OF THE twmttg Name of Book and Volume, Division Range Shelf. Received ___ University of California. THE MEDICAL LIBRARY Hi-' v. .} . F< > r urj I;A UD. \i . i >. Of San Francisco. PKESEFTED BY MES. -AND MISS FOURGEAUD. FOWNES' MANUAL OF CHEMISTRY, ELEMENTARY CHEMISTRY, THEORETICAL AND PRACTICAL. BY GEORGE FOWNES, F.R.S., LATE PROFESSOR OF PRACTICAL CHEMISTRY IN UNIVERSITY COLLEGE, LONDON. EDITED, WITH ADDITIONS, sr ROBERT BRIDGES, M. D., WCFESSOR OF CHEMISTRY IN THE PHILADELPHIA COLLEGE OF PHARMACY, ETC. LTO. A NEW AMERICAN, FROM TLfE LAST AND REVISED LONDON EDITION. WITH NUMEROUS ILLUSTRATIONS ON WOOD. PHILADELPHIA: BLANC HARD AND LEA. 1857. Entered, according to Act of Congress, in the year 1853, by KLAN CHARD AND LEA. in the Clerk's Office of the District Court of the United States for tha Eastern District of Pennsylvania^ ADVERTISEMENT NEW AMERICAN EDITION THE lamented death of the Author has caused the revision of this edition to fall into the hands of others, who have fully sustained its reputation by the additions which they have made, more especially in the portion devoted to Organic Chemistry, as set forth in their preface. This labour has been so thoroughly performed, that the American Editor has found but little to add, his notes con- sisting chiefly of such matters as the rapid advance of the science has rendered necessary, or of investigations which had apparently been overlooked by the Author's friends. These additions will be found distinguished by his initials. The volume is therefore again presented as an exponent of the most advanced state of Chemical Science, and as not unworthy a con- tinuation of the niaiked favour which it has received as an elementary text-book. PlIILADKLPHIA, October, 1853. PREFACE. THE design of the present volume is to offer to the student com- mencing 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 Che mical Investigations have made known to us. The work has no pre- tensions to be considered a complete treatise on the subject, but is intended to serve as an introduction to the larger and more compre- hensive 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 laboratory, and by exhibiting, by the aid of numerous wood-engravings, 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 followed in the lectures themselves, and to describe the non-metallic elements and some of their most important compounds before discussing the subject of the general philosophy of Chemical Science, and even (vii) Vlll PREFACE. before describing the principle of the equivalent quantities, or ex- plaining 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, ex- pressed in symbols. I have devoted as much space as could be afforded to the very im- portant 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. ADVERTISEMENT TO THE THIRD LONDON EDITION, THE correction of this Edition for the press was the daily occupa- tion of Professor Fownes, until a few hours previous to his death iu January, 1849. His wish and his endeavour, 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 nie 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, GKOSVEXOU STREET, Jan., 1850. ADVERTISEMENT FOURTH LONDON EDITION IT has been the endeavour of the Editors to include in the present edition of the Manual the progress of Chemistry since the Author's death. The foundation which he laid, and the form which he gave to tho work, remain untouched. But time has rendered it necessary that each portion should be revised ; and a few repairs, and some consider- able additions, especially in Organic Chemistry, have been made. Thus, several of the chapters on the Alcohols, the Organic Bases, Colouring Matters, &c., have been almost re-written. Still, such changes only have been made as the Editors believed the Author himself would have desired, if his life had been spared to Science. II. BENCE JONES. A. W. IIOFMANN. LON T DON, Seplemler, 1852. (xi) I TABLE OF CONTENTS. PAGE INTRODUCTION , , , 25 PART I. PHYSICS. OF DENSITY ASI SPECIFIC GRAVITY. 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. Elasticity of gases. Construction and use of the air-pump 34 Weight and pressure of the air. Barometer 37 Law of Mariotte; relations of density and elastic force; correction of volumes of gases for pressure 33 HEAT. Expansion. Thermometers 41 Different rates of expansion among metals; compensation-pendulum 44 Baniell's pyrometer 45 Expansion of liquids and gases. Ventilation. Movements of the atmo- sphere 46 Conduction of heat 52 Change of state. Latent heat 52 Ebullition ; steam 54 Distillation 58 Evaporation at low temperatures 50 Vapour of the atmosphere ; hygrometry 61 Liquefaction of permanent gases 62 Production of cold by evaporation 64 Capacity for heat. Specific heat 66 Sources of heat 68 2 (ziii) XIV CONTENTS. LIGHT. FACE Reflection, refraction, and polarization of light 71 Chemical rays 77 Radiation, reflection, absorption, and transmission of heat 79 MAGNETISM. Magnetic polarity; natural and artificial magnets..,. 86 Terrestrial magnetism.. 88 ELECTRICITY. Electrical excitation ; machines 92 Principle of induction; accumulation of electricity l3 Voltaic electricity 97 Thermo-electricity. Animal electricity 9U Electro-magnetism; magneto-electricity 100 Electricity of steam 10? PART II. CHEMISTRY OF THE ELEMENTARY BODIES. NON-METALLIC ELEMENTS. Oxygen 105 Hydrogen; water; binoxide of hydrogen 110 Nitrogen; atmospheric air'; compounds of nitrogen and oxygen 120 Carbon; carbonic oxide ; carbonic acid 127 Sulphur; compounds of sulphur and oxygen 131 Selenium 136 Phosphorus; compounds of phosphorus and oxygen 137 Chlorine; hydrochloric acid. Compounds of chlorine and oxygen 139 Iodine , 143 Bromine 143 Fluorine 149 Silicium 150 Boron 151 COMPOUNDS FORMED BY THE UNION OF THE JNON-METALLIC ELEMENTS AMONG THEMSELVES. Compounds of carbon and hydrogen. Light carbonetted hydrogen ; defiant gas; coal and oil-gases. Combustion, and the structure of flame 153 Nitrogen and hydrogen; ammonia , 162 CONTENTS. XV PAG a Sulphur, selenium, and phosphorus, with hydrogen 163 Nitrogen, with chlorine and iodine; chloride of nitrogen 167 Other compounds of non-metallic elements 168 Chlorine, with sulphur and phosphorus 168 DN THE GENERAL PRINCIPLES OF CHEMICAL PHILOSOPHY. Nomenclature 170 Laws of combination by weight 172 By volume 177 Chemical symbols 130 The atomic theory 182 Chemical affinity 183 Electro-chemical decomposition; chemistry of the voltaic pile 187 METALS. General properties of the metals 197 Crystallography 202 Isomorphism 209 Polybasic acids 212 Binary theory of the constitution of salts 213 Potassium 217 Sodium 224 Ammonium.. 232 Lithium 235 Barium 237 Strontium 239 Calcium 239 Magnesium 245 Aluminium 248 Beryllium (glucinum) 250 Yttrium, cerium, lanthanium, and didymium 251 Zirconium. Thorium 252 Manufacture of glass, porcelain, and earthenware 252 Manganese 256 Iron 259 Aridium 2G6 Chromium 267 Nickel 269 Cobalt. 271 Zinc 272 Cadmium 274. Bismuth 274 Uranium 276 Copper 277 Lead 279 Tin.... .. 282 XVI CONTENTS. PAOS Tungsten 284 Molybdenum 284 Vanadium 285 Tantalum (columbium) 28G Niobium and pelopium 286 Titanium 287 Antimony 287 Tellurium 290 Arsenic 291 Silver 296 Gold 299 Mercury 301 Platinum 307 Palladium 311 Khodium 312 Iridium 312 Kuthenium . 314 Osmium... .. 314 PART III. ORGANIC CHEMISTRY. INTRODUCTION ... 31G LAW OF SUBSTITUTION 317 THE ULTIMATE ANALYSIS OP ORGANIC BODIES 320 EMPIRICAL AND RATIONAL FORMULAE , 329 DETERMINATION OF THE DENSITY OP THE VAPOURS OF VOLATILE LIQUIDS .... 330 SACCHARINE AND AMYLACEOUS SUBSTANCES, AND THE PRODUCTS OF THEIR ALTERATION 333 Cane and grape-sugars ; sugar from ergot of rye ; sugar of diabetes insipi- dus; liquorice-sugar; milk-sugar; mannite... , , 333 Starch; dextrin; starch from Iceland-moss; inulin ; gum; pectin; lignin.. 337 Oxalic and saccharic acids , 341 Xyloidin ; pyroxylin; mucic acid 344 Suberic, mellitic, rhodizonic, and croconic acids 345 Fermentation of sugar. Alcohol 345 Lactic acid 349 Ether, and ethyl-compounds 351 Sulphovinic, phosphovinic, and oxalovinic acids 358 Heavy oil of wine 302 Olefiantgas; Dutch liquid; chlorides of carbon 362 CONTENTS. XVli PAGE Ethionic and isethionic acids 365 Chloral, &c 3C6 Mereaptan ; xanthic acid 367 Aldehyde; aldehydic acid; acetal 369 Acetic acid 371 Chloracctic acid 375 Acetone 376 Kakodyl 377 SUBSTANCES MORE OR LESS ALLIED TO ALCOHOL. Wood-spirit; methj'l-compounds 381 Sulphomethylic acid 384 Formic acid; chloroform 385 Formomethylal ; methyl-mercaptan 387 Potato-oil and its derivatives 388 Sulphamylic acid; valerianic acid 390 Chlorovalerisic and chlorovalerosic acids 393 Fusel-oil from grain-spirit; general view of the alcohols 393 Bitter-almond-oil and its products; ben/oyl-compounds 396 Benzoic-acid ; sulphobeuzoic acid; benzone and benzol 396 Sulphobenzide and hyposulphobenzic acid 398 Nitrobenzol, azobenzol, &c 399 Formobenzoic acid; hydrobenzamide; benzoin; benzile ; benzilic acid; benzimide, &c 400 Hippuric acid 402 Homologues of benzoyl-series 403 Salicin; salicyl and its compounds 403 Chlorosamide. Phloridzin. Cumarin 405 Cinnamyl and its compounds ; cinnamic acid ; chloro-cinnose 407 VEGETABLE ACIDS. Tartaric acid 410 Racemic acid 413 Citric acid 413 Aconitic or equisetic acid 414 Malic acid. 414 Fumaric and maleic acids 416 Tannic and gallic acids 416 AZOTIZED ORGANIC PRINCIPLES OP SIMPLE CONSTITUTION. Cyanogen; paracyanogen ; hydrocyanic acid 420 Amygdalin ; amygdalic acid 423 Metallic cyanides 424 Cyanic,, cyanuric, and fulminic acids 426 Chlorides, <&c., of cyanogen 429 2* XV111 CONTENTS. PAGE Ferro- and Atfricyanogen, and their compounds; Prussian blue 430 Cobaltocyanogen ; nitroprussides 433 Sulphocyanogen, and its compounds ; selenocyanogen ; melam ; melamine ; ammeline; ammelide , 434 Urea, and uric acid 436 Allantoin; alloxan; alloxanic acid; mesoxalic acid; mykomelinic acid; parabanic acid ; oxaluric acid ; thionuric acid ; uramile ; alloxantin ; murexide; murexan 438 Xanthic and cystic oxides 443 TflE YEGETO-ALKALIS, AND ALLIED BODIES. Morphine, and its salts 444 Narcotine ; opianic and hemipinic acids ; cotarnine 445 Codeine; thebaine ; pseudo-morphine; narceine ; ineconine 446 Meconic acid 446 Cinchonine and quinine; quinoidine 447 Kinic acid; kinone; hydrokinone 448 Strychnine and brucine ; veratrine 449 Conicine; nicotine; sparteine; harmaline; harmine; caffeine or theine; theobromine ; berberine ; piperine ; hyoscyamiae ; atropine ; solanine ; aconitine; delphinine; emetine; curarine 450 Gentianin ; populin ; daphnin ; hesperidin ; elaterin ; antiarin ; picrotoxin ; asparagin; santonin 451 ORGANIC BASES OP ARTIFICIAL ORIGIN. Bases of the ethyl-series. Ethylamine ; biethylamine ; triethylamine ; oxide of tetrethyl-ammonium 455 Bases of the methyl-series. Methylamine; bimethylamine ; triinethyla- mine; oxide of tetramethyl-ammoniiwh 457 Bases of the amyl-series. Amylamine ; biamylamine ; triamylamine ; oxide of tetramyl-ammonium 458 Bases of the phenyl-series. ^ Aniline ; chloraniline; nitraniline; cyaniline; melaniline 459 Bases homologous to aniline. Toluidine ; xylidine ; cuinidine. Naphthali- dine; chloronicine 462 Mixed bases. Ethylaniline ; biethylaniline ; oxide of triethylamyl-ammo- nium ; biethylamylamine ; oxide of methylobiethylamyl-ammonium ; methylethylamylamine ; ethylamylaniline ; oxide of metbyl-ethyl-amylo- phenyl-ammonium 463 BASES OP UNCERTAIN CONSTITUTION. Chinoline 464 Kyanol; leucol; picoliae 465 Petinine 465 Furfurine , ... 465 CONTENTS. XIX PAGE Fucusine ; amarine; thiosinnamine 466 Thialdine; alanine 467 Phosphorus-bases 468 Antimony-bases 469 ORGANIC COLOURING PRINCIPLES. Indigo; white indigo; sulphindylic acid 470 Isatin; anilic and picric acids ; chrysanilic and an thranilic acids 471 Litmus lecanorin; orcin; orcein, &c 474 Cochineal, madder, dye-woods, &c 477 Chrysammic, chrysolepic, and styphnic acids 47$ OlLS AND FATS. Fixed oils ; margarin, stearin, and olein ; saponification, and its products j glycerin 480 Palm and cocoa-oils. Elaidin and elaidic acid 483 Suberic, succinic, and sebacic acids 484 Butter. Butyric, caproic, caprylic, and capric acids 485 Wax; spermaceti; cholesterin; cantharidin 486 Acrolein; acrylic acid 487 Products of the action of acids on fats 487 Castor-oil; caprylic alcohol 488 Volatile oils. Oils of turpentin, lemons, aniseed, cumin, cedar, gaultheria, valerian, peppermint, lavender, rosemary, orange-flowers, rose-petals 488 Camphor; camphoric acid 492 Oils of mustard, garlic, onions, &c 492 Eesins. Caoutchouc 493 Balsams. Toluol, styrol 494 COMPONENTS OP THE ANIMAL BODY. Albumin, fibrin, and casein; protein 496 Gelatin and chondrin 500 Kreatin and kreatinine 502 Composition of the blood; respiration; animal heat 503 Chyle; lymph; mucus; pus 507 'Milk; bile; urine; urinary calculi 503 Nervous substance ; membranous tissue ; bones 51(5 The function of nutrition in the vegetable and animal kingdoms 518 PRODUCTS OF THE DESTRUCTIVE DISTILLATION, AND SLOW PUTREFACTIVE CHANGE OF ORGANIC MATTER. Substances obtained from tar. Paraffin ; eupione; picamar; kapnomor; cedriret; kreosote; chryscn and pyren 523 XX - CONTENTS. PAdE Coal-oil. Carbolic acid (hydrate of oxide of plienyl) 526 Naphthalin and paranaphthalin 529 Petroleum, naphtha, and other allied substances 530 APPENDIX. Hydrometer tables. Table of the tension of the vapour of water at differ- ent temperatures. Table of the proportion of real alcohol in spirits of different densities. Analyses of the mineral waters of Germany. Table of weights and measures 533 LIST OF ILLUSTRATIONS BY WOOD-CUTS. Fig. Pago 1 Specific-gravity bottle 28 2 " " 29 3 " " 29 4 " " 29 5 " " 30 6 " " beads 31 7 Hydrometer 32 8 Urinoraeter 32 9 Specific gravity 33 10 Elasticity of gases 34 11 Single air-pump 35 12 Double " 36 13 Improved" 36 14 " " 37 15 Barometer 38 16 " 39 17 " 40 18 Expansion of solids 41 19 " liquids 41 20 " gases 41 21 Differential thermometer 43 22 " 43 23 Difference of expansion in metals 44 24 Gridiron pendulum 44 25 Mercury 45 26 Compensation balance 45 27 Daniell's pyrometer 45 28 Expansion of mercury /. 47 29 Atmoppheric currents 50 30 " " 50 31 " " 51 32 Boiling paradox 55 33 Steam-bath 57 34 Steam-engine 57 35 Distillation 58 36 Liebig's condenser 59 37 Tension of vapour ; 59 38 " " . 60 89 Wet-bulb hygrometer (xxi) XX11 LIST OP ILLUSTRATIONS. 40 Condensation of gases ..................................................................... 63 41 Thilorier's apparatus .................................. ...................................... 64 42 Cold by evaporation ....................................................................... 65 43 Wollaston's cryophorus .................................................................... 65 44 Daniell's hygrometer ....................................................................... 65 45 Reflection of light ........................................................................... 72 46 Refraction of light ......................................................................... 72 47 " " .......................................................................... 72 48 " ................................................ .......... ................ 73 49 Spectrum ........................ . .............................................................. 74 50 ........................ . .............................................................. 74 51 Polarization of light ........................................................................ 75 52 " " ........................................................................ 76 53 " " ........................................................................ 76 54 Reflection of heat ........................................................................... 79 55 " " ........................................................................... 80 56 Effects of electrical current on the magnetic needle ............................... 82 57 " " " ................................ 82 58 Current produced by heat ................................................................. 83 59 Melloni's instrument for measuring transmitted heat .............................. 83 60 Magnetic polarity ........................................................................... 87 61 " " .......... , ................................................................ 87 62 Electro repulsion ............................................................................ 93 63 Electroscope .................................................................................. 93 64 Electric polarity .............................................................................. 93 65 Electrical machine .......................................................................... 95 66 " plate ..................................................................... 95 67 Leyden jar .................................................................................... 96 68 Electrophorus ................................................................................. 97 69 Volta's pile ....................................... ............................................. 98 70 Crown of cups ................................................................................ 98 71 Cruikshank's trough ........................................................................ 99 72 Effect of electrical current on the magnetic needle ............................. ;.. 100 73 Astatic needle ......................................................................... . ...... 101 74 Magnetism developed by the electrical current ..................... . ............... 101 75 " " " >" ..................................... 102 76 Electro-magnet ............................................................................... 102 77 Apparatus for oxygen ...................................................................... 105 78 Hydro-pneumatic trough .................................................................. 106 79 Transferring gases ........................................................................... 107 80 Pcpy's hydro-pneumatic apparatus ..................................................... 107 81 Apparatus for hydrogen .................................................................... Ill 82 Levity of hydrogen ......................................................................... HI 83 Diffusion of gases ........................................................................... 112 84 Daniell's safety-jet ........................................................................... 113 85 Musical sounds by hydrogen ............................................................. 114 86 Catalyse effect of platinum .............................................................. 115 LIST OP ILLUSTRATIONS. ZX111 Fig. l*ap;e 87 Decomposition of water 116 83 Eudiometer of Cavendish 116 89 Analysis of water 116 90 Preparation of nitrogen 120 91 Analysis of air 121 92 lire's eudiometer 122 93 Preparation of nitric acid 123 9i " protoxide of nitrogen 125 95 Crystalline form of carbon 127 96 " " " 127 97 " 127 98 " " " 127 99 Preparation of carbonic acid 129 100 Mode of forming caoutchouc connecting-tubes 129 101 Crystalline form of sulphur 131 102 Crystals of sulphur 131 103 Crystalline form of sulphur 131 104 Preparation of phosphorus 137 105 " chlorine 139 106 " hydrochloric acid 1 12 107 Safety-tube 113 108 Combustible under water 145 109 Preparation of hydriodic acid 1 17 110 silica 150 111 Blast furnace 157 112 Reverberatory furnace 157 113 Structure of flame 158 114 Mouth blowpipe 159 115 Structure of blowpipe flame 159 116 Argand spirit-lamp 159 117 Common " 159 118 Mitchell's " 16f 119 Gas " 16C 120 Davy's safe " 161 121 Hemming's safety-jet 161 122 Effect of metallic coil 161 123 Apparatus for sulphuretted hydrogen 164 124 Multiple proportions 181 125 Water in its usual state 18i< 126 " undergoing electrolysis 189 127 Voltameter 190 128 Decomposition without contact of metals 191 129 "Wollaston's voltaic battery 193 130 DanielFa constant " 193 131 Grove's '- " 194 132 Electrotype 195 133 Lead-tree ... .. 19 & XXIV LIST OF ILLUSTRATIONS. Fig. Pago 134 Wire-drawing 193 135 Wollaston's goniometer 203 136 Reflecting " 204 137 " " principles of 205 138 Crystals, regular system 206 139 " regular prismatic system 206 140 " right prismatic system 207 141 " oblique prismatic system 2(-7 142 " doubly oblique prismatic system 208 143 Crystals, rhombohedral system 208 144 " passage of cube to octahedron 209 145 " " " octahedron to tetrahedron 209 146 Alkalimeter 227 147 Apparatus fo\ determining carbonic acid 228 148 " " " 229 149 Iron manufacture. Blast-furnace 264 150 Crystals of arsenious acid 293 151 Subliming tube for arsenic 294 152 Marsh's test 295 153 Weighing tube 321 154 Combustion '. 321 155 Chaufier 322 156 Water tube 322 157 Carbonic acid bulbs -. 322 158 Apparatus complete 323 159 Bulb for liquids 324 160 Comparative determination of nitrogen 325 161 Pipette 325 162 Absolute estimation of nitrogen 326 163 Varentrap's and Will's method 327 164 Determination of the density of vapours 330 165 Starch granules 338 166 Preparation of ether 361 167 " defiant gas. 363 168 " Dutch liquid 363 169 Catalysis 371 170 Preparation of kakodyle 379 171 " benzoicacid , 397 172 " tannic acid 417 173 Uric acid crystals 438 174 Blood globules 504 Itf5 Pus " 508 176 Milk " 508 177 Trommer's test 514 178 Uric acid calculus 515 179 Urate of ammonia calculus 515 180 Fusible calculus '. 516 J81 Mulberry calculus 516 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 structure of the earth, the sea, and the air, and of the various organized or living be- ings 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 properties and relations of vast numbers of individual substances; and by this method alone. The science is entirely experimental, and all its conclusions the re- sults 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 opposition to effects termed physical, which are not attended by such consequences. Changes of decomposition or combination are thus easily distinguished from those temporarily brought about by heat, electricity, magnetism, 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 chem- 3 (25J 26 INTRODUCTION. ical 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 de- composed into quicklime and a gaseous body, carbonic acid. Both lime and carbonic acid are in their turn susceptible of decomposition, the first into a metal, calcium, and oxygen, and the second into carbon and oxygen. For this purpose, however, simple heat does not suffice, the resolution of these substances into their components demanding the exertion of a high degree of chemical energy. Beyond this second step of decomposition 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 ele- ments ; 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 physical constitution of gases, the chief phenomena of heat and electricity, and a few other subjects, forms such an indispensable introduction to Chemistry itself, that it is never 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. PAET I. PHYSICS. OF DENSITY AND SPECIFIC GRAVITY. IT is of great importance in 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 gravity 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. 1 In all cases of solids and liquids this standard of unity is pure water at the temperature of 60 Fahr. (15-5C). 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. The ordinary ex- pression of specific weight, therefore, is a number expressing how many times the weight of an equal bulk of water is contained 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 00, we mean that equal bulks of these two liquids and of distilled water possess weights in the proportion of the num- bers 1-85, 0-794, and 1 ; or 1850, 794, and 1000. It is necessary to be par- ticular about the temperature ; for, as will be hereafter shown, liquids are extremely expansible by heat ; otherwise, a constant bulk of the same liquid will not retain a constant weight. It will be proper to begin with the de- scription 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 liquor 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 figuro represented on the next page, (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 60 (15-5C). Such a flask is readily procured from any one of the Italian artificers, to be found in every large town, who manufacture cheap thermometers for sale. A counterpoise of the exact weight of the empty 1 In other words, density means comparative mass, and specific gravity comparative weight. These expressions, although really relating to distinct things, are often used quite indiffe- rently in chemical writings, and without practical inconvenience, since mass and weight are directly proportioual to each other. (27) 28 DENSITY AND SPECIFIC GRAVITY. _. _ bottle is made from a bit of brass, an old weight, or something of the kind, and carefully adjusted by filing : an easy task. The bottle is then grad- uated, by introducing water at 60, until it ex- actly 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 tem- perature of 60, 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. A watery liquid in a narrow glass tube always presents a curved surface from the molecular ac- tion of the glass, the concavity being upwards. It js better, on this account, in graduating the bottle, to make two scratches as represented in the draw- ing, 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, three-square file, the hard point of Thich, also, it may be observed, answers perfectly well for writing upon glass, in the absence of a proper diamond-pencil. The specific-gravity bottle above described differs from those commonly made for sale by the instrument-makers. These latter are constructed with a perforated stopper, so arranged that when the bottle is quite filled, the stopper put in its place, and the excess of liquid which flows through the hole wiped from the outside, a constant measure is always had. There are inconveniences attending the use of the stopper which lead to a preference of the open bottle with merely a mark on the neck, even when very volatile liquids are experimented with. 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 trifling 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 di- mensions, from scarcity of the liquid to be examined. The shape is also in reality of little moment ; any light phial with a narrow neck may be em- ployed, not quite so conveniently perhaps, as a specific-gravity bottle. The determination of the specific gravity of a solid is also an operation of great facility, although the principle is not so obvious. As it would be impossible to put in practice a direct method like that indicated for liquids, recourse is had to another plan. The celebrated theorem of Archimedes affords a solution of the difficulty. This theorem may be thus expressed : When a solid is immersed in a fluid, it loses a portion 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 important proposition, as well as to establish it by reasoning. The drawing (fig. 2) represents a little apparatus for the former purpose. This consists of a thin cylindrical vessel of brass, into the interior of which fits very accurately 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 precisely equal to the weight of an equal bulk of water, may then be proved by filling DENSITY AND SPECIFIC GRAVITY. 29 .he bucket to the brim, whereupon the equilibrium /vill be restored. 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 rectangular body, and so adjusted with respect to density, that it shall float indifferently in any part beneath the surface (fig. 3). Now the law of fluid pressure is to this effect : The pressure exerted by a fluid upon the containing vessel, or upon anything plunged beneath its surface, depends, first, upon the density of that fluid, and, secondly, upon the perpendicular height of the col- umn. It is independent of the form and lateral dimensions of the vessel or immersed body. More- over, owing to the peculiar physical constitution of fluids, this pressure is exerted equally in every di- rection, upwards, downwards, and laterally, with equal force. The floating body is in a state of equilibrium ; therefore the pressure downwards caused by its gravi- tation must be exactly compensated by the upward transmitted pressure of the column of water a, b. But this pressure downwards is obviously equal to the weight of an equal quantity of water, since the body of necessity displaces its own bulk Hence, the weight lost, or supported by the water, is the weight of a volume of water equal to that of the body immersed. 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 thus, 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 imagina- tion, into a multitude of little perpendicular prisms, or cylinders, 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- crystals : 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 horse-hair, immersed com- pletely (fig. 4) in pure water at 60 (15 -50), and again weighed. It now weighs less, the difference 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 3* Fig. 2. rig. 3. Fig. 4. 80 DENSITY AND SPECIFIC GRAVITY. times the latter number is contained in the former ; the quotient will be the density, water being taken = 1. For example : The quartz-crystals weigh in air 293-7 grains. When immersed in water, they weigh 180-1 Difference being the weight of an equal volume of water ... 113-6 293-7 = 2-58, the specific gravity required. The arbitrary rule is generally thus written : "Divide the weight in air by the loss of weight in water, and the quotient will be the specific 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, - 5 - namely, the weight of an equal bulk of air, is BO 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 (fig. 5), heavy enough to sink it, and suspended from the balance. The whole is then ex- actly weighed, immersed in water, and again weighed. The difference 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 weigh- ing 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 139-3 133-7 139^3 = ' 9598 ' In all such experiments, it is necessary to pay attention to the temperature 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. This difficulty is easily conquered 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; DENSITY AND SPECIFIC GRAVITY. 31 the sugar is next weighed in the air, then suspended by a horse-hair, and weighed in the oil ; the difference is the weight of an equal bulk of the latter ; a simple calculation gives the weight of a corresponding volume of water : Weight of sugar in air 400 grains. Weight of sugar in oil of turpentine 182-5 Weight of equal bulk of oil of turpentine 217-5 87 : 100 = 217-5 : 250, the weight of an equal bulk of water : hence the specific gravity of the sugar, !5 = l-6. 250 The substance to be examined may be in small fragments, or powder. Here the operation is also very simple. A bottle holding a known weight of water is taken ; the specific-gravity bottle already described answers per- fectly well. A convenient quantity of the substance is next carefully weighed out, and introduced into the bottle, which is then filled up to the mark on the neck with distilled water. It is clear that the vessel now contains less water by a quantity equal to the bulk of the powder than if it were filled in the usual manner. It is, lastly, weighed. In the subjoined experiment emery powder was tried. The bottle held, of water 1000 grains. The substance introduced weighed 100 Weight of the whole, had no water been displaced 1100 The observed weight is, however, only 1070 Hence water displaced, equal in bulk to the powder 30 100 -^TT = 3-333 specific gravity. 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 theorem of Archimedes affords the key to the general doctrine of the equilibrium of floating bodies, of which an application is made in the common hydrometer, 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 fluid specifically heavier than itself, it sinks down until it displaces a quantity of fluid 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 fluid, the position of equilibrium will involve the immersion of exactly 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 fluid of one-half the specific gravity of water, if such could be found, then it would 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 spe- cific gravity of a fluid. In this manner little glass beads (fig. G) of known specific gravities are sometimes employed in the arts to ascertain in a rude manner the specific gravity of liquids ; 32 DENSITY AND SPECIFIC GRAVITY. Fig. 7. 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. 7) in general use consists of a floating vessel of thin metal or glass, having a weight beneath to maintain it in an upright position, and a stem above bearing a divided scale. The use of the instrument 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 fluid will counterbalance its weight. For the same reason, in a liquid of less density, it sinks deeper. The hydrometer comes to rest almost immediately, and then the mark on the stem at the fluid-level may be read oif. Very extensive use is made of instruments of this kind in the arts ; these sometimes bear dif- ferent names, according to the kind of liquid for ./ \ which they are intended ; but the principle is the \-jjp L^ same in all. The graduation is very commonly (5 ^j^rrrrd^ arbitrary, two or three different scales being un- fortunately used. These may be sometimes re- duced, however, to the true numbers expressing the specific gravity by the aid of tables of com- parison drawn up for the purpose. A very convenient and useful instrument in the shape of a small hydrometer (fig. 8) for taking the specific gravity of urine, has lately 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. a The determination of the specific gravity of gases and vapours 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 concerned, but the pro- cesses are much more delicate, and involve be- sides certain corrections for differences of tem- perature and pressure, founded on principles yet to be discussed. It will be proper to defer the consideration of these matters for the present. The method of determining the specific gravity of a gas will be found described under the head of Fig. 8. 1 This and other instruments described or figured in the course of the work, may be had of Mr. Newman, 122 Kegent Street, upon the excellence of whose workmanship reliance may be safely placed. a The graduation of the urinometer is such that each degree represents 1-1000, thus giving the actual 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 1000 will epresent the density of the liquid. If, for example, the surface of the liquid coincide with 23 on the scale, the specific gravity will be 1023, about the average density of healthy urine. K B. DENSITY AND SPECIFIC GRAVITY. 33 Cl Oxygen," and that of the vapour of a volatile liquid in the Introduction to Organic Chemistry/ 1 The mode of determining the specific gravity of a liquid by means of a solid has been omitted in the text. It results from the theorem of Ar- chimedes, that if any solid be immersed in water and then in any other liquid, the loss of height 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 instance, let a piece of glass rod be suspended from the balance-pan and exactly counterpoised, 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 rod. Now wipe the glass dry, and having removed the additional weights, immerse it in the other liquid, and restore the equipoise as before, M^s 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, x^r example : The glass rod loses by immersion in water 171 jr *.4. The glass rod loses by immersion in alcohol 143 112 =i-836 the specific gravity required. R. B. Fig. 9. 3-1 PHYSICAL CONSTITUTION OP THE PHYSICAL CONSTITUTION OF THE ATMOSPHERE, AND OF GASES IN GENERAL. IT requires some little abstraction of mind to realize completely the singu- lar condition in which all things at the surface of the earth exist. We live at the bottom of an immense ocean of gaseous matter, which envelopes everything, 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 nothing 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 constitu- tion 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, fig. 10, closed at the bottom, in Figf 10- which moves a piston, air-tight, so that no air can escape between the piston and the cylinder. Suppose now the piston be pressed downwards with a certain force ; the air beneath it will be compressed into a smaller bulk, the amount of this compression depending on the force ap- plied ; if the power be sufficient, the bulk of the gas may be thus diminished to one hun- dredth part or less. When the pressure is re- moved, the elasticity or tension, as it is called, of the included air or gas, will immediately force up the piston until it arrives at its first position. Again, take b, fig. 10, 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 upwards, the air below will ex- pand, so as to fill completely the enclosed space, and this to an apparently unlimited ex- tent. 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 OF THE ATMOSPHERE. 35 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 to the particles of material bodies, when in a gaseous state, a self-repulsive energy. This statement is commonly made somewhat in this manner: master is under the influence of two opposite forces, one of which tends to draw the particles together, the other to separate them. By the preponde- rance of one or other of these forces, we have the three states called solid, liquid, arid 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 vapour. Various names are applied to these forces, and various ideas entertained concerning them ; the attractive forces bear the name of cohesion when they are exerted between particles of matter separated by a very small interval, and gravitation, when the distance is great. The repulsive principle is often thought to be identical with the principle of heat. Fig. 11. The ordinary air-pump, shown in section in fig. 11, consists essentially of ft metal 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 ex- hausted, and is furnished with a valve opening upwards. A similar valve, also opening upwards, is fitted to the piston ; these valves are made with slips of oiled silk. When the piston is raised from the bottom of the cy linder, 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. A3 the descent of the piston continues, the air included within the cylinder be- 3b PHYSICAL CONSTITUTION comes compressed, its elasticity is increased, and at length it forces ope? the upper valve, and escapes into the atmosphere. In this manner, a cy- linder 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. Fig. 12. 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, be- tween them, moved by a winch. By this contrivance the operation of exhaustion is much facilitated and the labour lessened. The arrangement is shown in fig. 12. A simpler and far superior form of air-pump is thus constructed: the cylinder, which may be of large dimen- sions, 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 the 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 enclosed 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 OF THE ATMOSPHERE, 37 Fig. 14. closes, a vacuum is left in the upper part, of the cylinder, into which the air of 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 favourable 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 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 upwards ; this may also be of metal, and contained within the body of the piston. Its use is to avoid the momentary condensation of the air in the receiver when the piston descends. The pump is worked by a lever in the manner represented in fig. 14. To return to the atmosphere. Air pos- sesses weight : a light flask or globe of glass, furnished with a stop-cock and ex- hausted by the air-pump, weighs consi- derably 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 atmosphere may be demonstrated by se- curely 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 con- cave, until it suddenly breaks. A thin square glass bottle, 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 conse- quence of the accidental formation of a partial vacuum within. After what has been said on the subject of fluid pressure, it will scarcely be ne- cessary to observe that the law of equality of pressure in all directions also holds good in the case of the atmosphere. The perfect mobility of the particles of air permits the transmission of the force ge- nerated 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, 88 PHYSICAL CONSTITUTION Fig .15. the latter, on being allowed access to the tube, would rise in its interior until the weight of the column balanced the pres- sure 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 ex- actly estimating the amount of pressure exerted by the atmo- sphere. Such an instrument is the barometer: a straight glass tube is taken, about 36 inches in length, and sealed by the blow-pipe flame at one extremity ; it is then filled with clean, dry mercury, care being taken to displace all air- bubbles, the open end stopped with a finger, and the tube in- verted in a basin of mercury. On removing the finger, tha 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 at- mospheric 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 instrument. The Royal Society of London possess a water- barometer at their apartments at Somerset House. Its con- struction was attended with great difficulties, and it has been 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 which ia thus expressed : The volume of a 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 pres- sure 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, is easily demonstrable by direct experiment. A glass tube, about 7 feet in length, is closed at one end, and bent into the form shown in fig. 16, the open limb of the siphon being the longest. It is next attached to a board furnished with a moveable 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 ATMOSPHERE. 39 1 e< the mercury in the open part of the tube stands Fig. 16. very nearly 30 inches above that in the closed portion. The pressure of an additional "atmosphere" has con- sequently 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 illustra- tion of the principle than for furnishing rigorous proof of the law; this has, however, been done. MM. Arago and Duloug 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. All gases are alike subject to this law, and all va- pours of volatile liquids, when remote from their points of liquefaction. 1 It is a matter of the greatest im- portance 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 fol- lowing 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 30 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 ; 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 practical pupil will do well to familiarize himself with these simple 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 diminish with the altitude, and very rapidly. The lower strata of air have to bear the weight of those above them ; they become, in consequence, deeper and more com- pi'essed 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 Volume of air. Height of barometer, in inches. 30 15 7-5 3-75 10-82 16 1-875 13-525 32 0-9375 16-23 64 0-46875 1 When near the liquefying point the law no longer holds; tho volume diminishes ttu/r rapidly than the theory indicates, a smaller amount of pressure being then sufficient 4X) PHYSICAL CONSTITUTION OP THE ATMOSPHERE. Fig. 17. The numbers in the first column form an arithmetical series, by the constant addition of 2-705 ; those in the second column an increasing geometrical series, each being the double of its prede- cessor; and those in the third, a decreasing geometrical series, in which each number is the half of that standing above it. In ascending in the air in a balloon, these effects are well ob- served ; the expansion of the gas within the machine, and the fall of the mercury in the barometer, soon indicate to the voya- ger 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, speedily led to the observation that the atmospheric pressure at the same level is not constant, but possesses, on the contrary, 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 distinguished ; 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 regular 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 pressure of the atmosphere. The marginal drawing represents a very convenient and economical siphon barometer for this purpose. A piece of new and stout tube, of about one-third of an inch in internal diameter, is procured at the glass-house, sealed at one extremity, and bent into the siphon form, as repre- sented. 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 by a stick or glass rod. The barometer is, Jastly, 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 ob- servation 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 at once read off. HEAT. 41 HEAT. IT will lie 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 altering their dimensions. 2. Conduction, or transmission of heat. 3. Change of state. 4. Capacity of bodies for 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 (fig. 18) be taken, of such magnitude as to fit accurately lowpipe flame, and the 42 HEAT. 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 remainder of the air is easily expelled, and the whole space filled with mercurial vapour, on the condensa- tion of which the metal is forced into the instrument by the pressure of the air, until it becomes completely filled. 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 tempera- tures 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 in the upper part of the tube, which is essential 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 certain fixed points, at the least two in number, 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 such 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, which is always the same under similar circumstances. A clean metallic vessel is 'taken, into which pure water is put and made to boil ; a thermometer placed in the boiling liquid just so deep as is necessary to cover the bulb, invariably marks the same degree of temperature so long as the height of the barometer re- mains unchanged. The tube having been carefully marked with a file at these two points, it remains to divide the interval into degrees ; this is entirely arbitrary. In the greater part of Europe and in America, the scale called centigrade is em- ployed; the space in question being 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 very inconvenient division of Fahrenheit is still in use ; the above 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 temperature of ebullition is expressed by the number 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 an uniform system has not been generally adopted in graduating thermometers ; this would rendfir unnecessary the labour which now so frequently has to be performed of translating the language of one scale into that of another. To effect this, presents, however, no great diffi- culty. Let it be required, for example, to know the degree of Fahrenheit' A scale which corresponds to 60 centigrade. 100 C. = 180 F., or 5 C. = 9 F. Consequently, 5 : 9 = 60 : 108. HEAT. 43 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 either scale, presents rather more apparent difficulty ; a little consideration, however, will render the method obvious, the interval between the two zero-points being borne in mind. 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. 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 (fig. 21), the atmosphere is completely excluded. The effects of expansion are in the one case complicated with those arising from changes of pressure, and in the other cease to be visible at all when the whole 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 can occur. Accordingly, such instruments are called differential thermometers, since they serve to measure differences of temperatures between the two portions of air, while changes affecting both alike are not indicated. Fig. 22 shows another form of the same instrument. Fig. 21. O Fig. 22. 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 instrument 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. All bodies are enlarged in their dimensions by the application of heat, and reduced by its abstraction, or, in other words, contract on being artiii* 44 HEAT. 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, all expand alike for the same increase of heat. 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 temperature 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 arti- ficially cooled, the brass contracts more than the iron, and the reverse of this effect is produced. Fig. 23. This fact has received a most valuable application. It is not necessary to insist on the importance of possessing instruments for tlie accurate mea- surement of time ; such are absolutely indispensable to the Fig. 24. successful cultivation of astronomical science, and not less use- ful to the navigator, from the assistance they give him in find- ing the longitude at sea. For a long time, notwithstanding the perfection of finish and adjustment bestowed 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 num- ber of beats made by a pendulum : now the time of oscillation of a pendulum depends principally upon its length ; any altera- tion in this condition will seriously aifect 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 tempera- ture ; so that a pendulum adjusted to vibrate seconds at 60 (15-5C) would go too slow when the temperature rose to 70 (21 -1C), from its elongation, and too fast when the tempera- ture fell to 50 (10C), 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 expansion 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 oppo- site direction of the brass or zinc, it is possible to maintain under all circumstances of temperature an invariable distance between the point? of suspension and of oscillation. This is often called the gridiron HEAT. 45 Fig. 26. pendulum ; fig. 24 will clearly illustrate its principle ; the shaded Fig. 25. bars are supposed to be iron and the others brass. A still simpler compensation pendulum (fig. 25) is thus con- structed. 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. 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 necessity subject to variation by change of temperature. To remedy the evil thus involved, the circumference of the balance- wheel is made of two metals having different rates of expansion, fast soldered together, the most expansible being on the outside. The compound rim is also cut through in two or more places, as represented in fig. 26. When the watch is exposed to a high tempera- ture, and the diameter of the wheel becomes enlarged by expansion, each segment is made, by the same agency, to assume a sharper curve, whereby its centre of gravity is thrown inwards, and the expansive effect com- pletely compensated. Many other beautiful appli- cations 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 tempera- tures above those capable of being taken by the thermometer. A rod of iron or platinum, about five inches long, is dropped into a tube of black- lead ware ; a little cylinder of baked porcelain is put over it, and secured in its place by a platinum strap and a wedge of porcelain. When the whole is exposed to heat, the expansion of the bar drives forward the cylinder, which moves with a certain degree of friction, and shows, by the extent of its displacement, the length- ening which the bar had undergone. It remains, therefore, to measure the amount of this displacement, whioh must be very small, even when the heat has been ex- ceedingly intense. This is effected by the contrivance shown in fig. 27, in which the motion of the longer arm of the lever carrying the vernier of the scale is nmltipled 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 congelation, and afterwards into another of the same metal in a boiling state, and marking off the interval. By this instrument the melting-point F3 S- 27. 46 HEAT. of cast iron was fixed at 2786 Fahrenheit (1530C) 3 and the greatest heat of a good wind-furnace at about 3300 (1815C). 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 obtained by MM. Lavoisier and Laplace. The fraction indicates the amount of expansion in length suffered by rods of the under- mentioned bodies in passing from 32 (0C) to 212 (100C). English flint glass Common French glass Glass without lead Another specimen Steel untempered Tempered steel Soft iron Gold Copper Brass Silver . Lead From the linear expansion, the cubic expansion (or increase of volume) may be easily calculated. When an approximation only is wanted, it will be sufficient to triple the fraction expressing the increase in one dimension. 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 indis- pensable to make provision for these changes of dimensions. A very useful little application of expansion by heat is that to the cutting 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 wished-for 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 Fluids. The dilatation of a fluid may be determined by fill- ing with it a thermometer, 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 re- sult being evidently the difference of the two. Liquids vary exceedingly in this particular. The following table is taken from Pe'clet's Elemens de Physique. Apparent Dilatation in Glass between 32 (0C) and 212 (100C). Water Hydrochloric acid, sp. gr. T137 .... Nitric acid, sp. gr. 1*4 . . , ' . . * Sulphuric acid, sp. gr. 1/85 , Ether jV Olive oil .* '-'.'' . . . . . . yV Alcohol ......... 7 Mercury -$* Most of these numbers must be taken as representing mean results. For there are few fluids which, like mercury, expand regularly between these temperatures. Even mercury above 212 (100C) expands irregularly, as the following table shows. HEAT. ,, 5* -UTS Absolute Expansion of Mercury for 180. Between 32 (0C) and 212 (100C) Between 212 (100C) and 392 (200C) .... Between 392 (200C) and 572 (300C) .... 3 V The absolute amount of expansion of mercury is, for many reasons, a point of great importance ; it has been very carefully determined by a me- thod independent of the expansion of the containing vessel. The apparatus employed for this purpose by MM. Dulong and Petit is shown in fig. 28, di- vested, however, of many of its subordinate parts. It consists of two up- right 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 hottest column will be the tallest, because the expansion of the metal diminishes its specific-gravity, and the law of hydrostatic equilibrium requires that the heights of such columns should be inversely as their den- sities. By the aid of the outer cylinders, one of the tubes is maintained Constantly at 32 (0C), 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 horizontal micrometer telescope, moving on a vertical divided scale. Fig. 28 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 32 (0C) be 6 inches high, and that at 212 (100C) 6-108 inches, the increase of height, 108 on 6,000, or ^l.^- part of the whole, must represent the absolute cubical expansion. The indications of the mercurial thermometer are inaccurate when very high ranges of temperature are concerned, from the increased expansibility of the metal ; on this account, a certain correction is necessary in many ex- periments, and tables for this purpose have been drawn up. 1 An exception to the regularity of expansion in fluids, exists in the case of water; it is so remarkable, and its consequences so important, that it ia necessary to advert to it particularly. Let a large thermometer-tube be filled with water at the common tempe- 1 Below 400 Fahrenheit (204-4C) the error may be neglected: at 500 (2GOC) it i? about 1; at 630 (332-5C) 6. Regiianlt. 48 HEAT. rature of the air, and then artificially cooled. The liquid will be observed to contract regularly, until the temperature falls to about 40 (4-4C), or 8 above the freezing-point. After this, a farther reduction of temperature causes expansion instead of contraction in the volume of the water, and this expansion continues until the liquid arrives at its point of congelation, when so sudden and violent an enlargement takes place, that the vessel is almost invariably broken. At the temperature of 40 (4-4C), or more correctly, perhaps, 39-5 (4-lC), water is at its maximum density; increase or dimi- nution of heat produces upon it, for a short time, the same effect. A beautiful experiment of Dr. Hope illustrates the same fact. If a tall jar filled with water at 50 (10C) or 60 (15-5C) and having in it two 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 attained the temperature of 40 (4-4C) after which it will re- main stationary. At length the upper thermometer will also mark 40 (4-4C) but still continue to sink as rapidly as before, while that at the bot- tom 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 be- comes denser in consequence, and falls to the bottom, its place being sup- plied 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 ac- quired its condition of maximum density, that is, until the temperature has fallen to 40 (4-4C). 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 behaviour of water is attended by the most beneficial consequences, in shielding the inhabitants of the waters from ex- cessive cold. The deep lakes of the North American Continent never freeze, the intense and prolonged cold of the winters of those regions being insuffi- cient to reduce the temperature of such masses of water to 40 (4-4C). 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. Sea-water has a maximum density at the same temperature as fresh water. The depths of the Polar Seas exhibit this temperature throughout the year, while the surface-water is in summer much above, and in winter much below, 40 (4'4C) ; in both cases being specifically lighter than water at that temperature. This gradual expansion of water cooled below 40 (4 0< 4C) must be carefully distinguished from the great and sudden increase of volume it exhibits in the act of freezing, and in which respect it resem- bles many other bodies which expand on solidifying. It may be observed that the force thus exerted by freezing water is enormous. 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 the following morn- ing split in fragments. 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 alike for equal increments of heat; and all vapours, 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. HEAT. 49 3. The rate of expansion is uniform for all degrees of heat. 4. The actual amount of expansion is equal to y^ part of the volume of the gas at Fahrenheit, for each degree of the same scale. 1 It will be unnecessary to enter into any description of the methods of in- vestigation by which these results have been obtained ; the advanced student will find in Pouillet's Siemens de Physique, and in the papers of MM. Magnus" and Regnault 3 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 tempera- ture ; this can be effected with great facility. Let it be required, for ex- ample, to find the volume which 100 cubic inches of any gas at 50 (10C) would become on the temperature rising to 60 (15 -5C). The rate of expansion is T ^ of the volume at for each degree ; or 460 measures at become 461 at 1, 462 at 2, - 460 -j- 50 = 510 at 50, and 460 -f- 60 = 520 at 60. Hence Meas. at 50. Meas. at 60. Meas. at 50. Meas. at 60. 510 : 520 = 100 ': 101-96. If this calculation is required to be made on the centigrade scale, it must be remembered that the zero of that scale is the melting point of ice. Above this temperature the expansion for each degree of the centigrade scale is _^_ of the original volume. This, and the correction for pressure, are operations of very frequent oc- currence 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 quite 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 which 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 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 exhi- bited by those gases which, as will hereafter be seen, are most easily lique- fied, such as carbonic acid, cyanogen, and sulphurous acid, and that the dis- crepancies become smaller and smaller as the elastic force is lessened ; so that, if means existed for comparing the different gases in states equally dis- tant from their points of condensation, there is reason to believe that the law would be strictly fulfilled. The experiments of MM. Dulong and Petit give for the rate of expansion -f^ of the volume at : this is no doubt too high. Those of Rudburg give T ^ T ; of Magnus T ^ ; and of Regnault ^ : the fraction ^- w is adopted in the test as a convenient number, sufficiently near the mean of the three pre- ceding, to answer all purposes. *0r the amount of expansion is equal to 1492d part of the Tolume the gas occupies at 320F. for each degree of Fahrenheit's scale. On the centigrade scale the expansion is 1-27M part of the bulk at (PC. - R. B. * PoggendorfPfl Aunaleu, iv. 1. Ann. Chim. et Phys., 3rd series, jv 5. and v. 52, 5 HEAT. Fig. 29. 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 pre- vails ; 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 low- est stratum of air, which, becoming expanded, rises, and gives place to another, and in this manner an ascending current is established, the colder and heavier air streaming in late- rally from the more temperate regions, north and south, to supply the partial vacuum thus occasioned. A circulation so commenced will be completed in obedience to the laws of hydro- statics, by the establishment of counter-cur- rents in the higher parts of the atmosphere, having directions the reverse of those on the surface. (Fig. 29.) 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 velo- city diminishes rapidly towards 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 towards the equator, to sup- ply the place of that raised aloft by its dimin- ished density, brings with it the degree of mo- mentum belonging to that portion of the earth's surface from which it set out, and as this momentum is less than that of the earth, under its new position, the earth itself travels faster than the air immediately over it, thus producing the effect of a wind blowing in a contrary direction to that of its own motion. The original north and south winds are thus deviated from their primitive directions, and made to blow more or less from the eastward, so that the combined effects of the unequal heating and of the movement of rotation is to generate in the northern hemi- sphere a constant north-east wind, and in the southern hemisphere an equally constant south-east wind. (Fig. 30.) 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, trans- ferred laterally towards the poles, is soon found to travel faster than the earth beneath it, producing the effect of a westerly wind, which modifies the primary current. The regularity of the trade-winds is much interfered with by the neigh- bourhood of large continents, which produce local effects upon a scale suf- ficiently 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 HEAT. 51 Fig. 31. 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 North- ern 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 hydro- static 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 downwards is the weight of the body added to the weight of the column of water above it ; the force which presses it upwards 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 upwards of the column of water, a c, fig. 31, is no longer compensated by the downward pressure of the corresponding column of solid and water above it ; the former force preponderates, and the body is driven upwards. If, on the contrary, the body be specifically heavier than the water, then the latter force has the ascendancy, and the body sinks. All things so described exist in a common chim- ney ; 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 a b repre- sents the whole atmosphere above it. When the air inside and outside the chimney is at the same temperature, equilibrium takes place, because 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 upwards 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 portion 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 noticed in summer time by the smoke from neighbouring chimneys finding its way into rooms which have been, for a considerable period, without fire. The ventilation of mines has long been conducted upon the same principle c 52 HEAT. 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 rarefying- the air within, and causing an ascending current, occasions fresh air to tra- verse every part of the mine, and sweep before it the noxious gases, but to* frequently present. CONDUCTION OP HEAT. Different bodies possess very different conducting powers with respect to heat: if two similar rods, the one of iron and 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 be taken as a specimen : Gold . . . 1000 Silver ... 973 Copper . . .898 Iron ... 374 Zinc . . .363 Tin ... 304 Lead ... 179 Marble . . .23-6 Porcelain . . 12-2 Fire-clay . . 11-4 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 favourable 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 circulation 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 communi- cated 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 ends of another spiral built into a small furnace at a lower level, and an unintermitting circulation of the liquid takes place as long as heat is applied. CHANGE OF STATE. If equal weights of water at 32 (0C) and water at 174 (78-8C) be mixed, the temperature of the mixture will be the mean of the two temper- atures, or 103 (39-4C). If the same experiment be repeated with snow, or finely powdered ice, at 32 (0C) and water at 174 (78 8C), the tem- perature of the whole will be still only 32 (0C), but the ict will have been wltcd HEAT. 2 Ib. water at 103 (39 -4C) ;32 1 Ib. of water at 32 (0C) \ 1 Ib. of water at 174 (78-8C) J lib. of ice at 32 (0C) \ 1 Ib. of water at 174 (78-8C) j 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 142 (78-8C). The heat, thus become insensible to the thermometer in effecting the lique- faction of the ice, is called latent heat, or, better, head of fluidity. Again, let a perfectly uniform source of heat be imagined, of such inten- sity that a pound of water placed over it would have its temperature raised 10 (5-5C) per minute. Starting with water at 32 (0C), in rather more than 14 minutes its temperature would have risen 142 (78-8) ; but the same quantity of ice at 32 (0C), exposed for the same interval of time, would not have its temperature 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 freezing- point without the formation of ice ; but then, if a little agitation be com- municated to the jar, or a grain of sand dropped into the water, a portion instantly solidifies, and the temperature of the whole rises to 32 (0C) ; 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 10 (5 0t 5C). 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 sulphate of soda 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. Crystal- lization 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. When* ever a solid becomes a liquid, a certain fixed and definite amount of heat disappears, or becomes latent ; and conversely, whenever a liquid becomes a solid, heat to a corresponding extent is given out. The amount of latent heat varies much with different substances, as will be seen by the table : Water l Sulphur Lead . 142 (78-SC) 145 (80 -5C) 162 (90 -5C) Zinc . Tin Bismuth .493 (273-8C) 500 (277 -7C) . 550 (305 -5C) When a solid substance can be made to liquefy by a weak chemical attrac- tion, 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 is plunged into the mass, the mercury sinks to ( 17-7C), while the whole, after a short period, becomes fluid by the attraction between the water and the salt ; such a mixture is very often used MM. De la Provostaye and Regnault, Ann. Chirn. et Pbys., 3d series, viii. 1. 5 * 54 HEAT. in chemical experiments to cool receivers and condense the vapours of vola- tile liquids. Powdered crystallized chloride of calcium and snow produce cold enough to freeze mercury. Even powdered nitrate of potassa, or sal- ammoniac, dissolved in water, occasions a very notable depression of tem- perature ; in every case, in short, in which solution is unaccompanied by energetic chemical action, cold is produced. No relation is to be traced between the actual melting-point of a sub- stance, and its latent heat when in a fused state. 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 accompa- nied by absorption of sensible heat, and the reverse by its disengagement. The latent heat of steam and other vapours may be ascertained by a similar mode of investigation to that employd in the case of water. When water at 32 (0C) is mixed with an equal weight of water at 212 (100C), the whole is found to possess the mean of the two temperatures, or 122 (50C) ; on the other hand, 1 part by weight of steam at 212 (100C) when condensed into cold water, is found to be capable of raising 5-6 parts of the latter from the freezing to the boiling-point, or through a range of 180 (100C). Now 180 X 5-6 = 1008; that is to say, steam at 212 (100C) in becoming water at 212, parts with enough heat to raise a weight of water equal to its own (if it were possible) 1008 (560C) of the ther- mometer. When water passes into steam, the same quantity of sensible heat becomes latent. The vapours of other liquids seem to have less latent heat than that of water ; the following table is by Dr. Ure, and serves well to illustrate this point : Vapour of water 967 (537-2C) alcohol 442 (246 -6C) ether 302 (167 -7C) petroleum 178 (98 -8C) oil of turpentine 178 (98-80) nitric acid 532 (295 -5C) liquor ammonise 837 (145 -OC) vinegar 875 (486 -1C) Ebullition is occasioned by the formation of bubbles of vapour 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 distinguishing liquids which much resemble each other. A few cases may be cited in. illustration : Substance. Boiling-point. Ether 96 (35-5C) Bisulphide of carbon 115 (46 -1C) Alcohol 177 (80 -5C) Water 212 (100 C) Nitric acid, strong 248 (120 C) Oil of turpentine 312 (155 -5C) Sulphuric acid , 620 (326 -2C) Mercury 662 (350 C) For ebullition to take place, it is necessary that the elasticity of the vapour should be able to overcome the cohesion of the liquid and the pressure upon its surface ; hence the extent to which the boiling-point may be modified. Water, under the usual pressure of the atmosphere, boils at 212 (100C) ; HEAT. 55 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 vapour, 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 vapour to an almost un- limited extent; a temperature of 350 (177C) or 400 (204C) 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 illustra- tive of the effect of diminished pressure in depressing the Fig. 32. boiling point of a liquid. A little water is made to boil for a few minutes in a flask or retort (fig. 32) 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 con- siderable time by the affusion of cold water, which, by con- densing the vapour within, occasions a partial vacuum. The nature of the vessel, or rather, the state of its sur- face, 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 1 that by particular management a much greater difference can be observed. If two similar glass flasks be taken, the one coated in the inside with a film of shellac, and the other completely cleansed by hot sulphuric acid, water heated over a lamp in the first will boil at 211 (99-4C), while in the second it will often rise to 221 (105C) or even higher ; a momentary burst of vapour 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 vapour, while the temperature sinks to 212 (100C), and there remains stationary. These remarkable effects must be attributed to an attraction between the surface of the vessel and the liquid. 3 1 Marcet, Ann. Chim. et Phys., 3d series, v. 449. 3 A remarkable modification of the relation between the temperature of liquids and the vessel containing them, results where the repulsive action predominates. When a small quantity of water is thrown into a red-hot platinum crucible, it assumes a spheroidal form, presents no appearance of ebullition, but only a rotary motion, and evaporates very slowly; but when the temperature falls to 300. this spheroidal condition is lost, the liquid boils and is soon dissipated. In the spheroidal state there is no contact between the water and metal, in consequence of the high tension of the small quantity of vapour which is formed and surrounds the globule, but on the fall in temperature, the tension lessens and with it the repulsive action, contact takes place and the heat is rapidly communicated to the liquid, which at once is converted into steam. So slight is the influence of the caloric of the vessel on the contained liquid in this condition, tliat if liquid sulphurous acid be poured on the globule, the water is by the sudden evaporation of the acid converted into ice at the bottom of the red-hot crucible. When a liquid which boils at a low temperature, is thrown on an- other heated nearly to ebullition and whose boiling-point is high, the spheroidal state is likewise assumed, as water on oil, spirits of turpentine, sulphuric acid, &c., and ether on water, &c. As connected with this phenomenon, it has been observed that perfect immunity from the caloric of highly heated liquids may be obtained by previously moistening the part to which the application is made with some fluid which evaporates at a low temperature. Thus the hand, while moistened with ether, may be plunged into boiling-water without even the sen- sation of heat. When wet with water it may be dipped into melted lead without injury or strong sensation of heat, and still less is perceived if alcohol or ether be used. A similar experiment has been performed with melted cast-iron as it runs from the furnace, and the 50 HEAT. 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 water, is affected by heat in precisely the same manner as the permanent gases ; its rate of expansion and increase of elastic force are the same. When water is present, however, this is no longer the case, but on the contrary, the elastic force increases in a far more rapid proportion. This elastic force of steam in contact with water, at different temperatures, has been very carefully determined by MM. Arago and Dulong, and very lately by M. Regnault. The force is expressed in atmospheres ; the abso- lute pressure upon any given surface can be easily calculated, allowing 14-6 Ib. 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 calcula- tions founded on the data so obtained. Pressure of steam Corresponding in atmospheres. temperature. F. C. 1 212 100 1-5 234 112 -2 2 251 121 -2 2-5 264 128 -8 3 275 135 3-5 285 140 -5 4 294 145-5 4-5 300 148 -8 5 308 153 -1 5-5 314 156 -2 6 320 160 6-5 326 163 -1 7 332 166 -2 7-5 337 169 -4 8 342 172 -2 9 351 177 -2 10 359 181 -2 11 367 186 -1 12 374 190 It is a very remarkable fact, that the latent heat of steam diminishes as the temperature of the steam rises, so that equal weights of steam thrown into cold water exhibit nearly the same heating power, although the actual temperature of the one portion may be 212 (100C), and that of the other 350 (176-2C) or 400 (204 -4C). This also appears true with temperatures below the boiling-point; so that it seems, to evaporate a given quantity of water the same absolute amount of heat is required, whether it be performed slowly at the temperature of the air, in a manner presently to be noticed, or whether it be boiled off under the pressure of twenty atmospheres. It is for this reason that the process of distillation in vacuo at a temperature which the hand can bear, so advantageous in other respects, can effect no direct saving in fuel. 1 dry parts subjected to the radiant caloric have been found more affected than that exposed to the melted metal. The immunity in the case of using water as the moistening agent arises from the fact that the temperature of the globule in the spheroidal state is much below the boiling-point of the liquid. R. B. ' The proposition in the text, of the sum of the latent and sensible heats of steam being a constant quantity, is known by the name of Watt's law, having been deduced by that illus- Pressure of steam Corresponding in atmospheres. temperature. P. c. 13 381 194 14 387 197 7 15 393 200 5 16 398 203 1 17 404 206 2 18 409 209 4 19 414 212 2 20 418 214 4 21 423 217 2 22 427 219 4 23 431 221 2 24 436 224 4 25 439 226 1 30 457 236 1 35 473 245 1 40 487 252 7 45 491 255 50 511 266 1 HEAT. 57 Fig. 33. 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 212 (100C), or higher, may be kept up in the pipes or other vessels in which the steam is contained by the expenditure of a vei-y 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 niters and other ob- jects 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. 33), surmounted by a double box or jacket, into which the substance to be dried is put, and loosely covered by a card. The apparatus 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. s ' 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 es- sentially of a cylinder of metal, a (fig. 34), in which works a closely-fitting solid piston, 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 interven- tion of an oscillating beam. A pipe commu- nicates with the interior of the cylinder, and also with a vessel surrounded with cold water, called the condenser, marked b in the sketch, and 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 the cylinder and the condenser, 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 engine itself at the proper moment, so that the piston is al- ternately 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 trious man from experiments of his own. It has always agreed well with the rough practical results obtained by engineers, and has lately been confirmed to a great extent, aHhough not completely, by a series of elaborate experiments by M. Kegnault. DS HEAT. high-pressure 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 steam-ships, 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 country, is now getting 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 duty of raising more than 100,000,000 Ib. of water one foot high by the consumption 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 employed 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 vapour at different tem- peratures, or to part a volatile liquid from a substance incapable of volatili- sation. 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 vapour is raised, and of a condenser, in which it returns to the liquid or solid con- dition. 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 and most generally useful arrangement for distillation on the small scale ; the retort is heated by a lamp or a char- Fig. 35. HEAT. 59 coal fire, and the receiver is kept cool, if necessary, by a wet cloth, or it may be surrounded with ice. (Fig. 35.) Fig. 36 Fig. 37 The condenser of Professor Liebig is a very valuable instru- ment in the laboratory ; it consists of a glass tube (fig. 36), tapering from end to end, fixed by perforated corks in the centre of a metal pipe, provided with tubes so arranged that a current of cold water may circulate through the apparatus. By putting a few pieces of ice into the little cistern, the temperature of this water may be kept at 32 (0C), and extremely volatile liquids condensed. Liquids evaporate at temperatures below their boiling-points ; in this case the evaporation takes place solely from the surface. Water, or alcohol, exposed in an open vessel at the temperature of the air, gradually dries up and disappears ; the more rapidly, the warmer and drier the air above it. This fact was formerly explained by supposing that air and gases in general had the power of dissolving and holding in solution certain quantities of liquids, and that this power in- creased with the temperature ; such an idea is incorrect. If a barometer-tube (fig. 37) 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 account for this depression, it must of necessity be imputed to the vapour which instantaneously rises from the water into the vacuum ; and that this effect is really due to the elasticity or tension of the aqueous vapour, is easily proved by exposing the barometer to a heat of 212 (100C), when the depression of the mercury will be complete, and it will stand at the same level within and without the tube, indicating that at that temper- ature the elasticity of the vapour is equal to that of the atmo- sphere, 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 with water at different temperatures, tLo 60 HEAT. tension of the aqueous vapour for each degree of the thermometer may be accurately determined by its depressing eifect 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 a vacuum, and in this way the tension may be very conve- niently expressed. The following table was drawn up by Dr. Dalton, to "whom we owe the method of investigation. Temperature. F. C. Tension in inches of mercury. 32 ... .... ..... 0-200 40 50 ... 4-4 ... 10 0-263 0-375 60 70 80 90 ... 15-5 ... 21-1 ... 26-6 ... 32-2 0-524 0-721 1-000 1-360 100 110 120 ... 37-7 ... 43-3 ... 48-8 1-860 2-530 3-330 Temperature. Tension in inches F. C. of mercury. 130 ... 54-4 4-34 140 150 160 ... 60 ... 65-5 5-74 7-42 9-46 ... 71-1 170 ... 76-6 12-13 180 ... 82-2 15-15 190 200 212 ... 87-7 ... 93-3 19-00 23-64 30-00 ...100 Fig. 38. Other liquids tried in this manner are found to emit vapours of greater or less tension, for the same temper- ature, 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 vapour until a much greater heat is applied ; and that given off by mercury itself in warm summer weather, although it may by very delicate means be detected, is far too little to exercise any effect upon the barometer. In the case of water, the evapora- tion is quite distinct and perceptible at the lowest tem- peratures, 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 was impossible. There exists for each vapour a state of density which it cannot pass without losing its gaseous condition, and becoming liquid ; this point is called 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 at- tempt to increase the density of this vapour by com- pressing 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 (fig. 38), and the latter slowly sunk into a very deep cistern of mercury, it will be found that the height of the column of mercury in the tube above that in the cistern remains unaltered until the upper extremity of the barometer approaches the surface of the metal in the reservoir. It will be observed also, that, as the tube sinks, the little stratum of liquid ether increases in thick- ness, but no increase of elastic force occurs in the vapour above it, and, consequently, no increase of density; for tension and density are always, under ordinary circum- stances at least, directly proportionate to each other in the same vapour. HEAT. 61 The point of maximum density of a vapour is dependent upon the tem- perature ; it increases rapidly as the temperature rises. This is well shown in the case of water. Thus, taking the specific gravity of atmospheric air at 212 (100C) = 1000, that of aqueous vapour in its greatest possible state of compression for the temperature will be as follows : Temperature. Specific gravity. Weight of 100 cubic inches. F. C. 32 5-690 0-136 grains. 50 10- 10-293 0-247 60 15-5 14-108 0-338 100 37-7 46-500 1-113 150 65-5 170-293 4-076 212 100 625-000 14-962 The last number was experimentally found by M. Gay-Lussac ; the others are calculated upon that by the aid of Dr. Dalton's table of tensions. Thus, there are two distinct methods by which a vapour may be reduced to the liquid form ; pressure, by causing increase of density until the point of maximum density for the particular temperature is reached ; and cold, by which the point of maximum density is itself lowered. The most powerful eifects are of course produced when both are conjoined. For example, if 100 cubic inches of perfectly transparent and gaseous vapour of water at 100 (37-7C), in the state above described, had its tem- perature reduced to 50 (10C), not less than 0-87 l grain of fluid 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 vapour rises, and the condition of max- imum density is assumed in the same manner as if the space were perfectly empty ; the sole difference lies in the length of time required. 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 resistance to the rise of the vapour. 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 vapour will be found to have risen from it as if no gas had been present, the quantity depending entirely on the temper- ature to which the whole is subjected. The tension of this vapour 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. Vapour of water exists in the atmosphere at all times, and in all situa- tions, and there plays a most important part in the economy of nature. The proportion of aqueous vapour present in the air is subject to great variation, and it often becomes exceedingly important to determine its quantity. This >s easily done by the aid of the foregoing principles. If the aqueous vapour 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 vapour of water, the slightest reduction of tempera- ture will cause the deposition of a portion in the liquid form. If, on the contrary, as is almost always in reality the case, the vapour of water be below its state of maximum density, that is, in an expanded condition, 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, 1 100 cubic inches aqueous vapours at 100 (37-7C), weighing 1-113 grain, wruld at 50*" (10C), become reduced to 10'2'J cubic inches, weighing - &47 grain 62 HEAT. 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 tem- perature 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 a deposition of 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 way of example, that the latter were 70 (21-1C), and the dew-point 50 (10C) ; the elasticity of the watery vapour present would correspond to a Maximum density proper to 50 (10C), and would support a column of mercury 0-375 inch high. If the barometer on the spot stood at 30 inches, therefore, 29-625 inches would be supported by the pressure of the dry air, and the remaining 0-375 inch by the vapour. 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 vapour, occupying the same space, and having tensions indicated by the numbers just mentioned. A cubic foot, or 1728 cubic inches of vapour at 70 (21-1C), would become reduced by con- traction, according to the usual law, to 1662-8 cubic inches at 50 (10C) ; this vapour would be at its maximum density, having the specific gravity pointed out in the table ; hence 1662-8 cubic inches would weigh 4-11 grains. The weight of the aqueous vapour contained in a cubic foot of air will thus be ascertained. In England the difference between the temperature of the air and the dew-point seldom reaches 30 ( 1-2C) ; but in the Deccan, with a temperature of 90 (32 -2C), the dew-point has been seen as low as 29 ( 1-6C) making the degree of dryness 61. l Another method of finding the proportion of moisture present in the air is to observe the rapidity with which evaporation takes place, and which is always in some relation to the degree of dryness. The bulb Fig. 39. of a thermometer is covered with muslin, and kept wet with water ; evaporation produces cold, as will presently be seen, and accordingly the thermometer soon sinks below the ac- tual temperature of the air. When it comes to rest, the degree is noticed, and from a comparison of the two tempe- ratures an approximation to the dew-point can be obtained by the aid of a mathematical formula contrived for the pur- pose. This is called the wet-bulb hygrometer ; it is often made in the manner shown in fig. 39, 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 in connexion with the little water reservoir. The perfect resemblance in every respect which vapours 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 extent 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 vapours of volatile liquids in a state very far removed from that of their maximum density. The subjoined table represents the results of Mr. Faraday's first investigations, Mr. Daniell, Introduction to Chemical Philosophy, p. 154. HEAT. 63 with the pressure in atmospheres, and the temperature at which the con- densation took place. 1 Atmospheres. Temperature. P. C. Sulphurous acid 2 45 7-2 Sulphuretted hydrogen 17 50 10 Carbonic acid 36 32 Chlorine 4 60 15-5 Nitrous oxide 50 45 7 -2 Cyanogen 3-6 45 7 -2 Ammonia 6-5 50 10 Hydrochloric acid 40 50 10 The method of proceeding was very simple ; the materials were sealed up in a strong narrow tube (fig. 40), together with a little pressure-gauge, con- Fig. 40. sisting of a slender tube closed at one end, and having within it, near the open extremity, a globule of mercury. The gas being disengaged by the application of heat, or otherwise, accumulated in the tube, and by its own pressure brought about condensation. 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 tem- perature, produced by means to be presently described, olefiant gas, hydri- odic and hydrobromic acids, phosphoretted hydrogen, and the gaseous fluorides of silicon and boron, were successively liquefied. Oxygen, hydro- gen, nitrogen, nitric oxide, carbonic oxide, and coal-gas, refused to liquefy at the temperature of 166 ( 74-4C) while subjected to pressures vary- ing in the different cases from 27 to 58 atmospheres. 3 Sir Isambard Brunei, and, more recently, M. Thilorier, of Paris, suc- ceeded in obtaining liquid carbonic acid in great abundance. The apparatus of M. Thilorier (fig. 41) consists of a pair of extremely strong metallic ves- sels, one of which is destined to serve the purpose 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 are 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 pre- caution taken to prevent leakage under the enormous pressure the vessel has to bear. The receiver resembles the retort in every respect ; it has a similar stop-cock, and is connected with the retort by a strong copper tube and a pair of union screw-joints ; a tube passes from the stop-cock down- wards, and terminates near the bottom of the vessel. The operation is thus conducted : 2f Ib. of bicarbonate of soda, and 6$ 2b. of water at 100 (37-7C), are introduced into the generator; oil of vitriol * Phil. Trans, for 1823, p. 189. 3 Phil. Trans, for 1845, p. 155, to the amount of 1 J Ib. is poured into a copper cylindrical vessel, which is 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 ma- chine 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 mixture is favoured by swinging the whole backwards and forwards for a few mi- nutes, after which it may be suffered to remain a little time at rest. The receiver, surrounded with ice, is next connected to the generator, and both cocks opened ; the liquefied carbonic acid 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 quite ceased, the stop- cock itself unscrewed, and the sulphate of soda turned out. This operation must be repeated five or six times before any very considerable quantity of liquefied acid will have accumulated in the receiver. When the receiver thus charged has its stop-cock opened, a stream of the liquid is forcibly driven up the tube by the elasticity of the gas contained in the upper part of the vessel. It will be quite proper to point out to the experimenter the great personal danger he incurs in using this apparatus, unless the greatest care be taken in its management. A dreadful accident has already occurred in Park by the bursting of one of the iron vessels. The cold produced by evaporation has been already adverted to ; it is simply an effect arising from the conversion of sensible heat into latent by the rising vapour, and it may be illustrated in a variety of ways. A little ether dropped on the hand thus produces the sensation of great cold, and water contained in a thin glass tube, surrounded by a bit of rag, is speedily frozen when the rag is kept wetted with ether. HEAT. 65 Fig. 42. When a little water is put into a watch-glass, (fig. 42), supported by a triangle of wire over a shallow glass dish of sulphuric acid placed on the plate of a good air-pump, the whole covered with a low receiver, and the air with- drawn as perfectly as possible, the water is in a few minutes converted into a solid mass of ice, and the watch-glass very frequently broken by the expansion of the lower portion of water in the act of freezing, a thick crust first forming on the surface. The absence of the impediment of the air, and the rapid absorption of watery vapour by the oil of vitriol, induce such quick evaporation that the water has its tem- perature almost immediately reduced to the freezing-point. The same fact is shown by a beautiful instrument contrived by Dr. Wol- laston, called a cryophorus, or frost-carrier. It is made of glass, of the form represented in fig. 43, and contains a small quantity of water, the rest of the space being vacuous. "When all the water is turned into the bulb, and the empty extremity plunged into a mixture of ice and salt, the solidification of the vapour gives rise to such a quick evaporation from the surface of the water, that the latter freezes. Fig. 43. Fig. 44. All means of producing artificial cold yield to that derived from the poration of the liquefied carbonic acid, just mentioned. When a jet of liquid is allowed to issue into the air from a nar- row aperture, such an intense degree of cold is produced by the vaporization of a part, that the remainder freezes to a solid, and falls in a shower of snow. By suffering this jet of liquid to flow into a metal box provided for the purpose, shown in the drawing of the apparatus (fig. 44), a large quantity of the solid acid may be obtained ; it closely re- sembles snow in appearance, and when held in the hand occasions a painful sensation of cold, while it gradually disappears. Mixed with a little ether, and poured upon a mass of mercury, the latter is almost instantly frozen, and in this way pounds of the solidified metal may be obtained. The addi- tion of the ether facilitates the contact of the car- bonic acid with the mercury. The temperature of a mixture of solid carbonic acid $nd ether in the air, measured by a spirit- thermometer, was found to be 100 ( 76 -6C) ; when the same mixture was placed beneath the receiver of an air-pump, and exhaustion rapidly made, the temperature sank to 166 ( 110C). This was the method of obtaining extreme cold employed by Mr. Faraday in his last experiments on the liquefaction of gases. Under such circum- eva- that 36 HEAT. stances, the liquefied bydriodic, hydrobromic, and sulphurous acid gases, carbonic acid, nitrous oxide, sulphuretted hydrogen, cyanogen, and ammo nia, froze to colourless transparent solids, and alcohol became thick and oily. The principle of the cryophorus has been very happily applied by Mr. Daniell to the construction of a dew-point hygrometer ; fig. 44. It consists of a bent glass tube terminated by two bulbs, one of which is half filled with ether, the whole being vacuous as respects atmospheric air. A delicate ther- mometer is contained in the longer limb, the bulb of which dips into the ether ; a second thermometer on the stand serves to show the actual tempe- rature of the air. The upper bulb is covered with a bit of muslin. When an observation is to be made, the liquid is all transferred to the lower bulb, and ether dropped upon the upper one, until by the cooling effects of evapo- ration a distillation of the contained liquid takes place from one part of the apparatus to the other, by which such a reduction of temperature of the ether is brought about, that dew-is deposited on the outside of the bulb, which is made of black glass in order that it may be more easily seen. The differ- ence of temperature indicated by the two thermometers is then read off. CAPACITY FOR HEAT; SPECIFIC HEAT. Let the reader renew a supposition made when the doctrine of latent heat was under consideration ; let him imagine the existence of an uniform source of heat, and its intensity such as to raise a given weight of water 10 (5-5C) in 30 minutes. If, now, the experiment be repeated with equal weights of mercury and oil, it will be found, that instead of 30 minutes, 1 minute will suffice in the former case, and 15 minutes in the latter. This experiment serves to point out the very important fact, that different bodies have different capacities for heat ; that equal weights of water, oil, and mercury, require, in order to rise through the same range of tempera- ture, quantities of heat in proportion of the numbers 30, 15, and 1. This is often expressed by saying that the specific heat of water is 30 times as great as that of mercury, and the specific heat of oil 15 times as great. Again, if equal weights of water at 100 (37-7C), and oil at 40 (4-4C), be agitated together, the temperature of the whole will be found to be 80 (26 -6C), instead of 70 (21-1C), the mean of the two ; and if the tempera- tures be reversed, that of the mixture will be only 60 (15 -5C). Thus, at 7 : <::$ } * * -'* at 80 < 26 - 6C > Loss by the water, 20 (11-1C). Gai'n by the oil, 40 (22-2C). at 60 15 " 5C at 100 Gain of water, 20 (11-1C). Loss of oil, 40 (22 -2C). This shows the same fact, that water requires twice as much heat as oil to produce the same thermometric effect. There are three distinct methods by which the specific heat of various ubstances may be estimated. The first of these is by observing the quantity f ice melted by a given weight of the substance heated to a particular tem- perature ; the second is by noting the time which the heated body requires to cool down through a certain number of degrees ; and the third is the method of mixture, on the principle illustrated ; this latter method is pre- ferred as the most accurate. The determination of the specific heat of different substances has occupied the attention of many experimenters ; among these MM. Dulong and Petit, and recently M. Regnault, deserve especial mention. It appears that each solid and liquid has its own specific heat ; and it is probable that this, in- HEAT. 67 Btead of being a constant quantity, varies with the temperature. The de- termination of the specific heat of gases is attended with peculiar difficulties 1 on account of the comparatively large volume of small weights of gases. Satisfactory results have however been obtained by the method of mixing for the following gases. SPECIFIC HEAT AT 30 INCHES PRESSURE. Of equal volumes. Of equal weights. Air = l Water =1 Atmospheric air 1 1 0-2669 Oxygen 1 0-8848 0-2361 Hydrogen 1 12-3401 3-2936 Nitrogen 1 1-0318 0-2754 Carbonic oxide 1 1-0805 0-2884 Protoxide of nitrogen ... 1-227 0-8878 0-2369 Carbonic acid 1-249 0-8280 0-2210 Olefiantgas 1-754 1-5763 0-4207 Aqueous vapour 1-960 3-1360 0-8470 1 For the comparison of the specific heat of atmospheric air with that of water, we are indebted to Count Rumford ; for the comparison of the specific heat of the various gases, to Delaroche and Berard. Whenever a gas expands, heat becomes thereby latent. Hence the amount of heat required to raise a gas to a certain temperature increases the more we allow it to expand. Dulong has found that if the amount of heat re- quired to raise the temperature of a volume of gas (observed at the melting point of ice, and at the pressure of 30 inches) to a given height without its volume undergoing any change, be represented by 1, then if the gas is al- lowed to expand until the pressure is reduced again to 30 inches whilst the high temperature is kept up, the additional amount of heat which is required for this purpose is, for oxygen, hydrogen, or nitrogen 0,421 ; for carbonic acid 0,423 ; for binoxide of nitrogen 0,343 ; and for olefiant gas 0,240. If there be no source of heat from which this additional quantity can be obtained, then the gas is cooled during expansion, a portion of the free heat becoming latent. On the other hand, if a gas be compressed, this latent heat becomes free, and causes an elevation of temperature, which, under favourable circumstances, may be raised to ignition; syringes by^ which tinder is kindled are constructed on this principle. In the upper regions of the atmosphere the cold is intense ; snow covers the highest mountain-tops even within the tropics, and this is due to the increased capacity for heat of the expanded air. MM. Dulong and Petit observed in the course of iheir investigation a most remarkable circumstance. If the specific heats of bodies be computed upon equal weights, numbers are obtained, all different, and exhibiting no simple relations among themselves ; but if, instead of equal weights, quantities be taken in the proportion of the chemical equivalents, an almost perfect coin- cidence in the numbers will be observed, showing that some exceedingly in- timate connexion must exist between the relations of bodies to heat and thei* chemical nature ; and when the circumstance is taken into view, that relations of even a still closer kind link together chemical and electrical phenomena, it is not too much to expect that ere long some law may be dis- covered far more general than any with which we are yet acquainted. * The later determinations of Rcgnault vary from the above: thus in equal ^eights, Water = l; Atraospherie air he gives as 0-2377; Oxygen, 0-2182; Nitrogen, 0-2440; and Vapour of Water, 0-4750; and contrary to the results of Gay-Lussac, the specific heat of ait does not vary with the temperature. R. B. 68 HEAT. The following table is extracted from the memoirs of M. Regnault, witn whose results most of the experiments of Dulong and Petit closely coincide Substances. Specific heat of Specific heat of equal weights. equivalent weights. Water 1-00000 Oil of Turpentine 0-42593 Glass 0-19768 Iron 0-11379 3-0928 Zinc 0-09555 3-0872 Copper 0-09515 3-0172 Lead 0-03140 3-2581 Tin 0-05623 3-3121 Nickel 0-10863 3-2176 Cobalt 0-10696 3-1628 Platinum 0-03243 3-2054 Sulphur 0-20259 3-2657 Mercury 0-03332 3-7128 Silver 0-05701 6-1742 Arsenic 0-08140 6-1326 Antimony 0-05077 6-5615 Gold 0-03244 6-4623 Iodine 0-05412 6-8462 Bismuth 0-03084 2-1877 Of the numbers in the second column, the first ten approximate far too closely to each other to be the result of mere accidental coincidence ; the five that follow are very nearly twice as great; and the last is one-third less. 1 Independently of experimental errors, there are many circumstances which tend to show, that, if all modifying causes could be compensated, or their effects allowed for, the law might be rigorously true. The observations thus made upon elementary substances have been ex- tended by M. Regnault to a long series of compounds, and the same curious law found, with the above limitations, to prevail throughout, save in a few isolated cases, of which an explanation can perhaps be given. Except in the case of certain metallic alloys, where the specific heats were the mean of those of their constituent metals, no obvious relation can be traced between the specific heat of the compound body and of its compo- nents. The most general expression of the facts that can be given is the following : In bodies of similar chemical constitution, the specific heats are in an inverse ratio to the equivalent weights, or to a multiple or submultiple of the latter. Simple as well as compound bodies will be comprehended in this law. 3 SOURCES OP 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. : The equivalent of Bismuth being assumed as 71, but adopting 213, the number given under the head of bismuth, the specific heat of an equivalent weight will be 6-5688, or com- jdo with the five preceding. R. B. a Ann. Chim. et Phys. Ixxiii. 5; and the same, 3rd series, i. 129. HEAT. 6& 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 1 (|C) for every 45 feet, or 117 (65C) per mile. On the supposition that the rise continued at the same rate, at the depth of less than two miles the earth 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. 1 According to this idea, the earth must be looked upon as an intensely- heated, fluid spheroid, covered with a crust of solid badly-conducting mat- ter, cooled by radiation into space, and bearing somewhat the same propor- tion in thickness to the ignited liquid within, that the shell of an egg does 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. The smaller, and what may be called secondary, sources of heat, are very numerous ; they may be divided, for the present, into two groups, me- chanical motion and chemical combination. To the first must be referred ele- vation of temperature by friction and blows ; and to the second, the effects of combustion and animal respiration. With regard to the heat developed by friction, it appears to be indefinite in amount, and principally dependent upon the nature of the rubbing surfaces. An experiment of Count Rumford is on record, in which 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 a few ounces only. Sir H. Davy melted two pieces of ice by rubbing them together in vacuo at 32 (0C) ; and uncivilized men, in various parts of the world, have long been known to obtain fire by rubbing together two pieces of dry wood. The origin of the heat in these cases is by no means intelligible. Malleable metals, 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 diminished ; the rise of temperature is thus in some measure explained. 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 original physical state. 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 in all probability fixed and definite ; its intensity is dependent upon the time over which the action is extended. Science has already been en- riched by many admirable, although yet incomplete, researches on this im- portant but most difficult subject. It is not improbable that many of the phenomena of heat, classed at present under different heads, may hereafter be referred to one common cause, namely, alterations in the capacity for heat of the same body under different 1 The new Artesian well at Grenelle, near Paris, has a depth of 1794-5 English feet: itia bored through the chalk basin to the sand beneath ; the work occupied seven years and two months. The temperature of the water, which is exceedingly abundant, is 82 (27'7C) ; th mean temperature of Paris is 51 (10-5C); the difference is 31 (17'2C), which gives a rate of about 10 (|C) for 58 feet. 70 HEAT. physical conditions. For example, the definite absorption and evolution of sensible heat attending change of state may be simply due to the increased capacity for heat, to a fixed and definite amount, of the liquid over the solid, and the vapour over the liquid. The experimental proof of the facts is yet generally wanting ; in the very important case of water, however, the deci- dedly inferior capacity for heat of ice compared with that of liquid water seems fully proved from experiments on record. The heat of combination might perhaps, in like manner, be traced to con- densation of volume, and the diminution of capacity for heat which almost invariably attends condensation. The proof of the proposition in numerous cases would be within the reach of comparatively easy experimental inquiry LIGHT. 71 LIGHT. THE subject of light is so little connected xdth elementary chemistry, that very slight notice of some of the most important points will suffice. Two views have been entertained respecting the nature of light. Sir Isaac Newton imagined that luminous bodies emitted, or shot out, infinitely small particles in straight lines, which, by penetrating the transparent part of the eye and falling upon the nervous tissue, produced vision. Other phi- losophers 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 transmitted with inconceivable velocity through a highly elastic medium, of excessive tenuity, filling all space, and occupying the intervals between the particles of mate- rial substances, to which they gave the name of ether. The wave-hypothesis of light is at present most in favour, as it serves to explain certain singular phenomena, discovered since the time of Newton, with greater facility than the other. 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, at Copenhagen, found that this period appeared to be longer when the earth, in its passage round the sun, was most distant from the planet Jupiter, and, on the contrary, he observed that the periodic time appeared to be shorter when the earth was nearest to Jupiter. The difference, though very small, for a single revolution of the satellite, by the addition of many, so increases, during the passage of the earth from its nearest to its greatest distance from Jupiter, that is, in about half a year, that 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 space 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 the electrical agent. When a ray of light falls on a plane surface it may be disposed of in three ways ; it may be absorbed and disappear altogether ; it may be reflected, or thrown off, according to a particular law ; or it may be partly absorbed, partly reflected, and partly transmitted. The first happens when the surface is perfectly black and destitute of lustre ; the second, when a polished surface of any kind is employed; and the third, when the body upon which the light falls is of the kind called transparent, as glass or water. The law of reflection is extremely simple. If a line be drawn perpendi- cular to the surface upon which the ray falls, and the angle contained between the ray and the perpendicular measured, it will be found that the ray, after reflection, takes such a course as to make with the perpendiculai 72 LIGHT. Fig. 45. Fig. 46. an equal angle on the opposite of the latter. A ray of light, n, fig. 45, falling at the point p, will be reflected in the direction PR/, making the angle K/PP' equal to the angle BPP X ; or a ray from the point r falling upon the same spot will be reflected to r f in virtue of the same law. Farther, it is to be observed, that the incident and reflected rays are always contained in the same vertical 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 become permanently altered in direction when reflected from curved surfaces, becoming divergent or convergent according to the kind of curvature. It has just been stated that light passes in straight lines ; but this is only *rue so long as the medium through which it travels preserves the same density and the same chemical nature ; when this ceases to be the case, the ray of light is bent from its course into a new one, or, in optical lan- guage, is said to be refracted. Let r, fig. 46, be a ray of light falling upon a plate of some trans- parent substance with parallel sides, such as a piece of thick plate glass ; and a its point of contact with the upper surface. The ray, instead of holding a straight course and passing into the glass in the direc- tion 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. 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 refracted from a line perpendicular to the surface of the denser substance : in the former case the angle of incidence is said to be greater than that of refraction ; in the latter, it is said to be less. The amount of refraction, for the same medium, varies with the obliquity with which the ray strikes the surface. When perpendicular to the latter, it passes without change of direction at all ; and in other posi- tions, the refraction increases with the obli- quity. Let R, fig. 47, represent a ray of light fall- ing upon the surface of a mass of plate glass at the point A. From this point let a perpen- dicular be raised and continued into the new medium, and around the same point, as a centre, let a circle be drawn. According to the law just stated, the refraction must be to- wards the perpendicular ; in the direction AB/ for example. Let the lines a a, a r a/, at right angles to the perpendicular, be drawn, and their length compared by means of a scale of equal parts, and noted ; Fig. 47. LIGHT. 73 their length will be in the case supposed in the proportion of 3 to 2. These lines are termed the sines of the angles of incidence and refraction, re- spectively. Now let another ray be taken, such as r ; it is refracted in the same man~ ner to r', the bending being greater from the increased obliquity of the ray ; but what is very remarkable, if the sines of the two new angles of inci- dence and refraction be again compared they will still be found to bear to each other the proportion of 3 to 2. The fact is expressed by saying, that the ratio of the sines of the incidence and refraction is constant for the same medium. The plane of refraction coincides moreover with that of incidence. 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 powers of different bodies is to state the ratio borne by the sine of the angle of refrac- tion to that of incidence, making the former unity : this is called the index of refraction for the substance. Thus, in the case of glass, the index of re- fraction will be 1-5. When this is once known for any particular transparent body, the effect of the latter upon a ray of light entering it, in any position, can be calculated by the aid of the law of sines. Substances. Index of refraction. Tabasheer* 1-10 Ice 1-30 Water 1-34 Fluor spar 1-40 Plate glass 1-50 Rock crystal 1-60 Crysolite 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 When a luminous ray enters a mass of substance differing in refractive power from the air, and whose surfaces are not parallel, it becomes perma- nently deflected from its course and altered in its direction. It is upon this principle that the pro- Fig. 48. perties of prisms and lenses depend. To take an example. Let fig. 48 represent a triangular prism of glass, upon the side of which the ray of light B may be supposed to fall. This ray will of course be refracted in entering the glass towards a line perpendicular to the first surface, and again, from a line perpendicular to the second surface on emerging into the air. The result will be a total change in the direction of the ray. A convex lens is thus enabled to converge rays of light falling upon it, and a concave lens 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 +he electric spark, and of all ordinai'y 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 the shutter, or otherwise (fig. 49), and suffered to fall upon a 1 A siliceous deposit in the joints of the bamboo. 74 glass prism in the manner described above, it will not only be refracted from its straight course, but will be decomposed into a number of coloured rays, which may be received upon a white screen placed behind the prism. When solar light is employed, the colours are extremely brilliant, and spread into 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 experiment of Sir I. Newton, and from it he drew the inference that white light is com- posed of seven primitive colours, the rays of which are differently refran- gible by the same medium, and hence capable of being thus separated. The violet rays are most refrangible, and the red rays least- Sir D. Brewster is disposed to think, that out of Newton's seven primitive colours four are really compound, and formed by the superposition of the three remaining, namely, blue, yellow, and red, which alone deserve the name of primitive. When these three kinds of rays are mixed, or super- imposed, in a certain definite manner, they produce white light, but when one or two of them are in excess, then an effect of colour is perceptible, simple in the first case, and compound in the second. There are, according to this hypothesis, rays of all refrangibilities of each colour, and conse- quently white light in every part of the spectrum, but then they are une- qually distributed ; the blue rays are more numerous near the top, the yel- low towards the middle, and the red at the bottom, the excess of each colour producing its characteristic effect. In the diagram below (fig. 50) the inten- sity of each colour is represented by the height of a curve, and the effects of mixture will be intelligible by a little consideration. BLUB. Fig. 50. YELLOW. RED. SOLAR SPECTRUM. VIOLET. INDIGO. BLUE. GREEN. YELLOW. ORANGE. RED. Bodies of the same mean refractive power do not always equally disperse or spread out the differently coloured rays; because the principal yellow or red rays, for instance, are equally refracted by two prisms of different, ma- terials, it does not follow that the blue or the violet shall be similarly affected. Hence, prisms of different varieties of glass, or other transparent substances, give, under similar circumstances, very different spectra, both LIGHT. 75 as respects the length of the image, and the relative extent of the coloured bands. The colours of natural objects are supposed to result from the power which the surfaces of the bodies possess of absorbing some of the coloured rays, while they reflect or transmit, as the case may be, the remainder. Thus, an object appears red because it absorbs, or causes to disappear, a portion of the yellow and blue rays composing the white light by which it is illuminated. A ray of common light made to pass through certain crystals of a par- ticular order is found to undergo a very remarkable change. It becomes split or divided into two rays, one of which follows the general law of refrac- tion, and 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 carbonate of lime. 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 upon a plate of glass at an angle of 50 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, under the same angle, upon a second glass plate, it will be observed that there are two particular positions of the latter in which the ray ceases to be reflected. 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 condi- tion, and by employing a series of similar plates (fig. 51), held parallel to the first, this effect may be greatly in- creased ; 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 trans- mission in this manner is in an opposite state to that polarized by reflection ; that is, when examined by a second or analyzing plate, held at the angle before men- tioned, it will be seen to be reflected when the other dis- appears, and to be absorbed when the first is reflected. It is not every substance which is capable of polarizing light in this manner ; glass, water, and certain other bo- dies, 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. It is said that both rays are polarized in opposite directions. With a rhomb of transparent Iceland spar of toler- ably large dimensions the two oppositely-polarized rays may be widely sepa- rated and examined apart. There is yet another method of polarization, by the employment of plates of the mineral tourmaline cut parallel to the axis of the crystal. This body polarizes by simple transmission, the ray falling perpendicular to its surface ; a part of the light is absorbed, and the remainder modified in the manner described. When two such plates are held with their axes parallel, as in fig. 52, light traverses them both freely ; but when one of them is turned round in the manner shown in fig. 53, so as to make the axes cross at right angles, the light is almost wholly stopped, if the tourmalines be good. A plate of the mineral thus becomes an excellent test for discriminating be- tween the polarized light and that which has not undergone the change. Some of the most splendid phenomena of the science of light are exhibited 76 LIGHT. Fig. 52. Fig. 53. when thin plates of doubly-refracting substances are interposed between the polarizing arrangement and the analyzer. Instead of the tourmaline plate, which is always coloured, frequent use is made of two Nichol's prisms, or conjoined prisms of carbonate of lime, which, in consequence of a peculiar cutting and combination, possess the property of allowing only one of the oppositely polarized rays to pass. If the two Nichol's prisms are 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 tourmaline plates, when the two prisms cross one another. The phenomenon is the same with colourless as with coloured light. Supposing that polarized light, coloured, for example, by going through a plate of red glass, passed through the first Nichol's prism and was altogether obstructed in consequence of the position of the second prism, then if be- tween the two prisms a plate of rock crystal, formed by a section at right angles to the principal axis of the crystal, is interposed, the light polarized by the first prism by passing through the plate of quartz is enabled par- tially 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 required varies with the thickness of the plate of rock crystal, and also with the colour of the light that is employed. It increases from red in the following order, green, yellow, blue, violet. This property of rock crystal was discovered by Arago. The kind of polarization has been called circular polarization. No other crystals are known to produce the same effect. 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. Biot observed that many solutions of organic substances exhibit the pro- perty of circular polarization, though to a far less extent than rock crystal. Thus, solution of cane-sugar and tartaric acid possess right-handed polari- zation, whilst albumen, grape-sugar, and oil of turpentine, are left-handed. In all these solutions the amount of circular polarization increases with the concentration of the fluid and the thickness of the column of liquid 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 fluid exhibits, the liquid is put into a glass tube not less than from ten to twelve inches long, which is closed with glass plates, one of which should be coloured, red for example. 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 de- scription, the saccharometer, is chiefly used for determining the concentra- tion of solutions of sugar. LIGHT. 77 Faraday has made the remarkable discovery, that if a very strong electric current is passed round a substance which possesses the property of circular polarization, the amount of rotation is altered to a considerable degree. The luminous rays of the sun are accompanied, as already mentioned, by others which possess heating powers. If the temperature of the different coloured spaces in the spectrum be tried with a delicate thermometer, it will be found to increase from the violet to the red extremity, and when the prism is of some particular kinds of glass, the greatest effect will be mani- fest a little beyond the visible red ray. It is inferred from this that the chief mass of the heating rays of the sun are among the least refrangible components of the solar beam. Again, it has long been known that chemical changes both of combination and of decomposition, but more particularly the latter, could be effected by the action of light. Chlorine and hydrogen combine at common tempera- tures only under the influence of light, and parallel cases occur in great numbers in organic chemistry : the blackening and decomposition of salts of silver are familiar instances of the chemical powers of the same agent. Now it is not the luminous part of the ray which effects these changes ; they are produced by certain invisible rays accompanying the others, and which are found most abundantly in and beyond the violet part of the spectrum. It is there that the chemical effects are most marked, although the intensity of the light is exceedingly feeble. The chemical rays are thus directly op- posed to the heating rays in the common spectrum in their degree of refran- gibility, since they exceed all the others in this respect. In the year 1802, 1 Mr. Thomas Wedgwood proposed a method of copying paintings on glass by placing behind them white paper or leather moistened with a solution of nitrate of silver, which became decomposed and blackened by the transmitted light in proportion to the intensity of the latter; and Davy, in repeating these experiments, found that he could thus obtain tole- rably accurate representations of objects of a texture partly opaque and partly transparent, such as leaves and the wings of insects, and even copy with a certain degree of success the images of small objects obtained by the solar microscope. These pictures, however, required to be kept in the dark, and only examined by candle-light, otherwise they became obliterated by the blackening of the whole surface from which the salt of silver could not be removed. These attempts at light-painting attracted but little notice till the publication of Mr. Fox Talbot's 2 papers, read before the Royal Society, in January and February, 1839, in which he detailed two methods of fixing the pictures produced by the action of light on paper impregnated with chloride of silver, and at the same time described a plan by which the sen- sibility of the prepared paper may be increased to the extent required for receiving impressions from the images of the camera obscura. Very shortly afterwards, Sir John Herschel 3 proposed to employ solutions of the alkaline hyposulphites for removing the excess of chloride of silver from the paper, and thus preventing the farther action of light, and this plan has been found exceedingly successful. The greatest improvement, however, which the curious art of photogenic drawing has received, is due to Mr. Talbot, 4 who, in a communication to the Royal Society, described a method by which paper of such sensibility could be prepared as to permit its application to the taking of portraits of living persons by the aid of a good camera obscura, the time required for a perfect impression never ex- ceeding a few minutes. The portraits executed in this manner by Mr. Collen and others are beautiful in the highest degree, and leave little room for improvement in any respect. The process itself is rather complex, anj 1 Journal of the Royal Institution, i. 170. > Phil. Mag. March, 1839 8 Phil. Trans, for 1840, p. 1. phil. Mag. August. W 78 LIGHT. demands a great number of minute precautions, only to be learned by expe- rience, but which are indispensable to perfect success. The general plan is the following : Writing-paper of good quality is washed on one side with a moderately dilute solution of nitrate of silver, and left to dry spontaneously in a dark room ; when dry, it is dipped into a solution of iodide of potassium, and again dried. These operations should be performed by candle-light. When required for use, the paper thus coated with yellow iodide of silver is brushed over with a solution containing nitrate of silver, acetic acid, and gallic acid, and once more carefully dried by gentle warmth. This kalotype paper is so sensitive, that exposure to diffused daylight for one second suffices to make an impression upon it, and even the light of the moon produces the same effect, although a much longer time is required. The images of the camera obscura are at first invisible, but are made to appear in full intensity by once more washing the paper with the above mentioned mixture, and warming it before the fire, when the blackening effect commences and reaches its maximum in a few minutes. The picture is of course negative, the lights and shadows being reversed ; to obtain positive copies nothing more is necessary than to place a piece of ordinary photographic paper prepared with chloride of silver beneath the kalotype impression, cover them with a glass plate, and expose the whole to the light of the sun for a short time. Before this can be done, the kalotype must however be fixed, otherwise it will blacken, and this is effected by im- mersion in a solution of hyposulphite of soda, and well washing with water. Sir John Herschel has shown that a great number of other substances can be employed in these photographic processes by taking advantage of the singular deoxidizing effects of certain portions of the solar rays. Paper washed with a solution of a salt of sesquioxide of iron becomes capable of receiving impressions of this kind, which may afterwards be made evident by ferricyanide of potassium, or terchloride of gold. Vegetable colours are also acted upon in a very curious and apparently definite manner by the different parts of the spectrum. 1 The Daguerreotype, the announcement of which was first made in the summer of 1839 by M. Daguerre, who had been occupied with this subject from 1826, if not earlier, is another remarkable instance of the decomposing effects of the solar rays. A clean and highly-polished plate of silvered copper is exposed for a certain period to the vapour of iodine, and then transported to the camera obscura. In the most improved state of the pro- cess, a very short time suffices for effecting the necessary change in the film of iodide of silver. The picture, however, only becomes visible by exposing it to the vapour of mercury, which attaches itself, in the form of exceed- ingly minute globules, to those parts which have been most acted upon, that is to say, to the lights, the shadows being formed by the dark polish of the metallic plate. Lastly, the drawing is washed with a solution of hyposul- phite of soda to remove the undecomposed iodide of silver, and render it permanent. The images of objects thus produced bear the most minute examination with a magnifying glass, the smallest details being depicted with perfect fidelity. Great improvements have been necessarily made in the application of this beautiful art to taking portraits. By the joint use of bromine and iodine the plates are rendered far more sensitive, and the time of sitting is short- ened to a very few seconds. When the operation is completed the colour of the plate is much improved by the deposition of an exceedingly thin film of gold, which communicates a warm purplish tint, and removes the previous (lull leaden-grey hue, to most persons very offensive. 1 Phil. Trans. 1812, p. 1. RADIATION OF HEAT. 79 RADIATION, REFLECTION, ABSORPTION, AND TRANSMISSION OF HEAT. RADIATION OF HEAT. IF a red-hot ball be placed upon a metallic support, and left to itself, cooling immediately commences, and only stops when the temperature of the ball is reduced to that of the surrounding air. This effect takes place in three ways : heat is conducted away from the ball through the substance of the support; another portion is removed by the convective power of the air ; and the residue is thrown off from the heated body in straight lines or rays, which pass through air without interruption, and become absorbed by the surfaces of neighbouring objects which happen to be presented to their impact. This radiant or radiated heat resembles, in very many respects, ordinary light ; it suffers reflection from polished surfaces according to the same law ; it is absorbed by those that are dull or rough ; it moves with extreme velo- city ; and, finally, it traverses certain transparent media, undergoing refrac- tion at the same time, in obedience to the laws which regulate that pheno- menon in optics. The fact of the reflection of heat may be very easily proved. If a person stand before a fire in such a position that his face may be screened by the mantelshelf, and if he then take a bright piece of metal, as a sheet of tinned plate, and hold it in such a manner that the fire may be seen by reflection, at the same moment a distinct sensation of heat will be felt. The apparatus best fitted for studying these facts consists of a pair of con- cave metallic mirrors of the form called parabolic. The parabola is a curve possessing very peculiar properties, one of the most prominent being the following : A tangent drawn to any part of the curve makes equal angles with two lines, one of which pro- Fig. 54. ceeds from the point where the tangent touches the curve in a direction parallel to what is called the axis of the parabola, and the other from the same spot through a point in front of the curve, called the focus. It results from this that parallel rays, either of light or heat, falling upon a mirror of this particular curva- ture in a direction parallel to the axis of the parabola, will be all reflected to a single point at the focus ; and rays diverging from this focus, and impinging upon the mirror, will, after reflection, become parallel (fig. 54). If two such mirrors be placed opposite to each other at a considerable distance, and so adjusted that their axes shall be coincident, and a hot body placed in the focus of the one, while a thermometer occupies that of the other, the reflec- tion of the rays of heat will become manifest by their effect upon the instru ment. In this manner, with a pair of by no means very perfect mirrors, 18 inches in diameter, separated by an interval of 20 feet or more, amadou or 80 RADIATION OP II EAT. gunpowder may be readily fired by a red-hot ball in the focus of the oppo- site mirror (fig. 55). Fig. 55. The power of radiation varies exceedingly with different bodies, as may be easily proved. If two similar vessels of equal capacity be constructed of thin metal, and the surface of one highly polished, while that of the other is covered with lampblack, and both filled with hot water of the same temperature, and their rate of cooling observed from time to time with a thermometer, it will be constantly found that the blackened vessel loses heat much faster than the one with bright surfaces ; and since both are put on a footing of equality in other respects, this difference, which will often amount to many degrees, must be ascribed to the superior emissive power of the film of soot. By another arrangement, a numerical comparison can be made of these differences. A cubical metallic vessel is prepared, each of whose sides is in a different condition, one being polished, another rough, a third covered with lampblack, &c. This vessel is filled with water, kept constantly at 212 (100C) by a small steam-pipe. Each of its sides is then presented in succession to a good parabolic mirror, having in its focus one of the bulbs of the differential thermometer before described (fig. 22), the bulb itself being blackened. The effect produced on this instrument is taken as a measure of the comparative radiating powers of the different surfaces. The late Sir John Leslie obtained by this method of experiment the follow- ing results : Emissive power. Lampblack 100 Writing-paper 98 Glass 90 Plumbago 75 Emissive power. Tarnished lead 45 Clean lead 19 Polished iron 15 Polished silver 12 The best reflecting surfaces are always the worst radiators ; polished metal reflects nearly all the heat that falls upon it, while its radiating power- is the feeblest of any substance tried, and lampblack, which reflects nothing, radiates most perfectly. The power of absorbing heat is in direct proportion to the power of emis- sion. The polished metal mirror, in the experiment with the red-hot ball, remains quite cold, although only a few inches from the latter ; or, again, if a piece of gold leaf be laid upon paper, and a heated iron held over it 1 The formerly supposed influence of mere difference of surface has been called in question "by M. Melloni, who attributes to other causes the effects observed by Sir John Leslie and others, among which superficial oxidation and difference of physical condition with respect to hardness and density, are among the most important. With metals not subject to tarnish, scratching the surface increases the emissive power when the plates have been rolled or hammered, i. e. are in a compressed state, and diminishes it, on the contrary, when the metal has been cast and carefully polished without burnishing. In the case of ivory, marble, and jet, where compression cannot take place, no difference is perceptible in the radiating power of polished and rough surfaces. Ann. Chim. et Phys. Ixx. 435. RADIATION OF HE^T. 81 until the paper is completely scorched, it will be found that the film of metal lias perfectly defended that portion beneath it. The faculty of absorption seems to be a good deal influenced by colour ; Dr. Franklin found that when pieces of cloth of various colours were placed on snow exposed to the feeble sunshine of winter, the snow beneath them became unequally melted, the effect being always in proportion to the depth of the colour ; and Dr. Stark has since obtained a similar result by a dif- ferent method of experimenting. According to the late researches of Mel- loni, this effect depends less on the colour than on the nature of the colour- ing matter which covers the surface of the cloth. These facts afford an explanation of two very interesting and important natural phenomena, namely, the origin of dew, and the cause of the land and sea-breezes of tropical countries. While the sun remains above the horizon, the heat radiated by the surface of the earth into space is compen- sated by the absorption of the solar beams ; but when the sun sets, and this supply ceases, while the emission of heat goes on as actively as before, the surface becomes cooled until its temperature sinks below that of the air. The air in contact with the earth of course participates in this reduction of temperature ; the aqueous vapour present speedily reaches its point of max- imum density, and then begins to deposit moisture, whose quantity will de- pend upon the proportion of vapour in the atmosphere, and on the extent to which the cooling process has been carried. It is observed that dew is most abundant in a clear calm night, succeeding a hot day ; under these circumstances the quantity of vapour in the air is usually very great, and at the same time, radiation proceeds with most facility. At such times a thermometer laid on the ground will, after some time, indicate a temperature of 10 (5-5C), 15 (8-3C), or even 20 (11-1C) below that of the air a few feet higher. Clouds hinder the formation of dew, by reflecting back to the earth the heat radiated from its surface, and thus preventing the necessary reduction of temperature ; and the same effect is produced by a screen of the thinnest material stretched at a little height above the ground. In this manner gardeners often preserve delicate plants from destruction by the frosts of spring and autumn. The piercing cold felt just before and at sunrise, even in the height of summer, is the consequence of this refrigeration having reached its maximum. Wind also effectually prevents the deposition of dew, by constantly renew- ing the air lying upon the earth before it has had its temperature sufficiently reduced to cause condensation of moisture. Many curious experiments may be made by exposing on the ground at night, bodies which differ in their powers of radiation. If a piece of black cloth and a plate of bright metal be thus treated, the former will often be found in the morning covered with dew, while the latter remains dry. Land and sea-breezes are certain periodical winds common to most sea- coasts within the tropics, but by no means confined to those regions. It is observed, that a few hours after sunrise a breeze springs up at sea, and blows directly on shore, and that its intensity increases as the day advances, and declines and gradually expires near sunset. Shortly after, a wind arises in exactly the opposite direction, namely, from the land towards the sea, lasts the whole of the night, and only ceases with the reappearance of the sun. It is easy to give an explan-ation of these effects. When the sun shines at once upon the surface of the earth and that of the sea, the two become unequally heated from their different absorbing power ; the land becomes much the warmer. The air over the heated surface of the ground, being ex- panded by heat, rises, and has its place supplied by colder air flowing from the sea, producing the sea-breeze. When the sun sets, both sea and land begin to cool by radiation; the rate of the cooling of the latter will, how- 82 TRANSMISSION OP HEAT. ever, far exceed that of the former, and its temperature will rapidly fall. The air above becoming cooled and condensed, flows outwards in obedience to the laws of fluid pressure, and displaces the warmer air of the ocean. In this manner, by an interchange of air between sea and land, the otherwise oppressive heat is moderated, to the great advantage of those who inhabit such localities. The land and sea-breezes extend to a small distance only from shore, but afford, notwithstanding, essential aid to coasting navigation, since vessels on either tack enjoy a fair wind during the greater part of both day and night. TRANSMISSION OP HEAT; DIATHERMANCY. Rays of heat, in passing through air, receive no more obstruction than those of light under similar circumstances ; but with other transparent media the case is different. If a parabolic mirror be taken and its axis directed towards the sun, the rays both of heat and light will be reflected to the focus, which will exhibit a temperature sufficiently high to fuse a piece of metal, or fire a combustible body. If a plate of glass be now placed between the mirror and the sun, the effect will be but little diminished. Now, let the same experiment be made with the heat of a kettle filled with boiling water ; the heat will be concentrated by reflection as before, but, on interposing the glass, the heating effect at the focus will be reduced to nothing. Thus, the rays of heat coming from the sun traverse glass with facility, which is not the case with those emanating from the boiling water. In the year 1833, M. Melloni published the first of a series of exceedingly valuable researches on this subject, which are to be found in detail in various volumes of the Annales de Chemie et de Physique. 1 It will be necessary, in the first instance, to describe the method of operation followed by this philosopher. Not long before, two very remai'kable facts had been Fig. 56. discovered : Oersted, in Copenhagen, showed that a current of electricity, however produced, exercises a singular and perfectly definite action on a magnetic needle; and Seebeck, in Berlin, found that an electric current may be generated by the unequal effects of heat on different metals in contact. If a wire conveying an electrical current be brought near a magnetic needle, the latter will immediately alter its position and assume a new one, as nearly perpendicular to the wire as the mode of suspension and the magnetism of the earth will permit. When the wire, for example, is placed directly over the needle (fig. 56), while the current it carries travels from north to south, the needle is deflected from its ordinary direction and the north pole driven to the eastward. When the current is reversed, the same pole deviates to an equal amount towards the west. Placing the wire below the needle instead of above produces the same effect as reversing the current. When the needle is subjected to the action of two currents in opposite directions, the one above and the other below, Fig. 57. they will obviously concur in their effects. The same thing happens when the wire carry- ing the current is bent upon itself (fig. 57), and the needle .placed between the two por- tions ; and since every time the bending is re- peated, a fresh portion of the current is made to act in the same manner upon the needle, it is easy to see how a current too feeble to pro- duce any effect when a simple straight wire is 1 Translated also in Tayloi's Scientific Memoirs. TRANSMISSION OF HEAT. 83 employed, may be made by this contrivance to exhibit a powerful action on the magnet. It is on this principle that instruments called galvanometers, yalvanoscopes, or multipliers, are constructed , they serve, not only to indicate the existence of electrical currents, but to show by the effect upon the needle the direction in which they are moving. By using a very long coil of wire, and two needles, immovably connected, and hung by a fine filament of silk, almost any degree of sensibility may be communicated to the apparatus. When two pieces of different metals, connected together at each end, have one of their joints more heated than the other, an electric current is imme- diately set up. Of all the metals tried, bismuth and antimony form the most powerful combination. A single pair of bars, having one of their junc- tions heated in the manner shown in fig. 58, can develop a current strong enough to deflect a Fig. 58. compass-needle placed within, and, by ar- ranging a number in a series and heating their alternate ends, the intensity of the current may be very much increased. Such an arrangement is called a thermo-electric pile. M. Melloni constructed a thermo-electric pile of this kind, containing fifty-five slender bars of bismuth and antimony, laid side by side and soldered together at their alternate ends. He connected this pile with an exceedingly delicate multiplier, and found himself in the possession of an in- strument for measuring small variations of temperature far surpassing in delicacy the air-thermometer in its most sensitive form, and having great advantages in other respects over that instrument when employed for the purposes to which he devoted it. The substances whose powers of transmission were to be examined were cut into plates of a determinate thickness, and, after being well polished, arranged in succession in front of the little pile, the extremity of which was blackened to promote the absorption of the rays. (Fig. 59.) A perforated Fig. 59. screen, the area of whose aperture equalled that of the face of the piK was placed between the source of heat and the body under trial, while a second screen served to intercept all radiation until the moment of the ex- periment. After much preliminary labour for the purpose of testing the capabilities, of the apparatus and the value of its indications, an extended series of re- searches was undertaken and carried on during a long period with great success : some of the most curious results are given in the subjoined table. Four different sources of heat were employed in these experiments, dif fering in their degrees of intensity: the naked flame of an oil lamp ; a coU TRANSMISSION OF HEAT. of platinum wire heated to redness ; blackened copper at 734 (390C) ; and the same heated to 212 (100C). Substances. (Thickness of plate 0-1 inch, nearly.) Transmission of 100 rays of heat from A i 11 1| W.3 Pjj *' O l| *f 1 Rock-salt, transparent and colourless 92 78 65 54 46 39 39 38 37 18 11 9 8 8 6 92 69 65 23 38 28 24 28 28 16 2 2 6 92 42 65 13 24 6 6 6 6 3 4 92 33 65 20 3 Rock-salt muddy . Beryl Fluor-spar greenish . Iceland-spar .. , Rock-crystal Rock-crystal brown Tourmaline dark green ... .-. Sugar-candy Fluor-spar green translucent Ice pure and transparent On examining this remarkable table, which is an abstract of one much more extensive, the first thing that strikes the eye is the want of connection between the power of transmitting heat and that of transmitting light ; taking, for instance, the oil-lamp as the source of heat, out of a quantity of heat represented by 100 rays falling upon the pile, the proportion intercepted by similar plates of rock-salt, glass, and alum, may be expressed by the numbers, 8, 61, and 91 ; and yet these bodies are equally transparent with respect to light. Generally speaking, colour was found to interfere with the transmissive power, but to a very unequal extent ; thus, in fluor-spar, colour- less, greenish, and deep-green, the quantities transmitted were 78, 46, and 8, while the difference between colourless and brown rock-crystal was only 1. Bodies absolutely opaque, as wood, metals, and black marble, stopped the rays completely, although it was found that the faculty of transmission was possessed to a certain extent by some which were nearly in that condition, as thick plates of brown quartz, black mica, and black glass. When rays of heat had once passed through a plate of any substance, the interposition of a second similar plate occasioned much less loss than the first ; the same thing happened when a number were interposed ; the rays, after traversing one plate, being but little interrupted by others of a similar nature. The next point to be noticed is the great difference in the properties of the rays from different sources. Out of 100 rays from each source which fell on rock-salt, the same proportion was always transmitted, whether the rays proceeded from the intensely heated flame, the red-hot platinum wire, or the copper at 734 (390C) or 212 (100C) ; but this is true of no other substance in the list. In the case of plate-glass, we have the numbers 39< 24, 6. and 0, as representatives of the comparative quantities of heat trans TRANS MISSION OF HEAT. 85 mitted through the plate from each source ; or in the three varieties of fluor- spar, as below stated : Flame. Red-heat. 734 (390C). 212 (100C). Colourless 78 69 42 33 Greenish 46 38 24 20 Dark green 8 6 4 3 While one substance, beryl, out of 100 rays from an intensely heated source, suffers 54 to pass, and from the same number (that is, an equal quantity of heat) from metal at 212 (100C), none at all; another, fluor- spar, transmits rays from the two sources mentioned, in the proportion of 8 to 3. These, and many other curious phenomena, are fully and completely explained on the supposition, that among the invisible rays of heat differ- ences are to be found exactly analogous to those differences between the rays of light which we are accustomed to call colours. Rock-salt and air are the only substances yet known which are truly diathermanous, or equally transparent to all kinds of heat-rays ; they are to the latter what white glass or water is to light ; they suffer rays of every description to pass with equal facility. All other bodies act like coloured glasses, absorbing certain of the rays more abundantly than the rest, and colouring, as it were, the heat which passes through them. These heat-tints have no direct relation to ordinary colours ; their exist- ence is, nevertheless, almost as clearly made out as that of the coloured rays of the spectrum. Bodies at a comparatively low temperature emit rays of such a tint only as to be transmissible by a few substances ; as the tem- perature rises, .rays of other heat-colours begin to make their appearance, and transmission of some portion of these rays takes place through a greater number of bodies ; while at the temperature of intense ignition we find rays of all colours thrown out, some or other of which will certainly find their way through a great variety of substances. By cutting rock-salt into prisms and lenses, it is easy to show that radiant heat may be reflected like ordinary light, and its beams made to converge or diverge at pleasure ; and, lastly, to complete the analogy, it has been shown to be susceptible of polarization by transmission through plates of doubly-refracting minerals, in the same manner as light itself. 1 1 Dr. Forbes, Phil. Mag. for 1835; also M. Melloni, Ann. Chem. et Phys. Ixy. 5. 86 MAGNETISM. MAGNETISM. A PARTICULAR species of iron ore has long been remarkable for its pro- perty of attracting small pieces of iron, and causing them to adhere to its surface : it is called loadstone, or magnetic iron ore. If a piece of this loadstone be carefully examined, it will be found that the attractive force for particles of iron is greatest at certain particular points of its surface, while elsewhere it is much diminished, or even alto- gether absent. These attractive points, or centres of greatest force, are denominated poles, and the loadstone itself is said to be endued with mag- netic polarity. If one of the poles of a natural loadstone be rubbed in a particular man- ner over a bar of steel, its characteristic properties will be communicated to the bar, which will then be found to attract iron-filings like the loadstone itself. Farther, the attractive force will be greatest at two points situated very near the extremities of the bar, and least of all towards the middle. The bar of steel so treated is said to be magnetised, or to constitute an arti- ficial magnet. When a magnetised bar or natural magnet is suspended at its centre in any convenient manner, so as to be free to move in a horizontal plane, it ia always found to assume a particular direction with regard to the earth, one end pointing nearly north and the other nearly south. If the bar be moved from this position, it will tend to re-assume it, and, after a few oscillations, settle at rest as before. The pole which points towards the astronomical north is usually distinguished as the north pole of the bar, and that which points southward, as the south pole. A suspended magnet, either natural or artificial, of symmetrical form, serves to exhibit certain phenomena of attraction and repulsion in the presence of a second magnet, which deserve particular attention. When a north pole is presented to a south pole, or a south pole to a north, attraction ensues between them ; the ends of the bars approach each other, and, if permitted, adhere with considerable force ; when, on the other hand, a north pole is brought near a second north pole, or a south pole near another south pole, mutual repulsion is observed, and the ends of the bars recede from each other as far as possible. Poles of an opposite name attract, and of a similar name repel each other. Thus, a small bar or needle of steel, properly magnetized and suspended, and having its poles marked, becomes an instrument fitted not only to discover the exist- ence of magnetic power in other bodies, but to estimate the kind of polarity affected by their different parts. A piece of iron brought into the neighbourhood of a magnet acquires itself magnetic properties ; the intensity of the power thus conferred depends upon that of the magnet and upon the interval which divides the two ; be- coming greater as that interval decreases, and greatest of all when in actual contact. The iron under these circumstances is said to be magnetized by induction or influence, and the effect, which in an instant readies its maxi- mum, is at once destroyed by removing the magnet. When steel is substituted for iron in this experiment, the inductive action is hardly perceptible at first, and only becomes manifest after the lapse of a certain time ; in this condition, when the steel bar is removed from the mag- MAGNETISM. 87 net, it retains a portion of the induced polarity. It becomes, indeed, a per- manent magnet, similar to the first, and retains its peculiar properties for an indefinite period. A particular name is given to this resistance which steel always offers in a greater or less degree both to the development of magnetism and its sub- sequent destruction; it is called specific coercive power. The rule which regulates the induction of magnetic polarity in all cases is exceedingly simple, and most important to be remembered. The pole pro- duced is always of the opposite name to that which produced it, a north pole Fi g- 6 . developing south polarity, and a south pole north polarity. The north pole of the magnet, shown in fig. 60, induces south polarity in all the nearer extre- mities of the pieces of iron or steel which surround it, and a state similar to its own in all the more remote extre- mities. The iron thus magnetized is capable of exerting a similar inductive action on a second piece, and that upon a third, and so to a great number, the intensity of the force diminishing as the distance from the permanent mag- net increases. It is in this way that a magnet is enabled to hold up a number of small pieces of iron, or a bunch of filings, each separate piece becoming a magnet for the time by induction. Magnetic polarity, similar to that which iron presents, has been found only in some of the compounds of iron, in nickel, and in cobalt. Magnetic attractions and repulsions are not in the slightest degree inter- fered with by the interposition of substances destitute of magnetic proper- ties. Thick plates of glass, shellac, metals, wood, or of any substances except those above mentioned, may be placed between a magnet and a sus- pended needle, or a piece of iron under its influence, the distance being pre- served, without the least perceptible alteration in its attractive power, or force of induction. One kind of polarity cannot be exhibited without the other. In other words, a magnetic pole cannot be insulated. If a magnetized bar of steel be broken at its neutral point, or in the middle, each of the broken ends ac- quires an opposite pole, so that both portions of the bar become perfect magnets ; and, if the division be carried still farther, if the bar be broken into a hundred pieces, each fragment will be a complete magnet, having its own north and south poles. This experiment serves to show very clearly that the apparent polarity of the bar is the consequence of the polarity of each individual particle, the poles of the bar being merely points through which the resultants of all these forces pass : the large magnet is made up of an immense number of little magnets regularly arranged side by side (fig. 61), all having their north Fig. 61. ILJiUHUB 88 MAGNETISM. poles looking one way, and their south poles the other. The middle portion of such a system cannot possibly exhibit attractive or repulsive effects on an external body, because each pole is in close juxta-position with one of an opposite name and of equal power ; hence their forces will be exerted in op- posite directions and neutralize each other's influence. Such will not be the case at the extremities of the bar ; there uncompensated polarity will be found capable of exerting its specific power. This idea of regular polarization of particles of matter in virtue of a pair of opposite and equal forces, is not confined to magnetic phenomena ; it is the leading principle in electrical science, and is constantly reproduced in some form or other in every discussion involving the consideration of mole- cular forces. Artificial steel magnets are made in a great variety of forms; such as small light needles, mounted with an agate cap for suspension upon a fine point ; straight bars of various kinds ; bars curved into the shape of a horse- shoe, &c. All these have regular polarity communicated to them by cer- tain processes of rubbing or touching with another magnet, which require care, but are not otherwise difficult of execution. When great power is wished for, a number of bars may be screwed together, with their similar ends in contact, and in this way it is easy to construct permanent steel mag- nets capable of sustaining great weights. To prevent the gradual destruc- tion of magnetic force, which would otherwise occur, it is usual to arm each pole with a piece of soft iron or keeper, which, becoming magnetized by in- duction, serves to sustain the polarity of the bar, and even increases in sonm cases its energy. The direction spontaneously assumed by a suspended needle indicates that the earth itself has the properties of an enormous magnet, whose south pole is in the northern hemisphere. A line joining the two poles of such a needle or bar indicates the direction of the magnetic meridian of the place, which is a vertical plane coincident with the direction of the needle. The magnetic meridian of a place is not usually coincident with its geo- graphical meridian, but makes with the latter a certain angle called the de- clination of the needle ; in other words, the magnetic poles are not situated within the line of the axis of rotation. The amount of this declination of the needle from the true north and south not only varies at different places, but in the same place is subject to daily, yearly, and secular fluctuations, which are called the variations of declination. Thus, at the commencement of the 17th century, the declina- tion was eastward ; in 1660, it was ; that is, the needle pointed due north and south. Afterwards it became westerly, slowly increasing until the year 1818, when it reached 24 30', since which time it has been slowly di- minishing. If a steel bar be supported on a horizontal axis passing exactly through its centre of gravity, it will of course remain equally balanced in any posi- tion in which it may happen to be placed ; if the bar so adjusted be then magnetized, it will be found to take a permanent direction, the north pole being downwards, and the bar making an angle of about 70, with a hori- zontal plane passing through the axis. This is called the dip, or inclination of the needle, and shows the direction in which the force of terrestrial mag- netism is most energetically exerted. The amount of this dip is different in different latitudes ; near the equator it is very small, the needle remaining nearly or quite horizontal ; as the latitude increases the dip becomes more decided ; and over the magnetic pole the bar becomes completely vertical. Such a situation is in fact to be found in the northern hemisphere, consider- ably to the westward of the geographical pole, in Prince Regent's Inlet, lat. 70 & N. and longitude 96 46' W. ; the dipping-needle has here been MAGNETISM. 89 seen to point directly downwards, while the horizontal or compass-needle ceased to traverse. The position of the south magnetic pole has lately been determined, by the observations of Captain Ross, to be about lat. 73 S. and long. 130E. By observing a great number of points near the equator in which the dip becomes reduced to nothing, a line may be traced around the earth, called the magnetic equator, and nearly parallel to this, on both sides, a number of smaller circles, called lines of equal dip. These lines present great irreg- ularities when compared with the equator itself and the parallels of lati- tude, the magnetic equator deviating from the terrestrial one as much as 12 at its point of greatest divergence. Like the horizontal declination, the dip is also subject to change at the same place. Observations have not yet been made during sufficient time to determine accurately the law and rate of alte- ration, and great practical difficulties exist also in the construction of the instruments. In the year 1773 it was about 72 ; at the present time it is near 69 & in London. The inductive power of the magnetism of the earth may be shown by holding in a vertical position a bar of very soft iron ; the lower end will be found to possess north polarity, and the upper, the contrary state. On re- versing the bar the poles are also reversed. All masses of iron whatever, when examined by a suspended needle, will be found in a state of magnetic polarity by the influence of the earth ; iron columns, tools in a smith's shop, fire-irons, and other like objects, are all usually magnetic, and those made of steel permanently so. On board ship, the presence of so many large masses of iron, guns, anchors, water-tanks, c., thus polarized by the earth, causes a derangement of the compass-needles to a very dangerous extent ; happily, a plan has been devised for determining the amount of this local attraction in diiferent positions of the ship, and making suitable corrections. The mariner's compass, which is nothing more than a suspended needle attached to a circular card marked with the points, was not in general use in Europe before the year 1300, although the Chinese have had it from very early antiquity. Its value to the navigator is now very much increased by correct observations of the exact amount of the declination in various parts of the world. Probably every substance in the world contributes something to the mag- netic action of the earth ; for, according to the latest discoveries of Mr. Faraday, magnetism is not peculiar to those substances which have more especially been called magnetic, such as iron, nickel, cobalt, but it is the property of all matter, though to a much smaller degree. Very powerful magnets are required to show this remarkable fact. Large horse-shoe mag- nets, made by the action of the electric current, are most proper. The magnetic action on different substances which are capable of being easily moved, diifers not only according to the size, but also according to the nature of the substance. In consequence of this, Faraday divides all bodies into two classes. He calls the one magnetic, or, better, paramagnetic, and the other diamagnetic. The matter of which a paramagnetic (magnetic) body consists is attracted by both poles of the horse-shoe magnet ; on the contrary, the matter of a diamagnetic body is repelled. When a small iron bar is hung by untwisted silk between the poles of the magnet, so that its long diameter can easily move in a horizontal plane, it arranges itself axially, that is, parallel to the straight line which joins the poles, or to the magnetic axis of the poles; assuming at the end which is nearest the north pole, a south pole, and at the end nearest the south pole, a north pole. Whenever the little bar is removed from this position, after a few oscillations, it returns again to its previous position. The whole class of paramagnetic bodies behave in a pre- 8 * 90 MAGNETISM. cisely similar way under similar circumstances ; only in the intensity of the effects great differences occur. On the contrary, diamagnetic bodies have their long diameters placed equatorially, that is, at right angles to the magnetic axis. They behave, as if at the end opposite to each pole of the magnet, the same kind of polarity existed. In the first class of substances, besides iron, which is the best representa- tive of the elass, we have nickel, cobalt, manganese, chromium, cerium, titanium, palladium, platinum, osmium, aluminium, oxygen, and also most of the compounds of these bodies ; most of them, even when in solution. According to Faraday, the following substances are also feebly paramagnetic (magnetic) ; paper, sealing-wax, indian-ink, porcelain, asbestos, fluor-spar, minium, cinnabar, binoxide of lead, sulphate of zinc, tourmaline, graphite, and charcoal. In the second class are placed bismuth, antimony, zinc, tin, cadmium, sodium, mercury, lead, silver, copper, gold, arsenic, uranium, rhodium, iridium, tungsten, phosphorus, iodine, sulphur, chlorine, hydrogen, and many of their compounds. Also, glass free from iron, water, alcohol, ether, nitric acid, hydrochloric acid, resin, wax, olive oil, oil of turpentine, caoutchouc, sugar, starch, gum, and wood. These are diamagnetic. If diamagnetic and paramagnetic bodies are combined, their peculiar pro- perties are destroyed. In most of these compounds, occasionally, in conse- quence of the presence of the smallest quantity of iron, the peculiar mag- netic power remains more or less in excess. Thus green bottle glass and many varieties of crown glass are magnetic in consequence of the iron in them. In order to examine the magnetic properties of fluids they are placed in very thin glass tubes, the ends of which are closed by melting, they are then hung horizontally between the poles of the magnet. Under the influence of poles sufficiently powerful, they begin to swing, and accord- ing as the fluid contents are paramagnetic (magnetic), or diamagnetic, they assume an axial or equatorial position. Under certain circumstances substances which belong to the paramagnetic class behave as if they were diamagnetic. This happens in consequence of a differential action. Thus, for example, when a glass tube full of a dilute solution of sulphate of iron is allowed to swing in a concentrated solution of sulphate of iron, instead of in the air, it assumes an equatorial position. The air, in consequence of the oxygen in it, is itself paramagnetic (magnetic). Hence such bodies as appear to possess feeble diamagnetic properties, can only show their true properties when hung in a vacuum. Faraday has tried the magnetic condition of gases in different ways. One way consisted in making soap bubbles with the gas which he wished to in- vestigate, and bringing these near the poles. Soap and water alone is feebly diamagnetic. A bubble filled with oxygen was strongly attracted by the magnet. All other gases in the air are diamagnetic, that is, they are re- pelled. But, as Faraday has shown, in a different way, this partly arises from the paramagnetic (magnetic) property of the air. Thus he found that nitrogen, when this differential action was eliminated, was perfectly indif- ferent, whether it was condensed or rarified, whether cooled or heated. When the temperature is raised, the diamagnetic property of gases in the air is increased. Hence the flame of a candle or of hydrogen is strongly' repelled by the magnet. Even warm air is diamagnetic in cold air. For some time it has been believed that bodies in a crystalline form had a special and peculiar behaviour when placed between the poles of a magnet. [t appeared as though the magnetic directing power of the crystal had some peculiar relation to the position of its optic axis ; so that, independently of the magnetic property of the substance of the crystal, if the crystal was MAGNETISM. 91 positively optical, it possessed the power of placing its optic axis parallel with the line which joined the poles of the magnet, while optically negative crystals tried to arrange their axes at right angles to this line. This suppo- sition is disproved by the excellent investigation of Knoblauch and Tyndall. It follows from their observations that the peculiarity in regard to crystals is dependent on their internal state of cohesion, that is, on unequal com- pression in different directions. If crystalline, or even uncrystalline sub- stances are unequally compressed in different directions, they are found to possess a preponderating directive force in the direction in which they are most strongly compressed, so that when this direction does not coincide with the long diameter of the body, magnetic bodies will even arrange themselves equatorially, and diamagnetic bodies axially. ELECTRICITY. ELECTRICITY. IF glass, amber, or sealing-wax, be rubbed with a dry cloth, it acquires the power of attracting light bodies, as feathers, dust, or bits of paper ; this is the result of a new and peculiar condition of the body rubbed, called elec- trical excitation. If a light downy feather be suspended by a thread of white silk, and a dry glass tube, excited by rubbing, be presented to it, the feather will be strongly attracted to the tube, adhere to its surface for a few seconds, and then fall off. If the tube be now excited anew, and presented to the feather, the latter will be strongly repelled. The same experiment may be repeated with shellac or resin ; the feather in its ordinary state will be drawn towards the excited body, and after touching, again driven from it with a certain degree of force. Now, let the feather be brought into contact with the excited glass, so as to be repelled by that substance, and let a piece of excited sealing-wax be presented to it ; a degree of attraction will be observed far exceeding that exhibited when the feather is in its ordinary state. Or, again, let the feather be made repulsive for sealing-wax, and then the excited glass be presented ; strong attraction will ensue. The reader Avill at once see the perfect parallelism between the effects described and some of the phenomena of magnetism ; the electrical excite- ment having a twofold nature, like the opposite polarities of the magnet. A body to which one kind of excitement has been communicated is attracted by another body in the opposite state, and repelled by one in the same state. The excited glass and resin being to each other as the north and south poles of a pair of magnetized bars. To distinguish these two different forms of excitement, terms are em- ployed, which, although originating in some measure in theoretical views of the nature of the electrical disturbance, may be understood by the student as purely arbitrary and distinctive ; it is customary to call the electricity manifested by glass positive or vitreous, and that developed in the case of shellac, and bodies of the same class, negative or resinous. The kind of elec- tricity depends in some measure upon the nature of the surface ; smooth glass rubbed with silk or wool becomes ordinarily positive, but when ground or roughened by sand or emery, it acquires, under the same circumstances, a negative charge. The repulsion shown by bodies in the same electrical state is taken advan- tage of to construct instruments for indicating electrical excitement and pointing out its kind. Two balls of alder-pith (fig. 62), hung by threads or very fine metal wires, serve this purpose in many cases ; they open out when excited, in virtue of their mutual repulsion, and show by the degree of diver- gence the extent to which the excitement has been carried. A pair of gold leaves suspended beneath a bell jar, and communicating with a metal cap above (fig. 63), constitute a much more delicate arrangement, and one of great value in all electrical investigations. These instruments are called electroscopes or electrometers ; when excited by the communication of a known kind of electricity, they show, by an increased or diminished diver- gence, the state of an electrified body brought into their neighbourhood. ELECTRICITY. 93 Fig. 62. Fig. 63. One kind of electricity can no more be developed without the other than one kind of magnetism ; the rubber and the body rubbed always assume opposite states, and the positive condition on the surface of a mass of matter is invariably accompanied by a negative state in all surrounding bodies. The induction of magnetism in soft iron has its exact counterpart in elec- tricity ; a body already electrified disturbs or polarizes the particles of all surrounding substances in the same manner and according to the same law, inducing a state opposite to its own in the nearer portions, and a similar state in the more remote parts. A series of globes suspended by silk threads, in the manner represented in fig. 64, will each become electric by induction Fig. 64. when a charged body is brought near the end of the series, like so many pieces of iron in the vicinity of a magnet, the positive half of each globe looking in one and the same direction, and the negative half in the opposite one. The positive and negative signs are intended to represent the states. The intensity of the induced electrical disturbance diminishes with the distance from the charged body ; if this be removed or discharged, all the effects cease at once. So far, the greatest resemblance may be traced between these two sets of phenomena ; but here it seems in great measure to cease. The magnetic polarity of a piece of steel can awaken polarity in a second piece in contact with it by the act of induction, and in so doing loses nothing whatever of its power ; this is an effect completely different from the apparent transfer or discharge of electricity constantly witnessed, which in the air and in liquids often give rise to the appearance of a bright spark of fire. Indeed, ordinary magnetic effects comprise two groups of phenomena only, those namely of attraction and repulsion, and 'those of induction. But in elec- tricity, in addition to phenomena very closely resembling these, we have the effects of discharge, to which there is nothing analogous in magnetism, and which takes place in an instant when any electrified body is put in commu 94 ELECTRICITY. nicatioa with the earth by any one of the class of substances called con- ductors of electricity ; all signs of electrical disturbance then ceasing. These conductors of electricity, which thus permit discharge to take place through their mass, are contrasted with another class of substances called non-conductors or insulators. The difference, however, is only one of degree, not of kind ; the very best conductors offer a certain resistance to the elec- trical discharge, and the most perfect insulators permit it to a small extent. The metals are by far the best conductors ; glass, silk, shellac, and dry gas, or vapour of any sort, the very worst ; and between these there are bodies of all degrees of conducting power. Electrical discharges take place silently and without disturbance in good conductors of sufficient size. But if the charge be very intense, and the conductor yery small or imperfect from its nature, it is often destroyed with violence. When a break is made in a conductor employed in effecting the discharge of a highly-excited body, disruptive or spark-discharge, so well known, takes place across the intervening air, provided the ends of the conductor be not too distant. The electrical spark itself presents many points of interest in the modifications to which it is liable. The time of transit of the electrical wave through a chain of good conduct- ing bodies of great length is so minute as to be altogether inappreciable to ordinary means of observation. Professor Wheatstone's very ingenious ex- periments on the subject give, in the instance of motion through a copper wire, a velocity approaching that of light. Electrical excitation is apparent only upon the surfaces of bodies, or those portions directed towards other objects capable of assuming the opposite state. An insulated ball charged with positive electricity, and placed in the centre of the room, is maintained in that state by the inductive action of the walls of the apartment, which immediately become negatively electrified ; in the interior of the ball there is absolutely no electricity to be found, although it may be constructed of open metal gauze, with meshes half an inch wide. Even on the surface the distribution of electrical force will not always be the same; it will depend upon the figure of the body itself, and its position with regard to surrounding objects. The polarity will always be highest in the projecting extremities of the same conducting mass, and greatest of all when these are attenuated to points, in which case the inequality becomes so great that discharge takes place to the air, and the excited condition cannot be maintained. The construction and use of the common electrical machine, and other pieces of apparatus of great practical utility, will, by the aid of these prin- ciples, become intelligible. A glass cylinder (fig. 65) is mounted with its axis in a horizontal position, and provided with a handle or winch by which it may be turned. A leather cushion is made to press by a spring against one side of the cylinder, while a large metal conducting body, armed with a number of points next the glass, occupies the other ; both cushion and conductor are insulated by glass supports, and to the upper edge of the former a piece of silk is attached long enough to reach half round the cylinder. Upon the cushion is spread a quantity of a soft amalgam of tin, zinc, and mercury, 1 mixed up with a little grease ; this substance is found by experience to excite glass most powerfully. The cylinder, as it turns, thus becomes charged by friction against the rubber, and as quickly discharged by the row of points attached to the great conductor ; and as the latter is also completely insulated, its surface speedily acquires a charge of positive electricity, which may be 1 Part tin, 2 zinc, and 6 mercury. ELECTRICITY. Fig. 65. 93 communicated by contact to other insulated bodies. The maximum effect is produced when the rubber is connected by a chain or wire with the earth. If negative electricity be wanted, the rubber must be insulated and the con- ductor discharged. Another form of the electrical machine consists of a circular plate of glass (fig. 66) moving upon an axis, and provided with two pairs of cushions or Fig. 66. 96 ELECTRICITY. or rubbers, attached to the upper and lower parts of the wooden frame, covered with amalgam, between which the plate moves with considerable friction. An insulated conductor, armed as before with points, discharges the plate as it turns, the rubbers being at the same time connected 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 insu- lation. The rubbers also must be carefully dried before use, and the amal- gam renewed if needful ; 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 indirectly 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 which 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 fluid which the conductor receives from the ma- chine must especially accumulate at that spot to which another good con- ductor 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 con- nection with the earth, is placed opposite to it, we have an arrangement 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 nega- tive condition of the other, must be increased to a very considerable 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 Fig. 67. much greater difficulty, even when the plate of insulating matter is very thin. It is on this principle that instru- ments for the accumulation of electricity depend, among which the Leyden jar is the most important. A thin glass jar (fig. 67) is coated on both sides with tin- foil, care being taken to leave several inches of the upper part uncovered ; a wire, terminating in a metallic knob, communicates with the internal coating ; when the outside 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 posi- tive and negative, until a very great degree of intensity has been attained. On completing the connection between the two coatings by a metallic wire or rod, discharge oc- curs in the form of an exceedingly bright spark, accom- panied by a loud snap ; and if the body be interposed in the circuit, the peculiar and disagreeable sensation of the electric shock is felt at the mo- ment of its completion. By enlarging the dimensions of the jar, or by connecting together a number 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 shattered, many com- bustible substances set on fire, and all the well-known effects of lightning exhibited upon a small scale. ELECTRICITY. 97 T"ie electric spark is often very conveniently employed in chemical inqui- ries for firing gaseous mixtures in close 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. This is by the use of the electrophorus. A round tray or dish of tinned plate is ri S- 68 prepared (fig. 68), having a stout wire , } round its upper edge ; the width may be about twelve inches, and the depth half an 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 insulating handle. When a spark is wanted, the resinous plate is excited by striking with a dry, warm piece of fur, or a silk handkerchief; the cover is placed upon it, and touched by the finger. 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 poirits, sparks may be drawn as often as may be wished. It is not known to what cause the disturbance of the electrical equilibrium 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 maxi- mum 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 repre- sent the two coatings, and the intervening air the bad-conducting body or dielectric. The polarities of the opposed surface and of the insulating 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. W T hen these are capable of con- ducting 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 precautions 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 inge- nious plan for the purpose, which is now adopted, with tLe most complete success, in the British Navy. W r hen two solid conducting bodies are plunged into a liquid which acts upon them unequally, the electric equilibi'ium is also disturbed, the one ac- quiring the positive condition, and the other the negative. Thus, pieces of zinc and platinum put into dilute sulphuric acid, constitute an arrangement capable of generating electrical force ; the zinc being the metal attacked, becomes negative; and the platinum remaining unaltered, assumes the posi- tive 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, s r.d as these successive charges and discharges take place through the fluid and metals with inconceivable rapidity, the result is an apparently continuous notion, to which the term electrical current is given. It is necessary to guard against the idea which the term naturally suggests, 9 ELECTRICITY. of an actual bodily transfer of something through the substance of the con- ductors, like water through a pipe; the real nature of all these phenomena is entirely unknown, and may perhaps remain so ; the expression is conve- nient 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 elec- troscope ; but, by arranging a number of such alternations in a connected 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 instruments in- vented by Volta, called the pile, and crown of cups, depend upon this principle. Upon a plate of zinc (fig. 69) 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 plate of inactive metal, until a pile of about twenty alternations has been built up. If the two terminal plates be now touched with wet hands, the sensation of the electric shock will be experienced; but, unlike the momentary effect produced by the discharge of a jar, the sensation will be prolonged and continuous, 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 en- during 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 glasses (fig. 70) are arranged in a row or circle, each containing a piece of active and Tig. 70. piece of inactive metal, and a portion of exciting liquid ; zinc, copper, 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 alternations are concerned, the term " compound circuit" i npplied ; they are called also, indifferently, voltaic batteries. In every fo"j# of such ELEC.TRICITY. 99 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 pro- pagated through the liquid to the inactive conductor, and thence back again by the connecting wire, these extremities of the battery being always re- spectively negative and positive when the apparatus is insulated. In common parlance, 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 communica- tion; 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 arroAVS. 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 (fig. 71), which thus becomes divided into a series of Fig. 71. cells or compartments capable of receiving the exciting liquid. This appa- ratus 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 suffices to prepare it for use. The crown of cups was also put into a much more manageable form by Dr. Babington, and still farther 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 bat- teries, of which a description will be found towards the middle of this volume. The term " galvanism," sometimes applied to this branch of electrical science, is used in honour 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 instrument 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, inequality of temperature and conducting power in different metals placed 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. Two or three 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 apparatus 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. Although the fact that electricity is capable, under certain circumstances, both of inducing and of destroying magnetism, has long been known, from 100 ELECTRICITY. the effects of lightning on the compass-needle and upon small steel articles, as knives and forks, to which polarity lias suddenly been given by the stroke, it was not until 1819 that the laws of these phenomena were discovered by Professor (Ersted, of Copenhagen, and shortly afterwards fully developed by M. Ampere. The action which a current of electricity, from whatever source proceed- ing, 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 which is exerted in a direction perpendicular at once to that of the current, and to the line joining the pole arid the wire. Both poles of the magnet being thus acted upon at the same time, and in contrary 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 any way removed. This curious angular mo- tion may even be shown by suspending a magnet in such a way that one only of its poles shall be subjected to the current; a permanent 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 moveable con- nections 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 direction 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 north pole will be in the direction of the hands. Qr a little piece of apparatus (fig. 72) may be used if reference is Fig. 72. often requhed ; 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 latter 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, 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, and by 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 with their poles op- posed, 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, ELECTRICITY. 101 than one alone would be, all the actions of every part of the coil being strictly ..'oncui-rent. 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 arrangement is shown in fig. 73. Fig. 73. Fig. 74. The action between the pole and the wire is mutual, as may be shown by rendering the wire itself moveable and placing a magnet in its vicinity: on completing the circuit, the wire will be put in motion, and, if the arrange- ment permits, 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 magnetized 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 variety of arrangements, among which it will be sufficient to cite the beautiful little apparatus of Professor de la Rive. A short wide glass tube (fig. 74) is fixed into a cork ring of considerable size ; a little voltaic battery, consisting of a single pair of copper and zinc plates, is fitted to the tube, and to these the endg 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 mag- net held near it in the most perfect manner, as long as the current circu - lates. 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 of the poles. This effect is prodigiously increased by causing the current to circulate a number of times round the bar, which then acquires extraordi- nary magnetic power. A piece of soft iron, worked into the form of a horse- shoe (fig. 75), and surrounded by a coil of copper wire covered with silk or cotton for the purpose of insulation, furnishes an excellent illustration of the inductive energy of the current in this respect; when the ends of the 102 ELECTRICITY. Fig. 75. wire are put into communication 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. A current of electricity can thus develop magnetism in a transverse direction to its own ; in the same man- ner, 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 mo- mentary 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 os- cillations to a state of rest. On removing the magnet, 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. 76 represents a very powerful arrangement of this kind. Fig. 76. When two covereu 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 connexion 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 cur- rent. 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 ELECTRICITY. 103 turns of the coil ; when the circuit is closed, the first is moving in the oppo- site 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, is made and broken in rapid succession, we can increase in a remarkable manner the effects which are produced at the moment of breaking the circuit either at the place of interruption such as the spark-discharges ; or in secondary closing-con- ductors, such as the action on the nerves or the decomposition of water. M. Ampere discovered in the course of his investigations a number of extremely interesting phenomena resulting from the action of electrical cur- rents 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 were made to approach each other, strong attraction took place between them, and when in opposite directions, an equally strong repulsion. These effects, which are not difficult to demon- strate, have absolutely no relation that can be traced to ordinary electrical attractions and repulsions, from which they must be carefully distinguished ; they are purely dynamic, having to do with electricity in motion. M. Ampere founded upon this discovery a most beautiful and ingenious hypo- thesis of magnetic actions in general, which explains very clearly the influ- ence of the current upon the needle. The electricity exhibited under certain peculiar circumstances by a jet of steam, first observed by mere accident, but since closely investigated by Mr. Armstrong, and also by Mr. Faraday, is now referred to the friction, not of the pure steam itself, but of particles of condensed water, against the inte- rior of the exit-tube. It is very doubtful whether mere evaporation can cause electrical disturbance, 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 con- structed 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, c&teris 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. PART II. CHEMISTRY OF ELEMENTARY BODIES. THE term element or elementary substance is applied in chemistry to those forms or modifications of matter which have hitherto resisted all attempts to decompose them. Nothing is ever meant to be affirmed concerning 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 pos- sessed by science, many of the substances which now figure as elements may possibly be shown to be compounds ; this has already happened, and may again take place. The elementary bodies, at present recognised, amount to sixty-two in number ; of these, about forty-seven 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, although very con- venient 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 arid least numerous division. The elements are named as in the subjoined table, which, however, does not indicate the order in which they will be discussed. Non-metallic Elements. Oxygen Hydrogen Nitrogen Chlorine Iodine Bromine Fluorine Carbon Silicon Boron Sulphur Selenium Phosphorus Elements of interme- diate characters. Arsenic Telluriunc Metals. Antimony Gold Chromium Aluminium Vanadium Beryllium Tungsten (or Glucinum) (or Wolfram) Zirconium Molybdenum Norium Tantalum Thorium (or Columbium) Yttrium Niobium Cerium Pelopium Erbium Titanium Terbium Uranium Lantanum Platinum Didymium Palladium Bismuth Rhodium Tin Iridium Mercury Ruthenium Silver Osmium Lead Barium Strontium Calcium Magnesium Zinc Cadmium Nickel Cobalt Copper Iron Manganese Lithium Sodium Potassium (104) OXYGEN. 105 OXYGEN. Whatever plan of classification, founded on the natural relations of the elements, be adopted, in the practical study of chemistry, it will always be found most advantageous 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 dcphlogisticated air. The name oxygen l was given to it by Lavoisier some time afterwards. Oxygen exists in a free and uncom- bined state in the atmosphere, mingled with another gaseous body, nitrogen : no good direct means exist, however, for separating it from the latter, and, accordingly, it is always obtained for purposes of experiment by decom- posing 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 to- gether the mercury and the oxygen is so feeble, that simple exposure to heat suffices to bring about decomposition. The red precipitate is placed 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 the figure. 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 pneu- matic 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 pressure of the atmosphere, and entrance of air is prevented. When 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, Fig. 77. 1 From o|i> f> acid, and ywvddi, I give rise to. OXYGEN. it may be removed, still keeping its mouth below the water-level, and an- other substituted. The whole arrangement is shown in fig. 77. The experiment 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 por- tion of the salt called chlorate of potassa. 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 chloride of potassium. This plan, which is very easy of execution, is always adopted when very pure gas is required for analytical purpose. 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 oxide of manganese of commerce, which under these circumstances suffers decomposition, although not to the extent manifest in the red precipitate. If a little of the black oxide of manganese be finely powdered and mixed with chlorate of potassa, and this 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 obvious part in the change brought about. Whatever method be chosen and the same remark applies to the collec- tion 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 at- mospheric air of the apparatus. The practical management of gases is a point of great importance to the chemical student, and one with which ho must endeavour 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 sen- sibly 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 the same in depth, to admit the extremity of the delivery-tube beneath the jar, which stands securely upon the shelf. Fig. 78. OXYGEN. 107 Fig. 79. When the pneumatic trough is required of tolerably large dimensions, it maj with great advantage have the form and disposition represented in the cu\ (fig. 78) ; one end of the groove spoken of, which crosses the shelf or shallow portion, is shown at a. Gases are transferred from jar to jar with the utmost facility, by firsi 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 be- neath 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 found to be prevented. Ajar wholly or partially filled with gas at the pneumatic trough may b removed by placing beneath it a shallow basin, or even a common plate (fig. 79), so as to carry away enough water to cover the edge of the jar; and gas, 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 to blad- ders 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 manoeuvre, 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 some 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 (fig. 80), surmounted by a shallow trough or cistern, the communication be- tween the two being made by a couple of tubes, a b, furnished with cocks, fh, one of which passes nearly to the bottom of the drum, as shown in the sectional sketch. A short wide open tube, c, is inserted obliquely near the bottom of the vessel, into which a plug may be tightly screwed. A stop-cock, g, near the top, serves to transfer gas to a bladder or tube apparatus. A glass water- guage, de, affixed to the side of the drum, and communicating with both top and bot- tom, indicates the level of the liquid within. To use the gas-holder, the plug is first to be 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-leaknge occur, the escape of water is inconsidur- Fig. 80. 108 OXYGEN. able. 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 rise without hin- drance 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 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. Oi opening the cock of the neighbouring tube, the hydrostatic pressure of tl> i column of water will cause condensation 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 difficulty. Oxygen, when free or uncombined, is only known in the gaseous state, all attempts to reduce it to the liquid or solid condition by cold and pressure having completely failed. It is, when pure, colourless, 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 splendour 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 re- lighted 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 goodness 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 ajar 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 good gas, exhibits a most beautiful appearance of combustion. If the experiment be made in ajar standing on a plate, the fused globules of black oxide of iron 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 splendour which the eye is unable to support. In these and many other similar cases which might be mentioned, the same ultimate effect is produced as in atmospheric air; the action is, however, 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 ani- mals is an effect of the same nature as common combustion. The blood con- tains 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, which is usually taken as the standard of unity of specific gravity among gases. Its specific gravity is expressed by the number 1-1057; l 100 cubic inches at 60 (15-5C). and under the mean pressure of the atmosphere, that is, 30 inches of mercury, weigh 34-29 grains. It has been already remarked, that to determine with the last 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 * Dumas, Ann. China, et Phys., 3d series, iii. 275. OXYGEN. 100 methods -which may be adopted for this purpose ; the one below described appears, on the whole, to be the simplest and best. It requires, however, the most scrupulous care, and the observance of a number of minute pre- cautions, 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 convenient, and again weighed. Lastly, it is to be filled with dry air, the temperature and pres- sure 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 moist- ened 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 advantage, since by opening the stop-cock for a single instant when the globe has attained an equilibrium of temperature, the tension becomes exactly that of the air, so that all barometrical correction is avoided, unless the pressure of the atmosphere should sensibly vary during the time occupied by the expe- riment. It is hardly necessary to remark, that the greatest care must also be taken to purify arid 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 correction, or at least to diminish almost to nothing the errors involved by such a process. 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 rela- tions, potassa, soda, or the oxide of silver or of lead ; these are denominated alkaline or basic oxides, or sometimes salifiable bases. The oxides of the second group have properties exactly opposed to those of the bodies men- tioned ; oil of vitriol and phosphoric acid may be taken as the types or repre- sentatives of the class : they are called acids, and tend strongly to unite with the basic oxides. When this happens, what is called a salt is generated as sulphate of potassa, or phosphate of silver, each of these substances be- ing compounded of a pair of oxides, one of which is highly basic and the other highly acid. Then there remains a third g-roup of what may be termed neutral .oxides, from their little disposition to enter into combination. The black oxide of manganese, already mentioned, is an excellent example. It very frequently happens that a body is capable of uniting with oxygen in several proportions, forming a series of oxides, to which it is necessary to give distinguishing names. The rule in such cases is very simple, at least when the oxides of the metals are concerned. In such a series it is always found that one out of the number has a strongly-marked basic character ; to this the term protoxide is given. The compounds next succeeding receive the names of llnoxide or dent 'oxide, teroxide or tritoxide, &c., from the Latin or Greek numerals, the different grades of oxidation being thus indicated. If 110 HYDROGEN. tlier<* be a compound between the protoxide and binoxide, the name oxict-i is usually applied. So it is usual to call the highest oxide, not having distinctly acid characters, peroxide, from the Latin prefix, signifying excess. Any compound containing less oxygen than the protoxide, is called a sub- oxide. Superoxide or hyper oxide are words sometimes used instead of per- oxide. Ozone. It has long been known that dry oxygen, or atmospheric air, when exposed to the passage of a series of electric sparks, emits a peculiar and somewhat metallic odour. The same odour may be imparted to moist oxygen, by allowing phosphorus to remain for some time in it. A more accurate examination of this odorous air has shown that, in addition to the smell, it assumes several properties not exhibited by pure oxygen. One of its most curious effects is the liberation of iodine from iodide of potassium. The oxygen thus altered has been the subject of many researches lately, particularly by Prof. Schoenbein, of Basel, who proposed the name of ozone 1 for it. The true nature of ozone, however, is still unknown, most probably it is a peculiar modification of oxygen. HYDROGEN. Hydrogen is always obtained for experimental purposes by deoxidizing water, of which it forms the characteristic component. 2 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 vapour 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. When zinc is put into water, chemical action of the liquid upon the metal is imperceptible ; but if a little sulphuric acid be added, decomposition of the water ensues, the oxygen unites with the zinc, forming oxide of zinc, which is instantly dissolved by the acid, while the hydrogen, previously in union with the oxygen, is disengaged in the gaseous form. The reaction is represented in the subjoined diagram. Water {Hydrogen Free. \ Oxygen __^^ Zinc ' oxide of zinc Sulphate of Sulphuric acid /oxide of zinc It is not easy to explain the fact of the ready decomposition of water by zinc, in presence of an acid or other substance which can unite with the oxide so produced ; it is, however, a kind of reaction of very common oc- currence in chemistry. The simplest method of preparing the gas is the following. A wide-necked bottle is chosen, and fitted with a sound cork (fig. 81), perforated by two holes for the reception of a small tube-funnel reaching 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 evolution of gas is easily regulated by the supply of acid, and when enough has been dis- charged to expel the air of the vessel, it may be collected over water into a jar, or passed into a gas-holder. In the absence of zinc, filings of iron or araall nails may be used, but with less advantage. 1 From o>, I smell. 4 Ilence the name, from C^op, water, and ytvvdu. HYDROGEN. Ill Fig. 81. 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, pur- chased by weight of the maker, 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 gpirit-lamp, or even a candle or gas-jet. Corks may be perforated by a heated wire, and the hole rendered smooth and cylindrical by a round iile, or the in- genious cork-borer of Dr. Mohr, now to be had of most 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 colourless, tasteless, and inodorous, when quite pure. To obtain it in this condition, it must be prepared from the purest zinc that can be obtained, and passed in succession through solutions of potassa and nitrate of silver. When prepared from commercial zinc, it has a slight smell, which is due to impurity, and when iron has been used, the odoxir becomes very strong and disagreeable. It is inflammable, burning when kindled with a pale yellowish flame, and 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 pro- perties, it is incapable of sustaining life. In point of specific gravity, hydrogen is the lightest substance known; Dumas and Boussingault place its density between 0-0691 and 0-0695 ; * hence 100 cubic inches will weigh, under ordinary circumstances of pressure and temperature, 2-14 grains. When a gas is much lighter or much heavier than atmospheric air, it may often be collected and examined without the aid of the pneumatic trough. A bottle or narrow t iar may be filled with hydrogen without much admixture of air, by inverting it over the extremity of an upright tube delivering the gas (fig. 82). 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 stopper or glass plate. If the mouth of the jar be wide, it must be partially closed by a piece of card- board during the operation. This method of collecting gases by displacement is often extremely useful. Hydrogen was for- merly used for filling air-balloons, being made for the purpose 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 employing a high temperature in the manufacture. Although far inferior to pure hydrogen in buoyant power, it is found in practice to possess advan- tages over that substance, while its greater density is easily compensated by increasing the magnitude of the balloon. 1 Ann. China, et Plays. 3d. series, viii. vfl)l. Fig. 82. 112 HYDROGEN. There is a very remarkable property enjoyed by gases and vapours 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, these will be found, at the expira- tion of a certain period, depending much upon the narrowness of the tube and its length, uniformly mixed, even though the gases differ greatly in density, and the system has been arranged in a vertical position, with the heaviest 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 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 riot pass through narrow orifices with the same degree of facility. Professor Graham, to whom we are indebted for a very valuable investigation 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 Fig. 83. other half with oxygen, the two gases will penetrate the diaphragm at very different rates : four cubic inches of hy- drogen will pass into the oxygen side, while one cubic inca of oxygen travels in the opposite direction. The densities 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, or 4 to 1. By making the diaphragm of some flexible material, as a piece of membrane, the accumulation of the lighter gas on the side of the heavier may be rendered evident by the bulging of the membrane. The simplest and most striking method of making the experiment is by the use of Profes~ sor Graham's diffusion-tube (fig. 83). This is merely a piece of wide glass tube ten or twelve inches in length, 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 great 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 an uniform state, and the accumulation of poisonous gases and exhalations in towns and other confined localities prevented. A distinction must be carefully drawn between rcnl diffusion through small apertures, and the apparently similar passage of gas through wet or moist membranes and other substances, which is really due to temporary liquefac- tion or solution of the gas, and is an effect completely different from diffu- sion, properly so called. For exampb, the diffusive power of carbonic acid HYDROGEN. 113 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 be rendered explosive. 1 It has been stated, that, although the light emitted by the flame of pure hydrogen is exceedingly feeble, yet the temperature of the flame is very high. This temperature may be' still farther exalted by previously mixing the hydrogen with as much oxygen as it requires for combination, that is, as will presently be seen, exactly half its volume. Such a mixture burns like gunpowder, independently of the external air. When raised to the requisite temperature for combination, the two gases unite with explosive 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 precautions, a mixture of oxygen and hydrogen can be burned at a jet without communi- cation 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 only take place 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 phy- sical characters from that of a simple jet of hydrogen or any other combustible gas ; it is long and pointed, and very re- markable in appearance. The safety-jet of Mr. Hemming, the construction of which involves a principle not yet discussed, may be adapted to a com- mon bladder containing the mixture, and held under the arm, and the gas forced through the jet by a little pressure. Although the jet, properly constructed, is believed to be safe, it is best to use nothing stronger than a bladder, for fear of injury in the event of an explosion. The gases are often con- tained in separate 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 pecu- liar 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. 84). 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 steel file burns with the utmost brilliancy, throwing off showers of beautiful sparks ; an in- Fig. 84. 1 Professor Graham hns since published a very extensive scries of researches on the pas- Page of gases through narrow tubes, which will be found i a detail in the Philosophical Trau BCtions tor lo4o. p. 5^3. 10* 114 HYDROGEN. combustible oxidized body, as magnesia or lime, becomes so intensely ig- nited, as to glow with a light insupportable to the eye, and to be susceptible of employment as a most powerful illuminator, as a substitute 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 hydro- Fig. 85. g en (fig. 5^ 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 temperatures for any length of time without combination taking place, yet, under particular circumstances, they unite quietly and without explosion. Some 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 had the same property, provided their surfaces were absolutely clean. Neither is the effect strictly confined to platinum ; other metals, as palladium and gold, and even stones and glass, enjoy the same property, although 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 hydro- gen standing over water, combination of the two gases immediately begins, and the level of the water rapidly rises, the platinum becoming so hot, that drops of water accidentally falling upon it enter into ebullition. If the metal be very thin and exceedingly clean, and the gases very pure, then 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 preceding quiet combination of the two bodies. When the platinum is reduced to a state of division, and its surface thereby much extended, it becomes immediately red-hot in a mixture of hydrogen and oxygen, or hydrogen and air ; a jet of hydrogen thrown upon a little of the spongy metal, contained in a glass or capsule, becomes at once kindled, and on this principle machines for the production of instantaneous light have been constructed. These, however, only act well when constantly used ; the spongy platinum 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 pro- perty of condensing gases upon their surfaces, and that this faculty is enjoyed pre-eminently 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 tem- porary increase of density, whereupon combination ensues. Coal-gas and ether or alcohol vapour may be made to exhibit the phenome- non of quiet oxidation under the influence of this remarkable surface-action. 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. 115 A very pleasing experiment may be made by attaching such a coil ot wire to a card, and suspending it in a glass containing a few drops of ether (fig. 86), having previously made it red-hot in the flame of a spirit-lamp. The wire continues to glow until the Fig. 86. oxygen of the air is exhausted, giving rise to the pro- duction of an irritating vapour 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, Blow combustion of the spirit drawn up by the capillarity of the wick will take place, accompanied by the pungent vapours 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 beside the metals. The great discrepancy in physical properties is perhaps more apparent than real. Hydrogen is yet unknown in the solid condition, while, on the other hand, the vapour of the metal mercury is as transparent and colourless as hydrogen itself. This vapour 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 binoxide of hydrogen. It appears that the composition of water was first demonstrated in the year 1781, by Mr. Cavendish, 1 but the discovery of the exact proportions in which oxygen and hydrogen unite in generating that most important corn-- 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 compound 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 general application than the second, but in this particular instance both may be employed, although the results of the synthesis are most valuable. The most elegant example of analysis of water would probably be foun I in its decomposition 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 ; oxygen, in a state of perfect purity, is evolved from the water in contact with the plate belonging to the copper end of the battery, and hydrogen, equally pure, is disengaged at the plate connected with the zinc extremity, the middle portions of liquid remaining apparently unaltered By placing small graduated jars over the platinum plates, the gases can be * A claim to the discovery of the composition of water on behalf of Mr. James Watt, ha* been very strongly ur^ed, 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 zimulta- ne msly, and unknown to each other. 116 HYDROGEN. Fig. 87. Fig. 88. collected, and their quantities determined. Fig. 87 will show at a glance the whole arrangement ; the conducting wires pass through the bottom of the glass cup, and thence to the battery. When this experiment has been con- tinued 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 lately shown, is likewise decomposed into its constituents by heat. The effect is produced by intro- ducing platinum balls, ignited by electricity or other means, into water or steam. The two gases are, however, 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 filled with mercury, and exploded by the electric spark, all the mixture disappears, and the mercury is forced up into the tube, filling it completely. The same experiment may be made with the explosion-vessel or eudiometer of Mr. Caven- dish. (Fig. 88.) 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-cftck be then opened under water, the latter will rush in and fill the vessel, leaving merely a bubble of air, the result of an imperfect exhaustion. The process upon which most reliance is placed is that in which pure oxide of copper is reduced at a red heat by hy- drogen, and the water so formed collected and weighed. This oxide suffers no change by heat alone, but the momentary contact of hydrogen, or any common combustible matter at a high tem- perature, suffices to reduce a corresponding portion to the metallic state. Fig. 89 will serve to convey some idea of the arrangement adopted in re- searches of this kind. Fig. 89. A copious supply of hydrogen is procured by the action of dilute sul- phuric acid upon the purest zinc that can be obtained ; the gas is made to pass in succession through solutions of silver and strong caustic potassa, by which its purification is completed. After this, it is conducted through a HYDROGEN. 1] * tube Iliroe or four foet in length, filled with fragments of pumice-stone steeped in concentrated oil of vitriol, or with anhydrous phosphoric acid. These substances have such an extraordinary attraction for aqueous vapour, 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 appa- ratus containing the oxide of copper, represented at b; this consists of a two-necked flask of very hard white glass, maintained at a red heat by a spirit-lamp placed beneath. As the decomposition proceeds, the water pro- duced by the reduction of the oxide begins to condense 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 vapour by the cur- rent of gas which passes in excess. Before the experiment can be commenced, the oxide of copper, the purity of which is well ascertained, must be heated to redness for some time in a current of dry air ; it is then suifered to cool, and very carefully weighed with the 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 slowly applied to the oxide. The action is at first very energetic ; the oxide often exhibits the appearance of ignition ; as the decomposition proceeds, it becomes more sluggish, and requires the application of a good deal of 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 re-weighed. The loss of the oxide of copper gives the oxygen ; the gain of the receiver and its dry- ing-tube indicates the water, and the difference between the two, the hy- drogen. A set of experiments, made in Paris in the year 1820, 1 by MM. Dulong and Bcrzelius, 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. Quite recently the subject has been re-investigated by M. Dumas, 2 with the most scrupulous precision, and the above supposition fully confirmed. The composition of water may therefore be considered as established: it contains by weight 8 parts oxygen to 1 part hydrogen, and by measure, 1 volume oxygen to 2 volume* hydrogen. The densities of the gases, as al- ready mentioned, correspond very closely with these results. The physical properties of water are too well known to need lengthened description ; it is, when pure, colourless and transparent, destitute of taste and odour, and an exceedingly bad conductor of electricity of low tension. It attains its greatest density towards 40 (4-5C), freezes at 32 (0C), and boils under the pressure of the atmosphere at or near 212 (100C). It evaporates at all temperatures. One cubic inch at 62 (16-7C) weighs 252-45 grains. It is 815 times heavier than air; an imperial gallon weighs 70,000 grains or 10 lb. avoirdupois. To all ordinary observation, water is incompressible ; very accurate experiments have nevertheless shown that it does yield to a small extent when the power employed is very great ; the diminution of volume for each atmosphere of pressure being about 51-rnil- lionths of the whole. Clear water, although colourless in small bulk, is blue like the atmosphere when viewed in mass. This is seen in the deep ultramarine tint of the ocean, and perhaps in a still more beautiful manner in the lakes of Switzerland and other Alpine countries, and in the rivers which issue from them ;. the elightest admixture of mud or suspended impurity destroying the effect. * Ann. Chhu. et Phys. xv. 3SG. a Ann. China, et Phys. 3rd series, viii. 18ft 118 HYDROGEN. The same magnificent colour is visible in the fisstircs und caverns found in the ice of the glaciers, -which is usually extremely pure and transparent within, although foul upon the surface. Steam, or vapour of water, in its state of greatest density at 212 (100C), compared with air at the same temperature, and possessing an equal elastic force, has a specific gravity expressed by the fraction of 0-625. In this con- dition, it may be represented as containing, in every two volumes, two volumes of hydrogen, and one volume of oxygen. 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 filtration through a porous stone or a bed of sand will separate suspended impurities, but dis- tillation alone will free the liquid from those that are dissolved. In the pre- paration of distilled water, which is an article of large consumption 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 con- ducted 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, 1 of Brighton, the water being that of the Channel: 1000 grains contained Water 964-745 Chloride of sodium 27-059 Chloride of potassium 0-766 Chloride of magnesium 3-666 Bromide of magnesium 0-029 Sulphate of magnesia 2-296 Sulphate of lime 1-406 Carbonate of lime 0-033 Traces of iodine and ammoniacal salt 1000-000 Its specific gravity was found to be 1-0274 at 60 (15-5C). Sea- water is liable to variations of density and composition by the influence 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 sub- stances derived from the rocks they traverse ; such are the various mineral waters scattered over the whole earth, and to which medicinal virtues nre attributed. Some of these hold protoxide of iron in solution, and are effer- vescent from carbonic acid gas ; others are alkaline, probably from traver- sing 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 pro- duction of a hydrate of that base. Sometimes the attraction between the Phil. Mag. July, 1839. HYDROGEN. 119 water and the second body is so great that the compound is not decomposable by any heat that can be applied ; the hydrates of potassa and soda, and of phosphoric acid, furnish examples. Oil of vitriol is a hydrate of sulphuric acid, from which the water cannot be thus separated. Water very frequently combines with saline substances in a less intimate manner than that above described, constituting what is called water of crys- tallization, from its connexion with the geometrical figure of the salt. In this case it is easily driven off by the application of heat. Lastly, the solvent propei-ties 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 excep- tions to this law, one of the most remarkable of which is common salt, the solubility of which is nearly the same at all temperatures ; the hydrate and certain organic salts of lime, also, dissolve more freely in cold than in hot water. Water dissolves gases, but in very unequal quantities ; some, as hydrogen, oxygen, and atmospheric air, are but little acted upon; others, as ammonia and hydrochloric acid, are absorbed to an enormous extent ; and between these extremes there are various intermediate degrees. Generally, the colder the water, the more gas does it dissolve ; a boiling heat disengages the whole, if the gas be not very soluble. 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. Tui'ner inclosed in the upper part of a high-pressure steam-boiler, worked at 300 (149C), pieces of plate and crown glass. At the expiration 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 stalac- tites of siliceous matter, above an inch in length, depended from the little wire cage which inclosed the glass. This experiment tends to illustrate the changes which may be produced by the action of water at a high tempe- rature in the interior of the earth upon felspathic and other rocks. Some- thing of the sort is manifest in the Geyser springs of Iceland, which deposit siliceous sinter. 1 Binoxide of hydrogen, sometimes called oxygenated water, is an exceedingly interesting substance, but unfortunately very difficult of preparation. It is formed by dissolving the binoxide of barium in dilute hydrochloric acid, carefully cooled by ice, and then precipitating the baryta by sulphuric acid ; the excess of oxygen of the binoxide, instead of being disengaged as gas, unites with a portion of the water, and converts it into binoxide of hydrogen. This treatment is repeated with the same solution and fresh portions of the binoxide of barium until a considerable quantity of the latter has been con- sumed, and a corresponding amount of binoxide of hydrogen formed. The liquid yet contains hydrochloric acid, to get rid of which it is treated in suc- cession with sulphate of silver and baryta-water. The whole process re- quires the utmost care and attention. The binoxide of barium itself is pre- pared by exposing pure baryta, contained in a red-hot porcelain tube, to a stream of oxygen. The solution of binoxide of hydrogen may be concen- trated under the air-pump receiver until it acquires the specific gravity of 1-45. In this state it presents the aspect of a colourless, transparent, ino- dorous 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 212 (100C) it is decomposed with ex.. 1 Phil. Mag. Oct. 1834. 120 NITROGEN. plosive violence. Binoxide of hydrogen contains exactly twice as much xygen as water, or 16 parts to 1 part of hydrogen. NITROGEN. Nitrogen' constitutes about four-fifths of the atmosphere, and enters into a great variety of combinations. It may be prepared for the purpose of expe- riment by several methods. One of the simplest of these is to burn out the oxygen from a confined portion of air, by phosphorus, or by a jet of hy- drogen. A small porcelain capsule is floated on the water of the pneumatic trough, and a piece of phosphorus placed in it and set on fire. Fig. 90. (Fig. 90.) A bell-jar is then inverted over the whole, and suifered to rest on the shelf of the 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 bub- bles are expelled, after which the level of the water rises considerably. When the phosphorus becomes extinguished by exhaustion of the oxygen, and time has been given for the subsidence of the cloud of finely- divided, snow-like phosphoric acid, which floats in the residual gas, the nitrogen may be decanted into ano- ther vessel, and its .properties examined. Prepared by the foregoing process, nitrogen is con- taminated by a little vapour of phosphorus, which communicates its peculiar odour. A preferable me- thod is to fill a porcelain tube with turnings of copper, or, still better, with the spongy metal obtained by reducing the oxide by hydrogen ; to heat this tube to redness, and then pass through it a stream of atmospheric air, the oxygen of which is entirely removed during its pro- gress 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 chlo- rine combines with the hydrogen, and the nitrogen is set free with efferves- cence. In this manner very pure nitrogen can be obtained. In making this experiment, 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 formed by the contact of chlorine with an ammoniacal salt. Nitrogen is destitute of colour, taste, and smell ; it is a little lighter than air, its density being, according to Dumas, 0-972. 100 cubic inches, at 60 (15-5C), and 30 inches barometer, will therefore weigh 30-14 grains. Nitro- gen is incapable of sustaining combustion or animal existence, although, like hydrogen, 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 charac- terized by negative properties. The exact composition of the atmosphere has repeatedly been made the nibject of experimental research. Besides nitrogen and oxygen, the air Contains a little carbonic acid, a very variable proportion of aqueous vapour, n trace of ammonia, and, perhaps, a little carburetted hydrogen. The oxygen and nitrogen are in a state of mixture, not of combination, 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 a balloon; it hns been collected and examined in London and Paris, and many other districts ; still the proper- 1 i. e. Generator of nitre; also called azote, from a, priv.itive, and 0)7), life. NITROGEN. 121 tions of oxygen and nitrogen remain unaltered, the diffusive energy of the gases being adequate to maintain this perfect uniformity of mixture. The carbonic acid, on the contrary, being much influenced by local causes, varies considerably. In the following table the proportion of oxygen and nitrogen are given on the authority of M. Dumas, and the carbonic acid on that of De Saussure ; the ammonia, the discovery of which is due to Liebig, is too email in quantity for direct estimation. Composition of the Atmosphere. By weight. By measure. 77 parts 79-19 Nitrogen Oxygen . 23 " 20-81 100 100-00 Fig. 91. Carbonic acid, from 3-7 measures to 6-2 measures, in 10,000 measures of air. Aqueous vapour variable, depending much upon the temperature. Ammonia, a trace. 100 cubic inches of pure and dry air weigh, according to Dr. Prout, 31-0117 grains; the temperature being 60 F. (15-5C) and the baro- meter standing at 30 inches. 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 ni- trogen is suffered to flow into an exhausted glass globe, also previously weighed. The increase of weight after the experiment gives the information sought. An easier, but less accurate method, consists in intro- ducing into a graduated tube, standing over water (fig. 91), 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. Professor Liebig has lately proposed to use an alkaline solution of pyro-gallic 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 accuracy with unusual rapidity and facility of execution. Another plan is to mix the air with hydrogen and pass an electric spark ; after the 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 chemistry, it may be worth while describing the process in detail, as it is applicable, with certain obvious variations, to a number of analogous cases. A convenient form of apparatus for the purpose is the siphon eudiometer of Dr. Ure ; this consists of a stout glass tube, having an internal diameter i>f about one-third of an inch, closed at one end, and bent into the form represented in the drawing. (Fig. 92.) Two pieces of platinum wire, melted into the glass near the closed extremity, serve to give passage to the fcpark. The closed limb is carefully gi-aduated. When required for use, the 122 NITROGEN. rig. 92. instrument is filled with mercury and inverted into a vessel of the same fluid. A quantity of the air to be examined is then introduced, the manipulation being precisely the same as with experiments over water ; the open end is stopped with a finger, and the air transferred to the closed extremity. The instrument is next held upright, and after the level of the mer- cury 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 intro- duced, equal, as nearly as can be guessed, to about half the volume of the air. The eudiometer is once more brought into an 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 electrophorus, and explosion ensues. The air con- fined by the thumb in the open part of the tube acts as a spring and mode- rates the explosive effect. Nothing now remains but to equalize the level of the mercui-y 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 substance 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 3 21 ; oxygen in the hundred measures. The working pupil will do well to acquire dexterity in the use of this val- uable instrument, by practising the transference of gas or liquid from the one limb to the other, &c. In the analysis of combustible gases by explo- sion with oxygen, solution of caustic potassa is often required to be intro- duced into the closed part. Compounds of Nitrogen and Oxygen. There are not less than five distinct compounds of nitrogen and oxygen, thus named and constituted : NITROGEN. 123 Composition by weight. Nitrogen. Oxygen. Protoxide of nitrogen* 14 8 Binoxide of nitrogen 3 14 16 Nitrous acid 14 24 Hyponitric acid 3 14 32 Nitric acid 14 40 Nitric or Azotic Acid. In certain parts of India, and also 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, the solution filtered and made to crystallize, furnishes the highly important salt known in com- merce as nitre or saltpetre; it is a compound of nitric acid and potassa. To obtain liquid nitric acid, equal weights of powdered nitre and oil of vitriol are introduced into a glass retort, and heat applied by means of an Argand gas-lamp or charcoal chauffer. 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 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 operation may be stopped ; and when the retort is quite cold, water may be introduced to dissolve out the bisulphate of potassa. The reaction is thus explained. Nit JNltre Oil of vitriol Nitric acid Liquid nitric acid. Bisulphate of potassa. In the manufacture of nitric acid on the large scale, the glass retort is replaced by a cast-iron cylinder, and the receiver by a series of earthen con- densing vessels connected by tubes. (Fig. 93.) Nitrate of soda, found native n Peru, is often substituted for nitrate of potassa. Fig. 93. Liquid nitric acid so obtained has a specific gravity of 1-5 to 1-52 ; it has a ^ Aden yellow colour, which is due to nitrous or hyponitric acid held in solu- tion, and which, when the acid is diluted with water, gives rise by its decom- position to a disengagement of nitric oxide. It is exceedingly corrosive, staining the skin deep yellow, and causing total disorganization 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. 1 Otherwise called nitrous oxide. 1 Called by Professor Graham peroxide of nitrogen. * Otherwise called nitric oxide. 124 NITROGEN. Pure liquid nitric acid, in its most concentrated form, is obtained by mix ing the above with about an equal quantity of oil (if vitriol, re-distilling, collecting apart the first portion which comes 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 colourless as water; it has the sp. gr. 1-517 at 60 (15-5C), boils at 184 (84-5C), and consists of 54 parts real acid, and 9 parts water. Although nitric acid in a more dilute form acts very violently upon many metals, and upon organic substances generally, this is not the case with the compound in question ; even at a boiling heat it re- fuses 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. A second definite compound of real nitric acid and water exists, containing 54 parts of the former to 36 parts of the latter. Its sp. gr. at 60 (15-5C) is 1-424, and it boils at 250 (121 C). An acid weaker than this is concen- trated to this point by evaporation ; and one stronger, reduced to the same amount by loss of nitric acid and water in the form of the first hydrate. 1 Absolute nitric acid, in the separate state, was unknown up to 1849, when M. Deville succeeded in obtaining this remarkable substance by exposing nitrate of silver, which is a combination of nitric acid, silver, and oxygen, to the action of chlorine gas. Chlorine and silver combine, forming chloride of silver, which remains in the apparatus, whilst oxygen and anhydrous nitric acid separate. The latter is a colourless substance, crystallizing in six-sided columns, which fuse at 80 (30C), and boil between 113 and 122 (45 and 50C), when they commence to be decomposed. Anhydrous nitric acid has been found to explode sometimes spontaneously. It dissolves in water with evolution of much heat, forming hydrated nitric acid. It con- sists of 14 parts of nitrogen and 40 parts of oxygen. Nitric acid forms with bases a very extensive and important group of salts, the nitrates, which are remarkable for all being soluble in water. The hydrated acid 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 chlo- rine from common salt in the nitre, and sometimes of sulphate from acci- dental splashing of the pasty mass in the retort. To discover these impuri- ties, a portion is diluted with four or five times its bulk of distilled water, and divided between two glasses. Solution of nitrate of silver is dropped into the one, and solution of nitrate of baryta into the other ; if no change ensue in either case, the acid is free from the impurities mentioned. 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, water, or an alkaline solution being present. 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 pro- duction of nitric acid in the air. A very minute quantity of nitric acid is also produced by the combustion of hydrogen and other substances 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 precipitant can be found for this substance. One of the best tests is its power of bleaching u solution of indigo in sulphuric acid when boiled with that liquid. The 1 The two hydrates of nitric acid are thus expressed by symbols : NOs, HO and NOe, 4HO. No compound containing two equivalents of water appears to e-tist. NITROGEN. 125 absence of chlorine must be ensured in this experiment by means which will hereafter be obvious, otherwise the result is equivocal. Protoxide of Nitrogen; Nitrous Oxide; (laughing gas.) When solid nitrate of ammonia is heated in a retort or flask, 1 fig. 94, furnished with a perforated cork and bent tube, it is resolved into water and nitrous oxide. The nature of the decomposition will be understood from the subjoined diagram. Nitrate of Ammonia 80 Nitric acid 54 Ammonia 17 Water 9 (Nitrogen 14 Oxygen 8 ' Oxygen 8 Oxygen 24 ^---^ Nitrogen 14 -^ Hydrogen 3 Protox. nitrogen 22 "-^- Protox. nitrogen 22 ~~- Water 27 Water 9. Fig. 94. No particular precaution is required in the ope- ration, save due regulation of the heat, and the avoidance of tumultuous disengagement of the gas. Protoxide of nitrogen is a colourless, transparent, and almost inodorous gas, of distinctly sweet taste. Its specific gravity is 1-525; 100 cubic inches weigh 47-29 grains. It supports the combustion of a taper or piece of phosphorus with almost as much energy as pure oxygen ; it is easily distin- guished, however, from that gas by its solubility in cold water, which dissolves 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 difficulty ; it requires, at 45 (7-2C) 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 eudiometer, it explodes with violence, and liberates its own measure of nitrogen. Every two vol- umes of the gas must consequently contain two volumes of nitrogen and one volume of oxygen, the whole being condensed or contracted one-third; a constitution resembling that of vapour of water. 3 The most remarkable feature in this gas is its intoxicating power upon the animal system. It may be respired, if quite pure, or merely mixed with atmospheric air, for a short time, without danger or inconvenience. The effect is very transient, and is not followed by depression. Binoxide of Nitrogen ; Nitric Oxide. Clippings or turnings of copper are put into the apparatus employed for preparing hydrogen, 3 together with a little water, and nitric acid added by the funnel until brisk effervescence is excited. The gas may be collected over cold wa er, 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- 1 Florence oil-flasks, which may be purchased at a very trifling sum, constitute exceedingly, useful vessels for chemical purposes, and often supersede retorts or other expensive appa- ratus. The} r are rendered still more valuable by cutting the neck smoothly round with a hot iron, softening it in the flame of a good Argand gas-lamp, and then turning over the edge eo as to form a lip, or border. The neck will then bear a tight-fitting cork without risk of splitting. * See page 118. " See page 111. 11* 126 NITROGEN. other portion of the acid. Nitric acid is very prone to act thus upon certain metals. The gas obtained in this manner is colourless and transparent ; in contact with air or oxygen gas it produces deep red fumes, which are rea,dily ab- sorbed by water ; this character is sufficient to distinguish it from all other gaseous bodies. A lighted taper plunged into the gas is extinguished ; lighted phosphorus, however, burns in it with great brilliancy. The specific gravity of binoxide of nitrogen is 1-039; 100 cubic inches weigh 32-22 grains. It contains equal measures of oxygen and nitrogen gases united without condensation. When this gas is passed into a solution of protoxide of iron 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 substances. The compound is again decomposed by boiling. Nitrous Acid. Four measures of binoxide of nitrogen are mixed with one measure of oxygen, and the gases, perfectly dry, exposed to a temperature of ( 17-8C). They condense to a thin mobile green liquid. Its vapour is orange-red. Nitrous acid is decomposed by water, being converted into nitric acid and binoxide of nitrogen. For this reason it cannot be made to unite directly with metallic oxides ; nitrite of potassa may, however, be prepared by fusing nitrate of potassa, when part of its oxygen is evolved ; and many other salts of nitrous acid may be obtained by indirect means. Hyponitric Add. It has been doubted whether the terra acid applied to this substance be correct, since it seems to possess the power of forming salts only in a very limited degree ; the expression has, notwithstanding, been long sanctioned by use. Moreover, a beautiful crystalline lead-salt of this substance has been discovered by M. Peligot. It is formed by digesting nitrate of lead with metallic lead. It is chiefly the vapour of hyponitric acid which forms the deep red fumes always produced when binoxide of nitrogen escapes into the air. When carefully dried nitrate of lead is exposed to heat in a retort of hard glass, it is decomposed ; protoxide of lead remains behind, while the acid is resolved into a mixture of oxygen and hyponitric acid. By surrounding the receiver with a very powerful freezing mixture, the latter is condensed to the liquid form. It is then nearly colourless, but acquires a yellow, and ul- timately a red tint, as the temperature rises. At 82 (27 -8C) it boils, giving off its well-known red vapour, the intensity of the colour of which is greatly augmented by elevation of temperature. This substance, like the preceding, is decomposed by water, being resolved into binoxide of nitrogen and nitric acid. Its vapour is absorbed by strong nitric acid, which thereby acquires a yellow or red tint, passing into green, then into blue, and afterwards disappearing altogether on the addition of successive portions of water. The deep red fuming acid of commerce, called nitrons acid, is simply nitric acid impregnated with hyponitric gas. 1 Nitrogen appears to combine, under favourable circumstances, with metals When iron and copper are heated to redness in an atmosphere of ammonia, they become brittle and crystalline, but without sensible alteration of weight. M. Schrotter has shown that in the case of copper, at least, this effect is 1 Much doubt yet hangs over the true nature and relations of these two acids. According to M. Peligot, the only product of the union of binoxide of nitrogen and oxygen is hyponitric acid, which in the total absence of water is a white solid crystalline body, fusible at 16 ( 8-9C>. At common temperatures it is an orange-yellow liquid. The same product is ob- tained by heating perfectly dry nitrate of lead. From these experiments it would appear that iijtrous acid in a separate state is unknown. Ann. Chim. et Phys. 3d series, ii. 68. CARBON. 127 caused by the formation and subsequent destruction of a nitride, that is, a compound of nitrogen with copper. When ammonia is passed over protoxide of copper heated to 570 (298-9C), water is formed, and a soft brown powder produced, which when heated farther 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. 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 plumbago. It constitutes a large proportion of all organic structures, animal and vege- table : when these latter are exposed to destructive distillation in close ves- sels, a great part of this carbon remains, obstinately retaining some of the hydrogen and oxygen, and associated with the earthy and alkaline matter of the tissue, giving rise to the many varieties of charcoal, coke, &c. 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 curi- ous chemical nature confers upon it a high degree of scientific interest. Several localities in India, the island of Borneo, and more especially Brazil, furnish this beautiful substance. It is always distinctly crystallized, often quite transparent and colourless, 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, whose history cannot be traced. The crystalline form of the diamond is that of the regular octahedron or cube, or some figure geometrically con- nected with these ; many of the octahedral crystals exhibit a very peculiar appearance, arising from the faces being curved or rounded, which gives to the crystal an almost spherical figure. Fig. 95. Fig. 96. Fig. 97. Fig. 98. The diamond is infusible and inalterable 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 or- dinary redness in a vessel of oxygen, it burns with facility, yielding carbonic acid gas. This is the hardest substance known ; it admits of being split or cleaved 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 useful to the lapidary And seal-engraver. One very curious and useful application 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 glass ; a crystal of diamond having the rounded octahedral 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 deep split or cut, which penetrates to a considerable depth into the glass, and determines its fracture with perfect certainty. 128 CARBON. Graphite, or plumbago, appears to consist essentially of pure carbon, al- though most specimens contain iron, the quantity of which varies from n, 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 Cum- berland, where a kind of irregular vein is found- traversing the ancient slate- beds of that district. Crystals are not common ; when they occur, they 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 charcoal. 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 sul- phur; 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 colouring 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. 1 The property in question is possessed by all kinds of charcoal in a small degree. Charcoal made from box, or other dense wood, has a property of con- densing into its pores gases and vapours ; 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 effect, as well as that of the decolorizing power, no doubt depends in some way upon the same peculiar action of surface so remarkable in the case of platinum in a mixture of o ?ygen and hydrogen. 3 Compounds of Carbon and Oxygen. There are two direct inorganic compounds of carbon and oxygen, called carbonic oxide and carbonic acid ; their composition may be thus stated : Composition by weight. Carbon. Oxygen. Carbonic oxide 6 8 Carbonic acid 6 16 1 It removes from solution in water the vegetable bases, bitter principles and astringent substances, when employed in excess, requiring from twice to twenty times their weight for total precipitation. A solution of iodine in water, or iodide of potassium, is quickly de- prived of colour. 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 absorbed unaltered; the oxide in the salt may be reduced; or, the salts precipitated in a basic condition, the solution showing an acid reaction as soon as the carbon begins to act. It is in this last case especially that traces of the bases can be detected, the acid set free pre- venting their 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, Mem. Chim. Soc. 1845; Garrod, Pharm. Journ. 1845; Weppen, Ann. deChim. 1845. R. B. a 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. In the form of charcoal it conducts heat slowly and electricity readily. Car- bon is insoluble in water and not liable to be affected by air and moisture. It retards putre- faction. R. B. CARBON. 129 Carbonic Acid is always produced when charcoal burns in air or in 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 generating hydrogen may be again 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 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 Fig. 99. very conveniently, by displacement, if it be required dry, as shown in fig. 99. The long drying-tube is filled with fragments of chloride of calcium, 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. 1 Carbonic acid gas is colourless ; it has an agreeable pungent taste and odour, but cannot be respired for a moment without insensibility following. Its specific gravity is 1-524, 3 100 cubic inches weighing 47-26 grains. This gas is very hurtful to animal life, even when largely diluted with air ; it acts as a narcotic poison. Hence the danger arising from imperfect ven- tilation, the use of fire-places 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 cai'bonic acid is con- stantly disengaged during the process of respiration, which, as we have seen, (page 108,) is nothing but a process of slow combustion. This gas is some- times emitted in large quantity from the earth in volcanic districts, and it is constantly generated where organic matter is in the act of undergoing fer- mentive decomposition. The fatal " after-damp" of the coal-mines contains a large proportion of carbonic acid. 1 In connecting tube-apparatus for conveying tubes of caoutchouc about an inch long, are in- erprresaibly useful. These are made by bending a piece of sheet India-rubber, a, fig. 100, loosely round a glass tube or rod, o, and cutting off the superfluous portion with sharp scissors. The fresh-cut edges of the caoutchouc, pressed strongly together, cohere completely, provided they have not been soiled by touching with the fingers, and thu tube is perfect. The connectors are secured by two or three turns of thin silk cord. 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 breaking asunder. * MM. Dulong uud Berzelius. or cold liquids, not corrosive, littlt Fig. 100. '.30 CARBON. A lighted taper plunged into carbonic acid is instantly extinguished, even to the red-hot snuff. When diluted with three times its volume of air, it still has 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 carbonate of lime is very characteristic. Cold water dissolves about its own volume of carbonic acid, whatever be the density of the gas with which it is in contact ; the solution temporarily reddens litmus paper. In common soda-water, and also in effervescent wines, examples may be seen of this solubility of the gas. Even boiling Water absorbs a perceptible quantity. Some of the interesting phenomena attending the liquefaction of carbonic acid have been already described ; it requires for the purpose a pressure of between 27 and 28 atmospheres at 32 (0C), according to Mr. Addams. The liquefied acid is colourless 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 bisulphide of carbon, and is insoluble in water and fat oils. It is probably destitute when in this condition of all properties of an acid. 1 Carbonic acid exists, as already mentioned, in the air ; relatively, its quan- tity 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 latter having the power, by the aid of their green leaves, of decomposing carbonic acid, retaining the carbon, and expelling the oxygen. The presence of light is essential to this extraordinary effect, but of the manner of its execution 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 lime and mag- nesia. Carbonic Oxide. When carbonic acid is passed over red-hot charcoal or metallic iron, one-half of its oxygen is removed, and it becomes converted into carbonic oxide. 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. On heating the mixture the organic acid is resolved into water, carbonic acid, and carbonic oxide ; by passing the gases through a strong solution of caus- tic potassa, the first is withdrawn by absorption, while the second remains unchanged. Another, and it may be preferable method, is to heat finely- powdered yellow ferrocyanide of potassium with eight or ten times its weight of concentrated sulphuric acid. The salt is entirely decomposed, yielding a most copious supply of perfectly pure carbonic oxide gas, which may be col- lected over water in the usual manner. 3 Carbonic oxide is a combustible gas ; it burns with a beautiful pale blue flame, generating carbonic acid. It has never been liquefied. It is colour- less, has very little odour, and is extremely poisonous, even worse than carbonic acid. Mixed with oxygen, it explodes by the electric spark, but 1 When relieved of pressure it immediately boil?, and seven parts out of eight assume the gaseous state, the rest becoming solid at 90 (67'7C) (Mitchell). Solid carbonic acid mixed with ether produces in vacuo a very intense cold ( 165 [109-4C] Faraday), capable of solidifying many gases when aided by pressure. Liquid carbonic acid immersed in this mix- ture becomes a solid so clear and transparent that its condition cannot be detected until a portion again becomes liquid. R. B. a See a paner by the author, in Memoirs of Chem. Soc. of London, i. 251. 1 eq. crystal- lized ferrocyanide of potassium, and 6 eq. oil of vitriol, yield 6 eq. carbonic, oxide, 2 eq. sul phate of potassa. 3 eq. sulphate of ammonia, and 1 eq. protosulphate of iron. SULPHUR. 131 with some difficulty. Its specific gravity is 0-973 ; 100 cubic inches weigh 30-21 grains. The relation by volume of these oxides of carbon may thus be ma.de in- telligible : carbonic acid contains its own volume of oxygen, that gas suffer- ing no change of bulk by its conversion. One measure of carbonic oxide mixed with half a measure of oxygen and exploded, yields one measure of carbonic acid; hence carbonic oxide contains half its volume of oxygen. Carbonic oxide unites with chlorine under the influence of light, forming a pungent, suffocating compound, possessing acid properties, called phosgene gas, or chloro-carbonic acid. It is made by mixing equal volumes of car- bonic oxide and chlorine, both perfectly dry, and exposing the mixture to sunshine ; the gases unite quietly, the colour disappears, and the volume becomes reduced to one-half. It is decomposed by water. SULPHUR. This is an elementary body of great importance and interest. Sulphur is often found in a free state in connection with deposits of gypsum and rock- salt ; its occurrence in volcanic districts is probably accidental. Sicily fur- nishes 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 crys- tals of sulphur exhibit two distinct and incompatible forms, namely, an oc- tahedron Avith rhombic base (fig. 101), which is the figure of native sulphur, and that assumed when sulphur separates from solution at common tempe- ratures, as when a solution of sulphur in bisulphide of carbon is exposed to slow evaporation in the air; and a lengthened prism (fig. 103), having no relation to the preceding ; this happens when a mass of sulphur is melted, and, after partial cooling, the crust at the surface broken, and the fluid por tion poured out. Fig. 102 shows the result of such an experiment. Fig- 101. Fig. 102. Fig. 103. The specific gravity of sulphur varies according to the form in which it is crystallized. The octahedral variety has a specific gravity 2-045 ; the pris- matic variety a specific gravity 1-982. Sulphur melts at 232 (111-1C) ; at this temperature it is of the colour of amber, and thin and fluid as water ; when farther heated, it begins to thicken, and to acquire a deeper colour : and betAveen 430 (221 C) and 480 (249C), 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 its remarkable 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 tempera- ture last mentioned to the boiling-point, about 792 (400C), sulphur again 132 SULPHUR. becomes thin and liquid. In the preparation of commercial flowers of sul- phur, the vapour is conducted into a large cold chamber, where it condenses in minute crystals. The specific gravity of sulphur-vapour is 6-654. Sulphur is insoluble in water and alcohol ; oil of turpentine and the fat oils dissolve it, but the best substance for the purpose is bisulphide of car- bon. In its chemical relations sulphur bears great resemblance to oxygen ; to very many oxides there are corresponding sulphides, and these sulphides often unite among themselves, forming crystallizable compounds analogous to salts. Compounds of Sulphur and Oxygen. Composition by weight. Sulphur. Oxygen. Sulphurous acid 16 16 Sulphuric acid 1 16 24 Hyposulphurous acid 32 16 Hyposulphuric acid 32 40 Sulphuretted hyposulphuric acid 48 40 Bisulphuretted hyposulphuric acid 64 40 Trisulphuretted hyposulphuric acid 80 40 Sulphurous Acid. This is the only product of the combustion of sulphur in dry air or oxygen gas. It is most conveniently prepared by heating oil of vitriol with metallic mercury or copper clippings; a portion of the acid is decomposed, one-third of its oxygen being transferred to the metal, while the sulphuric acid becomes sulphurous. Sulphurous acid thus obtained is a colourless gas, having the peculiar suffocating odour of burning brimstone ; it instantly extinguishes flame, and is quite irrespirable. Its density is 2-21, 100 cubic inches weighing 68-69 grains. At ( 17-8C), under the pres- sure of the atmosphere, this gas condenses to a colourless, limpid liquid, very expansible by heat. Cold water dissolves more than thirty times its volume of sulphurous acid. The solution may be kept unchanged so long as air is excluded, but access of oxygen gradually converts the sulphurous into sulphuric acid, in the presence of water, although the dry gases may remain in contact for any length of time without change. When sulphurous acid and aqueous vapour are passed into a vessel cooled to below 17 or 21 ( 50 or 8C), a crystalline body forms, which contains about 24-2 acid to 75-8 water. One volume of sulphurous acid gas contains one volume of oxygen, and Jth of a volume of sulphur-vapour, 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. 1 The terminations ous and ic, applied to acids, signify degrees of oxidation, the latter being the highest; acids ending in ous form salts the names of which are made to end in UK, and those in ic terminate in ate, as sulphurous acid, sulphite of soda, sulphuric acid, sulphate of Boda. a The more advanced student will he glad to see these stated in equivalents by the use of symbols, hereafter to be explained, their relations becoming thereby much more evident. The numbers given are really the equivalent numbers, but are intended only to show the pro- portions of sulphur and oxygen, without any reference to other bodies. The following are the quantities required to saturate one equivalent of a base: Sulphurous acid SOj Sulphuric acid SOs Hyposulphurous acid S^Oa Hyposulphuric acid, Dithionic acid SsOs Sulphuretted hyposulphuric acid, Trithionic acid SsOs Bisulphuretted hyposulphuric acid, Tetrathionic acid 8402 Trisulphuretted hyposulphuric acid, Pentathionic acid SsO SULPHUR. 133 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 *bn a much smaller scale. The trough is best constructed of hard, sound wood, and so contrived as to economise as much as possible the expensive fluid 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 alkalis are soluble and crystallizable ; they are easily formed by direct com- bination. Sulphites of baryta, strontia, and lime, are insoluble in water, but soluble in hydrochloric acid. The strong acids decompose them ; nitric acid converts them into sulphates. Sulphuric Acid. Hydrated sulphuric acid has been known since the fifteenth century. There are two distinct processes by which it is at the present time prepared, namely, by the distillation of green sulphate of iron, and by the oxidation of sulphurous acid by nitrous acid. The first process is still carried on in some parts of Germany, especially in the neighbourhood of Nordhausen in Prussia ; the sulphate of iron, 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 temperature ; the remainder is driven off in vapour, which is condensed by the cold vessel. The product is a brown oily liquid, of about 1-9 specific gravity, fuming 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 mentioned, always followed as the more economical, depends upon the fact, that, when sulphurous acid, hyponitric acid, and water are present in certain propor- tions, the sulphurous acid becomes oxidized at the expense of the hyponitric acid, which by the loss of one-half of its oxygen sinks to the condition of binoxide of nitrogen. 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 constructed, 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 sometimes a jet of steam is also introduced. Lastly, an exit is provided 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 sulphurous acid, atmospheric air, nitric acid vapour, 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 acid, becoming hyponitric ; it does not remain in this state, however, but suffers farther deoxidation until it is reduced to binoxide of nitrogen. That substance in contact with free oxygen absorbs a portion of the latter, and once more becomes hyponitric acid, which is again destined to undergo de- oxidation by a fresh quantity of sulphurous acid. A very small portion of hyponiti-ic acid, mixed with atmospheric air and sulphurous acid, may thus in time convert an indefinite amount of the latter into sulphuric acid, by acting as a kind of carrier between the oxygen of the air and the sulphurous acid. The presence of water is essential to this reaction. We may represent the change by the diagram on the succeeding page : 134 SULPHUR. f Nitrogen 14 Binoxide of nitrogen 30 Jlyponitric acid 46 4 Oxygen 16 (Oxygen 16. Sulphurous acid Water 18 ^=^ Hydrated 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 ; it 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 humidity in the air within, and sulphurous and hyponitric acids are introduced by separate tubes, symptoms of chem cal action become immediately 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. 1 When thrown into water, it is resolved into sulphuric acid, binoxide of nitrogen, and nitric acid. This curious body is certainly very often produced in large quantity in the leaden chambers ; but that its production is indispensable to the success of the process, and con- stant when the operation goes on well, and the hyponitric acid is not in excess, may perhaps admit 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, it 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 there- abouts; it is then transferred to carboys, or large glass bottles fitted in bas- kets, for sale. In Great Britain this manufacture is one of great national importance, and is carried on to a vast extent. An inferior kind of acid is sometimes made by burning iron pyrites, or poor copper ore, as a substitute for Sicilian sulphur; this is chiefly used by the makers for their own con- sumption ; it very frequently contains arsenic. The most concentrated sulphuric acid, or oil of vitriol, as it is often called, is a definite combination of 40 parts real acid, and 9 parts water. It is a colourless, 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 15 ( 26-lC) it freezes; at 620 (326 -6C) it boils, and may be distilled without decomposition. Oil of vitriol has a most energetic attraction for water; it withdraws aqueous vapours from the air, and when diluted, great heat is evolved, so that the mixture always requires to be made with caution. Oil of vitriol is not the only hydrate of sulphuric acid ; 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 49 parts strong liquid acid and 9 parts water, congeals or crystallizes at a temperature above 1 M. Gaultier de Claubry assigned to this curious substance the composition expressed hy the formula 4110, 2NOa+5S0 3 , and this view has generally been received by recent chemical writers. M. de la Provostaye has since shown that a compound, possessing all the essential properties of the body in question, may be formed by bringing together, in a scaled glass tube, liquid sulphurous acid and liquid hyponitric acid, both free from water. The white crystalline solid soon begins to form, and at the expiration of twenty-six hours the reaction appears complete. The new product is accompanied by an exceedingly volatile greenish liquid having the characters of nitrous acid. The white substance, on analysis, was found to contain the elements of two equivalents of sulphuric acid and one of nitrous acid, or N03+2S03. M. de la 1'rovostaye very ingeniously explains the anomalies in the different analyses of the leaden chamber product, by showing that the pure substance forms crystal- lizable combinations with different proportions of liquid sulphuric acid. (Ann. Ohirn. et Fbys. Ixxiii. 362.) SULPHUR. 135 32 (0C), and remains solid even at 45 (7-2C). Lastly, when a very dilute acid is concentrated by evaporation in vacua over a surface of oil of vitriol, the evaporation stops when the real acid and water bear to each other the proportion of 40 to 27. When good Nordhausen oil of vitriol is exposed in a retort to a gentle heat, and a receiver cooled by a freezing mixture fitted to it, a volatile substance distils over in great abundance, which condenses into beautiful, white, silky crystals, resembling those of asbestus ; this bears the name o? anhydrous sulphuric acid. When put into water it hisses like .a hot iron, from the violence with which combination occurs ; exposed to the air even for a few moments, it liquefies by absorption of moisture, forming common liquid sulphuric acid. It forms an exceedingly curious compound with dry ammoniacal gas, quite distinct from ordinary sulphate of ammonia, and which indeed possesses none of the characters of a sulphate. This interest- ing substance may also be obtained by distilling the most concentrated oil of vitriol with a sufficient quantity of anhydrous phosphoric acid. Sulphuric acid, in all soluble states of combination, may be detected with the greatest ease by solution of nitrate of baryta, or chloride of barium. A white precipitate is produced, which does not dissolve in nitric acid. Hyposulphurous Acid. By digesting sulphur with a solution of sulphite of potassa- or soda, a portion of that substance is dissolved,- and the liquid, by slow evaporation, furnishes crystals of the new salt. The acid 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 pre- cipitates, and into sulphurous acid, easily recognized by its odour. 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 rela- tion to the art of photogenic drawing. Hyposulphuric Acid, Vilhionic Acid. This is prepared by suspending finely divided binoxide of manganese in water artificially cooled, and then transmitting a stream of sulphurous acid gas ; the binoxide becomes pro- toxide, half its oxygen converting the sulphurous acid into hyposulphuric. The hyposulphate of manganese thus prepared is decomposed by a solution of pure hydrate of baryta, and the barytic salt, in turn, by enough sul- phuric acid to precipitate the base. The solution of hyposulphuric acid may be concentrated by evaporation in vacuo, until it acquires a density of 1-347: pushed farther, it decomposes into sulphuric and sulphurous acids. It has no odour, is very sour, and forms soluble salts with baryta, lime, and provoxide of lead. Sulphuretted hyposulphuric Acid, Trithionic Acid. A substance accidentally formed by M. Langlois, 1 in the preparation of hyposulphite of potassa, by gently heating with sulphur a solution of carbonate of potassa, saturated with sulphurous acid. The salts bear a great resemblance to those of hypo- sulphurous acid, but differ completely in composition, while the acid itself is not quite so prone to change. It is obtained by decomposing the potassa salt by hydrofiuosilicic acid ; it may be concentrated under the receiver of the air-pump, but it is gradually decomposed into sulphur, sulphurous and sulphuric acids. Bisulphuretted hyposulphuric Acid, Tetrathionic Acid. This was discovered by MM. Foi-dos and Gelis.* When iodine is added to a solution of hyposul- jp> iN of soda, a large quantity of that substance is dissolved, and a clear, r 'V i^less solution obtained, which, besides iodide of sodium, contains a salt 1 Ann. Chim. et Phys. 3d scries, iv. 77. Ib. 3d series, vi. 464 186 SELENIUM. of a peculiar acid, richer in sulphur than the preceding. By suitable means, the new substance can be eliminated, and obtained in a state of solution. It very closely resembles hyposulphuric acid. The same .acid is produced by the action of sulphurous acid on subchloride of sulphur. Trisulphuretted hyposulphuric Add, Pentathionic. Add. Another acid of sulphur has been announced by M. Wackenroder, who formed it by the action of sulphuretted hydrogen on sulphurous acid. It is described as colourless and inodorous, of acid and bitter taste, and capable of being con- centrated to a considerable extent by cautious evaporation. It contains S 5 5 ; under the influence of heat, it is decompos-ed into sulphur, sulphurous and sulphuric acid and sulphuretted hydrogen. The salts of pentathionic acids are nearly all soluble. The baryta salt crystallizes from alcohol in square prisms. The acid is also formed when hyposulphate of lead is decomposed by sulphuretted hydrogen, and when protochloride of sulphur is heated with sulphurous acid. Sulphurous acid 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. 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 selenide of lead of Clausthal, in the Hartz. Selenium is a reddish-brown solid body, somewhat translucent, and having an imperfect metallic lustre. Its specific gravity, when rapidly cooled after fusion, is 4-3. At 212 (100C), or a little above, it melts, and at 650 (343-3C) boils. It is insoluble in water, shid exhales, when heated in the air, a peculiar and disagreeable odour, which has been compared to that of decaying horseradish. There are three oxides of selenium, two of which correspond respectively to sulphurous and sulphuric acids, while the third has no known analogue in the sulphur series. Composition by weight Selenium. Oxygen. Oxide of selenium 39-5 8 Selenious acid 39-5 16 Selenic acid 39-5 24 Oxide. Formed by heating selenium in the air. It is a colourless gas, slightly soluble in water, and has the remarkable odour above described. It has no ucid properties. Selenious Add. This is obtained by dissolving selenium in nitric acid, and evaporating to dryness. It is a white, soluble, deliquescent substance, of distinct acid properties, and may be sublimed without decomposition. Sul- phurous acid decomposes it, precipitating the selenium. Selenic Acid. Prepared by fusing nitrate of potassa or soda with selenium, precipitating the seleniate so produced by a salt of lead, and then decom- posing the compound by sulphuretted hydrogen. The hydrated acid strongly resembles oil of vitriol ; but, when very much concentrated, decomposes, by the application of heat, into selenious acid and oxygen. The seleniates bear the closest analogy to the sulphates in every particular. PHOSPHORUS. 137 Fig. 104. PHOSPHORUS. Phosphorus in a state of phosphoric acid is contained in the ancient un- etratified 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 inflexibility to the bony skeleton. This element 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 sulphate of lime washed. The liquid is then evaporated to a syrupy consistence, mixed with charcoal powder, and the desiccation com- pleted 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 con- /eyed to a chimney. (Fig. 104.) This manufac- ture is now conducted on a very great scale, the consumption of phosphorus, for the apparently 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 vapour 4-35, air being unity. At 108 (42-2C) it melts, and at 550 (287-7C) boils. It is insoluble in water, and is usually kept immersed in that liquid, but dissolves in oils, in native naphtha, and especially in bisulphide of carbon. When set on fire in the air, it burns with a bright flame, generating phosphoric acid. Phosphorus is exceedingly in- flammable ; 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 xindergoes by tho oxygen of the air, and upon it depends one of the methods employed for the analysis of the atmosphere, 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 vapour of ether, or some essential oil ; it may even be distilled in an atmosphere containing vapour of oil of turpentine in considerable quantity. Neither does the action go on in pure oxygen, at least at the temperature of 60 (15-5C), which is very remark- able ; but if the gas be rarefied, or diluted with nitrogen, hydrogen, or car bonic acid, oxidation is set up. According to the researches of Marchand, evaporation of phosphorus causes a luminosity, even when there is no ox ; da- tion. 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 for fifty hours common phosphorus to a temperature of about 404 to 482 (240 to 250C) in an atmosphere which is unable to act chemi- 12* 138 PHOSPHORUS. cally upon it. At this temperature it becomes red and opaque, and insoluble in bisulphide of carbon, whereby it may be separated from ordinary phos- phorus. It may be obtained in compact masses when common phosphorus is kept for eight days at a constant high temperature. It is a coherent, 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 392 (200C), nor has it any tendency to combine with the oxygen of the air. When heated to 500 (260C), it is reconverted into ordinary phosphorus. Compounds of Phosphorus and Oxygen. These are four in number, and have the composition indicated below. Composition by weight. Phosphorus. Oxygen. Oxide of phosphorus 64 8 Hypophosphorous acid 32 8 Phosphorous acid 32 24 Phosphoric acid l 32 40 Oxide of Phosphorus. When phosphorus is melted beneath the surface of hot water, and a stream of oxygen gas forced upon it from a bladder, com- bustion ensues, and the phosphorus is converted in great part into a brick- red powder, which is the substance in question. It is decomposed by heat into phosphorus and phosphoric acid. Hypophosphorous Acid. When phosphide of barium is put into hot water, that liquid is decomposed, giving rise to phosphoretted hydrogen, phos- phoric acid, hypophosphorous acid, and baryta ; the first escapes as gas, and the two acids remain in union with the baryta. By filtration the soluble hypophosphite 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 Acid. Phosphorous acid is formed by the slow combustion of phosphorus in the atmosphere ; or by burning that substance by means of a very limited supply of air, in which case it is anhydrous, and presents the aspect of a white powder. The hydrated acid is more conveniently prepared by adding water to the terchloride 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. By evaporating the solution to the con- sistence of syrup, the hydrochloric acid is expelled, and the residue on cooling crystallizes. Hydrated 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 hydrated phosphoric acid and pure phosphoretted hydrogen gas. Jt is composed of 56 parts real acid and 27 parts water. 2 The phosphites are of little importance. 1 Phosphoric Acid. When phosphorus is burned under a bell-jar by the aid of a copious supply of dry air, snow-like anhydrous phosphoric acid is pro- 1 In symbols Oxide of phosphorus PaO Hypophosphorous acid P Phosphorous acid P Oa -' Phosphoric acid P Os Equivalent of phosphorus, 32 2 Or,3HO, PO 3 . CHLORINE . 139 duced in great quantity. This substance exhibits as much attraction for water as anhydrous sulphuric acid ; 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. Once in the state of hydrate, the water cannot again be separated. When nitric acid of moderate strength is heated in a retort to which a receiver is connected, and fragments of phosphorus 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 off 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 hydrated acid may be obtained pure. This is the glacial phos- phoric acid of the Pharmacopoeia. A third method consists in taking the acid phosphate of lime produced by the action of sulphuric acid on bone-earth, precipitating it with a slight excess of carbonate of ammonia, separating by a filter the insoluble lime- salt, and then evaporating and igniting in a platinum vessel the mixed phosphate and sulphate of ammonia. Hydrated 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 atmo- spheric air, by the aid of a proper apparatus, not difficult to contrive, in which the process may be carried on continuously. The anhydrous acid 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 hydrate of phosphoric acid is exceedingly deliquescent, and requires to be kept in a closely stopped bottle. It contains 72 parts real acid, and 9 parts water. Phosphoric acid is a powerful acid ; its solution has an intensely sour taste, and reddens litmus paper ; it is not poisonous. There are few bodies that present a greater degree of interest to the chemist than this substance ; the extraordinary changes its compounds undergo by the action of heat, chiefly Fi &- 105< made known to us by the admirable researches of Prof. Graham, will be found described in connection with the general history of saline compounds. CHLORINE. This substance is a member of a small natural group containing besides iodine, bromine and fluorine. So great a degree of resemblance exists between these bodies in all their chemical relations, that the history of one will almost serve, with a few little alterations, for that of the rest. Chlorine ' is a very abundant substance ; in common salt it exists in combination with sodium. It is most easily prepared by pouring strong liquid hydrochloric acid upon finely-powdered black oxide of manganese, contained in a ret Sulphate of soda. The composition of this substance maybe 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 chlorine and 1 part 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 142 CHLORINE. cork and bent tube, in the manner represented in fig. 106 ; the latter passes through and below a second short tube into a wide-necked bottle, containing Fig. 106 a little \rater, into which the open tube dips. A bent tube is adapted to an- other hole in the cork of the wash-bottle, so as to convey the purified gas into a quantity of distilled water, by which it is instantly absorbed. The joints are mad-e air-tight by melting over the corks a little yellow wax. 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 condensation of the gas, it is necessary to surround the condensing-vessel with cold water. The simple wash-bottle figured in the drawing will be found an exceed- ingly 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 gas of any kind is to be passed through an alkaline or other solution. The open tube dipping into the liquid prevents the possibility of absorption, by which a partial vacuum would be occasioned, and the liquid of the second vessel iost 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. /Fig- 107.) Liquid poured into the funnel rises upon the opposite side of CHLORINE. 143 ihe 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 inte- Fig. 107 rior. 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 increased 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 absorption within is quickly compensated by the entrance of air through the liquid in the bulb. The plan employed on the great scale by the manufacturer is the same in principle as that described ; he merely substitutes a large iron cylinder for the flask, and vessels of stone-ware for those of glass. Pure solution of hydrochloric acid is transparent and colourless ; when strong, it fumes in the air by disengaging a little gas. It leaves no residue on evaporation, and gives no precipitate or milki- ness with solution of chloride of barium. 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 has usually a yellow colour, and is very impure, containing salts, sulphuric acid, chloride of iron, and organic matter. It may be rendered sufficiently good for most pur- poses 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, hyponitric acid and chlorine being evolved. This at least appears to be the final result of the action ; at a certain stage, however, two peculiar substances, con- sisting of nitrogen, oxygen, and chlorine, (chlorohyponitric acid 1 and chlo- ronitrous acid, 2 ) appear to be formed. It is chiefly the chlorine which attacks the metal. The presence of hydrochloric acid, or any other soluble chloride, is easily detected by solution of nitrate of silver. A white curdy precipitate is pro- duced, insoluble in nitric acid, freely soluble in ammonia, and subject to blacken by exposure to light. Compounds of Chlorine and Oxygen. Although these bodies never combine directly, they may be made to unite by circuitous means in five different proportions, as below : Composition by weight. Chlorine. Oxygen. Hypochlorous acid 35-5 8 Chlorous acid 35-5 24 Hypochloric acid 35-5 32 Chloric acid 35-5 40 Perchloric acid 3 35-5 56 Hypochlorous and chloric acids are generated by the action of chlorine on certain metallic oxides ; the former in the cold, the latter at a high tempe 1 NOa Cla. 3 NOaCl. * Hypochlorous acid CIO Chlorous acid ClOs Hypochloric acid C10< Chloric acid ClOs Perchloric add C107 144 (HLORINE. rature. Chlorous, hypochloric, and perchloric acids result from the decom- position of chloric acids. Hypochlorous Add. This is best prepared by the action of chlorine gas upon red oxide of mercury. It is a pale yellow gaseous body, containing, in every two measures, two measures of chlorine and one of oxygen. It is very freely soluble in water, and explodes, although with no great violence, by 'slight elevation of temperature. The odour of this gas is peculiar, and but remotely resembles that of chlorine. It bleaches powerfully, and acts upon certain of the metals in a manner which is determined by their re- spective attractions for oxygen and chlorine. It forms with the alkalis a series of bleaching salts. The preparations called chloride of, or chlorinated lime and soda, contain hypochlorous acid. A description of these will be found under the head of Salts of Lime. The reaction by which hypochlorous acid is produced may thus be illus- trated : Chlorine r== ^ Hypoehlorous acid. Oxide of f Mercury ^ """" mercury \ Oxygen ^___^^ Chlorine "- Chloride of mercury. The chloride of mercury, however, does not remain as such ; it combinea with another portion of the oxide, when the latter is in excess, forming a peculiar brown compound, an oxychloride of mercury. 1 Chlorous Acid. This substance is prepared by heating in a flask filled to the neck, a mixture of 4 parts of chlorate of potassa and 3 parts of arsenious acid with 12 parts of nitric acid previously diluted by 4 parts of water. During the operation, which must be performed in a water-bath, a greenish yellow gas is evolved, which is sparingly soluble in water, and cannot be condensed by exposure to a freezing mixture. It slowly combines with bases, producing a class of salts called chlorites. The process which gives rise to chlorous acid is rather complicated. The arsenious acid deprives the nitric acid of part of its oxygen, reducing it into nitrous acid, which is oxidized again at the expense of the chloric acid. This, by the loss of two- fifths of its oxygen, becomes chlorous acid. Hypochloric Acid ; Peroxide of Chlorine. Chlorate of potassa is made into a paste with concentrated sulphuric acid, and cooled ; this is introduced into a small glass retort, and very cautiously heated by warm water ; a deep yellow gas is evolved, which is the body in question ; it can be collected only \>y displacement, since mercury decomposes, and water absorbs the gas. Hypochloric acid has a powerful odour, 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 by danger, and should be performed only on a small scale. It is composed Hy measure of one volume of chlorine and two volumes of oxygen, con- 1 A very commodious method of preparing hypochlorous acid has lately been described by 31. Pelouze. Red oxide of mercury, prepared by precipitation and dried by exposure to a Btrong heat, is introduced into a glass tube, kept cool, and well washed, and dry chlorine gas is slowly passed over it. Chloride of mercury and hypochlorous acid are formed; the latter i? collected by displacement. When the flask or bottle in which the gas is received is exposed to artificial cold by the aid of a mixture of ice and salt, the hypochlorous acid condenses to a deep red liquid, slowly soluble in water, and very subject to explosion. It is remarkable that the crystalline oxide of mercury prepared by calcining the nitrate, or by the direct oxidation of the metal, is scarcely acted upon by chlorine under the circumstances described, Ami.. Cbim. et Phys. Cd series, vii. 179 CHLORINE. 145 Fig. 108. iensed into two volumes. 1 It may be liquefied by cold. The solution of the gas in water bleaches. Salts of this acid have not yet been obtained. The euchlorine of Davy, prepared by gently heating chlorate of potassa with dilute hydrochloric acid, is probably a mixture of chlorous acid and free chlorine. The production of chlorous acid from chlorate of potassa and sulphuric acid, depends upon the spontaneous splitting of the chloric acid into chlorous acid and perchloric acid, which latter remains in union with the potassa.* When a mixture of chlorate of potassa and sugar is touched with a drop of oil of vitriol, it is instantly set on fire ; the hypochloric acid disengaged being decomposed by the combustible substance with such violence as to cause inflammation. If crystals of chlorate of potassa be thrown into a glass of water, a few small fi-agments of phosphorus added, and then oil of vitriol poured down a narrow funnel reaching to the bottom of the glass, the phosphorus will burn beneath the surface of the water by the as- sistance of the oxygen of the hypochloric acid disen- gaged. Fig. 108. The liquid at the same time becomes yellow, and acquires the odour of that gas. Chloric Acid. This is the most important com- pound of the series. When chlorine is passed to saturation into a moderately strong hot solution of caustic potassa, or the carbonate of that base, and the liquid concentrated by evaporation, it furnishes, on cooling, flat tubular crystals of a colourless salt, consisting of potassa combined with chloric acid. The mother-liquor contains chloride of potassium. In this reaction a part of the potassa is decomposed; its oxygen combines with one portion of chlorine to form chloric acid, while the potassium is taken up by a second portion of the same substance. 3 From chlorate of potassa, chloric acid may be obtained by boiling the salt with a solution of hydrofluosilicic acid, which forms an almost insoluble salt with potassa, 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 syrupy 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 nitrate of baryta or silver; 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 solution of the acid has no bleaching power. Perchloric Acid. Prof. Penny has shown that when powdered chlorate of potassa is thrown by small portions into hot nitric acicl, j, change of the 1 In equivalents, as already stated, C10.J. ( 2 eq. chlorine 9 3 equiv. chloric acid-^ 8 eq. oxygen 1 fi eq. chlorine 6 eq. potassa 13 ( 7 eq. oxygen 1 eq. chlorine 5 cq. chlorine 1 eq. chlorine 5 eq. 5 eq. oxygen 1 eq. potassa 2 eq. hypochloric acid. 1 eq. perchloric acid. 5 eq. chloride potassium. 1 eq. chlorate pctassa. 146 IODINE. same description as that which happens when sulphuric acid is used takes place, but with this important difference, that the chlorine and 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 nitrate of potassa and perchlorate of potassa, which may be readily separated by their difference of solubility. By treating the potassa salt in the manner directed for chloric acid, the free acid may be obtained tolerably pure. It may be concentrated by evapo- ration, and even distilled without change. The solution fumes slightly in the air, and has a specific gravity of 1-65. It is very greedy of moisture, and has no bleaching properties. The perchlorates much resemble the chlo- rates ; they give off oxygen when heated to redness. The acid is the most stable of the compounds of chlorine and oxygen. IODINE. This remarkable substance 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 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 quantity in some aluminous slates of Sweden, and in several varieties of coal and turf. Kelp, or the half-vitrified ashes of sea-weeds, prepared by the inhabitants of the Western Islands and the northern shores of Scotland and Ireland, ia treated with water, and the solution filtered. The liquid is then concentrated by evaporation until it is reduced to a very small volume, the chloride of sodium, carbonate of soda, chloride of potassium, and other salts, being removed as they successively crystallize. The dark brown mother-liquor left contains very nearly the whole of the iodine ; this is mixed with sul- phuric acid and binoxide of manganese, 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 ; it requires in practice, however, careful management, otherwise the impuri- ties present in the solution interfere with the general result. The manganese is not really essential ; iodide of potassium or sodium, 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 colour and imper* feet metallic lustre, resembling that of plumbago ; the crystals are sometimes eery large and brilliant. Its density is 4-948. At 225 (107-2C) it fuses, and at 347 (175C) boils, the vapour having an exceedingly beautiful violet colour. 1 It is slowly volatile, however, at common temperatures, and exhales un odour much resembling that of chlorine. The density of the vapour is 8-716. Iodine requires for solution about 7000 parts of water, which never- theless acquires a brown colour ; in alcohol it is much more freely soluble. Solutions of hydriodic acid and the iodides of the alkaline metals also dis- solve a large quantity ; these solutions are not decomposed by water, which is the case with the alcoholic tincture. Thia substance stains the skin, but not permanently ; it has a very ener- getic action upon the animal system, and is much used in medicine. * Whence the name, fo><5>;j, violet-coloured. IODINE. 147 One of the most characteristic properties of iodine is the production of a splendid blue colour by contact with the organic principle 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 quan- Fig. 109. tity of chlorine- water, when the iodine, being displaced from combination, becomes capable of acting upon the starch. Hydriodic Acid. The simplest process for preparing hydriodic acid gas is to introduce into a glass tube (fig. 109), sealed at one extremity, a little iodine, then a small quan- tity of roughly-powdered glass moistened with water, upon this a few little 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 received over mercury. The experi- ment depends upon the formation of an iodide of phosphorus, and its subsequent decomposition by water, hydrated phospho- rous acid and iodide of hydrogen being produced. The glass merely serves to moderate the violence of the action of the iodine upon the phosphorus. Hydriodic acid gas greatly resembles the corresponding chlorine compound ; it is colourless, and highly acid ; it fumes in the air, and is very soluble in water. Its density is about 4-4. By weight it is composed of 127 parts iodine and 1 part hydrogen ; and by measure, of equal volumes of iodine-vapour and hydrogen united without condensation. Solution of hydriodic acid may be prepared by a process much less trou- blesome than the above. Iodine in fine powder is suspended in water, and a stream of washed sulphuretted hydrogen passed through the mixture ; sulphur is deposited, and the iodine converted into hydriodic acid. When the liquid has become colourless, it is heated to expel the excess of sulphu- retted hydrogen, and filtered. This solution cannot long be kept, especially if it be strong ; the oxygen of the air gradually decomposes the hydriodic acid, and iodine is set free, which, dissolving in the remainder, communicates to it a brown colour. Compounds of Iodine and Oxygen. The most important of these are the iodic and periodic acids. Composition by weight. Iodine. Oxygen. Iodic acid 127 40 Periodic acid l 127 56 Iodic Acid may be prepared by the direct oxidation of iodine by 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. 1 lOa, and I0r. 148 BROMINE. lodic acid is a very soluble substance; it crystallizes in colourless, six- sided tables, -which contain water. It is decomposed by heat, and its solution readily deoxidized by sulphurous acid. The iodates much resemble the chlorates ; that of potassa is decomposed by heat into iodide of potassium and oxygen gas. Periodic Acid. When solution of iodate of soda is mixed with caustic soda, and a current of chlorine transmitted through the liquid, two salts are formed, namely, chloride of sodium and a combination of periodate of soda with hydrate of soda, 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 periodate of silver ; from which the acid may be separated by the action of water, which resolves the salt into free acid and insoluble basic periodate. The acid itself may be obtained in crystals. It is permanent in the air, and capable of being resolved into iodine and oxygen by a high temperature, BROMINE. Bromine * dates back to 1826 only, having been discovered by M. Balard of Montpelier. It is found in sea-water, and is a frequent constituent of saline springs, chiefly as bromide of magnesium ; 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 a quantity of ether; the chlorine decomposes the bromide of magnesium, and the ether dissolves the bromine thus set free. On standing, the ethereal solution, having a fine red colour, separates, and may be removed by a funnel or pipette. Caustic potassa is then added in excess, und heat applied ; bromide of potassium and bromate of potassa are formed. The solution is evaporated to dryness, and the saline matter, after ignition to redness to decompose the bromate of potassa, heated in a small retort with binoxide of manganese and sulphuric 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 vapour, which condenses into drops beneath the liquid. Bromine is at common temperatures a red thin liquid of an exceedingly intense colour, and very volatile; it freezes at about 19 ( 7-2C), and boils at 145-4 (63C). The density of the liquid is 2'976, and that of the vapour 5-39. The odour 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. Hydrobromic Acid. This substance bears the closest resemblance in every particular to hydriodic acid ; it has the same constitution by volume, very nearly the same properties, and may )>e prepared by means exactly similar, substituting the one body for the other. The solution of hydrobromic acid has also the power of dissolving a large quantity of bromine, thereby acquir- ing a red tint. Hydrobromic acid contains by weight 80 parts bromine, and 1 part hydrogen. Bromic Acid. Caustic alkalis in presence of bromine undergo the same change as with chlorine, bromide of the metal and bromate of the oxide being produced; these may often be separated by the inferior solubility of 1 From 8puuos, a noisome smell : a very appropriate term. FLUORINE SILICIUM. 149 the latter. Bromic acid, obtained from bromate of baryta, closely resembles chloric acid ; it is easily decomposed. The bromates when heated lose oxygen and become bromides. No other compound of bromine and oxygen has yet been described. FLUORINE This element has never been isolated, at least in a state fit for examination ; its properties are consequently in great measure unknown ; from the obser- vations made, it is presumed to be gaseous, and to possess colour, like chlorine. The compounds containing fluorine can be easily decomposed, and the element transferred from one body to another; but its extraordinary chemical energies towards the metals and towards sUicium, a component of glass, have hitherto baffled all attempts to obtain it pure in a separate state. As fluoride of calcium it exists in small quantities in many animal substances ; such as bones. Several chemists have endeavoured to obtain it by decom- posing fluoride of silver by means of chlorine in vessels of fluor-spar, but even these experiments have not led to a decisive result. Hydrofluoric Acid. When powdered fluoride of calcium (fluor-spar) is heated with concentrated sulphuric acid in a retort of platinum or lead con- nected with a carefully cooled receiver of the same metal, a very volatile colourless liquid is obtained, which emits copious white and highly suffoca- ting fumes in the air. This was formerly believed to be the acid in an anhydrous state. M. Louyet, however, states that it still contains water, and that hydrofluoric acid, like hydrochloric acid, when anhydrous, is a gas. 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 and 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 vapour of the acid is also very advantageously applied to the same object in the fol- lowing 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 sulphuric acid added to form with the latter a thin paste. The glass is placed upon the basin, with the waxed side downwards, and gentle heat applied beneath, which speedily disengages the vapour of hydrofluoric acid. In a very few minutes the ope- ration is complete ; the glass is then removed and cleaned by a little warm oil of turpentine. When the experiment is successful, the lines are very ilear and smooth. No combination of fluorine and oxygen has yet been discovered Silicium, sometimes called silicon, in union with oxygen constituting silica, or the earth of flints, is a very abundant substance, and one of great im- portance. 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 silicium 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, tb contents of the tube are put into cold water, which removes the saline 13 150 SILICIU Fig. 110 matter and any residual potassium, and leaves untouched the silicium. 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 colour, denser, and incombustible, refusing to burn even when heated by the flame of the oxy-hydrogen blowpipe. Silica. This is the only known oxide ; it contains 21-3 parts silicium, and 24 parts oxygen. 1 Colourless transparent rock-crystal consists of silica very nearly in a state of purity ; common quartz, agate, calcedony, flint, and several other minerals, are also chiefly composed of this substance. The experiment about to be described, furnishes silica in a state of com- plete purity, and at the same time ex- hibits one of the most remarkable pro- perties of silicium, namely, its attraction 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. (Fig. 110.) The first effect is the disengagement of hydrofluoric acid ; this substance, how- ever, finding itself in contact with the silica of the powdered glass, undergoes decomposition, water and flouride of silicium being produced. The latter is a permanent gas, which escapes from the flask by the bent tube. By con- tact with a large quantity of water, it is in turn decomposed, yielding silica, which separates in a beautiful gelatinous condition, and an acid liquid which is a double fluoride of silicium and hydrogen, commonly called hydrofluo- silicic acid. 3 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 baryta and potassa, with which it forms nearly insoluble precipitates, the double fluoride of silicium and potas- sium being used, as was stated, in the preparation of silicium. The fluoride of silicium, instead of being conducted into water, may be collected over mercury; it is a permanent gas, destitute of colour, and very heavy. Ad- mitted into the air, it condenses the moisture of the latter, giving rise to a 1 Or, Si0 3 . * (1) Reaction of hydrofluoric acid upon silica: Fluorine - Hydrofluoric acid =- Gaseous fluoride of silicium. .Water. 2) Decomposition of fluoride of silicium by water: Fluoride of s mdumi Fluoride of silicium Hydrofluosilicic acid. BORON. 151 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. There is another method by which pure silica can be prepared, and which is also very instructive, inasmuch as it is the basis of the proceeding adopted in the analysis of all siliceous minerals. Powdered rock-crystal or fine sand is mixed with about three times its weight of dry carbonate of soda, and the mixture fused in a platinum crucible. When cold, the glassy mass is boiled with water, by which it is softened, and almost entirely dissolved. An excess of hydrochloric acid is then added to the filtered liquid, and the whole eva- porated to complete dryness. 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, sesquioxide of iron, lime, and many other bodies which may happen to be present, are removed. The silica is washed,, dried, and heated red-hot. The most prominent characters of silica are the following : it is a very fine, white, tasteless powder, not sensibly soluble in water or dilute acids (with the exception of hydrofluoric) unless recently precipitated. It dis- solves, on the contrary, freely in strong alkaline solutions. Its density is about 2-66. and it is only to be fused by the oxy-hydrogen blowpipe. Silica is in reality an acid, and a very powerful one ; insolubility in water prevents the manifestation of acid properties under ordinary circumstances. When heated with bases, especially those which are capable of undergoing fusion, it unites with them and forms true salts, which are sometimes solu- ble in water, as in the case of the silicates of potassa and soda when the proportion of base is considerable. Common glass is a mixture of several silicates in which the reverse of this happens, the silica, or as it is more cor- rectly called, silicic acid, being in excess. Even glass, however, is slowly acted upon by water. Finely-divided silica is highly useful in the manufacture of porcelain. This substance is closely related to silicium ; it is the basis of boracic acid. Boron is prepared by a process very similar to that described in the case of silicium, the double fluoride of boron and potassium being substituted for the other salt, and the operation conducted in a small iron vessel instead of a glass tube. It is a dull greenish-brown powder, which burns in the air when heated, producing boracic acid. Nitric acid, alkalis in a fused condi- tion, chlorine, and other agents, attack it readily. There is but one oxide of boron, namely, boracic acid, containing 10'9 parts boron and 24 parts oxygen. 1 Boracic acid 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 boracic acid combined with soda. Boracic acid crystallizes in transparent colourless plates, soluble in- about 25 parts of cold water, and in a much smaller quantity at a boiling heat ; the acid has but little taste, and feebly affects vegetable colours. When heated, it loses water, and melts to a glassy transparent mass, which dis- solves many metallic oxides with great ease. ..The crystals contain 34-9 parts real acid, and 27 parts water. They dissolve in alcohol, and the solu- tion burns with a green flame. 152 BORON. Glassy boracic acid in a state of fusion requires for its dissipation in vapour a very intense and long-continued heat; the solution in water cannot, however, be evaporated without very appreciable loss by volatilization ; hence it is probable that the hydrate is far more volatile than the acid itself. By heating in a glass flask or retort one part of the vitrified boracic acid, 2 of fluor-spar, and 12 of oil of vitriol, a gaseous fluoride of boron may be obtained, and received in glass jars standing over mercury. It is a trans- parent gas, very soluble in water, and very heavy ; it forms a dense fume in the air like the fluoride of silicium. 1 These two bodies are thus constituted : SiFg, and BF* COMPOUNDS OP CARBON AND HYDROGEN. 153 ON CERTAIN IMPORTANT COMPOUNDS FORMED BY THE UNION OP THE PRECEDING ELEMENTS AMONG THEMSELVES. 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 che- mistry, as they cannot be formed by the direct union of their elements, but always arise from the decomposition of a complex body of organic origin. It will be found convenient, notwithstanding, to describe two of them in this part of the volume, as they very well illustrate the important subjects of combustion, and the nature of flame. Light Carbonetted or Carburetted Hydrogen ; Marsh-gas; Fire-damp ; Gas of the Acetates. 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, which probably existed 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 carbonic acid ; the latter is easily absorbed by lime-water or caustic potassa. Until recently, 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 vapour of alcohol through a red-hot tube, contain large quantities of light carbonetted hydrogen, associated, however, with other substances which hardly admit of separation. M. Dumas was so fortunate as to discover 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 acetate of soda, 40 parts solid hydrate of potassa, and 60 parts quicklime in powder. This mixture is transferred to a flask or retort, and strongly heated ; the gas is disengaged in great abundance, and may be received over water. 1 Light carbonetted hydrogen is a colourless and nearly inodorous gas, which does not affect vegetable colours. It burns with a yellow flame, generating 1 Ann. Chiin. et Phys. Ixxiii. 93. The reaction consists in the conversion of the acetic acid, by the aid of the elements of water, into carbonic acid and light carbonetted hydrogen ; the instability of the organic acid at a high temperature, and the attraction of the potassa for carbonic acid, being the determining causes. The lime prevents the hydrate of potassa from fusing and attacking the glass vessels. This decomposition is best understood by putt'jig it In the shape of an equation. Acetic acid C^sOa ) f Carbonic acid, 2 eq. Ca 04. \Vater H J \ Marsh-gas, 2 eq. C 2 ll4 Cill404. 154 COMPOUNDS OP carbonic acid and watei\ It is not poisonous, and may be respired to a great extent without apparent injury. The density of this compound is about 0-559, 100 cubic inches weighing 17-41 grains; and it contains carbon and hydrogen associated in the proportion of 6 parts by weight of the former to 2 of the latter. 1 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 a gas remain which is entirely absorbable by a little solution of caustic potassa. Now carbonic acid contains its own volume of oxygen ; hence one- half of the oxygen added, that is, 100 measures, must have been consumed 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 carbonic acid. When chlorine is mixed with light carbonetted hydrogen over water, no change follows, provided light be excluded. The presence of light, however, brings about decomposition, hydrochloric acid, carbonic acid, and sometimes other products being produced. It is important to remember that the gas is not acted upon by chlorine in the dark. 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 potassa. A second wash-bottle, partly filled with oil of vitriol, is connected to the first, and furnished with a tube dipping into the water of the pneumatic trough. On the first application 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-vapour diminishes in quantity, and its place becomes in great part supplied by a permanent inflammable gas ; carbonic acid and sulphurous acid 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 vapour by the acid in the second, so that the olefiant gas is delivered tole- rably pure. The reaction is too complex to be discussed at the present mo- ment ; it will be found fully described in another part of the volume. Ole- fiant gas thus produced is colourless, neutral, and but slightly soluble in water. Alcohol, ether, oil of turpentine, and even olive oil, as Mr. Faraday hag observed, dissolve it to a considerable extent. 2 It has a faint odour 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 light car- bonetted hydrogen. This gas, when mixed with oxygen and fired, explodes with extreme violence. Its density is 981 ; 100 cubic inches weigh 30-57 grains. By the use of the eudiometer, as already described, it has been found that each measure of olefiant gas requires for complete combustion exactly three of oxygen, and produces under these circumstances two measures of car- bonic acid. Whence it is evident that it contains twice its own volume of hydrogen, combined with twice as much carbon as in marsh-gas. By weight, these proportions will be 12 parts carbon, and 2 parts hydrogen. Olefiant gas is decomposed by passing through a tube heated to bright redness ; a deposit of charcoal takes place, and the gas becomes converted 1 The two carbides of hydrogen here described are thus represented in equivalents: Li;ht carbonetted hydrogen C H 2 Olefiant gas CaHa * Olefiant gas, by pressure and intense cold, produced by the evaporation in a vacuum of eolid carbonic acid and ether, is condensed into a colourless transparent liquid, but not frozen, flraraday.) R B. CARBON AND HYDROGEN. 155 into light carbonetted hydrogen, or even into free hydrogen, if the temper- ature be very high. This latter change is of course attended by increase ,of volume. Chlorine acts upon olefiant gas 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 odour, to which the name chloride of hydrocarbon, or Dutch liquid, is given. It is from this peculiarity that the term olefiant is derived. A pleasing and instructive experiment may also be made by mixing in a tall jar two measures of chlorine and one of olefiant gas, and then quickly applying 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 mo- ment 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 of management to yield a good result. 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 tem- perature at which the process is conducted, the permanent gases becoming 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 products conducted into a long horizontal pipe of large dimensions, always half filled with liquid, into which dips the extremity of each separate tube ; this is called the hydraulic main. The gas and its ac- companying vapours are next made to traverse a refrigerator, usually a series of iron pipes, cooled on the outside by a stream of water ; here the condensation of the tar and ammoniacal liquid becomes complete, and the gas proceeds onwards to another part of the apparatus, in which it is to be deprived of the sulphuretted hydrogen and carbonic acid gases always present in the crude product. This is generally effected by hydrate of lime, which readily absorbs the compounds in question. The purifiers are large iron vessels, partly filled with a mixture of hydrate of lime and water, in which a churning machine or agitator is kept in constant motion to prevent the subsidence of the lime. The gas is admitted at the bottom of the vessel by a great number of minute apertures, and is thus made to present a large surface of contact to the purifying liquid. 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 be- comes an object of importance. Coal-gas thus manufactured and purified is preserved for use in immense cylindrical receivers, close 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 yet made in such an imperfect 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. 1 1 It may give some idea of the extent of this species of manufacture, to mention, that in- th? year 18G8. for lighting London and the suburbs alone, there were eighteen public gas work.*, and 2,500,009 invested in pipes and apparatus. The yearly revenue amounted to 156 COMBUSTION, AND Coal-gas varies much in composition, judging from its variable density and illuminating power, and from the analyses which have been made. The difficulties of such investigations are very great, and unless particular pre- caution be taken, the results are merely approximative. The purified gas is believed to contain the following substances, of which the first is most abun- dant, and the second most valuable. Light carbonetted hydrogen. Olefiant gas. Hydrogen. Carbonic oxide. Nitrogen. Vapours of volatile liquid carbides of hydrogen. 1 Vapour of bisulphide of carbon. Separated by Condensation and by the Purifiers. Tar and volatile oils. Sulphate of ammonia, chloride and sulphide of ammonium. Sulphuretted hydrogen. Carbonic acid. Hydrocyanic acid, or cyanide of ammonium. A very 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 de- composed and converted into permanent gas, which requires no purification, as it is quite free from the ammoniacal and sulphur compounds which vitiate the gas from coal. A few 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 80 atmospheres ; these were furnished with a screw-valve of pecu- liar construction, and exchanged for others when exhausted. The comparative high price of the material, and other circumstances, led to the abandonment of the undertaking. COMBUSTION, AND THE STRUCTURE OP FLAME. When any solid substance, capable of bearing the fire, is heated to a certain point, it emits light, the character of which depends upon the temperature. Thus, a bar of platinum or a piece of porcelain raised to a particular tempe- rature, become 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 oxy- hydrogen blowpipe, the light becomes exceedingly powerful and acquires a tint of violet. Bodies in these states are said to be incandescent or ignited. Again, if the same experiment be made on a piece of charcoal, similar eifects will be observed, but something in addition ; for whereas the platinum 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 450,000, and the consumption of coal in the same period to 180,000 tons, 1,460 millions of cubic feet of pas being made in the year. There were 134.300 private lights, and 30,400 street lamps. 890 tons of coal were used in the retorts in the space of twenty-four hours at mid- winter, and 7,120,000 cubic feet of gas consumed in the longest night. Dr. Ure, Dictionary of Arts and Manufactures. Since that time the production of gas has been very considerably Increased. 1 These bodies increase the illuminating power, and confer on the gas its peculiar odour. THE STRUCTURE OF FLAME. 157 disappears. This is what is called combustion in contradistinction 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 com- bustion, 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 arid hydrogen by the aid of the free oxygen of the air. The heat 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 1 to the point necessary to melt refrac- tory metals, and to bring about certain desired effects of chemical decom- position. 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, there being reason to believe that the quantity of heat evolved is 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 common 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 fire-place being closed on all sides, and no en- trance of air allowed, save between the bars of the grate. Such is the kind of furnace generally employed 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, in which a crucible is repre- sented, arranged in the fire for an operation of the kind mentioned. . m.) Pig. 111. Fig. 112 158 COMBUSTION, AND The " reverberatory" furnace (fig. 112) 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 reflected downwards by the arched form of the roof. Any degree of heat can be ob- tained in a furnace of this kind, from the temperature of dull redness, 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, enjoy, when sufficiently heated, the faculty of emitting light; the same power is possessed by gaseous bodies, but the temperature required to render a gas luminous is incomparably higher than in the cases already described. Gas or vapour in this condition constitutes flame, the actual temperature of which generally exceeds that of the white heat of solid bodies. The light emitted from pure flame is exceedingly feeble ; illuminating power is almost entirely dependent upon the presence of solid matter. The flame of hydrogen, or of the inixeM 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. Th piece of lime in the blowpipe flame cannot have a higher temperature than that of the flame itself; yet the light it throws off is infinitely greater. Flames burning in the air, and not supplied with oxygen Fig. 113. from another source, are, as already stated, hollow ; the che- mical action is necessarily confined to the spot where the two bodies unite. That of a lamp or candle, when carefully ex- \_ c amined, is seen to consist of three separate portions. The dark central part, A, fig. 113, easily rendered evident by de- pressing 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, B, which, in contact with a cold body, deposits soot. On the outside a second cone, c, is to be traced, feeble in its light-giving power, but having an exceedingly high temperature. The explanation of these ap- pearances is easy : 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 supply of oxygen limited, the hydrogen takes all, to the exclusion of a great part of the car- bon. Now this happens in the case under consideration, at some little dis- tance within the outer surface of the flame, namely, in the luminous portion ; the little oxygen which has penetrated thus far inwards is entirely consumed by the hydrogen, and the particles of deposited charcoal, which would, were they cooler, form smoke, become intensely ignited by the burning hydrogen, and evolve a light whose whiteness marks a very elevated temperature. In the exterior and scarcely visible cone, these particles of carbon undergo combustion. A jet of coal-gas exhibits these 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, and the illuminating power almost disappears. The common mouth blowpipe is a little instrument of high utility ; it is merely a brass tube, fitted with an ivory mouth-piece, 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 perhaps that contrived by Mr. Pepys, and shown in fig. 114. The flame so produced is very peculiar. Instead of the double envelope just described, two long pointed cones are THE STRUCTURE OF FLAME. 159 observed, which, when the blowpipe is good, and the aperture smooth and round, are very well de- fined, the outer one being yellowish, and the inner blue. Fig. 115. 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 com- bustible matter, possessing strong reducing or deoxidizing powers, while the highly heated air just beyond the point of the exterior cone ox- idizes 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 cir- cumstances, and observations of great value made in a very short time. The use of the instrument requires an even and uninterrupted blast of some duration, by a method easily acquired with a little patience ; it consists in employing for the purpose the muscles of the cheeks alone, respiration 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 apparatus. In this lamp the wick is cylindrical, the flame being supplied with air both inside and outside ; the combustion is greatly aided by the chimney, which is made of copper when the lamp is used as a source of heat. Fig. 116 exhibits, in sec- tion, 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 introduced, in order to prevent loss when the lamp is not in use. Glass spirit-lamps, fitted Fig. 116. Fig. 114. Fig. 115. Fig. 117. 1 When in use this aperture must always be open, otherwise an accident is sure to happen, the heat expands the air in the lump, and the epirit is forced out in a state of inflammation. 160 COMBUSTION, AND Fig. 119. with caps (fig. 117) to prevent evaporation, are very convenient for occa- sional use, being always ready and in order.' In London, and other large towns where coal-gas is to be had, that sub- stance is constantly used with the greatest economy and advantage in every respect as a source of heat. Retorts, flasks, capsules, and other vessels, can be thus exposed to an easily re- gulated and invariable temperature for many successive 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. 119, consist- ing of a common Argand gas-burner fixed on a heavy and low foot, and connected with a flexible tube of caoutchouc or other material, leaves nothing to desire. The kindling-point, or temperature at which combus- tion commences, is very different with different substan- ces ; phosphorus will sometimes take fire in the hand ; sulphur requires a temperature exceeding that of boil- ing water ; charcoal must be heated to redness. Among gaseous bodies the same fact is observed : hydrogen is inflamed by a red-hot wire ; carbonetted hydrogen re- quires 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 safe-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 ex- plosive, taking fire at a light, and burning with a pale blue flame ; and many fearful accidents have occurred from the ignition of large quantities of mixed air and gas 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 labours resulted in some exceedingly important discoveries respecting flame, of which the substance has been given, and which led to the construction of the lamp which bears his name. 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 other- wise, 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 cooling, and its transmission rendered impossible. In this experiment, high conducting power and diminished diameter com- pensate for diminution of length ; and to such an extent can this be carried, Fig. 118. 1 The ppirit-lamp represented in fisr. 118. is one contrived by Dr. Mitchell. "It is made of tinned iron. The alcohol is poured out by means of the hollow handle, and is admitted 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 con- sumed, and the flame kept uniform; and as the pipes which pass to the burner are so re- mote from the flame, the alcohol never be- comes heated so as to fly off through the vent-hole, and thus to cause greater waste and danger of explosion." A cylindrical chimney is an advantageous addition for many purposes. It may be made of tiri-plute or copper. R. B. THE STRUCTURE OP FLAME 161 Fig. 120. that metallic gauze, -which may be looked upon as a series of very short square tubes arranged side by side, arrests in the most complete manner the passage of flame in explosive mixtures, when of sufficient degree of fineness, depending upon the inflammability of the gas. Most providentially, the fire-damp mixture has an ex- ceedingly high kindling point ; a red heat does not cause in- flammation ; consequently, the gauze will be safe for this substance, when flame would pass in almost any other case. The miner's safe-lamp (fig. 120) is merely an ordinary oil- lamp, the flame of which is enclosed in a cage of wire gauze ; made double at the upper part, containing about 400 aper- tures 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, with- out 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, extinguished, while the in- terior of the gauze cylinder becomes filled with the burn- ing mixture of gas and air. As the atmosphere becomes purer, the wick is once more relighted. These appear- ances are so remarkable, that the lamp becomes an admi- rable indicator of the state of the air in different parts of the mine. 1 The same great principle has been ingeniously applied by Mr. Hemming to the construction of the oxy-hydrogen safety -jet formerly 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, forcibly driven into the centre of the bundle. Fig. 121. The arrangement thus presents a series of metal tubes, very long in proportion to their diameter, the cooling powers of which are so great as to prevent the pos- sibility of the passage of flame, even with oxygen and hy- drogen. 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 (fig. 122) into a short spiral, about 0-1 inch Fig. 122. Fig. 121. * This is the true use of the lamp, namely, to permit the viewer or superintendent, with- out risk to himself, to examine the state of the air in every part of the mine; not to enable workmen to continue their labours 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 either to adopt efficient means of ventilation, or to clof> workings of this dangerous character altogether. 162 NITROGEN AND HYDROGEN; AMMONIA. 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. 1 NITROGEN AND HYDROGEN; AMMONIA. When powdered sal-ammoniac is mixed with moist hydrate of lime, and gently heated in a glass flask, a large quantity of gaseous matter is disengaged, which must be collected over mercury, or by displacement, advantage being taken of its low specific gravity. Ammoniacal gas thus obtained is colourless ; it has a very powerful pun- gent odour, and a strong alkaline reaction to test-paper, by which it may be at once distinguished from nearly all other bodies possessing the same physi- cal characters. Under a pressure of 6-5 atmospheres at 60 (15 -5C), am- monia condenses to the liquid form. a Water dissolves about 700 times its volume of this remarkable gas, forming a solution which in a more dilute state has long been known under the name of liquor ammonice ; by heat, a great part is again expelled. The solution is decomposed by chlorine, sal- ammoniac being formed, and nitrogen set free. Ammonia has a density of 0-589; 100 cubic inches weigh 18-26 grains. It cannot be formed by the direct union of its elements, although it is some- times produced under rather remarkable circumstances by the deoxidation of nitric acid. The great sources of ammonia are the feebly-compounded azotized principles of the animal and vegetable kingdoms, which, when left to putrefactive change, or subjected to destructive distillation, almost inva- riably give rise to an abundant production of this substance. The analysis of ammoniacal 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 hydrogen gas, and 1 measure 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 will be in the proportion of 3 parts hydrogen to 14 parts nitrogen. 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 1 Where coal-gas is to be had, it may be advantageously used as a source, of heat, by taking advantage of the above-mentioned fact. On passing a current of gas through a wide vertical tube, open at the bottom to afford a free mixture with atmospheric air, but closed at Uie top by wire gauze, and then kindling the mixture after its escape through the meshes, it will burn with feeble illuminating power, but no loss of heat. When the proportion of the gas to the atmospheric air is such as not to allow the flame to become yellow, the combustion will be complete, and no carbonaceous deposit will be formed on cold bodies held over the fiames. The length and diameter of the cylinder are determined by the amount of gas to be burnt, and the length may be much decreased by interposing a second diaphragm of wire gauze about mid-length of the cylinder, the current of gas being introduced below this, by which means a more thorough and rapid mixture is made with the atmospheric air. Sir John Robinson, K. II. &c., Ed. New Phil. Journal, 1840. 11. B. At the temperature of 103 ( 75C), liquid ammonia freezes into a colourless solid, hMvicr than the liquid itself. (Faraday.) K. B. NITROGEN AND BORON. 163 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 water is put into the safety-funnel, heat cautiously applied to the flask, and the whole left to itself. The disengagement of ammonia is very regular and uniform. Chloride of calcium, with excess of hydrate of lime, remains in the flask.' The decomposition of the salt is usually represented in the manner shown by the subjoined diagram. {Ammonia Ammonia. Hydrochloric J Hydrogen ^^- Water, acid I Chlorine. _ calcium. Solution of ammonia should be perfectly colourless, leave no residue on evaporation, and when supersaturated by nitric acid, give no cloud or mud- diness with nitrate of silver. Its density diminishes with its strength, that of the most concentrated being about 0-875 ; the value in alkali of any sample of liquor ammoniae 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 Alkalimetry. When solution of ammonia is mixed with acids of various kinds, salts are generated, which resemble in the most complete manner the corresponding compounds of potassa and soda ; these are best discussed in connexion with the latter. Any ammoniacal salt can at once be recognized by the evolution of ammonia when it is heated with hydrate of lime, or solution of carbonate of potassa or soda. NITROGEN AND BORON. A combination of nitrogen with boron was first obtained by Balmain. Woehler prepared it by mixing one part of pure dry borax with two parts of dry sal-ammoniac, heating to redness, boiling with water and hydrochloric acid, filtering and washing with hot water, when the compound remained in the form of a white powder. As yet it has not been obtained quite free from oxygen. SULPHUR, SELENIUM, AND PHOSPHORUS, WITH HYDROGEN. Sulphuretted Hydrogen ; Hydrosulphuric Acid. There are two methods by which this important compound can be readily prepared, namely, by *he action of dilute sulphuric acid upon sulphide of iron, and by the decomposi- tion of sulphide of antimony by hydrochloric acid. The first method yields it most easily, and the second in the purest state. Protosulphide of iron is put into the apparatus for hydrogen, already several times mentioned, together with some 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 : Se Fig. 106, p. 142. SULPHUR WITH HYDROGEN. Sulphuretted hydrogen. Sulphuric acid ' ^ :=::;)fc - Sulphate of protoxide of iron. By the other plan, finely-powdered sulphide of antimony is put into a flask, to which a cork and bent tube can be adapted, and strong liquid hydro- chloric acid poured upon it. On the application of heat, a double inter- change occurs between the bodies present, sulphuretted hydrogen being formed, and chloride of antimony. The action only lasts while the heat is maintained. Hydrochloric acid { *$ ^^ Sulphuretted ^&*' Sulphide of antimony { ^^n^- ^=^Chloride of antimony. Sulphuretted hydrogen is a colourless gas, having the odour of putrid eggs ; it is most offensive when in small quantity, when a mere trace is pre- sent in the air. It is not irritating, but, on the contrary, powerfully narcotic. When set on fire, it burns with a blue flame, producing water and 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 ; 100 cubic inches weigh 36-33 grains. A pressure of 17 atmospheres at 50 (10C) reduces Fig. 123. jj. | Q j. ne iiq u jd f orm< Cold water dissolves its own volume of sulphuretted hydrogen, and the solution is often directed to be kept as a test ; it is so prone to decomposition, however, by the oxygen of the air, that it speedily 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 (fig. 123), to which a bit of bent tube is fitted by a cork, is supplied with a little sulphide of iron 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 instrument is again ready for use. When potassium is heated in sulphuretted hydrogen, the metal burns with great energy, becoming converted into sulphide, while pure hydrogen remains, equal in volume to the original gas. Taking this fact into account, and comparing the density of the gas with those of hydrogen and sulphur-vapour, it appears that every volume of sulphuretted hydrogen contains one volume of hydrogen and one-sixth of a volume of sulphur-vapour, the whole con- densed into one volume. This corresponds very nearly with its composition by weight, determined by other means, namely, 16 parts sulphur and 1 part hydrogen. When a mixture is made of 100 measures of sulphuretted hydrogen and 150 measures of pure cxygen, and exploded by the electric spark, complete combustion t-nsues, ana 100 measures of sulphurous acid gas result. Sulphuretted hydrogen is a frequent product of the putrefaction of organic tnatter, both animal and vegetable ; it occurs also in certain mineral springs, as at Harrowgate, and elsewhere. When accidentally present in the atmo- PERSULPHIDE OP HYDROGEN. 165 sphere 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, and it frequently affords the means also 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 sulphuretted hydrogen, water or hydrochloric acid being produced at the same time. All the metals are, in fact, precipitated whose sulphides are insoluble in water and in dilute acids. Sulphuretted hydrogen possesses itself the properties of an acid ; its solution in water reddens litmus paper. The best test for the presence of this compound is paper wetted with solution of acetate of lead. This salt is blackened by the smallest trace of the gas. Persulphide of Hydrogen. This substance corresponds in constitution and instability to the binoxide of hydrogen ; it is prepared by the following means: Equal weights of slaked lime and flowers of sulphur are boiled with 5 or 6 parts of water for half an hour, when a deep orange-coloured solution is produced, containing among other things persulphide of calcium. This is filtered, and slowly added to an excess of dilute sulphuric acid, with constant agitation. A white precipitate of separated sulphur and sulphate of lime makes its appearance, together with a quantity of yellow oily-looking matter, which collects at the bottom of the vessel ; this is persulphide of hydrogen. 1 If the experiment be conducted by pouring the acid into the solution of sulphide, then nothing but finely-divided precipitated sulphur is obtained. The persulphide is a yellow, viscid, insoluble liquid, exhaling the odour of sulphuretted hydrogen; its specific gravity is 1-769. It is slowly decom- posed even in the cold into sulphur and sulphuretted hydrogen, and instantly by a higher temperature, or by contact with many metallic oxides. This compound probably contains twice as much sulphur in relation to the other elements, as sulphuretted hydrogen. Hi/drogen and Selenium ; Selenietled Hydrogen. This substance is produced by the action of dilute sulphuric acid upon selenide of potassium or iron ; it very much resembles sulphuretted hydrogen, being a colourless gas, freely 1 The reaction which ensues when hydrate of lime, sulphur, and water, are boiled together, is rather complex; bisulphide or pentasulphide of calcium being formed, together with hypo sulphite of lime, arising from the transfer of the oxygen of the decomposed lime to another portion of sulphur. 2 pn 1'nip i ^ e( l' pa ^ c i um - ^_ -*- % e( L- bisulphide of calcium. I 2 eq. oxygen 4 eq. sulphur- 2 eq. sulphur - ^=- 1 eq. hyposulphurous acid. The bisulphide of calcium, decomposed by an acid under faA'ourable circumstances, yields a ealt of lime and bisulphide (persulphide) of hydrogen. 1 eq. bisulp. calcium * - ph _ - - 1 eq. bisulphide of hydropm. ______ , Sulphuric acid =^ l <*! sulphate of lime. When the acid is poured into the sulphide, sulphuretted hydrogen, water, and sulphate of lime, are 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 sul* stance, hydrochloric acid must be used in the place of sulphuric. 166 PHOSPHORUS WITH HYDROGEN. soluble in water, and decomposing metallic solutions like that subtance ; in- soluble 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 39-5 parts selenium, and 1 part hydrogen. Phosphorus and Hydrogen ; Phosphoretted Hydrogen. This body bears a slight analogy in some of its chemical relations to ammoniacal gas ; it is, however, destitute of alkaline properties. Phosphoretted hydrogen may be obtained in a state of purity by heating in a small retort hydrated phosphorous acid, which is by such treatment de- composed into phosphoretted hydrogen and hydrated phosphoric acid. 1 Thus obtained, the gas has a density of 1-24. It contains 32 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-vapour, condensed into two volumes. It possesses a highly disagreeable odour 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 potassa or hydrate of lime, water, and phosphorus ; 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. The alkali acts by its presence determining the decomposition of the water, in the same manner as sulphuric acid determines the decompo- sition of water when in contact with zinc. Water ... / H y dr S en 3^==- Phosphoretted hydrogen. Phosphorus Phosphorus. Lime ' -^^ Hypophosphite of lime. 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 re- quires caution; the bubbles should be singly admitted. When kept over water for some time, the gas loses this property, without otherwise suffering any appreciable change : but if dried by chloride of calcium, it may be kept unaltered for a much longer period. M. Paul Thenard has shown that the spontaneous combustibility of the gas arises from the presence of the vapour of a liquid phosphide of hydrogen, which can be procured in small quantity, by conveying the gas produced by the action of the water on phosphide of calcium through a tube cooled by a freezing mixture. This substance forms a colourless liquid of high refractive power and very great volatility. It does not freeze at ( 17-8C). In contact with air it inflames instantly, and its vapour in very small quantity communicates spontaneous inflammability to pure phosphoretted hydrogen, and to all other combustible gases. It is decomposed by light into gaseous phosphoretted hydrogen, and a solid phos- phide which is often seen on the inside of jars containing gas which has lost Decomposition of hydrated phosphorous acid by heat : f C 1 eq. phoaph. ^ l e< l- phosphoretted hydrogen, PIIj Ireal^cid 1 3 eq " P ho8 P h - ia (12 eq. oxygen | 3 eq. hydrog.' 12 eq. I 9 eq. hydrog. ^_^^ f3 eq. phos-) H _ d ,- twl nhofl . water \ 3 eq. oxygen _^=?--^. j pboric ac.> H y d rated phos- [ 9 eq. oxy|en - : ^^ 9 eq. water.) P honc acltL NITROGEN WITH CHLORINE, ETC. 167 the property of spontaneous inflammation by exposure to light. Strong acids occasion its instantaneous decomposition. Its instability is equal to that of binoxide of hydrogen. It is to be observed that the pure phospho- retted hydrogen gas itself becomes spontaneously inflammable if heated to the temperature of boiling water. 1 Phosphoretted hydrogen decomposes several metallic solutions, giving rise to precipitates of insoluble phosphides. With hydriodic acid it forms a crys- talline compound somewhat resembling sal-ammoniac. NITROGEN WITH CHLORINE AND IODINE. Chloride of Nitrogen. When sal-ammoniac or nitrate of ammonia is dis- solved in water, and a jar of chlorine gas inverted into the solution, the gas is absorbed, and a deep yellow oily liquid is observed to collect upon the surface of the solution, which ultimately sinks in globules to the bottom. This is chloride of nitrogen, 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 is 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 dan- gerous 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 is explained by the following diagram :- Chlorine ^^^ Chloride of nitrogen. Chlorine ^^^^^ Hydrochloric acid a Nitrogen - ""^ST* Hydrogen """" ydrochloric acid Hydrochloric acid. Chloride of nitrogen is very volatile, and its vapour is exceedingly irrita- ting to the eyes. It has a specific gravity of 1 -653. It may be distilled at 160 (71 0< 1C), although the experiment is attended with great danger. Between 200 (93-3C) and 212 (100C) it explodes with the most fearful violence. Contact with almost any combustible matter, as oil or fat of any kind, determines the explosion at common temperatures ; a vessel of porce- lain, 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 induce a belief that it contains hydrogen. 3 Iodide, of Nitrogen. When finely-powdered iodine is put into caustic am- monia it is in part dissolved, giving a deep brown solution, and the residue is converted into a black powder, which is the substance in question 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. Iodide of nitrogen is a black insoluble powder, which, when drv, explodes with the slightest touch, even that of a feather ; and sometimes without any obvious cause. The explosion is not nearly so violent as that of the com- * Ann. Chim. et Phys. 3rd series, xiv. 5. According to M. Th6nard, the new liquid phosphirt* of hydrogen contains Plh and the solid Pall. The gas is represented by the formula Plfc. 'Instead of NCI* it may in reality be Nil Cla. 168 OTHER COMPOUNDS OP pound last described, and is attended with the production of violent fumes of iodine. Dr. Gladstone has proved that this substance contains hydrogen, and that it may be viewed as ammonia, in which two-thirds of the hydrogen are replaced by iodine. OTHER COMPOUNDS OF NON-METALLIC ELEMENTS. Chlorine with Sulphur and Phosphorus. Chloride of Sulphur. The subchlo- ride is easily prepared by passing dry chlorine over the surface of sulphur kept melted in a small glass retort connected with a good condensing ar- rangement. The chloride distils over as a deep orange-yellow mobile liquid, of peculiar and disagreeable odour, which boils at 280 (137 -8C). 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. 1 Subchloride of sulphur is instantly decomposed by water ; hydrochloric and hyposulphurous acids are formed, and sulphur separated. The hypo- sulphurous acid in its turn decomposes into stilphur and sulphurous acid. Protochloride of sulphur is formed by exposing the above compound for a considerable time to the action of chlorine, and then distilling it in a stream of the gas. It has a deep red colour, is heavier than water, boils at 147 (63-9C), and contains twice as much chlorine as the subchloride. 3 Chlorides of Phosphorus. Terchloride. 3 This is prepared in the same man- ner as subchloride of sulphur, by gently heating phosphorus in dry chlorine gas, the phosphorus being in excess. Or, by passing the vapour of phos- phorus over fragments of calomel (subchloride of mercury) contained in a glass tube and strongly heated. It is a colourless, thin liquid, which fumes in the air, and possesses a powerful and offensive odour. Its specific gravity is 1-45. Thrown into water, it sinks to the bottom of that liquid, and be- comes slowly decomposed, yielding phosphorous acid and hydrochloric acid. This compound contains 32 parts phosphorus, and 106-5 parts chlorine. Pentachloridc of Phosphorus.* The compound formed when phosphorus is burned in excess of chlorine. Into a large retort, fitted with a cap and stop- cock, pieces of phosphorus are introduced ; the retort is then exhausted, and filled with dry chlorine gas. The phosphorus takes fire, and burns with a pale flame, forming a white, volatile, crystalline sublimate, which is the pen- tachloride. It may be obtained in larger quantity by passing a stream of chlorine gas into the preceding liquid terchloride, which becomes gradually converted into a solid, crystalline mass. Pentachloride of phosphorus is decomposed by water, yielding phosphoric and hydrochloric acids. Two bromides of phosphorus are known, closely corresponding in proper- ties and constitution with the chlorides. Several compounds of iodine and phosphorus appear to exist : they are fusible crystalline substances, which decompose by contact with water, and yield hydriodic and phosphorous, or phosphoric acid. Chlorine and Carbon. Several compounds of chlorine and carbon are known. They are obtained indirectly by the action of chlorine upon certain organic compounds, and are described in connection with the history of alcohol, &c. Iodine with Sulphur and Phosphorus. These compounds are formed by gently heating together the materials in vessels from which the air is ex- cluded. They present few points of interest. Chlorine with Iodine. Iodine readily absorbs chlorine gas, forming, when the cnlorine is in excess, a solid, yellow compound, and when the iodine pre- ponderates, a brown liquid. The solid iodide is decomposed by water, yield- ing hydrochloric and iodic acids. 5 S*C1. SC1. 3 PC1 3 . 'PCI* Hence it doubtless contains 1 eq. iodine, and 5 eq. chlorine, or ICle. NON- METALLIC ELEMENTS. 169 Another definite compound is formed by heating in a retort a mixture of 1 part iodine and 4 parts chlorate of potassa ; oxygen-gas and chloride of iodine are disengaged, and the latter may be condensed by suitable means, lodate and perchlorate of potassa remain in the retort. This chloride of iodine is a yellow, oily liquid, of suffocating smell and astringent taste ; it is soluble in water and alcohol without decomposition. tt probably consists of 127 parts iodine, and 35-5 parts chlorine. 1 Carbon and Sulphur. Bisulphide of Carbon. A wide porcelain tube is filled with pieces of charcoal, which have been recently heated to redness in a ;overed 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 downwards, 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 vapour, which, at that high temperature, combines with the carbon, forming an exceedingly volatile compound, which is condensed by the ice and collects at the bottom of the vessel. This is collected and re-distilled with very gentle heat in a retort connected with a good condenser. Bisulphide of carbon is a transparent colourless liquid of great refractive and dispersive power. Its density is 1-272. It boils at 110 (4o-3C), and emits vapour of considerable elasticity at common temper- atures. The odour of this substance is very repulsive. When set on fire in the air it burns with a blue flame, forming carbonic acid and sulphurous acid gases ; and when its vapour is mixed with oxygen it becomes explosive. It freely dissolves sulphur, and by spontaneous evaporation deposits the latter in beautiful crystals ; it also dissolves phosphorus Chlorides of Silicium and Boron. Both silicium and boron combine directly with chlorine. The chloride of silicium is most easily obtained by mixing finely-divided silica with charcoal-powder and oil, strongly heating the mix- ture in a covered crucible, and then exposing the mass so obtained in a por- celain 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 colourless and very volatile liquid, boiling at 122 (50C), of pungent, suffocating odour. In contact with water it yields hydrochloric acid and gelatinous silica. This substance contains 21-3 parts silicium, and 106-5 chlorine. 3 Bromide of Silicium may be obtained by a similar proceeding, the vapour of bromine being substituted for chlorine ; it resembles the chloride, but is less volatile. Chloride of Boron is a permanent gas, decomposed by water with produc- tion of boracic 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 boracic acid and char- coal. It resembles in constitution chloride of silicium. * Or single equivalents. 15 170 GENERAL PRINCIPLES OE ON THE GENERAL PRINCIPLES OF CHEMICAL PHILOSOPHY THE study of the non-metallic elements can be pushed to a very consider able extent, and a large amount of precise and exceedingly important infor- mation acquired, without much direct reference to the great fundamental laws of chemical union ; the subject cannot be discussed in this manner com- pletely. as will be obvious from occasional 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, furnish admirable illusti-ations 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 facilitated by constant references to examples of combinations, the elements and pro- ducts of which have been already described. So much more difficxilt 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 farther, however, it is absolutely necessary that these matters should be discussed ; the metallic compounds are so numerous and complicated, that the establishment of some general principle, some con- necting link, becomes indispensable. The doctrine of equivalents, and the laws which regulate the formation of saline compounds, supply this defi- ciency. In the organic department of the science, the most interesting perhaps of all, a knowledge of these principles, and, farther, an acqiiaintance or even familiarity with the beautiful system of chemical notation now in use, are absolutely required. This latter is found of very great service in the study of salts and other complex inorganic compounds, but in that of organic chemistry it cannot be dispensed with. It will be proper to commence with a notice of the principles which regu- late the modern nomenclature in use in chemical writings. NOMENCLATURE. In the early days of chemistry the arbitrary and fanciful names which were conferred by each experimenter on the new compounds he discovered sufficed to distinguish these from each other, and to render intelligible the description given of their production. Such terms as oil of vitriol, spirit of salt, oil of tartar, butter of antimony, sugar of lead, flowers of zinc, sal enixum, sal mirabile, &c., were then quite admissible. In process of time, however, when the number of known substances became vastly increased, the confu- sion of language produced by the want of a more systematic kind of nomen- clature became quite intolerable, and the evil was still farther increased by the frequent use of numerous synonyms to designate the same substance. In the year 1787, Lavoisier and his colleagues published the plan of the CHEMICAL PHILOSOPHY. 171 remarkable system of nomenclature, -which, with some important extensions since rendered necessary, has up to the present time to a great extent satisfied the wants of the science. It is in organic chemistry that the deficiencies of this plan are chiefly felt, and that something like a return to the old method has been rendered inevitable. Organic chemistry is an entirely new science which has sprung up since the death of these eminent men, and has to deal with bodies of a constitution or type differing completely from that of the inorganic acids, bases and salts which formed the subjects of the chemical studies of that period. The rapid progress of discovery, by which new com- pounds, and new classes of compounds, often of the most unexpected nature, are continually brought to light, sufficiently proves that the time to attempt the construction of a permanent systematic plan of naming organic bodies has not yet arrived. The principle of the nomenclature in use may be thus explained : Ele- mentary substances still receive arbitrary names, generally, but not always, referring to some marked peculiarity of the body ; an uniformity in the ter- mination of the word has generally been observed, as in the case of new metals whose names are made to end in turn. Compounds formed by the union of non-metallic elements with metals, or with other non-metallic elements, are collected into groups having a kind of generic name derived from the non-metallic element, or that most opposed in characters to a metal, and made to terminate in ide. 1 Thus we have oxides, chlorides, iodides, bromides, &c., of hydrogen and of the several metals ; oxides of chlorine ; chlorides of iodine and sulphur ; sulphides and phosphides of hydrogen and the metals. The nomenclature of oxides has been already described (p. 109). They are divided into three classes, namely, alkaline or basic oxides, neutral oxides, and oxides possessing acid characters. In practice the term oxide is usually restricted to bodies belonging to the first two groups, those of the third being simply called acids. Generally speaking, these acids are derived from the non-metallic elements, which yield no basic oxides ; many of the metals, however, yield acids of a more or less energetic description. The same element in combining with oxygen in more than one proportion may yield more than one acid ; in this case it has been usual to apply to the acid containing most oxygen the termination ic, and to the one containing the lesser quantity the termination ous. When more members of the same group came to be known, recourse was had to a prefix, hypo or hyper, (or per,) signifying deficiency or excess. Thus, the two earliest known acids of sulphur were named respectively sulphurous and sulp/niric acids ; subse- quently two more were discovered, the one containing less oxygen than sulphurous acid, the other intermediate in composition between sulphurous and sulphuric acids. These were called hyposulpliurous and hyposulphuric acids. The names of the new acids of sulphur of still more recent discovery are not yet permanently fixed ; Lavoisier's system, even in its extended form, fails to furnish names for such a lengthened series. Other examples of the nomenclature of acids with increasing proportions of oxygen are easily found ; as hypopliOKphor ous, phosphorous and phosphoric acids; hypochlorous, chlorous, hypochloric, chloric, and perchloric acids ; nitrous, hyponitric, and nitric acids, &c. The nomenclature of salts is derived from that of the acid they contain ; if the name of the acid terminate in ic, that of the salt is made to end in ate .* if in ous, that of the saline compounds ends in He. Thus, sulphuric acid forms sulphates of the various bases ; sulphurous acid, sulphites ; hyposulphurous acid, hyposulphites ; hyposulphuric acid, hyposuJphates, &c. The rule here is very simple and obvious. 1 Formerly the termination uret was likewise frequently used. 172 GENERAL PRINCIPLES OF The want of uniformity in the application of the systematic nomenclature is chiefly felt in the class of oxides not possessing acid characters, and in that of some analogous compounds. The old rule was to apply the word protoxide to the oxide containing least oxygen, to call the next in order bin- oxide, the third tritoxide, or teroxide ; &c. But latterly this rule has been broken through, and the term protoxide given to that oxide of a series in which the basic characters are most strongly marked. Any compound con- taining a smaller proportion of oxygen than this is called a suboxide. An example is to be found in the two oxides of copper ; that which was once called binoxide is now protoxide, being the most basic of the two, while the former protoxide is degi-aded into suboxide. The Latin prefix per, or rarely hyper, is sometimes used to indicate the highest oxide of a series destitute of acidity, as peroxide of iron, chromium, manganese, lead, &c. Other Latin prefixes, as scsqui, bi or bin, and quad, applied to the name of binary compounds or salts, have reference to the con- stitution of these latter expressed in chemical equivalents. 1 Thus, an oxido in which the proportion of oxygen and metal are in equivalents, as 1-5 to 1, or 3 to 2, is often called a sesquioxide ; if in the proportion of 2 to 1, a binoxide, &c. The same terms are applied to salts ; thus we have neutral sulphate of potassa, sesquisutphale of potassa, and bisulphate of potassa ; the first con- taining 1 equivalent of acid to 1 of base, the second 1-5 of acid to 1 of base, and the third 2 equivalents of acid to 1 equivalent of base. In like mannei we have neutral oxalate, binoxalate, and quadroxalate of potassa, the latte? having 4 eq. of acid to 1 eq. of base. Many other cases might be cited. The student will soon discover that the rules of nomenclature are ofter loosely applied, as when a Latin numeral prefix is substituted for one of Greet origin. We speak of tersulphide instead of tritosulphide of antimony These and other small irregularities are not found in practice to cause seri ous confusion. THE LAWS OF COMBINATION BY WEIGHT. The great general laws which regulate all chemical combination admit of being laid down in a manner at once simple and concise. They are four ir number, and to the following eifect: 1. All chemical compounds are definite in their nature, the rptK of tli6 elements being constant. 2. When any body is capable of uniting with a second in several pro- portions, these proportions bear a simple relation to each other. 3. If a body, A, unite with other bodies, B, C, T>, the quantities of B, C, D, which unite with A, represent the relations in which they unite among themselves, in the event of union taking place. 4. The combining quantity of a compound is the sum of the combining quantities of its components. (1.) Constancy of Composition. That the same chemical compound invari- ably contains the same elements united in unvarying proportions, is a propo- sition almost axiomatic; it is involved in the very idea of identity itself. The converse, however, is very far from being true ; the same elements com- bining in the same proportions do not of necessity generate the same substance. Organic chemistry furnishes numerous instances of this very remarkable fact, in which the greatest diversity of properties is associated with identity of chemical composition. These cases seem to be nearly confined to organic 1 See a few pages forward. CHEMICAL PHILOSOPHY. 173 chemistry ; only a few well-established and undoubted examples being known in the organic or mineral division of the science. (2.) Multiple Proportions. Illustrations of this simple and beautiful law abound on every side ; let the reader take for example the compounds of nitrogen and oxygen, five in number, containing the proportions of the two elements so described that the quantity of one of them shall remain con- stant: Nitrogen. Oxygen. Protoxide 14 8 Binoxide 14 16 Nitrous acid 14 24 Hyponitric acid 14 32 Nitric acid : 14 40 It will be seen at a glance, that while the nitrogen remains the same, the quantities of oxygen increase by multiples of 8, or the number representing the quantity of that substance in the first compound; thus 8, 8x2, 8x3, 8x4, and 8x5, gi ye respectively the oxygen in the protoxide, the binoxide, nitrous acid, hyponitric acid, and lastly, nitric acid. Again, carbonic acid contains exactly twice as much oxygen in proportion to the other constituent as carbonic oxide ; the binoxide of hydrogen is twice as rich in oxygen as water ; the corresponding sulphides exhibit the same phenomena, while the metallic compounds offer one continued series of illustrations of the law, although the ratio is not always so simple as that of 1 to 2. It often happens that one or more members of a series are yet deficient : the oxides of chlorine afford an example Chlorine. Oxygen. Hypochlorous acid 35-5 8 Chlorous acid 35-5 24 Hypochloric acid 35-5 32 Chloric acid 35-5 40 Perchloric acid 35-5 56 Here the quantities of oxygen progress in the following order: 8, 8x3, 8x4, 8x5, 8x7; a gap is manifest between the first and second substances; this remains to be filled up by future researches. The existence of a simple relation among the numbers in the second column is however not the less evident. Even when difficulties seem to occur in applying this principle, they are only apparent, and vanish when closely examined. In the highly complex sulphur series, given at p. 132, the numbers placed in each column are multiples of the lowest amongst them ; and, by making the assumption, which is not at all extravagant, that certain of the last-named bodies are in- termediate combinations, we may arrange the four direct compounds in such % manner that the sulphur shall remain a constant quantity. Sulphur. Oxygen. Hyposulphurous acid 32 16 Sulphurous acid 32 32 Hyposulphuric acid 32 40 Sulphuric acid 32 48 Compound bodies of all kinds are also subject to the law of multiples when they unite among themselves, or with elementary substances. There arc two sulphates of potassa and soda : the second contains twice as much acid in relation to the alkaline base as the first. There are three oxalatcs of potassa, namely, the simple oxalate, the binoxalatc, and the quadroxalate ; 15* 174 GENERAL PRINCIPLES OF the second has equally twice as much acid as the first ; and the third twice as much as the second. Many other cases might be cited, but the student, once in possession of the principle, will easily notice them as he proceeds. (3.) Law of Equivalents. It is highly important that the subject now to be discussed should be completely understood. Let a substance be chosen whose range of affinity and powers of combi- nation are very great, and whose compounds are susceptible of rigid and exact analysis ; such a body is found in oxygen, which is known to unite with all the elementary substances, with the single exception of fluorine. Now, let a series of exact experiments be made to determine the proportions in which the different elements combine with one and the same constant quantity of oxygen, which, for reasons hereafter to be explained, may be assumed to be 8 parts by weight ; and let these numbers be arranged in a column opposite the names of the substances. The result is a table or list like the following, but of course much more extensive when complete. Oxygen. Hydrogen 1 Nitrogen 14 Carbon 6 Sulphur 16 Phosphorus 32 Chlorine 35-5 Iodine 127 Potassium 39 Iron 28 Copper 31-7 Lead.... 103-7 Silver 108 &c. &c. Now the law in question is to this effect : If such numbers represent the proportions in which the different elements combine with the arbitrarily- fixed quantity of the starting substance, the oxygen, they also represent the proportions in which they unite among themselves, or at any rate bear some ex- ceedingly simple ratio to these proportions. Thus, hydrogen and chlorine combine invariably in the proportions 1 and 35-5 ; hydrogen and sulphur, 1 to 16; chlorine and silver, 35-5 to 108; iodine and potassium, 127 parts of the former to 39 of the latter, c. This rule is never departed from in any one instance. The term equivalent is applied to these numbers for a reason which will now be perfectly intelligible ; they represent quantities capable of exactly replacing each other in combination : 1 part of hydrogen goes as far in com- bining with or saturating a certain amount of oxygen as 28 parts of iron, 39 of potassium, or 108 of silver ; for the same reasons, the numbers are said to represent combining quantities, or proportionals. Nothing is more common than to speak of so many equivalents of this or that substance being united to one or more equivalents of a second ; by this expression, quantities are meant just so many times greater than these rela- tive numbers. Thus, sulphuric acid is said to contain 1 equivalent of sul- phur and 3 equivalents of oxygen; that is, a quantity of the latter repre- sented by three times the combining number of oxygen ; phosphoric acid is made up of 1 equivalent of phosphorus and 5 of oxygen ; the red oxide of iron contains, as will be seen hereafter, 3 equivalents of oxygen to every 2 equivalents of metal, &c. It is an expression which will henceforward be CHEMICAL PHILOSOPHY. 175 freely and constantly employed ; it is hoped, therefore, that it will be under- stood. The nature of the law will easily show that the choice of the body destined to serve for a point of departure is perfectly arbitrary, and regulated by con- siderations of convenience alone. A body might be chosen which refuses to unite with a considerable num- ber of the elements, and yet the equivalents of the latter would admit of being determined by indirect means, in virtue of the very peculiar law under discussion. Oxygen does not unite with fluorine, yet the equivalent of the latter can be found by observing the quantity which combines with the equi- valent quantity of hydrogen or calcium, already known. We may rest as- sured that if an oxide of fluorine be ever discovered, its elements will be associated in the ratio of 8 to 19, or in numbers which are either multiples or submultiples of these. The number assigned to the starting-substance is also equally arbitrary ; if, in the table given, oxygen instead of 8 were made 10, or 100, or even a fractional number, it is quite obvious that although the other numbers would all be different, the ratio, or proportion among the whole, would remain un- changed, and the law would still be maintained in all its integrity. There are in fact two such tables in use among chemists ; one in which oxygen is made = 8, and a second in which it is made = 100; the former is generally used in this country and England, and the latter still to a certain extent on the Continent. The only reason for giving, as in the pre- sent volume, a preference to the first is, that the numbers are smaller and more easily remembered. The number 8 has been chosen in this table to represent oxygen, from an opinion long held by the late Dr. Prout, and recently to appearance substan- tiated in some remarkable instances by very elaborate investigation, that the equivalents of all bodies are multiplies of that of hydrogen; and, conse- quently, by making the latter unity, the numbers would be all integers. The question must be considered as altogether unsettled. A great obstacle to such a view is presented by the case of chlorine, which certainly seems to be a fractional number; and one single well-established exception will be fatal to the hypothesis. As all experimental investigations are attended with a certain amount of error, the results contained in the following table must be looked upon merely as good approximations to the truth. For the same reason, small differences are often observed in the determination of the equivalents of the same bodies by different experimenters. 176 GENERAL PRINCIPLES OP TABLE OF ELEMENTARY SUBSTANCES, WITH THEIR EQUIVALENTS. Oxy. = 8. Aluminium.... 13*7 Oxy. = 100. 171-25 Oxy. = 8. Nickel 29-6 Oxy. = 100. 370 Antimony 129 Arsenic 75 1612-5 937-5 Niobium Nitrogen 14 175 Barium 68-5 850-25 Norium Beryllium 6-9 86-25 Osmium 99-6 1245 Bismuth 213 2662-5 Oxygen . 8 100 Boron 10-9 136-25 Palladium 53-3 666-25 Bromine . . . 80 1000 Pelopium Cadmium 56 Calcium 20 700 250 Phosphorus.... 32 Platinum 98-7 400 1233-75 Carbon 6 75 Potassium 39 487-5 Cerium 47 (?) 587-5 Rhodium 52-2 652-5 Chlorine 35-5 443-75 Ruthenium 52-2 65 9 -5 Chromium ... 26-7 333-75 Selenium .. . 39-5 493-75 Cobalt 29-5 368-75 Silicium 21-3 266-25 Copper 31 - 7 396-25 Silver 108 1350 Didymium . 50 (') 625 Sodium .... 23 287-5 Erbium Fluorine 19 237.5 Strontium 43-8 Sulphur 16 547-5 200 Gold 197 2462-5 Tantalum 184 2300 Hydrogen 1 Iodine 127 12-5 1587-5 Tellurium 64-2 Terbium 802-5 Iridium 99 1237-5 Thorium 59-6 745 Iron 28 350 Tin 58 725 Lanthanum ... 47 (?) Lead 103-7 587-5 1296-25 Titanium 25 Tungsten 92 312-5 1150 81-25 Uranium 60 750 Magnesium ... 12 Manganese.,.. 27-6 Mercury 100 150 345 1250 Vanadium 68-6 Yttrium Zinc 32-6 857-5 407-5 Molybdenum.. 46 575 Zirconium 33-6 420 (4.) Combining Numbers of Compounds. The law states that the equivalent or combining number of a compound is always the sum of the equivalents of its components. This is also a great fundamental truth, which it is neces- sary to place in a clear and conspicuous light. It is a separate and inde- pendent law, established by direct experimental evidence, and not deducible from either of the preceding. The method of investigation by which the equivalent of a simple body is determined, has been already explained ; that employed in the case of a com- pound is in nowise different. The example of the acids and alkalis may be taken as the most explicit, and at the same time most important. An acid and a base, combined in certain definite proportions, neutralize, or mask each other's properties completely, and the result is a salt ; these proportions are called the equivalents of the bodies, and they are very variable. Some acids have very high capacities of saturation, of others a much larger quantity must be employed to neutralize the same amount of base ; the bases them- selves present also similar phenomena. Thus, to saturate 47 parts of potassa, or 116 parts of oxide of silver, there are required CHEMICAL PHILOSOPHY. 177 40 parts sulphuric acid, 54 " nitric acid, 75-5 " chloric acid, 167 " iodic acid, 51 " acetic acid. Numbers very different, but representing quantities which replace each other in combination. Now, if a quantity of some base, such as potassa, be taken, which is represented by the sum of the equivalents of potassium and oxygen, then the quantity of any acid requisite for its neutralization, as de- termined by direct experiment, will always be found equal to the sum of the equivalents of the different components of the acid itself. 39= equivalent of potassium. 8= " oxygen. 47 = assumed equivalent of potassa. 47 parts of potassa are found to be exactly neutralized by 40 parts of real sulphuric acid, or by 54 parts of real nitric acid. These quantities are evidently made up by adding together the equivalents of their constituents : 1 equivalent of sulphur = 16 1 equivalent of nitrogen = 14 3 " oxygen = 24 5 " oxygen = 40 1 " sulphuric ackl = 40 1 " nitric acid = 54 And the same is true if any acid be taken, and the quantities of different bases required for its neutralization determined ; the combining number of the compound will always be found to be the sum of the combining num- bers of its components, however complex the substance may be. Even among such bodies as the vegeto-alkalis of organic chemistry, the same uni- versal rule holds good. When salts combine, which is a thing of very com- mon occurrence, as will hereafter be seen, it is always in the ratio of the equivalent numbers. Apart from hypothetical consideration, no d, priori reason can be shown why such should be the case ; it is, as before remarked, an independent law, established like the rest, by experiment. A curious observation was very early made to this effect : If two neutra . salts which decompose each other when mixed, be brought in contact, the new compounds resulting from their mutual decomposition will also be neutral. For example, when solution of nitrate baryta and sulphate of potassa are mingled, they both suffer decomposition, sulphate of baryta and nitrate of potassa being simultaneously formed, both of which are perfectly neutral. The reason of this will be at once evident ; interchange of elements can only take place by the displacement of equivalent quantities of matter on either side. For every 54 parts of nitric acid set free by the decomposition of the barytic salt, 47 parts of potassa are abandoned by the 40 parts of sulphuric acid with which they were previously in combination, now trans- ferred to the baryta. But 54 and 47 are the representatives of combining quantities ; hence the new compound must be neutra.. COMBINATION BY VOLUME. Many years ago, M. Gay-Lussac made the very important and interesting discovery that when gases combine chemically, union invariably takes placo either between equal volumes, or between volumes which bear a simple rela- tion to each other. This is not only true of elementary gases, but of com- 7.78 GENERAL PRINCIPLES OP bodies of this description, as it is invariably observed that the con- traction of bulk which so frequently follows combination itself also bears a simple relation to the volumes of the combining gases. The consequence of this is, that compound gases and the vapours of complex volatile liquids (which are truly gases to all intents and purposes) follow the same law as elementary bodies, when they unite with these latter or combine among them- selves. The ultimate reason of the law in question is to be found in the very remarkable relation established by the hand of Nature between the specific gravity of a body in the gaseous state and its chemical equivalent ; a rela- tion of such a kind that quantities by weight of the various gases expressed by their equivalents, or in other words, quantities by weight which combine, occupy under similar circumstances of pressure and temperature either equal volumes, or volumes bearing a similar proportion to each other. In the example cited below, equivalent weights of hydrogen, chlorine, and iodine- vapour, occupy equal volumes, whiLe the equivalent of oxygen occupies exactly half that measure. Cubic inches. 8-0 grains of oxygen occupy at 60 (15-5C) and 30 inches barom. 23-3 1-0 grain of hydrogen ............................................................ 46-7 35-5 grains of chlorine ............................................................ 46-2 127-0 grains of iodine-vapour (would measure) .............................. 46-7 If both the specific gravity and the chemical equivalent of a gas be known, its equivalent or combining volume can be easily determined, since it will be represented by the number of times the weight of an unit of volume (the specific gravity) is contained in the weight of one chemical equivalent of the substance. In other words, the equivalent volume is found by dividing the chemical equivalent by the specific gravity. The following table exhibits the relations of specific gravity, equivalent weight, and equivalent volume of the principal elementary substances. Sp. gravity. Equiv. weight. Equiv. volume. Hydrogen .................... 0-OG93 ............... 1-0 ............... 14-43 or 1 Nitrogen ..................... 0-972 ............... 14-0 ............... 14-37 1 Chlorine ...................... 2-470 ............... 35-5 ............... 14-33 1 Bromine-vopour ............ 5-395 ............... 80-0 ............... 14-82 1 Iodine-vapour ...... . ........ 8-716 ............... 127-0 ............... 14-57 1 Carbon- vapour 1 ............ 0-418 ............... 6-0 ............... 14-34 1 Mercury-vapour ............ 7-000 ............... 100-0 .............. 14-29 1 Oxygen ....................... 1-106 ............... 8-0 ............... 7-23 Phosphorus-vapour ........ 4-350 ........... ; ... 32-0 ............... 7-35 Arsenic-vapour ............ 10-420 ............... 75-0 ............... 7-19 Sulphur-vapour ............ 6-654 ............... 16-0 ............... 2-40 | Thus it appears that hydrogen, nitrogen, chlorine, bromine, iodine, carbon, and mercury, in the gaseous state, have the same equivalent volume ; oxygen, phosphorus, and arsenic, one-half of this ; and sulphur one-sixth. The fclight discrepancies in the numbers iu the third column result chiefly from urrors in the determination of the specific gravities. Compound bodies exhibit exactly similar results : * See farther on. CHEMICAL PHILOSOPHY. 179 Sp. gravity. Equiv. weight. Equiv. volume. Water-vnpour 0-625 .... 9-0 .... 14-40 or 1 Protoxide of nitrogen 1-525 .... 22-0 .... 14-43 Sulphuretted hydrogen 1-171 .... 17-0 .... 14-51 Sulphurous acid 2-210 .... 32-0 .... 14-52 Carbonic oxide 0-973 .... 14-0 ... 14-39 Carbonic acid 1-524 .... 22-0 .... 14-43 Light carbonetted hydrogen 0-559 .... 8-0 .... 14-31 Olefiantgas 0-981 .... 14-0 .... 14-27 Binoxide of nitrogen 1-039 .... 30'0 .... 28-87 Hydrochloric acid 1-269 .... 36-5 .... 28-70 Phosphorettcd hydrogen 1-240 .... 35-0 .... 28-22 Ammonia 0-589 .... 17-0 .... 28-86 Ether-vapour 2-586 .... 37-0 .... 14-31 Acetone-vapour 2-022 .... 29-0 .... 14-34 Benzol-vapour 2-738 .... 78-0 .... 28-49 Alcohol-vapour 1-613 .... 46-0 .... 28-52 In the preceding tables the ordinary standard of specific gravity for gases, atmospheric air, has been taken. It is, however, a matter of perfect indif- ference what substance be chosen for this purpose ; the numbers represent- ing the combining volumes will change with the divisor, but the proportions they bear to each other wilt remain unaltered. And the same remark applies to the equivalent weights ; either of the scales in use may be taken, provided that it be adhered to throughout. The law of volumes often serves in practice to check and corroborate the results of experimental investigation, and is often of great service in this respect. There is an expression sometimes made use of in chemical writings which it is necessary to explain, namely, the meaning of the words hypothetical den- sity of vapour, applied to a substance which has never been volatilized, such as carbon, whose real specific gravity in that state must of course be un- known; it is easy to understand the origin of this term. Carbonic acid con- tains a volume of oxygen equal to its own; consequently, if the specific gravity of the latter be subtracted from that of the former gas, the residue will express the proportion borne by the weight of the carbon, certainly then in a vaporous state, to that of the two gases. The specific gravity of carbonic acid is 1-5240 That of oxygen is 1-1057 0-4183 On the supposition that carbonic acid contains equal volumes of oxygen and this vapour of carbon, condensed to one-half, the latter will have the specific gravity represented by 0-4183 and the combining volume given in the table. But this is merely a supposition, a guess; no proof can be given that carbonic acid gas is so constituted. All that can be safely said is con- tained in the prediction, that, should the specific gravity of the vapour of carbon ever be determined, it will be found to coincide with this number, or to bear some simple and obvious relation to it. For many years past, attempts have been made to extend to solids and liquids the results of Gay-Lussac's discovery of the law of gaseous combi- nation by volume, the combining or equivalent volumes of the bodies in question being determined by the method pursued in the case of gases, namely, by dividing the chemical equivalent by the specific gravity. The ISO GENERAL PRINCIPLES OP numbers obtained in this manner representing the combining volumes of the various solid and liquid elementary substances, present far more cases of discrepancy than of agreement. The latter are, however, sufficiently nu- merous to excite great interest in the investigation. 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. Such is a brief account of the great laws by which chemical combinations, of every kind, are governed and regulated ; and it cannot be too often re- peated, that the discovery of these beautiful laws has been the result of pure experimental inquiry. They have been established on this firm and stable foundation by the joint labours of very many illustrious men ; they are the expression of fact, and are totally independent of all hypotheses or theories whatsoever. CHEMICAL NOTATION ; SYMBOLS. For convenience in communicating ideas respecting the composition, and supposed constitution, of chemical compounds, and explaining in a clear and simple manner, the results of changes they may happen to undergo, re- course is had to a kind of written symbolical language, the principle of which must now be explained. To represent compounds by symbols is no novelty, as the works of the Alchemists will show, but these have been mere arbitrary marks or characters invented for the sake of brevity, or sometimes perhaps for that of obscuiity. The plan about to be described is due to Berzelius ; it has been adopted, with slight modifications, wherever chemistry is pursued. Every elementary substance is designated by the first letter of its Latin name, in capital, or by the first letter conjoined with a second small one, the most characteristic in the word, as the names of many bodies begin alike. The single letter is usually confined to the earliest discovered, or most im- portant element. Farther, by a most ingenious idea, the symbol is made to represent not the substance in the abstract, but one equivalent of that sub- stance. Table of Symbols of the Elementary Bodies. Aluminium Al Antimony (Stibium) Sb Arsenic As Barium Ba Beryllium Be Bismuth Bi Boron Bo Bromine Br Cadmium Cd Calcium Ca Carbon C Cerium Ce Chlorine Cl Chromium Cr Cobalt Co Copper (Cuprum) Cu Didymium Dy Erbium Er Fluorine F Gold (Aurum) Au Hydrogen H Iodine I Iridium Ir Iron (Ferrum) Fe Lantanum Ln Lead (Plumbum) Pb Lithium L Magnesium Mg Manganese Mn Mercury (Hydrargyrum) .... II g Molybdenum Mo Nickel Ni Niobium Nb Nitrogen N Norium No Osmium Os Oxygen Palladium Pd CHEMICAL PHILOSOPHY. 181 Pelopium Pe Phosphorus P Platinum Pt Potassium (Kalium) K Rhodium R Ruthenium Ru Selenium Se Silicium Si Silver (Argentum) Ag Sodium (Natrium) Na Strontium Sr Sulphur S Tantalum Ta Tellurium Te Terbium Tb Thorium Th Tin (Stannum) Sn Titanium Ti Tungsten (Wolframium) W Vanadium V Uranium U Yttrium Y Zinc Zn Zirconium Zr Combination between bodies in the ratio of the equivalents is expressed by mere juxtaposition of the symbols, or sometimes by interposing the sign of addition. For example : Water HO, orH-f Hydrochloric acid HC1, or H -+ Cl Protoxide of iron FeO, or Fe -}- When more than one equivalent is intended, a suitable number is added, sometimes being placed before the symbol, like a co-efficient in algebra, sometimes appended after the manner of an exponent, but more commonly placed a little below on the right. Binoxide of hydrogen H -f- 20, or H0 a , or H0 2 Sulphuric acid S + 30, or go 3 , or S0 3 Hyposulphuric acid.. 2S + 50, or S 2 5 or S 2 5 Combination between bodies themselves compound is indicated by the sign of addition, or by a comma. When both are used in the same formula, the latter may be very conveniently applied, as Professor Graham has suggested, to indicate the closest and most intimate union. A number standing before symbols, inclosed within a bracket, signifies that the whole of the latter are to be multiplied by that number. Occasionally the bracket is omitted, when the number aft'ects all the symbols between itself and the next sign. A few examples will serve to illustrate these several points. Sulphate of soda NaO + S0 3 , or NaO , S0 3 Nitrate of potassa KO -j- N0 5 , or KO , N0 5 The base being always placed first. Double sulphate of copper and potassa CuO , S0 3 -f-KO , S0 3 The same in a crystallized state CuO , S0 3 -j-KO , S0 3 -f-6HO Common crystallized alum, or double sulphate of alumina and potassa, ia thus written : A1 2 3 , 3S0 3 +KO , S0 3 +24HO In expressing organic compounds, where three or more elements exist, the same plan is used. Sugar C 12 H n O n Alcohol C 4 H 6 2 Acetic acid HO , C 4 H 3 3 Morphine C 34 H, 9 N 6 Acetate of worphine C 34 H 19 N 6 , C 4 H,0. Acetate of soda NaO, C 4 H 3 3 16 182 GENERAL PRINCIPLES OP By such a system, the eye is enabled to embrace the whole at a glance, and gain a distinct idea of the composition of the body, and its relations to others similarly described. Some authors are in the habit of making use of contractions, which, how- ever, are by no means generally adopted. Thus, two equivalents of a sub- stance are indicated by the symbol with a short line drawn through or below it ; an equivalent of oxygen is signified by a dot, and one of sulphur by a comma. These alterations are sometimes convenient for abbreviating a long formula, but easily liable to mistakes. Thus, Sesquioxide of iron FeO 3 , or F eO 3 , or Fe, instead of Fe a 3 Bisulphide of carbon C, instead of CS 2 Crystallized alum as before AlS 3 -j-KS-j-24H. THE ATOMIC THEORY. That no attempt should have been made to explain the reason of the very remarkable manner in which combination occurs in the production of che- mical compounds, and to point out the nature of the relations between the different modifications of matter which fix and determine these peculiar and definite changes, would have been unlikely, and in contradiction with the speculative tendency of the human mind. Such an attempt, and a very inge- nious and successful one it is, has been made, namely, the atomic hypothesis of Dr. Dal ton. 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 farther diminished in magnitude ; they become, in short, atoms. 1 Now, however the imagination may succeed in figuring to itself the condition of matter on either view, it is hai-dly neces- sary to mention that we have absolutely no means at our disposal 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 pei'haps that of the sages of Egypt and Hindostan long before them. Dr. 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 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, farther, that the relative weights of the atoms are in the proportions of the equivalent numbers, and the hypothesis becomes capable of rendering consistent and satisfactory reasons for all the consequences of those beautiful laws of combination lately discussed. 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 produce 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 ; an atom 1 "Aro//oj that which cannot be cut. CHEMICAL PHILOSOPHY. 183 of nitrogen unites with one of oxygen to form laughing gas; -with two, to form binoxide of nitrogen; with three, to produce nitrous acid; with four, hyponitric acid ; and with five, nitric acid, perhaps something after the manner represented in fig. 124, in which the circle with a cross represents *Jie atom of nitrogen, and the plain circle that of oxygen. Fig. 124. Protoxide. Binoxide. Two atoms of one substance may unite themselves with three or even with seven of another, as in the case of one of the acids of manganese ; but such combinations are rare. The mode in which bodies replace, or may be substituted for, each other, is also perfectly intelligible, as a little consideration will show. Finally, the law which fixes the equivalent of a compound at the sum of the equivalents of the components, receives an equally satisfactory expla- nation. The difficulties in the general application of the atomic hypothesis are chiefly felt in attempting to establish some wide and universal relation be- tween combining number and combining volume, among gases and vapours, and in the case of the highly complex products of organic chemistry. These obstacles have grown up in comparatively recent times. On the other hand, the remarkable observations of the specific capacities for heat of equivalent quantities of the solid elementary substances, might be urged in favour of this or some similar molecular hypothesis. But even here serious discrep- ancies exist ; we may not take liberties with equivalent numbers determined by exact chemical research, and, in addition, a simple relation is generally found to be wanting between the capacity for heat of the compound and that of its elements. The theory in question has rendered great service to chemical science ; it has excited a vast amount of inquiry and investigation, which have contribu- ted very lai'gely to define and fix the laws of combination themselves. In more recent days it is not impossible, that, without some such hypothetical guide, the exquisitely beautiful relations which Mitscherlich and others have shown to exist between crystalline form and chemical composition, might never have been brought to light, or, at any rate, their discovery might have been greatly delayed. At the same time, it is indispensable to draw the broadest possible line of distinction between this, which is at the best but a graceful, ingenious, and, in its place, useful hypothesis, and those great general laws of chemical action which are the pure and unmixed result of inductive research. 1 Chemical Affinity. The 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 *The expression atomic weight IB very often substituted for that of equivalent weight, and Is, in fact, in almost every case to be understood as such : it is, perhaps, better avoided. 184 GENERAL PRINCIPLES OP 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 dis- tinguished from other modifications of attractive force which are exerted indiscriminately between all descriptions of substances, sometimes at enor- mous distances, and 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 re- pulsion 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 ; the attraction between the different members of these two groups is incomparably more feeble. Sulphur and phosphorus stand, as it were, mid-way ; they combine with substances of one and the other class, their properties separating them sufficiently from both. Acids are drawn towards alkalis, and alkalis toAvards 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 tem- perature 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 for- merly prevailed that the relations of affinity were fixed and constant between the same substances, and great pains were taken in the preparation of tables exhibiting what was called the precedence of affinities. The 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 exercise of one single force, but rather the joint effect of a number, so complicated and so variable in intensity, that it is but seldom possible to predict the consequences of any yet untried experiment. The following may serve as examples of the tables alluded to ; the first illustrates the relative affinities of a number of bases for sulphuric acid, each decomposing the combination of the acid with the base below it ; thus, magnesia decomposes sulphate of ammonia ; lime dis- places the acid from sulphate of magnesia, &c. The salts are supposed to be dissolved in water. The second table exhibits the order of affinity for oxygen of several metals, mercury reducing a solution of silver, coppsr one of mercury, &c. CHEMICAL PHILOSOPHY. 185 Sulphuric acid. Baryta, Lime, Strontia, Magnesia, Potassa, Ammonia. Soda, Oxygen. Zinc, Mercury, Lead, Silver. Copper, It will be proper to examine shortly some of these extraneous causes to 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, spontaneously separates 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 at all, but which oxidates superficially at a red-Beat, 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 lime in hydrochloric acid is mixed with a solution of carbonate of ammonia, double interchange ensues, carbonate of lime and hydrochlorate of ammonia being generated. Here the action can be shown to be in a great measure determined by the insolubility of the carbonate of lime. Again, dry carbonate of lime, powdered and mixed with hydrochlorate of ammonia, and the whole heated in a retort, gives a sublimate of carbonate of ammonia, while chloride of calcium remains behind. In this instance, it is no doubt the great volatility of the ammoniacal salt which chiefly determines the kind of decomposition. When iron-filings are heated to redness in a porcelain tube, and vapour of water passed over them, the water undergoes decomposition with the utmost facility, hydrogen is 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 vapour 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 atmosphere is suf- ficient to settle the point. An atmosphere of steam offers little resistance to the escape of hydrogen ; one of hydrogen bears the same relation to steam ; and this apparently trifling difference of circumstances is quite enough for the purpose. The decomposition of vapour 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 l-3000th 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 favourable to chemical com- oination. Thus carbon and nitrogen refuse to combine w'th gaseous hy- 16* 186 PRINCIPLES OF CHEMICAL PHILOSOPHY. drogen ; yet when these substances are simultaneously liberated from some previous combination, they unite with great ease, as when organic matters are destroyed by heat, or by spontaneous putrefactive change. There is a strange and extraordinary, and at the same time very extensive class of actions, grouped together under the general title of cases of disposing affin- ity. The preparation of hydrogen from zinc and sulphuric acid is one of the most familiar. A piece of polished zinc or iron, put into pure water, manifests no power of decomposing the latter to the smallest extent; it remains perfectly bright for any length of time. On the addition, however, of a little sulphuric acid, hydrogen is at once freely disengaged, and the metal becomes oxidized and dissolved. Now, the only intelligible function of the acid is to dissolve off the oxide as fast as it is produced ; but why is the oxide produced when acid is present, and not otherwise ? The question is very difficult to answer. Great numbers of examples of this curious indirect action might be adduced. Metallic silver does not oxidize at any temperature ; nay more, its joxide is easily decomposed by simple heat ; yet if the finely-divided metal be mixed with siliceous matter and alkali, and ignited, the whole fuses to a yellow transparent glass or silicate of silver. Platinum is attacked by fused hydrate of potassa ; hydrogen is probably disengaged while the metal is oxidized ; this is an effect which never happens to silver under the same cir- cumstances, although silver is a much more oxidable substance than plati- num. The fact is, that potassa forms with the oxide of the last-named metal a kind of saline combination, in which the oxide of platinum acts as an acid ; and hence its formation under the disposing influence of the power- ful base. In the remarkable decomposition 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 fewer in number and more definite, than in the event of simple destruction by a graduated heat. The preparation of light carbonetted hydrogen by the new artificial process, already described, is an excellent example. There is yet a still more obscure class of phenomena, in which effects are brought about by the mere presence of a substance, which itself undergoes no change whatever ; the experiment mentioned in the article on oxygen, in which that gas is obtained, with the greatest facility, by heating a mix- ture of chlorate of potassa and binoxide of manganese, is an excellent case in point. The salt is decomposed at a very far lower temperature than would otherwise be required. The oxide of manganese, however, is not in the slightest degree altered ; it is found, after the experiment, in the same state as before. The name katalysis is sometimes given to these peculiar actions of contact ; the expression is not significant, and may be for that reason the more admissible, as it suggests no explanation. It is proper to remark, that the contact-decompositions alluded to are sometimes mixed up with other effects, which are, in reality, much more in- telligible, as the action of finely-divided platinum upon certain gaseous mix- tures, in which the solid really seems to have the power of condensing the gas upon its greatly extended surface, and thereby inducing combination by bringing the particles within the sphere of their mutual attractions. CHEMISTRY OP THE VOLTAIC PILE. 1/7 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 ; pro- vided that the liquid be capable of conducting a current of a certain degree of energy, its decomposition 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 quiescent. In addition, the elements are not separated indifferently and at random at these two surfaces, but, on the contrary, make their appearance with per- fect uniformity and constancy at one or the other, according to their che- mical 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 termination of the battery itself, usually, but by no means necessa- rily, of metal, are designated poles or electrodes,* as by their intervention the liquid to be experimented on is made a part of the circuit. The process of decomposition by the current is called electrolysis,' 1 ' and the liquids, which, when thus treated, yield up their elements, are denominated 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 connected by wires with the extremities of an active battery, oxygen is disengaged at the positive electrode, and hydrogen at the negative, in the proportion of one measure of the former to two of the latter nearly. This experiment has before been described. 3 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. Iodide of potassium dissolved in water is decomposed in a similar man- ner, and with still greater ease ; the free iodine at the positive side can be recognized by its brown colour, or by the addition of a little gelatinous starch. Every liquid is not an electrolyte ; many refuse to conduct, and no decom- position can then occur ; alcohol, ether, numerous essential oils, and othei products of organic chemistry, besides a few saline inorganic compounds, act in this manner, and completely arrest the current of a very powerful battery. It is a very curious fact, and well deserves attention, that very nearly, if not all the substances acknowledged to be susceptible of electrolytic decomposi- tion, belong to one class; they are all binary compounds, containing single 1 From ri\tKrpov, and Wdy, a way. ' From rjXtvTpov, and Auw, I loose. * Page 115. 188 ELECTRO-CHEMICAL DECOMPOSITION; equivalents of their components, the latter being strongly opposed to ?ach other in their chemical relations, and held together by very powerful affinities. The amount of power required to effect decomposition varies greatly ; solution of iodide of potassium, melted chloride of lead, solution of hydro- chloric acid, water mixed with a little oil of vitriol, and pure water, demand in this respect very different degrees of electrical force, the resistance to decomposition increasing from the first-mentioned substance to the last. One of the most important and indispensable conditions of electrolysis is fluidity; bodies which when reduced to the liquid condition freely conduct and as freely suffer decomposition, become absolute insulators to the elec- tricity of the battery when they become solid. Chloride of lead offers a good illustration of this fact ; when fused in a little 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, all signs of decomposition cease, and at the same moment the magnetic needle reassumes its natural position. In the game manner the thinnest film of ice completely arrests the current of a pow- erful voltaic apparatus ; the instant the ice is liquefied at any one point, so that water-communication may be restored between the electrodes, the cur- rent again passes, and decomposition occurs. Fusion by heat, and solution in aqueous liquids, answer the purpose equally well. A fluid substance may conduct a strong current of electricity without being decomposed ; there are a few examples already known ; the electrolysis of a solid is, from its physi- cal properties, of course out of the question. Liquids often exhibit the property of conduction for currents strong enough to be indicated by the galvanometer, but yet incapable of causing decompo- sition in the manner described. These currents may be conveyed through extensive masses of liquids ; the latter seem, under these circumstances, to conduct after the manner of metals, without perceptible molecular change. 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 so often 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 alto- gether unaffected, directly at least ; severance from that previous combination 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 water, for example, is subjected to decomposition in a glass vessel with parallel sides, oxygen is disengaged 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 water 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 water, separated perhaps by an interval of four or five inches, may be respectively evolving pure oxygen and pure hydrogen. There is, it would seem, but one mode of explaining this and all similar cases of regular electrolytic decomposition; this is by assuming that all the particles of water between the electrodes, and by which the current is con- veyed, simultaneously suffer decomposition, the hydrogen travelling in one direction and the oxygen in the other. The neighbouring elements, thus brought into close proximity, unite and reproduce water, 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 oxygen between itself and the negative Jectrode ; when it reaches the latter, finding no disengaged particle of oxygen CHEMISTRY OF THE VOLTAIC PILE. 189 for its reception, it is rejected as it were from the series, and thrown off in a scphrate state. The same thing happens to each particle of oxygen, 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, uutil'at length it arrives at the positive plate or wire, and is disengaged. A succession of particles of hydrogen are thus continually thrown off from the decomposing mass at one extremity, and a corresponding succession of particles of oxygen at the other. The power of the current is exerted with equal energy in every part of the liquid conductor, although its effects only become manifest at the very extremities. The action is one of a Fig. 125. MMr II1@ Water in usual state. purely molecular or internal nature, and the metal terminations of the bat- tery merely serve the purpose of completing the connection between the latter and the liquid to be decomposed. The figures 125 and 126 are intended to assist the imagination of the reader, who must at the same time avoid re- garding them in any other light than that of a somewhat figurative mode of representing the curiotis phenomena described. The circles are intended to indicate the elements, and are distinguished by their respective symbols. Fig. 126. 1)@11I@1@I Water undergoing electrolysis. A distinction is to be carefully drawn between true and regular electro- lysis, and what is called secondary decomposition, brought about by the reaction of the bodies so eliminated upon the surrounding fluid, or upon the substance of the electrodes ; hence the advantage of platinum for the latter purpose when electrolytic actions are to be studied in their greatest sim- plicity, that metal being scarcely attacked by any ordinary agents. When, for example, a solution of nitrate or acetate of lead is decomposed by the current between platinum plates, metallic lead is deposited at the negative side, and a brown powder, binoxide of lead, at the positive : the latter sub- stance is the result of a secondary action ; it proceeds, in fact, from the nascent oxygen at the moment of its liberation reacting upon the protoxide of lead present in the salt, and converting it into binoxide, which is insoluble in the dilute acid. There is every reason to believe that when sulphuric and nitric acids seem to be decomposed by the current, the effect is really due to the water they contain becoming decomposed, and reacting by its hydrogen upon the acid ; for these bodies do not belong to the class of elec- trolytes, as already specified, and would probably refuse to conduct could they be examined in an anhydrous condition. If a number of different electrolytes, such as acidulated water, sulphato of copper, iodide of potassium, fused chloride of lead, &c., be arranged in a 190 ELECTRO-CHEMICAL DECOMPOSITION: Fig. 127. series, And the same current be made to traverse the whole, all will suffer decomposition at the same time, but by no means to the same amount. If arrangements be made by which the quantities of the eliminated elements can be accurately ascertained, it will be found, when, the decomposition has proceeded to some extent, that these latter will have been disengaged exactly in the ratio of the chemical equivalents. The same current which decomposes 9 parts of water will separate into thfiir elements 166 parts of iodide of po- tassium, 139-2 parts of chloride of lead, &c. Hence the very important conclusion : The action of the current is perfectly definite in its nature, pro- ducing a fixed and constant amount of decomposition, expressed in each electrolyte by the value of its chemical equivalent. From a very extended series of experiments, based on this and other me- thods of research, Mr. Faraday was enabled to draw the general inference that effects of chemical decomposition were always proportionate to the quantity of circulating electricity, and might be taken as an accurate and trustworthy measure of the latter. Guided by this highly important principle, he constructed his voltame- ter, an instrument which has rendered the great- est service to electrical science. This is merely an arrangement by which a little acidulated water is decomposed by the current, the gas evolved being collected and measured. By plac- ing 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. 127, 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 pneumatic trough, the tube of the instrument, which is filled to the neck with dilute sulphuric acid, being passed beneath the jar. The decompositions of 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 obstacles, 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, develope far more electricity, to judge from the chemical effects of such an arrangement, than very many turns of a large plate electrical machine in high action. Nevertheless, polar or electrolytic decomposition can be distinctly and satis- factorily 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 disturbance in that apparatus. Volta himself ascribed it to mere contact of dissimilar metals ; to what was denominated an electro-motive force, called into being by such contact ; the liquid merely serving the purpose of a conductor be- tween one pair of metals and that succeeding. Proof was supposed to be given of the fundamental position by an experiment in which discs of zino 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 CHEMISTRY OF THE VOLTAIC PILE. 191 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 tho battery always bore some kind of proportion to the chemical action upon the zinc ; that, for instance, when pure water was used the effect was extremely feeble; with a solution of salt, it became much greater; and, lastly, with dilute acid, greatest of all; so that some relation evidently existed between the chemical effect upon the metal, and the evolution of electrical force. The experiments of Mr. Faraday and Professor Daniell have given very great support to the chemical theory, by showing that contact of dissimilar metals is not necessary in order to call into being powerful electrical currents, and that the development of electrical force is not only in some way connected with the chemical action of the liquid of Fig. 128. the battery, but that it is always in direct proportion to the latter. One very beautiful experiment, in which decompo- sition of iodide of potassium by real electrolysis is performed by a current generated without any contact of dissimilar metals, can be thus made: A plate of zinc (fig. 128) 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 rivetting, and the latter bent into an arch. A piece of folded filter-paper is wetted with a so- lution of iodide of potassium, and placed upon the zinc ; the platinum plate is arranged opposite to the latter, with the end of its wire resting upon the paper, and then the pair plunged into a glass of dilute sulphuric acid, mixed with a few drops of nitric. A brown spot of iodine becomes in a moment evident beneath the extremity of the platinum wire ; that is, at the positive side of the arrangement. A strong argument in favour 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 plates, the one iron and the other copper, be connected by wires with a galvanometer, and then immersed in a solution of an alkaline sul- phide. 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 fii-st instance the copper is acted upon, and not the iron ; in the 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 arrange- ment. The liquid is either dilute sulphuric acid, sometimes mixed with a little nitric, or occasionally, where very slow and long-continued action is wanted, salt and water. To obtain the maximum effect of the apparatus with the least expenditure of zinc, that metal must be employed in a puio stale, or its surface must be covered by or amalgamated with mercury, 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 crowu of cups ; by each alternation of zinc, fluid, and copper, the current is urged forwards with increased energy, its intensity is augmented, but the actual 192 ELECTRO-CHEMICAL DECOMPOSITION; 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 elec- tricity 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 water 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, while the zinc undergoes tranquil and imperceptible oxidation and solution. Thus, exactly the same effects are seen to occur in every active cell of a closed circuit, which are witnessed in a portion of water undergoing electrolysis ; the oxygen appears at the positive side, with respect to the current, and the 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 elec- trolysis, 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 plumbago, partially embedded 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 the latter to some extent. 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 water, in order to evolve 1 grain of hydrogen from the latter, 33 grains of zinc must be oxidized 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 oxidation of an equivalent of zinc in the battery, is capable of effecting the decomposition of an equivalent of water, 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 chemical and electrical forces, and their remarkable quantitative or equivalent relations. It almost seems, to use an expression of Mr. Faraday, as if a transfer of chemical force took place through the substance of solid metallic conductors ; that chemical actions, called into play in one portion of the circuit, could be made at pleasure to exhibit their effects without loss or diminution in any other. There is an hypothesis, not of recent date, long countenanced and supported 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 chemical affinity ; or, on the other hand, that all chemical action is a manifestation of electrical force. One of the most useful forms of the common voltaic battery is that con- trived by Dr. Wollaston (fig. 129). The copper is made completely to encircle CHEMISTRY OF THE VOLTAIC PILE. 193 Fig. 129. the zinc j late, 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 sciewed 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 measure. A number of such batteries are easily connected together by straps of sheet copper, and admit of being put into action with great ease. The great objection to this and to all the older forms of the voltaic battery 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 sulphate of zinc, but still more on the coating of hydrogen, and at a later stage, on the precipitation of metallic zinc on the copper plates. It is self-evident that if the copper plate in the fluid became covered with zinc, it would electrically, act 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 substances separated from the liquid, is commonly called polarization. An instrument of immense value for the purposes of electro-chemical research, in which it is desired to maintain powerful and equable currents for many suc- cessive hours, has been contrived by Professor Daniell (fig. 130). Each cell of this "constant" battery con- sists of a copper cylinder 3 inches in diameter, and of a height varying from 6 to 18 inches. The zinc is employed in the form of a rod f of an inch in diameter, carefully amalgamated, and suspended in the centre of the cylinder. A second cell of porous earthenware or animal membrane intervenes between the zinc and the copper ; this is filled with a mixture of 1 part by mea- sure of oil of vitriol and 8 of water, and the exterior space with the same liquid, saturated with sulphate of copper. A sort of little colander is fitted to the top of the cell, in which crystals of the sulphate of copper are placed, so that tht Fig. 130. C 194 ELECTRO-CHEMICAL DECOMPOSITION; Fig. 131. strength of the solution may remain unimpaired. When a communication is made by a wire between the rod and the cylinder, a powerful current is pro- duced, 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 advantage of retaining its energy undiminished for a lengthened period. For the copper plates become covered with a compact precipitate of copper without tho evolution of any hydrogen, so long as the solution of sulphate of copper remains saturated. By this most excellent arrangement the sur- faces of the copper plates retain their original chemical properties unchanged. The polarization is avoided, and the chief cause of the gradual loss of powei is removed. Mr. Grove, on precisely the same principles, succeeded afterwards in fornv ing a zinc and platinum battery, the action of which is con- stant. To hinder the evolution of hydrogen on the plati- num plates he employed the oxidizing action of nitric acid. One of the cells in this battery is represented in the margin, in section (fig. 131). The zinc plate is bent round, so as to present a double surface, and well amalgamated ; within it stands a thin fiat 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 Wollaston'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, experiments 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 action. The zinc, as in the case of Professor Daniell's battery, is only consumed while the 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. The nitric acid suppresses the whole of the hydrogen, becoming thereby slowly deoxi- dized and converted into nitrous acid, which at first remains dissolved, but after some time begins to be disengaged from the porous cells in dense red fumes ; this constitutes the only serious drawback to this excellent instru- ment. 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 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. Mr. Smee has contrived an ingenious battery, in which silver covered witlf thin coating of finely-divided metallic platinum is employed in association \rith amalgamated zinc and dilute sulphuric acid. The rough surface appears to permit the ready disengagement of the bubbles of hydrogen. Within the last nine or ten 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 copying, ,r rather in multiplying, engraved plates and medals, by depositing upon their surfaces a thin coating of metallic copper, which, when separated from the original, exhibits, in reverse, a most faithful representation of the latter. CPIEMISTRY OP THE VOLTAIC PILE. 195 Fig. 132. By using this in its turn as a mould or matrix, an absolutely perfect fac- simile of the plate or medal is tbtained. In the former case, the impressions taken on paper are quite indistinguishable 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 indefinitely. The copper is very tough, and bears the action of the press perfectly well. The apparatus used in this and many similar processes is of the simplest possible kind. A trough or cell of wood (fig. 132) 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 sulphate of copper, sometimes mixed with a little acid, on the other. A plate of zinc is soldered to a wire or strap 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. Other metals may be precipitated in the same manner, in a smooth and compact form, by the use of certain precautions which have been gathered by experience. Electro-gilding and plating are now carried on very largely and in great perfection by Messrs. Elkington and others. Even non-conduct- ing bodies, as sealing-wax and plaster of Paris, may be coated with metal ; it is only necessary, as Mr. Murray has shown, to rub over them the thin- nest possible film of plumbago. Seals may thus be copied in a very few hours with unerring truth. M. 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 pro- ducts exactly resembled natural minerals, and, indeed, the experiments threw great light on the formation of the latter within the earth. 1 The common but very pleasing experiment of the lead tree is greatly de- pendent on electro-chemical action. When a piece of zinc is suspended in a solution of acetate of lead, the first effect is the decomposition of a portion of the latter, and the deposi- tion 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 en- tirely disappears. (Fig. 133.) The first portions of lead form with the zinc a voltaic arrangement of sufficient power to de- compose the salt, under the peculiar circumstances in which the latter is placed, the metal is precipitated upon the nega- tive portion, that is, the lead, while the oxygen and acid are taken up by the zinc. Professor Grove has contrived a battery, in which an elec- trical current, of sufficient intensity to decompose water, is produced by the reaction of oxygen upon hydrogen. Each element of this interesting appa- ratus consists of a pair of glass tubes to contain the gases, dipping into a vessel of acidulated water. Both tubes contain platinum plates, covered Tig. 133 1 Trait6 de 1'ElectricitS et du MagnStisme, iii. 239. 196 ELECTRO-CHEMICAL DECOMPOSITION. 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 hermeti- cally 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 galvano- scope. 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 indicates the de- composition of the liquid ; and when the experiment is made with a small voltameter, it is found that the oxygen and hydrogen disengaged, exactly equal in amount the quantities absorbed by the act of combination in -each tube of the battery. CHEMISTRY OF THE METALS. 197 CHEMISTRY OF THE METALS. "iuials constitute the second and larger group of elementary bodies Ji &veu* aunA,e/ of these are of very rare occurrence, being found only in a ft jr scarce mkerals; others are more abundant, and some few almost uni- versally diffused throughout the whole 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 pro- gress of civilization. If arsenic and tellurium bo included, the metals amount to forty-nine in number. Physical Properties. One of the most remarkable and striking characters possessed by the metals is their peculiar lustre ; this is so characteristic, that the expression metallic lustre has passed into common speech. This pro- perty is no doubt connected with the extraordinary degree of opacity which the metals present in every instance. The thinnest leaves or plates, the edges of crystalline laminae, arrest the passage of light in the most complete man- ner. An exception to this rule is usually made in favour of gold-leaf, which when held up to the daylight exhibits a greenish colour, as if it were really endued with a certain degree of translucency ; the metallic film is, however, always so imperfect, that it becomes 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. In point of colour, 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-grey tint of lead ; bismuth, it is true, has a pinkish colour, but it is very feeble. The differences of specific gravity are very wide, passing from potassium and sodium, which are lighter than water, to platinum, which is nearly twenty-one times heavier than an equal bulk of that fluid. Table of the Specific Gravities of Metals at 60 (15-5C), t Platinum 20-98 Gold 19-26 Tungsten 17-60 Mercury 13-57 Palladium 11-30 to 11-8 Lead 11-35 Silver 10-47 Bismuth 9-82 Uranium 9-00 Copper 8-89 Cadmium 8-60 1 Dr. Turner's Elements, eighth edition, p. 345. 198 CHEMISTRY OF THE METALS. Cobalt 8-54 Nickel 8-28 Iron 3-79 Molybdenum 7-40 Tin 7-29 Zinc 7-86 to 7-1 Manganese 6-85 Antimony 6-70 Tellurium 6-11 Arsenic 5-88 Aluminium 2-60 1 Magnesium ; 1-70 Sodium 0-972 ; Potassium 0-865 The property of malleability, or power of extension under the hammer or between the rollers of the flatting-mill, is enjoyed 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 alkalis, and mercury, when solidified, are also malleable. Zinc may be placed mid- way between the malleable and brittle division ; then perhaps bismuth, and, lastly, such metals as antimony and arsenic, which are altogether destitute of malleability. The specific gravity of malleable metals is usually very sensibly increased by pressure or blows, and the metals themselves 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 Fig. 134. as it involves the principle of tenacity, or power of re- sisting tension. The 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 (fig. 134), each being a little smaller than its predecessor, until the requisite degree of fineness is attained. 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 susceptible of being easily drawn into wire is the following : it is determined by observing the weights required to break asunder wires Irawn through tne 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, ex- * WShler. CHEMISTRY OP THE METALS. 199 tracted from the late Dr. Turner's excellent work, will give an idea of their relations to heat. The melting-points of the metals which only fuse at a temperature above ignition, and that of zinc, are on the authority of Mr. Daniell, having been observed by the help of the pyrometer before described : Melting points. F. C. Mercury 390 ,,390-44 Potassium 136 57-77 Sodium 194 90 Tin , 442 227-77 Fusible below J Cadmium (about) 442 277-77 a red heat 1 Bismuth 497 258-33 ' Lead 612 322-77 Tellurium rather less fusible than lead Arsenic unknown Zinc 773 411-66 ^Antimony just below redness 'Silver 1873 1022-77 Copper 1996 1091-11 Gold 2016 1102-22 Cast iron... 2786 1530 Pure iron ~) Nickel Cobalt i- Fusible only in an excellent wind- Manganese.... } furnace. Palladium .... J Infusible below 1 Molybdenum . 1 a red heat Uranium 1 T _ ,. ., , . . , Tungsten f Im perfectly melted in wind-furnace. Chromium J Titanium Cerium Osmium T ., Iridium ... [ Infusible m furnace ; 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 alkalis. 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 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, and cadmium, rise in vapour when heated to a bright redness ; arsenic and tellurium are volatile. CHEMICAL RELATIONS OF THE METALS ; CONSTITUTION OF SALTS. 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 very frequently lost. The alloys themselves are really true chemical compounds, and not mere mixtures of the consti- 200 CHEMISTRY OF THE METALS. tuent metals ; their properties often differ completely from those of the latter. The oxides of the metals may be divided, as already pointed out, into three classes ; namely, those which possess basic characters more or less marked, those which refuse to combine with either acids or alkalis, and those which have distinct acid properties. The strong bases are all protoxides ; they contain single equivalents of metal and oxygen ; the weaker bases are usually sesquioxides, containing metal and oxygen in the proportion of two equivalents of the former to three of the latter ; the peroxides or neutral compounds are still richer in oxygen, and, lastly, the metallic acids contain the maximum proportion of that element. The gradual change of properties by increasing proportions of oxygen is well illustrated by the case of manganese. Metal. Oxygen. Symbols. Characters. Protoxide 1 eq. ... 1 eq. ... MnO ... Strongly basic. Sesquioxide 2 eq. ... 3 eq. ... Mn 2 3 ... Feebly basic. Binoxide 1 eq. ... 2 eq. ... Mn0 2 ... Neutral. Manganic acid 1 eq. ... 3 eq. ... MnO., ") . , ., Permanganic acid 2 eq. ... 7 eq. ... Mn a 7 } StrOD ^ acid " The oxides of iron and chromium present similar, but less numerous gra- dations. When a powerful oxygen-acid and a powerful metallic base are united in such proportions that they exactly destroy each other's properties, the re- sulting salt is said to be neutral; it is incapable of affecting vegetable colours. Now, in all these well-characterized neutral salts, a constant and very remarkable relation is observed to exist between the quantity of oxygen in the base, and the quantity of acid in the salt. This relation is expressed in the following manner : To form a neutral combination, as many equiva- lents of acid must be present in the salt as there are of oxygen in the base itself. In fact, this has become the very definition of neutrality, as the action on vegetable colours is sometimes an unsafe guide. It is easy to see the application of this law. When a base is a protoxide, a single equivalent of acid suffices to neutralize it ; when a sesquioxide, not less than three are required. Hence, if by any chance, the base of a salt should pass by oxidation from the one state to the other, the acid will be in- sufficient in quantity by one-half to form a neutral combination. Sulphate of the protoxide of iron offers an example ; when a solution of this substance is exposed to the air, it absorbs oxygen, and a yellow insoluble sub-salt, or bwic-salt, is produced, which contains an excess of base. Four equivalents of the green compound absorb from the air two equivalents of oxygen, and give rise to one equivalent of neutral and one equivalent of basic sulphate of the sesquioxide, as indicated by the diagonal zigzag line of division. 1 eq. iron -f 1 eq. oxygen 1 eq. sulphuric acid. 1 eq. iron -j- 1 eq. oxygen 1 eq. sulphuric acid. j -f- 1 eq. oxygen from air 1 eq. iron -f 1 eq. oxygen I 1 eq. sulphuric acid. 1 eq. iron -j- 1 eq. oxygen 1 eq. sulphuric acid. -j- 1 eq. oxygen from air. Such sub-salts or basic salts are very frequently insoluble. The combinations of chlorine, iodine, bromine, and fluorine with the aetals possess in a very high degree the saline character. If, however, the definition formerly given of a salt be rigidly adhered to, these bodies must be excluded from the class, and with them the very substance from which the name is CHEMISTRY OP THE METALS. 01 derived, that is, common salt, which is a chloride of sodium To obviate this anomaly, it has been found necessary to create two classes of salts ; in the first division will stand those constituted after the type of common salt, which contain a metal and a salt-radical, as chlorine, iodine, &c. ; and in the second, those which, like sulphate of soda and nitrate of potassa, are gene- rally supposed to be combinations of an acid with an oxide. The names haloid 1 salts, and oxygen-acid, or oxy-salls, are given to these two kinds. When a haloid salt is dissolved in water, it might be regarded as a combi- nation of a metallic oxide with a hydrogen-acid, the water being supposed to undergo decomposition, its hydrogen being transferred to the salt-radical, and its oxygen to the metal. This view is unsupported by evidence of any value : it is much more probable, indeed, that no truly saline compounds of hydrogen-acids exist, at any rate in inorganic chemistry. When a solution of any hydrogen-acid is poured upon a metallic oxide, we may rather suppose that both are decomposed, water and a haloid salt of the metal being pro- duced. Take hydrochloric acid and potassa by way of example. Hydrochloric f Chlorine - ^ Chloride of potassium. acid ........ \ Hydrogen -^^_ -"~~" Pntassa / Potassium ^^-^^ -' \ Oxygen - ^^ Water. On evaporating the solution, the chloride of potassium crystallizes out. When hydrochloric acid and ammoniacal gases are mixed, they combine with some energy and form a white solid salt, sal-ammoniac. Now this sub- stance bears such a strong resemblance in many important particulars to chloride of potassium and common salt, that the ascription to it of a similai constitution is well warranted. If chloride of potassium, therefore, contain chlorine and metal, sal-ammo- niac may also contain chlorine in combination with a substance having the chemical relations of a metal, formed by the addition of the hydrogen of the acid to the elements of the ammonia. Hydrochloric / 1 eq. Chlorine -- Chlorine ... *| acid ....... \ 1 eq. Hydrogen g a l_ Ammonia ... ? eq " ^ ammonac. \\ eq. Nitrogen ^^. Ammonium J The term ammonium is given to this hypothetical body, NH 4 ; it is sup- posed to exist in all the ammoniacal salts. Thus we have chloride of ammonium, sulphate of the oxide of ammonium, &c. This view is very strongly supported by the peculiarities of the salts themselves, and by the existence of a series of substances intimately related to these salts in organic chemistry, as will hereafter be seen. Many of the sulphides also possess the saline character and are soluble in water, as those of potassium and sodium. Sometimes a pair of sulphides will unite in definite proportions, and form a crystallizable compound. Such bodies bear a very close resemblance to oxygen-acid salts ; they usually contain a protosulphide of an alkaline metal, and a higher sulphide of a non- metallic substance or of a metal which has little tendency to form a basic oxide, the two sulphides having exactly the same relation to each other as the oxide and acid of an ordinary salt. Hence the expressions sulphur-salt, sulphur-acid, and sulphur-base, which Berzelius applies to such compounds ; they contain sulphur in the place of oxygen. Thus, bisulphide of carbon is a sulphur-acid ; it forms a crystallizable compound with protosulphide of potassium, which is a sulphur-base. Were oxygen substituted for the sulphur in this product, we should have carbonate of potassa. 1 SXj, sea-salt, and ?<5oj, form. '22 CHEMISTRY OF THE METALS. KS-fCS 2 sulphur-salt. KO-fC0 2 oxygen-salt. These remarkable compounds are very numerous and interesting ; they have been studied by Berzelius with great care. Salts often combine together, and form what are called double salts, in which the same acid is in combination with two different bases. When sul- phate of copper and sulphate of potassa, or chloride of zinc and sal-ammoniac, are mixed in the ratio of the equivalents, dissolved in water, and the solution made to crystallize, double salts are obtained. These latter are often more beautiful, and crystallize better than their constituent salts. Many of the compounds called super, or acid salts, such as bisulphate of potassa, which have a sour taste and acid reaction to test-paper, ought strictly to be considered in the light of double salts, in which one of the bases is water. Strange as it may at first sight appear, water possesses considerable basic powers, although it is unable to mask acid reaction on vegetable colours ; hydrogen, in fact, very much resembles a metal in its chemical relations. Bisulphate of potassa will, therefore, be a double sul- phate of potassa and water, while oil of vitriol must be assimilated to neutral sulphate of potassa. KO-f S0 3 andHO-fS0 3 . "Water is a weak base ; it is for the most part easily displaced by a metallic oxide ; yet cases occur now and then in which the reverse happens, and water is seen to decompose a salt, in virtue of its basic power. There are few acid salts which contain no water ; as the bichromate of potassa, and a new anhydrous sulphate of potassa discovered by M. Jaque- lain. It will be necessary, of course, to adopt some other view in these cases. The simplest will be to consider them as really containing two equi- valents of acid to one of base. By water of crystallization is meant water in a somewhat loose state of com- bination with a salt, or other compound body, from which it can be disen- gaged by the mere application of heat, or by exposure to a dry atmosphere. Salts which contain water of crystallization have their crystalline form greatly influenced by the proportion of the latter. Green sulphate of iron crystal- lizes in two different forms, and with two different proportions of water, according to the temperature at which the salt separates from the solution. Many salts containing water effloresce in a dry atmosphere, crumbling to powder, and losing part or the whole of their water of crystallization ; while in a moist atmosphere they may be preserved unchanged. The opposite effect to this, or deliquescence, results from a strong attraction of the salt for water, in virtue of which it absorbs the latter from the air, often to the extent of liquefaction. Crystallization; Crystalline Forms. Almost every substance, simple and compound, capable of existence in the solid state, assumes, under favourable 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 edge of organization, and which, when in a 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 result of exceedingly slow changes constantly occurring within the earth ; it is invariably found that artificial crystals of salts, and 1 Ann. Chim. et Phys. Ixx. 311. CHEMISTRY OP THE METALS. 208 other soluble substances, which have been slowly and quietly deposited, always surpass in size and regularity those of more rapid formation. Solution in water or some other liquid is one very frequent method of effecting crystallization. If the substance be more soluble at a high than at a lower temperature, then a hot and saturated solution by slow cooling 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 sur- face of oil of vitriol, often proves very effective. Fusion and slow cooling may be employed in many cases ; that of sulphur s a good example ; the metals usually afford traces of crystalline figure when thus treated, which sometimes become very beautiful and distinct, as with bismuth. A third condition under which crystals very often form is in passing from a gaseous to a solid state, of which iodine affords a good in- stance. When by any of these means time is allowed for the symmetrical arrangement of the particles of matter at the moment of solidification, 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, not 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 carbonate of lime in the two modifications of calcareous spar and arragonite, both chemi- cally the same, but physically different. A fourth example might be given in the iodide of mercury, which also has two distinct forms, and even two distinct colours, offering as great a contrast as those of diamond and plum- bago. Fig. 135. 204 CHEMISTRY OP THE METALS. The angles of crystals are measured by means of instruments called goni- ometers, of which there are two kinds in use, namely, the old or common goniometer, and the reflective goniometer of Dr. Wollaston. The common goniometer consists of a pair of steel blades moving with friction upon a centre, as shown in the cut (fig. 135). The edges a a are carefully 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 di- vided semicircle, the contained angle is at once read off. An approximative measurement, within one or two degrees, can be easily obtained by this in- strument, provided the planes of the crystal be tolerably perfect, and large enough for the purpose. Some practice is of course required before even this amount of accuracy can be attained. The reflective goniometer is a very superior instrument, its indications be- ing correct within a fraction of a degree ; it is applicable also to the mea- surement 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. 136) will convey an idea of its nature and mode of use. Fig. 136. 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. A vernier, e, immovably fixed to the upright support, serves to mea- sure with great accuracy the angular motion of the divided circle. The crystal at / can thus be turned round, or adjusted in any desired position, without the necessity of moving the disc. 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. This will be easily intelligible by reference to fig. 137, in which a crystal having the form of a triangular prism 1 is shown in the two positions, the angle to be measured being that indicated by the letters e df. The lines a c, be, are perpendicular to the respective faces of the crystal, 1 The triangular prism has been chosen for the sake of simplicity; but a moment's con- sideration will show that the rule applies equally well to any other figure. CHEMISTRY OF THE METALS. 205 Fig. 137. consequently the internal angles dg c, dhc, are right angles. Now, since the sum of the internal angles of a four-sided rectilineal figure, as dgch, equal four right angles, or 360, the angle g dh (or e df) must of necessity be the supplement to the angle g c h, or that through which the crystal moves. All that is required to be done, therefore, is to measure the latter angle with accuracy, and subtract its value from 180 ; and this the gonio- meter 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-illumi- nated 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 too easily- visible 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 mea- sured shall nearly coincide with, or be parallel to, the axis of the instru- ment. 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. 136) 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. Following this image, the crystal is still cautiously turned until the upper black line seen by re- flection 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 su- perposed. 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 been correctly placed, so as to bring the edge into the required condition of parallelism with the axis of motion, the measurement of the angle may be made. 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 backwards, so that the 18 206 CHEMISTRY OF THE METALS. 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 opera- tion 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 o 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 remarkable 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 as follows : 1. The regular 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 show the terminations 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, iodide of potassium, the alums, fluor-spar, bisulphide of iron, garnet, spinelle, &c. 2. The square prismatic system. Three axes are here also observed, at right-angles to each other. Of these, however, two only are of equal length, the third being usually longer or shorter. The most important forms are : a right square prism, in which the latter axes terminate in the central point Fig. 139. a a. Principal, or vertical axis. I b. Secondary, or lateral axis. CHEMISTRY OF THE METALS. XOl 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 octahedra (3 and 4). Examples of these forms are to be found in zircon, native binoxide of tin, apophyllite, yellow ferrocyanide of potassium, &c. 3. The right prismatic system. This is characterized by three axes of un- equal lengths, placed at right-angles to each other, as in the right rectangular prism (1), the right rhombic prism (2), the right rectangular-based octahedron, (3), and the right rhombic-based octahedron (4). Fig. 140. a a. Principal axis. & b, c c. Secondary axes. The system is exemplified in sulphur crystalliied at a low temperature, arsenical iron pyrites, nitrate and sulphate of potassa, sulphate of baryta, &c. 4. The 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 per- pendicular to the other. To this system may be referred the four following a a. Principal axis. b b, c c. Secondary axes. forms: The oblique rectangular prism (1), the oblique rhombic prism (2), the oblique rectangular-based octahedron (3), the oblique rhombic-based octahe- dron (4). Such forms are taken by sulphur crystallized by fusion and cooling, real- gar, sulphate, carbonate and phosphate of soda, borax, green vitriol, and many other salts. 5. The doubly -oblique prismatic system. The crystalline forms comprehended in this division are, from their great apparent irregularity, exceedingly dif- ficult to studv and understand. In them are traced three axes, which may 208 CHEMISTRY OF THE METALS. be all unequal in length, and are all oblique to each other, as in the two doubly -oblique prisms (I and 2), and in the corresponding doubly-oblique octa- hedrons (3 and 4). Fig. 142. a a. Principal axis, as before. b b, o c. Secondary axes. Sulphate of copper, nitrate of bismuth, and quadroxalate of potassa, aiford illustrations of these forms. 6. The rhombohedral system. This is very important and extensive : it is characterized by the presence of four axes, three of which are equal, in the same plane, and inclined to each other at angles of 60, while the fourth or Fig. 143. a a. Principal axis. b 6. Secondary axes. principal axis is perpendicular to all. The regular six-sided prism (1), thh quartz-dodecahedron (2), the rhombohedron (3), and a second dodecahedron, whose faces are scalene triangles (4), belong to the system in question. Examples are readily found ; as in ice, calcareous spar, nitrate of soda, beryl, quartz or rock crystal, and the semi-metals, arsenic, antimony, and tellurium. 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 disti-ibuted unequally, but still in obedience to certain definite laws, then alterations of form are produced, giving rise to figures which have a direct geometrical connection with that from which they are derived. If, for example, in the cube, a regular omission of successive rows of particles of matter in a cer- tain order be made at each solid angle, while the crystal continues to increase elsewhere, the result will be the production of small triangular planes, CHEMISTRY OF THE METALS. 209 which, as the process advances, gradually usurp the whole of the surface of the crystal, and convert the cube into an octahedron. The new planes are called secondary, and their production is said to take place by regular decre- ments upon the solid angles. The same thing may happen on the edges of the cube ; a new figure, the rhombic dodecahedron, is then generated. Fig. 144. 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. Fig. 144. Passage of cube to octahedron. It is important to observe, that in all these deviations from what may be regarded as the primary or fundamental figure of the crystal, the modifying planes are in fact the planes of figures belonging to the same natural group or crystallographical system as the primary form, and having their axes coincident with those of the latter. 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. Crystals often cleave parallel to all the planes of the primary figure, as in calcareous spar, which offers a good illustration of this perfect cleavage. Sometimes 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 octahedron (fig. 145), and of the rhombohedric form by a similar change from the quartz-dodecahedron already figured. Fig. 145. Passage of octahedron to tetrahedron. 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 crystallized compounds without alteration of the characteristic geometrical figure. Such bodies are said to be isomorphous. 1 1 From 7 ff0 j, equal, and ftdp(f>n\ shape or form. 210 CHEMISTRY OF THE METALS. For example, magnesia, oxide of zinc, oxide of copper, protoxide of iron, and oxide of nickel, are allied by isomorphic relations of the most intimate nature. The salts formed by these substances with the same acid and similar proportions of water of crystallization, are identical in their form, and, when of the same colour, cannot be distinguished by the eye ; the sul- phates of magnesia and zinc may be thus confounded. The sulphates, too, all combine with sulphate of potassa and sulphate of ammonia, 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 sesquioxide of iron replace each other continually without change of crystalline figure ; the same remark may be made of potassa, soda, and ammonia, with an equivalent of water, or oxide of ammonium, these bodies being strictly isomorphous. The alumina in in common alum may be replaced by sesquioxide of iron ; the potassa by ammonia, or by soda, and still the figure of the crystal remains unchanged. These replacements may be partial only ; we may have an alum containing both potassa and ammonia, or alumina and sesquioxide of chromium. 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 sulphate of protoxide of iron and sulphate of copper, iso- morphous salts, yields on evaporation crystals containing both iron and copper. But if before evaporation the protoxide of iron be converted into sesquioxide by chlorine or other means, then the crystals obtained are free from iron, except that of the mother-liquor which wets them. The salt of sesquioxide of iron is no longer isomorphous with the copper salt, and easily separates from the latter. When compounds are thus found to correspond, it is inferred that the ele- ments composing them are also isomorphous. Thus, the metals magnesium, zinc, iron, and copper are presumed to be isomorphous ; arsenic and phos- phorus should present the same crystalline form, because arsenic and phos- phoric 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 ele- ments themselves are believed to be also isomorphous. Unfortunately, for obvious reasons, it is very difficult to observe the crystalline figure of most of the elementary bodies, and this difficulty is increased by the frequent di- morphism they exhibit. Absolute identity of value in the angles of crystals is not always exhibited 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 occasion no surprise, as there are reasons why such variations may be expected, the chief perhaps being the unequal effects of expansion by heat, by which the angles of the same crystals are changed by alteration of temperature. A good example is found in the case of the carbonates of lime, magnesia, man- ganese, iron, and zinc, which are found native crystallized in the form of obtuse rhombohedra (fig. 143, 3) not distinguishable from each other by the eye, or even by the common goniometer, but showing small differences when examined by the more accurate instrument of Dr. Wollaston. These com- pounds are isomorphous, and the measurements of the obtuse angles of theii rhombohedra as follows : CHEMISTRY OF THE METALS. 211 Carbonate of lime 105 5' " magnesia 107 25' " prot.ox. manganese 107 20 / " " iron 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 mea- sure 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 destruc- tion of what may be called the primitive type of the compound, these diffi- culties vanish. Another benefit conferred on science by the discoveries in question, is that of furnishing a really philosophical method of classifying elementary and compound substances, so as to exhibit their natural relationships ; it would be perhaps more proper to say that such will be the case when the isomorphic relations of all the elementary bodies become known, at present only a certain number have been traced. 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 of the metal from its relation to sesquioxide of iron, which is certainly so ; the black oxide of copper is inferred to be really the protoxide, although it contains twice as much oxygen as the red oxide, because it is isomorphous with magnesia and zinc, both undoubted protoxides. The subjoined table will serve to convey some idea of the most important families of isomorphous elements ; it is taken from Professor Graham's sys- tematic work, 1 to which the pupil is referred for fuller details on this inte- resting subject. Isomorphous Groups. (1-) (3.) (7.) Sulphur Barium Sodium Selenium Strontium Silver Tellurium. Lead. Gold (2.) (4.) Potassium Magnesium Tin Ammonium. Calcium Titanium. (8.) Manganese (5.) Chlorine Iron Platinum Iodine Cobalt Iridium Bromine Nickel Osmium. Fluorine Zinc (6.) Cyanogen. Cadmium Tungsten (9.) Copper Molybdenum Phosphorus Chromium Tantalum. Arsenic Aluminium Antimony Beryllium BismuthI Vanadium Zirconium. There is a law concerning the formation of double salts which may now be mentioned ; the two bases are never taken from the same isomorphous 1 Second edition, p. 149. 212 CHEMISTRY OF THE METALS. family. Sulphate of copper or of zinc may unite in this manner with sulphate of soda or potassa, but not with sulphate of iron or cobalt ; chloride of mag- nesium may combine with chloride of ammonium, bu't not with chloride of zinc or nickel, &c. It will be seen hereafter that this is a matter of some importance in the theory of the organic acids. Polybasic Acids. There is a particular class of acids in which a departure occurs from the law of neutrality formerly described ; these are acids re- quiring two or more equivalents of a base for neutralization. The phosphoric and arsenic acids present the best examples yet known in mineral chemistry, but in the organic department of the science cases very frequently occur. Phosphoric acid is capable of existing in three different states or modifica- tions, forming three separate classes of salts which differ completely in pro- perties and constitution. They are distinguished by the names tribasic, dibasic, and monobasic acids, according to the number of equivalents of base required to form neutral salts. Tribasic or Common Phosphoric Acid. "When commercial phosphate of soda is dissolved in water and the solution mixed with acetate of lead, an abundant white precipitate of phosphate of lead falls, which may be collected on a filter, and well washed. While still moist, this compound is suspended in distilled water, and an excess of sulphuretted hydrogen gas passed into it. The protoxide of lead is converted into sulphide, which subsides as a black insoluble precipitate, while phosphoric acid remains in solution, and is easily deprived of the residual sulphuretted hydrogen by a gentle heat. The soda-salt employed in this experiment contains the tribasic modifica- tion of phosphoric acid ; of the three equivalents of base, two consist of soda and one of water ; when mixed with solution of lead, a tribasic phosphate of the oxide of that metal falls, which when decomposed by sulphuretted hydro- gen, yields sulphide of lead and a hydrate of the acid containing three equivalents of water in intimate combination. {2 eq. soda ~~~7 ^ e< ^' ace * a ^ e f soda. 1 water / /^ " h y drated acetic acid. 1 ,, pnos-) phoric acid / 3 eq acetate f 2 eq * acetic acid of lead 1 3 I) oxide" oTlead- -?> l eq. tribasic phosphate of lead. {3 eq. lead 7 3 eq. sulphide of lead. 3 oxygen 1 ,, phos- phoric acid J 3 eq. sulphuretted f 3 eq. sulphur hydrogen \ 3 hydrogen ^ 1 eq. tribasic hydrate of phosphoric acid. The solution of tribasic hydrate may be concentrated by evaporation in vacuo over sulphuric acid until it crystallizes in thin deliquescent plates. The same compound in beautiful crystals, resembling those of sugar-candy, has been accidentally formed/ It undergoes no change by boiling with water, but when heated alone to 400 (204-4C) loses some of its combined water, arid becomes converted into a mixture of the bibasic and monobasic hydrates. At a red heat it becomes entirely changed to monohydrate, which, at a still higher temperature, sublimes. Tribasic phosphoric acid is characterized by the yellow insoluble salt it forms with protoxide of silver. 1 P61igot, Ann. Chim. et Phys. Ixxiii. 286. CHEMISTRY OF THE METALS. 213 Bibasic Phosphoric Acid, or Pyrophosphoric Acid. When common phos- phate of soda, containing 2NaO, HO, P0 5 +24HO, is gently heated, the 24 equivalents of water of crystallization are expelled, and the salt becomes anhydrous ; but if the heat be raised to a higher point, the basic water is also driven off, and the acid passes into the second or bibasic modification. If the altered salt be now dissolved in water, this new compound, the bibasic phosphate of soda, crystallizes out. When mixed with solution of acetate of lead, bibasic phosphate of lead is thrown down, which, decomposed by sulphuretted hydrogen, furnishes a solution of the bibasio hydrate. This solution may be preserved without change at common tem- peratures, but when heated, an equivalent of water is taken up, and the substance passes back again into the tribasic modification. Crystals of this hydrate have also been observed by M. Pe'Iigot. Their production was accidental. The bibasic phosphates soluble in water give a white precipitate with solution of silver. Monobasic, or Metaphosphoric Acid. When common tribasic phosphate of soda is mixed with solution of tribasic hydrate of phosphoric acid, and ex- posed, after proper concentration, to a low temperature, prismatic crystals are obtained, which consist of a phosphate of soda having two equivalents of basic water. NaO, 2HO, P0 5 -f-2HO. When this salt is very strongly heated, both the water of crystallization and that contained in the base are expelled, and monobasic phosphate of soda remains. This may be dissolved in cold water, precipitated with ace- tate of lead, and the lead-salt, as before, decomposed by sulphuretted hy- drogen. The solution of the monobasic hydrate is decomposed rapidly by heat, becoming converted into tribasic hydrate. It possesses the property of co- agulating albumen, which is not enjoyed by either of the preceding modifi- cations. Monobasic alkaline phosphates precipitate nitrate of silver white. The glacial phosphoric acid of pharmacy is, when pure, hydrate of mono- basic phosphoric acid : it contains HO, P0 5 . Anhydrous phosphoric acid, prepared by burning phosphorus in dry air, when thrown into water, forms a variable mixture of the three hydrates. When heated, a solution of the tribasic hydrate alone remains. 1 See also phosphates of soda. Binary Theory of Salts. The great resemblance in properties between the two classes of saline compounds, the haloid and oxy-salts, has very naturally led to the supposition that both might possibly be alike constituted, and that the latter, instead of being considered compounds of an oxide and an acid, might with greater propriety be considered to contain a metal in union with a compound salt-radical, having the chemical relations of chlorine and iodine. On this supposition sulphate and nitrate of potassa will be constituted in the same manner as chloride of potassium, the compound radical replacing the simple one. Old view. New view. KO-fSO, K-f-S0 4 KO-fN0 5 K-fN0 6 1 The three modifications of phosphoric acid possess properties so dissimilar that they might really be considered three distinct, although intimately related bodies. It is exceedingly remarkable, that when their salts are subjected to electro-chemical decomposition, the arid* travel unaltered, a tribasic salt giving at the positive electrode a solution of common phos- phoric acid; a bibasic salt, one of pyrophosphoric acid; and a monobasic salt, one of met* phosphoric acid (Professor Daniell and Dr. Miller, Phil. Trans, for 1844, p. 1). 214 CHEMISTRY OF THE METALS. Hydrated sulphuric acid will be, like hydrochloric acid, a hydride of a salt- radical, H+S0 4 . When the latter acts upon metallic zinc, the hydrogen is simply displaced, and the metal substituted ; no decomposition of water is supposed to occur, and, consequently, the difficulty of the old hypothesis is at an end. When the acid is poured upon a metallic oxide, the same reaction occurs as in the case of hydrochloric acid, water and a haloid salt are produced. All acids must be, in fact, hydrogen acids, and all salts haloid salts, with either simple or compound radicals. This simple and beautiful theory is not by any means new ; it was sug- gested by Davy, who proposed to consider hydrogen as the acidifying prin- ciple in the common acids, and lately revived and very happily illustrated by Liebig. It is supported by a good deal of evidence derived from various sources, and has received great help from a series of exceedingly interesting experiments on the electrolysis of saline solutions, by the late Professor Daniell. 1 The necessity of creating a great number of non-insoluble com- pounds is often urged as an objection to the new view ; but the same objec- tion applies to the old mode of considering the subject. Hyposulphurous acid and hyposulphuric acid are unknown in their free states. The com- pounds S 2 2 and S 2 4 are as hypothetical as the substances S 2 3 and S 2 6 . The same remark applies to almost every one of the organic acids ; and, what Is well worthy of notice, those acids which, like sulphuric, phosphoric, and carbonic acids, may be obtained in a separate state, are destitute of all acid properties so long as the anhydrous condition is retained. Some very interesting observations have been published lately by M. Ger- hardt, 1 which are likely to hasten a change in the notation of acids generally. It has been pointed out that sulphuric and nitric acid, which, according to the theory of oxygen acids, are considered as compounds respectively of teroxide of sulphur andpentoxide of nitrogen with water, S0 3 ,HO, and N0 5 , HO, may be considered likewise as hydrogen acids, analogous to hydro- chloric and hydrocyanic acid. Hydrochloric acid HC1 Hydrocyanic acid HON Sulphuric acid ") Hydrosulphanic acid / " Nitric acid \ HN0 6 . Hydronitranic acid.. / Among the many facts which have been adduced in favour of the theory of oxygen acids, the preparation of the so-called anhydrous acids S0 3 and NO (see pages 124 and 135) has always been considered as powerful props. On the other hand, the followers of the theory of hydrogen acidft have inva- riably called attention to the scarcity of the so-called anhydrous acids, and especially to the fact that, with a few exceptions, they are entirely wanting in Organic Chemistry. The researches of M. Gerhardt just referred to, have furnished the means of making the anhydrous organic acids ; but the circumstances under which they are produced exhibit these substances in a perfectly new light, and prove that they stand in a very different relation to the hydrated acids from what is generally assumed. If dry benzoate of soda be heated with chloride of benzoyl (see page 399) to a temperature of 266 (130C), a limpid liquid is formed, which is de- 1 See Darnell's Introduction to Chemical Philosophy, 2d edition, p. 533. 9 Chem. Soc. Quar. Jour. v. 127. CHEMISTRY OF THE METALS. 215 composed with deposition of chloride of sodium when heated a few degrees higher ; there is formed, at the same time, a white crystalline product, which has exactly the composition of anhydrous benzoic acid, for it contains Ci 4 H 6 3 or BzO, if we represent C M H 5 2 by Bz. The decomposition which takes place is represented by the following equation : BzO,NaO-fBzCl=NaCl-f2BzO. The new substance crystallizes in beautiful oblique prisms, fusible at 90 -4 (33C), and volatile without decomposition. It is insoluble in water, but readily dissolves in alcohol and ether ; these solutions are perfectly neutral to test-paper. Cold water has not the slightest effect upon this body j by boil- ing water it is gradually converted into benzoic acid. This change immedi- ately occurs with boiling solutions of the alkalis. Boiling alcohol converts it into benzoate of ethyl. From the mode of formation, it is evident that the substance in qxiestion cannot be regarded as anhydrous benzoic acid, al- though it agrees with that substance in composition. It is obviously a sort of a salt, benzoate of benzoyl, or benzoic acid in which one equivalent of hy- drogen is replaced by benzoyl. Benzoic acid BzO,HO New compound BzO,BzO. If an additional support for this view was required, it would be found in the circumstance that chloride of benzoyl acts in exactly the same manner upon cumate, cinnamate, and salicylate of soda, a series of compounds be- ing produced which are perfectly analogous to the preceding substance, but contain in the place of benzoyl cuminyl, C2oH ia 2 =Cm; cinnamyl, C, 8 H 7 2 = Ci; or salicyl, C 14 H 6 4 =S1. Benzoic acid BzO,HO Benzoate of benzoyl BzO,BzO Benzoate of cuminyl , BzO,CmO Benzoate of cinnamyl BzO,CiO Benzoate of salicyl BzO,S10. These substances are for the most part fusible, odourless solids, or oils heavier than water. With the alkalis they yield a mixture of the acids from which they have been produced. Several are not volatile without decompo- sition. A perfectly similar series of substances has been obtained with acetic acid. The acetic chloride, C1C 4 H 3 2 , corresponding to chloride of benzoyl, is formed in a most interesting process, namely, by the action of pentachloride of phosphorus (see page 168) upon acetate of soda, when chloride of sodium, oxichloride of phosphorus, PC1 3 2 , and chloride of acetetyl 1 are formed. NaO, C 4 H 3 3 4- PC1 5 = NaCl -f PCl 3 2 -f C 4 H 3 2 C1. The action of chloride of acetetyl upon dry acetate of soda gives rise to the formation of an oily liquid, which has the composition of anhydrous acetic acid, C 4 H,0 3 , but which in reality is acetate of acetetyl = C 4 H y 2 , 4 H 3 2 ,0. a This liquid boils at 278-6 (137C) ; it is not miscible at once 1 Acetetyl in order to distinguish it from acetyl, C 4 Hs. 3 This formula requires an equivalent of oxygen to produce two equivalents of anhydrous acetic acid. C P tassium ^ 1 eq. pentasulphide Aeq.hyposul- potassa 1 J e q. oxygen^ ^> of potassium, phite of po--j . tassai l "^ 1 " " J ] " ^ n " " r * posulph. -| 3 eq. sulphur- acid ( 8 eq. oxygen -^ 3 eq. sulphate of potassa. From both these mixtures the pentasulphide of potassium may be ex- tracted by alcohol, in which it dissolves. When the carbonate is fused with half its weight of sulphur only, then the tersulphide, KS 3 , is produced instead of that above indicated ; 3 eq. of po- tassa and 8 eq. of sulphur containing the elements of 2 eq. sulphide and 1 eq. hyposulphite. The effects described happen in the same manner when hydrate of potassa is substituted for the carbonate ; and also, when a solution of the hydrate is boiled with sulphur, a mixture of sulphide and hyposulphite always results. CHLORIDE OF POTASSIUM, KC1. This salt is obtained in large quantity in the manufacture of chlorate of potassa ; it is easily purified from any portions of the latter by exposure to a dull red-heat. It is also contained in kelp, and is separated for the use of the alum-maker. Chloride of potassium closely resembles common salt in appearance, as- suming, like that substance, the cubic form of crystallization. The crystals dissolve in three parts of cold, and in a much less quantity of boiling water ; they are anhydrous, have a simple saline taste, with slight bitterness, and fuse when exposed to a red-heat. Chloride of potassium is volatilized by a very high temperature. IODIDE OF POTASSIUM, KI. There are two different methods of preparing this important medicinal compound. (1.) When iodine is added to a strong solution of caustic potassa free from carbonate, it is dissolved in large quantity, forming a colourless solution containing iodide of potassium and iodate of potassa ; the reaction is the same as in the analogous case with chlorine. When the solution begins to be permanently coloured by the iodine, it is evaporated to dryness, arid cau- tiously heated red-hot, by which the iodate of potassa is entirely converted into iodide of potassium. The mass is then dissolved in water, and after fil- tration, made to crystallize. (2.) Iodine, water, and iron-filings or scraps of zinc, are placed in a warm situation until the combination is complete, and the solution colourless. The resulting iodide of iron or zinc is then filtered, and exactly decomposed with solution of pure carbonate of potassa, great care being taken to avoid excess of the latter. Iodide of potassium and carbonate of protoxide of iron, or zinc, are obtained ; the former is separated by filtration, and evaporated until the solution is sufficiently concentrated to crystallize on cooling, the washings of the filter being added to avoid loss. Iodide of iron { f Potassiu )tassa ^ Oxygen ^_^^ Carbonic acid ^~^v Carbonate of protoxido of iron. The second method is, on the whole, to be preferred. 224 SODIUM. Iodide of potassium crystallizes in cubes, which are often, from some un- explained cause, milk-white and opaque ; they are anhydrous, and fuse readily -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 iodide of potassium, like those of all the soluble iodides, dis- solves a large quantity of free iodine, forming a deep brown liquid, not de- composed by water. BROMIDE OF POTASSIUM, KBr. This compound may be obtained by pro- cesses exactly similar to those just described, substituting bromine for the iodine. It is a colourless and very soluble salt, quite indistinguishable in appearance and general characters from the iodide. The salts of potassa are colourless, when not associated with a coloured metallic oxide or acid. They are ail more or less soluble in water, and may be distinguished by the following characters : (1.) Solution of tartaric acid added to a moderately strong solution of a potassa-salt, gives, after some time, a white, crystalline precipitate of cream of tartar ; the effect is greatly promoted by strong agitation. (2.) Solution of bichloride of platinum, with a little hydrochloric acid, if necessary, gives, under similar circumstances, a crystalline yellow precipi- tate, which is a double salt of bichloride of platinum and chloride of potas- sium. 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 hydrofluosilicic acid, give rise to slightly-soluble white precipitates when added to a potassa-salt. (4.) Salts of potassa usually colour the outer blowpipe flame purple or violet ; this reaction is clearly perceptible only when the potassa-salts are pure. SODIUM. This metal was obtained by Davy very shortly after the discovery of po- tassium, and by similar means. It may be prepared in large quantity by decomposing carbonate of soda by charcoal at a high temperature. Six parts of anhydrous carbonate of soda are dissolved in a little hot water, and mixed with two parts of finely-powdered charcoal arid one part of charcoal in lumps. The whole is then evaporated to dryness, transferred to the iron retort before described, and heated in the same manner to white- ness. A receiver containing rock-oil is adapted to the tube, and the whole operation carried on in the same way as when potassium is made. The pro- cess, when well conducted, is easier and more certain than that of making potassium. Sodium is a silver-white metal, greatly resembling potassium in every re- spect; it is soft at common temperatures, melts at 194 (90C), and oxidizes very rapidly in the air. Its specific gravity is 0-972. Placed upon the sur- face of cold water, sodium decomposes that liquid with great violence, but seldom takes fire unless the motions of the fragment be restrained, and its rapid cooling diminished, by adding gum or starch to the water. With hot water it takes fire at once, burning with a bright yellow flame, and giving rise to a solution of soda. The equivalent of sodium is 23, and its S3 7 tnbol (Natrium) Na. There are two well-defined compounds of sodium and oxygen; the pro- toxide, anhydrous soda, NaO, and the binoxide, Na6 2 , or perhaps, teroxide Na0 3 ; they are formed by burning sodium in air or oxygen gas, and resem- ble in every respect the corresponding compounds of potassium. HYDRATE OF SODA, NaO, HO. This substance is prepared in practice by SODIUM. 225 TABLE OP Percentage of real soda. 77-8 DENSITY. Density. 1-40 Percentage of real soda. 29-0 63-6 1-36 26-0 53-8 1-32 23-0 46-6 1-29 19-0 41-2 1-23 16-0 36-8 1-18 13-0 34-0 1-12 9-0 .. 31-0 1-06 .. , 4-7 decomposing a somewhat dilute solution of carbonate of soda by hydrate of Hme ; the description of the process employed in the case of hydrate of po- tassa, and the precautions necessary, apply word for word to that of soda. The solid hydrate is a white, fusible substance, very similar in properties to hydrate of potassa. It is deliquescent, but dries up again after a time in consequence of the absorption of carbonic acid. The solution is highly al- kaline, and a powerful solvent for animal matter; it is used in large quan- tity 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 Dr. Dalton. Density. 2-00 1-85 1-72 1-63 1-55 1-50 1-47 1-44 CARBONATE OF SODA, NaO,C0 2 -f-10HO. Carbonate of soda was once ex- clusively obtained from the ashes of sea-weeds, and of plants, such as the Salsola soda, which grew by the sea-side, or, being cultivated in suitable lo- calities for the purpose, were afterwards subjected to incineration. The barilla, yet employed to a small extent in soap-making, is thus produced in several places on the coast of Spain, as Alicant, Carthagena, &c. That made in Brittany is called varec. Carbonate of soda is now manufactured on a stupendous scale from com- mon salt, or rather from sulphate of soda, by a process of which the follow- ing is an outline : A charge of GOOlb. of common salt 1 is placed upon the hearth of a well- heated reverberatory furnace, and an equal weight of sulphuric acid of sp. gr. 1-6 poured upon it through an opening in the roof, and thoroughly min- gled with the salt ; hydrochloric acid gas is disengaged, which is either allowed to escape by the chimney, or condensed by suitable apparatus, and the salt is converted into sulphate of soda. This part of the process takes for completion about four hours, and requires much care and skill. 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 cwt. is about the quantity operated on at once. When the decomposition is judged complete, the melted matter is raked from the surface into an iron trough, where it is allowed to cool. When cold, it is broken up into little pieces, and lixiviated with cold or tepid water. The solution is evaporated to dryness, and the salt calcined with a little saw-dust in a suitable furnace. The product is the soda-ash, or British alkali of com- merce, which, when of good quality, contains from 48 to 52 per cent, of pure soda, partly in the state of carbonate, and partly as hydrate, the re mainder being chiefly sulphate of soda and common salt, with occasional traces of sulphite or hyposulphite, and also cyanide of sodium. By dissolving 1 Graham, Elements, p. 393, vol. :. 226 SODIUM. Boda-ash in hot water, filtering the solution, and then allowing it to cool slowly, the carbonate is deposited in large transparent 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 sulphate of soda into sulphide of sodium by the aid of the combustible matter, and, secondly, in the double interchange of elements between that substance and the carbonate of lime. Sulphide of sodium/ S ul P hur ^ Sul P llide of calcium ' JLime{ C: Carbonate of lime * " \ Oxygen ( Carbonic acid ~^. Carbonate of soda. The sulphide of calcium combines with another proportion of lime to form a peculiar compound, which is insoluble in cold or slightly warm water. Other processes have been proposed, and even carried into execution, but the above, which was originally proposed by M. Leblanc, is found most ad- vantageous. The ordinary crystals of carbonate of soda contain ten equivalents of water, but by particular management the same salt may be had with fifteen, nine, seven, equivalents, or sometimes with only one. The common form of the crystal is derived from an oblique rhombic prism ; they efiloresce in dry air, and crumble to a white powder. Heated, they fuse in their water of crys- tallization ; 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 power- ful alkaline reaction. BICARBONATE OF SODA, NaO,C0 2 -J- HO,C0 2 . 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 ab- sorbed, while the crystals lose the greater part of their water, and pass into the new compound. Bicarbonate of soda, prepared by either process, is a crystalline white powder, which cannot be re-dissolved in warm water without partial decom- position. It requires 10 parts of water at 60 (15-5C) 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. A sesquicarbonate of soda containing 2NaO,3C0 2 -f-4HO has been described by Mr. Phillips ; like the sesquicarbonate of potassa, it is formed at plea- sure only with difficulty. This salt occurs native on the banks of the soda- lakes of Sokena in Africa, whence it is exported under the name of trona. Alkalimetry; Analysis of Hydrates and Carbonates of the Alkalis. The general principle of these operations consists in ascertaining the quantity of real alkali in a given weight of the substance examined, by finding how much of the latter is required to neutralize a known quantity of an acid, as sulphuric acict. The first step is the preparation of a stock of dilute sulphuric acid of determinate strength ; containing, for example, 100 grains of real acid in every 1,000 grain-measures of liquid : ' a large quantity, as a gallon or more, * The capacity of 1.000 grains of distilled water at 60 (155C). The grain-measure of water is often found a very convenient and useful unit of volume in chemical researches. Vessels graduated on this plan bear simple comparison with the imperial pnllon and pint, and fre- quently also enable ttte operator to measure out a liquid of known density instead of weigh- ing it. SODIUM. 227 may be prepared at once by the following means. The oil of vitriol is first examined; if it be good and of the sp. gr. 1-85 or near it, the process is ex- tremely simple ; every 49 grains of the liquid acid contains 40 grains of absolute acid ; the quantity of the latter required in the gallon, or 70,000 grain-measures of dilute acid, will be of course 7,000 grains. This is equi valent to 8.571 grains of the oil of vitriol, for Real acid. Oil of vitriol. 40 : 49 = 7000 : 8575 All that is required to be done, therefore, is to weigh out 8,575 grains of oil of vitriol, and dilute it with so much water, that the mixture, when cold, shall measure exactly one gallon. It very often happens, however, that the oil of vitriol to be used is not so strong as that above mentioned ; in which case it is necessary to discover its real strength, as estimated from its saturating power. Pure anhydrous car- bonate of soda is prepared by heating to dull redness, without fusion, the bicarbonate ; of this salt 53 grains, or 1 eq., correspond to 31 grains of soda, and neutralize 40 grains of real sulphuric acid. A convenient quantity is carefully weighed out, and added, little by little, to a known weight, say 100 grains, of the oil of vitriol to be tried, diluted with four or five times its weight of water, until the liquid, after warming, becomes quite neutral to test-paper. By weighing again the residue of the carbonate, it is at once known how much of the latter has been employed ; the amount of real acid in the hundred parts of the oil of vitriol is then easily calculated. Thus, suppose the quantity of carbonate of soda used to be 105 grains ; then, Carb. soda. Sulpb. acid. 53 : 40 = 105 : 79-24; 79-24 grains of real acid are consequently contained in 100 grains Fig. 146 of oil of vitriol ; consequently, 79-24 : 100 = 7000 : 8833-82 the weight in grains of the oil of vitriol required to make one gallon of the dilute acid. The " alkalimeter" is next to be constructed. This is merely a 1000-grain measure, made of a piece of even, cylindrical glass tube, about 15 inches long and 0-6 inch internal diameter, closed at one extremity, and moulded into a spout or lip at the other. Fig. 146. A strip of paper is pasted on the tube and suffered 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 weighing into it, in succession, 100, 200, 300, &c., grains of dis- tilled water at GO (15 -5C), until the whole quantity, amounting to 1,000 grains, 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 the bottom of the curve formed by the surface of the water. The smaller divisions of the scale, of 10 grains each, may then be made by dividing by compasses each of the spaces into ten equal parts. When the graduation is complete, arid 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. When this alkaliraeter is used 2*^8 SODIUM. with the dilute acid described, every division of the glass will correspond to one grain of real sulphuric acid. Let it be required, by way of example, to test the commercial value of soda-ash, or to examine it for scientific purposes : 50 grains of the sample are weighed out, dissolved in a little warm water, and, if necessary, the solution filtered ; the alkalimeter is then filled to the top of the scale with the test-acid, and the latter poured from it into the alkaline solution, which is tried from time to time with red litmus-paper. The addition of acid must of course be made very cautiously as neutralization advances. When the solution, after being heated a few minutes, no longer affects either blue or red test-paper, the measure of liquid employed is read off, and the quantity of soda present in the state of carbonate or hydrate in the 50 grains of salt found by the rule of proportion. Suppose 33 measures, consequently 33 grains of acid, have been taken ; then Sulph. acid. Soda. 40 : 31 = 33 : 25-57; the sample contains, therefore, 51-2 per cent, of available alkali. It will be easily seen that the principle of the process described admits of very wide application, and that, by the aid of the alkalimeter and carefully prepared test-acid, the hydrates and carbonates of potassa, soda, and am- monia, both in the solid state and in solution, can be examined with great ease aud accuracy. The quantity of real alkali in a solution of caustic am- monia may thus be determined, the equivalent of that substance, and the amount of acid required to neutralize a known weight, being inserted as the second and third terms in the above rule-of-three statement. The same acid answers for all. 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 (fig. 147) of three or four Fig. 147. 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 chloride of calcium, 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 examined 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 chloride of calcium tube are then adjusted, and the whole apparatus accurately counterpoised on the balance. This done, the flask is slightly inclined, so that the 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 of the tube. When the action has entirely ceased the liquid is heated 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 carbonic acid. The acid must be in excess after the experiment. When carbonate of lime is thus analyzed, strong hydrochloric acid must be substi- tuted for the oil of vitriol. Instead of the above apparatus, a neat arrangement may be used which SODIUM. 229 was first suggested by Will and Fresenius. It consists of two small glass flasks, A and B, fig. 148, the latter being somewhat smaller than the former. Both the flasks are 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 flask, whilst a second tube reach- Fig. 148. ing 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 analyse a carbonate, a suitable quan- tity (fifty grains) is put into A, together with some water. B is half filled with concentrated 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 d, whereby the air in A is likewise rarified. Im- mediately a portion of sulphuric acid ascends in the tube c, and flows over into flask A, causing a disengagement of carbonic acid, which escapes at rf, after having been perfectly dried by passing through the bottle B. This operation 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 carbonic acid in the compound analysed. 1 SULPHATE OF SODA, GLAUBER'S SALTS, NaO, S0 3 -}-10HO. This is a by- product in several chemical operations ; it may of course be prepared directly, if wanted pure, by adding dilute sulphuric acid to saturation to & solution of carbonate of soda. It crystallizes in a figure derived from an oblique rhombic prism ; the crystals contain 10 eq. of water, are efflores- cent, 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 91 -5 (33C), when a maximum is reached, 100 parts of water dissolving 322 parts of the salt. Heated beyond this point, the solubility diminishes, and a portion of sul- phate is deposited. A warm saturated solution, evaporated at a high tempe- rature, deposits opaque prismatic crystals, which are anhydrous. This salt has a slightly bitter taste, and is purgative. Mineral springs sometimes con- tain it, as at Cheltenham. BISULPHATE OF SODA, NaO,S0 3 -f HO,S0 3 -{- 3HO. This is prepared by adding to 10 parts of anhydrous neutral sulphate, 7 of oil of vitriol, evapo- rating the whole to dryness, and gently igniting. The bisulphate 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 simple sulphate ; a change which necessarily supposes the previous formation of a true anhydrous bisulphate, NaO,2S0 3 . HYPOSULPHITE OF SODA, NaO, S 2 2 . There are several modes of procu- ring this salt, which is now used in considerable quantity for photographic purposes. One of the best is to form neutral sulphite of soda, by passing a stream of well washed sulphurous acid gas into a strong solution of carbo- nate of soda, and then to digest the solution with sulphur at a gentle heat during several days. By careful evaporation at a modern temperature, the ealt is obtained in large and regular crystals, which are very soluble in water. 1 A conTenient modification of this has been made by Dr. Wetherill, (Journ. Frank, fust); and another by Schafiner. (Chem. Gazette, Jan. 15, 1853. R. B.) 230 SODIUM. NITRATE OF SODA ; CUBIC NITRE, NaO, N0 5 . Nitrate of soda occurs native, and in enormous quantity, at Atacama. in Peru, where it forms a regular bed, of great extent, covered with clay and alluvial matter. The pure salt commonly crystallizes in rhombohedrons, resembling those of calcareous spar, but is probably dimorphous. It is deliquescent, and very soluble in water. Nitrate of soda 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 su- perficial manure or top-dressing. PHOSPHATES OF SODA; COMMON TRIBASIC PHOSPHATE, 2NaO, HO, P0 5 -j-24 HO. This beautiful salt is prepared by precipitating the acid phosphate of lime obtained by decomposing bone-earth by sulphuric acid, with a slight excess of carbonate of soda. 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 14 equivalents of water, and having a form different from that above mentioned, have been obtained. A second tribasic phosphate, sometimes called subphosphate, 3NaO, P0 5 -f-24HO, is obtained by adding a solution of caustic soda to the prece- ding 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, except the loss of its water of crystallization. Its solution is strongly alkaline. A third tribasic phosphate, often called superphosphate or biphos- phate, NaO,2HO,P0 5 -J-2HO, may be obtained by adding phosphoric acid to the ordinary phosphate, until it ceases to precipitate chloride of barium, 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 phosphate of soda. Tribasic phosphate of soda, ammonia, and water ; microcosmic salt, NaO, NH 4 0,HO,P0 5 -j-8HO. Six parts of common phosphate of soda are heated with 2 of water until the whole is liquefied, when 1 part of powdered sal- ammoniac is added ; common salt separates, and may be removed by a filter, and from the solution, duly concentrated, the new salt is deposited in pris- matic crystals, which may be purified by one or two re-crystallizations. Microcosmic salt is very soluble. When gently heated, it parts with the 8 eq. of water crystallization, and, at a higher temperature, the water acting as base is expelled, together with the ammonia, and a very fusible compound, metaphosphate of soda, remains, which is valuable as a flux in blowpipe ex- periments. This salt is said to occur in the urine. BlBASIC PHOSPHATE OF SODA ; PYROPHOSPHATE OF SODA, 2 NaO,P0 5 -f 10HO. Prepared by strongly heating common phosphate of soda, dissolving the residue in water, and re-crystallizing. The crystals are very brilliant, per- manent in the air, and less soluble than the original phosphate ; their solution is alkaline. A bibasic phosphate, containing an equivalent of basic water, lias been obtained ; it does not, however, crystallize. MONOBASIC PHOSPHATE OF SODA; METAPHOSPHATE OF SODA, NaO,P0 5 . Obtained by heating either the acid tribasic phosphate, or microcosmic salt. It is a transparent 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 a beautifully crystalline mass is obtained. It may be separated by means of boiling water from the vitreous metaphosphate which will not crystallize. Another metaphosphate has been obtained by adding sulphate of soda to an excess of phosphoric acid, evaporating and heating to upwards of 000 (315-5C). Possibly these SODIUM. 231 several metamosphates may be represented by the formulae NaO,P0 5 ; 2NaO,i>P0 5 ; 3NaO,3P0 6 . The tribasic phosphates give a bright yellow precipitate with solution of nitrate of silver ; the bibasic and monobasic phosphates afford white precipi- tates with the same substance. The salts of the two latter classes, fused with excess of carbonate of soda, yield the tribasic modification of the acid. Phosphates intermediate between the monobasic and bibasic phosphates of soda, 3NaO,2P0 5 , and GNaO,5P0 5 . The first is produced by fusing 100 parts of anhydrous pyrophosphate of soda, and 76-87 parts of metaphosphate of soda. The white crystalline mass is reduced to powder, and quickly exhausted with water. The solution, on exposure to the atmosphere, yields small plates which are very soluble in water. The second is produced by fusing 100 parts of pyrophosphate of soda, and 307-5 of metaphosphate; it crystallizes with more difficulty than the prece- ding compound. MM. Fleitmann and Henneberg, the discoverers of these new phosphates, represent the different phosphates thus : Common phosphate ................................ 6NaO,2P0 5 Pyrophosphate ...................................... 6NaO,3P0 5 Metaphosphate ..................................... 6NaO,6P0 5 In each of which six equivalents of the base are combined with a different polymeric acid. BIBORATE OF SODA; BORAX, NaO,2B0 3 -f- 10HO. This compound occurs in the waters of certain lakes in Thibet and Persia ; it is imported in a crude state from the East Indies under the name of tincal. When purified, it con- stitutes the borax of commerce. Much borax is now, however, manufactured from the native boracic acid of Tuscany. 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 eq. of water of crystal- lization are expelled, and at a higher temperature the salt fuses, and assumes a glassy appearance on cooling ; in this state it is much used for blowpipe experiments, the metallic oxides dissolving in it to transparent beads, many of which are distinguished by characteristic colours. By particular manage- ment, crystals of borax can be obtained with 5 eq. 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 sol- dering metals, its action consisting in rendering the surfaces to be joined metallic, by dissolving the oxides, and sometimes enters into the composition of the glaze with which stoneware is covered. Neutral borate of soda may be formed by fusing together borax and car- bonate of soda in equivalent proportions, and then dissolving the mass in water. The crystals are large, and contain NaO,B0 3 -f 8HO. SULPHIDE OF SODIUM, NaS. Prepared in the same manner as the proto- sulphide of potassium ; it separates from a concentrated solution in octahe- dral crystals, which are rapidly decomposed by contact of air into a mixture of hydrate and hyposulphite of soda. It forms double sulphur-salts with sulphuretted hydrogen, bisulphide of carbon, and other sulphur-acids. Sulphide of sodium is supposed to enter into the composition of the beau- tiful pigment ultramarine, prepared from the lapis lazuli, and which is now ^mitated by artificial means. 1 CHLORIDE OF SODIUM ; COMMON SALT, NaCl. This very important sub 1 See Pharmaceutical Journal, ii. 53. 232 AMMONIUM. stance is found in many parts of the world in solid beds or irregular strata of immense thickness, as in Cheshire, for example, in Spain, Galicia, and many other localities. An inexhaustible supply exists also in the waters of the ocean, and large quantities are annually obtained from saline springs. The rock-salt is almost always too impure for use ; if no natural brine- spring exist, 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 sepa- rates, it is removed from the bottom of the vessels by means of a scoop, pressed while still moist into moulds, and then transferred to the drying- stove. When large crystals are required, as for the coarse-grained bay-salt used in curing provisions, the evaporation is slowly conducted. Common salt is apt to be contaminated with chloride of magnesium. When pure, this substance is not deliquescent in moderately dry air. It crystallizes in anhydrous cubes, which are often grouped together into pyra- mids, or steps. It requires about 2 parts of water at 60 (15-5C) for solu- tion, and its solubility is not sensibly increased by heat ; it dissolves to some extent in spirits, but is nearly insoluble in absolute alcohol. Chloride of sodium fuses at a red-heat, and is volatile at a still higher temperature. The economical uses of common salt are well known. The iodide and bromide of sodium much resemble the corresponding potas- sium-compounds : they crystallize in cubes which are anhydrous, and are very soluble in water. There is no good precipitant for soda, all the salts being very soluble with the exception of antimonate of soda, the use of which is attended with diffi- culties ; its presence is often determined by purely negative evidence. The yellow colour imparted by soda-salt to the outer flame of the blowpipe, and to combustible matter, is a character of some importance. AMMONIUM. In connection with the compounds of potassium and sodium, those formed by ammonia are most conveniently studied. Ammoniacal salts correspond in every respect in constitution with those of potassa and soda ; in all cases the substance which replaces those alkalis is hydrate of ammonia, or, as it is now almost generally considered, the oxide of a hypothetical substance called ammonium, capable of playing the part of a metal, and ismorphous with potassium and sodium. All attempts to isolate this substance have failed, apparently from its tendency to separate into ammonia and hydrogen gas. When a globule of mercury is placed on a piece of moistened caustic po- tassa, and connected with the negative side of a voltaic battery of very moderate power, while the circuit is completed through the platinum plate upon which rests the alkali, decomposition of the latter takes place, and an amalgam of potassium is rapidly formed. If this experiment be now repeated with a piece of sal-ammoniac instead of hydrate of potassa, a soft solid, metalline mass is also produced, which has been called the ammoniacal amalgam, and considered to contain ammo- nium in combination with mercury. A still simpler method of preparing this extraordinary compound is the following : A little mercury is put into a test-tube with a grain or two of potassium or sodium, and gentle heat ap- plied; combination ensues, attended by heat and light. When cold, the fluid amalgam is put into a capsule, and covered with a strong solution of sal-ammoniac. The production of ammoniacal amalgam instantly com- mences, the mercury increases prodigiously in vclume, and becomes quite AMMONIUM. 233 pasty. The increase of weight is, however, quite trifling ; it varies from i-gVoth to T 2 o-o o th P art - Left to itself, the amalgam quickly decomposes into fluid mercury, ammo- nia, and hydrogen. It is difficult to offer any opinion concerning the real nature of this com- pound : something analogous occurs when pure silver is exposed to a very high temperature, much above its melting-point, in contact with air or oxy- gen gas ; the latter is absorbed in very large quantity, amounting, accord ing to the observation of Gay-Lussac, to 20 times the volume of the silver, and is again disengaged on lessening the heat. The metal loses none of its lustre, and is not sensibly altered in other respects. The great argument in favour of the existence of ammonium is founded on the perfect comparison which the ammoniacal salts bear with those of the alkaline metals. The equivalent of ammonium is 18 ; its symbol is NH 4 . CHLORIDE OF AMMONIUM; (MURIATE OF AMMONIA;) SAL-AMMONIAC, NH 4 C1. Sal-ammoniac was formerly obtained from Egypt, being extracted by sub- limation 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 slight excess of hydrochloric acid, by which the alkali is neutralized, and the carbonate and sulphide 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 sub- limation in large iron vessels lined with clay, surmounted 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 favourable circumstances, in distinct cubes or octahedrons ; 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, in a much smaller quantity of hot water. By heat, it is sub- limed without decomposition. The crystals are anhydrous. Chloride of ammonium forms double salts with chloride of magnesium, nickel, cobalt, manganese, zinc, and copper. SULPHATE OF OXIDE OF AMMONIUM ; SULPHATE OF AMMONIA, NH 4 O, S0 3 -{-HO. Prepared by neutralizing carbonate of ammonia by 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, which lose an equivalent of water when heated. It is entirely de- composed, and driven off by ignition, and, even to a certain extent, by long boiling with water, ammonia being expelled and the liquid rendered acid. CARBONATES OF AMMONIA. These compounds have been carefully exam- ined by Professor Rose, of Berlin, 1 and appear very numerous. The neutral, anhydrous carbonate, NH 3 ,C0 2 , is prepared by the direct union of carbonic acid with ammoniacal gas, both being carefully cooled. The gases combine in the proportions of one measure of the first to two of the second, and give rise to a pungent, and very volatile compound, which condenses in white flocks. It is very soluble in water. The pungent, transparent, carbonate of ammonia of pharmacy, which is prepared by subliming a mixture of sal- ammoniac and chalk, always contains less base than that required to form a neutral carbonate. Its composition vai'ies a good deal, but in freshly pre- 1 Annalen der Pharmacic, xxx. 45 20* 234 AMMONIUM. pared specimens approaches that of a sesquicarbonate of oxide of ammonium, 2 NH 4 0,3C0 2 . When heated in a retort, the neck of which dips into mer- cury, it is decomposed, with disengagement of pure carbonic acid, into neutral hydrated carbonate of ammonia, and several other compounds. Ex- posed to the air at common temperatures, it disengages neutral carbonate of ammonia, loses its pungency, and crumbles down to a soft, white powder, which is a bicarbonate, containing NH 4 0,C0 2 -f-HO,C0 2 . This is a permanent combination, although still volatile. When a strong solution of the commer- cial sesquicarbonate is made with tepid water, and filtered, warm, into a close vessel, large and regular crystals of bicarbonate, having the above com- position, are sometimes deposited after a few days. These are inodorous, quite permanent in the air, and resemble, in the closest manner, crystals of bicarbonate of potassa. NITRATE OF OXIDE OF AMMONIUM ; NITRATE OF AMMONIA, NH 4 0,N0 5 . Easily prepared by adding carbonate of ammonia to slightly diluted nitric acid until neutralization has been reached. By slow evaporation at a mode- rate temperature it crystallizes in six-sided prisms, like those of nitrate of potassa ; but, as usually prepared for making nitrous oxide, by quick boiling, until a portion solidifies completely on cooling, it forms a fibrous and indis- tinct crystalline mass. Nitrate of ammonia dissolves in 2 parts of cold water, is but feebly deli- quescent, and deflagrates like nitre on contact with heated combustible matter. Its decomposition by heat has been already explained. 1 SULPHIDES OF AMMONIUM. Several of these compounds exist, and may be formed by distilling with sal-ammoniac the corresponding sulphides of potassium or sodium. The double sulphide of ammonium and hydrogen, NH 4 S-J-IIS, commonly called hydrosulphate of ammonia, or, more correctly, hydrosulphate of sul- phide of ammonium, is a compound of great practical utility ; it is obtained by saturating a solution of ammonia with well-washed sulphuretted hydrogen gas, until no more of the latter is absorbed. The solution is nearly colourless 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 metallic solutions, which are very often characteristic, and is of great service in analytical chemistry. 3 When dry ammoniacal gas is brought in contact with anhydrous sulphuric acid, a white crystalline compound is produced, which is soluble in water. In a freshly prepared cold solution of this substance neither sulphuric acid nor ammonia can be found ; but after standing some time, and especially if heat be applied, it passes into ordinary sulphate of ammonia. A compound of dry ammoniacal gas and sulphurous acid also exists ; it is a yellow soluble substance, altogether distinct from sulphite of ammonia. * Page 125. 3 PHOSPHATES OF OXIDE OF AMMONIUM; COMMON TRIE ASIC PHOSPHATE, 2 NH 4 0,HO,P05-f HO. This salt is formed by precipitating the acid phosphate of lime with an excess of carbonate of ammonia. The solution is allowed to evaporate spontaneously or by a gentle heat. In the latter case ammonia is lost and it becomes necessary to saturate the acid set free, previous to crystallization. It crystallizes in six-sided tables derived from oblique quadrangular prisms. Its crystals are efflorescent, soluble in alcohol, and soluble in four times its weight of cold water. Its solution has an alkaline, slightly saline taste and alkaline reaction. By teat ammonia is disengaged. The acid tribasic phosphate, NH40,2HO,P05+4HO, is formed when a solution of the common phosphate is boiled as long as ammonia is given off. It crystallizes in four-sided pi'isms. Its crystals are permanent, soluble in 5 parts of cold water, acid in taste and reaction. Another tribasic phosphate, SNEUO.POs subphosphate is formed by adding ammonia to either of tne above It falls as a slightly soluble granular precipitate. R. B. LITHIUM. 235 Dry carbonic acid and ammonia also unite to form a volatile white powder, as already mentioned. When certain salts, especially chlorides in an anhydrous state, are exposed to ammoniacal gas, the latter is absorbed with great energy, and the combi- nations formed are riot always easily decomposed by heat. The chlorides of copper and silver absorb, in this manner, lai'ge quantities of the gas. All these compounds must be carefully distinguished from the true ammoniacal salts containing ammonium or its oxide. There is supposed to be yet another compound of hydrogen and nitrogen to which the term amidogen has been given. When potassium is heated in the vapour of water, this substance is decomposed, hydrogen is evolved, and the metal converted into oxide. When the same experiment is made with dry ammoniacal gas, hydrogen is also set free, and an olive-green crystalline compound produced, supposed to contain potassium in union with a new body, NH 2 , having an equivalent of hydrogen less than ammonia. When ammonia is added to a solution of corrosive sublimate, a white pre- cipitate is obtained, which has been long known in pharmacy. Sir R. Kane infers, from his experiments, that this substance should be looked upon as a compound of chloride of mercury with amide of mercury. The latter salt has not been obtained separately ; still less has amidogen itself been isolated. It has been thought that ammonia may be considered an amide of hydrogen, analogous to water or oxide of hydrogen, capable of entering into combina- tion with salts, and other substances, in a similar manner, yielding unstable and easily decomposed compounds, which offer a great contrast to those of the energetic This may be formed, as already mentioned, by exposing baryta, heated to full redness in a porcelain tube, to a current of pure oxygen gas. The binoxide is grey, and forms a white hydrate with water, which is not decomposed by that liquid in the cold, but dissolves in small quantity. The binoxide may also be made by heating pure baryta to redness in a platinum crucible, and then gradually adding an equal weight of chlorate of potassa ; binoxide of barium and chloride of potassium are produced. The latter may be extracted by cold water, and the binoxido left in the state of hydrate. It is interesting chiefly in its relation to bin- oxide of hydrogen. When dissolved in dilute acid, it is decomposed by bichromate of potassa, oxide of silver, chloride of silver, sulphate and car bonate of silver. CHLORIDE OF BARIUM, BaCl-f-2HO. This valuable salt is prepared by dissolving the native carbonate in hydrochloric acid, filtering the solution, From 0apvs, heavy, in allusion to the great specific gravity of the native carbonate and Bulpnate. 238 BARIUM. and evaporating until a skin 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 sulphate is reduced to fine powder, and intimately mixed with one-third of its weight of powdered coal ; the mixture is pressed into an earthen crucible 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 com- bustible matter of the coal. The black mass obtained is powdered and boiled in water, by which the sulphide is dissolved ; the solution is filtered hot, and mixed with a slight excess of hydrochloric acid ; chloride of barium and sul- phuretted hydrogen are produced ; the latter escaping with effervescence. Lastly, the solution is filtered to separate any little insoluble matter, and eva- porated to the crystallizing point. The crystals of chloride of barium are flat, four-sided tables, colourless and transparent. They contain 2 equivalents of water, easily driven off by heat; 100 parts of water dissolve 43-5 parts at GO (15-5C), and 78 parts at 223 (106 -50), which is the boiling-point of the saturated solution. NITRATE OF BARYTA, BaO, N0 5 . The nitrate is prepared by methods exactly similar to the above, nitric acid being substituted for the hydro- chloric. It crystallizes in transparent colourless octahedrons, which are anhydrous. They require for solution 8 parts of cold, and 3 parts of boil- ing water. This salt is much less soluble in dilute nitric acid than in pure water ; errors sometimes arise from such a precipitate of crystalline nitrate of baryta being mistaken for sulphate. It disappears on heating, or by large affusion of water. SULPHATE OF BARYTA; HEAVY-SPAR; BaO,S0 3 . Found native, often beau- tifully crystallized. This compound is always produced when sulphuric acid or a soluble sulphate is mixed with a solution of a barytic salt. It is not sensibly soluble in water or in any dilute acid, even nitric ; hot oil of vitriol dissolves a little, but the greater part separates again on cooling. Sulphate of baryta is used as a pigment, but often for the purpose of adulterating white-lead ; the native salt is ground to fine powder and washed with dilute sulphuric acid, by which its colour is improved, and a little oxide of iron probably dissolved out. The specific gravity of the natural sulphate is as high as 4-4 to 4-8. SULPHIDE OF BARIUM, BaS. The protosulphide of barium is obtained in the manner already described ; the higher sulphides may be formed by boil- ing this compound with sulphur. Protosulphide of barium crystallizes in thin and nearly colourless plates from a hot solution, which contain water, and are not very soluble ; they are rapidly altered by the air. A strong solution of sulphide may be employed in the preparation of hydrate of baryta, by boiling it with small successive portions of black oxide of copper, until a drop of the liquid ceases to precipitate a salt of the lead black ; the liquid being filtered, yields, on cooling, crystals of hydrate. In this reaction, besides hydrate of baryta, hyposulphite of that base, and sulphide of copper are produced ; the latter is insoluble, and is removed by the filter, while most of the hyposulphite remains in the mother-liquor. CARBONATE OF BARYTA, BaO, C0 2 . The natural carbonate is called withe- rite; the artificial is formed by precipitating the chloride or nitrate with an alkaline 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 baryta-salts. Solutions of hydrate and nitrate of baryta and of the chloride of barium are constantly kept in the laboratory as chemical tests, the first being em- STRONTIUM. 239 ployed to effect the separation of carbonic acid from certain gaseous mix- tures, and the two latter to precipitate sulphuric acid from solution. The soluble salts of baryta are poisonous, which is not the case with those of the base next to be described. STRONTIUM. The metal strontium may be obtained from its oxide by means similar to those described in the case of barium ; it is a white metal, heavy, oxidizable n the air, and capable of decomposing water at common temperatures. The equivalent of strontium is 43-8, and its symbol is Sr. PROTOXIDE OF STRONTIUM ; STRONTIA ; SrO. This compound is best pre- pared by decomposing the nitrate by the aid of heat ; it resembles in almost every particular the earth baryta, forming, like that substance, a white hy- drate, soluble in water. A hot saturated solution deposits crystals on cool- ing, which contain 10 equivalents of water. The hydrate has a great at- traction for carbonic acid. BINOXIDE OP STRONTIUM, Sr0 2 . The binoxide is prepared in the same manner as binoxide of barium ; it may be substituted for the latter in mak- ing binoxide of hydrogen. The native carbonate and sulphate of strontia, met with in lead-mines and other localities, serve for the preparation of the various salts by means ex- actly similar to those already described in the case of baryta ; they have a very feeble degree of solubility in water. CHLORIDE OF STRONTIUM, SrCl. The chloride crystallizes in colourless needles or prisms, which are slightly deliquescent, and soluble in 2 parts of cold and still less of boiling water ; they are also soluble in alcohol, and the solution, when kindled, burns with a crimson flame. The crystals contain 6 equivalents of water, which they lose by heat ; at a higher temperature the chloride fuses. NITRATE OF STRONTIA, SrO,N0 5 . This salt crystallizes in anhydrous oc- tahedrons, 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." 1 CALCIUM. This is a silver-white and extremely oxidable metal, obtained with great difficulty by means analogous to those by which barium and strontium are procured. The equivalent of calcium is 20 ; its symbol is Ca. PROTOXIDE OF CALCIUM ; LIME ; CaO. This extremely important com- pound may be obtained in a state of considerable purity by heating to full redness, for some time, fragments of the black bituminous marble of Derby., shire or Kilkenny. If required absolutely pure, it must be made by ignit- ing to whiteness, in a platinum crucible, an artificial carbonate of lime, pro- cured by precipitating the nitrate by carbonate of ammonia. Lime in an impure state is prepared for building and agricultural purposes by calcining 1 RED-FIRE: Grns. Dry nitrate of strontia 800 Sulphur 225 Chlorate of potassa 200 Lampblack 50 The ptrontia or baryta-salt, the sulphur, and the lampblack, must be finely powdered and intimately mixed, after which the chlorate of potassa should be added in rather coarse pow- der, and mixed without much rubbing with the other ingredients. The red-fire composition has teen known to ignite spontaneously. GREEN-FIRE : Grns Dry nitrate of baryta 46t Sulphur 150 Chlorate of potassa 100 Lampblack 240 CALCIUM. in a kiln of suitable construction, the ordinary limestones which abound in many districts ; a red-heat, continued for some hours, is sufficient to disen- gage the whole of the carbonic acid. In the best contrived lime-kilns the process is carried on continuously, broken limestone and fuel being con- stantly thrown in at the top, and the burned lime raked out at intervals from beneath. Sometimes, when the limestones contain 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 infusi- ble, 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 equivalent of water ; the latter can be again expelled by a red-heat. This hydrate is soluble in water, but far less so than either the hydrate of baryta or of strontia, and what is very remarkable, the colder the water, the larger the quantity of the compound which is taken up. A pint of water at 60 (15-5C) dissolves about 11 grains, while at 212 (100C) only 7 grains are retained in solution. The hydrate has been obtained in thin delicate crystals by slow evaporation under the air-pump. Lime-water is always prepared for chemical and pharmaceutical purposes by agitating cold water with excess of hydrate of lime in a closely-stopped vessel, and then, after subsidence, pouring off the clear liquid, and adding a fresh quantity of water, for another occasion ; 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 carbonic acid from the atmosphere. It is used, like baryta-water, as a test for that substance, and also in medicine. Lime- water prepared from some varieties of limestone may contain potassa. The hardening of mortars and cements is in a great measure due to the 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 favourable circumstances, to acquire extreme hardness with age. Lime-cements which resist the action of water, contain the oxides of iron, silica, and alumina ; they require to be carefully prepared, and the stone not over-heated. When ground to powder and mixed with water, solidification 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-argillaceous iron- stone 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 promoted, and other important objects, as the destruction of certain hurtful compounds of iron in marsh and peat-land, is often attained. The addition of lime pro- bably serves likewise to liberate potassa from the insoluble silicate of that base contained in the soil. BINOXIDE OF CALCIUM, Ca0 2 . This is stated to resemble binoxide of barium, and to be obtainable by a similar process. CHLORIDE OF CALCIUM, CaCl. Usually prepared by dissolving marble in hydrochloric acid ; also a by-product in several chemical manufactures. The salt separates from a strong solution in colourless, prismatic, and exceed- ingly deliquescent crystals, which contain 6 equivalents of water. By heat this water is expelled, and by a temperature of strong ignition the salt 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 a fused condition, is of great practical use in desiccating gases, for which purpose the latter are slowly transmitted through tubes CALCIUM. 241 filled with fragments of the salt. Chloride of calcium is also freely soluble in alcohol, which, when anhydrous, forms with it a definite crystallizable compound. SULPHIDE OF CALCIUM. The simple sulphide is obtained by reducing sulphate of lime at a high temperature by charcoal or hydrogen ; it is nearly colourless, and but little soluble in water. By boiling together hydrate of lime, water, and flowers of sulphur, a red solution is obtained, which on cooling deposits crystals of bisulphide, which contain water. When the sulphur is in excess, and the boiling long continued, a pentasulphide is generated ; hyposulphurous acid is, as usual, formed in these reactions. PHOSPHIDE OF CALCIUM. When the vapour of phosphorus is passed over fragments of lime heated to redness in a porcelain tube, a chocolate-brown compound, the so-called phosphide of lime, is produced. This substance is probably a mechanical mixture of phosphide of calcium, and phosphate of lime. It yields spontaneously inflammable phosphoretted hydrogen when put into water. 1 SULPHATE OF LIME ; GYPSUM ; SELENITE ; CaO, S0 3 . Native sulphate of lime in a crystalline condition, containing 2 equivalents of water, is found in considerable abundance in some localities ; it is often associated with rock- salt. When regularly crystallized, it is termed selenite. Anhydrous sulphate of lime is also occasionally met with. The salt is formed by precipitation when a moderately concentrated solution of chloride of calcium is mixed with sulphuric acid. Sulphate of lime is soluble in about 500 parts of cold water, and its solubility is a little increased by heat. It is more soluble in water containing chloride of ammonium or nitrate of potassa. The solution is precipitated by alcohol. Gypsum, or native hydrated 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 2GO (126-6C), by which the water of crystallization is expelled, and afterwards reduced to fine powder. When mixed with water, it solidifies 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. Ai'tificial coloured marbles, or scagliola, are frequently prepared by inserting pieces of natural stone in a soft stucco containing this substance, and polishing the surface when the cement has become hard. Sulphate of lime is one of the most common impurities of spring water. The peculiar property water acquires by the presence in it of lime, is termed hardness. It manifests itself by the effect such waters have upon the palate, and particularly by its peculiar behaviour with soap. Hard waters yield a lather with soap only after the whole of the lime-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 waters is based.* The hardness produced by sulphate of lime is called permanent hard- ness, since it cannot be remedied. CARBONATE OF LIME ; CHALK; LIMESTONE; MARBLE; CaO, C0 2 . Carbo- nate of lime, often more or less contaminated by protoxide of iron, clay, and organic 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 1 According to M. Paul Thenard, the phosphide of calcium existing in this mixture, has the compositions PCa 2 . By coming in contact with water, it yields liquid phosphoretted hydrogen, PCaa + 2110= 2CaO + P1I 2 (Page 166). The greater portion of the liquid phosphide is immediately decomposed into solid and gaseous phosphoretted hydrogen. 5PH2 = 3PII 3 + P 2 H. a Journal of the Pharmaceutical Society, vol. vi. p. 526. 242 CALCIUM. they have been subjected since their deposition. The most ancient and highly 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 carbonate of lime or calcareous spar, which have evidently been slowly deposited from a watery solution. Carbo- nate of lime 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, is 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 pro- duced disappears on agitation, and a transparent solution of carbonate of lime in excess of carbonic acid is obtained. This solution is decomposed completely by boiling, the carbonic acid being expelled, and the carbonate precipitated. Since all natural waters contain dissolved carbonic acid, it if to be expected that lime in this condition should be of very common occur- rence ; and such is really found to be the fact ; rivei% and more espcciallj .spring water, almost invariably containing carbonate of lime thus dissolved 3n limestone districts, this is often the case to a great extent. The hardnesi (" water, which is owing to the presence of carbonate of lime, is called tem- porary, 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 becomes thus carbo- nated, are precipitated. Upon this principle, Prof. Clark's process of soft- ening water is based. This process is of considerable importance, since a supply of hard water to towns is in many respects a source of great inconve- nience. As has been already mentioned, the use of such water, for the pur- poses 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. 1 The beautiful stalactitic incrustations of lime-stone caverns, and the deposits of calc-sinter or travertin upon various objects, and upon the ground in many places, are thus explained by the solubility of carbonate of lime in water containing carbonic acid. Crystallized carbonate of lime exhibits the curious property of dimorphism ; calcareous spar and arragonite, although possessing the same chemical com- position, both containing single equivalents of lime and carbonic acid, and nothing besides, have different crystalline forms, different densities, and dif- ferent optical properties. The former occurs very abundantly in crystals derived from an obtuse rhomboid, whose angles measure 105 5 X and 74 55' : its density varies from 2'5 to 2-8. The rarer variety, or arragonite, is found in crystals whose pri- mary form is a right rhombic prism ; a figure having no geometrical relation to the preceding; it is, besides, heavier and harder. PHOSPHATES OF LIME. A number of distinct compounds of lime and phos- phoric acid probably exist. Two tribasic phosphates, 2CaO, I10,P0 5 , and >CaOP0 5 , are produced when the corresponding soda-salts are added in so- lution to chloride of calcium ; the first is slightly crystalline, and the second gelatinous. When the first phosphate is digested with ammonia, or dissolved in acid and re-precipitated by that alkali, it is converted into the second. 1 Many proposals have been made to prevent the formation of boiler-deposits. The most efficient appears to be the method of Dr. Kitterband, which consists in throwing into the boiler a small quantity of sal-ammoniac, when carbonate of ammonia is formed, which is volatilized with the steam, chioride of calcium remaining in solution. It need scarcely be 2iioutv>tted that this plan is inapplicable in the case of permanently hard waters. CALCIUM. 243 IVe earth of bones consists principally of what appears to be a combi- nation of these two salts. Another phosphate, containing 2 equivalents of basic water, has been described, which completes the series; it is formed by dissolving either of the preceding in phosphoric, hydrochloric, or nitric acid, and evaporating until the salt separates on cooling in small platy crys- tals. It is this substance which yields phosphorus, when heated with char- coal, in the ordinary process of manufacture before described. Bibasic and monobasic phosphates of lime also exist. These phosphates, although inso- luble in water, dissolve readily in dilute acids, even acetic acid. FLUOKIDK OF CALCIUM; FLUOR-SPAR; CaF. This substance is important as the most abundant natural source of hydrofluoric acid and the other fluorides. It occurs beautifully crystallized, in various colours, in lead-veins, the crystals having commonly the cubic, but sometimes the octahedral form, parallel to the faces of which latter figure they always cleave. Some varie- ties, when heated, emit a greenish phosphorescent light. The fluoride is quite insoluble in water, and is decomposed by oil of vitriol in the manner already mentined, vide p. 149. CHLORIDE OF LIME; BLEACHING-POWDER. When hydrate of lime, very slightly moist, is exposed to chlorine gas, the latter is eagerly absorbed, and a compound produced which has attracted a great deal of attention ; this is the bleaching-powder of commerce, now manufactured on an immense scale, for bleaching linen and cotton goods. It is requisite, in preparing this sub- stance, to avoid with the greatest care all elevation of temperature, which may be easily done by slowly supplying the chlorine in the first instance. The product, when freshly and well prepared, is a soft, white powder, which attracts moisture from the air, and exhales an odour sensibly diiferent from that of chlorine. It is soluble in about 10 parts of water, the unaltered hy- drate being left behind ; the solution is highly alkaline, and bleaches feebly. When hydrate of lime is suspended in cold water, and chlorine gas trans- mitted through the mixture, the lime is gradually dissolved, and the same peculiar bleaching compound produced ; the alkalis also, either caustic or carbonated, may by similar means be made to absorb a large quantity of chlorine, and give rise to corresponding compounds ; such are the " disinfect- ing solutions" of M. Labarraque. The most consistent view of the constitution of these curious compounds is that which supposes them to contain salts of hypochlorous acid, a substance as remarkable for bleaching powers as chlorine itself; and this opinion seems borne out by a careful comparison of the properties of the bleaching-salts with those of the true hypochlorites. Hypochlorous acid can be actually ob- tained from good bleaching-powder, by distilling it with dilute sulphuric or nitric acid, in quantity insufficient to decompose the whole ; when the acid is used in excess, chlorine is disengaged. 1 If this view be correct, chloride of calcium must be formed simultaneously with the hypochlorite, as in the following diagram : Chlorine ^.Chloride of calcium. Lime { I. Calcium Chlorine Lime : - ^^-ITypochlorite of lime. When the temperature of the hydrate of lime has risen during the absorption of the chlorine, or when the compound has been subsequently exposed to heat, its bleaching properties are impaired or altogether destroyed ; it then contains chlorate of lime and chloride of calcium ; oxygen, in variable quan- 1 M. Cay-Lussac, Ann. Chim. et Phys. 3rd serios, v. 29G 244 CALCIUM. tity, is usually set free. The same change seems to ensue by long keeping, even at the common temperature of the air. In an open vessel it is speedily destroyed by the carbonic acid of the atmosphere. Commercial bl caching- powder thus constantly varies in value with its age, and with the care origi- nally bestowed upon its preparation ; the best may contain about 30 percent, of available chlorine, easily liberated by an acid, which is, however, far short of the theoretical quantity. The general method in which this substance is employed for bleaching is the following : the goods are first immersed in a dilute solution of chloride of lime and then transferred to a vat containing dilute sulphuric acid. De- composition ensues ; both the lime of the hypochlorite and the calcium of the chloride are converted into sulphate of lime, while the free hypochlorous and hydrochloric acids yield water and free chlorine. The chlorine thus disengaged in contact with the cloth, causes the destruc- tion of the colouring matter. This process is often repeated, it being unsafe to use strong solutions. White patterns are on this principle imprinted upon coloured cloth, the figures being stamped with tartaric acid thickened with gum-water, and then the stuff immersed in the chloride bath, when the parts to which no acid has been applied remain unaltered, while the printed portions are bleached. For purifying an offensive or infectious atmosphere, as an aid to proper ventilation, the bleaching-powder is very convenient. The solution is exposed in shallow vessels, or cloths steeped in it are suspended in the apartment, when the carbonic acid of the air slowly decomposes it in the manner above described. An addition of a strong acid causes rapid disengagement of chlorine. The value of any sample of bleaching-powder may be easily determined by the following method, in which the loosely combined chlorine is estimated by its effect in peroxidizing a protosalt of iron, of which two equivalents re- quire one of chlorine ; the latter acts by decomposing water and liberating a corresponding quantity of oxygen 78 (more correctly 78-16) grains of green sulphate of iron are dissolved in about two ounces of water, and acidu- lated by a few drops of sulphuric or hydrochloric acid ; this quantity will require for peroxidation 10 grains of chlorine. Fifty grains of the chloride of lime to be examined are next rubbed up with a little tepid water, and the whole transferred to the alkalimeter l before described, which is then filled up to with water, after which the contents are well mixed by agitation. The liquid is next gradually poured into the solution of iron, with constant stirring until the latter has become peroxidized, which may be known by a drop ceasing to give a deep blue precipitate with ferricyanide of potassium. The number of grain-measures of the chloride solution employed may then be read off, since these must contain 10 grains of serviceable chlorine, the quantity of the latter in the 50 grains may be easily reckoned. Thus, sup- pose 72 such measures have been taken, then Measures. Grs. chlorine. Measures. Grs. chlorine. 72 : 10 == 100 : 13-89 The bleaching-powder contains, therefore, 27-78 per cent. 3 Baryta, strontia, and lime are thus distinguished from all other substances, and from each other. Caustic potassa, when free from carbonate, and caustic ammonia, occasion 110 precipitates in dilute solutions of the earths, especially of the first two, the hydrates being soluble in water. 1 Tide p. 227. 2 Graham's Elements, vol. i. p. 414. MAGNESIUM. 245 Alkaline carbonates, and carbonate of ammonia, give white precipitates, /nsoluble in excess of the precipitant, with all three. Sulphuric acid, or a sulphate, added to very dilute solutions of the earths in question, gives an immediate white precipitate with baryta, a similar pre- cipitate after a short interval with strontia, and occasions no change with the lime-salt. The precipitates with baryta and strontia are quite insoluble in nitric acid. Solution of sulphate of lime gives an instantaneous cloud with baryta, and one with strontia after a little time. Sulphate of strontia is itself suffi- ciently soluble to occasion turbidity when mixed with chloride of barium. Lastly, the soluble oxalates give a white precipitate in the most dilute so- lutions of lime, which is not dissolved by a drop or two of hydrochloric nor by an excess of acetic acid. This is an exceedingly characteristic test. The chlorides of strontium and calcium dissolved in alcohol colour the flame of the latter red or purple ; salts of baryta communicate to the flame a pale green tint. MAGNESIUM. A few pellets of sodium are placed at the bottom of a test-tube of hard German glass, and covered with fragments of fused chloride of magnesium, the heat of a spirit-lamp is then applied until reaction has been induced; this takes place with great violence and elevation of temperature, chloride of sodium being formed, and metallic magnesium set free. When the tube and its contents are completely cold, it is broken up, and the fragments put into cold water, by which the metal is separated from the salt. Magnesium is a white, malleable metal, fusible at a red-heat, and not sen- sibly acted upon by cold water ; it is oxidized by hot water. Heated in the air, it burns and produces magnesia, which is the only oxide. Sulphuric and hydrochloric acids dissolve it readily, evolving hydrogen. The equivalent of this metal is 12, and its symbol Mg. MAGNESIA; CALCINED MAGNESIA; MgO. This is prepared with great ease by exposing the magnesia alba of pharmacy 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 5,000 parts of water at 60 (16-6C) and 36,000 parts at 212 (100C). The al- kalinity 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. CHLORIDE OF MAGNESIUM, MgCl. When magnesia, or its carbonate, is dissolved in hydrochloric acid, there can be no doubt respecting the simul- taneous production of chloride of magnesium and water ; but when this so- lution comes to be 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 chlo- rine for hydrogen ; hydrochloric acid is expelled, and magnesia remains, If, however, sal-ammoniac or chloride of potassium happen to be 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 am- monia, 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 porce- lain crucible. Sal-ammoniac sublimes, and chloride of magnesium 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 21* 246 MAGNESIUM. 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. SULPHATE OF MAGNESIA EPSOM SALT; MgO,S0 3 -}-7HO. This salt occurs in sea-water, and in that of many mineral springs, and is now manufactured in large quantities by acting on magnesian lime-stone by diluted sulphuric acid, and separating the sulphate of magnesia from the greater part of the slightly soluble sulphate of lime by the filter. The crystals are derived from a right rhombic prism ; they are soluble in an equal weight of water at 60 (15-5C), and in a still smaller quantity at 212 (100C). The salt has a nauseous bitter taste, and, like many other neutral salts, purgative properties. When exposed to heat, 6 equivalents of water readily pass off, the seventh being energetically retained. Sulphate of magnesia forms beau- tiful double salts with the sulphates of potassa and ammonia, which contain 6- equivalents of water of crystallization. CARBONATE OF MAGNESIA. The neutral carbonate, MgO,C0 2 , occurs native in rhombohedral crystals, resembling those of calcareous spar, embedded in talc-slate : a soft earthy variety is sometimes met with. When magnesia alba is dissolved in carbonic acid water, and the solution left to evaporate spontaneously, small prismatic crystals are deposited, which consist of carbonate of magnesia, with 8 equivalents of water. The magnesia alba itself, although often called carbonate of magnesia, is not so in reality; it is a compound of carbonate with hydrate. It is pre- pared by mixing hot solutions of carbonate of potassa or soda, and sulphate of magnesia, the latter being kept in slight excess, boiling the whole a few minutes, during which time much carbonic acid is disengaged, and then 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 4(MgO,C0 2 )-f MgO,HO-f 6HO. Magnesia alba is slightly soluble in water, especially when cold. PHOSPHATE OF MAGNESIA, 2MgO,HO,P0 5 + 14HO. This salt separates in small colourless prismatic crystals when solutions of phosphate of soda and sulphate of magnesia are mixed and suffered to stand some time. Prof. Graham states that it is soluble in about 1,000 parts of cold water, but Berzelius describes a phosphate which only requires 15 parts of water for solution : this can hardly be the same substance. Phosphate of magnesia exists in the grain of the cereals, and can be detected in considerable quantity in beer. PHOSPHATE OF MAGNESIA AND AMMONIA, 2MgO,NH 4 0,P0 5 +12IIO. When a soluble phosphate is mixed with a salt of magnesia, and ammonia or its carbonate 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 scarcdy so in saline liquids. When heated, it is resolved into bibasic phosphate (pyrophosphate) of mag- nesia, containing 35-71 per cent, of magnesia. At a strong red-heat it fuses to a white enamel-like mass. The phosphate of magnesia and ammonia sometimes forms an urinary calculus. In practical analysis, magnesia is often separated from solutions by bringing it into this state. The liquid, free from alumina, lime, &c., is mixed with phosphate of soda and excess of ammonia, and gently hen ted for a short time. The precipitate is collected upon a filter and thoroughly washed with water containing a little sal-ammoniac, after which it is dried, ignited to redness, and weighed. The proportion of magnesia is then easily calculated. MAGNESIUM. 247 SILICATES OP MAGNESIA. The following natural compounds belong to this class: Steatite or soap-stone, MgO,Si0 3 , a soft, white, or pale-coloured, amor- phous substance, found in Cornwall and elsewhere ; Meerschaum, MgO,Si0 3 -J- HO, from which pipe-bowls are often manufactured ; Chrysolite, 3MgO,Si0 3 , a crystallized mineral, sometimes employed for ornamental purposes ; a por- tion of magnesia is commonly replaced by pi'otoxide of iron which communi- cates a green colour ; Serpentine is a combination of silicate and hydrate of magnesia ; Jade, an exceedingly hard stone, brought from New Zealand, con- tains silicate of magnesia combined with silicate of alumina ; its green Colour is due to sesquioxide of chromium ; Augite and hornblende are essentially double salts of silicic acid, magnesia, and lime, in which the magnesia is more or less replaced by its isomorphous substitute, protoxide of iron. The salts of magnesia are strictly isomorphous with those of the protox- ides of zinc, of iron, of copper, &c. ; they are usually colourless, and are easily recognised by the following characters : A gelatinous white precipitate with caustic alkalis, including ammonia, insoluble in excess, but soluble in solution of sal-ammoniac. A white precipitate with the carbonates of potassa and soda, but none with carbonate of ammonia in the cold. A white crystalline precipitate with soluble phosphates, on the addition of a little ammonia. 248 ALUMINIUM. SECTION III. METALS OF THE EARTHS PROPER. ALUMINUM OR ALUMINIUM. ALUMINA, the only known oxide of this metal, is a substance of very abun- dant occurrence in nature in the state of silicate, as in felspar and its asso- ciated minerals, and in the various modifications of clay thence derived. Aluminium is prepared in the same manner as magnesium, but with rather more difficulty ; a platinum or iron tube closed at one extremity may be em- ployed. Sesquichloride of aluminium is first introduced, and upon that about an equal bulk of potassium loosely wrapped in platinum foil. The lower part of the tube is then heated so as to sublime the chloride and bring its vapours in contact with the melted potassium. The reduction takes place with great disengagement of heat. The metal, separated by cold water from the alkaline chloride, has a tin-white colour and perfect lustre. It is ob- tained in small fused globules by the heat of reduction, which are malleable, and have a specific gravity of 2-6. When heated in the air or in oxygea, it takes fire and burns with brilliancy, producing alumina. Aluminium has for its equivalent the number 13-7 ; its symbol is Al. ALUMINA, A1 2 3 . This substance is inferred to be a sesquioxide, from its isomorphism with the red oxide of iron. It is prepared by mixing solution of alum with excess of ammonia, by which an extremely bulky, white, gela- tinous precipitate of hydrate of alumina is thrown down. This is washed, dried, and ignited to whiteness. Thus obtained, alumina constitutes a white, tasteless, coherent mass, very little acted upon by acids. The hydrate, on the contrary, when simply dried in the air, or by gentle heat, dissolves freely in dilute acid, and in caustic potassa or soda, from which it is precipitated by the addition of sal-ammoniac. Alumina is fusible before the oxyhydro- gen blowpipe. The mineral called corundum, of which the ruby and sap- phire are transparent varieties, consists of nearly pure alumina in a crystal- lized state, with a little colouring oxide ; emery, used for polishing glass and metals, is a coarse variety of corundum. Alumina is a very feeble base, and its salts have often an acid reaction. SESQUICHLORIDE OF ALUMINIUM, A1 2 C1 3 . The solution of alumina in hydro- chloric acid behaves, when evaporated to dryness, like that of magnesia, the chloride being decomposed by the water, and alumina and hydrochloric acid produced. The chloride may be thus prepared : Pure precipitated alumina is dried and mixed with lampblack, and the mixture strongly calcined in a covered crucible. It is then transferred to a porcelain tube fixed across a furnace, and heated to redness in a stream of chlorine gas, when the alu- mina, yielding to the attraction of the chlorine on the one hand, and the carbon on the other, for each of its constituents, suffers decomposition, car- bonic oxide being disengaged, and sesquichlovide of aluminium formed ; the latter sublimes, and condenses in the cool part of the tube. ALUMINIUM. 249 Sesquichloride of aluminium is a crystalline yellowish substance, exces- sively greedy of moisture, and very soluble. Once dissolved, it cannot be again recovered. It is said to combine with sulphuretted and phosphoretted hydrogen, and with ammonia. SULPHATE OF ALUMINA, Al 2 3 ,3S0 3 -f-18HO. Prepared by saturating dilute sulphuric acid with hydrate of alumina, and evaporating. It crystal- lizes in thin, pearly plates, soluble in 2 parts of water; it has a sweet and astringent taste, and an acid reaction. Heated to redness, it is decomposed, leaving pure alumina. Two other sulphates of alumina, with excess of base, are also described, one of which is insoluble in water. Sulphate of alumina combines with the sulphates of potassa, soda, and ammonia, forming double salts of great interest, the alums. Common alum, the source of all the preparations of alumina, contains Al 2 3 ,3S0 3 -f-KO, SO., -J-24HO. It is manufactured, on a very large scale, from a kind of slaty clay, loaded with bisulphide of iron, which abounds in certain parts. This is gently roasted, and then exposed to the air in a moistened state; oxygen is absorbed, the sulphur becomes acidified, sulphate of protoxide of iron and sulphate of alumina are produced, and afterwards separated by lixiviation with water. The solution is next concentrated, and mixed with a quantity of chloride of potassium, which decomposes the iron-salt, forming proto- chloride of iron and sulphate of potassa, which latter combines, with the sulphate of alumina, to alum. By crystallization, the alum is separated from the highly soluble chloride of iron, and afterwards easily purified by a repetition of that process. Other methods of alum-making exist, and are sometimes employed. Potassa-alum crystallizes in colourless, transparent octahedrons, which often exhibit the faces of the cube. It has a sweetish and astringent taste, reddens litmus paper, and dissolves in 18 parts of water at 60 (15-5C), and in its own weight of boiling water. Exposed to heat, it is easily rendered anhydrous, and, by a very high temperature, decom- posed. The crystals have little tendency to change in the air. Alum is largely used in the arts, in preparing skins, dyeing, &c. ; it is occasionally contaminated with oxide of iron, which interferes with some of its applica- tions. The celebrated Roman alum, made from alum-stone, a felspathic rock, altered by sulphurous vapours, was once much prized on account of its free- dom from this impurity. A mixture of dried alum and sugar, carbonized in an open pan, and then heated to redness, out of contact of air, furnishes the pyrophorus of Homberg, which ignites spontaneously on exposure to the atmosphere. The essential ingredient is, in all probability, finely divided sulphide of potassium. Soda-alum, in which sulphate of soda replaces sulphate of potassa, has a form and constitution similar to that of the salt described ; it is, however, much more soluble, and difficult to crystallize. Ammonia-alum, containing NH 4 0,S0 3 , instead of KO,S0 3 , very closely re- sembles common potassa-alum, having the same figure, and appearanci, and constitution, and nearly the same degree of solubility as that substance It is sometimes manufactured for commercial use. When heated to redness, it yields pure alumina. Few of the other salts of alumina, except the silicates, present points of interest ; these latter are of great importance. Silicates of alumina entei into the composition of a number of crystallized minerals, among which felspar occupies, by reason of its abundant occurrence, a prominent place Granite, porphyry, trachyte, and other ancient unstratified rocks, consist in great part of this mineral, which, under peculiar circumstances, by no means well understood, and particularly by the action of the carbonic acid of the air, suffers complete decomposition, becoming converted into a soft, friable mass of earthy matter. This is the origin of clay ; the change itself is seen 250 BERYLLIUM. in great perfection in certain districts of Devonshire and Cornwall, the felspar of the fine white granite of those localities being often disintegrated to an extraordinary depth, and the rock altered to a substance resembling soft mortar. By washing, this finely divided matter is separated from the quartz and mica, and the milk-like liquid, being collected in tanks and suffered to stand, deposits the suspended clay, which is afterwards dried, first in the air and afterwards in a stove, and employed in the manufacture of porcelain. The composition assigned to unaltered felspar is A1 2 3 , 3Si0 3 -f-KO,Si0 3 , or alum, having silicic acid in the place of sulphuric. The exact nature of the change by which it passes into porcelain clay is unknown, although it evi- dently consists in the abstraction of silica and alkali. 1 When the decomposing rock contains oxide of iron, the clay produced is coloured. The different varieties of shale and slate result from the alteration of ancient clay-beds, apparently in many instances by the infiltration of water holding silica in solution; the dark appearance of some of these deposits is due to bituminous matter. It is a common mistake to confound clay with alumina ; all clays are es- sentially silicates of that base ; they often vary a good deal in composition. Dilute acids exert little action on these compounds ; but by boiling with oil of vitriol, alumina is dissolved out, and finely divided silica left behind. Clays containing an admixture of carbonate of lime are termed marls, and are recognized by effervescing with acids. A basic silicate of alumina, 2A1 2 3 , Si() 3 , is found crystallized, constituting the beautiful mineral called cyamte. The compounds formed by the union of the silicates of alumina with other silicates are almost innumerable ; a soda-felspar, albife, containing that alkali in place of potassa, is known, and there are two somewhat similar lithia-compounds spodumene and petalile. The zeolites belong to this class: analdme, nepheline. mesotype, &c., are double silicates of soda and alumina, with water of crystallization. Slilbite, heulan- diie, laumonite, prehniie, &c., consist of silicate of lime, combined with silicate of alumina. The garnets, axinite, mica, &c., have a similar composition, but are anhydrous. Sesquioxide of iron is very often substituted for alumina in these minerals. Alumina, when in solution, is distinguished without difficulty. Caustic potassa and soda occasion white gelatinous precipitates of hydrate of alumina, freely soluble in excess of the alkali. Ammonia produces a similar precipitate, insoluble in excess of the reagent. The alkaline carbonates and carbonate of ammonia precipitate the hydrate, with escape of carbonic acid. The precipitates are insoluble in excess. BERYLLIUM (GLUCINUM). This metal is prepared from the chloride in the same manner as aluminium, ft is fusible with great difficulty, not acted upon by cold water and burns ,vhen heated in the air, producing berylla. The equivalent of beryllium is 6-9, and the symbol Be. A specimen of white porcelain clay from Dartmoor, Devon, gave the author the following result on analysis : Silica 47-20 Alumina, \vith trace of iron and manganese 38-80 Lime 0-24 Water 12-00 Alkali and loss 1-76 100-00 CERIUM, L A N T II A N I U M , AND DIDYMIUM 251 BERYLLA, Be 2 3 , is a rare enrth found in the emerald, beryl, and euclas>: y from which it may be extracted by a tolerably simple process. It very much resembles alumina, but is distinguished from that substance by its solubility, when freshly precipitated, in a cold solution of carbonate of ammonia, from which it is again thrown down .on boiling. The salts of berylla have a sweet taste, whence its former name gluciua (^AvKuf). The metal of a very rare earth, yltria, contained in a few scarce minerals The name is derived from Ytterby, a place in Sweden, where one of these, gadolinite, is found. It is obtained from the chloride by the process alreadj described ; it resembles in character the preceding metal. Ordinary yttria is stated by Professor Mosander to be a mixture of the oxides of not less than three metals, namely, Yttrium, erbium, and terbium, which differ in the characters of their salts, and in other particulars. The first is a very powerful base, the two others are weak ones. They are separated with extreme difficulty. CERIUM, LANTIIANIUM, AND DIDYMIUM. The oxides of these very rare metals are found associated in the Swedish mineral cerite ; the equivalent of cerium is about 47, and its symbol Ce. This metal forms a protoxide CeO, and a sesquioxide Ce 2 3 . The crude sesquioxide of cerium obtained by precipitating the double sulphate of cerium and potassa directly derived from cerite by carbonate of potassa, has been shown by Mosander to contain in addition to sesquioxide of cerium, the oxides of two other metals, to which the above names were given. After ignition it is red-brown. The complete separation of these three bodies is attended with the greatest difficulty, and has indeed been, only partially accomplished. 1 Oxide of cerium may be obtained pure by heating the mixture of the three oxides first with diluted and afterwards with concentrated nitric acid, which gradually removes the whole of the oxides of latlmnium and didymium. The yellow oxide of cerium, obtained by igniting the nitrate, is a mixture of proto- and sesquioxide, which are extremely difficult to obtain in a sepa- rate state. The salts of the former are colourless, and are completely pre- cipitated by sulphate of potassa; the sulphate of the sesquioxide is yellow, arid forms a beautiful double salt with sulphate of potassa, which is decom- posed by water. The metal cerium has been obtained from the chloride by the action of sodium. Oxide of lanthanium, as pure as it has been obtained, forms a very pale salmon-coloured powder, unchanged by ignition in open or close vessels. In contact with water it gives a snow-white bulky hydrate which has an alkaline reaction, and decomposes ammoniacal salts by boiling. Its salts are crystallizable, colourless, sweet, and astringent, and are precipitated by sulphate of potassa. A tolerably pure lanthanium-salt may be obtained by slowly crystallizing an acid solution containing the sulphates of lanthanium and didymium, picking out the rose-coloured crystals (containing didymium), and the viole* ones (containing lanthanium and didymium), adding the solution of the latter to the mother-liquor, and repeating the process. In this manner the whole of the didymium-salt may be finally separated by crystallization. Metallic lanthanium is prepared like cerium. The occasional brown colour of crude oxide of cerium is due to oxide of 1 A synopsis of the various methods for the separation of cerium, lanthanium, and didy miuiu has been given by Mr. U. Watts. Chem. Soc. Quar. Jour. ii. 140. 252 ZIRCONIUM THORIUM GLASS. didymium. In a pure state, it forms a brown powder, soluble in acids, and generating a series of red crystallizable salts, from which caustic potassa precipitates a violet- blue hydrate, quickly changing by exposure to the air. It communicates to glass an amethystine colour. 1 ZIRCONIUM. Prepared by heating the double fluoride of zirconium and potassium with potassium, and separating the salt with cold water. The metal is black, and acquires a feeble lustre when burnished. It takes fire when heated iu the air. The equivalent of zirconium is 33-6, and its symbol Zr. ZIRCONIA, Zr 2 3 , is a rare earth, very closely resembling alumina, found together with silica, in the mineral zircon. The salts are colourless and have an astringent taste. Svanberg has rendered it probable that an undescribed metallic oxide exists in certain varieties of zircon, for the metal of which he proposes the name of norium. THORIUM. The metal of an earth from a very rare mineral, thorite ; it agrees in character with aluminium, and is obtained by similar means. The equivalent of thorium is 59-6, and its symbol Th. THORIA, ThO, is remarkable for its great specific gravity, and is otherwise distinguished by peculiar properties which separate it from all other substances. 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 sili- cates included among the earthly minerals. Compounds identical with some of these are also occasionally formed in artificial processses, 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 silicate of lead ; crown and plate-glass belong to the former division ; flint- fflass, 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 black oxide of iron, derived from the impure materials. The principle of the glass manufacture is very simple. Silica, in the shape of sand, is heated with carbonate of potassa or soda, and slaked lime or oxide of lead ; at a high temperature, fusion and combi- nation occur, and the carbonic acid is expelled. When the melted mass has become perfectly clear and free from air-bubbles, it is left to cool until it as- sumes 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 oxide of iron. Red-lead, one of the higher oxides, is preferred to litharge, although immediately reduced to 1 Annalen der Cbemie und Pharmacie, xlviii. 210. GLASS. 253 protoxide by the heat, the liberated oxygen serving to destroy any combus- tible matter which might accidentally find its way into the crucible and stain the glass by reducing a portion of the lead. Potassa gives a better 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 collect- ing a proper quantity of soft, pasty glass at the end of his bloiv-pipe, an iron tube, five or six feet in length, terminated by a mouth-piece of wood ; he then commences 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 obvi- ate 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, trans- ferred 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 movement given to the rod. Plate-glass is cast upon a flat metal table, and after very care- ful annealing, ground true and polished by suitable machinery. Tubes are made by rapidly drawing out a hollow cylinder ; and from these a great va- riety of useful 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 portions 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 : Bohemian plate-glass (excellent). 1 Silica 60-0 Potassa 25-0 Lime 12-5 97-5 English flint-glass." Silica 51-93 Potassa 13-77 Oxide of lead 33-28 98-98 The difficultly-fusible white Bohemian tube, so invaluable in organic che- mistry, has been found to contain in 100 parts : Silica 72-80 Lime, with trace of alumina 9-68 Magnesia -40 Potassa 16-80 Traces of manganese, &c., and loss -32 Different colours are often communicated to glass by metallic oxides. Thus, oxide of cobalt gives deep blue ; oxide of manganese, amethyst ; sub- oxide of copper, ruby-red ; black oxide of copper, green ; the oxides of iron, dull green or brown, &c. These are either added to the melted con 1 Mitscherlich, Lehrbuch. ii. 187 Faraday. 22 254 PORCELAIN AND EARTHENWARE. tents 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 re-heated until fusion of the colouring matter occurs ; such is the practice of enam- elling and glass-painting. 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 carbonate of potassa or soda, and the product treated with water, the greater part dissolves, yielding a solution from which acids precipitate gelatinous silica. This is the soluble glass sometimes mentioned by chemical writers ; its solution has been used for rendering muslin and other fabrics of cotton or linen less combustible. 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 purposes 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 charac- ters. In porcelain the body of the ware is very compact and translucent, and breaks with a conchoidal 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 com- pact and partly glassy character of porcelain is the result of the admixture with the clay of a small portion of some substance, fusible at the temperature to which the ware is exposed when baked or fired, and which, 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 silicate of lime, or alkali. The clay employed in porcelain-making is always directly derived from the decomposed felspar, none of the clays of the secon- dary strata being pure enough for the purpose ; it must be white, and free from oxide of iron. To dimmish the retraction which this substance under- goes in the fire, a qantity 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 impal- pable powder. The utmost pains are taken to eifect perfect 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 completely 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 sub- stance, 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 fire-places, and surmounted by a lofty dome. Dry wood or coal is consumed as fuel, and its flame directed into the interior, and made to circulate around and among the earthen cases, or seggars 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 colours This operation has sometimes to be repeated more than once. EARTH EN WAUl. 255 The manufacture of porcelain in Europe is of modern origin ; the Chinese have possessed the art t'rorn the commencement of the seventh century, and their ware is, in some respects, altogether unequalled. The materials em- ployed by them are known to be kaolin, or decomposed felspar; peluntze, or quartz reduced to fine powder ; and the ashes of fern, which contain carbonate of potassa. STONEWARE. This is a coarse kind of porcelain, made from clay containing oxide of iron and a little lime, to which it owes its partial fusibility. The gla- zing is performed by throwing common salt into the heated furnace ; this is vo- latilized, and decomposed by the joint agency of the silica of the ware, and of the vapour of water always present ; hydrochloric acid and soda are pro- duced, 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 secondary clay, mixed with a considerable quantity of silica. The articlea are thoroughly dried and fired, after which they are dipped into a readily fusible glaze-mixture, of which oxide of lead 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 colours, 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 ware. 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 employed for the same purpose ; and powdered coke has been also used with the earth ; such cru- cibles bear rapid changes of temperature with impunity. 256 MANGANESE. SECTION IV. OXTDABLE METALS PROPER, WHOSE OXIDES FORM POWERFUL BASES. MANGANESE. 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, carbide of manganese, may be best 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 Hes- sian or Cornish crucible with moist charcoal-powder, introduced a little at a time, arid 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 cracible becomes red-hot, after which it is urged to its maxi- mum for an hour or more. When cold, the crucible is broken up, and the metallic button of manganese extracted. Manganese is a greyish-white metal, resembling some varieties of cast- iron ; it is hard and brittle, and destitute of magnetic properties. Its spe- cific gravity is about 8. It is fusible with great difficulty, and, when free from iron, oxidizes in the air so readity, that it requires to be preserved in naphtha. Water is not sensibly decomposed by manganese in the cold. Dilute sulphuric acid dissolves it with great energy, evolving hydrogen. The equivalent of manganese is assumed to be 27-6; its symbol is Mn. Oxides of Manganese. Seven different oxides of this metal are described, but two out of the number are, probably, secondary compounds. Protoxide MnO Sesquioxide Mn 2 3 Binoxide Mn0 2 Proto-sesquioxide (red oxide) Mn 3 4 =MnO, Mn 2 3 Varvicite Mn 4 7 =Mn 2 3 2Mu0 2 Manganic acid Mn0 3 Permanganic acid Mn 2 O 7 PROTOXIDE, MnO. When carbonate of manganese is heated in a stream of hydrogen gas, or of vapour of water, the carbonic acid is disengaged, and a green-coloured powder left behind, which is the protoxide. Prepared at a dull red-heat only, the protoxide is so prone to absorb oxygen from the air, that it cannot be removed from the tube without change ; but when at a higher temperature it appears more stable. This oxide is a very powerfal \ MANGANESE. 257 bane, being isomorphous with magnesia and zinc ; it dissolves quietly in dilute acids, neutralizing them completely and forming salts, which have often a beautiful pink colour. When alkalis are added to solutions of these compounds the white hydrated oxide first precipitated speedily becomes brown by passing into a higher state of oxidation. SsaQuioxiDE, Mn 2 3 . This compound occurs in nature in the state of hydrate ; a very beautiful crystallized variety is found at Ilefeld, in the Harts. It is produced artificially, by exposing to the air the hydrated prot- oxide, and forms the principal part of the residue left in the iron retort when oxygen gas is prepared by exposing the native binoxide to a moderate red- heat. The colour of the sesquioxide is brown or black, according to its origin or mode of preparation. It is a feeble base, isomorphous with alu- mina ; for, when gently heated with diluted sulphuric acid, it dissolves to a red liquid, which, on the addition of sulphate of potassa or of ammonia, deposits octahedral crystals having the constitution of common alum ; these are, however, decomposed by water. Strong nitric acid resolves this oxide into a mixture of protoxide and binoxide, the former dissolving, and the latter remaining unaltered ; while hot oil of vitriol destroys it by forming sulphate of the protoxide, and liberating oxygen gas. Heated with hydro- chloric acid, chlorine is evolved, as with the binoxide, but to a smaller extent. BINOXIDE, Mn0 2 . 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 protoxide. Biaoxide of man- ganese has a black colour, is insoluble in water, and refuses to unite with acids. It is decomposed by hot hydrochloric 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 a very large quantity for making chlorine, and as it is subject to great alteration of value from an admixture of the sesquioxide and several impurities, it becomes desirable to possess means of assaying ditferent 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 a very fine powder, are put into the little vessel employed in the analysis of carbonates, 1 together with about half an ounce of cold water, and 100 grains of strong hydro- chloric acid ; 50 grains of crystallixed oxalic acid are then added, the cork carrying the chloride of calcium tube is fitted, and the whole quickly weighed or counterpoised. The application of a gentle heat suffices to deter- mine the action : the disengaged chlorine converts the oxalic acid into car- bonic acid, with the help of the elements of water, two equivalents of car- bonic acid representing one of chlorine, and consequently one of binoxide of manganese. Now, the equivalent of the latter substance, 43-6, is so nearly equal to twice that of carbonic acid, 22, that the loss of weight suffered by the apparatus when the reaction has has become complete, and the residual gas has been driven off by momentary ebullition, may be taken to represent the quantity of real binoxide in the. 50 grains of the sample It is obvious that the little apparatus of Will and Fresenius, described at page 229, may be used with the same advantage. RED OXIDE, Mn 3 4 , or probably MnO-fMn 2 3 . This oxide is also found native, and is produced artificially by heating to whiteness the binoxide or sesquioxide, or by exposing the protoxide 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 higher oxides already 'See page 228. 258 MANGANESE. described. Borax and glass in a fused state dissolve this substance, and acquire the colour of the amethyst. VARVICITE, Mn 4 7 , or Mn 2 3 -j-2Mn0 2 . A natural production, discovered by Mr, Phillips, among certain specimens of manganese-ore from Warwick- shire ; it has also been found at Ilefeld. It much resembles the binoxide, but is harder and more brilliant, and contains water. By a strong heat, varvicite is converted into red oxide, with disengagement of aqueous vapour and oxygen gas. CHLORIDE OF MANGANESE, MnCl. This salt may be prepared in a state of purity from the dark brown liquid residue of the preparation of chlorine from binoxide of manganese 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, evaporated to perfect dryness, and then slowly heated to dull ignition in an earthen vessel, with constant stirring. The chloride of iron is thus either volatilized or converted by the remaining water into insoluble sesquioxide, while the manganese-salt is unaffected. On treating the greyish-looking powder thus obtained with water, the chloride of manganese is dissolved out, and may be separated by filtration from the sesquioxide of iron. Should a trace of the latter yet remain, it may be got rid of by boiling the liquid for a few minutes with a little carbonate of man- ganese. The solution of chloride has usually a delicate pink colour, which becomes very manifest when the salt is evaporated to dryness. A strong solution deposits rose-coloured tabular crystals, which contain 4 equivalents of water ; these are very soluble and deliquescent. The chloride is fusible at a red-heat, is decomposed slightly at that temperature by contact of air, and is dissolved by alcohol, with which it forms a crystallizable compound. SESQUICHLORIDE, Mn 2 C1 3 . When precipitated sesquioxide of manganese is put into cold dilute hydrochloric acid, it dissolves quietly, forming a red solution of sesquichloride. Heat disengages chlorine, and occasions the pro- duction of protochloride. SULPHATE OF PROTOXIDE OF MANGANESE, MnO,S0 3 -f-7HO. A beautiful rose-coloured and very soluble salt, isomorphous with sulphate of magnesia. It is prepared on a large scale for the use of the dyer, by heating, in a close vessel, binoxide of manganese and coal, and dissolving the impure protoxide thus obtained in sulphuric acid, with the 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 the sulphate of sesquioxide of iron is decomposed. Water then dissolves out the pure sulphate of manga- nese, leaving the sesquioxide of iron behind. The salt is used to produce a permanent brown dye, the cloth steeped in the solution being aftewards passed through a solution of bleaching-powder, by which the protoxide is changed to insoluble hydrate of the binoxide. Sulphate of manganese sometimes crystallizes with five equivalents of water. It forms a double salt with sulphate of potassa. CARBONATE OF MANGANESE. Prepared by precipitating the protochloride by an alkaline carbonate. It is insoluble and buff-coloured, or sometimes nearly white. Exposed to heat, it loses carbonic acid, and absorbs oxygen. MANGANIC ACID, Mn0 3 . When an oxide of manganese is fused with an alkali, an additional quantity of oxygen is taken up from the air, and a deep green saline mass results, which contains a salt of the new acid, thus formed under the influence of the base. The addition of nitre, or chlorate of potassa, facilitates the production of manganic acid. Water dissolves this compound very readily, and the solution, concentrated by evaporation in vacuo, yields green crystals. IRON. PERMANGANIC ACID, Mn 2 7 . When manganate of potassa, free from any great excess of alkali, is put into a large quantity of water, it is resolved into hydrated binoxide of manganese, which subsides, and a deep purple liquid, containing permanganate of potassa. This effect is accelerated by heat. The changes of colour accompanying this decomposition are very re- markable, and have procured for the substance the name mineral chameleon ; excess of alkali hinders, in some measure, the reaction, by conferring greater stability on the manganate. Permanganate of potassa is easily prepared on a considerable scale. Equal parts of very finely powdered binoxide of man- ganese and chlorate of potassa are mixed with rather more than one part of hydrate of potassa dissolved in a little water, and the whole 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 colour, and are not very soluble in cold water. The manganates and permanganates are decomposed by contact with organic matter ; the former are said to be iso- morphous with the sulphates, and the latter with the perchlorates. Salts of the protoxide of manganese are very easily distinguished by reagents. The fixed caustic alkalis, and ammonia, give white precipitates, insoluble in excess, quickly becoming brown. The carbonates of the fixed alkalis, and carbonate of ammonia, give white precipitates, but little subject to change, and insoluble in excess of carbonate of ammonia. Sulphuretted hydrogen gives no precipitate, but sulphide of ammonium throws down insoluble, flesh-coloured sulphide of manganese, which is very characteristic. Ferrocyanide of potassium gives a white precipitate. Manganese is also easily detected by the blowpipe ; it gives with borax an amethystine bead in the outer or oxidizing flame, and a colourless one in the inner flame. Heated upon platinum foil with carbonate of soda, it yields a green mass of manganate of soda. IRON. This is by very far the most important member of the group of metals under discussion ; there are few substances to which it yieids in interest, when it is considered how very intimately the knowledge of the properties and uses of iron is connected with human civilization. Metallic iron is of exceedingly rare occurrence ; it has been found at Canaan, in Connecticut, 1 forming a vein about two inches thick in mica-slate, but it 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 contain, in common with the iron of the undoubted meteorites, nickel. In an oxidized condition, the presence of iron may be said to be universal ; it constitutes great part of the common colouring matter of rocks and soils ; it is contained in plants, and forms an essential component of the blood of the animal body. In the state of bisulphide it is also very common Pure iron may be prepared, according to Mitscherlich, by introducing into 1 Phillip's Mineralogy, fourth edit. p. 208. 260 IRON. a Hessian crucible 4 parts of fine iron wire cut smull, and 1 part of black oxide of iron. This is covered with a mixture of white sand, lime, and car- bonate of potassa, 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 carbon and silicum pre- sent in the wire having been removed by the oxygen of the oxide. Pure iron has a white colour and perfect lustre ; it is extremely soft and tough, and has a specific gravity of 7-8. The 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 g^th of an inch in diame- ter bearing a weight of 601b. It is very difficult of fusion, and before be- coming 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 oxide by hydrogen gas, takes fire spontane- ously 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 pre- sence of a little acid vapour.* At a red-heat iron decomposes water, evolving hydrogen, and passing into the black oxide. Dilute sulphuric and hydro- chloric acids dissolve it freely with separation of hydrogen. Iron is strongly magnetic up to a red-heat, when it loses all traces of that remarkable pro- perty. The equivalent of iron is 28, and its symbol Fe. Four compounds of iron and oxygen are described. Protoxide FeO Sesquioxide (peroxide) Fe 2 3 Protosesquioxide (black oxide) Fe 3 4 =FeO, Fe 2 3 Ferric acid FeO 3 PROTOXIDE, FeO. This is a very powerful base, neutralizing acids com- pletely, and isomorphous with magnesia, oxide of zinc, &c. It is almost unknown in a separate state, from its extreme proneness to absorb oxygen and pass into the sesquioxide. When a salt of this substance is mixed with caustic alkali or ammonia, a bulky whitish precipitate of hydrate of the pro- toxide falls, which becomes nearly black when boiled, the water being sepa- 1 When obtained at a heat below redness. R. B. 9 The rusting of iron proceeds with rapidity after it once begins, extending from the point first affected. Iron rust contains ammonia, resulting from the combination of the nascent hydrogen of decomposed water uniting with dissolved nitrogen. This is an important point in medico-legal investigations, as it is considered, that, when stains on a steel instrument yield ammonia by the action of potassa, the presence of organic matter is proved ; but as rust rontains ammonia, it becomes necessary to ascertain its absence, or drive it off, previous to \ (A-rauug with potassa. R. B. IRON. 261 rated. This hydrate exposed to the air, very rapidly changes, becoming green and ultimately red-brown. The soluble salts of protoxide of iron have commonly a delicate pale green colour, and a nauseous metallic taste. SKSQI T IOXIDE, Fe 2 3 . A feeble base, isomorphous with alumina. Sesqui- oxide of iron occurs native, most beautifully crystallized as specular iron ore in the island of Elba, and elsewhere ; also as red and brown hcematites, the latter being a hydrate. It is artificially prepared by precipitating a solution of sulphate of the sesquioxide or the sesquichloride of iron by excess of am- monia, and washing, drying, and igniting the yellowish-brown hydrate thus produced ; fixed alkali must not be used in this operation, as a portion is re- tained by the oxide. In fine powder, this oxide has a full red colour, and is used as a pigment, being prepared for the purpose by calcination of the sul- phate of the protoxide ; the tint varies somewhat with the temperature to which it has been exposed. This 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. Sesquioxide of iron is not acted upon by the magnet. 1 BLACK OXIDE; MAGNETIC OXIDE ; LOADSTONE, Fe 3 4 , or probably FeO-f- Fe 2 O 3 . A natural product, one of the most valuable of the iron ores, often found in regular octahedral crystals, which are magnetic. It may be pre- pared by mixing due proportions of salts of the protoxide and sesquioxide of iron, precipitating them by excess of alkali, and then boiling the mixed hydrates, when the latter unite to a black sandy substance, 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 vapour. It is incapable of forming salts. FERRIC ACID, Fe0 3 . A very remarkable compound of recent discovery. The simplest mode of preparing it is to heat to full redness, for an hour, in a covered crucible, a mixture of one part of pure sesquioxide of iron, and four parts of dry nitre. The brown, porous, deliquescent mass is treated when cold with ice-cold water, by which a deep amethystine red solution of ferrate of potassa is obtained. This gradually decomposes even in the cold, evolving oxygen gas, and depositing sesquioxide ; by heat the decomposition is very rapid. The solution of ferrate of potassa gives no precipitate with salts of lime, magnesia, or strontia, but when mixed with one of baryta, a deep crimson, insoluble compound falls, which is a ferrate of that base, and is very permanent. PROTOCHLORIDE OF IRON, Fed. Formed by transmitting dry hydrochloric acid gas over red-hot metallic iron, or by dissolving iron in hydrochloric acid. The latter solution yields, when duly concentrated, green crystals of the pro- tochloride, containing 4 equivalents of water ; they are very soluble and deliquescent, and rapidly oxidize in the air. SESQUICHLORIDE OF IRON, Fe 2 Cl 3 . Usually prepared by dissolving sesqui- 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 chloride of potassium and sal-ammoniac. When evaporated to dryness and strongly heated, much of the chloride is decom- posed, yielding sesquioxide and hydrochloric acid ; the remainder sublimes, and afterwards condenses in the form of small brilliant red crystals, which deliquesce rapidly. The solution of sesquichloride of iron is capable of dis- solving a large excess of recently precipitated hydrate of the sesquioxide, by *In the form of hydrate, FesOa+BIIO, as recently precipitated from the persulphate hy am- mouia, it constitutes the antidote for amsnious acid. The affinity for water in this case is not strong the hydrate gradually decomposing even when kept under water, its colour pivwiuf from yellowish brown to red. 11. B. 262 IRON. which it acquires a much darter colour. Anhydrous sesquichloride of iron is also produced by the action of chlorine upon the heated metal. PROTIODIDE OF IRON,, Fel. This is an important medicinal preparation; it is easily made by digesting iodine with water and metallic iron. The so- lution 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. 1 A sesqui-iodide of iron exists, which is yellowish-red and soluble. SULPHIDES OF IRON. Several compounds of iron and sulphur are de- scribed ; of these the two most important are the following. Protosulphule, FeS, is a blackish, brittle substance, attracted by the magnet, formed by heating together iron and sulphur. It is dissolved by dilute acids with evo- lution of sulphuretted hydrogen gas, and is constantly employed 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 filings 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 of iron, FeS , iron pyrites, is a natural product, occurring in rocks of all ages, and evidently formed in many cases by the gradual de- oxidation of sulphate of iron by organic matter. It has a brass-yellow colour, is very hard, not attracted by the magnet, and not acted upon by dilute acids. Exposed to heat, sulphur is expelled, and an intermediate sul- phide, analogous probably to the black oxide, is produced. This substance also occurs native, under the name of magnetic pyrites. The bisulphide is sometimes used in the manufacture of sulphuric acid. Compounds of iron with phosphorus, carbon, and silicium exist, but little is known respecting them in a definite state. The carbide 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 hurtful substance in bar-iron, as it renders it brittle or cold-shorj. SULPHATE OF PROTOXIDE OF IRON; GREEN VITRIOL, FeO,S0 3 -}-7HO. This beautiful and important salt may be obtained by directly dissolving iron in dilute sulphuric acid ; it is generally prepared, however, and that on a very large scale, by contact of air and moisture with common iron pyrites, which, by absorption of oxygen, readily furnishes 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 equiva- lents of water, have been obtained. Sulphate of protoxide of iron forms double salts with the sulphates of potassa and ammonia. SULPHATE OF SESQUIOXIDE OF IRON, Fe 2 3 ,3S0 3 . Prepared by adding to a solution of the protosalt 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-coloured amorphous mass, which, when put into water, very slowly dissolves. With the sulphates of potassa and ammonia, this salt yields compounds having the form an.d constitution of the alums ; the crystals are nearly destitute of colour. These latter are decomposed by water, and sometimes by long keep- ing when in a dry state. They are best prepared by exposing to spontaneous evaporation a solution of sulphate of sesquioxide of iron to which sulphate of putassa or of ammonia has been added. Or protevrted from the action of oxygen by pure honey, or other saccharine substance, h the proportion of one part to three of the solution. H. B. IRON. 263 NITRATE OF THE PROTOXIDE OF IRON, FeO,N0 5 . When dilute cold nitric acid is made to act to saturation upon protosulphide of iron, and the solu- tion evaporated in vacuo, pale green and very soluble crystals of protonitrate are obtained, which are very subject to alteration. The nitrate of the ses- quioxide 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. CARBONATE OF PROTOXIDE OF IRON, FeO,C0 2 . The -white precipitate ob- tained by mixing solutions of protosalt of iron and alkaline carbonate ; it cannot be washed and dried without losing carbonic acid and absorbing oxygen. This substance occurs in nature as spathoseiron ore, associated with variable quantities of carbonate of lime and of magnesia; and 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 carbonic acid ; such waters are known by the rusty matter they deposit. No carbonate of the sesquioxide is known. The phosphates of iron are all insoluble. 1 Salts of the protoxide of iron are thus distinguished : Caustic alkalis, and ammonia, give nearly white precipitates, insoluble in excess of the reagent, rapidly becoming green, and ultimately brown, by ex- posure to air. Alkaline carbonates, and carbonate of ammonia, throw down the white carbonate, also very subject to change. Sulphuretted hydrogen gives no precipitate, but sulphide of ammonium throws down black protosulphide of iron, soluble in dilute acids. Ferrocyanide of potassium gives a nearly white precipitate, becoming deep blue on exposure to air. Salts of the sesquioxide are thus characterized : Caustic alkalis, and ammonia, give foxy-red precipitates of hydrated ses- quioxide, insoluble in excess. The carbonates behave in a similar manner, the carbonic acid escaping. Sulphuretted hydrogen gives a nearly white precipitate of sulphur, and reduces the sesquioxide to protoxide. Sulphide of ammonium gives a black precipitate, slightly soluble in excess, Ferrocyanide of potassium yields Prussian blue. Tincture or infusion of gall-nuts strikes intense bluish-black with the most dilute solutions of salts of sesquioxide of iron. Iron Manufacture. This most important branch of industry consists, aa now conducted, of two distinct parts ; viz., the production from the ore of a fusible (carbide) of iron, and the subsequent decomposition of the carbide, 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 carbonate of iron mixed with clay ; sometimes lime and magnesia are also present. It is broken in pieces, 1 PHOSPHATE OP PROTOXIDE OF IRON, 2FeO, IIO,P0 5 , is formed when a solution of common phosphate of soda is added to a solution of protosulphate of iron. It fa II a as a white preci- pitate, prndually becoming bluish by the action of the air; it is soluble in acids, from which ammonia asam precipitates it, and re-dissolves the precipitate when added in excess The blue phosphate contains perphosphate. PHOSPHATE OF SESQUIOXIDE OF IRON is formed by adding common phosphate of soda to per- sulphate or porchloride of iron; a white precipitate is produced insoluble in ammonia unless an excess of phosphate of soda be present. Digested with the fixeO alkalis or ammonia it becomes brown. 11. B. 264 IRON. and exposed to heat in a furnace resembling a lime-kiln, by which the water >md carbonic acid are expelled, and the ore rendered dark-coloured, denser, and also magnetic ; it is then ready for reduction. The furnace in which this operation is performed is usually of very large dimensions, fifty feet or more in height, and constructed of brick work with great solidity, the interior being lined with excellent fire-bricks ; the figure will be at once understood from the sectional drawing (fig. 149). The furnace is close at Fig. 149. the bottom, the fire being maintained by a powerful artificial blast introduced by two or three tuyere-pipes, as shown in the section. The materials, con- sisting of due proportions of coke or carbonized coal, roasted ore, and lime- stone, are constantly supplied from the top, the operation proceeding con- tinuously night imd day, often for years, or until the furnace is judged to require repair. ID 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 carbide by cementation, while the silica and alumina unite with the lime, purposely added, to a kind of glass or slag, nearly free from oxide of iron. The carbide 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 suffered to run into rude moulds of sand by opening an orifice at the IRON. 265 bottom of the recipient, previously stopped with clay. Such is the origin of crude or or cast-iron, of which there are several varieties, distinguished by differences of colour, hardness, and composition, and known by the names of grey, black, and ivhitc iron. The first is for most purposes the best, as it admits of being filed and cut with perfect ease. The black and grey 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 furaace. 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 by an operation called puddling ; previous to which, however, it commonly undergoes a process the theory of which is not perfectly intelligible. It is remelted, 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 ordi- nary 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 of 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 a view of pro- moting more rapid oxidation. 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 und*r an immense hammer, moved by machinery, by which each becomes quickly fashioned into a rude bar. This is re-heated, 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, Avhich are afterwards piled or bound together, again raised to a welding heat, and hammered or rolled into a single bar ; and this process of piling or fagotting 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 carbon and silicium ; when strongly heated with oxide of iron, those compounds un- dergo decomposition, the carbon and siliciu.ni becoming oxidized at the ex- pense of the oxygen of the oxide. As this change takes place, the metal gradually loses its fusibility, but retains a certain degree of adhesiveness, BO 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, some- times made with charcoal. Steel. A very remarkable, and most useful substance, prepared by heat- ing iron in contact with charcoal. Bars of Swedish iron are embedded in charcoal powder, contained in a large rectangular crucible or chest of 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 17 266 A R I D I U M . per cent, of carbon, becoming harder, and at the same time fusible, with a certain diminution, however, of malleability. The active agent in this ce- mentation process is probably carbonic oxide ; the oxygen of the air in the crucible combines with the carbon, to form that substance, which is after- wards decomposed by the heated iron, one half of its carbon being abstracted by the latter. The carbonic acid thus formed takes up an additional dose of carbon from the charcoal, and again becomes carbonic oxide, the oxygen, or rather the carbonic acid, acting as a carrier between the charcoal and the Tietal. The product of this operation is called blistered steel, from the blis- ered and rough appearance of the bars ; the texture is afterwards improved nd equalized by welding a number of these bars together, and drawing the whole out under a light tilt-hammer. The most perfect kind of steel is that which has undergone fusion, having been cast into ingot-moulds, and afterwards hammered : of this all fine cut- ting 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, in 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 stiffness or pastiness is observed in the residual metal, it is withdrawn, and hammered or rolled into bars. The wootz, or native steel of India, is probably made in this manner. Annealed cast-iron, sometimes called run-steel, is now much employed as a substitute for the more costly products of the forge ; the articles, when cast, are embedded in powdered iron ore, or some earthy material, and, after be- ing exposed to a moderate red-heat for some time, are allowed slowly to cool, by which a very extraordinary degree of softness and malleability is attained. It is very possible that some little decarbonization may take place during this process. The most remarkable property of steel is that of becoming exceedingly hard when quickly cooled ; when heated to redness, and suddenly quenched in cold water, steel, in fact, becomes capable of scratching glass with fa- cility ; if re-heated to redness, and once more left to cool slowly, it again becomes nearly as soft as ordinary iron, and, between these two conditions, 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 doivn, by exposure to a proper degree of annealing heat, which is often judged of by the colour of the thin film of oxide which appears on the polished surface. Thus, a temperature of about 480 (221C), indicated by n, faint straw-colour, gives the proper temper for razors ; that for scissors, pen-knives, &c., will be comprised between 470 (243C) and 490 (254C), and be attended by a full yellow or brown tint. Swords and watch-springs require to be softer and more elastic, and must be heated to 550 (288C) or 560 (293C), or until the surface becomes deep blue. Attention to these colours has now become of less importance, as metal baths are often sub- stituted for the open fire in this operation. ARIDIUM. ARILIUM (from "Apqs, Mars, and ttios, appearance) from the resemblance of its oxide to oxide of iron. Ulgren considers this as a new metal. He found it in the chrome iron from Roros, and in iron ore from Oernstolso. Tbere are sti! 1 doubts hanging over the existence of this metal. CHROMIUM. 267 CHROMIUM. 4/HROMIUM is found in the state of oxide, in corabinntion with oxide of i^jn, in some abundance in the Shetland Islands, and elsewhere ; as chro- mate of lead, it constitutes a very beautiful mineral, from which it was first obtained. The metal itself is got in a half-fused condition by mixing the oxide with one-fifth of its weight of charcoal-powder, inclosing the mixture in a crucible lined with charcoal, and then subjecting it to the very highest heat of a powerful furnace. It is hard, greyish-white, and brittle; of 5-9 specific gravity, and exceedingly difficult of fusion. Chromium is but little oxidable, being scarcely attacked by the most powerful acids ; it forms at least four compounds with oxygen, corresponding to, and probably ismor- phous with, those of iron. The equivalent of chromium is 26-8 ; its symbol is Cr. PROTOXIDE or CHROMIUM, CrO. When potassa is added to a solution of the protochloride of chromium, a brown precipitate falls, which speedily passes to deep foxy red, with disengagement of hydrogen. Tfie protoxide, in the state of the pale greenish hydrate, is perhaps obtained when ammonia is substituted for potassa in the preceding experiment. This substance is a powerful base, forming pale blue salts, which absorb oxygen with extreme avidity. The double sulphate of protoxide of chromium and potassa con- tains 6 eq. of water, like the other members of the same group. PROTOSESQUIOXIDE OF CHROMIUM, CrO-f O 2 3 , is the above brownish-red precipitate produced by the action of water, upon the protoxide. The de- composition is not complete without boiling. This oxide corresponds with the magnetic oxide of iron, and is not salifiable. SESQUIOXIDE OF CHROMIUM, O 2 3 . When chromate of mercury, prepared by mixing solutions of the nitrate of suboxide of mercury and of chromate or bichromate of potassa, is exposed to a red-heat, it is decomposed, pure sesquioxide of chromium having a fine green colour, remaining. In this state the oxide is, like alumina after ignition, insoluble in acids. From a solution of sesquioxide of chromium in potassa or soda, green gelatinous hydrated sesquioxide of chromium is separated on standing. When finely powdered and dried over sulphuric acid, its formula is Cr 2 3 -f 6HO. A hy- drate may also be had by boiling a somewhat dilute solution of bichromate of potassa, strongly acidulated by hydrochloric acid, with small successive portions of sugar or alcohol ; in the former case, carbonic acid escapes ; in the latter a substance called aldehyde and acetic acid are formed, substances with which we shall become acquainted in organic chemistry, and the chromic acid of the salt becomes converted into sesquichloride of chromium, the colour of the liquid changing from red to deep green. A slight excess of ammonia precipitates the hydrate from this solution. It has a pale purplish- green colour, which becomes full green on ignition ; an extraordinary shrink- ing of volume and sudden incandescence is observed when the hydrate is decomposed by heat. Anhydrous sesquioxide in a beautifully crystalline condition may be prepared by heating to full redness in an earthen crucible bichromate of potassa. One-half of the acid suffers decomposition, oxygen being disengaged, and oxide of chromium left. The melted mass is then treated with water, which dissolves out neutral chromate of potassa, and the oxide is, lastly, washed and dried. Sesquioxide of chromium commu- nicates a fine green tint to glass, and is used in enamel-painting. The sesquioxide of chromium is a feeble base, resembling, and isomor- phous with, sesquioxide of iron and alumina ; the salts it forms have a green or purple colour, and are said to be poisonous. The sulphate of sesquioxide of chromium is prepared by dissolving the hydrated oxide in dilute sulphuric acid. It unites with the sulphates of po- 268 CHROMIUM. tassa and of ammonia, giving rise to magnificent salts which crystallize in regular octahedrons of a deep claret colour, and possess a constitution re- sembling that of common alum, the alumina being replaced by sesquioxide of chromium. The finest crystals of chromium-alum are obtained by spon- taneous evaporation, the solution being apt to be decomposed by heat. PROTOCIILORIDE OF CHUOMIUM, CrCl. The violet-coloured sesqnichloride of chromium, contained in a porcelain or glass tube, is heated to redness in a current of perfectly dry and pure hydrogen gas ; hydrochloric acid is dis- engaged, and a white foliated mass is obtained, which dissolves in water with great elevation of temperature, yielding a blue solution, which, by ex- posure to the air, absorbs oxygen with extraordinary energy, acquiring a deep green colour, and passing into the state of oxychloride of chromium, 2O 2 C1 3 , Cr 2 3 . The protochloride of chromium is one of the most powerful reducing or deoxidizing agents known. SESQUICHLORIDE or CHROMIUM, Cr 2 Cl 3 . This substance is readily obtained in the anhydrous condition by heating to redness in a porcelain tube a mix- ture of sesquioxide of chromium and charcoal, and passing dry chlorine gas over it. The sesquichloride sublimes, and is deposited in the cool part of the tube, in the form of beautiful crystalline plates of a pale violet colour. According to M. Peligot, it is totally insoluble in water under ordinary cir- cumstances, even at a boiling heat. It dissolves, however, and assumes the deep green hydrated state in water containing an exceedingly minute quan- tity of the protochloride in solution. The hydration is marked by the evo- lution of much heat. This remarkable effect must probably be referred to the class of actions known at present under the name of katalysis. 1 The salts of the sesquioxide of chromium are easily recognized. Caustic alkalis precipitate the hydrated oxide, easily soluble in excess. Ammonia, the same, but nearly insoluble. Carbonates of potassa, soda, and ammonia, throw down a green precipitate of carbonate and hydrate, slightly soluble in a large excess. Sulphuretted hydrogen causes no change. 1 Sulphide of ammonium precipitates the hydrate of the sesquioxide. CHROMIC ACID, Cr0 3 . Whenever sesquioxide of chropnium is strongly heated with an alkali, in contact with the air, oxygen is absorbed and chromic acid generated. Chromic acid may be obtained nearly pure, and in a state of great beauty, by the following simple process : 100 measures of a cold saturated solution of bichromate of potassa are mixed with 150 measures of oil of vitriol, and the whole suffered to cool ; the chromic acid crystallizes in brilliant crimson-red prisms. The mother-liquor is poured off, and the crystals placed upon a tile to drain, being closely covered by a glass or bell-jar. a Chromic acid is vei-y deliquescent and soluble in water ; the solution is instantly reduced by contact with organic matter. Chromate of Potassa, KO,Cr0 3 . This is the source of all the preparations of chromium ; it is made directly from the native chrome-iron ore, which is a compound of the sesquioxide of chromium and protoxide of iron, analogous to magnetic iron ore, by calcination with nitre or with carbonate of potassa, *he stone being reduced to powder, and heated for a long time with the alkali in a reverberatory furnace. The product, when treated with water, yields a yellow solution, which by evaporation deposits anhydrous crystals of the same colour, isomorphous with sulphate of potassa. Chromate of potassa has a cool, bitter, and disagreeable taste, and dissolves in 2 parts of water at 60 (15-5C). 1 See page 186. ' Mr. Warriiigton ; Proceedings of Chom. Soc. i. 18. NICKEL. 269 Bichromate of Potassa, KO,2Cr0 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 an oblique rhombic prism. It melts when heated, and is soluble in 10 parts of water, and the solution has an acid reaction. Chromate of Lead, PbO,O0 3 . On mixing solution of chromate or bichro- mate of potassa with nitrate or acetate of lead, a brilliant yellow precipitate falls, which is the compound in question; it is the chrome-yellow of the painter. When this compound is boiled with lime-water, one-half of the acid is withdrawn, and a subchromate of an orange-red colour left. The subchromate is also formed by adding chromate of lead to fused nitre, and afterwards dissolving out the soluble salts by water ; the product is crystal- line, and rivals vermilion in beauty of tint. The yellow and orange chrome- colours 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. Chromate of Silver, AgO,Cr0 3 * This salt precipitates as a reddish brown powder when solutions of chromate of potassa and nitrate of silver are mixed. It dissolves in hot dilute nitric acid, and separates, on cooling, in small ruby-red platy crystals. The chromates of baryta, zinc, and mercury are insoluble ; the first two are yellow, the last is brick-red. Perchromic Acid is obtained, according to Barreswill, by mixing chromic acid with dilute binoxide of hydrogen or bichromate of potassa with a dilute but very acid solution of binoxide of barium in hydrochloric acid, when a liquid is formed of a blue colour, which is removed from the aqueous solution by ether. The composition of this very unstable compound is per- haps O a O r A salt of chromic acid is at once recognised by its behaviour with solu- tions of baryta and lead ; and also by its colour and capability of furnishing, by deoxidation, the green sesquioxide of chromium. CHLOROCHROMIC ACID, Cr0 2 -f-Cl.' 3 parts of bichromate of potassa and 8J parts of common salt are intimately mixed and introduced into a small glass retort ; 9 parts of oil of vitriol are then added, and heat applied as long as dense red vapours arise. The product is a heavy deep red liquid resembling bromine ; it is decomposed by water, with production of chromic and hydrochloric acids. NICKEL. Nickel is found in tolerable abundance in some of the metal-bearing veins of the Hartz mountains, and in a few other localities, chiefly as arsenide, the kupfernickd of mineralogists, so called from its yellowish-red colour; 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- Baits. This metal is found in meteoric iron, as already mentioned. Nickel is easily prepared by exposing the oxalate to a high white heat, m * If this formula be trebled, we obtain Cr 3 OeCl3 = 2CrO.),OCl3, and the substance becomes u compound of 2 eq. of chromic acid and 1 eq. of terchloridc of chromium. The terchloridc of chromium is not known in the free state. 23* 270 NICKEL. a crucible lined with charcoal. It is a white, malleable metal, having a den- sity of 8-8, a high melting point, and a less degree of oxidability than iron, since it is but little attacked by dilute acids. Nickel is strongly magnetic, but loses this property when heated to 660 (349C). This metal forms two oxides, only one of which is basic. The equivalent of nickel is 29-6; its symbol is Ni. PROTOXIDE OF NICKEL, NiO. This compound is prepared by heating to redness the nitrate, or by precipitating a soluble salt with caustic potassa, and washing, drying, and igniting the apple-green hydrated oxide thrown down. It is an ash-grey powder, freely soluble in acids, which it completely neutralizes, being isomorphous with magnesia, and the other members of the same group. The salts of this substance, when hydrated, have usually a beautiful green colour; in the anhydrous state they are yellow. SESQUIOXIDE, OR PEROXIDE OF NICKEL, Ni 2 3 . This oxide is a black in- soluble substance, prepared by passing chlorine through the hydrated oxide suspended in water ; chloride of nickel is formed, and the oxygen of the oxide decomposed transferred to a second portion. It is also produced when a salt of nickel is mixed with a solution of bleaching-powder. The sesqui- oxide is decomposed by heat, and evolves chlorine when put into hot hydro- chloric acid. CHLORIDE OF NICKEL, NiCl. This is easily prepared by dissolving oxide or carbonate of nickel in hydrochloric acid. A green solution is obtained which furnishes crystals of the same colour, containing water. When ren- dered anhydrous by heat, the chloride is yellow, unless it contain cobalt, in which case it has a tint of green. SULPHATE OF NICKEL, NiO,S0 3 -f7HO. This is the most important of the gaits of nickel. It forms green prismatic crystals, containing 7 equivalents of water, which require 3 parts of cold water for solution. Crystals with 6 equivalents of water have also been obtained. It forms with the sulphates of potassa and ammonia beautiful double salts, NiO,S0 3 -f KO,S0 3 -f 6HO and NiO,S0 3 -f NH 4 0, S0 3 -f6HO. 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 preparing the metal. CARBONATE OF NICKEL. When solutions of sulphate or chloride of nickel and of carbonate of soda are mixed, a pale green precipitate falls, which is a combination of carbonate and hydrate of nickel. It is readily decomposed by heat. Pure salts of nickel 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 aqua regia. The solution is gently evaporated to dryness, the residue treated with boiling water, and the inso- luble arsenate of iron removed by a filter. The liquid is then acidulated with hydrochloric acid, treated with sulphuretted hydrogen 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 of bicarbonate of soda is gradually added, by which the sesquioxide of iron may be completely separated without loss of nickel- Bait. Lastly, the filtered solution, boiled with carbonate of soda in excess, yields an abundant pale green precipitate of carbonate of nickel, 1 from which all the other compounds may be prepared. 1 This precipitate may still contain cobalt, which can only be separated from it by very complicated processes, for which the more advanced studont is referred to ' Liebig and Koyp'ts Annual Report," ii. 334. COBALT. 271 The salts of nickel are well characterized by their behaviour with re- agents. Caustic alkalis 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 colour. Carbonate of potassa and soda give pale green precipitates. Carbonate of ammonia, a similar precipitate, soluble in excess, with blue colour. Ferrocyanide of potassium gives a greenish-white precipitate. Cyanide of potassium produces a green precipitate, which dissolves in an excess of the precipitant to an amber-coloured liquid which is re-precipitated by addition of hydrochloric acid. Sulphuretted hydrogen occasions no change, if the nickel be in combina- tion with a strong acid. Sulphide of ammonium throws down black sulphide of nickel. 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 copper, 60 of zinc, and 40 of nickel. This alloy is very malleable, and takes a high polish. COBALT. This substance bears, in many respects, an extraordinary resemblance to the metal last described ; it is often associated with it in nature, and may be obtained from its compounds by similar means. Cobalt is a white, brittle 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 hodrochlorio and sulphuric acids. It is strongly magnetic. There are two oxides of this metal, corresponding in properties and constitution with those of nickel. The equivalent of cobalt is 29-55 : its symbol is Co. PROTOXIDE OF COBALT, CoO. This is a grey 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 sulphate or chloride of cobalt with carbonate of soda, and washing and drying and igniting the precipitate. When the cobalt-solution is mixed with caustic potassa a beautiful blue pre cipitate falls, which when heated becomes viulet, and at length dirty red, from absorption of oxygen and a change in the state of hydration. SESQUIOXIDE OF COBALT, Co 2 3 . The sesquioxide is a black, insoluble, neutral powder, obtained by mixing solutions of cobalt and of chloride of lime. CHLORIDE OF COBALT, CoCl. The chloride is easily prepared by dissolving the oxide in hydrochloric acid ; it gives a deep rose-red solution, which, when sufficiently strong, deposits hydrated crystals of the same colour. When the liquid is evaporated by heut to a very small bulk, it deposits anhy- drous crystals which are blue ; these latter by contact with water again dissolve to a red liquid. A dilute solution of chloride of cobalt constitutes the well-known blue sympathetic ink ; characters written on paper with this liquid are invisible from their paleness of colour until the salt has been rendered anhydrous by exposure to heat, when the letters appear blue. When laid aside, moisture is absorbed, and the writing once more dis- appears. Green sympathetic ink is a mixture of the chlorides of cobalt and kiickel. 272 ZINC. Chloride of cobalt may be prepared directly from cof/alt-glancc, the native arsenide, by a process exactly similar to that described in the case of nickel. SULPHATK OF COBALT, CoO,S0 3 -f- 7HO. This salt forms deep red crystals, requiring for solution 24 parts of cold water ; they are identical in form with those of sulphate of magnesia. It combines with the sulphates of po- tassa and ammonia, forming double salts, which contain as usual six equiva- lents of water. A solution of oxalic acid added to one of sulphate of cobalt occasions, after some time, the separation of nearly the whole of the base in the state of oxalate. CARBONATE OF COBALT. The alkaline carbonates produce in solution of cobalt a pale peach-blossom coloured precipitate of combined carbonate and hydrate, containing 3(CoO,HO)4-2(CoOCO a ). The salts of cobalt have the following characters: Solution of potassa gives a blue precipitate, changing by heat to violet and red. Ammonia gives a blue precipitate, soluble with difficulty in excess, with brownish red colour. Carbonate of soda affords a pink precipitate. Carbonate of ammonia, a similar compound, soluble in excess. Ferrocyanide of potassium gives a greyish-green precipitate. Cyanide of potassium affords a yellowish-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. Sulphuretted hydrogen produces no change, if the cobalt be in combination with a strong acid. Sulphide of ammonium throws down black sulphide of cobalt. Oxide of cobalt is remarkable for the magnificent blue colour 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 sub- stance called smalt, used as a pigment, consists of glass coloured by oxide of cobalt ; it is thus made : The cobalt ore is roasted until nearly free from arsenic, and then fused with a mixture of carbonate of potassa 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 arsenide ; this is the speiss of which mention has already been made. The glass, when com- plete, is removed and poured into cold water ; it is afterwards ground to powder and elutriated. Cobalt-ultramarine is a fine blue colour prepared by mixing 16 parts of freshly precipitated alumina with 2' parts of phosphate or arsenate of cobalt : this mixture is dried and slowly heated to redness. Ey daylight the colour is pure blue, but by artificial light it is violet. Zaffer is the roasted cobalt ore mixed with a quantity of siliceous sand, 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 colour to glass. ZINC. Zinc is a somewhat abundant metal ; it is found in the state of carbonate and sulphide associated with lead ores in many districts, both in Britain and ZINC. 273 on the Continent ; large supplies are obtained from Silesia. The native car- bonate, 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, mixed with fragments of coke or charcoal, and then distilled at a full red-heat in a large earthen retort ; carbonic oxide escapes, while the reduced metal volatilizes and is condensed by suitable means, generally with minute quantities of arsenic. 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 250 (121C) and 300 (149C) it is, on the contrary, malleable, and may be rolled or hammered without danger of fracture, and, what is very remarkable, after such treat- ment, retains it malleability when cold : the sheet-zinc of commerce is thus made. At 400 (204 -4C) it is so brittle that it may be reduced to powder. At 773 (411-6C) it melts: at a bright red-heat it boils arid volatilizes, and, if air, be admitted, burns with a splendid green light, generating the oxide. Dilute acids dissolve zinc very readily ; it is constantly employed in this manner in preparing hydrogen gas. The equivalent of zinc has been fixed at 32 G ; its symbol is Zn. PROTOXIDE OF ZINC, ZnO. Only one oxide of this metal is known to exist; it is a strong base, isomorphous with magnesia; it is prepared either by burning zinc in atmospheric air, or by heating to redness the carbonate. Oxide of zinc is a white tasteless powder, insoluble in water, but freely dis- solved by acids. When heated it is yellow, but turns white again on cooling. SULPHATE OF ZINC ; WHITE VITRIOL; ZnO, S0 3 -(-7HO. This salt is hardly to be distinguished by the eye from the sulphate of magnesia ; it is pre- pared by dissolving the metal in dilute sulphuric acid, or, more economically, by roasting the native sulphide, or blende, which by absorption of oxygen becomes in great part converted into sulphate of the oxide. The altered mineral is thrown hot into water, and the salt obtained by evaporating the clear solution. Sulphate of zinc has an astringent metallic taste, and is used in medicine as an emetic. The crystals dissolve in 1\ parts of cold, and in a much smaller quantity of hot water. Crystals containing 6 equiva- lents of water have been observed. Sulphate of zinc forms double salts with the sulphates of potassa and ammonia. CARBONATE OF ZINC, ZnO,C0 2 . The neutral carbonate 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 3'ields pure oxide of zinc. CHLORIDE OF ZINC, ZnCl. The chloride 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 chloride of zinc is sometimes used as a bath for obtaining a graduated heat above 212 (100C). Chloride of zinc unites with sal-ammoniac and chloride of potas- sium to double salts ; the former of these, made by dissolving an equivalent of zinc in the requisite quantity of hydrochloric acid, and then adding an equivalent of sal-ammoniac, is very useful in tinning and soft-soldering copper and iron. A salt of zinc is easily distinguished by appropriate reagents. Caustic potassa and soda give a white precipitate of hydrate, freely soluble in excess of alkali. Ammonia behaves in the same manner ; an excess re dissolves the precipi late instantly. 274 CADMIUM BISMUTH. The carbonates of potassa and soda give white precipitates, insoluble in excess. Carbonate of ammonia gives also a white precipitate, which is re-dissolved by an excess. Ferrocyanide of potassium gives a white precipitate. Sulphuretted hydrogen causes no change. 1 Sulphide of ammonium throws down white sulphide of zinc. The applications of metallic zinc to the purposes of roofing, the construc- tion of water-channels, &c., are well known; it is sufficiently durable, but inferior in this respect to copper. This metal was discovered in 1817 by Stronger; it accompanies the ores of zinc, and, being more volatile than that substance, rises first in vapour when the calamine is subjected to distillation with charcoal. Cadmium resembles tin in colour, but is somewhat harder ; it is very malleable, has a density of 8-7. melts below 500 (260C), and is nearly as volatile as mer- cury. 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 equivalent of cadmium is 56 ; its symbol is Cd. PROTOXIDE OF CADMIUM, CdO. The oxide may be prepared by igniting either the carbonate or the nitrate ; in the former case it has a pale brown colour, and in the latter a much darker tint and a crystalline aspect. Oxide of cadmium is infusible ; it dissolves in acids, producing a series of colourless salts. SULPHATE OF CADMIUM, CdO,S0 3 -[-4HO. This is easily obtained by dis- solving the oxide or carbonate in dilute sulphuric acid ; it is very soluble in water, and forms double salts with the sulphates of potassa and of ammonia, which contain CdO,S0 8 -f KO,S0 5 +6HO, and CdO,S0 3 4 NH 4 0,S0 3 -f6HO. CHLORIDE OF CADMIUM, CdCl. This is a very soluble salt, crystallizing in small four-sided prisms. SULPHIDE OF CADMIUM is a very characteristic compound, of a bright yellow colour, fusible at a high temperature. It is obtained by passing sulphuretted hydrogen gas through a solution of the sulphate, nitrate, or chloride. The salts of cadmium are thus distinguished : Fixed caustic alkalis give a white precipitate of hydrated oxide, insoluble in excess. Ammonia gives a similar white precipitate, readily soluble in excess. The alkaline carbonates, arid carbonate of ammonia, throw down white carbonate of cadmium, insoluble in excess of either precipitant. Sulphuretted hydrogen and sulphide of ammonium precipitate the yellow sulphide of cadmium. BISMUTH. Bismuth is found chiefly in the metallic state, disseminated through an earthy matrix, from which it is separated by simple exposure to heat. The metal is highly crystalline and very brittle; it has a reddish- white colour, and a density of 9-9. Cubic crystals of great beauty may be obtained by : With neutral solutions, or zinc-salts of an organic acid, a white precipitate ensues. BISMUTH. 275 slowly cooling a considerable mass of this substance until solidification has commenced, and then piercing the crust, and pouring out the fluid residue. Bismuth melts at about 500 (2GOC), and volatilizes at a high temperature : it is little oxidized by the air, but burns when strongly heated with a bluish flame. Nitric acid, somewhat diluted, dissolves it freely. The equivalent of bismuth is 213, its symbol is Bi. TEROXIDE OF BISMUTH, Bi0 3 . This is the base of all the salts. It is a straw-yellow powder, obtained 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. BISMUTHIC ACID, Bi0 5 . If teroxide of bismuth be suspended in a strong solution of potassa, and chlorine be passed through this liquid, decomposition of water ensues ; hydrochloric acid being formed and the teroxide converted into the pentoxide. To separate any teroxide which may have escaped oxi- dation, the powder is treated with dilute nitric acid, when the bismuthic acid is left as a reddish powder, which is insoluble in water. This substance combines with bases, but the compounds are not very well known. When heated it loses oxygen, an intermediate oxide Bi0 4 being formed, which may be considered as bismuthate of bismuth, 2Bi0 4 =Bi0 3 ,Bi0 5 . NITRATE OF BISMUTH, Bi0 3 ,N0 5 -f-9HO. When bismuth is dissolved in moderately strong nitric acid to saturation, and the whole left to cool, large, colourless, transparent crystals of the neutral nitrate are deposited. Water decomposes these crystals; and an acid solution containing a little bismuth is obtained, and a brilliant white crystalline powder is left, which varies to a certain extent in composition according to the temperature and the quan- tity of water employed, but which frequently consists of a basic nitrate of the teroxide Bi0 3 ,3N0 5 -f-2IIO. A solution of nitrate of bismuth, 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 larger proportion of teroxide of bismuth. This remarkable decomposition illustrates at once the basic property of water, and the feeble affinity of teroxide of bismuth for acids, the nitric acid dividing itself between the two bases. The decomposition of a neutral salt by water is by no means an uncommon occurrence in the history of the metals ; a solution of terchlo- ride of antimony exhibits the same phenomenon; certain salts of mercury are aft'ected in a similar manner, and other cases might perhaps be cited, less conspicuous, where the same change takes place to a smaller extent. The basic nitrate of teroxide of bismuth was once extensively employed as a cosmetic, but is said to injure the skin, rendering it yellow and leather-like. It has been used in medicine. The other salts of bismuth possess few points of interest. Bismuth is sufficiently characterized by the decomposition of the nitrate by water, and by the blackening the nitrate undergoes when exposed to the action of sulphuretted hydrogen gas. A mixture of 8 parts of bismuth, 5 parts of lead, and 3 of tin, is known tinder the name of fusible metal, and is employed in taking impressions from dies and for other purposes; it melts below 212 (100C). The discrepan- cies so frequently observed between the properties of alloys and those of their constituent metals, plainly show that such substances must be looked upon as true chemical compounds, and not as mere mixtures ; in the present case the proof is complete, for the fusible metal has lately been obtained in crystals. 276 URANIUM. URANIUM. This metal is found in a few minerals, as pitchblende and uranite, of which the former is the most abundant. It appears from the recent interesting re- searches of M. Peligot, that the substance hitherto taken for metallic ura- nium, obtained by the action of hydrogen gas upon the black oxide, is no* in reality the metal, but a protoxide, capable of uniting directly with acids, and, like the protoxide of manganese, not decomposable by hydrogen at a red-heat. The metal itself can be obtained only by the intervention of po tassium, applied in the same manner as in the preparation of magnesium. It is described as a black coherent powder, or a white malleable metal, ac- cording to the state of aggregation, not oxidized by air or water, but emi- nently combustible when exposed to heat. It unites also with great violence with chlorine and with sulphur. M. Peligot admits three distinct oxides of uranium, besides two other compounds of the metal and oxygen, which he designates as suboxides. The equivalent of uranium is 60. Its symbol is U. PROTOXIDE OF URANIUM, UO. This is the ancient metal ; it is prepared Vy several processes, one of which has been already mentioned. It is a brown powder, sometimes highly crystalline. When in minute division it is pyrophoric, taking fire in the air, and burning to black oxide. It forms with acids a series of green salts. A corresponding chloride exists, which forms dark green octahedral crystals, highly deliquescent and soluble in water. M. Peligot attributes a very extraordinary double function to this substance, namely, that of acting as a protoxide and forming salts with acids, and that of combining with chlorine or oxygen after the fashion of an elementary body. PROTOSESQUIOXIDE OF URANIUM; BLACK OXIDE; U 4 5 , or 2UO-f-U 2 3 . The black oxide, formerly considered as protoxide, is produced when both protoxide and sesquioxide are strongly heated in the air, the former gaining, and the latter losing, a certain quantity of oxygen. It forms no salts, but is resolved by solution in acids into protoxide and sesquioxide. SESQUIOXIDE OF URANIUM, U 2 3 . The sesquioxide is the best known and most important of the three ; it forms a number of extremely beautiful yel- low salts. When caustic alkali is added to a solution of nitrate of sesqui- oxide of uranium, a yellow precipitate of hydrated oxide falls, which, re- tains, however, a portion of the precipitant. The hydrate cannot be exposed to a heat sufficient to expel the water without a commencement of decompo- sition. A better method of obtaining the sesquioxide is to heat by means of an oil-bath the powdered and dried crystals of the nitrate to 480 (249C), until no more nitrous fumes are disengaged. Its colour in this state is chamois-yellow. NITRATE OF SESQUIOXIDE OF URANIUM, U 2 3 ,N0 5 -f 6HO ; or (U 2 2 ) 0, N0 5 -}-6HO; U 2 2 being the supposed quasi-metal. This nitrate is the starting point in the preparation of all the compounds of uranium ; it may be pre- pared from pitchblende by dissolving the pulverized mineral in nitric acid, evaporating to dryness, adding water and filtering ; the liquid furnishes, by due evaporation, crystals of nitrate of uranium, which are purified by a repetition of the process, and, lastly, dissolved in ether. This latter solu- tion yields the pure nitrate. The green salts of uranium are peroxidized by boiling with nitric acid. A yellow precipitate with caustic alkalis, convertible by heat into black oxide; a brown precipitate with sulphide of ammonium; and none at all with pult)huietted hydrogen gas, sufficiently characterize the salts of sesqui- COPPER. 277 oxide of uranium. A solution suspected to contain protoxide may be boiled with a little nitric acid, and then examined. The only application of uranium is that to enamel-painting and the stain- ing of glass ; the protoxide giving a fine black colour, and the sesquioxide a delicate yellow. COPPER. Copper is a metal of great value in the arts of life ; it sometimes occur in the metallic state, crystallized in octahedrons, but is more abundant h the condition of red oxide, and in that of sulphide combined with sulphide of iron, or yellow copper ore. Large quantities of the latter substance are annually obtained from the Cornish mines and taken to South Wales for re- duction, which is effected by a somewhat complex process. The principle of this may, however, be easily made intelligible. The ore is roasted in a reverberatory furnace, by which much of the sulphide of iron is converted into oxide, while the sulphide of copper remains unaltered. The product of this operation is then strongly heated with siliceous sand ; the latter combines with the oxide of iron to a fusible slag, and separates from the heavier copper-compound. When the iron has, by a repetition of these pro- cesses been got rid of, the sulphide of copper 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 car- bonaceous 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 remaining 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. Copper has a well-known yellowish-red colour, 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 red-heat, and seems to be a little volatile at a very high temperature. Copper undergoes no change in dry air; exposed to a moist atmosphere, it becomes covered with a strongly adherent 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 acid ; nitric acid, even dilute, dissolves it readily with evolution of binoxide of nitrogen. Two oxides are known which form salts ; a third, or peroxide, is said to exist. The equivalent of copper is 31-7; its symbol Cu. PROTOXIDE OF COPPER ; BLACK OXIDE ; CuO. This is the base of the ordinary blue and green salts. It is prepared by calcining metallic copper at a red-heat, with full exposure to air, or, more conveniently, by heating to redness the nitrate, which suffers complete decomposition. When a salt of this oxide is mixed with caustic alkali in excess, a bulky pale blue precipi- tate of hydrated oxide falls, which, when the whole is raised to the boiling- point, becomes converted into a heavy dark brown powder; this also is an- hydrous 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. Protoxide of copper is soluble in acids, and forms a, series of very important salts, being isomorphous with magnesia. . SUBOXIDE OP COPPER; RED OXIDE; Cu 2 0. The suboxide 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 sul- phate of copper, and then putting in an excess of caustic potassa ; the blue solution, heated to ebullition, is reduced by the sugar and deposits suboxide 278 COPPER. It often occurs m beautifully transparent ruby-red crystals, associated with other ores of copper, and can be obtained in this state by artificial means. This substance forms colourless salts -with acids, -which are exceedingly instable, and tend to absorb oxygen. The suboxide communicates to glass a magnificent red tint, while that given by the protoxide is green. SULPHATE OF COPPER; BLUE VITRIOL; CuO,S0 3 -f-^HO. This beautiful salt is prepared by dissolving oxide of copper in sulphuric acid, or, at less expense, by oxidizing the sulphide. It forms large blue crystals, soluble in 4 parts of cold and 2 of boiling water ; by heat it is rendered anhydrous and nearly white, and a very high, temperature decomposed. Sulphate of copper combines with the sulphates of potassa and of ammonia, forming pale blue salts which contain 6 equivalents of water, and also with ammonia, gene rating a remarkable compound of deep blue colour, capable of crystallizing. NITRATE OF COPPER, CuO,N0 5 -f- 8HO. The nitrate 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 subnitrate is known ; it is green. Nitrate of copper also combines with ammonia. CARBONATES OF COPPER. When carbonate of soda is added in excess to a solution of sulphate of copper, the precipitate is at first pale blue and flocculent, but by warming it becomes sandy, and assumes a green tint ; in this state it contains CuO,C0 2 -f-CuO,HO-J-HO. This substance is prepared as a pigment. The beautiful mineral malachite has a similar composition, but contains one equivalent of water less. Another natural compound, not yet artificially imitated, occurs in large transparent crystals of the most intense blue; it contains 2(CuO,C0 2 )-L-CuO,HO. Verdiler, made by decom- posing nitrate of copper by chalk, is said, however, to have a somewhat similar composition. CHLORIDE OF COPPER, CuCl-(-2HO. The chloride is most easily prepared by dissolving the black oxide in hydrochloric acid, and concentrating the green solution thence resulting. It forms green crystals, very soluble in water and in alcohol; it colours 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 becomes con- verted into the subchloride. The latter is a white fusible substance, but little soluble in water, and prone to oxidation; it is formed when copper- filings or copper-leaf are put into chlorine gas. ARSENITE OF COPPER ; SCHEELE'S GREEN. This is prepared by mixing solutions of sulphate of copper and arsenite of potassa ; it falls as a bright green insoluble powder. The characters of the protosalts of copper are well marked. Caustic of potassa gives a pale blue precipitate of hydrate, becoming blackish-brown anhydrous protoxide on boiling. Ammonia also throws down the hydrate ; but, when in excess, re-dissolves it, yielding an intense purplish blue solution. Carbonates of potassa and soda give pale blue precipitates, insoluble in excess. Carbonate of ammonia, the same, but soluble with deep blue colour. Ferrocyanide of potassium gives a fine red-brown precipitate of ferrocya- nide of copper. Sulphuretted hydrogen and sulphide of ammonium afford black sulphide of copper. The alloys of copper are of great importance. Brass consists of copper alloyed with from 28 to 34 per cent, of zinc; the latter. may be added di- LEAD. 279 irectly to tlie melted copper, or granulated copper may be heated with cala- minc and charcoal-powder, as in the old process. Gun-metal, a most trustvv oi'tliy and 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 parts tin, 6 parts zinc, and 1 part lead. The brass of the ancients is an alloy of copper with tin. This abundant and useful metal is altogether obtained from the native sul- phide, or galena, no other lead-ore being found in quantity. The reduction is effected in a reverberatory furnace, into which the crushed lead ore is intro- duced 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 temperature raised, when the sulphate and sulphide react upon each other, producing sulphurous acid and metallic lead. 1 Lead is a soft bluish metal, possessing very little elasticity; its specific gravity is 11-45. It may be easily rolled out into plates, or drawn into coarse wire, but has a very trifling degree of strength. Lead melts at 600 (315 -5C) or a little above, and at a white-heat boils and volatilizes. By slow cooling it may be obtained in octahedral crystals. In moist air this metal becomes coated with a film of grey matter, thought to be suboxide, and when exposed to the atmosphere in a melted state it rapidly absorbs oxygen. Dilute acids, with the exception of nitric, act but slowly upon lead. Chemists are fami- liar with four oxides of lead, only one of which possesses basic properties. The equivalent of lead is 103-7 ; its symbol is Pb. PROTOXIDE; LITHARGE: MASSICOT; PbO. This 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 protoxide which has undergone fusion. Protoxide of lead has a delicate straw-yellow colour, is very heavy, and slightly soluble in water, giving an alkaline liquid. At a red-heat it melts, and tends to crystallize on cooling. In a melted state it attacks and dissolves siliceous matter with astonishing facility, often pene- trating an earthen crucible in a few minutes. It is easily reduced when heated with organic substances of any kind containing carbon or hydrogen. Protoxide of lead forms a large class of salts, which are colourless if the acid itself be not coloured. RED OXIDE; RED-LEAD; Pb 3 4 , or 2PbO+Pb0 2 . The composition of this substance is not very constant ; it is prepared by exposing for a long time to the air, at a very faint red-heat, protoxide of lead which has not been fused ; it is a brilliant red and extremely heavy powder, decomposed with evolution of oxygen by a strong heat, and converted into a mixture of pro- toxide and binoxide by acids. It is used as a cheap substitute for vermilion. BlNOXIDE OF LEAD ; PUCE OR. BROWN OXIDE t PbOg. This Compound is obtained without difficulty by digesting red-lead in dilute nitric acid, when nitrate of protoxide is dissolved out and insoluble binoxide left behind in the form of a deep brown powder. The binoxide is decomposed by a red-heat, yielding up one-half of its oxygen. Hydrochloric acid converts it into chlo- ride of lead with disengagement of chlorine ; hot oil of vitriol forms with it {Oxide of f Lead Free, lead { Oxygen -===- 2 Sulphurous acid. Sulphuric j Sulphur ~^ acid ( 3 Oxygen Sulphide of lead { **** 280 LEAD. sulphate of lead, and liberates oxygen. The binoxide is very useful in sepa- rating sulphurous acid from certain gaseous mixtures, sulphate of lead being then produced. SUUOXIDE OF LEAD, Pb 2 0. When oxalate of lead is heated to dull redness in a retort, a grey pulverulent substance is left, which is resolved by acids into protoxide of lead and metal. It absorbs oxygen with great rapidity when heated, and even when simply moistened with water and exposed to the air. NITRATE OF LEAD, PbO,N0 5 . The nitrate may be obtained by dissolving carbonate of lead 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 binoxide. It crystallizes in anhydrous octahedrons, which are usually milk-white and opaque ; it dissolves in 7% parts of cold water, and is decomposed by heat, yielding nitrous acid, oxygen, and pro- toxide of lead, which obstinately retains traces of nitrogen. \Vhen a solution of this salt is boiled with an additional quantity of oxide of lead, a portion of the latter is dissolved, and a basic nitrate generated, which may be had in crystals. Carbonic acid separates this excess of oxide in the form of a white compound of carbonate and hydrate of lead. Neutral and basic compounds of oxide of lead with nitrous, and the elements of hyponitric acid, have been described. These last are probably formed by the combination of a nitrite with a nitrate. CARBONATE OF LEAD; WHITE-LEAD; PbO,C0 2 . Carbonate of lead is some- times found beautifully crystallized in long white needles, accompanying other metallic ores. It may be prepared by precipitating in the cold a solu- tion of the nitrate or acetate by an alkaline carbonate ; when the lead solu- tion is boiling, the precipitate is a basic salt, containing 2(PbO,C0 2 )-j-HO, PbO ; it is also manufactured to an immense extent by other means for the use of the painter. Pure carbonate of lead 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 pow- dered litharge with the neutral salt. This solution is then brought into con- tact with carbonic acid gas ; 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 car- bonic acid, these processes being susceptible of indefinite repetition, when 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 pre- pared, 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 ar- ranged 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 decomposing bark, and in this manner a pile of many alternations is constructed. After the lapse of a con- siderable time the pile is taken down and the sheets of lead 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 vapour of vinegar raised by the high temperature of the fermenting matter merely to act as a carrier between the carbonic acid evolved from the tan LEAD 281 and the oxide of lead formed under the influence of the acid vapour; a neu- tral acetate, a basic acetate, and a carbonate being produced in succession, the action gradually travelling from the surface inwards. The quantity of acetic acid used is, in relation to the lead, quite trifling, 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. When clean metallic lead is put into pure water and exposed to the atmo- sphere, a white, crystalline, scaly powder begins to show itself in a few hours, and very rapidly increases in quantity. This substance may consist of hydrated protoxide of lead, formed by the action of the oxygen dissolved in the water and from 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 very insoluble in water. When common river or spring "water is substituted for the pure liquid, this effect is less observable, the little sulphate, almost invariably present, causing the deposition of a very thin but closely adherent film of sulphate of lead upon the surface of the metal, which protects it from farther 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 contaminated with lead, and the cistern 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 containing car- bonic acid. CHLORIDE OF LEAD, PbCl. This salt is prepared by mixing strong solu- tions of acetate of lead and chloride of sodium ; or by dissolving litharge in boiling dilute hydrochloric acid, and setting aside the filtered solution to cool. Chloride of lead crystallizes in brilliant, colourless needles, which require 135 parts of cold water for solution. It is anhydrous ; it melts when, heated, and solidifies on cooling to a horn-like substance. IODIDE OF LEAD, Pbl. The iodide of lead separates as a brilliant yellow precipitate Avhen a soluble salt of lead is mixed with iodide of potassium. This compound dissolves in boiling water, yielding a colourless solution, which deposits the iodide on cooling in splendid golden-yellow scales. The soluble salts of lead thus behave with reagents : Caustic potassa and soda precipitate a white hydrate, freely soluble in excess. Ammonia gives a similar white precipitate, not soluble in excess. The carbonates of potassa, soda, and ammonia, precipitate carbonate of lead, insoluble in excess. Sulphuric acid or a sulphate causes a white precipitate of sulphate of lead, insoluble in nitric acid. Sulphuretted hydrogen and sulphide of ammonium throw down black sulphide of lead. An alloy of 2 parts of lead and 1 of tin constitutes plumber's 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. 1 Ammonia gives no immediate precipitate with the acetate. 24* 282 TIN. SECTION V. OXIDABLE METALS PROPER, WHOSE OXIDES FORM WEAK BASES OR ACIDS. THIS valuable metal occurs in the state of oxide, and more rarely as sul- phide ; the principal tin mines are those of the Erzgebirge in Saxony and Bohemia, Malacca, and more especially Cornwall. In Cornwall the tin-stone is found as a constituent 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 second stream-tin. Oxide of tin 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 cast into large blocks, which, after being assayed, receive the stamp of the Duchy. 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 colour, approaching to 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 442 (227-77C). 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 easily attacked and dissolved by hydrochloric acid, with evolution of hydrogen ; nitric acid acts with great energy, converting it into a white hydrate of the binoxide. There are two well-marked oxides of tin, which act as feeble bases or acids, according to circumstances, and a third, which has been less studied. The equivalent of tin is 58 ; its symbol is Sn. PROTOXIDE OF TIN, SnO. When solution of protochloride of tin is mixed with carbonate of potassa, a white hydrate of the protoxide falls, the car- bonic acid being at the same time extricated. When this is carefully washed, dried, and heated in an atmosphere of carbonic acid, it loses water, and changes to a dense black powder, which is permanent in the air, but takes fire on the approach of a red-hot body, and burns like tinder, producing binoxide. The hydrate is freely soluble in caustic potassa; the solution decomposes by keeping into metallic tin and binoxide. SESQUIOXIDE OF TIN, Sn 2 3 . The sesquioxide is produced by the action of hydrated sesquioxide of iron upon protochloride of tin ; it is a greyish, Blimy substance, soluble in hydrochloric acid, and in ammonia. This oxide has been but little examined. BINOXIDE OF TIN, Sn0 2 . This substance is obtained in two different states, having properties altogether dissimilar. When bichloride of tin is precipi- tated by an alkali, a white bulky hydrate appears, which is freely soluble in TIN. 282 acids. If, on the other hand, the bichloride be boiled with excess of nitric acid, or if that acid be made to act directly on metallic tin, a white sub- stance is produced, which refuses altogether to dissolve in acids, and pos- sesses properties differing in other respects from those of the first modifica- tion. Both these varieties of binoxide of tin have the same composition, and when ignited, leave the pure binoxide of a pale lemon-yellow tint. Both dissolve in caustic alkali, and are precipitated with unchanged proper- ties by an acid. The two hydrates redden litmus-paper. 1 PROTOCHLORIDE OF TIN, SnCl. The protochloride is easily made by dis- solving metallic tin in hot hydrochloric acid. It crystallizes in needles con- taining 2 equivalents of water, 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. The anhydrous chloride may be obtained by distilling a mixture of calomel and powdered tin, prepared by agitating the melted metal in a wooden box until it solidifies. The chlo- ride is a grey, resinous-looking substance, fusible below redness, and volatile at a high temperature. Solution of protochloride of tin is employed as a deoxidizing agent ; it reduces the salts of mercury and other metals of the same class. BICHLORIDE or PERCHLORIDE OF TIN, SnCl 2 . This is an old and very cu- rious compound, formerly called fuming liquor of Libavius. It is made by exposing metallic tin to the action of chlorine, or, more conveniently, by distilling a mixture of 1 part of powdered tin, and 5 parts of corrosive sub- limate. The bichloride is a thin, colourless, mobile liquid ; it boils at 248 (120C), and yields a colourless invisible vapour. It fumes in the air, and when mixed with a third part of water, solidifies to a crystalline mass. The solution of bichloride is much employed by the dyer as a mordant; it is com- monly prepared by dissolving metallic tin in a mixture of hydrochloric and nitric acids, care being taken to avoid too great elevation of temperature. SULPHIDES OF TIN. Protosulphide, SnS, is prepared by fusing tin with ex- cess of sulphur, and strongly heating the product. It is a lead-grey, brittle substance, fusible by a red-heat, and soluble with evolution of sulphuretted 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 yel- lowish-grey, and easily decomposed by heat. Bisulphide, 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 protochloride of tin sublime, while the bisulphide remains at the bottom of the vessel in the form of brilliant gold-coloured scales ; it is used as a substitute for gold-powder. Salts of tin are thus distinguished : Protoxide. Caustic alkalis ; white hydrate, soluble in excess. Ammonia; carbonates of potassa, 1 , TT ,.. , , , . , ,, soda, and ammonia ..... .. ........ l^ hlte h y drate ' nearl y msoluble lu J excess. Binoxide. Caustic alkalis ; white hydrate, soluble in excess. Ammonia ; white hydrate, slightly soluble in excess. 1 Fremy lias called the first of these oxides stannic acid SnOa. The second he has na'ned nactastannic acid Sn 6 0io. S 5C) ; the product has a dark red colour and is highly crystalline ; it is the re.d precipitate of the old writers. (2) By cautiously heating any of the nitrates of either oxide to complete decomposition, when the acid is decomposed and expelled, oxidizing the metal to a maximum, if it happen to be in the con- dition of a suboxide. The product is in this case also crystalline and very dense, but has a much paler colour than the preceding ; while hot it is nearly black. It is by this method that the oxide is generally prepared ; it is apt to contain undecomposed nitrate, which may be discovered by strongly lioating a portion in a test-tube : if red fumes are produced or the odour of nitrous acid exhaled, the oxide has been insufficiently heated in the process of manufacture. (3) By adding caustic potassa in excess to a solution of corrosive sublimate, by which a bright yellow precipitate of oxide is thrown down, which only differs from the foregoing preparations in being destitute of crystalline texture and much more minutely divided. 3 It must be well washed and dried. Red oxide of mercury is slightly soluble in water, communicating to the latter an alkaline reaction and metallic taste ; it is highly poisonous. When htrongly heated, it is decomposed, as before observed, into metallic mercury and oxygen gas. NITRATES OF THE OXIDES OF MERCURY. Nitric acid varies in its action upon mercury, according to the temperature. When cold and somewhat diluted, only salts of the grey oxide are formed, and these are neutral or 1 By referring to cyanogen, it will be perceived that when the equivalent of mercury is considered to be 100, the constitution of the cyanide of mercury is analogous to the other metallic cyanides, but when taken at 200, it Lecomes a bicyanide, and then differs from all others. R. B. * This precipitate is considered by Shauflfner to be a hydrate, HgO,3IIO, for by exposure tr> the temperature of 392, it loses water amounting to over 20 per cent, of its weight. 11. B. MERCURY, OR QUICKSILVER. 303 basic (i. e. with excess of oxide), 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 salt of the red oxide produced. Both classes of salts are apt to be decomposed by a large quantity of water, giving rise to insoluble, or sparingly soluble, compounds containing an excess of base. Neutral nitrate of the suboxide, Hg 2 0,N0 5 -f-2HO, forms large colourless 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, after some time, deposited, containing 3Hg 2 0,2N0 5 -j-3HO ; this is also decomposed by water. The two salts are easily distinguished when rubbed in a mortar with a little chloride of sodium ; the neutral compound gives nitrate of soda and calomel ; the basic salt, nitrate of soda and a black compound of calomel with oxide of mercury. A black substance, called Hahnemanri's soluble mercury, is produced when ammonia in small quantity is dropped into a solution of the nitrate of the suboxide ; it contains 3Hg 2 0, N0 5 -}-NH 3 , or, according to Sir R. Kane, 2HgO,N0 5 -f-NH 3 ; the composition of this preparation evidently varies according to the temperature and the concentration of the solutions. Nitrates of the Protoxide (Red Oxide) of Mercury. By dissolving red oxide of mercury in excess of nitric acid and evaporating gently, a syrupy liquid is obtained, which, enclosed in a bell-jar over lime or sulphuric acid, de- posits voluminous crystals and crystalline crusts. The crystals and crusts have the same composition, 2(HgO,N0 5 )-j-HO. The same substance is de- posited from the syrupy liquid as a crystalline powder by dropping it into concentrated nitric acid. The syrupy liquid itself appears to be a definite compound containing HgO,N0 5 -j-2HO. By saturating hot dilute nitric acid with the red oxide, a salt is obtained on cooling which crystallizes in needles, permanent in the air, containing 2HgO,N0 5 -f- HO. The preceding crystal- lized salts are decomposed by water, with production of compounds more and more basic as the washing is prolonged or the temperature of the water raised. The nitrates of the protoxide of mercury combine with ammonia. Sulphate of the Suboxide of Mercury, Hg 2 0,S0 3 , falls as a white crystalline powder when sulphuric acid is added to a solution of the nitrate of the sub- oxide : it is but slightly soluble in water. Sulphate of the protoxide, HgO, S0 3 , is readily prepared by boiling together oil of vitriol and metallic mer- cury until the latter is wholly converted into a heavy white crystalline pow- der, 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 employed. Water decomposes the sulphate, dissolving out an acid salt and leaving an insoluble, yellow, basic compound, formerly called turpeth or turbith mineral, containing, according to Kane's analysis. 3IIgO,S0 3 . Long-continued washing with hot water entirely removes the remaining acid, and leaving pure protoxide of mercury. SUBCHLORIDE OF MERCURY; CALOMEL; Hg 2 Cl. This very importont sub- f.tarice may be easily and well prepared by pouring a solution of the nitrate of the suboxide 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 generally pro- cured by another and more complex process. Dry sulphate of the red oxide is rubbed in a mortar with as much metallic mercury as it already contains, and a quantity of common salt, until the globules disappear, and an uniform mixture has been produced. This is subjected to sublimation, the vapour of the calomel being carried into an atmosphere of steam, or into a chamber containing air ; it i? thus condensed in a minutely-divided ^tate, and the la- 304 MERCURY, OR QUICKSILVER. borious process of pulverization of the sublimed mass avoided. The reaction is thus explained: 1 f 1 eq. mercury^ Calomel, Hg g Cl. 1 eq. sulphate I 1 eq. oxygen ^.^ of mercury j 1 eq. sul- ^ phuric acid. 1 eq. metallic mercury 1 eq. common S 1 eq. chlorine salt \ 1 eq. sodium ^* Sulphate of soda. Pure calomel is a heavy, white, insoluble, tasteless powder; it rises in vapour at a temperature below redness, and is obtained by ordinary subli- mation as a yellowish-white crystalline mass. It is as insoluble in cold di- luted nitric acid as the chloride of silver ; boiling-hot strong nitric acid oxi- dizes and dissolves it. Calomel is instantly decomposed by an alkali, or by lime-water, with production of sub-oxide. It is sometimes apt to contain a little chloride, which would be a very dangerous contamination in calomel employed for medical purposes. This is easily discovered by boiling with water, filtering the liquid, and adding caustic potassa. Any corrosive sub- limate is indicated by a yellow precipitate. PROTOCHLORIDE OF MERCURY ; CORROSIVE SUBLIMATE ; HgCl. The chlo- ride may be obtained by several different processes. (1) When metallic mercury is heated in chlorine gas, it takes fire and burns, producing this substance. (2) It may be made by dissolving the red oxide in hot hydro- chloric acid, when crystals of corrosive sublimate separate on cooling. (3) Or, more economically, by subliming a mixture of equal parts of sulphate of the red oxide of mercury and dry common salt ; and this is the plan gene- rally followed. The decomposition is thus easily explained : a {1 eq. mercury -^ Corrosive sublimate. 1 eq. oxygen 1 eq. sul- ) ^phuric acid / ,. f 1 eq. chlorine ^ ^^~-~^>^ 1 eq. common salt j l ? | god}um ^-Sulphate of soda. The sublimed protochloride forms a white, transparent, crystalline mass, of great density; it melts at 509 (265C), and boils and volatilizes at a somewhat higher temperature. It is soluble in 16 parts of cold and 3 of boiling water, and crystallizes from a hot solution in long white prisms. Al- cohol and ether also dissolves it with facility ; the latter even withdraws it from a watery solution. Chloride of mercury combines with a great number * If the grey oxide be considered as protoxide, the sulphate will be sulphate of the binox- Me. HgOa, 2SOs, and the decomposition will stand thus : , , , ( 1 eq. mercury ^ 2 eq. calomel, HgCl. leq. sulphate J 2 oxyg en v ^^^ of mercury } 2 J* sulphuric aeid/><<^ 1 eq. metallic mercury ^-^^^ 2 eq. common I 2 eq. chlorine ^ ^^Sw gilt I 2 eq. sodium -^> 2 eq. sulphate of soda. Or on the other supposition : 1 ea sulphate of f l eq - mercur y ^ Bichloride of mercury. - 1 eq. suipnaie or j 2 eq oxygen mcrcury (2^. sulphuric acid . . ,. f 2 eq. chlorine -<^ \ '^^^ 2 %* common salt j 2 godium _^=^ 2 eq. sulphate of soda. MERCURY, OR QUICKSILVER. 305 of other metallic chlorides, forming a series of beautiful double salts, of which the ancient sal alembroth may be taken as a good example : it contains HgCl-f- NII 4 Cl-f- HO. Corrosive sublimate absorbs ammoniacal gas with grea* avidity, generating a compound supposed to contain 2IgCl-j-NH 8 . When excess of ammonia is added to a solution of corrosive sublimate, p white insoluble substance is thrown down, long known under the name of white, pre ipitate. Sir P^obert Kane, who has devoted much attention to the salts of mercury, represents this white precipitate as a double amide and chloride of mercury, or HgCl-f-HgNH 2 , 2 equivalents of chloride of mercury and 1 of ammonia, yielding 1 equivalent of the new body and 1 of hydro- chloric acid. A corresponding black compound, Hg 2 Cl-J- HgNH" 2 , is produced when ammonia is digested with calomel, which must be carefully distin- guished from the suboxide. Several compounds of protochloride of mercury with protoxide of mercury also exist. These are produced by several processes, as when an alkaline carbonate or bicarbonate is added in varying proportions to a solution of corrosive sublimate. They differ greatly in colour and physical character, and are mostly decomposed by water. Corrosive sublimate forms insoluble compounds with many of the azotized organic principles, as albumin, &c. It is perhaps to this property that its great antiseptic virtues are due. Animal and vegetable substances are pre- served by it from decay, as in Mr. Kyan's method of preserving timber and cordage. Albumin is on this account an excellent antidote to corrosive sub- limate in cases of poisoning. SUBIODIDE OF MERCURY, Hg 2 T. ^he subiodide is formed when a solution of iodide of potassium is added to nit-rate of the suboxide of mercury ; it separates as a dirty yellow, insoluble precipitate, with a cast of green. It may be prepared by rubbing together in a mortar mercury and iodine in the proportion of 2 equivalents of the former to 1 of the latter, the mixture being Moistened from time to time with a little alcohol. PROTIODIDE OF MERCURY, Hgl. When solution of iodide of potassium is mixed with protochloride of mercury, a precipitate falls, which is at first yellow, but in a few moments changes to a most brilliant scarlet, which colour is retained on drying. This is the neutral iodide ; it may be made, although of rather duller tint, by triturating single equivalents of iodine and mercury with a little alcohol. When prepared 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 iodide of potassium. The iodide of mercury exhibits a very remarkable case of dimorphism, attended with difference of colour, the latter being red or yellow, according to the figure assumed. Thus, when the iodide is suddenly exposed to a high temperature, it becomes bright yellow throughout, and yields a copious sublimate 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 spontaneously after a certain lapse of time. On the other hand, by a very slow and careful heat- ing, 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. 1 SUBSULPHIDE OF MERCURY, PIg 2 S. The black precipitate thrown down from a solution of the nitrate of suboxide of mercury by sulphuretted hydro- gen, is a subsulphide ; it is decomposed by heat into metallic mercury and neutral sulphide. 1 Memoirs of Chemical Society of London, !. 85. 2G * 306 MERCURY, OR QUICKSILVER. SULPHIDE OF MERCURY ; ARTIFICIAL CINNABAR ; VERMILION ; HgS. Sul- phuretted hydrogen gas causes a precipitate of a white colour when passed in small quantity into a solution of corrosive sublimate or nitrate of the red oxide ; this is a combination of sulphide with the salt itself. An excess of the gas converts the whole into sulphide, the colour at the same time chang- ing to black. When this black sulphide is sublimed, it becomes dark red and crystalline, but undergoes no change of composition; it is then cinnabar. The sulphide is most easily prepared by subliming an intimate mixture of 6 parts of mercury and 1 of sulphur, and reducing to a very fine powder the resulting cinnabar, the beauty of the tint depending much upon the extent to which division is carried. The red or crystalline sulphide may also be formed directly, without sublimation, by heating the black precipitated sub- stance in a solution of pentasulphide of potassium; the sulphide of mercury 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 acid ; it resists the action both of caustic alkali in solution, and of strong mineral acids, even nitric, and is only attacked by aqua regia. When protoxide of mercury is put into a large excess of pure caustic ammonia, a compound is obtained, the colour of which varies with the statw of the oxide. If the latter be amorphous, it is pale yellow; if crystalline, then the action of the ammonia is much less energetic, and the product darker in colour. This substance possesses very extraordinary properties, those, namely, of* a most powerful base, and probably belongs to the same class as the compound bases containing platinum, described under that metal. The body in question bears a temperature of 260 (126 -5C), with- out decomposition, becoming brown and anhydrous by the loss of 3 equiva- lents of water. In this state it contains NH 3 Hg 4 3 =NH 2 Hg 2 0-f2Hg() or NHg 4 0-}-2HO. It is insoluble in water, alcohol, and ammonia; cold solu- tion of potassa has no action on the hydrate, but at a boiling heat some ammonia is disengaged. The anhydrous base is only acted on by hydrate of potassa in fusion. It combines directly and energetically with acids, form- ing well-defined compounds ; it absorbs carbonic acid with avidity from the air, like baryta or lime. It even decomposes ammoniacal salts by boiling, expelling the ammonia and combining with the acid. 1 The salts of mercury are all 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 carbonate of soda. The metal is precipitated from its soluble combinations by a plate of copper, and also by a solution of protochloride of tin, used in excess. The behaviour of the protochloride and soluble salts of the red oxide with austic potassa and ammonia is also highly characteristic. 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, where light and heat are produced ; besides this, many of the amalgams crystallize after a while, becoming solid. The amalgam of 1 Ann. Cbim. ct Phys. 3d serie xviii. 333. PLATINUM. 307 tin used in silvering looking-glasses, and that of silver sometimes employed for stopping hollow teeth, are examples. PLATINUM. Platinum, palladium, rhodium, indium, ruthenium, and osmium, form a small 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 Ceylon, and in a few other places. It has never been seen in the rook, which, however, is judged, from the accompanying minerals, 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-hydrochloric acid, con- taining 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 yel- lowish-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- monio-chloride. This substance is washed with a little cold water, dried and heated to redness ; metallic platinum in spongy state is left. Although this metal cannot be fused into a compact mass by any furnace-heat, yet the same object may be accomplished by taking advantage of its property of welding, like iron, at a very 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 ham- mered, or subjected to powerful pressure by suitable means. If this opera- tion has been properly conducted, the platinum will now be in a state to bear forging into a bar, which can afterwards be rolled into plates, or drawn into wire, at pleasure. Platinum is in point of colour 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. It is the (except Iridium) heaviest sub- stance 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 high value in the construction of chemical vessels. It is dissolved by aqua regia, and superficially oxidized by fused hydrate of potassa, 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, where the division is pushed much farther. It is easily prepared by boiling a solution of bichloride of platinum to which an excess of carbonate of soda and a quan- tity of sugar have been added, until the precipitate formed after a little time becomes perfectly black, and the supernatant liquid colourless. The black powder is collected on a filter, washed, and dried by gentle heat. This sub- stance appears to possess the property of condensing 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 on 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 508 PLATINUM. loses these peculiarities, which, are no doubt the result of its excessively com- minuted state. Platinum forms two compounds with oxygen, chlorine, &c. The equivalent of platinum is 98-7. l Its symbol is Pt. PROTOXIDE OF PLATINUM, PtO. When protochloride of platinum is di- gested with caustic potassa, a black powder, soluble in excess of alkali, is pro- duced : this is the protoxide. It is soluble in acids with brown colour, and the solutions are not precipitated by sal-ammoniac. When binoxide of pla- tinum is heated with solution of oxalic acid, it is reduced to protoxide, which remains dissolved. The liquid has a dark blue colour, and deposits fine cop- per-red needles of oxalate of the protoxide of platinum. BINOXIDE OF PLATINUM, PtO ? . This is best prepared by adding nitrate of baryta to sulphate of the binoxide of platinum ; sulphate of baryta and nitrate of the binoxide are produced. From the latter, caustic soda precipi- tates one-half of the binoxide of platinum. The sulphate is itself obtained by acting with strong nitric acid upon the bisulphide of platinum, which falls as a black powder when a solution of bichloride is dropped into sulphide of potassium. The hydrate of the binoxide is a bulky brown powder, which, when gently heated, becomes black and anhydrous. It may also be formed by boiling bichloride of platinum 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 alkalis and alkaline earths, giving rise to a series of double compounds, which are not precipitated by excess of alkali. A combination of binoxide of platinum with ammonia exists, which is explosive. Both oxides of plati- num are reduced to the metallic state by ignition. PROTOCHLORIDE OF PLATINUM, PtCl. The protochloride is produced when bichloride of platinum, dried and powdered, is exposed for some time to a heat of 400 (204 -50), by which half of the chlorine is expelled ; also, when sulphurous acid is passed into a solution of the bichloride until the latter ceases to give a precipitate with sal-ammoniac. It is a greenish-grey pow- der, insoluble in water, but dissolved by hydrochloric acid. The latter solu- tion, mixed with sal-ammoniac or chloride of potassium, deposits a double salt in fine red prismatic crystals, containing in the last case, PtCl-f-KCl. The corresponding sodium-compound is very soluble and difficult to crystal- lize. The protochloride is decomposed by heat into chlorine and metallic platinum. BICHLORIDE OR PERCHLORIDE OF PLATINUM, PtClj. This substance is al- ways formed when platinum is dissolved in nitro-hydrochloric acid. The acid solution yields on evaporation to dryness a red or brown residue, deli- quescent, and very soluble both in water and alcohol ; the aqueous solution has a pure orange-yellow tint. Bichloride of platinum combines to double salts with a great variety of metallic chlorides ; the most important of these compounds are those containing the metals of the alkalis and ammonium. Bichloride of platinum and chloride of potassium, PtCl 2 , KC1, forms a bright yel- low crystalline precipitate, being produced whenever solutions of the chlo- rides of platinum and of potassium are mixed, or a salt of potassa, mixed with a little hydrochloric acid, added to bichloride of platinum. It is feebly soluble in water, still less soluble in dilute alcohol, and is decomposed with some difficulty by heat. It is readily reduced by hydrogen at a high tem- perature, furnishing a mixture of chloride of potassium and platinum-black ; the latter substance may thus, indeed, be very easily prepared. The sodium- salt, PtClj, NaCl-f-6HO, is very soluble, crystallizing in large, transparent, yellow-red prisms of great beauty. The ammonio- chloride of platinum, Ptd 2 , NH 4 C1, is indistinguishable, in physical characters, from the potassium-salt; 9S-94, Prof. Andrews, Chem. Gar., Oct. 1852. PLATINUM. 309 it is thrown down as a precipitate of small, transparent, yellow, octahedral crystals when sal-ammoniac is mixed with chloride of platinum ; 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. Compounds of platinum with iodine, bromine, sul- phur, and phosphorus have been formed, but are comparatively unim- portant. Some very extraordinary compounds have been derived from the proto- chloride of platinum. When ammonia in excess is added to a hot solution of the protochloride of platinum and ammonium, a green crystalline salt separates after a time, which is quite insoluble in water, and is not affected by hydrochloric or sul- phuric acids, ammonia, or even a boiling-hot solution of potassa. This sub- stance is known as the green salt of Magnus, and contains the elements of protochloride of platinum and ammonia, or PtCl-}-NH 3 . When the above compound is heated with concentrated nitric acid, it be- comes converted into a white, granular, crystalline powder, which on addition of water dissolves, leaving a residue of metallic pfatiuum. The solution yields on standing small, brilliant, colourless prisms of a substance very so- luble in water, containing the*elements of protochloride of platinum, ammo- nia, nitric acid, and an additional equivalent of oxygen : PtCl,N 2 H 6 0-fN0 5 . The platinum and chlorine in this curious body are insensible to ordinary reagents, and ammonia is evolved from it only on boiling with caustic alkali ; the presence of nitric acid can be detected immediately by gently heating a small portion with copper-filings and oil of vitriol. Prom this substance a series of salt-like bodies can be obtained, some of which have been carefully studied by M. Gros. Thus, when treated with hydrochloric acid, the nitric acid is wholly displaced, and a compound formed which crystallizes in small, transparent, yellowish octahedrons, sparingly soluble in boiling water, con- taining PtCl,N 2 H 6 Cl. With sulphuric acid it gives a substance which crys- tallizes in small, sparingly soluble, colourless needles, containing PtCl, N 2 H 6 0-f-S0 3 . The oxalic acid compound is white and insoluble; it contains PtCl,N 2 tJ 6 0-f-C 2 3 . Crystallizabie compounds containing phosphoric, tar- taric, citric, malic, formic, and even carbonic acids, were obtained by similar means. These substances have very much the characters of salts of a com- pound base or quasi-meta.1 containing PtCl,N 2 H 6 , and which yet remains un- known in a separate state. M. Raewsky has repeated and extended the observations of M. Gros. MM. lleiset and Peyrone have also described two other basic bodies con- taining platinum in the same remarkable condition : these differ from the preceding in being free from chlorine. Protochloride of platinum put into ammonia becomes rapidly converted into a green powder, which, by boiling, slowly dissolves ; the solution, on evaporation and cooling, furnishes beautiful yellowish crystals of the chlorine- compound of one of these bases, compounded of platinum and the elements of ammonia. The crystals contained PtN 2 H 6 Cl-j-HO. The equivalent of water is easily expelled by heat, and regained by absorption from the air. The green salt of Magnus, boiled with ammonia, yields the same product. A solution of this substance, mixed with nitrate of silver, gives chloride of silver and the nitrate of the new base, which crystallizes on evaporation in fine, white, transparent needles, containing PtN 2 H g O+NO g . The sulphide, iodide, and bromide are also crystallizable. Two carbonates exist. By adding baryta-water to a solution of the sulphate, or by treating the chloride witb protoxide of silver, and evaporating the filtered liquid in vucuo, a whittt, 310 PLATINUM. crystalline, deliquescent mass is obtained, which is the hydrate of the base, PtN 2 H 6 0-j-HO. It is almost comparable in point of alkalinity with potassa itself, absorbing carbonic acid with energy, and decomposing ammoniaoal salts. When this hydrate is heated to 230 (110C), it abandons water and ammonia, and leaves a greyish, porous, insoluble mass containing PtNII 3 ,0. This is probably an isomeric modification of the second base, whose salts are mentioned below. When a solution of the iodide, PtN 2 H 6 I, is long boiled, it deposits a spar- ingly soluble yellow powder, the composition of which is expressed by the formula PtNH 3 I : this is the iodine-compound of a second basic substance, PtNH 3 ; and from it by double decomposition a series of analogous salts can be obtained. When the iodine-compound is treated with protoxide of silver, the base itself is obtained in the form of a powerfully alkaline solution. The green salt of Magnus has the same composition as the chloride of this new base, which is yellow and soluble in boiling water, and may be converted into it. The salts of the first base are generally convertible into those of the second by heat, and the converse change may also be often effected by ebul- lition with ammonia. The subject of the platinum-bases appears,to be by no means exhausted. Only quite recently another remarkable basic compound containing ammonia and platinum has been discovered by M. Gerhardt. The chloride of Keiset's second base, the compound PtNH 3 Cl, when treated with chlorine, absorbs this element, and becomes converted into a lemon-yellow powder, consisting of small octahedrons, and having the composition PtNH 3 Cl 2 . Boiled with nitrate of silver, this substance yields chloride of silver and, according to the quantity of nitric acid present, a salt, PtNH 3 2 ,2N0 5 , or PtNlT 3 2 ,N0 5 -j- 3HO. On adding ammonia to the latter nitrate, a crystalline precipitate takes place, which consists of PtNIJ 3 2 -{-2HO. This substance, which is slightly soluble in water, may be viewed as the hydrated base existing in the bichloride and in the nitrates previously described. The bichloride, or a solution of binoxide of platinum, can be at once re- cognized by the yellow precipitate with sal-ammoniac, decomposable by heat, vith production of spongy metal. Bichloride of platinum and the sodio-chloride of platinum are employed in analytical investigations to detect the presence of potassa, and separate it from soda. For the latter purpose, the alkaline salts are converted into chlorides, and in this condition mixed with four times their weight of sodio- chloride of platinum 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 chloride of potassium 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 chloride of sodium "by difference; 100 parts of potasso-chloride of platinum correspond to 35 06 parts of chloride of potassium. 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 the caustic alkali roughens and corrodes the metal. The experimenter must be particularly careful to avoid introducing any oxide of any easily fusible metal, as that of lead or tin, into a platinum crucible. If reduction should by any means occui, these metals will at once alloy themselves with the pla- PALLADIUM. 311 tinum, and the vessel will be destroyed. A platinum crucible must never be put naked into the fire, but be always placed within a covered earthen crucible. PALLADIUM. The solution of crude platinum, from which the greater part of that metal has been precipitated by sal-fimmoniac, is neutralized by carbonate of soda, and mixed with a solution of cyanide of mercury ; cyanide of palladium separates as a whitish insoluble substance, which, on being washed, dried, and heated to redness, yields metallic palladium in a spongy state. The pal- ladium is then welded into a mass, in the same manner as platinum. Palladium closely corresponds with platinum in colour, a.ppearance, and difficult fusibility ; it is also very malleable and ductile. In density it differs very much from that metal, being only 11-8. Palladium is more oxidable than platinum. 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 aqua regia. There are two compounds of palladium and oxygen. The equivalent of palladium is 53-3: its symbol is Pd. PROTOXIDE OF PALLADIUM, PdO. This is obtained by evaporating to dry- ness, 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 carbonate of soda is added to the above solution. It is decomposed by a strong heat. BINOXIDE OF PALLADIUM, Pd0. 2 . The pure binoxide is very difficult to obtain. When solution of crustic potassa is poured, little by little, with constant stirring, upon the double chloride of palladium and potassium in a dry state, the latter is converted into a yellowish-brown substance, which is the binoxide, in combination with water and a little alkali. It is but feebly soluble in acids. PROTOCIILORIDE OF PALLADIUM, PdCl. The solution of the metal in aqua, regia yields this substance when evaporated to drynesss. It is a dark brown mass, soluble in water when the heat has not been too great, and forms double salts with many metallic chlorides. The potassio- and ammonio- chlorides of palladium are much more soluble than those of platinum ; they have a brownish-yellow tint. BICHLORIDE OF PALLADIUM only exists in solution, and in combination with the alkaline chlorides. It is formed when the protochloride of palladium is digested in aqua regia. The solution has an intense brown colour, and is decomposed by evaporation. Mixed with chloride of potassium or sal-ammo- niac, it gives rise to a red crystalline precipitate of double salt which is but little soluble in water. A sulphide of palladium, PdS, is formed by fusing the metal with sulphur, or by precipitating a solution of protochloride by sulphuretted hydrogen. A palladium-salt is well marked by the pale yellowish-white precipitate with solution of cyanide of mercury, convertible by heat into the spongy metal. This precipitate is a double salt, having the formula PdCy,HgCy, HO. Palladium is readily alloyed with other metals, as copper : one of these compounds, namely, the alloy with silver, has been applied to useful pur- poses. A native alloy of gold with palladium is found in the Brazils, and imported into England. S12 RHODIUM IRIDIUM. The solution from which platinum and palladium have been separated iu the manner described is mixed with hydrochloric acid, and evaporated to dryness. The residue is treated with alcohol of specific gravity 0-837, 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 ; chloride of sodium is dissolved out, and metallic rhodium re- mains. Thus obtained, rhodium is a white, coherent, spongy mass, which is more infusible and less capable of being welded than platinum. Its spe- cific 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 potassa. None of the acids, singly or conjoined, dissolve this metal, unless it be in the state of alloy, as with pla- tinum, in which it is attacked by aqua regia. The equivalent of rhodium is 52-2 ; its symbol is R. PROTOXIDE OF RHODIUM, RO, is obtained by roasting finely divided me- tallic rhodium. It is but little known. SESQUIOXIDE OF RHODIUM, R 2 3 . Finely-powdered metallic rhodium is heated in a silver crucible with a mixture of hydrate of potassa and nitre ; the fused mass boiled with water leaves a dark brown, insoluble substance, consisting of sesquioxide of rhodium in union with potassa. This is digested with hydrochloric acid, which removes the potassa and leaves a greenish- grey hydrate of the sesquioxide of rhodium, insoluble in acids. A soluble modification of the same substance, retaining, however, a portion of alkali, may be had by adding an excess of carbonate of potassa to the double chlo- ride of rhodium and potassium, and evaporating. SESQUICHLORIDE OF RHODIUM, R 2 C1 3 . The pure sesquichloride is prepared by adding hydrofluosilicic acid to the double chloride of rhodium and potas- sium, evaporating the filtered solution to dryness, and dissolving the residue in water. It forms a brownish-red deliquescent mass, soluble in water, with a fine red colour. It is decomposed by heat into chlorine and metallic rho- dium. The chloride of rhodium and potassium, R 2 Cl 3 -f-2KCl-f-2HO, j s p re _ pared by heating in a stream of chlorine a mixture of equal parts finely powdered rhodium and chloride of potassium. This salt has a fine red colour, is soluble in water, and crystallizes in four-sided prisms. Chloride of rhodium and sodium is also a very beautiful red salt, obtained by a similar process; it contains R 2 Cl 3 -j-3NaCl-f 18HO. The chloride of rhodium and ammonium resembles the potassium-compound. SULPHATE OF RHODTUM, R^O^SSOj. The sulphide of rhodium, obtained by precipitating one of the salts by a soluble sulphide, is oxidized by strong nitric acid. The product is a brown powder, nearly insoluble in nitric acid, but dissolved by water ; it cannot be made to crystallize. Sulphate of rho- dium and potassium, is produced when metallic rhodium is strongly heated with bisulphate of potassa. It is a yellow salt, slowly soluble in cold water. An alloy of steel with a small quantity of rhodium is said to possess ex- tremely valuable properties. IRIDIUM. When crude platinum is dissolved in aqua regia, a small quantity of a grey scaly metallic substance usually remains behind, having altogether resisted the action of the acid ; this is a native alloy of iridium and osmium. It is reduced to powder, mixed with an equal weight of dry chloride of sodium, and heated to redness in a glass tube, through which a stream of moist chlo- IRIDIUM. 813 rine gas is transmitted. The farther extremity of the tube is connected with a receiver containing solution of ammonia. The gas, under these circum- stances, is rapidly absorbed, chloride of iridium and chloride of osmium be- ing produced : the former remains in combination with the chloride of so- dium ; 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 double chloride of iridium and sodium is dissolved out : this is mixed with an excess of carbonate of soda, and evaporated to dryness. The residue is ignited in a crucible, boiled with water, and dried ; it then consists of a mixture of sesquioxide of iron, and a combination of oxide of iridium with soda ; it is reduced by hydrogen at a high temperature, and treated successively with water and strong hydro- chloric acid, by which the alkali and the iron are removed, while metallic iridium is left in a divided state. By strong pressure and exposure to a white heat, a certain degree of compactness may be communicated to the metal. Iridium is a white brittle metal, fusible with great difficulty before the oxy-hydrogen blowpipe. 1 It is not attacked by any acid, but is oxidized by fusion with nitre, and by ignition to redness in the air. The equivalent of iridium is 99. Its symbol is Ir. OXIDES OF IRIDIUM. Four of these compounds are described. Protoxide of iridium, IrO, is prepared by adding caustic alkali to the protochloride, and digesting the precipitate in an acid. It is a heavy black powder, inso- luble in acids. It may be had in the state of hydrate by precipitating the protochloride of iridium and sodium by caustic potassa. The hydrate is so- luble in acids with dirty green colour. Sesquioxide, Ir 2 $ , is produced when iridium is heated in the air, or with nitre ; it is best prepared by fusing in a silver crucible a mixture of carbonate of potassa and the terchloride of iridinm and potassium, and boiling the product with water. This oxide ia bluish-black, and is quite insoluble in acids. It is reduced by combustible substances with explosion. Binoxide of iridium, Ir0 2 , is unknown in a sepa- rata state ; it is supposed to exist in the sulphate, produced when the sul- phide is oxidized by nitric acid. A solution of sulphate heated with excess of nlkali evolves oxygen gas, and deposits sesquioxide of iridium. Teroxide cf iridium, Ir0 3 , is produced when carbonate of potassa is gently heated with the terchloride of iridium ; it forms a greyish-yellow hydrate, which con- tains alkali. CHLORIDES OF IRIDIUM. Protochloride, IrCl, is formed when the metal i? brought in contact with chlorine at a dull red-heat; it is a dark olive-green insoluble powder. It is dissolved by hydrochloric acid, and forms double salts with the alkaline chlorides, which have a green colour. The sesquichlo- ride, Ir 2 Cl 3 , 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 metallic chlorides. Bichloride of iridium is obtained in solution by adding hydrofluosilicic acid to the bichloride of iridium and potassium, formed when chlorine is passed over a heated mixture of iridium and chloride of potassium. It forms with metallic chlorides a numter of double salts, which resemble the platinum -compounds of the same order. Terchloride cf iridium, IrCl 3 , is unknown in a separate state. Terchloride of iridium ana potassium is obtained by heating iridium with nitre, and then dissolving the 1 It is the heaviest substance known, its specific gravity, according to Professor Hare, beln* 21-S. Proceedings of the Amer. Phil. Soc. May and June, 1842. It? B 27 till RUTHENIUM OSMIUM. whole in aqua rer/ici, and evaporating to dryness. The excess of chloride of potassium may be extracted by a small quantity of water. The crystallized salt has a beautiful red colour. The variety of tints exhibited by the diffe- rent soluble compounds of iridium is very remarkable, and suggested the name of the metal, from the word iris. Platinum, palladium, and iridium combine with carbon when heated in the flame of a spirit-lamp ; they acquire a covering of soot, which, when burned, leaves a kind of skeleton of spongy metal. RUTHENIUM. M. Claus has described under this name a new metal contained in the residue from crude platinum, insoluble in aqua reyia. It closely resembles iridium in its general characters, but yet possesses distinctive features of its own. It was obtained in the form of small angular masses, with perfect metallic lustre, very brittle and infusible. Its specific gravity is 8-6. It resists the action of acids, but oxidizes readily when heated in the air. The equivalent of ruthenium is 52-2, and its symbol Ku. OXIDES OF RUTHENIUM. Protoxide of ruthenium, RuO, is a greyish-black metallic-looking powder, obtained by heating bichloride of ruthenium with excess of carbonate of soda in a stream of carbonic acid gas, and then wash- ing away the soluble saline matter. It is insoluble in acids. The sesquioxide, l\u 2 O 3 . in the anhydrous condition is a bluish-black powder formed by heating the metal in the air. It is also precipitated by alkalis from the sesquichlo- ride as a blackish-brown hydrate, soluble in acids with orange-yellow colour. The binoxide, Ru0 2 , is a deep blue powder, procured by roasting the bisul- phide. A hydrate of this oxide is known in an impure condition. An acid of ruthenium is also supposed to exist. Sesquichloride of ruthenium, Hu 2 Cl 3 , is an orange-yellow soluble salt of astringent taste ; when the solution is heated, it becomes green and finally blue, by reduction, in all probability, to protochloride. Sesquichloride of ruthenium forms double salts with the chlorides of potassium and ammonium. OSMIUM. The solution of osmic acid in ammonia, already mentioned, is gently boated for some time in a loosely-stopped vessel ; its original yellow colour becomes darker, and at length a brown precipitate falls, which is a combination of sesquioxide of osmium with ammonia : it results from the reduction of the osmic acid by the hydrogen of the volatile alkali. A little of the precipitate is held in solution by the sal-ammoniac, but may be recovered by heating the clear liquid with caustic potassa. The brown substance is dissolved in hydrochloric acid, a little chloride of ammonium added, and the whole evapo- rated to dryness. The residue is strongly heated in a small porcelain retort; the oxygen of the oxide combines with hydrogen from the ammonia, vapour of water, hydrochloric acid, and sal-ammoniac are expelled, and osmium left behind, as a greyish porous mass, having the metallic lustre. In the most compact state in which this metal can be obtained, it has a luish-white colour, and, although somewhat flexible in thin plates, is yet asily reduced to powder. Its specific gravity is 10; it is neither fusible nor volatile. It burns when heated to redness, yielding osmic acid, which volatilizes. Osmate of potassa is produced when the metal is fused with nitre. When in a finely divided state, it is oxidized by strong nitric acid. The equivalent of osmium is 99-6 ; its symbol is Os. OXIDES OF OSMIUM. Five compounds of osmium with oxygen are known. Protoxide, OsO, is obtained, in combination with a little alkali, vhen caustic potassa is added to a solution of protochloride of osmium and potassium. It is a dark green powder, slowly soluble in acids. Sesquioxide f Os 2 3 , has OSMIUM. 315 already been noticed ; it is generated by the deoxidation of osmate of am- monia ; it is black, and but little soluble in acids. It always contains ammonia, and explodes feebly when heated. Binoxide of osmium, Os0 2 , is pre- pared by strongly heating in a retort a mixture of carbonate of soda and the bichloride of osmium and potassium, and treating the residue with water, and afterwards with hydrochloric acid. The binoxide is a black powder, insoluble in acids, and burning to osmic acid when heated in the air. Osmious acid Os0 3 is known only in combination. On adding alcohol to a solution of osmate of potassa, the alcohol is oxidized at the expense of the osmic acid, and a rose-red crystalline powder of osmite of potassa is produced. On at- tempting to separate the acid, it is decomposed into the binoxide and osmic acid. Osmic acid, Os0 4 , is by far the most important and interesting of the oxides of this metal. It is prepared by heating osmium in a current of pure oxygen gas ; it condenses in the cool part of the tube in which the experi- ment is made in colourless transparent crystals. Osmic acid melts and even boils below 212 (100C) ; its vapour has a peculiar offensive odour, and is exceedingly irritating and dangerous. Water slowly dissolves this substance. It has acid properties, and combines with bases. Nearly all the metals pre- cipitate osmium from a solution of osmic acid. By the action of ammonia on osmic acid, a new acid has been formed, containing osmium, nitrogen, and oxygen. It has been called osman-osmic acid or osmamic acid. Some doubts are hanging over the formula of this substance. It produces salts with many bases. CHLORIDES OF OSMIUM. ProtocMoride, OsCl, is a dark green crystalline substance, formed by gently heating osmium in chlorine gas. It is soluble in a small quantity of water, with green colour, but decomposed by a large quantity into osmic and hydrochloric acids and metallic osmium. It forms double salts with the metallic chlorides. The sesquichloride, Os 2 Cl 3 , has not been isolated ; it exists in the solution obtained by dissolving the sesquioxide in hydrochloric acid. Bichloride, OsCl 2 , in combination with chloride of potassium, is produced when a mixture of equal parts metallic osmium and the last-named salt is strongly heated in chlorine gas. It forms fine red oc- tahedral crystals, containing OsCl 2 -}-KCl. Osmium combines also with sulphur and with phosphorus. PAKT III. ORGANIC CHEMISTRY. INTRODUCTION. ORGANIC substances, whether directly derived from the vegetable or ani- mal kingdom, or produced by the subsequent modification of bodies which thus originate, are remarkable as a class for a degree of complexity of con- stitution far exceeding that observed in any of the compounds yet described. And yet the number of elements which enter into the composition of these substances is extremely limited ; very few, comparatively speaking, contain more than four, viz., carbon, hydrogen, oxj^gen, and nitrogen; sulphur and phosphorus are occasionally associated with these in certain mineral pro- ducts ; and compounds containing chlorine, bromine, iodine, arsenic, anti- mony, zinc, &c., have been formed by artificial means. This paucity of elementary bodies is compensated by the very peculiar and extraordinary properties of the four first-mentioned, which possess capabilities of combi- nation to which the remaining elements are strangers. There appears to be absolutely no limit to the number of definite, and often crystallizable, sub- stances which can be thus generated, each marked by a perfect individuality of its own. The mode of association of the elements of organic substances is in gene- ral altogether different from that so obvious in the other division of the science. The latter is invariably characterized by what may be termed a binary plan of combination, union taking place between pairs of elements, and the compounds so produced again uniting themselves to other compound bodies in the same manner. Thus, copper and oxygen combine to oxide of copper, potassium and oxygen to potassa, sulphur and oxygen to sulphuric acid ; sulphuric acid, in its turn, combines both with oxide of copper and oxide of potassium, generating a pair of salts, which are again capable of uniting to form the double compound, CuO,S0 8 -}-KO,S0 3 . The most complicated products of inorganic chemistry may be thus shown to be built up by this repeated pairing on the part of their constituents. With organic bodies, however, the case is strikingly different ; no such ar- rangement can here be traced. In sugar, C l2 H n O n , or morphine, C 34 H 19 N0 6 , or the radical of bitter almond oil, C 14 H 5 2 , and a multitude of similar cases, the elements concerned are, as it were, bound up together into a single whole, which can enter into combination with other substances, and be thence disengaged with properties unaltered. A curious consequence of this peculiarity is to be found in the compara- tively instable character of organic compounds, and their general proneness to decomposition and change, when the balance of opposing forces, to which they owe their existence, becomes deranged by some external cause. If a complex inorganic substance be attentively considered, it will usually be found that the elements are combined in such a manner as to satisfy the most powerful affinities, and to give rise to a state of very considerable per- manence and durability But in the case of an organic substance containing (310) INTRODUCTION TO ORGANIC CHEMISTRY. 317 three or four elements associated in the way described, this is very far from being true: the carbon and oxygen strongly tend to unite to form carbonic acid ; the hydrogen and oxygen attract each other in a powerful manner, and the nitrogen, if that body be present, also contributes its share to these internal sources of weakness by its disposition to generate ammonia. While the opposing forces remain exactly balanced, the integrity of the compound is preserved; but the moment one of them, from some accidental cause, acquires preponderance over the rest, equilibrium is destroyed and the organic principle breaks up into two or more new bodies of simpler and more permanent constitution. The agency of heat produces this effect by exalting the attraction of oxygen for hydrogen and carbon ; hence the almost universal destructibility of organic substances by a high temperature. Mere molecular disturbance of any kind may cause destruction when the insta- bility is very great. As a general rule, it may be assumed that those bodies which are most complex from the number of elements, and the want of simplicity in their equivalent relations, are by constitution weakest, and least capable of resist- ing the action of disturbing forces ; and that this susceptibility of change diminishes with increased simplicity of structure, until it reaches its minimum in those bodies which, like the carbides of hydrogen, like cyanogen, and oxalic acid, connect, by imperceptible gradations, the organic and the mineral departments of chemical science. The definite organic principles of the vegetable and animal kingdoms form but a very small proportion of the immense mass of compounds included within the domain of organic chemistry: by far the greater number of these are produced by modifying by suitable means the bodies furnished by the plant or the animal, and which have themselves been formed from the elements of the air by processes for the most part unknown, carried on under the control of vitality. Unlike these latter, the artificial modifications referred to, by oxidation, by the action of other powerful reagents, by the influence of heat, and by numerous other sources of disturbance, are, for the most part, changes of descent in order of complexity, new products being thus generated more simple in constitution and more stable in character than the bodies from which they were derived. These, in turn, by repetition of puch treatment under perhaps varied circumstances, may be broken up into other and still simpler organic combinations ; until at length the binary compounds of inorganic chemistry, or bodies so allied to them that they may be placed indifferently in either group, are by such means reached. Organic Substitution-products: Law of Substitution. The study of the action of chlorine, bromine, iodine, and nitric acid upon various organic substances has led to the discovery of a very remarkable law regulating the formation of chlorinetted and other analogous compounds, which, without being of necessity absolute in every case, is yet of sufficient generality and import- ance to require careful consideration. This peculiar mode of action consists in the replacement of the hydrogen of the organic substance by chlorine, bromine, iodine, the elements of hyponitric acid, and more rarely other stib- stances of the same class, equivalent for equivalent, without the destruction of the primitive type or constitution of the compound so modified. The hydrogen thus removed takes of course the form of hydrochloric or hydro- bromic acid, &c., or that of water, by combination with another portion of the active body. Strange as it may appear, and utterly opposed to the ordi- nary views of the functions of powerful salt-radicals, this loss of hydrogen and assumption of the new element do actually occur with a great variety of substances belonging to different groups with comparatively trifling dis- turbance of physical and chemical properties ; the power of saturation, tho density of the vapour, and other pccularities of the original substance rcmuiu 27* 318 INTRODUCTION TO * the same, saving the modification they may suffer from the difference of the equivalent weights of hydrogen and the bodies by which it is replaced. This change may take place by several successive steps, giving rise to a series of substitution-compounds, which depart more and more in properties from the original substance with each successive increase in the proportion of the replacing body. The substitution may even be total, the whole of the hydrogen being lost, and its place supplied by a similar number of equiva- lents of the new element. And even in these extreme cases, of very common occurrence, however, with one class of substances, the resulting compound retains generally the stamp of its origin. Although numerous examples of these changes will be found described in detail in the following pages, it will be well perhaps to mention here two or three cases by way of illustration. Dutch-liquid, the compound formed by the union of equal measures of olefiant gas and chlorine, containing C 4 H 4 C1 2 , is affected by chlorine in obedience to the law of substitution ; one, two, three, four equivalents of hydrogen being successively removed by the prolonged action of the gas aided by sunshine, and one, two, three, or four equivalents of chlorine intro- duced in place of the hydrogen withdrawn as hydrochloric acid. In the last product, the sesquichloride of carbon, C 4 C1 6 , the replacement is total ; the intermediate products are volatile liquids not differing very much in general characters from Dutch-liquid itself. A great number of compound ethers of the ethyl- and methyl-series are attacked by chlorine and bromine in a similar manner ; indeed, the majority of the examples of the law in question are to be found in the history of this class of bodies. Concentrated acetic acid, placed in a vessel of dry chlorine and exposed to the sun, gives rise to chloracetic acid, containing C 4 C1 3 3 ,HO, and in which, consequently, the whole hydrogen of the real acid is replaced by chlorine. Chloracetic acid is a stable substance, of strong acid characters, and forms a series of salts, some of which bear no slight resemblance to the normal ace- tates. Basic substitution-products have been obtained indirectly ; chloraniline, bromaniline, and iodaniline are the most striking examples. These will be found fully described in the sections on organic bases. The action of fuming nitric acid upon organic substances very commonly indeed gives rise to substitution-products containing the elements of hypo- nitric acid, N0 4 , in place of hydrogen. The benzoyl-compounds, and several of the essential oils natural and derived from resins, will be found to furnish illustrations. In formulae representing substitution-compounds retaining some hydrogen, the practice is often adopted of placing the substituting body beneath or be- sides this residual hydrogen, and uniting them by a bracket on each side. Thus, the formulae of the first two products of the action of chlorine on Dutch- liquid are thus written : C1 2 , and C 4 { } C1 2 , or C 4 , (H,C1) C1 2 and C 4 (H 2 C1 2 ) C1 2 . And pyroxlin, or gun-cotton, which is supposed to be a substitution-product from lignin, C 24 H 2 p0 20 , having 5 equivalents of hydrogen replaced by the ele- ments of hyponitric acid, will stand : 5N0 4 } *0' or C 24 [H 16 (N0 4 ) 5 ] 20 . fsomeric bodies, or substances different in properties, yet identical in com-> position, are of constant occurrence in organic chemistry, and stand, indeed, among its most striking and peculiar features. Every year brings to light fresh examples of compounds so related. In most cases, discordance in pr<- ORGANIC CHEMISTRY. 811 perties is fairly and properly ascribed to difference of constitution, the ele- ments being differently arranged. For instance, formic ether and acetate of methyl are isomeric, both containing C 6 H 6 4 ; but then the first is supposed to consist of formic acid, C 2 H0 3 , combined with ether, C 4 H 6 ; while the second is imagined in accordance with the same views, to be made up of ace- tic acid, C 4 Hp0 3 , and the ether of wood-spirit, C 2 H 3 0. And this method of explanation is generally sufficient and satisfactory ; when it can be shown that a difference of constitution, or even a difference in the equivalent num- bers, exists between two or more bodies identical in ultimate composition, the reason of their discordant characters becomes to a certain extent intelli- gible. Organic bodies may be thus classified : 1 . Quasi-elementary Substances, and their compounds. These affect the disposition and characters of the true elements, and, like the latter, evince a tendency to unite on the one hand with hydrogen and the metals, and on tho other with chlorine, iodine, and oxygen. The former are designated organic salt-radicals, and the latter organic salt-basyles. Few of either kind have been yet isolated, and it is very possible that very many of them are unable to exist in a separate state. Some of these quasi-elements are among the most important and interesting substances in organic chemistry. 2. Organic Salt-bases, not being the oxides of known radicals. The prin- cipal members of this class are the vegeto-alkalis ; they form crystallizable compounds with acids, organic and inorganic, and even possess in some cases a distinct alkaline reaction to test-paper. 3. Organic acids, not being compounds of known radicals. These bodies are very numerous and important. Many of them have an intensely sour taste, redden vegetable blues, and are almost comparable in chemical energy with the acids of mineral origin. 4. Neutral non-azotized substances, containing oxygen and hydrogen in the proportions to form water. The term neutral, as applied to these compounds, is not strictly correct, as they usually manifest feeble acid properties by com- bining with metallic oxides. This group comprehends the sugars, the dif- ferent modifications of starch, gum, &c. 5. Neutral azotized substances ; the albuminous principles and their allies, the great components of the animal frame. These are in the highest degree complex in constitution, and are destitute of the faculty of crystalliatioH. 6. Carbides of Hydrogen, their oxides and derivatives. 7. Fatty bodies. 8. Compound acids, containing the elements of an organic substance in com- bination with those of a mineral or other acid. These bodies form a largo and very interesting class, of which sulphovinic acid may be taken as the type or representative. . 9. Colouring principles, and other substances not referable to either of the preceding classes. The action of heat on organic substances presents many important and interesting points, of which a few of the more prominent may be noticed. Bodies of simple constitution and of some permanence, which do not sublime unchanged, as 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 numerous pyro-acids, of which many examples will occur in the succeeding pages, are thus produced. Carbonic acid and water are often eliminated under these circumstances. If the heat be sud- denly raised to redness, then the regularity of the decomposition vanishes, whUe the products become more uncertain and more numerous ; carbonic acid and watery vapor are succeeded by inflammable gases as carbonic oxide 320 THE ULTIMATE ANALYSIS OF and carbonetted hydrogen ; 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 destructive distillation. If the organic substance contain nitrogen, arid be 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 carbo- naceous 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 au excess of strong alkaline base, as potassa 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 escaping in some volatile form. Thus, benzoic acid distilled with hydrate of lime, at a dull red-heat, yields carbonate of lime and a bicarbide of hydrogen, ben- zole ; woody fibre and caustic potassa, heated to a very moderate tempera- ture, yield ulmic acid and free hydrogen ; with a higher degree of heat, oxalic acid appears in the place of the ulmic ; and, at the temperature of ignition, carbonic acid, hydrogen being the other product. The spontaneous changes denominated decay and putrefaction, to which many more of the complicated organic, and, more particularly, azotized prin - ciples are subject, have lately attracted much attention. By the expression decay, 1 Liebig and his school understand a decomposition of moist organic matter, freely exposed to the air, by the oxygen of which it is gradually burned and destroyed, without sensible elevation of temperature ; the term putrefaction, on the other hand, is limited to changes occurring in and be- neath the surface of water, the effect being a mere transposition of ele- ments, or metamorphosis of the organic body. The conversion of sugar into alcohol and carbonic acid furnishes, perhaps, the simplest case of the kind. It is proper to remark, however, that contact of oxygen is indispensable, in the first instance, to the change, which, 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 de- cay ; and if the decay or its cause, namely, the absorption of oxygen, be presented, no putrefaction occurs. The most putrescible substances, as ari- imal flesh intended for food, milk, and highly azotized vegetables, are pre served indefinitely, by enclosure in metallic cases, from which the air has been completely removed and excluded. Some of the curious phenomena of communicated chemical activity, where a decomposing substance seems to involve others in destructive change, Which, without such influence^ would have remained in a permanent and quiescent state, will be found noticed in their proper places, as under the head of Vinous Fermentation. These actions are yet very obscure, and re- quire to be discussed with great caution. THE ULTIMATE ANALYSIS OF ORGANIC BODIES. As organic substances cannot be produced at will from their elements, the analytical method of research is alone applicable to the investigation of their exact chemical composition ; hence the ultimate analysis of these substances becomes a matter of great practical importance. The operation is always executed by causing complete combustion of a known weight of the body to 1 Or eremacausis, that is, slow burning. ORGANIC BODIES. 321 be examined, in such a manner that the carbonic acid and water produced shall be collected, and their quantity determined ; the carbon and hydrogen they respectively contain may from these data be easily calculated. When nitrogen, sulphur, phosphorus, chlorine, &c., are present, special and sepa- rate means are resorted to for their estimation. The method to be described for the determination of the carbon and hy- drogen owes its convenience and efficiency to the improvements of Professor Liebig ; it has superseded all other processes, and is now invariably employed in inquiries of the kind. With proper care, the results obtained are wonder- fully correct; and equal, if not surpass in precision, those of the best mineral analyses. The principle upon which the whole depends is the fol- lowing : When an organic substance is heated with the oxides of copper, lead, and several other metals, it undergoes complete combustion at the ex- pense of the oxygen of the oxide, the metal being at the same time reduced, either completely or to a lower state of oxidation. This effect takes place with greatest ease and certainty with the black oxide of copper, which, al- though unchanged by heat alone, gives up oxygen to combustible matter with extreme facility. When nothing but carbon and hydrogen, or those bo- dies together with oxygen, are present, one experiment suffices ; the carbon and hydrogen are determined directly, and the oxygen by difference. It is of course indispensable that the substance to be analyzed should possess the physical characters of purity, otherwise the inquiry cannot lead to any good result ; if in the solid state, it must also be freed with the most scrupulous care from the moisture which many substances retain with great obstinacy. If it will bear the application of moderate heat, this desiccation is very easily accomplished by a water or steam-bath ; in other cases, expo- sure at common temperatures to the absorbent powers of a large surface of oil of vitriol in the vacuum of an air-pump must be substituted. The operation of weighing the dried powder is conducted in a narrow open tube (tig. 153), about 2J or 3 inches long; the tube and substance are weighed together, and, when the Fig. 153. latter has been removed, the tube with any little adherent matter is re- weighed. This weight, sub- tracted from the former, gives the weight of the sub- stance employed in the experiment. As only 5 or 6 grains are used, the weighings should not evolve a greater error than -o^th part of a grain. The protoxide of copper is best made from the nitrate by complete ignition in an earthen crucible : it is reduced to powder, and re-heated just before use, to expel hygroscopic moisture, which it absorbs, even while warm, with avidity. The combustion is performed in a tube of hard white Bohemian glass, having a diameter of 0-4 or 0-5 inch, and in length varying from 14 to 18 inches ; this kind of glass bears a moderate red-heat without becoming soft enough to lose its shape. One end of the tube is drawn out to a point, as shown in fig. 154, and closed; the other is simply heated to fuse and soften the sharp edges of the glass. The tube is now two-thirds filled with the ye* Fig. 154. Oxide copper. Mixture. Oxide copper. 322 THE ULTIMATE ANALYSIS OP warm protoxide of copper, nearly the whole of which is transferred to a small porcelain or Wedgwood mortar, and very intimately mixed with the organic substance. The mixture is next transferred to the tube, and the mortar rinsed with a little fresh and hot oxide, which is added to the rest ; the tube is, lastly, filled to within an inch of the open end with oxide from the crucible. A few gentle taps on the table suffice to shake together the contents, so as to leave a free passage for the evolved gases from end to end. The arrangement of the mixture and oxide in the tube is represented in the sketch. The tube is then ready to be placed in the furnace or chauffer : this latter is constructed of thin sheet-iron, and is furnished with a series of supports of equal height, which serve to prevent flexure in the combustion-tube when softened by heat. Fig. 155. The chauffer is placed upon flat bricks or a Fig. 155. piece of stone, so that but little air can enter the grating, unless the wholo be purposely raised. A slight inclination is also given towards the extremity occupied by the mouth of the combustion-tube, which passes through a holo provided for the purpose. To collect the water produced in the experiment, a small light tube of the form represented in fig. 156, filled with fragments of spongy chloride of cal- cium, is attached by a perforated cork, thoroughly dried, to the open ex- Fig. 156. Fig. 157. tremity of the combustion-tube. The carbonic acid is condensed into a solu- tion of caustic potassa, of specific gravity 1-27, which is contained in a small glass apparatus on the principle of a Woulfe's bottle, shown in fig. 157. The connection between the latter and the chloride of calcium-tube is com- pleted by a little tube of caoutchouc, secured with silk cord. The whole is shown in fig. 158, as arranged for use. Both the chloride of calcium-tube und the potass-apparatus are weighed with the utmost care before the ex- periment. The tightness of the junctions may be ascertained by slightly rarefying the included air by sucking a few bubbles from the interior through the liquid, using the dry lips, or better, a little bent tube with a perforated cork : / the difference of the level of the liquid in the two limbs of the potass- ORGANIC BOD IES. 323 apparatus be preserved for several minutes, the joints are perfect. Red- hot charcoal is now placed around the anterior portion of the combustion- Fig. 158. Drawing of the whole arrangement. tube, containing the pure oxide of copper, and when this is red-hot, the- fire is slowly extended towards the farther extremity by shifting the moveable screen ^, represented in the drawing. The experiment must be so conducted, that an uniform stream of carbonic acid shall enter the potass-apparatus by bubbles which may be easily counted : when no nitrogen is present, these bubbles are towards the termination of the experiment almost completely absorbed by the alkaline liquid, the little residue of air alone escaping. In the case of an azotized body, on the contrary, bubbles of nitrogen gas, pass through the potassa-solution during the whole process. When the tube has become completely heated from end to end, and no more gas is disengaged, but, on the other hand, absorption begins to be evident, the coals are removed from the farther extremity of the combustion- tube, and the point of the latter broken off. A little air is drawn through the whole apparatus, by which the remaining carbonic acid and watery vapour are secured. The parts are, lastly, detached, and the chloride of calcium tube and potass-apparatus re-weighed. The following account of a real experiment will serve as an illustration ; the substance examined was crystallized sugar. Quantity of sugar employed 4-750 grains. Potass-apparatus weighed after experiment.... 781-13 " " before experiment.. 773-82 Carbonic acid 7-31 Chloride of calcium-tube after experiment 226-05 " " before experiment ... 223-30 Water 2-75 7-31 gr. carbonic acid=l-994 gr. carbon: and 2-75 gr. water=0-3056 gi hydrogen ; or in 100 parts of sugar,' * Th theoretical composition of sugar CwHuOn, reckoned to 100 parts gives Carbon 42-11 Hydrogen 6-43 Oxygen 51'46 100-00 324 THE ULTIMATE ANALYSIS OF Carbon 41-98 Hydrogen 6-43 Oxygen, by difference 51-59 100-00 When the organic substances cannot be mixed with the protoxide of copper in the manner described, the process must be slightly modified to meet the particular case. If, for example, a volatile liquid is to be examined, it is enclosed in a little glass bulb with a narrow stem, which is weighed before and after the introduction of the liquid, the point being hermetically sealed. The combustion-tube must have, in this case, a much greater length ; and, as the protoxide of copper cannot be introduced hot, it must be ignited and cooled out of contact with the atmosphere, to pre- Fig. 159. vent absorption of watery vapour. This is most conveniently effected by transferring it, in a heated state, to a large platinum crucible, to which a close-fitting cover can be adapted. When quite cold, the cover is removed, and instantly replaced by a dry glass funnel, by the assistance of which the oxide may be directly poured into the com- bustion-tube, with mere momentary exposure to the air. A little oxide is put in, then the bulb, with its stem broken at a, fig. 159, a file-scratch having been previously made ; and lastly, the tube is filled with the cold and dry protoxide of copper. It is arranged in the chauffer, the chloride of calcium tube and potass-apparatus adjusted, and then, some six or eight inches of oxide having been heated to redness, the liquid in the bulb is, by the approximation of a hot coal, expelled, and slowly converted into vapour, which, in passing over the hot oxide, is completely burned. The experiment is then terminated in the usual manner. Fusible fatty substances, and volatile concrete bodies, as camphor, require rather different management, which need not be here described. Protoxide of copper, which has been used, may be easily restored by moistening with nitric acid, and ignition to redness ; it becomes, in fact, rather improved than otherwise, as after frequent employment its density is increased, and its troublesome hygroscopic powers diminished. For sub- stances which are very difficult of combustion, from the large proportion of carbon they contain, and for compounds into which chlorine enters as a con- stituent, fused and powdered chromate of lead is very advantageously sub- stituted for the protoxide of copper. Chromate of lead freely gives up oxygen to combustible matters, and even evolves, when strongly heated, a little of that gas, which thus ensures the perfect combustion of the organic body. Analysis of azotized Substances. The presence of nitrogen in an organic compound is easily ascertained by heating a small portion with solid hydrate of potassa in a test-tube ; the nitrogen, if present, is converted into ammo- nia, which may be recognized by its odour and alkaline reaction. There are several methods of determining the proportion of nitrogen in azotized organic substances, the experimenter being guided in his choice of means by the nature of the substance and its comparative richness in that element. The carbon and hydrogen are first determined in the usual manner, a longer tube than usual is employed, and four or five inches of its anterior portion filled witn spongy metallic copper, made by reducing the protoxide by hydrogen ; this serves to decompose any nitrous acid or biu oxide of nitrogen, which may ORGANIC BODIE S. 325 1*3 formed in the act of combustion. During the experiment some idea of the abundance or paucity of the nitrogen may be formed from the number of hubbies of incondensible gas which traverse the solution of potassa. In the case of compounds abounding in nitrogen, and readily burned by protoxide of copper, a method may be employed, which is very easy of execu- tion ; this consists in determining the ratio borne by the liberated nitrogen to the carbonic acid produced in the combustion. A tube of hard glass, of the usual diameter, and about 15 inches long, is sealed at one end; a little of the organic substance, mixed with protoxide of copper, is introduced, and allowed to occupy about two inches of the tube ; about as much pure oxide is placed over it, and then another portion of a similar mixture ; after which the tube is filled up with a second and larger portion of the pure oxide, and quantity of spongy metallic copper. A short bent tube, made mcveable by a caoutchouc joint, is fitted by a perforated cork, and made to dip into a mercurial trough, while the combustion-tube itself rests in the chauffer. (Fig. 160.) Fig. 160. 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. Com- bustion of the first portion of the mixture takes place, the gaseous products sweeping before them nearly the whole of the air of the apparatus. Figt 161> 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 col- lected in a graduated jar, until the operation is at an end. The volume is then read off, and some strong solution of caustic po- tassa thrown up into the jar by a pipette with a curved extremity. (Fig. 161.) When the absorption is complete, the residual volume of nitrogen is observed, and compared with that of the mixed gases, proper correction being made for difference 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 ni- trogen of the residual atmosphtric air becomes so great as to de- stroy all confidence in the result of the experiment; and the same thing happens when the substance is incompletely burned by pro- toxide of copper; other means must then be .employed. The 1 Volumes of the two gases represents equivalents; for 100 cubic inches carbonic acid weigh 47'26 grains. 100 nitrogen 30'14 47-26 : 30-14 = 22 : 14-01 The last two terms are the equivalent numbers: one equivalent of carbonic vl too tain* one equivalent of carbon. 326 THE ULTIMATE ANALYSIS OF absolute, method of determination, also known by the name of Dumas's me- thod, may be had recourse to when the foregoing, or comparative method, fails from the tirst cause mentioned ; it gives excellent results, and is appli- cable to all azotized substances. A tube of good Bohemian glass, 28 inches long, is securely sealed at one end; into this enough dry bicarbonate of soda is put to occupy 6 inches. A little pure protoxide of copper is next introduced, and afterwards the mix- ture 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 remain- der of the tube, amounting to nearly one-half of its length, is then filled up with pure protoxide of copper and spongy metal, and a round cork, perfo- rated by 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, fig. 1G2, and the combustion-tube arranged in the furnace. A few coals ar e now applied to the farther end of the tube, so as to decompose a portion of the bicarbonate of soda, the remainder of the carbonate as well as of the other part of the tube being protected from the heat by a screen n. The current of carbonic acid 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 de- pressed under the level of a mercurial trough, and the gas, which is evolved, collected in a test-tube filled with concentrated potassa-solution. If the gas be perfectly absorbed, or, after the introduction of a considerable quantity, only a minute bubble be left, the air maybe considered as expelled. The next step is to fill a graduated glass-jar two-thirds with mercury and one-third with a strong solution of potassa, and to invert it over the delivery-tube, as represented in fig. 162. This done, fire is applied to the tube, commencing at the front end, and gradually proceeding to the closed extremity, which yet contains some unde- composed bicarbonate of soda. This, when the fire at length reaches it, yields up carbonic acid, which chases forward the nitrogen lingering in the tube. The carbonic acid generated during the combustion is wholly absorbed by the potassa 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 properly corrected for temperature, pressure, and aqueous vapour, and its weight determined by calculation. When the operation has been very successful, and all pre- cautions minutely observed, the result still leaves an error in excess, amount- ing to 03 or 05 per cent., due to the residual air of the apparatus, or that condensed into the pores of the protoxide of copper. A most elegant process for estimating nitrogen in all organic compounds, except those containing the nitrogen in the form of nitrous, hyponitric and ORGANIC BODIES. 827 nitric acids, has been put into practice by MM. Will and Varrentrapp. When a non-azotized organic substance is heated to redness with a large excess of hydrate of potassa or soda, it suffers complete and speedy combustion at the expense of the water of the hydrate, the oxygen combining with the carbon of the oi-ganic matter to carbonic acid, 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 proportion of nitrogen can be easily calculated. An intimate mixture is made of 1 part caustic soda, and 2 or 3 parts quick- lime, 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 strong 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 to deliquescence of the alkali, fa- cilitates mixture with the organic substance, and prevents fusion and lique- faction. A proper quantity of the substance to be analyzed, from 5 to 10 grains namely, 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 ordi- nary 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 collected in a little ap- paratus of three bulbs (fig. 163) containing moderately strong hydrochloric Fig. 163. acid, attached by a cork to the combustion-tube. Matters being thus ad- justed, fire is applied to the tube commencing with the anterior extremity. When ignited throughout its whole length, and when no more gas issues from the apparatus, the point of the tube is broken, 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 bichloride of platinum 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 bi- chloride of platinum, but leaves untouched the yellow crystalline double chloride of platinum and ammonium. The latter* is collected upon a small weighed filter, washed with the same mixture of alcohol and ether, dried at 212 (100C), and weighed ; 100 parts correspond to G-272 parts of nitrogen ; or, the salt with its filter maybe very carefully ignited, arid 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. 228 ULTIMATE ANALYSIS OF ORGANIC BODIES. Bodies very rich in nitrogen, as urea, must be mixed with about an quantity of pure sugar, to furnish incondensible gas, and thus diminish the violence of the absorption which otherwise occurs ; and the same precaution must be taken, for a different reason, with those which contain little or no hydrogen. A modification of this process has been lately suggested by M. Peligot, which is very convenient if a large number of nitrogen-determinations are to be made. By this plan the ammonia, instead of being received in hydro- chloric acid, is conducted into a known volume (from % to 1 cubic inch) of a standard solution of sulphuric acid, contained in the ordinary nitrogen- bulbs. After the combustion is finished, the acid containing the ammonia is poured out into a beaker, coloured 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, fig. 136, described under the head of alkali- metry (page 227). The volume of lime-solution necessary to neutralize the same amount of acid, which is used for condensing the ammonia, having been ascertained by a preliminary experiment, it is evident that the differ- ence of the quantities used in the two experiments gives the ammonia col- lected during the combustion in the acid ; the amount of nitrogen may thus be calculated. If, for instance, an acid be prepared, containing 20 grains of pure hydrated sulphuric acid (S0 3 ,HO) in 1,000 grain-measures 200 grain-measures of this acid the quantity introduced into the bulbs cor- respond to 1-38 grains of ammonia, or 1-14 grains of nitrogen. The alka- line solution is so graduated that 1,000 grain-measures will exactly neutra- lize 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 solution, it is evident that - = 60 grain-measures were saturated 1000 by the ammonia, and the quantity of nitrogen is obtained by the proportion 1-14 v 60 200 : 1-14 = 60 : z, wherefrom z = ^ == 0-342 grains of nitrogen. j\j(j Estimation of Sulphur in organic compounds. When bodies of this class containing sulphur are burned with protoxide of copper, a small tube con- taining binoxide of lead must be interposed between the chloride of calcium tube and the potass-apparatus to retain any sulphurous acid which may be formed. It is better, however, to use chromate of lead in such cases. The proportion of sulphur is determined by oxidizing a known weight of the sub- stance by strong nitric acid, or by fusion in a silver vessel with ten or twelve times its weight of pure hydrate of potassa and half as much nitre. The sulphur 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 salt of baryta. Phosphorus is, in like manner, oxidized to phosphoric acid, the quantity of which is determined by precipitation in combination with sesquioxide of iron, or otherwise. Estimation of Chlorine. The case of a volatile liquid containing chlorine is of most frequent occurrence, and may be taken as an illustration of the general plan of proceeding. The combustion with protoxide of copper 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 chloride of copper into the chloride of calcium tube. Chromate of lead 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 EMPIRICAL AND RATIONAL FORMULAE. 329 filled with fragments of pure quick-lime. The lime is brought to a red- hent, and the vapour of the liquid driven over it, -when the chlorine dis- places oxygen from the lime, and gives rise to chloride of calcium. When cold, the contents of the tube are dissolved in the dilute nitric acid, filtered, and the chlorine precipitated by nitrate of silver. EMPIRICAL AND RATIONAL 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 rational formula, on the contrary, aims at describing the exact composition of one equivalent, or combining proportion of the substance, by stating the absolute number of equivalents of each of its elements essential to that object, 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 ; the rational requires in addition a knowledge of its combining quantity, which can only be obtained by direct experiment, by synthesis, or by the careful examination of one or more of its most definite compounds. Farther, the rational 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 C 4 H 3 3 , which exhibits the simplest relations of the three elements, and at the same time expresses the quantities of these, in equivalents, required to make up an equivalent of acetic acid ; hence, it is both empirical and rational. On the other hand, the empirical formula of crystallized kinic acid is C 7 H 6 6 , while its rational formula, determined by its capacity of saturation, is double, or C 14 H 12 12 , otherwise written C 14 H n O n ,HO. In like manner, the empi- rical formula of the artificial alkaloids furfurine. and amarine are respectively C 15 H 6 N0 3 and C 21 H 9 N. The equivalents of these substances, that is to say, the quantities required to form neutral salts with one equivalent of any well- defined monobasic acid, will, however, be expressed by the formulae C 30 H ia N 2 6 and C 42 H 1S N 2 ; hence these latter deserve the name of rational. The deduction of an empirical formula from the ultimate analysis is very asy ; the case of sugar, already cited, may be taken as an example. This contains, according to the analysis, in 100 parts Carbon 41-98 Hydrogen 6-43 Oxygen 51-59 10CHX) If each of these quantities be divided by the equivalent of the element, the quotients will express in equivalents the relations existing between them ; 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, who is obliged to use more indirect means. 41-98 51-59 = 6-99; 6-43; -g-=6-44, or 699 eq. carbon, 643 eq. hydrogen, and 644 eq. oxygen. It will be evident, in the first place, that the hydrogen and oxygen are present in the proportions to form water, or as many equivalents of one as of the other. Again, the equivalents of carbon and hydrogen are nearly in 330 DETERMINATION OF THE DENSITY OF VAPOURS. the proportion of 12 : 11, so that the formula G l2 li n O u 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 with 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 experiment, viz., two or three-tenths per cent, deficiency in the carbon, and not more than one-tenth per cent, excess in the hydrogen. Carbon 6x12=72 Hydrogen 11 eq. = ll Oxygen 8x11=88 171 171 : 72=100 : 42-11 171 : 11 = 100 : 6-43 171 : 88=100 : 51-46 Organic acids and salt-radicals have their proper equivalents 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 protoxide of lead or metallic silver left behind. If the protoxide of lead be mixed with globules of reduced metal, the quantity of the latter must be ascertained by dissolving away the oxide by 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, on the con- trary, or a basyle, has its equivalent 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. DETERMINATION OF THE DENSITY OF VAPOURS. The determination of the specific gravity of the vapour of a volatile sub- stance is frequently a point of great importance, inasmuch Fig. 164. as it gives the means, in conjunction 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 : A light glass globe, fig. 164, about three inches in diameter, is taken, and its neck softened and drawn out in the blowpipe-flame, as repre- sented in the figure, this is accurately weighed. About one hundred grains of the volatile liquid are then intro- duced, by gently warming the globe and dipping the point into the liquid, which is then forced upwards by the pres- sure of the air as the vessel cools. The globe is next firmly attached by wire to a handle, 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 temperature considerably above that of the boiling-point of the liquid. The latter becomes rapidly converted into vapour, which escapes by the nar- row orifice, chasing before it the air of the globe. When the issue of vapour has wholly ceased, and the temperature of the bath, Care- fully 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 beneath the surface of water which has been boiled and cooled out of contact of air, or better, mercury. The liquid enters the globe, and, if the expulsion of the air by the vapour has been complete, filla DETERMINATION OF THE DENSITY OF VAPOURS. 331 it ; if otherwise, an air-bubble is left, whose volume can be easily ascertained by pouring the liquid from the globe into ajar graduated to cubic inches, and then re-filling the globe, and repeating the same observation. The capacity of the vessel is thus at the same time known ; and these are all the data required. An example will render the whole intelligible. Determination of the density of the vapour of Acetone. Capacity of globe 31-61 cubic inches Weight of globe filled with dry air at 52 (11-11C) and 30-24 inches barometer 2070-88 grains. Weight of globe filled with vapour at 212 (100C) temp, of the bath at the moment of sealing the point, and 30-24 inches barometer 2076-81 grains. Residual air, at 45 (7-22C), and 30-24 inches barometer 0-60 cubic inch. 31-61 cub. inches of air at 52 and 30-24 in bar. =32-36 cub. inches at 60 (15-C) and 30 inch, bar., weighing 10-035 grains. Hence, weight of empty globe 2070-8810-035=2060-845 grains. 0-6 c. inch of air at 45=0-8 c. inch at 212 ; weight of do. by calculation =0-191 grain. 31-61 0-8 = 30-81 cubic inches of vapour at 212 and 30-24 in. bar., which, on the supposition that it could bear cooling to 60 without liquefaction, would, at that temperature, and under a pressure of 30 inch, bar., become reduced to 24-18 cubic inches. Hence, Weight of globe and vapour 2076-810 grains. ,, residual air 0-191 2076-619 Weight of globe 2060-845 Weight of the 24-18 cubic inches of vapour 15-774 Consequently, 100 cubic inches of such vapour must weigh... 65-23 100 cubic inches of air, under similar circumstances, weigh 31-01 65-23 - - =2-103, the specific gravity of the vapour in question, an being unity. In the foregoing statement a correction has been, for the sake of simpli city, omitted, which, in very exact experiments, must not be lost sight of, viz., the expansion and change of capacity of the glass globe by the elevated temperature of the bath. The density so obtained will be always en this account a little too high. The error to which the mercurial thermometer is, at high temperatures, liable, tends in the opposite direction. 2 DETERMINATION OP THE DENSITY OF VAPOURS. It is easy to compare the actual specific gravity of the vapour found in the manner above described with the theoretical specific gravity deduced from the formula of the substance: The formula of acetone, is C 8 H 3 0. In combining volumes this is repre- sented by 3 vols. of the hypothetical vapour of carbon, 3 vols. of hydrogen, and half a volume of oxygen. Or the weight of the unit of volume of ace- tone-vapour will be equal to three times the specific gravity of carbon-va- pour, three times that of hydrogen, and one-half that of oxygen added together, one volume of the compound vapour containing 6 volumes of its components : 3 vols. hypothetical vapour of carbon 0-41 83x3 = 1-2549 3 vols. hydrogen 0-0693x3=0-2079 \ vol. oxygen =0-5528 Theoretical specific gravity 2-0156 CANE AND GRAPE-SUGAR. 333 SECTION I. NON-AZOTIZED BODIES OF THE SACCHARINE AND AMYLACEOUS GROUP. SUGAK, STARCH, GUM, LIGN1N, AND ALLIED SUBSTANCES. THE members of this remarkable and very natural group present several interesting cases of isomerism. They are characterized by their feeble aptitude to enter into combination, and also by containing, with perhaps one exception, oxygen and hydrogen in the proportions to form water. Table of Saccharine and Amylaceous Substances. Cane-sugar, crystallized C^H^O^ Cane-sugar, in combination Grape-sugar, crystallized Grape-sugar, in combination Milk-sugar, crystallized Milk-sugar, in combination Sugar from Secale cornutum C 24 H 26 26 Mannite C 6 H 7 6 Starch, unaltered, dried at 212 (100C) Amidin, or gelatinous starch Dextrin, or gummy starch Starch from Cetraria Islandica Gum- Arabic Gum-tragacanth ........................................ 24^20^20 Lignin, or cellulose CANE-SUGAR; ORDINARY SUGAR, C^H^O^- This most useful substance 13 found in the juice of many of the grasses, in the sap of several forest- trees, in the root of the beet and the mallow, and in several other plants. It ia extracted most easily and in greatest abundance from the sugar-cane, culti- vated for the purpose in many tropical countries. The canes are crushed between rollers, and the expressed juice suffered to flow into a large vessel where it is slowly heated nearly to its boiling-point. A small quantity of hydrate of lime mixed with water is then added, which occasions the separa- tion of a coagulum consisting chiefly of earthy phosphates, waxy matter, :t peculiar albuminous principle, and mechanical impurities. The clear liquid separated from the coagulum thus produced is rapidly evaporated in open pans heated by a fierce fire made with the crushed canes of the preceding year, dried in the sun and preserved for the purpose. When sufficiently concentrated the syrup is transferred to a shallow vessel, and left to crys- tallize, during which time it is frequently agitated in order to hasten the change and hinder the formation of large crystals. It is, lastly, drained 334 CANE AND GRAPE-SUGAR. from the dark uncrystallizable syrup, or molasses, and sent into commerce, under the name of raw or Muscovado sugar. The refining of this crude pro- duct is effected by re-dissolving it in water, adding a quantity of albumen in the shape of serum of blood or white of egg, and sometimes a little lime- water, and heating the whole to the boiling-point; the albumen coagulates, and forms a kind of net-work of fibres, which inclose and separate from the liquid all mechanically suspended impurities. The solution is decolorized by filtration through animal charcoal, evaporated to the crystallizing-point, and put into conical earthen moulds, where it solidifies, after some time, to a confusedly-crystalline mass,, which is drained, washed with a little clean syrup, and dried in a stove ; the product is ordinary loaf-sugar. When the crystallization is allowed to take place quietly and slowly, sugar-candy re- sults, the crystals under these circumstances acquiring large volume and regular form. The evaporation of the decolorized syrup is best conducted in strong close boilers exhausted of air ; the boiling-point of the syrup is reduced in consequence from 230 (110C) to 150 (65-5C) or below, and and the injurious action of the heat upon the sugar in great measure pre- vented. Indeed, the production of molasses in the rude colonial manufacture is chiefly the result of the high and long-continued heat applied to the cane- juice, and might be almost entirely prevented by the use of vacuum-pans, the product of sugar being thereby greatly increased in quantity, and so far improved in quality as to become almost equal to the refined article. In many parts of the continent of Europe sugar is manufactured on a large scale from beet-root, which contains about 8 per cent, of that substance. The process is far more complicated and troublesome than that just described, and the product much inferior. When refined, however, it is scarcely to be distinguished from the preceding. The inhabitants of the Western States of America prepare sugar in considerable quantity from the sap of the sugar- maple, Acer saccharinum, which is common in those parts. The tree is tapped in the spring by boring a hole a little way into the wood, and inserting a small spout to convey the liquid into a vessel placed for its reception. This is boiled down in an iron pot, and furnishes a coarse sugar, which is almost wholly employed for domestic purposes, but little finding its way into com- merce. Pure sugar slowly separates from a strong solution in large, transparent colourless crystals, having the figure of a modified oblique rhombic prism. It has a pure, sweet taste, is very soluble in water, requiring for solution only one-third of its weight in the cold, and is also dissolved by alcohol, but with more difficulty. When moderately heated it melts, and solidifies on cooling to a glassy amorphous mass, familiar under the name of barley sugar: at a higher temperature it blackens and suffers decomposition ; and the same effect is produced, as already remarked, by long-continued boiling of the aqueous solution, which loses its faculty of crystallizing and acquires colour. The crystals have a specific gravity of 1-6, and are unchanged in the air. The deep brown soluble substance called caramel, used for colouring spirits, and other purposes, is a product of the action of heat upon cane-sugar. It contains C Z 4Hi 8 Oi8, and is isomeric with cane-sugar in combination. The following is the composition assigned to the principal compounds of cane-sugar by M. Peligot, who has devoted much attention to the subject. 1 Crystallized cane-sugar C 24 H 18 0, 8 -f-4HO Compound of sugar with common salt C 24 H 18 18 -|-NaCl-f-3HO Compound of sugar with baryta C 24 H 18 0, 8 -f-2BaO-f 4110 Compound of sugar with lime C 24 H 18 18 -f 2CaO-f4HO Compound of sugar with protoxide of lead .... C 24 H 18 0, 8 -f-4PbO 1 Ann. Chim. ct Phys. Ixyii. 113. CANE AND GRAPE-SUGAR. 335 The compounds with baryta and lime are prepared by digesting sugar at a gentle heat with the hydrates of the earths. The lime-compound has a bitter taste, and is more soluble in cold water than in hot. Both are readily decomposed by carbonic acid, crystals of carbonate of lime being occasion- ally produced. The combination with protoxide of lead is prepared by mix- ing sugar with a solution of acetate of lead, adding excess of ammonia, and drying the white insoluble product out of contact with air. The compound with common salt is crystallizable, soluble, and deliquescent. GRAPE-SUGAR; GLUCOSE; SUGAR OF FRUITS, C 24 H 28 2S . This variety of ugar is very abundantly diffused through the vegetable kingdom ; it may be extracted in large quantity from the juice of sweet grapes, and also from honey, of which it forms the solid crystalline portion, by washing with cold alcohol, which dissolves the fluid syrup. It may also be prepared by arti- ficially modifying cane-sugar, starch, and woody fibre, by processes presently to be described. The appearance of this substance, to an enormous extent, in the urine, is the most characteristic feature of the disease called diabetes. Grape-sugar is easily distinguished by several important peculiarities from cane-sugar: it is much less sweet, and less soluble in water, requiring 1 parts of the cold liquid for solution. Its mode of crystallization is also completely different ; instead of forming, like cane-sugar, bold, distinct crys- tals, it separates from its solutions in water and alcohol in granular warty masses, which but seldom present crystalline faces. When pure, it is nearly white. When heated, it melts, and loses 4 eq. of water, and at a higher temperature blackens and suffers decomposition. Grape-sugar combines with difficulty with lime, baryta, and oxide of lead, and is converted into a brown or black substance when boiled with solution of caustic alkali, by which cane-sugar is but little affected. It dissolves, on the contrary, in strong oil of vitriol without blackening, and gives rise to a peculiar com- pound acid, whose baryta-salt is soluble. Cane-sugar is, under these cir- cumstances, instantly changed to a black mass resembling charcoal. When solutions of cane and grape-sugar are mixed with two separate por- tions of solution of sulphate of copper, and caustic potassa added in excess to each, deep blue liquids are obtained, which, on being heated, exhibit dif- ferent characters ; the one containing cane-sugar is at first but little altered ; a small quantity of red powder falls after a time, but the liquid long retains its blue tint: with the grape-sugar, on the other hand, the first application of heat throws down a copious greenish precipitate, which rapidly changes to scarlet, and eventually to dark red, leaving a nearly colourless solution. This is an excellent test for distinguishing the two varieties of sugar, or dis- covering an admixture of grape with cane-sugar. Grape-sugar unites with common salt, forming a soluble compound of sweetish saline taste, which crystallizes in a regular and beautiful manner. Compounds of Grape-sugar, according to Peligot. Crystalline grape-sugar dried in the air ............ C24H 21 21 -}-7HO The same, dried at 266 (130C) ..................... C^H^Ogi-f 3110 Compound of grape-sugar with common salt ...... C 24 H 2l 21 -f-NaCl-f-5HO The same, dried at 206 (130C) ..................... C^riajO^-j-NaCl-j^HO Compound of grape-sugar with baryta ............. C^H^O^-j- 3BaO-f 7HO Compound of grape-sugar with lime ................ Compound of grape-sugar with protoxide of lead Sulphosaccharic Acid, C 24 H 20 20 ,S0 3 . Melted grape-sugar is cautiously mixed with concentrated sulphuric acid, the product dissolved in water, and neutralized with carbonate of baryta ; sulphate of baryta is formed together with a soluble sulphosaccharate of that earth, from which the acid itself 336 CANE AND GRAPE- SI) GAR. may be afterwards eliminated. It is a sweetish liquid, forming a variety of soluble salts, and very prone to decompose into sugar and sulphuric acid. Action of dilute Acids upon Sugar. Cane-sugar dissolved in dilute sulphuric acid is gradually but completely converted, at the common temperature of the air, into grape-sugar. The same solution, when long boiled, yields a brownish-blaok and nearly insoluble substance, which is a mixture of two distinct bodies, one having the appearance of small shining scales, and the other that of a dull brown powder. The first, called by Boullay and Mala- guti ulmin, and by Liebig sacchulmin, is insoluble in ammonia and alkalis ; the second, ulmic acid, the sacchulmic acid of Liebig, dissolves freely, yielding dark brown solutions precipitable by acids. By long-continued boiling witii water, sacchulmic acid is converted into sacchulmin. Both these substances have the same composition, expressed by the empirical formula C 2 HO. Hy- drochloric acid in a dilute state, produces the same effects. 1 Action of Alkalis upon Sugar. When lime or baryta is dissolved in a solu- tion of grape-sugar, and the whole left to itself several weeks in a close vessel, the alkaline reaction will be found to have disappeared from the for- mation of an acid substance. By mixing this solution with basic acetate of lead, a voluminous white precipitate is obtained, which, when decomposed by sulphuretted hydrogen, yields sulphide of lead, and the new acid, to which the term kalisaccharic or glucic is applied. Glucic acid is very soluble and deliquescent, has a sour taste and acid reaction: its salts, with the exception of that containing protoxide of lead, are very soluble. It contains C 8 H 5 6 . When grape-sugar is heated in a strong solution of potassa, soda, or baryta, the liquid darkens, and at length assumes a nearly black colour. The addi- tion of an acid then gives rise to a black flocculent precipitate of a substance called melasinic acid, containing C 24 H 12 10 . Cane-sugar long-boiled with alkalis undergoes the same changes, being probably first converted into grape-sugar. SUGAR FROM ERGOT OF RYE. This variety of sugar, extracted by alcohol from the ergot, crystallizes in transparent colourless prisms, which have a sweet taste, and are very soluble in water. It differs from cane-sugar in not reducing the acetate of copper when boiled with a solution of that substance. It contains C 24 H 26 26 . SUGAR OF DIABETES INSIPIDUS. A substance having the other properties of a sugar, but destitute of sweet taste, has been described by M. Thenard as having been obtained from the above-mentioned source. It was capable of furnishing alcohol by fermentation, and of suffering conversion into grape- sugar by dilute sulphuric acid. Its composition is unknown. LIQUORICE-SUGAR ; GLYCYRRHIZIN. The root of the common liquorice yields a large quantity of a peculiar sweet substance, which is soluble in water, but refuses to crystallize ; it is remarkable for forming with acids compounds which have but sparing solubility. Glycyrrhizin cannot be made to ferment. The formula of this substance is not definitely settled. SUGAR OF MILK; LACTIN, C 24 H 24 02 t . This curious substance is an impor- tant constituent of milk ; it is obtained in large quantities by evaporating whey to a syrupy state, and purifying the lactin, which slowly crystallizes out by animal charcoal. It forms white, translucent, four-sided prisms, of great 1 Under the names ulmin and ulmic add (humin and humic add, cre.nic and y the formula C 4 H 6 2 : it is pro- duced by the breaking up of an equivalent of grape-sugar, C 24 H 2g 28 , into 4 eq.of alcohol, 8 of carbonic acid, arid 4 of water. It is grape-sugar alomj which yields alcohol, the ferment in the experiment above related first con- verting the cane-sugar into that substance. Milk-sugar may sometimes appa- rently be made to ferment, but a change into grape-sugar always really pre- cedes the production of alcohol. The spirit, first obtained by distilling a fermented saccharine liquid is very weak, being diluted with a large quantity of water. By a second distilla- tion, 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 commerce 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 this by re-distilling it with half its weight of fresh quick-lime. 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 colourless, limpid liquid, of pungent and agreeable taste and odour; its specific gravity at 60 (15-5C) is 0-7938, and that of its vapour 1-613. It is very inflammable, burning with a pale bluish flame, free trorn smoke, and has never been frozen. Alcohol boils at 173 (78-4C) when ;n the anhydrous condition ; in a diluted state the boiling-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 degrees , t\\s takes place not only with pure alcohol, but with rectified ALCOHOL. 347 gpirix. It is misciblo with water in all proportions, and, indeed, has a great attraction for the latter, absorbing its vapour from the air, and abstracting the moisture from membranes and other similar substances immersed in it. The solvent powers of alcohol are very extensive ; it dissolves a great num- ber of saline compounds, and likewise a considerable proportion of potassa. "With many of these substances it forms definite compounds. The substance which is produced by potassa, contains C 4 H 5 0,KO ; it may be likewise formed bv acting with potassium upon anhydrous alcohol, when hydrogen is evolved. Alcohol dissolves, moreover, many organic substances, as the vegeto-alkalis, rosins, essential oils, and various other bodies; hence its great use in chemi- cal investigations and in several of the arts. The strength of commercial spirit is inferred from its density, when free from sugar and other substances added subsequent to distillation ; 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 0-9108 at 60 (15 -5C), and contains 49 J per cent, by weight of real alcohol. 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 wines of France and Germany it sometimes falls as low as 12 per cent. Strong ale contains about 10 per cent., ordinary spirits, as brandy, gin, whisky, 40 to 50 per cent., or occasionally more. These latter owe their characteristic flavours to certain essential oils, present in very small quantity, either generated in the act of fermentation or pur- posely 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 decom- position, and in that state becomes a ferment to the sugar, which is gradu- ally converted into alcohol. If the sugar be in excess, and the azotized mat ter deficient, the resulting wine remains sweet ; but if, on the other hand, the proportion of sugar be small, and that of albumin 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 colour 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 ia disengaged under pressure, and retained in solution in the liquid. The pro- cess 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 tartrate of potassa, with a little tartrate of lime and colouring matter, and is the source of all the tartaric acid met with in commerce. The salt in question exists in the juice in considerable 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 removed as the sugar disappears. It is this circumstance which renders grape-juice alone fit for making good wine : when that of gooseber- ries 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 recourse 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. lleer is a well-known liquor, of great antiquity, prepared from germinated grain, generally barley, and is used" in countries where the vine does not 348 ALCOHOL. 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 favour 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-dry- ing. During this process, the curious substance already referred to, dias- tase, is produced, and a portion of the starch, of the grain converted into sugar, and rendered soluble. In brewing, the crushed malt is infused in water at about 170 (76. 6C), and the mixture left to stand during the space of two hours or more. The easily soluble diastase has thus an opportunity of acting upon the unaltered starch of the grain, and, changing it into dextrin and sugar. The clear liquor, or wort, strained from the exhausted malt, is then pumped in a cop- per boiler, and boiled with the requisite quantity of hops, for communicating a pleasant bitter flavour, and conferring on the beer the property of keep- ing without injury. The flowers of the hop contain a bitter, resinous prin- ciple, called lupulin, and an essential oil, both of which are useful. 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 fei-meiitation, to which it would oth- erwise 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 in- duced. 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 carbonic acid. Highly coloured 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 cara- mel ; 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 greyish-yellow soft solid, nearly insoluble 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 transparent 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 fermentive process. No yeast is ever produced in liquids free from azotized matter; that added for the purpose of exciting fermenta- tion in pure sugar is destroyed, and rendered 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 ; oth- erwise, it speedily spoils. The distiller, who prepares spirits from grain, makes his wort, or irash, 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 bis infusion with hops, but proceeds at once to the fermentation, which LACTIC ACID. 319 he pushes as far as possible by large and repeated doses of yeast. Alcohol is manufactured iu 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 distilled. The potato-spirit is contami- nated by a very offensive volatile oil, again to be mentioned ; the crude pro- duct from corn contains a substance of a similar kind. The business 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 ; th yeast added to the dough converts the small portion of sugar the meal natu rally contains into alcohol and carbonic acid. The gas thus disengaged forces the tough and adhesive materials into bubbles, which are still farther 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. Sometimes carbonate of ammonia is employed with the same view, being completely volatilized by the high temperature of the oven. Bread is now sometimes made by mixing a little hydrochloric and carbonate of soda in the dough ; if proper proportions be taken, and the whole throughly mixed, the operation appears to be very successful. The use of leaven is one 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 fermenta- tion, in the same manner as yeast, but less perfectly ; it is apt to communicate a disagreeable sour taste and odour. LACTIC ACID ; LACTIC ACID FERMENTATION ; BUTYRIC ACID FERMENTATION. Azotized albuminous substances, which in an advanced state of putrefactive change act as alcohol-ferments, often possess, at certain periods of decay, the property of inducing an acid /fermentation in sugar, the consequence of which is the conversion of that substance into lactic acid. Thus, the azotized matter of malt, when suffered to putrefy in water for a few days, acquires the power of acidifying the sugar which accompanies it, while in a more advanced state of decomposition it converts, under similar circumstances, the sugar into alcohol. The glutin of grain behaves in the same manner: wheat flour, made into a paste with water, and left four or five days in a warm situation, be- comes a true lactic acid ferment; if left a day or two longer, it changes its character, and then acts like common yeast. Moist animal membranes, in a slightly decaying condition, often act energetically in developing lactic acid. Cane-sugar, probably by previously becoming grape-sugar, and the sugar of milk, both yield lactic acid, the latter, however, most readily, the grape- sugar having a strong tendency towards the alcoholic change. A good method of preparing lactic acid is the following. An additional quantity of milk- sugar is dissolved in ordinary milk, which is then set aside in a warm place, until it becomes sour and coagulated. The casein of the milk absorbs oxygen from the air, runs into putrefaction, and acidifies a portion of the sugar. The lactic acid formed, after a time coagulates and renders insoluble the casein, and the production of that acid ceases. By carefully neutralizing, however, the free acid by carbonate of soda, the casein becomes soluble, and, resuming its activity, changes a fresh quantity of sugar into lactic acid, which may be also neutralized, and by a sufficient number of repetitions of this process all the sugar of milk present may, in time, be acidified. When this has taken place, the liquid is boiled, filtered, and evaporated to dryness in a water-bath. The residue is treated with hot alcohol, which dissolves out the lactate of soda. The alcoholic solution may then be decomposed by the cautious addition of sulphuric acid, which precipitates sulphate rf soda, inso- luble in spirit The free acid may, if needful, be neutralized with lime, and tne resulti JT; nit purified by re-crystallization and the use of animal char- coal, after jrh t\ it may be decomposed by oxalic acid 350 LACTIC ACID. The following process will be found more economical on a large scale : A mixture is made of two gallons of milk, which may be stale or skimmed milk, six pounds of raw sugar, twelve pints of water, eight ounces of putrid cheese, and four 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 86 (80C), with occasional stirring. At the end of two or three weeks it will be found converted into a semi-solid mass or pudding of lactate of lime, which may be drained, pressed, and purified by re-crystallization from water. The lactate of lime may be decomposed by the necessary quantity of pure oxalic acid, the filtered liquor neutralized with carbonate of zinc, and, after a second filtration, evaporated until the zinc-salt crystallizes out on cooling. The latter may, lastly, be re-dissolved in water, and decomposed by sul- phuretted hydrogen, in order to obtain the free acid. If in the first part of the process the solid lactate of lime be not removed at the proper period from the fermenting liquid, it will gradually re-dissolve and disappear. On examination the liquid will then be found to consist chiefly of a solution of butyrate of lime. This second stage of the process, to which the name of butyric add fer- mentation has been given, is attended with an evolution of hydrogen and carbonic acid. It will be mentioned more in detail in the Section on Oils and Fats. 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. It has been supposed to exist in the blood, urine, and other animal fluids ; recent researches have, however, failed to detect it in either blood or urine, although it has been shown by Liebig to exist in considerable quantity in the juice of flesh or muscle. Lactic acid has been lately produced artificially in a most remarkable manner by the action of nitrous acid upon alanine. (See the Section on Organic Bases.) Solution of lactic acid may be concentrated in the vacuum of the air- pump, over a surface of oil of vitriol, until it acquires the aspect of a colour- less, 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. It forms soluble salts with all the metallic oxides. The syrupy acid contains C 6 H 5 6 -f-HO, or C 12 H 10 ]0 -f2HO, the water being basic, and susceptible of replacement by a metallic oxide. When syrupy lactic acid is heated in a retort to 266 (130C), water con- taining a little actic acid distils over, and the residue on cooling forms a yel- lowish solid fusible mass, very bitter, and nearly insoluble in water. This is anhydrous lactic acid, C 6 H 5 5 . Long-continued boiling with water converts it into ordinary lactic acid. When this substance is farther heated it decom- poses, yielding numerous products. One of these is lactide, formerly errone- ously called anhydrous lactic acid, a volatile substance, crystallizing in brilliant colourless rhombic plates, which, when put into water, slowly dis- solve, with production of common lactic acid. Lactide contains C 6 H 4 4 ; it combines with ammonia, forming lactamide, C 6 H 7 N0 4 , a colourless, crystalli- zable, soluble substance, resembling in its chemical relations oxamide. Another product of the action of heat on lactic acid is lactone, a colourless volatile liquid, boiling at 198 (92-2C.) Acetone is also formed, and carbonic oxide and carbonic acid are disengaged. A salt of lactic acid, gently heated with five or six parts of oil of vitriol, yields an enormous quantity of perfectly pure carbonic oxide gas. The most important and characteristic of the lactates are those of lime and the oxide of zinc. ETHER. 851 LACTATE OF LIME, CaO,C 6 TT 5 5 -]-5HO, exists ready-formed, to a small ex- teat, in Nux vomica. "When pure, it crystallizes in tufts of minute -wliite needles grouped in concentric layers. It dissolves in 10 parts of cold, and indefinitely in boiling water, melting in its water of crystallization at that temperature. LACTATE OF ZINC, ZnO,C 6 H 5 5 -j-3HO, is deposited from a hot solution in small brilliant 4-sided prismatic crystals, which require for solution 58 parts of cold and 6 of boiling water. LACTATE OF PROTOXIDE OF IRON, FeO,C 6 H 5 5 -j-3HO, is now used in medi- cine. It is prepared by adding alcohol to a mixture of lactate of ammonia and protochloride of iron, when the salt is precipitated in the form of small yellowish needles. When the expressed juice of the beet is exposed to a temperature of 90 (32 -9C) or 100 (37-7C) for a considerable time, the sugar it contain? suffers a peculiar kind of fermentation, to which the term viscous has been applied. Gases are evolved which contain hydrogen, and when the change appears complete, and the products come to be examined, the sugar is found to have disappeared. Mere traces of alcohol are produced, but, in place of that substance, a quantity of lactic acid, mannite, and a mucilaginous sub- stance resembling gum-Arabic, and said to be identical with gum in com- position. Pure sugar can be converted into this substance ; by boiling yeast or the glutin of wheat in water, dissolving sugar in the filtered solution, and ex- posing it to a tolerably high temperature, the viscous fermentation is set up, and a large quantity of the gummy principle generated. A little gas is at the same time disengaged, which is a mixture of carbonic acid and hydrogen. PRODUCTS OF THE ACTION OF ACIDS ON ALCOHOL. ETHER; OXIDE OF ETHYL. When equal weights of rectified spirit and oil of vitriol are mixed in a retort, the latter connected with a good condensing arrangement, and the liquid heated to ebullition, a colourless and highly vo- latile liquid, long known under the name of ether, or sulphuric ether, distils over. The process must be stopped as soon as the contents of the retort blacken and froth, otherwise the product will be contaminated with other substances, which then make their appearance. The ether obtained may be mixed with a little caustic potassa, and re-distilled by a very gentle heat. Pure ether is a colourless, transparent, fragrant liquid, very thin and mo- bile. Its sp. gr. at 60 (15-5C) is about 0-720; it boils at 96 (35-5C) under the pressure of the atmosphere, and bears without freezing the se- verest cold. When dropped on the hand it occasions a sharp sensation of cold, from its rapid volatilization. Ether is very combustible ; it burns with a white flame, generating water and carbonic acid. Although the substance itself is one of the lightest of liquids, its vapour is very heavy, having a density of 2-586. Mixed with oxygen gas, and fired by the electric spark, or otherwise, it explodes with the utmost violence. Preserved in an imper- fectly-stopped vessel, ether absorbs oxygen, and becomes acid from the pro- duction of acetic acid ; this attraction for oxygen is increased by elevation of temperature. It is decomposed by transmission through a red-hot tube Into olefiant gas, light carbonetted hydrogen, and a substance yet to be de- scribed, aldehyde. 852 COMPOUND ETHERS. Ether is tniscible with alcohol in all proportions, but not with water; it dissolves to a small extent in that liquid, 10 parts of water taking up 1 part, or thereabouts, of ether. It may be separated from alcohol, provided the quantity of the latter be not excessive, by an addition of water, and in this manner samples of commercial ether may be conveniently examined. Ether is a solvent for oily and fatty substances generally, and phosphorus to a small extent, a few saline compounds and some organic principles, but its powers in this respect are much more limited than those of alcohol or water. Ether was the first part of a great number of analogous substances in which the property of producing temporary insensibility to pain was recog- nized. In surgical operations, the use of ether is now superseded by that of chloroform. Ether is found by analysis to contain C 4 H 5 ; it, therefore, differs from al- cohol, C 4 II 6 2 , by the elements of water. Alcohol is often regarded as the hydrate of ether; but as ether cannot be made to combine with water di- rectly, and as alcohol cannot be converted into ether by the abstraction of water by the aid of substances known to possess a high affinity for that body, such a view was always looked upon as hypothetical. R,ecent experiments have, in fact, shown that a very different relation exists between alcohol and ether. We shall return to these researches, when we consider the theory of the production of ether, which will be discussed partly in connection with the history of sulphovinic acid, and partly with that of the methyl-com- pounds. COMPOUND ETHERS ; ETHYL-THEORY ; ETHYL. The so-called compound ethers constitute a very large and important class of substances derived from alcohol, and containing either the elements of ether, in combination with those of an oxygen-acid, inorganic or organic, or the elements of ole- fiant gas in union with those of a hydrogen-acid. The relations of these compounds to alcohol and the acids are most simply and clearly illustrated by comparing them with ordinary salts, in which the metal is replaced by a salt-basyle termed ethyl, containing C 4 H 5 . This substance forms haloid.-salts by combining with chlorine, iodine, bromine, &c., and its oxide, identical or isomeric with common ether, with oxygen-acids, like basic metallic oxides in general. A body containing carbon and hydrogen in the proportions indi- cated by the formula C 4 H 5 , has been lately obtained by Dr. Frankland, from one of the members of this group of compounds, and describe" under the name of ethyl. It is formed by exposing iodide of ethyl in sealed tubes, to the action of metallic zinc, at a temperature of 320 (160C).' In this re- action, the iodine of the iodide of ethyl C 4 H 5 I combines with the zinc, and ethyl is set free. On opening the sealed tubes, and allowing the gas, which is ethyl mixed with several secondary products (especially olefiant gas), to pass into a freezing mixture, the temperature of which is kept below 9 ( 23C), the ethyl condenses to a colourless mobile liquid. It is not at- tacked by concentrated sulphuric and nitric acids. Chlorine acts upon it under the influence of light, but not in the dark. Hitherto no compound ether has been reproduced from ethyl. The ethyl-theory, proposed by the sagacity of Liebig long before the separation of ethyl itself, will be found highly useful as an aid to the memory ; it must not, however, be forgotten that the compound ethers are distinguished by important characters from real and undoubted salts. Table of Ethyl- Compounds. Ethyl, symbol Ae C 4 H 5 Oxide of ethyl; ether C 4 !1 5 Hydrate of the oxide; alcohol C 4 II 5 0,HO 1 See also, zinc-ethyl, page 368. COMPOUND ETHERS. 353 Chloride of ethyl C 4 H 5 C1 Bromide of ethyl C 4 H 5 Br Iodide of ethyl C 4 H 5 l Cyanide of ethyl C 4 H 5 Cy Nitrate of oxide of ethyl C 4 H 5 0,N0 5 Nitrite of oxide of ethyl C 4 H 5 0,N0 3 Oxalate of oxide of ethyl C 4 H 5 0,C 2 3 Hydride of ethyl C 4 H 5 H Zinc-ethyl C 4 H 5 Zn &c. &c. The ethers of many of the acids may be formed by the direct action of these latter upon alcohol at a high temperature, the elements of water being displaced by those of the acid; this is chiefly conspicuous with the volatile acids. A more ready general method of forming them, however, is to distil a mixture of alcohol, sulphuric acid, and a salt of the acid the ether of which is required. The fatty acids, which in general cannot be distilled without more or less decomposition, yield their ethers with great facility by the action of hydrochloric acid gas upon an alcoholic solution of the acid. The compound ethers are mostly volatile aromatic liquids, in a few cases crystallizable solids, without action on vegetable colours, sparingly soluble in water, but dissolved in all proportions by alcohol and ether. They are not acted upon in the cold by alkaline carbonates, but suffer decomposition with more or less difficulty when heated with aqueous solutions of caustic alkali, a salt of the acid of the ether being usually generated, and alcohol formed and set free. An alcoholic solution of hydrate of potassa or soda is more active in this respect. The same kind of decomposition is often brought about by the prolonged contact of boiling water. CHLORIDE OF ETHYL; LIGHT HYDROCHLORIC ETHER; AeCl. 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 of alcohol is poured upon 4 parts of dry common salt in a retort, aud heat applied ; in either case the vapour of the hydrochloric ether should be con- ducted through a little tepid water in a wash-bottle, and then conveyed .'.nto a small receiver surrounded by ice and salt. It is purified from adhering water by contact with a few fragments of fused chloride of calcium. Hy- drochloric ether is a thin, colourless, and excessively volatile liquid, of a penetrating, aromatic, and somewhat alliaceous odour. At the freezing point of water, its sp. gr. is 0-921, and it boils at 50 (12-5C) ; it is soluble in 10 parts of water, is not decomposed by solution of nitrate of silver, but is quickly resolved into chloride of potassium and alcohol by a hot solution of caustic potassa. BROMIDE OF ETHYL; HYDROBROMIC ETHER; AeBr. This is prepared by distilling a mixture of 8 parts bromine, 1 part phosphorus, and 32 parts alcohol. The phosphorus is converted into phosphorous acid by the oxygen of the alcohol, when the ethyl combines with the bromine ; 3 equivalents of alcohol, 3 equivalents of bromine, and 1 equivalent of phosphorus, yield 3 equivalents of bromide of ethyl, 3 equivalents of water, and 1 equivalent of phophorous acid. It is a very volatile liquid, boiling at 106 (41 C), of penetrating taste and smell, and superior in density to water. IODIDE OF ETHYL ; HYDRIODIC ETHER ; Ael. Obtained by gradually mix- ing, with precaution, 1 part of phosphorus, 5 parts of alcohol, and 10 parts of iodine (1 eq. of phosphorus, 3 eq. of alcohol, and 3 eq. of iodine), and distilling. The reaction is analagous to that described in the case of the bromide. Iodide of ethyl is a colourless liquid, of penetrating and ethereal odour, having a density of 1-92, and boiling at 158 nOC). It becomes red 30* 354 COMPOUND ETHERS. by contact with air 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. SULPHIDE or ETHYL ; AeS. Formed by the action of chloride of ethyl upon a solution of the protosulphate of potassium. It is colourless, has a disagreeable garlic odour, and boils at 180 (82C). CYANIDE OF ETHYL, AeCy. This is produced when a mixture of sulphovi- nate of potassa and cyanide of potassium, both in a dry state, is slowly heated. It is colourless, when perfectly pure it has a powerful, not disa- greeable odour, and a sp. gr. of 0-788. It boils at 190-4 (88C). This substance has lately been studied by Drs. Kolbe and Frankland. They have found that cyanide of ethyl differs from the ordinary ethers in its deportment with the alkalis. Instead of yielding cyanide of potassium and alcohol, it is converted into ammonia and propionic acid, C 5 H 5 3 ,HO, a peculiar acid closely allied to acetic acid, and which will be noticed more in detail under the head of acetone. Cyanide of ethyl, in this reaction, absorbs 4 equiva- lents of water : 1 eq. of cyanide of ethyl.... C 6 H 5 N I 1 eq. of propionic acid C 6 H 6 O 4 4 eq. of water I1 4 4 | 1 eq. of ammonia H 3 N C 6 H 9 N0 4 (See cyanide of methyl.) When acted upon by potassium, cyanide of ethyl furnishes a gas, the nature of which is not definitely settled ; the residue contains cyanide of potassium and an organic alkali cyanethine, which con- tains C 18 H 15 N 3 , nnd is formed by the coalescence of three equivalents of the cyanide. SULPHITE OF OXIDE OF ETHYL; SULPHUBOUS ETHER ; AeO,S0 2 This sub- stance was obtained by adding absolute alcohol in excess to subchloride of sulphur. Hydrochloric acid is evolved, and sulphur deposited, while the sulphite of ethyl distils as a limpid strongly smelling liquid, of sp. gr. 1-085, boiling at 338 (170C), it is slowly decomposed by water. SULPHATE OF OXIDE OF ETHYL; SULPHURIC ETHER; AeO,S0 3 . This sub- stance has been only recently obtained. It is formed by passing the vapour of anhydrous sulphuric acid into perfectly anhydrous ether. A syrupy liquid is produced, which is shaken with 4 vols. of water and 1 vol. of ether, when two layers are formed; the lower contains sulphovinic acid, and various other compounds, while the upper layer consists of an ethereal solution of sul- phate of ethyl. At a gentle heat the ether is volatilized, and the sulphate of ethyl remains as a colourless liquid. It cannot be distilled without decom- position. PHOSPHATE OF OXIDE OF ETHYL ; PHOSPHORIC ETHER. See phosphovinic acid. NITRATE OF OXIDE OF ETHYL; NITRIC ETHER; AeO.N0 3 . The nitrate likewise has only recently been obtained ; it is prepared by cautiously dis- tilling a mixture of equal weights of alcohol and moderately strong nitric acid, to which a small quantity of nitrate of urea has been added. The ac- tion of nitric acid upon alcohol is peculiar ; the facility with which that acid is deoxidized by combustible bodies, leads, under ordinary circumstances, to the production of nitrous acid on the one hand, and an oxidized product of alcohol on the other, a nitrite of the oxide of ethyl being generated instead of a nitrate. M. Millon has shown that the addition of urea, from reasons to be explained when this compound will be described, entirely prevents the formation of that substance, and at the same time preserves the alcohol from oxidation by undergoing that change in its place, the sole liquid product COMPOUND ETHERS. 355 being the new ether. 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 odour ; and is not decomposed by an aque- ous solution of caustic potassa, although that substance dissolved in alcohol Attacks it even in the cold, with production of nitrate of potassa. Its vapoui ts apt to explode when strongly heated. NITRITE OF OXIDE OF ETHYL; NITROUS ETHER; AeO,N0 3 . Pure nitrous ether can only be obtained by the direct action of the acid itself upon alcohol. 1 part of potato-stai-ch, and 10 parts of nitric acid, are gently heated in a capacious retort or flask, and the vapour of nitrous acid thereby evolved 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 care- fully avoided. The product of this operation is a pale yellow volatile liquid, possessing an exceedingly agreeable odour of apples ; it boils at 62 (16-6C), and has a density of 0-947. It is decomposed by potassa, without darkening, into the nitrite of the base, 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 introduced 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 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 lo jsely stopped, and left two or three days in a cool place, .after which it is found to contain two layers of liquids, of which the uppermost is the ether. It is puri- fied by rectification. A somewhat similar product may be obtained by care- fully distilling a mixture of 3 parts rectified spirit and 2 of nitric acid of 1-28 sp. gr. ; the tire must be withdrawn as soon as the liquid boils. The siceet spirits of nitre of pharmacy, prepared by distilling three pounds of alcohol with four ounces of nitric acid, is a solution of nitrous ether, alde- hyde, and perhaps other substances, in spirit of wine. CARBONATE OF OXIDE OF ETHYL ; CARBONIC ETHER; AeO,C0 2 . Fragments of potassium 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 Ihe receiver as a colourless, limpid liquid of aromatic odour and burning taste. It boils at 259 (126C), and is decomposed by an alcoholic solution of potassa into carbonate of that base and alcohol. The reaction which gives rise to this substance is unexplained. SILICIC AND BORACIC ETHERS. A number of these compounds appear to exist, containing different proportions of the acids. Silicic ether, containing 3Ae(),Si0 3 , was obtained by M. Ebelmen by the action of anhydrous alcohol upon chloride of silicium. It is a colourless, limpid, aromatic liquid, of sp, gr. 0-933, boiling at 329 (165C), and decomposed by water with production of silicic acid and alcohol. In contact with moist air it is gradually resolved into translucent hydrate of silica, which becomes in the end hard enough to scratch glass. By substituting ordinary spirit for absolute alcohol, other compounds containing a larger portion of silicic acid are obtained. Horacic ether was procured by a similar process, substituting the chloride of boron for chloride of silicium. It formed a thin, limpid liquid of agreeable odour, having the sp. gr. of 0-885, and boiling at 246 (118C). It is decom- posed by water. Its alcoholic solution burns with a fine green flame, throw ing oif a thick smoke of boracic acid. It contains 3AeO,Bo0 3 . A .second 356 COMPOUND ETHERS. boracic ether in the form of a solid glassy fusible substance, containing AeO,2Bo0 3 , was formed by the action of fused boracic acid upon absolute alcohol. It is volatile in the vapour of alcohol only, and is decomposed by water. Of the ethers of the organic acids, the following are the most important: OXALATE OF THE OXIDE OF ETHYL; OXALIC ETHER; AeO,C 2 3 . This COm- pound is most easily obtained by distilling together 4 parts binoxala-te of potassa, 5 parts oil of vitriol, and 4 parts 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 retort, the first portions 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 volatilized spirit may condense.' After 6 or 8 hours' digestion, the mixture generally contains only traces of oxalic acid which is not etherified. Pure oxalic ether is a colourless, oily liquid, of pleasant aromatic odour, and 1-09 sp. gr. It boils at 363 (183 -8C) is but little soluble in water, and is readily decomposed by caustic alkalis into an oxalate and alcohol. With solution of ammonia in excess, it yields oxamide and alcohol. C 4 H 5 0, C 2 3 +NH 3= C 2 2 ,NH 2 +C 4 H/>,IIO. This is the best process for preparing oxamide, which is obtained perfectly white and pure. (See page 343.) 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 so- luble in hot alcohol, and separates, on cooling, in colourless, transparent, scaly crystals. They dissolve in water, and are both fusible and volatile. The name oxamethane is given to this body ; it consists of C 8 H 7 N0 6 =C 4 H 5 0, C 4 H 2 N0 6 , i. e., the ether of oxamic acid (see page 343). 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 the sunshine, a white, colourless, crystalline, fusible body is produced, insoluble in water and instantly decomposed by alcohol. It contains C 6 C1 5 4 , or oxalic ether in which the whole of the hydrogen is replaced by chlorine. ACETATE OF OXIDE OF ETHYL; ACETIC ETHER; AeO,C 4 H 3 3 . Acetic ether is conveniently made by heating together in a retort 3 parts of acetate of potassa, 3 parts of strong alcohol, and 2 of oil of vitriol. The distilled pro- duct is mixed with water, to separate the alcohol, digested first with a little chalk, and afterwards with fused chloride of calcium, and, lastly, rectified. The pure ether is an exceedingly fragrant, limpid liquid; it has a density of 0-890, and boils at 165 (73-8C). Alkalis decompose it in the usual manner. When treated with ammonia, it yields acetamide, a crystalline substance soluble in water and alcohol, which contains C 4 H 5 N0 2 ==C 4 H 3 2 ,NH 2 , i. e., acetate of ammonia 2 equivalents of water. Its formation is analogous to that of oxamide. Alkalis and acids reconvert it into ammonia and acetic acid. When treated with nitrous acid, it yields acetic acid, water and ni- trogen gas, C 4 H 5 N0 2 -f N0 3 =C 4 H 3 3 ,HO-j-H04-2N. FORMATE OF THE OXIDE OF ETHYL; FORMIC ETHER; AeO,C 2 H0 3 . A mix- ture of 7 parts of dry formate of soda, 10 of oil of vitriol, and 6 of strong alcohol, is to be subjected to distillation. The formic ether, separated by the addition of Avater to the distilled product, is agitated with a little mag- nesia, and left several days in contact with chloride of calcium. Formic ether is colourless, has an aromatic smell, and density of 915, and boils at 13H C (5G' J C). Watei diss >lves tlrs substance to a small extent. COMPOUND ETHERS. 357 The ethers of many of the vegetable acids have been obtained and de- scribed. The ethers of cyanic and cyanuric acids have been formed and studied. The description of these remarkable substances and of their important pro- ducts of decomposition is postponed until the history of the acids themselves has been given. ETHERS or THE FATTY ACIDS. Normal stearic ether has not yet been ob- tained. By passing hydrochloric acid gas into an alcoholic solution of stearic acid, Redtenbacher succeeded in obtaining the compound AeO,HO,C 6S H 66 5 . It resembled white wax, was inodorous and tasteless, melted at 86 (30C), and could not be distilled without decomposition. It was readily decomposed by boiling with caustic alkalis. Margaric ether is prepared by a similar mode of proceeding. "When purified from excess of acid by agitation with succes- sive small quantities of weak spirit, and afterwards made to crystallize slowly from the same menstruum, it forms regular, brilliant, colourless crys- tals, fusible at 70 (21 -1C), and distilling without decomposition ; when less pure it is in great part destroyed by this latter process. Margaric ether contains AeOjC^AggOg. An oleic ether, and corresponding compounds of seve- ral other less important fatty acids, have been formed and described. They greatly resemble each other in characters. BUTYRIC AND VALERIANIC ETHERS, AeO,C 8 H 7 3 , and AeO,Ci H 9 3 . The ether-compounds of these acids are easily obtained by the preceding process. They are fragrant volatile liquids, having an odour resembling that of the rind of the pine-apple. They are used for flavouring brandy. They are lighter than water, boil at a high temperature, and possess the constitution and general character of the class of bodies to which they belong. (ENANTTIIC ETHER. The aroma possessed by certain wines appears due to the presence of the ether of a peculiar acid called cenanthic, and which is pro- bably generated during fermentation. When such wines are distilled on the large scale, an oily liquid passes over towards the close of the operation, which consists, in great measure, of the crude ether ; it may be purified by agitation with solution of carbonate of potassa, freed from water by a few fragments of chloride of calcium, and re-distilled. (Enanthic ether is a thin, colourless liquid, having a powerful and almost intoxicating vinous odour ; it has a density of 0-862, boils at 482 (250C), and is but sparingly soluble in water, although, like the compound ethers in general, it dissolves with facility in alcohol. It contains C 22 H ]2 4 , or AeO,C 18 H, 7 O s . A hot solution of caustic potassa instantly decomposes oenanthic ether ; alcohol distils over, and oenanthate of potassa remains in the retort ; the latter is readily decomposed by warm dilute sulphuric acid, with liberation of oenanthic acid. Purified by repeated washing with hot water, cenanthic acid presents the appearance of a colourless, inodorous oil, which at 77 (25C) becomes a soft solid, like butter. It reddens litmus paper, and dissolves easily in solutions of the alkaline carbonates and in spirit, and very much resembles the fatty acids, to be hereafter described, the products of saponi- fication. The acid thus obtained is a hydrate, composed of C 18 H, 7 3 -f-HO. An acid of exactly the same composition has been obtained from Pelargonium roseum, and described by the name of pelargonic acid. It, is likewise pro- duced, together with a host of similar acids, by the action of nitric acid upon oleic acid. (Enanthic ether may be reproduced by distilling a mixture of 5 parts sulphovinate of potassa, and 1 part hydrated cenanthic acid, or perhapsf better, by the ordinary process for the ethers of the fatty acids. CHLOROCARBONIC ETHER. Although the constitution of this suostance is doubtful, it may be here described. Absolute alcohol is introduced into a glass-globe containing chlorocarbonic acid (phosgene gas, p. 131) : the gas ia absorbed in large quantity, and a yellowish liquid produced, from which 358 COMPOUND ACIDS CONTAINING water separates the chlorocarbonic ether. When freed from water by chlo- ride of calcium, and from adhering acid by rectification from litharge, it forms a thin, colourless, neutral liquid, which burns with a green flame. Its den- sity is 1-133; it boils at 202 (94-5C). The vapour, mixed with a large quan- tity of air, has an agreeable odour, but when nearly pure is extremeiy suffo- cating. It contains C 6 H 5 C10 4 =C 4 H 5 0,C 2 C10 8 . The density of the vapour is 3-82. The action of ammonia, gaseous or liquid, upon this substance, gives rise to a very curious product, called by M. Dumas ur ethane ; sal-ammoniac is at the same time formed. Urethane is a white, solid, crystallizable body, fusible below 212 (100C), and distilling unchanged, when in a dry state, at about 356 (180C) ; if moisture be present, it is decomposed, with evolution of ammonia. Water dissolves this substance very easily ; the solution is not affected by nitrate of silver, and yields, by spontaneous evaporation, large and distinct crystals. It contains C 6 H 7 N0 4 , or elements of carbonic ether and urea, whence the name. COMPOUND ACIDS CONTAINING THE ELEMENTS OF ETHER. SULPHOVINIC ACID, C 4 H 5 0,2S0 3 ,HO. Strong rectified spirit of wine is mixed with a double weight of concentrated sulphuric 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 with chalk; much sulphate of lime is produced. The latter is placed upon a cloth filter, drained, and pressed ; 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 pro- duct is sulphovinate of lime, in beautiful colourless, transparent crystals, con- taining CaO,C 4 H 6 0,2S0 3 4-2HO. They dissolve in an equal weight of cold water, and effloresce in a dry atmosphere. A similar salt, containing baryta, BaO,C 4 H 5 0,2S0 3 -f-2HO, equally soluble, and still more beautiful, may be produced by substituting, in the above pro- cess, carbonate of baryta for chalk ; from this substance the hydrated acid may be procured by exactly precipitating the base by dilute sulphuric acid, and evaporating the filtered solution, in vacuo, at the temperature of the air. It forms a sour syrupy liquid, in which sulphuric acid cannot be recognized, and is very easily decomposed by heat, and even by long exposure in the vacuum of the air-pump. All the sulphovinates are soluble ; the solutions are decomposed by ebullition. The lead-salt resembles the barytic com- pound. That of potassa, easily made by decomposing sulphovinate of lime by carbonate of potassa, is anhydrous ; it is permanent in the air, very solu- ble, and crystallizes well. Sulphovinate of potassa, distilled with concentrated sulphuric acid, gives ether; with dilute sulphuric acid, alcohol : and with strong acetic acid, acetic ether. Heated with hydrate of lime or baryta, the sulphovinates yield a sul- phate of the base and alcohol. PHOSPHOVINIC ACID, C 4 H 5 0,P0 5 ,2HO. This acid is bibasic. The baryta- salt is prepared by heating to 180 (82-2C) 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 bj- carbonate of baryta. The solution of phosphovinate, separated by filtration from the insoluble phos- phate, id evaporated at a moderate temperature. The salt crystallizes in bril- liant 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 68 (20C). The THE ELEMENTS OF ETHER. 359 crystals contains 2BaO,C 4 H 5 0,P0 5 -fl2HO. From this substance the hydra- ted acid may be obtained by precipitating the baryta by dilute sulphuric acid, and evaporating the filtered liquid in the vacuum of the air-pump ; it forms a colourless, syrupy liquid, of intensely sour taste, which sometimes exhibits appearances of crystallization. It is very soluble in water, alcohol, and ether, and easily decomposed by heat when in a concentrated state. The phosphovinates of lime, silver, and lead possesses but little solubility ; those of the alkalis, magnesia, and strontia are freely soluble. Voegeli has lately observed that, by the action of syrupy phosphoric acid upon alcohol, together with phosphovinic acid, another acid is formed, to which he gives the name phosphobiethylic acid, phosphovinic acid being designated by phosphethylic acid. The baryta silver and lead-salt of this acid are more soluble than the corresponding phosphovinates. The lead- salts atid lime-salts are anhydrous, and contain respectively PbO,2C 4 H 5 0,P0 5 and CaO,2C 4 H 5 0,P0 5 . The former of these salts, when heated to a temperature between 356 and 374 (180 and 190C), yields an aromatic, limpid liquid, which is tribasic phosphoric ether, 3C 4 H 5 0,P0 5 . It boils at 288 -5 (142 -6C). Its formation is represented by the equation : 2(PbO,2C 4 H 5 0,P0 5 ) = 3C 4 H 5 0,P0 5 -f2PbO,C 4 H 5 0,P0 5 . OXALOVINIC ACID, C 4 H 5 0,2C 2 3 .HO. Oxalic ether is dissolved in anhy- drous alcohol, and enough alcoholic solution of caustic potassa added to neutralize one-half of the oxalic acid present, whereupon the potassa-salt of the new acid precipitates in the form of crystalline scales, insoluble in alcohol, but easily dissolved by water. The free acid is obtained as a sour and exceedingly instable liquid by the addition of hydrofluosilicic acid to a solution of the preceding salt in dilute alcohol. It forms with baryta a very soluble salt. A tartrovinic acid has been described, and many other compounds of the same type exist. Another, and a different view, is very frequently taken of the substances just described, and of many analogous compounds. The sulphovinates, phosphovinates, &c., are supposed to possess a constitution resembling that . of ordinary double salts, one of the bases being a metallic oxide, and the second ether. Thus, anhydrous sulphovinate of baryta is written BaO,S0 8 4-C 4 H 5 0,S0 3 , or double sulphate of baryta and ether ; hydrated sulphovinic acid is HO,S0 3 -f-C 4 H 5 0,S0 3 , or bisulphate of ether. There are, however, grave objections against this mode of viewing the subject: in every true double salt the characters both of acid and bases remain unchanged ; alum gives the reactions of sulphuric acid, of alumina, and of potassa; while in sulphovinic acid or sulphovinate not a trace of sulphuric acid can be detected by any method short ef actual decomposition, by heat or otherwise. If sulphovinate of baryta contain sulphate of baryta ready formed, it is very difficult to understand how that salt can be decomposed by an addition of sulphuric acid. The student must, however, bear in mind that all views of the constitution of complex organic compounds must, of necessity, be to a great extent hypothetical, and liable to constant alteration with the progress of science. Products of the Decomposition of Sulphovinic Acid by Heat. A solution of sulphovinic acid, or, what is equivalent to it, a mixture, in due proportions, of oil of vitriol and strong alcohol, undergoes decomposi- tion when heated, yielding products which differ with the temperature to 360 COMPOUND ACIDS CONTAINING which the liquid is subjected. The cause of the decomposition is to be traced to the instability of the compound itself, and to the basic power of water, and the attraction of sulphuric acid for the latter, in virtue of which it determines the production of that substance, and liberates the elements of the ether. When the sulphovinic acid is so far diluted as to boil at 260 (126 -6C) or below, or when a temperature not exceeding this is applied to a stronger solution by the aid of a liquid bath, the compound acid is resolved into sul- phuric acid, which remains behind in the retort or distillatory vessel, while alcohol, and mere traces of ether, are volatilized. An acid whose boiling-point lies between 260 and 310 (126-6 and 154 -5C) is decomposed by ebullition into hydrated sulphuric acid and ether, which is accompanied by small quantities of alcohol. Lastly, when, by the addition of a large quantity of oil of vitriol, the boiling-point of the mixture is made to rise to 320 (160C) and above, the production of ether diminishes, and other substances begin to make their appearance, of which the most remarkable is olefiant gas. The mixture in the retort blackens, sulphurous acid and carbonic acid are disengaged, a yellow, oily aromatic liquid passes over, and a coaly residue is left, which contains sulphur. The chief and characteristic product is the olefiant gas ; the others may be considered the result of secondary actions. The three modes of decomposition may be thus contrasted : Below 260 C 4 H 5 0,2S0 3 ,HO-f2HO = C 4 B 5 0,HO-f 2(S0 3 ,HO) 260 310 C 4 H 6 0,2S0 3 ,HO+ HO = C 4 H 5 -f-2(S0 3 ,HO) Above 320 C 4 H 5 0,2S0 3 , HO = C 4 H 4 + 2(S0 8 ,HO) The ether-producing temperature is thus seen to be circumscribed within narrow limits; in the old process, however, in which a mixture of equal weights of alcohol and sulphuric acid is subjected to distillation, these con- ditions can be but partially complied with. At first the temperature of the mixture is too low to yield ether in any quantity, and towards the end of the process, long before all the suphovinic acid has been decomposed, it becomes too high, so that olefiant gas and its accompanying products appear instead. The remedy to this inconvenience consists in restraining the temperature of ebullition of the mixture within its proper bounds by the introduction of a constant supply of alcohol, to combine with the .liberated sulphuric acid, and reproduce the sulphovinic acid as fast as it becomes destroyed. The im- proved, or continuous ether-process, in which the same acid is made to ethe- rify an almost indefinite quantity of spirit, may be thus elegantly conducted upon a small scale. A wide-necked flask is fitted with a sound cork, perforated by three aper- tures, one of which is destined to receive a thermometer, with the graduation on the stem ; a second, the vertical portion of a long narrow tube, termina- ting in an orifice of about ^ of an inch in diameter ; and the third, a wide bent tube, connected with "the condenser, to carry off the volatile products. A mixture is made of 8 parts by weight of concentrated sulphuric 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 ther- mometer very shortly indicates a temperature of 300 (149C) ; when this happens, alcohol of the above density is suffered slowly to enter by the narrow tube, which is put in communication with a reservoir of that liquid, consisting of a large bottle perforated by a hole near the bottom, and fur- nished with a small brass stop-cock, fitted by a cork ; the stop-cock is secured to the end of the long tube by a caoutchouc connecter, tied, as usual with silk cord. As the tube passes nearly to the bottom of the flask, the alcohol gets thoroughly mixed with the acid liquid, the hydrostatic pressure of the THE ELEMENTS OF ETHER. Fig. 166. 361 fluid column being sufficient to ensure the regularity of the flow ; the quan- tity is easily adjusted by the aid of the stop-cock. For condensation, a Liebig's condenser may be used, supplied with ice- water. The arrangement is figured above (fig. 166). The intensity of heat, and the supply of alcohol, must be so adjusted that the thermometer may remain at 300 (149C), or as near that temperature as possible, while the contents of the flask are 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. This loss of acid constitutes the only limit to the duration of the process, which might otherwise continue indefinitely. On the large scale, the flask may be replaced by a vessel of lead, the tubes 1 Fig. 106. Apparatus for the preparation of ether, a. Flask containing the mixture of oil of vitriol and alcohol, b. Reservoir with stop-cock, for supplying a constant stream of alcohol s. Wide bent tube connected with the condenser for conveying away the vapours, d. The thermometer for regulating the temperature of the boiling liquid. 31 362 OLEFIANT GAS. being also of the same metal ; the stem of the thermometer may be made ta pass air-tight through the cover, and heat may, perhaps, be advantageously applied by high-pressure steam, or hot oil, circulating in a spiral of metal tube, immersed in the mixture of acid and spirit. The crude ether is to be separated from the water on which it floats, agi- tated with a little solution of caustic potassa, 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 spontaneous separation before mentioned does not occur, from the accidental presence of ^arger quantity than usual of undecomposed alcohol ; the addition of a little *^ter, however, always suffices to determine it. We shall once more return to the formation of ether, when we discuss the ,_. >thyl-compounds. HEAVY OIL OP WINE. When a mixture of 1\ parts of concentrated sulphu- ric acid, and 1 part of rectified spirit of wine, of 0-833 sp. gr., is subjected to distillation, a little ether comes over, but is quickly succeeded by a yel- lowish, oily liquid, which may be freed from sulphurous acid by agitation with water, and from ether and undecomposed alcohol by exposure in the vacuum of the air-pump, beside two open capsules, the one containing hy- drate of potassa, and the other concentrated sulphuric acid. This substance may be prepared in larger quantity by the destructive distillation of dry sul- phovinate of lime ; alcohol, oil of wine, and a small quantity of an exceed- ingly volatile liquid, yet imperfectly examined, are produced. Pure oil of wine is colourless, or greenish, of oily consistence, and heavier than water ; it has an aromatic taste, and an odour resembling that of peppermint. Its boiling point is tolerably high. It is soluble in alcohol and ether, but scarcely so in water. By analysis it is found to contain C 8 H 9 0,2S0 3 , or per- haps C 4 H 4 ,S0 3 -|-C 4 H 5 0,S0 3 ; that is, neutral sulphate of ether, in combina- tion with the sulphate of a hydro-carbon, etherole. In contact with boiling water, oil of wine is resolved into sulphovinic acid, and a volatile liquid, known by the name of light, or sweet oil of wine ; with an alkaline solution, this effect is produced even with greater facility. Light oil of wine, left in a cool place for several days, deposits crystals of a white solid matter, which is tasteless, and has but little odour ; it is called etherin. The fluid residual portion is yellowish, oily, and lighter than water ; it has a high boiling-point, solidifies at a very low temperature, and is freely soluble in alcohol and ether; it bears the name of etherole. Both etherole and etheriu have the same composition, namely C 4 H 4 , and are consequently isomeric with olefiant gas. OLEPIANT GAS ; ETHYLINE. This substance may also be advantageously prepared on the principle described, by restraining the temperature within certain bounds, and preventing the charring and destruction of the alcohol, which always occurs in the old process, and which, at the same time, leads to the production of sulphurous and carbonic acids, which contaminate the gas. If the vapour of alcohol be passed into somewhat diluted sulphuric acid, maintained at a boiling-heat, it is absorbed with production of sulphovinic acid, which is shortly afterwards decomposed into water and olefiant gas. The process is thus conducted : A wide-necked flask (fig. 167), containing rectified spirit of wine, is fitted with a cork, through which pass an ordinary safety-tube, with a little water, and the bent glass tube, intended to convey the vapour of the spirit into the acid. The latter must be of such strength, as to have a boiling-point between 320 and 330 C (160 and 165 -5C) ; it is prepared by diluting strong oil of vitriol with rather less than half its weight of water. The acid is placed in a second and larger flask, also closed by a cork, into which are inserted two tubes and a thermometer. The first is DUTCH -LIQUID Fig. 167. 363 piece of straight tube, wide enough to allow the tube conveying the alcohol- vapour to pass freely down it, and dipping a little way into the acid ; the second is a narrow bent tube, the extremity of which is immersed in the water of the pneumatic trough. Both flasks are heated ; and as soon as it is seen that the acid is in a state of tranquil ebullition, while the thermometer marks the temperature above mentioned, the spirit is made to boil, and its vapour carried into the acid, which very soon begins to evolve olefiant gas and vapour of water, accompanied by a little ether and oil of wine, but no sulphurous acid. The acid liquid does not blacken, and the experiment may be carried on as long as may be desired. This is a very elegant and instructive, although somewhat troublesome, method of preparing the gas. The essential parts of the apparatus are shown in fig. 167. CHLORIDE OF OLEFIANT GAS ; DUTCH-LIQUID. It has long been known that when equal measures of olefiant gas and chlorine are mixed over water, absorp- tion 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, fig. 168, having a narrow neck at the lower part, dipping 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 olefiant gas being 364 CHLORIDES OF CARBON. kept a little in excess. The chlorine should be washed with water, and the olefiant gas passed through strong oil of vitriol, to remove vapour of ether ; the presence of sulphurous and carbonic acids is not injurious. Combina- tion takes place very rapidly, and the liquid product trickles down the sides of the globe into the receiver. When a considerable quantity has been col- lected, it is "agitated first with water, and afterwards with concentrated sul- phuric acid ; it is, lastly, purified by re-distillation. If impure olefiant gas be employed, the crude product contains a large quantity of a substance called by M. Regnault chloro-sulphuric acid, S0 2 C1, which, on contact with water, is converted, by the decomposition of the latter, into sulphuric and hydrochloric acids. Pure Dutch-liquid is a thin, colourless liquid, of agreeably fragrant odour, and sweet taste ; it is slightly soluble in water, and readily so in alcohol and ether. It is heavier than water, and boils when heated to 180 (82 -3C) ; it is unaffected by oil of vitriol and solid hydrate of potassa. When in- flamed, it burns with a greenish, smoky light. This substance yields, by analysis, C 4 H 4 C1 2 . When Dutch-liquid is treated with an alcoholic solution of caustic potassa, it is slowly resolved into chloride of potassium, which separates, and into a new and exceedingly volatile substance, containing C 4 H 3 C1, whose vapour requires to be cooled down to ( 17 -7C) before it condenses. At this temperature it forms a limpid, colourless liquid. Chlorine is absorbed by this substance, and a compound produced, which contains C 4 H 3 C1 3 ; this is in, turn decomposed by an alcoholic solution of hydrate of potassa into chloride of potassium and a new volatile liquid, C 4 H 2 C1 2 . BROMIDE AND IODIDE OF OLEFIANT GAS, C 4 H 4 Br 2 and C 4 H 4 I 2 . These compounds correspond to Dutch-liquid ; they are produced by bringing olefiant gas in contact with bromine and iodine. The bromide is a colour- less liquid, of agreeable, ethereal odour, and has a density of 2-16; it boils at 265 (129-5C), and solidifies, when cooled, to near ( 17-7C). The iodide is a colourless, crystalline, volatile substance, of penetrating odour ; it melts at 174 (78-8C), resists the action of sulphuric acid, but is decom- posed by caustic potassa. PRODUCTS OF THE ACTION OF CHLORINE ON DUTCH-LIQUID ; CHLORIDES OF CARBON. Dutch-liquid readily absorbs chlorine gas, and yields several new compounds, produced by the abstraction of successive portions of hydrogen, and its replacement or substitution by equivalent quantities of chlorine. This regular substitution of chlorine, bromine, iodine, &c., in place of hydrogen, as before stated, is a phenomenon of constant occur- rence in reactions between these bodies and very many organic compounds. In the present case four such steps may be traced, giving rise, in each instance, to hydrochloric acid and a new substance. Three out of the four new products are volatile liquids, containing C 4 H 3 C1 3 ,C 4 H 2 C1 4 and C 4 HC1 5 ; the fourth C 4 C1 6 in which the substitution of chlorine for hydrogen is com- plete, is the chloride of carbon, long ago obtained by Mr; Faraday by putting Dutch-liquid into a vessel of chlorine gas, and exposing the whole to the influence of light. Sesquichloride or Per chloride of Carbon, C 4 C1 6 , is a white, solid, crystalline substance, of aromatic odour, insoluble in water, but easily dissolved by alcohol and ether ; it melts at 320 (160C), and boils at a temperature a little above. It burns with difficulty, and is unaffected by both acids and alkalis. It is prepared as above stated. Protochloride of Carbon, C 4 C1 4 . When the vapour of the preceding sub- stance is transmitted through a red-hot porcelain tube filled with fragments of glass or rock-crystal, it is decomposed into free chlorine, and a second chloride of carbon, which condenses in the form of a volatile, colourless ETHIONIC AND ISETHIONIC ACIDS. 365 liquid, which has a density of 1-55, and boils at 248 (120C). The density ol its vapour is 5-82. It resembles in chemical relations the perchloride. Subchloride of Carbon, C 4 C1 2 , is produced when the protochloride is passed many successive times through an ignited porcelain tube; it is a white, volatile, silky substance, soluble in ether. Bichloride of Carbon, C 2 C1 4 . A fourth chloride of carbon is known and will be described here, although it is not derived from the alcohol group. It is formed by passing the vapour of bisulphide of carbon together with chlo- rine, through a red-hot porcelain-tube. A mixture of chloride of sulphur and bichloride of carbon is formed, which is distilled with potassa, when the chloride of sulphur is decomposed, and pure bichloride passes over. It is a colourless liquid of 1-56 sp. gr., and boils at 170-6 (77C). An alco- holic solution of potassa converts this compound into a mixture of chloride of potassium and carbonate of potassa. The same compound is formed by exhausting the action of chlorine upon marsh-gas and chloride of methyl in the sunshine. COMBUSTIBLE PLATINUM-SALTS OF ZEISE. A solution of bichloride of pla- tinum in alcohol is mixed with a little chloride of potassium dissolved in hy- drochloric acid, and the whole digested some hours at a high temperature. The alcohol is distilled off, the acid residue neutralized by carbonate of potassa, and left to crystallize.' The distilled liquid contains hydrochloric ether and aldehyde. The platinum-salt forms yellow, transparent, prismatic crystals, which become opaque on heating from loss of water ; when intro- duced into the flame of a spirit lamp, the salt burns vividly, leaving metallic platinum. It is soluble in 5 parts of warm water. When dried at 212 (100C), this substance contains Pt 2 Cl 2 ,C 4 H 4 - r -KCl. Corresponding com- pounds, containing Pt 2 Cl 2 ,C 4 H 4 -}-NaCl, and Pt^CJ^-j-NI^Cl, are known to exist. The chloride of potassium can be separated from the above compound by the cautious addition of bichloride of platinum ; the filtered solution yields by evaporation in vacuo a yellow, gummy, acid mass. The solution is slowly decomposed in the cold, and rapidly at a boiling heat, with separation of a black precipitate. These compounds are of uncertain constitution. PRODUCTS OF THE ACTION OF ANHYDROUS SULPHURIC ACID ON ALCOHOL AND OLEFIANT GAS. "When anhydrous alcohol is made to absorb the vapour of anhydrous sul- ohuric acid, a white, crystalline, solid substance is produced, fusible at a gentle heat, which, when purified from adhering acid, is found to consist of carbon, hydrogen, and the elements of sulphuric acid, in the relation of the equivalent numbers, or probably C 4 H 4 ,4S0 3 . To this substance Magnus applies the name sulphate of carbyl. A body very similar in appearance and properties, and probably identical with this, had previously been produced by M. Regnault, by passing pure and dry olefiant gas over anhydrous sul- phuric acid contained in a bent tube. When the crystals of sulphate of carbyl are dissolved in alcohol, water added, the whole neutralized by carbonate of baryta, and the filtered solu- tion concentrated by very gentle heat to a small bulk, and then mixed with a quantity of alcohol, a precipitate falls, which consists of baryta, in com- bination with a peculiar acid closely resembling the sulphovinic, but yet differing in many important particulars. By the cautious addition of iilute 31* 366 CHLORAL. sulphuric acid, the base may be withdrawn, and the hydrate of the new acid left in solution ; it bears the name of ethionic acid, and contains C 4 H 5 0,4S0 3 -f- 2 HO. The ethionat.es differ completely from the sulphovinates ; all are soluble in water, and appear to be anhydrous. Those of lime, baryta, and oxide of lead refuse to crystallize ; the ethionates of potassa, soda, and ammonia, on the contrary, may readily be obtained in good crystals. When a solution of ethionic acid is boiled, it is decomposed into sulphuric acid, and a second new acid, the isethionic, isomeric with sulphovinic acid. The isethionic acid and its salts are very stable : their solutions may be boiled without decomposition. The isethionates of baryta, lead, copper, potassa, soda, and ammonia crystallize with facility, and cannot be confounded with the sulphovinates. The hydrated acid contains C 4 H 5 0,2S0 3 -f-HO. The action of anhydrous sulphuric acid on ether, as has been already men- tioned, gives rise to the formation of neutral sulphate of ethyl (see page 354.) Together with this substance sulphuric acid and several other acids methionic and althionic are obtained, which are not yet sufficiently studied. PRODUCTS OF THE ACTION OF CHLORINE ON ALCOHOL, ETHER, AND ITS COMPOUNDS. CHLORAL. Perfectly dry chlorine is passed into anhydrous alcohol to saturation; the gas is absorbed in large quantity, and hydrochloric acid abundantly produced. Towards the end of the process the reaction must be aided by heat. When no more hydrochloric acid appears, the current of chlorine is interrupted, and the product agitated with three times its volume of concentrated sulphuric acid ; on gently warming this mixture in a water- bath, the impure chloral separates as an oily liquid, which floats on the surface of the acid ; it is purified by distillation from fresh oil of vitriol, and afterwards from a small quantity of quick-lime, which must be kept com- pletely covered by the liquid, until the end of the operation. Chloral has been obtained from starch, by distillation with hydrochloric acid and binoxide of manganese. Chloral is a thin, oily, colourless liquid, of peculiar and penetrating odour, which excites tears ; it has but little taste. When dropped upon paper it leaves a greasy stain, which is not, however, permanent. It has a density of 1-502, and boils at 201-2 (94C). Chloral is freely soluble in water, alcohol, and ether ; it forms, with a small quantity of water, a solid, crystal- line hydrate ; the solution is not affected by nitrate of silver. Caustic baryta and lime decompose the vapour of chloral when heated in it with appearance of ignition ; the oxide is converted into chloride, carbon is deposited, and car- bonic oxide set free. Solutions of caustic alkalis also decompose it, with production of a formate of the base, and a new volatile liquid, chloroform. Chloral contains C 4 HC1 3 2 . When chloral is preserved for any length of time, even in a vessel herme- tically sealed, it undergoes a very extraordinary change; it becomes con- verted into a solid, white, translucent substance, insoluble chloral, possessing exactly the same composition as the liquid itself. The new product is but very slightly soluble in water, alcohol, or ether ; when exposed to heat, alone >r in contact with oil of vitriol, it is re-converted into ordinary chloral. So- lution of caustic potassa resolves it into formic acid and chloroform. Bro- mine acts upon alcohol in the same manner as chlorine, and gives rise to a product very similar in properties to the foregoing, called brt>mal, which coiu ALCOHOL. SG7 tains C 4 TIBr 3 2 . It forms a crystallizable hydrate with water, and is decom po^ed by strong alkaline solutions into formic acid and bromoform. A cor- responding iodine-compound probably exists. Chlorine acts in a different manner upon alcohol which contains water ; when very dilute, the principal products are hydrochloric acid and aldehyde, the change being one of oxidation at the expense of the water. With strong spirit the reaction is more complex, one of its products being a volatile, oily, colourless liquid, of uncertain composition, long known under the name of heavy muriatic ether. The mode of action of dry chlorine on pure ether conforms strictly to the law of substitution before mentioned ; the carbon remains intact, while a portion or the whole of the hydrogen is removed, and its place supplied by an equivalent quantity of chlorine. Ether exposed to a current of the dry gas for a considerable period, the temperature being at first artifically reduced, yields a heavy oily product, having the odour of fennel. This is found by analysis to contain C 4 H 3 C1 2 0, or ether, in which 2 eq. of chlorine have been substituted for 2 eq. of hydrogen. It may be termed bichlori- netted ether. By the farther action of chlorine, aided by sunlight, the re- maining hydrogen is removed, and a white crystalline solid substance, closely resembling sesquichloride of carbon produced. This is composed of C 4 C1 5 ; it is called pentachlorinetted ether. In a substance called cloretheral, C 4 H 4 C10, accidentally formed by M. d'Arcet, in the preparation of Dutch- liquid, from the ether-vapour mixed with the olefiant gas, we have evidently the first member of this series. With the compound ethers, the same remarkable law is usually followed. The change is, however, often complicated by the appearance of secondary products. Thus, chlorinelted acetic ether, a dense, oily liquid, very different from common acetic ether, was found to contain C 8 H 6 C1 2 4 , being a substi- tution product of C g H 8 4 =C 4 H 5 0,C 4 H 3 3 ; and chtorinetted formic ether, C 6 H 4 C1 2 4 , is formed, in like manner, by the substitution of 2 eq. chlorine for 2 eq. hydrogen in ordinary formic ether, C 6 H 6 4 =C 4 H 5 0,C 2 H0 3 . A most remarkable and interesting set of compounds, due to substitution of this kind, are formed by the action of chlorine on chloride of ethj?!, or light hydrochloric ether. When the vapour of this substance is brought into con- tact with chlorine gas, the two bodies combine to a colourless oily liquid, very like Dutch-liquid, but yet differing from it in several important points ; it has, however, precisely the same composition, and its vapour has the same density. By the prolonged action of chlorine three other compounds are successively obtained, each poorer in hydrogen and richer in chlorine than the preceding, the ultimate product being the well-known sesquichloride of carbon of Mr. Faraday. Hydrochloric ether C 4 TI 5 C1 Monochlorinetted hydrochloric ether C 4 H 4 C1 2 Bichlorinetted C 4 U 3 C1 3 Trichlorinetted C 4 H 2 C1 4 Quadrichlorinetted C 4 H C1 5 Sesquichloride of carbon C 4 C1 6 DERIVATIVES OF ALCOHOL CONTAINING SULPHUR. MERCAPTAN. A solution of caustic potassa, of 1-28 or 1-3 sp. gr., is satu rated with sulphuretted hydrogen, and mixed in a retort with an equal volume of solution of sulphovinate of lime of the same density. The retort i*> oon- o68 ALCOHOL. nected 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 ea t sily sepa- rated by a funnel. The product thus obtained is a colourless, limpid liquid, of sp. gr. 0-842, but slightly soluble in water, easily miscible, on the con- trary, with alcohol. It boils at 97 (36C). The vapour of mercaptan has a most intolerable odour of onions, which adheres to the clothes and person with great obstinacy ; it is very inflammable, and burns with a blue flame. Mercaptan contains C 4 H 6 S 2 =C 4 H 5 S,HS ; or alcohol, having sulphur in the place of oxygen. When brought into contact with red oxide of mercury, even in the cold, violent reaction ensues, 1 water is formed, and a white substance is produced, soluble in alcohol, and separating from that liquid in distinct crystals, which contain C 4 H 5 S,IIgS. This compound is decomposed by sulphuretted hydro- gen, sulphide of mercury being thrown down, and mercaptan reproduced. By adding solutions of the oxides of lead, copper, silver, and gold, to an alcoholic solution of mercaptan, corresponding compounds containing those metals are formed. Caustic potassa produces no effect upon mercaptan, but potassium displaces hydrogen, and gives rise to a crystallizable compound soluble in water. XANTHIC ACID. The elements of ether and those of bisulphide of carbon combine in presence of an alkali to a very extraordinary substance, possess- ing the properties of an oxygen-acid, to which the name xanthic is applied, tm account of the yellow colour of one of its most permanent and charac- teristic salts, that of oxide of copper. Hydrate of potassa is dissolved in 32 parts of alcohol of 0-800 sp. gr. ; into this solution bisulphide of carbon is dropped until it ceases to be dissolved, or until the liquid loses its alka- linity. The whole is then cooled to ( 17-8C), when the potassa-salt separates in the form of brilliant, slender, colourless prisms, which must be quickly pressed between folds of bibulous paper, and dried in vacuo. It i? freely soluble in water and alcohol, but insoluble in ether, and is gradually destroyed by exposure to air by oxidation of a part of the sulphur. Hy- drated xanthic acid may be prepared by decomposing the foregoing com- pound by dilute sulphuric or hydrochloric acid. It is a colourless, oily liquid, heavier than water, of powerful and peculiar odour, and very com- bustible ; it reddens litmus-paper, and ultimately bleaches it. Exposed to gentle heat, it is decomposed into alcohol and bisulphide of carbon ; this happens at a temperature of 75 (23 -8C). Exposed to the air, or kept be- neath the surface of water open to the atmosphere, it becomes covered with a whitish crust, and is gradually destroyed. The xanthates of the alkalis and of baryta are colourless and crystallizable ; the lime-salt dries up to a gummy mass ; the xanthates of the oxides of zinc, lead, and mercury are white, and but feebly soluble, that of copper is a flocculent, insoluble sub- stance, of beautiful yellow colour. Hydrated xanthic acid contains C 6 Il5S 4 0,HO ; or C 4 H 5 0,C 2 S 4 ,HO. In the salts this water is replaced by one equivalent of a metallic oxide. DERIVATIVES OF ALCOHOL CONTAINING METALS. ZINC-ETHYL. In heating iodide of ethyl with zinc in sealed glass-tubes (see compound ethers; ethyl-theory, p. 352) a white substance remains in the tube, which is a mixttire of iodide of zinc and a peculiar volatile com- 1 Whence the name, mercurium captans. ALCOHOL. 369 pound, to -which Dr. Frankland has given the name zinc-ethyl. It may be separated from the residue by distilling it in a current of hydrogen, when it it is obtained in the form of a liquid of a disagreeable odour, which contains C 4 H 5 Zn. In contact with atmospheric air it is rapidly oxidized. When mixed with water, this compound is decomposed with evolution of a carbo- netted hydrogen, having the formula G 4 H 6 =C 4 H 5 ,H, which may be viewed as the hydride of ethyl. STIBETHYL. Iodide of ethyl when distilled with an alloy of antimony and potassium, yields a curious substance, which MM. Loewig and Schweizer have described under the name of stibethyl. It contains SbC 12 H 15 =Sb 3 (C 4 H 5 ). We shall return to this substance when speaking of the compound ammonias. 1 PRODUCTS OF THE OXIDATION OF ALCOHOL. When alcohol and ether burn with flame in free air, the products of their combustion are, as with all bodies of like chemical nature, carbonic acid and water. Under peculiar circumstances, however, these substances undergo partial oxidation, in which the hydrogen alone is affected, the carbon re- maining untouched. The result is the production of certain compounds, which form a small series, supposed by some chemists to contain a common radical, to which the name acetyl is applied. It is derived from ethyl by the oxidation arid removal of 2 eq. of hydrogen. Table of Acetyl- Compounds. Acetyl (symbol Ac) C 4 TT 3 Oxide of acetyl (unknown) C 4 H 3 Hydrate of oxide of acetyl; aldehyde C 4 H 3 0,HO Acetylous acid ; aldehydic acid C 4 H 3 O 2 ,HO Acetylic acid ; acetic acid C 4 H 3 3 ,HO Acetyl and its protoxide are alike hypothetical. ALDEHYDE, C 4 H 4 2 or AcO,HO. This substance is formed, as already no- ticed, among other products, when the vapour of ether or alcohol is trans- mitted through a red-hot tube ; also, by the action of chlorine on wealr alcohol. It is best prepared by the following process : 6 parts of oil of vitriol are mixed with 4 parts of rectified spirit of wine, and 4 parts of water ; this mixture is poured upon 6 parts of powdered binoxide of man- ganese, contained in a capacious retort, in connection with a condenser, cooled by ice-cold water. Gentle heat is applied ; and when 6 parts of liquid have passed over, the process is interrupted. The distilled product is put into a small retort, with its own weight of chloride of calcium, and redis- tilled; the operation is repeated. The aldehyde, still retaining alcohol, and other impurities, is mixed with twice its volume of ether, and saturated with dry ammoniacal gas ; a crystalline compound of aldehyde and ammonia separates, which may be washed Avith a little ethei-, and dried in the air. From this substance the aldehyde may be separated by distillation in a water-bath, with sulphuric acid, diluted with an equal quantity of water; by careful rectification from chloride of calcium, at a temperature not ex- ceeding 87 (30-5C), it is obtained pure and anhydrous. Bfomicthyl, BiCi2lIi5=Bi 3(C4H 6 ). Stanothyl, SnOJI 5 and tellurethyl, TeC4H 5 have also been produced by similar reactions and some of their compounds investigated. It. B. 370 ALDEHYD1C ACID. Aldehyde ' is a limpid, colourless liquid, of characteristic ethereal odour, which, when strong, is exceedingly suffocating. It has a density of 0-790, boils at 72 (22 -3C), and mixes, in all proportions, with water, alcohol, and ether ; it is neutral to test-paper, but acquires acidity on exposure to air, from the production of acetic acid ; under the influence of platinum-black this change is very speedy. When a solution of this compound is heated with caustic potassa, a remarkable brown, resin-like substance is produced, the so-called aldehyde-resin. Gently heated with protoxide of silver, it reduces the latter without evolution of gas, the metal being deposited on the inner surface of the vessel as*a brilliant and uniform film ; the liquid contains alde- hydate of silver. When treated with hydrocynic acid, aldehyde yields a substance called alanine, which was already noticed, when treating of lactic acid, and which will be described more in detail in the section on vegeto-alkalis, under the head of bases from aldehyde. The action of sulphuretted hydrogen upon the ammonia-compound gives rise to the formation of thialdine, noticed likewise under the head of bases from aldehyde. The ammonia-compound above mentioned forms transparent, colourless crystals of great beauty ; it has a mixed odour of ammonia and turpentine ; it dissolves very easily in water, with less facility in alcohol, and with diffi- culty in ether; it melts at about 170 (76C), and distils unchanged at 212 (100C). Acids decompose it, with production of ammoniacal salt and sepa- ration of aldehyde. The crystals, which are apt to become yellow, and lose their lustre in the air, contain C 4 H 4 2 -f-NH 3 . When pure aldehyde is long preserved in a close-stopped vessel, it is sometimes found to undergo spontaneous change into one, and even two iso- meric modifications, differing completely in properties from the original compound. In a specimen kept some weeks at 32 (0C), transparent acicular crystals were observed to form in considerable quantity, which, at a tempe- rature little exceeding that of the freezing-point of water, melted to a colour- less liquid, miscible with water, alcohol, and ether ; a few crystals remained, which sublimed without fusion, and were probably composed of the second substance. This new body received the name elaldehyde; it was found to be identical in composition with aldehyde, but to differ in properties and in the density of its vapour; the latter has a sp. gr. of 4-515, while that of alde- hyde is only 1-532, or one-third of that number. It refuses to combine with ammonia, is not rendered brown by potassa, and is but little affected by solution of silver. The second modification, or met aldehyde, is sometimes produced in pure aldehyde, kept at the common temperature of the air, even in hermetically- sealed tubes ; the conditions of its formation are unknown. It forms colour- less, transparent, prismatic crystals, which sublime without fusion at a temperature above 212 (100), and are soluble in alcohol and ether, but not in water. They also were found, by analysis, to have the same composition as aldehyde. The substance which we have described by the term of chloral may be viewed as bichlorinetted aldehyde. ALDEHYDIC ACID, C 4 H 8 2 ,HO. When solution of aldehydate of silver, obtained by digesting oxide of silver in excess with aldehyde, is precipitated oy sulphuretted hydrogen, an acid liquid is obtained, which neutralizes alkalis, and combines with the oxides of the metals. It is very easily decom- posed. Aldehydate of silver, mixed with baryta- water, gives rise to aldehy- date of baryta and oxide of silver : if this precipitate be heated in the liquid, * Alcohol dehydrogenatus. ACETIC ACID. 371 the metal is reduced, and neutral acetate of baryta formed ; whence it is in- ferred that the new acid contains the elements of the acetic acid, minus an equivalent of oxygen. ACETAL. This substance is one of the products of the slow oxidation of alcohol-vapour under the influence of platinum- black. Spirit of wine is poured into a large, tall, glass-jar, to the depth of about an inch, and a shallow capsule, containing slightly -moistened platinum -black, arranged above the surface of the liquid ; the jar is loosely covered by a glass plate, and left during two or three weeks, in a warm situation. At the expiration of that period the liquid is found highly acid ; it is. to be neutralized with carbonate of potassa, as much chloride of calcium added as the liquid will dissolve, and the whole subjected to distillation, the first fourth only being collected. Fused chloride of calcium added to the distilled product now throws up a light oily liquid, which is a mixture of acetal with alcohol, aldehyde, and acetic ether. By fresh treatment with chloride of calcium, and long exposure to gentle heat in a retort, the aldehyde is expelled. The acetic ether is destroyed by caustic potassa, and the alcohol removed by washing with water, after which the acetal is again digested witli fused chloride of calcium, and re-distilled. Pure acetal is a thin, colourless fluid, of agreeable ethereal odour of sp. gr. 0-821 at 72 (22 -2C), and boiling at 220 (104C). It is soluble in 18 parts of water, and miscible in all proportions with alcohol and ether. It is unchanged in the air ; but, under the influence of platinum-black, becomes converted into aldehyde, and eventually into acetic acid. Nitric and chromic acids produce a similar eifect. Strong boiling solution of potassa has no action on this substance. Acetal contains C 12 H. 4 4 , or the elements of 2 eq. ether and 1 eq. aldehyde, C 12 H ]4 4 =2C 4 H 5 0+C 4 H 4 2 . When a coil of fine platinum wire is heated to redness, and plunged into a mixture of ether, or alcohol-vapour and atmospheric air, it determines upon its surface the partial combustion of the former, and gives rise to an excessively pungent acrid vapour, which may be con- densed to a colourless liquid by suitable means. The Fi S- 169 - heat evolved in the act of oxidation is sufficient to main- tain the wire in an incandescent state. The experiment may be made by putting a little ether into an ale-glass, fig. 169, and suspending over it the heated spiral from a card ; or by slipping the coil over the wick of a spirit- lamp, so that the greater part may be raised above the cotton; the lamp is supplied with ether or spirit of wine, lighted for a moment, and then blown out. The coil continues to glow in the mixed atmosphere of air and combustible vapour, until the ether is exhausted. This is the lamp without flame of Sir H. Davy. A ball of spongy platinum may be substituted for the coil of wire. The condensed liquid contains acetic and formic acids with aldehyde and aldehydic acid. ACETIC ACID. Pure alcohol, exposed to the air, or thrown into a vessel of oxygen gas, fails to suifer the slightest change by oxidation ; when diluted with water, it remains also unaffected. If, on the other hand, spirit of wine be dropped upon dry platinum-black, the oxygen condensed into 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 vapour of acetic acid is abundantly evolved. It is almost unnecessary to add, that the platinum itself undergoes no change in this experiment. 372 ACETIC ACID. 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 vine- gar, 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 86 (30C). Such is the plan adopted at Orleans. 1 In England vinegar of an inferior description is pre- pared 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. A little sulphuric acid is afterwards added, with a view of checking farther decomposition, or mothering, by which the product would be spoiled. There is another source of acetic acid besides the oxidation of alcohol : when dry, hard wood, as oak and beech, is subjected to destructive distilla- tion at a red-heat, acetic acid is found among the liquid condensable pro- ducts 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 char- coal of excellent quality remains in the retort. The acid liquid is subjected to distillation, the first portion being collected apart for the sake of a pecu- liar volatile body, shortly to be described, which it contains. The remainder is saturated with lime, concentrated by evaporation, and mixed with solu- tion of sulphate of soda; sulphate of lime precipitates, while the acetic acid is transferred to the soda. The filtered solution is evaporated to its crystallizing-point ; the crystals are drained as much as possible from the dark, tarry mother-liquid, 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 acetate of soda, thus obtained, readily yields hydrated acetic acid by distillation with sulphuric acid. The strongest acetic acid is prepared by distilling finely powdered anhy- drous acetate of soda with three times its weight of concentrated oil of vitriol. The liquid is purified by rectification from sulphate of soda, acci- dentally thrown up, and then exposed to a low temperature. Crystals of hydrate of acetic acid form in large quantity, which may be drained from the weaker fluid portion, and then suffered to melt. Below 60 (15-5C) this substance forms large, colourless, transparent crystals, which above that temperature fuse to a thin, colourless liquid, of exceedingly pungent and well-known odour ; 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. The hydrate of acetic acid in the liquid condition has a density of 1-063, and boils at 246 (119C) ; its vapour is inflammable. Acetic acid forms a great number of exceedingly important salts, all of which are soluble in water ; the acetates of silver and mercury are the least soluble. The hydrate of acetic acid contains C 4 H 3 3 ,HO = Ac0 3 ,HO ; it. is formed 1 Dumas, Chimie appliquSe aux Arts, vi. 537. ACETIC ACID. 373 from alcohol by the substitution of 2 eq. of oxygen for 2 eq. of hv.lrogen. The water is basic, and can be replaced by metallic oxides. A different view regarding the constitution of this acid has been proposed by Prof. Kolbe ; it is chietiy based upon the remarkable decomposition which acetic acid under- goes when submitted to the action of the galvanic current. We shall return to this subject when speaking of valerianic acid. 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 sometim.es employed in the process. The strength of any sample of acetic acid cannot be safely inferred from its density, but is easily determined by observing the quantity of dry carbonate of soda necessary to saturate a known weight of the liquid. 1 ACETATE OF POTASSA, KO,C 4 H 3 3 . This salt crystallizes with, great diffi- culty ; it is generally met with as a foliated, white, crystalline mass, obtained by neutralizing carbonate of potassa by acetic acid, evaporating to dryness, and heating the salt to fusion. The acetate is extremely deliquescent, and soluble in water and alcohol ; the solution is usually alkaline, from a little loss of acid by the heat to which it has been subjected. From the alcoholic solution, carbonate of potassa is thrown down by a stream of carbonic acid. ACETATE OF SODA, NaO,C 4 H 3 3 -j-6HO. The mode of preparation of this salt on the large scale has been already described; it forms large, transpa- rent, colourless crystals, derived from a rhombic prism, which are easily rendered anhydrous by heat, effloresce in dry air, and dissolve in 3 parts of cold, and in an equal weight of hot water, it is also soluble in alcohol. The taste of this substance is cooling and saline. The dry salt undergoes the igneous fusion at 550 (287-8C), and begins to decompose at 600 (315-5C). ACETATE OF AMMONIA; SPIRIT OF MINDERERUS ; NH 4 Q,C 4 H 3 3 . The neu- tral solution obtained by saturating strong acetic acid by carbonate of am- monia cannot be evaporated without becoming acid from loss of base ; the salt passes off in large quantity with the vapour of water. Solid acetate of ammonia is best prepared by distilling a mixture of equal parts of acetate of lime and powdered salammoniac ; chloride of calcium remains in the retort. A saturated solution of the solid salt in hot water, suffered slowly to cool in a close vessel, deposits long slender crystals, which deliquesce in the air. Acetate of ammonia has a sharp and cooling, yet sweet, taste ; its solution becomes alkaline on keeping, from decomposition of the acid. Acetate of ammonia when distilled with anhydrous phosphoric acid, loses 4 eq. of water, being converted into a colourless liquid inmiscible with water, of an aromatic odour, and boiling at 170 (77C) which has received the name of acetonitrile C 4 H 3 N. When boiled with acids or alkalis it re-assimi- lates the 4 eq. of water, being converted again into acetic acid and ammonia. This substance is the type of a class ; great many ammonia-salts of acids, analogous to acetic acid, undergoing a similar change when treated with an- hydrous phosphoric acid. It is likewise obtained by a perfectly different process, which will be described when treating of the methyl-compounds. (See cyanide of methyl, page 383, and also acetic ether, page 356.) The acetates of lime, baryta, and stronlia, are very soluble, and can be pro- cured in crystals ; acetate of magnesia crystallizes with difficulty. ACETATE OF ALUMINA, A1 2 3 ,3C 4 H 3 3 . This salt is very soluble in water, and dries up in the vacuum of the air-pump to a gummy mass, without trace * AcetYc acid increases in density by the addition of water, and reaches its maximum 1.079 when 30 parts have been mixed with 100 of the strongest acid; it then decreases in density and when 13u parts have been added its specific gravity is the same as the hydrate, 1.0(33 The most ready method to test its .strensrlh is to suspend in it a fragment of pure marble of known weight; the loss of weight resulting will be five sixths of the weight of the hydratwl acid present, 50 parts of carbonate of liine being required to saturate 60 parts of acetio cid.-K. B. 374 ACETIC ACID. of crystallization. If foreign salts be present, the solution of the acetate becomes turbid on heating, from the separation of a basic compound, which re-dissolves as the liquid cools. Acetate of alumina is much employed in calico-printing ; it is prepared by mixing solutions of acetate of lead and alum, and filtering from the insoluble sulphate of lead. The liquid is thick- ened with gum or other suitable material, and with it the design is impressed upon the cloth by a wood-block, or by other means. Exposure to a moderate degree of heat drives oiF the acetic acid, and leaves the alumina in a state capable of entering into combination with the dye-stuif. Acetate of manganese forms colourless, rhombic, prismatic crystals, perma- nent in the air. Acetate of protoxide of iron crystallizes in small greenish- white needles, very prone to oxidation; both salts dissolve freely in water. Acetate of sesquioxide of iron is a dark-brownish red, uncrystallizable liquid, of powerful astringent taste. Acetate of cobalt forms a violet-coloured, crys- talline, deliquescent mass. The nickel-salt separates in green crystals, which dissolve in 6 parts of water. ACETATE OP LEAD, PbO, C 4 H 3 8 -j-3HO. This important salt is prepared on a large scale by dissolving litharge in acetic acid ; it may be obtained in colourless, transparent, prismatic crystals, but is generally met with in com- merce as a confusedly crystalline mass, somewhat resembling loaf-sugar. From this circumstance, and from its sweet taste, it is often called sugar of lead. The crystals are soluble in about l\ parts of cold water, effloresce in dry air, and melt when gently heated in their water of crystallization ; the latter is easily driven off, and the anhydrous salt obtained, which suffers the igneous fusion, and afterwards decomposes, at a high temperature. Acetate of lead is soluble in alcohol. The watery solution has an intensely sweet, and at the same time astringent, taste, and is not precipitated by ammonia. It is an article of great value to the chemist. BASIC ACETATES (SUBACETATES) OP LEAD. Sesqui-basic acetate is produced when the neutral anhydrous salt is so far decomposed by heat as to become converted into a porous white mass, decomposable only at a much higher temperature. It is soluble in water, and separates from the solution evapo- rated to a syrupy consistence in the form of crystalline scales. It contains 3PbO,2C 4 H 3 3 . A sub-acetate with 3 eq. of base is obtained by digesting at a moderate heat 7 parts of finely-powdered litharge, 6 parts of acetate of lead, and 30 parts of water. Or, by mixing a cold saturated solution of neu- tral acetate with a fifth of its volume of caustic ammonia, and leaving the whole some time in a covered vessel ; the salt separates in minute needles, which contain 3PbO,C 4 H 3 3 -j-HO. The solution of sub-acetate prepared by the first method is known in pharmacy under the name of Goulard water, A third sub-acetate exists, formed by adding a great excess of ammonia to a solution of acetate of lead, or by digesting acetate of lead with a large quan- tity of oxide. It is a white, slightly crystalline substance, insoluble in cold, and but little soluble in boiling water. It contains 6PbO,C 4 H 3 3 . The solu- tions of the sub-acetates of lead have a strong alkaline reaction, and absorb carbonic acid with the greatest avidity, becoming turbid from the precipita tion of basic carbonate. ACETATE OP COPPER. The neutral acetate, CuO,C 4 H 3 3 ~j-HO, is prepared by dissolving verdigris in hot acetic acid, and leaving the filtered solution to cool. It forms beautiful dark-green crystals, which dissolve in 14 parts of cold and 5 parts of boiling water, and are also soluble in alcohol. A solution oi this salt, mixed with sugar and heated, yields suboxide of copper in the form of minute red octahedral crystals ; the residual copper solution is not precipitated by an alkali. Acetate of copper furnishes, by destructive disti. 1 lation, strong acetic acid, containing acetone, and contaminated with copper. The salt i sometimes called distilled verdiyris, and is used as a pigment. CHLORACETIC ACID. 375 BASIC ACETATES (SUB-ACETATES) OF COPPER. Common verdigris, made by spreading the marc of grapes upon plates of copper exposed to the air during several weeks, or by substituting, with the same view, pieces of cloth dipped in crude acetic acid, is a mixture of several basic acetates of copper which have a green or blue colour. One of these, 3CuO,2C 4 H 3 3 -f-6HO, is obtained by digesting the powdered verdigris in warm water, and leaving the soluble part to spontaneous evaporation. It forms a blue, crystalline mass, but little soluble in cold water. When boiled, it deposits a brown powder, which is a sub-salt with large excess of base. The green insoluble residue of the verdigris contains 3CuO,C 4 H 3 3 -|-3HO : it may be formed by digesting neutral acetate of copper with the hydrated oxide. By ebullition with water it is resolved into neutral acetate and the brown sub-salt. ACETATE or SILVER, AgO,C 4 H 3 3 , is obtained by mixing acetate of potassa with nitrate of silver, and washing the precipitate with cold water to remove the nitrate of potassa. It crystallizes from a warm solution in small colour- less needles, which have but little solubility in the cold. Acetate of suboxide of mercury forms small scaly crystals, which are as feebly soluble as those of acetate of silver. The salt of the red oxide of mercury dis- solves with facility. CHLORACETIC ACID. 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 the new product, the chloracetic acid, with a small quantity of oxalic acid. The liquid at the bottom contains the same substances, together with the unaltered acetic acid. Hydrochloric and carbonic acid gases are at the same time produced, together with suffocating vapour, resembling chloro-carbonic aci'd. The crystalline matter is dissolved out with a small quantity of water, added to the liquid contained in the bottle, and the whole placed in the vacuum of the air-pump, with capsules containing fragments of caustic potassa, and concentrated sul- phuric acid. The oxalic acid is first deposited, and afterwards the new sub- stance in beautiful rhombic crystals. If the liquid refuses to crystallize, it maybe distilled with a little anhydrous phosphoric acid, and then evaporated. The crystals are spread upon bibulous paper to drain, and dried in vacuo. Chloracetic acid is a colourless and extremely deliquescent substance; it has a faint odour, and a sharp, caustic taste, bleaching the tongue and destroying the skin; the solution is powerfully acid. At 115 (46C) it melts to a clear liquid, and at 390 (218-8C) boils and distils unchanged. The density of the fused acid is 1 -617 ; that of the vapour, which is very irri- tating, is probably 5-6. The substance contains, according to the analysis of M. Dumas, C 4 C1 3 3 .HO, or the elements of hydrated acetic acid from which 3 eq. of hydrogen have been withdrawn, and 3 eq. of chlorine substi- tuted. Chloracetic acid forms a variety of salts, which have been examined and described: it combines also with ether, and with the ether of wood-spirit. These compounds correspond to the ethers of the other organic acid. Chlora- cetale of potassa crystallizes in fibrous, silky needles, which are permanent in the air, and contain KO,C 4 Cl 3 3 -f- HO. The ammomacal salt is also crys- tallizable and neutral ; it contains NH 4 0,C 4 C1 3 3 -J-5HO. Chloracetate of silver is a soluble compound, crystallizing in small greyish scales, which are easily altered by light; it gives, on analysis, AgO,C 4 C] 3 3 , and is consequently anhydrous. When chloracetic acid is boiled with an excess of ammonia, it is decom- posed, with production of chloroform and carbonate of ammonia. C 4 H C1 3 4 =C 2 H C1 8 and C 2 4 . 376 ACETONE. With caustic potassa, it yields a smaller quantity of chloroform, chloride of potassium, carbonate and formate of potassa. The chloride and the for- mate are secondary products of the reaction of the alkali upon the chloro- form. Normal acetic maybe reproduced from this curious substitution-compound. When an amalgam of potassium and mercury is put into a strong aqueous solution of chloracetic acid, chemical action ensues, the temparature of tht liquid rises, without disengagement of gas, and the solution is found to con- tain acetate of potassa, chloride of potassium, and some caustic potassa. ACETONE; PYR.OACETIC SPIRIT. When metallic acetates in an anhydrous state are subjected to destructive distillation, they yield, among other pro- ducts, a peculiar inflammable, volatile liquid, designated by the above names. It is most easily prepared by distilling carefully dried acetate of lead in a large earthen or coated glass retort, by a heat gradually raised to redness; the retort must be connected with a condenser well supplied with cold water. Much gas is evolved, chiefly carbonic acid, and the volatile product, but slightly contaminated with tar, collects in the receiver. The retort is found after the operation to contain minutely divided metallic lead, which is some- times pyrophoric. The crude acetone is saturated with carbonate of po- tassa, and afterwards rectified in a water-bath from chloride of calcium. This compound may also be prepared by passing the vapour of strong acetic acid through an iron tube heated to dull redness ; the acid is resolved into acetone, carbonic acid, carbonic oxide, and carbonetted hydrogen. Pure acetone is a colourless limpid liquid, of peculiar odour; it has a density of 0-792, and boils at 132 (55-5C) ; the density of its vapour, 2-022. Acetone is very inflammable, and burns with a bright flame; it is miscible in all proportions with water, alcohol, and ether. The simplest formula of this substance which is produced by the resolution of acetic acid into acetone and carbonic acid, is C 3 H 3 ; but it is probable that this for- mula should be doubled. When acetone is distilled with half its volume of Nordhausen sulphuric acid, an oily liquid is obtained, which in a state of purity has a feeble garlic odour. It is lighter than water, and very inflammable. It contains C 18 H 12 , and is produced by the abstraction of the elements of water from acetone. It has received the name mesitilole. If pentachloride of phosphorus be dropped into carefully cooled acetone, and the whole mixed with water, a heavy oily liquid separates, which is stated to contain C 6 H 5 C1. When this is dissolved in alcohol, and mixed with caustic potassa, a second oily pro- duct results. This is lighter than water, has an aromatic odour, and con- tains C 6 II 6 0. Sir Robert Kane has described a number of other compounds formed by the action of acids, and other chemical agents, on acetone, from which he has inferred the existence of an organic salt-basyle, containing C 6 H 5 , and to which the name of mesityl has been given. Zeise, on the other hand, has shown that by the action of chloride of platinum upon acetone, a yellow crystallizable compound can be obtained, having a composition expressed by the formula C 6 H 5 0-f-PtCl 2 . Acetic acid is not the only source of acetone ; it is produced in the de- structive distillation of citric acid, and may be procured from sugar, starch, and gum by distillation with 8 times their weight of powdered quick-lime The acetone is, in this case, accompanied by an oily, volatile liquid, sepa- rable by water, in which it is insoluble. This substance is called metacetone or propione ; it contains C 5 H 5 0, its boiling-point is 212 (100C). PROPIONTC ACID. Metacetone distilled with a mixture of bichromate of potassa and sulphuric acid yields, among other products, rnetacetonic or pro- vtonic acid C 8 H 5 3 ,HO, a volatile acid, very closely resembling acetic acid, KAKODYL AND ITS COMPOUNDS. 377 and chiefly distinguished from that substance by the high degree of solu- bility of its soda-salt. Mr. Morley has lately shown that propionate of ba- ryta when submitted to destructive distillation, yields again propione. Pro- pionic acid is one of the products of the action of hydrate of potassa in a melted state upon sugar, and is also generated by the fermentation of gly- cerin. The formation of this substance by the action of potassa upon cy- anide of ethyl has been already mentioned, page 354. When acetate of potassa is heated with a great excess of caustic alkali it is converted, as already remarked, 1 into carbonic acid and light carbonetted hydrogen, by the reaction of the oxygen of the water of the hydrate upon, the carbon of the acid. C 4 H 3 3 ,HO=C 2 4 -{- C 2 H 4 . KAKODYL AND ITS COMPOUNDS. The substance long known under the name of fuming liquor of Cadet, pre- pared by distilling a mixture of dry acetate of potassa and arsenious acid, has been shown by M. Bunsen to be the oxide of an isolable organic basyl, capable of forming a vast number of combinations, displacing other bodies, and being in turn displaced by them, in the same manner as a metal. The investigation of this difficult subject reflects the highest honour on the pa- tience and skill of the discoverer. Kakodyl, so named from its poisonous and offensive nature, contains three elements, viz., carbon, hydrogen, and arsenic. Table of the most important Kakodyl- Compounds. Kakodyl (symbol Kd) C 4 H 6 As. Oxide of kakodyl KdO. Chloride of kakodyl KdCl. Chloride of kakodyl and copper KdCl-{-Cu 2 Cl. Oxy-chloride of kakodyl 3KdCl-j-KdO. Terchloride of kakodyl KdCl 3 . Bromide of kakodyl KdBr. Iodide of kakodyl Kdl. Cyanide of kakodyl KdCy. Kakodylic acid Kd0 3 . Kakodylate of silver AgO,Kd0 3 . Kakodylate of kakodyl KdO,Kd0 3 . Sulphide of kakodyl KdS. Sulphide of kakodyl and copper KdS-j-3CuS. Tersulphide of kakodyl KdS 3 . Sulphur-salts containing tersulphide ) KdS,KdS 3 AuS,KdS 3 . of kakodyl / CuS,KdS 3 PbS,KdSj. Selenide of kakodyl KdSe. OXIDE OF KAKODYL; CADET'S FUMING LIQUID ; ALKARSIN; KdO. Equal weights of acetate of potassa and arsenious acid are intimately mixed, and introduced into a glass retort connected with a condenser and tubulated re- ceiver, cooled by ice : a glass tube is attached to the receiver to carry away the permanently-gaseous products to some distance from the experimenter. See page 153. 378 KAKODYL AND TTS COMPOUNDS. Heat is then applied to the retort, which is gradually increased to redness. At the close of the operation, the receiver is found to contain two liquids, besides a quantity of reduced arsenic : the heavier of these is the oxide of kakodyl in a coloured and impure condition ; the other chiefly consists of water, acetic acid, and acetone. The gas given off during distillation is principally carbonic acid. The crude oxide of kakodyl is repeatedly washed by agitation with water, previously freed from air by boiling, and afterwards re-distilled from hydrate of potassa in a vessel filled with pure hydrogen gas. All these operations must be conducted in the open air, and the strictest pre- cautions adopted to avoid the accidental inhalation of the smallest quantity of the vapour or its products. Oxide of kakodyl is a colourless, ethereal liquid of great refractive power; it is much heavier than water, having a density of 1-462. It is very slightly soluble in water, but easily dissolved by alcohol ; its boiling-point approaches 302 (150C), and it solidifies to a white crystalline mass at 9 ( 12-6C). The odour of this substance is extremely offensive, resembling that of arse- netted hydrogen : the minutest quantity attacks the eyes and the mucous membrane of the nose; a larger dose is highly dangerous. When exposed to the air, oxide of kakodyl emits a dense white smoke, becomes heated, and eventually takes fire, burning with a pale flame, and producing carbonic acid, "water, and a copious cloud of arsenious acid. It explodes when brought into contact with strong nitric acid, and inflames spontaneously when thrown into chlorine gas. The density of the vapour of this body is about 7-5. Oxide of kakodyl is generated by the reaction of arsenious acid on the elements of acetone, carbonic acid being at the same time formed ; the accompanying products are accidental : 2 eq. acetone C 6 H 6 O 2 , and 1 eq. arsenious acid, As0 3 =l eq. oxide kakodyl, C 4 H 6 AsO, and 2 eq. carbonic acid, C 2 4 . CHLORIDE or KAKODYL, KdCl. A dilute alcoholic solution of oxide of kakodyl is cautiously mixed with an equally dilute solution of corrosive sublimate, avoiding an excess of the latter; a white, crystalline, inodorous precipitate falls, containing KdO-{-2HgCl : when this is distilled with con- centrated liquid hydrochloric acid, it yields corrosive sublimate, water, and chloride of kaltodyl, which distils over. The product is left some time in contact with chloride of calcium and a little quicklime, and then distilled alone in an atmosphere of carbonic acid. The pure chloride is a colourless liquid, which does not fume in the air, but emits a vapour even more fearful in its effects, and more insupportable in odour than that of the oxide. It is heavier than water, and insoluble in that liquid, as also in ether; alcohol, on the other hand, dissolves it with facility. The boiling-point of this compound is a little above 212 (100C) ; its vapour is colourless, is spontaneously in- flammable in the air, and has a density of 4-56. Dilute nitric acid dissolves the chloride without change ; with the concentrated acid ignition and explo- sion occur. Chloride of kakodyl combines with subchloride of copper to a white, insoluble, crystalline double salt, containing KdCl-}-Cu 2 Cl, and also with oxide of kakodyl. KAKODYL, IN A FREE STATE, may be obtained by the action of metallic zinc, iron, or tin upon the above-described compound. Pure and anhydrous chloride of kakodyl is digested for three hours, at a temperature of 212 (100C), with slips of clean metallic zinc contained 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 ia 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 kakodyl itself. This is rendered quite pure by distil- lation from a fresh quantity of zinc, the process being conducted in the little KAKODYL AND ITS CO M POUNDS. 379 apparatus shown in the margin (fig. 170), -which is made Fig. 170. from a piece of glass tube, and is intended to serve the pur- pose both of retort and receiver. The zinc is introduced into the upper bulb, and then the tube drawn out in the manner represented. The whole is then filled with carbonic acid, and the lower extremity put into communication with a little hand-syringe. On dipping the point a into the crude kakodyl and making a slight movement of exhaustion, the liquid is drawn up into the bulb. Both extremities are then sealed in the blow-pipe flame, and after a short diges- tion at 212 (100C) or a little above, the pure kakodyl is distilled off into the lower bulb, which is kept cool. It forms a colourless, transparent, thin liquid, much resemb- ling the oxide in odour, and surpassing that substance in inflammability. When poured into the air, or into oxygen gas, it ignites instantly ; the same thing happens with chlo- rine. With very limited access of air it throws off white fumes, passing into oxide, and eventually into kakodylic acid. Kakodyl boils at 338 (170C), and when cooled to 21 ( 6-lC) crystallizes in large, transparent, square prisms. It combines directly with sulphur and chlorine, and in fact may readily be made to furnish all the compounds previously derived from the oxide. It constitutes the most perfect type of an organic quasi-metal which chemistry yet possesses. Kakodyl is decomposed by a temperature inferior to redness into metallic arsenic, and a mixture of 2 measures light carbonetted hydrogen, arid 1 measure olefiant gas. Chloride of kakodyl forms a hydrate, which is thick and viscid, and readily decomposable by chloride of calcium, which withdraws the water. In the preparation of the chloride, and also in other operations, a small quantity of a red amorphous powder is often obtained, called erytrarsin. This is inso- luble in water, alcohol, ether, and caustic potassa, but is gradually oxidized by exposure to the air, with production of arsenious acid. It contains C 4 H 6 3 As 3 . IODIDE or KAKODYL, Kdl. This is a thin, yellowish liquid, of offensive odour, and considerable specific gravity, prepared by distilling oxide of kakodyl with strong solution of hydriodic acid. A yellow crystalline sub- stance is at the same time formed, which is an oxy-iodide. Bromide and fluoride of kakodyl have likewise been obtained and examined. SULPHIDE OF KAKODYL, KdS, is prepared by distilling chloride of kakodyl with a solution of the bisulphide of barium and hydrogen. It is a clear, thin, colourless liquid, smelling at once of alkarsin and mercaptan, insoluble in water, and spontaneously inflammable in the air. Its boiling-point is high, but it distils easily with the vapour of water. This substance dissolves sulphur, and generates tersulphide of kakodyl, KdS 3 , which is a sulphur- acid, and combines with the sulphides of gold, copper, bismuth, lead, and antimony. CYANIDE OF KAKODYL, KdCy. The cyanide is easily formed by distilling alkarsin with strong hydrocyanic acid, or cyanide of mercury. Above 91 (32 P- 7C) it is a colourless, ethereal liquid, but below that temperature it crystallizes in colourless, four-sided prisms, of beautiful diamond lustre. It boils at about 284 (140C), and is but slightly soluble in water. It requires to be heated before inflammation occurs. The vapour of this substance is most fearfully poisonous; the atmosphere of a room is said to be so far con- taminated by the evaporation of a few grains, as to cause instantaneous numbness of the hands and feet, vertigo, and even unconsciousness. KAKODYLIC ACID (ALKARGEN) ; Kd0 3 . This is the ultimate product of th 880 KAKODYL AND ITS COMPOUNDS. action of oxygen at a low temperature upon kakodyl or its oxide ; it is best prepared by adding oxide of mercury to that substance, covered with a layer of water, and artificially cooled, until the mixture loses all odour, and after- wards decomposing any kakodylate of mercury, that may have been formed, by the cautious addition of more alkarsin. The liquid furnishes, by evapo- ration to dryness and solution in alcohol, crystals of the new acid. The sulphide, and other compounds of kakodyl, yield, by exposure to air, the same substance. Kakodylic acid forms brilliant, colourless, 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 very soluble in water and in alcohol, but not in ether ; the solution has an acid reaction. When mixed with alkalis and evaporated, a gummy, amorphous mass results. With the oxides of silver and mercury, on the other hand, it yields crystallizable com- pounds. It unites with oxide of kakodyl, and forms a variety of combinations with metallic salts. Alkargen is exceedingly stable ; it is neither affected by red, fuming nitric acid, aqua regia, nor even chromic acid in solution ; it may be boiled with these substances without the least change. It is deoxi- dized, however, by phosphorous acid and protochloride of tin to oxide of kakodyl. Dry hydriodic acid gas decomposes it, with production of water, iodide of kakodyl, and free iodine; hydrochloric acid, under similar circum- stances, converts it into a corresponding terchloride, which is solid and crys- tallizable. Lastly, what is extremely remarkable, this substance is not in the least degree poisonous. PARAKAKODYLIC OXIDE. When air is allowed access to a quantity 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 kakodylic acid. Long exposure to air, or the passage of a copious current through the mass, heated to 158 (70C), fails to induce crystallization of the whole. If in this state water be added, everything dissolves, and a solution results which contains kakodylic acid, partly free, and partly in combination with the oxide of kakodyl. When this liquid is distilled, water, having the odour of alkarsin, passes over, and afterwards an oily liquid, which is the new compound. Impure kakodylic acid remains in the retort. Parakakodylic oxide, purified by rectification from caustic baryta, is a colourless, oily liquid, strongly resembling alkarsin itself in odour, relations to solvents, and in the great number of its reactions. It neither fumes in the air, however, nor takes fire at common temperatures ; its vapour, mixed with air, and heated to 190 (87-8C), explodes with violence. By analysis, t is found to have exactly the same composition as ordinary oxide of kakodjl. WOOD-SPIRIT AND ITS DERIVATIVES. 881 SECTION II. SUBSTANCES MORE OR LESS ALLIED TO ALCOHOL. WOOD-SPIRIT AND ITS DERIVATIVES. IN the year 1812, Mr. P. Taylor discovered, among the liquid products of the destructive distillation of dry-wood, a peculiar volatile inflammable liquid, much resembling spirit of wine, to which allusion has already been made. This substance has been shown by MM. Dumas and Pe"ligot to be really a second alcohol, forming an ether, and a series of compounds, exactly corresponding with those of vinous spirit, and even more complete, in some points, than the latter. Wood-spirit, like ordinary alcohol, may be regarded as a hydrated oxide of a body like ethyl, containing C 2 H 3 , called methyl. 1 A very great number of compound methyl-ethers have been described; they present the most complete parallelism of origin, properties, and consti- tution with those derived from common alcohol. Wood-spirit Series. Methyl (symbol, Me) C 2 H 2 Oxide of methyl , C 2 fJ 3 Hydride of methyl (marsh gas) C 2 H 3 H Chloride of methyl C 2 H 3 C1 Iodide of methyl &c C 2 H 3 l Zinc-methyl C 2 H 3 Zn Wood-spirit C 2 H 3 0,HO Sulphate of oxide of methyl C 2 H 3 0,S0 3 Nitrate of oxide of methyl &c C 2 H 3 0,N0 5 Sulphomethylic acid C 2 H 3 0,2S0 3 ,HO Formic acid C 2 H 3 ,HO Chloroform C 2 H Cl, HYDRATED OXIDE OF METHYL; PYROXYLIC SPIRIT; WOOD-SPIRIT; MeO,HO The crude wood-vinegar probably contains about T ^ part of this sub stance, 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 by hydrate of lime, the clear liquid separated from the oil which floats on the surface, and from the sediment at the bottom of the vessel, and again distilled. A volatile liquid, which burns like weak alcohol, is obtained ; this may be strengthened in the same manner as ordinary spirit, by rectification, and ultimately rendered pure and anhydrous, by careful distillation from quick-lime by the heat of a water-bath. Pure wood-spirit is a colourless, thin liquid, of peculiar odour, quite different from that of alcohol, and burning, disagreeable taste ; it boils 1 From fifQu, wine, and v\>], wood ; the termination v\tj, or yl, is very frequently employed in the sms" 1 of mutter, material. 382 WOOD-SPIRIT AND ITS DERIVATIVES. at 152 (66-6C), and has a density of 0-798 at 08 (20C). The dsnsity of its vapour is 1-12. Wood-spirit mixes in all proportions with water, when pure ; it dissolves resins and volatile oils as freely as alcohol, and is often substituted for alcohol in various processes in the arts, for which purpose it is prepared on a large scale. It may be burned instead of ordinary spirit, in lamps; the flame is pale-coloured, like that of alcohol, and deposits no soot. Wood-spirit dissolves caustic baryta ; the solution deposits, by evapo- ration in vacuo, acicular crystals, containing BaO-f-MeO,HO. Like alcohol, it dissolves chloride of calcium in large quantity, and gives rise to a crystal- line compound, resembling that formed by alcohol, and containing, according to Kane, CaCl-f2(MeO,HO). OXIDE OF METHYL ; WOOD-ETHER ; MeO. One part of wood-spirit and 4 parts of concentrated sulphuric acid are mixed and exposed to heat in a flask fitted with a perforated cork and bent tube ; the liquid slowly blackens, and emits large quantities of gas, which may be passed through a little strong solution of caustic potassa, and collected over mercury. This is the wood-spirit ether, a permanently gaseous substance, which does not liquefy at the temperature of 3 ( 16-1C). It is colourless, has an ethereal odour, and burns with a pale and feebly luminous flame. Its specific gravity is 1-617. Cold water dissolves about 36 times its volume of this gas, acquiring thereby the characteristic taste and odour of the substance ; when boiled, the gas is again liberated. Alcohol, wood-spirit, and concentrated sulphuric acid, dissolve it in still larger quantity. Under the head of ether it has been mentioned that the generally received relation of this substance to the other ethyl-compounds had been rendered doubtful by recent researches. The same remark of course applies to me- thylic ether, which is in every respect analogous to common ethers. It was first proposed by Berzelius. and has long been urged by MM. Laurent and Gerhardt, that the composition of alcohol being expressed by the formula C 4 H 6 2 , the true formula of ether was C 8 H, 2 , and not C 4 H ? 0. The cor- rectness of this view has lately been established by a series of beautiful ex- periments carried out by Prof. Williamson. He found that the substance produced by dissolving potassium in alcohol, which has the formula C 4 II 5 0, KO, when acted upon by iodide of ethyl, furnishes iodide of potassium and perfectly pure ether. This reaction may be expressed by the two following equations : C 4 H 5 0,KO -j- C 4 H,I = KI -f 2C 4 H 5 0, or C 4 H 6 0,KO -f C 4 H 5 E = KI -f- C 8 H 10 2 . T'aat in this reaction, not two equivalents of ether, as represented in the first equation, but a compound C 8 H, 2 is formed, as expressed in the second, is clearly proved by substituting, when acting upon the compound C 4 H 5 0,KO, for the iodide of ethyl, the corresponding methyl-compound. In this case neither common ether nor methyl-ether is formed, but an intermediate com- pound C 6 H 8 2 C 4 H 5 0,C 2 H 3 0. This substance is insoluble in water, and has a peculiar odour similar to that of ether, but boils at 50 (10C). It is very probable that the substances, which have been described by the terms ethyl and methyl, likewise are not C 4 H. and C 2 H 3 , but C g H 10 and C 4 H 6 . The limits of this elementary work will not permit us to enter into the details of this question, which is still under the discussion of scientific chemists. CHLORIDE OF METHYL, MeCl. This compound is most easily prepared by heating a mixture of 2 parts of common salt, 1 of wood-spirit, arid 3 of con- centrated sulphuric acid ; it is a gaseous body, which may be conveniently collected over water, as it is but slightly soluble in that liquid. Chloride of methyl is colourless ; it has a peculiar odour and sweetish taste, and burns. WOOD-SPIRIT AND ITS DERIVATIVES. 883 when kindled, with a pale flame, greenish towards the edges, like most com- bustible chlorine-compounds. It has a density of 1-731, and is not liquefied at ( 17-7C). The gas is decomposed by transmission through a red-hot tube, with slight deposition of carbon, into hydrochloric acid gas and a car- bonetted hydrogen, which has been but little examined. IODIDE OF METHYL, Mel, is a colourless 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 2-257, and boils at 111 (43-8C). The density of its vapour is 4-883. The action of zinc upon iodide of methyl in sealed tubes furnishes a colourless gas, appa- rently a mixture of several substances, among which methyl may occur. 1 The residue contains iodide of zinc together with a volatile substance of very disagreeable odour, which absorbs oxygen with so much avidity, that it takes fire when coming in contact with the air. It is zinc-methyl, C 4 H 5 Zn, cor- responding to zinc-ethyl. (See page 368.) "When mixed with water it yields oxide of zinc and light carbonetted hydrogen. CYANIDE OF METHYL, MeCy. If a dry mixture of sulphomethylate of baryta and cyanide of potassium are heated in a retort, a very volatile liquid of a powerful odour distils over. It generally contains hydrocyanic acid and water, from which it is separated by distillation, first over red oxide of mer- cury, and then over anhydrous phosphoric acid. When thus purified, it has an agreeable aromatic odour, and boils at 170-6 (77C). When boiled with potassa, it undergoes a decomposition analogous to that of cyanide of ethyl, (see page 354)'; it absorbs 4 eq. of water, and yields acetic acid and am- monia. I C 4 H 3 0,HO = C 4 H 4 4 0-4 H 3 N C 4 H 7 N0 4 C 4 H 7 N0 4 It has been mentioned that this compound may be obtained by abstracting 4 eq. of water from acetate of ammonia by means of phosphoric acid. (See (page 373.) Compounds of methyl with bromine, fluorine, and sulphur have also "been obtained. SULPHATE OF OXIDE OF METHYL, MeO,S0 3 . This interesting substance is prepared by distilling 1 part of wood-spirit with 8 or 10 of strong oil of vitriol : the distillation may be carried nearly to dryness. The oleaginous liquid found in the receiver is agitated with water, and purified by rectifica- tion from powdered caustic baryta. The product, which is the body sought, is a colourless oily liquid, of alliaceous odour, having a density of 1-324, and boiling at 370 (1877C). 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 temperature, into sulphomethylic acid and wood-spirit, which is thus reproduced by hydration of the liberated methylic etheY. Anhydrous lime or baryta have no action on this summit ; their hydrates, however, and those of potassa and soda, decompose it instantly, with production of a sul phornethylate of the base, and wood-spirit. When neutral sulphate of methyl is heated with common salt, it yields sulphate of soda and chloride of methyl ; with cyanide of mercury or potassium, it gives a sulphate of the base, and cyanide of methyl ; with dry formate of soda, sulphate of soda and formate of methyl. These reactions possess great interest. 1 The same compound is believed to occur among the substances produced by the action of a galvanic current upon acetic acid. See valeriauic acid, page 392. 384 WOOD-SPIRIT AND ITS DERIVATIVES. NITRATE OP OXIDE OF METHYL, MeO,N0 5 . One part of nitrate of potassa is introduced into a retort, connected with a tubulated receiver, to which is attached a bottle, containing salt and water, cooled by a freezing, mixture ; a second tube serves to carry off the incondensible gases to a chim- ney. A mixture of one part of wood-spirit and 2 of oil of vitriol is made, and immediately poured upon the nitre ; reaction commences at once, and requires but little aid from external heat. A small quantity of red vapour is seen to arise, and an ethereal liquid condenses, in great abundance, in the receiver, and also in the bottle. When the process is at an end, the distilled products are mixed, and the heavy oily liquid obtained separated from the water. It is purified by several successive distillations by the heat of a water-bath from a mixture of chloride of calcium and litharge, and, lastly, rectified alone in a retort, furnished with a thermometer passing through the tabulature. The liquor begins to boil at about 140 (60C) ; the temperature soon rises to 150 (65-5C), at which point it remains constant; the product is then col- lected apart, the first and most volatile portions being contaminated with hydrocyanic acid and other impurities. Even with these precautions, the nitrate of methyl is not quite pure, as the analytical results show. The pro- perties of the substance, however, remove any doubts respecting its real nature. Nitrate of methyl is colourless, neutral, and of feeble odour ; its density is 1-182; it boils at 150 (65-5C), and burns, when kindled, with a yellow flame. Its vapour has a density of 2-64, and is eminently explosive; when heated in a flask or globe to 300 (140C), or a little above, it explodes with fearful violence ; the determination of the density of the vapour is, conse- quently, an operation of danger. Nitrate of methyl is decomposed by a solu- tion of caustic potassa into nitrate of that base and wood-spirit. OXALATE or OXIDE OF METHYL, MeO, C 2 3 . This beautiful and interest- ing substance 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, exposed to the air, quickly evaporates, leaving the oxalic methyl-ether in the form of rhombic transparent crystalline plates, which may be purified by pressure between folds of bibulous paper, and re-distilled from a litlle oxide of lead. The product is colourless, and has the odour of common oxalic ether ; it melts at 124 (51-1C), and boils at 322 (161 C). It dissolves freely in alcohol and wood-spirit, and also in water, which, how- ever, rapidly decomposes it, especially when hot, into oxalic acid and wood- spirit. The alkaline hydrates effect the same change even more easily. Solu- tion of ammonia converts it into oxanide and wood-spirit. With dry amrno- niacal gas it yields a white, solid substance, which crystallizes from alcohol in pearly cubes ; this new body, designated oxamelhylane, or oxamate of methyl, contains C 6 H 5 N0 6 =C 2 H 3 0,C 4 H 2 N0 6 . Many other salts of oxide of methyl have been formed and examined. The acetate, MeO,C 4 H 3 8 , is abundantly obtained by distilling 2 parts of wood- spirit with 1 of crystallizable acetic acid, and 1 of oil of vitriol. It much resembles acetic ether, having a density of 0-919, and boiling at 136 (57-8C) ; the density of its vapour is 2-563. This compound is isomeric with formic ether. Formate of methyl, MeO,C 2 H0 3 , is prepared by heating in a retort equal weights of sulphate of methyl and dry formate of soda, it is very vola- tile, lighter than water, and is isomeric with hydrate of acetic acid. Chloro- carbonic methyl-ether is produced by the action of that gas upon wood-spirit ; it is a colourless, thin, heavy, and very volatile liquid, containing C 4 H 3 C10 4 =C 2 II 3 0,C 2 C10 3 . It yields with dry ammonia a solid crystallizable substance, called urethylane, C 4 H 5 N0 4 . (See page 358.) SULPHOMETHYLIC ACID, MeO,2S0 3 ,HO. Sulphomethylate of baryta is prepared in the same manner as the sulphovinate ; 1 part of wood-spirit is WOOD-SPIRIT AND ITS DERIVATIVES. 385 Blowij mixed with 2 parts of concentrated sulphuric acid, the whole heated to ebullition, and left to cool, after which it is diluted with water and neu- tralized with carbonate of baryta. The solution is filtered from the inso- luble sulphate, and evaporated, first in a water-bath, and afterwards in vacua to the due degree of concentration. The salt crystallizes in beautiful square colourless tables, containing BaO,C 2 H 3 0,2S0 3 -{-2HO, which effloresce in dry air, and are very soluble in water. By exactly precipitating the base from this substance by dilute sulphuric acid, and leaving the filtered liquid to eva- porate in the air, hydrated sulphomethylic acid may be procured in the form of a sour, syrupy liquid, or as minute acicular crystals, very soluble in water and alcohol. It is very instable, being decomposed by heat in the same manner as sulphovinic acid. Sulphomethylate of potassa crystallizes in small, nacreous, rhombic tables, which are deliquescent; it contains KO, C 2 H 3 0,2S0 3 . The lead-salt is also very soluble. FORMIC ACID. As alcohol by oxidation under the influence of finely-divided platinum gives rise to acetic acid, so wood-spirit, under similar circumstan- ces, yields a peculiar acid product, produced by the substitution of 2 eq. of oxygen for 2 eq. of hydrogen, to which the term formic is given, from its oc- currence in the animal kingdom, in the bodies of ants. The experiment may be easily made by inclosing wood-spirit in a glass jar with a quantity of platinum-black, and allowing moderate excess of air; the spirit is gra- dually converted into formic acid. There has not been found an interme- diate product corresponding to aldehyde. Anhydrous formic acid, as in the salts, contains C 2 H0 3 . or the elements of 2 eq. carbonic oxide, and 1 eq. water. Pure hydrate formic acid, C 2 TI0 3 ,HO, is obtained by the action of sulphu- retted hydrogen on dry formate of lead. The salt, reduced to fine powder, is very gently heated in a glass tube connected with a condensing apparatus, through which a current of dry sulphuretted hydrogen gas is transmitted. It forms a clear, colourless liquid, which fumes slightly in the air, of exceed- ingly penetrating odour, boiling at 209 (98-5C), and crystallizing in large brilliant plates when cooled below 32 (0C). The sp. gr. of the acid is 1-235; it mixes with water in all proportions; the vapour is inflammable, and burns with a blue flame. A second hydrate, containing 2 eq. of water, exists; its density is 1-11, and it boils at 223 (106-1C). In its concen- trated form this acid is extremely corrosive; it attacks the skin, forming a blister or an ulcer, painful and difficult to heal. A more dilute acid may be prepared by a variety of processes : starch, sugar, and many other organic substances often yield formic acid when heated with oxidizing agents ; a con- venient method is the following : 1 part of sugar, 3 of binoxide of manga- nese, and 2 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 carbonic acid has subsided, heat is cautiously applied, and a considerable quantity of liquid distilled over. This is very impure ; it contains a vola- tile oily matter, and some substance which communicates a pungency not proper to formic acid in that dilute state. The acid liquid is neutralized with carbonate of soda, and the resulting formate purified by crystallization, and if needful, by animal charcoal. From this, or any other of its salts, solution of formic acid may be readily obtained by distillation with dilute sulphuric acid. It has an odour and taste much resembling those of acetic acid, reddens litmus strongly, and decomposes the alkaline carbonates with effervescence. Another process for making formic acid consists in distilling dry oxalic acid, mixed with its own weight of sand or pumice-stone in a glass retort. Carbonic oxide and carbonic acid are disengaged, while a very acid liquid distils, which is formic acid contaminated with a small quantity of oxa-io 33 886 WOOD -SPIRIT AND ITS DERIVATIVES. ncid. By redistilling this mixture pure distilled formic acid is obtained. This process yields a very strong acid, but only a small quantity in pro- portion to the oxalic acid employed. Formic acid, in quantity, may be extracted from ants by distilling the insects with water, or by simply macerating them in the cold liquid. Formic acid is readily distinguished from acetic acid by heating it with a little solution of oxide of silver or mercury ; the metal is reduced, and pre- cipitated in a pulverulent state, while carbonic acid is extricated; this re- action is sufficiently intelligible. The protochloride of mercury is reduced, by the aid of the elements of water, to calomel, carbonic acid arid hydro' chloric acids being formed. The most important salts of formic acid are the following: Formate of soda crystallizes in rhombic prisms containing 2 eq. of water; it is very so- luble, and is decomposed like the rest of the salts by hot oil of vitriol with evolution of pure carbonic oxide. Fused with many metallic oxides, it causes their reduction. Formate of potassa is with difficulty made to crys- tallize from its great solubility. Formate of ammonia crystallizes in square prisms ; it is very soluble, arid is decomposed by a high temperature into hydrocyanic acid and water, the elements of which it contains, NH 4 0,C 2 H0 8 4HO=C 2 NH. This decomposition is perfectly analogous to that of acetate of ammonia, see page 373. The salts of baryta, strontia, lime, and magnesia form small prismatic crystals, soluble without difficulty. Formate of lead crystallizes in small, diverging, colourless needles, whtieh require for solution 40 parts of cold water. The formates of manganese, protoxide of iron, zinc, nickel, and cobalt, are also crystallizable. That of copper is very beautiful, constituting bright blue, rhombic prisms of considerable magni- tude. Formate of silver is white, but slightly soluble, and decomposed by the least elevation of temperature. CHLOBOFOEM. This substance is produced, as already remarked, when an aqueous solution of caustic alkali is made to act upon chloral. It may be obtained with greater facility by distilling alcohol, wood-spirit, or acetone with a solution of chloride of lime. 1 part of hydrate of lime is suspended in 24 parts of cold water, and chlorine passed through the mixture until nearly the whole lime is dissolved. A little more hydrate is then added to restore the alkaline reaction, the clear liquid mixed with 1 part of alcohol or wood-spirit, and, after an interval of 24 hours, cautiously distilled in a very spacious vessel. A watery liquid containing a little spirit and a heavy oil collect in the receiver; the latter, which is the chloroform, is agitated with water, digested with chloride of calcium, and rectified in a water-bath. It is a thin, colourless liquid of agreeable ethereal odour, much resembling that of Dutch-liquid, and sweetish taste. Its density is 1-48, and it boils at 141-8 (61C) ; the density of its vapour is 4-116. Chloroform is with diffi- culty kindled, and burns with a greenish flame. It is nearly insoluble in water, and is not affected by concentrated sulphuric acid. Alcoholic solution of potassa decomposes it with production of chloride of potassium and for- mate of potassa. Chloroform may be prepared on a larger scale by cautiously distilling to- gether good commercial chloride of lime, wa,ter and alcohol. The whole product distils over with the first portions of water, so that the operation may be soon interrupted with advantage. This substance has been called strongly into notice from its remarkable effects upon the animal system in producing temporary insensibility to pain when its vapour is inhaled. Chloroform contains C 2 HC1 3 ; it is changed to formic acid by the substitu- tion of three eq. of oxygen for the three eq. of chlorine removed by the alkaline metal. WOOD- SPIRIT AND ITS DERIVATIVES. 387 .Bromoform, C 2 HBr 3 , is a heavy, volatile liquid, prepared by a similar pro- cess, bromine being substituted in the place of chlorine. It is converted by alkali into bromide of potassium and formate of potassa. lodoform, C 2 IIT 3 , is a solid, yellow, crystallizable substance, easily obtained by adding alco- holic solution of potassa to tincture of iodine, avoiding excess, evaporating the whole to dryness, and treating the residue with water. lodoforni is nearly insoluble in water, but dissolves in alcohol, and is decomposed by al- kalis in the same manner as the preceding compounds. FORMOMETHYLAL. This is a product of the distillation of wood-spirit with dilute sulphuric acid and binoxide of manganese. The distilled liquid is saturated with potassa, by which the new substance is separated as a light oily fluid. When purified by rectification, it is colourless, and of agreeable aromatic odour; it has a density of 0-855, boils at 170 (41C), and is com- pletely soluble in three parts of water. It contains C 6 H 8 4 . It corresponds to acetal, and may be viewed as a compound of 2 eq. of ether, with 1 eq. of the yet unknown aldehyde of the methyl-series, Cfl^^ss^C^^CfB.^. METHYL-MERCAPTAN is prepared by a process similar to that recommended for ordinary mercaptan, sulphomethylate of potassa being substituted for the sulphovinate of lime. It is a colourless liquid, of powerful alliaceous odour, and lighter than water; it boils at 68 (20C), and resembles mer- captan in its action on red oxide of mercury. PRODUCTS OF THE ACTION OF CHLORINE ON THE COMPOUNDS OF METHYL. Chlorine acts upon the methylic compounds in a manner strictly in obedi- ence to the law of substitution ; the carbon invariably remains intact, and every proportion of hydrogen removed is replaced by an equivalent quantity of chlorine. Methylic ether and chlorine, in a dry and pure condition, yield a volatile liquid product, containing C 2 H 2 C10 ; the experiment is at- tended with great danger, as the least elevation of temperature gives rise to a violent explosion. This product in its turn furnishes, by the continued action of the gas, a second liquid, containing C 2 HC1 2 0. The whole of the hydrogen is eventually lost, and a third compound, C 2 C1 3 0, produced. Chloride of methyl, C 2 II 3 C1, in like manner gives rise to three successive products. The first, C 2 H 2 C1 2 , is a neAV volatile liquid, much resembling chloride of olefiant gas ; the second, C 2 HC1 3 , is no other than chloroform ; the third is bichloride of carbon, C 2 C1 4 . Some of these substances, especially chloroform and bichloride of carbon, have been obtained also by the action of chlorine on light carbonetted hy- drogen (marsh-gas), which thus becomes connected with the methyl-series. It may be regarded as hydride of methyl, a view which is likewise sup- ported by its formation from zinc-methyl (see page 382) ; thus we have the following series. Hydride of methyl C 2 H 3 H. Light carbonetted hydrogen. Chloride of methyl C 2 H 3 C1. Chlorinetted chloride of methyl C 2 H 2 C1 2 . Bichlorinetted " " C 2 I1C1 3 . Chloroform. Trichlorinetted " " C 2 C1 4 . Bichloride of carbon. The acetate of methyl, C 6 H 6 4 , gives C ? H 4 C1 2 4 , and C 6 H 3 C1 3 4 ; the other methyl^ethers are without doubt affected in a similar manner. Commercial wood-spirit is very frequently contaminated with other sub- stances, some of which are with great difficulty separated. It sometimes contains aldehyde, often acetone and propione, and very frequently a vola- tile oil, which is precipitated by the addition of water, rendering the whole turbid. The latter is a mixture of several hydrocarbons, very analogous to those contained in coal-tar. A specimen of wood-spirit, from Wattwyl, in Switzerland, was found by Gmeiin to contain a volatile liquid, differing ii) 388 POTATO-OIL AND ITS DERIVATIVES. some respects from acetone, to winch he gave the term lignone. A verj similar substance is described by Schweizer and Weidmarm, under the name of xylite. Lastly, Mr. Scanlan has obtained from wood-spirit a solid, yellowish-red, crystallizable substance called eblanin. It is left behind in the retort when the crude spirit is rectified from lime ; it is insoluble in water, sublimes without fusion at 273 (133-9C), and contains, according to Dr. Gregory. C 21 H 9 4 . POTATO-OIL AND ITS DERIVATIVES. In the manufacture of potato-brandy the crude spirit is found to be con- taminated with an acrid volatile oil, called fusel-oil, which is extremely diffi- cult to separate in a complete manner. Towards the end of the distillation, it passes over in considerable quantity ; it may be collected apart, agitated with several successive portions of water to withdraw the spirit, with which it is mixed, and re- distilled. According to the researches of M. Cahours, this substance exhibits properties indicative of a constitution analogous to that of alcohol; it maybe considered as the hydrate of the oxide of the hydrocarbon, called amyl, containing C 10 H n . The ether of potato-oil, and a variety of other compounds, corresponding in every point to those of ordi- nary alcohol, have been formed, as will be manifest from an inspection of the following table : Amyl (symbol Ayl) C, II n Amyl-ether C, H n O Hydride of amyl C 10 H n tf Potato-oil C 10 H n O,HO Chloride of amyl C 10 H U C1 Bromide of amyl C, H n Br Iodide of amyl C, H U I Zinc-amyl C, H n Zn Acetate of amyl C 10 H 11 0,C 4 H 3 8 Sulphamylic acid C 10 H n O,2S0 3 ,110 Amylene C 10 H 10 Valerianic acid C 10 H 9 3 ,HO. HYDRATED OXIDE OF AMYL; FUSEL OIL; AylOJIO. The crude fusel-oil of potato-brandy is washed with water, and distilled in a retort furnished with a thermometer, the bulb of which dips into the liquid. The portion which distils between 260.(126-GC) and 280 (137-8C) is collected apart and re-distilled in the same manner, until an oil is obtained, having a fixed boiling-point at 268 269 (131-1C 131-7C). Thus purified, it is a thin fluid oil, exhaling a powerful and peculiarly suffocating odour, and leaving a burning taste ; it inflames with some difficulty, and then burns with a pure blue flame. Its density is 0-818. It undergoes little change by contact with air under ordinary circumstances; but when warmed, and dropped upon platinum-black, it oxidizes to valerianic acid, which bears the same relation to this substance that acetic acid does to ordinary alcohol, or formic acid to methyl-alcohol. The action of heat upon fusel-oil has been lately studied by Captain Reynolds. The vapour of this alcohol, when passed through a red-hot glass- tube, yields a mixture of gases, among which a carbo-hydrogen Ce'He pre- dominates, which has the chemical character of olefiant gas, and to which the name propylene has been given. The separation of this gaseous mixture has hitherto failed, but on bringing the gas in contact with chlorine a compound C 9 H 6 C 2 is formed. This is a heavy liquid boiling at 217 0> 4 (103 y C). It is in every respect analogous to the Dutch-liquid (see page 303), originating under similar circumstances from olefiant gas. POTATO-OIL AND ITS DERIVATIVES. 389 IMYL-ETIIER, AylO. If amyl-alcohol is distilled with concentrated sul- ] ,-i-ie acid, a mixture of several substances is obtained, which has to be 8 M irated by distillation. After several rectifications an oil is obtained, wh eh has a sp. gr. 0-779 and boils at 848-8 (176C). This is amyl-ether. The composition is C, H H 0, or, if we adopt the double formulae, C^II^C^. Intermediate ethers between amyl- and ethyl-, and likewise between amyl- nnd metliyl-ether have been prepared. They contain respectively C 14 Hie0 2 = C 4 H 5 0,C 10 H U and C 12 H 14 2 =C 2 H 3 0,C lp II u O. CHLORIDE OF AMYL, Ayl Cl. The chloride is procured by subjecting to distillation equal weights of potato-oil and pentachloride of phosphorus, washing the product repeatedly with alkaline water, and rectifying it from chloride of calcium. Less pure it may be obtained by saturating fusel-oil with hydrochloric acid. It is a colourless liquid, of agreeable aromatic odour, insoluble in water, and neutral to test-paper; it boils at 215 (101-7C), and ignites readily, burning with a flame green at the edges. By the long-continued action of chlorine, aided by powerful sunshine, a new product, or chlorinetted chloride of ami/I, was obtained in the form of a vola- tile colourless liquid, smelling like camphor, and containing C 10 H 3 C 9 ; the whole of the hydrogen could not, however, be removed. BROMIDE OF AMYL, Ayl Br, is a volatile, colourless liquid, heavier than water. It is obtained by distilling fusel-oil, bromine and phosphorus together. (See bromide of ethyl, page 853.) Its odour is penetrating and alliaceous. The bromide is decomposed by an alcoholic solution of potassa with production of bromide of the metal. IODIDE OF AMYL, Ayl I, is procured by distilling a mixture of 15 parts of potato-oil, 8 of iodine, and 1 of phosphorus. It is colourless when pure, heavier than water, volatile without decomposition at 294 -8 (146C) and resembles in other respects the bromide ; it is partly decomposed by expo- sure to light. Iodide of amyl, when heated in sealed tubes with zinc to 374 (190C) yields amyl, a colourless liquid of an ethereal odour contain- ing C 10 H n , and boiling at 311 (155C). Together with this substance there is formed iodide of zinc and zinc-amyl C 10 H n Zn, which, when coming in contact with water, is decomposed into oxide of zinc and hydride of amyl H n H, which is an exceedingly volatile substance, boiling at 8b' CYANIDE OF AMYL, Ayl Cy. Colourless liquid of 0-806 sp. gr., and boiling at 294-8 (14GC), which is obtained by distilling cyanide of potassium with sulphamylate of potassa. Boiled with potassa, this compound acid under- goes a decomposition analogous to that of cyanide of ethyl and methyl, (see pages 354 and 383;) it absorbs 4 eq. of water, and furnishes ammonia and the potassa-salt of caproic acid C 12 II 12 4 , one of the constituents of butter, (^ 12 U 11 N-f4IIO = C 12 H 12 4 +NH 3 . AOKTATK OF OXIDE OF AMYL, Ayl 0,C 4 II 3 3 . This interesting product is eiihily obtained by submitting to distillation a mixture of 1 part of potato-oil, 2 parts of acetate of potassa, and 1 part of concentrated sulphuric acid ; it is purified by washing with dilute alkali, and distillation from chloride of cal- cium. It presents the appearance of a colourless, limpid liquid, which is in- soluble in water, soluble in alcohol, boils at 272 (133-8C), and becomes converted by an alcoholic solution of potassa into an acetate of that base, with reproduction of fusel-oil. This ether possesses in a remarkable manner the odour of the Jargonelle-pear. It is now manufactured upon a large scale for flavouring liquors and confectionaiy. CARBONATE OF OXIDE OF AMYL, Ayl 0,C0 2 . This ether has been lately obtained by Mr. Medlock by saturating fusel-oil with phosgene-gas (chloro- cnrbonic acid). A compound analogous to chloro-carbonic ether AylO,C 2 C10., is lirst produced, which, when treated with water, yields hydrochloric and car- 390 POTATO-OIL AND ITS DERIVATIVES. borne acids, together with carbonate of amyl (AylO,C 2 C10 3 -[-HO=AylO, C0 2 -f-HCl-j-C0 2 ). Carbonate of amyl is a colourless liquid of an aromatic odour, boiling at 438 -8 (226C). Alcoholic solution of potassa converts this ether into fusel-oil, carbonate of potassa being formed at the same time. Sulphide of amyl, amyl-mercaptan, and numerous other compounds of like nature, have been described. SULPHAMYLIC ACID. When equal weights of potato-oil and strong sul- phuric acid are mixed, heat is evolved, accompanied by blackening and par- tial decomposition. The mixture diluted with water, and saturated with carbonate of baryta, affords sulphate of that base, and a soluble salt cor- responding to the sulphovinate. The latter may be obtained in a crystalline state by gentle evaporation, and purified by re-solution and the use of ani- mal charcoal. It forms small, brilliant, pearly plates, very soluble in water and alcohol, containing BaO,Cj H u O,2S0 3 -f-HO. The baryta may be pre- cipitated from the salt by dilute sulphuric acid, and the hydrated sulpha- mylic 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 potato-oil and sulphuric acid. The potassa-salt forms groups of small radiated needles, very soluble in water. The sulphamylates of lime and protoxide of lead are also soluble and crystallizable. AMYLENE. By the distillation of potato-oil with anhydrous phosphoric acid, a volatile, colourless, oily liquid is procured, quite different in proper- ties from the original substance. It is lighter than water, boils at 102 -2 (39C), and contains no oxygen. Its composition is represented by the formula C 10 H, ; consequently it not only corresponds to the olefiant gas in the alcohol-series, but is isomeric with that substance. Like olefiant gas it combines directly with chlorine and bromine, giving rise to compounds Cj H 10 Cl 2 and Ci H ]0 Br 2 . The vapour, however, has a density of 2-68, which is 2J times that of olefiant gas, every measure containing 5 measures of hydrogen. Together with this substance several other hydrocarbons are formed, especially the one to which the name paramylene has been given. It con- tains C 20 H 20 , and boils at 320 (160C). VALERIANIC OR VALERIC ACID. M. Dumas has shown that when a mixture of equal parts of quicklime and hydrate of potassa is moistened with alcohol, and the whole subjected to a gentle heat, out of contact of air, the alcohol is oxidized to acetic acid, with evolution of pure hydrogen gas. At a higher temperature the acetate of potassa produced is in turn decomposed, yielding carbonate of potassa and light carbonetted hydrogen. Wood-spirit, by similar treatment, yields hydrogen and formate of potassa, which, as the heat increases, becomes converted into carbonate, with continued disengage- ment of hydrogen. In like manner potato-oil, the third alcohol, suffers under similar circumstances, conversion into a new acid, bearing to it the same relation that acetic acid does to common alcohol, and formic acid to wood- spirit, hydrogen being at the same time evolved. The body thus produceJ is found to be identical with a volatile oily acid distilled from the root Vale- riana offLcinalis. In preparing artificial valerianic acid, the potato-oil is heated in a fiask with about ten times its weight of the above-mentioned alkaline mixture during the space of 10 or 12 hours ; the heat is applied by a bath of oil or fusible-metal raised to the temperature of 390 (198-8C) or 400 (204-4C). When cold, the nearly white solid residue is mixed with water, an excess of sulphuric or phosphoric acid added, 'and the whole subjected to distillation. The distilled liquid is supersaturated with potassa, evaporated nealy to dryness to dissipate any undecomposed potato-oil, and then mixed POTATO-OIL AND ITS DERIVATIVES. 891 with somewhat diluted sulphuric acid in excess. The greater part of the valevianic acid then separates as an oily liquid, lighter than water; this is a terhydrate of the acid, containing three equivalents of water, one of which is basic. When this hydrate is distilled alone, it undergoes decomposition ; water, with a little of the acid, first appears, arid eventually the pure acid, in the form of a thin, fluid, colourless oil, of the persistent and characteristic odour 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. Valerianic acid has a density of 0-937 ; it boils at 370 (175 C C). Placed in contact with water, it absorbs a certain quantity, and is itself to a certain extent soluble. The salts of this acid present but little interest, as few among them seem to be susceptible of crystallizing. The liquid acid is found by analysis to contain C 10 H 9 3 ,HO, and the silver-salt, AgO,C 10 H 9 3 . The ether-cornpound of valerianic acid has been already mentioned (page 357). By treatment with ammonia this ether is converted into valeranride C 10 H n N0 2 =C 10 H 9 2 ,NH 2 , (analogous to acetamide,) which, under the influ- ence of anhydrous phosphoric acid loses 2 more eq. of water, becoming vale- ronitrile C, H 9 N=C 8 H 9 ,C 2 N or cyanide of butyl. The former is a fusible crystalline substance, the latter a volatile liquid, having a boiling point of 257 (125C). It was first obtained by the action of oxydizing agents upon gelatin. (See Section VIII on the components of the animal body.) A more advantageous mode of preparing valerianic acid is the following : 4 parts of bichromate of potassa in powder, 6 parts of oil of vitriol, and 8 parts of water are mixed in a capacious retort ; 1 part of pure potato-oil is then 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 potassa, and the aqueous solution sepa- rated mechanically from a pungent, colourless, oily liquid, which floats upon it, and which is valerianate of amyl. The alkaline solution is then evaporated to a small bulk and decomposed by sulphuric acid as already directed. Valerianic acid is found in angelica root, in the bark of Viburnum opulus, and probably exists in many other plants ; it is generated by the spontaneous decomposition of azotized substances, mineral and vegetable, and is produced in many chemical reactions in which oxidizing agents are employed. If an open jar be set in a plate containing a little water, and having beneath it a capsule with heated platinum-black, upon which potato-oil is slowly dropped in such quantity as to be absorbed by the powder, the sides of the jar become speedily moistened with an acid liquid, which collects in the plate, and may be easily examined. This liquid, saturated with baryta-water, evaporated to dryness, and the product distilled with solution of phosphoric acid, yields valerianic acid. 1 Some very beautiful, and for the progress of organic chemistry, highly important results, have lately been obtained by the action of electricity, upon valerianic acid. By submitting a solution of valerianate of potassa to a gal- vanic current, produced by 4 elements of Bunsen's battery, Dr. Kolbe ob- served that potassa and pure hydrogen were evolved at the negative pole, while at the positive pole valerianic and carbonic acids, an odorous inflam- mable gas, and an ethereal liquid, made their appearance. The inflammable gas obtained in this reaction is a carbohydrogen C 8 H g which had been pre- 1 Anhydrous valerianic acid is formed by the reaction between valerianate of potassa and oxychloride of phosphorus, 5(KO, CioH 9 3 ) and PC1 3 02=2KOP0 5! and 3KC1, and 5(CioII 9 07). It is an oleaginous liquid lighter than water. Boiling water changes it slowly into the bydratod and. while this transformation is rapidly atlected by solutions of the alkalies. It boils at 410 (216C), and distils unchanged. II. li. 392 POTATO-OIL AND ITS DERIVATIVES. viously isolated by Mr. Faraday from the oily products separated from Com- pressed oil gas. This substance, to which the name butylene has been given, is perfectly analogous to the olefiant gas (ethylene), propylene and amylene which have been previously described. It combines with chlorine and bro- mine, forming substances analogous to Dutch liquid. The oily liquid formed together with anrylene, in the electrolysis of valerianic acid, is a mixture of several substances, among which a hydrocarbon, of the remarkable compo- sition C 8 H 9 , predominates. This body, to which the name butyl or valyl has been given, is a colourless liquid, of an agreeable ethereal odour, and boils at 22G-4 (108C). Kolbe believes that this hydrocarbon must be viewed as a compound analogous to methyl, ethyl, and amyl, with which we have become acquainted, and that it forms the radical of an alcohol yet to be dis- covered, having the formulaC 8 H 9 0,HO and analogous to methyl-, ethyl-, and amyl-alcohols, an alcohol which, by oxidation, would yield the acid C 8 H 7 3 , HO, i. e., butyric acid, just as the three alcohols mentioned are converted respectively into formic, acetic, and valeric acids. Kolbe considers butyl to be one of the proximate constituents of valeric acid, which he views as an intimate combination of butyl with oxalic acid, butyl-oxalic acid C 10 H 9 3 ,HO C 8 II g ,C 2 3 HO. According to this view, the transformation of valeric acid under the influence of the galvanic current is readily explained. The oxy- gen evolved at the positive pole by the electrolysis of water oxidizes the oxa- lic to carbonic acid, and liberates the butyl, portions of which are farther attacked by the oxygen, and deprived of 1 eq. of hydrogen, thus giving rise to the simultaneous evolution of butylene. If this view holds good for butyric acid, it must be equally true of propionic, acetic, and formic acid, and of a great number of analogous acids, which will be described in the subsequent chapters of this Manual. Propionic acid will be ethyl-oxalic acid, acetic acid methyl-oxalic, and lastly,- formic acid hydrogen-oxalic acid, thus Formic acid C 2 H0 3 , H0= H ,C 2 3 ,HO Acetic acid ,.. C 4 H 3 3 ,HO=C 2 H 3 ,C 2 3 ,HO Propionic acid C 6 H 5 3 ,HO=C 4 H 5 ,C 2 3 ,HO Valeric acid Ci H 9 3 ,HO=C 8 H 9 ,C 2 3 ,HO ' This view is borne out by the electrolytic decomposition of acetic acid, which yields a gas, considered by Kolbe to be methyl. Several collateral facts have furnished additional support to this theory, amongst which may be quoted the remarkable deportment of the ammonia-salts of these acids under the influence of anhydrous phosphoric acid. In this reaction, oxalic, formic, * Butyric acid constitutes the fifth member of this series as a combination of propyl with oxalic acid or propyl-oxalic acid, Butyric acid C 8 H 9 On,IIO=C6ll7,C203.IIO As valyl is formed from valeric acid, so the decomposition of butyric acid should yield propyl Cell 7 , the oxide of which CellvO has b;en detected in cod-liver oil in combination with oleic nnd margaric acid. Butylic alcohol of Wurtz appears to fill up this vacancy in the alcohol series. It was extracted from rectified potato-oil by fractional distillations, retaining that which posses between 226- 4 (103) and 244-4 (118). By subsequent purification a liquid is obtained which boils at 233-6(112), is lighter than water, has the odour of amylic alcohol, but less disagrw- able. Fused potassa changes it into butyric acid with the liberation of hydrogen. Its com- position is C 8 U, Oa=C 8 H9qjIO ; or hydrate of oxide of valyl. Butylic alcohol, when mixed with its own weight of strong sulphuric acid and after twenty- four hours' repose saturated with carbonate of potassa, yields sulphate and Bulphobntylate of potassa. The latter dissolves readily in boiling absolute alcohol, from which it is deposited in anhydrous pearly crystals of the composition KO,CsIIa0.2S03. The eyanate and eyanuratc of butylic ether yield with potassa a nitrogenous product, Imtylauiiii, NITaC&ITg, in the same way as the cyanales and cyanurates of ethyl, methyl, nr amyl, yield respectively cthylamin. NHaC-jIIs, mcthylamin Nllj&tft aud amylamin Nlla CIIn.-K. 15. FUSEL-OIL OF GE A I N - S P I R I T . 893 acetic, propionic, and valeric acids yield respectively cyanogen and the cya- nides of hydrogen, methyl, ethyl, and butyl. NH 4 0, C 2 3 _4HO= C 2 N NH 4 0, H, C 3 3 4HO= H, C 2 N NH 4 0,C 2 II a ,C 2 3 4HO = C 2 R 3 ,C 2 N NH 4 0,C 4 H 5 ,C 2 3 4HO=C 4 H 6 ,C 2 N NH 4 0,C 8 H 9 ,C 2 3 4HO=C 8 H 9 ,C 2 N We have seen, moreover, that the cyanides of methyl and ethyl, when treated with the alkalis are readily reconverted into acetic and propionic acid, and in the Section on cyanogen it will be shown that this substance and hydro- cyanic acid are indeed easily convertible into oxalate and formate of ammonia. All these facts are readily intelligible by the view proposed by Dr. Kolbe. CHLOROVALERISIC ACID. When dry chlorine is passed for a long time into pure valerianic acid, in the dark, the gas is absorbed in great quantity, and much hydrochloric acid produced; towards the end of the operation a little heat becomes necessary. The product is a semi-fluid transparent substance, heavier than water, odourless, and of acrid burning taste. It does not congeal when exposed to a very low temperature, but acquires complete fluidity when heated to 86 (30C). It cannot be distilled without decomposition. When put into water it forms a thin, fluid hydrate, which afterwards dissolves to a considerable extent. This body is freely soluble in alkalis, from which it is again precipitated by the addition of an acid. Chlorovalerisic acid contains C 10 (H 6 Cl,)O ai HO. CHLOROVALEROSIC ACID. This is the ultimate product of the action of chlorine on the preceding substance, aided by exposure to the sun. It re- sembles chlorovalerisic acid in appearance and properties, being semi-fluid and colourless, destitute of odour, of powerful pungent taste, and heavier than water. It can neither be solidified by cold, nor distilled without decom- position. In contact with water, it forms a hydrate containing 3 eq. of that substance, which is slightly soluble. In alcohol and ether it dissolves with facility. It forms salts with bases, of which the best defined is that of silver. Chlorovalerosic acid is composed of C 10 (H 5 C1 4 )0 3 ,HO. FUSEL-OIL OF GRAIN-SPIRIT. The fusel-oil separated in large quantities from grain-spirit by the London rectifiers consists chiefly of potato-oil (hy- drated oxide of amyl) mixed with 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 oenanthic and margaric acids. These last-named substances form the principal part of the nearly solid fat produced in this manner in whisky-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 odour resembling that of some of the umbelliferous plants, and is unaifected by solution of caustic potassa. According to Mr. Rowney, the fusel-oil of the Scotch distilleries contains in addition a certain quantity of capric acid C 20 H 20 4 which is one of the constituents of butter. The fusel-oil of marc-brandy of the south of France was found by M. Balard to contain potato-oil and oenanthic ether. Potato-oil has been separated from the spirit distilled from beet-molasses, and from artificial grape-sugar made by the aid of sulphuric acid. Although much obscurity yet hangs over the history of these substances, it is generally supposed that they are products of the fermentation of sugar, and have an origin contemporaneous with that of common alcohol. It is impossible to leave the history of the alcohols without alluding to eoine results of great importance for the elucidation of organic compounds 394 HOMOLOGOUS SERIES. generally, which the study of these substances has elicited. When describing the three alcohols, discussed in the preceding chapter, we have repeatedly pointed out the remarkable analogy presented by the properties and the general deportment of these three bodies. If we compare the composition of the three alcohols, Methyl-alcohol C 2 H 4 2 Ethyl-alcohol C 4 H 6 2 Amyl-alcohol C 10 H, 2 2 we find that their formulge present an unmistakable symmetry. All three contain the same amount of oxygen, only the carbon and hydrogen vary.^ This variation, however, takes place in very simple relations. Thus we find the difference of ethyl- and methyl-alcohol to be C 4 H 6 2 C 2 H 4 2 = C 2 ILj the difference of amyl- and methyl-alcohol to be C 10 H 12 O 2 C 2 1I 4 2 = C g H 8 =4C 2 H 2 . The same elementary difference of course prevails likewise be- tween all the derivatives of the three alcohols. Iodide of methyl C 2 H 3 I Iodide of ethyl C 4 H 5 I = C 2 F 3 T -f C 2 H 2 Iodide of amyl C, H n I C 2 H 3 l -f 4C 2 H 2 or Formic acid C 2 H 3 ,HO Acetic acid C 4 H 3 3 ,HO = C 2 H0 3 ,HO-f C 2 TT 2 Valeric acid C 10 H 9 3 ,HO = C 2 [I0 3 ,HO-(-4(yi 2 Methylic, ethylic, and amylic alcohols are by no means the only members of this class which are known. In the succeeding sections of this work will be noticed a series of compounds evidently of a perfectly analogous character which have been discovered. By submitting castor-oil to a series of pro- cesses, M. Bouis has formed an alcohol, which has been called "caprylio alcohol." According to M. Dumas, spermaceti contains another analogous substance, cetylic alcohol, which is a solid : and Mr. Brodie has prepared two alcohols, cerotylic and mellisic, from ordinary bees' wax. The compo- sition of these substances stands in exactly the same relation to that of the preceding alcohols, which we have pointed out, as will be seen from the fol- lowing table : Caprylic alcohol C] 6 H is2 = C 2 H 42 + "C 2 TI 2 Cetylic alcohol C 32 H 34 2 = C 2 H 4 2 -f 15C 2 H 2 Cerotylic alcohol ^^5 6 z = C 2 FI 4 2 + 26C 2 H 2 Melissic alcohol C 60 H 62 2 = C 2 H 4 2 -f 29C 2 H 2 These four alcohols, when submitted to the action of oxidizing agents, nre converted into four acids, analogous to formic and acetic acid, and which stand to each other, and to formic and acetic acid, in exactly the same rela- tion as the various alcohols. Caprylic acid C 16 H I5 3 ,IIO = C 2 H0 3 ,HO 4- 7C 2 TT 2 Cetylic acid C 32 H 31 3 ,HO = C 2 H0 3 ,HO -f 15r 2 H 2 Cerotylic acid C 54 H 53 3 ,HO = C 2 H0 3 .HO -f 2GC 2 H 2 Melissic acid C 60 H 59 3 ,HO = C 2 H0 3 ,HO -f 29C 2 H 2 A glance at these tables shows that all the alcohols known differ from methyl-alcohols by C 2 H 2 , or a multiple of it. At the same time, it is evi- dent that the series by no means regularly ascends. Thus we perceive that between ethylic and aniylic alcohols two compounds are possible ; in like ir.anner two between amylic and caprylic .alcohols. Even now the parallel series of volatib acids is far more complete than HOMOLOGOUS SERIES. 395 that of the alcohols. At present the following members of this group are known, which are placed in juxtaposition with the collateral alcohols : Methyl-alcohol C 2 H 4 2 Formic acid C 2 H 2 4 Ethyl-alcohol C 4 H 6 2 Acetic acid C 4 H 4 4 (Tetryl-alcohol) C 6 H 8 2 Propionic acid C 6 H 6 4 (Butyl-alcohol) C 8 H 10 2 Butyric acid C 8 H 8 4 Amyl-alcohol C 10 H, 2 2 Valeric acid C, H 10 4 C i2 H i4 2 Caproic acid .... C 12 U 12 4 Ci 4 M 16 2 (Enanthylic acid C 14 H 14 4 Capryl-alcohol C, 6 I1 18 2 Caprylic acid C 16 H, 6 O 4 Ci3 H 2o2 Pelargonic acid C 18 H 18 O 4 ^20^22^2 Capric acid C 20 H 20 4 &c. &c. &c. c. We might continue the series of acids uninterruptedly to C 38 H 38 4 (balcnic acid), and with intervals even much higher up to acids containing 54 and even more equivalents of carbon. Most of the acids belonging to this series have been separated from fats, and hence this series is frequently designated by the name of the series of fatty acids. A series of analogous substances whose composition varies by C 2 H 2 , or a multiple of it, is called a series of homologous bodies a name first used by M. Gerhardt, to whom we are much indebted for the elucidation of this sub- ject. It is evident that there exist as many such homologous series as there are derivatives of any one of the alcohols. We may construct a series of homologous radicals, or ethers, or hydrocarbons. Methyl .... Ethyl . C 2 H 3 C, H- Methyl-ether.. Ether Co H 3 ( IL Ethylene C 2 H 2 C PI Propyl? ... Butyl Amyl , Caproyl .. .. c u J , .. C s H, .. 10 H,, .. U, 8 li u CIXJ (Tetryl-ethcr). Amy l -ether.... 4 5 C P H 7 C. IT 8 O C, o n n O U H I3 C M H ]5 C la H 17 Propylene .... Butylene Amylene Caproylene... Caprylene .... 4 4 C 6 H 6 cXo c!x 4 2 C 18 "ie All these series of homologous bodies still present numerous gaps; none perhaps more than that of the alcohols which may be taken as the prototype of all the rest ; but since the existence of these homologous series was first pointed out, many gaps have been filled, and it may be expected that before long the rapid strides of organic chemistry will render them complete. The properties of the various members belonging to homologous series gradually change as we ascend in the series. The most characteristic alte- ration is the diminution of volatility. A regular difference between the boiling points of homologous substances was first pointed out by H. Kopp As an example may be taken the series of fatty acids : Boiling points. Differences. Formic acid C 2 IT 2 4 209 98-5 1 * ' Acetic acid C 4 H 4 4 246 119 If ^ S ' Propionic acid C c IJ 6 O 4 284 140 Butyric acid C 8 H g 4 314-6 157 175 18 Caproic acid C 12 H, 2 4 3S8-4 198 From this table it is evident that the boiling temperature of the homolo- gous acids rises on an average 36 -3 (19-9C) for every increment of C 2 H V A. similar regular difference has been observed in the boiling points of manj 396 BITTER- ALMOND OIL homologous compounds. As yet, however, the number of cases in -which discrepancies occur is very considerable. The substances discussed in the next three sections have but little relation to the alcohols ; they may, however, be here most conveniently described. BITTER-ALMOND OIL AND ITS PRODUCTS. The volatile oil of bitter almonds possesses a very high degree of interest, from its study having, in the hands of MM. Liebig and Wohler, led to the first discovery of a compound organic body capable of entering into direct combination with elementary principles, as hydrogen, chlorine, and oxygen, and playing in some degree the part of a metal. The oil is supposed to be the hybride of a salt-basyle, containing C 14 H 5 2 , called benzoyl, from its re- lation to benzoic acid, which radical is to be traced throughout the whole series ; it has been isolated, and will be described among the products of distillation of the benzoates. Table of Benzoyl- Compounds. Benzoyl, symbol Bz C 14 TT 5 2 Hydride of benzoyl ; bitter-almond oil Ci 4 H 5 2 FI Hydrated oxide of benzoyl; benzoic acid C, 4 H 5 2 0,HO Chloride of benzoyl C, 4 H 5 2 C1 Bromide of benzoyl C 14 H 5 2 Br Iodide of benzoyl C 14 H 5 2 I Sulphide of benzoyl C 14 H 5 2 S. HYDRIDE or BENZOYL ; BITTER-ALMOND OIL ; BzII. This substance is pre- pared in large quantities, principally for the use of the perfumer, by dis- tilling with water the paste of bitter almonds, from which the fixed oil has been expressed. It certainly does not pre-exist in the almonds ; the fat oil obtained from them by pressure is absolutely free from every trace of this principle ; it is formed by the action of water upon a peculiar crystallizablo substance, hereafter to be described, called amygdalin, aided in a very ex- traordinary manner by the presence of the pulpy albuminous matter of the seed. The crude oil has a yellow colour, and contains a very considerable quantity of hydrocyanic acid, the origin of which is contemporaneous with that of the oil itself: it is agitated with dilute solution of protochloride of iron mixed with hydrate of lime in excess, and the whole subjected to dis- tillation; water passes over, accompanied by the purified essential oil, which is to be left for a short time in contact with a few fragments of fused chlo- ride of calcium" to free it from water. Pure hydride of benzoyl is a thin, colourless liquid, of great refractive power, and peculiar and very agreeable odour; its density is 1-043, and its boiling-point 356 (180C): it is soluble in about 30 parts of water, and is miscible in all proportions with alcohol and ether. Exposed to the air, it greedily absorbs oxygen, and becomes converted into a mass of crystallized benzoic acid. Heated with hydrate of potassa, it disengages hydrogen, and yields benzoate of the base. The vapour of the oil is inflammable, and burns with a bright flame and much smoke. It is very doubtful whether pure bitter-almond oil is poisonous; the crude product, sometimes used for im- parting an agreeable flavour to puddings, custards, &c., and even publicly gold for that purpose, is in the highest degree dangerous. OXIDE OF BENZOYL ; BENZOIC ACID ; BzO. This is the sole product of the oxidation at a moderate temperature of bitter-almond oil ; it is not, how- ever, thus obtained for the purposes of experiment and of pharmacy. Seve- ral of the balsams yield benzoic acid in great abundance, more especially the concrete resinous variety known under the name of gum-benzoin. When AND ITS PRODUCTS. 897 this substance is exposed to a gentle heat in a subliming vessel, the benzoic acid is volatilized, and may be condensed by a suitable arrangement. The simplest and most efficient apparatus for this arid all similar operations is the contrivance of Dr. Mohr : Fi S- 17 it consists of a shallow iron pan, (fig. 171,) over the bottom of which the substance to be sublimed is thinly spread ; a sheet of bibulous-paper, pierced with a number of pin-holes, is then stretched over the vessel, and a cap made of thick, strong drawing or cartridge- paper, 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 vapour 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, colourless crystals, which exhale a fragrant odour, not belonging to the acid itself, but due to 4 the small quantity of a volatile oii. A more productive method of preparing the acid is to mix the powdered gum- benzoin very intimately with an equal weight of hydrate of lime, to boil this mixture with water, and to decompose the filtered solution, concentrated 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 eifected 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 212 (100C), and sublimes at a temperature a little above; it boils at 462 (238 -8C), and emits a vapour 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 a boiling heat. The crystals obtained by sub- limation, or by the cooling of a hot aqueous solution, contain an equivalent of water, which is basic, or C, 4 H 5 3 ,HO. All the benzoates have a greater or less degree of solubility ; they are easily formed, either directly or by double decomposition. Benzoates of the alkalis and of ammonia are very soluble, and somewhat difficult to crystalli/e. Kenzoate of lime forms groups of small colourless needles, which require 20 parts of cold water for solution. The salts of baryta and strontia are soluble with difficulty in the cold. Neutral benzoate of the sesquiozide of iron is a soluble compound ; but the basic salt obtained by neutralizing as nearly as possible by ammonia a solution of sesquioxide of iron, and then adding ben- zoate of ammonia, is quite insoluble. Sesquioxide of iron is sometimes thus separated from other metals in practical analysis. Neutral and basic benzoate of lead are freely soluble in the cold. Benzoate of silver crystallizes in thin transparent plates, which blacken on exposure to light. Some re- markable products, obtained by the action of chlorine upon a solution of benzoate of potassa, will be mentioned in the section on the Organic Bases. NITROBENZOIC ACID. When benzoic acid is boiled for several hours with fuming nitric acid, until red fumes cease to appear, it yields a new acid body, in which the elements of hyponitric acid are substituted for an equivalent of hydrogen of the original benzoic acid. Nitro-benzoic acid greatly resembles benzoic acid in character, and contains C 14 H 4 N0 7 ,HO=C 14 (FI 4 N0 4 )0 3 ,HO. The remarkable transformation of the amide of this acid, of nitro-benzimide, will be noticed under the head of aniline. SULPHOBENZOIC ACID. Benzoic acid is soluble without change in conccn trated oil of vitriol, and is precipitated by the addition of water ; it combines, however, with anhydrous sulphuric acid, generating a compound acid analo- 34 398 BITTER-ALMOND OIL gous to the sulphovinic, but bibasic, forming a neutral and an acid scries of suits. The baryta-compound is easily prepared by dissolving in water the viscid mass produced by the union of the two bodies, and saturating the solution with carbonate of baryta. On adding hydrochloric acid to the filtered liquid, and allowing the whole to cool, acid sulphobenzoate of baryta crys- tallizes out. This salt has an acid reaction, and requires 20 parts of cold water for solution ; the neutral salt is much more soluble. The hydrated acid is easily obtained by decomposing the sulphobenzoate of baryta by dilut sulphuric acid ; it forms a white, crystalline, deliquescent mass, very stabK and permanent, which contains C 14 H 5 3 ,2S0 3 ,2HO. BENZONE, BENZOPHENONE. When dry benzoate of lime is distilled at a high temperature, it yields a thick, oily, colourless liquid, of peculiar odour. This is a mixture of several compounds, from which, however, a crystalline sub- stance C I3 H 5 0, or C 26 II ](? 2 , may be isolated, to which the name benzone or benzophenone has been given. Carbonate of lime remains in the retort ; the reaction is thus perfectly analogous to that by which acetone is produced by the distillation of a dry acetate. CaO,C 14 H 5 3 =C 13 H 5 0-f-CaO,C0 2 . The benzophenone is, however, always accompanied by secondary products, due to the irregular and excessive temperature, solid hydrocarbons, carbonic oxide, and benzol, a body next to be described. BKNZOL, or BENZINE. If crystallized benzoic acid be mixed with three times its weight of hydrate of lime, and the whole distilled at a temperature slowly raised to redness in a coated glass or earthen retort, water, and a volatile oily liquid termed benzol, pass over, while carbonate of lime, mixed with excess of hydrate of lime, remains in the retort. The benzol separated from the water, and rectified, forms a thin, limpid, colourless liquid, of strong agreeable odour, insoluble in water, but miscible with alcohol, having a den- sity of 0-885, and b.oiling at 176 (80C) ; the sp. gr. of its vapour is 2-738. Cooled to 32 (0C), it solidifies to a white, crystalline mass. Benzol contains carbon and hydrogen only, in the proportion of 2 eq. of the former to 1 of the latter, or probably C 12 H 6 . It is produced by the resolution of the benzoic acid into benzol and carbonic acid, the water taking part in the reaction. C M H 6 4 =C I8 H 6 +2CO a . Benzol is identical with the bicarbide of hydrogen, many years ago dis- covered by Mr. Faraday in the curious liquid condensed during the compres- sion of oil-gas, of which it forms the great bulk, being associated with an excessively volatile hydrocarbon, containing carbon and hydrogen in the ratio of the equivalents, the vapour of which required for condensation a temperature of ( 17-7C). This is the substance which has been de- scribed under the name of butylene, when treating of valeric acid (see page 392). A copious source of benzol has been lately shown by Mr. Mansfield to exist in the lightest and most volatile portions of coal-tar oil, which will be noticed in its place under the head of that substance. . SuLPiioBENziDE AND HYPOSULPHOBENzic ACID. Benzol combines directly with anhydrous sulphuric acid, to a thick viscid liquid, soluble in a small quantity of water, but decomposed by a larger portion, with separation of a crystalline matter, the sulphobenzide, which may be washed with water, in which it is nearly insoluble, dissolved in ether, and left to crystallize by spontaneous evaporation. It is a colourless, transparent substance, of great importance, fusible at 212 (100C), bearing distillation without change, and resisting the action of acids and other energetic chemical agents. Sulpho- benzide contains C^IIgSO^. It may be viewed as benzol in which 1 eq. of AND ITS PRODUCTS. 809 hydrogen has been replaced by 1 eq. of sulphurous acid. The fiei liquid from which the preceding substance has been separated, neutralized by carbonate of baryta and filtered, yields hi/posulphobenzate of baryta, which is a soluble salt, but crystallizes in an imperfect manner. By double decompo- sition with sulphate of copper, a compound of the oxide of that metal is obtained, which forms fine, large, regular crystals. The hydrate of hyposul- phobenzic acid is prepared by decomposing the copper-salt with sulphuretted hydrogen ; a sour liquid is obtained, which furnishes, by evaporation, a crystalline residue, containing C ]2 H 5 S0 2 -j-HO,S0 3 . The salts of potassn, soda, ammonia, and of the oxides of zinc, iron, and silver, crystallize freely. This compound acid can be prepared by dissolving benzol in Nordhausen sulphuric acid. NITROBENZOL. Ordinary nitric acid, even at a boiling temperature, has no action on benzol ; the red fuming acid attacks it, with the aid of heat, with great violence. The product, on dilution, throws down a heavy, oily, yel- lowish, and intensely sweet liquid, which has an odour resembling that of bitter-almond oil. Its density is 1-209; it boils at 415 (212-8C), and dis- tils but not without being slightly changed. It is but little affected by acids, alkalis, or chlorine, and is quite insoluble in water. Nitrobenzol contains C, 2 H 5 N0 4 , and may be viewed as benzol, in which 1 eq. of hydrogen is re- placed by 1 eq. of hyponitric acid. When nitrobenzol is heated with an al- coholic solution of caustic potassa, and the product subjected to distillation, a red oily liquid passes over ; this is a mixture of several substances from which, on cooling, large red crystals separate, which are nearly insoluble in water, but dissolve with facility in ether and alcohol. This compound, which is called azobenzol, melts at 149 (65), and boils at 379 (192-2C) ; it contains C 12 H 5 N. Together with the azobenzol an oil is produced, which contains C, 2 H 7 N, and has, like ammonia, the power of combining with acids. It has received the name of aniline, and will be described in the section on organic bases. The reaction which gives rise to azobenzol and aniline in this case, is not yet perfectly understood, several other substances being si- multaneously produced, and a large quantity of nitrobenzol being charred. Nitrobenzol may, however, be entirely converted into aniline, by a most ele- gant process, discovered by Zinin, namely, by the action of sulphide of am- monium, which will be noticed when treating of aniline. BJNITROBENZOL. If benzol is dissolved in a mixture of equal volumes of concentrated nitric and sulphuric acids, arid the liquid be boiled for some minutes, it solidifies on cooling to a mass of crystals, which are easily fu- sible, insoluble in water, and readily soluble in alcohol. They contain Cj 2 H N 2 8 =C 12 (H 4 2N0 4 ), and may be viewed as benzol in which 2 eq. of hydrogen are replaced by 2 eq. of hyponitric acid. Benzol and chlorine combine when exposed to the rays of the sun ; thii product is a solid, crystalline, fusible substance, insoluble in water, contain- ing C, 2 n 6 Cl 6 , called chlorobenzol When this substance is distilled, it is de- composed into hydrochloric acid, and a volatile liquid, chloroi/enzide, composed of C 12 [F 3 C1 3 . In its chemical relations, benzol exhibits the character of a substance anal- ogous to hydride of methyl (marsh-gas), hydride of ethyl, and hydride t>f ainyl. Benzol C 12 TT 5 TT. = Hydride of Phenyl. Sulphobenzol C 12 H 5 S0 2 . Nitrobenzol C, 2 1I 5 N0 4 . The ??eohol belonging to this hydride is known; it contains C ]2 tT 6 <> 2 _- t C 12 H/?,HO, and will be described among the volatile principles of coal-tar OF BENZOYL, BzCl. This compound is prepared by passing dr% 400 BITTER -ALMOND OIL chlorine gas through pure bitter-almond oil, as long as hydrochloric acid continues to be formed ; the excess of chlorine is then expelled by heat. Chloride of benzoyl is a colourless liquid of peculiar, disagreeable, arid pun- gent odour. Its density is 1-106. The vapour is inflammable, and burns with a tint of green. It is decomposed slowly by cold, and quickly by boil- ing water, into benzoic and hydrochloric acids ; with an alkaline hydrate, benzoate of the base, and chloride of the metal, are generated. BENZAMIDE. When pure chloride of benzoyl and dry ammoniacal gas are presented to each other, the ammonia is energetically absorbed, and a white, solid substance produced, which is a mixture of sal-ammoniac and a highly interesting body, benzamide. The sal-ammoniac is removed by washing with cold water, and the benzamide dissolved in boiling water, and left to crys- tallize. It forms colourless, transparent, prismatic, or platy crystals, fusible at 239 (115C), and volatile at a higher temperature. It is but slightly soluble in cold, freely in boiling water, also in alcohol and ether. Benza- mide corresponds to oxamide, both in composition and properties : it con- tains C 14 H 7 N0 2 =Cj 4 H 5 2 ,NH 2 , or benzoate of oxide of ammonium, minus 2 eq. of \vater, and it suffers decomposition by both acids and alkaline solu- tions, yielding, in the first case, a salt of ammonia and benzoic acid, and, in the second, free ammonia and a benzoate. When distilled it loses again 2 eq. of water, and becomes benzoriitrile. (See farther on.) IODIDE OF BENZOYL, Bzl. This is prepared by distilling the chloride of benzoyl with iodide of potassium ; it forms a colourless, crystalline, fusible mass, decomposed by water and alkalis, in the same manner as the chloride. The broi lide of benzoyl, BzBr, has very similar properties. The sulphide, BzS, is a yellow oil, of offensive smell, which solidifies, at a low temperature, to a soft, crystalline mass. Cyanide of benzoyl, BzCy, obtained by heating the chloride with cyanide of mercury, forms a colourless, oily, inflammable liquid, of pungent odour, somewhat resembling that of cinnamon. All these compounds yield benzamide with dry ammonia. FORMOBENZOIC ACID. Crude bitter-almond oil is dissolved in water, mixed with hydrochloric acid, and evaporated to dryness : the residue is boiled with ether, which dissolves out the new substance, and leaves sal-ammoniac. Formobenzoic acid forms small, indistinct, white crystals, which fuse, and afterwards suffer decomposition by heat, evolving an odour resembling that of the flowers of the hawthorn, and leaving a bulky residue of charcoal. It is freely soluble in water, alcohol, and ether, has a strong acid taste and reac- tion, and forms a series of crystallizable salts with metallic oxides. This sub- stance contains C, 6 H 7 6 ,HO=C 14 H 6 2 -}-C 2 HOg,HO, or the elements of bitter- almond oil, and formic acid : it owes its origin to the peculiar action of strong mineral acids on the hydrocyanic acid of the crude oil, by which that body suffers resolution into formic acid and ammonia. It is decomposed by oxi- dizing bodies, as binoxide of manganese, nitric acid, and chlorine, into bitter- almond oil and carbonic acid. HYDROBENZAMIDE. Pure bitter-almond oil is digested for some hours at about 120 (49C) with a large quantity of strong solution of ammonia ; the resulting white crystalline product is washed with cold ether, and dissolved in alcohol ; the solution, left to evaporate spontaneously, deposits the In/dro- benzamide in regular, colourless crystals, which have neither taste nor smell. This substance melts at a little above 212 (100C), is readily decomposed by heat, dissolves with ease in alcohol, but is insoluble in water; the alco- holic solution is resolved by boiling into ammonia and bitter-almond oil ; a similar change happens with hydrochloric acid. Hydrobenzamide contains C 4? H 19 N 2 , or the elements of 3 equivalents of bitter-almond oil, and 2 of ammonia, minus 6 equivalents of water. When impure bitter-almond oil is employed in this experiment, the products are different, several other com- AND ITS PRODUCTS. 401 pounds being obtained. But even with the pure oil frequently a great variety of substances are formed. The hydrobenzamide when submitted to the action of chemical processes furnishes a great number of derivatives, of which, how- ever, only one substance, namely, amarine, will be described in the section on the organic bases. BENZOIN. This substance is found in the residue contained in the retort from which bitter-almond oil has been distilled with lime and oxide of iron, to free it from hydrocyanic acid ; it is a product of the action of alkalis and alkaline earths on the crude oil, and is said to be only generated in the presence of hydrocyanic acid. It is easily extracted from the pasty mass, by dissolving out the lime and oxide of iron by hydrochloric acid, and boiling the residue in alcohol. Benzoin forms colourless, transparent, brilliant, prismatic crystals, tasteless and inodorous; it melts at 248 (120C), and distils without decomposition. Water, even at a boiling heat, dissolves but a small quantity of this body ; boiling alcohol takes it up in a larger propor- tion ; it dissolves in cold oil of vitriol, with violet colour. Benzoin contains C 14 II C 2 , orC 28 H 12 4 , and is, consequently, an isomeric modification of bitter- almond oil. BEXZILE. This curious compound is a product of the action of chlorine on benzoin ; the gas is conducted into the fused benzoin as long as hydrochloric acid continues to be evolved. It is likewise formed by treating benzoin with fuming nitric acid. The crude product is purified by solution in alcohol. It forms large, transparent, sulphur-yellow crystals, fusible at 200 (93 -3C), unaltered by distillation, and quite insoluble in water. It dissolves freely in alcohol, ether, and concentrated sulphuric acid, from which it is precipitated by water. Benzile is composed of C 14 H 5 2 , or C 28 H 10 4 , and is therefore i&o- meric with the radical of the benzoyl-series. BENZOLIC ACID. Benzoin and benzile dissolve with the violet tint in an alcoholic solution of caustic potassa ; by long boiling the liquid becomes colourless, and is then found to contain a salt of a peculiar acid, called the benzilic, which is easily obtained by adding hydrochloric acid to the filtered liquid, and leaving the whole to cool. Benzilic acid forms small, colourless, transparent crystals, slightly soluble in cold, more readily in boiling water : it melts at 248 (120C), arid cannot be distilled without decomposition. It dissolves in cold concentrated sulphuric acid with a fine carmine-red colour- Ben zilic acid contains C 28 H n 5 ,HO, or 2 eq. benzile and 1 eq. water. BENZONITRILE. When benzoate of ammonia is exposed to destructive dis- tillation, among other products a yellowish volatile oil makes its appearance, having exactly the odour of bitter-almond oil. It is heavier than water, slightly soluble in that liquid, boils at 376 (191-1C), and contains C 14 H 5 N. It is benzoate of ammonia, 4 eq. of water, (NH 4 0,C ]4 H 5 3 4HO=Ci 4 H 5 N,) and stands to this salt in the same relation as cyanogen to oxalate, hydro- cyanic acid to formate, and cyanide of methyl to acetate of ammonia. Ben- zonitrile likewise maybe viewed as a cyanide, when it becomes a member of the^phenyl-series, C 14 H 5 N=C 12 U 5 C 2 N. BUXZOYL. Benzoate of copper by dry distillation cautiously conducted gives a residue containing salicylic and benzoic acids, and an oily distilled product which crystallizes on cooling. This substance possesses the odour of the geranium, melts at 158 (70C), and contains C 14 H 5 2 . It was dis- covered by Ettling, and subsequently studied by Stenhouse, and is evidently the radical of the benzoyl-series. By heating with hydrate of potassa it ia instantly converted into benzoic acid with disengagement of hydrogen. BENZIMIDE. This is a white, inodorous, shining, crystalline substance occasionally found in crude bitter-almond oil. It is insoluble in water, and but slightly dissolved by boiling alcohol and ether. Oil of vitriol dissolves it with dark indigo-blue colour, becoming green by the addition of a little water. 402 BITTER-ALMOND OIL AND ITS PRODUCTS. This reaction is characteristic. Benzimide contains C 28 H U N0 4 . It may be viewed as derived from an acid benzoate of ammonia by tlie separation of 4 eq. of water. A great number of other compounds derived from bitter-almond oil, directly or indirectly, have been described by M. Laurent and others. Many of these contain sulphur, sulphuretted hydrogen and sulphide of ammonium being employed in their preparation. HIPPUKIG ACID. This interesting substance is in some measure related to the benzoyl-compounds. It occurs, often in large quantity, in combination "with potassa or soda, in the urine of horses, cows, and other graminivorous animals. It is prepared by evaporating in a water-bath perfectly fresh cow-urine to about a tenth of its volume, filtering from the deposit, and then mixing the liquid with excess of hydrochloric acid. Cow-urine fre- quently deposits hippuric acid without concentration, when mixed with a considerable quantity of hydrochloric acid, in which the acid is less soluble than in water. The brown crystalline 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 colour, and begins to exhale the odour of that substance ; it is then filtered, and left to cool. The still impure acid is re-dissolved in water, neutralized with carbonate of soda, and boiled for a short time with animal charcoal ; the hot filtered solution is, lastly, decom- posed by hydrochloric acid. Hippuric acid in a pure state crystallizes in long, slender, milk-white, and exceedingly frangible square prisms, which have a slight bitter taste, fuse on the application 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 tem- Derature, hippuric acid undergoes decomposition, yielding benzoic acid, ben- zoate of ammonia, and a fragrant oily matter, with a coaly residue. "With hot oil of vitriol, it gives off benzoic acid : boiling hydrochloric acid con- verts it into benzoic acid and glycocine (gelatin-sugar) which is described in the Section on Animal Chemistry. Hippuric acid contains C 18 H 8 N0 5 ,HO. The constitution of hippuric acid has been frequently discussed by che- mists. Very different views have been proposed. The most probable one is, that it is the amidogen compound of a peculiar acid glycobenzoic acid. If hippuric acid be treated with nitrous acid, it undergoes the decomposition peculiar to amidogen-compounds, which has been explained when treating of oxamide (page 343). A new non-nitrogenous acid is formed together with water and pure nitrogen C^H 8 N0 5 ,KO-f NO ?: =C]sH 7 7 ,HO-fHO-f 2N. Glycobenzoic acid is a crystalline substance, slightly soluble in water, but readily dissolved by alcohol and ether. It may be viewed as a conjugate acid, containing benzoic and glycolic acids 2 eq. of water C ]S H 7 7 ,HO = C, 4 Hg0 4 ,C 4 H 4 6 2HO. Under the influence of boiling water it splits indeed into benzoic and glycolic acids. Glycocine must be considered a- glycolamide NH 4 0,C 4 H 3 5 2HO = C 4 H 5 N0 4 , and this explains the conver- sion of hippuric acid into benzoic acid and glycocine. If, in the preparation of hippuric acid, the urine be in the slightest degree putrid, the hippuric acid is all destroyed during the evaporation, ammonia 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 hippuric acid, which is then found in the urine. BENZOYL-SERIES. 403 HOMOLOGUES OF THE BENZOYL-SERIES. Toluylic Add, C 16 H 7 3 ,HO. This substance, which differs from benzoic acid bv C 2 H 2 , has been lately discovered by Mr. Noad, who obtained it by the action of very dilute nitric acid upon cymol, a carbo-hydrogen occurring in cumin-oil. It is a substance exhibiting the closest analogy with benzoic acid both in its physical characters and in its chemical relations. Like benzoic acid, when treated with fuming nitric acid, it yields a nitro-acid, nitrotoluylic acid, C 16 H 6 N0 7 ,HO = C 16 (H e N0 4 )O a ,HO ; distilled with lime or baryta, it furnishes a hydro-carbon C 14 H g , homologous to benzol. The latter substance, which has received the name of toluol, is also obtained from other sources, especially from coal-tar and Tolu balsam. An acid of the formula C 18 H 9 3 ,HO, is not yet known, but we may con- fidently expect that the progress of science will not fail to elicit this sub- stance ; even now we are acquainted with a hydrocarbon C, 6 H 10 , homologous to benzol and toluol. This substance, which is called xylol, is found in wood-tar and coal-gas-naptha, and stands to the unknown acid C, 8 H 9 3 HO in the same relation as benzol to benzoic acid. Should the above acid be discovered, we may with certainty predict that, when distilled with excess of lime, it will yield xylol. Cumic acid, C 2o H n 3 ,HO. Another acid, homologous to benzoic acid, was discovered some time ago, by MM. Cahours and Gerhardt. It is formed by the oxydation of one of the constituents of cumin-oil, cuminol C 20 II 12 2 , which corresponds to oil of bitter almonds. It likewise yields a nitro-acid, nitro-cumic acid C 20 H 10 N0 7 ,HO = C 20 (H 10 N0 4 )0 3 ,HO, and when distilled is converted into cumol Ci 8 Hj 2 , a hydrocarbon, homologous to benzol, toluol, and xylol. Of the next series only the hydrocarbon is known. This is cymol C 20 H 14 , the substance which, as has been mentioned above, is the source of toluylic acid. The homology of these substances is clearly exhibited by the following table : Hydrides. Acids. Hydrocarbons derived from the acid. Benzoyl-series C 14 H 5 2 H C 14 H 5 8 ,HO C, 2 H 6 Toluyl-series C 16 H 7 3 ,HO C 14 H 8 Xylyl-series C 16 H 10 Cumyl-series C 20 tt n 2 H C 20 H U 3 ,HO C, 8 H 12 Cymyl-series C 20 H, 4 This table shows that up to the present moment only the series of hydro- carbons is without a gap, while two acids and three hydrides remain to be discovered. SALICYL AND ITS COMPOUNDS. SALICIN. The leaves and young bark of the poplar, willow, and several other trees contain a peculiar crystallizable, bitter principle, called salicin, which in some respects resembles the vegeto-alkalis cinchonine and quinine, being said to have febrifuge properties. It differs essentially, however, from these bodies in being destitute of nitrogen, and in not forming salts with acids. Salicin may be prepared by exhausting the bark with boiling water, concentrating the solution to a small bulk, digesting the liquid with powdered protoxide of lead, and then, after freeing the colution from lead by a stream of sulphuretted-hydrogen gas, evaporating until the salicin crys- 104 S AL I C Y L . tallizcs out on cooling. It is purified by treatment with animal charcoal and re-crystallization. Salicin forms small, white, silky needles, of intensely bitter taste, which have no alkaline reaction. It melts and decomposes by heat, burning with a bright flame, and leaving a Fesidue of charcoal. It is soluble in 5-6 parts of cold water, and in a much smaller quantity when boiling hot. Oil of vitriol colours it deep red. The last experiments of M. Piria give for sali- cin the formula C 26 H 18 O, 4 . When salicin is distilled with a mixture of bichromate of potassa and sul- phuric acid, it yields, among other products, a yellow, sweet-scented oil, which is found to be identical with the volatile oil distilled from the flowers of the Spiraea ulmaria, or common meadow-sweet. This substance appears to be the hydride of a compound salt-radical, salicyl, containing C 14 H 5 4 ; it has the properties of a hydrogen-acid. Table of Salicyl- Compounds. Salicyl (symb. SI) C 14 F 5 4 Hydrosalicylic acid C, 4 H 5 OJI Salicylide of potassium Cj 4 II 5 4 K Hydrochlorosalicylic acid C, 4 (H 4 C1)0 4 H Hydriodosalicylic acid C, 4 (H 4 I) 4 II Hydrobromosalicylic acid C 14 (H 4 Br)0 4 H Salicylic acid C 14 H 5 5 ,HO HTDROSALTCYLIC ACID ; SALICYLOUS ACID ; ARTIFICIAL OIL OP MEADOW- SWEET, S1H. One part of salicin is dissolved in 10 of water, and mixed in a retort with 1 part of powdered bichromate of potassa and 2 parts of oil of vitriol diluted with 10 parts of water; gentle heat is applied, and after the cessation of the effervescence first produced, the mixture is distilled. The yellow oily product is separated from the water, and purified by rectifica- tion from chloride of calcium. It is thin, colourless, and transparent, but acquires a red tint by exposure to the air. Water dissolves a sensible quan- tity of this substance, acquiring the fragrant odour of the oil, and the cha- racteristic property of striking a deep violet colour with a salt of sesquioxide of iron, a property however which is also enjoyed by salicylic acid. Alcohol and ether dissolve it in all proportions. It has a density of 1-173, and boils at 385 (166 -1C), when heated alone. Hydrosalicylic acid decomposes the alkaline carbonates even in the cold ; it is acted upon with great energy by chlorine and bromine. By analysis it is found to contain C 14 H 6 4 , or the same elements as crystallized beuzoic acid; and the density of its vapour is also the same, being 4-276. SALICYLIDK OF POTASSIUM, KS1. This compound is easily prepared by mixing the oil with a strong solution of caustic potassa ; it separates, on agi- tation, as a yellow crystalline mass, which may be pressed between folds of blotting-paper, and re-crystallized from alcohol. It forms large, square, golden-yellow tables, which have a greasy feel, and dissolve very easily both in water and alcohol ; the solution has an alkaline reaction. When quite dry, the crystals are permanent in the air ; but in a humid state they soon become greenish, and eventually change to a black, soot-like substance, in- soluble in water, but dissolved by spirit and by solution of alkali, called melanic acid. Acetate of potassa is formed at the same time. Melanic acid contains C 20 II g O I0 . The crystals of salicylide of potassium contain water "vhich cannot be expelled without partial decomposition of the salt. SALICYLIDE OF AMMONIUM, NH 4 S1, crystallizes in yellow needles which are quickly destroyed with production of ammonia and the hydride. Salicylide of l>a-iu'in, BaC 14 lT 6 -{-2110, forms fine yellow acicular crystals, which are SALICYL. 405 but slightly soluble in the cold. Salicylide of copper is a green insoluble powder, containing CuC, 4 H 5 4 . Salicylide of copper by destructive distillation gives, among other products, hydride of salicyl and a solid body forming colourless prismatic crystals, fusible and volatile. It is insoluble in water, dissolved by alcohol and ether, and is unaffected by fusion with hydrate of potassa. Nitric acid converts it into anilic and picric acids. (See indigo). It contains C 14 H 5 3 , and is iso- meric with anhydrous benzoic acid. CHLOROHYDRO-SALICYLIC ACID, C ]4 (H 4 C1)0 4 ,H. Chlorine acts very strongly upon the hydride of salicyl ; the liquid becomes heated, and disengages large quantities of hydrochloric acid. The product is a slightly yellowish crys- talline mass, which, when dissolved in hot alcohol, yields colourless tabular crystals of the pure compound, having a pearly lustre. This substance is insoluble in water ; it dissolves freely in alcohol, ether, and solutions of the fixed alkalis ; from the latter it is precipitated unaltered by the addition of an acid. It is not even decomposed by long ebullition with a concentrated solution of caustic potassa. Heated in a retort, it melts and volatilizes, con- densing in the cool part of the vessel in long, snow-white needles. The odour of this substance is peculiar and by no means agreeable, and its taste is hot and pungent. Chlorohydro-salicylic acid combines with the metallic oxides ; with potassa it forms small red crystalline scales, very soluble in water. The correspond- ing compound of barium, prepared from the foregoing, by double decompo- sition, is an insoluble crystalline, yellow powder, containing Ba C 14 (H 4 C1)0. BUOMOIIYDRO-SALICYLIC ACID, C 14 (H 4 Br)0 4 ,H. The bromide-compound is prepared by the direct action of bromine on the hydride of salicyl ; it crys- tallizes in small colourless needles, and very closely resembles in properties the chloride. The hydride of salicyl dissolves a large quantity of iodine, acquiring thereby a brown colour, but forming no combination ; the iodide may, however, be procured by distilling iodide of potassium with chlorohy- dro-salicylic acid. It sublimes as a blackish-brown fusible mass. CIILOUOSAMIDE. The action of dry ammoniacal gas on pure chlorohydro- salicylic acid is very remarkable ; the gas is absorbed in large quantity, and a solid yellow, resinous-looking compound produced, which dissolves in boiling ether, and separates as the solution cools in fine yellow iridescent crystals ; this and a little water are the only products, not a trace of sal- ammoniac can be detected. Chlorosamide is nearly insoluble in water ; it dissolves without change in ether, and in absolute alcohol ; with hot rectified spirit it is partially decomposed, with disengagement of ammonia. Boiled with an acid, it yields an ammoniacal salt of the acid and chlorohydro-sali- cylic acid ; with an alkali, on the other hand, it gives free ammonia, while chlorohydro-salicylic acid remains dissolved. Chlorosamide contains C w (HuCljJNjOgj it is formed by the addition of 2 eq. of ammonia to 3 eq. of chlorohydro-salicylic acid, and the subsequent separation of 6 eq. of water A corresponding and very similar substance, bromosamide, is formed by the action of ammonia on bromohydro-salicylic acid. SALIGENIN. This curious substance is a product of the decomposition of salicin under the influence of the emulsion or synaptase of sweet almonds ; it is also generated by the action of dilute acids. In both cases the salicin is resolved into saligenin and grape sugar. Saligenin forms colourless, na- creous scales, freely soluble in water, alcohol, and ether. It melts at 180 (82C), and decomposes at a higher temperature. Dilute acids at a boiling heat convert it into a resinous-looking substance, C 14 H 6 9 , called saliretin. Many oxidizing agents, as chromic acid and oxide of silver, convert this sub- stance into hydride of salicyl: even platinum-black produces this effect. IU aqueous solution gives a deep indigo-blue colour with salts of ses^uioxide oi 406 S A L I C Y L . iron. Saligenin contains C, 4 TI 8 4 . Hence the transformation of salicin is represented by the equations : C 24 TI 28 28 = 2C 14 ir g 4 Salicin. Grape-sugar. Saligenin. Salicin yields with chlorine substitution-compounds containing that ele- ment, which are susceptible of decomposition by synaptase, with production of bodies termed chloro- and bichloromliyenin. Chlorosaligenin very closely resembles normal saligenrn, and contains C 14 (H 7 C1)0 4 . Certain products, called by M. Piria helicin, helicoidin, undanilotic acid, are described as result- ing from the action of dilute nitric acid upon salicin. With strong acid at a high temperature nitro-salicylic acid (anilic acid) C 14 (H 4 NO 4 )0 5 ,HO, is pro- duced. SALICYLIC ACID, S10,HO. This compound is obtained by heating hydride of salicyl with excess of solid hydrate of potassa ; the mixture is at first brown, but afterwards becomes colourless ; hydrogen gas is disengaged during the reaction. On dissolving the melted mass in water, and adding a slight excess of hydrochloric acid, the salicylic acid separates in crystals, which are purified by re-solution in hot water. This substance very much resembles benzoic acid ; it is very feebly soluble in cold water, is dissolved in large quantities by alcohol and ether, and may be sublimed with the utmost ease. It is charred and decomposed by hot oil of vitriol, and attacked with great violence by strong, heated nitric acid. Salicylic acid contains C I4 H 5 6 ,HO. Salicylic acid can also be prepared with great ease by fusing salicin with excess of hydrate of potassa, and also by the action of a concentrated and hot solution of potassa upon the volatile oil of Gaulthcria procumbens, which is the methyl-compound of this acid occurring in nature (see essential oils containing oxygen). When salicylic acid is mixed with powdered glass or sand arid exposed to strong and sudden heat in a retort, it is almost entirely converted into carbonic acid and hydrate of phenyl, C, 2 B 6 2 , a substance found in considerable proportion in coal-tar-naphta, and the same change happens to many of its salts with even greater facility. PHLOKIDZIN. This is a substance bearing a great likeness to salicin, found in the root-rind of the apple and cherry-tree, and extracted by boiling al- cohol. It forms fine, colourless, silky needles, soluble in 1000 parts of cold water, but freely dissolved by that liquid when hot ; it is also soluble with- out difficulty in alcohol. It contains C 42 H 2l () 20 -f-4IIO. Dilute acids convert phloridzin into grape-sugar and a crystallizabie sweet substance called phlo- retin, C^H^O^. C 24 IT 2 /) 2 Phloridzin. Grape-sugar. Phloretin. CUMARIN. The odoriferous principle of the tonka-bean. It may be often seen forming minute colourless crystals under the skin of the seed, and be- tween the cotyledons. It is best extracted by macerating the sliced beans 111 hot alcohol, and, after straining through cloth, distilling off the greater part of the spirit. The syrupy residue deposits on standing crystals of cu- inarin, which must be purified by pressure from a fat oil which abounds in the beans, and then crystallized from the hot water. So obtained, cumarin forms slender, brilliant, colourless needles, fusible at 122 (50C), and dis- tilling without decomposition at a higher temperature. It has a fragrant odour and burning taste ; it is very slightly soluble in cold water, mor* CINNAMYL AND ITS COMPOUNDS. 407 freely in hot water, and also in alcohol. It is unaffected by dilute acids and alkalis, which merely dissolve it. Boiling nitric acid converts it into picric acid, and a hot concentrated solution of potassa into cumaric, and eventually into salicylic acid. Cumarin exists in several other plants, as the Mc.lilotw. ojficinalis, the Asperula adorata, and the Anthoxanthum odoratum. According to M. Bleibtreu it contains C 18 H 6 4 . Cumaric acid is C 18 H 8 6 . CINNAMYL AND ITS COMPOUNDS. The essential oil of cinnamon seems to possess a constitution analogous to that of bitter-almond oil; it passes by oxidation into a volatile acid, tho cinnamic, which resembles in the closest manner ben/oic acid. The radical assumed in these substances bears the name of cinnamyl ; it has not been isolated. Table of Cinnamyl- Compounds. Cinnamyl (symbol Ci) C, 8 H 7 2 Chloride of cinnamyl C, 8 H 7 2 C1 Hydride of cinnamyl; oil of cinnamon C lg H 7 2 H Hydrated oxide of cinnamyl; cinnamic acid C, 8 H 7 2 0,HO Cinnamylic alcohol C IS H 9 0,HO Cinnamate of cinnamylic ether Ci 8 H 9 0,C, 8 lL 7 O 3 HYDRIDE OF CINNAMYL ; OIL OF CINNAMON ; CUT. Cinnamon of excellent quality is crushed, infused twelve hours in a saturated solution of common salt, and then the whole subjected to rapid distillation. Water passes over, milky from essential oil, which after a time separates. It is collected and left for a short time in contact with chloride of calcium. This fragrant and costly substance has, like most of the volatile oils, a certain degree of solu- bility in water ; it is heavier than that liquid, and sinks to the bottom of the receiver in which the distilled products have been collected. It contains, according to M. Dumas, Ci 8 U 8 2 . CINNAMTC ACID, Ci(),HO. When pure oil of cinnamon is exposed to tho air, or inclosed in a jar of oxygen, it is quickly converted by absorption of gas into a mass of white crystalline matter, which is hydrated cinnamic acid; this is the only product. Cinnamic acid is found in Peruvian and Tolu bal- sams, associated with benzoic acid, and certain oily and resinous substances ; .it may 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 hydrate of lime ; this mixture is boiled for some time in a large quantity of water, and filtered hot. On cool- ing, cinnamate of lime crystallizes out, while benzoate of lime remains in solution. The impure salt is re-dissolved 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 cin- namic acid separates in small plates or needle-formed crystals of perfect whiteness. From the original mother-liquor much benzoic acid can be pro- cured. 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 248 (120C), and enters into ebullition and distils without change at 560 (293-3C); the vapour is pungent and irritating. Cinnamic acid is much less soluble, both in hot and cold water, than benzoic; a hot saturated solu- tion becomes on cooling a soft-solid mass of small nacreous crystals. It dissolves with perfect ease in alcohol. Boiling nitric acid decomposes cin- 408 CINNAMYL AND ITS COMPOUNDS. namic :tcid with great energy, and with production of copious red fumes ; bitter almond-oil distils over, and benzoic acid remains in the retort in which the experiment is made. When cinnamic acid is heated in a retort with a mixture of strong solution of bichromate of potassa and oil of vitriol, it is almost instantly converted into benzoic acid, which afterwards distils over with the vapour of water: the odour of bitter-almond-oil is at the same time very perceptible. The action of chlorine is different ; no benzoic acid is formed, but other products, which have not been perfectly studied. Cinnamic acid forms with bases a variety of salts which are very similar to the benzoates. The crystallized acid contains C 18 H 7 3 ,HO. When dis- tilled with an excess of lime or baryta, cinnamic acid undergoes a decompo- sition analogous to that of benzoic acid; an oily liquid cinnamol C 16 H g distils over, whilst a carbonate of the alkaline earth remains behind, C 18 H 8 4 -{~ 2BaO=2(BaO,Cp g ) + C 18 H 6 . This oil is also found in liquid storax, and is frequently described by the term styrol. (See resins and balsams.) CHLOROCINNOSE. This is the ultimate product of the action of chlorine on oil of cinnamon by the aid of heat. When purified by crystallization from alcohol, it forms brilliant, colourless needles, fusible, and susceptible of vola- tilization without change. It is not affected by boiling oil of vitriol, and may be distilled without decomposition in a current of ammoniacal gas. Chlorocinnose contains C 18 H 4 C1 4 2 ; it is formed by the substitution in the oil of cinnamon of 4 eq. of chlorine for 4 eq. of hydrogen. The true chloride of cinnamyl, Ci Cl, seems to be first formed in considerable quantity, and subsequently decomposed by the continued action of the chlorine ; it has not been separated in a pure state ; it appears as a very thin, fluid oil, convertible into a crystalline mass by strong solution of potassa. When cinnamon-oil is treated with hot nitric acid, it undergoes decompo- sition, being converted into hydride of benzoyl and benzoic acid. With a boiling solution of chloride of lime the same thing happens, a benzoate of the base being generated. If the oil be heated with solution of caustic potassa it remains unaffected ; with the solid hydrate, however, it disengages pure hydrogen, and forms a potassa-salt, which appears to be the cirmamate. When brought into contact with cold concentrated nitric acid, a crystalline, yellowish, scaly compound is obtained, which is decomposed by water with separation of the oil. With ammonia a solid substance is produced, which also appears to be a direct compound of the two bodies. Two varieties of oil of cinnamon are met with in commerce of very unequal value, viz. that of China, and that of Ceylon ; the former being considered the best : both are, however, evidently impure. The pure oil may be ex- tracted from them by an addition of cold, strong nitric acid ; the crystalline matter which forms after the lapse of a few hours, separated and decomposed by water, yields ure hydride of cinnamyl. There can be no doubt that the cinnamic acid in Tolu and Peru balsams is gradually formed by the oxidation of a substance very closely related to the alcohols. When these balsams are first imported they are nearly fluid, but gradually acquire consistence by keeping. By the aid of an alcoholic solution of potassa, a compound, sometimes oily, sometimes solid, may be separated from these balsams, which cannot be distilled without partial de- composition. This compound, described respectively under the name of cinnamein (when oily), and styracin (when solid), when distilled with hydrate of potassa, is converted into cinnamic acid and a neutral substance, which likewise occurs in an oily and crystalline modification, and has been called, respectively, peruvin and styrone. These substances are related to each other in a very remarkable manner. Peruvin may be viewed as the alcohol of CINNAMYL AND ITS COMPOUNDS. 409 cinnamic acid, when cinnamein becomes the compound ether consisting of alcohol and cinnamic acid. This relation will become obvious by the fol- lowing formulae : Ethyl-series. Alcohol C 4 H 5 0,HO Acetic acid C 4 H 3 3 ,HO Acetic ether C 4 H 5 0,C 4 H 3 3 Cinnamyl-series. Peruvin C, S H 9 0,HO Cinnamic acid C, 8 H 7 3 , HO Cinnamein C 18 H 9 0,C, 8 II 7 3 "When treated with oxidizing agents, peruvin yields cinnamic aoid, or its products of decomposition, oil of bitter-almonds and benzoic acid. 410 VEGETABLE ACIDS. SECTION III. VEGETABLE ACIDS. THE vegetable acids constitute a very natural and important family or group of compounds, many ot which possess the property of acidity, i. e, acid reaction to litmus paper, and power of forming stable, neutral, and often crystallizable compounds with bases, to an extent comparable with that of the mineral acids. Some of these bodies are very widely diffused through the vegetable kingdom ; others are of much more limited occurrence, being found in some few particular plants only, and very frequently in combina- tion with organic alkaline bases, in conjunction with which certain of them will be found described. Many of the vegetable acids are polybasic ; and it is remarkable that in the new products, or pyro-acids, to which they often give rise under the influence of heat, this character is usually lost. The particular acids now to be described are for the most part of extensive and general occurrence ; mention will be made of some of the rarer ones ia connection with their respective sources. Table of Vegetable Acids. Tartaric acid C 8 H 4 10 ,2Hl> Racemic acid C 8 H 4 10 ,2HO Citric acid C 12 H 5 0,,,3HO Aconitic, or equisetic acid C 4 H 3 ,HO Malic acid , C g H 4 8 ,2HO Fumaric acid C 4 H 3 ,HO Tannic acid C 19 H 5 9 ,3HO Gallic acid C 7 H 3 ,2HO TARTARIC ACID. This is the acid of grapes, of tamarinds, of the pine- apple, and of several other fruits, in which it occurs in the state of an acid potassa-salt; tartrate of lime is also occasionally met with. The tartaric acid of commerce is wholly prepared from the tartar or argol, an impure acid tartrate of potassa, deposited from wine, or rather grape-juice, in the act of fermentation. This substance is purified by solution in hot water, the use of a little pipe-clay, and animal charcoal to remove the colouring-matter of the wine, and subsequent crystallization; it then constitutes cream of tartar, and serves for the preparation of the acid. The salt is dissolved in boiling water, and powdered chalk added as long as effervescence is excited, or the liquid exhibits an acid reaction ; tartrate of lime and neutral tartrate of potassa result ; the latter is separated from the former, which is insoluble, by filtration. The solution of tartrate of potassa is then mixed with excess of chloride of calcium, which throws down all the remaining acid in the form of lime-salt; this is washed, added to the former portion, and then the whole digested with a sufficient quantity of dilute sulphuric acid to with- draw the base and liberate the organic acid. The filtered solution is cau- tiously evaporated to a syrupy consistence and placed to crystallize in a wa^m situation. VEGETABLE ACIDS. 411 Tartaric acid forms colourless, transparent crystals, often of large size, which have the figure of an oblique rhombic prism more or less modified ; these .are permanent in the air, and inodorous ; they dissolve with great facility in water, both hot and cold, and are also soluble in alcohol. The solution reddens litmus strongly, and has a pure acid taste. The aqueous solution, as has been mentioned (page 76), possesses right-handed polariza- tion. This solution is gradually spoiled by keeping. Tartaric acid is bibasic; the crystals contain C 8 H 4 IO ,2HO. This substance is consumed in large quantities by the calico-printer, being employed to evolve chlorine from solution of bleaching-powder in the production of white or discharged pat- terns upon a coloured ground. TARTKATE OF POTASSA. NEUTRAL TARTRATE ; SOLUBLE TARTAR ; 2KO, CgTI 4 Oj . The neutral salt may be procured by neutralizing cream of tartar with chalk, as in the preparation of the acid, or by adding carbonate of potassa to cream of tartar to saturation : it is very soluble, and crystallizes with difficulty in right rhombic prisms, which are permanent in the air, and have a bitter, saline taste. ACID TARTRATE OF POTASSA; CREAM OF TARTAR; KO,HO,CgH 4 1() . The origin and mode of preparation of this substance have been already de- scribed. It forms small transparent or translucent prismatic crystals, irre- gularly grouped together, which grit between the teeth. It dissolves pretty freely in boiling water, but the greater part separates as the solution cools, leaving about ^ or less dissolved in the cold liquid. The salt has an acid reaction, and a sour taste. When exposed to heat in a close vessel, it is de- composed with evolution of inflammable gas, leaving a mixture of finely- divided charcoal and pure carbonate of potassa, from which the latter may be extracted by water. Cream of tartar is almost always produced when tartaric acid in excess is added to a moderately strong solution of a potassa- salt, and the whole agitated. TARTRATTS OF SODA. Two compounds of tartaric acid with soda are known: a neutral salt, 2NaO,C 8 H 4 0, -f-4HO ; and an acid salt, NaO,HO, C g H 4 0, -f-2HO. Both are easily soluble in water, and crystallize. Tartaric acid and bicarbonate of soda form the ordinary effervescing draughts. TARTRATE OF POTASSA AND SODA ; ROCHELLE OR SEIGNETTE SALT ; KO, NaO,C 8 H 4 Oi -f-10HO. This beautiful salt is made by neutralizing with car- bonate of soda a hot solution of cream of tartar, and evaporating to the consistence of thin syrup. It separates in large, transparent, prismatic crystals, the faces of which are unequally developed ; these effloresce slightly in the air, and dissolve in 1J parts of cold water. Acids precipitate cream of tartar from the solution. Rochelle salt lias a mild, saline taste, and is used as a purgative. TARTRATES OF AMMONIA. The neutral tartrate is a soluble and efflorescent salt, containing 2NH 4 0,C 8 H 4 10 - r -2HO. The add tartrate, NH 4 0,HO,C 8 H 4 10 , closely resembles ordinary cream of tartar. A salt corresponding to Rochelle salt also exists, having oxide of ammonia in place of soda. The tartrates of lime, baryta, strontia, magnesia, and of the oxides of most of the metals proper, are insoluble, or nearty so, in water. TARTRATE OF ANTIMONY AND POTASSA; TARTAR EMETIC. This salt is easily made by boiling teroxide of antimony in solution of cream of tartar ; it is deposited from a hot and concentrated solution in crystals derived from an octahedron with rhombic base, which dissolve without decomposition in 15 parts of cold, and 3 of boiling water, and have an acrid and extremely dis- agreeable taste. The solution is incompatible with, and decomposed by, both acids and alkalis ; the former throw down a mixture of cream of tartar and teroxide of antimony, and the latter, the teroxide, which is again dissolved by great excess of the reagent. Sulphuretted hydrogen separates all the 412 VEGETABLE ACIDS. antimony in the state of tersulphide. Heated in a dry state on charcoal before the blowpipe, it yields a globule of metallic antimony. The a contain KO,Sb0 3 ,C 8 H 4 10 -f2H0. 1 An analogous compound containing arsenious. acid (AsO s ) in plac^ of ter- oxide of antimony has been described. It has the same crystalline; loan as tartar-emetic. A solution of tartaric acid dissolves hydrated sesquioxide of iron in large quantity, forming a brown liquid which has an acid reaction, and dries up by gentle heat to a brown, transparent, glassy substance, destitute of all traces of crystallization. It is very soluble in water, and the solution is not pre- cipitated by alkalis, fixed or volatile. Indeed, tartaric acid added in sufficient quantity to a solution of sesquioxide of iron or alumina, entirely prevents the precipitation of the bases by excess of ammonia. Tartrate and ammoni- acal tartrate of iron are used in medicine, these compounds having a less disagreeable taste than most of the iron-preparations. Solution of tartaric acid gives white precipitates with lime- and baryta- water, and with acetate of lead, which dissolve in excess of the acid ; with neutral salts of lime and baryta no change is produced. The effect on solu- tion of potassa-salts has been already noticed. ACTION OF HEAT ON TARTARIC ACID. When crystallized tartaric acid is exposed to a temperature of 400 (204-5C) or thereabouts, it melts, loses water, and passes through three different modifications, called in succession tartralic, tartrelic, and anhydrous tartaric acid. The two first are soluble in water, and form salts, which have properties completely different from those of ordinary tartaric acid. The third substance, or anhydrous acid, is a white insoluble powder. All three, in contact with water, slowly pass into common tartaric acid. Their composition is thus expressed : Ordinary tartaric acid C 8 H 4 ]0 ,2HO Tartralic acid 2C 8 H 4 0, ,3HO Tartrelic acid C 8 H 4 10 ,HO Anhydrous acid C 8 H 4 10 The analogy borne by these bodies to the several modifications of phos- phoric acid will be at once evident. PYROTARTARIC ACID. When crystallized tartaric acid is subjected to destructive distillation, a heavy acid liquid containing this substance passes over, accompanied by a large quantity of carbonic acid ; in the retort is left a semi-fluid black mass, which, by farther heating, gives combustible gases, an empyreumatic oil, and a residue of charcoal. The distilled product exhales a powerful odour of acetic acid, and is with great difficulty purified. Pyrotartaric acid forms a series of salts, and an ether; it is supposed to con~ tain C 6 H 3 5 ,HO. A second pyro-acid sometimes separates in crystals from the preceding compound, and may be obtained in larger quantity by the destruc- tive distillation of cream of tartar; it is composed of C 5 H 3 3 ,HO. When tartaric acid is heated to 400 (204 -5C) with excess of hydrate of pota.xsa, it is resolved without charring or secondary decomposition into oxa- 1 According to Dumas, KO.SbOs.Csl^Oio-fHO. Dried at 212 (100C), an equivalent of water is lost, and at 428 (220C), two additional equivalents, leaving the compound KO,SbOs, (MI 3 Otj, which can no longer contain ordinary tartaric acid. Nevertheless, when dissolved in water, ILe crystals again take up the elements of water and reproduce the original salt. VEGETABLE ACIDS. 413 lie and acetic acids, which remain in union with the base, and only undergo decomposition at a much higher temperature. RACEMIC ACID ; PARATARTARIC ACID. The grapes cultivated in certain districts of the Upper Rhine, and also in the Vosges, in France, contain, in association with tartaric acid, another and peculiar acid body, to which the term racemic acid is given ; it is rather less soluble than tartaric acid, and separates first from the solution of that substance. Between these two acids, however, the greatest possible resemblance exists ; they have exactly the same composition, and yield, when exposed to heat, the same products ; the salts of racemic acid correspond, in the closest manner, with the tartrates. A solution of this acid precipitates a neutral salt of lime, which is not the case with tartaric acid. A solution of racemic acid does not rotate the plane of polarization. Racemic acid has been lately the subject of some exceedingly interesting researches by M. Pasteur, which have thrown much light upon the relation of this acid to tartaric acid. If racemic acid be saturated with potassa, or soda, or with most other bases, crystals are obtained, which are identical in form and physical properties. By saturating racemic acid, however, with two bases, by forming, for instance, compounds corresponding to Rochelle- salt, which contain potassa and soda or ammonia and soda, and allowing the solution to crystallize slowly, two varieties of crystals are produced, which may be distinguished by their form, namely, as the image and the reflection of the image, or as right-handed and left-handed. If the two kinds of crystals are carefully selected and separately crystallized, in each case crys- tals of the one variety only are deposited. The composition, the specific gravity, and, in fact, most of the physical properties of these two varieties of racemate of potassa and soda, are invariably the same. They diifer, how- ever, somewhat in their chemical characters, and especially in one point, they rotate the plane of polarization in opposite directions. (See page 76.) M. Pasteur assumes in the two varieties of crystals the existence of two modifications of the same acid, which he distinguishes, according as the salts possess right- or left-handed polarization, by the terms deztroracemic and levoracemic acids. These acids can be separated by converting the above compounds into lead- or baryta-salts, and decomposing them by means of sulphuric acid. In this manner two crystalline acids are obtained, identical in every respect excepting in their deportment with polarized light, and in their crystals behaving as image and reflection. It is very probable, not to say certain, that dextroracemic acid is nothing but common tartaric acid. A mixture of equal parts of the two acids has no longer the slightest effect on polarized light, and exhibits in every respect the deportment of racemic acid. CITRIC ACID. Citric acid is obtained in large quantity from the juice of limes and lemons ; it is found in many other fruits, as in gooseberries, cur- rants, &c., in conjunction with another acid, the malic. In the preparation of this acid, the juice is allowed to ferment a short time, in order that muci- lage and other impurities may separate and subside ; the clear liquor is then carefully saturated with chalk, which forms, with the citric acid, an insoluble compound. This is thoroughly washed, decomposed by the proper quantity of sulphuric acid, diluted with water, and the filtered solution evaporated to a small bulk, and left to crystallize. The product is drained from the, mother- liquor, re-dissolved, digested with animal charcoal, and again concentrated to the crystallizing-point. Citric acid forms colourless, prismatic crystnls, which have a pure and agreeable acid taste; they dissolve, with great ease, in r )oth hot and cold water; the solution strongly reddens litmus, and, when lorg kept, is subject to spontaneous change. Citric acid is tribasic; it j formula in the gently dried and anhydrous silver 35* 414 VEGETABLE ACIDS. salt is Ci 2 H 5 O n . The hydrated acid crystallizes with two different quantities of water, assuming two different forms. The crystals, which separate by spontaneous evaporation from a cold saturated solution, contain Cj 2 H 5 O n , 3FIO-f-2HO, the last being water of crystallization ; while, on the other hand, those which are deposited from a hot solution contain but 4 equivalents of water altogether, three of which are basic. Citric acid is entirely decomposed when heated with sulphuric and nitric acids ; the latter converts it into oxalic acid. Caustic potassa, at a high temperature, resolves it into acetic and oxalic acids. 1 When subjected to the action of chlorine, the alkaline citrates yield among other products chloroform. The citrates are very numerous, the acid forming, like ordinary phosphoric acid, three classes of salts, which contain respectively 3 eq. of a metallic oxide, 2 eq. of oxide and 1 eq. of basic water, and 1 eq. oxide and 2 eq. basic water, besides true basic salts, in which the water of crystallization is perhaps replaced by a metallic oxide. The citrates of the alkalis are soluble and crystallizable with greater or less facility ; those of baryta, strontia, lime, lead, and silver are insoluble. Citric acid resembles tartaric acid in its relations to sesquioxide of iron ; it prevents the precipitation of that substance by excess of ammonia. The citrate, obtained by dissolving the hydrated sesquioxide 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 ammonio-citrate of iron are elegant medicinal preparations. Very little is known respecting the composition of these curious compounds ; the absence of crystallization is a great bar to inquiry. Citric acid is sometimes adulterated with tartaric ; the fraud is easily detected by dissolving the acid in a little cold water, and adding to the solu- tion a small quantity of acetate of potassa. If tartaric acid be present, a white crystalline precipitate of cream of tartar will be produced on agitation. ACONITIC, on EQUISETIC ACID. When crystallized citric acid is heated in a retort until it begins to become coloured, and to undergo decomposition, and the fused, glassy product, after cooling, dissolved in water, an acid is obtained, differing completely in properties from citric acid, but identical with an acid extracted from the Aconitum napellus and the Equisetum fluviatile. Aconitic acid forms a white, confusedly-crystalline mass, permanent in the air, and very soluble in water, alcohol, and ether ; the solution has an acid and astringent taste. The salts of aconitic acid possess but little interest; that of baryta forms an insoluble gelatinous mass ; aconitate of lime, which has a certain degree of solubility, is found abundantly in the expressed juice of the monkshood, and aconitate of magnesia in that of the equisetum. Hydrated aconitic acid contains C 4 H0 3 ,HO; it is formed in the artificial process above described, by the breaking up of 1 eq. of hydrated citric acid, C, 2 HgO, 4 , into 2 eq. of water and 3 eq. of hydrated aconitic acid. There are, however, invariably many secondary products formed, such as acetone, carbonic oxide, and carbonic acid. The farther action of heat upon aconitic acid gives rise to several new acids, especially citraconic and itaconic acids, both expressed by the formula C 5 H 2 3 ,HO. The limits of this elementary work will not permit us to enter into a description of these farther products of decomposition. MALIC ACID. This is the acid of apples, pears, and various other fruits ; it is often associated, as already observed, with citric acid. An excellent * The easy resolution of tartaric and citric acids into a mixture of oxalic and acetic adds by the action of heat, aided by the presence of a powerful base, has led to the idea of the pos- sible pre-existence of these last-named bodies in the two vegetable acids, which may thus be compounded of two acids of simpler constitution, forming coupled or conjugate acids, of which several have been supposed to exist. These views, although sometimes useful, are not at present supported by evidence of great importance. VEGETABLE ACIDS. 415 process for preparing the acid in question is that of Mr. Everitt, who has demonstrated its existence, in great quantity, in the juice of the common garden rhubarb ; it is accompanied by acid oxalate of potassa. The rhubarb stalks are peeled, and ground or grated to pulp, which is subjected to pres- sure. The juice is heated to the boiling-point, neutralized with carbonate of potassa, and mixed with acetate of lime ; insoluble oxalate of lime falls, which is removed by filtration. To the clear and nearly colourless liquid, solution of acetate of lead is added as long as a precipitate continues to be produced. The malate of lead is collected on a filter, washed, diffused through water, and decomposed by sulphuretted hydrogen. 1 The filtered liquid is carefully evaporated to the consistence of syrup, and left in a dry atmosphere until it becomes converted into a solid and somewhat crystalline mass of malic acid: regular crystals have not been obtained. From the berries of the mountain-ash (sorbus aucuparia) in which malic acid is like- wise present in considerable quantity, especially at the time they commence to ripen, the acid may be prepared by the same process. Malic acid is bibasic, its formula being C g H 4 8 ,2HO; it forms a variety of salts, some of which are neutral, others acid. In the presence of fer- menting substances, especially of putrifying casein, it is itself decomposed, yielding succinic, acetic, and carbonic acid. 3(C 8 H 4 8 ,2HO) = 2(C 8 H 4 6 ,2HO)-f C 4 H 3 3 ,HO-f4C0 2 -f-2HO. Malic acid. Succinic acid. Acetic acid. Sometimes also butyric acid and hydrogen are observed among the products of this decomposition. Malic acid is colourless, 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. The most characteristic of the malates are the acid malate of ammonia, NH 4 0,IIO, C 8 H 4 S , which crystallizes remarkably well, and the malate of lead, which is insoluble in pure water, but dissolves, to a considerable extent, in warm dilute acid, and separates, on cooling, in brilliant, silvery crystals which con- tain water. The acid may, by this feature, be distinguished. The acid ma- late of lime, CaO,IIO,C 8 U 4 8 -f6HO, is also a very beautiful salt, freely solu- ble in warm water. It is prepared by dissolving the sparingly soluble neutral malate of lime in hot dilute nitric acid, and leaving the solution to cool. Recent researches of M. Piria have established a most intimate relation between malic acid and two substances asparagin and aspartic acid, which will be described in one of the succeeding sections. These compounds may be viewed as malamide and malauiic acid, analogous to oxamide and oxamic acid. Oxalic acid a . . C 4 G ,2HO Malic acid . . C,H 4 8 ,2HO Neutral oxalate of\ p n 9xriT r\ f Neutral malate oH n TI n oxrtr A ammonia . . j^A,2ISH 4 j aramonia . . } C 8 H 4 8 ,2NH 4 Oxamide. . .}C 4 TI 4 N 2 4 { ^ mide ' as P a ~ } C 8 H 8 NA Knojalate of am- 1 ^^Hfl { *^* of am- J C^H Oxamic acid . }c 4 H t NO.,HO 1 If the acid be required pure, crystallized malate of lead must lie used, the freshly preci- pitated suit invariably carrying down a quantity of lime, which cannot be removed by simple waflbiug. 3 We have here doubled the formula of oxalic acid, when it becomes bibasic, like malic acid. There are, in fact, many features in the history of oxalic acid, which render it probable tha. it is bibasic. In the text we have still retained the generally received formula. 416 VEGETABLE ACIDS. Hitherto neither asparagin nor aspartic acid have been actually obtained from malic acid. On the contrary, these substances are converted with the greatest facility into malic acid. On passing a current of nitrous acid into a solution of asparagin or aspartic acid, pure nitrogen is evolved, malic being liberated. C 9 H 8 N 2 6 + 2N0 8 = C 8 H 4 8 ,2HO + 2110 -f 4N Asparagin. Malic acid. FUMARTC AND MALEIC ACIDS. If malic acid be heated in a small retort, nearly filled, it melts, emits water, and enters into ebullition ; a volatile acid passes over, which dissolves in the water of the receiver. After a time, small solid, crystalline scales make their appearance in the boiling liquid, and increase in quantity, until the whole becomes solid. The process may now be interrupted, and the contents of the retort, after cooling, treated with cold water ; unaltered malic acid is dissolved out, and the new sub- stance, having a smaller degree of solubility, is left behind; it is called fumaric acid, from its identity with an acid extracted from the common fumitory. Fumaric acid forms small, white, crystalline laminae, which dissolve freely in hot water and alcohol, but require for that purpose 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 phenomenon often observed in organic bodies of small volatility. Fumaric acid forms salts, which have been examined by M. Rieckher, and an ether, which, by the action of ammonia, yields a white, amorphous, insoluble powder, called fumar amide, corresponding in properties and constitution with oxamide. Hydrated fumaric acid contains C 4 H0 3 ,HO; hence it is isomeric with aconitic acid. The volatile acid produced simultaneously with the 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 ; it has a strong acid taste and reaction, and is convertible by heat into fumaric acid. Hydrated maleic acid contains C 8 H 2 6 ,2HO. Maleic and fumaric acids are thus seen to have precisely the same composition ; they are formed by the separation of 2 eq. of water from hydrated malic acid. TANNIC AND GALLIC ACIDS. These are substances in which the acid character is much less strongly marked than in the preceding bodies ; they constitute the astringent principles of plants, and are widely diffused, in one form or other, through the vegetable kingdom. It is possible that there may be several distinct modifications of tannic acid, which differ among themselves in some particulars. The astringent principle of oak-bark and nut-galls, for example, is found to precipitate salts of sesquioxide of iron bluish-black, while that from the leaves ef the sumach and tea-plant, as well as infusions of the substances known in commerce under the name of Ttino and catechu, are remarkable for giving, under similar circumstances, precipitates which have a tint of green. The colour of a precipitate is, however, too much influenced by external causes to be relied upon as a proof of essential difference. Unfortunately, the tannic acid or acids refuse to crystallize ; one most valuable test of individuality is therefore lost. After the reaction with salts of sesquioxide of iron, the most character- istic feature of tannic acid and the other astringent infusions referred to, is that of forming insoluble compounds with a great variety of organic, and especially animal substances, as solutions of starch and gelatin, solid mus- eular fibre and skin, &c., which then acquire the property of resisting putre- VEGETABLE ACIDS. 417 Pig. 172. faction ; it is on this principle that leather is manufactured. Gallic acid, on the contrary, is useless in the operation of tanning. Tannic Acid of the Oak. This substance may be prepared by the elegant and happy method of M. Pelouze, from nut-galls, -which are excrescences produced on the leaves of a species of oak, the Quercus infect oria, by the puncture of an insect. A glass vessel, having somewhat the figure of that represented in the margin, fig. 172, is loosely stopped at its lower extremity by a bit of cotton wool, and half or two-thirds filled with pow- dered Aleppo-galls. Ether, prepared in the usual manner by rectification, and containing, as it invariably does, a little water, is then poured upon the powder, and the vessel loosely stopped. The liquid, which after some time collects in the receiver below, consists of two distinct strata ; the lowest, which is almost colourless, is a very strong solution of nearly pure tannic acid in water ; the upper consists of ether holding in solution gallic acid, colouring matter, and other impurities. The carefully-separated heavy liquid is placed to evaporate over a surface of oil of vitriol in the vacuum of the air-pump. Tannic acid, or tannin, thus obtained, forms a slightly yellowish, friable, porous mass, without the slightest tendency to crystal- lization. It is very soluble in water, less so in alcohol, and very slightly soluble in ether. It reddens litmus, and pos- sesses a pure astringent taste without bitterness. A strong solution of this substance mixed with mineral acids gives rise to precipitates, which consist of combinations of the tannic acid with the acids in question ; these compounds are freely soluble in pure water, but scarcely so in acid solutions. Tannic acid precipitates albumin, gelatin, salts of the vegeto- alkalis, and several other substances ; it forms soluble com- pounds with the alkalis, which, if excess of base be present, rapidly attract oxygen, and become brown by destruction of the acid ; the tannates of baryta, strontia, and lime are sparingly soluble, and those of the oxides of lead and antimony insoluble. Salts of protoxide of iron are unchanged by solution of tannic acid ; salts of the sesquioxide, on the contrary, give with it a deep bluish-black precipitate, which is the basis of writing-ink ; hence the value of an infusion of tincture of nut-galls as a test for the presence of that metal. The action of acids upon tannic acid gives rise to the for- mation of gallic acid, which will be presently described, with simultaneous separation of grape-sugar. Hence tannic acid would appear to be a conju- gated sugar-compound. Tannic acid, carefully dried, contains Cjgl^Og-f-^HO. 1 Tannic acid, closely resembling that obtained from galls, may be extracted by cold water from catechu ; hot water dissolves out a substance having feeble acid properties, termed catechin. This latter compound, when pure, crystallizes in fine colourless needles, which melt when heated, and dissolve very freely in boiling water, but scarcely at all in the cold. Catechin dis- solves also in hot alcohol and ether. The aqueous solution acquires a red tint by exposure to air, and precipitates acetate of lead and corrosive subli- mate white, reduces nitrate of silver on the addition of ammonia, but fails to form insoluble compounds with gelatin, starch, and the vegeto-alkalis. It 1 This formula is scarcely established beyond a doubt. M. Strecker, who has obseryed the formation of sugar from tannic acid, represents this substance by the formula OoIl^Oac, and its change under the influence of acids by the equation 2C*oIIi80a6-r8IIO = 8(C 7 H03,2IIO) Tannic acid. Gallic acid. Grape-sugar. 418 VEGETABLE ACIDS. strikes a deep green colour with the salts of scsquioxide of iron. This body is said to be convertible by heat into tannic acid. The formula which has been assigned to catechin is C ]5 H 6 6 . Japonic and rubic acids are formed by the action of alkali in excess upon catechin ; the first in the caustic condition, and the second when in the state of carbonate. Japonic acid is a black and nearly insoluble substance, so- luble in alkalis and precipitated by acids, containing C 12 H 4 4 ,HO ; it is per- haps identical with a black substance of acid properties, formed by M. Peligot, by heating grape-sugar with hydrate of baryta. Rubic acid has been but little studied ; it is said to form red insoluble compounds with the earths and certain oxides of the metals. Several acids closely allied to tannic acid have been found in coffee and Paraguay tea. GALLIC ACID. Gallic acid is not nearly so abundant as tannic acid ; it is produced by an alteration of the latter. A solution of tannic acid in water exposed to the air, gradually absorbs oxygen, and deposits crystals of gallic acid, formed by the destruction of the tannic acid. The simplest method of preparing this acid in quantity is to take powdered nut-galls, which, when fresh and of good quality, contain 30 or 40 per cent, of tannic acid, with scarcely more than a trace of gallic, to mix this powder with water to a thin paste, and to expose the mixture to the air in a warm situation for the space of two or three months, adding water from time to time to replace that lost by drying up. The mouldy, dark-coloured mass produced may then be strongly pressed in a cloth, and the solid portion boiled in a con- siderable quantity of water. The filtered solution deposits on cooling abun- dance of gallic acid, which may be drained and pressed, and finally purified by re-crystallization. It forms small, feathery, and nearly colourless crys- tals, which have a beautiful silky lustre; it requires for solution 100 parts of cold, and only 3 parts of boiling water ; the solution has an acid and as- tringent taste, and is gradually decomposed by keeping. Gallic acid does not precipitate gelatin ; with salts of protoxide of iron no change is pro- duced, but with those of the sesquioxide a deep bluish-black precipitate falls, which disappears when the liquid is heated, from the reduction of the sesquioxide to the protoxide at the expense of the gallic acid. The salts of gallic acid present but little interest ; those of the alkalis are soluble, and readily destroyed by oxidation in presence of excess of base, the solution acquiring after some time a nearly black colour ; the gallates of most of the other metallic oxides are insoluble. Gallic acid, dried at 212 (100C), contains C 7 H0 3 ,2HO; the crystals con- tain an additional equivalent of water. The insoluble residue of woody fibre and other matters from which the gallic acid has been withdrawn by boiling water, contains a small quantity of another acid substance, which may be extracted by an alkali, and after- wards precipitated by an addition of hydrochloric acid, as a greyish inso- luble powder. It contains C 7 H 2 4 , when dried at 248 (120C), or gallic acid minus 1 eq. of water. The term ellagic acid is given to this substance. M. Pelouze once observed its conversion into ordinary gallic acid. The conversion of tannic into gallic acid by oxidation is accompanied by a disengagement of carbonic acid, the volume of which equals that of the oxygen absorbed : the oxidizing action must therefore be confined to the car- bon, and may perhaps be thus represented : 1 eq. tannic acid Ci 8 H 8 12 ) ("2 eq. gallic acid .... C 14 H C 0, ls=-J2eq. water H 2 2 8 eq. oxygen 8 j (4 eq. carbonic acid C 4 8 Ci 8 ^8 2o C 18 n 8 20 VEGETABLE ACIDS. 410 Much of the gallic acid is subsequently destroyed, in all probability only a part of that first produced escaping. The changes which gallic acid suffers when exposed to heat are very in- teresting. Heated in a retort by means of an oil-bath, the temperature of which is steadily maintained at 420 (215C), or thereabouts, it is resolved into carbonic acid, and a new acid which sublimes into the neck of the re- tort in brilliant, crystalline plates, of the most perfect whiteness ; an insig- nificant residue of black matter remains behind. The term pyrogallic acid is given to the volatile product. It dissolves with facility in water, but the solution cannot be evaporated without blackening and decomposition; it communicates a blackish-blue colour to salts of the protoxide of iron, and reduces those of the sesquioxide to the state of protoxide. An alkaline so- lution of this acid absorbs a very considerable quantity of oxygen, and has lately been employed with great advantage by Professor Liebig for the pur- pose of determining the amount of oxygen in atmospheric air. (See page 121.) The acid characters of this substance are very indistinct. Pyrogallic acid contains C 6 H 3 3 . When dry gallic acid is suddenly heated to 480 (249C), or above, it is decomposed into carbonic acid, water, and a second new acid, the metagallic^ which remains in the retort as a black, shining mass, resembling charcoal ; a few crystals of pyrogallic acid are formed at the same time. Metagallic acid is insoluble in water, but dissolves in alkalis, and is again precipitated as a black powder by the addition of an acid. It combines with the oxides of lead and silver, and is composed of C 6 H a O ? . Pyrogallic acid, also, exposed to the requisite temperature, yields metagallic acid, with separation of water. Tannic acid, under similar circumstances, furnishes the same products as gallic acid. Dr. Stenhouse has shown that pyrogallic acid may be procured in considerable quantity by carefully heating the dried aqueous extract of gall-nuts in Dr. Moh's subliming apparatus, already described. All these changes admit of simple explanation. C 7 H 3 5 = C 6 H 3 3 + C0 2 Dry gallic acid. Pyrogallic acid. C 6 H 3 3 = C 6 H 2 2 -f HO Pyrogallic acid. Metagallic acid. 3(C 18 H 6 9 ,3HO) == 6(C 7 H0 3 ,2HO) + 2C 6 H,0 3 Tannic acid. Gallic acid. Pyrogallic acid. These phenomena present admirable illustrations of the production of pyrogen-acids by the agency of heat. 420 CYANOGEN. SECTION IV. AZOTIZED ORGANIC PRINCIPLES OF SIMPLE CONSTITUTION. CYANOGEN, ITS COMPOUNDS AND DERIVATIVES. CYANOGEN' forms the most perfect type of a quasi-simple sub-radical that chemistry presents, as kakodyl does of the basyle class ; it is interesting also from being the first-discovered body of the kind. Cyanogen may be prepared with the utmost ease by heating in a small retort of hard glass the salt called cyanide of mercury, previously reduced to powder, and well dried. The cyanide undergoes decomposition, like the oxide under similar circumstances, yielding metallic mercury, a small quan- tity of a brown substance of which mention will again be made, and cyanogen itself, a colourless, permanent gas, which must be collected over mercury. It has a pungent and very peculiar odour, remotely resembling that of peach- kernels, or hydrocyanic acid ; exposed while at the temperature of 45 (7-2C) to a pressure of 3-6 atmospheres, it condenses to a thin, colourless, transparent liquid. Cyanogen is inflammable ; it burns with a beautiful pur- ple, or peach-blossom coloured flame, generating carbonic acid and liberating nitrogen. The specific gravity of this gas is 1-806 ; it is composed of carbon and nitrogen in the proportion of 2 equivalents of the former to 1 equivalent of the latter, or C 3 N ; this is easily proved by mixing it with twice its mea- sure of pure oxygen, and firing the mixture in the eudiometer ; carbonic acid is formed equal in volume to the oxygen employed, and a volume of nitrogen equal to that of the cyanogen is set free. Cyanogen, in its capacity of quasi- element, is designated by the symbol Cy. Water dissolves 4 or 5 times its volume of cyanogen-gas, and alcohol a much larger quantity; the solution rapidly decomposes, yielding oxalate of ammonia, C 2 N-f-4HO = NH 4 0,C 2 3 , brown insoluble matter, and other products. PARACYANOGEN. This is the brown or blackish substance above referred to, which is always formed in small quantity when cyanogen is prepared by heating the cyanide of mercury, and probably also, by the decomposition of solutions of cyanogen and of hydrocyanic acid. It is insoluble in water and alcohol, is dissipated by a very high temperature, and contains, according to Professor Johnson, carbon and nitrogen in the same proportions as in cya- nogen. CYANIDE OF HYDROGEN ; HYDROCYANIC OR PRUSSIC ACID, II Cy. This very important compound, so remarkable for its poisonous properties, was disco- vered as early as 1782, by Scheele. It may be prepared in a state of purity, and anhydrous, by the following process : A long glass tube filled with dry cyanide of mercury, 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-mixture. Gentle heat is applied to the tube, the contents of which * So called from Kvavos, Hue, and ytwu., I generate. CYANOGEN. 421 suffer decomposition in contact with the gas, sulphide of mercury and cya- nide of hydrogen being produced ; the latter is condensed in the receiver to the liquid form. A little of the cyanide of mercury should be left undecom- posed, to avoid contamination of the product by sulphuretted hydrogen. The pure acid is a thin, colourless, and exceedingly volatile liquid, which has a density of 0-7058 at 45 (7 -60), boils at 79 (26 -1C), and solidifies, when cooled to ( 17-8C) ; its odour is very powerful and most charac- teristic, 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 pro- portions. 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 vapour should be carefully avoided in all experiments in which hydrocyanic acid is concerned, as it produces headache, giddiness, and other disagreeable symp- toms ; ammonia and chlorine are the best antidotes. The acid in its pure form can seldom 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 favours this decomposition. Even in a dilute condition it is apt to decompose, becoming brown and turbid, but not always 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, tho hydrochloric for example, the whole solidifies to a crystalline paste of sal- ammoniac and hydrated formic acid ; a reaction which is explained in a very simple manner, 1 eq. of hydrocyanic acid and 4 eq. water, yielding 1 eq. of ammonia and 1 eq. of formic acid. C 2 N,H -f 4HO = NH 3 -f C 2 HO,,HO On the other hand, when dry formate of ammonia is heated to 392 (200C), it is almost entirely converted into hydrocyanic acid and water. NH 4 0,C 8 HO., = C 2 N,H -f 4HO. Aqueous solution of hydrocyanic acid may be made by various means. The most economical, and by far the best, where considerable quantities are wanted, is to decompose at a boiling-heat the yellow ferrocyanide of potas- sium by diluted sulphuric acid. For example, 500 grains of the powdered ferrocyanide may be dissolved in four or five ounces of warm water, and introduced into a capacious flask or globe capable of being connected by a perforated cork and wide bent tube with a Liebig's condenser well supplied with cold water ; 300 grains of oil of vitriol are diluted with three or four times as much water and added to the contents of the flask ; distillation is carried on until about one-half of the liquid has distilled over, after which the process may be interrupted. The theory of this process has been care- fully studied by Mr. Everitt ; ' it is sufficiently complicated. ' 6 eq. carbon _____ ^~s? Insoluble yellow salt. 6 eq. carbon 2 eq. ferrocy- 3 eq. nitrogen' anide of po-<{ 3 eq. nitrogen, tassium 1 eq. potassium- 3 eq. potassium. 2 eq. iron 3 ea water f 3 eq * h y dr g ea ^^^ ^3 eq. hydrocyanic acid. \ 3 eq. oxygen __ ____ __ __ _^\. 6 eq. sulphuric acid - ==^> 3 eq. bisulphate of po- tassa. 36 Phil. Magazine. Feb. 1835. 422 CYANOGEN, The substance described in the preceding diagram as insoluble yellow salt i- mains in the flask after the reaction, together with the bisulphate of potassa ; it contains the elements of 2 eq. cyanide of iron, and 1 eq. cyanide potas- sium, but its constitution is unknown. On exposure to the air, it rapidly becomes blue. When hydrocyanic acid is wanted for 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 examination is best made by precipitating with excess of nitrate of silver a known weight of the acid to be tried, collecting the insoluble cyanide of silver upon a small lilter previously weighed, washing, drying, and lastly re-weighing the whole. From the weight of the cyanide that of the hydrocyanic acid can be easily calculated, an equivalent of the one corresponding to an equivalent of the other; or the weight of the cyanide of silver may be divided by 5, which will give a close approximation to the truth. Another very elegant method for determining the amount of hydrocyanic acid in a liquid has been lately suggested by Prof. Liebig. It is based upon the property possessed by cyanide of potassium of dissolving a quantity of cLloride of silver sufficient to produce with it a double cyanide containing equal equivalents of cyanide of silver and of potassium (KCy, AgyCy). Hence a solution of hydrocyanic acid, which is super-saturated with potassa, and mixed with a few drops of solution of common salt, will not yield a perma- nent precipitate with nitrate of silver 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 eq. of hydrocyanic acid to 1 eq. of silver, i. e. 108 : 54 = silver consumed : z. It is a common remark, that the hydrocyanic acid made from ferrocyanide of potassium keeps better than that made by other means. The cause of this is ascribed to the presence of a trace of mineral acid. Mr. Everitt ac tually 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 cyanide of potas- sium by solution of tartaric acid: 100 grains of crystallized tartaric acid in powder, 44 grains of cyanide of potassium, 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 filtration or other treatment need be employed. The production of hydrocyanic acid from bitter-almonds has been already mentioned in connection with the history of the volatile oil. Bitter-almonds, the kernels of plums and peaches, the seeds of the apple, the leaves of the cherry-laurel, and various other parts of plants belonging to the great natural order, rosacece, yield on distillation with water, a sweet-smelling liquid, con- taining hydrocyanic acid. This is probably due in all cases to the decompo- sition of the amygdalin, pre-existent in the organic structure. The change in question is brought about, in a very singular manner, by the presence of a soluble azotized substance, called emulsin or synaptase, which forms a large proportion of the white pulp of both bitter and sweet almonds. This sub- stance bears a somewhat similar relation to amygdalin, that diastase, which ITS COMPOUNDS AND DERIVATIVES. 423 it closely resembles in many particulars, does to starch. Hydrocyanic acid exists ready-formed to a considerable extent in the juice of the bitter cassava. AMYGDAI/IN is prepared with facility by the following process: The paste of bitter-almonds, from which the fixed oil has been expressed, is exhausted with boiling alcohol : this coagulates and renders inactive the synaptase, while at the same time it dissolves out the amygdalin. The alcoholic liquid is distilled in a water-bath, by which much of the spirit is recovered, and the syrupy residue diluted with water, mixed with a little yeast, and set in a warm place to ferment ; a portion of sugar, present in the almonds, is thus destroyed. The filtered liquid is then evaporated to a syrupy state in a water-bath, and mixed with a quantity of alcohol, which throws down the amygdalin as a white crystalline powder ; the latter is collected on a cloth filter, pressed, re-dissolved in boiling alcohol, and left to cool. It separates in small crystalline plates, of pearly whiteness, which are inodorous and nearly tasteless ; it is decomposed by heat, leaving a bulky coal, and diffusing the odour of the hawthorn. In water, both hot and cold, amygdalin is very insoluble : a hot saturated solution deposits, on cooling, brilliant prismatic crystals, which contain water. In cold alcohol it dissolves with great diffi- culty. Heated with dilute nitric acid, or a mixture of dilute sulphuric acid and binoxide of manganese, it is resolved into ammonia, bitter-almond oil, benzoic acid, formic acid, and carbonic acid ; with permanganate of potassa, it yields a mixture of cyanate and benzoate of that base. I Amygdalin is composed of C^H^NO^, Synaptase itself has never been obtained in a state of purity, or fit for analysis ; it is described as a yellowish-white, opaque, brittle mass, very soluble in water, and coagulable, like albumin, by heat, in which case it loses its specific property. In solution it very soon becomes turbid and pu- trefies. The decomposition of amygdalin tinder the influence of this body may be elegantly studied by dissolving a portion in a large quantity of water, and adding a little emulsion of sweet-almond ; the odour of the volatile oil immediately becomes apparent, and the liquor yields, on distillation, hydro- cyanic acid. The nature of the decomposition may be thus approximately represented : II eq. hydrocyanic acid C 2 H N 2o q .Wtter-almondil C M H 12 4 2 cq.SL'add :::::: *$* 5 eq. water H 5 5 It may be observed that in preparing bitter-almond oil the paste should be well mixed with about 20 parts of warm water, and the whole left to stand some hours before distillation ; the heat must be gently raised to avoid coagulating the synaptase before it has had time to act upon the amygdalin. Almond-paste, thrown into boiling water, yields little or no bitter-almond oil. AMYGDALIC ACID. When amygdalin is boiled with an alkali or an alkaline earth, it is decomposed into ammonia, and a new acid called the amygdalic, which remains in union with the base. This is best prepared by means of baryta-water, the ebullition being continued as long as ammonia is evolved. From the solution thus obtained, the baryta may be pi-ecipi- tated by dilute sulphuric acid ; the filtered liquid is evaporated in a water- bath. Amygdalic acid forms a colourless, transparent, amorphous mass, very soluble in water, and deliquescent in moist air ; the solution has an acid taste and reaction. It is converted by oxidizing agents into fitter- 424 CYANOGEN, almond oil, formic, and benzoic acids. The amygdalates are mostly soluble, but have been but little studied ; the acid contains C 40 H 26 24 ,IIO. The presence of hydrocyanic acid is detected with the utmost ease; its remarkable odour and high degree of volatility almost sufficiently charac- terize it. With solution of nitrate of silver 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 a dry state, metnllia silver being left; the chloride, under the same circumstances, merely fuses, but undergoes no chemical change. Tha 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 acid. The liquid to be examined is mixed with a few drops of solution of sulphate of protoxide of iron and an excess of caustic potassa, and the whole exposed to the air for 10 or 15 minutes, with agitation ; hydrochloric acid is then added in excess, which dissolves the oxide of iron, and, if hydrocyanic acid be present, leaves Prussian blue as an insoluble powder. The reaction becomes quite intel- ligible when the production of a ferrocyanide, described a few pages hence, is understood. See page 432. Another elegant process for detecting hydrocyanic acid is mentioned in the article upon hydrosulphocyanic acid. The most important of the metallic cyanides are the following ; they bear the most perfect analogy to the haloid-salts. CYANIDE OF POTASSIUM, KCy. When potassium is heated in cyanogen gas, it takes fire and burns in a very beautiful manner, yielding cyanide of the metal ; the same substance is produced when potassium is heated in the vapour of hydrocyanic acid, hydrogen being liberated. If pure nitrogen gas be transmitted through a white-hot tube, containing a mixture of car- bonate of potassa and charcoal, a considerable quantity of cyanide of potas- sium is formed, which settles in the cooler portions of the tube as a white amorphous powder; carbonic oxide is at the same time extricated. 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 carbonate of potassa in a close vessel, a very abundant pro- duction of cyanide of potassium results, which cannot however be advan- tageously extracted by direct means, but in practice is always converted into ferrocyanide, which is a much more stable substance, and crystallizes better. There are several methods by which cyanide of potassium may be pre- pared for use. It may be made by passing the vapour of hydrocyanic acid into a cold alcoholic solution of potassa ; the salt is deposited in a crystal- line form, and may be separated from the liquid, pressed and dried. Ferro- cyanide of potassium, heated to whiteness in a nearly close vessel, evolves nitrogen and other gases, and leaves a mixture of charcoal, carbide of iron, and cyanide of potassium, which latter salt is not decomposed unless the temperature be excessively high. Mr. Donovan recommends the use in this process 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 tempera- ture ultimately raised to whiteness ; when no more gas issues, the tube is stopped with a cork, and, when the whole is completely 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 below, aud preserved in a well-stopped bottle ; the black substance contains much ITS COMPOUNDS AND DERIVATIVES. 425 cyanide, which may be extracted by a little cold water. It would be better, perhaps, in the foregoing process, to deprive the ferrocyanide of potassium of its water of crystallization before introducing it into the iron vessel. Professor Liebig has published a very easy and excellent process for making cyanide of potassium, which does not, however, yield it pure, but mixed with cyanate of potassa. For most of the applications of cyanide of potassium, as, for example, electro-plating and gilding, for which a con- siderable quantity is now required, this impurity is of no consequence. 8 parts of ferrocyanide of potassium are rendered anhydrous by gentle heat, and intimately mixed with 3 parts of dry carbonate of potassa; this mix- ture is thrown into a red-hot earthen crucible, and kept in fusion, with occa- sional stirring, until gas ceases to be evolved, and the fluid portion of the mass becomes colourless. The crucible is left at rest for a moment, and then the clear salt decanted from the heavy black sediment at the bottom, which is principally metallic iron in a state of minute division. In this experiment, 2 eq. of ferrocyanide of potassium and 2 eq. carbonate of potassa yield 5 eq. cyanide of potassium, 1 eq. cyanate of potassa, 2 eq. iron, and 2 cq. carbonic acid. The product may be advantageously used, instead of ferrocyanide of potassium, in the preparation of hydrated hydro- cyanic acid, by distillation with diluted oil of vitriol. Cyanide of potassium forms colourless, cubic or octahedral crystals, deli- quescent in the air, and exceedingly soluble in water; it dissolves in boiling alcohol, but separates in great measure on cooling. It is readily fusible, and undergoes no change at a moderate red, or even white-heat, when excluded from air ; otherwise, oxygen is absorbed and the cyanide of potassium becomes cyanate of potassa. Its solution always has an alkaline reaction, and exhales when exposed to the air the smell of hydrocyanic acid ; it is decomposed by the feeblest acids, even the carbonic acid of the atmosphere, and when boiled in a retort is slowly converted into formate of potassa with separation of ammonia. This salt is anhydrous ; it is said to be as poisonous as hydrocyanic acid itself. Cyanide of potassium has been derived from a curious and unexpected source. In some of the iron-furnaces in Scotland where raw-coal is used fur fuel with the hot blast, a saline-looking substance is occasionally observed to issue in a fused state from the tuyere-holes of the furnace, and concrete on the outside. This proved, on examination by Dr. Clark, to be principally cyanide of potassium. CYANIDE OF SODIUM, NaCy, is a very soluble salt, corresponding closely with tiie foregoing, and obtained by similar means. CYANIDE OF AMMONIUM, NH 4 Cy. This is a colourless, crystallizable, and very volatile substance, prepared by distilling a mixture of cyanide of potas- sium and sal-ammoniac, or by mingling the vapour of anhydrous hydrocyanic acid with ammoniacal gas, or, lastly, according to the observation of M. Langlois, by passing ammonia over red-hot charcoal. It is very soluble in water, subject to spontaneous decomposition, and is highly poisonous. CYANIDE OF MERCURY, HgCy. One of the most remarkable features in the history of cyanogen is its powerful attraction for certain of the less oxidable metals, as silver, and more particularly mercury and palladium. Dilute hydrocyanic acid dissolves finely-powdered red oxide of mercury with the utmost case; the liquid loses all odour, and yields on evaporation crys- tals of cyanide of mercury. Cyanide of potassium is in like manner decom- posed by red oxide of mercury, hydrate of potassa being produced. Cyanide of mercury is generally prepared from common ferrocyo,nide of potassium ; 2 parts of the salt are dissolved in 15 parts of hot water, and 3 parts of dry sulphate of mercury added ; the whole is boiled for 15 minutes, and filtered hot from the oxide of iron, which separates. The solution, on cooling, 30* 120 CYANOGEN, deposits the new salt in crystals. Cyanide of mercury forms white, trans- lucent prisms, much resembling those of corrosive sublimate ; it is soluble in 8 parts of cold water, and in a much smaller quantity at a higher tempe- rature, and also in alcohol. The solution has a disagreeable, metallic taste, is very poisonous, and is not precipitated by alkalis. Cyanide of mercury is used in the laboratory as a source of cyanogen. CYANIDE OF SILVEK, AgCy, has been already described. Cyanide of zinc, ZnCy, is a white insoluble powder, prepared by mixing acetate of zinc with hydrocyanic acid. Cyanide of cobalt, CoCy, is obtained by similar means ; it is dirty white, and insoluble. Cyanide of palladium forms a pale, whitish precipitate when the chloride of that metal is mixed with a soluble cyanide, including that of mercury. Tercyanide of gold, AuCy 8 , is yellowish-white and insoluble, but freely dissolved by solution of cyanide of potassium. Protocyanide of iron has not been obtained, from the tendency of the metal to pass into the radical, and generate a ferrocyanide. An insoluble green compound containing FeCy,F 2 Cy B was formed by M. Pelouze by passing chlo' rine gas into a boiling solution of ferrocyanide of potassium. CYANIC AND CYANURIC ACIDS. These are two remarkable isomeric bodies, related in a very close and intimate manner, and presenting phenomena of great interest. Cyanic acid is the true oxide of cyanogen ; it is formed in conjunction with cyanide of potassium, when cyanogen gas is transmitted over heated hydrate or carbonate of potassa, or passed into a solution of the alkaline base, the reaction resembling that by which chlorate of potassa and chloride of potassium are generated when the oxide and the salt-radical are presented to each other. Cyanate of potassa is, moreover, formed when the cyanide is exposed to a high temperature with access of air; unlike the chlorate, it bears a full red-heat without decomposition. Hydrated Cyanic Acid, CyO,HO, 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, with- out any other product, into hydrated cyanic acid, which condenses in the receiver to a limpid, colourless liquid, of exceedingly pungent and penetra- ting odour, like that of the strongest acetic acid ; it even blisters the skin. When mixed with water, it decomposes almost immediately, giving rise to bicarbonate of ammonia. This is the reason why the hydrated acid cannot be separated from a cyanate by a stronger acid. A trace of cyanic acid, however, always escapes decomposition, and communicates to the carbonic acid evolved a pungent Bmell similar to that of the sulphurous acid. The cyanates may be easily distinguished by this smell, and by the simultaneous formation of an ammo- nia-salt, which remains behind. The pure hydrated cyanic acid cannot be preserved ; shortly after its pre- paration it changes spontaneously, with sudden elevation of temperature, into a solid, white, opaque, amorphous substance, called cyamelide. This curious body has the same composition as hydrated cyanic acid ; it is inso- luble in water, alcohol, ether, and dilute acids ; it dissolves in strong oil ef vitriol by the aid of heat, with evolution of carbonic acid and production of ammonia ; boiled with solution of caustic alkali, it dissolves, ammonia is disengaged, and a mixture of cyanate and cyanurate of the base generated. By dry distillation it is again converted into the hydrate of cyanic acid. CYANATE OF POTASSA, KO,CyO. The best method of preparing this salt, is, according to Liebig, to oxidize cyanide of potassium by means of litharge. The cyanide, already containing a portion of cyanate, described p. 425, is re-melted in an earthen crucible, and finely powdered protoxide of lead added ITS COMPOUNDS AND DERIVATIVES. 427 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, powdered and boiled with alcohol ; the hot filtered solution deposits crystals of cyanate of potassa on cooling. The great de-oxidizing power exerted by cyanide of potassium at a high temperature promises to render it a valuable agent in many of the finer metallurgic operations. Another method of preparing the cyanide is to mix dried and finely-pow- dered ferrocyanide of potassium with half its weight of equally dry binoxide of manganese ; to heat this mixture in a shallow iron ladle with free expo- sure to air and frequent stirring until the tinder-like combustion is at an end, and to boil the residue in alcohol, which extracts the cyanate of potassa. This salt crystallizes from alcohol in thin, colourless, transparent plates, which suffer no change in dry air, but on exposure to moisture become gra- dually converted, without much alteration of appearance, into bicarbonate of potassa, ammonia being at the same time disengaged. Water dissolves the cyanate of potassa in large quantity ; the solution is slowly decomposed in the cold, and rapidly at a boiling heat, into bicarbonate of potassa and am- monia. When a concentrated solution is mixed with a small quantity of dilute mineral acid, a precipitate falls, which consists of acid cyanurate of potassa. Cyanate of potassa is reduced to cyanide of potassium by ignition with charcoal in a covered crucible. Cyanate of potassa, mixed with solutions of lead and silver, gives rise to insoluble cyanates of the oxides of those metals, which are white. CYANATE OF AMMONIA ; UREA. When the vapour of hydrated 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, cyanate of ammonia. It dissolves in water, and, if mixed with an acid, evolves carbonic acid gas ; with an alkali, it yields ammonia. If the solution be heated, or if the crystals be merely exposed a certain time to the air, a por- tion of ammonia is dissipated, and the properties of the compound completely changed. It may now be mixed with acids without the least symptoms of decomposition, while cold caustic alkali, on the other hand, fails to discharge the smallest trace of ammonia. The result of this curious metamorphosis of the cyanate is a substance called urea, a product of the animal body, the chief and characteristic constituent of urine. This artificial formation of one of the products of organic life cannot fail to possess great interest. Its dis- covery is due to Prof. Wohler. The properties of urea, and the most advan- tageous methods of preparing it, will be found described a few pages hence. CYANURIC ACID. The substance called melam, of which farther mention will be made, is dissolved by gentle heat in concentrated sulphuric acid, the solution mixed with 20 or 30 parts of water, and the whole maintained at a temperature approaching the boiling-point, until the specimen of the liquid, on being tried by ammonia, no longer gives a white precipitate : several days are required. The liquid, concentrated 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 sub- stance melts, boils, disengages 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 little and little until the liquid becomes nearly colourless ; it is then mixed with water, and suffered to cool, whereupon the cyanuric acid separates. The urea may likewise be decomposed very con- ysniently by gently heating it in a tube, while dry chlorine gas passes over it. A mixture of cyanuric acid and sal-ammoniac results, which is separated by dissolving in water. 428 CYANOGEN; Cyanurie acid in a pure state forms colourless crystals, seldom of large size, derived from an oblique rhombic prism, -which effloresce in a dry atmo- sphere from loss of water. It is very soluble in cold water, and requires 24 parts for solution at a boiling heat; it reddens litmus feebly, has no odour, and but little taste. This acid is tribasic ; the crystals contain C 6 N 3 3 ,3HO -J-4HO, and are easily deprived of the 4 eq. of water of crystallization. In point of stability, it offers a most remarkable 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 an anhydrous state, containing C 6 N 3 3 ,8HO. 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 : Cyanate of ammonia is converted by heat into urea. Urea is decomposed by the same means into cyanuric acid and urea. Cyanuric acid is changed by a very high temperature into hydrated cyanic acid. In the latter reaction, 1 eq. of hydrated cyanuric acid splits into 3 eq. hy- drated cyanic acid. C 6 N 3 3 ,3HO=:3(C 2 NO,HO). CYANATE AND CYANURATE OF OXIDE OF ETHYL. If a dry mixture of cya- nate of potassa and sulphovinate of potassa be distilled, a product is ob- tained which consists of a mixture of the above ethers. They are separated without difficulty, the cyanate boiling at 140 (GOC), while the boiling point of the cyanurate is much higher, namely, 528 -8 (276C). Cyanate of ethyl is a mobile liquid, the vapour of which excites a flow of tears. The com- position of cyanate of ethyl is C 6 H 5 N0 2 =C 4 H 5 0,C 2 NO=AeO,CyO. The formation is represented by the equation KO,CyO-f-KO,AeO,2S0 3 =AeO, CyO-f 2(KO,SO,). The cyanurate of ethyl contains 3AeO,C 6 N 3 3 ; it arises in this reaction from the coalescence of 3 eq. of cyanate of ethyl. It may be likewise obtained by distilling a mixture of sulphovinate of potassa with cyanurate of potassa. Cyanurate of ethyl is a crystalline mass, slightly so- luble in water, readily soluble in alcohol and ether, fusing at 185 (85C). By substituting for sulphovinate of potassa, salts of sulphomethylic and sul- phamylic acid, the corresponding methyl- and amyl-compouuds may be ob- tained. 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 isomeric both with cyanic and cyanuric acids, originates in the peculiar action exercised by ni- trous acid upon alcohol in presence of a salt of silver or mercury. Neither absolute fulminic acid nor its hydrate has ever been obtained. Fulminate of silver is prepared by dissolving 40 or 50 grains of silver, which need not be pure, in ^ oz. by measure of nitric acid of sp. gr. 1-37 or thereabouts, by the aid of a little heat ; a sixpence answers the purpose very well. To the highly acid solution, while still hot, 2 measured ounces of al- cohol are added, and heat applied until reaction commences. The nitric acid oxidizes part of the alcohol to aldehyde and oxalic acid, becoming itself re- duced to nitrous acid, which in turn acts upon the alcohol in such a manner as to form nitrous ether, fulminic acid, and water. 1 eq. nitrous ether and 1 eq. of nitious acid containing the elements of 1 eq. fulminic acid and 5 P.I}, water. C 4 H 5 0, NO, -f N0 3 = C 4 N 2 2 -f 5110. ITS COMPOUNDS AND DERIVATIVES. The fulminate of silver 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 or bottle. This is the only safe method of keeping the salt. Fulminate of silver is soluble in 36 parts of boiling water, but the greater part crystallizes out on cooling ; it is one of the most dangerous substances to handle that chemistry presents ; it explodes when strongly heated, or when rubbed or struck with a hard body, or when touched with concentrated sulphuric acid, with a degree of violence almost indescribable ; the metal is reduced, and a large volume of gaseous matter suddenly liberated. Strange to say, it may, when very cautiously mixed with oxide of copper, be burned in a tube with as much facility as any other organic substance. Its composition thus determined is expressed in the formula 2AgO,C 4 N 2 2 . The acid is evidently bibasic ; when fulminate of silver is digested with caustic potassa, one-half of the oxide is precipitated, and a compound pro- duced containing AgO,KO,C 4 N 2 2 , which resembles the neutral silver-salt, and detonates by a blow. Corresponding compounds containing soda and oxide of ammonium exist ; but a pure fulminate of an alkaline metal has never been formed. If fulminate of silver be digested with water and cop- per, or zinc, the silver is entirely displaced, and a fulminate of the new metal produced. The zinc-salt mixed with baryta-water gives rise to a precipitate of oxide of zinc, while fulminate of zinc and baryta, ZnO,BaO,C 4 N 2 2 , re- mains in solution. Fulminate of mercury 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 vapours are disengaged, to- gether with a large quantity of nitrous ether and aldehyde ; these are some- times condensed and collected for sale, but are said to contain hydrocyanic acid. The fulminate of mercury separates from the hot liquid, and after cooling may be purified from an admixture of reduced metal by solution in boiling water and re-crystallization. It much resembles the silver-salt in appearance, properties, and degree of solubility, and contains 2Hg 2 0,C 4 N 2 2 . It explodes violently by friction or percussion, but, unlike the silver-corn, pound, merely burns with a sudden and almost noiseless flash when kindled in the open air. It is manufactured on a large scale for the purpose of charging percussion-caps ; sulphur arid chlorate of potassa, or more fre- quently nitre, are added, and the powder, pressed into the cap, is secured by a drop of varnish. The relations 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. Cyanate of silver AgO , C 2 N 0. Fulminate of silver 2Ag() , C 4 N 2 2 . Cyanurate of silver 3AgO , C 6 N 3 3 . Until quite recently, beyond the accidental one of identity of composition, no relation existed between fulminic acid and its isomers. Mr. Gladstone has, however, shown that, when a solution of fulminate of copper is mixed with excess of ammonia, filtered, treated with sulphuretted hydrogen in excess, and again filtered from the insoluble sulphide of copper, the liquid obtained is a mixed solution of urea and sulphocyanide of ammonium. CHLORIDES OF CYANOGEN. Chlorine forms two compounds with cyanogen 430 FERROC YANO G EN AND ITS COMPOUNDS. or its elements, which are isomeric, and correspond to cyanic and cyanuric acids. Gaseous chloride of cyanogen, CyCl, is formed by conducting chlorine gas into strong hydrocyanic acid, or by passing chlorine over moist cyanide of mercury contained in a tube sheltered from the light. It is a permanent and colourless gas at the temperature of the air, of insupportable pungency, and soluble to a very considerable extent in water, alcohol, and ether. At ( 17 -8C) it congeals to a mass of colourless crystals, which at 5 ( 15C) melt to a liquid whose boiling-point is 11 ( 11-6C). At the tem- perature 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 it gradually passes into the solid modification. Solid chloride of cyanogen 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 colourless needles, which exhale a powerful and offensive odour, compared by some to that of the excrement of mice ; it melts at 284 (140C), and sublimes unchanged at a higher tem- perature. When heated in contact with water, it is decomposed into cyanuric and hydrochloric acids. This compound may be represented by the formula CyCl 3 , or C 6 N 3 ,C1 3 . It dissolves in alcohol and ether without decomposition. BROMIDE and IODIDE or CYANOGEN correspond to the first of the preceding compounds, and are prepared by distilling bromine or iodine with cyanide of mercury. They are colourless, volatile, solid substances, of powerful odour. FERROCYANOGEN AND ITS COMPOUNDS. When a solution of cyanide of potassium is digested with iron-filings at a gentle heat in an open vessel, oxygen is absorbed from the air, the iron dis- solves quietly and disappears, and a highly alkaline, yellow liquid is obtained, which on evaporation deposits lemon-yellow crystals containing potassium in combination with a new salt-radical composed of the metal iron and the ele- ments of cyanogen ; in the mother-liquid hydrate of potassa is found. 3 eq. cyanide of potassium, 1 eq. iron, and 1 eq. oxygen, yield 1 eq. of the new salt, and 1 eq. of potassa. 3KCy-f Fe-f-0 = KO-f K 2 ,C 6 N 3 Fe. The new substance is called ferrocyanogcn, and is designated by the symbol Cfy ; it is bibasic, neutralizing 2 equivalents of metal or hydrogen, and con- tains the elements of 3 equivalents of cyanogen combined with 1 eq. of iron. It has never been isolated. When iron in filings is heated in a small retort with a solution of cyanide of potassium, it is dissolved with evolution of hydrogen, caustic potassa and the new substance being generated ; the oxygen in this case is derived from the decomposition of water. Sulphide of iron and cyanide of potassium give rise, under similar circumstances, to sulphide of potassium and ferrocyanide of potassium. HYDROFKRROCYANIC ACID, Cfy2H. Ferrocyanide of lead or copper, both of which are insoluble, may be suspended in water, and decomposed by a stream of sulphuretted hydrogen gas. The filtered solution, evaporated in the vacuum of the air-pump over a surface of oil of vitriol, furnishes the acid in a solid form. If the aqueous solution be agitated with ether, nearly the whole of the acid separates in colourless, crystalline laminae ; it may even be made in large quantity by adding hydrochloric acid to a strong solution of ferrocyunide of potassium in water free from air, and shaking the whole with fether. The crystals may be dissolved in alcohol, and the acid again thrown down by ether, which possesses the remarkable property of precipi- tating this subistauce from solution, irydroferrocyanic acid differs completely FERROCYANOGEN AND ITS COMPOUNDS. 431 from hydrocyanic acid ; its solution in water has a powerfully acid taste and reaction, and decomposes alkaline carbonates with effervescence ; it refuses to dissolve oxide of mercury in the cold, but when heat is applied, undergoes decomposition, forming cyanide of mercury and a peculiar compound of iron, cyanogen, and oxygen, with reduction of some of the oxide. In a dry state the acid is very permanent, but when long exposed to the air in contact with water it becomes entirely converted into Prussian blue. This interesting substance was discovered by Mr. Porrett. FERROCYANIDE OF POTASSIUM, frequently called Yellow prussiate of potash, K 2 Cfy-f3HO, or K 2 C 6 N 3 Fe-f3HO. This most beautiful salt is manufactured on a large scale by the following process, which will now be easily intelligi- ble: Dry refuse animal matter of any kind is fused at a red-heat with im- pure carbonate of potassa and some iron-filings in a large iron vessel, from which the air should be excluded as much as possible ; cyanide of potassium 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 purified by re- solution. If a sufficient quantity of iron be not present, great loss is incurred by the decomposition of the cyanide into formate of potassa and ammonia. Ferrocyanide of potassium forms large, transparent, yellow crystals, derived from an octahedron with a square base; they cleave with facility in a direction parallel to the base of the octahedron, and are tough and diffi- cult to powder. They dissolve in 4 parts of cold, and in 2 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 3 eq. of water, and becomes anhydrous ; at a high temperature it yields cyanide of potassium, carbide of iron, and various gaseous products ; if air be ad- mitted, the cyanide becomes cyanate. The ferrocyanides are often described as double salts in which protocy- anide of iron is combined with other metallic cyanides, or with hydrogen. Thus, hydroferrocyanic acid is written FeCy,2HCy, and ferrocyanide of potassium, FeCy,2KCy-{-3HO; the oxygen and hydrogen of the water of crystallization being respectively adequate to convert the metals into pro- toxide and the cyanogen into hydrocyanic acid. This view has the merit of simplicity, and will often prove an useful aid to the memory, but there are insuperable objections to its adoption as a sound and satisfactory theory. Ferrocyanide of potassium is a chemical reagent of great value ; when mixed in solution with neutral or slightly acid salts of the metals proper, it gives rise to precipitates which very frequently present highly characteristic colours. In most of these compounds the potassium of the base is simply displaced by the new metal : the beautiful brown ferrocyanide of copper contains, for example, Cu 2 Cfy or Cu 2 C 6 N 3 Fe, and that of lead, Pb 2 Cfy. With salts of protoxide of iron it gives a bluish precipitate, which becomes rapidly dark blue by exposure to air ; this appears to be a compound of the neutral ferrocyanide of iron, Fe 2 Cfy, with ferrocyanide of potassium. When a ferrocyanide is added to a solution of salt of sesquioxide cu iron, Prussian blue is produced. Although this remarkable substance has now been long known, and many elaborate researches have been made with a view of determining its exact composition, the problem cannot yet be said to be completely solved. This difficulty arises in great measure from the existence of several distinct deep blue compounds formed under different cir- 1 The sulphur is derived from the reduced sulphate of the crude pearl-ashes used in thi* i&n.niif;ictiirfi. 432 FERROCYANOGEN AND ITS COMPOUNDS. * cumstances, and having many properties in common, which have been fre- quently confounded. The following is a summary of the account given by Berzelius, who has paid much attention to this subject. Ordinary Prussian Blue, Ci 8 N 9 Fe 7 , or Fe 4 Cfy 3 . This is best prepared by adding nitrate of sesquioxide of iron to solution of ferrocyanide of potas- sium, keeping the latter in slight excess. It forms a bulky precipitate of the most intense blue, which shrinks to a comparatively small compass when well washed and dried by gentle heat. In a dry state it is hard and brittle, much resembling in appearance the best indigo ; the fresh-fractured surfaces have a beautiful copper-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 ; con- centrated oil of vitriol converts it into a white, pasty mass, which again becomes blue on the addition of water. Alkalis destroy the colour in- stantly ; they dissolve out a ferrocyanide, and leave sesquioxide of iron. Boiled with water and red oxide of mercury, it yields a cyanide of the metal, and sesquioxide of iron. Heated in the air, Prussian blue burns like tinder, leaving a residue of sesquioxide of iron. Exposed to a high temperature in a close vessel, it disengages water, cyanide of ammonium, and carbonate of ammonia, and leaves carbide of iron. This substance forms a very beautiful pigment, both an oil and a water-colour, but has little permanency. The Prussian blue of commerce is always exceedingly impure ; it contains alumina and other matters, which greatly diminish the brilliancy of the colour. The production of Prussian blue by mixing sesquioxide salt of iron and ferrocyanide of potassium or sodium may thus be elucidated: 3 eq. ferrocyanide J 3 eq. ferrocyanogen ^^^-- Prussian blue. potassium \ 6 eq. potassium 2 eq. nitrate of C 4 eq. iron sesquioxide of -I 6 eq. oxygen iron ( 6 eq. nitric acid ~~^*" 6 eq. nitrate of po- tassa. In the above formula no account is taken of the elements of water which Prussian blue certainly contains ; in fact it must be looked upon as still requiring examination. The theory of the beautiful test of Scheele for the discovery of hydrocy- anic acid, or any soluble cyanide, will now be clearly intelligible. The liquid is mixed with a salt of protoxide of iron and excess of caustic alkali ; the protoxide of iron quickly converts the alkaline cyanide into ferrocy- anide. By exposure for a short time to the air, another portion of the hydrated oxide becomes peroxidized ; when excess of acid is added, this is dissolved, together with the unaltered protoxide ; and thus presented to the ferrocyanide in a state fitted for the production of Prussian blue. Basic Prussian Blue, Fe 4 Cfy 3 -f-Fe 2 3 . This is a combination of Prussian blue with sesquioxide of iron ; it is formed by exposing to the air the white or pale blue precipitate caused by a ferrocyanide in a solution of protosalt of iron. It differs from the preceding in being soluble in pure water, although not in a saline solution. The blue precipitate obtained by adding nitrate of sesquioxide of iron to a large excess of ferrocyanide of potassium, is a mixture of insoluble Prussian blue with a compound containing that substance in union with fer- rocyanide of potassium, or Fe 4 Cfy 3 4-2K 2 ^O r - This also dissolves in water as soon as the salts have been removed by washing. FERRIC Y A NOGEN AND ITS COMPOUNDS. 433 The other ferrocyanides may be despatched in a few words. The soda-salt, Na 2 Cfy~|-12HO, crystallizes in yellow four-sided prisms, which are efflorescent in the air and very soluble. Ferrocyanide of ammonium, (NII 4 )C 2 fy-f-3HO, is isomorphous with ferro- cyanide of potassium ; it is easily soluble, and is decomposed by ebullition. Ferrocyanide of barium, Ba 2 Cfy, prepared by double decomposition, or by boiling Prussian blue in baryta-water, forms minute yellow, anhydrous crys- tals, which have but a small degree of solubility even in boiling water. The corresponding compounds of strontium, calcium, and magnesium, are more freely soluble. The ferrocyanides of silver, lead, zinc, manganese, and bis- muth 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. Ferrocyanides with two basic metals are occasionally met with ; when, for example, concentrated solutions of chloride of calcium and ferrocyanide of potassium are mixed, a sparingly-soluble crystalline precipitate falls, con- taining KCaCfy, the salt-radical being half saturated with potassium, and half with calcium ; many similar compounds have been formed. FERRI-, OR FKRRIDCYANOGEN, C 12 N 6 Fe 2 ; or Cfdy. This name is given to a substance, by some thought to be a new salt-radical, isomeric with ferro- cyanogen, but differing in capacity of saturation ; it has never been isolated. Ferricyanide, of potassium is thus prepared: Chlorine is slowly passed, with agitation, into a somewhat dilute and cold solution of ferrocyanide of potas- sium, until the liquid acquires a deep reddish-green colour, and ceases to precipitate a salt of the sesquioxide of iron. It is then evaporated until a skin begins to form upon the surface, filtered, and left to cool ; 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 solu- ble in 4 parts of cold water; the solution has a dark greenish colour. The crystals burn when introduced into the flame of a candle, and emit sparks. Ferricyanide of potassium contains K 3 Cfdy ; hence the radical is tribasic ; the salt is formed by the abstraction of an equivalent of potassium from 2 eq. of the yellow ferrocyanide of potassium. It is decomposed by excess of chlorine, and by deoxidizing agents, as sulphuretted hydrogen. The term red prussiate of potash is often, but very improperly, given to this sub- stance. Ferricyanide of hydrogen is obtained in the form of a reddish-brown acid Tiquid, by decomposing ferricyanide of lead with sulphuric acid ; it is very instable, and is resolved, by boiling, into a hydrated sesquicyanide of iron, an insoluble dark green powder, containing Fe 2 Cy 3 -j-3HO, and hydrocyanic acid. The ferricyanides of sodium, ammonium, and of the alkaline earths, are soluble ; those of most of the other metals are insoluble. Ferricyanide of potassium, added to a salt of the sesquioxide of iron, occasions no precipi- tate, but merely a darkening of the reddish-brown colour of the solution ; with protoxide of iron, on the other hand, it gives a deep blue precipitate, containing Fe 3 Cfdy, which, when dry, has a brighter tint than that of Prus- sian blue ; it is known under the name of TurnbulVs blue. Hence, ferri- cyanide of potassium is as excellent a test for protoxide of iron, as the yellow ferrocyanide is for the sesquioxide. COBALTOCYANOGEN. A series of compounds analogous to the preceding, containing cobalt in place of iron, have been formed and studied ; a hydro- gen-acid has been obtained and a number of salts, which much resemble those of ferricyanogen. Several other metals of the same isomorphous family are found capable of replacing iron in these circumstances. NITROPRTISSIDES. The action of nitric acid upon ferrocyanides and ferri- cyanides 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 37 434 SULPHOCYANOGEN, ITS COMPOUNDS. appears to be MjjFe 2 Cy 5 NO, 'which exhibits a close relation with th parts of ether, 2000 parts cold and 54 of hot water. Has a strong alkaline reaction, and forms crystallizable salts. It is probably identical with daturine, It. I >. 4 Crystallizes from an alcoholic solution in small grains; soluble readily in alcohol anri ether, and also in 100 parts cold and 50 boiling water; has a sharp, bitter taste, and alkaline reaction. Its salts are not crystallizable. R. B. 452 VEGETO- ALKALIS. It crystallizes in golden-yellow needles, is sparingly soluble in cold water, more soluble in hot water, and freely dissolved by alcohol and ether. Its composition is C 14 TI 5 5 . POPULIN. This substance closely resembles salicin in appearance and solu- bility, but has a penetrating sweet taste ; it is found accompanying salicin in the bark and leaves of the aspen. According to recent researches of Piria, popwlin contains C 40 H 22 Oi 6 -j-4HO. It is a conjugate compound of salicin and benzoic acid. CAOao = C,4 H A + C 26 H 18 14 -L2HO Crystall. Populin. Benzoic acid. Salicin. By the action of reagents it is converted into benzoic acid, and the products of decomposition of salicin. With dilute acid it yields benzoic acid, grape- sugar, and saliretin ; when treated with a mixture of sulphuric acid and bichromate of potassa, it furnishes a considerable quantity of hydride of Balicyl. DAPHNIN. Extracted from the bark of the Daphne mezereum; it forms colourless, radiated needles, freely soluble in hot water, alcohol and ether. HESPERIDIN. A white, silky, tasteless substance, obtained from the spongy part of oranges and lemons. It dissolves in 60 parts of hot water ; also in alcohol and ether. ELATERIN. The active principu of Momordica elaterium. It is a white, silky, crystalline powder, insoluble in water. It has a bitter taste, and ex- cessively violent purgative properties. Alcohol, ether, and oils dissolve it. Exposed to heat, it melts and afterwards volatilizes. It contains C 20 H, 4 5 . ANTIARIN. The poisonous principle of the Upas antiar. It forms small, pearly crystals, soluble in 27 parts of boiling water, and also in alcohol, but scarcely so in ether; it cannot be sublimed without decomposition. Intro- duced into a wound, it rapidly brings on vomiting, convulsions, and death. Antiarin contains C 14 H, 5 . PICROTOXIN. It is to this substance that Cocculux indicus owes its active properties. Picrotoxin forms small, colourless, stellated needles, of inex pressibly bitter taste, which dissolve in 25 parts of boiling ale v hol. It con- tains C 10 H 6 4 . ASPARAGIN. This, and the two following, are azotized bodies. Asparagin is found in the root of the marsh-mallow, in asparagus sprouts, and in several other plants. The mallow-roots are chopped small, and macerated in the cold with milk of lime : the filtered liquid is precipitated by carbonate of ammonia, and the clear solution evaporated in a water-bath to a syrupy state. The impure asparagin, which separates after a few days, is purified by re-crys- tallization. Asparagin forms brilliant, transparent, colourless crystals, which have a faint cooling taste, and are freely soluble in water, especially when hot. When dissolved in a saccharine liquid, which is afterwards made to ferment, when heated with water under pressure in a close vessel, or when boiled with an acid or an alkali, it is converted into ammonia and a new acid, the aspartic. Asparagin contains C 8 H 8 N 2 6 , and aspartic acid C 8 H 7 N0 8 . The remarkable relation in which these substances stand to malic acid has been already noticed under the head of malic acid (see p. 415). SANTONIN. This substance is the crystalline principle of several varieties of Artemisia. In order to obtain it, the seeds are crushed, and digested with lime and spirit of wine, when a yellow liquid is obtained, from which the alcohol is separated by distillation. The residuary liquid is saturated with acetic acid, when the santonin crystallizes. This substance is easily eoluble in water and alcohol, and contains C 30 TI, 8 6 . Santonin possesses the character of a weak acid. ORGANIC BASES OF ARTIFICIAL ORIGIN. 453 ORGANIC BASES OF ARTIFICIAL ORIGIN. The constitution of the alkaloids, which occur ready formed in nature, is not yet clearly understood. The fact that all these substances contain nitrogen, the alkaline reaction, which the greater part of them exhibits with vegetable colours, and especially their faculty of combining with acids to crystallizable salts, establish an obvious relation between the alkaloids and ammonia. This has never been doubted, and the views of chemists have been divided only as to the form of this relation. At a certain time Berzelius assumed that all the alkaloids contained ammonia ready formed, and that their basic properties were due to this ammonia. According to this view the formulae of quinine and morphine would be Quinine C 20 H ]2 N0 2 =C 20 H 9 2 ,NH 3 Morphine C^H^NO^C^HjeO^NH.^ This view, in the general form in which it was proposed, is certainly inad- missible. It is supported by very scanty experimental evidence, and was never universally adopted. There may be some alkaloids so constituted as represented by the theory of Berzelius. There are, however, a great many, the constitution of which is obviously different. Several of these substances have been lately the subject of extensive and careful inquiries ; but these researches, although they have established their formulae and increased our knowledge regarding their salts, have as yet elicited but few facts which promise to afford a clearer insight into the nature of these bodies. On the other hand, the labours of the last ten years have brought to light a very numerous group of substances perfectly analogous to the alkaloids which are found in plants, but produced by artificial processes in the labo- ratory. These bodies, which are termed artificial alkaloids or artificial or- ganic bases, are mostly volatile. Their constitution is much simpler than that of the native bases. The very processes which give rise to their forma- tion often permit a very clear insight into the mode in which the elements are grouped, and in the relation existing between these substances and am- monia. In a former section of this volume (page 232), it has been stated that the majority of chemists incline to assume in the ammoniacal salts the existence of a compound metal ammonium NH 4 , Chloride of ammonium, NH 4 C1 Sulphate of ammonia, NH 4 0,S0 8 . Now, recent researches have shown, that in these salts, 1, 2, 3, or even the 4 eq. of hydrogen may be replaced by compound radicals, containing vari- able proportions of carbon and hydrogen, without any change in their fun- damental properties. It is evident that we obtain in this manner, in addi- tion to the ammoniacal salts, four new series of compounds very ciosety allied to the former. Let A B C D represent a series of such radicals capable of replacing hydrogen, then the following series of salts may be brmed: - Ammonia-salts N^ 5 > Cl N^ >0,SO First group of compound ammonia-salts 454 ORGANIC BASES OF ARTIFICIAL ORIGIN. 0,S0 3 . Second group of com- pound ammonia-salts Third group of compound ammonia-salts Fourth group of com- pound ammonia-salts It need scarcely be mentioned that it is by no means necessary that the several hydrogen-equivalents in ammonia should be replaced by different radicals, as assumed in the preceding table. Substances of the formula) are even more easily prepared and more frequently met with. This synopsis shows that the number of salts capable of being derived from the ordinary ammoniacal salts, must be very considerable. Even now a very extensive series has been prepared, although the number of radicals at our disposal at present is still comparatively limited. It has been mentioned that all attempts at isolating both ammonium and its oxides have hitherto failed (see page 232). On treating chloride of am- monium or sulphate of ammonia with mineral oxides, such as potassa, lime, and baryta, decomposition ensues, chloride of potassium or sulphate of po- tassa, &c., is formed, and the separated oxide of ammonium splits into ammonia-gas and water, NH 4 0=NH 3 -j-HO (see page 162). The compound ammonia-salts are likewise decomposed by mineral oxides. With the three first classes the change is perfectly analogous to that of am- moniacal salts, the separated oxide is decomposed into water and a volatile base, the properties of which, according to the nature of the replacing radi- cals, are more or less closely approximated to those of ammonia itself. We arrive in this manner at three groups of organic bases, differing from one another by the amount of hydrogen which is replaced ; they have been dis- tinguished by the terms amidogen-, imidogen-, and nitrile-bases. A r A B N H (II (A N^ H id H IH IH Ammonia. Amidogen- Imidogen- Nitrile-bases. bases. bases. The last group of ammoniacal salts, in which the 4 eq. of hydrogen are replaced by radicals, differ in their deportment from the former classes, ^fhese salts are not decomposed by potassa, but yield, by appropriate treat- ment, a series of substances of a very powerfully alkaline character, which ute expressed by the general formulae : (A N> B ORGANIC BASES OF ARTIFICIAL ORIGIN. 455 are evidently analogous to hydrated oxide of ammonium ; from which they di:Fer, however, in a remarkable manner, by their powerful stability. These general statements will become more intelligible if we elucidate them bv the description of several individual substances ; the limits of this work compel us. however, to confine ourselves to the more important members of this already very numerous group, which is moreover daily increasing. It may at once be stated that by far the greater number of these compounds are derived from the alcohols or substances analogous to them, and that the radicals which in the preceding sketch have been designated by the letters A, B, C, and D, are chiefly the hydrocarbons previously described under the names ethyl, methyl, and amyl. BASES OF THE ETHYL-SERIES. ETHYLAITINE, Ethyl-ammonia, C 4 H 7 Nr= (H 2 ,C 4 H 5 )==N(H 2 Ae). On digest- ing bromide or iodide of ethyl (see page 353) with an alcoholic solution of ammonia, the alkaline reaction of the ammonia gradually disappears. On evaporating the solution on the water-bath a white crystalline mass is obtained, which consists chiefly of bromide of ethyl-ammonium, AeI-j-NH 3 =N(H 3 Ae)I. On distilling this salt in a retort provided with a good con- denser, with caustic lime, the ethylamine is liberated and distils over, NH 2 AeI-f KO=N(H 2 Ae) -f HO-f- KI. Another method of preparing this compound, and indeed the method by which this remarkable substance was first obtained by M. Wurtz, consists in submitting cyanate of ethyl to the action of hydrate of potassa. In describ- ing cyanic acid (see page 426), the interesting change has been mentioned, which this substance undergoes when treated with boiling solution of potassa. In this case cyanic acid splits into 2 eq. of carbonic acid and 1 eq. of am- monia ; cyanate of ethyl (see page 428) suffers a perfectly analogous decom- position, and instead of ammonia we obtain ethylamine. Hydrated cyanic acid. C 2 NO,AeO + 2(KO,HO)=2(KO,C0 2 )-fN(H 2 Ae) Cyanate of Ethylamine. ethyl. Cyanur.te of ethyl, isomeric with the cyanate, likewise furnishes ethylamine. Ethylamine is a very mobile liquid of 0-6964 sp. gr., at 46-4 (8C), which boils at 64-4 (18C). The sp. gr. of the vapour is 1-57. It has a most powerfully ammoniacal odour, and restores the blue colour to reddened litmus paper. It produces white clouds, with hydrochloric acid, and is absorbed by water with great avidity. With the acids it forms a series of neutral crystallizable salts perfectly analogous to those of ammonium. This substance imitates, moreover, in a remarkable manner, the deport- ment of ammonia with metallic salts. It precipitates the salts of magnesia, alumina, iron, manganese, bismuth, chromium, uranium, tin, lead, and mer- cury. Zinc-salts yield a white precipitate which is soluble in excess. Like ammonia, ethylamine dissolves chloride of silver, and yields with copper- salts a blue precipitate, which is soluble in an excess of ethylamine. On adding ethylamine to oxalic ether, a white precipitate of elhyl-oxamide. N(HAe),C 2 2 , is produced ; even a compound analogous to oxamic acid (see page 343) has been obtained. Ethylamine may, however, be readily distin- 456 ORGANIC BASES OP ARTIFICIAL ORIGIN. guished from ammonia ; its vapour is inflammable, and it produces, with bichloride of platinum, a salt N(H 3 Ae)Cl,PtCl 2 , crystallizing in golden scales, which are rather soluble in water. If ethylamine is treated with chlorine, it furnishes chloride of ethyl-ammonium and a yellow liquid of a penetrating odour exciting tears, which contains ]X T Cl 2 Ae. This substance is bichlor ethyl- amine. When treated with potassa it is converted into ammonia, acetate of potassa, and chloride of potassium, NCl 2 ,C 4 H 6 -f 3KO-f HO=KO,C 4 H 3 3 -f- NH S + 2KC1. JtiLhylamine-urea. On passing into a solution of ethylamine, the vapour of hydrated cyanic acid, the liquid becomes hot, and deposits after evaporation, fine crystals of ethylamine-urea, C4H 7 N-fC 2 NO,HO==C 6 H 8 N 2 2 =C 2 (H 3 ,C 4 H 5 )N 2 2 =C 2 (H 3 Ae)N 2 2 . This substance, which may be received as ordinary urea (see page .436), in which 1 eq. of hydrogen is replaced by ethyl, may be prepared also by treating cyanic ether with ammonia, C 4 H 5 0,C 2 NO-|-NU 3 C 6 H 8 N 2 2 . Ethylamine urea is very soluble in water and alcohol ; the concentrated aqueous solution, unlike that of ordinary urea, yields no pre- cipitate with nitric acid; but on gently evaporating the mixture, a very soluble crystalline nitrate of ethylamine-urea is obtained. Boiled with po- tassa, this substance yields a mixture of equal equivalents of ammonia and ethylamine, C 2 (H 3 Ae)N 2 2 -f 2(KO,HO)=2(KO,C0 2 ) -f NH 3 -f N(H 2 Ae). BIETHYLAMINE, Biethyl ammonia, CgHuN NII,2C 4 H 5 =N(HAe 2 ). A mix- ture of solution of ethylamine and bromide of ethyl, heated in a sealed tube for several hours, solidifies to a crystalline mass of bromide of biethyl- ammonium, N(H 2 Ae)-j- AeBr=N(H 2 Ae 2 )Br. The bromide, when distilled with potassa, furnishes a colourless liquid, still very alkaline, and soluble in water, but less so than ethylamine. This compound boils at 133 (55C). It forms beautifully crystallizable salts with acids. A solution of chloride of biethyl-ammonium furnishes with bichloride of platinum, a very soluble double salt, N(H 2 Ae 2 )Cl,PtCl 2 , crystallizing in orange-red grains, very diffe- rent from the orange-yellow leaves of the corresponding ethyl-ammonium- salts. Biethylamine-urea. Biethylamine probably behaves with cyanic acid like ammonia and ethylamine, giving rise to biethylamine-urea. This substance has been produced by the action of cyanic ether upon ethylamine, C 4 H 5 0, C 2 NO+C 4 H 7 N == C 10 H 12 N 2 2= C 2 (H 2 2C 4 H 5 )N 2 2 ^C 2 (H 2 Ae 2 )N 2 2 . Biethyla- mine-urea is very crystallizable, and readily forms a crystalline nitrate. Boileu with potassa, biethylamine-urea yields pure ethylamine, C 2 (H 2 Ae 2 )N 2 2 +2(KO,HO)=2(KO,C0 2 )-f-2N(H 2 Ae). TRIETHYLAMINE, Triethy I- ammonia, C 12 H 15 N=N3C 4 H 5 = NAe 3; The for- mation of this body is perfectly analogous to those of ethylamine and bie- thylamine. On heating for a short time a mixture of biethylamine with bromide of ethyl in a sealed glass tube, a beautiful fibrous mass of bromide of triethyl-ammonium is obtained, from which the triethylamine is sepa- rated by potassa. Triethylamine is a colourless, powerfully alkaline liquid, boiling at 195 -8 (91C). The salts of this base crystallize remarkably well. "With bichloride of platinum it forms a very soluble double salt, N(HAe 3 ) Cl,PtCl 2 , which crystallizes in magnificent large orange-red rhombs, Hydrated Oxide of Tetrethyl - ammonium, C gp H 2 ,NO a = N4(C 4 H 5 )0,HO = NAe 4 0,HO. When anhydrous triethylamine is mixed with dry iodide of ethyl, a powerful reaction ensues, the mixture enters into ebullition, and so- lidifies on cooling to a white crystalline mass of iodide of tetrethyl-ammonium, NAe 3 -}- AeI = NAe 4 T. The new iodide is readily soluble in hot water, from which it crystallizes on cooling in beautiful crystals of considerable size. This substance is not decomposed by potassa ; 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 casa ORGANIC BASES OF ARTIFICIAL ORIGIN. 457 sulphate or nitrate of silver be employed, we obtain together with iodide of silver, the sulphate or nitrate of oxide of tetrethyl-ammonium, which crys- tallize on evaporation; on the other hand, if the iodide be treated with freshly precipitated protoxide of silver, the oxide of tetrethyl-ammonium itself is separated. On filtering off the silver-precipitate, a clear colourless liquid is obtained, which contains the isolated base in solution. It is of a strongly alkaline reaction, and has an intensely bitter taste. Solution of oxide of tetrethyl-ammonium has a remarkable analogy to potassa and soda. Like the latter substance, it destroys the epidermis and saponifies fatty substances with formation of true soaps. With the salts of the metals, this substance exhibits exactly the same reactions as potassa. On evaporating a solution of the base in vacuo, long slender needles are deposited, which are evidently the hydrate of the base, with an additional amount of water of crystallization. After some time these needles disappear again, and a semi-solid mass is left, which is the hydrate of oxide tetrethyl-ammonium. A concentrated solution of this substance in water may be boiled without decomposition, but on heating the dry substance, it is decomposed into pure triethylamine and olefiant gas. N Ae 4 0, HO = 2 HO -f N Ae s 4. C 4 H 4 . Oxide of tetrethyl-ammonium forms neutral-salts with the acids. They are mostly very soluble ; several yield beautiful crystals. The platinum salt, NAe 4 Cl,PtCl 2 , forms orange-yellow octahedrons, which are of about the same solubility as the corresponding bichloride of platinum and potassium. Oxide of tetrethyl-ammonium is obviously perfectly analogous to the hitherto hypothetical oxide of ammonium. It is a compound of remarkable stability, the existence and properties of which must be regarded as power- ful supports of the ammonium-theory. BASES OF THE METHYL-SERIES. METHYLAMINE, Methylammonia, C 2 H 5 N = N(H t ,C 2 H 3 ) = N(H 2 Me). The formation and the method of preparing this compound from the cyanate of methyl, is perfectly analogous to those of ethylamine (see page 455) ; how- ever, 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. The crystalline residue, which is the chloride of methyl-ammonium, when distilled with dry lime, yields methylamine gas, which, like ammonia gas, has to be collected over mercury. It is distin- guished from ammonia, by a slightly fishy odour, and by the facility with which it burns. Methylamine is liquefied about 32 (0C), its sp. gr. is 1-08. This substance is the most soluble of all gases, at 53-6 (12C) 1 volume of water absorbs 1040 volumes of 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 ethyl- amine. Methylamine appears to be produced in a great number of pro- cesses of destructive distillation ; it has been formed by distilling several of the natural organic bases, such as codeine, morphine, caffeine, and several others, with caustic potassa ; frequently a mixture of several bases are produced in this manner. Among the numerous derivatives already obtained with this substance, methylamine-urea C 2 (H 3 Me)N 2 2 , and bimethylamine-urea C 2 (H 2 Me 2 )N 2 2 , and even a methyl-ethylamine-urea C 2 (H 2 MeAe)N 2 2 may be quoted. The latter substance has been produced by the action of cyanate of ethyl upon methyl- amine. Even a series of platinum-bases analogous to those produced by the 39 458 ORGANIC BASES OF ARTIFICIAL ORIGIN. action of ammonia upon protochloride of platinum (see page 309), have been obtained with methylamine. BLMETHYLAMINE has not yet been prepared in a pure state. TRIMETHYLAMINE, trimethyl-ammonia, C 6 H 9 N = N3C 2 H 3 = NMe 3 . This substance is readily obtained in a state of perfect purity, by submitting oxide of tetramethyl-ammonium (see the following compound) to the action of heat. It is gaseoxis at the common temperature, but liquefies at about 48-2 (0C) to a mobile fluid of very powerfully alkaline reaction. Tri- methylamine produces with acids very soluble salts. The platinum-salt N(HMe 8 )Cl.PtCl r is likewise very soluble and crystallizes in splendid orange- red octahedrons. According to Mr. Winkles, large quantities of trimethyl- umine are found in the liquor in which salt herrings are preserved. HYDRATED OXIDE OF TETRAMETHYL-AMMONIUM, C 8 II 13 N0 2 N4C 2 H 3 ,0, HO = NMe 4 0,HO. The corresponding iodide may be obtained by adding iodide of methyl to the preceding compound. Both substances unite with a sort of explosion. The same iodide is prepared, however, with less diffi- culty, simply by digesting iodide of methyl with an alcoholic solution of am- monia. 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 compound form in largest quantity, and may be separated by crystallization, the iodide of tetramethyl- ammonium being rather difficultly soluble in water. From the iodide the base itself is separated by means of protoxide of silver. The properties are similar to those of the corresponding ethyl-compound. It differs, how- ever, from oxide of tetrethyl-ammonium in its behaviour when heated (see page 457), yielding as it does trimethylamine, and pure methyl-alcohol, NMe 4 0,HO=NMe 3 -f MeO,HO. 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 more copious state- ment given in page 455, and confine ourselves to a brief observation of their principal properties. AMYLAMINE, amy I- ammonia, C 10 H )3 N=N(H 2 ,C 10 H 11 )=N(H 2 Ayl), colour- less liquid of a peculiar penetrating aromatic odour, slightly soluble in water, to which it imparts a strongly alkaline reaction. With the acids it forms crystalline salts, which have a fatty lustre. Amylamine boils at 199-4 (93C). An amyfamine-urea has been prepared. BIAMYLAKINE, biamy I- ammonia, C^H^N N(H,2C 10 H n )==N(HAyl 2 ), aro- matic liquid, less soluble in water, and less alkaline than amylamine. It boiiS at about 338 (170C). TRIAMYLAMINE, triamyl-ammonia, C 30 H 33 N=N3C, H u =NAyl 3 , colourless liquid of properties similar to those of the two preceding bases, but boiling at 494 -6 (257C). The salts of triamylamine are very insoluble in water, and fuse, when heated, to colourless liquids, floating upon water. HYDRATED OXIDE OF TETRAMYL-AMMONIUM, C 40 H 45 N0 2 =N4Ci H u ,0,HO =NAyl 4 0,HO. This substance is far less soluble than the corresponding bases of the methyl- and ethyl-series. On adding potassa to the aqueous solution the compound separates as an oily layer. On evaporating the solution in an atmosphere free from carbonic acid, the alkali may be ob- tained in splendid crystals of considerable size. When submitted to distilla- tion it splits into water, triamylamine, and amylene (see page 390), NAylO, II()=2HO+NAyl 8 -|-C 10 H 10 . ORGANIC BASES O ARTIFICIAL ORIGIN. 459 BASES OF THE PHENYL-SKRIES. ANILINE, phenylamine, C, 2 H 7 N = N(H 2 ,C I2 H 5 ) = N(II 2 Pyl). Under the head of salicylic acid (see page 406, and also page 399), a volatile crystal- line substance has been noticed by the name of hydrated oxide of phenyl. This substance, of which a fuller description is given in Section IX., imitates to a certain extent the deportment of an alcohol, but several very character- istic transformations of the alcohols, and especially the conversion into the corresponding acid, have not as yet been realized. The organic base, how- ever, which is derived from this alcohol in the same manner as methylamine, ethylamine, and arnylamine, from methyl-, ethyl-, and amyl-alcohol, is known under the term aniline, a name given to it on account of its relation to the indigo-series. Aniline cannot be produced from phenyl-alcohol by the same processes which have furnished the bases of the other alcohols, neither bro- mide nor iodide of phenyl having as yet been obtained. However, on heating phenyl-alcohol with ammonia in sealed tubes, aniline is produced, PylO,IU> _j_NH 3 =2HO-4-N(H 2 Pyl). This process, however, although interesting as establishing clearly the relation of aniline and phenyl-alcohol, is not calcu- luted to yield large quantities of this substance. Aniline is invariably obtained either from indigo or from nitrobenzol. Powdered indigo boiled with a highly-concentrated solution of hydrate of potassa dissolves with evolution of hydrogen gas to a brownish-red liquid containing a peculiar acid, the chrysantUc, which becomes gradually converted into another acid, the anthranilic (see page 474). If this matter be trans- ferred to a retort and still farther heated, it swells up and disengages ani- line, 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 accom- panied, and re-distilled, it is obtained nearly colourless. The formation of aniline from indigo is represented by the following equation : C 16 H 5 N0 2 -f2(KO,HO)-f2HO=C 12 H 7 N-f-4(KO,C0 2 )-|-4H. Indigo. Aniline. In order to prepare aniline from nitrobenzol (see page 399), this substance is submitted to a process discovered by Zinin, which has proved a very abun- dant source of artificial organic bases. An alcoholic solution of nitro-benzol is treated with ammonia and sulphuretted hydrogen, until after some hours a precipitate of sulphur takes place. The brown liquid is now saturated again with sulphuretted hydrogen, and the process repeated until sulphur is no longer separated. The reaction may be remarkably accelerated by occasion- ally heating or distilling the mixture. The liquid is then mixed with excess of acid, filtered, boiled to expel alcohol and unaltered nitrobenzol, and then distilled with excess of caustic potassa. The transformation of nitrobenzoi into aniline is represented by the equation : C, 2 H 5 N0 4 -f6HS=C l2 H 7 N+4HO-f6S Nitrobenzol. Aniline. If the aniline be required quite pure, it must be converted into oxalate, the salt several times crystallized from alcohol, and again decomposed by hydrate of potassa. 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 (see page 474), and occasionally in other reactions. \Vhcn pure, aniline forms a thin, oily, colourless liquid, of faint vinous 460 ORGANIC BASES OF ARTIFICIAL ORIGIN. odour, and aromatic, burning taste. It is very volatile, but nevertheless has a high boiling-point, 359 -6 (182C). 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 destitute of alkaline reaction to test-paper, but is quite remarkable for the number and beauty of the crystallizable compounds it forms with acids. Two extraordi- nary reactions characterize this body and distinguish it from all others, viz., that with chromic acid, and that with solution of hypochlorite of lime. The former gives with aniline a deep greenish or bluish-black precipitate, and the latter an extremely beautiful violet-coloured compound, the fine tint of which is, however, very soon destroyed. 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 (see page 471). When isatin is distilled with an exceedingly con- centrated solution of caustic potassa, it is, like indigo, resolved into aniline, carbonic acid, and free hydrogen. In like manner, when chlorisatin or bichlorisatin, two chloro-substitutes of isatin, are similarly treated, they yield products analogous to aniline, but containing one or two equivalents of chlo- rine respectively in place of hydrogen. The chloraniline, C, 2 (H 6 C1)N, and bichlor aniline, C 12 (H 5 C1 2 )N, thus produced, cannot be obtained directly, how- ever, from aniline by the action of chlorine, thus differing from ordinary substitution-compounds ; but aniline may be reproduced from them by the same re-agent, which is capable of reconverting chloracetic acid into ordi- nary acetic acid, namely, an amalgam of potassium (see page 375). They are the first cases on record of organic bases containing chlorine. Chloraniline forms large, colourless octahedrons having exactly the odour 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, indifferent to vegetable colours, and, except in being solid at common temperatures, re- sembles aniline in the closest manner. It forms numerous and beautiful crystallizable salts. If aniline be treated with chlorine-gas, the action goes farther, trie hlor aniline, C 12 (H 4 C1 3 )N, being produced, a volatile crystalline body which has no longer any basic properties. The corresponding bromine- compounds have also been formed and described. Nitraniline. If nitrobenzol be heated with fuming nitric acid, or, still better, with a mixture of that acid and oil of vitriol, it is converted into a substance called binitrobenzol, containing C 12 H 4 N 2 8 , or nitrobenzol in which an additional equivalent of hydrogen is replaced by the elements of hyponi- tric acid (see page 399). When this is dissolved in alcohol and subjected to the reducing action of sulphide of ammonium in Zinin's process, it furnishes a new substance of basic properties, nitraniline, having the constitution of a hyponitric acid substitution-product of ordinary aniline. The attempts to prepare it direct from aniline by means of nitric acid were unsuccessful, the principal product being usually carbazotic acid. Nitraniline forms yellow, acicular crystals, but little soluble in cold water, although easily dissolved by alcohol and ether. When warmed it exhales an aromatic odour, 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 bromaniline fails to give with hypochlorite of lime the characteristic reaction of the normal compound. Nitraniline forms crystallizable salts, of which the hydrochlorate is the best known. This substance contains the elements of aniline with an equivalent of hy- drogen replaced by hyponitric acid, or C, 2 H 6 N 2 4=: C 12 (H 6 N0 4 )N. Cy aniline is formed by the action of cyanogen upon aniline ; it is a crys- ORGANIC BASES OP ARTIFICIAL ORIGIN. 461 talline substance capable of combining with acids like aniline, but very prone to decomposition. Cyaniline contains C 14 H 7 N 2 =C 12 H 7 NCy. Hence it is formed by the direct union of 1 eq. of cyanogen and 1 eq. of aniline. Melaniline. The action of dry chloride of cyanogen upon anhydrous ani- line gives rise to the formation of a resinous substance, which is the chlo- rine-compound of a very peculiar basic substance to which the name me- laniline has been given. Dissolved in water and mixed with potassa, the above salt furnishes melaniline in form of an oil, which rapidly solidifies to a beautiful crystalline mass. Melaniline contains C^n^Ng. The following equation represents its formation : 2C 12 H 7 N-f- CgNClrsCajIlMNaCl. Melaniline, when treated with chlorine, bromine, iodine, or nitric acid, yields basic substitution-products, in which invariably 2 eq. of hydrogen are displaced. It combines with 2 eq. of cyanogen. The constitution of the substitution-products of aniline is readity intelli- gible ; it is evident that these substances owe their origin to a double sub- stitution, namely, first, of 1 equivalent of hydrogen in ammonia by phenyl ; and, secondly, of one or several equivalents of hydrogen in phenyl by chlorine, bromine, &c. The arrangement of the elements may be conveni- ently illustrated by the following formula} : Ammonia NH 3 Aniline NH 2 ,C 12 H 5 Chloraniline NH 2 ,C 12 (H 4 C1) P.romaniline NH 2 ,C 12 (H 4 Br) Bibromaniline NH 2 ,C I2 (H 3 Br 2 ) Tribromaniline NH 2 ,C I2 (H 2 Br 3 ) Nitraniline NH 2 ,C, 2 (H 4 N0 4 ) The constitution of cyaniline and melaniline is not so readily understood. Aniline-compounds corresponding to the amides and amidog en-acids, &c. Tn describing the ammonia-salts of various acids, attention has been repeatedly called to the power possessed by many of them to yield several new groups of compounds by the loss of a certain amount of water (see pages 343 and 415). These groups are perhaps best elucidated by the derivatives of oxalio acid- NH 4 0,C 2 3 2HO = C 2 2 N 2 TI Neutral oxalate of Oxauiido. ammonia. NH 4 0,C 2 3 ,HO,C 2 3 2TIO = C/VNtf/^O.JTO Cinoxalate of ammonia. Oxamic acid. NH 4 0,C 2 3 4HO = C a N Neutral oxalate of Oxalonitrile or ammonia. cyanogen. The terms corresponding to oxamide and oxamic acid have also been o taincd in the aniline-series; they are produced by the distillation of neutr: and acid oxalate of aniline, and have been called oxanilide and oxanilic acid. Oxatrilide = C 14 H 6 N0 2 = C 2 2 ,N(IIPyl) Oxanilic acid = C, 6 H 8 N0 6 = C 2 O 2 ,N(HPyl),C a 3 ,HO. Compounds analogous to the nitrilcs nave not been obtained in the aniline- 462 ORGANIC BASES OF ARTIFICIAL ORIGIN. series, and the reason is intelligible if we glance at the formula of oxaluto of aniline, N(H 3 Pyl)0,C 2 3 . It is obvious that 4 eq. of water cannot be eliminated from this salt without touching the hydrogen of the phenyl, i. e., without destroying the compound altogether. A great many anilides and anilic acids have been formed. Aniline-urea. On passing the vapour of cyanic acid into aniline, the sub- stance becomes hot, and solidifies on cooling to a crystalline mass, containing C 14 H 8 N 2 2 =C 2 (H 3 Pyl)N 2 2 . This is the composition of aniline-urea. This substance, however, does not combine with acids like the ureas (see pages 427 and 456), it is only isomeric with the true aniline-urea, which is obtained by another process. Among the derivatives of benzoic-acid, nifrobenzoic acid, C 14 (H 4 N0 4 )0 3 ,HO, (see page 397,) has been mentioned. The ether of this acid, C 4 H 6 0,Cj 4 (H 4 N0 4 )0 3 , like oxalic ether, and many other ethers, furnishes an amide when treated with ammonia. This substance, nitrobcn- zamide, C 14 (H 4 N0 4 )0 2 ,NH 2 , under the influence of sulphide of ammonium, suffers a change, which is perfectly analogous to that of nitrobenzol under similar conditions (see page 459). The mixture soon deposits sulphur, and yields, on evaporation, crystals of aniline-urea. C 14 H 6 N 2 6 -f-6HS = C 14 H 8 N 2 2 -f4HO + 6S Nitrobenzamide. Aniline-urea. This substance, which was discovered by M. Chancel, combines with nitric and hydrochloric acid, and even with bichloride of platinum. liases homologous to Aniline. In a former section of this Manual (page 403), a series of hydrocarbons has been mentioned, which are homologous to benzol. Each of these sub- stances, when treated with fuming nitric acid, yields a nitro-substitute cor- responding to nitrobenzol, which, under the influence of sulphuretted hydro- gen, is converted into a basic compound homologous to aniline. We thus obtain the following group : Benzol, C 12 H 5 H Nitrobenzol, C 12 H 5 N0 4 Aniline, N(H 2 .C, 2 ir 5 ) Toluol, C 14 H 7 H Nitrotoluol, C 14 H 7 N0 4 Toluidine, N(H 2 ,C 14 H 7 ) Xylol, C 16 H 9 H Nitroxylol, C ]6 H 9 N0 4 Xylidine, N(H 2 ,C 16 H 9 ) Cumol, C 18 H n H Nitrocumol, C 18 H 1 ,N0 4 Cumidine, N(H 2 ,C 18 If n ) TOLUIDINE, C 14 H 9 N==N(H 2 ,C 14 H 7 )=N(H a Tyl). This is prepared exact/y like aniline. Toluidine forms colourless platy crystals, very sparingly soluble in water, but easily in alcohol, ether, and oils ; it is heavier than water, has an aro- matic taste and odour, and a very feeble alkaline reaction. At 104 (40C) it melts, and at 388 (198C), boils, and distils unchanged ; it forms a series of beautiful crystallizable salts. XYLIDINE, C 16 H n N=N(H 2 ,C 16 H 9 )==N(H 2 Xyl). Of this compound little more than the existence is known. CUMIDINE, C 18 H w N=N(H 2 ,C I8 Hp):=N(H 2 Cyl). This substance is an oil which boils at 437 (225C). It forms magnificent salts with the acids. The following two bases are likewise closely allied to the group of aniline- bases, both by their mode of formation and by their constitution. NAPHTHALIDINE, C 20 TI 9 N=N(H 2 ,C 2o H 7 )=N(H 2 Nyl). This substance is interesting, as being one of the first of its kind produced by Zinin's process. It is obtained by the action of sulphide of ammonium upon an alcoholic solution of nitronaphihalase, one of the numerous products of the action of nitric acid upon the hydrocarbon naphthalin, which will be noticed in the last section of the Manual. When pure it forms colourless silky needles, ORGANIC BASES OF ARTIFICIAL ORIGIN. 163 fusible, and volatile without decomposition. It has a powerful, not disagree- able odour and burning taste, is nearly insoluble in water, but readily dis- solves in alcohol and ether ; the solution has no alkaline reaction. Naph- thalidine forms numerous crystallizable salts. CHLORONICINE, C IO (H 6 C1)N=NH 2 C IO (H 4 C1). A substance of the above composition has been lately discovered by Saint Evre, and deserves special notice, because it may be viewed as a chloro-substitute of the natural alkaloid nicotine (see page 450), which contains C 10 H 7 N. It is obtained by the following rather complicated series of reactions. A stream of chlorine is passed through a solution of benzoate of potassa to which some free alkali has been added, when a deposit forms consisting of chlorate of potassa and the potassa-salt of a new chlorinetted acid Ci 2 (H 4 Cl)0 3 ,HO. This acid, which is derived from benzoic acid by the removal of 2 eq. of carbon in the form of carbonic acid and by the introduction of 1 eq. of chlorine in the place of 1 eq. of hydrogen, has received the name of chloroniceic acid. It forms cauliflower-like crystals, fusible at 302 (150C), and boiling at 419 (215C). It is volatile without decomposition ; when submitted to distilla- tion with lime it yields a chlorinetted hydrocarbon chloronicene C, (H 5 C1), which is converted into nitrochloronicene C 10 ,(H 4 C1N0 4 ) by the action of fuming nitric acid. This, lastly, when treated with sulphide of ammonium furnishes chloronicine. It forms brown flakes, which dissolve in a great deal of water ; the solution, however, has no alkaline reaction. It forms crys- tallizable salts with hydrochloric and acetic acids, and a fine platinum-salt. The perfect analogy in the derivatives from chloroniceic acid to that of aniline and benzoic acid, is obvious from the following table : Benzoic acid C 14 H 6 4 Chloroniceic acid C, 2 (H 5 C1)0 4 Benzol Cj 2 H 6 Chloronicene C 10 (H 5 C1) Nitrobenzol C 12 (H 5 N0 4 ) Nitrochloronicene Ci (H 4 ClN0 4 ) Aniline C 12 H 5 ,H 2 N Chloronicine C, (H 4 C1)H 8 N. Up to the present moment chloronicine has not yet been converted into nicotine, nor has nicotine been transformed into chloronicine. MIXED BASES. In one of the preceding paragraphs it has been mentioned that the several hydrogen-equivalents in ammonium may be replaced by different hydro-carbon radicals. In fact, on treating aniline or toluidine with bromide, or iodide of ethyl, as described under the head of ethylamine, the following series of compounds are obtained : Aniline N(H 2 Pyl) Toluidine N(H 2 Tyl) Ethylaniline N(HPylAe) Ethylotoluidine N(HTylAe) Biethylaniline N(PylAe 2 ) Biethylotoluidine N(TylAe 2 ) Ammonium base N(PylAe 3 )0,HO Ammonium-base 1 N(TylAe 3 )0,HO ETHYLANILINE (ethylophenylamine) and BIETHYLANILINE (biethylopheny- lamine) are liquids greatly resembling aniline. They boil respectively at 399-2 (204C) and 41 6 -5 (213-6C). The ammonium-base, to which the name Oxide of biethylophenyl-ammonium may be given, is soluble in water, with a powerful alkaline reaction, corresponding in its general properties to oxide of tetrethyl-ammonium (see page 456). The series of bases which may be possibly obtained by changing the radicals is almost without limit ; even now a considerable variety has been produced, of which however only 1 Unpublished researches of Messrs R. Morley and John Abel. 4G4 BASES OF UNCERTAIN CONSTITUTION. a few will be mentioned here, as remarkable for the diversity of the materials With which they are constructed. HYDRATED OXIDE OF TRIETHYLAMYL-AMMONIUM, C 22 H 27 N0 2 = N(3C 4 TT 5 , C, II n )0,HO = N(Ae ? Ayl)0,HO. Triethylamiue (see page 456), when boiled with iodide of amyl is slowly converted into a crystalline mass of iodide of Tricthylamyl-ammonium. The base liberated with protoxide of silver and submitted to distillation yields olefiant gas, and BTETHYLAMINE, C 18 H 21 N=N(2C 4 H 5 ,C 10 H n ) = N(Ae 2 Ayl), a liquid boiling at 309-2 (154C). This compound is most powerfully attacked by iodide of methyl. Both substances immediately solidify to a beautifully crystalline iodide from which protoxide of silver separates. HYDRATED OXIDE OF METHYLO-BIETHYLAMYL-AMMONIUM, C 20 H 25 N0 2 =N (C2H 3 ,2C 4 H 5 ,C 10 H u )0,HO==N(MeAe a Ayl),0,HO. This substance, which is a powerfully alkaline base, soluble in water, when distilled undergoes the same decomposition as the other members of the fourth group of bases, yielding olefiant gas, and METHYLETHYLAMYLAMINE, or ammonia, in which 1 eq. of hydrogen is replaced by methyl, another by ethyl, and a third by amyl, C, 6 H, 9 N = N(0 2 H 3 ,C 4 H 5 ,C, H u )=N(MeAeAyl). This is a basic oil of a peculiar aromatic odour, boiling at 275 (135C) and forming crystallizable salt with the acids. ETHYLAMYLANILINE, C 26 H 21 N = N(C ]2 H5,C 4 H 5 ,C 1? H n ) = N(rylAeAyl). Ethylaniline (see page 463) treated with iodide of amyl yields the iodide of the above base, which is separated by distillation with potassa. It is an aromatic oil, boiling at 503 -5 (262C). The action of iodide of methyl upon, this substance gives rise to a new iodide from which protoxide of silver sepa- rates, and HYDRATED OXIDE OF METHYL-ETIIYL-AMYLO-PHENYL-AMMONTUM, C^H^NOg N(C 2 H 3 ,C 4 H 5 ,C )0 H n ,C 12 TT 5 )0,HO = N(MeAeAylPyl)0,HO. This compound is very soluble in water, is powerfully alkaline, and of an extremely bitter taste. The composition, established by the examination of a platinum-salt, is certainly remarkable, for this compound contains the radicals of not less than four different alcohols. BASES OF UNCERTAIN CONSTITUTION In addition to the artificial bases which have just been described, several others have been formed by processes less simple and less calculated to afford a clear insight into their constitution. The destructive distillation of nitro- genous substances has furnished a rich harvest of similar substances. A few of the most interesting may be briefly mentioned. CHINOLEINE (LEUCOLINE) C, g H 8 N. Quinine, cinchonine, strychnine, and probably other bodies of this class, when distilled with a very concentrated solution of potassa, yield an oily product resembling aniline in many respects, and possessing strong basic powers; it is, however, less volatile than that substance, and boils at 460 (235C). When pure it is colourless and has a faint odour 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. Chinoleinc has no alkaline reaction, but forms salts with aciJs, which, gene- rally speaking, do not crystallize very freely. BASES OF UNCERTAIN CONSTITUTION. 465 Bases from Coal-tar Oil. KYANOL and LEUKOL. The volatile basic bodies described tinder these names have lately been identified, the first with aniline and the second with chinoleine. They are separated from the coal-oil by agitating large quanti- ties of that liquid with hydrochloric or diluted sulphuric acid, and then dis- tilling the acid liquid with excess of potassa or lime. They are readily sepa- rated by distillation. PICOLINE C 12 H 7 N. Dr. Anderson has described under the foregoing name a third volatile, oily base, present in certain varieties of coal-tar-naphtha, being there associated with aniline, chinoleine, and several other volatile sub- stances but imperfectly understood. It is separated without difficulty from the two bases mentioned by distillation, in virtue of its superior volatility. Picoline, when pure, is a colourless, transparent, limpid liquid, of powerful and persistent odour, and acrid, bitter taste. It is unaffected by a cold of ( 17'7C). 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 272 (183-3C). It mixes in all propor- tions with pure water, but is insoluble in caustic potassa and most saline solutions. The alkalinity of this substance is exceedingly well marked ; it restores the blue colour of reddened litmus, and forms a series of crystalliza- ble salts. This substance, as seen from the above formula, is isomeric with aniline, but numerous characteristic reactions completely distinguish it from this body. 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 volatile organic bases. Together with some of the substances already de- scribed, such as methylamine, ethylamine, picoline, and analine, Dr. Ander- son has found in it a peculiar base. PETININE C 8 H n N. The properties of this substance are very analogous to those of Methylamine, and triethylamine. It has the same composition as biethylamine, but differs from it by its higher boiling-point, which is 175 (79 -5C), that of biethylamine being 133 (55C) (see page 455). Some chemists are inclined to explain this difference by assuming that petinine is an ammonia-base, containing the radical butyl, which was mentioned under the head of valeric acid (see page 392), in one word that it is bulylamine N(H 2 , C 8 H 9 ), homologous to ethylamine. This assumption may be correct, but is not as yet supported by any experimental evidence. Bases obtained by the action of Ammonia upon Volatile Oils. FURFITRINE. When sulphuric acid diluted with an equal bulk of water is carefully mixed with twice its weight of wheat-bran, and the adhesive pasty mass obtained exposed in a proper vessel to the action of a current of stearn which is afterwards condensed by a worm or refrigerator, a liquid is obtained which holds in solution a peculiar volatile oil, to which the term furfurole has been given. By re-distillation several times repeated, the first half of the liquid only being collected, the furfurole can be extracted from the water, and then by distillation alone obtained in a state of purity. It has a pale yellow colour, and a fragrant odour like that of oil of cassia ; its specific gravity is 1-165, and it boils at 325 (1G2-8C), distilling unchanged. It dis- solves in all proportions in alcohol and to a very considerable extent in water, and is roadily destroyed by strong acids and caustic alkalis, especially when aided by heat. Furfurole contains C 6 II 2 0. The specific gravity of its vapour ia 3493. 466 BASES OP UNCERTAIN CONSTITUTION. The product of furfurole is very greatly increased and the operation much facilitated by previously depriving the bran of all starch, glutin, and soluble matter by steeping it in a cold dilute solution of caustic potassa, and wash- ing and drying by gentle heat or in the sun. Maceration in cold water fer some time answers the same purpose, owing to the lactic acid formed in that case. In contact with solution of ammonia, furfurole becomes converted in the space of a few hours into a yellowish-white, crystalline, insoluble substance, furfurolamide, Ci 5 H 6 N0 3 ; this body is slowly decomposed in contact with water, and instantly by an acid into ammonia and furfurole. It may be crys- tallized from alcohol, however, in which it dissolves without much change. When boiled with a somewhat dilute solution of caustic potassa, no ammonia is disengaged, but the substance is slowly dissolved if the quantity of liquid be considerable, and the solution deposits on cooling small, white, silky needles of a substance having the same composition as furfurolamide itself. There is no other product. This new body, to which the name furfurine has been given, is a powerful organic base, forming with acids, a series of beau- tiful crystallizable salts, and decomposing at a boiling heat the saline com- pounds of ammonia. Furfurine is very sparingly soluble in cold water, but dissolves in about 135 parts at 212 (100C). 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 intensely bitter. Furfurine contains in 1 equivalent C^H^N^. 1 FUCUSINE. By treating several varieties of fucus with sulphuric acid in exactly the same manner as in the preparation of furfurole, Dr. Stenhouse obtained a series of substances, which he designates by the terms fucusol, fucusamide, and fucusine. They have exactly the same composition as the corresponding terms in the furfurole-series, and also most of their properties, but differ in some details. AMARINE (BENZOLINE). The hydrobenzamide of M. Laurent, C 42 H )8 N 2 , produced by the action of ammonia on pure bitter-almond-oil (see page 400), when long boiled with a solution of caustic potassa, suffers the same kind of change as furfurolamide, becoming entirely converted into a new body iso- meric with hydrobenzamide, having the characters of a salt-base, and to which the preceding name has been given. Precipitated by ammonia from a cold solution of the hydrochlorate or sulphate, amarine separates in white curdy masses, which when washed and dried become greatly reduced in volume. In this state it is singularly electric by friction with a spatula. Ifc 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 the form of small, colourless, prismatic crystals. Below 212 (100C) it melts, and on cooling assumes a glassy or resinous condition. Strongly heated in a retort, it decomposes with production of ammonia, and a volatile oil not yet examined, and a new body, pyrobenzolin, which appears to be a neutral substance, insoluble in water, dissolved by boiling alcohol, and containing a large quantity of nitrogen. It is fusible by moderate heat, and on cooling becomes a mass of colourless radiating needles or plates. The salts of amarine are mostly sparingly soluble : the sulphate, nitrate, and hydrochlorate are crystallizable and very definite. Amarine contains C 42 Hi 8 N 2 . THIOSINNAMINE. The volatHe oil distilled from black mustard-seed, C S H 5 NS 2 , which will be noticed farther on, in contact with solution of ammonia, f This remarkable substance, the nearest approach to the native alkaloids yet made, wat discovered by the author of this Manual. EDS. BASES OF UNCERTAIN CONSTITUTION. 467 yields a compound having the characters of an organic base, and forming colourless, prismatic crystals, bitter in taste and soluble in water. The solution does not aifect test-paper. It melts when heated, but cannot be sublimed. Acids combine with it, but form no crystallizable salts: the double salts of the hydrochlorate with bichloride of platinum and corrosive subli- mate are the most definite. This substance contains sulphur; its formula is C 8 H S N 2 S 2 . It is the only product of the action of ammonia on the oil. Thiosinnamine is decomposed by metallic oxides, as protoxide of lead, with production of a metallic sulphide and a new body of basic properties, free from sulphur, called sinnamine. This latter substance crystallizes very slowly from a concentrated aqueous solution in brilliant, colourless crystals which contain water. It has a powerful bitter taste, is strongly alkaline to test-paper, and decomposes ammoniacal salts by boiling. With the excep- tion of the oxalate, it forms no crystallizable salts. Sinnamiue contains in the crystallized state C 8 H 6 N 2 ,HO. When mustard-oil is treated with protoxide of lead or baryta, the whole of the sulphur is withdrawn, and carbonic acid and another basic substance produced, which, when pure, crystallizes in colourless plates, soluble in water and in alcohol ; the solution has a distinct alkaline reaction. Sinapoline, the body so formed, contains C uH 12 N 2 2 . Bases from Aldehyde. THIALDINE The crystalline compound of aldehyde with ammonia (see page 369), is dissolved in 12 to 16 parts of water, mixed with a few drops of caustic ammonia, and then the whole subjected to a feeble stream of sul- phuretted hydrogen. After a time the liquid becomes turbid and deposits a white crystalline substance, which is the body in question. 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, regu- lar, rhombic crystals, having the figure of those of common gypsurn. The crystals are heavier than water, transparent and colourless. They refract light strongly. The substance has a somewhat aromatic odour, melts at 110 (43-8C), and volatilizes slowly at common temperatures. It distils unchanged with the vapour 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 colours, but dissolves freely in acids, forming crystalli- zable salts. Heated with hydrate of lime it yields chinoleine. Thialdine contains C I2 H ]3 NS 4 . A very similar compound containing selenium exists. ALANINE. This substance is likewise obtained from aldehyde. Ii Has been only recently discovered by Strecker, who obtained it in a reaction, which promises many interesting results. If an aqueous solution of the am- monia-compound of aldehyde be treated with hydrocyanic and hydrochloric acid, chloride of ammonium is formed, together with hydrochlorate of aid- nine. On adding to this solution a mixture of alcohol and ether, the greater portion of the chloride of ammonium is precipitated ; the filtrate is then treated with protoxide of lead to remove a small quantity of ammonium and hydrochloric acid, and separated from the lead by sulphuretted hydrogen The liquid thus obtained deposits feathery crystals of alanine. The compo- sition of alanine is C 6 H.N0 4 , and its formation represented by the equation: C 4 II 4 2 + HC 2 N 4. 2IIO=C 6 H 7 N0 4 Aldehyde. Hydrocyanic Alaniae. acid. 468 APPENDIX TO THE ORGANIC BASES. Alaninc crystallizes in rhombic prisms of the lustre of mother-of-pearl. They are pretty soluble in cold, but more so in boiling water; the solution has a sweetish taste, but no effect upon vegetable colours. Alanine is a weak base; as yet only a crystalline nitrate has been obtained, but several combinations with metallic oxides have been produced. This substance has the same com- position as lactamide (see page 351), urethane (see page 358), and sarcosine, which will be described in the section on the components of the animal body. But it is only isomeric with these substances, from which it differs in its physical and chemical properties. The most interesting feature in the his- tory of alanine is its behaviour with nitrous acid. Under the influence of this reagent it is converted into lactic acid, identical in every respect with that obtained in the fermentation of sugar (see page 349). This reaction is represented by the following equation : C 6 H 7 N0 4 +N0 3 =C 6 H 5 O s ,HO+2N-f-HO Alanine. Lactic acid. APPENDIX TO THE ORGANIC BASES. All the numerous members of this extensive group, which have been con- sidered in the preceding section, invariably contain nitrogen. Recent re- searches, however, have shown that two series of analogous substances exist which contain phosphorus and antimony, in the place of nitrogen. These remarkable compounds, which are not yet sufficiently known, will be briefly noticed in the subsequent paragraphs. Phosphorus-bases. If a current of chloride of methyl (see page 382) be passed over a layer of phosphide of calcium (see page 241), heated to about 356 (180C), a mixture of several phosphoretted bodies is produced, which are partly liquid arid partly solid. M. Paul Thenard, who has investigated this subject, has separated from this mixture three compounds, containing carbon, hydrogen, and phosphorus, which he believes to correspond to the three hydrides of phosphorus (see page 166). Phosphoretted Phosphoretted hydrogens. methyl-bodies. P 2 H P 2 C 2 H 3 =P 2 Me PH 2 P2C 2 H 3 =PMe 2 PH 3 P3C 2 H 3 =PMe 3 . As far as can be seen from the results obtained by M. Thenard, which have not yet been published in detail, the two last substances are powerful bases analogous to the bases of the nitrogen-series. These substances are very readily decomposed, one of them is even spontaneously inflammable, BO that their preparation and study has been attended with great difficulty and even danger, circumstances which sufficiently account for the insuffi- ciency of the description. It is evident that the last body is the phospho- retted analogue of trimethylamine, triethylamine, and triamylamine, and the question arises whether the second may not be viewed as the phospho- retted bimethylamine, and whether farther researches will not establish the existence of the whole series of the phosphoretted bases corresponding to ihe compound ammonia? previously described. APPENDIX TO THE ORGANIC BASES. 469 Antimony-bases. Among tLe derivatives of alcohol, a compound of antimony with 3 eq. of ethyl has been briefly noticed see page (438; under the name of stibethyl. The composition of this remarkable compound approximates it to triethyla- T,ie,h y ,aine NAe 3 ........................................ SbAe A closer examination has shown that this substance differs in many points from triethylamine, but that in one very essential character, the two sub- stances agree in the most perfect manner. The properties of stibethyl are the following; it is a transparent, very mobile liquid, of a penetrating odour of onions. It boils at 317 (158-3C). In contact with atmospheric air, it emits a dense white fume and frequently even takes fire, burning with a white brilliant flame. It combines directly with 2 eq. of oxygen, sulphur, chlorine, and iodine. Binoxide of stibethyl, SbAe 3 2 , forms a viscid transparent mass soluble in water and alcohol. It is extremely bitter and not poisonous. This sub- stance cannot be volatilized without decomposition. Binoxide of stibethyl combines with acids, giving rise to the formation of crystallizable salts con- taining 2 eq. of acid. Bisulphide of stibethyl, SbAe-jSg. Beautiful crystals of silvery lustre, so- luble in water and alcohol. Their taste is bitter, and their odour similar to that of mercaptan. The solution of this compound exhibits the deportment of an alkaline sulphide ; it precipitates the solution of the metals as sul- phides, a soluble salt of stibethyl being formed at the same time. This de- portment, indeed, affords the simplest means of preparing the salts of stibe- thyl. Bichloride of stibethyl, SbAe 3 Cl 2 . Colourless liquid of the odour of oil of turpentine. Biniodide of stibethyl, SbAe 3 I 2 . Colourless needles of intensely bitter taste. The analogy of stibethyl with triethylamine is best exhibited in its deport- ment with iodide of ethyl. The two substances combine to a new iodide, containing SbAe 4 I, from which a powerful alkaline base may be separated by the action of protoxide of silver. This substance, which must evidently be analogous to oxide of tetrethyl-ammonium, NAe 4 0,HO SbAe 4 0,HO, has not yet been minutely examined. A series of analogous substances exist in the methyl-series. They have been examined by M. Landolt, who has described several of its compounds, separated the methyl-antimony-base corresponding to oxide of tetrethyl- ammonium. The iodide, SbMe 4 T, produced by the action of iodide of methyl upon stibraethyl, 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 protoxide of silver, it yields a powerfully alkaline solution exhibiting al! the properties of potassa, from which, on evaporation, a white crystalline mabs, the hydrate of the base, SbMe 4 0,HO, crystallizes. This compound forms an acid sait with sulphuric acid, which crystallizes in tables. It contains SbMeXXSO. -j-HO,S0 3 . 40 470 ORGANIC COLOURING rRINCITLES. SECTION VI. ORGANIC COLOURING PRINCIPLES. THE organic colouring principles are substances of very considerable prac- tical importance in relation to the arts ; several of them, too, have been made the subjects of extensive and successful chemical investigation. With the exception of one red dye, cochineal, they are all of vegetable origin. The art of dyeing is founded upon an affinity or attraction existing between the colouring matter of the dye and the fibre of the fabric. In woollen and silk this affinity is usually very considerable, and to such tissues i permanent stain is very easily communicated, but with cotton and flax it is much weaker. Recourse is then had to a third substance, which does possess in a high degree such affinity, and with this the cloth is impregnated. Alumina, sesquioxide of iron, and oxide of tin are bodies of this class. When an infusion of some dye-wood, as logwood, for example, is mixed with alum and a little alkali, a precipitate falls, consisting of alumina in combination with colouring matter, called a lake; it is by the formation of this insoluble substance within the fibre that a permanent dyeing of the cloth is effected. Such applications are termed mordants. Sesquioxide of iron usually gives rise to dull, heavy colours ; alumina and oxide of tin, especially the latter, to brilliant ones. It is easy to see, that, by applying the mordant partially to the cloth, by a wood-block or otherwise, a pattern may be produced, as the colour will be removed bv washing from the other portions. INDIGO. Indigo is the most important member of the group of blue colouring matters. It is the product of several species of the genus indigofera, which grow principally in warm climates. When the leaves of these plants are placed in a vessel of water and allowed to ferment, a yellow substance is dissolved out, which by contact of air becomes deep blue and insoluble, and finally precipitates. This, washed and carefully dried, constitutes the indigo /f commerce. It is not contained ready-formed in the plant, but is pro- duced by the oxidation of some substance there present. Neither is the fermentation essential, as a mere infusion of the plant in hot water deposits 'ndigo by standing in the air. Indigo comes into the market in the form of cubic cakes, which, rubbed ith a hard body, exhibit a copper-red appearance; its powder has an in- tensely deep blue tint. The best is so light as to swim upon water. In addition to the blue colouring matter, or true indigo, it contains at least half its weight of various impurities, among which may be noticed a red resinous matter, the indigo-red of Berzelius ; these may be extracted by boiling the powdered indigo in dilute acid, alkali, and afterwards in alcohol. Pure indigo is quite insoluble in water, alcohol, oils, dilute acids, and alkalis ; it dissolves in about 15 parts of concentrated sulphuric acid, forming INDIGO. 471 a deep blue pasty mass, entirely soluble in water, and often used in dyeing; this is sulpkindyUc or sulphindigotic acid, a compound analogous to sulphovinio acid, capable of forming with alkaline bases blue salts, which, although easily soluble in pure water, are insoluble in saline solutions. If an insufficient quantity of sulphuric acid has been employed, or digestion not long enough continued, a purple powder is left on diluting the acid mass, soluble in a large quantity of pure water. The Nordhausen acid answers far better for dissolving indigo than ordinary oil of vitriol. Indigo may, by cautious man- agement, be volatilized; it forms a fine purple vapour, which condenses in brilliant copper-coloured needles. The best method of subliming this sub- stance is, according to Mr. Taylor, to mix it with plaster of Paris, make the whole into a paste with water, and spread it upon an iron plate. 1 part in- digo, and 2 parts plaster, answer very well. This, when quite dry, is heated by a spirit-lamp ; the volatilization of the indigo is aided by the vapour of water disengaged from the gypsum, and the surface of the mass becomes covered with beautiful crystals of pure indigo, which may be easily removed by a thin spatula. At a higher temperature, charring and decomposition take place. In contact with de-oxidizing agents, and with an alkali, indigo suffers a very curious change ; it becomes soluble and nearly colourless, perhaps re- turning to the same state in which it existed in the plant. It is on this prin- ciple that the dyer prepares his indigo-vat: 5 parts of powdered indigo, 10 parts of green vitriol, 15 parts of hydrate of lime, .and GO parts of water, are agitated together in a close vessel, and then left to stand. The hydratecl protoxide of iron, in conjunction with the excess of lime, reduces the indigo to the soluble state ; a yellowish liquid is produced, from winch acids pre- cipitate the white or de-oxidized indigo as a flocculent insoluble substance, which absorbs oxygen with the greatest avidity, and becomes blue. Cloth steeped in the alkaline liquid, and then exposed to the air, acquires a deep and most permanent blue tint by the deposition of solid insoluble indigo in the substance of the fibre. Instead of the iron-salt and lime, a mixture of dilute caustic soda and grape-sugar dissolved in alcohol may be used ; the sugar becomes oxidized to formic acid, and the indigo reduced. On allowing a solution of this description to remain in contact with the air, it absorbs oxygen and deposits the indigo in the crystalline condition. The following formulae represent the composition of the bodies described: Blue insoluble indigo C l6 H 5 N 2 White, or reduced indigo 1 C 16 II 6 N 2 Sulphiudylic acid C 16 H 4 N 0,2S0 3 , HO. Products of the Decomposition of Indigo. The products of the destructive modification of indigo by powerful chemical agents of an oxidizing nature are both numerous and interesting, inasmuch as they connect this substance in a very curious manner with several other groups of organic bodies, especially with those of the salicyl- and phenyl- series. Many of them are exceedingly beautiful, and possess very remarkable properties. ISATIN. One part of indigo reduced to fine powder, and rubbed to a paste with water, is gently heated with a mixture of one part of sulphuric acid and one part of bichromate of potassa dissolved in 20 or 30 parts of water ' Properly liydrogc.nized indigo, if the above be the correct view: white indigo may, how evor, be viewed as a hydrate, arid blue indigo as an oxide, of one and the fame substance. White inrli^o Ci 6 H 5 N O+IIO BloeiutUgo Ciell 5 NO+0 472 INDIGO. The indigo dissolves with very slight disengagement of carbonic acid towards the end, forming a yellow-brown solution, which on standing deposits impure {satin in crystals. These are collected, slightly washed and re-dissolved in boiling water ; the filtered solution deposits on cooling the isatin in a state of purity. Or, powdered indigo may be mixed with water to a thin paste, heated to the boiling-point in a large capsule, and nitric acid added by small portions until the colour disappears ; the whole is then largely diluted with boiling water, and filtered. The impure isatin. which separates on cooling is washed with water containing a little ammonia, and re-crystallized. Both these processes require careful management, or the oxidizing action proceeds too far, and the product is destroyed. Isatin forms deep yellowish-red prismatic crystals of great beauty and lustre ; it is sparingly soluble in cold water, freely in boiling water, and also in alcohol. The solution colours the skin yellow, and causes it to emit a very disagreeable odour. It cannot be sublimed. Isatin contains the elements of indigo plus 2 eq. of oxygen, or C )6 H 5 N0 4 . A solution of potassa dissolves isatin with purple colour ; from this solu- tion acids precipitate the isatin unchanged. When boiled, however, the colour is destroyed, and the liquid furnishes on evaporation crystals of the potassa-salt of a new acid, the isatinic, containing C 16 H 6 N0 5 .HO. In the free state this is a white and imperfectly crystalline powder, soluble in water, and easily decomposed into isatin and water. By chlorine, isatin is converted into the substitution-product chlorisatin, C 16 (H 4 C1)N0 4 , a body closely resembling isatin itself in properties. If an alcoholic solution and excess of chlorine be employed, other products make their appearance, as chloranile, C 12 C1 4 4 , trichlorophenol, C 12 (H 3 C1 3 )0 2 , and a resinous substance. The former of these substances, the position of which in the kinone-series has been already noticed (page 449), yields other pro- ducts with potassa and ammonia. Bromisatin is easily formed. The changes which isatin, and its chlorinetted and brominetted congeners, undergo when {submitted to the action of fusing hydrate of potassa has been already con- sidered in the section on the vegeto-alkalis (see page 459). Exposed to the action of sulphuretted hydrogen and sulphide of ammo- nium, isatin furnishes several new compounds, as isathyde, sulfesathyde, sulfa- sathyde. A hot solution of isatin, when treated with sulphide of ammonium, gives rise to a deposit of sulphur, a white crystallized substance being produced at the same time ; it has received the name of isathyde, and contains CjgHg N0 4 . It is obvious that it bears to isatin the same relation as white to blue indigo. If the sulphide of ammonium be replaced by sulphuretted hydro- gen, bisulphisathyde, Ci 6 H 8 N0 2 S 2 , is produced, which is unlike the former; 2 eq. of oxygen, being replaced by 2 eq. of sulphur. An alcoholic solution of potassa converts this into sulphisathyde, Ci 6 H 6 N0 3 S, in which only half of the oxygen in isatin is replaced by sulphur. Under the influence of cold aque- ous solution of potassa, bisulphisathyde yields indin, C 16 H 6 N0 2 , which is iso- ineric with white indigo. When treated with boiling potassa, indin fixes the elements of 2 eq. of water, and becomes indinic acid, C 16 H 7 N0 3 ,HO, the po- lassa-salt of which forms fine black needles. Ammoniacal gas and solution of ammonia yield with isatin a series of in- teresting substances containing the nitrogen of the ammonia in addition to that of the isatin. ACTION OF CHLORINE ON INDIGO. In the dry state chlorine has no action whatever on indigo, even at the temperature of 212 (100C). In contact with water, the blue colour is instantly destroyed, and cannot again be re- stored. The same thing happens with the blue solution of sulphindylic acid. When chlorine is passed into a mixture of powdered indigo and water until INDIGO. 473 the colour disappear!?, and the product is then distilled in a retort, water containing hydrochloric acid and a mixture of two volatile bodies, trichlor- aniline, C, 2 (II 4 C! 3 )N, and trichlorophenol, C ]2 (H 3 C! 3 )0 2 , pass over into the receiver, while the residue in the retort is found to contain chlorisatin, al- ready mentioned, and bichlorixatin, C ]6 (H 3 C1 2 )N0 4 , much resembling that sub- stance, but more freely soluble in alcohol. Both these bodies yield acids in contact with boiling solution of potassa, by assimilating the elements of water. The action of bromine on indigo is very similar. ANILIC AND PICRIC ACIDS. Artilic or indigotic acid is prepared by adding powdered indigo to a boiling mixture of 1 part of nitric acid and 10 parts of water, until the disengagement of gas ceases, filtering the hot dark- coloured liquid, and allowing it to stand. The impure anilic acid so ob- tained is converted into the lead-salt, which is purified by crystallization and the use of animal charcoal, and then decomposed by sulphuric acid. Anilic acid forms fine white or yellowish needles, which have a feeble acid taste and very sparing degree of solubility in cold water. In hot water and in alcohol it dissolves easily. It melts when heated, and on cooling assumes a crystalline structure. By careful management it may be sublimed un- changed. Anilic acid contains C, 4 H 4 N0 9 .HO=C I4 (H 4 N0 4 )0 5 ,HO. It has been mentioned that the same acid is readily prepared from salicylic acid (see page 40G). Hence it is more appropriately called nitro-salicylic acid. Picric, carbazotic, or nitrophenisic acid, is one of the ultimate products of the action of nitric acid upon indigo and numerous other substances, as nilk, wool, several resins, especially that of Xanthorhaza hastilis (yellow gum of Botany Bay), salicin and some of its derivatives, cumarin, and certain bodies belonging to the phenyl-series. It may be prepared from indigo by adding that substance in coarse powder and by small portions to ten or twelve times its weight of boiling nitric acid of sp. gr. 1-43. When the last of the indigo has been added, and the action, at first extremely violent, has became moderated, an additional quantity of nitric acid may be poured upon the mixture, and the boiling kept up until the evolution of red fumes nearly ceases. When cold, the impure picric acid obtained may be removed, con- verted into potassa-salt, several times re-crystallized, and, lastly, decom- posed by nitric acid. In the pure state it forms beautiful pale yellow scaly crystals, but slightly soluble in cold water, and of insupportably bitter taste. Picric acid is used in dyeing ; it forms a series of crystallizable salts of yel- low or orange colour : that of potassa forms brilliant needles, and is so little soluble in cold water, that a solution of picric acid is occasionally used as a precipitant for that base. The alkaline salts of this acid explode by heat with extraordinary violence. The crystals of picric acid contain C, 2 H 2 N 3 13 ,HO. If a solution of picric acid be distilled with hydrochlorite of lime, or a mixture of chlorate of potassa and hydrochloric acid, an oily liquid of a penetrating odour is obtained, having a sp. gr. of 1-6G5, and boiling between 237 and 239 (114 and 115C). The substance, chloropicrin, was disco- vered by Stenhouse, who gives the formula C 4 C1 7 N 2 10 ; MM. Gerhardt and Cahours assign to it the formula C 2 C1 3 N0 4 . According to the latter formula, which is more probable, chloropicrin would be chloroform, in which the hy- drogen is replaced by the elements of hyponitric acid : Chloroform C 2 (HC1 3 ) ; Chloropicrin C 2 (N0 4 C1 3 ). PRODUCTS OF THE ACTION OF HYDRATE OF POTASSA UPON INDIGO. One of the most remarkable of these, aniline, has been already described (see page 459). When powdered indigo is boiled with a very concentrated solution of caustic potassa, it is gradually dissolved with the exception of some brown- ish flocculent matter, and the liquid on cooling deposits yellow crystals of 40* 474 LICHENS. the potassa-salt of a new acid, the chrysanilic, which can be procured in a purer state, by dissolving the crystals in water, filtering from reproduced indigo, and adding a slight excess of mineral acid. Chrysanilic acid can be obtained in indistinct crystals from weak alcohol ; it is supposed to contain C 28 H 10 N 2 5 ,HO, but it is very probable that it is a mixture of several sub- stances, especially isatinic acid. When this substance is boiled with mineral acids, it is decomposed into another new acid, the anthranilic, which remains in solution, and a blue in- soluble matter resembling indigo ; a similar effect is slowly produced by the action of the air upon an alcoholic solution of chrysanilic acid. Anthranilic acid is colourless, sparingly soluble in cold water, easily soluble in alcohol. It melts when heated, sublimes under favourable circumstances, but decom- poses entirely when heated in a narrow tube into carbonic acid and aniline. It contains C, 4 H 6 N0 3 ,HO. By treatment with nitrous acid, anthranilic acid is converted into salicylic acid C 14 H 6 N0 3 ,HO-f N0 3 =C 14 II 5 5 ,HO-fHO-f2N. According to M. Cahours, pure indigo can also be converted into salicylic acid by fusion with hydrate of potassa ; a particular temperature is required, somewhat above 570 (298C), and the operation is by no means always successful. Litmus is used by the dyer as a red colouring matter ; the chemist employs it in the blue state as a test for the presence of acid, by which it is instantly reddened. In preparing test-papers for chemical use with infusion of litmus, good writing or drawing-paper, free from alum and other acid salts, should be chosen. Those sheets which after drying exhibit red spots or patches, may be reddened completely by a little dilute acetic acid, and used, with much greater advantage than turmeric-paper, to discover the presence of free alkali, which restores the blue colour. Many lichens, when exposed in a moistened state to the action of ammonia, yield purple or blue colouring principles, which, like indigo, do not pre- exist in the plant itself. Thus, the Roccella tinctoria, the Variolaria orcina, the Lecanora tar tar ea, &c., when ground to paste with water, mixed with putrid urine or solution of carbonate of ammonia, and left for some time freely exposed to the air, furnish the archil, litmus, and cudbear of commerce, very similar substances, differing chiefly in the details of the preparation. From these the colouring matter is easily extracted by water or very dilute solution of ammonia. The lichens have been extensively examined by Schunk, Stenhouse, and several other chemists. The whole subject has been lately revised by Dr. Strecker, whose formulae have been adopted in the following succinct ac- count : ERYTHRIC ACID. The lichen Roccella tinctoria, from which the finest kind of archil is prepared, is boiled with milk of lime, the filtered solution is pre- cipitated by hydrochloric acid, and the precipitate dried and dissolved in warm, not boiling, alcohol, from which on cooling crystals of ery thric acid are deposited. This is a very feeble acid, colourless, inodorous, difficultly solu- ble in cold and even in boiling water, readily soluble in ether. Its solution, when mixed with chloride of lime, assumes a blood-red colour. Boiled with water for some time, erythric acid absorbs 2 eq. and yields picro-erythrin, a crystallizable, bitter principle, and a new acid presently to be described, which is termed by some chemists lecanoric, by others orselHnic acid. If the ebullition be continued, the orsellinic acid undergoes a farther change, being converted into a crystalline substance, orcin, of which mention will shortly be made. LICHENS. 475 The composition of these various substances is expressed by the following formulae : Erythric acid C 20 H 11 )0 Orsellinic acid C 16 H 8 g Picro-erythrin , C 24 H 16 14 Orcin C^H 8 4 And the successive changes which occur by ebullition are represented by the following equation: 20^,0,0+ 2HO = C, 6 H 8 Og + JW^eOw Erythric acid. Orsellinic acid. Picro-erythrin. Orsellinic acid. Orcin. ALPHAORSELLIC ACID is obtained from the South American variety of Roccella tinctoria. The preparation and the properties of this substance are perfectly analogous to those of erythric acid. Alphaorsellic acid contains C 32 H 14 14 ; by boiling with baryta-water it likewise furnishes orsellinic acid. C^H M 14 +2HO = 2C, 6 H 8 8 Alphaorsellic Orsellinic acid. acid. If the ebullition be continued too long, a great portion of the orsellinio acid is converted into orcin. ORSELLINIC ACID, formerly frequently called lecanoric acid, whether pre- pared from erythric or alphaorsellic acid, forms crystals which are far more soluble in water than either of the acids from which it has been prepared. Its taste is somewhat bitter. Boiled with water, it yields, as has been stated, orcin ; under the influence of air and ammonia, it assumes a beauti- ful purple colour. If the lichens, instead of being treated with milk of lime, be exhausted with boiling alcohol, the erythric and alphaorsellic acids are likewise decom- posed ; but instead of orsellinic acid, the ether of this substance, C 4 H 6 0, C 16 H 7 7 , is formed. This ether was formerly described under the namo pseudo-erythrin until Mr. Schunk pointed out the true nature of the sub- stance. Orsellinate of ethyl may be likewise produced by boiling pure orsellinic acid with alcohol. It crystallizes in colourless lustrous plates, which are readily soluble in boiling water, alcohol, and ether. BETAORSELLIC ACID is found in Roccella tinctoria grown at the Cape ; it ia obtained like erythric and alphaorsellic acid, which it resembles in proper- ties. Betaorsellic acid contains C^FIjgOjg ; by boiling with water, it yields likewise orsellinic acid, together with hair-like crystals of a silvery lustre, of a substance called roccellinin, which has the composition C 18 H 8 7 . Betaorsellic acid. Orsellinic acid. Roccellinin. The decomposition of betaorsellic acid is obviously analogous to that of erythric acid, the roccellinin representing the picro-erythrin. Evernic acid is extracted by milk of lime from Evernia prunastri, which was formerly believed to contain orsellinic acid. Evernic acid is very diffi- cultly soluble even in boiling water ; it assumes a yellow colour with chlo- 476 LICHENS. ride of lime. When boiled with the alkalis, it yields another crystalline acid, everninic acid, differing from the preceding by its free solubility in boiling water. The composition of evernic acid is represented by the for- mula C 34 H 16 14 , that of everninic acid by C 18 H 10 Og. Evernic acid, when boiled for a considerable time with baryta, yields orcin ; everninic acid does not give a trace of this substance ; it is therefore probable that evernic acid, under the influence of alkalis, yields in addition to everninic acid likewise orsellinic acid, from which the orcin is derived, and that this decomposition is represented by the equation : Evernic acid. Orsellinic acid. Everninic acid. PARELLIC ACID. Lecanora parella contains an acid probably analogous to erythric, alphaorsellic, betaorsellic, and evernic acids, the composition of which is, however, still unknown. By boiling with baryta it yields orsellinic acid andpardlic acid, C )8 H 6 O g . ORCIN is the general product of decompositions of the acids previously described under the influence of heat or alkaline earths. Orcin is best prepared by boiling lecanoric or orsellinic acid, pure or im- pure, with baryta-water, precipitating the excess of baryta by carbonic acid, and evaporating the filtered liquid to a small bulk. It forms, when pure, large, square prisms, which have a slightly yellowish tint, an intensely sweet taste, and a high degree of solubility both in water and alcohol. When heated, orcin loses water and melts to a syrupy liquid which distils un- changed. The crystals of orcin contain C 14 H 8 4 ,2HO. ORCEIN. When ammonia is added to a solution of orcin, and the whole exposed to the air, the liquid assumes a dark red or purple tint, by absorp- tion of oxygen ; a slight excess of acetic acid then causes the precipitation of a deep red powder, not very soluble in water, but freely dissolving in ammonia and fixed alkalis, with a purple or violet colour. This is an azo- tized substance, formed from the elements of the ammonia and the orcin, called orcein ; it probably constitutes the chief ingredient of the red dye- stuff of the commercial articles before mentioned. The composition of orcein is less certain than that of orcin; it probably contains C, 4 H 7 N0 6 , when its formation from orcin, under the joint influence of oxvgen and ammonia, would be represented by the equation : C, 4 H 8 4 ,2HO + 60-fNH, = C 14 H 7 N0 6 Orcin. Orcein. Other substances are occasionally present in lichens ; thus, the Usnea barbata and several other lichens contain usnic acid, a substance crystallizing from alcohol in fine yellowish-white needles with metallic lustre, having the formula C 34 H 18 14 . It gives no orcin by distillation, but a substance similar to it, which probably contains C 38 H ]8 6 , and has been designated by the name of betaorcin. Its formation, which is attended by an evolution of car- bonic acid, is represented by the equation : Usnic acid. Betaorcin. The Parmelia parietina furnishes another new substance, cltrysophamc acid, crystallizing in fine golden-yellow needles and containing C 10 H 4 3 . It is a very stable substance, and may be sublimed without much decomposition. RED AND YELLOW Dl 8. 477 RED AND YELLOW DYES. COCHINEAL. This is a little insect, the Coccus cacti, which lives on several species of cactus, which are found in warm climates, and cultivated for the purpose, as in Central America. The dried body of the insect yields to water and alcohol a magnificent red colouring matter, precipitable by alumina and oxide of tin ; carmine is a preparation of this kind. In cochineal the colour- ing matter is associated with several inorganic salts, especially phosphates and nitrogeuetted substances. Mr. Warren De La Rue, who has published a very elaborate investigation of cochineal, 1 has separated the pure colouring matter, which he calls carminic acid, by the following process. The aqueous decoction of the insect is precipitated by the acetate of lead, and the impure carminate of lead washed and decomposed by hydrosulphuric acid ; the colouring matter thus separated is submitted again to the same treatment. A solution of carminic acid is thus obtained, which is evaporated to dryness, re-dissolved in absolute alcohol, and digested with crude carminate of lead, whereby a small quantity of phosphoric acid is separated, and lastly mixed with ether, which separates a trace of a nitrogenetted substance. The residue now obtained on evaporation is pure carminic acid. It is a purple- brown mass, yielding a fine red powder, soluble in water and alcohol in all proportions, slightly soluble in ether. It is soluble without decomposition in concentrated sulphuric acid, but readily attacked by chlorine, bromine, and iodine, which change its colour to yellow. It resists a temperature of 276-8 (136C), but is charred when heated more strongly. Carminic acid is a feeble acid. The composition of the substance, dried at 248 (120C), is represented by C 28 H 14 0, 6 , which formula was corroborated by the analysis of a copper-compound, CuO,C 28 H 14 16 . By the action of nitric acid upon carminic acid, together with oxalic acid, a splendid nitrogenetted acid, crystallizing in yellow rhombic plates, is ob- tained. This substance, to which the name nitrococcusic acid was given, is bibasic ; it contains C, 6 H 3 N 3 0, 6 ,2HO. It is soluble in cold, and more so in boiling water, readily soluble in alcohol and ether. Nitrococcusic acid is evidently derived from a non-nitrogenous compound in which part of the hydrogen is replaced by the elements of hyponitric acid. Like the sub- stances of this class, it explodes when heated. In the mother-liquor, from which the carminic acid has been separated, Mr. Warren De La Rue discovered a white, crystalline, nitrogenetted sub- stance, for which he established the formula C IS H,,N0 6 . This substance is identical with tyrosine, which will be mentioned in the section on Animal Chemistry. MADDER. The root of the Rubia tinctorum, cultivated in southern France, the Levant, &c., is the most permanent and valuable of the red dye-stuffs. In addition to several yellow colouring matters, which are of little impor- tance for the purposes of the dyer, madder contains two red pigments which are called alizarin andpurpurin. These substances have been the subject of very extensive researches by Debus, Higgins, and especially by Schunk. The latest papers on madder have been published by Wolff and Strecker, whose formulae are quoted in the following abstract. ALIZARIN. The aqueous decoction of madder is precipitated by sulphurio acid, and the precipitate washed and boiled with sesquichloride of aluminum, which dissolves the red pigments; an insoluble brownish residue remaining behind. The solution, when mixed with hydrochloric acid, yields a precipi- tate consisting chiefly of alizarin, however, still contaminated with purpurin. The impure alizarin thus obtained may be farther purified by again throwing 1 Mem. of the Chem. Soc. vol. iii. p. 454. 478 RED AND YELLOW DYES. down the alcoholic solution with hydrate of alumina, and boiling the preci- pitate with a concentrated solution of soda, which leaves a pure compound of alumina and alizarin behind. From this the alizarin is separated by hydrochloric acid, and re-crystallized from alcohol. Pure alizarin crystal- lizes in splendid red prisms, which may be sublimed. It is but slightly solu- ble in water and in alcohol, but dissolves in concentrated sulphuric acid with a deep red colour. On addition of water, the colouring matter is re-precipi- tated unchanged. It is also soluble in alkaline liquids, to which it imparts a magnificent purple colour. It is insoluble in cold solution of alum. Ali- zarin is the chief colouring matter of madder ; it contains C 2o H 6 6 -j-4IIO, arid is a feeble acid ; but a few definite compounds with mineral oxides have been prepared, among which a lime-compound, C 20 H 6 6 ,3CaO-f-3HO, may be quoted. The action of nitric acid upon alizarin gives rise to the formation of oxalic acid and phthalic acid, a substance which will again be men- tioned among the products of decomposition of naphthalin. C 20 H 6 6 -f 2HO + 80 = 2(C 2 3 ,HO) + C 16 II 6 8 Alizarin. Phthalic acid. PURPURIX. Madder is allowed to ferment and then boiled with a strong solution of alum. The solution, when mixed with sulphuric acid, yields a red precipitate, which is purified by re-crystallization from alcohol. Purpurin thus obtained crystallises in red needles, which contain C, 8 H 6 6 -f-2HO, i. e., 2 eq. of carbon less than alizarin. When treated with nitric acid, purpurin, like alizarin, furnishes oxalic and phthalic acids. Purpurin likewise con- tributes to the tinctorial properties of madder, but less so than alizarin. Together with alizarin and purpurin, several other substances occur in madder, among which may be noticed an orange pigment, rttbfadn, convertible by oxidizing agents into a peculiar acid, rubiacic acid, a yellow pigment, xanthin, a bitter principle, rubian, sugar, pectic acid, and several resins, &c. Garancin is a colouring material, which is produced by the action of sul- phuric acid upon madder. This substance possesses a higher tinctorial power than madder itself. The beautiful Turkey red of cotton cloth is a madder-colour ; it is given by a very complicated process, the theory of which is not perfectly elucidated. An abstract of it will be found in Prof. Graham's " Elements of Chemistry." SAFFLOWER. This substance contains a yellow and a red colouring matter, the latter being insoluble in water, but soluble in alkaline liquids. The saf- flower may be exhausted with water acidulated with acetic acid, and the solution mixed with acetate of lead, and filtered from the dark-coloured impure precipitate. The lead-compound of the yellow pigment may then be thrown down by addition of ammonia, and decomposed by sulphuric acid. In its purest form the yellow matter forms a deep yellow, uncrj'stallizable, and very soluble substance, very prone to oxidation. In its lead-compound it has probably the composition G^H 12 13 . The red matter or carthanrin is obtained from the residual safflower by a dilute solution of carbonate of soda ; pieces of cotton wool are immersed in the liquid, and acetic acid gradually added. The dried cotton is then digested in a fresh quantity of the alkaline solution, and the liquid supersaturated with citric acid, which throws down the carthamin in carmine-red flocks. It forms, when pure and dry, an amorphous, brilliant, green powder, nearly insoluble in water, but soluble in alcohol with splendid purple colour. It contains C 14 II 8 7 . Brazil-wood and Logwood give red and purple infusions, which are largely jsed in dyeing ; the colouring principle of logwood is termed hematoxylin, RED AND YELLOW DYES. 479 and has been obtained in crystals. This substance contains C 40 H 7 )5 -{-8IIO, Acids brighten these colours, and alkalis render them purple or blue. Among yellow dyes, quercitron-bark, fustic-ivood, and saffron may be men- tioned, and also turmeric ; these all give yellow infusions to water, and furnish more or less permanent colours. Purree or Indian yellow, a body of unknown origin, used in water-colour painting, according to the researches of Stenhouse and Erdmann, is a com- pound of magnesia with a substance termed purreic or euxanthic acid. The latter, when pure, crystallizes in nearly colourless needles, sparingly soluble in cold water, and of sweetish bitter taste. It forms yellow compounds with the alkalis and earths, and is decomposed by heat with production of a neutral crystalline sublimate, purrenone or euxanthone. Purreic acid contains ^40^i6^2i purrenone C 13 H 4 4 . By the action of chlorine, bromine, and nitrio acid, a series of substitution-products are formed. Certain of the products of the action of nitric acid upon aloes resemble very much some of the derivatives of indigo, without, however, it seems, being identical with them. Powdered aloes, heated for a considerable time with excess of moderately strong nitric acid, yields a deep red solution, which deposits on cooling a yellow crystalline mass. This, purified by suitable means, constitutes chrysammic acid ; it crystallizes in golden-yellow scales, which have a bitter taste, and are but sparingly soluble in water. Its potassa- salt has a carmine-red tint, and exhibits a green metallic lustre, like that of murexide. The formula of chrysammic acid is not perfectly established. It is probably C 14 HN 2 O n ,HO. Like picric acid, it yields with chloride of lime, chloropicrin. The mother-liquor from which the chrysammic acid has been deposited contains a second acid, the chrysolepic, which also forms golden- yellow, sparingly soluble, scaly crystals. The potassa-salt forms small, yellow prisms, of little solubility. It explodes by heat. Chrysolepic acid contains C, 2 H 2 N 3 13 ,HO ; it is isomeric and possibly identical with picric acid. To these may be added the styphnic acid recently described by MM. Boettger and Will, produced by the action of nitric acid of sp. gr. 1-2 upon assafcetida and several v tier gum-resins and extracts. Purree, when treated with excess of nitric acid, likewise yields styphnic acid. It crystallizes, when pure, in slender, yellowish-white prisms, sparingly soluble in water, readily dissolved in alcohol and ether. It has a purely astringent taste, and stains the skin yellow. By gentle heat it melts, and on cooling becomes crystalline ; suddenly and strongly heated, it burns like gunpowder. It also furnishes chloropicrin. The salts of this substance mostly crystallize in orange-yellow needles, and explode with great violence by heat. Styphnio acid contains C, 2 H 2 N 3 Oi 5 ,HO, i. e., picric acid+2 eq. of oxygen. It may be viewed as a nitro-substitute of the same acid, C 12 H 5 3 ,HO, which, by the in- troduction of chlorine in the place of hydrogen, furnishes chloroniceic acid (see page 463). Hypothetical niceic acid C !2 H 5 ,0 3 ,HO ChloKmiceic acid t. C 12 (H 4 C1)0 8 ,HO Trinitroniceic acid Ci 2 H 2 (N0 4 )30 3 ,HO. 480 OILS AND FATS. SECTION VII. OILS AND FATS. THE oils and fats form an interesting and very natural group of substances, which have been studied with great success. The vegetable and animal fats agree so closely in every respect, that it will be convenient to discuss them nnder one head. Oily bodies are divided into volatile and fixed: the former are capable of being distilled without decomposition, the latter are not. When dropped or spread upon paper, they all produce a greasy stain ; in the case of a vola- tile oil, this stain disappears when the paper is warmed, which never happens with a fixed fatty substance. All these bodies have an attraction, more or less energetic, for oxygen : this in some cases reaches such a height as to occasion spontaneous inflammation, as in the instance of large masses of cot- ton or flax moistened with rape or linseed oil. The effect of this absorption of oxygen leads to a farther classification of the fixed oils into drying and non-drying oils, or those which become hard and resinous by exposure to air, and those which thicken slightly, become sour and rancid, but never solidify. To the first class belong the oils used in painting, as linseed, rape, poppy- seed, and walnut ; and to the second, olive and palm-oils, and all the oils and fats of animal origin. The parts of plants which contain the largest quanti- ties of oil are, in general, the seeds. Olive-oil is, however, obtained from the fruit itself. The leaves of many plants are varnished on their upper surface with a covering of waxy fat. Among the natural orders, that of the cruciferce is conspicuous for the number of oil-bearing species. The fixed oils in general have but feeble odour, and scarcely any taste ; whenever a sapid oil or fat is met with, it is invariably found to contain some volatile oily principle, as in the case of common butter. They are all insolu- ble in water, and but slightly soluble in alcohol, with the exception of castor- oil ; in ether and in the essential oils, on the other hand, they dissolve in large quantity. The consistence of these substances varies from that of the thinnest olive- oil to that of solid, compact suet; and this difference proceeds from the vari- able proportions in which the proximate solid and fluid fatty principles are associated in the natural product. All these bodies may, in fact, by mere mechanical means, or by the application of a low temperature, be separated into two, or sometimes three, different substances, which dissolve in, or mix with each other, in all proportions. Thus, olive oil exposed to a cold of 40 (4-5C) deposits a large quantity of crystalline solid fat, which may be separated by filtration and pressure ; this is termed margarin, from its pearly aspect. That portion of the oil which retains its fluidity at this, or even an inferior degree of cold, has received the name olein or elain. Again, a solid animal fat may, by pressure between folds of blotting-paper, be made much harder, more brittle, and more difficult of fusion. The paper becomes im- pregnated with a permanently fluid oil, or olein, while the solid part is found to consist of a mixture of two solid fats, one resembling the margarin of olive- OILS AND FATS. 481 oil, and the other having a much higher melting-point, and other properties Which distinguish it from that substance ; it is called stearin. These remarks apply to all ordinary oils and fats : it is, however, by no means proved that the olein and margarin of all vegetable and animal oils are identical; it is very possible that there may be essential differences among them, more especially in the case of the first-named substance. Fixed fatty bodies, in contact with alkaline solutions at a high tempera- ture, undergo the remarkable change termed saponification. "When stearin, inargarin, or olein, are boiled with a strong solution of caustic potassa or soda, they gradually combine with the alkali, and form a homogeneous, viscid, transparent mass, or soap, freely soluble in warm water, although in- soluble in saline solutions. If the soap so produced be afterwards decom- posed by the addition of an acid, the fat which separates is found completely changed in character ; it has acquired a strong acid reaction when applied in a melted state to test-paper, and it has become soluble with the greatest facility in warm alcohol ; it is in fact a new substance, a true acid, capable of forming salts, and a compound ether, and has been generated out of the elements of the neutral fat under the influence of the base. Stearin, when thus treated, yields stcaric acid, margarin gives margaric acid, olein gives oleic acid, and common animal fat, which is a mixture of the three neutral bodies, affords by saponification by an alkali and subsequent decomposition of the soap, a mixture of the three fatty acids in question. These bodies are not, however, the only products of saponification ; the change is always accompanied by the formation of a very peculiar sweet substance, called glycerin, which remains in the mother-liquor from which the acidified fat has been separated. The process of saponification itself proceeds with perfect facility in a close vessel ; no gas is disengaged ; the neutral fat, of whatso- ever kind, is simply resolved into an alkaline salt of the fatty acid, or soap, and into glycerin. 1 STEARIN AND STEARIC ACID. Pure animal stearin is most easily obtained by mixing pure mutton-fat, melted in a glass flask, with several times its weight of ether, and suffering the whole to cool. Stearin crystallizes out, while margarin and olein remain in solution. The soft pasty mass may then be transferred to a cloth, strongly pressed, and the solid portion still farther purified by re-crystallization from ether. It is a white friable substance, in- soluble in water, and nearly so in cold alcohol ; boiling spirit takes up a small quantity. Boiling ether dissolves it with great ease, but when cold retains only -^^^ of its weight. The melting-point of pure stearin, which is one of its moVt important physical characters, may be placed at about 130 (54-5C). When stearin is saponified, it yields, as already stated, glycerin and stearic acid. The latter crystallizes from hot alcohol in milk-white needles, which are inodorous, tasteless, and quite insoluble in water. It dissolves in its own weight of cold alcohol, and in all proportions at a boiling heat; it is likewise soluble in ether. Alkaline carbonates are decomposed by steario acid. Exposed to heat, it fuses, and at a higher temperature, if air be ex- cluded, volatilizes unchanged. The melting-point of stearic acid is about 158 (70C). MARGARIN AND MARGARIC ACID. The ethereal mother-liquor from which stearin has separated in the process just described yields on evaporation a soft-solid mixture of margarin and olein with a little stearin. By compres- 1 We aro indebted to M. Chevreul for the first series of scientific researches on the fixed oils and fats, and on the theory of saponification. These admirable investigations are detailed in the early volumes of the " Annales de Chiinie et de Physique," and were afterwards pub- lished in a separate form in 1823, under the title of " Rechf.rches chimiques sur les Corps gra* d'Oi'igine animate." 41 482 OILS AND FATS. sion between foldrf of blotting-paper, and re-solution in ether, it is rendered tolerably pure. In this state margarin very much resembles stearin ; it is, however, more fusible, melting at 116 (46-6C), and very much more solu- ble in cold ether. By saponification it yields glycerin and margaric acid. The properties of this last-named substance resemble in the closest mannei those of stearic acid ; it is different in composition, however, more solubl in cold spirit, and has a lower melting-point, viz., 140 (GOC) or there- abouts. Its salts also resemble those of stearic acid. A more or less impure mixture of stearic and margaric acids is nof very extensively used as a substitute for wax and spermaceti in the manu- facture of candles. It is prepared by saponifying tallow by lime, decom- posing the insoluble salt so formed by boiling with dilute sulphuric acid, and then pressing out the fluid or oily portion from the acidified fat. The solid part of olive-oil is said to be a definite compound of true mar- garin and olein, inasmuch as its melting-point, 68 (20C), is constant; it gives by saponification a mixture of margaric and oleic acids. OLEIN AND OLEIC ACID. It is doubtful whether a perfectly pure olein has yet been obtained ; the separation of the last portions of margarin, with which it is always naturally associated, is a task of extreme difficulty. Any fluid oil, animal or vegetable, which has been carefully decolorized, and filtered at a temperature approaching the freezing-point of water, may be taken as a representative of the substance. Oleic acid much resembles olein in physical characters, being colourless and lighter than water, but it has usually a-distinct acid reaction, a sharp taste, and is miscible with alcohol in all proportions. When submitted to the action of nitric acid, it yields almost the whole series of acids, of which formic, acetic, propionic, butyric, &c., are members, and which has been mentioned in a previous section of this work (see page 395). When stearic or margaric acid, or ordinary animal fats, are exposed to destructive distillation, they yield margaric acid, a fatty body incapable of saponification, termed margarone, a liquid carbide of hydrogen, and various permanent gases. The neutral fats furnish besides an extremely pungent and even poisonous, volatile principle, called acrolein, described farther on. In the manufacture of ordinary soaps both potassa and soda are used ; the former yielding soft, and the latter hard soaps. Animal and vegetable fats are employed indifferently, and sometimes resin is added. Composition of the preceding Substances. The following are the formulae at present assigned to the fatty acids in question : they are chiefly founded on investigations made at Giessen. Stearic acid C 68 H 66 5 ,2HO Margaric acid C 68 H 66 6 ,2IIO. Margaric is thus seen to differ from stearic acid in containing 1 eq. of oxy- gen more, and stearic acid can actually be converted into margaric by the action of oxidizing agents. Stearic acid is bibasic, and in its crystallized state contains 2 eq. of water. Margaric acid, as represented by the above formula, is likewise bibasic, but many chemists consider it as a monobasic acid 34113303,110; its bibasic nature being, in fact, by no means so we".l established as that of stearic acid. The subject requires farther examina- tion, especially since an opinion has lately been expi-essed, that stearic and margaric acids are isomeric modifications of the same acid. 1 1 According to Huntz, margaric acid is a mixture of stearic and palmitic acids, and that one part of stearic acid mixed with 9-10 parts of palmitic acid (melting at 144; G'2-2C), pro- duced a compound fusing at 140(COC). and possessing all the properties and ultimate corn- position of margaric acid. Moreover, when margaric acid obtained from mutton-fat was acted on by acetate of baryta, the first precipitate gave an acid melting at 135 '5 (57C), and soliii- OILS AND FATS. 483 r)l ,2HO. The remarkable pro- duction of this substance from malic acid by a process of fermentation has been already mentioned (see page 415). Sebacic add is a constant product of the destructive distillation of oleic acid, olein, and all fatty substances containing tbose bodies; it is extricated by boiling the distilled matter with water ; it has also been lately formed by the action of potassa on castor-oil (see page 488). It forms small pearly crystals resembling those of benzoic OILS AND FATS. 485 aoicl. It has a faint acid taste, is but little soluble in cold water, melts when heated, arid sublimes unchanged. Sebacic acid is composed of C 10 H 8 3 ,HO or C 20 H 16 6 ,2HO. BUTTER ; VOLATILE ACIDS OF BUTTER. Common butter chiefly consists of n solid crystallizable, and easily fusible fat, a fluid oily substance, and a yellow colouring matter, besides mechanical impurities, as casein. The oily part appears to be a mixture of olein and a peculiar odoriferous fatty prin- ciple, butyrin, not yet isolated, which by saponification yields four distinct volatile acids, the butyric, the caproic, the caprylic, and the capric : these are most easily obtained by saponifying butter with potassa or soda, adding an excess of sulphuric acid, and distilling. The acid watery liquid obtained may then be saturated with an alkali, evaporated to a small bulk, and then distilled with excess of sulphuric or phosphoric acid in a retort. The mixed acids are separated by taking advantage of the unequal solubility of their baryta-salts ; the less soluble salts of the mixture, amounting to about ^ of the whole mass, contain capric and caprylic acids ; the larger and more soluble portion, the caproic and butyric acids. BUTYRIC ACID, when pure, is a thin colourless liquid, of pungent rancid odour and sour taste. It is miscible in all proportions with water and alcohol. Its density is 0-963, and it boils and distils unchanged at 327 (lt>4C). It is attacked by chlorine, with production of oxalic acid and of a chlorinetted compound not examined. Butyric acid contains C 8 H 7 3 ,HO. CAPROIC ACID forms a colourless liquid, of sp. gr. 0-922, boiling at 388 -4 (198C); it has a feeble odour, somewhat resembling that of acetic acid, Mid is much less soluble in water than butyric acid. It contains C 12 H H 3 ,HO. The artificial formation of this acid from cyanide of amyl has been already noticed (see page 390). Caproic acid has been lately submitted to the action of the galvanic current. Messrs. Brazier and Gossleth have proved that it is analogous to that of valeric acid, and that the principal product is the hydro- carbon amyl C 10 H n previously obtained by Dr. Frankland by the action of zinc upon iodide of amyl (see page 390). CAPRYLIC ACID is chiefly remarkable for exhaling a powerful and disgusting odour of perspiration. It contains Cj 6 H, 5 3 ,HO. This acid has been lately obtained by a very interesting reaction, namely, by the oxidation of the new caprylic alcohol discovered by M. Bouis among the products of decomposition of castor oil (see page 488). CAPRIC ACID much resembles the caproic ; it has a mixed odour of acetic acid and the smell of the goat, and is very sparingly soluble in water. Its formula is C 20 H, 9 3 ,HO. The simple relation existing between the formulae of the volatile acids of butter, which are all members of the series of fatty acids, has been already pointed out (see page 395). These acids exist ready formed in rancid butter and in cheese, associated with valeric acid. They are produced in small quantity by the saponifica- tion of most animal and some vegetable fats, and are generated, as has been mentioned already (see page 482), together with other products, by the action of nitric acid upon oleic acid. Butyric acid has been observed also as a product of the spontaneous decomposition of fibrin, and pre-exists in the leguminous fruit known as St. John's bread. Whale and seal oil yield by saponification a volatile acid greatly resembling the preceding, called phocenic or delphinic acid ; it was formerly believed to be a peculiar acid, but it is according to recent experiments nothing but valeric acid. Butyric acid has acquired a certain degree of importance from the curious discovery of M. Pelouze, that sugar, under particular circumstances, is sus ceptible of becoming converted into that substance. A tolerably strong 41* 486 OILS AND FATS. solution of common sugar mixed with a small quantity of casein and some chalk, and exposed for some time to a temperature of 95 (35C), yields, by a species of fermentation, in which the casein is the active ferment, a large amount of butyrate of lime ; carbonic acid and hydrogen gases are extricated during the whole period. This change may be thus expressed (W^ = 4HO-f8H-f8CO a -f 2(C 8 H 7 3 ,HO) Grape-sugar. Butyric acid. The mixture directed for lactic acid answers well (see page 350) , laciate of lime is first formed in large quantity, and afterwards gradually dissolved and converted into butyrate, which may be decomposed by sulphuric acid and distilled. This is an exceedingly interesting case of the half-artificial formation of an animal product. WAX. Common bees-ivax, freed from its yellow colouring matter by bleaching, may be separated by boiling alcohol into two different proximate principles, cerin and myricin. The first is a white crystalline substance, soluble in about 16 parts of boiling spirit, and melting at 144 (62-2C) ; it is the more abundant of the two. It is easily saponified by a solution of caustic potassa. According to Brodie's valuable experiments it consists chiefly of cerotic acid 54115303,110, which belongs to the series of fatty acids (see page 395). The same body in a very interesting form of combi- nation exists in Chinese wax, which, according to Brodie, is a compound ether containing cerotic acid combined with the ether of cerotylic alcohol C 54 H 55 0,HO. It may be viewed as cerotate of oxide of cerotyl C 34 H 55 0, C^Hg-jOg corresponding to the acetic ether of the wine-alcohol-series. When heated with potassa it undergoes the changes peculiar to compound ethers; yielding on the one hand cerotate of potassa, and on the other hand cerotylic alcohol. Myricin is very much less soluble in alcohol, and rather more fusible. It is saponified with difficulty by a dilute solution of caustic potassa, palmitic acid C 32 H 31 3 ,HO (see page 484), combines with the po- tassa, and a substance C 60 H 61 O,HO, belonging to the series of alcohols, is set free, which has been termed melissic alcohol. Hence myricin is like- wise a compound ether, namely, palmitate of oxide of melissyl C 92 H S2 4 = CeoHoAC^fW SPERMACETI. The soft-solid matter found in very large quantity in a remarkable cavity in the head of the spermacetic whale, when submitted to pressure, yields, as is well known, a most valuable fluid oil, and a crystal- line, brownish substance, which, when purified, becomes the beautiful snow- white article of commerce, spermaceti. This substance appears, by the most recent experiments, to be a neutral fatty body of the constitution of compound ethers, and not, as formerly supposed, a mixture of several proxi- mate principles. It melts at 120 (48 -8C), and when cooled under favour- able circumstances, forms distinct crystals. Boiling alcohol dissolves it in small quantity, and ether in much larger proportion. Spermaceti is sapo- nified with great difficulty : two products are obtained, a substance CggHg/Xj belonging to the series of alcohols (see page 394), to which the name cetylic (ethalic) alcohol has been given, and cetylic (ethalic) acid C 32 H 32 4 ; the fii-st is a crystallizable fat, whose melting-point is nearly the same as that of spermaceti itself, but its solubility in alcohol is much greater; it is also readily sublimed without decomposition. Cetylic acid stands to cetylic alcohol in the same relation as acetic acid to ordinary alcohol, and may be actually procured from the latter by oxidation ; it resembles in many re- spects margaric acid. By oxidation by nitric acid, spermaceti yields a large quantity of succinic acid. * Spermaceti is composed of C^Hg/^suCag^OjCg.^^ ; it is cctylate of OILS AND FATS. 487 oxide of cetyl, and represents in the cetyl-series the acetic ether of the common alcohol-series. 1 CHOLESTERIN. This substance is found in small quantity in various parts of the animal system, as in the bile, in the brain and nerves, and in 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 cholesterin crystallizes in brilliant, colourless plates. It has the characters of a fat, is insoluble in water, taste- less and inodorous ; it is freely soluble in boiling water, and also in ether. It altogether resists saponification. Cholesterin melts at 278 (136C), and contains probably C 26 H 2 20. CANTHARIDIN, the active principle of the Spanish fly, may be here men- tioned. It is a colourless, crystallizable, fatty body, extracted by ether or alcohol from the insect ; it is insoluble in water and dilute acids, and vola- tile when strongly heated. The vapour attacks the eyes in a very painful manner. Cantharidin contains C 10 H 6 4 . ACROLEIN. When a neutral fat is subjected to destructive distillation, it furnishes, as already mentioned, among other products, an excessively vola- tile acrid substance, which attacks the eyes arid the mucous membrane of the nose most distressingly. As the neutral fats alone yield this body, and the fatty acids never, it is known to arise from the elements of the glycerin ; and glycerin itself under certain circumstances may be made to produce acrolein abundantly. It is best prepared by distilling glycerin with bisul- phate of potassa ; both the preparation and purification are attended with great difficulties. Pure acrolein is a thin, colourless, highly volatile liquid, lighter than water, and boiling at 126 (52-9C). Its vapour is irritating beyond descrip- tion. It is sparingly soluble in water, freely in alcohol and ether. Accord- ing to M. Redtenbacher it contains C 6 H 4 2 . When exposed for some time to the air, or when mixed with oxide of silver, acrolein oxidizes with avidity, and passes into acrylic acid, which re- sembles in very many particulars acetic and propionic acids ; it contains C 6 H 3 3 ,HO. Acrolein by keeping undergoes partial decomposition, yielding a white, flocculent, indifferent body, disacryle ; the same substance is some- times produced together with acrylic acid by exposure to the air. In con- tact with alkalis, acrolein suffers violent decomposition, producing, like aldehyde, a resinous body. The action of sulphuric acid upon olive-oil has been studied by M. Fre"my. When the oil is slowly and cautiously mixed with half its volume of concen- trated sulphuric acid, all rise of temperature being avoided, a homogeneous liquid is obtained, which, when mixed with a little water, separates into two layers, the undermost consisting of sulpho-glyceric and free-sulphuric acid, and the upper and syrupy portion of two compound acids, the sulphomargaric and sulpholeic. These latter dissolve in a large quantity of water, but after some time undergo decomposition into sulphuric acid and several new fatty acids, to which the names metamargaric, hydromargaric, hydromargaritic, metoleic, and hydroleic were given. The first three are derived from the ele- , _ 1 According to the investigations of ITeintz, the composition of spermaceti is of a Tory coirplex diameter, consisting of a series of acids differing in constitution by Calls combined with ethal. vi/,. : Margethal = margarate of oxide of cetyl C24lIs303,C 3 2ir g3 Palmetlial = palmitate C32FI 3I 3 ,C 32 H 33 O Cetethal = cetate CsuIl^Oii.CaaHasO Myristethal = myri.tate CihllaiOs.CssIlasO Cocethal = cocinate CiellasOsjCi.HasO. R. B. 488 OILS AND FATS. tnents of the sulphomargaric acid; they are solid and crystallizable, and much resemble ordinary margaric acid, differing slightly from that substance nnd from each other in their melting-points, degree of solubility in alcohol, &c. The metoleic and hydroleic acids are fluid, and are derived from the sulpholeic acid of the mixture. They yield carbonic acid and liquid hydro- carbons by destructive distillation. The composition of these fatty acids is yet uncertain, but in all probability they only differ from margaric and oleic acids by the elements of water. The action of sulphuric acid upon the oil is thus somewhat similar to the effect of saponification, the neutral fat being resolved into margaric and oleic acids and glycerin, the whole of which then combine with the elements of sulphuric acid to form compounds belong- ing to the large group of substances of which sulphovinic acid is the typical member. The sulphuric saponification of fatty bodies is now carried out on & very large scale for producing cheaper varieties of "stearin candles." For this pui'pose, inferior fatty bodies, such as palm-oil, are mixed with 5 or 6 per cent, of concentrated sulphuric acid, and exposed to a temperature of 350 (177C) produced by overheated steam. After cooling, the black mass thus obtained crystallizes to a tolerably solid fat, which is washed once or twice with water, and then submitted to distillation by the aid of steam, heated to about 560 (293-5C). The product of the distillation, which is beautifully white, may be at once used for making candles ; frequently, however, it un- dergoes the processes of cold and hot pressing, whereby a much more solid fat is obtained. CASTOR OIL, which differs in some respects from the ordinary vegetable oils, yields, by oxidation with nitric acid, a peculiar product, namely, a vola- tile fatty acid to which the term cenanlhylic has been applied. It forms a colourless, oily liquid of aromatic odour and burning taste, and slightly soluble in water. It refuses to solidify at a very low temperature, and can- not be distilled alone without some decomposition, although its vapour passes over readily with that of water. This body has distinct acid properties, forms a series of salts and an ether, and contains C ]4 H 13 3 , HO. Under the influence of the galvanic current it undergoes a decomposition similar to that of valei-ic acid, according to Messrs. Brazier and Gossleth, the principal product being, together with a hydrocarbon containing equal equivalents of carbon and hydrogen, an oily substance C 12 H 13 , boiling at 395 -6 (202C), to which the name caprogl has been given, and which may be viewed as the radical of the alcohol of caproic acid C ]2 H 13 0,HO, still to be discovered. Castor-oil has lately become the source of a new alcohol in the hands of M. Bouis. According to his researches, there is present in castor-oil a pecu- liar oleic acid, ricinoleic acid, which contains CggH^Og.HO, i. e., 2 eq. of oxygen more than common oleic acid. If this acid, or more conveniently castor-oil itself, be heated with solid hydrate of potassa, an oily liquid distils over, boiling at 356 (180C), which is the alcohol of caprylic acid. It con- tains C, 8 H 17 0,HO, and is readily converted into caprylic acid (see page 485), by treatment with oxidizing agents. The residue in the retort contains sebacate of potassa. This transformation is represented b; T the following equation : CssH^OsJIO -f 2(KO,IIO) -_= 2KO,C 20 II J6 06 -f C 16 H 17 0,HO -f 2H Ricinoleic acid. Sebacate of potassa. Caprylic alcohol. VOLATILE OILS. The volatile oils of the vegetable kingdom are exceedingly numerous : they are secreted by plants, and confer upon their flowers, fruits, leaves, and VOLATILE OILS. 489 wood their peculiar odours. These substances are mostly procured by dis- tilling the plant, or part of the plant, with water ; their points of ebullition always lie above that of water; nevertheless, at 212 (100C) the oils emit: vapour of very considerable tension, which is carried over mechanically, and condensed with the steam. The milky, or turbid liquid obtained, when left at rest, separates into oil and water. Sometimes the oil is heavier than the water, and sinks to the bottom ; sometimes the reverse happens. The volatile oils, when pure, are colourless: they very frequently, how- ever, have a yellow, and in rarer cases, a green colour, from the presence of impurity. The odour of these substances is usually powerful, and their taste pungent and burning. They resist saponification completely, but when exposed to the air frequently become altered by slow absorption of oxygen, and assume the character of resins. They mix in all proportions with fat oils, and dissolve freely both in ether and alcohol ; from the latter solvent they are precipitated by the addition of water. As already mentioned, the volatile oils communicate a greasy stain to paper, which disappears by warm- ing ; by this character any adulteration with fixed oils can be at once de- tected. A solid, crystalline matter, corresponding to the margarine of the common oils, frequently separates from these bodies ; it bears the general name of slearoptene, and differs probably in almost every case. The essential oils may be conveniently divided into three classes; viz., those consisting of carbon and hydrogen only ; those consisting of carbon, hydrogen, and oxygen ; and those containing in addition sulphur and nitrogen. Oils composed of Carbon and Hydrogen. OIL, or ESSENCE OF TURPENTIN. This substance may be taken as the type or representative of the class ; it is obtained by distilling with water the soft or semi-fluid balsam called in commerce crude turpentine, which exudes from various pines and firs, or flows from wounds made for the purpose in the wood. The solid product left after distillation is common resin. Oil of tur- pentin, when farther purified by rectification, is a thin, colourless liquid, of powerful and well-known odour: its density in the liquid state is 0-865, and that of its vapour 4-764; it boils at 812 (155-5C). In water it dis- solves to a small extent, and in strong alcohol and ether much more freely ; with fixed oils it mixes in all proportions. Strong sulphuric acid chars and blackens this substance ; concentrated nitric acid and chlorine attack it with such violence that inflammation sometimes ensues. Oil of turpentin is composed of C 5 H 4 or C 20 H, 6 . With hydrochloric acid the oil forms a curious compound, which has been called artificial camphor from its resemblance in odour and appearance to that substance. It is prepared by passing dry hydrochloric acid gas into the pure oil, cooled by a freezing mixture. After some time, a white, crys- talline substance separates, which may be strained from the supernatant brown and highly acid liquid, and purified by alcohol, in which it dissolves very freely. This substance is neutral to test-paper, does not aifect nitrate of silver, and sublimes without much decomposition ; it contains C 20 H 17 ,C1, or perhaps C 20 H 16 ,HC1. The dark mother-liquid contains a somewhat similar, but fluid compound. Different specimens of oil of turpentin yield very variable quantities of these substances, which may, perhaps, arise from the co-existence of two very similar and isomeric oils in the ordinary article. When these hydrochlorates are decomposed by distillation with lime, they yield liquid oily products differing in some particulars from the original oil of turpentin, but have the same composition as that substance. That from the solid has received the name of camplnjlcne, and that from the liquid com- pound lerebylene. The hypothetical and non-isolable modifications of the oii 490 VOLATILE OILS. supposed to exist in the solid comphor are termed respectively camphene and terebene. Anothef Isomeric compound, colophene, is produced by distilling oil of tur- pentin with concentrated sulphuric acid. It is a viscid, oily, colourless liquid, of high boiling-point, and exhibiting by reflected light a deep bluish tint, a phenomenon often remarked in bodies of this class. Bromine and iodine also form compounds with oil of turpentin. Oil of turpentin is very largely used in the arts, in painting, and as a sol- vent for resins in making varnishes. Bottles in which rectified oil of turpentin, not purposely rendered anhy- drous, has been preserved, are often studded in the interior with groups of beautiful, colourless, prismatic crystals, which form spontaneously. These have the composition of a hydrate of oil of turpentin. These crystals contain !y chemical change that can be traced in the act of coagulation is the loss of alkali and soluble salts, which are removed by the hot water. A solution of ordinary albumin gives precipitates with excess of sulphuric, hydrochloric, nitric, and nze/a-phosphoric acids; but neither with acetic nor with common or tribasic phosphoric acid. These precipitates, which, though soluble in water, are insoluble in an excess of dilute acid, are looked upon as direct compounds of albumin with the acids in question. Most of the metallic salts, as those of copper, lead, mercury, &c., form insoluble com pounds with albumin, and give precipitates with its solution; hence the value of white of egg as an antidote in cases of poisoning with corrosive sublimate. Alcohol, added in large quantity, precipitates albumin. Tannic acid, or infusion of galls, gives with it a copious precipitate. By these cha- racters the presence of albumin may be readily discovered, and its identi- fication eifected ; a very feebly alkaline liquid, if containing albumin, coagu- lates by heat, becomes turbid on the addition of nitric acid, and previously acidulated by acetic acid, gives a precipitate with solution of corrosive sublimate. It must be remembered, that a considerable quantity of alkali, and very minute quantities of the mineral acids, prevent coagulation by heat, and the addition of acetic acid, indispensable to the mercury-test, produces the same effect. The chemical composition of albumin has been carefully studied ; it con- tains in 100 parts: Carbon 53-5 Hydrogen 7-0 Nitrogen 15-5 Oxygen 22-0 Phosphorus 0-4 Sulphur 1-6 100-0 The existence of unoxidized sulphur in albumin is easily shown ; a boiled egg blackens a silver spoon from a trace of alkaline sulphide formed or sepa- rated during the coagulation ; and a solution of albumin in excess of caustic potassa, mixed with a little acetate of lead, gives on boiling a black preci- pitate containing sulphide of lead. FIBRIN. This substance is found in solution in the blood. It is procured by washing the coagulum of blood in a cloth until all the soluble portions are removed, or by agitating fresh blood with a bundle of twigs, when the fibrin attaches itself to the latter, and is easily removed and cleansed by repeated washing with cold water. The only impurity then remaining is a small quantity of fat, which can be extracted by ether. In the fresh state fibrin forms long, white, elastic filaments ; it is quite tasteless, and inso- luble in both hot and cold water. By long-continued boiling it is partly dissolved. When dried in vacuo, or at a gentle heat, it loses about 80 per cent, of water, and becomes translucent and horny; in this state it closely resembles coagulated albumin. Fresh fibrin wetted with concentrated acetic acid, forms, after some hours, a transparent jelly, which slowly dissolves in pure water ; put into a very dilute caustic alkali, fibrin dissolves com- pletely, and the solution exhibits many of the characters of albumin. Phos- phoric acid produces a similar eifect. Boiled with strong hydrochloric acid for several hours, fibrin is converted into a mixture of leucinc (see page 477) and tyrosine (see page 500). The fibrin of arterial and venous blood is not absolutely the same : wnen the venous fibi'in of human blood is triturated in a mortar with H time? its 42* 498 COMPONENTS OF THE ANIMAL BODY. weight of water and ^ of its weight of nitrate of potassa, and the mixture is left 24 hours or more at a temperature of 100 120 (37-7 48-8C), it becomes gelatinous, slimy, and eventually entirely liquid; in this condition it exhibits all the properties of a solution of albumin which has been neu- tralized by acetic acid. It coagulates by heat, it is precipitated by alcohol, corrosive sublimate, &c., and when largely diluted it deposits a flocculent substance, not to be distinguished from insoluble albumin. 1 With arterial fibrin, on the contrary, no such liquefaction happens, and even the fibrin of venous blood, when long exposed to the air, or to oxygen gas, loses the pro- perty in question. In the soluble state, fibrin is in great measure unknown ; when withdrawn from the influence of life, it coagulates spontaneously after a certain interval, giving rise to the production of the clot which appears in blood left to itself, and which consists of a kind of fine net-work of fibres, swollen with liquid serum, and inclosing the little red colouring particles of the blood, hereafter to be described. Mr. Mulder found dried fibrin, carefully freed from fat, to be composed as follows : Carbon 52-7 Hydrogen 6-9 Nitrogen 15-4 Oxygen 23-5 Phosphorus 0-3 Sulphur 1-2 100-0 The ash, or incombustible portion of fibrin, varying from 0-7 to 2-5 per cent, consists chiefly of the phosphate of lime. CASEIN. This is the characteristic azotized component of milk, and the basis of the various preparations termed cheese ; it is not known to occur in any other secretion. Casein very closely resembles albumin in many par- ticulars, and may even be occasionally confounded with it. Like that sub- stance, it is insoluble in water when in a state of purity, and only assumes the soluble condition in the presence of free alkali, of which, however, a very small quantity suffices for the purpose. To prepare casein, fresh milk is gently warmed with dilute sulphuric acid, the coagulum produced well washed with water, dissolved in a dilute solution of carbonate of soda, and placed in a warm situation to allow the fat or butter to separate from the watery liquid. The latter is then removed by a siphon, and re-precipitated by sul- phuric acid. These precipitations and re-solutions in dilute alkali are several times repeated. Lastly, the insoluble casein is well washed with boiling water, and treated with ether to remove the last traces of fat. In this state it is a white curdy substance, not sensibly soluble in pure water or in alcohol, but dissolved with great ease by water containing a little caustic or carbo- nated alkali. It is also soluble to a certain extent in dilute acids, from which it may be precipitated by cautious neutralization. The precipitate formed by an acid in a strong solution of casein contains acid in combination, which, however, may be entirely removed by washing. In the moist state casein reddens litmus-paper, and masks the reaction of an alkaline car- bonate When incinerated, it leaves about 0-3 per cent, of incombustible matter. A solution of casein in very dilute alkali, as in milk, does not coagulate on boiling. On evaporation the surface becomes covered by a skin, and the * Ik'Lig, Handwortcrbuch tier Chcmic, i. 881. COMPONENTS OF THE ANIMAL BODY. 499 whole eventually dries up to a translucent mass. Acetic acid precipitates casein, which is a distinctive character between that substance and albumin. By fusion with hydrate of potassa casein yields valerianic and butyric acids, besides other products. The most striking property of casein is its coagulability by certain animal membranes. This is well seen in the process of cheese-making, in the pre- paration of the curd. A piece of the stomach of the calf, with its mucous membrane, is slightly washed, put into a large quantity of milk, and the whole slowly heated to about 122 (50 C C). In a short time after this tem- perature has been attained, the milk is observed to separate into a solid, white coagulum, or mass of curd, and into a yellowish, translucent liquid called whey. The curd contains all the casein of the milk, much of the fat, and much of the inorganic matter ; the whey retains the milk-sugar and the soluble salts. It is just possible that this mysterious change may be really due to the formation of a little lactic acid from the milk-sugar, under the joint influence of a slowly decomposing membrane and the elevated tempe- rature, and that this acid may be sufficient in quantity to withdraw the alkali which holds the casein in solution, and thus occasion its precipitation in the insoluble state. The loss of weight the membrane itself suffers in this operation is very small ; it has been found not to exceed T ^ 5 5 part. Casein has been carefully analysed by Mulder ; it contains in 100 parts Carbon 53-83 Hydrogen 7-15 Nitrogen 15-65 x ff n l 23-37 fculpnur ) 100-00 When precipitated by acetic acid and washed with alcohol and ether it contains about 1 per cent, of sulphur. When not treated with acid it con- tains about 6 per cent, of phosphate of lime. A comparison of the composition of these three bodies described is very remarkable, as it shows that they are very closely related in composition. The fibrin contains rather a larger quantity of oxygen than the albumin, and the casein contains no phosphorus. As, however, it is very doubtful whether these substances have been obtained in an unmixed and pure state no for- mulae can be given. PROTEIN. Mulder observed that when albumin, fibrin, or casein was dis- solved in a moderately strong solution of caustic alkali, and digested at 140 (60 -C), or thereabouts, in an open vessel until the liquid ceased to blacken with a salt of lead, and then filtered, and mixed with a slight excess of acetic acid, a copious, snow-white flocculent precipitate fell, and a faint odour of sulphuretted hydrogen was evolved. The new substance he called pro- tein. 1 He stated that it was free from sulphur and phosphorus, and that it was by the combination of different quantities of these elements with pro- tein, that albumin, fibrin, and casein, were produced, the protein pre-existing in each of these substances. It is, however, now admitted, that neither by the above-mentioned treatment, nor in any way, can a substance free from sulphur be obtained, and the protein must therefore be considered as one of the first products of the decomposition of albumin, fibrin, and casein, bv moderately strong caustic alkali. When albumin, fibrin, or casein, are boiled in strong solution of potas??a 1 So called from -xpurtvu, Ital-e the first plate; in allusion to its alleged important relation* to the albumiuous principles. 500 COMPONENTS OF THE ANIMAL BODY. as long as ammoniacal vapours are given off, the liquid then neutralized with sulphuric acid, evaporated to dryness, and the product exhausted by boiling alcohol, three compounds are dissolved out, viz., a soluble, brown extract-like substance, erythroprotide ; a soluble straw-yellow substance, pro- tide, and a curious crystallizable principle, leucine, which forms small colour- less scales, destitute of taste and odour, soluble in water and alcohol, and in concentrated sulphuric acid without decomposition. When heated, it sub- limes unchanged. Leucine contains C I2 H )3 N0 4 , (see page 501). Binoxide and Teroxide of Protein. These names were given by Mulder to products of the long-continued action of boiling water upon fibrin in contact with air; they are said to be the chief ingredients also of the buffy coat of blood in a state of inflammation, being produced at the expense of the fibrin. 1 They cannot be obtained free from sulphur. Binoxide of protein is quite insoluble in water, but dissolves in dilute acids ; when dry, it is dark coloured. The soluble part of the fibrin-decoction contains teroxide of protein, which somewhat resembles, and has been confounded with, gelatin. It is freely soluble in boiling water, and in dilute alkalis. Coagulated albumin is slowly dissolved by boiling water, and said to be converted into this sub- stance. The solution in cold water gives a precipitate with nitric acid which is re-dissolved on the application of heat, and re-precipitated when cooled. A substance closely resembling this in its reactions and composition has been found in the urine of a patient suffering from molleties ossium.* When chlorine gas is passed to saturation into a solution of ordinary albu- min, or either fibrin or casein dissolved in ammonia, a white, flocculent, in- soluble substance falls, which, when washed and dried, becomes a soft yel- lowish powder. This is supposed to be a compound of chlorous acid and protein ; when digested with ammonia, it yields sal-ammoniac and teroxide of protein. GELATIN AND CHONDRIN. Animal membranes, skin, tendons, and even bones, dissolve in water at a high temperature more or less completely, but with very different degrees of facility, giving solutions which on cooling ac- quire a soft-solid, tremulous consistence. The substance so procured is termed gelatin ; it does not pre-exist in the animal system, but is generated from the membranous tissue by the action of hot water. The jelly of calves' feet, and common size and glue, are familiar examples of gelatin in different conditions of purity. Isinglass, the dried swimming-bladder of the stur- geon, dissolves in water merely warm, and yields a beautifully pure gelatin. ]n this state it is white and opalescent, or translucent, quite insipid and in- odorous, insoluble in cold water, but readily dissolving by a slight elevation of temperature. Cut into slices and exposed to a current of dry air, it shrinks prodigiously in volume, and becomes a transparent, glassy, brittle mass, which is soluble in warm water, but insoluble in alcohol and ether. Exposed to destructive distillation, it gives a large quantity of ammonia, in- flammable gases, nauseous empyreumatic oil, and leaves a bulky charcoal containing nitrogen. In a dry state, gelatin may be kept indefinitely ; in contact with water, it putrefies. Long-continued boiling gradually alters it, und the solution loses the power of forming a jelly on cooling. 1 part of dry gelatin or isinglass dissolved in 100 parts of water solidifies on cooling. An aqueous solution of gelatin is precipitated by alcohol, which withdraws the water ; corrosive sublimate in excess gives a white flocculent precipitate, and the same happens with solution of nitrate of the sub- and protoxide of mercury ; neither alum, acetate, nor basic acetate of lead affect a solution of gelatin. With tannic acid or infusion of galls, gelatin gives a copious, * Mnldpr, Annalon dor Chcmie und Pharmacio, xlvii. 323. a Se Philosophical Trans. 1848. COMPONENTS OF THE ANIMAL BODY. 501 whitish, curdy precipitate, which coheres on stirring to an elastic mass, quite insoluble in water, and incapable of putrefaction. Chlorine passed into a solution of gelatin occasions a dense white precipi- tate of chlorite of gelatin, which envelopes each gas-bubble, and ultimately forms a tough, elastic, pearly mass, somewhat resembling fibrin. Boiling with strong alkalis converts gelatin, with evolution of ammonia, into leucine, and a sweet crystallizable principle, gelatin-sugar, or glycocoll, or better, ^glycocine containing C 4 H 5 N0 4 . This remarkable substance was first formed by the action of cold concentrated sulphuric acid upon gelatin, and has lately been obtained by the action of acids upon hippuric acid, which is thereby resolved into benzole acid and glycocine (see page 402). It forms colourless crystals, freely soluble in water, and unites to crystallizable com- pounds with a great number of bodies, acids, bases and salts. Glycociue, when treated with nitrous acid, yields an acid homologous to lactic acid (sea page 402), to which the name of glycolic acid has been given. C 4 H 5 N0 4 -f- N0 3 = C 4 H 4 6 -f 2N-f HO Glycocine. Glycolic acid. This substance, which is but imperfectly studied, appears to be present like- wise in the mother-liquor from which the fulminate of silver has been deposited. There exists a remarkable relation between glycocine, alanine, and leucine, two substances which have been previously described (pages 467 and 500). These three bodies are homologous, as will be seen from the following formulae : Glycocine C 4 H 5 N0 4 Alanine C 6 H 7 N0 4 Leucine C 12 H 13 N0 4 . The deportments of these three substances with nitrous acid is perfectly alike. Leucine, according to M. Strecker, yields a new acid Cj 2 H, 2 6 homo- logous to glycolic and lactic acids, which has not yet been perfectly ex- amined. When a dilute solution of gelatin is distilled with a mixture of bichromate of potassa and sulphuric acid, it yields a number of extraordinary products, as acetic, valerianic, benzoic, and hydrocyanic acids, and two volatile oily principles termed valeronitrile and valeracetonitrile. The former is a thin colom-less liquid, of aromatic odour, like that of hydride of salicyl ; it is lighter than water, boils at 257 (125C), and contains Cj H ? N. The latter much resembles the first, but boils at 158 (70C), and contains CggH^NgOe- Alkalis convert valeronitrile into valerianic acid and ammonia, and valera- cetonitrile into valerianic and acetic acids and ammonia. It is very pro- bable that the latter compound is a mixture of acetonitrile and valeronitrile. Dry gelatin, subjected to analysis, has been found to contain in 100 parts : Carbon 50-05 Hydrogen 647 Nitrogen 1835 Oxygen 25-13 100-00 From these numbers the formulae C 13 II, N 2 5 , and C 52 H 40 N 8 20 , have been deduced. The cartilage of the ribs and joints yields a gelatin differing in some re- spects from the preceding; it is called, by way of distinction, chondrin. 502 COMPONENTS OF THE ANIMAL BODY. Acetate of lead and solution of alum precipitate this substance, which is not the case with common gelatin. To chondrin the formulas C 32 H 26 N 4 14 , and C 48 H 40 N 6 2o have been given. If a solution of gelatin, albumin, fibrin, casein, or probably any one of the more complex azotizecl animal principles, be mixed with solution of sul- phate of copper, and then a large excess of caustic potassa added, the greenish precipitate first formed is re-dissolved, and the liquid acquires a purple tint of indescribable magnificence and great intensity. Gelatin is largely employed as an article of food, as in soups, &c. ; but its value in this respect has been much overrated. In the useful arts, size ard glue are consumed in great quantities. These are prepared from the clip- pings of hides, and other similar matters, inclosed in a net, and boiled with water in a large cauldron. The strained solution gelatinizes on cooling, and constitutes size. Glue is the same substance in a state of desiccation, the size being cut into slices and placed upon nettings, freely exposed to a cur- rent of air. Gelatin is extracted from bones with much greater difficulty . the best method of proceeding is said to be to inclose the bones, previously crushed, in strong metallic cylinders, and admit high-pressure steam, which attacks and dissolves the animal matter much more easily than boiling water ; or, to steep the bones in dilute hydrochloric acid, thereby removing the earthy phosphate, and then dissolve the soft and flexible residue by boiling. There is an important economical application of gelatin, or rather of the material which produces it, which deserves notice, viz., to the clarifying of wines and beer from the finely divided and suspended matter which often renders these liquors muddy and unsightly. When isinglass is digested in very dilute cold acetic acid, as sour wine or beer, it softens, swells, and assumes the aspect of a very light transparent jelly, which, although quite insoluble in the cold, may be readily mixed with a large quantity of watery liquid. Such a preparation, technically called finings, is sometimes used by brewers and wine-merchants for the purpose before-mentioned ; its action on the liquor with which it is mixed seems to be purely mechanical, the gela- tinous matter slowly subsiding to the bottom of the cask, and carrying with it the insoluble substance to which the turbidity was due. KREATIN AND KREATININE. Kreatin was first observed by Chevreul, and has lately been studied very carefully by Professor Liebig, who obtained it from the soup of boiled meat; it is best prepared from the juice of raw flesh by the following 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 colouring 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 kreatin is gradually deposited in crystals, which are easily purified by re-solution in water and digestion with a little animal charcoal. When pure, kreatin forms colourless, brilliant, prismatic crystals, which become dull by loss of water at 212 (100C). They dissolve readily in boil- ing water, sparingly in cold, and are but little soluble in alcohol. The aqueous solution has a weak bitter taste, followed by a somewhat acrid sen- sation. In an impure state the solution readily putrifies. Kreatin is a neu- tral body, not combining either with acids or alkalis. In the crystallized state it contains C 8 H 9 N 3 4 ,2HO. By the action of strong acids, kreatin is converted into Jcreatinine, a power- ful organic base, with separation of the elements of water. The new sub- stance forms colourless prismatic crystals, and is much more soluble in water COMPOSITION OF THE BLOOD. 503 than kreatin ; it has a strong alkaline reaction, forms -with acids crystalli- fcable salts, and contains C 8 H 7 N 3 2 . Kreatinine pre-exists to a small extent in the juice of flesh, together with lactic acid and other bodies yet imperfectly examined. It is also found in conjunction with kreatin in urine. When kreatin is long boiled with solution of caustic baryta, it is gradually resolved into urea, subsequently decomposed into carbonic acid and ammo- nia, and a new organic body of basic properties, sarcosine. The latter, when pure, forms colourless transparent plates, extremely soluble in water, sparingly soluble in alcohol, and insoluble in ether. When gently heated they melt and sublime without residue. Sarcosine forms with sulphuric acid a crystallizable salt, and contains C 6 H 7 N0 4 , being isomeric with lactamide, alariine, and urethane. The mother-liquid from flesh from which the kreatine 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 preci- pitated in a white amorphous condition by alcohol. It probably contains C, H 6 N 2 0, ,H0. 1 Recently, moreover, a kind of sugar, which however does not ferment, has been found in the juice of flesh. It was discovered by Scherer, who calls it inosite, and gives the composition C, 2 H 12 O l2 -f-4HO, This substance crystallizes in beautiful crystals. COMPOSITION OF THE BLOOD ; RESPIRATION. The blood is the general cir- culating fluid of the animal body, the source of all nutriment and growth, and the general material from which all the secretions, however much they may differ in properties and composition, are derived. Food or nourish- ment from without can only be made available by being first converted into blood. It serves also the scarcely less important office of removing and carrying off principles from the body which are hurtful, or no longer re- quired. In all vertebrated animals the blood has a red colour, and probably in all cases a temperature above that of the medium in which the creature lives. In the mammalia this is very apparent, and in the birds still more so. The heat of the blood is directly connected with the degree of activity of the respiratory process. In man the temperature of the blood seldom varies much from 98 (36-6C), when in a state of health, even under great vicissi- tudes of climate; in birds it is sometimes as high as 109 (42 -SC). To these two highest classes of the animal kingdom, the mammifers and the birds, the observations about to be made are intended especially to apply. In every creature of this description two kinds of blood are met with, which differ very considerably in their appearance, viz., that contained in the left side of the heart and in the arteries generally, and that contained in the right side of the heart and in the veins : the former, or arterial blood, has a bright red colour, the latter, the venous blood, is blackish purple. Farther, the conversion of the dark into the florid blood may be traced to what takes place during its exposure to the air in the lungs, and the oppo- site change, to what takes place in the capillaries of the general vascular system, or the minute tubes or passages, distributed in countless numbers throughout the whole body, which connect the extremities of the arteries arid veins. When compared together, little difference of properties or com- position can be found in the two kinds of blood ; the fibrin varies a little, that from venous blood being, as already mentioned, soluble in a solution of nitrate of potassa, which is not the case with arterial fibrin." It is very prone, besides, to absorb oxygen, and to become in all probability partly changed to the substance called binoxide of protein, which no doubt exists 1 Liebig, Chemistry of Food. 504 COMPOSITION OF TIIE BLOOD/ in the fibrin of arterial blood. The only other notable point of difference ia in the gaseous matter the blood holds in solution, carbonic acid predomina- ting in the venous, and free oxygen in the arterial variety. In its ordinary state the blood has a slimy feel, a density varying from 1-053 to 1-057, and a decidedly alkaline reaction ; it has a saline and disa- greeable taste, and, when quite recent, a peculiar odour or halitus, which almost immediately disappears. An odour may, however, afterwards be de- veloped by an addition of sulphuric acid, which is by some considered char- acteristic of the animal from which the blood was obtained. The coagulation of blood in repose has been already noticed, and its cause traced to the spontaneous solidification of the fibrin : the effect is best seen when the blood is received into a shallow vessel, and left to itself some time. No evolution of gas or absorption of oxygen takes place in this process. By strong agitation coagulation may be prevented ; the fibrin in this case sepa- rates in cohering filaments. To the naked eye the blood appears a homogeneous fluid, but it is not so in reality. When examined by a good microscope, it Fi S- 174> is seen to consist of a transparent and nearly colourless liquid, in which tloat about a countless multitude of little round red bodies, to which the colour is due ; these are the blood-discs or blood- corpuscles of microscopic observers. Fig. 174. They are accompanied by colourless globules, fewer and larger, the white corpuscles of the blood. The blood-discs are found to present different appearances in the blood of different animals: in the mammifers they look like round red or yel- lowish discs, thin when compared with their diam- eter, being flattened or depressed on opposite sides. In birds, lizards, frogs, and fish, the cor- puscles are elliptical. In magnitude, they seem to be pretty constant in all the members of a spe- cies, but differ with the genus and order. In man they are very small, varying from ^^^ to s oW f an ^ nc ^ ' in breadth, while in the frog the long diameter of the ellipse measures at least four times as much. The corpuscles consist of an envelope containing a fluid in which the red colouring-matter of the blood is dissolved. The coagulation of blood effects a kind of natural proximate analysis ; the clear, pale serum, or fluid part, is an alkaline solution of albumin, containing various soluble salts ; the clot is a mechanical mixture of fibrin and blood globules, swollen and distended with serum, of which it absorbs a large but variable quantity. When the coagulum of blood is placed upon bibulous paper, and drained as much as possible from the fluid portion, and then put into water, the en- velope, which consists of globulin, dissolves and sets free the colouring matter, forming a magnificent crimson solution, which has many of the characters of a dye-stuff. It contains albumin and globulin, and coagulates by heat and by the addition of alcohol ; this albumin and globulin cannot be sepa- rated, and attempts to isolate the hematosin or red pigment have consequently failed. From its extreme susceptibility of change, it is not known in a state of purity. The above watery solution, exposed with extensive surface in a warm place, dries up to a dark red, brittle mass, which is again soluble in water. After coagulation it becomes quite insoluble, but dissolves like albumin in caustic alkalis. Carbonic and sulphurous acids blacken the reel solution ; oxygec, or atmospheric air, heightens its colour ; protoxide of nitrogen COMPOSITION OF THE BLOOD. 505 renders it purple ; while sulphuretted hydrogen, or an alkaline sulphide, changes it to a dirty greenish black. Jiematosin differs from the other animal principles in containing as an es- sential ingredient a remarkable substance not found elsewhere in the animal system, viz., the oxide of the metal iron. If a little of the dried clot of blood be calcined in a crucible and digested with dilute hydrochloric acid, a solution will be obtained rich in oxide of iron ; or if the solution of colouring matter just referred to be treated with excess of chlorine gas, the yellow liquid separated from the greyish coagulum formed will be found to give in a striking manner the well-known reactions of the sesquioxide of iron. There is little doubt either about the condition of the metal ; sesquioxide of iron is with- drawn from the dry clot by the cautious addition of sulphuric acid, and without much alteration of the colour of the mass. 1 It is well known that certain organic matters, as tartaric acid, prevent the precipitation of sesqui- oxide of iron by alkalis, and its recognition by ferrocyanide of potassium, and it is very likely that the blood may contain a substance or substances capable of doing the same. Jiematosin, necessarily in a modified state, contains, according to Mulder, in '100 parts : Carbon 65-3 Hydrogen 5-4 Nitrogen 10-4 Oxygen 11-9 Iron ... . 7-0 100-0 The following table represents the composition of healthy human blood a whole ; it is on the. authority of M. Lecanu. a (10 (2-) Water 780-15 785-58 Fibrin 2-10 3-57 Albumin 65-09 69-41 Colouring matter 133-00 119-63 Crystallizable fat 2-43 4-30 Fluid fat 1-31 2-27 Extractive matter of uncertain nature, soluble in 1 -\ "a i QO both water and alcohol f Albumin in combination with soda 1-26 2-01 Chlorides of sodium and potassium ; carbonates, "I Q.O-T IT.QA phosphates, and sulphates of potassa and soda... j Carbonates of lime and magnesia; phosphates of^ o.in 1.40 lime, magnesia, and iron; sesquioxide of iron... J Loss 2-40 2-59 1000-00 1000-00 In healthy individuals of different sexes these proportions are found to vary slightly, the fibrin and colouring matter being 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 albu 1 Liebig, Ilandworterbuch, i. 885. a Ann. Chim. et de Pbys. xlviil. 320 506 FUNCTION OF RESPIRATION. min, 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. Closely connected with the subject of the composition of the blood are those of respiration, and of the production of animal heat. The simplest view that can be taken of a respiratory organ in an air-breath- ing animal, is that of a little membranous bag, saturated with moisture, and containing air, over the surface of which meanders a minute blood-vessel, whose contents, during their 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 mem- branes are imbued. In some of the lower classes of animals, where respira- tion is sluggish and inactive, these air-cells are few and large ; but in the higher kinds they are minute, and greatly multiplied in number, in order to gain extent of surface, each communicating with the external air by the wind- pipe and its ramifications. Respiration is performed by the agency of the muscles which lie between and about the ribs, and by the diaphragm. The lungs are not nearly emptied of air at each expiration. Under ordinary circumstances about 15 cubic "inches only are thrown out, while by a forced effort as much as 50 or 60 cubic inches may be expelled. This is repeated about 18 times per minute when the individual is tranquil and undisturbed. The expired air is found to have undergone a remarkable change ; it is loaded with aqueous vapour, while a very large proportion of oxygen has disappeared, and its place been supplied by carbonic acid ; air once breathed containing enough of that gas to extinguish a taper. The total volume of the air seems to undergo but little change in this process, the carbonic acid being about equal to the oxygen lost. This, however, is found to depend very much upon the nature of the food ; it is likely that when fatty sub- stances, containing much hydrogen, are used in large quantities, a disappear- ance of oxygen will be observed. Nitrogen is in small quantity exhaled from the blood. In health no nitrogen is absorbed ; the food invariably containing more of that element than the excretions. Whatever may be the difficulties attending the investigation of these sub- jects, and difficulties there are, as the discrepant results of the experiments prove, one thing is clear : namely, that quantities of hydrogen and carbon are daily oxidized in the body by the free oxygen of the atmosphere, and their products expelled from the system in the shape of water and carbonic acid. Now, if it be true that the heat developed in the act of combination is a constant quantity, and no proposition appears more reasonable, the high temperature of the body 'may be the simple result of this exertion of chemi- cal force. 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 does not exceed 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, secretion, and all the mysterious functions of animal life, are un- doubtedly 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 carbonic acid produced is held in solution by the now venous blood, and probably confers, in great measure, upon the latter its dark colour 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 carbonic acid is conveyed outwards^ FUNCTION OF RESPIRATION. 507 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 colour, and its capability of supporting life. Much of this oxygen is, no doubt, simply dis- solved in the serum ; the corpuscles, according to Professor Liebig, act as carriers of another portion, in virtue of the iron they contain, that metal being alternately in the state of sesquioxide, and of carbonate of the pro- toxide, of sesquioxide in the arteries, and of carbonate of protoxide in the veins, by loss of oxygen, and acquisition of carbonic acid. M. Mulder con- siders the fibrine to act in the same manner ; being true fibrin in the veins, and, in part at least, an oxide of proteine 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 effects 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, 1 to 14 ounces ; the whole of which is thrown off in the state of carbonic acid, 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 habit, who follow in- door pursuits in warm rooms, consume a much smaller quantity; their respiration 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 nir, 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 appetite 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, to 77 ounces ; that consumed by a cow, to 70 ounces. The determination was made in the manner just mentioned, viz., by comparing the quantity and composition of the food. CHYLE. A specimen, examined by MM. Tiedemann and Gmelin, taken from the thoracic duct of a horse, was found closely to resemble, in compo- sition and properties, ordinary blood ; the chief difference was the compara- tive absence of colouring matter, the chyle having merely a reddish-white tint. It coagulated, after standing four hours, and gave a red-coloured clot, small in quantity, and a turbid, reddish-yellow serum. The milky appear- ance of chyle is due to fat globules, which sometimes confei the same character upon the serum of blood. LYMPH. Under the name of lymph, two or more fluids, very different in their nature, have been confounded, namely, the fluid taken up by the absor- bents of the alimentary canal, which is simply chyle, containing both fibrin and albumin, and the fluid poured out, sometimes in prodigious quantities, from serous membranes, which is a very dilute solution of albumin, contain Animal Chemistry, p. 14. 508 MILK, BILE, URINE Fig. 175. ing a portion of soluble salts of the blood. The liquor amnii of the pregr nant female, and the fluid of dropsy, are of this character. Mucus AND Pus. The slimy matter effused upon the surface of variou? 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, probably varies a good deal in its nature in different situations. It is com- monly either colourless or slightly yellow, and translucent or transparent: it is quite insoluble in water, forming, in the moist state, a viscid, gelatinous mass. In dilute alkalis it dissolves with ease, and the solution is precipi- tated by an addition of acid. Pus, the natural secretion of a wounded or otherwise injured surface, is commonly a creamy, white, or yellowish liquid, which, under the microscope, ap- pears to consist of multitudes of minute globules (fig. 175, a) ; dilute acetic acid renders them transparent, and shows the internal nuclei (6). It is neither acid nor alkaline. Mixed with water, it communi- cates a milkiness to the latter, but after a time subsides. Caustic alkali does not dissolve pus, but converts it into a trans- parent, gelatinous substance, which can be drawn out into threads. The peculiar ropincss thus produced with an alkali is not peculiar to pus. Healthy mucus owes its sliminess to an alkaline fluid acting on the mucous globules. MILK, BILE, URINE, AND URINAKY CALCULI. 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 animals and in those which live exclusively on vegetable food. The proportions of the constituents may, however, sometimes differ to a considerable extent. It will be seen hereafter that the substances present in milk are wonderfully adapted to its office of providing materials for the rapid growth and develop- ment of the animal frame. It contains an azotized matter, casein, nearly identical in composition with muscular flesh, fatty principles, and a peculiar sugar, and lastly, various salts, among which may be mentioned phosphate of lime, held in complete solution 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 mi- croscope of even moderate power, it is seen to consist of a perfectly transparent fluid, in which float about numbers of transparent globules (fig. 17G); these consist of fat, surrounded by an albuminous envelope, which can be broken mechanically, as in churning, or dissolved by the chemical action of caustic potassa, 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 temperature 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 remaining watery liquid is expelled from between them and separated. The bultcr 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. AND URINARY CALCULI. 509 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 flavour is unfortunately somewhat impaired by this process. The consistence of butter, in other words, the proportions of margarin 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 about 120 (49C), 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 colouring-matter, and then subjected to strong and increasing pressure. The fresh cheese so prepared being con- stantly kept cool and dry, undergoes a particular kind of putrefactive fer- mentation, very little understood, by which principles are generated which communicate a particular taste and odour. The goodness of cheese, as well as much of the difference of flavour perceptible in different samples, de- pends 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. 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 condition. 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 phosphate of lime. 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 M. Haidlefc, 1 the follow- ing statement of its composition in 1000 parts has been deduced : Water 873-00 Butter 30 00 Casein 48-20 Milk-sugar 43-90 Phosphate of lime 2-31 " magnesia 0-42 " iron 0-07 Chloride of potassium 1-44 Sodium 0-24 Soda in combination with casein..., .... 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. BILE. This is a secretion of a very different character from the pre- teding ; the largest internal organ of the body, the liver, is devoted to its 1 Aunalcn der Chcmic und Phurmacic, xlv. 263. 43* 510 MILK, BILE, URINE, preparation, which is said to take place from venous, instead of arterial blood. The composition of the bile has been made the subject of much in- vestigation ; the following is a summary of the most important facts which have been brought to light. 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 odour, a most nauseous, bitter taste, a distinctly alkaline reaction, and is miscible with water in all proportions. When evaporated to dryness at 212 (100C), and treated with alcohol, the greater part dissolves, leaving behind an in- soluble jelly of mucus of the gall-bladder. This alcoholic solution contains colouring-matter and cholesterin; from the former it maybe freed by diges- tion 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 colourless liquid. The colouring-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. Acetate of lead partially precipitates it ; the tribasic acetate precipitates it com- pletely ; the precipitate is readily soluble in acetic acid, in alcohol, and to a certain extent in excess of acetate of lead. When carbonized by heat, and! incinerated, bile leaves between 11 and 12 per cent, of ash, consisting chiefly of carbonate of soda, with a little common salt and alkaline phosphate. The recent beautiful researches of Strecker, show that bile is essentially a mixture of the soda-salts of two peculiar conjugate acids very distinctly resembling the resinous and fatty acids. One of these contains nitrogen, but no sulphur, and is termed cholic acid, or better, glycho-cholalic, being a conjugated compound of a non-nitrogenous acid, cholalic acid, 1 with the nitro- genetted substance glycocine (see page 501), the other containing nitrogen and sulphur, has received the name choleic acid, or better, tauro-cholalic acid, being a conjugated compound of the same cholalic acid with a body to be presently described under the name of taurin, containing both nitrogen and sulphur. The relative proportion in which these acids occur in bile, remains pretty constant with the same animal, but varies considerably with different classes of animals. GLYCO-CHOLALIC 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, stellated crystals which consist of glyco-cholalate of soda and potassa. These mixed crystals were first obtained by Platner, and they compose his so-called crystallized bile, Glyco-cholalic acid may be obtained by decomposing the glyco-cholalate of soda by 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 G 52 H 42 NO n ,I10. When boiled with a solution of potassa, the acid divides into cholalic acid C^HgpO^HO, and glycocine or gelatin- sugar : C fig H 42 N0 11 ,HO+2HO = C 48 F S9 9 ,HO+C 4 PI 5 N0 4 Glyco-cholalic acid. Cholalic acid. Glycocine. 1 Also called cholic acid by some authors. AND URINARY CALCULI. 511 Boiled with concentrated sulphuric or hydrochloric acids, it yields likewise glycocine, but instead of cholalic acid, another white amorphous acid, cho- loidinic acid (C 48 H 39 9 = cholalic acid 1 eq. of water), or if the ebullition has continued for some time, a resinous substance, from its insolubility in water called dyslysin, (C^HggOg = cholalic acid 4 eq. of water.) TATJRO-CHOLALIC ACID is thus procured. Ox bile is freed as far as pos- sible from glyco-cholalic acid by means of neutral acetate of lead, and it is then precipitated by basic acetate of lead, to which a little ammonia is added. The precipitate is decomposed by carbonate of soda, when tolerably pure tauro-cholalate of soda is obtained. By decomposing the tauro-cholalate of lead by sulphuretted hydrogen, tauro-cholalic acid is liberated. This substance, however, which was previously called choleio acid and bilin, has never been obtained in the pure state. Its formula, as inferred from the study of its products of decomposition, would be C 52 H 44 NS 2 13 ,HO. When boiled with alkalis it divides into cholalic acid and tauriue : C 52 H 44 NS 2 13 ,HO-f-2HO = C 48 H 39 9 ,HO-f C 4 H 7 NS 2 6 Tauro-cholalic acid. Cholalic acid. Taurin. With boiling acids it gives likewise taurin, but instead of cholalic acid, either choloidinic acid or dy sly sin, according to the duration of the ebulli- tion. TAURIN, C 4 H 7 NS 2 6 , crystallizes in colourless regular hexagonal prisms, which have no odour 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 filtration and evaporation, the acid residue is treated with five or six times its bulk of boiling alcohol, from which the taurin separates on cooling. CHOLALIC or CHOLIC ACID, C 48 H 39 9 ,HO, crystallizes in tetrahedra. It is soluble in sulphuric 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 colour is produced, which constitutes Pettenkofer's test for bile. At 383 (195C) it loses an atom of water, and is converted into chloloidinic acid, which change, as has been pointed out, is also produced by ebullition with acids. Cholalic acid is best obtained by boiling the resinous mass precipitated by ether from the alcoholic solution of the bile with a dilute solution of potassa for 24 or 36 hours, till the amorphous potassa-salt that has separated begins to crystallize. The dark-coloured soft mass removed from the alkaline liquid, dissolved in water, and hydrochloric acid added, a little ether causes the deposition of the cholalic acid in crystals. One of the colouring-matters of the bile forms the chief part of the con- cretions sometimes met with in the gall-bladders of oxen, and which are much valued by painters in water-colours, as forming a magnificent yellow pigment. It dissolves in caustic alkali without change of colour, and when mixed with excess of nitric acid becomes successively green, blue, violet, red, and even- tually yellow. The composition of this substance is unknown. Another colouring-matter is dark green, and is considered by Berzelius, as identicaj with the pigment 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 tin- name hyockolic acid has been given, which may be prepared in the following manner: fresh pigs' bile is mixed with a solution of sulphate of soda, the precipitate obtained is dissolved in absolute alcohol, and decolorized by animal charcoal. From this solution ether throws down a soda-salt, yield- 612 MILK, BILE, AND URINE. ing, on addition of sulphuric acid, hyocholic acid as a resinous mass, which is dissolved in alcohol and re-precipitated by water. Hyocholic acid contains C 54 H 43 NO, . When heated with solutions of the alkalis, the acid undergoes a decomposition perfectly analogous to that of glyco-cholalic acid, hyocholic acid, splitting into glycocine and a crystalline acid, very soluble in alcohol, less so in ether, which has been termed hyocho- lalic add. This substance contains C 50 H 39 7 ,HO, and the change is repre- sented by the following equation: C 54 H 43 N0 10 +2HO == C 60 U 39 7 ,HO + C 4 H 5 N0 4 Hyocholic acid. Hyocholalic acid. Glycocine. Hence hyocholic acid might be called glyco-hyocholalic add. When boiled with acids, glyco-hyocholalic acid yields likewise glycocine, but instead of hyocholalic acid, a substance representing the dyslysin of the ordinary bile, which might be termed hyodyslysin. The composition of hyodyslyin is C 50 H 38 6 = hyocholalic acid 2 eq. HO. Pigs' bile contains a very trifling quantity of sulphur, probably in the form of a sulphuretted acid corresponding to the tauro-cholalic acid of ox-bile. Rtrecker believes this acid to contain C 54 H 45 NS 2 Oi 2 : it might be called tauro- hyocholalic add, which when boiled with an alkali would yield taurin and hyocholalic acid. The sulphuretted acid must be present in pigs' bile in very minute quantity ; it is even less known than tauro-cholalic acid. The once celebrated oriental bezoar-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 lithofdlinic add. To procure this sub- stance, the calculi are reduced to powder and exhausted with boiling al- cohol ; the dark solution is decolorized by animal charcoal, and left to eva- porate by gentle heat, whereupon the lithofellinic acid is deposited in small, colourless, transparent six-sided prisms. It is insoluble in water, amd with difficulty soluble in ether, but dissolves with ease in alcohol : it melts at 202 (95 -5C), and at a higher temperature burns with a smoky flame, leaving but little charcoal. Lithofellinic acid dissolves without decompo- sition in concentrated acetic acid, and in oil of vitriol ; it forms a soluble salt with potassa, and dissolves also in ammonia, but crystallizes out un- changed on evaporation. By analysis, lithofellinic acid is found to consist of C^HagO^HO. 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 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 in- troduced 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 sulphates, chlorides, phosphates of lime, and magnesia, alkaline salts, and certain yet imperfectly known principles, including an odoriferous and a colouring substance (see foot-note to p. 513). Healthy human urine is a transparent, light amber-coloured liquid, which, while warm, emits a peculiar, aromatic, and not disagreeable odour. This is lost on cooling, while the urine at the same time occasionally becomes turbid from a deposition of urate of ammonia, which re-dissolves with slight elevation of temperature. It is very decidedly acid to test-paper ; ' this acidity has been ascribed to acid phosphate of soda, to free uric acid, and * The degree of acidity appears to be constantly changing. See Philosophical Trans. 18481 MILK, BILE, AND URINE. 513 to free lactic acid ; lactic acid can, however, hardly co-exist with urate of ammonia, and the amorphous buff-coloured deposit obtained from fresh urine by spontaneous evaporation in vacua is not uric acid, but the ammonia-salt of that substance, modified as to crystalline form by the presence of minute quantities of chloride of sodium. 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 neutral potassa or soda-salts of a vegetable acid, as tartaric or acetic acid ; the acid of the salt is burned in the blood in the process of respiration, and a por- tion of the base appears in the urine in the state of carbonate. The urine is often alkaline in cases of retention, from carbonate of ammonia 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 1-028 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 production of crystals of nitrate of urea, whereas with urine of the usual degree of con- centration many hours will elapse before the nitrate begins to separate. The quantity 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 bo assumed as a mean. When kept at a moderate temperature, urine, after some days, begins to decompose ; it exhales an offensive odour, becomes alkaline from the pro- duction of carbonate of ammonia, and turbid from the deposition of earthy phosphates. The carbonate of ammonia is due to the putrefactive decomposition of the urea, which gradually disappears, the ferment, or active agent of the change, being apparently the mucus of the bladder, a portion of which is always voided with the urine. It has been found also that the yellow adhesive deposit from stale urine is a most powerful ferment 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 sulphide of am- monium ; this is formed by the de-oxidation of sulphates by the organic matter. The highly offensive odour and extreme pungency of the decom- posing liquid may be prevented by previously mixing the urine, as Liebig suggests, with sulphuric or hydrochloric acid, in sufficient quantity to satu- rate all the ammonia that can be formed. The following is an analysis of human urine, by Berzelius. 1000 part? contained Water 933-00 Urea 30-10 Lactates and extractive matter 1 17-14 * All dark -coloured, uncry stall izable substances, soluble both in water and alcohol, were confounded by the old chemists under the general name of extractive matter. The progress of modern science constantly tends to extricate from this confused mass one by one the many definite organic principles therein contained in a more or less modified form, and to restrict within narrower limits the application of the term. In the above instance, the colouring matter of the urine, and it may be several other substances, are involved. Professor Lio);iNH 2 Pyl C 2 (H 3 Pyl)N0 2 AeO,HO AeO,KO AeO,2S0 3 ,HO AeO Aecl AeCy AeO,Ae,C 2 3 NHjjAe C 2 (H 3 Ae)N0 2 Ethyl-alcohol Oxide of ethyl-potassa Sulphovinic acid Oxide of ethyl Chloride of ethyl ( Cyanide of ethyl (pro- \ pio nitrile) Propionate of ethyl Ethylamine Ethyl-urea. Chlorophenisic acid. This is the characteristic and principal product of the action of chlorine on hydrate of oxide of phenyl. The pure substance is not necessary for the preparation of this body, those portions of crude coal-oil which boil between 360 400 (182-2 204-5C) answering verj well. The oil is saturated with chlorine, and distilled in the open air, the first and last portions being rejected; the product is again treated with 528 VOLATILE PRINCIPLES OF COAL-TAR. chlorine until the whole solidifies. The crystals are drained and dissolved in hot dilute solution of ammonia ; on cooling, the sparingly soluble chloro- phenisate of ammonia crystallizes out. This is dissolved in pure water, de- composed by hydrochloric acid, washed, and, lastly, distilled. Chlorophenisic acid forms exceedingly fine, colourless, silky needles, which melt when gently heated ; it has a very penetrating, persistent, and charac- teristic odour, is very sparingly soluble in water, but dissolves freely in alcohol, ether, and hot concentrated sulphuric acid. It slowly sublimes at common temperatures, and distils with ebullition when strongly heated. Chlorophenisic acid forms well-defined salts, and contains C, 2 (H 2 C1 3 )0,HO. By the action of a great excess of chlorine an analogous acid richer in chlo- rine is formed. It is called chlorophenusic acid, and contains C ]2 C1 6 0,HO. Jlroruophenisic acid is prepared by analogous means, and possesses a consti- tution and character greatly resembling those of the chlorine-compound. Nitrophenasic acid. On distilling phenyl-alcohol with very dilute nitric acid, beautiful yellow needles are obtained, soluble in ammonia and potassa, and yielding a beautiful red silver-salt. This substance is nitrophenasic acid, Ci 2 H 4 N0 5 ,HO==C,,2(H 4 N0 4 )(),H(). Nitrophenesic and nitrophenisic acids may be prepared directly from the oil which is employed in the preparation of Chlorophenisic acid. The oil is carefully mixed in a large open vessel with rather more than its own weight of ordinary nitric acid. The action is very violent. The brownish-red substance produced is slightly washed with water, then boiled with dilute ammonia, and filtered hot. A brown mass remains on the filter, which is preserved to prepare nitrophenisic acid, and the solution deposits on cooling a very impure ammoniacal salt of nitro- phenesic acid, which requires several successive crystallizations, after which it is decomposed by nitric acid and the product crystallized from alcohol. Nitrophenesic acid forms blonde-coloured prismatic crystals, very spar- ingly soluble even in boiling water, but freely soluble in alcohol. It has no odour. Its taste, at first feeble, becomes after a short time very bitter. At 219 (104C) it melts, and on cooling crystallizes. In very small quantity it may be distilled without decomposition, but when briskly heated it often detonates, but not violently. The salts of this acid are yellow or orange and very beautiful : they are mostly soluble in water, and detonate feebly when heated. The acid contains C 12 ^I 3 N 2 9 JIO=:C 12 H 3 (N0 4 ) 2 0,HO. Nitro- phenisic acid is identical with picric or carbazotic acid (see page 473). It may be prepared with great economy from impure nitrophenesic acid, or from the brown mass insoluble in dilute ammonia already referred to. It is purified by a process similar to that employed in the case of the preceding substances. Nitrophenisic acid contains Ci 2 H 2 N 3 I3 ,HO=C, 2 H 2 (N0 4 ) 8 0,H0. 1 The following table exhibits the relation of these substitution-products : Phenyl-alcohol C, 2 H 5 0,HO = Phenol Chlorophenisic acid C, 2 (H 2 C1 3 ) 0,HO = Trichlorophenol Nitrophenasic acid C 12 (H 4 NO 4 ) 0,HO = Nitrophenol Nitrophenesic acid C 12 (H 3 [N0 4 ] 2 ) 0,HO = Binitrophenol Nitrophenisic acid Ci 2 (H 2 [N0 4 ] 3 ) 0,HO = Trinitrophenol. The neutral portion of coal-tar naphtha consists of a great variety of hy- drocarbons, partly liquid, partly solid. The liquid hydrocarbons have been already described (see pages 398 and 403). They are chiefly benzol, toluol, xylol, cumol, and cymol? The solid hydrocarbons are naphihalin and para- naphthalin together with several similar substances less perfectly known. 1 Ann. Chiin. et Phys. 3d series, iii. 195. 4 The same hydrocarbons have been lately found by M. Cahours in the oily liquids pre ripitateu by water from commercial wood-spirits (see page o87). VOLATILE PRINCIPLES OP COAL-TAR. 529 NAPHTIIALIN. When, in the distillation of coal-tar, the last portion of the volatile oily product is collected apart and left to stand, a quantity of solid, crystalline matter separates, -which is principally composed of the substance in question. An additional quantity may be obtained by pushing the distillation until the contents of the vessel begin to char ; the naphthalin then condenses in the solid state, but dark-coloured and very impure. By simple sublimation, once or twice repeated, it is obtained perfectly white. In this state naphthalin forms large, colourless, transparent, brilliant, crys- talline plates, exhaling a faint and peculiar odour, which has been compared to that of the narcissus. Naphthalin melts at 176 (80C) to a clear, colour- less liquid, which crystallizes on cooling; it boils at 413 (211-6C), and evolves a vapour whose density is 4-528. When strongly heated in the air, it inflames and burns with a red and very smoky light. It is insoluble in cold water, but soluble to a slight degree at the boiling temperature ; alcohol and ether dissolve it easily ; a hot saturated alcoholic solution deposits fine iridescent crystals on cooling. Naphthalin is found by analysis to contain C 10 II 4 or C 20 H 8 . Naphthalin dissolves in warm concentrated sulphuric acid, forming a red liquid, which, when diluted with water, and saturated with carbonate of baryta, yields salts of at least two distinct acids, analogous to sulphovinio acid. One of these, the sulphonaphthalic acid of Mr. Faraday, crystallizes from a hot aqueous solution in small white scales, which are but sparingly soluble in the acid. The free acid is obtained in the usual manner by de- composing the baryta-salt with sulphuric acid ; it forms a colourless, crys- talline, brittle mass, of acid, metallic taste, very deliquescent, and very solu- ble in water. The second baryta-salt is still less soluble than the preceding. The composition of sulphonaphthalic acid is C 20 H 7 S 2 5 ,HO. Fuming nitric acid at a high temperature attacks naphthalin ; the products are numerous, and have been attentively studied by M. Laurent. The same chemist has described a long series of curious products of the action of chlo- rine on naphthalin. Nitric acid gives rise to a great number of nitro-sub- stitutes, the most interesting of which, is the compound known by the namo nitronaphthalase, which, when submitted to Zinin's process, is converted into naphthalidine (see page 462). Among the derivatives of naphthalin, a com- pound deserves to be mentioned, which has been described under the name of phthalic acid. This acid has not yet been produced directly from naphtha- lin, but may be obtained by boiling one of the products of the action of chlo- rine upon naphthalin, namely, the tetrachloride of naphthalin (C^HgC^) with nitric acid. The same substance is formed by submitting alizarin to the action of nitric acid. Phthalic acid crystallizes in yellow plates ; it is but slightly soluble in cold water, but dissolves freely in alcohol and ether. Phthalio acid is bibasic, and contains Ci 6 H 4 O tJ ,2HO; when heated it loses 2 eq. of water, and becomes Cj 6 H 4 6 . Treated with fuming nitric acid it yields a nitro-acid, nitro-phtha- lic acid, C 16 (H 3 N0 4 ) 6 , 2HO. When distilled with baryta it is converted into benzol : C ]6 H 6 8 -f4BaO = 4(BaOCO a )-fC J2 H 6 Ththalic acid. Benzol. The formation of phthalic acid from alizarin has established a most inte- resting connection between the naphthalin and alizarin-series. It would be of great interest if naphthalin, which is produced /n enormous quantities in the manufacture of coal-gas, but has not yet found any useful application, could be converted by chemical processes into alizarin. That there is a hope of such a conversion being possible, is even now pointed out by the close 45 530 PETROLEUM, NAPHTHA,, analogy *f one of the chlorine products of naphthalin, of chloronaphthalit acid, both in composition and properties with alizarin. This substance con- tains C 20 (H 5 C1)0 6 , and may be viewed as chloralizarin : Alizarin C 20 H 6 6 Cloronaphthalic acid C 20 (H 5 C1)0 6 . Chloronaphthalic acid produces most beautifully coloured compounds with the metallic oxides. The history of the formation of naphthalin is rather interesting ; it is per- haps the most stable of all the more complex compounds of carbon and hydro- gen : in a vessel void of free oxygen it may be heated to any extent without decomposition ; and, indeed, where other carburets of hydrogen are exposed to a very high temperature, as by passing in vapour through a red-hot porcelain tube, a certain quantity of naphthalin is almost invariably pro- duced. Hence its presence in coal and other tar is mainly dependent upon the temperature at which the destructive distillation of the organic substance has been conducted. Lampblack very frequently contains naphthalin thus accidentally produced. PARANAPHTHALIN. This substance occurs in the naphthalin of coal-tar, and is separated by the use of alcohol, in which ordinary naphthalin is freely soluble, whilst paranaphthalin is almost totally insoluble ; in other respects it much resembles naphthalin. The crystals obtained by sublimation are, however, usually smaller and less distinct. It melts at 356 (180C), and boils at 570 (299C), or above. Its best solvent is oil of turpentin. Para- naphthalin has the same composition as naphthalin itself; the density of its vapour is, however, different, viz., 6-741. Its composition may be repre- sented by the formula C^H^. PETROLEUM, NAPHTHA, AND OTHER ALLIED SUBSTANCES. Pit-coal, lignite or broivn coal, jet, bitumen of various kinds, petroleum or rock-oil, and naphtha, and a few other allied substances more rarely met with, are looked upon as products of the decomposition of organic matter, espe- cially vegetable matter, beneath the surface of the earth, in situations where the conditions of contact with water, and nearly total exclusion of atmo- spheric air, are fulfilled. Deposited at the bottom of seas, lakes, or rivers, and subsequently covered up by accumulations of clay and sand, hereafter destined to become shale and gritstone, the organic tissue undergoes a kind of fermentation, by which the bodies in question, or certain of them, are slowly produced. Carbonic acid and light carbonetted hydrogen are by-pro- ducts of the reaction ; hence their frequent disengagement, the first from beds of lignite, and the second from the farther advanced and more perfect coal. The vegetable origin of coal has been placed beyond doubt by microscopic research ; vegetable structure can be thus detected even in the most mas- give and perfect varieties of coal when cut into thin slices. In coal of infe- rior quality, much mixed with earthy matter, it is evident to the eye ; the leaves of ferns, reeds, and other succulent plants, more or less resembling those of the tropics, are found in a compressed state between the layers of shale or slaty clay, preserved in the most beautiful manner, but entirely converted into bituminous coal. The coal-mines of Europe, and particularly those of our own country, furnish an almost complete fossil-flora ; a history of many of the now lost species which once decorated the surface of the earth. In the lignites the woody structure is much more obvious. Beds of this material are found in very many of the newer strata, above the true coal, to which they are consequently posterior. As an article of fuel, brown-coal is AND OTHER ALLIED SUBSTANCES. 531 tf comparatively small value ; it resembles peat, giving but little flame and Mnitting a disagreeable, pungent smell. Jet, used for making black ornaments, is a variety of lignite. The true bitumens are destitute of all organic structure ; they appear to have arisen from coal or lignite by the action of subterranean heat, and very closely resemble some of the products yielded by the destructive dis- tillation of those bodies. They are very numerous, and have yet been but imperfectly studied. 1. Mineral pitch, or compact bitumen, the asphaltum or Jew's pitch of some authors. This substance occurs abundantly in many parts of the world ; as, in the neighbourhood of the Dead Sea in Judea ; in Trinidad, in the famous pitch lake, and elsewhere. It generally resembles in aspect common pitch, being a little heavier than water, easily melted, very inflammable, and burning with a red, smoky flame. It consists principally of a substance called by M. Boussingault asphaltene, composed of C 20 H, 6 3 . It is worthy of remark, that M. Laurent found paranaphthalin in a native mineral pitch. 2. Mineral tar seems to be essentially a solution of asphaltene in an oily fluid called petrolene. This has a pale yellow colour and peculiar odour ; it is lighter than water, very combustible, and has a high boiling point. It has the same composition as the oils of turpentin and lemon-peel, namely Ci H 8 . Asphaltene contains, consequently, the elements of petrolene, to- gether with a quantity of oxygen, and probably arises from the oxidation of that substance. 3. Elastic bitumen ; mineral caoutchouc. This curious substance has only been found in three places ; in a lead-mine at Castleton, in Derbyshire ; at Montrelais, in France ; and in the State of Massachusetts. In the two latter localities it occurs in the coal-series. It is fusible, and resembles in many respects the other bitumens. Under the names petroleum and naphtha are arranged various mineral oils which are observed in many places to issue from the earth, often in con- siderable abundance. There is every reason to suppose that these owe their origin to the action of internal heat upon beds of coal, as they are usually found in connection with such. The term naphtha is given to the thinner and purer varieties of rock-oil, which are sometimes nearly colourless ; the darker and more viscid liquids bear the name of petroleum. Some of the most noted localities of these substances are the following : The north-west side of the Caspian Sea, near Baku, where beds of marl are found saturated with naphtha. Wells are sunk to the depth of about 30 feet, in which naphtha and water collect, and are easily separated. In some parts of this district so much combustible gas or vapour rises from the ground, that when set on fire, it continues burning, and even affords heat for economical purposes. A large quantity of an impure variety of petroleum comes from the Birman territory in the East Indies : the country consists of sandy clay, resting on a series of alternate strata of sandstone and shale. Beneath these occurs a bed of pale blue shale loaded with petroleum, which lies immediately on coal. A petroleum-spring exists at Colebrook Dale, in Shropshire. The sea near the Cape de Verde Islands has been seen covered with a film of rock-oil. The finest specimens of naphtha are furnished by Italy, where it occurs in several places. In proof of the origin attributed to these substances, an experiment of Dr. Reichenbach may be cited, who, by distilling with water about 100 Ib. of pit-coal, obtained nearly 2 ounces of an oily liquid exactly resembling the natural naphtha of Amiano, in the Duchy of Parma. The variations of colour and consistence in different specimens of these bodies certainly depends in great measure upon the presence of pitchy and 532 PETROLEUM, NAPHTHA, ETC. fatty substances dissolved in the more fluid oil. Dr. Gregory found paraffin in petroleum from Rangoon. The boiling-point of rock-oil varies from about 180 to near 600 (82 -2 to 315 -50) ; a thermometer inserted into a retort in which the oil is under- going distillation, never shows for any length of time a constant tempera- ture. Hence it is inferred to be a mixture of several different substances. Neither do the different varieties of naphtha give similar results on analysis ; they are all, however, carbides of hydrogen. The use of these substances in the places where they abound is tolerably extensive ; they often serve the inhabitants for fuel, light, &c. To the chemist pure naphtha is valuable, as offering facilities for the preservation of the more oxidable metals, as potas- sium and sodium. The following are of rarer occurrence : Retinite, or Retinasphalt, is a kind of fossil resin met with in brown coal ; it has a yellow or reddish colour, is fusible and inflammable, and readily dissolved in great part by alcohol. The soluble portion has been called retinic acid by Prof. Johnston. Hatchetin is a somewhat similar substance met with in mineral coal at Merthyr-Tydvil, and also near Loch Fyne, in Scotland. Idrialin is found associated with native cinnabar, and is extracted from the ore by oil of turpentin, in which it dissolves. It is a white, crys- talline substance, scarcely volatile without decomposition, but slightly soluble in alcohol and ether, and composed of C 49 H, 4 ; it is generally associated with a hydrocarbon idryl, which contains C 42 H 14 . Ozokerite, or fossil wax, is found in Moldavia, in a layer of bituminous ehale ; it is brownish and has a somewhat pearly appearance ; it is fusible below 212 (100C), and soluble with difficulty in alcohol and ether, but easily in oil of turpentin. It appears to contain more than one definite principle. APPENDIX. 45* (688) 534 APPENDIX. HYDROMETER TABLES. COMPARISON OF THE DEGEEES OF 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 63 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 66 1-583 5 1-034 31 1-256 67 1-600 6 1-041 32 l-2dl 58 1-617 7 1-048 83 1-277 69 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 1-094 39 1-345 65 1-747 14 1-101 40 1-357 66 1-767 15 1-109 41 1-369 67 1-788 16 1-118 42 1-381 68 1-809 17 1-126 43 1-395 69 1-831 18 1-134 44 1-407 70 1-854 19 1-143 45 1-420 71 1-877 20 1-152 46 1-434 72 1-900 21 1-160 47 1-448 73 1-924 22 1-169 48 1-462 74 1-949 23 1-178 49 1-476 75 1-974 24 1-188 50 1-490 76 2-000 25 1-197 51 1-495 APPENDIX. 535 2. Baumffs 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 64 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 0913 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 M. Francoeur ; they are taken from the Handworterbuch der Chemie of Liebig and Poggendorff. Baume'a 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 Baume". In the United Kingdom, Twaddell's hydrometer is a good deal used for dense liquids. This instrument is so graduated that the real sp. gr. 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 gp. gr., water being 1000. Thus 10 Twaddell indicates a sp. gr. of 1050, or 1-05; 90 Twaddell, 1450, or 1-45. In the Customs and Excise, Sike's hydrometer is used. 536 APPENDIX. ABSTRACT OF DR. DALTON'S TABLE OP THE ELASTIC FORCE OP VAPOUR OF WATER AT DIFFERENT TEMPERATURES, EXPRESSED IN INCHES OP MERCURY. Temperature. Force. Temperature. Force. Temperature. Force. Fah. Cent. Fah. Cent. Fah. Cent. 32 0-0 0-200 57 13-88 0-474 90 32 -2 1-36 33 0-55 0-207 68 14-4 0-490 95 35 1-58 34 1-1 0-214 59 15 0-507 100 370.77 1-86 35 lo-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 17-77 0-597 125 51-66 3-75 40 40.4 0-263 65 18-3 0-616 130 540.4 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 5-74 43 6-l 0-294 68 20 0-676 145 62-77 6-53 44 6-66 0-305 69 20 -55 0-698 150 65 -5 7-42 45 7-2 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 0-796 190 870.77 1900 49 90.4 0-363 74 23-3 0-823 200 93-3 23-64 50 10 0-375 75 23-88 0-851 210 98 -88 28-84 51 10-55 0-388 76 24-4 0-880 212 100 30-00 52 11-1 0-401 77 25 0-910 220 104-4 34-99 53 ll-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 55 12-77 0-443 80 26-66 1-000 250 121-1 58-21 56 13-3 0-458 85 29-44 1-170 300 148 -88 111-81 APPENDIX. 537 TABLE OF THE PROPORTION BY WEIGHT OF ABSOLUTE OR REAL ALCOHOL IN 100 PARTS OF SPIRITS OF DIFFERENT SPECIFIC GRAVITIES. (FOWNES.) Sp.Gr. 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 43 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 67 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 i 538 APPENDIX. DR. SCHWEITZER'S OF THE PRINCIPAL MINERAL WATERS OF GERMANY Grains of Anhydrous Ingredients in One Pound Troy. Carlsbad. Ems. Schlesischer. Obersalz- Brunnen. Carbonate of Soda 7-2712 8-0625 7-6211 Ditto of Lithia. . 0-0150 0-0405 Ditto of Baryta 0-0022 Ditto of Strontia 0-0055 0-0080 0-0170 Ditto of Lime 1-7775 0-8555 1-5464 Ditto of Magnesia 1-0275 0-5915 1-5496 Ditto (proto) of Manganese Ditto (proto) of Iron Sub-Phos of Lime . 0-0048 0-0208 0-0012 0-0028 0-0120 0-0026 0-0356 Ditto of Alumina 0-0019 0-0014 Sulphate of Potassa 0-4050 0-3160 Ditto of Soda 14-9019 2-5106 Ditto of Lithia Ditto of Lime Ditto of Strontia Nitr of Magnesia . Chlor. of Ammonium 0-0164 Ditto of Potassium 0-0338 Ditto of Sodium 5-9820 5-7255 0-8682 Ditto of Lithium.. Ditto of Calcium Ditto of Magnesium Ditto of Barium Ditto of Strontium ... . Bromide of Sodium .... . 0-0051 Iodide of Sodium Fluoride of Calcium 0-0184 0-0014 Silica 0-4329 0-3104 0-2423 Total 31-4606 16-0525 14-7309 Carbonic Acid Gas in 100 l cubic inches j r Temperature 58 Sprud. 165 (73-8C) Neub. 138 (58-8C) 51 Kess. 117 (47 -2C) 98 58 (14-5C) Analyzed by... Miihl. 128 (53-3C) Ther. 122 (50C) Berzelius. Kran. 84 (28-8C) Struve. Struve. APPENDIX. TABLE OF ANALYSES AND OF THE SARATOGA CONGRESS SPRING OF AMERICA. Saratoga Congress Spring. Kissengen. Ragozi. Marienbad. Kreutbr. Auschowitz. Ferdinands- Brunnen. Eger. Franzens- Brunnen. 0-8261 5-3499 4-5976 3-8914 0-0858 0-0507 0-0282 0-0672 5-8531 4-1155 0-0202 0-0173 0-0592 4-8180 1-3185 0-0121 0-1397 0-0028 2-9509 2-0390 2-0288 0-1319 0-0040 3-0085 2-2867 0-0692 0-2995 0-0023 1-3501 0-5040 0-0322 0-1762 0-0172 0-0040 0-0092 0-1379 1-2540 28-5868 16-9022 18-3785 5-5485 .... 0-1004 0-0326 0-0364 1-6256 19-6653 39-3733 10-1727 6-7472 6-9229 3-6599 0-1613 0-3331 0-0046 0-0069 0-0023 0-1112 0-1609 0-2908 0-5023 0-3548 32-7452 114 50 (10C) Schweitzer. 56-7136 96 53 (11-6C) Struve. 51-6417 105 53 (11-CC) Berzelius. 34-4719 146 49 (9-5C) Steinman. 31-6670 154 54 (12-2C) Berzelius. 540 APPENDIX. DR. SCHWEITZER'S OF THE PRINCIPAL MINERAL WATERS OF GERMANY Grains of Anhydrous Ingredients in One Pound Troy. Pyrmont. Spa Pouhon. Fachingen. Carbonate of Soda 0-5531 12-3328 Ditto of Lithia Ditto of Baryta Ditto of Strontia Ditto of Lime 4-7781 0-7387 1-8667 Ditto of Magnesia 0-8421 1-2983 Ditto (proto) of Manganese 0-0364 0-0389 OOQ-I Sub-Phos of Lime . . 0-0102 0-0061 Ditto of Alumina 0-0110 0-0064 Sulphate of Potassa 0-0314 0-0593 Ditto of Soda 1-6092 0-0^81 0-1267 Ditto of Lithia 0-0067 Ditto of Lime 5-0 9 65 Ditto of Strontia 0-0154 Ditto of Magnesia 2-3684 Chlor. of Ammonium Ditto of Potassium Ditto of Sodium 0-3371 3-2337 Ditto of Lithium Ditto of Magnesium . . 0-8450 Ditto of Barium Ditto of Strontium Bromide of Sodium . . Iodide of Sodium Alumina Silica 0-3727 0-3739 0-0657 Total 15-4221 3-2691 18-9300 Carbonic Acid Gas in 100 ~ 160 136 135 Temperature (F.) 56 (13-3C) 50 (10C) 50 C10C) Analyzed bv Struve. Struve. Bischoff. APPENDIX. 541 TABLE OF ANALYSES AND OF THE SARATOGA CONGRESS SPRING OF AMERICA, Continued. Sellers. Seidschiitz. Ptillna. Kreuznach. Elisen- Brunnen. Adelheids- Quelle. 4-6162 5-2443 0-0902 0-0014 0-0094 0-0144 0-0387 1-4004 1-5000 5-1045 0-8235 0-0032 0-5775 4-8045 0-2058 1-1812 0-0072 0-4703 0-2980 OOli 0-0095 0-1495 0-0121 0-0007 0-0020 0-0117 0-0088 0-0026 0-2978 3-6705 3-6000 0-0066 17-6220 92-8500 1-1287 1 -9500 0-0347 62-3535 5-9302 69-8145 0-2685 0-7287 0-1845 12-9690 54-6917 0-0562 28-4608 9-7358 1-2225 14-7495 0-2366 0-5494 0-2304 0-3060 0-0013 00024 0-1500 0-0086 0-0166 0-2265 0-0900 0-1320 0-2355 0-1922 21-2982 126 58 (14-5C) Struve. 98-0133 20 58 (14-5C) Struve. 188-4806 7 58 (14-5C) Struve. 68-0190 12 47 (8-3C) Struve. 35-4739 10 58 (14-5C) Struve. 4G 542 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. The 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 French 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 mlire of France = 39-37 incbei. " decimetre = 3-937 " centimetre = 0-394 " millimetre = 00394 INDEX. ABSORPTION of heat... PAGE 80 .. 334 ACIDS continued. PA OK 394 ACIDS cont. PATE 510 .. 394, 486 447 glyco-hyo-cholalic... 512 402, 501 336 371 chelidonic ... 356 chloracetic .. 318, 375 141 Acetate of acetetvl 215 Acetate of oxide of amyl... 389 Acetate^ 373 446 145 402 131 336 Acetetj'l . . 215 chlorochromic.... chlorohydrosalic' chlorohyponitric chloronaphthalic 269 rlic 405 143 147 371, 395 214, 215 ... 356 148 141 530 420 At' 483 463 hydroferricyanic... . 433 430 376 143 373 528 149 369 chlorosulphuric. .. 130, 364 144 149 371, 395 487 anhydrous 214, 215 414 chlorovalerisic.... 393 hydromar IS* 484 292 447 135 291 345 407 i"asuric 449 415, 452 300 472 403 491 503 123 426 itaconic 414 395 426, 427 iodic 147 401 485 136 396 215 413 isatinic . .. 472 442 345 betaorsellic 475 dithionic 135 418 275 491 kakodylic 379 . 151 elaidio 484 336 US ella< r ic 418 kinie 447,448 349 bromo-hydrosalicylic.... 405 equisetic 414 474 475, 476 413 3 Q 3 485 486 492 366 lithic 433 492 345 lithofellinic .. . 512 capric caproic 394, 485 39 i, 485 479 415 evernic 475 maleic 416 caprylic carbazotic 391, 485 473 $26 everninic ferric formic 476 261 385 C ( 4 malic .... 414 259 481 129 400 446 liquefaction of.... carminic 3 477 517 fulminic 428 416 404 ... 336 gallic . ... . 416,418 39* cerotic . . 486 clvco-bcnzoic .... ... 402 mellitir ... 31* 544 INDEX. ACII>S cont. PAGE ACIDS emit. PAOE ricinoleic 488 AQB metacetonic 376 rubiacic 478 meta"-allic 419 rubic . ... 418 Alanine 350 370 467 metamargaric 488 saccharic 343 Albite ' * <>50 metapectic 340 sacchulmic 336 Albumin 495 metaphoFphoric 213 salicylic 406 methionic 366 palicylous 404 Alcohol 346 metoleic 487 sebacic 484 mucic 344 selenic 136 butyl- 392 3Q r > muriatic 141 selenious 136 capryl- 305 488 rnykomelinic 440 gtearic 481 cerotyl- 395' 486 myri^tic 484 inyronic 493 suberic 345, 484 ethal- 486 nitric 123 succinic 484 nitra^inic 490 sulphamylic 390 nitrobcnzoic 397 sulphindi |r otic 471 nitrococcusic 477 pulphindylic 471 tures 537 sulpho p lyc< i ric 483 sulpholeic . 487 nitropheni. e ic 528 sulphomarnaric 487 Aldehydic acid 370 nitrosalicylic 406,473 sulphomethylic 383, 384 Alembroth, sal 305 nitrotoluylic 403 sulphonaphthalic 529 Algaroth, powder of 289 nitrous 126 sulphophenic 526 Alizarin 477 Alkalimeter 227 oenanthylic 395, 488 Alkalimetry.... 226 oleic 482 sulphovinic 358 Alkaloids 444 sulphuric 133 artificial 453 opianic 445 sulphuric, anhydrous... 135 Alkargen.... 379 orsellinic 474,475 sulphurous 132 Alkarsin 377 oxalic 341 Allantoin 438 oxalovinic 359 tannic 416 Alliaria officinalis oil of 493 tartaric .. . . 410 oxalinic.... 461 tartralic 412 Alloxantin ... 441 451 palmitic . 484 tartrelic . . . 412 Alloys 199 parabanic 440 tartrovinic 359 of copper 278 tauro-cholalic 511 Allyl .. .. 493 parellic 476 tauro-hyo-cholalic 512 oxide of. 493 poetic 341 telluric 290 sulphide of 493 tellurous 290 pontathionic 136 tctrathionic . 135 Aloes 479 toluylic 403 periodic 148 trithionic 135 Althionic acid 366 ulmic 336 Alums . . 249 phosphethylic 359 uric 436, 438 Roman . 249 phosphobiethylk. 359 Alumina 248 phosphoric 138 valerianic 390, 395 acetate of. 373 valeric 390, 395, 492 analytical remarks on 250 bibasic 213 xantbic 368 silicates of 249 glacial 213 salts 202 monobasic 213 anhydrous 214 Aluminium 248 tribasic 212 bibasic 212 chloride of 248 fatty 345 hydrogen- theory of. 214 Amalgam, ammoniacal 232 phthalic 529 picric 473 monobasic 212 notation of. 213 Amalgam 199, 306 Amalic acid 450 pimaric . ... 494 oxygen- theory of. 214 Arnarine 401 466 pinic 493 polybasic 212 Amber 484 494 terminology of 132 Amidin ' S38 tribasic 212 Amidogen 235 vegetable 410 Aconitates 414 Ammelide 436 pyrogallic . . . . 419 Aconitic acid 414 Ammeline 436 Aconituin acid of 414 pyrophosphoric 213 pyrotartaric 412 Aconitum napellus 451 Acrolein 482, 487 Acrylic acid 487 alum 249 analytical remarks on.. 235 benzoate of 307 retinic 532 Affinity, chemical 183 cyan ate of 427 rhodizonic ... 345 After-damp of coal-mines 129 j malate of..... .... 415 INDEX. 545 AMMONIA cont. PAGE oxalate of 343 PAGE Aspartic acid 415, 452 PAGR Bceberine 451 purpurate of. 442 Aspen 452 Beer . . 347 tartrate of 411 urate of .. 438 Asphaltene 531 Beetroot, sugar from 334 Bell metal 279 Ammonium 201,232 cyanide of 425 Astatic needle 101 Bengal light 290 Atmosphere, chemical re- lations of 120 Benzamide 400 ferrocyanide of. 433 Benzile 401 salicylide of 404 composition and ana- lysis of ' 121 Benzilic acid 401 Benzimide 401 Amorphous quinine 448 Amy-dalle acid 423 physical constitution of 34 purifying 244 vapour of water in 61 Atmospheric electricity... 97 Atomic theory . . 182 Benzoates 397 Amygdalin 396, 423 Amylaceous group 333 Amyl and its compounds 388 scries, bases of the 458 Benzoate of benzoyl 215 of phenyl 527 Benzoic acid 396,452 anhydrous 215 Atomic weight 183 Atoms 182 -urea 458 Atropa belladonna . .. 451 Benzoin 480 Benzol . 398 Amylene . .. 390 Attenuation of wort 348 Attraction. . .. 183 Benzol, homologues of.... 462 Benzoline 466 Amylic ether 389 Augite 247 Ben zone 398 Amylotriethyl - ammo- nium, oxide of 464 Auric acid 300 Auschowitz, water of. 539 Axes of crystals 206 Benzonitrile 401 Benzophenone 398 Benzoyl . . 401 Analysis, ultimate, of or- ganic bodies 320 Axinite 250 and its compounds 396 benzoate of 218 Azobenzol 399 Analysis of carbonates.... 228 Analytical method of che- mical research 115 Azotic acid 123 Berberine . 451 B. Badian-oil 491 Berberis vulgaris 451 Bergamot, oil of 490 Berthollet's fulminating silver 299 Auilic acid 406. 473 Aniline 399,459,463 Balenic acid 395 Balsams 493 Beryl 251 homologues of 462 -urea 462 Balsam Canada 494 Berylla .. . 251 copaiba 494 Beryllium 2oO Anilotic acid 406 Peru . . .. 408 495 Betaorcin 476 Animal heat 507 Tolu 403 408 495 Betaorsellic acid 475 Bezoar stones 512 body, components of.... 496 Aniseed, oil of. 490 Barilla 225 Barium 237 Anisic acid 490 Anioin 4 ( '0 Bibasic acids 212 Anisol 491 Barley eivar . 33 1 Biborate of soda 231 Bicarbonate of potassa.... 221 Bicarbonate of soda 226 Bichloraniline 460 Auisyl, hydride of. 490 Authranilic acid 459, 474 Baryta and its hydrate 237, 238 acetate of 373 Antimonic acid 288 Bichlorethylamine 456 Antimony 287 analytical remarks on.. 238 Bichloride of tin , 283 bases 469 Bichlorisatin 473 crude 289 fulminate of 429 Bichlorokinone 449 potassa, tartrate of. 411 tartrate of 411 Bichloro^aligenin 406 Bases 109 Bichromate of potassa 269 Biethylamine 456 Arabia 340 from aldehyde 467 amidogeu- 454 from animal oil 465 Archil 474 Ar^and lamp . . 159 -urea . 456 Argol 347 410 Biethyl-amylamine 464 Aricine 448 organic, containing chlorine 4CO Biethylaniline . 463 Aridium 266 Biethyl-phenylamine 463 Biethyl-phenyl-ammo- Arrow poison of central Biethylo-toluidine 463 Arrowroot 339 artificial, containing Biliary calculi 487 Bile 509 Arsenic and its corn- mixed artificial 463 test of Pettenkofer 611 Bilin 511 nitrile- 454 analytical details 293 detection in organic mixtures... . 293 from volatile oils by Binary theory of salts 213 Binitrobenzol 399, 460 Arsenious acid 291 organic, artificial 453 Binitrotoluol 495 Artemisia 452 Binoxide of barium 237 of protein 500 of tin 282 Arterial blood 503 containing platinum.... 309 Bissorin 340 Aswdbetida 479 oil of 493 AspMi-agin 415, 452 Appnragofi 452 40 * Battery, constant 193 Baume's hydrometer 535 Bay salt 232 Biscuit 254 Bismuth 274 Analytical remarks 276 546 INDEX. PAGE Bismuthic acid 275 PAOE Cadmium 274 PAOB Bisulphate of potassa 221 of soda . > 229 analytical remarks 274 Caffeine 450 Casein 498 Bisulphide of carbon 169 Bitter almonds, oil of 396 nmrexide 451 Calamine 273 Cassius, purple. 283 Castor-oil... 488 Catechu 416 417 pounds .. 239 elastic 531 fluoride of 243 Cedrene 491 Black flux 294 analytical remarks 244 Cedriret. . .. 624 Bleaching 244 Calc sinter. '.. .. ... 242 Cellulose 341 Bleaching powder 243 Calculi, biliary 487 Cement 240 testing its value 244 urinary 443, 515 Cements, lime 240 gaits 144 fusible 516 Blende 273 mulberry 516 Blood . . . 503 Calomel 303 Cerasin 340 Camphene 489 Cerebric acid 517 circulation of the 503 Camphogen 492 Cerebrolein . .. 517 Campholene , 492 Cerin 486 discs 504 Cerite 251 globules 504 Camphor 492 Cerium . 251 artificial 489 Camphoric acid 492 tyl 486 Blowpipe 158 Camphylene 489 Ccrotic acid 486 Blue ink 432 Canada balsam 494 Cerotyl .... ' 486 light .. . 290 Cane-su^ar 333 Cerotylic acid 394 Prussian 432 Candle, flame of.. 158 alcohol 394 486 Turnbull's 433 Candles, stearin 488 Cetyl-series ' 487 Boilers, deposits in 242 Boilin" 1 point 54 Canthridin 487 Caoutchouc 494 Cctylic acid 394, 486 alcohol 394 486 Bones 518 mineral 531 Chalk 241 Boracic acid 151 tubes (note) 129 stones 438 ether .. 355 Caoutchoucin 494 Chameleon mineral 259 Borax 231 Capric acid 395 Capivi, oil of . 490 petable 128 Borneol 492 Caproic acid 395,485 Chelidonic acid . 447 Boron . 151 Caproyl 395, 488 chloride of 109 Caprylicacid 395, 488 alcohol. . . . 396 488 Brass 278 Caramel 334 Chinese wax ' 486 Brazil wood 478 Carbamide 437 Chinoline 464 Bread 349 Carbazotlc arid 473 Chinoidine 448 Brewing 348 Carbides of hydrogen 153 Chloracetates 375 British gum . . 339 Carbolic acid 526 Chloracetic acid 318 375 Brornal 367 Carbon 127 Chloral 366 370 chloride of. 365 Bromanisal 491 bisulphide of 169 Chloranile 449 Bromic acid 148 compounds with oxy- Chloraniline 460 gen 128 of arsenic 292 estimation in organic Chloretheral 367 of benzoyl. . . 400 bodies 321 Chlorhydric acid . . 141 Carbonate of baryta 238 Chloric acid 145 of ethyl 353 of copper 278 Chloride of aluminium 248 of potassium 224 of lead 280 Bromine 148 of lime 241 of amyl 389 Bromi^atin . 472 of magnesia 246 of antimony. 288 Bromoform 367 387 of oxide of amyl 378 of arsenic 292 of potassa 219 of barium 237 of silver . .. 298 of benzoyl 399 of soda 225 of zinc 273 of calcium 240 Brucine 444 Carbonates 130 Bunsen's battery 194 analysis of. 228 of cinnamyl 408 Butter 485 508 of ammonia 233 of antimony 288 Carbonetted hydrogen, Butyl 392 light 153 of ethyl 353 Butylene 392 398 Carbonic acid 129 of ""old 300 Butylic alcohol 392 395 ether . ... 355 Butyric acid 395 485 oxide 130 ether 357 Carbyl, sulphate of. 365 of kakodyl 378 Butyrin 485 Carlsbad, water of 538 of lime 243 C. Carminic acid 477 of methyl 382 Cacao butter 484 Cadet's fuming liquid 377 Carthauiin.... ... 478 of nitre con ... ... 167 INDEX. 547 CnLoniDK cont. PAGE of oleliant gas 363 PAGE Citrates 414 PAQB Cumin oil 491 of phenyl 527 Citric acid 413 Cuminol . 403 491 Clarifying wines and beer 502 Cumol . 403 462* 49'' Clay iron-stone 263 Curarine 451 origin of 249 Curd 499 of silicium 169 Cyanates .... 427 of silver . 298 Coal, brown 530 Cyanethine 354 of sodium 231 Cyamelide 426 Cobalt 271 Cyanic acid 426 O f zi nc 273 analytical remarks on.. 272 Cyanide of amyl 389 Chlorides of carbon 365 366 cyanide of 426 Chlorine 139 acetate of. 374 of ethyl 354 Cobalto-cyanogen 433 of hydrogen 420 Cobalt-ultramarine 272 of kakodyl 379 bodies 328 of methyl 383 peroxide of 144 Coccus cacti 477 Chlorisatin .. . 472 Cochineal 477 Cyanides 424 Cocinic acid . . .... 484 Cyaniline 460 Chlorobenzide 399 Cocoa-oil 484 Cyanite 250 Chloro-carbonic acid 131 Codeine 446 ether 357 Cohesion 184 Coke 128 Colchicine 450 Chloroform 366 386 Collodion 344 tives 420 Chloro-hydro-salicylicacid 405 Colophene 490 iodide of... . . 430 Colophony 493 Cymol 403 491 Chlorometry 244 Columbium . . . . 286 Cystic oxide 443* 516 Chloroniceic acid 463 Combination by volume.. 177 by weight 172 D. Chloronicine 463 Dammar resin 494 Combustion 156 Daniell's battery 193 Comenic acid 447 Dutch liquid 155, 318, 363 Common salt 231 Datura stramonium 451 Chloro-naphthalic acid 630 Daturine 451 Chloropicrin 473,479 Combination, laws of. 172 Daphne mezereum 452 Chloro-saligenin 406 Daphnin 452 Decay 320 Chloro-sulph uric acid 136 364 Declination, magnetic ... 88 Chlorous acid 144 Conduction of heat 52 Decolorization by charcoal 128 Ohlorovalerisic acid . 393 Conicine 450 Deliquescence 202 Conine 450 Delphinic acid 485 Cholesterin 487 Constant battery 193 Delphinine... 451 Cholestrophane . 450 Cotarnine 446 Delphinium staphisagria 451 Cholic acid 510 Copaiba balsam 494 Dew, origin and cause of 81 Choloidinic acid 511 Copal 494 Density .... 27 Chondria 500 Copper 277 Density of vapours, deter- Chroruate of lead 267 mination of 330 alloys of 278 Dextrin .. 338 Chrome-yellow 269 analytical remarks on.. 278 Dextro-racemic acid 413 Chromic acid . . 268 ferrocyanide of 433 Diabetes 335, 514 Chromium 267 salicylide of 404 analytical remarks 268 Cork 484 Dialuric acid 442 Chrysammic acid 479 Corn-oil 393 Diamagnetic bodies 89 Corundum 248 Diamond 127 Chry^en 525 Diastase 339 Chrysolite 247 Didymium 251 Chrysophanic acid 476 Crown-^lass 252 Diffusion H2 Chyle 507 Crucibles 255 false 507 Cinchomne 447 Digestion 521 Ciuchovatine 448 Crystals 202 Dimorphism 203 Cinnabar 301 306 Crystallization 202 Dippel's oil 46& Crystalline forms 202 Disacryle . . 487 Cinnamic acid 407 Crystallization, water of 202 Disinfection 141, 244 Cinnamol 408 4% Cube 206 Cinnamyl and its com- Cubcbs, oil of 490 Disposing influence 186 pounds 407 Cudbear . . 474 Distillation 58 Circular polarization of Cumaric acid 407 dry or destructive 319 li.rht 76 Dithionic add 1^5 Circulation of the blood 503 filmic 'icid 403 4 ( tl Citraconic ucid.... ... 4U Cumidiue.... ... 402 Double salts 202 548 INDEX. PAGE Draconic acid 491 ETHER cont. PAGE hydriodic 353 PAOB Ferricyanide of hydrogen 433 Fcrricyanides 433 Dragons' blood 494 hydrobromic 353 light hydrochloric 353 margaric 357 muriatic, heavy 367 nitric 354 Dropsy fluid of ... 508 Dyes, red and yellow 477 Dyeing, action of. 470 Dvslvsin. .... 511 Ferr idcy an ogen 433 Ferrocyanides 426, 431, 433 E. Earthenware 254,255 Eblanin 388 nitrous 355 Fibrin . 497 oenanthic 357 Fire blue 290 oxalic 356 oxamic 356 damp 153 red and green 239 Ebullition 54 phosphoric 354, 359 preparation of. 360 Flame, structure of. 156 Flint-glass 252 Effervescing draughts 411 silicic 355 Florence flasks 125 E-er, water of. 539 sulphuric . . 354 Fluids, expansion of 46 Fluoride of boron 152 Egg. white of 496 Elaidic acid 484 Elaidin 484 valerianic 357 Etherin 362 of calcium 243 of silicium 150 Elain 480 Etherole . 362 Fluorine 149 Elais guianensis 483 Fluor-spar . . .... 243 Elaldehyde 370 Food 518 Elaterin 452 Ethionic acid 366 Formates 386 Formic acid 385, 395 ether . 356 Electric eel 99 Ethyl 352 bromide of 353 Electric machine ... 94 chloride of. 353 cyanide of ... 354 Electricity 92 Formo-methylal 387 Formula? 329 Electro-chemical decompo- sition . 187 iodide of 353 oxide of. 351 oxidfe of, compounds of, with acids, see Ether. 351 oxide of, cyanate of 428 oxide of, cyanurate of... 428 series, bases of 455 sulphide of 354 empirical . 329 Electrodes 187 rational 329 Electrolysis 187 French weights and mea- sures 542 Electro-magnetism 100 Frigorific mixtures 53 Electro-plating 195 Electrolytes 187 Fucusamide 466 Electrotype 194 -theory 352 Fucusine 466 Elementary bodies 103 substances, table of 176 substances, table of sym- bols 180 -zinc 368 Ethylimine 455 Fucusol 466 Fulminates 428 -urea . 456 Fulminating silver of Ber- thollet 299 Ethylamylaniline 464 Elements ... 104 Fulminic acid 428 Elemi oil of 490 Ellao-ic acid 418 Ethylene 362 Funiaric acid 416 Emerald 251 Ethylophenylamine 464 Ethylo-tolufdine 464 Furfurine 465 Emery .... 248 Furfurolamide . 466 Ethyl-oxamide 455 Furfurol 465 Ems, water of 538 Emulsin 422 Euchlorine 145 Furnace, reverberatory... 157 Fusel-oil 3^8 Euchrone 345 Epsom salt ... 246 of grain-spirit 393 Fusible metal 275 Equator, magnetic 89 Equisetic acid 413 Equisetum, acid of. 414 Equivalents, table of. 176 Eudiometer 116, 122 Euclase 250 Fustic wood 479 Eupion 523 G. Gadolinite 251 Euxanthic acid 479 law of 174 p, ,. tq Galena 279 Erbium 251 ap ra i n Gallates . 418 Gallic acid 416,418 Erytrarsin 379 Galls, nut 417 Erythric acid 474 F 1 h t "" 41 Erythroprotide 500 of fluids 46 Galvanometer 83 Galvanoscope 83,101 Essence of turpentin 489 Essential oils 488 of gases 48 of solids 44 F. Fachingen, water of 540 Fats 480 Garanciu 478 Garlic oil of 493 Ethalicacid .... 486 alcohol 486 G arnets 251 Ether 351 Gas, coal and oil 155 acetic, chlorinetted 367 boracic. . . 355 Fatty acids 395 Gases diffusion of . . 112 Fecula 337 expansion of. 48 management of 106, 111 122, 129, 132 physical constitution of 34 butyric 357 Felspar 249 Fennel-oil 491 chlorocarbonic ~. 357 cyanic 428 Fermentation 345 butyric 349 lactic 349 Gas-holder . . 107 vinous . 346 Gastric juice 521 Gaultheria procumbens, oil of 40G fcriiiic, ehlormctk'd 30? INDEX. 549 PAGE Gelatin 500 TEAT cont. PAGE PAGB Ilydrosulphocyanic ncid.. 435 Hydrosulphuric acid 163 Hygrometer, dew-point... 66 wet-bulb 62 -sugar 501 capacity for specific 66 Gentianin . . 451 German silver 271 latent 53 Geyser springs of Iceland lift Gildin- 301 phenomena of 41 radiation ... .79 Glass, coloured 253 reflection 79 manufacture of. 25'2 transmission 82 variety of 252 Heavy spar 238 Hyodyslysin 512 soluble 254 Helicin . 406 Glauber's salt 229 Gliadin 519 Helicoidin 406 Hemihedral crystals 209 Ilypochlorous acid 144 Globulin 504 Hypophosphorous acid.... 138 Hyposulphate of silver... 298 Hyposulphate of soda 229 Hyposulphite of silver.... 298 Glucic acid 330 Hematite 261 Glucinum 252 Hematosin 504 Glucose 334 Glue 502 Gluten 337, 519 Herrings, liquor of salt.... 458 Hesperidin 452 Hyposulphobenzic acid... 398 Hyposulphuric acid 135 bisulphuretted 135 Glutin . 337 Glycerin 481, 483 Heulandite " . . 251 Glyco-benzoic acid 402 Glycocine 402, 501 Hippuric acid 402 Homologous, term 396 trisulphuretted 136 Glycocoll 501 Ilomologues of aniline.... 462 of benzol 462 Hyposulphurous acid 136 I. Glyco-cholalic acid 510 Glyco-hyocholalic acid 512 Glycolamide 402 of the glycocine-series... 501 of the salicyl-series 491 Glycolic acid 402 501 Idrialin 532 Glycyrrhizin , 336 Hop 348 Goniometry . 204 oil of . 490 Inclination, magnetic 88 Incrustations in boilers.. 242 Indian yellow 479 Gold, analytical remarks. 300 and its compounds 299 Horn silver 298 Horse-radish, oil of. 493 Huano 443 Indigo 470 -dust 299 red 470 .leaf 300 Humicacid 336 vat 240 standard of England.... 299 Humus 336 white, or de-oxidized.... 471 Indin 472 Hydrate of oil of turpen- tin 489 Indinic acid 472 Inosinic acid .. 503 Grape su^ar 334 Hydride of aiiisyl 490 Hydride of benzoyl 396 Inosite 503 Graphite 128 Ink label 494 Grass oil 490 Hydride of cinnamyl 407 Hydriodic acid 147 ether 353 blue, sympathetic 271 Inulin 239 lodic acid 147 'Greenheart timber 451 Green fire 239 Hydrobenzamide . 400 Iodide of amyl 388 Green salt of Magnus 30 Groups, isomorphous 211 Hydrobromic acid 148 of arsenic ... 292 ether 353 of benzoyl 400 Hydrocarbon, chloride of 155 Hydrochloric acid 141 ether heavy 367 of ethyl . . .. 353 Guano .. 443 of kakodyl 379 Gum .. 340 Hydrocyanic acid 420 Hydroferricyanic acid 433 Hydroferrocyanic acid 430 Hydrofluoric acid 149 arabic 340 of methyl 383 IJritish 339 of silver 299 Hydrofluosilicic acid 150 Iodine 146 chloride of. 168 Gun cotton .... . 344 antimonetted 289 lodoform 387 Gun metal 279 arsenetted 292 binoxide of. 115, 119 lode-sulphuric acid 136 Iridium 312 H. Hahnemann's soluble mercury . 303 estimation in organic bodies 321 analytical remarks on.. 263 and its compounds 259 cyanide of 426 persulpmae.... ^> Ilalitus 504 protoxide, lactate of..... 351 sesquioxide, benzoate of 397 Isatin 471 Haloid salts 201 Hardness of water 241 permanent... . 241 Hydrokinone, colourless.. 44S Isatinic acid 472 temporary 242 Ilarmaline 450 Hydroleic acid 487 Ilydromargaric acid 487 Hydromargaritic acid 487 Hydrometer tables 534 Hvdrosalicvlic acid 404 Isatyde 472 Isethionic acid 3C Harmine 450 llatchetin 530 Isomeric bodies 318 Heat, absorption 81 Isomorphism.. .... 209 550 INDEX. PAGE Isomorphous 209 LECANORA cont. PAG?. PAGE Manganese, acetate of. 374 and its compounds 256 assay of. 257 Manna sugar 337 I laconic acid ... 414 J. Legumin 520 Lemons 418 Japonic acid 418 oil of 490 Lpucine 500 Mannite 337 Jet 530 Jew's pitch 531 Leucoline 464 Leukol 465 Maple, sugar from 334 Marble 241 Levo-racemic acid 413 artificial coloured 241 Marc-brandy, fusel-oil of.. 393 K. Kakodyl 377 -compounds 377 Kakodylic acid 379 Leyden jar 9G Lichens 474 Light 71 blue or Bengal 290 ether 357 Margarin 4SO 481 Marienbad, water of 539 Marietta's law 38 Lignin 341 Marsh gas 153 Lignite 530 Marsh mallow 452 Kelp 'l4fi Lignone 388 Lime 289 Marls 250 Massicot 279 Kinic acid 447 448 acetate of 373 Mastic 494 Meadow-sweet, oil of. 404 Measures 542 Kino 416 Kinone 448 analytical remarks 244 benzoate of 3^7 Kish 1^8 Meat 518 Kissingen, llagozi water.. 539 Kreatin 502 carbonate of. 241 Meconic acid 446 chloride of . .. 243 Meconine 446 Kreatinine 450 50 9 lactate of 351 Meerschaum 247 Kreosote .' 524 malate of. 415 oxalate of . . 343 Mel am 436 Melamine 43Q Kyanol 465 phosphates of 24' 7 Melaniline 461 Kyan's method of preserv- ing timber 305 L. Labarraque's disinfecting fluid 243 tartrate of 411 Limestone 241 Liquefaction of gases 62 Melasinic acid 336 Mclissic acid 394 alcohol 394 486 Mellite .. 345 Mellitic acid 345 Label ink . . 494 Litharge ^70 Mellon 435 Lac 494 Lithia 235 Membranous tissues 516 Membranes, mucous 508 Mercaptan 367 Lactamide 35o Lithicacid . .. . ... 438 Lactates 350 Lithium . 235 Lactic acid 349 Lithofellinic acid 512 methyl- 387 Lactide 350 Lactin . 336 Loadstone 8 61 acetates of 375 analytical remarks on... 306 Lake 470 Lamp, argand 159 Logwood 478 Lupulin 348 fulminate of 429 flame of. 159 safety 161 Lungs 506 its compounds... 302 gpirit .. . 159 M. Madder 477 Mesitilol 376 Meityl 376 Lampblack 128 Mesotype 250 Land and sea breezes, cause 81 Magnesia 245 acetate of 373 Mesoxalic acid 440 Metacetone 376 aconitate of 414 Metacctonic acid 376 alba 246 Metaldehyde 370 Laumonite 250 analytical remarks on.. 247 Meta^allic acid 419 Laurel oil 490 Metals 197 Luvender oil of 492 Lead 279 silicates of 247 Metamargaric acid 487 Metapectiu 340 acetates of 374 sulphate of . . . 246 alloys of . 281 tartrate of 41 1 Metappctic acid 340 analytical remarks on... 281 benzoate of 397 binoxide of. 279 Metaphosphoric acid 213 Metastyrol 495 Meteorites 259 chloride of. 245 Magnetism 86 malate of . 415 Magnus, green salt of. 309 Malachite 278 Methionic acid 366 Methyl 381 -plaster 483 protoxide of. 279 Mai amic acid 415 Methylamine 457 red 279 Malamide 415 Malates 415 -urea 457 Methyl-ammonia 457 Methyl-compounds... 381.382 Methyl-ether 382 Methyl-ethyl-amylamine. 44 -urea 4o7 sugar of. 374 -tree 195 Mai eic acid 416 white 280 Leaven 349 Malic acid 414 Malleability of metals 198 Malting 348 JiC"anoraparella 476 INDEX. 551 PAGE Methyl -ethyl -amylophe- NITRATE cont. PAOE of baryta . ... 238 OIL cont. PAOH nvlammonium, oxide of 464 of bismuth 275 of lead 280 of hops 490 Methyl-mercaptan 387 of oxide of methyl 384 of potassa . 220 of soda 230 Metbyl-salicylate of, oxide of silver 298 of 491 Nitrates 124 of mustard .... 492 Methyl-series bases of the 457 of mercury 302 of onions 493 Metoleic acid 487 Nitre 220 Metre 542 cubic 230 of orange peel 490 Mica . 250 sweet spirits of 355 Microcosniic salt 230 Nitric acid 123 Milk 508 acid fumin " 126 spirit from . . . 509 ether 354 of rose petals . 492 Milk-sucrar 336 oxide 126 Nitrile-bases . . .. 455 of valerian 492 waters table of 538 Nitro-benzoic acid 397 of vitriol 134 Molasses 334 Nitro-benzol .. 399, 462 of wine, heavy and li^ht 362 Molybdenum 284 Oils . 480 Nitro-cumic acid 403 dryin ' or non-drying... 480 Nitro-cumol 462 volatile 488 Mordant 283 Nitrogen 120 Olefiant gas 154 Mordants. 470 binoxide of 126 and its compounds 362 Morphia 444 chloride of 167 Oleic acid 482 Olein .... .. 480, 482 Mortar 240 Olive oil 488 Mosaic gold ... 283 bodies 324 Onions, oil of. 493 Mueic acid 344 iodide of 167 Opianic acid . ... 445 Mucus 508 Nitro-phenesic acid 528 Opium 444 Mulberry calculus 516 Nitro-phenisic acid 528 Orange flowers, ofl of 492 oil of -peel 490 Multiplier 83 Nitro-salicylamide 492 Orcein 476 Nitro-salicylic acid 406 473 Orcin 474, 476 Murexide . . 442 Nitro-toluol .. 462, 495 Organic bases 444 caiFein 450 Nitro-toluylic acid 403 bases, artificial 453 Muriatic add 141 Nitrous acid 126 substances, action of ether ... 355 heat on 319 oxide 125 substances, classificar \itro-xylol 462 tion 319 Must 347 substances, composition Mustard oil of 492 Norium 352 elementary 316 Notation chemical 180 substances, decomposi- Mvkomelinic acid 440 Nutgalls 417 tion of 319 Myricin 492 Nutrition, plastic ele- substances, ultimate Myristicacid 484 ments of 520 Orpiment 292 Myrouicacid 493 0. Orsellinic acid 474, 475 N. Oxalate of oxide of methyl 384 Naphtha 531 ether 357 Oxalates 342 Niphthalidine 462 (Enanthylic acid 395 Oxalic acid 341 Niphthaliu 462 529 Oil gas 155 ether 356 Narceine 446 of alliaria ofilcinilis 493 Oxalo-nitrile 461 of aniseed 490 Oxalc-vinic acid 359 Oxaluricacid 440 Nepheline 250 of badian .. .. 491 Oxamethane 356 Oxamic acid 343 ether 356 Nickel 269 Oxamide 343 Oxanilic acid 461 lottate ol o/ ot ceaar wood Oxanilide 461 Nicotine 450, 469 ofelemi 490 Oxide, cystic 443 f 11 i t^S Niobium 286 \itran iline 460 of cubebs 490 of amyl, hydrated 38 of benzoyl 396 Nitraniside 490 of gaultheria procum- of bismuth 275 Nitrate of ammonia 234 bene 406,491 552 INDEX. OXIDE cont. PAGE of kakodyl 377 PJIENTL cont. PAGE chlorite of. 527 POTASSA cont. PAGE ol methyl 382 cyanide of 527 hydrated oxide 26 series, bases of. 459 chlorate of... 221 of methyl, hydrated.... 381 xanthic 443 cyanate of 426 nitrate of 9 20 Oxides 109 of antimony 288 Philosophy, chemical 170 Phloretin 406 perch lor ate of. 222 sulphate of 2''! Phloridzin 406 of hydrogen 115 of mercury .. 302 Phocenic acid 485 urate of 438 Phorone 492 Potassium and its com- of platinum 308 of potassium 218 Phosphate of lime 241 Phosphate of magnesia... 246 of magnesia and ammo- nia 246 bromide of 224 of silver 297 chloride of 2 9 3 of sodium 224 of zinc .. ... 273 Oxygen 105 Phosphate of soda 230 Phosphethylic acid 359 Phosphide of calcium 241 Phosphobiethylic acid 359 Phosphoretted hydrogen. 166 Phosphoric acid 138 -acids 201 salicylide of 404 Oxy-hydrogen, flame and sulphocyanide of. 434 Potuto-oil 488 safety-jet 161 Oxy-salts 201 Precipitate white 305 Ozone 110 acid, anhydrous 213 acid, bibasic 213 Prehni^e 250 P. Palladium, cyanide of 311, 426 Palmitate of oxide of me- lissyl 486 Proof-spirit 347 acid, glacial 213 acid, monobasic 213 acid tribasic 212 Proportionals 174 Proportions, multiple 173 ether 354 359 Palmitin 485 Phosphorous acid 138 Phosphorus 137 Palmitic acid 485 Protein 499 Papaverine 446 -bases 468 chloride of 168 binoxideof. 500 Parabanic acid 440 compounds of. 138 Protide 500 Paracyanogen 420 Paraffin 523 Phosphovinic acid 358 Protochloride of tin 2S3 Parakakodylic oxide 380 Param agnetic bodies 89 Paramide 345 Phthalic acid t 529 Picamar 524 Prussiate of potash, red... 433 ycl'ow 4^1 Picoline. 465 Picric acid. 473, 528 Parainylene 390 Picro-erythrin 475 Frussic aciu....^ 4^lJ Paranaphthalin 530 Parapectin 340 Picrotoxin 452 Pimaric acid 494 Paratartaric acid 413 Pinic acid 493 Parellic acid . . 476 Piperine 451 Purple of Cassias 283 Purpurate of ammonia... 442 Parmelia parietina 476 Pear, flavour of. 389 Pitch 523 Pearlash 219 Pit-coal 530 Pectio acid 340 Plants, supply of carbon to 130 Pcctiu 840 Pelargonic acid 357,395 Plaster of Paris 241 Purrenone 470 Peutathionic acid 136 Pepper, oil of. 490 Platinum and its com- pounds 307 Pus 508 Putrefaction 3 9 Peppermint, oil of. 492 Pepin 521 analytical remarks 310 bases 309 Pyrites 262 Perchlorate of potassa ... 222 Perchloric acid 145 black .... 307 Pyroacetic spirit 376 surface-action of.... 114, 115 Plumbago 128 Polarity, magnetic 86 Percussion-caps 429 Periodic acid 148 Pyrobenzolin 466 Peroxide of chlorine 144 Persulphide of hydrogen. 165 Peru balsam 408 Pyrogen acids 419 Pontil or puntil 253 Populin 452 Peruvin 408 Porcelain 254 Pyrophorus of Horn berg.. 249 Pyrophosphoric acid 213 Petalite 250 clay 250 Porphyroxine 446 Pettenkofer's bile-test 511 Potash 218 crude 219 Petrolene . 531 Potassa 218 Q. Quercitron bark 479 Petuntze .. 255 acetate of 373 Phenetol 527 alum 249 I'henol 491 526 analytical remarks on.. 224 Quicksilver . . 301 Phenyl 524 Quina . 447 alcohol 459 527 bicirbonate of ^*^0 Oiiiniilinn.... ... 448 benzcaterf ... 527 bisuluhide of. 221 1 Quinine.... ,...447 INDEX. 553 Quinine, amorphous PAGE 448 464 PAC.E Saponification 4S1 ! Saratoga Congress spring 539 448 R. 79 Schlesischer Obersalz- 413 292 Sca-liola 241 477 Sea^water 118 lied fire 239 Sebacic acid 484 Red lead 279 Seed lac 494 79 ggo-o-ars 254 of light Refraction, double... of light 71 75 72 499 Serdchutz, water of. 541 SeiTiette salt 411 Selenic acid 136 Selcnietted hydrogen 165 Selenious acid 136 493 506 Selenite . .. 241 506 Se^nium 136 532 lletinite 532 Reverberatory furna ce.... 158 .. .. 312 Serpentine . 247 Seruni of blood 504 Rhodizonic acid 345 488 Silica 150 Silicates of alumina 249 of magnesia , 247 Ilocella tinctoria Rocellinin . . . 474, 475 475 Silicic ether 355 . ... 411 Silicium 149 Rock oil 532 chloride of 169 Rock salt 232 fluoride of 150 249 492 analytical remarks 299 Rubia tinotorum.... 477 478 cyanide of 426 Jlubiacic acid 478 Rubian 478 Rubic acid 418 standard of England.... 299 Rust 260 Ruthenium 314 Sinapoline 467 S. Saccharic acid 343 Size . 502 Shellac 494 333 Skin 517 336 Smee's battery . . 194 Sacchulmin Safety-lamp 336 161 Smalt 272 Soap * 481 478 Saffron 479 Soap-test of Dr. Clark 241 339 Sal-alembroth .. Rflfi a l um 249 Sal-ammoniac 233 Salicin 403, 452 Salicyl and its compounds 403 hydride of 452 analytical remarks on... 232 ash 225 ash, testing its value.... 228 bicarbonate of 226 Salicylate of oxide of me- thyl 401 hydrate of 224 Salicylic acid 406 Salicylides 404 tartrates of. 411 Salicylous acid . 404 urate of . 438 405 Sodium 224 Pal ire tin 405 cyanide of 44 Saliva 521 Salsola soda Salt, definition 225 109 oxides of. 224 of sorrel Salts, super or acid binary theory of. constitution of.... 342 202 '.'.'.'.'.'.'. 199 OQ9 Solder 281 Solids, expansion of. 44 Sorrel, salt of 342 Spa Pouhon, water of. 540 neutral 200 Spar'teine 450 Specific gravities of metals 197 gravity of solids and Saltpetre Sandarac . 123, 220 494 Santonin 45*^ 47 PAGE Specific heat 66 Speculum metal 279 Spectrum 74 peiss 269 Spermaceti 486 Spirit from milk 509 of Mindererus 373 pyroxylic 381 Spirits, table of spec. gr. of 537 Spudomene 250 Springs 118 Starch 337 State, change of, by heat.. 52 Steambath 57 Steam engine 57 specific gravity of. 118 latent heat of 53 Stearic acid 481 Stearin 481 candles 482,483 Stearoptene 489 Steatite 247 Steel 265 Stibethyl 3C9, 469 StScklac 494 Stillbite 250 Stoneware 255 Strontia 239 acetate of. 373 - tartrateof 411 Strontium and its com- pounds 239 Strychnine 449 Styphnic acid 479 Styracin 408 Styrol 408, 495 Styrone 408 Suberic acid 345, 484 Sublimate, corrosive 304 Sublimation 58 Substitution, law of. 317 products, organic 317 Succinicacid 484 Sugar 833 candy 334 copper, test for the va- rieties of. 335 from diabetes 335 from diabetes insipidus 336 from starch or dextrine 338 gelatin- 402,501 of lead - 374 of milk 336 Sulphamylic acid 390 Sulphasatyde 472 Sulphate of alumina 249 of ammonia 233 of baryta 238 of carbyl 365 of copper 278 oflime 241 of magnesia 248 of oxide of methyl 384 ofpotassa 221 of silver 2! is of soda 229 of zinc 273 Sulphates of mercury 303 Sulphesatyde 472 Sulphide of allyl 493 of amyl 390 of arsenic 292 554 INDEX. SULPHIDE cont. PAGE of barium 238 of benzoyl 400 of calcium 241 of ethyl 354 of kakodyl 379 of silver 299 of sodium 231 Sulphides 132 of ammonium 234 of antimony 289 of mercury 306 of potassium 222 of tin 283 test for 434 Sulphindigotic acid 471 Sulphindy lie acid 471 Sulphite of oxide of ethyl 354 Sulphites 133 Sulphobenzide 398 Sulphobenzoic acid 397 Sulphocyanide of allyl.... 493 Sulphocyanides 434 Sulphocyanogen and its compounds 434 Sulphoglyceric acid 483 Sulpholeic acid 487 Sulphomethylic acid 383, 384 Sulphomargaric acid 487 Sulphonaphthalic acid 529 Sulphophenic acid 526 Sulphosaccharic acid 335 Sulphotoluolic acid 495 Sulphovinic acid 358 decomposed by heat 359 Sulphur 131 acids 201 auratum 289 bases 201 chloride of. 168 compounds with oxygen 132 estimation in organic bodies 328 salts 201 Sulphuretted hydrogen... 163 Sulphuric acid 133 ether 354,366 Sulphurous acid 132 ether 354 Super salts 202 Surface -action of plati- num, charcoal, gold, &c 114, 115, 128 Sylvic acid 493 Symbols 180 Synthetical method of chemical research 115 Systems of crystals 206 Synaptase 422 T. Tannates 417 Tannic acid 416, 417 Tannin 416, 417 Tanning 417, 517 Tantalum 286 Tapioca 339 Tar 523 mineral 531 -oil stearin 523 Tartar 410 cream of. 411 emetic 288, 411 oluble 411 PAGE Tartaric acid 410 TURPENTIN cont. PAOH Venetian 494 Type metal . .. ... 290 Tartralic acid 412 Tyrosine 477 497 Tartrates 411 Twaddell's hydrometer.... 535 II. Ulmic acid 336 Tartrelic acid 412 Tartrovinic acid 359 Taurin 511 Tauro-cholalic acid 511 Ulmin 336 Tauro-hyo-cholalic acid... 512 Teeth .. 518 Ultramarine . 231 Telluric acid 290 Uramile 441 Tellurium 290 Uramilic acid 441 Tension 24 Urites 438 Tension of vapours 59 Terbium 251 Urea 427,436 Terebene ... 490 Terebylene 489 Uric acid 436, 438, 515 Tetra-chloro-kinone 449 Tetra-methyl-ammonium, hydrated oxide of 458 Tetramyl-ammonium. hy- Urinary calculi 443, 515 Urine 512 TIsnif arid 476 Tetrathiomc acid 135 V. Tetrethyl-ammonium, ox- ide of 456 Thebaine.' 446 Valenmide ' 391 Theine 450 Valerianic acid 390 492 Theobromine 451 ether 357 Thermo-electrical pheno- mena 83 Valerian, oil of 492 Valeric acid 390, 395, 492 Valerene 483 Thermometer 42 Thialdine 370, 467 Valerol 492 Thionuric acid 441 Valeronitrile 391, 501 Valyl .. 392 Thoria 252 Vanadium 285 Thorite 252 Vapour of water, tension. 636 Vapours, determination of thedensityof. 330 maximum density of.... 60 tension of 59 Thorium 252 Tin 282 analytical remarks on.. 283 Tinned plate 284 Tissue, membranous 516 Titanium 287 Tolene . 495 Varec 225 Variolaria 474 Tolu balsam 408, 495 Vegetable acids 410 Toluidine 462, 463 Toluol 403,462,495 nutrition 522 Vegeto-alkalis . 444 Toluylic acid 403 Venous blood 503 Tonka bean 406 Trade winds 50 Ver atria 449 Transmission of heat 82 Travertin 242 Veratrine 449 Verdigris 374 Verditer 278 Triamyl-ammonia 458 Tribasic acids 212 Vermilion 306 Vinous fermentation 346 Viscous fermentation 351 Vitriol blue 278 Trichlor-aniline 460 Trichloro-kinone 449 Triethylamine 456 Triethyl-ammonia 456 Triethyl-stibin 469 Trimethylamine ,.. 458 Trimethyl-ammonia. 458 Trithionic acid 135 Trona 226 oil of . 134 oil of fuming 134 Volatile oils 488 Volume, combination by. 177 VoHaic battery 98 Tungsten 284 pile, chemistry of the... 187 Voltameter ~ 190 Turkey red 478 Turnbull's blue 433 W. Wash, distiller's 348 Water 115 hydrated oil of. 490 oil of. 489 analysis of 115 INDEX. 555 WATER cont. PAGE distilled 118 expansion by heat 47 hardness of 241,242 of crystallization 202 oxygenated 119 tension of its vapour.... 59 Wax 486 fossil 532 Weights 542 specific 27 Welding 199 Whey 499, 508 White lead 280 precipitate 305 Titriol 273 Winds 50 Wine 347 clarifying of. 502 Wintergreen oil 406 Witherite . 238 PAGE Wolframium 284 Wood ether 382 spirit 381 Woody tissue 341 Wootz 2F8 Wort 348 Xanthic acid 368 oxide 443,516 Xanthin 478 Xanthorrhceahastilis 473 Xylidine 462 Xylite 388 Xyloidin 341 Xylol 348 Y. 346,348 PAGE Yellow dyes 477 Yttria 251 Yttrium 251 Z. Zaffer 272 Zeise's combustible pla- tinum salt 365 Zeolites 250 Zinc 272 analytical remarks 273 cyanide of. 426 -ethyl 368 fulminate of. 429 lactateof. 351 Zinin's process 479 Zircon 252 Zirconia 252 Zirconium 252 THE END. CATALOGUE OF MEDICAL, SURGICAL, AND SCIENTIFIC WORKS, PUBLISHED BY BLANCHAKD & LEA, PHILADELPHIA. 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