UC-NRLF B 3 HEl ^3M LIBRARY OF THE DENTAL DEPARTMENT, UNIVERSITY OF CALIFORNIA. This book must be returned within four days. Fine, five cents each day for further detention. '4 /?-z>f- FOWNES MANUAL OF CHEMISTRY. -^ ^C J>h&f/-»-~^ f^ f' ^i NTARY CHEMISTRY, THEORETICAL AND PEACTICAL BY ^ GEORGE FOWNES, F.R.S., lATS PROFESSOK OF PBAX3TICAL CHXMISTRT IN CNIVEBSITX COLLEGE, LONSOir. EDITED, WITH ADDITIONS, BT ROBERT BRIDGES, M. D., PR0PES80E OF CHEMISTRY IX THE PHILADELPHIA COLLEQB OF PHARMACT, ETC. ETC. WITH NUMEROUS ILLUSTRATIONS ON WOOD. PHILADELPHIA: BLANCHARD AND LEA 1857. 1^ Entered, according to Act of Congress, in the year 1863, by BLANCHARD AND LEA, in the Clerk's Office of the District Court of the United States for the Eastern District of Pennsylvania. COLLINS, PRINTER ADVERTISEMENT TO THE 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 marked favour which it has received as an elementary text-book. Philadelphia, October, 1853. 1* (T) Digitized by tine Internet Arcinive in 2007 witii funding from . IVIicrosoft Corpoi-ation littp://www.arcliive.org/details/fownesmanualofchOOfownricli 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 aa 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 (yii) VIU 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. Univebsitt CoLLEaE, 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 in 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 me he should "do no more," — he had "finished his work." At his request I have corrected the press throughout, and made a few alterations that appeared desirable in the only part which he had left unaltered, the Animal Chemistry. The index and the press have also been corrected throughout by his friend Mr. Robert Murray. H Bence Jones, M.D. ), Geosvknok Stebet, Jan.y 1850. (ix) ADVERTISEMENT TO THE 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 the 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. H. Bence Jones. A. W. HOFMANN. « London, September, 1852. (^) TABLE OF CONTENTS, PAGI Introduction 25 PART I. PHYSICS. Of densitt and specific gravity. Methods of determining the specific gravities of fluids and solids 27 Construction and application of the hydrometer 32 Of the physical constitution op 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 38 Heat. Expansion. — Thermometers 41 Different rates of expansion among metals; compensation-pendulum 44 Daniell's pyrometer 45 Expansion of liquids and gases. — Ventilation. — Movements of the atmo- sphere 46 Conduction of heat 62 Change of state. — Latent heat 52 Ebullition; steam 54 Distillation 58 Evaporation at low temperatures 59 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 , (xiii) XIV CONTENTS. LiaHT. PAOB Reflection, refraction, and polarization of light 71 Chemical rays 77 Kadiation, reflection, absorption, and transmission of heat 79 Magnetism. Magnetic polarity; natural and artificial magnets 86 Terrestrial magnetism 88 Electricitt. "* Electrical excitation; machines 92 Principle of induction ; accumulation of electricity 93 Voltaic electricity 97 Thermo-electricity .-^Animal electricity 99 Electro-magnetism; magneto-electricity 100 Electricity of steam 10? PART II. CHEMISTRY OF THE ELEMENTARY BODIES. NON-HETALLIC 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 Seleniuip 136 Phosphorus; compounds of phosphorus and oxygen 137 Chlorine; hydrochloric acid. — Compounds of chlorine and oxygen 139 Iodine 143 Bromine 148 Fluorine 149 Silicium 150 Boron 151 COMPOTTNDS FORMED BY THE UNION OP THE NON-METALLIC ELEMENTS AMONG THEMSELVES. ' Compounds of carbon and hydrogen. — Light carbonetted hydrogen ; olefiant gas; coal and oil-gases. — Combustion, and the structure of flame 163 Nitrogen and hydrogen; ammonia 162 CONTENTS. XV PA.GB Sulphur, selenium, and phosphonis, 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 GENSBAL PBUtCIPLES OF CHEKICAL PHILOSOPHT. Komenclature 170 Laws of combination by weight 172 By volume 177 Chemical symbols ISO 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 25G Iron 259 Aridium 206 Chromium 267 Nickel 269 Cobalt 271 Zinc 272 Cadmium 274 Bismuth 274 Uranium 276 Copper 277 Lead 279 Tin 2S2 XVl CONTENTS. Tungnten , 284 Molybdenum 284 Vanadium 285 Tantalum (columbium) 286 Niobium and pelopium 286 Titanium 287 Antimony 287 Tellurium 290 Arsenic 291 Silver 296 Gold 299 Mercury 301 Platinum 307 Palladium 311 Rhodium 312 Iridium 312 Euthenium 314 Osmium 314 PART III. ORGANIC CHEMISTRY. Introduction 316 Law of substitution 317 The ultimate analysis op organic bodies 320 Empirical and rational formuljs 329 Determination op the density op the vapours op volatile liquids .... 330 Saccharine and amylaceous substances, and the products op their alteration 333 Cane and grape-sugars j 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 361 Sulphovinic, phosphovinic, and oxalovinic acids 358 Heavy oil of wine 362 Olefiantgas; Dutch liquid; chlorides of carbon 362 CONTENTS. XTll PAOB Ethionio and isethionio acids 365 Chloral, &o 366 Mercaptan ; xanthic acid 367 Aldehydej aldehydic acid; acetal 369 Acetic acid 371 Chloracetic acid 375 Acetone 376 Kakodyl , 377 Substances hore or less allied to alcohol. Wood-spirit; methyl-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 chlorovalerosio acids 393 Fusel-oil from grain-spirit; general view of the alcohols 393 Bitter-almond-oil and its products; benzoyl-compounds 396 Benzoic-acid ; sulphobenzoic acid ; benzone and benzol 396 Sulphobenzide and hyposulphobenzio acid 398 Nitrobenzol, azobenzol, &c 399 Formobenzoic acid; hydrobenzamide ; benzoin; benzile; benzilio 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 411 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, Ac^, of cyanogen 429 2* XVlll CONTENTS. PAGE Ferro- and .Wricyanogen, and their compounds; Prussian blue 430 Cobaltocyanogen ; nitroprussides 433 Sulphocyanogen, and its compounds ; selenocyanogen ; melam ; melamine ; ammeline; ammelide , 434 Urea, and uric acid 436 Allantoinj alloxan; alloxanic acid; mesoxalio acid; mykomelinio acid; parabanic acid ; oxaluric acid ; thionuric acid ; uramile ; alloxan tin ; murexide; murexan 438 Xanthio and cystic oxides 443 The vegkto-alkalis, and allied bodies. Morphine, and its salts 444 Narcotine; opianio and hemipinic acids ; cotarnine 445 Codeine; thebaine; pseudo-morphine; narceine; meconine 446 Meconic acid 446 Cinchonine and quinine; quinoidine 447 Kinio acid; kinone; hydrokinone 448 Strychnine and brucine ; veratrine 449 Conicine; nicotine; sparteine; harmaline; harmine; caffeine or theine; theobromine; berberine ; piperine; hyoscyamine; 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 j oxide of tetrethyl-ammonium , 455 Bases of the methyl-series. — Methylamine; bimethylamine; trimethyla- mine; oxide of tetramethyl-ammonium 457 Bases of the amyl-series. — Amylamine ; biamylamine ; triamylamine ; oxide of tetramyl-ammonium 468 Bases of the phenyl-series. — Aniline; chloraniline ; nitraniline; cyaniline; melaniline 459 Bases homologous to aniline. — Toluidine ; xylidine ; cumidine. Naphthali- dine; chloronicine 462 Mixed bases. — Ethylaniline; biethylaniline ; oxide of triethylamyl-ammo- nium ; biethylamylamine ; oxide of methylobiethylamyl-ammonium ; methylethylamylamine ; ethylamylaniline ; oxide of methyl-ethyl-amylo- phenyl-ammonium 463 Bases of uncertain constitution. Chinolin* T. 464 Kyanol; leucol; picoline 465 Petinine 466 Furfurine 465 CONTENTS. XIX PAQB Fucusine; amarine; thiosinnamine 466 Thialdinoj alanine 467 Phosphorus-bases 468 Antimony-bases 469 Organic colouring principles. Indigo; white indigo; sulphindylic acid 470 Isatin; anilic and picric acids ; chrysanilio and anthranilic acids 471 Litmus — lecanorin; orcin; orcein, Ac 474 Cochineal, madder, dye-woods, Ac 477 Chrysammic, chrysolepic, and styphnic acids 479 QiLS and fats. Fixed oils ; margarin, stearin, and olein ; saponification, and its products ; 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 Ca«tor-oU; caprylic alcohol 488 Volatile eila. — Oile 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, Ac 492 Resins. — Caoutchouc 493 Balsams. — Toluol, styrol 494 Components op the animal body. Albumin, fibrin, and casein; protein 496 Gelatin and chondrin 600 Kreatin and kreatinine •. 602 Coojposition of the blood ; respiration; animal heat 603 Chyle; lymph; mucus; pus 507 Milk; bile; urine; urinary calculi 608 Nervous substance ; membranous tissue ; bones 616 The function of nutrition in the vegetable and animal kingdoms 618 Products op the destructive distillation, and slow putbefactivi: CHANGE OP organic MATTER. Bubstances obtained from tar. — Paraffin; eupione; picamar; kapnomorj cedriret; kreosote; chrysen and pyren , 623 XX CONTENTS. , PAQH Coal-oil. — Carbolic acid (hydrato of oxide of phenyl) 626 Naphthalin and paranaphtballn 529 Petroleum, naphtha, and other allied substances 530 A.PPENDIX. 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 " *• « 39 5 " * 10 6 " •* beads 31 7 Hydrometer 32 8 Urinometer 32 9 Specific gravity 33 10 Elasticity of gases 34 11 Single air-pump 35 12 Double " 36 13 Improved" 36 14 " " Z7 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 Atmospheric currents 50 30 « « 50 31 " " 51 32 Boiling paradox 55 .S3 Steam-bath 57 34 Steam-engine 57 35 Distillation 66 36 Liebig's condenser 59 37 Tension of vapour 69 38 " " 60 89 Wet-bulb hygrometer 62 (xxi) XXll 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 Keflection of light 72 46 Refraction of light 72 47 " " 72 48 " " 73 49 Spectrum 74 50fc « 74 51 Polarization of light 75 62 " " .) 76 63 " " 76 64 Reflection of heat 79 66 « " 80 56 Effects of electrical current on the magnetic needle 82 67 « " " " 82 58 Current produced by heat 83 69 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 66 Electrical machine 95 66 " " plate 95 67 Leyden jar 96 68 Electrophorus 97 69 Volta'spile 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 Pepy's hydro-pneumatic apparatus 107 81 Apparatus for hydrogen Ill 82 Levity of hydrogen Ill 83 Diffusion of gases 112 84 Daniell's safety-jet 113 85 Musical sounds by hydrogen 114 U Cataly*'c effect of platinum 115 LIST OF ILLUSTRATIONS. XXlll Fig. l^age 87 Decomposition of water 116 88 Eudiometer of Cavendish 116 89 Analysis of water • • 116 90 Preparation of nitrogen 120 91 Analysis of air 121 92 Ure's eudiometer 122 93 Preparation of nitric acid 123 94 " protoxide of nitrogen 125 95 Crystalline form of carbon 127 96 " " " 127 97 « " « f27 98 " " " « 127 99 Preparation of carbonic acid 129 100 Mode of forming caoutchono 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 142 107 Safety-tube 143 108 Combustible under water 145 109 Preparation of hydriodic acid 147 110 « silica - 150 HI Blast furnace 167 112 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 « 16C 119 Gas « 16C 120 Davy's safe " t 161 121 Hemming's safety-jet 161 122 Effect of metallic coil 161 123 Apparatus for sulphuretted hydrogen 16< 124 Multiple proportions 18i 125 Water in its usual state 18J 126 " undergoing electrolysis 189 127 Voltameter 190 128 Decomposition without contact of metals 191 129 Wollaston's voltaic battery 193 130 Daniell's constant « 193 131 Grove's *• " 194 132 Electrotype 195 133 Lead-tree 295 XXIV LIST OP ILLUSTRATIONS. Fig. Page 134 Wire-drawing 198 135 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 207 142 " doubly oblique prismatic system 208 143 Crystals, rhombohedral system 208 144 " passage of cube to octahedron 209 145 " « " octahedron to tetrahedron 200 146 Alkalimeter 227 147 Apparatus foi determining carbonic acid 228 148 " " " " " 229 149 Iron manufacture. Blast-furnace 264 150 Crystals of arsenious acid 293 151 Subliming tube for arsenic 294 152r Marsh's test 295 153 Weighing tube 321 154 Combustion .- 321 155 Chauffer 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 " benzoic acid.... 397 172 « tannic acid 417 173 Uric acid crystals 438 174 Blood globules 504 \Sb Pus " 608 176 Milk " 508 177 Trommer's test 514 178 Uric acid calculus 515 179 Urate of ammonia calculus 515 180 Pusiblo calculus 516 181 Mulberry calculus 516 MANUAL OF CHEMISTRY INTRODUCTION. Thb 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 suflFering 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 (26) 26 INTEODUCTION. 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. PART I.— PHYSICS. OF DENSITY AND SPECIFIC GRAVITY. It is of great importance in the ontset to trnderstand 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.* 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 60°, 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 figure 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° -50). Such a flask is readily procured from any one of the Italian artificers, to be foimd in every large town, who manufacture cheap thermometers for sale. A counterpoise of the exact weight of the empty * In other words, density means comparative mass, and specific gravity comparative weight. These expressions, although really relating to distinct things, axe often used quite indiffe- rently in chemical writings, and without practical inconvenience, fiince maae and weight are d'rectly proportional to each other. (27) 28 DENSITY AND SPECIFIC GRAVITY. Fig. 1. 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 is 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 \»hich, 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 difi'ers 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 facUity, 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 suspendeu 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 tie bucket to the brim, whereupon the equilibrium ffill 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°-5C), 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. Fig. 3. 30 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 -■-■o.g = 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, Fig. 5. namely, the weight of an equal bulk of air, is so trifling that it is usually neglected. Sometimes the body to be examined is lighter than water, and floats. In this case it is first weighed and afterwards attached to a piece of metal (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 difterence 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 60-0 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 — ^•9^^8- 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 diflBculties. 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. 81 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, !1« = 1.6. 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 QQ- = 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 ^^S- 6. 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, / p«^ 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. 6) ff^ ' 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 indifl'erently 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 off". 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 same in all. The graduation is very commonly arbitrary, two or three difi'erent 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.* 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 difi^erences 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. ' This and other instruments described or figured in the course of the work, may be had of rtr. Newman, 122 Regent Street, upon the excellence of whose workmanship reliance may be safely placed. * 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. — & B. DENSITY AND SPECIFIC GRAVITY. 33 •♦ Ojcygen," and that of the vapour of a volatile liquid in the Introduction to Organic Chemistry/ * 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 veight sustained in each case will give the relative weights of equal hulks 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, ">L!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, jfo* example : — The glass rod loses by immersion in water 171 f* *«•«. The glass rod loses by immersion in alcohol 143 — =.•836 the specific gravity required. — R. B. Fig. 9. m PHYSICAL CONSTITUTION OF THE PHYSICAL CONSTITUTION OP THE ATMOSPHERE, AND OF GASES IN GENERAL. Fig. 10. 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 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. Wc are quite safe in the assumption, that, for ail 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: matter is under the influence of tw^o 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, and gaseous. When the particles of matter, in consequence of the direction and strength of their mutual attractions, possess only a very slight power of motion, a solid substance results ; when the forces are nearly balanced, we have a liquid, the particles of which in the interior of the mass are free to move, but yet to a certain extent are held together ; and, lastly, when the attractive power seems to be completely overcome by its antagonist, we have a gas or 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 A 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 transmitteel pressure from above, and communication with the receiver is cut oflF. As the descent of the piston continues, the air included within the cylinder be- 36 PHYSICAL CONSTITUTION comes compressed, its elasticity is increased, and at length it forces opep 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. Pig. 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 ■""ig. 18. 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 stufiing-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 "'^ sufi"ers 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 OP THE ATMOSPHERE. 87 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 toe 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, tmtil 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 measureji, 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 bj 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, the fluid sinks away from the top of the tube, until it stands at the height of about 30 inches above the level of that in the basin. Here it remains supported by, and balancing the 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 is thus expressed : — The volume of a gas is inversdy as the pressure ; the density and elastic force are directly as the pressure, and inversely a« 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 Marietta, 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 thp 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 I bi 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 Dulong published, in the year 1830, an account of certain experiments made by them in Paris, in which the law in question had been verified to the extent of 27 atmospheres. All gases are alike subject to this law, and all va- pours of volatile liquids, when remote from their points of liquefaction.' 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- f .,^ ■'!H):i^ pressed 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 _ Height of barometer, sea, in miles. Volume of air. 1 in inches. 30 2-705 2 5-41 4 8- 115 8 10-82 16 13-525 32 0-9375 16-23 fid ft./lAa7K * When near the liquefying point the law no longer holds; the volume diminishes m(/rt rapidly than the theory indicates, a smaller amount of pressure being then sufficient. 40 PHYSICAL CONSTITUTION OP THE ATMOSPHERE. f I' 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 2-6 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 vrith 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 T)osition, 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, lastly, attached to a board, and furnished with a long scale, made to slide, which may be of box-wood, with a slip of ivory at each end. When an 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 be convenient to consider the subject of Heat under several sec- tions, and in the following order : — 1. Expansion of bodies, or effects of variations of temperature in altering their dimensions. 2. Conduction, or transmission of heat. 3. Change of state. 4. Capacity of bodies fop 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 ^0 a gauge when cold, heated considerably, and again applied to the guage, it will be found to have become enlarged in all its dimensions. When cold, it will once more enter the gauge. Again, if a quantity of liquid contained in a glass bulb (fig. 19), furnished with a narrow neck, be plunged into hot water, or exposed to any other Fig. 18. I Fig. 19. Fig. 20. 1= ft source of heat, the liquid will mount in the stem, showing that its volume has been increased. Or, if a portion of air be confined in any vessel (fig. 20), the application of a slight degree of heat will suffice to make it occupy a space sensibly larger. This most general of all the effects of heat furnishes in the outset a prin- ciple, by the aid of which an instrument can be constructed capable of taking cognizance of changes of temperature in a manner equally accurate and con- venient : such an instrument is the thermometer. A capillary glass tube is chosen, of uniform diameter ■ one extremity is closed and expanded into a bulb, by the aid of the \»lowpipe flame, and the 4 * 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 oif 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 render 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 difl&- culty. Let it be required, for example, to know the degree of Fahrenheifa scale which corresponds to 60° centigrade. 100° C. == 180° F., or 6° 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 aff'ected 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 diflFerences of temperatures between the two portions of air, while changes afi'ecting both alike are not indicated. Fig. 22 shows another form of the same instrument. Fig. 21. 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 artifi- 44^ HEAT. oially 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 lo insiij^ on the importance of possessing instruments for the accurate mea- surement of time ; such are absolutely indispensable to the figr 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 nun^ ber of beats made by a pendulum : now the time of oscillation of a pendulum de-pends principally upon its length ; any altera- tion in this condition will seriously affect the rate of the clock. The material of which the rod of the pendulum is composed is subject to expansion and contraction by changes of 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° (10°C), 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 c'rcumstances of temperature fin invariable distance between the point? of If jspensiou and of oscillation. This is often called the gridiron HEAT. 45 ■ Fig. 26. pendulum ; fig. 24 will clearly illustrate its principle ; the shaded Fig. 26. 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, which 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 multipled 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. 'Qy this instrument the melting-point Fig. 27. 46^ HEAT. of cast iron was fixed at 2786° Fahrenheit (1530°C), and the greatest. heat of a good wind-furnace at about 3300° (1815°C). . The actual amount of expansion which diflferent 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° (0°C) to 212° (100°C). English flint glass TTi'S Soft iron ¥«2 Common French glass ri^T Gold Glass without lead . ttVi Copper Another specimen Tir^ff Brass Steel untempered 9?T Silver . . T^T Tempered steel T Lead ^r Prom 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 P^clet's Elemens de Physique. Apparent Dilatation in Glass between 32° (0°C) and 212° (100°C). Water 2I Hydrochloric acid, sp. gr. 1-137 . . • • 2V Nitric acid, sp. gr. 1*4 jf Sulphuric acid, sp. gr. 1*85 Xf Ether ^ yV Olive oil Y2 Alcohol ^ Mercury -si 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° (lOOoC) expands irregularly, as the following table shows. HEAT 47 Absolute Expansion of Mercury for 180°. Between 32° (0°C) and 212° (100°C) .... s\-^ Between 212° (100°C) and 392° (200°C) .... 5^35 Between 392° (200°C) and 572° (300°C) .... 3^3. 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° (0°C), 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° (0°C) be 6 inches high, and that at 212° (100°C) 6108 inches, the increase of height, 108 on 6,000, or -^^.-^ 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. ' 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 is necessary to advert to it particularly. Let a large thermometer-tube be filled with water at the common tempe- 1 Below 400° Fahrenheit (204O-4C) the error may be neglected; at 500° (260OC) it is alxmt 1"; at 630° (332°-5C) 6°. — Regnault. 48 HEAT. V rature of the air, and then artificially cooled. The liquid will be observed to contract regularly, until the temperature falls to abc/lit 40° (4°-4C), or S° 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 60 sudden and violent an enlargement takes place, that the vessel is almost invariably broken. At the temperature of 40° (4° -40), or more correctly, perhaps, 39°-5 (4°'1C), 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° (10°C) 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° -40) after which it will re- main stationary. At length the upper thermometer will also mark 40° (4° -40) 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 tintil the whole mass of water has ac- quired its condition of maximum density, that is, until the temperature has fallen to 40° (4° -40). 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° -40). 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 throughQut the year, while the surface-water is in summer much above, and in winter much below, 40° (4° -40) ; in both cases being specifically lighter than water at that temperature. This gradual expansion of water cooled below 40° (4° -40) 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 ip 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. «9 8, The rate of expansion is uniform for all degrees of heat. 4. The actual amount of expansion is equal to ^^^ part of the volume of the gas at 0° Fahrenheit, for each degree of the same scale.' 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 Elemms de Physique, and in the papers of MM. Magnus' and Regnault =* 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 60° (10°C) would become on the temperature rising to 60° (15° -SC). The rate of expansion is ^\^ of the volume at 0° for each degree ; or 460 measures at 0° become 461 at 1°, 462 at 2°, •• 460 -f 50 = 510 at 50°, and 460 -f- 60 = 520 at 60°. Hence Meas. at 50°. Meas. at 60°. Meae. at 50°. Meas. at 60°. 510 : 620 = 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 la\T would be strictly fulfilled. The experiments of MM. Dulong and Petit give for the rate of expansion Tj^ of the volume at 0° : this is no doubt too high. Those of Rudburg give Tflj ; of Magnus ^-*^ ; and of Regnault ^^^ : the fraction j^j^ 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 eqnal to 1492d part of tlie volume the gas occupies at 320F. for each decree of Fahrenheit's scale. On the centigrade scale the expansiou ie l-27.3d part of the bulk at OOC. — R. B. ■ PoggendorlTs Anualeu, iv. 1. • Ann. Chim. et Phys., 3rd series, iv 5. and v, 62. 5 50 HEAT. The ready expansibility of air by heat gives rise to the ptenomena 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, »orth 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 equator-ial 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 '.s the case in the Indian Ocean. They usually extend from about the 28th HEAT. 51 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 Fig. 31. body be lighter than an equal bulk of water ; the pi-essure 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 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 toi frequently present. CONDUCTION OF 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 Tin . 304 Silver . 973 Lead . 179 Copper . . 898 Marble . . 28-6 Iron 374 Porcelain . 12-2 Zinc . 363 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° (OoC) and water at 174° (78°-8C) be mixed, the temperature of the mixture will be the mean of the two tomper- aturea, or 103° (39°-4C). If the same experiment be repeated with snow, or finely powdered ice, at 32° (0°C) and water at 174° (78° 8C), the tem- perature of the whole will be still only 32° (0°C), but the ict will have been 'neltid HEAT. 63 = 2 lb. water at 103° (39° -40) 1 lb. of water at 82° (0°C) 1 lb. of water at 174° (78°-8C) 1 lb. of ice at 32° (0°C) I _ 2 lb water at 32° ^0°C^ 1 lb. of water at 174° (78°-8C) / — ^ ^^^ ^^^^r at 6Z (U c; 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° -SC). 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° (0°C), in rather more than 14 minutes its temperatm-e would have risen 142° (78° -8) ; but the same quantity of ice at 32° (0°C), 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° (0°C) ; 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° -50). Tliis curious condition of instable equilibrium shown by the very oold 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 cr;y1^tallized sulphate of soda iu 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 ' . 142° (78°-8C) Zinc . .493° (273°-8C) Sulphur . . 145 (80 -50 Tin . 500 (277 -70) Lead . . 162 (90 -50) Bismuth . . 550 (305 -50) 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 0° ( — 17° -70, 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. Chim. et Phys., 3d series, viii. 1. 6* 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° (0°C) is mixed with an equal weight of water at 212° (100°C), the whole is found to possess the mean of the two temperatures, or 122° (50°C) ; on the other hand, 1 part by weight of steam at 212° (100°C) 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° (100°C). Now 180 X 5-6 = 1008; that is to say, steam at 212° (100°C) in becoming water at 212°, parts with enough heat to raise a weight of water equal to its own (if it were possible) 1008° (560°C) 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 -60) ether 302 (167 -70) petroleum 178 (98 -80) " oil of turpentine 178 (98 -80) " nitric acid 532 (295 -SC) " liquor ammoniaB 837 (145 -OC) " vinegar 875 (486 -IC) 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 -IC) Alcohol 177 (80 -SC) Water 212 (100 C) Nitric acid, strong 248 (120 C) Oil of turpentine 312 (155 -50) Sulphuric acid , 620 (326 -20) 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° (100°C) ; 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 sui-face. 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° (177°C) or 400° (204°C) 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, Avhich, 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 ' 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° -40), while in the second it will often rise to 221° (105°C) 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° (100°C), and there remains stationary. These remarkable effects must be attributed to an attraction between the surface of the vessel and the liquid.^ * Marcet, Ann. Chim. et Phys., 3d scries, v. 449. ' A remarkable modification of the relation between the temperature of liquids and tli» 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 anJ 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 ha.s bcseu performed with melted cast-iron as it runs from the furnace, and th* 56 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 aifected 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 lb. to each atmosphere. The experiments were carried to twenty-five atmospheres, at which point the difiBculties and danger became so great as to put a stop to the inquiry ; ihe 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 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 41& 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 60 511 266 -1 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° (100°C), and that of the other 250° (176°-2C) or 400° (204o-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.» 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 t-ext, of the sum of the latent and sensible heatg of steam Unng a constaiit quantity, is known by the name of Watt's law, having been deduced by that illu»- Pressure of steam Corres ponding in atmospheres. temperature. 1 .... 212° 100° 1-5 .... 234 112 -2 2 .- 251 121 -2 2-5 .... 264 128 -8 8 .... 275 135 3-5 .... 285 140-5 4 .... 294 145-5 4-5 .... 300 148 -8 6 .... 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 HEAT. 57 Fig. 34. 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 Fix. 33. 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° (100°C), or higher, may be kept up in the pipes or other vessels in which the steam is contained by the expenditure of a very small quantity of the latter. Steam-baths of various forms are used in the arts with great convenience, and also by the scientific chemist for drying filters and other 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. 83), surmounted by a double box or jacket, into which the substance to be di-ied 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. 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 liaa always agreed well with the rouarh practical results obtained by engineers, and has lately been confirmed to a great extent, aJVhough not completely, by a series of elaborate cxperimonts by M, Uegnault. 68 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 lb. 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- zation. 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. H EAT. 69 coal lire, and the receiver is kept cool, if necessary, by a wet cloth, or it may be surrounded with ice. (Fig. 35.) Fis:.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° (0°C), 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° (100°C), 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, the 60 HEAT tension of the aqueous vapour for each degree of the thermometer may be accurately determined by its depressing effect upon the mercurial column ; the same power which forces the latter down one inch against the pressure of the atmosphere, would of course elevate a column of mercury % 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. Tension in inches C. of mercury. 0° 0-200 4-4 0-263 Temperature. 40 60 ... 10 0-375 60 ... 15-5 0-524 70 ... 21-1 0-721 80 ... 26-6 1-000 90 ... 32-2 1-360 100 ... 37-7 1-860 110 ... 43-3 2-530 120 ... 48-8 3-330 Temperature, C. F 130 140 150 160 170 180 190 200 212 Tension in inches of mercury. .. 54-4 4-34 .. 60 5-74 .. 65-5 7-42 .. 71-1 9-46 .. 76-6 1213 .. 82-2 15-15 .. 87-7 1900 .. 93-3 23-64 ..100 3000 u 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 iu 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° (100°C) = 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° 0° 5-G90 0136 grains. 50 10- 10-293 0-247 60 15-5 14108 0-338 100 37-7 46-500 1113 150 65 5 170-293 4076 212 100 625000 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 effects 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° (10°C), not less than 0-87 ' grain of fluid water would necessarily separate, or very neai'ly 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 ^ 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, * 100 cubic inches aqueous vapours at 100° (37°-70), weighing 1-113 grain, would at SO' (10°C), become reduced to 10-29 cubic inches, weighing 0-247 graia 6 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° (10°C) ; the elasticity of the watery vapour present would correspond to a Maximum density proper to 60° (10°C), 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 1G62-8 cubic inches at 50° (10°C) ; this vapour would be at its maximum dcnsitj'', 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°.' 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- ienaation took place.' Atmospheres. Temperature. l\ C. Sulphurous acid 2 45° 7o-2 Sulphuretted hydrogen 17 60 10 Carbonic acid 36 32 Chlorine 4 60 15-5 Nitrous oxide 60 46 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 \n 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, defiant 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 diflFerent cases from 27 to 58 atmospheres.' 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 : 2| lb, of bicarbonate of soda, and 6j it), of water at 100° (37°-7C), are introduced into the generator ; oil of vitriol » Phil. Trans, for 1823, p. 189. ' Phil. Trans, for 1845, p. 15,V u to the amount of Ij- lb. is poured into a copper cylindrical vessel, -vvhicli 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 driveti 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 Pari* by the bursting of one of the iron vessels. The cold produced by evaporation has been already adverted to; it is simply an eflfect 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 sufl'ering 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 and ether in the air, measured by a spirit- thermometer, was found to be — 10G° ( — 76° -GC) ; when the same mixture was placed Iseneath the receiver of an air-pump, and exhaustion rapidly made, the temperature sank to — 166° ( — 110°C). This was the method of obtaining extreme cold employed by Mr. Faraday in his last experiments on the liquefaction of gases. Under such circum- 6* eva- that 36 HEAT. stances, the liquefied hydriodic, hydrobromic, and sulphnrons acid gases, carbonic acid, nitrous oxide, sulphuretted liydrogen, 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° -50) 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° (37o-7C), and oil at 40° (4o-4C), be agitated together, the temperature of the whole will be found to be 80° (26° -GC), 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° -SC). Thus, 1 lb. Z^i "* '400 *(I°'4C) } 8'™ " ■"-'"■« -' 8»° (26-6C) , hence Loss by the water, 20° (11°-1C). Gain by the oil, 40° (22°-2C). \ lb." TifaT '' lit (l7°7C) } g^^^ ^ ^^^*^^*^ ^' ^0° (l^^-^C) 5 ^^^^'^ 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 Tetit, and recently M. Regnault, deserve especial mention. It appears that each Bolid and liquid has its own specific heat ; and it is probable that this, in- HEAT. b < Btead of being a constant quantity, varies with the temperature. The de- termination of the specific heat of gases is attended with peculiar diflSculties 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 = 1 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 Ditrogen ... 1-227 0-8878 0-2369 Carbonic acid 1-249 0-8280 0-2210 defiant gas 1-754 1-5763 0-4207 Aqueous vapour 1-960 3-1360 0-8470' 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 defiant 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. Dulohg 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 difi"erent, and exhibiting no simple relations among themselves ; but if, instead of equal weights, quantities bo 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 their 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 Regnault vary from the above: thus in equal •«reij5hti«, ■Water = l; Atmospheric air he gives a.s 0-2o77; Oxyi^en, .0-2182; Nitrogen, 0-2440; and Vapour of Water, 0-4750; and contrary to the results of Gay-Lussac, the specific heat of ttir does not vary with the temperature. — R. B. 68 HEAT. The following table is extracted from the memoirs of M. Regnault, witii 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 011379 80928 Zinc 009555 3-0872 Copper t 0-09515 3-0172 Lead 0-03140 3-2581 Tin 0-05623 3-3121 Nickel 0-10863 3-2176 Cobalt 0-l«696 3-1628 Platinum 003243 3-2054 Sulphur 0-20259 3-2657 Mercury 0-03332 3-7128 Silver 0-05701 61742 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.' 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.'* SOURCES OF HEAT. The first and greatest source of heat, compared with which all others are totally insignificant, is the sun. The luminous rays are accompanied by rays of a heating nature, which, striking against the surface of the earth, elevate its temperature ; this heat is communicated to the air by convection, as already described, air and gases in general not being sensibly heated by the passage of the rays. ' 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 coiu- ■,'ido with the five preceding. — R. B. " Ann. Chim. et Phys. Ixxiii. 5; and the same, 3rd series, i. 129. _ ^ HEAT. 6t7 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° (65°C) 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.' 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 el,rth 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° (0°C) ; 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 « The new Artesian well at Grenelle, near Paris, has a depth of 1794-5 English feet : it is bored through the chalk basin to the sand beneath ; the work occupied seyen years and two months. The temperature of the water, which is exceedingly abundant, is 820 (270-7C) ; tha mean temperature of Paris is 51o (10O-5C); the difference is 31° (170-2C), which gives a rat« of about 1° (|oC) 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 littie connected >rith elementary chemistry, that very slight notice of some of the most important points will suflfice. 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. Romer, 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. Romer 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 m 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 raj^ 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, r, fig. 45, falling at the point r, will he reflected in the direction pr'', making the angle r-'pp^ equal to the angle rpp^ ; or a ray from the point r falling upon the same spot will be reflected to r^ 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 ar^ for example. Let the lines a — a, a' — a^, at right angles to the perpendicular, be drawn, and their length compared by means of a scale of equal parts, and noted ; 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 8 to 2. The fact is expressed by saying, that the ratio of the sinea 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 i7idex 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' 110 Ice 1-30 Water 1-34 Fluor spar 1-40 Plate glass 1-60 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 200 Phosphorus 2-20 Diamond 2-50 Chromate of lead 3 00 Fig. 48. 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- 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 +lie electric spark, and of all ordinary flames, is of a compound nature. If a ray of light from any of the sources mentioned be admitted into a dark room by a small hole in the shutter, or otherwise (fig. 49), and suffered to fall upon a A siliceous deposit in tlie 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. Fig. 50. YELLOW. RED. SOLAE SPECTRUM. 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 56° 45', the portion of the ray which suffers reflection will be found to have acquired properties which it did not before possess ; for on throwing it, 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 he polarized. The light which passes through the first or polarizing plate, is also to a certain extent in this peculiar condi- Fig. 51. tion, and by employing a series of similar plates (fig. 51), R 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 trnn- mission in this manner is in an opposite state to tli: polarized by reflection ; that is, when examined by :i '•, 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 mannei 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. •when thin plates of doubly-refraoting 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, possfiss 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-lianded 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, whicl\^ 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. Lia^T. 7? 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- lures 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,* 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'^ 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^ 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,* 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, and » Journal of the Royal Institution, i. 170. a Phil. Mag. March, 1839 » Phil. Trans, for 1840, p. 1. * phil. Mag. August. 1841. 7 * 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.' The Daguerreotype, the announcement of which was first made in the summer of 1889 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 geld, wliich communicates a warm purplish tint, and removes the previous dull leaden-grey hue, to most persons very offensive. ' Phil. Trans. 1842, p. 1, RADIATION OP 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 interi'uption, 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 fi'om 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 HEAT. gunpowder ma/ be readily fired by a red-hot ball in the focus of the oppo- site mirror (fig. 55). Fig. 05. The power of radiation varies exceedingly with- diflferent bodies, as may be easily proved. If two similar vessels of equal capacity be constructed of thin metal, atid 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 difl^erences. A cubical metallic ves.sel is prepared, each of whose sides is in a diff'erent condition, one being polished, another rough, a third covered with lampblack, &c. This vessel is filled with water, kept constantly at 212° (100°C) by a small steam-pipe. Each of its sides is then presented in succession to a good pai'abolic 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 EmissiTe 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 • The formerly supposed influence of mere diflFerence of surface has been called in question t)y M. Melloni, who attributes to other causes the eflfects 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, Bcratching 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 wuiiating power of polished and rough surfaces. — Ann. Chim. et Phys. Ixx. 435. RADIATION OP HEaT. 81 until the paper is completely scorched, it will be found that the film of metal has 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 efl'ect 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 afi'ord 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 abimdant 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 explanation 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 0,P, 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 OF HEAT; DIATHERMANCY. Bays 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.* It will be necessary, in the f iTst instance, to describe the method of operation followed by this philosopher. Not long before, two very remarkable 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 tlie 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 • Translated also in Tayloi's Scientific Memoirs. TRANSMISSION OF H !£ *A'^ . 83 Fig. 58. employed, may be made by this contrivance to exhibit a powerful action on the magnet. It is on this principle that instruments called galvanometers^ galvanoscopes, 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 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. 69. screen, the area of whose aperture equalled that of the face of the pi** 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 coiJ 84 TRANSMISSION OF HEAT. of platinum wire heated to redness ; blackened copper at 734° (390°C) ; and the same heated to 212° (100°C). Substances. (Thickness of plate 0-1 inch, nearly.) Transmission of 100 rays of heat from Ah Rock-salt, transparent and colourless. Fluor-spar, colourless Rock-salt, muddy Beryl Fluor-spar, greenish Iceland-spar Plate-glass Rock-crystal Rock-crystal, brown Tourmaline, dark green Citric acid, transparent Alum, transparent Sugar-candy Fluor-spar, green, translucent Ice, pure and transparent 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 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 pUe, 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- Jess, greenish, and deep-green, the quantities transmitted were 78, 46, and 8, while the diflFerence 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 diflFerence in the properties of '■.he 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° (390°C) or 212° (100°C); 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 trana TRANSMISSION or HEAT. 85 mitted through the plate from each source ; or in the three varieties of fluor- spar, as below stated : — Flame. Eed-heat. 784° (3900C). 212° (lOOOC). 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, sufiFers 54 to pass, and from the same number (that is, an equal quantity of heat) from metal at 212° (100°C), 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 difi'erences 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 raya of all colours thrown out, some or other of which wiU 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.' * Dr. Forbes, Phil. Mag. for 1835; also M. Melloni, Ann. Chem. et Phys. Ixv. 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 is 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 reaches 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 Fig. 60. 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 ofi'ers 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 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 aa 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. / 8B 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 dijB&cult 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 eacli 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 som^ 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^ 5^ N. and longitude 96° W 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. 130° E. 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 ia 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° 5^ 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. AH 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 different 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, differs 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 Bilk 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 dremoved from this position, after a few oscillations, it returns again to its previous position. The whole class of paramagnetic bodies behave in a nre- 8* 90 MAGNETISM. cisely similar way under similar circumstances ; only in the intensity of the effects great diflferences 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 class, we have nickel, cobalt, manganese, chromium, cerium, titanium, palladium, platinum, osmium, aluminium, oxygen, and also most of the compoimds 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 diff"erential 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 difi*erent 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 difi'erent way, this partly arises from the paramagnetic (magnetic) property of the air. Thus he found that nitrogen, when this difi"erential 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. It 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 pi*operty 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 diflFerent 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 themselvei equatorially, and diamagnetic bodies axially. 1» ^2 ELECTEICITY. 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 tne result of a new and peculiar condition of the body rubbed, called elec- trical excitation. If a liglit 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 oflF. 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 will 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 electricat 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. ^ -Q+ Q* -Q' 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 eflFect 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 Tery 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,' 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. Tig. 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. M 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 nibbers being at the same time connected with the ground by the wood-work of the machine, or by a stiip 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 Ley den 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 Trie 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 ^ig- 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 points, 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 electiicity 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. When 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 the most complete success, in the British Navy. When two solid conducting bodies are plunged into a liquid which acts upon them unequally, the electric equilibrium 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 , and as these successive charges and discharges take place through the fluid and metals with inconceivable rapidity, the result is an apparently continuous action, to which the term electrical current is given. It is necessary to guard against the idea which the term naturally suggests, 9 9S ELECTRICITY Fig. 69. of an actual bodily transfer of siometliing 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 \netals 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 nuryber of cups or glasses (fig. 70) are arranged in a row or circle, each containing a piece of active and Fig. 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 arc concerned, the term " compound circuit " i« npplied ; tJiey are called also, indifferently, voltaic batteries. In every f<>~i» of such ELECTRICITY. S9 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 arrows. In the modification of Volta's original pile, made by Mr. Cruikshank, the zinc and copper plates are soldered together and cemented water-tight into. a mahogany trough (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 thfe 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. Th. 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 npon small steel articles, as knives and forks, to which polarity has 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 and 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 cui-rent, 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. Or a little piece of apparatus (fig. 72) may be used if reference is Fig. 72. A "'""iiiiial (s '" iiiiiiiiBpi often requiitfd; 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 asfa/ic, unaffected, or nearly so, by the magnetism of the earth ; and the needles being both acted apon in the same manner by the current, are urged with much greater force, ELECTRICITY. 101 than «ne aloile would be, all the actions of every part of the coil being strictly concurrent. A divided circle is placed below the upper needle, by which the angular motion can be measured ; and the whole is enclosed in glass, to shield the needles from the agitation of the air. The arrangement is shown in fig. 73, Fig. 73. rig. 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 ends of the spiral are soldered. On filling the tube with dilute acid and floating the whole in a large basin of water, the helix will be observed to arrange itself in the magnetic meridian, and on trial it will be found to obey a 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 oi- 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 eflfect 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 9 * 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 & ♦ransverse 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 Bteel 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 oonnexion 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 ♦uru in a ooil 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 flowiug 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, cceteris 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. Thb 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 ai 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 and 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. MetalB. Oxygen Antimony Gold Barium Hydrogen Chromium Aluminium Strontium Nitrogen Vanadium Beryllium Calcium Chlorine ^ Tungsten (or Glucinum) Magnesium Iodine ^ (or Wolfram) Zirconium Zinc Bromine ^ Molybdenum Norium Cadmium Fluorine Tantalum Thorium Nickel Carbon - (or Columbium) Yttrium Cobalt Silicon . Niobium Cerium Copper Boron Pelopium Erbium Iron Sulphur Titanium Terbium Manganese Selenium - Uranium Lantanum Lithium Phosphorus Platinum Didymium Sodium Palladium Bismuth Potassium Elements of interme- diate characters. Rhodium Iridium Tin Mercury Arsenic Ruthenium Silver Telluriuff Osmium Lead (104) OXYGEN, im ox YO EN. 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 dephlogisticated air. The name oxygen ' 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. From ^(uf, acid, and ycvvdia, I i^ve rise to. UQ 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 sufiicient. 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 sufi'ers 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 othef 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 pomt of great importance to the chemical student, and one with which he 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 i)f 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 cux (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 firs* 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. A jar wholly or pai'tially 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, ff, 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. AH three stop-cocks are then to be closed, and the plug removed. The pressure of the atmosphere retains the water in the gas holder, and if no air-leakage occur, the escape of water is inconsider- 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 th « 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 difl&culty. 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 aflBxed to a wire, and plunged with a single point red-hot into a jar of oxygen, it burns with great brilliancy, throwing off beautiful scintillations, until, if the oxygen be in excess, it is completely consumed. An iron wire, or, still better, a steel watch-spring, armed at its extremity with a bit of lighted amadou, and introduced into a vessel of good gas, exhibits a most beautiful appearance of combustion. If the experiment be made in a jar 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-feplendour 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; • 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 iiflBculty, but at the same time of very great importance. There are several » Dumas, Ann. Chiin. et Phys., 3d series, iii. 275. OXYGEN. 109 methods which may be adopted for this purijose ; 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 Avith fragments of pumice moist- ened with oil of vitriol, or some other extremely hj'groscopic 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 and dry the air used as the standard of comparison, and to bring both gas and air as nearly as possible to the same temperature, to obviate the necessity of a 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 group 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 tias a strongly-marked basic character; to this the term protoxide is given. The compounds next succeeding receive the names of binoxide or dentoxide, teroxide or tritoxide, &c., from the Latin or Greek numerals, the difrerent grades of oxidation being thus indicated. If 10 110 HYDROGEN. ther-* be a compound between the protoxide and binoxide, the name sesqui- oxiai 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 hyperoxide are words sometimes used instead of per- oxide. Ozone. — It has long been known that dry oxygen, or atmospherio 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 » for it. The true nature of ozone, however, is still unknown, most probably it is a peculiar modification of oxygen. HYDKOGBN. Hydrogen is always obtained for experimental purposes by deoxidizing water, of which it forms the characteristic component.' If a tube of iron or porcelain, containing a quantity of filings or turnings of iron, be fixed across a furnace, and its middle portion be made red-hot, and then the 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 j 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 small nails may be used, but with less advantage. » From S^w, I smell. ' Hence the name, from u^wfi, water, and ytwaw. HYDROGEN, 111 Iig.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 epirit-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 file, 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 odour 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 jar 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, whUe its greater density is easily TompensateJ by increasing the magnitude of the balloon. Fig. 82. * Ann. Cliira. et Phys. 3d. series, viii. Ail. Vl^ 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 not pass through narrow orifices with the same degree of facility. Professor Graham, to wliom 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 inch 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 censtitution of gaseous bodies ; it is the principal means by which the atmosphere is preserved in an uniform jjtate, and the accumulation of poisonous gases and exhalations in towns and other confined localities prevented. A distinction must be carefully drawn between real 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 example, 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.* 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- * Professor Graham has since published a very exten;?ive series of researches on the pas- Bage of jrases through narrow tubes, which will be found in detail in the Pbilosonhi'^al Tran* actions for 1846, p. 573. 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, gen (fig_ 85), a series of musical sounds are sometimes produced by ^j 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 tjirust 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 efi"ect 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 eff"ects, 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, slow combustion of the spirit drawn up by the capillarity of the wick will take place, accompanied by the pungent ^"^"CT^ vapours just mentioned, which may be modified, and C;J~Z^ 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,' but the discovery of the exact proportions in which oxygen and hydrogen unite in generating that most important com- pound has from time to time to the present day occupied the attention of some of the most distinguished cultivators of chemical science. There are two distinct methods of research in chemistry : the analytical, or that in which the 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 ^ith 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, han been very strongly urged, and supported by such evidence that the reader of the controversy may be led to the conclusion that the discovery was made by both parties nearly limulta- ne lusly, and unknown to each other. ^ T16 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-cock 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 cliange 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 vb'ch its purification is completed. After this, it is conducted through a HYDROGEN. 11 7 tube three or four feet 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 suffered 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 eff'ect 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 receivei 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,* by MM. Dulong and Berzelius, gave as a mean result for the composition of water by weight, 8-009 parts oxygen to 1 part hydrogen ; numbers so nearly in the proportion of 8 to 1, that the latter have usually been assumed to be true. Quite recently the subject has been re-investigated by M. Dumas,'^ 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 volumes 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° (4o-5C), freezes at 32° {0°G), and boils under the pressure of the atmosphere at or near 212° (100°C). 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-mil- 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 slightest admixture of mud or suspended impurity destroying the effect. » Ann. Chim. et Phys. xv. 386. « Ann. Chim. et Phys. 3rd series, viii. 189i 118 HYDROGEN. The same maguificent colour is visible in the fissures and caverns found in the ice of the glaciers, which is usually extremely pure and transparent within, although foul upon the surface. Steam, or vapour of water, in its state of greatest density at 212° (100°C), 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,' 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 are attributed. Some of these hold protoxide of iron in solution, and are efi^er- 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 properties of water far exceed those of any other liquid known. Among salts, a very large proportion are soluble to a greater or less extent, the solubility usually increasing with the temperature, so that a hot saturated solution deposits crystals on cooling. There are a few 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. Turner inclosed in the upper part of a high-pressure steam-boiler, worked at 300° {149°C), 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.* Binozide of hydrogen, sometimes called oxygenated icaier, is an exceedingly interesting substance, but unfortunatiely very difficult of preparation. It is formed by dissolving the binoxide of barium in dilate 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 concep- 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 efi^ervescence, due to the escape of oxygen gas ; near 212° (100°C) it is decomposed with ex. » 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 suffered 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°-6C), 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 mbject of experimental research. Besides nitrogen and oxygen, the air itontains a little carbonic acid, a very variable proportion of aqueous vapour, R 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 has been collected and examined in London and Paris, and many other districts ; still the propor- * i. e. Generator of nitre ; also called azote, from a, privative, and ^w^, life. NITROGEN. 121 tions of oxygen and nitrogen remain unaltered, the diflFusive 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 small in quantity for direct estimation. Composition of the Atmospfiere. By weight. Nitrogen 77 parts Oxygen 23 " By measure. .. 79-19 .. 20-81 Tig. 91. 100 100-00 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 Br. Front, 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, 3aref\illy 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), i known quantity of the air to be examined, and then passing into the latter a stick of phosphorus aflSxed 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 accuracv 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 »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 spark. The closed limb is carefully graduated. When required for use, th* tS2 NITROGEN. Fig. 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 oflF. 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 oflF; 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 efi'ect. Nothing now remains but to equalize the level of the mercury by pouring a little more into the instrument, and then to read off the volume for the last time. What is required to be known from this experiment is the diminution the mixture suffers by explosion ; for since the hydrogen is in excess, and since that 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 CO — s 21 ; oxygen in the hundred measures. 3 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- Bion 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' 14 16--N0«- Nitrous acid 14 24-^/03 Hvponitric acid' 14 82 •= W O y Nitric acid 14 40r. '^{OiT Nitric or Azotic Acid. — It. 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 js 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. Nitre Nitric acid Potassa Oil of vitriol {g^yj[^^.^^^.^ 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 ^>lden 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. « Otherwise called nitrous oxide. , '/ 1 » Called by Professor Graham peroxide of nitrogen. • Otherwise called nitric oxide, O-v 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 of 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° -50) 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.' 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 86° (30°C), and boil between 113° and 122° (45° and 50°C), 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 niti-e, 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 lias 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 |s not so easily detected in solution in small quantities as many other acids. Owing to tlie solubility of all its compounds, no precipitant can be found for this substance. One of the best tests is its power of bleaching a solution of indigo in sulphtiric acid when boiled with that liquid. The * The t-wo hydrates of nitric acid are thus expressed by symbols : — NOe, HO and NOe, 4H0. No compound containing two equivalents of water appears to exist. 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; Nitrou* Oxide; (laughing gas.) — When solid nitrate of ammonia is heated in a retort or flask,' 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. . ^ 80 I Nitrogen 14 Oxygen Oxygen Oxygen 24 Nitrogen 14 Hydrogen 3 Water 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.^ 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,^ together with a little water, and nitric acid added by the funnel until brisk efi"ervescence 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- * 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. They 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 edgo 6o 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* 120 NITROGEN. other portion of the acid. Nitric acid is Tery 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 readily 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 1039; 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 0° ( — 17° -80). 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 Acid. — It has been doubted whether the term 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. P^ligot. 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 nitrous acid, is simply nitric acid impregnated with hyponitric gas.' 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 * Much doubt yet hangs over the true nature and relations of these two acids. According to M. P^ligot, the only product of the union of binoxide of nitrogen and oxygen is hyponitrii- acid, which in the total absence of water is a white solid crj'stalline body, fusible at 16<^ ( — 8°-9Cy. 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 •^hat nitrous acid in a separate stafe is unknown. Ann. Chim. et Phys. 3d series, ii. 58. CARBON. 12t cauged 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. 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. " t" 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 a mere trace up to five per cent. Graphite is a somewhat rare mineral ; the finest, and most valuable for pencils, is brought from Borrowdale, in 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 difi"erent 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.' 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 efi'ect, as well as that of the decolorizing power, no doubt depends in some way upon the Bame peculiar action of surface so remarkable in the case of platinum in a mixture of otygen and hydrogen.' 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, o r) Carbonic oxide 6 ............ 8 ^ i; Carbonic acid 6 16- d O^ • It removes fi-om solution in water the vegetable bases, bitter principles and astringent Bubstanccs, 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. Arseuious acid U 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 ba.sic condition, the solution showing an acid reaction as soon as the carlx)n 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 bo dissolved out by boiling with an acid solution. — Warrington, Mem. Chim. Soc. 1845; Garrod, Pharm. Journ. 1845; Weppen, Ann. deChim. 1845. — R. B. • 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 putr*> faction. — R.B. CARBON m 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 ifl 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. .>g^.i«i>=>e>!to^MaiVrVtVr'f^W«-Trlr- 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.* 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,' 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 carbonic 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. • In connecting tube-apparatus for conyeying gases or cold liquids, not corrosive, little tubes of caoutchouc about an inch long, are in- expressibly 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 the 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 and Berzelius. 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° (0°C), 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.' 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 prefei'able 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.^ Carbonic oxide is a combustible gas ; it burns with a beautiful pale blue 6ame, 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 • When relieved of pressure it immediately boils, and seven parts out of eight assume the gaseous state, the rest becoming solid at — 90° (07°-7C) (Mitchell). Solid carbonic acid mixed witli 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 caunot be detected until a portion again becomes liquid. — R. B. '» See a paper by the author, in Memoirs of Chcm. 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. suJ phate of potassa- 3 eq. sulphate of ammonia, and 1 eq. protosulphate of iron. SU LPHUR, 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 made 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, suflfocating compound, possessing acid properties, called phosgeno gas, or chioro-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. c 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 with 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. Pig. 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 between 430° (221°C) and 480° (249°C), 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° (400°C), 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 le^-j*-* Sulphuric acid* 16 24 -'^•j Hyposulphurous acid 32 16't>^®^ Hyposulphuric acid 32 40-«^iOs- Sulphuretted hyposulphuric acid 48 40-Sj Oj Bisulphuretted hyposulphuric acid* 64 ......... 40^5 y o Trisulphuretted hyposulphuric acid 80 40= ^jg- ^ 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 suifocating 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 0° ( — 17°-8C), under the pres- sure of the atmosphere, this gas condenses to a colourless, limpid liquid, very expansible by heat. Cold water dissolves rtore 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° ( — 6° or — 8°C), 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 |th 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. * The terminations ous and ic, applied to acids, signify degrees of oxidation, the latter being the highest; acids ending in cms form salts the names of which are made to end in ite. and those in ic terminate in ate, as sulphurous acid, sidphite, of soda, sulphuric acid, sulphate of Boda. * The more advanced student will be glad to see these stated in equivalents by the use of symbols, hereafter to be explained, their relations becoming thereby much more evident. The liumbers 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 'he quantities required to saturate one equivalent of a base : Sulphurous acid SOu Sulphuric acid SO3 Hyposulphurous acid SaOj „ Hyposulphuric acid, Dithionic add : SaOe Sulphuretted hyposulphuric acid, Trithionic acid SsOs Bisulphuretted hyposulphuric acid, Tetrathionic acid S4O9 . Trisulphuretted hyposulphuric acid, Pentathionic add 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 on 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 Add. — 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 hyponitric 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 : — 12 134 SULPHUR. {Nitrogen 14 ^ Binoxide of nitrogen 30 Oxygen 16 Oxygen 16^ Sulphurous acid 64{«"^';g'--^|; 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 sulphui'ic acid, nitrous acid, and a little water.' 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 oflF 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°'1C) it freezes; at 620° (326° '60) 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, gi'eat 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 * M. Gaultier de Claubry assigned to this curious substance the composition expressed hy the formula 4H0, 2NOs+5S03, 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 sealed glass tube, liquid sulphurous acid and liquid hyponitric axiid, 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 NO3+2SO3. M. de la Provostaye very ingeniously explains the anomalies in the diflerent analyses of the leaden chamber product, by showing that the pure substance forms crystal- lizable combinations with different proportions of liquid sulphuric acid. (Ann. Ohim. et Fbys. Ixxiii. 362.) SULPHUR. 135 32° (0°C), and remains solid even at 45° (7°-2C). Lastly, when a very dilute acid is concentrated by evaporation in vacuo 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 of 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 vijtriol 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, Dithionic 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 protoxide of lead. Sulphuretted hyposulphuric Acid, Trithionic Acid. — A substance accidentally formed by M. Langlois,' 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 tliose 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 hydrofluosilicic acid ; it may be concentrated under the receiver of the air-pump, but it is gradually decomposed into sulphur, sulphurous and sulphuric acids. Bisulphuretted hypositvphuric Acid, Tetrathionic Acid. — This was discovered by MM. Fordos and G61is.» When iodine is added to a solution of hyposul- pVit*^ of soda, a large quantity of that substance is dissolved, and a cleai, rvv p^ess solution obtained, which, besides iodide of sodium, contains a salt » Ann. Chim. et Phys. 3d sanes, iv. 77. • 27;. 3(1 serie?. vi. ii4r- 136 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. Trisulplmretled hypomlphuric Acid, Pentathionic Acid. — Another acid of sulphur has been announced by M. Wackenroder, who foi-med 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 S5O5 ; under the influence of heat, it is decompo&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° (lOOoC), or a little above, it melts, and at 650° (343° -30) boils. It is insoluble in water, and exhales, when heated in the air, a peculiar and disagreeable odour, which has been compared to that of decaying horseradish. Ther^ are three oxides of selenium, two of which correspond respectively to sulphurous and sulphuric acids, while the thii-d has no known analogue in the sulphur series. Composition by weight Selenium. Oxygen. Oxide of selenium 39-6 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 acid properties. Selenious Acid. — 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 illuminatius power, and confer on th« 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 and 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 to the point necessary to melt refrac- tory metals, and to bring about certain desired eflFects 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 efi'ected by two distinct methods ; it may be forced into the fire by bellows or blowing- machinesj 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. (Fig. HI.) Fig. 111. Fig. 112 ^_j| 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 tlie 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 mixed gases, is scarcely visible in full daylight ; in a dusty atmosphere, however, it becomes much more luminous by igniting to intense whiteness the floating particles with which it comes in contact. The piece of lime in the blowpipe flame cannot have a higher temperature than that of the flame itself; yet the light it throws oif 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- /A----C amined, is seen to consist of three separate portions. The //\\ dark central part, a, fig. 113, easily rendered evident by de- // -\-\ --— B pressing upon the flame a piece of fine wire-gauze, consists of (/ A u combustible matter drawn up by the capillarity of the wick, ll / Vj'""-^ ^^^ volatilized by the heat. This is surrounded by a highly \\\ \jj luminous cone or envelope, b, which, in contact with a cold m hody, deposits soot. On the outside a second cone, c, is to r-ft-j be traced, feeble in its light-giving power, but having an UaJ 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 PLAMB. 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. ' When in use this aperture must, always he open, otherwise an accident is pure to happen, the beat expands the air in the lamp, and the spirit 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 difi'erent with diff"erent 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 eff'ect 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. * The spirit-lamp represented in fig. 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 ©f the fountain. By such an arrangement of parts, the alcohol may be added as it is con- sumed, and the flame kept uniform; and aa the pipes which pass to the burner are so re- mote from the flame, the alcohol never be- comes heated bo 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 madti of tin-plate or copper. — R. B. THE STRUCTURE OF FLA. ME 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 degx-ee 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 efl'ects 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 difi'erent parts of the mine.' The same great principle has been ingeniously applied by Mr, Hemming to the construction of the oxy-hydrogea 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, Thejetmay 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 01 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 eitlier to adopt efileient nveajis of ventilation, or to clos** 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.* NITROGEN AND HTDEOGEN ; 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° -oC), am- monia condenses to the liquid form.'* 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 pi-oportion 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 * Where coal-gas is to be had, it may be adTantageously 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 ine 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 utmosphei-ic 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 tiumes. The length and diameter of the cylinder are determined by the amount of gas to be burni, 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 •lohn Kobinson, K. H. &c., Ed. New Phif. Journal, 1840.— R. B. » At the temperature of — 103° ( — 75°C), liquid ammonia freezes into a colourless solid, hwAvicr than the liquid Itself —(Faraday.)— R. 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, rem*ains in the flask.' The decomposition of the salt is usually represented in the manner shown by the subjoined diagram. {Ammonia Ammonia. Hydrochloric ^ Hydrogen ' Z-"^ Water, acid I-™- { ?:&" ^Chloride of 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 yield.>i 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 : — » See Fig. 106, p. 142. J64 SULPHUR WITH HYDROGEN. Sulphide of iron { ^J'JP^"^ Water | Hydrogen \ Oxygen _ Sulphuric acid Sulphuretted hydrogen. 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 { chlorife"' Sulphide of antimony { ^^^^^J^'^' Sulphuretted hydrogen. -Chloride of antimony. Fig. 123. 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° (10°C) reduces it to the liquid form. 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 fittecf 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 liydrogen. When a mixture is made of 100 measures of sulphuretted hydrogen and 150 measures of pure oxygen, and exploded by the electric spark, complete combustion ensues, ana 100 measures of sulphurous acid gas result. Sulphuretted hydrogen is a frequent product of the putrefaction of organic matter, both animal and vegetable ; it occurs also in certain mineral springs, »s at Harrowgate, and elsewhere. When accidentally present in the atmo- PERSULPHIDE OF 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 oDy-looking matter, which collects at the bottom of the vessel ; this is persulphide of hydrogen.^ 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. Hydrogen and Selenium ; Selenietted 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 * The reaction which ensnes when hydrate of lime, sulphur, and water, are hoiled together, is rather complex; bisulphide or pentasulphide of calcium being formed, together with hypo Bulphite of lime, arising from the transfer of the oxygen of the decomposed lime to another portion of sulphur. 2 ea lime \ ^ ^^- <^^'*^^"°^ -> 2 eq. bisulphide of calcium. ^* 12 eq. oxygen . '" ■ 1 eq. hyposulphurous acid. The bisulphide of calcium, decomposed by an acid under favourable circumstances, yields • salt of lime and bisulphide (persulphide; of hydrogen. 1 eq. bisulp. calcium j ^ eq. sulp^hur --^^ 1 eq. bisulphide of hydrogen. 1 eq. water \ } ^- ^lyt^rogeu ^ } 1 eq. oxygen Sulphuric acid -^==^^ "^ ^l- sulphate of Ume. 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 Bub- stance, hydrochloric acid must be used in the place of sulphuric. 166 PHOSPHORUS WITH HYDROGEN. soluble in water, and decomposing metallic solutions like that suLtance ; 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 39-6 parts selenium, and 1 part hydrogen. Phosphorus and Hydrogen ; Pkosphoretted 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.* 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 thq 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 / Hydrogen --^::^=^ Phosphoretted hydrogen. ... "^Oxygen Phosphorus . Phosphorus^ _^^^ Lime -~==rs^ TTypnphnsphitft 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 suff'ering any appreciable change : but if dried by chloride of calcium, it may be kept •unaltered for a much longer period. M. Paul Th6nard has shown that the ipontaneous 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 Hot freeze at 0° ( — 17° -80). In contact with air it inflames instantly, and lis vapour in very small quantity communicates spontaneous inflammability lo pure phosphoretted hydrogen, and to all other combustible gases. It is decomposed by light into gaseous phosphoretted hydrogen, and a solid phos- ,»hide which is often seen on the inside of jars containing gas which has lost • Decomposition of hydrated phosphorous acid by heat : — ,1 eq. phosphoretted hydrogen, PHj i tq. hydtafed ;^»l odphorous Hydrated phos- phoric acid. NITROGEN WITH CHLORINE, ETC. 167 the property of spontaneous inflammation by exposure to light. Strong acida 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 spontanemisly inflammable if heated to the temperature of boiling water,* Phosphoretted hydrogen decomposes several metallic solutions, giving rise to precipitates of insoluble phosphides. With hydriodic acid it forms a crys- talline compound somewhat resembling sal-ammoniac. NITROGEN WITH CHLORINK 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 expenment : — 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 chloi-ide 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 ,^ " ""^"Z^^ ' Hydrochloric acid {^ Nitrogen -"^"^^^ ) Hydrogen " Hydrochloric 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°-1C), although the experiment is attended with great danger. Between 200° (93° -SC) and 212° (100°C) 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.'* 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 blacli 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 dry, 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. Th^nard, the new liquid phosphide of hydrogen contains PHa and the solid PaH. The gas is represented by the formula PH3. • Instead of NCla, it may in reality be NH Cla. 168 OTHER COMPOUNDS OF pound ^ast 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 ELKMENTS. 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.* Subchloride of sulphur is instantly decomposed by water ; hydrochloric and hyposulphurous acids are formed, and sulphur separated. The hypo- Bulphurous acid in its turn decomposes into sulphur 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.' Chlorides of Phosphorus. — Terchloride.^ — 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. Pentachloride 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.* « SgCl. » SCI. » PCla. « PC1», ■ Hemce it doubtless contains 1 eq. iodine, and 5 eq chlorine, or IClt. NON-MEI'ALLIC 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. It probably consists of 127 parts iodine, and 35-5 parts chlorine.' 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 jovered crucible, and fixed across a furnace in a slightly inclined position, [nto 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° (43°-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° (50°C), 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.* 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. » Or SiCI». 16 170 GENERAL PRINCIPLES OJ? 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 illustrations of the general laws referred to, but the study of their leading characters and relations does not of necessity involve a previous knowledge of these laws themselves. It is thought that by such an arrangement the comprehension of these very important general principles may become in some measure facilitated by constant references to examples of combinations, the elements and pro- ducts of which have been already described. So much more difificult 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 acquaintance 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 conferrea 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. Id 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 difi'ering 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, sufi&ciently 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 ium. 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.^ 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 sulphuric 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 hyposulphurom 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 hypophosphor ous, phosphorous Siud phosphoric acids; hypochlorous, chlorous, hypochloric, chloric, and perchloric Sicids; nitrous, hyponitric, a,nd 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 r if in ous, that of the saline compounds ends in ite. Thus, sulphuric acid forms sulphates of the various bases ; sulphurous acid, sulphites ; hyposulphurous acid, hyposulphites ; hyposulphuric acid, hyposulphates, &c. The rule here is very simple and obvious. * Formerly the termination uret was likewise firequently 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 iritoxide, 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 degraded into suboxide. The Latin prefix per, or rarely hi/per, 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 sesgui, 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.' Thus, an oxide 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, sesquisutphate 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, binoxalatc, 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 Greek 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 combinatirvn«» admit of being laid down in a manner at once simple and concise. They are four ir number, and to the following effect : — 1. All chemical compounds are definite in their nature, the r?t'o of th':, 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, D, 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 ' 8«e a few pages forward. CHEMICAL PHILOSOPHY. 173 chemistry ; only a few weTl-establisbed and undoubted examples being known in tb^^ganic or mineral division of the science. P^g^^^i^.p-^ultijple Proportions. — Illustrations of this simple and beautiful law ^T^bound 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, give 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 correspouding sulphides exhibit the same phenomena, while the metallic compounds oflFer 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 35-6 8 Chlorous acid 85-5 24 H3'pochloric acid 35-5 32 Chloric acid 35-5 40 Perchloric acid 35-6 66 Here the quantities of oxygen progi'ess 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 are 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 oxalates of potassa, namely, the simple oxalate, the binoxalate, and the quadroxalat© ; 15* 174 GENERAL PRINCIPLES OP tlie 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 aflBnity 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 8 Hydrogen 1 Nitrogen 14 Carbon 6 Sulphur 16 Phosphorus , 32 Chlorine 35-5 Iodine 127 Potassium 39 Iron 28 Copper 81-7 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, 1?5 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 difi'erent, 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 hypothefsis. 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 difl'ereut experimenters. '. 176 GENERAL PRINCIPLES OF TABLE OF ELEMENTABY SUBSTANCES, WITH THEIR EQUIVALENTS. Oxy. = 8. Aluminium..., 13-7 Antimony 129 Arsenic 75 Barium 68-5 Beryllium 6-9 Bismuth 213 Boron 10-9 Bromine 80 Cadmium 56 Calcium 20 Carbon 6 Cerium 47 (?) Chlorine 35-5 Chromium 26-7 Cobalt 29-5 Copper 31-7 Didymium 50 (?) Erbium Fluorine 19 Gold 197 Hydrogen 1 Iodine 127 Iridium 99 Iron 28 Lanthanum ... 47 (?) Lead 103-7 Lithium 6-5 Magnesium ... 12 Manganese.... 27-6 Mercury 100 Molybdenum.. 46 )xy. = 100. Oxy.=8. Oxy.=100. 171-25 Nickel ... 29-6 370 1612-5 Niobium 937-5 Nitrogen.... ... 14 175 856-25 Norium 86-25 Osmium ... 99-6 1245 2662-5 Oxygen ... 8 100 136-25 Palladium .. ... 63-3 666-25 1000 Pelopium 700 Phosphorus. ... 32 400 250 Platinum.... ... 98-7 1233-75 75 Potassium .. ... 39 487-5 587-5 Rhodium ... ... 52-2 652-5 443-75 Ruthenium . ... 52-2 652-5 333-75 Selenium ... ... 39-5 493-75 368-75 Silicium ... 21-3 266-25 396-25 Silver . 108 1350 625 Sodium ... 23 287-5 Strontium... ... 43-8 547-5 237.5 Sulphur ... 16 200 2462-5 Tantalum... ...184 2300 12-5 Tellurium... ... 64-2 802-5 1587-5 Terbium 1237-5 Thorium .... .., 59-6 745 350 Tin ... 58 725 587-5 Titanium ... ... 25 312-5 1296-25 Tungsten.... ... 92 1150 81-25 Uranium.... ... 60 760 150 Vanadium.. ... 68-6 857-6 345 Yttrium 1250 Zinc ... 32-6 407-5 575 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, 64 *' 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 eqjoivalent of sulphur =16 1 equivalent of nitrogen = 14 3 *' oxygen = 24 5 " oxygen = 40 1 " sulphuric acid = 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 neuira . 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 neutrai COMBINATION BY VOLUME, Many years ago, M. Gay-Lussac made the very important and interestrag discovery that when gases combine chemically, union invariably takes place 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 ?.78 GENERAL PRINCIPLES OP ^ouud bodies of this description, as it is invariably observed that the con- Iraction 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- Belves. 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 85-5 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. gra'^ty. Equiv. weight. Equiv. volume. Hydrogen 00693 1-0 14-43 or 1 Nitrogen 0-972 14-0 14-37 " 1 Chlorine 2-470 35-5 14-33 " 1 Bromine-vopour 5-395 800 14-82 " 1 Iodine-vapour 8-716 127-0 14-57 '* 1 Carbon- vapour' 0-418 6-0 14-34 " 1 Mercury-vapour 7-000 100-0 14-29 " 1 Oxygen 1-106 80 7-23"^ Phosphorus-vapour 4-350 ... 320 735 " | Arsenic-vapour 10-420 75-0 7-19 " | Sulphur-vapour 6-654 160 2-40"^ Thus it appears that hydrogen, nitrogen, chlorine, bromine, iodine, carbon, and mercury, in the gaseous state, have the same equivalent volume ; oxygen, phosphoi-us, and arsenic, one-half of this ; and sulphur one-sixth. The falight discrepancies in the numbers in the third column result chiefly from errors in the determination of the specific gravities. Compound bodies exhibit exactly similar results : — * See farther on. CHEMICAL PHILOSOPHY. 179 gp. gravity. Equiv. weight. Equiv. volume. Water-vapour 0-625 .... 90 .... 14-40 or 1 Protoxide of nitrogen 1-625 .... 220 .... 14-43"! Sulphuretted hydrogen 1-171 .... 17-0 .... 14-51 " 1 Sulphurous acid 2-210 .... 32-0 .... 14-52 " 1 Carbonic oxide 0-973 .... 14-0 ... 14-39 " 1 Carbonic acid 1-524 .... 220 .... 14-43"! Light carbonetted hydrogen 0-559 .... 80 .... 14-31 " 1 Olefiantgas 0-981 .... 14-0 .... 14-27"! Binoxide of nitrogen 1-039 .... 30-0 .... 28-87 " 2 Hydrochloric acid 1-269 .... 365 .... 28-70 " 2 Phosphoretted hydrogen 1-240 .... 35-0 .... 28-22 " 2 Ammonia 0589 .... 17-0 .... 28-86 " 2 Ether-vapour 2-586 .... 370 .... 14-31 " 1 Acetone-vapour 2-022 .... 290 .... 14-34 " 1 Benzol-vapour 2-738 .... 78-0 .... 28-49 " 2 Alcohol-vapour 1-613 .... 460 .... 28-52 " 2 « 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 will 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 gi-eat 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 ,:^ravity. The 180 GENERAL PRINCIPLES OF numbers obtained in this manner representing the combining volumes of the Yarious 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 obscurity. 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 CI 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) .... Hg Molybdenum Mo Nickel Ni Niobium Nb Nitrogen N Norium No Osmium Os Oxygen O Palladium Pd CHEMICAL PHILOSUPHY, 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 I'h 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 Uie sign of addition. For example : — Water HO, or H + Hydrochloric acid HCl, or H + CI Protoxide of iron FeO, or Fe -J- 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 -}- 20, or HO', or HOj Sulphuric acid 8 + 30, or SO", or SO3 Hyposulphuric acid.. 2S4-60, or S^' or S^Og 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 affects all the symbols between itself and the next sign. A few examples will serve to illustrate these several points. Sulphate of soda NaO + SO3 , or NaO , SO3 Nitrate of potassa KO -j- NOg , or KO , NO5 The base being always placed first. Double sulphate of copper and potassa CuO , SOg-f-KO , SO, The same in a crystallized state CuO , SOg-fKO , SOg-j-BHO Common crystallized alum, or double sulphate of alumina and potassa, is thus written : — AI2O3 , SSOg-fKO , SO3+24HO In expressing organic compounds, where three or more elements exist, the ^amo plan is used. Sngar CijHiiO,, Alcohol CXO2 Acetic acid HO , C4H3O3 Morphine Cg^HjgN Og Acetate of morphine Cg^HjgN Og , C^H^O, Acetate of soda NaO , C.H„0, 16 ' 4 8 s 182 GENERALPRINCIPLESOF 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', or F eO% or Fe, instead of Fcj Oj Bisulphide of carbon C, instead of CSa Crystallized alum as before AlSg-f KS-f-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, aioms.'^ Now, however the imagination may succeed in figuring to itself the condition of matter on either view, it is hardly 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 perhaps 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 atora * "Aro/toj, 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, hvponitric 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. ©OC^O 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 difiiculties 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 tills 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 largely 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.* 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 is very often substituted for that of equivalent weight, and is, in fact, in almost every case to be understood as such : it is, ->fti-haps, better avoided. 184 GENERAL PRINCIPLES OF bodies, in such a way as to give rise to a neio substance, having, for the most part, propei'ties completely in discordance with those of its components. The attraction thus exerted between diflFerent kinds of matter is to* be dis- tinguished from other modifications of attractive force which arc 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 aflinity 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 towards acids, while union among themselves rarely, if ever, takes place. Nevertheless, chemical combination graduates so imperceptibly into mere mechanical mixture, that it is often impossible to mark the limit. Solution is the result of a weak kind of affinity existing between the substance dis- solved and the solvent ; an affinity so feeble as completely to lose one of its most prominent features when in a more exalted condition, namely, power of causing elevation of temperature ; for in the act of mere solution the 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, etrontia, 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 mercui-y 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-heat, and again becomes reduced when the tempei*ature 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 tiie 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 uxygeu 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- Dination. 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 oflF 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 oxide 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 mQYQ 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 liriuging the particles within the sphere of their mutual attractions. CHEMISTRY OF THE VOLTAIC PILE. 1^ T 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,^ 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.^ 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 other 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 * From i^\tKTpov, and i^df, a way. • From fi^tKTpov, and Auw, I loose. » Page 115. 1?<8 ELECTRO-CHEMICAL DECOMPORITTONj 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 eflfect 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 resistaftce 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 Bame moment the magnetic needle reassumes its natural position. In the Bame 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 electrode ; 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 oflF in a separate 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, until 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. .©1©1®1©M®1® 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 curious phenomena described. The circles are intended to indicate the elements, and are distinguished by their respective symbols. © Fig. 126. ©, © ®T®1©T® ®1®®® © 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 sulphurio 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, siJphate of copper, iodide of potassium, fused chloride of lead, &c., be arranged in ft 19) 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 their 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 eflfects 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 qua?itity 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 CHEMISTEY OF THE VOLTAIC PILE. 191 this experiment is made, the smaller is the eflFect observed ; and hence it is judged highly probable that the whole may be due to accidental causes, against which it is almost impossible to guard. On the other hand, the observation was soon made that the power of the battery always 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 sulphui'ic 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 first 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 «oltaic 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 pure state, 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 crown of cups ; by each alternation of zinc, fluid, and copper, the current is urged forwai'ds with increased energy, its intensity is augmented, but the actuai 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 •hy 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 respefct 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, vrithout 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 afiinity ; 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- U'ived by Dr. Wollaston (fig. 129). The copper is made completely to encircle OHEMISTEY OF THE VOLTAIC PILE. 193 Fig. 129. ihe zinc jlatc, 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, 2J- 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 Kg. 130. 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 r r 194 ELECTRO-CHEMICAL DECOMPOSITION Fig. 131. strength of the solution may remain unimpaired. When a communication \^ 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 the 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 form 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 flat cell of porous earthenware, filled with strong nitric acid, and the whole is immersed in a mixture of 1 part by measure of oil of vitriol and 6 of water, contained either in one of the cells of 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 j>ortable, 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 nitrio 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 fames ; 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, an^ 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 with thin coating of finely-divided metallic platinum is employed in association with 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 slightlj* mentioned. Mr. Spencer and Professor Jacobi have employed it in copying, or 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. CHEMISTRY OF 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 multipliied 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.' 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 efi^ect 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 Fig. 133 * Traits de I'Electridtfi et du Magn6tisme, 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, &o., 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 <««ch tube of the battery. CHEMISTRY OF THE METALS. 197 CHEMISTRY OF THE METALS. Tj'w >fiji&.l3 constitute the second and larger group of elementary bodies i gveaf fluniLer of these are of very rare occurrence, being found only in a ft »;r sca\ ce mirerals ; 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- gi'ess of civilization. If arsenic and tellurium bo included, the metals amount to forty-nine ia 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 laminse, 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 acertain 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° (15o-5C).' 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 1 900 Copper .' 8-89 Cadmium 8-60 »Dr. Turner's Elements, eighth edition, p. 345. 17» 198 CHEMISTRY OP 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 611 Arsenic 5-88 Aluminium 2-60* 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 foimd 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 /^\ r\ 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 Wi w order of tenacity among the metals susceptible of being Vl/ 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 : Iron Gold Copper Zinc Platinum Tin Silver Lead Metals differ as much In fusibility as in density ; the following table, ex- » WaWsr. CHEMISTRY OP THE METALS. 199 Fusible below a red heat 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 — 39° — 39°-44 Potassium 136 57-77 Sodium 194 90 Tin 442 227-77 Cadmium (about) 442 277-77 Bismuth 497 258-33 Lead 612 322-77 Tellurium — rather less fusible than lead Arsenic — unknown Zinc 773 411-66 ^Antimony— just below redness fSilver 1873 1022-77 Copper 1996 1091-11 Gold ;. : 2016 1102-22 Cast iron 2786 1530 Pure iron ' Nickel Cobalt Manganese.... Palladium .... Molybdenum . Tungsten ^ Imperfectly melted in wind-fumace. Chromium... Infusible below < a red heat Fusible only in an excellent wind- furnace. Titanium . Cerium.... Osmium... Iridium ... Rhodium . Platinum . Tantalum Infusible in furnace ; fusible by oxy- hydrogen blowpipe. 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 EELATIONS 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- Oxygen. Symbols. Characters. leq. . 3 eq. . 2 eq. . .. MnO ... .. MdoO. ... .. MnOa ... Strongly basic. Feebly basic. Neutral. 3 eq. . 7eq. ., Strongly acid. 200 CHEMISTRY OP 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. Protoxide 1 eq. Sesquioxide 2 eq. Binoxide 1 eq. Manganic acid 1 eq. Permanganic acid 2 eq. 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 neuti'al 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 b-isic-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 -j- 1 eq. oxygen 1 eq. sulphuric acid. 1 eq. iron -|- 1 eq. oxygen 1 eq. sulphuric acid. i ~\- 1 eq. oxygen from air 1 eq. iron -|- 1 eg. oxygen 1 1 eq. sulphuric acid. 1 eq, iron -\- 1 eq. oxygen 1 eq. sulphuric acid. -|- 1 eq. oxygen from air. Such sub-salts or basic salts are very frequently insoiuble. The combinations of chlorine, iodine, bromine, and fluorine with the uietals 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 OF 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, io^e, &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 '^ salts, and ozy gen-acid, or ozy-salts, 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 -^,^ Potassa lo™"^__:r-^„. I Oxygen ^=s>^^yater. 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 similar 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 f 1 eq. Chlorine Chlorine ... ^ acid (1 eq. Hydrogen '" gal- Ammonia ... / ? ^^- S.y.'^'^^^''^^^^^::::^^ 1 ammoniac. \ 1 eq. Nitrogen ^^^^^^^^ Ammonium J The term ammonium is given to this hypothetical body, NH^ ; 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-add, 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 crj^tallizable 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. * £A(, sea-salt, and Hhoi, form. 2vy2 CHEMISTRY OP THE METALS. KS + CSj sulphur-salt. "'•'■' KO-f-COj 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 Bulphate of potassa. KO+SO, and HO-f SO,. 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 diflFerent 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 fav(?urable 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 » Ann. Chim. et Phys. Ixx. 311. CHEMISTRY OP THE METALS. 203 other soluble substances, "w^liich 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 beautif\il 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 tiiere 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- Burement 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. Pig. 136. a is a divided circle or disc of brass, the axis of which passes stiffly and without shake through the support h. 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 ver> 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' is shown in the two positions, the angle to be measured being that indicated by the letters e df. The lines ac, he, are perpendicular to the respective faces of the crystal, • The triangular prism has been chosen for the sake of Eimplicity; but a moment's con- sideration will show that the rule applies equally well to any oUier figure. CHEMISTRY OT THE METALS. 205 Fig. 137. consequently the internal angles dgc, dhc, are right angles. Now, since the sum of the internal angles of a four-sided rectilineal figure, as dgck, equal four right angles, or 360°, the angle ffdh (or e df) must of necessity be the supplement to the angle g ch, 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 METALfl. angle of motion is not obtained, but its supplement, or the angle of thfe 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 'rystal 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 tystems ; 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. -4 y ''"tt' / a— a. Principal, or vertical axis. b — 6. Secondary, or lateral axis. CHEMISTRY OF THE METALS. 207 of each side (1) ; a second right square prism, in which the axes terminate in the edges (2) ; a corresponding pair of rir/ht 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. h — 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 Fig. 141. a — a. Principal axis. 6 — 6, 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 in'egularity, exceedingly dif- ficult to studv and understand. In them are traced three axes, which may 208 CHEMISTRY OP THE METALS, be all unequal in length, and are all oblique to each other, as in the two doubly -oblique prisms (1 and 2), and in the corresponding doubly-oblique octa- hedrons (3 and 4). Fig. 142. a — a. Principal axis, as before. 6 — &, c — c. Secondary axes. Sulphate of copper, nitrate of bismuth, and quadroxalate of potassa, afford illustrations of these forms. 6. The rhombohedral system. — This is very important and extensive : it is characterized by the presence o^ 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, 6 — 6. Secondary axes. principal axis is perpendicular to all. The regular six-sided prism (1), thb 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 distributed 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, CHEiMISTRY OF THE METALS. 209 ■which, as the process advances, gradually usurp the whoTe 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 tetraliedron 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.^ 18 From 7(705, equal, and u6p(}>Tt, shape or form. 210 CHEMISTRY OP 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'' " protox. 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,' to which the pupil is referred for fuller details on this inte resting subject. liomoTjphous 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 ' Second edition, p. 149. 212 CHEMISTRY OP 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, but 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 trihasic, bibasic, and monobasic acids, according to the number of equivalents of base required to form neutral salts. Tribasic or Comvion 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. f 2 eq. soda — y 2 eq. acetate of soda. Phosphate J 1 » water y y ^ " ^y Crated acetic acid. of soda 1 1 ,, phos-l [ phoric acid / Q ^^ ..««*„*« r 2 eq. acetic acid' 3 eq. acetate 1 ^ ^ ^^^^..^ ^^^^. ""^ ^^^^ 1 3 ',; oxide of lead ^^ ^ e^- tribasic phosphate ^ of lead. {3 eq. lead . 7 3 eq. sulphide of lead. 3 „ oxygen 1 „ phos- phoric acid 3 eq. sulphuretted f 3 eq. sulphur' hydrogen t 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, and 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. » Peligot, Ano. Cbim. et Pbys. Ixxiii. 286. OHEMISTEY OP THB METALS. 218 Bibasi* Phosphoric Acid^ or Pyrophosphoric Acid. — When common phos- phate of soda, containing 2NaO, HO, POg-f 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 tho substance passes back again into the tribasic modification. Crystals of this hydrate have also been observed by M. P^ligot. Their production was accidental. The bibasic phosphates soluble in water give a white precipitate with solution of silver. Monobasic, or Metaphosphoric Add. — When common tribasic phosphate of Boda 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, 2H0, PO5+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, PO5. 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.* 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 compovmd 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. KO4-SO3 K-f-SO^ KO-f-NOg K-fNOg * 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 acidi travel unaltered, a tribasic salt giving at the positive electrode a solution of common pho9. 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 OP THE METALS. Hydrated sulphnric acid will be, like hydrochloric acid, a hydride of a salt- radical, H+SO4. 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.* 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 SgOg and S2O4 are as hypothetical as the substances SjOg and SjOg. 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 jproperties so long as the anhydrous condition is retained. Some very interesting observations have been published lately by M. Ger- hardt,» 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 and pentoxide of nitrogen with water, SOg,!!©, and NO5, HO, may be considered likewise as hydrogen acids, analogous to hydro- chloric and hydrocyanic acid. Hydrochloric acid HCl Hydrocyanic acid HCaN Sulphuric acid \ ttoq Hydrosulphanic acid j * Nitric acid S HNO«. 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 SO, and NOs (see pages 124 and 135) has always been considered as powerful props. On the other hand, the followers of the theory of hydrogen acids 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 diflferent 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° (130°C), a limpid liquid is formed, which is de- ' See Danieirs Introduction to Chemical Philosophy, 2d edition, p. 533. • 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 CwHgOj or BzO, if we represent C14H5O3 by Bz. The decomposition which takes place is represented by the following equation : — B20,NaO+BzCl=:NaCl+2BzO. The new substance crystallizes in beautiful oblique prisms, fusible at 90° -4 (33°C), 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 ; 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 question 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, CaoHi203=Cm ; cinnamyl, CigH^O'zss Ci; or salicyl, CuS50i=:Sl. 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, CIC4H3O2, 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, PCI3O3, and chloride of acetetyP are formed. NaO,C4H303+Pa5=NaCl-fPCl302-fC4H302Cl. The action of chloride of acetttyl upon dry acetate of soda gives rise to the formation of an oily liquid, which has the composition of anhydrous acetic acid, C^HgOg, but which in reality is acetate of acetetyl = C4H.,02, 04H3O2,O.' This liquid boils at 278°-6 (137°C) ; it is not miscible at once * Acetetyl in order to distinguish it from acetyl, C4HS. ' This formula requires an equivalent of oxygen to produce two equivalents of anhydrous acetic acid. C4H903,C4H3O2O + O=2(C4H3O3,O). In the reaction hetween acetate of soda and chloride of acetyle, an equivalent of oxygen from the soda converts the acetetyl into anhydrous acetic acid with the formation of chloride of sodium. NaO.C4H308 + G4H j03Cl=2(C4H303) + NaCl. Acetetyle here spoken of, is from its composition acetous or aldehydic add. — R. B. 216 CHEMISTRY OP THE METALS. with cold water, but only after continued agitation. Hot water dissolves it at once with formation of acetic acid. The application to inorganic compounds of the method, by means of which these substances are produced, promises in future very important materials for the elaboration of several of the most interesting questions with which chemists are engaged at the present moment. The general application of the binary theory still presents a few difficul- ties. But it is very probable that the progress of discovery will ultimately lead to its universal adoption, which would greatly simplify many parts of the science. One great inconvenience will be the change of nomenclature mvoUed. CLASSIFICATION OF METALS. 1. Metals of the Alkalis. Potassium, Lithium, Sodium, Ammouiuni. » 2. Metals of the Alkaline Earths. Barium, Calcium, Strontium, Magnesium. 3. Metals of the Earths Proper. Aluminium, Norium, Beryllium, Thorium, Yttrium, Cerium, Erbium, Lantanum, Terbium, Didymium. Zirconium, 4. Ozidahle Metals proper ^ whose Oxides form powerful Bases. Manganese, ■ Zinc, Iron, Cadmium, Chromium, Bismuth, Nickel, Lead, Cobalt, Uranium. Copper, 5. Oxidable Metals Proper, whose Oxides form weak Bases, or Adds. Vanadium, Titanium, Tungsten, Molybdenum, Tantalum, Tin, e Antimony, Arsenic, Niobium, Tellurium, Pelopium, Osmium. 6. are reduced by Heat ; Noble Metals, Metals Proper, whose Oxides Gold, Palladium, Mercury, Silver, Iridium, Ruthenium, Platinum, Rhodium. ^ /his hypothetical substance is merely placed with the metals for the sake of couvenlenoe, I «flll be apparent in the sequel. POTASSIUM. 217 SECTION I. METALS OF THE ALKALIS. POTASSIUM. Potassium was discovered by Sir H. Davy in 1807, who obtained it in very small quantity by exposing a piece of moistened hydrate of potassa to the action of a powerful voltaic battery, the alkali being placed between a pair of platinum plates put into connection with the apparatus. Processes have since been devised for obtaining this curious metal in almost any quantity that can be desired. An intimate mixture of carbonate of potassa and charcoal is prepared by calcining, in a covered iron pot, the crude tartar of commerce ; when cold, it is rubbed to powder, mixed with one-tenth part of charcoal in small lumps, and quickly transferred to a retort of stout hammered iron ; the latter may be one of the iron bottles in which mercury is imported, a short and some- what wide iron tube having been fitted to the aperture. The retort is placed upon its side, in a furnace so constructed that the flame of a very strong fire, fed with dry wood, may vrrap round it, and maintain every part at an uniform degree of heat, approaching to whiteness. A copper receiver, divided in the centre by a diaphragm, is connected to the iron pipe, and kept cool by the application of ice, while the receiver itself is partly filled with naphtha or rock-oil, in which the potassium is to be preserved. Arrange ments being thus completed, the fire is gradually raised until the requisite temperature is reached, when decomposition of the alkali by the charcoal commences, carbonic oxide gas is abundantly disengaged, and potassium distils over, and falls in large melted drops into the liquid. The pieces of charcoal are introduced for the purpose of absorbing the melted carbonate of potassa, and preventing its separation from the finely divided carbonaceous matter. If the potassium be wanted absolutely pure, it must be afterwards re-dis- tilled in an iron retort, into which some naphtha has been put, that its vapour may expel the air, and prevent the oxidation of the metal. Potassium is a brilliant white metal, with a high degree of lustre ; at the common temperature of the air it is soft, and may be easily cut with a knife, but at 32° (0°C) it is brittle and crystalline. It meltfe completely at 136^' (57° -770), and distils at a low red heat. The density of this remarkable metal is only 0-865, water being unity. Exposed to the air, potassium oxidizes instantly, a tarnish covering the surface of the metal, which quickly thickens to a crust of caustic potassa. Thrown upon water, it takes fire spontaneously, and burns with a beautiful purple flame, yielding an alkaline solution. When brought into contact with a little water in ajar standing over mercury, the liquid is decomposed with great energy, and hydrogen liberated. Potassium is always preserved under the surface of naphtha. The equivalent of potassium (kalium) is 39 j and its symbol, K 19 2ii POTASSIUM. There are two compounds of this metal with oxygen, — potassa and teroxide of potassium. Potassa, Potash, or Protoxide of Potassium, KO, is produced when potassium is heated in dry air ; the metal burns, and becomes entirely con- verted into a volatile, fusible, white substance, which is anhydrous potassa. Moistened with water, it evolves great heat, and forms the hydrate. The hydrate of potassa, KO, HO, is a very important substance, and one of great practical utility. It is always prepared for use by decomposing the 4;arbonate by hydrate of lime, as in the following process, which is very con- venient: — 10 parts of carbonate of potassa are dissolved in 100 parts of water, and heated to ebullition in a clean untinned iron, or still better, silver vessel ; 8 parts of good quicklime are meanwhile slaked in a covered basin, and the resulting hydrate of lime added, little by little, to the boiling solu- tion of carbonate, with frequent stirring. When all the lime has been in- troduced, the mixture is suffered to boil a few minutes, and then removed from the fire, and covered up. In the course of a very short time, the solu- tion will have become quite clear, and fit for decantation, the carljonate of lime, with the excess of hydrate, settling down as a heavy, sandy precipi- tate. The solution should not effervesce with acids. It is essential in this process that the solution of carbonate of potassa be dilute, otherwise the decomposition becomes imperfect ; the proportion of lime recommended is much greater than that required by theory, but it is always proper to have an excess. The solution of hydrate, or, as it is commonly called, caustic potassa, may be concentrated by quick evaporation in the iron or silver vessel to any desired extent ; when heated until vapour of water ceases to be disengaged, and then suffered to cool, it furnishes the solid hydrate, containing single equivalents of potassa and water. Pure hydrate of potassa is a white solid substance, very deliquescent and soluble in water ; alcohol also dissolves it freely, which is the case with com- paratively few of the compounds of this base ; the solid hydrate of com- merce, which is very impure, may thus be purified. The solution of this substance possesses, in the very highest degree, the properties termed alka- line ; it restores the blue colour to litmus which has been reddened by an acid ; neutralizes completely the most powerful acids ; has a naseous and peculiar taste, and dissolves the skin, and many other organic matters, when the latter are subjected to its action. It is constantly used by surgeons as a cautery, being moulded into little sticks for that purpose. Hj irate of potassa, both in the solid state and in solution, rapidly absorbs carbonic acid from the air ; hence it must be kept in closely stopped battles. When imperfectly prepared, or partially altered by exposure, it efferreoces with an acid. The water in this compound cannot be displaced by heat, the hydrate vo- latilizing as a whole at a very high temperature. The following table of the densities and value in real alkali of different "o'lutions of hydrate of potassa is given on the authority of Dr. Dalton. _ ,. Percentage of J^ensity. real alkali. 1-68 51-2 1-60 46-7 162 42 9 1-47 39-6 1-44 36 8 1-42 34-4 1-39 32-4 1-36 29-4 1-33 26-3 1-28 28-4 1 23 19-5 1-19 16-2 115 130 111 9-5 106 4-7 POTASSIUM. 219 Teroxide op potassium, KO3. — This is an orange-yellow fusible substance, generated when potassium is burned in excess of dry oxygen gas, and also formed, to a small extent, when hydrate of potassa is long exposed, in a melted state, to the air. When nitre is decomposed by a strong heat, per- oxide of potassium is also produced. It is decomposed by water into potassa, which unites with the latter, and into oxygen gas. Carbonate of potassa, KO, C02-f-2HO. — Salts of potassa containing a vegetable acid are of constant occurrence in plants, where they perform im- portant, but not yet perfectly understood, functions in the economy of those beings. The potassa is derived from the soil, which, when capable of sup- porting vegetable life, always contains that substance. When plants are burned, the organic acids are destroyed, and the potassa left in the state of carbonate. It is by these indirect means that carbonate, and, in fact, nearly all the salts of potassa, are obtained ; the great natural depository of the alkali is the felspar of granitic and other unstratified rocks, where it is combined with silica, and in an insoluble state. Its extraction thence is attended with too many difficulties to be attempted on the large scale ; but when these rocks disintegrate into soils, and the alkali acquires solubility, it is gradually taken up by plants, and accumulates in their substance in a condition highly favourable to its subsequent applications. Potassa-salts are always most abundant in the green and tender parts of plants, as may be expected, since from these evaporation of nearly pure water takes place to a large extent ; the solid timber of forest trees contains comparatively little. In preparing the salt on an extensive scale, the ashes are subjected to a process called lixiviation ; they are put into a large cask or tun, having an aperture near the bottom, stopped by a plug, and a quantity of water is added. After some hours the liquid is drawn off, and more water added, that the whole of the soluble matter may be removed. The weakest solutions are poured upon fresh quantities of ash, in place of water. The solutions are then evaporated to dryness, and the residue calcined, to remove a little brown organic matter ; the product is the crude potash or pearlash of com- merce, of which very large quantities are obtained from Russia and America. This salt is very impure ; it contains silicate and sulphate of potassa, chloride of potassium, &c. The purified carbonate of potassa of pharmacy is prepared from the crude article, by adding an equal weight of cold water, agitating, and filtering; most of the foreign salts are, from their inferior degree of solubility, left behind. The solution is then boiled down to a very small bulk, and suffered to cool, when the carbonate separates in small crystals containing 2 equiv. of water, which are drained from the mother-liquor, and then dried in a stove. A still purer salt may be obtained by exposing to a red-heat purified cream of tartar (acid tartrate of potassa), and separating the carbonate by solution in water and crystallization, or evaporation to dryness. Carbonate of potassa is extremely deliquescent, and soluble in less than its own weight of water; the solution is highly alkaline to test-paper. It is insoluble in alcohol. By heat the water of crystallization is driven off, and by a temperature of full ignition the salt is fused, but not otherwise changed This substance is largely used in the arts, and is a compound of great im- portance. Bicarbonate of potassa, KO, COj-fHO, CO,. — When a stream of car- bonic acid gas is passed through a cold solution of carbonate of potassa, the gas is rapidly absorbed, and a white, crystalline, and less soluble substance separated, which is the new compound. It is collected, pressed, le-dissolved in warm water, and the solution left to crystallize. 220 POTASSIUM. Bicarbonate of potassa is much le^s soluble than simple carbonate ; it re- quires for that purpose 4 parts of cold water. The solution is nearly neutral to test-paper, and has a much milder taste than the preceding salt. When boiled, carbonic acid is disengaged. The crystals, which are large and beau- tiful, derive their form from a right rhombic prism ; they are decomposed by heat, water and carbonic acid being extricated, and simple carbonate left behind. Nitrate of potassa ; nitre ; saltpetre, KO, NOg. — This important compound is a natural product, being disengaged by a kind of efflorescence from the surface of the soil in certain dry and hot countries. It may also be produced by artificial means, namely, by the oxidation of ammonia in pres- ence of a powerful base. In France, large quantities of artificial nitre are prepared by mixing animal refuse of all kinds with o' "♦ mortar or hydrate of lime and earth, and placing the mixture in heaps, pr/»*cted from the rain by a roof, but freely exposed to the air. From time to time the heaps are watered with putrid urine, and the mass turned over, to expose fresh surfaces to the air. When much salt has been formed, the mixture is lixiviated, and the solution, which contains nitrate of lime, mixed with carbonate of potassa ; carbonate of lime is formed, and the nitric acid transferred to the alkali. The filtered solution is then made to crystallize, and the crystals purified by re-solution and crystalliza- tion several times repeated. , All the niti'e used in this country comes from the East Indies ; it is dis- solved in water, a little carbonate of potassa added to precipitate lime, and then the salt purified as above. Nitrate of potassa crystallizes in anhydrous six-sided prisms, with dihedral summits; it is soluble in 7 parts of water at 60° (15°-5C), and in its own weight of boiling water. Its taste is saline and cooling, and it is without action on vegetable colours. At a temperature below redness it melts, and by a strong heat is completely decomposed. When thrown on the surface of many metals in a state of fusion, or when mixed with combustible matter and heated, rapid oxidation ensues, at the expense of the oxygen of the nitric acid. Examples of such mixtures are found in common gunpowder, and in nearly all pyrotechnic compositions, which burn in this manner independently of the oxygen of the air, and even under water. Gunpowder is made by very intimately mixing together nitrate of potassa, charcoal, and sulphur, in proportions which approach 1 eq. nitre, 3 eq. carbon, and 1 eq. sulphur. These quantities give, reckoned to 100 parts, and compared with the pro- portions used in the manufacture of the English government powder,' the following results : — Theory. Proportions in practioe. Nitrate of potassa 74-8 75 Charcoal 13-3 15 Sulphur 11-9 10 100- 100 The nitre is rendered very pure by the means already mentioned, freed from water by fusion, and ground to fine powder : the sulphur and charcoal, the latter being made from light wood, as dogwood or elder, are also finely groimd, after which the materials are weighed out, moistened with water, and thoroughly mixed, by grinding under an edge-mill. The mass is then subjected to great pressure, and the mill-cake thus produced broken in pieces, * Dr. M'CuUoeh, Ency. Brit. POTASSIUM. 221 and placed in sieves made of perforated vellum, moved by macHiuery, each containing, in addition, a round piece of heavy wood. The grains of powder broken oflf by attrition fall through the holes in the skin, and are easily sepa- rated from the dust by sifting. The powder is, lastly, dried by exposure to steam-heat, and sometimes glazed or polished by agitation in a kind of cask mounted on an axis. When gunpowder is fired, the oxygen of the nitrate of potassa is trans ferred to the carbon, forming carbonic acid ; the sulphur combines with the potassium, and the nitrogen is set free. The large volume of gas thus pro- duced, and still farther expanded by the very exalted temperature, suffi- ciently accounts for the explosive effects. Sulphate of potassa, K0,S03. — The acid residue left in the retort when nitric acid is prepared is dissolved in water, and neutralized with crude car- bonate of potassa. The solution furnishes, on cooling, hard transparent crystals of the neutral sulphate, which may be re-dissolved in boiling water, and re-crystallized. Sulphate of potassa is soluble in about 10 parts of cold, and in a much smaller quantity of boiling water ; it has a bitter taste, and is neutral to test-paper. The crystals much resemble those of quartz in figure and ap pearance ; they are anhydrous, and decrepitate when suddenly heated, which is often the case with salts containing no water of crystallization. They are quite insoluble in alcohol. BisuLPHATE OF POTASSA, KO.SOg -|- H0,S03. The neutral sulphate iu powder is mixed with half its weight of oil of vitriol, and the whole evapo- rated quite to dryness in a platinum vessel, placed under a chimney ; tlie fused salt is dissolved in hot water, and left to crystallize. The crystals have the figure of flattened rhombic prisms, and are much more soluble than the neutral salt, requiring only twice their weight of water at G0° (lo°-5C), and less than half that quantity at 212° (100°C). The solution has a sour taste and strong acid reaction. BisuLPHATE OF POTASSA, ANHYDROUS, KO,2S03. — Equal weights of neutral sulphate of potassa and oil of vitriol are dissolved in a small quantity of warm distilled water, and set aside to cool. The anhydrous sulphate crys- tallizes out in long delicate needles, which if left several days in the mother- liquor disappear, and give place to crystals of the ordinary hydrated bisul- phate above described. This salt is decomposed by a large quantity of water.' Sesquisulphate OF POTASSA, 2(KO,S03) -j- H0,S03. — A salt, crytallizing in fine needles resembling those of asbestos, and having the composition stated, was obtained by Mr. Phillips from the nitric acid residue. M. Jacque- lain was unsuccessful in his attempts to reproduce this compound. Chlorate of potassa, KOjClOg. — The theory of the production of chloric acid, by the action of chlorine gas on a solution of caustic potassa, has been already described (p. 145). Chlorine gas is conducted by a wide tube into a strong and warm solution of carbonate of potassa, until absorption of the gas ceases. The liquid is, if necessary, evaporated, and then allowed to cool, in order that the slightly soluble chlorate may crystallize out. The mother-liquid affords a second crop of crystals, but they are much more contaminated by chloride of potas- Bium, It may be purified by one or two re-crystallizations. Chlorate of potassa is soluble in about 20 parts of cold, and 2 of boiling water ; the crystals are anhydrous, flat, and tabular ; in taste it somewhai resembles nitre. Heated, it disengages oxygen gas from both acid and base, and leaves chloride of potassium. By arresting the decomposition when the * Jacquelain, Ann. China, et Phys. vol. vii. p. 31^ 19* ^ ^ 222 POTASSIUM. evolution of gas begins, and re-dissolving the salt, perchlorate of potassa and chloride of potassium may be obtained. This salt deflagrates violently with combustible matter, explosion often occurring by friction or blows. When about one grain weight of chlorate and an equal quantity of sulphur are rubbed in a mortar, the mixture ex- plodes with a loud report ; hence it cannot be used in the preparation of gun- powder instead of nitrate of potassa. Chlorate of potassa is now a large article of commerce, being employed, together with phosphorus, in making instantaneous light matches. Peechlorate of potassa, KO.CIO,. — This has been already noticed under the head of perchloric acid. It is best prepared by projecting powdered chlorate of potassa into warm nitric acid, when the chloric acid is resolved into perchloric acid, chlorine, and oxygen gases. The salt is separated by crystallization from the nitrate. Perchlorate of potassa is a very feebly soluble salt ; it requires 55 parts of cold water, but is more freely taken up at a boiling heat. The crystals are small, and have the figure of an octahedron, with square base. It is decomposed by heat, in the same manner as chlorate of potassa. Sulphides of potassium. — There are not less than five or six distinct compounds of potassium and sulphur, of which, however, only three are of sufficient importance to be noticed here ; these are the compounds, contain- ing KS, KS3, and KSg. Simple ov proiosulphide of potassium, is formed by directly combining the metal with sulphur, or by reducing sulphate of potassa at a red-heat by hy- drogen or charcoal powder. Another method is to take a strong solution of hydrate of potassa, and after dividing it into two equal portions, saturate the one with sulphuretted hydrogen gas, and then add the remainder. The whole is then evaporated to dryness in a retort, and the residue fused. The protosulphide is a crystalline cinnabar-red mass, very soluble in water. The solution has an exceedingly ofi'ensive and caustic taste, and is decom- posed by acids, even carbonic acid, with evolution of sulphuretted hydrogen, and formation of a salt of the acid used. This compound is a strong sulphur- base, and unites with the sulphides of hydrogen, carbon, arsenic, &c., forming crystallizable saline compounds. One of these, KS-j-HS, is produced when hydrate of potassa is saturated with sulphuretted hydrogen, as before men- tioned. The higher sulphides are obtained by fusing the protosulphide with dif- ferent proportions of sulphur. They are soluble in water, and decomposed by acids, in the same manner as the foregoing compound, with this addition, that the excess of sulphur is precipitated as a fine white powder. Hepar sulphuris is a name given to a brownish substance, sometimes used in medicine, made by fusing together different proportions of carbonate of potassa and sulphur. It is a variable mixture of the two higher sulphides with hyposulphite and sulphate of potassa. When equal parts of sulphur and dry carbonate of potassa are melted to- gether at a temperature not exceeding 482° (250°C.), the decomposition of the salt is quite complete, and all the carbonic acid is expelled. The fused mass dissolves in water, with the exception of a little mechanically-mixed sulphur, with dark brown colour, and the solution is found to contain nothing besides pentasulphide of potassium and hyposulphite of potassa. {2 eq. potassium__ _^ 2 eq. of pentasulphide of po- 2 eq. oxygen ^^^'^^'^ sium. 1 eq. potassa ]^[^^]^><;;[^ 12 eq. sulphur {1^ ^^; ^IJIpJ^J"^!:^^^. 1 ,q. hyposulphite of po- tassa. POTASSIUM. 223 When the mixture has been exposed to a temperature approaching that of ignition, it is found on the contrary to contain sulphate of potassa, arising from the decomposition of the hyposulphite which then occurs. 4 eq r 1 eq- potassium 1 eq. pentasulphide 4eq.hyposul- potassa j 3 e?' tasTaV ^-^"""^ of potassium. phiteofpo-4, , I deq.potassa^ ^ tassa. 1 ^ ®^- ^y- f ^ ®^' sulphur- *^^^* 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 tho-carbonate ig fused with half its weight of sulphur only, then the tersulphide,^KS3, 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, KCl. — 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. — "Kere 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 potassivim 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, and 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 / 1°^^^® ^^ ^^^^^^ °^ potassium. \ Iron — V. } (■ Potassium • Potassa I Oxygen -~^__\^ Carbonic acid "^ Carbonate of protoxide 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 ealt 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- Bolves 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 geujral characters from the iodide. The salts of potassa are colourless, when not associated with a coloured metallic oxide or acid. They are all more or less soluble in waiter, 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 and 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° (90°C), 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 symbol (Natrium) Na. There are two well-defined compounds of sodium and oxygen ; the pro- toxide, anhydrous soda, NaO, and the binoxide, NaOg, or perhaps, teroxide NaOg ; 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 decomposing a somewhat dilute solution of carbonate of soda by hydrate of lime ; 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 splid 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. TABLE OP DENSITY. Density. 2-00 1-85 1-72 1-63 1-55 1-50 1-47 1-44 Percentage of real soda. 77-8 1-40 63-6 1-36 53-8 1-32 46-6 1-29 41-2 1-23 36-8 M8 34-0 1-12 31-0 106 Density. Percentage of real sis lazuli, and which is now >mitated by artificial means.* Chloride op sodium ; commox salt, NaCl. — This very important sub- • See Pharmaceutical Journal, ii. 53. 232 AMMONIUM. stance is found in many parts of the world in solid beds or ii'regular strata of immense thickness, as in Clieshire, 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 2J 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 diifi- 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, tlie mercury increases prodigiously in vclume, and becomes quite AMMONIUM. 233 pasty. The increase of weight is, however, quite trifling ; it varies from Left to itself, the amalgam quickly decomposes into fluid mercury, ammo- nia, and hydrogen. It is difficult to ofter 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^. Chloride of ammonium; (Muriate of Ammonia;) sal-ammoniac, NH^Cl. — 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 op ammonium ; sulphate of ammonia, NH^O, SOg-j-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,' and appear very numerous. The neutral^ anhydrous carbonate, NHgjCOj, 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 mixtiire of sal- ammoniac and chalk, always contains less base than that required to form a neutral carbonate. Its composition vaines a good deal, but in freshly pre- * Annalen der Pharmacie, xxx. 45 20* 234 AMMONIUM. pared specimens approaches that of a sesquicarbonate of oxide of ammonium, 2 NH^OjSCOj. — 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 NH40,C02+HO,C02. 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, NH40,N05. — 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.* 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^S-f-HS, 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, sufiTering 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.'' 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. ^Phosphates of Oxide op Ammonium; Common Tribasic Phosphate, 2 NH40,H0,P05-f-H0. — 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 obliqiie quadrangular prisms. Its crystals are eflBlorescent, soluble in alcohol, and soluble in four times its weight of cold water. Its solution has an alkaline, slightly saline taate and alkaline reaction. By heat ammonia is disengaged. The acid tribasic phosphate, NH40,2HO,P06+4HO, is formed when a solution of the common phosphate is boiled as long as ammonia is given oflf. It crystallizes in four-sided prisms. Its crystals aie permanent, soluble in 5 parts of cold water, acid in taste and reaction. Another tribasic phosphate, 3NH40,P06 subphosphate is formed by adding ammonia to either of tne abov9 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 not always easily decomposed by heat. The chlorides of copper and silver absorb, in this manner, large 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, NHg, 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 quasi-nxQiiiX ammonium ; the views of chemists upon this sub- ject are, however, still divided. The ammoniacal salts are easily recognised ; they are all decomposed or volatilized by a high temperature ; and when heated with hydrate of lime, or solution of alkaline carbonate, evolve ammonia, which may be known by its odour and alkaline reaction. The salts are all more or less soluble, the acid tartrate of ammonia and the double chloride of ammonium and platinum being among the least so ; hence the salts of ammonia cannot be distinguished from those of potassa by the tests of tartaric acid and platinum-solution. A connecting link between this class of metals and the next succeeding. Lithium is obtained by electrolyzing, in contact with mercury, the hydrate of lithia, and then decomposing the amalgam by distillation. It is a white metal like sodium, and very oxidable. The equivalent of lithium is 6-5, and its symbol L. The oxide, lithia, LO, is found in petalite, spodumene, lepidolite, and a few other minerals, and sometimes occurs in minute quantities in mineral springs. From petalite it may be obtained, on the small "scale, by the fol- lowing process : — The mineral is reduced to an exceedingly fine powder, mixed with five or six times its weight of pure carbonate of lime, and the mixture heated to whiteness, in a platinum crucible, placed within a well- covered earthen one, for twenty minutes or half an hour. The shrunken coherent mass is digested in dilute hydrochloric acid, the whole evaporated to dryness, acidulated water added, and the silica separated by a filter. The solution is then mixed with carbonate of ammonia in excess, boiled and filtered ; the clear liquid is evaporated to dryness, and gently heated in a 236 LITHIUM. platinum crucible, to expel the sal-ammoniac. The residue is then, wetted "with oil of vitriol, gently evaporated once more to dryness, and ignited ; pure fused sulphate of lithia remains. This process will serve to give a good idea of the general nature of the operation by which alkalis are extracted in mineral analysis, and theii quantities determined. The hydrate of lithia is much less soluble in water than those of potassa and soda ; the carbonate and phosphate are also sparingly soluble salts. The chloride crystallizes in anhydrous cubes which are deliquescent. Sul- phate of lithia is a very beautiful salt ; it crystallizes in lengthened prisms containing one equivalent of water. It gives no double salt with sulphate of alumina. The salts of lithia colour the outer flame of the blowpipe carmine-red. BARIUM. 237 SECTION II. METALS OF THE ALKALINE EARTHS. Barium was obtained by Sir H. Davy by means similar to those mentioned in the case of lithium ; it is procured more advantageously, by strongly heat- ing baryta in an iron tube, through which the vapour of potassium is con- veyed. The reduced barium is extracted by quicksilver, and the amalgam distilled in a small green glass retort. Barium is a white metal, having the colour and lustre of silver ; it is mal- leable, melts below a red heat, decomposes water, and gradually oxidizes in the air. The equivalent of this metal has been fixed at 68-5 ; its symbol is Ba. Pkotoxide of barium; baryta, BaO. — Baryta,' or barytes, occurs in nature in considerable abundance as carbonate and sulphate, forming the veinstone in many lead-mines ; from both these sources it may be extracted with facility. The best method of preparing pure baryta is to decompose the crystallized nitrate by heat in a capacious crucible of porcelain until red vapours are no longer disengaged ; the nitric acid is resolved into nitrous acid and oxygen, and the baryta remains behind in the form of a greyish spongy mass, fusible at a high degree of heat. When moistened with water, it combines to a hydrate with great elevation of temperature. The hydrate is a white, soft powder, having a great attraction for carbonic acid, and soluble in 20 parts of cold and 2 of boiling water ; a hot saturated solution deposits crystals on cooling, which contain BaO, H0-|-9H0. Solu- tion of hydrate of baryta is a valuable re-agent; it is highly alkaline to test-paper, and instantly rendered turbid by the smallest trace of carbonio acid. BiNOXiDE OF BARIUM, BaOg- — 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 binoxide 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+2H0. — This valuable salt is prepared by dissolving the native carbonate in hydrochloric acid, filtering the solution, » From /3ap«5j, heavy, in allusiou to the great specific gravity of the native carbonate and •ulphale. 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 00° (15o-5C), and 78 parts at 223" (106°-5C), which is the boiling-point of the saturated solution. Nitrate of baryta, BaO, NOj. — 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; BaOjSOg. — 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, COj. — 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 eflFect 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 OF STRONTIUM, Sr02. — 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, SrOjNOg. — 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."* 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 I>erby- 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 * Rei>-Fire :— Grns. Dry nitrate of strontia 800 Sulphur 225 Chlorate of potassa 200 Lampblack 60 Green-Pire: — Qma. Dry nitrate of baryta 45c Sulphur 150 Chlorate of potassa 100 Lampblack 2f The strontia 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 compoeiUoit has Veen known to ignite spontaneously. 240 CALCIUM. in a kiln of suitable construction, the ordinary limestones which abonnd 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° (100°C) 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 phai*maceutical 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, CaOj. — 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. ^ Sulphate of lime ; gypsum ; selenite ; CaO, SO3. — 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 260° (126° -eC), 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. Artificial 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 eflFect 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 pertnanent hard- ness, since it cannot be remedied. Carbonate of lime ; chalk ; limestone ; marble ; CaO, CO^. — 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 * According to M. Paul Thenard, the phosphide of calcium existing in this mixture, has the compositions PCaj. By coming in contact with water, it yields liquid phosphoretted hydrogen, PCaa + 2II0 = 2CaO + PH,— (Page 166). The greater portion of the liquid phosphide is immediately decomposed into solid auil gaseous phosphoretted hydrogen. — 5PH2 = 3PH3 + F»H. * Journal of the Pharmaceutical Society, voi. vi. p. b'iii. 21 242 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 Bhow that the animals inhabited fresh -water ; marine species and corals are, liowever, 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 9 little lime-water be poured into a vessel of that gas, the turbidity first pro- duced disappears on agitation, and a transparent solution of carbon»*te of lime in excess of carbonic acid is obtained. This solution is decomposeo 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 ; river, and more especially spring water, almost invariably containing carbonate of lime thus dissolved ]n limestone districts, this is often the case to a great extent. The hardnest of 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, ano 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.* The beautiful stalactitic incrustations of lime-stone caverns, and the deposits of calc-siuter 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 diflFerent crystalline forms, diflFerent densities, and dif- ferent optical properties. The former occurs very abundantly in crystals derived from an obtuse rhomboid, whose angles measure 106° 6'' 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. PiiOSPHATES OF LIME. — A number of distinct compounds of lime and phos- phoric acid probably exist. Two trihasic phosphates, 2CaO,HO,P05, and ^CaOPOg, 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. * Many proposals have been made to prevent the formation of boiler-deposits. The most efficient appears to be the method of Dr. Ritterband, which consists in throwing into the boiler a small quantity of sal-ammoniac, when carbonate of ammonia is formed, which is TolatiUzed with the steam, cBioride of calcium remaining in solution. It need scarcely be i!»ontioned that this plan is inapplicable in the case of permanently hard waters. CALCIUM. 24ii Tne 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 chai*- 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. Fluoeide OF calcium; fluor-spae; 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. Chloeide 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 gi-eatest 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 diflferent 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 insuflScient to decompose the whole ; when the acid is used in excess, chlorine is disengaged.' 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 SY?^"" % I Calcium Chlorine Lime " '"--^^^ ^ ^"^ •Hypochlorite 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- • M. Gay-Lussac, Ann. Chim. et Phys. 3rd serios, v. 296 244 CALCIUM. tity, is usuxtlly 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 bleaching- 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 per cent, 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 stufi" 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 efi'ect 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 7816) 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 ' 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." Baryta, strontia, and lime are thus distinguished from all other substances, and from each other. Caustic potassa, when fi-ee fropi carbonate, and caustic ammonia, occasion no precipitates in dilute solutions of the earths, especially of the first two, the hydrates being soluble in water. • Vide p. 227. " Graham's ElementH, vol. i. p. 414. MAGNESIUM, 245 '" x\lkaline carbonates, and carbonate of ampaonia, give white precipitates, /nsoluble in excess of the precipitant, with all three. Sulphuric acid, or a sulphate, added to very dilate 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 sufl&- 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 puj'ple ; 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 phawnacy 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° (15°-oC) and 36,000 parts at 212° (100°C). 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, ia 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 oxyge<^ 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 solntions, 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 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; MgOjSOg-f-THO. — 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° (100°C). The salt has a nauseous bitter taste, and, like many other neutral salts, purgative {)roperties. 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, MgOjCOj, 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 3 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,C02)-f-MgO,HO-i- 6H0. Magnesia alba is slightly soluble in water, especially when cold. Phosphate of magnesia, 2MgO,HO,P05-|- 14H0. — 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,NH40,P05-{-12HO. — 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 lightly soluble in pure water, but scarcely 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 heated tor 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. MAGNEBIUM. 247 Silicates of magnesia. — The following natural compounds belong to thia class : — Steatite or aoap-stcne, MgO,Si03, a soft, white, or pale-coloured, amor- phous substance, found iu Cornwall and elsewhere ; Meerschaum, MgOjSiOg-l- HO, from which pipe-bowls are often manufactured ; — Chrysolite, 3MgO,Si03, a crystallized mineral, sometimes employed for ornamental purposes ; a por- tion of magnesia is commonly replaced by protoxide 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 ALUxMINIUM. 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 malleabk , and have a specific gravity of 2-6. When heated in the air or in oxygen, it takes fire and burns with brilliancy, producing alumina. Aluminium has for its equivalent the number 13-7; its symbol is Al. Alumina, ALOg. — 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, AlgClg. — 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 othei-, for each of its constituents, suffers decomposition, car- bonic oxide being disengaged, and sesquichloride 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, AlgOgjSSOj-j-l^HO. — 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 Al203,3SOj-fKO,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 ia 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° -50, 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 ia largely used in the arts, in prepai'ing 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 pyrojjhorus 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^OjSOg, instead of KOjSOg, very closdy re- sembles common potassa-alum, having the same figure, and appearance, 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, suflfers complete decomposition, becoming converted into a soft, friable mass of earthy matter. This is the origin of clay ; the change itself U 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 sufi'ered 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 AlgOg, SSiOg-f-KO.SiOg, 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.' When the decomposing rock contains oxide of iron, the clay produced is coloured. The difi"erent 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, SAlgOg, SiOg, is found crystallized, constituting the beautiful mineral called cyanite. The compounds formed by the union of the silicates of alumina with other silicates are almost innumerable ; a soda-felspar, albile, containing that alkali in place of potassa, is known, and there are two somewhat similar lithia-compounds spodumene and petalite. The zeolites belong to this class: analcime, nepheline, mesotype, &c., are double silicates of soda and alumina, with water of crystallization. Slilbite, heulan- dite, laumonite, prehnite, &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. BERYI-LIUM (GLUCINUM). This metal is prepared from the chloride in the same manner as aluminium, it 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, with trace of iron and manganese 38-80 Lime 0-24 Water 12-00 Alkali and loss 1-76 100-00 CERIUM, LANTHANIUM, AND DIDYMIUM 251 Berylla, BcjOg, is a rare earth found in the emerald, beryl, and euclasCy 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 boifing. The salts of berylla have a sweet taste, whence its former name glucina {yXvKvs)' YTTRIUM. The metal of a very rare earth, yttria, 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, LANTHANIUM, 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 foi-ms a protoxide CeO, and a sesquioxide CejOg. 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.* 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 lathanium 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, and 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 lattei to the mother-liquor, and repeating the process. In this manner the whole of the didpnium-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 * A synopsis of the various methods for the separation of cerium, lanthanium, and didy mium has been given by Mr. H. Watts. Chem. Sec. 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.' 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, ZrgOg, 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. THOBIUM. 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 suJBFered 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, naiftely, 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- glass, and the material of artificial gems to the latter. The lead promotes fusibility, and confers also density and lustre. Common green bottle glass contains no lead, but much silicate of 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 * Annalen der Chemie und Pharmacie, xlvlii. 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 blow-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 arc 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).* Silica 60-0 Potassa 250 Lime 12*5 97-5 English flintrglass.* Silica 51-93 Potassa 13-77 Oxide of lead 33-28 98-98 The diflBcultly-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 * Mitscherlich, L«hrbuch, ii. 187 ■ FaracUy. 22 ..*_v4i>.*. 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 diminish 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 effect 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 ah 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 fui'nace 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. EARTHENWARE. 255 The mamifacture of porccTain in Europe is of modern origin ; the Chinese have possessed the art from 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 ; petunlze, 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 articles 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 M A N a A N E s SECTION IV. OXIDABLE METALS PROPER, WHOSE OXIDES FORM POWERFl L 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, and rammed as hard as possible. A smooth cavity is then scooped in the centre, into which the above-mentioned mixture is compressed, and covered with charcoal-powder. The lid of the crucible is then fixed, and the whole arranged in a very powerful wind-furnace. The heat is slowly raised until the crucible becomes red-hot, after which it is urged to its 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 difl5culty, and, when free from iron, oxidizes in the air so readily, that it requires to be preserved in naphtha. Water is not sensibly decomposed by manga^iese 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 diflFerent oxides of this metal are described, but two out of the number are, probably, secondary compounds. Protoxide MnO Sesquioxide Mn^Oj Binoxide MnOj Proto-sesquioxide (red oxide) Mng04=MnO, MugOg Varvicite Mn407=Mn2032MnOa Manganic acid MnOg Permanganic acid MugO^ 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 powerful MANGANESE. 257 bac^e, 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. Sesquioxide, MujOg. — This compound occurs in nature in the state of hydrate ; a very beautiful crystallized variety is found at Ilefeld, in the Hartx. 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, MnO^. — 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. Binoxide 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 dill'erent 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,' 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 countei-poised. 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, 43-0, is so nearly equal to twice that of carbonic acid, 22, that the loss of weight guttered by the apparatus when the reaction has has become complete, and the residual gas has been driven olf 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, MUgO^, or probably MnO-j-MngOg. — This oxide is also found native, and is produced artificially by heating to whitene^^s 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, incapa>)le of forming salts, and acted upon by acids in the same manner as the two higher oxides ah'eady " Sec page 228. 22* 258 MANGANESE. described. Borax and glass in a fused state dissolve this substaLce, and acquire the colour of the amethyst. Varvicite, Mn^O,, or Mn203-J-2Mn02. — A natural prodviCtion, 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, Muj Clg. — 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,SOg-|-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 buif-coloured, or sometimes nearly white. Exposed to heat, it loses carbonic acid, and absorbs oxygen. Manganic acid, MnOg. — 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. 259 Pebmangantc acid, Mn^O^. — 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 \iydrate 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 e:^cess 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. This is by very far the most important member of the group of metals under discusgion ; there are few substances to which it yields 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,' 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 ' Phillip's Mineralogy, fourth edit. p. 20i. 260 IRON. a Hessian crucible 4 parts of fine iron wire cut smuU, and 1 part of black oxide of iron. This is covered with a mixture of white sand, lime, and car- bunate 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'jth of an inch in diame- ter bearing a weight of 601b. It is very difiicult 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 Band 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) FCgOg Protosesquioxide (black oxide) Fe304=FeO, FcgOg Ferric acid FeOg 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- » When obtained at a heat l)e1ow redness.— R. B. ^ Tlic rusting of iron proceeds with rapidity after it once begins, extending from the point first affecti ^ • -j. x /. ^ i t.j Sulphide of ammonTum } ^^^^^ precipitate of protosulphide. Binoxide. Caustic alkalis ; white hydrate, soluble in excess. Ammonia ; white hydrate, slightly soluble in excess. « Fremy has called the first of these oxides stannic acid SnOa. The second he hait na'ned metastannic acid SnsOio. See also H. Rose Pogg. Ann. Ixxv. 1, who thinks that there ar* other modifications of this oxide of tin. 284 TUNGSTEN — MOLYBDENUM. Alkaline carbonates ; white hydrates, slightly soluble in excess Carbonate of ammonia ; white hydrate, insoluble. Sulphuretted hydrogen ; yellow precipitate of sulphide. Sulphide of ammonium ; the same, soluble in excess. Terchloride of gold, added to a dilute solution of protochloride of tin, gives rise to a brownish-purple precipitate, called purple of Cassius, very characteristic, whose nature is not thoroughly understood ; it is supposed to be a combination of oxide of gold and sesquioxide of tin, in which the latter acts as an acid. Heat resolves it into a mixture of metallic gold and binox- ide of tin. Purple of Cassius is employed in enamel-painting. The useful applications of tin are very numerous. Tinned-plate consists of iron superficially alloyed with this metal ; pewter, of the best kind, is chiefly tin, hardened by the admixture of a little antimony, &c. Cooking vessels of copper are usually tinned in the interior. TUNGSTEN (WOLFBAMIUM). Tungsten is found, as tungstate of protoxide of iron, in the mineral wolf- ram, tolerable abundant in Cornwall ; a native tungstate of lime is also oc- casionally met with. Metallic tungsten is obtained in the state of a dark grey powder, by strongly heating tungstic acid in a stream of hydrogen, but requires for fusion an exceedingly high temperature. It is a white metal, very hard and brittle; it has a density of 17-4. Heated to redness in the air, it takes fire, and reproduces tungstic acid. The equivalent of tungsten is 92, its symbol is W (wolframium). BiNOXiDE OF TUNGSTEN, WOj- — This is most easily prepared by exposing tungstic acid to hydrogen, at a temperature which does not exceed dull red- ness. It is a brown powder, sometimes assuming a crystalline appearance and an imperfect metallic lustre. It takes fire when heated in the air, and burns, like the metal itself, to tungstic acid. The binoxide forms no salts with acids. Tungstic acid, WOj. — When tungstate of lime can be obtained, simple digestion in hot nitric acid is sufficient to remove the base, and liberate the tungstic acid in a state of tolerable purity: its extraction from wolfram, which contains tungstic acid or oxide of tungsten in association with the oxides of iron and manganese, is more difficult. Tungstic acid is a yellow powder, insoluble in water, and freely dissolved by caustic alkalis. When strongly ignited in the open air, it assumes a greenish tint. Intehmediate or blue oxide of tungsten, W205,=W02,W03. — This sub- Btance is obtained by heating tungstate of ammonia, or by exposing the brown binoxide to the action of hydrogen at a very low temperature. The same compound appears to be produced if tungstic acid be separated froni one of its salts, by hydrochloric acid and the liquid be digested with metallic zinc, when the solution or the precipitate assumes a beautiful blue colour, which is very characteristic of this metal. Two chlorides and two sulphides of tungsten are known to exist. molybdenum. Metallic molybdenum is obtained by exposing molybdic acid in a charcoal- lined crucible to the most intense heat that can be obtained. It is a white, brittle, and exceedingly infusible metal, having a density of 8-6, and oxi- lizing, when heated in the air, to molybdic acid. The equivalent of molybdenum is 46 ; its symbol is Mo. Peotoxide of molybdenum, MoO. — Molybdate of potassa is mixed with VANADIUM. 285 excMS of hydrochloric acid, by which the molybdic acid first precipitated is re-dissolved ; into this acid solution zinc is put : a mixture of chloride of zinc and protochloride of molybdenum results. A large quantity of caustic potassa is then added, which precipitates a black hydrate of the protoxide of molybdenum, and retains in solution the oxide of zinc. The freshly pre- cipitated protoxide is soluble in acids and in carbonate of ammonia ; when heated in the air, it burns to binoxide. BiNOxiDE OF MOLYBDENUM, MoOg. — This is obtained in the anhydrous con- dition by heating molybdate of soda with sal-ammoniac, the molybdic acid being reduced to binoxide by the hydrogen of the ammoniacal salt ; or, in a hydrated condition, by digesting metallic copper in a solution of molybdic acid in hydrochloric acid, until the liquid assumes a red colour, and then adding a large excess of ammonia. The anhydrous binoxide is deep brown, and insoluble in acids ; the hydrate resembles hydrate of sesquioxide of iron, and dissolves in acids, yielding red solutions. «lt is converted into molybdic acid by strong nitric acid. Molybdic acid, M0O3. — The native bisulphide of molybdenum is roasted, at a red-heat, in an open vessel, and the impure molybdic acid thence re- sulting dissolved in ammonia. The filtered solution is evaporated to dryness, the salt taken up by water, and purified by crystallization. It is, lastly, decomposed by heat, and the ammonia expelled. Molybdic acid is a white crystalline powder, fusible at a red-heat, and slightly soluble in water. It is dissolved with ease by the alkalis. It forms two series of salts, namely, neutral molybdates MO,Mo03, and acid molybdatea MO,2Mo03. Three chloi'ides, and as many sulphides of molybdenum, are described. VANADIUM. Vanadium is found, in small quantity, in one of the Swedish iron ores, and also as vanadate of lead. It has also been discovered in the iron slag of Stafi"ordshire. The most successful process for obtaining the metal is said to be the following: — The liquid chloride of vanadium is introduced into a bulb, blown in a glass tube, and dry ammcniucal gas passed over it; the latter is absorbed, and a white saline mass produced. When this is heated by the flame of a spirit-lamp, chloride of ammonium is volatilized, and metallic vanadium left behind. It is a white brittle substance, of perfect metallic lustre, and a very high degree of infusibility ; it is neither oxidized by air or water, nor attacked by sulphuric, hydrochloric, or even hydrofluoric acid ; aqua regia dissolves it, yielding a deep blue solution. The equivalent of vanadium is 68-6 ; its symbol is V. Protoxide of vanadium, VO. — This is prepared by heating vanadic acid in contact with charcoal or hydrogen ; it has a black colour, and imperfect metallic lustre, conducts electricity, and is very infusible. Heated in the air, it burns to binoxide. Nitric acid produces the same efi"ect, a blue nitrate of the binoxide being generated. It does not form salts. Binoxide of vanadium, VOj. — The binoxide is obtained by heating a mixture of 10 parts protoxide of vanadium, and 12 of vanadic acid in a vessel filled with carbonic acid gas; or by adding a slight excess of carbonate of soda to a salt of the binoxide; in the latter case it falls as a greyish-whito hydrate, readily becoming brown by absorption of oxygen. The anhydrous oxide is a black insoluble powder, convertible by heat and air into vanadic acid. It forms a series of blue salts, which have a tendency to become green and ultimately red, by the production of vanadic acid. Binoxide of vanadium also unites with alkalis. Vanadic acid, VO3. — The native vandate of lead is dissolved in nitric acid, and the lead and arsenic precipitated by sulphuretted hydrogen, which at the same time reduces the vanadic acid to binoxide of vanadium. The %M TANTALUM — NIOBIUM AND PELOPIUM. bhie filtered solution is then evaporated to dryness, and the residue digested in amnronia, which dissolves out the vanadic acid reproduced during evapo- ration. Into this solution a lump of sal-ammoniac is put; as that salt dis- solves, vanadate of ammonia subsides as a white powder, being scarcely solu- ble in a saturated solution of chloride of ammonium. By exposure to a tem- perature below redness in an open crucible, the ammonia is expelled, and vanadic acid left. It has a dark-red colour, and melts even below a red- heat ; water dissolves it sparingly, and acids with greater ease ; the solutions easily suffer deoxidation. It unites with bases, forming a series of red or yellow salts, of which those of the alkalis are soluble in water. Chlokides of vanadium. — The bichloride is prepared by digesting vanadic acid in hydrochloric acid, passing a stream of sulphuretted hydrogen, and evaporating the whole to dryness. A brown residue is left, which yields a blue solution with water and an insoluble oxi chloride. The icrchloride is a yellow liquid obtained by jJlissing chlorine over a mixture of protoxide of vanadium and charcoal. It is converted by water into hydrochloric and vanadic acids. Two sulphides, corresponding to the chlorides, exist. TANTALUM (COLUMBIUm). This is an exceedingly rare substance; it is found in the minerals iantalite atid ytlro-fantalite, and may be obtained pure by heating with potassium the double fluoride of tantalum and potassium. It is a grey metal, but little acted on by the ordinary acids, and burning to tantalic acid when heated in the air, or when fused with hydrate of potassa. The equivalent of tantalum is 184 ; its symbol is T. BiNOXiDK OF TANTALUM, TOg. — When tantalic acid is heated to whiteness in a crucible lined with charcoal, the greater part is converted into this sub- stance. It is a dark-brown powder, insoluble in acids, and easily changed by oxidation to tantalic acid. Tantalic acid, TO3. — The powdered ore is fused with three or four times its weight of carbonate of potassa, and the product digested with water; from this solution acids precipitate a white hydrate of the body in question. It is soluble in acids, but forms with them no definite compounds ; with al- kalis it yields, on the contrary, crystallizable salts. The specific gravity of the acid varies 7-03 to 8-26. NIOBIUM AND PELOPIUM. The oxides of these two metals exist in the tantalite of Bodenmais in Ba- varia. "When the supposed tantalic acid from this source is mixed with dry powdered charcoal, and heated to redness in a current of chlorine gas, a sublimate is obtained of a yellow, readily fusible, and very volatile substance, the 'chloride of pelopium, and a white, infusible, less volatile body, the chlo- ride of niobium. The true chloride of tantalum, from the Finland tantalite, much resembles chloride of pelopium. The American tantalite contains nio- bic, pelopic, and tungstic acids, the former in greatest quantity. All these chlorides are decomposed by water, with production of hydro- chloric acid and the insoluble acids of the metals in the hydrated state. In properties these bodies greatly resemble each other. When heated to redness, they exhibit strongly the phenomenon of incandescence. While hot, tantalic acid remains white, pelopic acid is rendered slightly yellowish and has a spe- cific giavity varying from 5-79 to. 6-37, and niobic acid becomes dark yellow, with a specific gravity between 4-56 and 6-26. Tantalum, niobium, and pelopium may be obtained in a finely-divided me- tallic state by the action of ammonia on their respective chlorides at a high TITANIUM — ANTIMONY. 287 temperature. So prepared, they are black, pulverulent, not acted on bj water, but burning, when heated in the air, to acids. TITANIUM. Crystallized oxide of titanium is found in nature in the forms of titaniU and anaiate. Occasionally in the slag adherent to the bottom of blast-fumacea in which iron ore is reduced small brilliant copper-coloured cubes, hard enough to scratch glass, and in the highest degree infusible are found. Thia substance, of which a single smelting furnace in the Hartz produced as much as 80 pounds, was formerly believed to be metallic titanium. Recent re- searches of Wohler, however, have shown it to be a combination of cyanide of titanium with nitride of titanium. When these crystals are powdered, mixed with hydrate of potassa and fused, ammonia is evolved, and titanate of potassa is formed. Metallic titanium in a finely divided state may be ob- tained by heating fluoride of titanium and potassium with potassium. There are two compounds of this substance with oxygen; viz. an oxide and an acid : very little is known respecting the former. The equivalent of titanium is 25 ; its symbol is Ti. Titanic acid, Ti02. — Titanate, or titaniferous iron ore, is reduced to fine powder and fused with twice its weight of carbonate of potassa, powdered, dissolved in dilute hydrofluoric acid when titanofluoride of titanium and potassium soon begins to separate. From its hot aqueous solution snow-like titanate of ammonia is precipitated by ammonia, which is easily soluble in hydrochloric acid, and when ignited gives pure titanic acid. When pure the acid is quite white ; it is, when recently precipitated from solutions, soluble in acids, but the solutions are decomposed by mere boiling. After ignition it is no longer soluble, passing over into metatitanic acid. Titanic acid, on the whole, very much resembles silica, and is probably often overlooked and confounded with that substance in analytical researches. Bichloride of titanium. — This is a colourless, volatile liquid, resembling bichloride of tin ; it is obtained by passing chlorine over a mixture of titanic acid and charcoal at a high temperature. It unites very violently with water. On passing the vapour with hydrogen through a red-hot tube, hydrochloric acid and a new compound TijClj are formed. antimony. This important metal is found chiefly in the state of sulphide. The ore is freed by fusion from earthy impurities, and is afterwards decomposed by heating with metallic iron or carbonate of potassa, which retains the sulphur. Antimony has a bluish-white colour and strong lustre ; it is extremely brittle, being reduced to powder with the utmost ease. Its specific gravity is 6-8 ; it melts at a temperature just short of redness, and boils and vola- tilizes at a white-heat. This metal has always a distinct crystalline, platy structure, but by particular management it may be obtained in crystals, which are rhombohedral. Antimony is not oxidized by the air at common temperatures ; strongly heated, it burns with a white flame, producing ter- oxide, which is often deposited in beautiful crystals. It is dissolved by hot hydrochloric acid with evolution of hydrogen and production of terchloride. Nitric acid oxidizes it to antimonic acid, which is insoluble in that men- struum. There are three compounds of antimony and oxygen ; the first has doubtful basic properties, the second is indifferent, and the third is an acid The equivalent of antimony is 129. Its symbol is Sb (stibium). Teroxide of antimony, SbOg. — This compound may be prepa>ed by several methods : as by burning metallic antimony at the bottom of a large red-hot crucible, in which case it is obtained in brilliant crystals ; or by pouring ^o'aiion of terchloride of aniimony into water, and digesting thi 288 ANTIMONY. resulting precipitate with a solution of carbonate of soda. The teroxide thus produced is anhydrous ; it is a pale buff-coloured powder, fusible at a red-heat, and volatile in a close vessel, but in contact with air, it, at a high temperature, absorbs oxygen and becomes changed to the intermediate oxide. There exists a sulphate, nitrate, and oxalate of teroxide of antimony. When boiled with cream of tartar (bitartrate of potassa), it is dissolved, and the solution yields, on evaporation, crystals of tartar-emetic, which is almost the only compound of teroxide of antimony with an acid which bears admixture with water without decomposition. An impure oxide for this purpose is sometimes prepared by carefully roasting the powdered sulphide in a rever- beratory furnace, and raising the heat at the end of the process, so as to fuse the product; it has long been known under the name of glass of antimony. Intermediate oxide, Sb04 = Sb03,Sb05. — This is the ultimate product of the oxidation of the metal by heat and air ; it is a greyish white powder, infusible, and destitute of volatility ; it is insoluble in water and in acids, except when recently precipitated. "When treated with tartaric acid or bitartrate of potassa, teroxide of antimony is dissolve^ TO ORGANIC CHEiMISTRY. 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 such treatment under perhaps varied circumstances, may be broken «p 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, ai'C 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 sub- 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, the density of the vapour, and other pecularities of the original substance remain 27* 518 INTEODUCTION 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 oases by way of illustration. Dutch-liquid, the compound formed by the union of equal measures of olefiant gas and chlorine, containing C4H4CI2, 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, C4CI5, 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 €401303,110, 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, NO4, 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 formulsB 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 : — C4 { ^{ } Cl„ and C4 { ^j2 } CI2. or C4, (H3CI) Cl^ and C4 (H.Cl^) CI,. And pyroxlin, or gun-cotton, which is supposed to be a substitution-product from lignin, C^^^O^q, having 6 equivalents of hydrogen replaced by the ele- ments of hyponitric acid, will stand: — ^^^ { 5NO4 } ^2o> or C,4 [H,5 (NO4),] 0^. Isomeric 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 pT<»- ORGANIC CHEMISTRY. 3K 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 CgHg04 ; but then the first is supposed to consist of formic acid, C2HO3, combined with ether, C4HgO ; while the second is imagined in accordance with the same views, to be made np of ace- tic acid, C4H3O3, and the ether of wood-spirit, CjHgO. And this method of explanation is generally suflBcient 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-elementaTy 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 the other with chlorine, iodine, and oxygen. The former are designated organic gait-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 crystallization. 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. Colouiing principles f 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 maybe 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, while 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, and 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 an 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,* 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 prevented, no putrefaction occurs. The most putrescible substances, as an- imal flesh intended for food, milk, and highly azotized vegetables, are pre served indefinitely, by enclosure in metalKc 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 OP OHGANTC BODIES. A» 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 » Or erema&iitsis, that is, slow burning. ORGANIC BODIES. 821 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 (fig. 153), about 2^ 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 oW*^ P^^* 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. (^a 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 whole be purposely raised. A slight inclination is also given towards the extremity occupied by the mouth of the combustion-tube, which passes through a hole 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. e=s=^^^ tremity of the combustion-tube. The carbonic acid is condensed into a solu- tion of caustic potassa, of specific gravity 1-27, which is conttiined 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. Tlie 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 : f the difference of the level of the liquid in the two limbs of the potass- ORGANIC BODIES. 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 gx hydrogen ; or in 100 parts of sugar,' • The theoretical composition of sugar CuHnOu, reckoned to 100 parts gives — Carbon 42-11 Hydrogen 6-43 Oxygen 61-46 lOO-OO 324 THE ULTIMATE ANALYSIS OP CarI)on 41-98 Hydrogen 6*43 Oxygen, by diflFerence 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. "^cnt absorption of watery vapour. This is most conveniently eflfected 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. /Inah/sis 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 biD oxide of nitrogen, which may ORGANIC BODIES. 325 h» formed in the act of combustion. During the experiment some idea of thtt abundance or paucity of the nitrogen may be formed from the number of bubbles 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 a quantity of spongy metallic copper. A short bent tube, made moveable 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, j-jg. igl. 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 atmospheric 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 * 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 term? are the equivalent numbers: one equiralent of carbonic v>i lOot on* equivalent of carbon, 28 U 326 THE ULTIMATE ANALYSIS OP 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 first cause mentioned ; it gives excellent results, and is appli- cable to all azotized substances. A tube of good Bohemian glass, ^8 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. 162, and the combustion-tube arranged in the furnace. A few coals Fig. 162. 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 cwicentrated potassa-solution. If the gas be perfectly absorbed, or, after the introduction of a considerable quantity, only a minute bubble be left, the air may be 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- oomposed 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 0-3 or 0-5 per cent., due to the residual air of the apparatus, or that ooiidensed into the pores of the protoxide of copper. A most elegant "process for estimating nitrogen in all organic compounds, tfTcept 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 lieated 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 organic matter to carbonic acid, which is retained by the alMlli, 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° (100°C), and weighed ; 100 parts correspond to 6-272 parts of nitrogen ; or, the salt with its filter may be very carefully ignited, and 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 228 ULTIMATE ANALYSIS OF ORGANIC BODIES. Bodies very rich in nitrogen, as urea, must be mixed with about an equwv quantity of pure sugar, to furnisli 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 hydrogelH A modification of this process has been lately suggested by M. P^ligot, 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- b\ilbs. After the combustion is finished, the acid containing the ammonia is poured out into a beaker, coloui-ed 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 calcvilated. If, for instance, an acid be prepared, containing 20 grains of pure hydrated sulphuric acid (SOgjHO) 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 200 X 300 solution, it is evident that — —^- — = 60 grain-measures were saturated by the ammonia, and the quantity of nitrogen is obtained by the proportion 1-14 X 60 200 : 1-14 = 60 : a;, wherefrom z = — —- — = 0-342 grains of nitrogen. 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 FORMULA. 329 filled witli fragments of pure quick-lime. The lime is iDrought to a red- heat, 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. EMPIBICAL AND KATIONAL FOBMUL^. 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 C4H3O3, 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^HgOg, while its rational formula, determined by its capacity of saturation, is double, or CJ4H12O12, otherwise written C(4Hj,0jj,H0. In like manner, the empi- rical formula of the artificial alkaloids /wr/wn/je and amarine are respectively CigHgNOg and CajHgN. 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 CgjHjj N20g and C^gHjgNj ; hence these latter deserve the name of rational. The deduction of an empirical formula from the ultimate analysis is very easy ; the case of sugar, already cited, may be taken as an example. This contains, according to the analysis, in 100 parts Carbon 41-98 Hydrogen 6-43 Oxygen 51-59 100^ 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 — g— =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 »f the other. Again, the equivalents of carbon and hydrogen are nearly in 28 * 330 DETERMINATION OP TH* DENSITY OP VAPOURS. the proportion of 12 : 11, so that the formula CjgHjiOjj 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 diflFerence 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 : 72=100 : 42-11 171 : 11 = 100 : 6-43 171 : 88=100 : 51-46 171 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 VAPOUES. 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 OP THE DENSITY OP VAPOURS. 331 it ; if otherwise, an air-bubble is left, whose volume can be easily ascertained by pouring the liquid from the globe into a jar graduated to cubic inches, and then re-filling the globe, and repeating the same observation. Thf capacity of the vessel is thus at the same time known ; and these are all thd 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° (100°C) temp, of the bath at the moment of sealing the point, and 30-24 inches barometer 2076-81 grains. Residual air, at 45° (7° -220, 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 2070-88—10-035=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 hear 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 "1*"1 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. J32 DETERMINATION OF 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 CjHgO. 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 0-4183 x 3=1-2549 3 vols, hydrogen 0-0693x3=0-2079 J vol. oxygen =0-5528 Theoretical specific gravity 2-0156 CANE AND GRAPE-SUGAE. 833 SECTION I. NON-AZOTIZED BODIES OF THE SACCHARINE AND AMYLACEOUS GROUP. SUaAR, STARCH, GUM, LIGNIN, 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 C24H22O22 Cane-sugar, in combination 024H,gO,g Grape-sugar, crystallized C24H2802g Grape-sugar, in combination 024H2i02i Milk-sugar, crystallized C24H24O24 Milk-sugar, in combination ^^fin^i^ Sugar from Secale cornutum 024H2gO26 Mannite Cg H^ Og Starch, unaltered, dried at 212° (lOOoC) C24H20O20 Amidin, or gelatinous starch OjjiHgoOgo Dextrin, or gummy starch O24H2QO20 Starch from Cetraria Islandica O24H20O20 Inulin O24H21O21 Gum- Arabic C24H22O22 Gum-tragacanth O24H20O20 Lignin, or cellulose O24H20O20 Cane-sugar ; ordinary sugar, C24H22O22. — This most useful substance is 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 is 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, a 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 834 CANE AND GRAPE-SUGAR. from the dark uncrystallizable syrup, or molasses, and sent into commerce, under the name of rato 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, wheie 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° (110°C) 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 liiany 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 C24H18O18, and is isomeric with cane-sugar in combination. The following is the composition assigned to the principal compounds of cane-sugar by M. P^ligot, who has devoted much attention to the subject.' Crystallized cane-sugar C24ll,80,8-f 4H0 Compound of sugar with common salt CjiHigOjg-i-NaCl-j-SHO Compound of sugar with baryta C24Hj80,g-j-2BaO-f-4HO Compound of sugar with lime C24HigO,g-j-2CaO-|-4HO (Compound of sugar with protoxide of lead .... C24H,gOig-f-4PbO » Ann. Chim. et Phys. Ixrii. 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. Gkapb-sugar ; glucose ; sugar of fruits, C24H28O28. — 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 IJ 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. AVhen solutions o'f 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 C24H2i02i + 7HO The same, dried at 266° (130°C) C24H2i02i-|-3HO Compound of grape-sugar with common salt C24H2i02i-f NaCl-f 5H0 The same, dried at 266° (130°C) C24H2i02i-fNaCl-f 2H0 Compound of grape-sugar with baryta C24H2i02i-|--3BaO-f 7H0 Compound of grape-sugar with Ume CgiHgAi-f ^CaO-f 7H0 Compound of grape-sugar with protoxide of lead C24H2i02i-}-6PbO Sulphosaccharic Acid, C24H2o02p,S03. — 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-SUGAR. may be afterwards eliminated. It is a sweetish liquid, forming a variety of Boluble 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 MZmm, 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 with water, sacchulmic acid is converted into sacchulmin. Both these substances have the same composition, expressed by the empirical formula CjHO. Hy- drochloric acid in a dilute state, produces the same eflFects.* Action of Alkalis upon Sugar. — When lime or bf^ryta 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 CgHgOg. 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 fiocculent precipitate of a substance called melasinic acid, containing C24Hj20,o. Cane-sugar long-boiled with alkalis undergoes the same changes, being probably first converted into grape-sugar. Sugar from ergot of bye. — 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 C24H2603g. Sugar of diabetes insipidus. — A substance having the other properties of a sugar, but destitute of sweet taste, has been described by M. Th^nard as having been obtained from the above-mentioned source. It was capable of furnishing alcohol by fermentation, and of suflFering 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, C24H24O2J.— 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 ' Under the names ulmin and vlmic acid (humin and Mimic acid, crenic and a^o-crenic acids,) have been confounded a number of brown or black uncrystallizable substances, produced by the action of powerful chemical agents upon sugar, lignin, &c., or generated by the putrefactive d9cay of vegetable fibre. Common garden mould, for example, treated with dilute, boi^ng polution of caustic potassa, vields a deep brown solution, from which acids precipitate a floo- culent, brown substance, having but a slight degree of solubility in water. This is generally jiilled tdmic or humic acid, and its origin ascribed to the reaction of the alkali on the ulmin or hvmus of the soil. It is known that these iKxiies differ exceedingly in composition; th^ «r«> Uw itt^ of ready investigation. MANNITE— STARCH. 337 hardness. It is slow and diflBcult of solution in cold water, requiring for that purpose 5 or 6 times its weight ; it has a feeble sweet taste, and in the solid state feels gritty between the teeth. When heated, it loses water, and at a high temperature blackens and decomposes. Milk-sugar forms several com- pounds with protoxide of lead, and is converted into grape-sugar by boiling with dilute mineral acids. It is not directly fermentable, but can be made, under particular circumstances, to furnish alcohol. Manna-sugar ; mannitb, C6H7O8 or CjjHj^Oij. — This is the chief compo- nent of manna, an exudation from a species of ash ; it is also found in the juice of certain other plants, and in several sea-weeds, and may be formed artificially from ordinary sugar by a peculiar kind of fermentation. It is best prepared by treating manna with boiling alcohol, and filtering the solu- tion whilst hot ; the mannite crystallizes on cooling in tufts of slender colour- less needles. It is fusible by heat without loss of weight, is freely soluble in water, possesses a powerfully sweet taste, and has no purgative properties. Mannite refuses to ferment. This substance combines with sulphuric acid, giving rise to a new acid, the composition of which is not yet definitely established. It is likewise acted on by concentrated nitric acid. The product of this action will be noticed farther on. The substance formerly described as mushroom-sugar is merely mannite. Starch ; fecula. — This is one of the most important and widely diffused of the vegetable proximate principles, being found to a greater or less extent in every plant. It is most abundant in certain roots and tubers, and in soft stems: seeds often contain it in large quantity. From these sources the fecula can be obtained by rasping or grinding to pulp the vegetable structure, and washing the mass upon a sieve, by which the torn cellular tissue is re- tained, while the starch passes through with the liquid, and eventually settles down from the latter as a soft, white, insoluble powder, which may be washed with cold water, and dried with very gentle heat. Potatoes treated in this manner yield a large proportion of starch. Starch from grain may be pre- pared in the same manner, by mixing the meal with water to a paste, and washing the mass upon a sieve : a nearly white, insoluble substance called gluten or glutin remains behind, which contains a large proportion of nitrogen. The glutin of wheat-flour is extremely tenacious and elastic. The value of meal as an article of food greatly depends upon this substance. Starch from grain is commonly manufactured on the large scale by steeping the material in water for a considerable period, when the lactic acid, always developed under such circumstances from the sugar of the seed, disintegrates, and in part dissolves the azotized matter, and greatly facilitates the mechanical separation of that which remains. A still more easy and successful process has lately been introduced, in which a very dilute solution of caustic soda, containing about 200 grains of alkali to a gallon of liquid is employed with the same view. Excellent starch is thus prepared from rice. Starch is inso- luble in cold water, as indeed its mode of preparation sufficiently shows ; it is equally insoluble in alcohol and other liquids which do not effect its de- composition. To the naked eye it presents the appearance of a soft, white, and often glistening powder ; under the microscope it is seen to be altogether destitute of crystalline structure, but to possess, on the contrary, a kind of organization, being made up of multitudes of little rounded transparent bodies, upon each of which a series of depressed parallel rings surrounding a central spot or hilum, may often be traced. The starch-granules from dif- ferent plants vary both in magnitude and form ; those from the Canna coc- cinea, or tons les mois, and potato being largest : and those from wheat, and the cereals in general, very much smaller. The figure on the next page (Fig. 165) will sei ve to convey an idea of the appearance of the granules gf potato-starch, highly magnified. 29 338 DEXTRIN. Fig. 165. "When a mixture of starch and water is heated to near the boiling-point of the latter, the granules burst and disappear, producing, if the proportion of starch be considerable, a thick gelatinous mass, very slightly opalescent from the shreds of very fine membrane, the envelope of each separate granule. By the addition of a large quantity of water, this gelatinous starch, or amidin, may be so far diluted as to pass in great measure through filter-paper. It is very doubtful, however, how far the substance itself is really soluble in water, at least when cold ; it is more likely to be merely suspended in the liquid in the form of a swollen, transparent, insoluble jelly, of extreme tenuity. Gelatinous starch, exposed in a thin layer to a dry atmosphere, becomes converted into a yel- lowish, horny substance, like gum, which, when put into water, again softens and swells. Thin gelatinous starch is precipitated by many of the metallic oxides, as lime, baryta, and protoxide of lead, and also by a large addition of alcohol. Infusion of galls throws down a copious yelloAvish precipitate containing tannic acid, which re-dissolves when the solution is heated. By far the most characteristic reaction, however, is that with free iodine, which forms with starch a deep indigo-blue compound, which appears to dissolve in pure water, although it is insoluble in solutions containing free acid or saline matter. The blue liquid has its colours destroyed by heat, temporarily if the heat be quickly withdraw, and permanently if the boiling be long con- tinued, in which case the compound is decomposed and the iodine volati- lized. Starch in the dry state, put into iodiue-water, acquires a purplish- black colour. The unaltered and the gelatinous starch, in a dried state, have the same composition, namely, (^24^2{P9o''' ^ compound of starch and protoxide of lead was found to contain, when dried at 212° (100°C), C^J^^o^^Q-if-^VhO. Dextrin. — When gelatinous starch is boiled with a small quantity of dilute sulphuric, hydrochloric, or, indeed, almost any acid, it speedily loses its consistency, and becomes thin and limpid, from having suffered conver- sion into a soluble substance, resembling gum, called dextrin.' The experi- ment is most conveniently made with sulphuric acid, which may be after- wards withdrawn by saturation with chalk. The liquid filtered from the nearly insoluble gypsum may then be evaporated in a water-bath to dry- ness. The result is a gum-like mass, destitute of crystalline structure, soluble in cold water, and precipitable from its sohition by alcohol, and capable of combining with protoxide of lead. When the ebullition with the dilute acid is continued for a considerable period, the dextrin first formed undergoes a farther change, and becomes converted into grape-sugar, which can be thus artificially produced with the greatest facility. The length of time required for this remarkable change depends upon the quantity of acid present ; if the latter be very small, it is necessary to continue the boiling many successive hours, replacing the water which evaporates. With a larger proportion of acid, the conversion is much more speedy. A mixture of 16 parts potato-starch, 60 parts water, and 6 parts sulphuric acid, may be kept boiling for about four hours ; the liquid neutralized with chalk, filtered, and rapidly evaporated to a small * Fpoio its a-tion en polarized light, twisting the plane of polarization towards the right htaid. DEXTRIN — STARCH — INULIN. 889- bulk. By digestion with animal charcoal and a second filtration much of the colour will be removed, after which the solution may be boiled down to a thin syrup and left to crystallize ; in the course of a few days it solidifies to a mass of grape-sugar. There is another method of preparing this sub- stance from stared which deserves particular notice. .Germinating seeds, and buds in the act of development, are found to contain a small quantity of a peculiar azotized substance, formed at this particular period from the glutin or vegetable albuminous matter, to which the name diastase is given. This substance possesses the same curious property of effecting the conver- sion of starch into dextrin, and ultimately into grape-sugar, and at a much lower temperature than that of ebullition. A little infusion of malt, or ger- minated barley, in tepid water, mixed with a large quantity of thick gela- tinous starch, and the whole maintained at 160° (71°C), or thereabouts, occasions complete liquefaction in the space of a few minutes from the pro- duction of dextrin, which in its turn becomes in three or four hours con- verted into sugar. If a greater degree of heat be employed, the diastase is coagulated and rendered insoluble and inactive. Very little is known respecting diastase itself; it seems very much to resemble vegetable albumin, but has never been got in a state of purity. The change of starch or dextrin into sugar, whether produced by the action of dilute acid or by diastase, takes place quite independently of the oxygen of the air, and is unaccompanied by any secondary product. The acid takes no direct part in the reaction ; it may, if not volatile, be all with- drawn without loss after the experiment. The whole affair lies between the starch and the elements of water ; a fixation of the latter occuring in the new product, as will be seen at once on comparing their composition. The sugar, in fact, so produced, very sensibly exceeds in weight the starch em- ployed. Dextrin itself has exactly the same composition as the original starch. Dextrin is used in the arts as a substitute for gum ; it is sometimes made in the manner above described, but more frequently by heating dry potato- starch to 400° (204° -oC), by which it acquires a yellowish tint and becomes soluble in cold water. It is sold in this state under the appellation of British Gum. Starch is an important article of food, especially when associated, as in ordinary meal, with albuminous substances. Arrow-root, and the fecula of the Canna coccinea, are very pure varieties, employed as articles of diet ; arrow-root is obtained from the Maranta arundinacea, cultivated in the West Indies ; it is with difficulty distinguished from potato-starch. Tapioca is prepared from the root of the latropha manihot, being thoroughly purified from its poisonous juice. Cassava is the same substance modified while moist by heat. Sago is made from the soft central portion of the stem of a palm-tree. Starch from Iceland Moss. — The lichen called Cetraria Mandica, puri- fied by a little cold solution of potassa from a bitter principle, yields when boiled in water a slimy and nearly colourless liquid, which gelatinizes on cooling, and dries up to a yellowish amorphous mass, which does not dissolve in cold water, but merely softens and swells. A solution of this substance in warm water is not affected by iodine, although the jelly, on the contrary, is rendered blue. It is precipitated by alcohol, acetate of lead, and infusion of galls, and is converted by boiling with dilute sulphuric acid into grape- sugar. According to Mulder, linen-starch likewise contains Q24^2QOiQ. The jelly from certain algoi, as that of Ceylon, and the so-called Carragheen moss^ closely resembles the above. Inultn. — This substance, which differs from common starch in some im portant particulars, is found in the root of the Tnula helenium. the Helianthut 840 auM. iuberosus, the dahlia, and several other plants ; it may be easily obtained by washing the rasped root on a sieve, and allowing the inulin to settle down from the liquid ; or by cutting the root into thin slices, boiling these in water, and filtering while hot ; the inulin separates as the solution cools. It is a white, amorphous, tasteless substance, nearly insoluble in cold water, but freely dissolved by the aid of heat ; the solution is precipitated by alco- hol, but not by acetate of lead or infusion of galls. Iodine communicates a brown colour. Inulin has been analyzed by Mr. Parnell, who finds it to contain, when dried at 212° (100°G), C24H2,02,. Gum. — Gum-Arabic, which is the produce of an acacia, may be taken as the most perfect type of this class of bodies. In its purest and finest con- dition, it forms white or slightly yellowish irregular masses, which are des- titute of crystalline structure, and break with a smooth conchoidal fracture. It is soluble in cold water, forming a viscid, adhesive, tasteless solution, from which the pure soluble gummy principle, or arabin, is precipitated by alcohol and by basic acetate of lead, but not by the neutral acetate.' Ara- bin is composed of C24H22O22, and is consequently isomeric with crystallized cane-sugar. Mucilage, so abundant in linseed, in the roots of the mallow, in salep, the fleshy root of Oi'chis mascula, and in other plants, differs in some respects from the foregoing, although it agrees in the property of dissolving in cold water. The solution is less transparent than that of gum, and is precipi- tated by neutral acetate of lead. Gum iragacanth is chiefly composed of a kind of mucilage to which the name bassorin has been given, and which refuses to dissolve in water, merely softening and assuming a gelatinous aspect. It is dissolved by caustic alkali. Cerasin is the term given to the insoluble portion of the gum of the cherry-tree ; it resembles bassorin. The composition of these various substances has been carefully examined by M. Schmidt, who finds that it closely agrees with that of starch. Mucilage in- variably contains hydrogen and oxygen in the proportion in which they form water, and when treated with acid, yeild grape-sugar. Pectin, or the jelly of fruits, is, in its physical properties, closely allied to the foregoing bodies. It may be extracted from various vegetable juices by precipitation by alcohol. It forms, when moist, a transparent jelly, soluble in water, and tasteless, which dries up to a translucent mass. It is to this substance that the firm ^consistence of currant and other fruit jellies is to be ascribed. According to M. Fremy, the composition of pectin is C'64^48^64- -^y ebullition with water and with dilute acids it is changed into two isomeric modifications, to which the names parapectin and metapectin have been given. In contact with bases, these three substances become converted into pectic acid, which, except that it possesses feeble acid proper- ties, and is insoluble in water, resembles in the closest manner pectin itself. By long boiling with solution of caustic alkali, a farther change is produced, and a new acid, the metapectic, developed, which does not gelatinize. The salts of these two acids are incapable of crystallizing. Their composition is represented by the following formulee : — Pectic acid 2HO,C32H2o02g Metapectic acid 2HO,C24Hi502 Much doubt still exists respecting the composition of the various bodies of the pectin-series ; they do not appear, from the analyses yet made, to con * The precipitate produced by sub-salts of lead is a compound of arabine and oxide of lead, CVHmOM-f 2PbO. By the action of very dilute sulphuric acid arabine is slowly changed into dextrine, and by proloneed contact into glucose. Nitric acid decomposes gum and produceB first mucic and ultimately oxalic acid. — JK. B. OXALIC ACID. 341 tain oxygen and hydrogen in equal equivalents, and consequently scarcely belong to the starch-group. Lignin; ceclulose. — This substance constitutes the fundamental mate- rial of the structure of plants ; it is employed in the organization of cells, and vessels of all kinds, and forms a large proportion of the solid parts of every vegetable. It must not be confounded with ligneous or woody tissue, which is in reality cellulose, with other substances superadded, which encrust the walls of the original membraneous cells, and confer stiffness and inflex- ibility. Thus woody tissue, even when freed as much as possible from colouring matter and resin by repeated boiling with water and alcohol, yields on analysis a result indicating an excess of hydrogen above that required to form water with the oxygen, besides traces of nitrogen. Pure cellulose, on the other hand, is a terniary compound of carbon and the ele- ments of water, closely allied in composition to starch, if not actually isomeric with that substance.* The properties of lignin may be conveniently studied in fine linen or cotton, which are almost entirely composed of the body in question, the associated vegetable principles having been removed or destroyed by the variety of treatment to which the fibre has been subjected. Pure lignin is tasteless, insoluble in water and alcohol, and absolutely innutritions ; it is not sensibly affected by boiling water, unless it happen to have been derived from a soft or imperfectly developed portion of the plant, in which case it is disintegrated and rendered pulpy. Dilute acids and alkalis exert but little action on lignin, even at a boiling temperature ; strong oil of vitriol converts it, in the cold, into a nearly colourless, adhesive substance, which dissolves in water, and presents the character of dextrin. This curious and interest- ing experiment may be conveniently made by very slowly adding concen- trated sulphuric acid to half its weight of lint, or linen cut into small shreds, taking care to avoid any rise of temperature, which would be attended with charring or blackening. The mixing is completed by trituration in a mor- tar, and the whole left to stand a few hours ; after which it is rubbed up with water, and warmed, and filtered from a little insoluble matter. The solution may then be neutralized with chalk, and again filtered. The gummy liquid retains lime, partly in the state of sulphate, and partly in combina- tion with a peculiar acid, composed of the elements of sulphuric or hypo- sulphuric acid, in union with those of the lignin, to which the name sulpho- lignic acid is given. If the liquid, previous to neutralization, be boiled during three or four hours, and the water replaced as it evaporates, the dextrin becomes entirely changed to grape-sugar. Linen rags may, by these means, be made to furnish more than their own weight of that sub- stance. Lignin is not coloured by iodine. PKODUCTS ARISING FROM THE ALTERATION OP THE PRECEDING SUBSTANCES BY CHEMICAL AGENTS. ACTION OF NITRIC ACID. Oxalic Acid, Q^O^MO-^-^TiO. — This important compound occurs ready formed in several plants, in combination with potassa as an acid salt, or with lime. It is now manufactured in large quantities as an article of > Dumas, Chimie appliquee aux Arts, vi. 6. 29* M2 OXALICACID. commerce, by the action of nitric acid on sugar, starch, and dextrin. With the exception of gum and sugar of milk, which yield another product, all the substances comprehended in the saccharine and starch group furnish oxalic acid, as the chief and characteristic result of the long-continued action of moderately strong nitric acid at an elevated temperature. One part of sugar is gently heated in a retort with 5 parts of nitric acid of sp. gr. 1-42, diluted with twice its weight of water; copious red fumes are disengaged, and the oxidation of the sugar proceeds with violence and rapidity. When the action slackens, heat may be again applied to the vessel, and the liquid concentrated, by distilling off" the superfluous nitric acid, until it deposits crystals on cooling. These are drained, re-dissolved in a small quantity of hot water, and the solution set aside to cool. The acid separates from a hot solution in colourless, transparent crystals derived from an oblique rhombic prism, which contain three equivalents of water, one of these being basic and inseparable, except by substitution ; the other two may be expelled by a very gentle heat, the crystals crumbling down to a soft white powder, which may be sublimed in great measure without decomposition. The crystallized acid, on the contrary, is decomposed by a high temperature into carbonic and formic acids and carbonic oxide, without Bolid residue. The crystals of oxalic acid dissolve in 8 parts of water at 60° (15°-5C), and in their own weight, or less, of hot water ; they are also soluble in spirit. The aqueous solution has an intensely sour taste and most powerful acid re- action, and is highly poisonous. The proper antidote is chalk or magnesia. Oxalic acid is decomposed by hot oil of vitriol into a mixture of carbonic oxide and carbonic acid ; it is slowly converted into carbonic acid by nitric acid, whence arises a considerable loss in the process of manufacture. The binoxides of lead and manganese effect the same change, becoming reduced to protoxides, which combine with the unaltered acid. Oxalic acid is formed from sugar by the replacement of the whole of its hydrogen by an equivalent quantity of oxygen. 1 eq. sugar =C24HjgOig) / 12 eq. oxalic acid= €554 0^ 36 eq. oxygen= Ogg j "~ 1 18 eq. water = HjgOjg C24H18O54 ^24^18^54 The most important salts of oxalic acid are the following : — Neutral oxalate of potassa, KO,C203-j-HO. — This is prepared by neutralizing oxalic acid by carbonate of potassa. It crystallizes in transpa- rent rhombic prisms, which become opaque and anhydrous by heat, and dis- solve in 3 parts of water. Oxalate of potassa is often produced when a variety of organic substances are cautiously heated with excess of caustic alkali. BiNoxALATE OP POTASSA, KO,2C20g-(-3HO. — Sometimes called salt of sorrel, from its occurrence in that plant. This, or the substance next to be mentioned, is found also in the rumez and oxalis acetosella, and in the garden rhubarb, associated with malic acid. It is easily prepared by dividing a so- lution of oxalic acid, in hot water, into two equal portions, neutralizing one with carbonate of potassa, and adding the other; the salt crystallizes on cooling, in colourless rhombic prisms. The crystals have a sour taste, and require 40 parts of cold, and 6 of boiling water for solution. QuADKOXALATE OF POTASSA, KO,4C203-}- 7H0. — Prepared by a process similar in principle to that last described. The crystals are modified octahe- drons, and are less soluble than those of the binoxalate, which the salt in other respects resembles. Oxalate of soda, NaOjCjOj, has but little solubility; a binoxalate exists. OXALIC ACID. 343 Oxalate op ammonia, NH40,C203-f HO. — This beautiful salt is prepared by neutralizing by carbonate of ammonia a hot solution of oxalic acid. It crystallizes in long, colourless, rhombic prisms, which effloresce in dry air from loss of water of crystallization. They are not very soluble in cold water, but freely dissolve by the aid of heat. Oxalate of ammonia is of great value in analytical chemistry, being employed to precipitate lime from its solutions. When oxalate of ammonia is heated in a retort, it is completely decomposed, yielding water, ammonia and carbonate of ammonia, cyanogen and carbonic acid gases, and a small quantity of a peculiar greyish white sublimate. The latter bears the name of oxamide ; it is a very remarkable body, and forms the type of a large class of substances containing the ele- ments of an ammoniacal salt, minus those of water. Oxamide is composed of CgHgNOg, i.e., NH40,C203 — 2H0, or the elements of 1 eq. amidogen, and 2 eq. carbonic oxide. It is insoluble in water and alcohol : when boiled with an alkali it furnishes an oxalate of the base, and ammonia, which is expelled; and when heated with an acid, it produces an ammoniacal salt. When treated with nitrous acid it likewise reproduces oxalic acid, pure nitrogen being evolved C2H2N02+N03=C203,H0-f.H04.2N. Oxamide is the representa- tive of a tolerably large class of bodies having very analogous chemical rela- tions, and apparently a common constitution. Oxamide is obtained purer and more abundantly from oxalic ether ; its preparation will be found des- cribed under the head of that substance. Oxalate of ammonia, when dis- tilled with anhydrous phosphoric acid, loses four equivalents of water and yields a considerable quantity of cyanogen, NH40,C203 — 4H0 = C^N. There are, however, other compounds simultaneously produced. The hinoxalate of ammonia is still less soluble than the oxalate. When this salt is heated in an oil-bath to 450° (232° -20), among other products an acid called the ozamic is generated, containing C4HjN05,HO, i.e., NH4O, CjOg.HOjCaOj — 2H0, and may be viewed as a compound of oxalic acid with oxamide. It forms soluble compounds with lime and baryta. When heated with alkalis it yields ammonia and oxalate ; hot oil of vitriol resolves it into carbonic oxide and carbonic acid ; and water converts it, at a boiling tem- perature, into binoxalate of ammouia. Oxamic acid too, is interesting as the type of a very large class of similarly constructed compounds. Oxalate op lime, CaO,C203-|-2HO. — This compound is formed whenever oxalic acid or an oxalate is added to a soluble salt of lime ; it falls as a white powder, which acquires density by boiling, and is but little soluble in hydro- chloric, and entirely insoluble in acetic acid. Nitric acid dissolves it easily. When dried at 212° (100°C) it retains an equivalent of water, which may be driven oiF by a rather higher temperature. Exposed to a red-heat in a close vessel, it is converted into carbonate of lime, with escape of carbonic oxide. The oxalates of baryta, zinc, manganese, protoxide of iron, copper, nickel, and cobalt, are nearly insoluble in water; that of magnesia is sparingly soluble, and that of the sesquioxide of iron freely soluble. The double oxalate of chro- mium and potassa, made by dissolving in hot water 1 part bichromate of po- tassa, 2 parts binoxalate of potassa, and 2 parts crystallized oxalic acid, is one of the most beautiful salts known. The crystals appear black by re- tiected light from the intensity of their colour, which is pure deep blue ; they are very soluble. The salt contains 3(KO,C203) -f Cr203,3C203-f HO. A corresponding compound containing sesquioxide of iron has been formed ; it crystallizes freely, and has a beautiful green colour. Saccharic acid, CgH407,HO. — This substance was once thought to be identical with malic acid, which is not the case ; it is formed by the action of dilute nitric acid on sugar, and is often produced in the preparation of oxalic acid, being, from its superior solubility, found in the mother-liquor from which the oxalic acid has crystallized. It may be made by heating to- 344 SACCHARIC ACID. gether 1 part sugar, 2 parts nitric acid, and 10 parts water. When the re- action seems terminated, the acid liquid is diluted, neutralized with chalk, and the filtered liquid mixed with acetate of lead. The insoluble saccharate of lead is washed, and decomposed by sulphuretted hydrogen The acid slowly crystallizes from a solution of syrupy consistence in long colourless needles ; it has a sour taste, and forms soluble salts with lime and baryta. When mixed with nitrate of silver, it gives no precipitate, but, on the addi- tion of ammonia, a while insoluble substance separates, which is reduced, by gently warming the whole, to metallic silver, the vessel being lined with a smooth and brilliant coating of the metal. Nitric acid converts the sac- charic into oxalic acid. Xyloidin and pyroxylin. — When starch is mixed with nitric acid of spe- cific gravity 1-5, it is converted without disengagement of gas into a trans- parent, colourless jelly, which, when put into water, yields a white, curdy, insoluble substance : this is the new body xyloidin. When dry, it is white and tasteless, insoluble even in boiling water, but freely dissolved by dilute nitric acid, and the solution yields oxalic acid when boiled. Other sub- stances belonging to the same class also yield xyloidin ; paper dipped into the strongest nitric acid, quickly plunged into water, and afterwards dried, becomes in great part so changed; it assumes the appearance of parchment, and acquires an extraordinary degree of combustibility. If pure finely divided ligneous matter, as cotton-wool, be steeped for a few minutes in a mixture of nitric acid of sp. gr. 1 -5 and concentrated sul- phuric acid, squeezed, thoroughly washed and dried by very gentle heat, it will be found to have increased in weight about 70 per cent., and to have be- come in the highest degree explosive, taking fire at a temperature not much above 300° (148° -80), and burning without smoke or residue. This is pyroxylin, the gun-cotton of Professor Schoenbein. It difi^ers from xyloidin in composition, in its mode of combustion, and in resisting the action of cer- tain liquids, as ether containing a little alcohol, which dissolve xyloidin with facility. To a solution of this description the name collodion has been given ; it is used in surgery. Both xyloidin and pyroxylin appear to the substitution-compounds, in which the elements of hyponitric acid replace Tespectively 3 and 5 equiva- lents of hydrogen in those of water in starch and lignin. The analytical results are not very uniform, but the formulae which best agree with them are, xyloidin C24H,7N3032, and pyroxylin C24H,5N504o.' An analogous compound is produced by the action of nitric acid upon mannite (vide p. 337). This substance may be crystallized from spirit, and contains CgH^NgOig ; it may be viewed as mannite, in which three equiva- lents of hydrogen are replaced by hyponitric acid. Mucic ACID C,2HgO,4,2HO. — Sugar of milk and gum, heated with nitric acid somewhat diluted, furnish, in addition to a small quantity of oxalic acid, ' Pyroxylin obtained by the mixture of nitric and sulphuric acids, or by the action of a well cooled mixture of two parts of nitrate of potassa and three parts of concentrated sul- phuric acid, has the composition as given in the text, but is wholly insoluble in ether, or a mixture of ether and alcohol. When, however, the cotton-wool is steeped in the mixture of nitre and sulphuric acid at the temperature produced by their mixture, the resulting com- pound is readily soluble in ether and a mixture of ether and alcohol forming a transparent, viscid solution. Ammonia passed through this solution renders it quite fluid. The ammo- uiacal solution acted on by a large quantity of water yields a light white precipitate, inso- luble in water, while nitrate of ammonia remains in solution. The composition of the pre- cipitate is intermediate between xyloidin and pyroxylin, CQ4H16N4O36 four equivalents ot hydrogen being replaced by four of hyponitric acid or four equivalents of the elements of V ater by four of nitric acid. It may be dried without alteration at the boiling temperature ; by heat it explodes with a slight residue of carbon. The mixture of sulphuric and nitric acid forms from gum, glucose, and dextrine, explosive products wh''h have not yet been fully examined. (Bechamp. Ann. Ch. et Phys. FeU 185?^ — E.B FERMENTATION OF &UGAR 845 a wliito nearly insoluble substance called mucic acid. It may be easily pre- pared by heating togethe*Hn a flask or retort 1 part of milk-sugar, or gum, 4 parts of nitric acid, and 1 of water ; the mucic acid is afterwards collected upon a filter, washed and dried. It has a slightly sour taste, reddens vege- table colours, and forms salts with bases. It requires for solution 66 parts of boiling water. Oil of vitriol dissolves it with red colour. Mucic acid is decomposed by heat, yielding, among other products, a volatile acid, the pyromucic, which is soluble in water, and crystallizes in a form resembling that of benzoic acid. Pyromucic acid is monobasic ; it contains CjoHjOg.HO. Suberic acid, Ci5H,20g,2HO, is formed by the action of nitric acid on the peculiar ligneous matter of cork, and also on certain fatty bodies ; it much resembles mucic acid, but is more soluble in water. It is a bibasic acid. See farther on, Section VII., Oils and Fats. The following bodies are closely allied in composition to oxalic acid : — Mellitic acid, 0403,110. — This substance occurs, in combination with alumina, in a very rare mineral called mellite or honey-stone, found in deposits of imperfect coal, or lignite. It is soluble in water and alcohol, and is crys- tallizable, forming colourless needles. It combines with bases : the melli- tates of the alkalis are soluble and crystallizable ; those of the earths and metals proper are mostly insoluble. Mellitate of ammonia yields by distillation two curious compounds, para- niide and euchronic acid. The former is a white, amorphous, insoluble sub- stance, containing CgHN04, (i.e., bimellitate of ammonia — 4 eq. of water), and convertible by boiling with water into bimellitate of ammonia. The latter forms colourless, sparingly soluble crystals containing in the anhy- drous state C,jN0g,2H0. In contact with metallic zinc and deoxidizing agents in general, euchronic acid yields a deep blue insoluble substance called euchrone. Rhodizonic and croconic acids. — When potassium is heated in a stream of dry carbonic oxide gas, the latter is absorbed in large quantity, and a black porous substance generated, which, when put into water, evolves in- flammable gas, and produces a deep red solution containing the potassa-salt of a peculiar acid; the rhodizonic; by adding alcohol to the liquid, th^j rho- dizonate of potassa is precipitated. This and the lead-salt are the only two compounds which have been fully examined ; the acid itself cannot be iso- lated. Rhodizonate of potassa is composed of C^O^SKO ; hence the acid would appear to be tribasic. When solution of rhodizonate of potassa is boiled, it becomes orange-yel- low from decomposition of the acid, and is then found to contain oxalate of potassa, free potassa, and a salt of an acid to which the term croconic is applied. This acid can be isolated ; it is yellow, easily crystallizable, and soluble both in water and alcohol. Crystallized croconic acid contains CA^HO. THE FERMENTATION OF SUGAR, AND ITS PRODUCTS. The term fermentation is applied in chemistry to a peculiar metamorpho- sis of a complex organic substance, by a transportation of its elements under the agency of an external disturbing force, different from ordinary chemical attraction, and more resembling those obscure phenomena of contact already noticed, to which the expression katalysis is sometimes applied. The expla nation which Liebig has suggested of the cause and nature of the fermen- tative change is a very happy one, although of necessity only hypothetical It has long been known that one of the most indispensable conditions of tkal process is the presence in the fermenting liquid of certain azotized substan- ces, called ferments, whose decomposition proceeds simultaneously with that of the body undergoing metamorphosis. They all belong to the class of al • 346 FERMENTATION OF SUGAR. buminous principles, bodies which in a moist condition putrefy and decom- pose spontaneously. It is imagined that when thUse substances, in the act of undergoing change, are brought into contact with neutral ternary com- pounds of small stability, as sugar, the molecular disturbance of the body, already in a state of decomposition, may be, as it were, propagated to the other, and bring about destruction of the equilibrium of forces to which it owes its being. The complex body under these circumstances, breaks up into simpler products, which possess greater permanence. Whatever may be the ultimate fate of this ingenious hypothesis, it is certain that decom- posing azotized bodies not only do possess very energetic and extraordinary powers of exciting fermentation, but that the kind of fermentation set up is, in a great degree, dependent on the phase or stage of decomposition of the ferment. Alcohol ; vinous fermentation. — A solution of pure sugar, in an open or close vessel, may be preserved unaltered for any length of time ; but, if putrescible azotized matters be present, in the proper state of decay, the sugar is converted into alcohol, with escape of carbonic acid. Putrid blood, white of egg, or flour-paste, will efl'ect this; by far the most potent alcoholic ferment is, however, to be found in the insoluble, yellowish, viscid matter deposited from beer in the act of fermentation, called yeast. If the sugar be dissolved in a large quantity of water, a due proportion of active yeast added, and the whole maintained at a temperature of 70° (21 -IC) or 80° (26° -60), the change will go on with great rapidity. The gas disengaged will be found to be nearly pure carbonic acid ; it is easily collected and ex- amined, as the fermentation, once commenced, proceeds perfectly well in a close vessel, as a large bottle or flask, fitted with a cork and conducting- tube. When the efi'ervescence is at an end, and the liquid has become clear, it will yield alcohol by distillation. Such is the origin of this important com- pound ; it is a product of the metamorphosis of sugar, under the influence of a ferment. The composition of alcohol is expressed by the formula C4Hg02 : it is pro- duced by the breaking up of an equivalent of grape-sugar, C24H2g02g, into 4 eq. of alcohol, 8 of carbonic acid, and 4 of water. It is grape-sugar alone 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 0-8.35, 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 aeveral days. The alcohol is distilled off by the heat of a watei'-bath. Pure alcohol is a colourless, limpid liquid, of pungent and agreeiible taste and odour; its specific gravity at 60° (15°-5C) is 0-7938, and that of its vapour l-Olo, It is very inflammable, burning with a pale bluish flame, free trom smoke, and has never been fi-ozen. Alcohol boils at 173° (78°-lC) when hi 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 many degrees, tlr^s takes place not only with pure alcohol, but with rectified ALCOHOL. S4T spirK. It is miscihlc 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 C4H50,KO ; it may be likewise formed by acting with potassium upon anhydrous alcohol, when hydrogen is evolved. Alcohol dissolves, moreover, many organic substances, as the vegeto-alkalis, resins, 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 0-91Q8 at 60° (15° -SC), and contains 49J 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 oflF 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 is 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 goosebei'- 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. Beer is a well-known liquor, of great antiquity, prepared from germinated grain, generally barley, and is used in countries where the vine does not 848 ALCOHOL. flourish. The operation of mailing 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 fermentation, 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 sufi^ered to run its full course, but is always stopped at a par- ticular point, by separating the yeast, and drawing ofl^ 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 ofi^ensive. Under the microscope it exhibits a kind of organized appearance,being made up of little transparent globules, which sometimes coliere 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 dxStiller, who prepares spirits from grain, makes his wort, or wash, much in the same manner as the brewer ; he uses, however, with the malt a large quantity of raw grain, the starch of which sufi"ers conversion into sugar by toe diastase of the malt, which is sufficient for his purpose. He does not boil his infusion with hops, but proceeds at once to the fermentation, which LACTIC ACID. 849 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 fei'raentation 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 ; butyhic 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 suflficient 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 decompohed by tho 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 resultia? nit purified by re-crystallization and the use of animal char- coal, after wh,fh it may be decomposed by oxalic aoid 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° (30°C), 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 v^U 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 acid 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 CgHgOg-j-HO, or C,2HjqO,o-|-2HO, the water being basic, and su|ceptible of replacement by a metallic oxide. 'vhen syrupy lactic acid is heated in a retort to 266° (130°C), water con- taining a little actio 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, CgHgOg. 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 CgH404 ; it combines with ammonia, forming lactamide, CgH7N04, 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° -20.) 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. 351 Lactate of lime, CaO.CgHsOg-f-^IIO, exists ready-formed, to a small ex- tent, in Nux vomica. When pure, it crystallizes in tufts of minute white needles grouped in concentric layers. It dissolves in 10 parts of cold, and indefinitely in boiling water, molting in its water of crystallization at that temperature. Lactate of zinc, ZnOjCgHgOg-f-^HO, is deposited from a hot solution in small brilliant 4-sided prismatic ci'ystals, which require for solution 68 parts of cold and 6 of boiling water. Lactate of protoxide of iron, FeOjCgHgOg-j-SHO, 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° -90) or 100 ACIDS CONTAINING ■which the liquid is subjected. The cause of the decomposition is to bt 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° -60 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° -SC) 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° (160°C) and above, the production of ether diminishes, and other substances begin to make their appearance, of which the most remarkable is defiant 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 defiant gas ; the others may be considered the result of secondary actions. The three modes of decomposition may be thus contrasted : — Below 260°— C4H50,2S03,HO+2HO = C4H50,H0-f 2(S03,H0) 260°— 310°— C4H50,2S03,HO-f HO = C.HgO -f 2(S03,HO) Above 320°— C4H60,2S03,H0 = C4H4 -f-^lSOa.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 defiant 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 J^ of an inch in diameter ; and the third, a wide bent tube, connected with me condenser, to carry ofi" 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° (149°C) ; 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 IHE ELEMENTS OF ETHER. Pig. 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° (149°C), or as near that temperature as possible, while the contents of the flask are maintained in a state of rapd 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 « Fig. 166. Apparatus for the preparation of ether, a. Flask containing the mixture of oil of Titriol and alcohol, b. Reservoir with stop-cock, for supplying a constant stream of alcchol c. Wide bent tube connected with the condenser for convejing away the vapours- d. Th« thermometer for regulating the temperature of the boiling liquid. 31 862 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 a larger quantity than usual of undecomposed alcohol ; the addition of a little water, however, always suffices to determine it. We shall once more return to the formation of ether, when we discuss the methyl-compounds. Heavy oil of wine, — When a mixture of 2^ 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- phoviuate 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 C8HgO,2S03, or per- haps 04114.803-1-041150,803; 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 siveet 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 etherin have the same composition, namely C^H^, and are consequently isomeric with defiant gas. Olefiant 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 alwfiys 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, throiigh 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= (160° and 165° -.50) ; 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-Ll 3UTD. Fig. 167. 363 Fig. 168. 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 defiant 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 op 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 864 CHLORIDES or CARBON. kept a little in excess. The chlorine should be washed with water, and the defiant 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- phui'ic acid ; it is, lastly, purified by re-distillation. If impure defiant gas be employed, the crude product contains a large quantity of a substance called by M, Regnault chloro-sulphuric acid, SOgCl, 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 ther. It is heavier than water, and boils when heated to 180° (82° -SC) ; t is unaffected by oil of vitriol and solid hydrate of potassa. When in- liamed, it burns with a greenish, smoky light. This substance yields, by ualysis, C4H4CI2. "V^en Dutch-liquid is treated with an alcoholic solution of caustic potassa, is slowly resolved into chloride of potassium, which separates, and into a ■.^ .J and exceedingly volatile substance, containing C4H3CI, whose vapour . ^quires to be cooled down to 0° ( — 17°-7C) before it condenses. At this I- mperature it forms a limpid, colourless liquid. Chlorine is absorbed by tliis substance, and a compound produced, which contains C4H3CI3 ; this is in turn decomposed by an alcoholic solution of hydrate of potassa into chloride of potassium and a new volatile liquid, C4H2CI2. Bromide and iodide of olefiant gas, C4H4Br2 and C4H4I2. — 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 0° (— 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 ov 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 ciilorine. This regular substitution of chlorine, bromine, iodine, &c., in I'lace of hydrogen, as before stated, is a phenomenon of constant occur- • ' ice in reactions between these bodies and very many organic compounds. ii the present case four such steps may be traced, giving rise, in each u),-3tance, to hydrochloric acid and a new substance. Three out of the four new products are volatile liquids, containing C4HgCl3,C4H2Cl4 and C4HCI5; the fourth C4Clg 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. Sesguichloride or Perchloride of Carbon, C4Clg, is a white, solid, crystalline sul»stance, of aromatic odour, insoluble in water, but easily dissolved by alcohol and ether; it melts at 320° (160°C), 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. Frotochloride of Carbon, C4CI4. — 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, colourlesa ETHIONIC AND ISET 11 IONIC ACIDS. 365 liquid, which has a density of 1-55, and boils at 248° (120<»C). The density ol its vapour is 5-82. It resembles in chemical relations the perchloride. Subchloride of Carbon, C4CI2, 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, C2CI4. — 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 (77°C). 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 Zeisb. — 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" (100°C), this substance contains Pt2Cl2,C4H4-|-KCl. Corresponding com- pounds, containing Pt2Cl2,C4H4-j-NaCl, and Pt2Cl2,C4H4-}-NH4Cl, 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 OLEriANT 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 C4H4,4S03. To this substance Magnus applies the name sulphate of carbyl. A body very similar in appearance and properties, and probably identical with this, had previovLsly 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 dilute 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 C4H50,4S0j-f- 2 HO. The ethionates 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 C4H50,2S03-j-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 hlorine 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 aftei-wards 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 : eea 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 20lo-2 (94°C). 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 C4HCI3O2. When chloral is preserved for any length of time, even in a vessel heime- 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 brumal, which con. ALCOHOL. 6K)i tains C^HBrgOj. It forma a crystallizable hydrate with water, and is aecom • posed by strong alkaline solutions into formic acid and bromoform. A cor- responding iodine-compound probably exists. ♦ Chlorine acts in a diflFerent 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 elher. 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 e(iuivalent 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 ia found by analysis to contain C4HgCl30, 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 C4CI5O ; it is called pentachlorinetted ether. In a substance called cloretheral, C4H4CIO, accidentally formed by M. d'Arcet, in the preparation of Dutch- liquid, from the ether-vapour mixed with the defiant 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 secondai-y products. Thus, chlorinetted acetic ether, a dense, oily liquid, very different from common acetic ether, was found to contain C8HgCl204, being a substi- tution product of CgHg04= 04X150,0411303; and chlorinetted formic ether, 0511401204, is formed, in like manner, by the substitution of 2 eq. chlorine for 2 eq. hydrogen in ordinary formic ether, 0gHgO4=04H5O,C2HO3. A most remarkable and interesting set of compounds, due to substitution of this kind, are formed by the action of chlorine on chloride of ethyl, 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 C4H5CI Monochlorinetted hydrochloric ether C4H4OI2 Bichlorinetted C4H3OI3 Trichlorinetted C4H2CI4 Quadrichlorinetted C4H Olg Sesquichloride of carbon C4 Olg DEBIVATIVES 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 Bolution of sulphovinate of lime of the same density. The retort li con- ALCOHOL. ti'6<5tt5a T^fth a ^ood"iiaili3etJSfer, and heat is applied by means of a Tbath of" Bait and water, Mercaptan and water distil over together, and are easily 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° (36°C). 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 C4HgS2=C4H5S,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,' water is formed, and a white substance is produced, soluble in alcohol, and separating from that liquid in distinct crystals, which contain C^HgSjHgS. 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 orystallizable 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, on 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 12 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 0° ( — 17° -80, 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 is 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° -80). 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 €5115840, HO ; or C4H50,C284,H0. In the Baits 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 mixture of iodide of zinc and a peculiar volatile com- * Whence the name, mercurium captans. ALCOHOL. . 369 pound, to which t)r. 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^HgZn. 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 C4Hg=C4H5,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 SbCjjHjgzsSb 3 (C4H5). We shall return to this substance when speaking of the compound ammonias.* 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 and removal of 2 eq. of hydrogen. Table of Acetyl- Compounds. Acetyl (symbol Ac) C4H3 Oxide of acetyl (unknown) C4H3O Hydrate of oxide of acetyl; aldehyde C4H30,HO Acetylous acid ; aldehydic acid C4H302,HO Acetylic acid ; acetic acid €411303,110 Acetyl and its protoxide are alike hypothetical. Aldehyde, C4H4OJ 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 weak 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 with a little ether, 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. » Bismaethyl, BiCuHi6=Bi 3(C4H5). Stanethyl, SnC4Hs and tellurethyl, TeC4H5 have alsc been produced by similar reactions and some of their compounds investigated. — R. B. SYO ALDEHYDIC 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° -30), 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° (76°C), and distils unchanged at 212° (100°C). 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 C4H4O2+NH3. 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° (0°C), 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 elaldehtjdc ; 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 metaldehyde, 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, CJIsOg.HO. — When solution of aldehydate of silver, obtained by digesting oxide of silver in excess with aldehyde, is precipitated Dy sulphuretted hydrogen, an acid liquid is obtained, which neutralizes alkalis, and combines with the oxides of the metals. It is very easily decom- posed. Aldehylate 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 with fused chloride of calcium, and re-distilled. Pure acetal is a thin, colourless fluid, of agreeable ethereal odour of sp. gr. 821 at 72° (22o-2C), and boiling at 220° (104°C). 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 eff"ect. Strong boiling solution of potassa has no action on this substance. Acetal contains CJ2HJ4O4, or the elements of 2 eq. ether and 1 eq. aldehyde, C^2^ljfi^=2C^\i^O+C^E^02. 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 Fig. 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 suffer the slightest change by oxidation ; when diluted with water, it remains also unaffected. If, on the other hand, s^it S^ v9ipe 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. J, 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 Buffering 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° (30°C). Such is the plan adopted at Orleans.' 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° (119°C) : 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 C4H303,H0 = Ac03,H0; it is formed * Dumas, Chimie appliqu^e aux Arts, vi. 537. ACETIC ACID. S73 from alcohol by the substitution of 2 eq. of oxygen for 2 eq. of hy irogen. The water is basic, and can be replaced by metallic oxides. A different vie-w regarding the constitution of this acid has been proposed by Prof. Kolbe ; it is chiefly 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 sometimes 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.* Acetate of potassa, K0,C4H303. — This salt crystallizes with, great diflS- 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,C4H303-}-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 Minderekus ; NH40,C4H308. — 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 oif 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, suflFered 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° (77°C) which has received the name of acetonitrile C4H3N. 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, analagous 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 strontia are very soluble, and can be pro- cured in crystals ; acetate of magnesia crystallizes with difficulty. Acetate of alumina, Al203,3C4H303. — This salt is very soluble in water, and dries up in the vacuum of the air-pump to a gummy mass, without trace * Acetic acid increases in density by the addition of water, and reaches its maximum 1.07S when 30 parts have been mixed with 100 of the strongest acid; it then decreases in densit>. and when 135 parts have been added its specific gravity is the same as the hydrate, 1.063° The most ready method to test its strength 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 hydrated acid present, 50 parts of carbonate of lime being required to saturate 60 parta of aceti* acid.— R. B. 82 374 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 off the acetic acid, and leaves the alumina in a state capable of entering into combination with the dye-stuff. 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 of lead, PbO, C^HgOg-fSHO. — 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 1\ 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 (subacetatbs) of lead. — Sesgui-lasic 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,2C4H303. 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,C4H303-}-HO. The solution of sub-acetate prepared by the first method is known in pharmacy under the name of Goulard tvater. 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 GPbO.QHgOg. 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 of copper. — The neutral acetate, CuO,C4H303-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 ot this salt, mixed with sugar and heated, jdelds 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] lation, strong acetic acid, containing acetone, and contaminated with copper. The salt i» sometimes called distilled verdigris, and is used as a pigment CHLORACETTC 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 -^veeks, 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,2C4H303-(-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 SCuOjC^HgOg-f-SHO : it may be formed by digesting neutral acetate of copper with the hydrated oxide. I5y ebullition with water U is resolved into neutral acetate and the brown sub-salt. Acetate of silver, AgO,C4H303, 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 acid. 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 may be 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° (46°C) 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, C4Cl303,H0, 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- cetate of potassa crystallizes in fibrous, silky needles, which are permanent in the air, and contain KCC^ClgOg+HO. The ammoniacal salt is also crys- tallizable and nexitral ; it contains NH40,C4Cl303-(-5H0. Chloracetate ofsilvei is a soluble compound, crystallizing in small greyish scales, which are easily altered by light; it gives, on analysis, AgO,C4Cl303, and is cotsequently anhydrous. When chloracetic acid is boiled with an excess of ammonia, it is decoin posed, with production of chloroform and carbonate of ammonia. C,TI C\0^=C^\{ Clg and i\0^. 576^ 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 the 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; pyroacetic 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 Lirge 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°oC); 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 CgHgO ; 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 CigHjj, 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 CgHgCl. 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 CgHgO. Sir llobert 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 CgHg, 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 CgllgO-f-PtCV 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 metaceione ov propione ; it contains CgHgO, its boiling-point is 212° (100°C). Propionic acid. — Metacetone distilled with a mixture of bichromate of potassa and sulphuric acid yields, among other products, metacetonic or pro- pionic acid CgHgOjjHO, 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,' 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. C4H303,H0 = C204-f C2H4. 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 off^ensive nature, contains three elements, viz., carbon, hydrogen, and arsenic. Table of the most important Kakodyl- Compounds. Kakodyl (symbol Kd) C4H6AS. Oxide of kakodyl KdO. Chloride of kakodyl KdCl. Chloride of kakodyl and copper KdCl-j-CugCl. Oxy-chloride of kakodyl 3KdCl-f-KdO. Terchloride of kakodyl KdClg. Bromide of kakodyl KdBr. Iodide of kakodyl Kdl. Cyanide of kakodyl KdCy. Kakodylic acid KdOg. Kakodylate of silver AgO,Kd03. Kakodylate of kakodyl KdO.KdOg. Sulphide of kakodyl KdS. Sulphide of kakodyl and copper KdS-f-3CuS. Tersulphide of kakodyl KdSg. Sulphur-salts containing tersulphide \ KdS.KdSs— AuS,KdS3. of kakodyl / CuS,KdS3— PbS,KdSj. Selenide of kakodyl KdSe. Oxide op kakodyl; Cadet's ruMiNa liquid ; alkarsin ; KdO. — Equal ^eights 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 carty away the permanently-gaseous products to some distance from the experimenter. » See page 153. S78 KAKODYL AND ITS 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° (150°C), and it solidifies to a white crystalline mass at 9° r — 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 CgHgOg, and 1 eq. arsenious acid, AsOgssrI eq. oxide kakodyl, C4HgAsO, and 2 eq. carbonic acid, C2O4. Chlobide of 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 kakodyl, 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° (100°C) ; 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-f-CugCl, 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° (100°C), with slips of clean metallic zinc contained in a bulb blown upon a glass tulje, previously filled with carbonic acid gas, and hermetically sealed. The metal dissolves quietly without evolution of gas. When the action is complete, and the whole cool, the vessel is observed to contain a white saline mass, which on the admission of a little water dissolves, and liberates a heavy oily liquid, the 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 COMPOUNDS. 379 apparatus shown in the margin (fig. 170), which is made Fig.lTO. 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° (100°C) 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° (170°C), 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 th© 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, and 1 measure defiant 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^HeOgASg. Iodide of 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 jiuoride 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, KdSj, which is a sulphui-- 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°-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° (140°C), and is but slightly soluble in water. It requii-es to be heated before inflammation occurs. The vapour of tlfis 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) ; KdOj.— This is the ultimate product of th« SSO 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 ot 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° (70°C), 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, U is found to have exactly the same composition as ordinary oxide of kakodjil. WOOD-SPIRIT AND ITS DERIVATIVES. 881 SECTION II. SUBSTANCES MORE OR LESS ALLIED TO ALCOHOL. WOOD-SPIEIT 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 Peligot 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 C2H3, called methyls 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) CjHj Oxide of methyl CgHgO Hydride of methyl (marsh gas) CgHjH Chloride of methyl CgHgCl Iodide of methyl &c GgHgl Zinc-methyl CgHgZn Wood-spirit CgHgO.HO Sulphate of oxide of methyl CaHgOjSOg Nitrate of oxide of methyl &c CgHjO.NOg Sulphomethylic acid C2H30,2S08,HO Formic acid CjH Og.HO Chloroform CgH CI,, Hydrated oxide op methyl; pyroxylic spirit; wood-spirit; MeO,HO — The crude wood-vinegar probably contains about j^^ 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 ' From iJiiQv, wine, and i\rj, wood ; the termination v\^, or yl, is very frequently, employed in the sjd9> of matter, material. 382 WOOD-SPIRIT AND ITS DERIVATIVES. at 152° (66°-6C), and has a density of 0-798 at 68° (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 Boot. Wood-spirit dissolves caustic baryta ; the solution deposits, by evapo- ration in vacuo, acicular crystals, containing BaO-(-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+2(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 ^4^6^2' *^® *''^® formula of ether was CgHjoOg, and not C4H5O. The cor- rectness of this view has lately been established by a series of beautiful ex- periments carried out by Prof. Williamson. lie found that the substance produced by dissolving potassium in alcohol, which has the formula C^IIjO, 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 :— C4H50,KO -f C4H5I = KI -f 2C4II5O, or C4H50,K0 -f C4H5I = KI -f- C«H,„02. Tiat in this reaction, not two equivalents of ether, as represented in the first equation, but a compound CgHjoOg is formed, as expressed in the second, is clearly proved by substituting, when acting upon the compound C4H50,K0, 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 CgHgOj = 041150,021130. This substance is insoluble in water, and has a peculiar odour similar to that of ether, but boils at 50° (10°C). It is very probable tliat the substances, which have been described by the terms ethyl and methyl, likewise are not C4H5 and CjHg, but CgH,Q and C4Hg. 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, and 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 bum^ 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 0° ( — 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° (430-8C). 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.* 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, C4H5Zn, cor- responding to zinc-ethyl. (See page 368.) "When mixed with water it yields oxide of zinc and light carbonetted hydrogen. Cyanide op 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 (77°C). 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. MeCy = C.HgN I C4H30,HO = C.H^ O4 C4H,N04 I C4H,N04 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,S03. — 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° (187°7C). 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 ether. 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 phomethylate 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. * The same compound is believed to occur among the substances produced by the action of a galvanic current upon acetic acid. See valerianic acid, page S92. «J84 WOOD-SPIRIT AND ITS DERIVATIVES. Nitrate of oxide of jiethyl, MeOjNOg. — 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 oflF 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° (60°C); 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, remeve 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° (140°C), or a little above, it explodes with fearful violence ; the determination of the density of the vapour is, conse- quenth', 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 of oxide of methyl, MeO, CgOj. — 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 efl'ect the same change even more easily. Solu- tion of ammonia converts it into oxanide and wood-spirit. With dry ammo- niacal gas it yields a white, solid substance, which crystallizes from alcohol in pearly cubes ; this new body, designated ozamethylane, or oxamate of methyl, contains CgH5N06=C2H30,C4H2N05. Many other salts of oxide of methyl have been formed and examined. The acetate, MeO,C4n30g, is abundantly obtained by distilling 2 parts of wood- spirit with 1 of ci'ystallizable 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.CgHOj, 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 C4H3CIO4 ssCallgOjCgClOgv It yields with dry ammonia a solid crystallizable substance, called urethylane, C4H5NO4. (See page 358.) Sulphomethylic acid, MeO,2S08,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 b1owi> 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 vacuo to the due degree of concentration. The salt crystallizes in beautiful square colourless tables, containing BaO,C2H30,2S03-f-2HO, which efiloresce 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. Sulphomethylale of potassa crystallizes in small, nacreous, rhombic tables, which are deliquescent; it contains KO, C2H30,2S03. The lead-salt is also very soluble. Formic acid. — As alcohol by oxidation under the influence of finely-divided platinfum 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 /orm/c 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 CgHOg, or the elements of 2 eq. carbonic oxide, and 1 eq. water. Pure hydrate formic acid, C2H03,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° (08°-5C), and crystallizing in large brilliant plates when cooled below 32° (0°C). 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 efi^ervescence 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 lifjuid 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 saltSj 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 eff"ervescence. 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 aciJ coutamiuated with a small quantity of oia-iy 33 y»d WOOD-SPIRIT AND ITS DERIVATIVES. acid. 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 and 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, and is decomposed by a high temperature into hydrocyanic acid and water, the elements of which it contains, NIl40,C2H08 — 4H0=C2NH, This decomposition is perfectly analogous to that of acetate of ammonia, see page 373. The salts of baryta, stroniia, lime, and magnesia form small prismatic crystals, soluble without difficulty. Formate of lead crystallizes in small, diverging, colourless needles, which 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. Chlorofokm. — 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 bollect 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 1410-8 (61 °C) ; 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 1)y 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, water 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 CjHClg; 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, CgHBrs, 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. Iodoform, C2HI3, 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. Iodoform 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 (Ustillation 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° (41°C), and is com- pletely soluble in three parts of water. It contains CgHgO^. 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, C^Hg04=2C2H30,C2H202. Metuyl-meecaptan 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° (20°C), 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 C2H2CIO ; 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 CaHCljO. The whole of the hydrogen is eventually lost, and a third compound, CgClgO, produced. . Chloride of methyl, CgHgCl, in like manner gives rise to three successive products. The first, CgHgClg, is a new volatile liquid, much resembling chloride of olefiant gas ; the second, CgHClg, is no other than chloroform ; the third is bichloride of carbon, C2CI4. 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 CgHgH. Light carbonetted hydrogen. Chloride of methyl CjHgCl. Chlorinetted chloride of methyl CgHgCla- * Bichlorinetted " «' CgHClg. Chloroform. Trichlorinetted « " GfX^. Bichloride of carbon. The acetate of methyl, C6H6O4, gives CgH4Cl204, and C6n3Cl304 ; 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 propioue, 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, wq,s found by Gmeliu to contain a volatile lifiuid, differing in 388 POTATO-OIL AND ITS D ER I V A T I "V E S . some respects from acetone, to which he gave the term lignone. A verj similar substance is described by Schwcizer and Weidmann, 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, C2iH904. 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 may be considered as the hydrate of the oxide of the hydrocarbon, called amyl, containing C,oH,j. 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) ^lo^n Amyl-ether C,qHj,0 Hydride of amyl CiqHjjH Potato-oil CiqH,, 0,110 Chloride of amyl C,oH,,Cl Bromide of amyl CioH,,Br Iodide of amyl C,gH,iI Zinc-amyl CioH,jZn Acetate of amyl C,oH,jO,C4H303 Sulphamylic acid CioHijO,2S03,HO Amylene ^xo^io Valerianic acid CjoHgOg.HO. Hydrated oxide op amyl; fusel oil; AylO,HO. — 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° (12G°-6C) and 280° (137° -80) 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 CeHe pre- dominates, which has the chemical character of defiant gas, and to which the name ■propijlene has been given. The separation of this gaseous mixture has hitherto failed, but on bringing the gas in contact with chlorine a compound CgHeCa is formed. This is a heavy liquid boiling at 21 7° -4 (103°C). It is in every respect analogous to the Dutch-liquid (see page 363), originating nuder similar circumstances from defiant gas. POTATO-OIL AND ITS DERIVATIVES. 389 VMYL-ETHER, AylO. If amyl-alcohol is distilled with concentrated sul- \ cr'ic acid, a mixture of several substances is obtained, which has to be 8v^ irated by distillation. After several rectifications an oil is obtained, wh.ch has a sp. gr. 0-779 and boils at 348°-8 (170°C). This is amyl-ether. The composition is C,olli,0, or, if we adopt the double formulas, C20H22O2. Intermediate ethers between amyl- and ethyl-, and likewise between amyl- and methyl-ether have been prepared. They contain respectively C14H16O2 =:C4H50,C,oH,iO and C,2H,402 = C2H30,C,oH,iO. CuLOBiDE OF AMYL, Ayl CI. — 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 amyl, was obtained in the form of a vola- tile colourless liquid, smelling like camphor, and containing CioH^P^ ; the whole of the hydrogen oould not, however, be removed. Bbomide 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 353.) 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 {146°Cj 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° (190°C) yields aniT/l, a colourless liquid of an ethereal odour contain- ing CjqH,,, and boiling at 311° (155°C). Together with this substance there is formed iodide of zinc and zinc-amyl C,oIIj,Zu, which, when coming in contact with water, is decomposed into oxide of zinc and hydride of amyl C,qH,2=:Ci(,H,iH, which is an exceedingly volatile substance, boiling at 86° (3U°C). Cyanide of amyl, Ayl Cy. — Colourless liquid of 0-800 sp. gr., and boiling at 294°-8 (14G°C), which i.s 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 C12H12O4, one of the constituents of butter, C,2H„N+4HO=C,2H,204+NH3. Acetate of oxide of amyl, Ayl OjCJIgOg. — This interesting product is easily 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° -30, 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 largo scale for flavouring liquors and confectionary. Carbonate of oxide op amyl, Ayl 0,C02- — This ether has been lately obtained by Mr. Medlock by saturating fusel-oil with phosgene-gas (chloro- carbonic acid). A compound analogous to chloro-carbonic ether AylO,C2C103 is first produced, which, when treated with water, yields hydrochloric and car- 33* o90 POTATO-OIL AND ITS DERIVATIVES. bonic acids, together with carbonate of amyl (AylOjCjClOa-f II0=AylO, C02-\-llGl-j-C02)' Carbonate of amyl is a colourless liquid of an aromatic odour, boiling at 438° -8 (226oC). Alcoholic solution of potassa converts this ether into fusel-oil, carbonate of potassa being furmed at the same time. Sulphide of amyl, aviyl-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,CjoHiiO,2S03-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 (39°C), and contains no oxygen. Its composition is represented by the formula CioH,q ; consequently it not only corresponds to the defiant gas in the alcohol-series, but is isomeric with that substance. Like defiant gas it combines directly with chlorine and bromine, giving rise to compounds CjjjIIioCIa and Ci^IIj^Brg. The vapour, however, has a density of 2-68, which is 2^ times that of defiant gas, every measure containing 5 measures of hydrogen. Together with this substance several other hydrocarbons are formed, espQcially the one to which the name paramylene has been given. It con- tains CaoIIao. and boils at 320° (160°C). Valekianic 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 produce J is found to be identical with a volatile oily acid distilled from the root Vale- riana officinalis. In preparing artificial valerianic acid, the potato-oil is heated in a flask 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° (198o-8C) or 400° (204° -40). 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. 391 ■with Roracwhat diluted sulphuric acid in excess. The greater part of the valeTianic 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, and 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 bums when inflamed with a bright, yet smoky light. Valerianic acid has a density of 0-937 ; it boils at 370° (175°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 CjoHgOg.HO, and the silver-salt, AgOjCi^^HgOg. The ether-compound of valerianic acid has been already mentioned (page 357). By treatment with ammonia this ether is converted into valeramide CioHjiN02=Ci(,H902,NH2, (analogous to acetamide,) which, under the influ- ence of anhydrous phosphoric acid loses 2 more eq. of water, becoming vale- ronitrile C,QHgN=CgHg,C2N or cyanide of butyl. The former is a fusible crystalline substance, the latter a volatile liquid, having a boiling point of 257° (125°C). 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.' 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 CgHg which had been pre- * Anhydrous valerianic acid is formed by the reaction between valerianate of potassa and oxychloriJe of phosphorus, 5(K0, C10II9O3) and PCl30a=2KOP05, and 3KC1, and 5(CioIIj07). It is an oleaginous liquid lighter than water. Boiling water rrbanpes it flowly into th« hydrateil arid, while this transformation is rapidly affected by solutions of the alkalies. It boils at 41'/^ (215^'C), and distils unchanged.— 11. U. 892 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 amylene, in the electrolysis of valerianic acid, is a mixture of several substances, among which a hydrocarbon, of the remarkable compo- sition CgHg, 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 226°-4 (108°C). 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 formula CgHgO, HO and analogous to methyl-, ethyl-, and amyl-alcohols, an alcohol which, by oxidation, would yield the acid CgH^Og, 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 CjoHgOgjHO :=CgHg,C203HO. 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...'. Cj HO3, H0= H ,C203,HO Acetic acid , C4 H303,HO=C2H3,C203,HO Propionic acid Cg H503,HO=C4H5,C203,HO Valeric acid CioH903,HO=C8Hg,C203,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 combiaation of propyl with oxalic acid or propyl-oxalic acid. Butyric acid C8H903,HO=C6H7,C303,HO As valyl is formed from valeric acid, so the decomposition of butyric acid should yield propyl Call'', the oxide of which CbIItO has b^en detected in cod-liver oil in combination with oleic and 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 passes between 2260-4 (103°) and 2440-4 (118°). By subsequent purification a liquid is obtained which boils at 2330-6 (112°), is lighter than water, has the odour of amylic alcohol, but less disagree- able. Fused potassa changes it into butyric acid with the liberation of hydrogen. Its com- position is Ceirio02=C8H90,HO, 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 sulphobutylate of potassa. The latter dis.folves readily in boiling absolute alcohol, from which it is deposited in anhydrous pearly crystals of the composition K0,C8ll9O.2S0s. The cyaiiate and cyanurate of butylic ether yield with potassa a nitrogenous product, Imtylamin, NllaCBlTg, in the same way as the cyanates and cyanurates of ethyl, methyl, or amyl, yiel.t vospectively rthylamin, NII2C4II6, methylamin NHsCaHs, and amylamin NHa CioHu.— K. B. FUSEL-OIL OF GRAIN-SPIRIT. 393 acetic, propionic, and valeric acids yield respectively cyanogen and the cya- nides of hydrogen, methyl, ethyl, and butyl. NH4O, C2O3— 4H0= CgN NH4O, II, C2O3— 4H0= H, CjN NH40,C2H3,C203— 4HO = C2H3,C2N NH40,C4H5,C2O3— 4H0=C4H.,C2N NH40,C8H9,C203— 4HO=C8H9,C2N 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. Chlorovalebisic 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 littlo 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° (30°C). 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,o(H6Cls)03,HO. Chloeovalerosic 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 Ci(,(H5Cl4)03,H0. 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 arayl-conipounds 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 unaflPected 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 C20H20O4 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 contemDoraneous with that of common alcohol. It is impossible to leave the history of the alcohols without alluding to Bome results of great importance for the elucidation of organic compounds 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 Cj H^ Og Ethyl-alcohol C4 Hg Og Amyl-alcohol CioHjaOg we find tfiat their formulae 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 diflFerence of ethyl- and methyl-alcohol to be C4HgO, — CgH^Oj = CgHa, the difi^erence of amyl- and methyl-alcohol to be C10H12O2 — Ca^A = CgHg =4C2H2. The same elementary diff"erence of course prevails likewise be- tween all the derivatives of the three alcohols. Iodide of methyl Cj Hg I Iodide of ethyl C4 Hg I = CJTgl -f C^Ho Iodide of amyl CioH^jI = CgHgl -f- 4C2H2 or Formic acid Cg H OgjHO Acetic acid JO^ Hg 03,H0 = C2H03,H0-f. C2H2 Valeric acid CjoHg Og.HO = C2HOg,HO + 4C2H2 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: — CapryUc alcohol CigHigOa = CgH^Og + 7C2H2 Cetylic alcohol C32H34O2 = C2HA -f l^CaHg CerotyUc alcohol C^HgA = C2H4O2 -f 26C2H2 Melissic alcohol CeoHggOg = CgHA -f 29C2H2 These four alcohols, when submitted to the action of oxidizing agents, are 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 CjgHisOgJIO = CgHOgJIO -}- IC^II^ Cetylic acid C32ll3,03,HO = C2H03,HO -f l^C^l^ Cerotylic acid CsJisgOgJIO = C2fI03,HO -{- 2OC2H2 Melissic acid G^o^^^(\,UO = C2H03,HO -f 29C2II2 A glance at these tables shows that all the alcohols known differ from methyl-alcohols by C2H2, or a multiple of it. At tlic same time, it is evi- dent that the series by no means regularly ascends. Thus we perceive tliat between ethylic and amylic alcohols two compounds are possible ; in like icanner 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 arc known, which are placed in juxtaposition with the collateral alcohols: — Methyl-alcohol Cg H4 Oj Ethyl-alcohol .... C4 H, O2 (Tetryl-alcohol)..... .... Ce H3 0, (Butyl-alcohol) .... C3 H,A Amyl-alcohol .... CjoHjaOg C12H14O2 CuHteO^ Capryl-alcohol .... ClgHigOg C 18^20^2 G20H22O2 &c. &c. Formic acid Cj H2O4 Acetic acid C4 H^ O4 Propionic acid Cg Hg O4 Butyric acid Cg Hg 0^ Valeric acid C,oH,q04 Caproic acid C12HJ2O4 (Enanthylic acid CJ4HJ4O4 Caprylic acid C,gH,g04 Pelargonic acid Cj8H,804 Capric acid ^'2o^2(Pa &c. &c. We might continue the scries of acids uninterruptedly to C3gH3g04 (balenic 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 C2H2, 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. Ethyl Propyl?.. Butyl Amyl Caproyl .. .H3 C4H5 Cg H7 CjjHjj Methyl-ether.. Cg H3 Ether C4 H5 (Tetryl-ether). Cp H^ O Amyl-ether . Ci^HjgO Ethylene C4 H4 Propylene .... Cg Hg Butylene Cg Hg Amylene C,oH,g Caproylene... C,2H,2 CigHi^O Caprylene .... CjgHjg 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. F, 209° 246° 284° 314°-6 388°-4 Formic acid Cg Hj O4 Acetic acid C4 H4 O4 Propionic acid Cg Ilg O4 Butyric acid Cg Hg O4 Valeric acid C,oH,o04 Caproic acid ^12^1204 From this table it is evident that the boiling temperature of the homolo- c. 98° 119° 140° 157° 175° 198° Dififerences. F. C. 37° 20°-5 38° 21° 30° .7'' 33°-4 18° 410.4 23° f ous acids rises on an average (19° -90) for every increment of Call^ 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 describea. BITTEU-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 €,411502, 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!j4pT502 Hydride of benzoyl; bitter-almond oil C14H5O2H Hydrated oxide of benzoyl; benzoic acid C,4H5020,HO Chloride of benzoyl C,4H502C1 Bromide of benzoyl C,4H502Br Iodide of benzoyl C14H5O2T Sulphide of benzoyl C14H5O2S. Hydride of benzoyl ; bitter-almond oil ; BzH. — 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 crystallizable 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° (180°C) : 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 sold 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 coucrete resinous variety known under the name of gum-benzoin. When AND ITS PEODUCTS. 397 vhis 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 and all similar operations is the contrivance of Dr. Mohr : Fig. 171. 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 pl.aced upon a sand-bath and slowly heated to tlie 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 the small quantity of a volatile oil. 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 efi"ected 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° (100°C), and sublimes at a temperature a little above; it boils at 462° (238° -SC), 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 aflFected 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 Cj^HgOgJIO. 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 crystallize. Benzoate of lime forms groups of small colourless needles, which require 20 parts of cold water for solution. The salts of baryta and sirontia are soluble with difficulty in the cold. Neutral benzoate of the sesqiiioxide 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,4H4N07,HO=C,4(H4N04)03,HO. The remarkable transformation of the amide of this acid, of niiro-benzamide, 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 combineB. however, with anhydrous sul^^huric acid, generating a compound acid aaalo* 84 398 BITTER-ALMOND OIL gous to the sulph«vinic, but bibasic, forming a neutral and an acid series of Baits. 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 stabU and permanent, which contains Ci4H503,2SOs,2HO. Benzone, benzophbnonb. — 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 C13H5O, or CjeHigOg, 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,Ci4H503=Ci3H60-f-CaO,COa. The benzophenone is, however, always accompanied by secondary pi*oducts, due to the irregular and excessive temperature, solid hydrocarbons, carbonic oxide, and benzol, a body next to be described. Benzol, 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 boiling at 176<^ (80 and is therefore iso- 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° (120°C), and cannot be distilled without decomposition. It dissolves in cold concentrated sulphuric acid with a fine carmine-red colour, Benzilic acid contains CggHjjOg.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 C14H5N. It is benzoate of ammonia, — 4eq. of water, (NH40,C,4H503 — 4H0=Ci4H5N,) 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 may be viewed as a cyanide, when it becomes a member of the phenyl-series, Ci4H5N=Ci2H5C2N. Benzoyl. — 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° (70°C), and contains C14H5O2. It was dis- covered by Ettling, and subsequently studied by Stenhouse, and is evidently the radical of the benzoyl-series. I5y heating with hydrate of potassa it is 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. 34^ 402 BITTER-ALMOND OIL AND ITS PROLUCTS. This reaction is characteristic. Benzimide contains C28lI,,N04. It may be viewed as derived from an acid benzoate of ammonia by the 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. HippuBic 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 s, 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 forma salts with bases, many of which are crystallizable. Exposed to a high tera- 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 CigHgN05,H0. 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 aTnidogen-compounds, which has been explained when treating of oxamide (page 343). A new non-nitrogenous acid is formed together with water and pure nitrogen Ci^HgNOgJIO-f N03=C,8ll707,HO + HO+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 CigHi^O^jHO =C,4H604,C4H406— 2H0. Under the influence of boiling water it splits indeed into benzoic and glycolic acids. Glycocine must be considered a- glycolamide NH40,C4H305— 2HO = C4H5N04, 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 tjecretion. 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 acitl, which is then found in the urine. BENZOYL-SERIES. 403 HOMOLOGUES OP THE BENZOYL-SEHIES. Toluylic Acid, Cigll^OgJIO- — This substance, -which difibrs from benzoic acid by CgHg, 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, Ci6H6N07,HO = C,^(H6N04)03,I10; distilled with lime or baryta, it furnishes a hydro-carbon C,4Hg, 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 CigHgOg.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,gH,(,, 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 CigllgOgHO 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, C2oH,i03,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 CgoHjjOj, which corresponds to oil of bitter almonds. It likewise yields a nitro-acid, nitro-cumic acid C2oH,qN07,HO = C2o(HjoN04)03,HO, and when distilled is converted into cumol CigHij, a hydrocarbon, homologous to benzol, toluol, and xylol. Of the next series only the hydrocarbon is known. This is cymol CgoH,^, the substance which, as has been mentioned above, is the source of toluylio acid. The homology of these substances is clearly exhibited by the following table : — Hydrides. Acids. Hydrocarbons derived from the acid. Benzoyl-series C,4H502H Ci4H503,HO CijHe Toluyl-series CigH^Oa.HO Ci4Hg Xylyl-series C,gH,o Cumyl-series CgoHuOgH C2oHii03,HO C,8H,2 Cymyl-series C20H14 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 bo discovered. •* SALICTL 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 I)owdere(l protoxide of lead, and then, after freeing the fcolution from lead by a stream of sulphuretted-hydrogen gas, evaporating until the salicin crys- i04 S AL I C Y L . tallizes out on cooling. It is purified bj 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 residue 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 C26H,gO,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 Spiroea ulmaria, or common meadow-sweet. This substance appears to be the hydride of a compound salt-radical, salicyl, containing C14H5O4 ; it has the properties of a hydrogen-acid. Table of Salicyl- Compounds. Salicyl (symb. SI) • C^Ji^ 0< Hydrosalicylic acid ^u^^i ^J^ Salicylide of potassium ^,4115 O4K Hydrochlorosalicylic acid C,4(H4C1)04H Hydriodosalicylic acid Ci4{H4l) O4H Hydrobromosalicylic acid C,4(H4Br)04H Salicylic acid C14H5 05,H0 Hydrosalicylic acid ; salicylous acid ; artificial oil of meadow- sweet, SIH. — 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 Ci4Hg04, or the same elements as crystallized benzoic acid ; and the density of its vapour is also the same, being 4-276. Salicylide of potassium, KSl. — 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 mcla)iic acid. Acetate of potassa is formed at the same time. Melanic acid contains C^U^O^q. The crystals of salicylide of potassium contain water Thich cannot be expelled without partial decomposition of the salt. Salicylide of ammonium, NH4SI, crystallizes in yellow needles which are quickly desiroyed with production of ammonia an«l tlie hydride. Salicylide of barium^ BaC,4H50 -j^-2H0, forms fine yellow acicular crystals, which are s A L I c y L . 405 but slightly soluble in the cold. Salicylide of copper is a green insoluble powder, containing CUC14H5O4. 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 hj'drate of potassa. Nitric acid converts it into anilic and picric acids. (See indigo). It contains C14H5O3, and is iso- meric with anhydrous benzoic acid. Chlorohydro-salioylic acid, C,4(H4C1)04,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 iai" 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 Cj4(H4Cl)0. Bromohydro-salicylic acid, Cj4(H4Br)04,H. — The bromide-compound ia 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. Chlorosamide. — 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 relnains dissolved. Chlorosamide contains G^ (H,5Cl3)N20g; 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*^ (82°C), and decomposes at a higher temperature. Dilute acids at a boiling heat convert it into a resinous-looking substance, Ci4Hg02, 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. Iti aqueous solution gives a deep indigo-blue colour with salts of sesquioxide oi 406 SALICYL. iron. Saligenin contams C,4Hj,04. Hence the transformation of salicin is represented by the equations : — 2C26H,80h+8HO = C,J{,,0,, = 2C,4H30^ Salitln. 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 hichlorosaligenin. Chlorosaligenin very closely resembles normal saligenin, and contains C,4(H7C1)04. Certain products, called by M. Piria helicin, helicoidin, and anilotic acid, are described as result- ing from the action of dilute nitric acid upon salicin. With strong acid at a liigh temperature nitro-salicylic add (anilic acid) C|4(H4N04)05,HO, is pro- duced. Salicylic acid, S10,H0. — 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 maybe 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 C14H5 05,H0. 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 Gaultheria 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 Band and exposed to strong and sudden heat in a retort, it is almost entirely converted into carbonic acid and hydrate of phenyl, CijHgOj, a substance found in considerable proportion in coal-tar-naphta, — and the same change happens to many of its salts with even greater facility. PiiLORiDziN. — 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 C42H24O20+4HO. Dilute acids convert phloridzin into grape-sugar and a crystallizable sweet substance called phlo- retin, C2oH,40io. 2(C42H2402o -f4HO ) = C24H2,02g -f 2C3oPThO,o Phloridzin. Grape-sugar. Phloretin. CuMARiN. — The odoi'iferous 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 in hot alcohol, and, after straining through cloth, distilling olf the greater part of the spirit. The syrupy residue deposits on standing crystals of cu- marin, which must be purified by pressure from a iat oil which abounds in the beans, and then crystallized from the hot water. So obtained, cumarin forms slender, brilliant, colourless needles, fusible at 122° (50°C), 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, moru 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 Melilotm officinalis^ the Asperula adorata, and the Anthozanthum odoratum. According to M. Bleibtreu it con " ~ ~ ' ~ 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, the cinnamic, which resembles in the closest manner benzoic acid. The radical assumed in these substajiccs bears the name of cinnamyl ; it has not been isolated. Table of Cinnamyl- Compounds. Cinnamyl (symbol Ci) CigH^Oj Chloride of cinnamyl CigH^OjCI Hydride of cinnamyl ; oil of cinnamon CjgH^OjH Hydrated oxide of cinnamyl; cinnamic acid Cj8H7020,nO Cinnamylic alcohol Cj8HgO,HO Cinnamate of cinnamylic ether CigHgOjCigll^Og Hydride of cinnamyl ; oil of cinnamon ; CiH. — 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, CjgHgOg. Cinnamic acid, CiO,HO. — When pure oil of cinnamon is exposed to the 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° (120°C), 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 iecomposeg cin- 408 CINNAMYL AND ITS COMPOUNDS. namic acid 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 benzoatcs. The crystallized acid contains CjgH^OgjHO. 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,gHg distils over, whilst a carbonate of the alkaline earth remains behind, CigHgO,,4- 2BaO=2(BaO,C02) + C,8TIg. 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,8lT4Cl402 ; it is formed by the sul>stitution in the oil of cinnamon of 4 eq. of chlorine for 4 cq. of hydrogen. The true chloride of cinnamijl, Ci CI, seems to be first formed in considerable quantity, and subsequently decomposed by the continued action of the chlonne ; 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 liydride of benzoyl and benzoic acid. With a boiling solution of chloride of lime the same thing happens, a bcnzoate 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 liydrogen, and forms a potassa-salt, which appears to be the cinnamate. 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 lai)se of a few hours, separated and decomposed by water, yields nre 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 cinnamei7i (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 styronc. These substances are related to each other vn 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-serieR. Alcohol C4H50,HO Acetic acid C4H303,H0 Acetic ether C4H50,C4H303 Cinuamyl-series. Peruvin C„HgO,HO Cinnamein CigHgOjCjgH^Oj When treated with ox^^iizing agents, peruvin yields cinnamic aftid, or its products of decomposition, oil of bitter-almonds and benioic acid. Sv*: 410 VEGETABLE ACID 6. SECTION III. VEGETABLE ACIDfl. 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 Q^^0^Q,2TiK. Racemic acid C8H40,o,2HO Citric acid C,2H50,„3HO Aconitic, or equisetic acid C4H 0^,110 Malic acid C8H408,2HO Fumaric acid C4H OgjHO Tannic acid Ci8H509,3HO Gallic acid C,H 03,2HO Taktaric 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 creavi 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 war'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^H40io,2HO. This substance is consumed in large quantities by the calico-printer, being employed to evolve chlorine from somtion of bleach ing-powder in the production of white or discharged pat- terns upon a coloured ground. Tartrate of potassa. Neutral tartrate ; soluble tartar ; 2K0, CgH^Oig. — 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,CgIT40,o. — 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,CgH40,o-f-4HO ; and an acid salt, NaO,HO, CgH40,(,-|-2IIO. Both are easily soluble in water, and crystallize. Tartaric acid and bicarbonate of soda form the ordinary ejfervescing draughts. Tartrate of potassa and soda ; Rochelle or seignette salt ; KO, NaO,CgH4O,Q-j-10nO. — 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 1^ parts of cold water. Acids precipitate cream of tartar from the solution. Rochelle salt has a mild, saline taste, and is used as a purgative. Tartrates of ammonia. — The neutral tartrate is a soluble and efflorescent salt, containing 2NH^O,C8H40,o-f2HO. The add tartrate, NH40,HO,C8H40,o, 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 nearly 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 ^s/ rstals contain KO.SbOg.CgH^Oio-f 2H0.» An analogous compound containing arsenious acid (AsOg) in plact* of ter- oxide of antimony has been described. It- has the same crystalline form 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° -50) or thereabouts, it melts, loses water, and passes through three different modifications, called in succession tariralic, 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 comipon tartaric acid. Their composition is thus expressed : — Ordinary tartaric acid CgH40,o,2HO Tartralic acid 2C8H40io,3HO Tartrelic acid C8H40io,HO Anhydrous acid C8H4O1Q 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 CgHgOgjHO. 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 0511303,110, When tartaric acid is heated to 400° (204° -50) with excess of hydrate of potassa, it is resolved without charring or secondary decomposition into oxa- » According to Dumas, KO,Sb03,C8H40i(>4-HO. Dried at 212° (lOOOC), an equiv.ilent of water is lost, and at 428° (220°C), two additional equivalents, leaving the compound KO,SbOs, CeH^Os, which can no longer contain ordinary tartaric acid. Nevertheless, when dissolved in water^ the crystals again take up the elements of water and reproduce the original salt. VEGETABLE ACIDS. 413 he *ti(i aceti' *cids, which remain in union with the base, and only undergo decomposition at a much higher temperature. Racemic acid ; paratartario 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 ealts 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 satm-ating 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 arer 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 twp 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 lend- br 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 eftect 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 frviits, as in gooseb^mes, cur- rants, &c., in conjunction with another acid, the malic. In the preparation of this acid, the juice is allowed to fferment 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- liqnor, re-dissolved, digested with animal charcoal, and again concentrated to the crystallizing-point. Citric acid forms colourless, prismatic crystals, wh;ch have a pure and agreeable acid taste; they dissolve, with great ease, in '^oth hot and cold water ; the solution strongly reddens litmus, and, when lorg kept, is subject to spontaneous change. Citric acid is tribasic; its formula in the gentW dried and anhydrous silver 35* 414 ^ VEGETABLE ACIDS. Bait is C12H5O,,. 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 CjjHjOu, 3HO-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.* 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 cry stalliz able 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 ii*on ; 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 amiponio-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, OR 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, confusedlj^-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 ; aconilate 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 C4H03,HO; it is formed in the artificial process above described, by the breaking up of 1 eq. of hydrated citric acid, C,2HgOx4, 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, Tfee farther action of heat upon aconitic acid gives rise to several new acids, especially citraconic and ilaconic acids, both expressed by the formula CgHjOj.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 those last-named bodies in the two vegetable acids, -w-hich 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, pxe not at present supported by ovidenco of great impoi-tance. 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.* 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 C8H40g,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(C8H408,2HO) = 2(C8H406,2HO) + C4H303,HO-f 4C02+2HO. Malic acid. Succinic acid. Acetic ^cid. 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, NH40,H0, CgH408, 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,HO,CgH40g-f-6HO, 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 malamic acid, analogous to oxamide and oxamic acid. Oxalic acid ' . . 0406,2HO Malic acid . . C,H408,2HO Neutral oxalate of | c^Oe,2NH40 { ^^^J^fj^^^^*';^} C8H408,2NH40 ammonia ^ ^ ^. 1 r- TTTM n / Malamide ; aspa- 1 n tt x: r. Oxamide . . . }C4H4NA { '^^17'.' '."'"} ^s^sNA Binoxalate of am- \ n c\ rxn xru n J Bimalate of am- monia . . . |C406,HO,NH40 I ^^^.^ _ _ ^ |v.8ra4V^8,xiu,i.xa4i^ Oxamicacid . }C4H,N0„H0 {^^.ttTJl^M \'"] ^^^^NO.HO ' If the acid be required pure, crystallized malate of lead must be used, the freshly preci- pitated salt invariably carrying down a quantity of lime, which cannot be removed by simple washing. 'We have here doubled the formula of oxalic acid, when it becomes bibasic, like malic aciil. 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 nitroxis acid into a solution of asparagin or aspartic acid, pure nitrogen is evolved, malic being liberated. C^HgNjOe 4- 2NO3 = 08H408,2irO + 2110 + 4N Asparagin. Malic acid. FuMARic 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 laminse, 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. Fumavic acid forms salts which have been examined by M, Pdeckher, and an ethor, 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 C4H03,H0; 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 CgH206,2HO. 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 diflpused, 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 pi-inciple 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, ns well as infusions of the substances known in commerce under the name of kino 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 tlie 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- cular fibre and skin, &c., which then acquire ^he property of resisting putre- VEGETABLE ACIDS. 417 Fig. 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 infectoria, 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 f stringent 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 CigHjOg-j-SHO.' 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 » 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 CioHisQagj and its change under the influence of acids by the equation 2CwniH036+SH0 = 8(C'7H03,2HO) -|- Cu^H^Om Tannic acid. Gallic acid. Grape-BUgar. 418 VEGETABLE ACIDS. strikes a deep green colour with the salts of sesquioxide of iron. This body is said to be convertible by heat into tannic acid. The formula which has been assigned to catechin is CjgHgOg. Japonic and ruhic 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 ^.^^fi^^fd ; it is per- haps identical with a black substance of acid properties, formed by M. P61igot, 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° (100°C), contains 07HO3,2HO; 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 C7H2O4, when dried at 248° (120°C), 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 CjgHgOia) ("2 eq. gallic acid .... C,4HgOjo I = -I 2 eq. water 8 eq. oxygen Og j (4 eq. carbonic acid water HjO 2 VEGETABLE ACIDS. 410 Much of the gallic acid is subsequently destroyed, in all probability onlj 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° (215°C), 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. Pyiogallic acid contains CgHgO^. When dry gallic acid is suddenly heated to 480° (249°C), 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 CgHaOj. 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. C7H3O5 = C6H3O3 4. CO2 Dry gallic acid. Pyrogallic acid. C8H3O3 = CgH^Oj 4- HO Pyrogallic acid. Metagallic acid. ^(CigHsOg.SHO) = 6(C7H03,2HO) + 2C6H3O3 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° -20) 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 CjN ; 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, C2N+4H0 = NH40,C203, 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, HCy. — 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 Kvavoi, blue, and ytvvdbi^l 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°-6C), boils at 79° (26°-lC), and solidifies, when cooled to 0° ( — 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, the 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. CjN,H + 4H0 = NHg -f C2H03,H0 On the other hand, when dry formate of ammonia is heated to 392° {ZOO°C), it is almost entirely converted into hydrocyanic acid and water. NH^O.CaHO, ^ C2N,H -}- 4H0. 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- eium 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 fo\ir 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 1:=:^ Insoluble yellow salt. 6 eq. carbon 2 eq. ferrocy- 3 eq. nitrogen, anideof po--^ 3 eq. nitrogen, tassium | 1 eq. potassium - I 3 eq, potassiums \^2 eq. iron 3 ea water / ^ ^^- ^^y^^^ogen ^*^-- — ^^-3 gq. hydrocyanic acid. ^ \ 3 eq. oxygen — — -__>^ 6 eq. sulphuric acid -^ *- 3 eq. bisulphate of po- t assa. «6 • Phil. Magazine. Feh. 1S35. 422 CYANOGEN, The substance described in the preceding diagram as insoluble yellow salt le- 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 filter 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 6, 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 chloride 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 thi»n 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- Btance 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. Amygdalin 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. Amygdalin is composed of C40H27NO22. 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 under 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 : — 1 eq. amygdalin, C4oH2,N022 1 eq. hydrocyanic acid C gH N 2 eq. bitter-almond oil G2%^n ^\ sugar C gH^ 0^ 2 eq. formic acid C 4H ^ Og 5 eq. water H « 0= C.nH^NO 22" 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 precipi- 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 titter- 424 CYANOGEN, almond oil, formic, and benzoic acids. The amygdalates are mostly soluble, but have been but little studied ; the acid contains C4oH2g024,HO. The presence of hydrocyanic acid is detected with the utmost ease ; it9 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, metallic 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, and preserved in a well-stopped bottle ; the black substance contains much ITS COMPOUNDS AND DERIVATIVES. 425 cyanide, which may he 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 eq. 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 for 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 soditjm, NaCy, is a very soluble salt, corresponding closely with the foregoing, and obtained by similar means. Cyanide of ammonium, NH4Cy. — This is a colourless, crystalHzable, 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 ease ; 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 ferrocyanide 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 cooliug, iJ6 * i26 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 silver, AgCy, has been already described. Cyanide of zinc, ZnCy, is a white insoluble powder, pi-epared by mixing acetate of zinc with hydi'ocyanic 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, AuCyg, is yellowish-white and insoluble, but freely dissolved by solution of cyanide of potassium. Proiocyanide 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,F2Cy8 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. Ilydrated 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. C,NO,HO-f2HO=C204+NH8. 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 smell 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 adied ITS COMPOUNDS AND DERIVATIVES. 427 by small portions ; the oxide is instantaneously reduced, and the metal, at fii"st 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 fexposure 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- veniently 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, CyaBuric acid in a pure state forms colourless crystals, seldom of large size, derived from an oblique rhombic prism, -which eflBoresce 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 CgNgOj.SHO -}-4H0, 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, cyanio 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 CgNjOgjSHO. 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. C6N303,3HO=3(CaNO,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 difificulty, the cyanate boiling at 140° (60°C), while the boiling point of the eyanurat.e is much higher, namely, 528° -8 (276°C). Cyanate of ethyl is a mobile liquid, the vapour of which excites a flow of tears. The com- position of cyanate of ethyl is C6H5N02=C4lT50,C2NO=AeO,CyO. The formation is represented by the equation KO,CyO-f-KO,AeO,2S03=AeO, CyO-j-2(KO,SO,). The cyanurate of ethyl contains SAeOjCgNgOg; 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° (85°C). By substituting for sulphovinate of potassa, salts of sulphomethylic and sul- phamylic acid, the corresponding methyl- and amyl-compounds 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 pi*epared by dissolving 40 or 50 grains of silver, which need not be pure, in f 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 eq. water. C4H50,N0,-f N03==:C,No024-5HO. ITS COMPOUNDS AND DERIVATIVES. 4ii^ 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,C4N202. 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,C4N20j|, 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,C4N202, 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 2Hg20,C4N202. 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 and 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 , CjN 0. Fulminate of silver 2AgO , C^^^'^i- Cyanurate of silver 3AgO , CgNgOg. 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 FERROCYANOQEN 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 0° ( — 17°'8C) it congeals to a mass of colourless crystals, which at 6° ( — 15°C) melt to a liquid whose boiling-point is 11° ( — llo-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 ofi'ensive odour, compared by some to that of the excrement of mice ; it melts at 284° (140°C), 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 CyoClg, or CgNgjClg. It dissolves in alcohol and ether without decomposition. Bromide and iodide of 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-l-0 = KO+Kg.CgNgFe. The new substance is called ferrocyanogen, 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 easels 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. Hydroferrocyanio ACID, Cfy2H. — Ferrocyanide of lead or copper, both of which are insoluble, may be suspended in water, and decomposed by a stream of sulpluiretted 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 sej^arates in colourless, crystalline laminie ; it may even be made in large quantity by adding hydrochloric acid to a strong solution of ferrocyanide 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 subotance from solution. Hydroferrocyanic acid differs completely PERROCTANOQEN AND ITS COMPOUNDS. 431 from hydrocyanic acid ; its solution in water has a powerfully acid taste and reaction, and decomposes alkaline carbonates with eflFervescence ; 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, KgCfy+SHO, or KgCgNgFe-f-SHO.— 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 qtiantity. 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,2IICy, and ferrocyanide of potassium, FeCy,2KCy-f-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 moit of these compounds the potassium of the base is simply displaced by the new metal : the beautiful brown ferrocyanide of copper contains, for example, CugCfy or CugCgNgFe, and that of lead, PbgCfy. 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, FcgCfy, with ferrocyanide of potassium. When a ferrocyanide is added to a solution of salt of sesquioxide oi 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 gi-eat measure from the existence of several distinct deep blue compounds formed under different cir- * The sulphur is derived from the reduced sulphate of the crude pearl-asl*** i'«^ in thi* aaxLufacture. 432 PERROCYANOGEN AN D 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, CjgNgFe^, or Fe^Cfyg. — 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 / 3 eq. ferrocyanogen ^^„^ ' Prussian blue. potassium \ 6 eq. potassium 2 eq. nitrate of T 4 eq. iron sesquioxide of ■< 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. Ry 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, Fe4Cfy3-}-Fe203. — 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 ii"on 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 Fe4Cfy3-f-2K2Cfy. This also dissolves in water as soon as the salts have been removed by washing. FERRICYANOGEN AND ITS COMPOUNDS. 433 The other ferrocyanides may be despatched in a few words. The soda-salt, NagCfy--f-12H0, crystallizes in yellow four-sided prisms, which are efflorescent in the air and very soluble. Ferrocyanide of ammonium, (NH4)C2fy-f-3HO, is isomorphous with ferro- cyanide of potassium ; it is easily soluble, and is decomposed by ebullition. Ferrocyanide of barium, BagCfy, 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 ferridcyanogen, CigNgFeg ; 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 ia pm-ified 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 KgCfdy ; 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 prussiaie 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 liquid, 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 FcjCyg-f-SHO, 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" FejCfdy, which, when dry, has a brighter tint than that of Prus- sian blue ; it is known under the name of TurnbuU's 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. Nttroprussides. — The action of nitric acid upon ferrocyanides and fern- cyanides gives rise to the formation of a very interesting series of new salt::*, which were discovered by Dr. Playfair. The general formula of these saltd 37 434 SULPHOCYANOGEN, ITS COMPOUNDS. appears to be MjFejCygNO, which exhibits a close relation with th(«e of the ferro- and ferricjanides. 2M2Cfy = M4 Fej Cy^ = ferrocyanides. Mj Fog Cyg = ferricyanides. Mg Fcj < ^^ =s nitroprussides. According to this formula, the formation of the nitroprusside would con- sist in the reduction of the nitric acid to the state of protoxide of nitrogen, which replaces 1 eq. of cyanogen in 2 eq. of ferrocyanide. The formation of these salts is attended by the production of a variety of secondary pro- ducts, such as cyanogen, oxamide, hydrocyanic acid, nitrogen, carbonic acid, &c. One of the finest compounds of this series is the nitroprusside of sodium, Nag.FeCygNO-f-^HO, which is readily obtained by treating 2 parts of the powdered ferrocyanide with 5 parts of common nitric acid, previously diluted with its own volume of water. The solution, after the evolution of gas has ceased, is digested on the water-bath, until salts of protoxide of iron no longer yield a blue but a slate-coloured precipitate. The liquid is now allowed to cool, when much nitrate of potassa, and occasionally oxamide, is deposited ; it is filtered and neutralized with carbonate of soda, which yields a green or brown precipitate, and furnishes a ruby-coloured filtrate. This, on evaporation, gives a crystallization of nitrate of potassa and soda, toge- ther with the new salt. The crystals of the latter are selected and purified by crystallization ; they are rhombic, and of a splendid ruby colour. The soluble nitroprussides strike a most beautiful violet tint with soluble sul- phides. This reaction is recommended by Dr. Plavfair as the most delicate test for alkaline sulphides. SULPHOCYANOGEN, ITS COMPOUNDS AND DERIVATIVES. The elements of cyanogen combine with sulphur, forming a very important and well-defined salt-radical, called sulphocyanogetiy which contains C2NS2, and is monobasic ; it is expressed by the symbol Csy. SuLPHOCYANiDE OF POTASSIUM, KCsy. — Yellow ferrocyanide of potassium, deprived of its water of crystallization, is intimately mixed with half its weight of sulphur, and the whole heated to tranquil fusion in an iron pot, and kept some time in that condition. When cold, the melted mass is boiled with water, which dissolves out a mixture of sulphocyanide of potassium and Bulphocyanide of iron, leaving little behind but the excess of sulphur em- ployed in the experiment. This solution, which becomes red on exposure to the air from the oxidation of the iron, is mixed with carbonate of potassa, by which the oxide of iron is precipitated, and potassium substituted ; an excess of the carbonate must be, as far as possible, avoided. The filtered liquid is concentrated, by evaporation over an open fire, to a small bulk, and left to cool and crystallize. The crystals are drained, purified by re-solution, if necessary, or dried by inclosing them, spread on filter-paper, over a surface of oil of vitriol, covered by a bell-jar. The reaction between the sulphur and the elements of the yellow salt is easily explained : 1 eq. of ferrocyanide of potassium, and G eq. sulphur, yielded 2 eq. of sulphocyanide of potassium, and 1 eq. of sulphocyanide of iron. KgCfy =CeN3Fe,K2-J- 6S=2(KC2NS2)-f FeCaNSg. Anothe* and perhaps simpler process consists in gradually heating to low redness in a covered vessel a mixture of 46 parts of dried ferrocyanide of SULPHOC YANOGEN, ITS COMPOUNDS. 435 potassium, 32 of sulphur, and 17 of pure carbonate of potassa. The mass is exhausted by water, the aqueous solution evaporated to dryness and ex- tracted with alcohoL The alcoholic liquid deposits splendid crystals on cool- ing or evaporation. The new salt crystallizes in long, slender, colourless prisms, or plates, which are anhydrous ; it has a bitter, saline taste, and is destitute of poi- sonous properties ; it is very soluble in water and alcohol, and deliquesces when exposed to a moist atmosphere. When heated, it fuses to a colourless liquid, at a temperature far below that of ignition. When chlorine is passed into a strong solution of sulphocyanide of potas- sium, a large quantity of a bulky, deep yellow, insoluble substance, resem- bling some varieties of chromate of lead, is produced, together with chloride of potassium, which tends to choke up the tube delivering the gas ; the liquid sometimes assumes a deep red tint, and disengages a pungent vapour, pro- bably chloride of cyanogen. This yellow matter may be collected on a filter, well washed with boiling water, and dried : it retains its brilliancy of tint. The term sulphocyanogen has generally been applied to this substance, from its supposed identity with the radical of the sulphocyanides ; it is, however, invariably found to contain both oxygen and hydrogen, and a formula much more complex than that belonging to the true sulphocyanogen, namely CgHj N4SgO, has been lately assigned to it. The yellow substance is quite insoluble in water, alcohol, and ether; it dissolves in concentrated sulphuric acid, from which it is precipitated by dilution. Caustic potassa also dissolves it, with decomposition; acids throw down from this solution a pale yellow, insoluble body, having acid properties. When heated in a dry state, the so-called sulphocyanogen evolves sulphur and bisulphide of carbon, and leaves a curious, pale straw-yellow substance, called mellon, which coniains CgN^, and is known to combine with hydrogen and the metals. Mellon bears a dull red-heat without decomposition, but is resolved by strong ignition inta a mixture of cyanogen and nitrogen gases. It is quite insoluble in water^ alcohol, and dilute acids. Hydrosulphocvanic acid, HCsy, is obtained by decomposing sulphocya- nide of lead, suspended in water, by sulphuretted hydrogen. The filtered solution is colourless, very acid, and not poisonous ; it is easily decomposed, in a very complex manner, by ebullition ; and by exposure to the air. By neutralizing the liquid with ammonia, and evaporating very gently, to dry- ness, sulphocyanide of ammonium, NH4Csy, is obtained as a deliquescent, saline mass. This salt may be conveniently prepared by digesting hydro- cyanic acid with yellow sulphide of ammonium, and boiling oif the excess of the latter (NH^Sj-f-HCyrrsNH^Csy-f-HS). The sulphocyanides of ^ocfmm, barium, strontium, calcium, manganese, and iron are colourless, and very soluble ; those of lead and silver are white and insoluble. A soluble sulpho- cyanide, mixed with a salt of the sesquioxide of iron, gives no precipitate but causes the liquid to assume a deep blood-red tint, exactly similar to that caused under similar circumstances by meconic acid ; hence the occasional use of sulphocyanide of potassium as a test for iron in the state of sesqui- oxide. The great facility with which hydrocyanic acid may be converted into sulphocyanide of ammonium enables us to ascertain the presence by the iron-test just described. The cyanide to be examined is mixed in a watch- glass with some hydrochloric acid and covered with another watch-glass, to which a few drops of yellow sulphide of ammonium adhere. On heating thv mixture, hydrocyanic acid is disengaged, which combines with the sulphide of ammonium, and produces sulphocyanide of ammonium ; this, after the expulsion of the excess of sulphide, yields the red colour with solution of sesquioxide of iron. Selbnocyanoqen. — A series of salts containing selenium, and corresponding h 436 UREA; URIC acid and its products. in their composition and properties with sulphocyanides, exist. They have been lately studied by Mr. Crookcs. Melam. — Such is the name given by Liebig to a curious buflf-coloured, insoluble, amorphous substance, obtained by the distillation at a high tem- perature of sulphocyanide of ammonium. It may be prepared in large quantity by intimately mixing 1 part of perfectly dry sulphocyanide of po- tassium with 2 parts of powdered sal-ammoniac, and heating the mixture for some time in a retort or flask ; bisulphide of carbon, sulphide of ammo- nium, and sulphuretted hydrogen are disengaged and volatilized, while a mixture of melam, chloride of potassium, and some sal-ammoniac remains ; the two latter substances are removed by washing with hot water. Melam contains Cj^HgNjj ; it dissolves in concentrated sulphuric acid, and gives, by dilution with water and long boiling, cyanuric acid. The same substance is produced with disengagement of ammonia when melam is fused with hydrate of potassa. When strongly heated, melam is resolved into mellon and ammonia. If melam be boiled for a long time in -a moderately strong solution of caustic potassa, until the whole has dissolved, and the liquid be then concen trated, a crystalline substance separates on cooling, which is called melamine, By re-crystallization it is obtained in colourless crystals, having the figure of an octahedron with rhombic base ; it is but slightly soluble in cold water, fusible by heat, and volatile with trifling decomposition. It contains CgHgNc and acts as a base, combining with acids to crystallizable compounds. A second basic substance called ammeline, very similar in properties to mela- mine, is found in the alkaline mother-liquor from which the melamine has separated ; it is thrown down on neutralizing the liquid with acetic acid. The precipitate, dissolved in dilute nitric acid, yields crystals of nitrate of ammeline, from which the pure ammeline may be separated by ammonia. It forms a brilliant white powder of minute needles, insoluble in water and alcohol, and contains CgHjNgOj. When ammeline is dissolved in concentrated sulphuric acid, and the solution mixed with a large quantity of water, or, better, spirit of wine, a white, insoluble powder falls. Which is designated ammelide, and is found to contain C,2HgN90g. When long boiled with dilute sulphuric acid, melamine, ammeline, and ammelide are converted into cya- nuric acid and ammonia. UREA ; UEIC ACID AND ITS PRODUCTS. These bodies are closely connected with the cyanogen-compounds, and may be most conveniently discussed in the present place. Urea. — Urea may be extracted from its natural source, the urine, or it may be prepared by artificial means. Fresh urine is concentrated in a water-bath, until reduced to an eighth or a tenth of its original volume, and filtered through cloth from the insoluble deposit of urates and phosphates. The liquid is mixed with about an equal quantity of a strong solution of oxalic acid in hot water, and the whole vigorously agitated and left to cool. A very copious fawn-coloured crystalline precipitate of oxalate of urea is obtained, which may be placed upon a cloth filter, slightly washed with cold water, and pressed. This is to be dissolved in boiling-hot water, and pow- dered chalk added until efi"ervescence ceases, and the liquid becomes neutral. The solution of urea is filtered from the insoluble oxalate of lime, warmed with a little animal charcoal, again filtered, and concentrated by evaporation, avoiding ebullition, until crystals form on cooling; these are purified by a repetition of the last part of the process. Urea can be extracted in great abundance from the urine of horses and cattle, duly concentrated, and from which the hippuric acid has been separated by the addition of hydrochloric acid ; oxalic acid then throws down the oxalate in such quantity as to render urea; uric acid and its products. 437 the whole semi-solid. Another process consists in precipitating the evapo- rated urine with concentrated nitric acid, when nitrate of urea is precipitated, which is re-crystallized with animal charcoal, and lastly decomposed by car- bonate of baryta. A mixture of nitrate of baryta and urea is formed, which is evaporated to dryness on the water-bath, and exhausted with alcohol, from which the urea crystallizes on cooling. By artificial means, urea is produced by heating solution of cyanate of ammonia. The following method of proceeding yields it in any quantity that can be desired. Cyanate of potassa, prepared by Liebig's process,' is dissolved in a small quantity of water, and a quantity of dry neutral sulphate of ammonia, equal in weight to the cyanate, added. The whole is evapo- rated to dryness in a water-bath, and the dry residue boiled with strong alcohol, which dissolves out the urea, leaving the sulphate of potassa and the excess of sulphate of ammonia untouched. The filtered solution, con- centrated by distilling oflF a portion of the spirit, deposits the urea in beau- tiful crystals of considerable magnitude. Urea forms transparent, colourless, four-sided prisms, which are soluble in an equal weight of cold water, and in a much smaller quantity at a high temperature. It is also readily dissolved by alcohol. It is inodorous, has a cooling, saline taste, and is permanent in the air, unless the latter be very damp. When heated, it melts, and at a higher temperature, decomposes with evolution of ammonia and cyanate of ammonia ; cyanuric acid remains, which bears a much greater heat without change. The solution of urea is neutral to test-paper ; it is not decomposed in the cold by alkalis or by hydrate of lime, but at a boiling heat emits ammonia, and forms a carbonate of the base. The same change happens by fusion with the alkaline hydrates. Brought into contact with nitrous acid, it is decomposed instantly into a mixture of nitrogen and carbonic acid gases ; this decomposition explains the use of urea in preparing nitric ether (see page 354). With chlorine it yields hydrochloric acid, nitrogen, and carbonic acid. Crystallized urea is anhydrous; it contains C2n4N202, or the elements of cyanate of oxide of ammo- nium. It differs from carbonate of ammonia by the elements of water ; hence it might with some propriety be called carbamide. It is easily converted into carbonate of ammonia by assimilating the oxygen and hydrogen of 2 eq. of water. A solution of pure urea shows no tendency to change by keeping, and is not decomposed by boiling ; in the urine, on the other hand, where it is associated with putrctiable organic matter, as mucus, the case is ditfe- rent. In putrid urine no urea can be found, but enough carbonate of ammonia to cause brisk eifervescence with an acid ; and if urine, in a recent state, be long boiled, it gives off ammonia and carbonic acid from the same source. Urea acts as a salt-base ; with nitric acid it forms a sparingly soluble compound, which crystallizes, when pure, in small, indistinct, colourless plates, containing single equivalents of urea, nitric acid, and water. When colourless nitric acid is added to urine, concentrated to a fourth or a sixth of its volume, and cold, the nitrate crystallizes out in large, brilliant, yellow laminae, which are very insoluble in the acid liquid. The production of this nitrate is highly characteristic of urea. The oxalate, when pure, crys- tallizes in large, ti-ansparent, colourless plates, which have an acid reaction, and are sparingly soluble ; it contains an equivalent of water. Urea forma several compounds with metallic salts, e. g., with those of mercury. On mixing a liquid containing urea with a solution of nitrate of protoxide of mercury, a white precipitate takes place, which is a compound of urea with 4 eq. of protoxide of mercury. If the nitric acid which is thus set free, be » See page 427. o7* 488 URIC ACID AND ITS PRODUCTS. neutralized by the addition of an alkali or baryta-water, the whole of the urea is removed from the liquid in the form of tlie above compounds. Prof. Liebig, to whom we are indebted for this observation, has based upon this deportment a process of determining the amount of urea in urine. The de- tails of this method, which is equally interesting to the chemist and the physiologist, have not yet been published. A series of substances analogous to urea, which have lately been disco- vered and described under the name of methylamine-urea, ethylamine-urea, biethylamine-urea, &c., will be noticed in the section on the vegeto-alkalis. Uric, or lithic acid. — This is a product of the animal organism, and has never been formed by artificial means. It may be prepared from human urine by concentration, and addition of hydrochloric acid ; it crystallizes out after some time in the form of small, reddish, translucent grains, very difficult to purify. A much preferable method is, to employ the solid white excrement of serpents, which can be easily procured ; this consists almost entirely of uric acid and urate of ammonia. It is reduced to powder, and boiled in dilute solution of caustic potassa ; the liquid, filtered from the in- significant residue of feculent matter, and earthy phosphates, is mixed with excess of hydrochloric acid, boiled for a few minutes, and left to cool. The product is collected on a filter, washed until free from chloride of potassium, and dried by gentle heat. Uric acid, thus obtained, forms a glistening, snow-white powder, tasteless, inodorous, and very sparingly soluble. It is seen Fig. 173. under the microscope to consist of minute, but regular crystals (fig. 173). It dissolves in concen- /Oy ^^& trated sulphuric acid without apparent decomposi- t->'c^^X^ tion, and is precipitated by dilution with water. By destructive distillation, uric acid yields cyanic, hydrocyanic, and carbonic acids, carbonate of am- monia, and a black coaly residue, rich in nitrogen. C^/A '^^^& ^ I^y fusion with hydrate of potassa, it furnishes ^ \-J B C^*^ carbonate and cyanate of the base, and cyanide of "^^^[[fil j~-N ^25 the alkaline metal. When treated with nitric acid ^^ wJ Q and with binoxide of lead, it undergoes decomposi- tion in a manner to be presently described. Uric acid is found by analysis to contain C,oH2N^04,2HO. It is a bibasic acid. The only salts of uric acid that have attracted any attention are those of the alkalis; acid urate of potassa contains KO,HO,C,oH2N404; it is deposited from a hot, saturated solution of uric acid in the dilute alkali as a white, sparingly soluble concrete mass, composed of minute needles ; it requires about 500 parts of cold water for solution, is rather more soluble at a high temperature, and much more soluble in excess of alkali. Urate of soda re- sembles the salt of potassa ; it forms the chief constituent of the gouty con- cretions in the joints, called chalk-stones. Urate of ammonia is also a sparingly soluble compound, requiring for the purpose about 1000 parts of cold water ; the solubility is very much increased by the presence of a small quantity of certain salts, as chloride of sodium. This is the most common of the urinary deposits, forming a buflf-coloured or pinkish cloud or muddiness, which dis- appears by re-solution when the urine is warmed ; the secretion from which this is deposited has an acid reaction. It occurs also as a calculus. The following substances result from the oxidation of uric acid by binoxide of lead and nitric acid ; they are some of the most beautiful and interesting bodies known, most of which have been discovered by Liebig and Wohler. Allantoin. — Allantoin occurs ready formed in the allantoic liquid of the f'Xtal calf. It is produced artificially by boiling together water, uric acid, URIC ACID AND ITS PRODUCTS. 4S9 and pure, freshly prepared binoxide of lead ; the filtered liquid, duly concen- trated by evaporation, deposits crystals of allantoin on cooling, which are purified by re-solution and the use of animal charcoal. It forms small but most brilliant prismatic crystals, which are transparent and colourless, des- titute of taste, and without action on vegetable colours. Allantoin dissolves in 1 60 parts of cold water, and in a small quantity at the boiling temperature. It is decomposed by boiling with nitric acid, and by oil of vitriol when con- centrated and hot, being in this case resolved into ammonia, carbonic acid, and carbonic oxide. Heated with concentrated solution of caustic alkalis, it is decomposed into ammonia and oxalic acid, which latter combines with the base. These reactions are explained by the analysis of the substance, which shows it to be composed of the elements of oxalate of ammonia minus those of three equivalents of water, or C4H3N2O3. The production of allantoin from uric acid and binoxide of lead is also per- fectly intelligible ; 1 eq. of uric ncid, 2 eq. of oxygen from the binoxide, and 3 eq. of water, contain the elements of allantoin, 2 eq. of oxalic acid, and 1 eq. of urea. C10H4N4O6+2OX _ f C^HgN.Oa-f 2(H0,C,03) -f 3H0 / "^ I -f-CgH^NjOj. The insoluble matter from which the solution of allantoin is filtered con- sists in great part of oxalate of lead, and the mother-liquor from wliich the crystals of allantoin have separated, yields, on farther evaporation, a large quantity of pure urea. Alloxan. — This is the characteristic product of the action of concentrated nitric acid on uric acid in the cold. An acid is prepared, of sp. gr. 1-45, or thereabouts, and placed in a shallow open basin ; into this a third of its weight of dry uric acid is thrown, by small portions, with constant agitation, care being taken that the temperature never rises to any considerable extent. The uric acid at first dissolves with copious eifervescence of carbonic acid and nitrogen, and eventually, the whole becomes a mass of white, crystal- line, pasty matter. This is left to stand some hours, drained from the acid liquid in a funnel whose neck is stopped with powder and fragments of glass, and afterwards more effectually dried upon a porous tile. This is alloxan in a crude state ; it is purified by solution in a small quantity of water, and crystallization. Alloxan crystallizes with facility from a hot and concentrated solution, slowly suffered to cool, in solid, hard, anhydrous crystals of great regularity, which are transparent, nearly colourless, have a high lustre, and the figure of a modified rhombic octahedron, A cold solution, on the other hand, left to evaporate spontaneously, deposits large foliated crystals, which contain 6 eq. of water ; they efl[loresce rapidly in the air. Alloxan is very soluble in water ; the solution has an acid reaction, a disagreeable astringent taste, and stains the skin, after a time, red or purple. It is decomposed by alkalis, and both by oxidizing and de-oxidizing agents ; its most characteristic property is that of forming a deep blue compound with a salt of protoxide of iron and an alkali. Alloxan contains Cgll^NjOig ; its production is thus illustrated : 1 eq. of uric acid, 4 eq. of water, and 2 eq. of nitric acid, contain the elements of alloxan, 2 eq. carbonic acid, 2 eq. of free nitrogen, 1 eq. of nitrate of am- pionia: — ^ +2JhO,NO^'^ } =CsH,N30,o-f 2C0,+N,-f NH,0,NO,. When to a solution of alloxan, heated to 140° (60°C), baryta-water is added as long as the precipitate first produced re-dissolves, and the filtered solutiot. 440 URIC ACID AND ITS PRODUCTS. is then left to cool, a substance is deposited in small, colourless, pearly crys- tals, which consists of baryta in combination with a new acid, the alloxanic. From this salt the base may be separated by the cautious addition of dilute sulphuric, acid : the filtered liquid by gentle evaporation yields alloxanic acid in small radiated needles. It has an acid taste and reaction, decomposes car- bonates, and dissolves zinc with disengagement of hydrogen. It is a bibasic acid, and contains in the hydrated state CgH2N20g,2HO ; hence it is isomeric with alloxan. The alloxanates of the alkalis are freely soluble ; those of the earths dissolve in a large quantity of tepid water^ and that of silver is quite insoluble and anhydrous. If a warm saturated solution of alloxanate of baryta is heated to ebullition,. a precipitate falls, which is a mixture of carbonate and alloxanate of baryta with an insoluble salt of a second new acid, the mesoxalic ; the solution is found to contain unaltered alloxanate of baryta and urea. Mesoxalic acid is best prepared by slowly adding solution of alloxan to a boiling-hot solution of acetate of lead ; the heavy granular precipitate of mesoxalate of lead thus produced is washed and decomposed by sulphuretted hydrogen ; urea is also formed in this experiment. Hydrate of mesoxalic acid is crystallizable ; it has a sour taste and powerfully acid reaction, and resists a boiling heat : it forms sparingly soluble salts with baryta and lime, and a yellowish insoluble compound with oxide of silver, which is reduced with effervescence when gently heated. This remarkable acid contains as hydrate €304,2110, and is consequently bibasic ; it is formed by the resolution of alloxan into urea, and 2 eq. of mesoxalic acid : — C8H4N20,o+2IIO=C2H4NgOj+2(HO,C80^). When ammonia in excess is added to a solution of alloxan, the whole heated to ebullition, and afterwards supersaturated with dilute sulphuric acid, a yellow, light precipitate falls, which increases in quantity as the liquid cools. This is mykomelinic add; it is but feebly soluble in water, easily dis- solved by alkalis, and forms a yellow compound with oxide of silver. Myko- melinic acid contains C^H5N405 ; it is produced by the conversion of alloxan and 2 eq. of ammonia into 1 eq. of mykomelinic acid and 5 eq. of water. Parabanic Acid. — This is the characteristic product of the action of moderately strong nitric acid on uric acid "or alloxan, by the aid of heat ; it is conveniently prepared by heating together 1 part of uric acid and 8 parts of nitric acid until the reaction has nearly ceased ; the liquid is evaporated to a syrupy state, and left to cool ; the acid is drained from the mother- liquid and purified by re-crystallization. Parabanic acid forms beautiful colourless, transparent, thin, prismatic crystals, which are permanent in the air ; it is easily soluble in water, has a pure and powerful acid taste, and reddens litmus strongly. Neutralized with animonia, and mixed with nitrate of silver, it gives a white precipitate. Crystallized parabanic acid contains ^6^2^4'2H^ ; its production is thus explained : 1 eq. of uric acid, 2 eq. of water, and 4 eq. of oxygen from the nitric acid, yield 1 eq. of parabanic acid, 4 eq. of carbonic acid, and 2 eq. of ammonia ; or, alloxan and four additional equivalents of oxygen furnish 1 eq. of parabanic acid, 2 eq. of carbonic acid, and 4 eq. of water. The alkaline parabanates undergo a singular change by exposure to heat ; if a solution of the acid be saturated with ammonia, boiled for a moment, and then left to cool, a substance separates in tufts of beautiful colourless needles ; this is the ammonia-salt of an acid called the oxaluric. The hy- drated acid is procured by adding an excess of dilute sulphuric acid to a hot and strong solution of oxaliirate of ammonia, and cooling the whole rapidly It forms a white, crystalline powder, of acid taste and reaction, capable of combining with bases : the salts of baryta and lime are sparingly URIC ACID AND ITS PRODUCTS. 441 soluble ; that of silver crystallizes from the mixed hot solution of nitrate of silver and oxalnrate of ammonia in long, silky needles. Oxaluric acid ia composed of CeHgNjO^jHO; or the elements of 1 eq, of parabanic acid and 3 eq. of water. A solution of oxaluric acid is resolved by ebullition into free oxalic acid and oxalate of urea. Thionuric acid. — A cold solution of alloxan is mixed veith a saturated solution of sulphurous acid in water, in such quantity that the odour of the gas remains quite distinct ; an excess of carbonate of ammonia mixed with a little caustic ammonia is then added, and the whole boiled for a few minutes. On cooling, thionurate of ammonia is deposited in great abundance, forming beautiful colourless, crystalline plates, which by solution in water and re-crystallization acquire a fine pink tint. A solution of this salt gives with acetate of lead a precipitate of insoluble thionurate of the oxide of that metal, which is at first white and gelatinous, but shortly becomes dense and crystalline ; from this compound the hydrated acid may be obtained by the aid of sulphuretted hydrogen. It forms a white, crystalline mass, per- manent in the air, very soluble in water, of acid taste and reaction, and capable of combining directly with bases. When its solution is heated to the boiling-point, it undergoes decomposition, yielding sulphuric acid and a very peculiar and nearly insoluble substance, called uramile. Thionuric acid is bibasic; the hydrate contains C8ll5N3S20,2,2HO ; or the elements of alloxan, an equivalent of ammonia, and 2 eq. of sulphurous acid. Uramile. — The product of the decomposition by heat of hydrated thionu- ric acid. Thionurate of ammonia is dissolved in hot water, mixed with a small excess of hydrochloric acid, and the whole boiled in a flask ; a white, crystalline substance begins in a few moments to separate, which increases in quantity until the contents of the vessel often become semi-solid ; this is uramile. After cooling, it is collected on a filter, washed with cold water to remove the sulphuric acid, and dried by gentle heat, during which it fre- quently becomes pinkish. Examined by a lens, it is seen to consist of minute acicular crystals. It is tasteless and nearly insoluble in water, but dissolves in ammonia and the fixed alkalis. The ammoniacal solution be- comes purple in the air. It is decomposed by strong nitric acid, alloxan and nitrate of ammonia being generated. Uramile contains CgHgNgOg ; or thionuric acid minus the elements of 2 eq. of sulphuric acid. Uramilic acid. — When a cold saturated solution of thionurate of ammo- nia is mixed with dilute sulphuric acid, and evaporated in a water-bath, instead of uramile, another substance, uramilic acid, is formed and deposited in slender, colourless prisms, soluble in 8 parts of cold water. Uramilic acid dissolves in concentrated sulphuric acid without apparent decomposi- tion ; it has a feeble acid taste and reaction, and combines with bases. The salts of the alkalis are easily soluble ; those of the earths much less so, and that of the oxide of silver is insoluble. Uramilic acid contains CjcHj^NgOiB ; 2 eq. of uramile and 3 eq. of water contain the elements of uramilic acid and 1 eq. of ammonia. It is a substance difficult of preparation. Alloxantin. — This is the chief product of the action of hot dilute nitrio acid upon uric acid ; the surest and best method of preparing it, however, is by passing a stream of sulphuretted-hydrogen gas through a moderately strong and cold solution of alloxan. The impure mother-liquid from which the crystals of alloxan have separated answers the purpose perfectly well* it is diluted with a little water, and a copious stream of gas transmitted through it. Sulphur is deposited in large quantity, mixed with a white, crystalline substance, which is the alloxantin. The product is drained upon a filter, slightly washed, and then boiled in water ; the filtered solution deposits the alloxantin on cooling. Alloxantin forms small, four-sided, oblique rhombic prisms, colourless and transparent ; it is soluble with diffi- culty in cold water, but more freely at a boiling temperature. The solution 442 URIC ACID AND ITS PRODUCTS. reddens litmus, gives with baryta-water a violet-coloured precipitate, which disappears on heating, and when mixed with nitrate of silver produces a black precipitate of metallic silver. Heated with chlorine or nitric acid, it is changed by oxidation to alloxan. The crystals become red when exposed to ammoniacal vapours. Alloxan tin contains CgHjNgOjo ; or alloxan plus 1 equivalent of hydrogen. This substance is readily decomposed ; when a stream of sulphuretted hydrogen is passed through a boiling solution, sulphur is deposited and an acid liquid produced, supposed to contain a new acid, to which the term dialuric is applied. When neutralized by ammonia it yields a salt which crystallizes in colourless silky needles, containing NH40,C8N204 -j- 3H0 They become deep red when heated to 212° (100°C) in the air. A hot satu- rated solution of alloxantin mixed with a neutral salt of ammonia instantly assumes a purple colour, which hoAvever quickly vanishes, and the liquid becomes turbid from the formation of uramile ; the liquid is then found to contain alloxan and free acid. With oxide of silver, alloxatin disengages carbonic acid, reduces a poi'tion of the metal, and converts the remainder of the oxide into oxalurate. Boiled with water and binoxide of lead, allox- antin gives urea and carbonate of lead. MuEEXiDE ; PURPUBATE OF AMBiONiA OF Dr, Pbout. — There are several different methods of preparing this magnificent compound. It may be made directly from uric acid, by dissolving that substance in dilute nitric acid, evaporating to a certain point, and then adding to the warm, but not boiling liquid, a very slight excess of ammonia. In this experiment alloxantin is first produced, which becomes afterwards partially converted into alloxan ; the presence of both is requisite to the production of murexide. This pro- cess is, however, very precarious, and often fails altogether. An excellent method is to boil for a few minutes in a flask a mixture of 1 part of dry uramile, 1 part of red oxide of mercury, and 40 parts of water, to which two or three drops of ammonia have been added ; the whole assumes in a short space of time an intensely deep purple tint, and when filtered boiling- hot, deposits, on- cooling, splendid crystals of murexide, unmixed with any impurity. A third, and perhaps even still better process, is that of Dr. Gre- gory : 7 parts of alloxan and 4 parts of alloxantin are dissolved in 240 parts of boiling water, and the solution added to -about 80 parts of cold, strong solution of carbonate of ammonia ; the liquid instantly acquires such a depth of colour as to become opaque, and gives on cooling a large quantity of mu- rexide ; the operation succeeds best on a small scale. Murexide' crystallizes in small square prisms,, which by reflected light exhibit a splendid green metallic lustre, like that of the wing-cases of the rose-beetle and other insects ; by transmitted light they are deep purple-red. It is soluble with difiiculty in cold water, much more easily at a boiling tem- perature, and is insoluble in alcohol and ether. Mineral acids decompose it with separation of murexan, and caustic potassa dissolves it, with production of a most magnificent purple colour, which disappears when the solution is boiled. Murexide contains, according to Liebig and Wohler, CigTT^NgOg; its production may be thus explained; 2 eq. of uramile and 3 eq. of oxygen from the protoxide of mercury give rise to murexide, 1 eq. of alloxatiic acid, and 3 eq, of water. 2CJI5N3O6 -f CO = C,2n6N50y,CJIN04 + 3110. Or, on the other hand, 1 eq. of alloxan, 2 eq. of alloxantin, and 4 eq. of ammonia, yield 2 eq. of murexide and 14 eq. of water. CaH^N^O^o + ^CsH,N,0,o -f 4NH3 = 2C,,H,NA + 14H0. * 80 called from the I'yrian dye, said to hav been prepared from a species oimurea^ a shell- fish XANTIIIC OXIDE, &c. 443 MuREXAN ; PURPURIC A€iD OP Dr. Prout. — Lie"big directs this subjjtance to be prepared by dissolving murexide in caustic potassa, heating the liquid until the colour disappears, and then adding an excess of dilute suphuric acid. It separates in colourless or slightly yellowish scales, nearly insoluble in cold water. In ammonia it dissolves, and the solution acquires a purple colour by exposure to the air, the murexide being then produced. Murexan is said to contain CgH4Nj05. This substance, and its relation to murexide, require re-examination. A series of substances closely related to the derivatives of uric acid, will be noticed under the head of Caffeine (see page 450). Connected with uric acid by similarity of origin, but not otherwise, are two curious and exceedingly rare substances, called zanthic oxide and cystic oxide. Xanthic oxide was discovered by Dr. Marcet ; it occurs as an urinary cal- culus, of pale brown colour, foliated texture, and waxy lustre, and is ex- tracted by boiling the pulverized stone in dilute caustic potassa and precipi- tating by carbonic acid. The xanthic oxide falls as a white precipitate, which on drying becomes pale yellow, and resembles wax when rubbed. It is nearly insoluble in water and dilute acids. Its characteristic property is to dissolve without evolution of gas in nitric acid, and to give on evaporation a deep yellow residue, which becomes yellowish-red on the addition of xmmonia or solution of potassa. Xanthic oxide gives on analysis CsH^NgOj. Cystic oxide. — Cystic oxide calculi, although very rare, are more frequently met with than those of the preceding substance ; they have a pale colour, a concentric structure, and often a waxy external crust. The powdered cal- culus dissolves in great part without effervescence in dilute acids and alkalis, including ammonia ; the ammoniacal solution deposits, by spontaneous evapo- ration, small, but beautiful colourless crystals, which have the form of six- sided prisms and square tables. It forms a saline compound with hydro- chloric acid. Caustic alkalis disengage ammonia from this substance by continued ebullition. Cystic oxide contains sulphur; it is composed of Uric acid is perfectly well characterized, even when in very small quantity, by its behaviour with nitric acid. A small portion heated with a drop or two of nitric acid in a small porcelain capsule dissolves with copious effer- vescence. When this solution is cautiously evaporated nearly to dryness, and, after the addition of a little water, mixed with a slight excess of am- monia, the deep red tint of murexide is immediately produced. Impure uric acid, in a remarkable state of decomposition, is now importer into this country in large quantities, for use as a manure, under the nam« of guano or huano. It comes from the barren and uninhabited islets of thi western coast of South America, and is the production of the countless birdd that dwell undisturbed in those regions. The people of Peru have used it for ages. Guano usually appears as a pale brown powder, sometimes with whitish specks ; it has an extremely offensive odour, the strength of which, however, varies very much. It is soluble in great part in water, and the solution is found to be extremely rich in oxalate of ammonia, the acid having been generated by a process of oxidation. Guano also contains a peculiar substance called guanine^ which closely corresponds with xanthic oxide. Like urea, it combines with acids, forming a series of crystallizable salts. Guanine cotitainB r TT x,0,. 444 VEGETO ALKALIS. SECTION V. THE VEGETO-ALKALIS. The vegeto-alkalis, or alkaloids, or organic bases, constitute a remarkable and most interesting group of bodies ; they are met with in various plants, always in combination with an acid, which is in many cases of peculiar nature, not occurring elsewhere in the vegetable kingdom. They are, for the most part, sparingly soluble in water, but dissolve in hot alcohol, from which they often crystallize in a very beautiful manner on cooling. Several of them, however, are oily, volatile liquids. The taste of these substances, when in solution, is usually intensely bitter, and their action upon the animal economy exceedingly energetic. They all contain a considerable quantity of nitrogen, and are very complicated in constitution, having high combining numbers. It is probable that these bodies are very numerous. None of the organic bases occurring in plants have yet been formed by artificial means ; analogous substances have, however, been thus produced. MoiiPHiNK, OR MORPHIA. — This is the chief active principle of opium ; it is the best and most characteristic type of the group, and the earliest known, dating back to the year 1803. Opium, the inspissated juice of the poppy-capsule, is a very complicated substance, containing, besides morphine, a host of other alkaloids in very variable quantities, combined with sulphui'ic acid and an organic acid called the meconic. In addition to these, there are gummy, resinous, and colouring matters, caoutchouc, &c., besides mechanical impurities, as chopped leaves. The opium of Turkey is the most valuable, and contains the largest quantity of morphine ; that of Egypt and of India are considerably inferior. It has been produced in England of the finest quality, but at great cost. If ammonia be added to a clear, aqueous infusion of opium, a very abundant bufi'-coloured or brownish-white precipitate falls, which consists principally of morphine and narcotine, rendered insoluble by the withdrawal of the acid. The product is too impure, however, for use. The chief diflSculty in the preparation of these substances is to get rid of the colouring matter, which adheres with great obstinacy, re-dissolving with the precipitates, and being again in part thrown down when the solutions ate saturated with an alkali. The following method, which succeeds well upon a small scale, will serve to give the student some idea of a process very commonly pursued when it is desired to isolate at once an insoluble organic base, and the acid with which it is in combination : — A filtered solution of opium in tepid water is mixed with acetate of lead in excess : the precipitated meconate of lead is separated by a filter, and through the solution containing acetate of morphine, now freed to a considerable extent from colour, a stream of sulphuretted hydrogen is passed. The filtered and nearly colourless liquid, from which the lead has been thus removed, may be warmed to expel the excess of gas, once more filtered, and then mixed with a slight excess of caustic ammonia, which throws down the morphine and narcotine ; these may be separated by boiling Mher, in which the latter is soluble. The meconate of lead, well washed, VEGETO-ALKALIS. 445 suspended in water, and decomposed by sulphuretted hydrogen, yields solu- tion of meconic acid. ]florphine and its salts are advantageously prepared, on the large scale, by the process of Dr. Gregory. A strong infusion of opium is mixed with a solution of chloride of calcium, free from iron; meconate of lime, which is nearly insoluble, separates, while the hydrochloric acid is transferred to the alkaloids. By duly concentrating the filtered solution, the hydrochlorate of morphine may be made to crystallize, while the narcotine, and other bodies, are left behind. Repeated recrystallization, and the use of animal charcoal, then suffice to whiten and purify the salt, from which the base may be pre- cipitated in a pure state by ammonia. Other processes have been proposed, as that of M. Thiboum^ry, which consists in adding hydrate of lime in excess to an infusion of opium, by which the meconic acid is rendered insoluble, while the morphine is taken up with ease by the alkaline earth. By exacUij neutralizing the filtered solution with hydrochloric acid, the morphine is pre- cipitated, but in a somewhat coloured state. Morphine, when crystallized from alcohol, forms small, but very brilliant prismatic crystals, which are transparent and colourless. It requires at least 1000 parts of water for solution, tastes slightly bitter, and has an alkaline reaction. These efi'ects are much more evident in the alcoholic solution. It dissolves in about 30 parts of boiling alcohol, and with great facility in dilute acids ; it is also dissolved by excess of caustic potassa or soda, but scarcely by excess of ammonia. When heated in the air, morphine melts, inflames like a resin, and leaves a small quantity of charcoal, which easily burns away. Morphine, in powder, strikes a deep bluish colour with neutral salts of sesquioxide of iron, decomposes iodic acid with liberation of iodine, and forma a deep yellow or red compound with nitric acid ; these reactions are by some considered characteristic. Crystalline morphine contains Cg^HigNOg-j-SIIO. The most characteristic and best-defined salt of this substance is the hydrochlorate. It crystallizes in slender, colourless needles, arranged in tufts or stellated groups, soluble in about 20 parts of cold water, and in its own weight at a boiling temperature. The crystals contain 6 eq. of water. The sulphate, nitrate, and phosphate are crystallizable salts ; the acetate crystallizes with great difficulty, and is usually in the state of a dry powder. The arti- ficial meconate is sometimes prepared for medicinal use. Narcotine. — The marc, or insoluble portion of opium, contains much nar- cotine, which may be extracted by boiling with dilute acetic acid. From the filtered solution the narcotine is precipitated by ammonia, and afterwards purified by soiutioTi in boiling alcohol, and filtration through animal charcoal. Narcotine crystallizes in small, colourless, brilliant prisms, which are nearly insoluble in water. The basic powers of narcotine are very feeble ; it is des- titute of alkaline reaction, and, although freely soluble in acids, refuses, for the most part, to form with them crystallizable compounds. According to Dr. Blyth, narcotine contains C4gH25NO,4. Narcotine yields some curious products by the action of oxidizing agents, as a mixture of dilute sulphuric acid and binoxide of manganese, or a hot solution of bichloride of platinum. They have been chiefly studied by Wohler and Blyth, and lately also by Anderson. The most important of these is opianic acid, a substance forming colourless, prismatic, reticulated crystals, sparingly soluble in cold water, easily in hot. It melts when heated, but does not sublime. After fusion it becomes quite insoluble in dilute alkalis, but without change of composition. This acid forms crystallizable salts and an ether : it contains CjoHgOgHO. The ammonia-salt, by evaporation to dry- ness, yields -a nearly white insoluble powder, called opiammon, containing C^gHjgNOig, convertible by strong acids into opianic acid and ammonia. Sul- 446 VEGETO-ALKALIS. phurous acid yields with opianic acid two products containing sulphur. A mixture of binoxide of lead, opianic acid, and sulphuric acid gives rise to a crystallizable bibasic acid termed hemipinic acid, containing C2oHgO,o,2HO. A basic substance, cotarnine, CagHigNOg, is contained in the mother-liquor from which opianic acid has crystallized ; it forms a yellow crystalline mass, very soluble, of bitter taste, and feebly alkaline reaction. Its hydrochlorate is a well-defined salt. Another basic substance, narcogenine, was accidentally produced in an attempt to prepare cotarnine by bichloride of platinum. It formed large orange-coloured needles, and contained CggHjgNOio. Codeine. — Hydrochlorate of morphine, prepared directly from opium as in Gregory's process, contains codeine-salt. When dissolved in water, and mixed with a slight excess of ammonia, the morphine is precipitated, and the codeine left in solution. Pure codeine crystallizes, by spontaneous evapo- ration, in colourless transparent octahedrons; it is soluble in 80 parts of cold, and 17 of boiling water, has a strong alkaline reaction, and forms crys- tallizable salts. Codeine is composed of CgeHjiNOg. This has lately been the subject of a careful investigation by Dr. Anderson, who has prepared a great number of its derivatives, all of which establish the formula given. Trebaine or paramorphine. — This substance is contained in the preci- pitate formed by hydrate of lime in a strong infusion of opium in Thibou- m6ry's process for morphine. The precipitate is well washed, dissolved in dilute acid, and mixed with ammonia in excess, and the thebaine thrown down, crystallized from alcohol. It forms when pure colourless needles like those of narcotine, but sparingly soluble in water, readily soluble in the cold in alcohol and ether. It melts when heated, and decomposes at a high tem- perature. With dilute acids it forms crystallizable compounds, and when isolated and in solution has a powerful alkaline reaction. The composition of thebaine is CggHjjNOg. A series of other bases, pseudo-morphine, narceine, meconine, papaveriney opianine, and porphyroxine, are also, at least occasionally, contained in opium; they are of small importance, and comparatively little is known respecting them. Meconic acid is obtained from the impure meconate of lead, as already mentioned. The solution is evaporated in the vacuum of the air-pump. A more advantageous method is to decompose the impure meconate of lime, obtained in Dr. Gregory's morphine-process, by warm dilute hydrochloric acid ; to separate the crystals of acid meconate of lime, which form on cooling, and to repeat this (operation until the whole of ^he base has been removed, which may be known by the acid being entirely combustible, with- out residue, when heated in the flame of a spirit-lamp upon platinum foil. It is with the greatest difficulty obtained free from colour. Meconic acid crystallizes in little colourless, pearly scales, which dissolve in 4 parts of hot water. It has an acid taste and reaction, forms soluble compounds with the alkalis, and insoluble salts with lime, baryta, and the oxides of lead and silver. The most remarkable feature in this substance is its property of striking a deep blood-red colour with a salt of the sesqui- oxide of iron, exactly resembling that developed, under similar circum- stances, by a sulphocyanide. The meconate of iron may, however, be dis- tinguished from the latter compound, as Mr. Everitt has shown, by an addi- tion of corrosive sublimate, which bleaches the sulphocyanide, but has little effect upon the meconate. This is a point of considerable practical impor- tance, as in medico-legal inquiries, in which evidence of the presence of opium is sought for in complex organic mixtures, the detection of meconic %cid is usually the object of the chemist; and since traces of alkaline sul- VEG.ETO-ALKALIS. 447 phocyanide are to be found in the saliva, it becomes very desiraole to remove that source of error and ambiguity. Crystallized meconic acid contains Cj4HO,j,3HO-j-6HO. When a solution of meconic acid in water, or, still better, in a mineral acid, is boiled, or when the dry acid is exposed in a retort to a temperature of 400° (204°-5C), it is decomposed, yielding a new bibasic acid, the comenicy containing C,2H20g,2HO, which much resembles in properties meconic acid. Water and carbonic acid are at the same time extricated. At a higher tem- perature comenic acid itself is resolved into a second new acid, the pyrome- conic, which sublimes, and afterwards condenses in brilliant colourless plates. It is monobasic, and contains CjoHgOg.HO. The salts of meconic acid and comenic acid, together with several derivatives of these substances, have been lately studied by Mr. How,' but our space will not permit us to describe these compounds. An acid much resembling the meconic has been extracted from the Cheli- doniuin majus ; it is combined with lime, and associated with malic and fu- maric acids. Chelidonic acid is bibasic, forming three classes of salts, and a pyro-acid with evolution of water and carbonic acid when exposed to a high temperature. It crystallizes in slender colourless needles of considerable solubility, containing C,4H20io,2HO-f 3H0. CiNCHONiNE AND QUININE. — It is to thcsc vegcto-alkalis that the valuable medicinal properties of the Peruvian barks are due. They are associated in the bark with sulphuric acid, and with a special acid, not found elsewhere, called the kinic. Cinchonine is contained in largest quantity in the pale bark, or Cinchona condaminea ; quinine in the yellow bark, or Cinchona cordifolia ; the Cinchona oblongifoUa contains both. The simplest, but not the most economical, method of preparing these substances, is to add a slight excess of hydrate of lime to a strong decoction of the ground bark, in acidulated water; to wash the precipitate which ensues, and boil it in alcohol. The solution, filtered while hot, deposits the vegeto-alkali on cooling. When both bases are present, they may be sepa- rated by converting them into sulphates; the salt of quinine is the least soluble of the two, and crystallizes first. Pure cinchonine or cinchonia, crystallizes in small, but beautifully bril- liant, transparent four-sided prisms. It is but very feebly soluble in water, dissolves readily in boiling alcohol, and has but little taste, although its salts are excessively bitter. It is a powerful base, neutralizing acids completely, and forming a series of crystallizable salts. Quinine, or quina, much resembles cinchonine ; it does not crystallize so well, however, and is much more soluble in water ; its taste is intensely bitter. Cinchonine is composed of CjjoHijNO, and Quinine of CgoHjaNOg.' Sulphate of quinine is manufactured on a very large scale for medicinal use ; it crystallizes in small white needles, which give a neutral solution. Nevertheless, this substance is a basic salt, and contains 2C20H jjN 03,803 -f- 8H0. The solubility of this compound is much increased by the addition of a little sulphuric acid, whereby the neutral salt CgoHigNOajSO^-f-SHO is formed. A very interesting compound has been lately produced by Dr. » Chem. Sec. Quar, Jour. Vol. IV. page SaS. ^ Some doubts are still hanging over the composition of cinchonine and quinine. Accord- ing to M. Lavrent these substances contain respectively CsjHiMNsO^, and CsellMNaOi. If these formulte be adopted the basic sulphate of commerce would become a neutral, the neutr 0,;C„ H, CArnsol. Oil of cumin is a mixture of two bodies, separable in great measure by distillation, cr/mol, a liquid hydrocarbon, containing C2oH,4, the most volatile portion of the oil, and cuminol, a colourless transparent oil, of powerful odour, easily changed in the air, and only to be distilled in a current of carbonic acid gas. Cuminol contains CgoHijOg, and is consequently isomeric with the solid essence of aniseed. By oxidation, this substance, which is homologous to oil of bitter almonds, yields cumicacid, a white, fatty, volatile substance, insolu- ble in water, having but little odour, and crystallizing in prismatic tables. It contains CgoHijOg.HO (see homologues of benzoic acid, page 403). Oil of cedar-wood, in like manner, contains two substances, a solid crys- talline compound, having the formula C32H2g02, and a volatile liquid hydro- carbon, cedrene, C32H24, which can also be obtained by distilling the solid with anhydrous phosphoric acid. Oil of gaultheria procumbens. — This very remartable substance is now known in commerce under the name of winter-green-oil ; it consists almost wholly of a definite principle which distils unchanged at 435° (223° -80), and contains, according to the analysis of M. Cahours, CigHgOg. When mixed with dilute caustic potassa, it solidifies to a crystalline mass, which is a potassa- salt, gaultherate of potassa, and from which the oil may be separated again unchanged on the addition of an acid. When distilled, however, with a con- centrated solution of caustic potassa, the oil of gaultheria is resolved into salicylic acid and wood-spirit, thus exactly resembling in its behaviour the compound ethers which have been described in a previous section of the Manual (see page 352). This oil is, in fact, a veritable compound ether, salicylate of oxyde of methyl, C2N30,Ci4H505=:C,gng06, furnished by nature herself. With ammonia the oil jHields salicylamide, C,4n7N04=C,4Hg04,NH2, isomeric with anthranilic acid (see page 474), which is converted by fuming 492 VOLA.TILE OILS. nitric acid into the nitro-substitute, nitro-salicylamide (anilamide) Cj^CH^ N04.)()^,NH2, crj'stalliziug in yellowish-white needles. Gaultheria oil is iso- meric with anisic acid (see page 491), and yields by distillation at a high tem- perature with anhydrous lime and baryta, anisol C,4Hg05, the same volatile oily liquid which is obtained from anisic acid by a similar process. Oil of valerian. — The oil obtained by distilling valerian-root with water has usually a viscid consistence, a yellowish colour, and a powerful and dis- agreeable odour. It consists of at least three principles, namely, valeric acid, borneene (see camphor), a light volatile liquid hydrocarbon, much resembling and isomeric with oil of turpentin, and valerol, a neutral oily body, much less volatile than the preceding, of feeble odour, and convertible by oxidizing agents into valeric acid. It contains Cj^Hj^O^. Borneene, under certain circumstances not well understood, assimilates the elements of water and yields the solid camphor of Borneo, or horneol. Camphob. — Common camphor yields a good example of a concrete essen- tial oil ; it is obtained by distilling with water the wood of the Laurus cam- phora. When pure, it forms a solid, white, crystalline, and translucent mass, tough, and diflBcult to powder, and having a powerful and very fami- liar odour. It melts when gently heated, and boils, distilling unchanged at a high temperature. It slowly sublimes at the temperature of the air, and often forms beautiful crystals on the sides of bottles or jars containing it exposed to the light. Camphor is very sparingly soluble in water, but readily soluble in alcohol, ether, and strong acetic acid. It contains CjoHgO, or ^20^16^2- By the action of nitric acid aided by heat, camphor is gradually oxidized and dissolved with production of camphoric acid; this substance forms small colourless needles or plates, of acid and bitter taste, sparingly soluble in cold water, and containing CioH703,HO. It melts when heated, and yields by distillation a colourless, crystalline, neutral substance, containing CiqH, O3, improperly termed anhydrous camphoric acid. When camphorate of lime is submitted to distillation, it yields a volatile oil containing oxygen, in its formation and constitution similar to acetone (page 376) or benzophenone (page 898). This substance, jpAorone, contains Cgtl^O or C, 8111402. By the action of anhydrous phosphoric acid it loses water and furnishes the hydrocarbon cumol, CigHjj (see page 403). When camphor in vapour is passed over a mixture of hydrate of potassa and quicklime strongly heated in a tube, it is resolved without disengage- ment of gas into an acid body termed camphoUc acid, white, crystalline, and sparingly soluble in water, containing CjoHj^OgJIO. By distillation with anhydrous phosphoric acid, this acid gives a volatile hydrocarbon, campko- lene. Camphor itself, by a similar mode of treatment, yields a colourless volatile liquid, CjoH,^, formerly called camphogen, but since found to be iden- tical with the hydrocarbon, cymol, occurring in oil of cumin. The camphor of Borneo, procured from the Dryahalanops camphora, contains CgoHjgOg ; it is accompanied by borneene, identical with that of the oil of valerian, and yields the same substance when distilled with anhydrous phos- phoric acid. Nitric acid converts it into common camphor. The oils of peppermint, lavender, rosemary, orange-flowers, rose-petals, and manv others, belong to the class of oxygenated essential oils. Essential Oils containing Sulphur. In the preparation of the sulphuretted volatile oils, distillatory vessels of copper, tia, or lead must be avoided, as those metals are attacked by the Rulphur. In other respects their manufacture offers no peculiarities. Oil of mustabd. — The most remarkable member of the class is the oil obtained by distillation from black mustard-seed. White mustard yields RESINS AND BALSAMS. 493 sone. Both varieties give, by expression, a bland fat oil. The volatile oil doeri not pre-exist in the seed, but is formed in the same manner as bitter- almond-oil, by the joint action of water and a peculiar coagulable albuminous matter upon a substance yet inperfectly known, present in the grain, and termed myronic acid. The distilled oil, when pure, is colourless ; it has a most powerful, pungent and suffocating smell, and a density of 1-015. Applied to the skin, it pro- duces almost instant vesication. It boils at 289° (145° -80). Water dis- solves it in small quantity, and alcohol and ether very freely. The oil itself, at a high temperature, dissolves both sulphur and phosphorus, and deposits them in a crystalline form on cooling. It is oxidized with violence by nitric acid, and by aqua regia. Alkalis decompose it by the aid of heat, with pro- duction of ammonia, an alkaline sulphide, and a sulphocyanide. The re- markable compound with ammonia, thiosinnamine, has been already described (see page 466.) Mustard-oil gives by analysis CgHgNSg." The oil of horse-radish, and that obtained from the roots of the Alliaria officinalis by distillation with water, are identical with the oil of black mus- tard-seed. Oil op garlic. — The crude oil procured by distilling the sliced bulbs with water is not a homogeneous product; by the action of metallic potassium, however, renewed until it is no longer tarnished, a small portion of oxyge- netted oil which it contains may be decomposed and withdrawn, after which the sulphuretted compound may be obtained pure by re-distillation. In this state it forms a colourless liquid, lighter than water, of high refractive power, possessing in a high degree the peculiar odour of the plant, and capable of being distilled without decomposition. It contains CgHjS. Garlic-oil dis- solved in alcohol, and mixed with solutions of platinum, silver, and mercury, gives rise to crystalline compounds having the characters of double salts, containing the elements of the oil with the sulphur replaced by oxygen or chlorine. A curious and interesting relation exists between the oils of mustard and garlic : in both these substances, we may assume the existence of a radical CgHg, to which the name allyl has been given, when mustard-oil becomes the sulphocyanide, and garlic-oil the sulphide of allyl. Mustard-oil CgHjNS =C6n5C2NS2. Sulphocyanide of allyl. Garlic-oil CgH^S =061158. Sulphide of allyl. This relation has been experimentally established. By mixing the oil with hydrate of soda and quicklime, and exposing the whole in an hermeti- cally-sealed tube to a temperature superior to that of boiling water, sulpho- cyanide of sodium is produced, together with an oily substance which is oxide of allyl, a substance chiefly known in combination, and which is the oxyge- netted constituent of crude garlic-oil. Again, if mustard-oil be treated in a similar manner with sulphide of potassium, sulphocyanide of potassium and garlic-oil are formed. On the other hand, when the compound of garlic-oil and chloride of mercury is gently heated with sulphoc3''anide of potassium, mustard-oil, with all its characteristic properties, is called into existence. The oils of assafostida, and onions, contain sulphur, and consequently belong to the same series ; they have not yet been thoroughly examined. RESINS AND BALSAMS. Common resin, or colophony, furnishes perhaps the best example of the class. The origin of this substance has been already described. It is a mixture of two distinct bodies, having acid properties j cailled j)inic and sylvie 42 494 RESINS AND BALSA IMS. aeids, separable from each other by their difference of solubility in cold an J somewhat dilute alcohol, the former being by far the more soluble of the two. Pure sylvic acid crystallizes in small, colourless, rhombic prisms, inso- luble in water, soluble in hot, strong alcohol, in volatile oils, and in ethei*. It melts when heated, but cannot be distilled without decomposition. The properties of pinic acid are very similar. Both have the same composition, viz., CgoHijOj. A third resin-acid, also isomeric with the preceding, the pimaric, has been found in the turpentin of the Pinus maritima of Bordeaux. Lac is a very valuable resin, much harder than colophony, and easily so- luble in alcohol; three varieties are known in commerce, viz., stick-lac, seed- lac, and shellac. It is used in varnishes, and in the manufacture of hats, and very largely in the preparation of sealing-wax, of which it forms the chief ingredient. Crude lac contains a red dye which is partly soluble in water. Lac dissolves in considerable quantity in a hot solution of borax ; Indian ink, rubbed up with this liquid, forms a most excellent label-ink for the laboratory, as it is unaffected by acid vapours, and, when once dry, becomes nearly in- soluble in water. Mastic, Dammar-resin, and sandarac are resins largely used by the varnish- maker. Dragon's-blood is a resin of a deep red colour. Copal is also a very valuable substance ; it differs from the other resins, in being with difficulty dissolved by alcohol and essential oils. It is miscible, however, in the melted state with oils, and is thus made into varnish. Amber appears to be a fossil resin ; it is found accompanying brown-coal or lignite. Caoutchouc. — This curious, and now most useful substance, is the produce of several trees of tropical countries, which yield a milky juice, hardened by exposure to the air. In a pure state, it is nearly white, the dark colour of commercial caoutchouc being due to the effects of smoke and other impuri- ties. Its physical characters are well known. It is softened, but not dis- solved by boiling water ; it is also insoluble in alcohol. In pure ether, rectified native naphtha, and coal-oil, it dissolves, and is left unchanged on the evaporation of the solvent. Oil of turpentin also dissolves it, forming a viscid, adhesive mass, which dries very imperfectly. At a temperature a little above the boiling-point of water caoutchouc melts, but never afterwards returns to its former elastic state. Few chemical agents affect this substance ; hence its great practical use, in chemical investigations, for connecting ap- paratus, &c. Analysis shows it to contain nothing but carbon and hydrogen. By destructive distillation caoutchouc yields a large quantity of thin vola- tile oily liquid, of naphtha-like odour, to which the name caoutchoucin has been applied. This is probably a mixture of several hydrocarbons, scarcely to be separated from each other by distillation or otherwise. It dissolves caoutchouc with facility. A substance much resembling caoutchouc in certain respects, and of simi- lar origin, has lately been introduced under the name of guttapercha. It is capable of many useful applications in the laboratory. Most of the resins, when exposed to destructive distillation, yield liquid, oily pyro-products, usually carbides of hydrogen, which have been studied with partial success. Great difficulties occur in these investigations ; the task of separating from each other, and isolating bodies which scarcely differ but in their boiling-points, is exceedingly troublesome. Balsams are also, as before hinted, natural mixtures of resins with volatile oils. These differ very greatly in consistence, some being quite fluid, others solid and brittle. By keeping, the softer kinds often become hard. Balsams may be conveniently divided into two classes, viz., those which, like common and Venice turpentin, Canada balsam, copaiba balsam, &c., are merely natural varnishes, or solutions of resins in volatile oils, and those which contain beu- BESINS AND BALSAMS. 495 «oic or cinnamic acid in addition, as Peru and Tolu balsams^ and the solid resinous benzoin commonly called gum-benzoin. Tolu-balsam, by distillation with water, yields three products; namely, benzoic acid, cinnamein, and tolene, a volatile colourless hydrocarbon, boiling at 338° (170°C), and containing CjoHg. The balsam freed in this manner from essential oils, exposed to destructive distillation, yields in succession a vis- cous liquid which crystallizes in the receiver, and a thin liquid heavier than water ; carbonic acid and carbonic oxide are largely evolved, and the retort is afterwards found to contain a residue of charcoal. The solid product is chiefly a mixture of benzoic and cinnamic acids ; the volatile oil contains at least two substances differing in their boiling-points, and easily separated, namely, toluol (benzoene), which has been mentioned already as a derivjitive of toluylic acid (see page 403), and an oily liquid heavier than water, of high boiling-point, and having the composition and characters of benzoic ether. Toluol is a thin, colourless liquid, insoluble in water, sparingly soluble in alcohol, more freely in ether ; it has the odour of benzol ; its sp. gr. is 0-870, and it boils at 226° (107°-5C). The density of its vapour is 3-26, and its for- mula C,4H^. It combines with fuming sulphuric acid to the compound sul- photuolic acid: with nitric acid it yields two products, nilrotoluol, C14H7NO4, and biniirotoluol, Cj4HgN208. The former is fluid, heavier than water, and bears a great resemblance in odour and other properties to nitrobenzol ; the latter is a solid, fusible, crystallizable substance. The conversion of nitro- toluol into the organic base toluidine, has been already described (see page 462). Liquid siorax distilled with water, holding in solution a little carbonate of soda, yields a small and variable quantity of volatile oil, not homogeneous, but from which, by careful distillation, a liquid volatile hydrocarbon, termed styrol, can be extracted in a state of purity. It is thin and colourless, of powerful aromatic odour, refuses to solidify when cooled to 0° ( — 17°-8C), and boils at 293° (145° -C). Its sp. gr. is 0-924; it is nearly insoluble in water, but mixes freely with alcohol and ether. Styrol contains CjgHg, and is consequently isomei-ic with benzol. This substance is also produced by the action of lime or baryta upon cinnamic acid (see page 408), whence it is more appropriately termed cinnamol. When a portion of styrol is hermetically sealed in a glass tube, and then exposed for half an hour to a temperature approaching 400° (204° -50) by means of an oil-bath, it undergoes a most remarkable change, becoming con- verted into a solid, transparent, glassy, fusible substance, called metastyrol, isomeric, as might be expected, with styrol itself. The same change is slowly produced by the influence of sunshine. A portion of metastyrol is always formed when styrol is distilled in a retort without water. Metastyrol is again convertible by distillation at a high temperature into liquid styrol. Certain of the products of the distillation of dragon's-blood appear to be identical with these bodies. 496 COMPONENTS OF THE ANIMAL BODY. SECTION VIII. COMPONENTS OF THE ANIMAL BODY. Albuminous principles, albumin. — The fluid portion of blood which has been some time drawn from the living body, and the white of eggs, con- tain this substance as their chief and characteristic ingredient. In the purest form in which albumin has yet been obtained it is insoluble, or nearly 80, in water. If clear serum of blood, or white of egg mixed with a little water and filtered, be exactly neutralized by acetic acid, and then largely diluted with pure cold water, a copious flocculent precipitate falls, which may be collected on a filter, and washed. In this state it is nearly colour- less, inodorous, and tasteless ; it dissolves with facility in water containing an exceedingly small quantity of caustic alkali, and gives a solution which has all the characters of the original liquid. When dried by gentle heat, it shrinks to a very small bulk, and becomes a translucent, horny mass, which softens in water, and exhales when exposed to heat the usual ammo- niacal products of animal matter, leaving a bulky coal, very difficult of com- bustion. When white of egg is thinly spread upon a plate and exposed to evaporation in a warm place, it dries up to a pale yellow, brilliant, gum-like substance, destitute of all traces of crystalline structure. In this state it may be preserved unchanged for any length of time, the presence of water being in all cases necessary to putrefactive decomposition. The dried white of egg may also be exposed to a heat of 212° (100°C) without alteration of properties. When put into slightly warm water, it softens, and at length in great measure dissolves. When reduced to fine powder and washed upon a filter with cold water, common salt, sulphate, phosphate, and carbonate of soda are dissolved out, together with mere traces of organic matter, while a soft swollen mass remains upon the filter, which has all the characters of pure albumin obtained by precipitation. When dried and incinerated, this leaves nothing but a little phosphate of lime. It thus appears likely that albumin is really an insoluble substance, and that its soluble state in the animal system is due to the presence of a little alkali. When natural albumin is exposed to heat it solidifies, or coagulates. The temperature required for this purpose varies with the state of dilution. If the quantity of albumin be so great that the liquid has a slimy aspect, a heat of 145° or 150° (62°-5 or 69°-5C) suffices, and the whole becomes solid, white, and opaque ; in a very dilute condition, boiling is required, and the albumin then separates in light, finely divided flocks. Thus changed by heat, albumin becomes quite insoluble in water; it dries up to a yellow, transparent, horny substance, which when macerated in water resumes its former whiteness and opacity. In dilute caustic alkali it dissolves with facility, and in this respect resembles the insoluble albumin just desci'ibed; it differs, however, from the latter in not being soluble in a strong solution COMPONENTS OF THE ANIMAL BODY. 497 of nitrate of potassa, -which dissolves with great ease that substance. The or>ly 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 Twe'a-phosphoi'ic 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- tication effected ; 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 63'5 Hydrogen 7-0 Nitrogen 15-5 Oxygen 22 Phosphorus 0-4 Sulphur 1-6 1000 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. FiBKiN. — 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 tibrin 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 effect. Boiled with strong hydrochloric acid for several hours, fibrin is converted into a mixture of leucine ('see page 477) and tyrosine (see page 500). The fibrin of arterial and venous blood is not absolutely the same ; wnen the venous fibrin of human blood is triturated in a mortar with 1 \ times its 42 * 498 COMPONENTS OF THE ANIMAL BODY. weight of water and J of its weight of nitrate of potassa, and the mixture ia 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,' 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 235 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 ' Liebig, llandwcirterbtich der Cbemie, i. 881. COMPONENTS OF THE ANIMAL BODY. 499 •whole eventually dries up to a translueent 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). 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 y^'o^ part. Casein has been carefully analysed by Mulder ; it contains in 100 parts — Carbon 53-83 Hydrogen 7-15 Nitrogen 15-65 Oxygen \ 00.07 Sulphur/ "^^"^^ 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° ((30° -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.' 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, by moderately strong caustic alkali. When albumin, fibrin, or casein, are boiled in strong solution of potai*pa • So called from rpwrtt'd), Iial:e the first pUi£i; in allusion to its alleged important relationo te tb« iilbumiuous 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, err/throprotide ; a soluble straw-yellow substance, joro- 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 CiaHjgNO^, (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.' 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 »;oloured. 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 molleiies 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. Jn 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 maybe kept indefinitely; in contact with water, it putrefies. Long-continued boiling gradually alters it, and 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, >■ Mr.ldpr, Annalen der Chemie und Pharmade, xlvii. 323. » Se« Philosophical Trans. 1818. COMPONENTS OP THE ANIxMAL BODY. 601 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 C4HgN04. 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 i3 thereby resolved into benzoic 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. Glycocine, when treated with nitrous acid, yields an acid homologous to lactic acid (see page 402), to which the name of glycolic acid has been given. C4H5NO4 + NO3 = C4H4O6 + 2N+H0 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 glycociue, 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 C4H5NO4 Alanine C6H7NO4 Leucine Ci2H,3N04. The deportments of these three substances with nitrous acid is perfectly alike. Leucine, according to M. Strecker, yields a new acid CjjHjaOg 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 colourless liquid, of aromatic odour, like that of hydride of salicyl ; it is lighter than water, boils at 257° (125oC), and contains CjoHgN. The latter much resembles the first, but boils at 158° (70°C), and contains C2eH24N206. 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 5005 Hydrogen 6 47 Nitrogen 18-35 Oxygen 2513 100-00 From these numbers the formulae CigHioNjOg, and CgaH^oNgOzo, 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 CgaH^eN^Oj^, and C^gH^oNgOao have been given. If a solution of gelatin, albumin, fibrin, casein, or probably any one of the more complex azotized 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 Talue in this respect has been much overrated. In the useful arts, size and 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- tinouij 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° (100°C). 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 C8HgN304,2HO. By the action of strong acids, kreatin is converted into kreatinine, a power- ful organic base, with separation of the elements of water. The new sub- •tence forms colourless prismatic crystals, and is much more soluble in water COMPOSITION or THE BLOOD. 503 than kreatin ; it has a strong alkaline reaction, forms with acids crystalli- zable salts, and contains CgH^NgOj. 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 C6H7NO4, being isomeric with lactamide, alanine, 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 Cio^^6^2^io'HO.' 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 Cj2Hj20j2-J-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 moi-e 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° -60), when in a state of health, even under great vicissi- tudes of climate; in birds it is sometimes as high as 109° (42°-8C). 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 difi'er 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 and 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 * Liebig, Chemistry of Food. 504 COMPOSITION OF THE BLOOD/ in the fibtin of arterial blood. The only other notable point of diflference is 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 eflfect 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 fibi'in 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 ^^"- ^'^'** is seen to consist of a transparent and nearly © colourless liquid, in which float about a countless ^^ O 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. (^ Q They are accompanied by colourless globules, fewer and larger, the white corpuscles of the blood. The blood-discs are found to present difterent appearances in the blood of difi'erent 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 coi*- ® © ^.o(\ phosphates, and sulphates of potassaand soda... j ' Carbonates of lime and magnesia; phosphates of\ (,,/^ , j.^ lime, magnesia, and iron ; sesquioxide of iron... / 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 ■ * Liebijr, Ilandwdrlerbuch, i. 885. « Ann. Chim. et de Phys. xlviH. 320 43 606 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 tlie 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 diapliragm. 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 hea»t developed in the act of combination is n 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 doe?; 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 coynbuation 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 conjecTture. 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 Tncmbrane, 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 caj^.ability 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, b^- 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 laody 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,' 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 air, a greater weight of oxygen is taken into the lungs, and absorbed into the blood at each inspiration. In this manner the temperature of the body is kept up, notwithstanding the piercing external cold ; a most marvellous adjustment of the nature of the food, and even of the inclinations and appetite of the man, to the circumstances of his existence, enable him to bear Avith 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 colouiing 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 chiuacter upon the serum of blood. LvMPH. — 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 * Auim:il Chemi.stiy, p. l-l. 508 MILK, BILE, URINE, ing a portion of soluble salts of the blood. The liquor amnii of the preg nant female, and the fluid of dropsy, are of this character. Mucus ANn Pus. — The slimy matter effused ^lpon the surface of vnriou!^ mucous membranes, as tlie lining of the alimentary canal, that of the blad- der, of the nose, lungs, &c., to which the general name mitcns 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 Avith ease, and the solution is precipi- tated by an addition of acid. Pus, the natural secretion of a wounded or otherwise injured surfixce, is J,. ...^ commonly a creamy, white, or yellowish '^* '"'■ liquid, which, under the microscope, ap- lP«9\yr.jj!i*(?^ {fSfi^^ijK pears to consist of multitudes of minute ©;^# y ©gS© globules (fig. 175, «); dilute acetic acid ^^/t^^/^r^ ^^^^ renders them transparent, and shows the ^(®>vW @ ^2 W^ internal nuclei {b). It is neither acid nor >>® ® ^ 4!^ ® ^ alkaline. Mixed with water, it communi- ^ ^% ig"^ ® ff^"5^ c^^^s ^ milkiness to the latter, but after a xsvy^ vi^ ^t^ ^ ^j^^g 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 ropiticss 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 URINARY 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- ^ O o *^5 °^ croscope of even modernte power, it is seen to ® co (P* 9 o*"*" o'°^ consist of a perfectly transparent fluid, in which o o »• "^ O" tf* ^"•'^* nbout numbers of transparent gloludo? ^o^o^f o^o^f^SfQO® (fig- l'^')« tJi^'^e consist of fat, surrounded by ® X^®qSV@° *^<%<^ *^" albuminous envelope, which can be broken ^^@o?® *^ 0° o *> mechanically, as in churning, or dissolved by ^°'^'^^i^^ Q w^^Q* *^'^ chemical action of caustic potassa, after « o®®."®^®® ^o 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 tlie f3 earthy phosphates being often thrown down from nearly neutral urine u^der such circumstances ; the phosphatic precipitate is, however, instantly dissolved by a drop of nitric acid. in diabetes the urine contains grape-sugar, the quantity of which com- monly increases with the progress of the disease, until it becomes enormous, the urine acquiring a density of 1040 and beyond. It does not appear that the urea is deficient alsoluteb/, although more difficult to discover from being mixed with such a mass of syrup. The smallest trace of sugar maj' be discovered in urine by Tromraer's test, (fig. 177,) formerly mentioned : a few drops of solution of sulphate of copper are added to the urine, and afterwards an excess of caustic potassa ; if sugar be present, a deep-blue liquid results, which, on boiling, deposits red suboxide of copper. With proper management, this test is very valuable ; it will even detect sugar in the blood of diabetic patients.' Urine containing sugar, when mixed with a little yeast, and put in a warm place, readily undergoes vinous fer- mentation, and afterwards yields, on distillation, weak alcohol, contaminated with ammonia. ^ The urine of children is said sometimes to contain benzoic acid ; it is pos- Bible that this may be hippuric acid. When benzoic acid is taken, the urine after a few hours yields on concentration, and the addition of hydrochloric acid, needles of hippuric acid, soiled by adhering uric acid. yielded a volatile acid in a notable quantity, which turned out to be acetic acid; a little ben- zoic acid was also noticed, and traced to a small amount of hippuric acid in the recent urine. The acid reaction of urine is ascribed to an acid phosphate of soda, produced by the partial Wecomposition of some of the common phosphate, the reaction of which is alkaline, by the organic acids (uric and hippuric) generated in the system, aided by the sulphuric acid con- .itantly produced by the oxidation of the protein-compounds of the food, or rather of the body. — Lancet, June. 1814. Still more recently Llebig has announced the discovery in the urine of kreatin and krea- tinine, already descriVod. Putrid urine contains kreatinine only. ' Dr. Bencc Jones, Med. Chirur. Trans, vol. xxvi. Great care must be taken in nsinj^thia *«!.^t. which depcnils on the instantaneous reiluction of the oxide of copper. By long boiling rery many organic substances pi-oduce this reaction. URINARY CALCULI 515 The deposit of buff-coloured or pinkish amorphous urate of ammonia, which so fi-equently occurs in urine upon cooling, after unusual exercise or Bliglit derangements of health, may be at once distinguished from a deposit of ammonio-magnesian pliospliate by its instant disappearance on the appli- cation of heat. Tlie earthy phosphates, besides, are hardly ever deposited from urine which has an acid reaction. The nature of the red colouring mutter which so often stains urinary deposits, especially in the case of free uric acid, is yet unknown. The yellow principle of bile has been observed in urine in severe cases of jaundice. The urine of the carnivorous mammifera is small in quantity, and highly acid ; it 'has a very offensive odour, and quickly putrefies. In composition it resembles that of man, and is rich in urea. In birds and serpents the uriue is a white pasty substance, consisting almost entirely of urate of ammo- nia. In herbivorous animals it is alkaline and often turbid from earthy car- bonates and phosphates ; urea is still the chai-acteristic ingredient, while of uric acid there is scarcely a trace; hippuric acid is usually, if not always, present, sometimes to a very large extent. AVhen the urine putrefies, this hippuric acid, as already noticed, becomes changed to benzoic acid. Urinary calculi. ^Stouy concretions, differing much in physical charac- ters and in chemical composition, are unhappily but too frequently formed in the bladder itself, and give rise to one of the most distressing complaints to which humanity is subject. Although many endeavours have been made to find some solvent or solvents for these calculi, and thus supersede the necessity of a formidable surgical operation for their removal, success has been but very partial and limited. Urinary calculi are genei'ally composed of concentric layers of crystalline or amorphous mattei% of various degrees of hardness. Very frequently the central point or nucleus is a small foreign body; curious illustrations of this "will be seen in any large collection. Calculi are not confined to man; the lower animals are subject to the same affliction; they have been found in horses, oxen, sheep, pigs, and almost constantly in rats. The following is a sketch of the principal characters of the different varie- ties of calculi : — 1. Uric Acid. — These are among the most common; externally they are smooth or warty, of yellowish or brownish tint ; they liave an imperfectly crystalline, dis- tinctly concentric structure, and are tolerably hard. Fig. 178.- Before the blowpipe the uric acid calculus burns away, leaving no ash. It is insoluble in water, but dissolves with f:icility in caustic potassa, with but little ammoniacal odour; the solution mixed with acid gives a copious white curdy precipitate of uric acid, which speedily becomes dense and crystalline. Cautiously heated with nitric acid, and then mixed willi a little ammonia, it gives the cha- racteristic reaction of uric acid, viz., deep pur- ple-red murexide. 2. Urate of Ammonia. — Calculi of urate of ammonia much resemble the preceding ; they are easily distinguished, however. Fig, 179, The powder boiled in water dissolves, and the solution gives a precipitate of uric acid when niixed with hydrochloric acid. It dissolves also in hot carbonate of potassa with copious '"•volution of ammonia. Fig. 178. Fii,^ 179. 618 URINARY C ALCU LI. Fig. 180. Fig. 181. 3. Fusible Calculus ; Fhosphate of Lime tvith Fhos^phate of Magnesia and Ammonia. — This is one of the most common kinds. The stone? are usually white or pale-coloured, smooth, earthy, and soft ; they often attain a large size. Fig. 180. Before the blowpipe this substance blackens from animal matter which earthy calculi always contain ; then becomes white, and melts to a bead with comparative facility. It is insoluble in caustic alkali, but • readily soluble in dilute acids, and the solution Is precipitated by ammonia. Calculi of unmixed phosphate of lime are rare, as also those of phosphate of magnesia and ammonia ; the latter salt is Bometimes seen forming small, brilliant crystals in cavities in the fusible calculus. 4. Oxalate of Lime Calculus; Mulberry Calculus. — The latter name is de- rived from the rough, warty character, and dai-k blood-stained aspect of this variety; it is perhaps the worst form of calculus. Fig. 181. It is ex- ceedingly hard ; the layers are thick and imper- fectly crystalline. Before the blowpipe the oxa- late of lime burns to carbonate by a moderate red-heat, and, when the flame is strongly urged, to quicklime. It is soluble in moderately strong hydrochloric acid by heat, and very easily in ni- tric acid. When finely powdered and long boiled in a solution of carbonate of potassa, oxalate of potassa may be discovered in the filtered liquid, when carefully neutralized by nitric acid, by white precipitates with solu- tions of lime, lead, and silver. A sediment of oxalate of lime in very minute, transparent, octahedral crystals, only to be seen by the microscope, is of common occurrence in urine in which a tendency to urate of ammonia deposits exists, 6. Cystic and Xanthic Oxides have already been described : they are very rare, especially the latter. Calculi of cystic oxide are very crystalline, and often present a waxy appearance externally ; sediments of cystic oxide are sometimes met with. As before mentioned, this substance is a definite crys- tallizable organic principle, containing sulphur to a large amount ; it is solu- ble both in acids and alkalis. When the solution in nitric acid is evaporated to dryness, it blackens ; when dissolved in a large quantity of caustic potassa, a drop of solution of acetate of lead added, and the whole boiled, a black pre- cipitate containing sulphide of lead makes its appearance. By these charac- ters cystic oxide is easily recognized. Xanthic oxide, also a definite organic principle, is distinguished by the peculiar deep-yellow colour produced when its solution in nitric acid is evapo- rated to dryness ; it is soluble in alkalis, but not in hydrochloric acid. Very many calculi are of a composite nature, the composition of the dif- ferent layers being occasionally changed, or alternating ; thus, urate of am- monia and oxalate of lime are not unfrequently associated in the same Btont. NERVOUS SUBSTANCE ; MEMBRANOUS TISSUE ; BONES. Nervous substance, — The brain and nerves consist of an albuminous substance, containing several remarkable fatty principles, capable of being extracted by alcohol and ether, some of which are yet very imperfectly known, and about 80 per cent, of water. Besides cholesterin, and a little ordinary fat, separated in the manner mentioned, M. Fr^my describes two MEMBRANOUS TISSUES. 617 new bodies,' cerebric acid and oho-phosphoric acid. The first is solid, white, and ci'ystalline, soluble without difficulty in boiling alcohol, and forming with hot water a soft, gelatinous mass. It melts when heated, and decom- poses almost immediately afterwards, exhaling a peculiar odour, and leaving a quantity of charcoal which contains free phosphoric acid, and is in conse- quence very difficult to bui'n. It combines with the alkalis, but forms in- soluble compounds. Cerebric acid contains in 100 parts — Carbon 66-7 Hydrogen 20-6 Nitrogen , 2-3 Oxygen 195 Phosphorus 0-9 100-0 The oleo-phosphoric acid has been even less perfectly studied than the preceding substance. It is of soft oily consistence, soluble in hot alcohol and ether, and saponifiable. When boiled with water, it is resolved into a fluid neutral oil, called cerebrolein, and phosphoric acid, which dissolves. The oily matter of the brain is sufficient in quantity to form with the albuminous portion a kind of emulsion, which, when beaten up, remains long suspended in water. Membranous tissues ; skin. — The composition of the many gelatin- giving tissues of the body is in great measure unknown ; even that of gela- tin itself is very doubtful, as several different substances may very possibly be confounded under this name. Dr. Scherer* has given, among many others, analyses of the middle coat of the arteries, which will serve as an example of a finely organized, highly elastic membrane, and of the coarse epidermis of the sole of the foot, with which it may be contrasted : — Artery coat. Epidermis. Carbon 53-75 61-04 Hydrogen 708 6-80 Nitrogen 15-36 17-23 Oxygen 23 81 24-93 100-00 100-00 A little sulphur was found in the epidermis. Hair, horn, nails, wool, and feathers have a nearly similar composition ; they all dissolve with disen- gagement of ammonia in caustic potassa, and the solution, when mixed with acid, deposits a kind of protein common to the whole. It is useless assign- ing foi-mulse to substances yet so little understood. The principle of tanning, of such great practical value, is easily explained. When the skin of an animal, carefully deprived of hair, fat, and other im- purities, is immersed in a dilute solution of tannic acid, the animal matter gradually combines with that substance as it penetrates inwards, forming a perfectly insoluble compound, which resists putrefaction completelj' ; this is leather. In practice, lime-water is used for cleansing and preparing the skin, and an infusion of oak-bark, or sometimes catechu, or other astringent matter, for the source of tannic acid. The process itself is necessarily a slow one, as dilute solutions only can be safely used. Of late years, how- ever, vai-ious contrivances, some of which shoAV great ingenuity, have been adopted with more or less success, for quickening the operation. All leather is not tanned ; glove-leather is dressed with alum and common salt, and ' Ann. Chim et Pbyp. 3rd series, ii. 463. " Anna] en der Chomie und rharmacic; xl. 50. 44 618 ANIMAL NUTRITION. afterwards treated with a preparation of the yolks of eggs, which contain an albuminous matter- and a yellow oil. Leather of this kind still yields a size by the action of boiling water. Boxes. — Bones are constructed of a dense celliilar tissue of membra- nous matter, made stiff and rigid by insoluble earthy salts, of which phos- phate of lime (SCaOjPOg) is the most abundant. Tlie proportions of earthy and animal matter vary very much with the kind of bone and with the age of the individual, as will be seen in the following table, in which the corres- ponding bones of an adult and of a still-born child are compared : — ADULT. CHILD. Inorganic Organic Inorganic Organic matter. matter. matter. matter. Femur 62-49 ... 87-51 57-51 ... 42-49 Humerus 63 02 ... 30-98 58 08 ... 41-92 Radius 60-51 ... 89-49 56-50 ... 43-50 Os temporum 63-50 ... 30-50 55-90 ... 44-10 Costa 67-49 ... 42-51 53-75 ... 46-25 The bones of the adult being constantly richer in earthy salts than those of the infant. The following complete comparative analysis of human and ox-bones ia due to Berzelius : — Human bones. Ox-bones. Animal matter soluble by boiling .... 32-17 ") ^q.90 Vascular substance 1-13/ losphate of lime, with a little ) ro m tt or uoride oi calcium / Ph( ill Carbonate of lime 11-30 3-85 Phosphate of magnesia 1-16 2-05 Soda, and a little common salt 1-20 8-45 10000 10000 The teeth have a very similar composition, but contain less animal matter ; their texture is much more solid and compact. The enamel does not contain more than 2 or 3 per cent, of animal matter. ON THE FUNCTION OF NUTRITION IN THE ANIMAL AND VEGETABLE KINGDOMS. The constant and unceasing waste of the animal body in the process of respiration, and in the various secondary changes therewith connected, ne- cessitates an equally constant repair and renewal of the whole frame by the deposition or organization of matter from the blood, which is thus gradually impoverished. To supply this deficiency of solid material in the circulating fluid is the office of the food. The sti-iking contrast which at first appears in the nature of the food of the two great classes of animals, the vegetable feeders and the carnivorous races, diminishes greatly on close examination : it will be seen, that, so far as the materials of blood, or, in other words, those devoted to the repair and sustenance of the body itself, are concerne i, the process is the same. In a flesh-eating animal great simplicity is observed in the construction of the digestive organs: the stomach is a mere enlarge- ment of the short and simple alimentary canal ; and the reason is plain : thf food of the creature, flesh, is absolutely identical in composition with its own blood, and with the body that blood is destined to nourish. In tiie sto- mach it undergoes mere solution, being brought into a state fitted for absorp- tion by the lacteal vessels, by which it is nearly all taken up, and at once conveyed into the blood; the excrements of such animals are little more ANIMAL NUTRITION. 519 than the comminuted bones, feathers, hair, and other matters which refuse to dissolve in the stomach. The same condition, that the food employed for tlie nourishment of the body must have the same or nearly the same chen)i- cal composition as the body itself, is really fulfilled in the case of animals that live exclusively on vegetable substances. It has been shown' that cer- tain of the azotized principles of plants, which often abound, and are never altogether absent, have a chemical composition and assemblage of properties which assimilate them in the closest manner, and it is believed even identify them, with the azotized principles of the animal body ; vegetable albumin, fibrin, and casein are scarcely to be distinguished from the bodies of the same name extracted from blood and milk. If a portion of wheaten flour be made into a paste with water, and cau- tiously washed on a fine metallic sieve, or in a cloth, a greyish, adhesive, elastic, insoluble substance will be left, called gluten or glutin, and a milky liquid will pass through, which by a few hours' rest becomes clear by de- positing a quantity of starch. If now this liquid be boiled, it becomes again turbid from the production of a flocculent precipitate, which, when collected, washed, dried, and purified from fat by boiling with ether, is found to have the same composition as animal albumin. The glutin itself is a mixture of true vegetable fibrin, and a small quantity of a peculiar azotized matter called gliadin, to which its adhesive properties are due. The gliadin may be extracted by boiling alcohol, together with a thick, fluid oil, which is separable by ether ; it is gluey and adhesive, quite insoluble in water, and, when dry, hard and translucent like horn ; it dissolves readily in dilute caus- tic alkali, and also in acetic acid. The fibrin of other grain is unaccompa- nied by gliadin ; barley and oatmeal yield no glutin, but incoherent filaments of nearly pure fibrin. Vegetable albumin in a soluble state abounds in the juice of many soft succulent plants used for food ; it may be extracted from potatoes by mace- rating the sliced tubers in cold water containing a little sulphuric acid. It coagulates when heated to a temperatm-e dependent upon the degree of con- centration, and cannot be distinguished when in this state from boiled white of egg in a divided condition. Almonds, peas, beans, and many of the oily seeds, contain a principle which bears the most striking reseinblance to the casein of milk. When a solution of this substance is heated, no coagulation occurs, but a skin forms on the surface, just as with boiled milk. It is coagulable by alcohol, and by acetic acid : the last being a character of importance. Such a solution mixed with a little sugar, an emulsion of sweet almonds, for instance, left to itself, soon becomes sour and curdy, and exhales an offensive smell ; it is then found to contain lactic acid. All these substances dissolve in caustic potassa with production of a small quantity of alkaline sulphide; the filtered solutions mixed with excess of acid give precipitates of protein. The following is the composition in 100 parts of vegetable albumin and fibrin ; it will be seen that they agree very closely with the results before given: — Albumin. Fibrin. Carbon 5501 54-60 Hydrogen 7-23 7-30 Nitrogen 15-92 15-81 Oxygen, sulphur, and phosphorus 21-84 22-29 10000 10000 Liebig, Ann. der Cbeni. uud riiarm. xxxix. 129. 520 ANIMAL NUTRITION. The composition of vegetable casein, or legumin, has not been so well ma-la out; so much discrepancy appears in the analyses as to lead to the suppo- sition that different substances have been operated upon. The great bulk, however, of the solid portion of the food of the herbivora consists of bodies which do not contain nitrogen, and therefore cannot yield tjustenance in the manner described : some of these, as vegetable fibre or lig- nin, and waxy matter, pass unaltered through the alimentary canal ; others, as starch, sugar, gum, and perhaps vegetable fat, are absorbed into the sys- tem, and afterAvards disappear entirely: they are supposed to contribute very largely to the production of animal heat. On these principles. Professor Liebig ' has very ingeniously made the dis- tinction between what he terms plastic elements of nutrition and elements of respiration ; to the former class belong Vegetable fibrin, Vegetable albumin, Vegetable casein, Animal flesh. Blood. To the latter, Fat, Starch, Gum, Cane-sugar, Grape-sugar, Milk-sugar, Pectine, Alcohol ? In a flesh-eating animal the waste of the tissues is very rapid, the tem- perature being, as it were, kept up in great measure by the burning of azotized matter ; in a vegetable feeder it is probably not so great, the nou' azotized substances being consumed in the blood in the place of the organic fabric. When the muscular movements of a healthy animal are restrained, a genial temperature kept up, and an ample supply of food containing much amyla- ceous or oily matter given, an accumulation of fat in the system rapidly takes place ; this is well-seen in the case of stall-fed cattle. On the other hand, when food is deficient, and much exercise is taken, emaciation results. These efi'ects are ascribed to difference in the activity of the respiratory function ; in the first instance, the heat-food is supplied faster than it is consumed, and hence accumulates in the form of fat; in the second, the conditions are re- versed, and the creature is kept in a state of leanness by its rapid con- sumption. The fat of an animal appears to be a provision of nature for the maintenance of life during a certain period under circumstances of privation. The origin of fat in the animal body has recently been made the subject of much animated discussion ; on the one hand it was contended that satis- factory evidence exists of the conversion of starch and saccharine substances into fat, by separation of carbon and oxygen, the change somewhat resem- bling that of vinous fermentation : it was argued, on the other side, that oily or fatty matter is invariably present in the food supplied to the domestic ani- mals, and that this fat is merely absorbed and deposited in the body in a slightly modified state. The question has now been decided in favour of the first of these views, which was enunciated by Professor Liebig, by the very chemist who formerly advocated the second opinion. By a series of very Oeautiful experiments, MM. Dumas and Milne Edwards proved that bees exclusively feeding upon sugar were still capable of producing wax, whicli was pointed out as a veritable fact. • Auiinal Chemistry, p. 96. ANIMAL NUTRITION. -621 It is not known in what manner di(jesfion, the reduction in the stomach of Jie food to a nearly fluid condition, is performed. The natural secretion of that organ, the gastric juice, is said to contain a very notable quantity of free hydrochloric acid. Dilute hydrochloric acid, aided by a temperature of 98° (;iG°-GC) or 100° (37°-7C), dissolves coagulated albumin, fibrin, &c. ; but many hours are required for that purpose. The gastric secretion has been supposed to contain a peculiar organic principle called pepsin, said to have been isolated, to which this power of dissolving albuminous substances in conjunction with the hydrochloric acid is attributed. In the saliva a pecu- liar organic principle exists, which causes the conversion of starch into sugar. If starch is held in the mouth even for two minutes, this change is found to occur. The active cause of this change has been looked on as a kind of ani- mal diastase. The food of animals, or rather that portion of the food which is destined to the repair and renewal of the frame itself, is thus seen to consist of sub- stances identical in composition with the body it is to nourish, or requiring but little chemical change to become so. The chemical phenomena observed in the animal system resemble so far those produced out of the body by artificial means, that they are all, or nearly all, so far as is known, changes in a descending series ; albumin and fibrin are probably more complex compounds than gelatin or the membrane which furnishes it ; this, in turn, has a far greater complexity of constitution than urea, the regular form in which rejected azotized matter is conveyed out of the body. Tiie animal lives by the assimilation into its own substance of the most complex and elaborate products of the organic kingdom ; — products which are, and, apparently, can only be, formed under the influence of vege- table life. The existence of the plant is maintained in a manner strikingly dissimilar: the food supplied to vegetables is wholly inorganic ; the carbonic acid and nitrogen of the atmosphere, the water which falls as rain, or is deposited aa dew ; the minute trace of ammoniacal vapour present in the air ; the alkali and saline matter extracted from the soil; — such are the substances which yield to plants the elements of their growth. That green healthy vegetables do possess, under circumstances to be mentioned immediately, the property of decomposing carbonic acid absorbed by their leaves from the air, or con- veyed thither in solution through the medium of their roots, is a fact posi- tively proved hj direct experiment, and rendered certain by considerations of a very stringent kind. To eftect this very remarkable decomposition, the influence of light is indispensable ; the ditfuse light of day suffices in some degrees, but the direct rays of the sun greatly exalt the activity of the pro- cess. The carbon separated in this manner is retained in the plant in union with the elements of water, with which nitrogen is also sometimes associated, while the oxygen is thrown ofi" into the air from the leaves in a pure and gaseous condition. The eS"ect of ammoniacal salts upon the growth of plants is so remarkable, as to leave little room for doubt concerning the peculiar function of the am- monia recently discovered in the air. Plants which in their cultivated state contain, and consequently require, a large supply of nitrogen, as wheat, and the cereals in general, are found to be greatly benefited by the application to the land of such substances as putrefied urine, which may be looked upon as a solution of carbonate of ammonia, the guano'- of the South Seas, which » Onano is tlie partially decomposed duno; of birds, found in immense quantity on some of the barren islets of the western coast of South America, as that of Teru. More recently, similar deposits have been found on the coast of Southern Africa. The guano now imported into England from these localiiies is usually a soft, brown powder, of various shades of Bolour. White specks of boue eavLli, and sometimes masses of saline matter, may be founa 522 VEGETABLE NUTRITION. , usually contains a large proportion of ammoniacal salt, and even of a pure sulphate of ammonia. Some of these manures doubtless owe a part of their value to the phosphates and alkaline salts they contain ; still, the chief efi'ect is certainly due to the ammonia. Upon the members of the vegetable kingdom thus devolves the duty of building up, as it were, out of the inorganic constituents of the atmosphere, — the carbonic acid, the water, and the ammonia, — the numerous complicated organic principles of the perfect plant, many of which are afterwards des- tined to become the food of animals, and of man. The chemistry of vege- table life is of a very high and mysterious order, and the glimpses occasion- ally obtained of its general nature are few and rare. One thing, however, is manifest, namely, the wonderful relations between the two orders of or- ganized beings, in virtue of which the rejected and refuse matter of the one is made to constitute the essential and indispensable food of the other. While the animal lives, it exhales incessantly from its lungs, and often from its skin, carbonic acid ; when it dies, the soft parts of its body undergo a series of chemical changes of degradation, which terminate in the production of carbonic acid, water, carbonate of ammonia, and, perhaps, other products in small quantity. These are taken up by a fresh generation of plants, which may in their turn serve for food to another race of animals. In it. That which is most recent, and prob.ably most valuable as manure, often contains un- decomposed uric acid, besides much oxalate or bydrochlorate of ammonia, and alkaline phos- phates, and other salts: it has a most offensive odour. The specimens taken from oldei deposits have but little smell, are darker in colour, contain no uric acid, and much less am- n)oniacal salt; the chief components are bone-earth, a peculiar dark-coloured organic matteri and soluble inorganic sal to. See also page 443. SUBSTANCES OBTAINED FROM TAR. 523 SECTION IX. ON CERTAIN PRODUCTS OF THE DESTRUCTIVE DISTILLATION AND SLOW PUTREFACTIVE CHANGE OF ORGANIC MATTER. SUBSTANCES OBTAINED FKOM TAR. There are three principal varieties of tar: — (1.) Tar of the wood-vinegar maker, procured by the destructive distillation of dry hard wood; (2.) Stockholm tar, so largely consumed in the arts, as in ship-building, &c., ■which is obtained by exposing to a kind of rude distillatio per descensum the roots and useless parts of resinous pine and fir-timb6r; and, lastly, (3.) Coal or mineral tar, a by-product in the manufacture of coal-gas. This is viscid, black, and ammoniacal. All these tars yield by distillation, alone or with water, oily liquids of extremely complicated nature, from which a number of curious products, to be presently described, have been procured; the solid brown or black resi- due constitutes pitch. Hard-wood tar furnishes the following: — Paraffin ; tar-oil stearin. — This remarkable substance is found in that part of the wood-oil which is heavier than water; it is extracted by re- distilling the oil in a retort, collecting apart the last portions, gradually adding a quantity of alcohol, and exposing the whole to a low temperature. Thus obtained, paraffin appears in the shape of small, colourless needles, fusible at 110° (43°-3C) to a clear liquid, which on solidifying becomes glassy and transparent. It is tasteless and inodorous ; volatile without decomposition; and burns, when strongly heated, with a luminous yet smoky flame. It is quite insoluble in water, slightly soluble in alcohol, freely in ether, and miscible in all propoi'tions, when melted, with both fixed and volatile oils. The most energetic chemical reagents, as strong acids, Jilkalis, chlorine, &c., fail to exert the smallest action on this substance; it is not known to combine in a definite manner with any other body, whence its extraordinary name, from paritm ajjinis. Paraffin contains carbon and hydrogen only, and in the same proportions as in olefiant gas, or CH. M. Lewy, of Copenhagen, makes it CgoHji. The rational formula is unknown. EupiONE.' — This is the chief component of the light oil of wood-tar; i* occurs also in the tar of animal matters, and in the fluid product of the dis* tillation of rape-seed oil. Its separation is effected by the agency of concen- trated sulphuric acid, or of a mixture of sulphuric acid and nitre, which oxidizes and destroys most of the accompanying substances. In a pure state, it is an exceedingly thin, colourless liquid, of agreeable aromatic odour, but destitute of taste ; it is the lightest known liquid, having a den- sity of 655. At 116° (46°6C) it boils and distils unchanged. Dropped upon paper, it makes a greasy stain, which after a time disappears. Eupione is very inflammable, and burns with a bright luminous flame. In water it is • From tZ, gfiod, Insautiful. and itiov, fat. 624 SUBSTANCES OBTAINED FROM TAR. quite insoluble, in rectified spirit nearly so, but with ether and oils freely miscible. Eupione is a hydrocarbon ; according to M. Hess it consists of CglTg. It is very probable that eupione frequently contains and sometimes entirely consists of hydride of amyl (see page 389). Other volatile oils, having a similar origin, and perhaps a similar compo- sition, but differing from the above in specific gravity and boiling-point, are sometimes confounded with eupione. The study of these substances presents ' many serions difl[iculties. It is even doubtful whether the eupione be not formed by the energetic chemical agents employed in its sitpposed purifica- tion, and this remark applies with even greater force to the next three or four tar-products to be noticed. PiCAMAR.' — A component of the heavy oil of wood ; it is a viscid, colour- less, oily liquid, of feeble odour, but intensely bitter taste. Its density is 1-095, and it boils at 518° (270°C). It is insoluble in water, but dissolves in all proportions in alcohol, ether, and the oils. The most characteristic property of picamar is that of forming with the alkalis and ammonia crys- talline compounds, which, although decomposed by water, are soluble with- out change in spirit. The composition of this substance is unknown. Kapnomor.'' — Such is the name given by Dr. Reichenbach to another oily liquid obtained from the same source as the last, by a long and complex process, in which strong solutions of caustic potassa are freely used. It is described as a colourless volatile oil, of high boiling-point, and rather lighter than water; it has an odour of ginger, and a taste feeble at first, but after- wards becoming connected with an insupportable sense of sufi'ocation. Water refuses to dissolve it; alcohol and ether take it up easily; and oil of vitriol combines with it, giving rise to a complex acid, the potassa-salt of Wliich is crystallizable. Its composition is unknown. CEnKiRRT.' — The lighter oil of hard-wood tar contains a substance, separ- able from the eupione, &c., by caustic alkalis, which in contact with oxidizing agents, as sulphate of sesquioxide of iron, chromic acid, or even atmos- pheric air, yields a mass of small, red, reticulated crystals, infusible by heat, and soluble in concentrated sulphuric acid with deep indigo-blue colour. This substance is insoluble in water, alcohol, and ether ; nothing is known respecting its composition. Kreosotk.* — This is by far the most important and interesting body of the group ; its discovery is due to Dr. Reichenbach ; it is the principle to which wood-smoke owes its power of curing and preserving salted meat and other provisions. Kreosote is most abundantly contained in the heavy oil of beech-tar, as procured from the wood-vinegar maker, and is thence ex- tracted by a most tedious and complicated series of operations ; it certainly pre-exists, however, in the original material. The tar is distilled in a me- tallic vessel, and the ditt'erent products collected apart ; the most volatile portion, which is lighter than water, and consists chiefly of eupione, is re- jected ; the second portion is denser, and contains the kreosote, and is set aside; the distillation is stopped when paraffin begins to pass over in quan- tity. The impure kreosote is first agitated with carbonate of potassa to remove adliering acid, separated, and re-distilled, the first part being again rejected; it is next strongly shaken with a solution of phosphoric -acid, and again distilled ; a quantity of ammonia is thus separated. Afterwards, it is dissolved in a solution of caustic potassa of specific gravity 1-12, and de- ' From pix, and amm'us, in allusion to its bitter taste. * From KUiiVdi, smoke, ftoipa, pan. ' From cixlrium, the- old name for acid tar-water, and rete, a net. * Derived from Kpfai, tiesb, and ffuJ^w, I preserve. SUBSTANCES OBTAINED FROM TAR. 525 canted from the insoluble oil which floats on the surface ; this alkaline liquid is boiled, and left some time in contact with air, by which it acquires a brown colour from the oxidation of some yet unknown substance present in the crude product. The compound of kreosote and alkali is next decomposed by sulphuric acid : the separated kreosote is again dissolved in caustic potassa, boiled in the air, and the solution decomposed by acid, and this treatment repeated until the product ceases to become coloured by the joint influence of oxygen and the alkaline base. When so far purified, it is well washed with water, and distilled. The first portion contains water; that which succeeds is pure kreosote. In this condition kreosote is a colourless, somewhat viscid oily liquid, of great refractive and dispersive power. It is quite neutral to test-paper ; it has a penetrating and most peculiar odour, that, namely, of smoked meat, and a pungent and almost insupportable taste when placed in a very small quantity upon the tongue. The density of this substance is 1-037, and its boiling-point 397° (202° -SC). It inflames with difficulty, and then burns with a smoky light. When quite pure, it is inalterable by exposure to the air ; much of the kreosote of commerce becomes, however, under these cir- cumstances, gradually brown. 100 parts of cold water take up about IJ parts of kreosote ; at a high temperature rather more is dissolved, and the hot solution abandons a portion on cooling. The kreosote itself absorbs water also to a considerable extent. In acetic acid it dissolves in much larger quantity. Alcohol and ether mix with kreosote in all proportions. Concentrated sulphuric acid, by the aid of heat, blackens and destroys it. Caustic potassa dissolves kreosote with great facility, and forms with it a definite compound, which crystallizes in brilliant pearly scales. Kreosote consists of carbon, hydrogen, and oxygen, but its exact compo- sition is yet uncertain. The formula C,4Hg02 has been given. The most remarkable and characteristic feature of the compound in ques- tion is its extraordinary antiseptic power. A piece of animal flesh steeped in a very dilute solution of kreosote dries up to a mummy-like substance, but absolutely refuses to putrefy. The well-known efficacy of impure wood- vinegar in preserving provisions is with justice attributed to the kreosote it contains ; and the effect of mere wood-smoke is also thus explained. In a pure state, kreosote is sometimes employed by the dentist for relieving tooth- ache arising from putrefactive decay in the substance of the tooth. Chrysen and pyren. — M, Laurent extracted from pitch, by distillation at a high temperature, two new solid bodies, to which he gave the preceding names ; they condense together, with a quantity of oily matter, partly in the necK of the retort, and partly in the receiver, and are separated by the aid of ether. Chrysen, so called from its golden colour, is a pure yellow, crystal- line powder, which fuses by heat, and sublimes without much decomposition. It is insoluble in water and alcohol, and nearly insoluble in ether: warm oil of vitriol dissolves it, with the development of a beautiful deep-green colour. Boiling nitric acid converts it into an insoluble red substance, which has not been studied. Chrysen is composed of CgH. Fyrm differs from the preceding substance in being colourless, crystal- lizing in small, soft, micaceous scales, soluble in boiling alcohol and ether. It is fusible and volatile. Pyren contains C5H2. Oil of ordinary tar, obtained by distillation alone, or with water, consists in great measure of unaltered oil of turpentin, mixed, however, with em- pyreumatic oily products, which give it a powerful odour and a dark colour The residual pitch contains much pine-resin, and thus differs from the solid portion of the hard wood-tar so frequently mentioned. 626 VOLATILE PRINCIPLES OP COAL-TAR. Volatile Principles of Coal- Tar. Co.al-tar yields on distillation a large quantity of thin, dark-c«Ioured, volatile oil, which, when agitated with dilute sulphuric acid to remove am- monia, and twice rectified with water, becomes nearly colourless : it is very volatile, lighter than water, very inflammable, and possesses in a high degree the property of dissolving caoutchouc, on which account it is vei*y exten- sively used in the manufacture of water-proof fabrics containing that material. This coal-oil is a mixture of a great variety of liquids and solids dissolved in the oil. By the action of acids and alkalis, this mixture may be conve- niently divided into three separate groups. (1) A group of basic compounds soluble in acids; (2) an acid portion soluble in alkalis; and (3) a group of neutral constituents. The basic constituents form but a small part of coal-tar-oil. They are ex- tracted by agitating successively large quantities of the oil with hydrochloric acid, and afterwards distilling the acid watery liquid obtained with excess of hydrate of lime. The bases thus obtained consist chiefly of picoline (see page 465), aniline (see page 459), and leucoline (see page 464), and are separated by distillation ; these three compounds boiling at very different temperatures. The acid portion of coal-tar-oil consists essentially of carbolic acid or phenol. Carbolic acid ; phenol. — Common coal-tar-oil is agitated with a mixture of hydrate of lime and water, the whole being left for a considerable time ; the aqueous liquid is then separated from the undissolved oil, deconiposed by hydrochloric acid, and the oily product obtained purified by cautious dis- tillation, the first third only being collected. Or crude coal-oil is subjected to distillation in a retort furnished with a thermometer, and the portion which passes over between the temperatures of 300° — 400° (149° — 204°-5C) collected apart. This product is then mixed with a hot strong solution of caustic potassa, and left to stand ; a whitish, somewhat crystalline, pasty mass is obtained, which by the action of water is resolved into a light oily liquid and a dense alkaline solution. The latter is withdrawn by a syphon, decomposed by hydrochloric acid, and the separated oil purified by contact with chloride of calcium and re-distillation. Lastly, it is exposed to a low temperature, and the crystals formed drained from the mother-liquor and carefully preserved from the air. Pure carbolic acid forms long colourless prismatic needles, which melt at 95° (35°C) to an oily liquid, boiling at 370° (180°C), and greatly resembling kreosote' in many particulars, having a very penetrating odour and burning taste, and attacking the skin of the lips. Its sp. gr. is 1-065. It is slightly soluble in water, freely in alcohol and ether, and has no acid reaction to test-paper. The crystals absorb moisture with avidity, and liquefy. It co- agulates albumin. Sulphur and iodine dissolve in it; nitric acid, chlorine, and bromine attack it with energy. Carbolic acid contains CigHjO,!^. In its chemical deportment carbolic acid stands very near the alcohols, a fact to which allusion has been made already in former sections (see pages 399 and 401) ; we may assume in it a compound radical, phenyl, CijHgrrsPyl, analogous to ethyl, when carbolic acid becomes Pyl 0,110, or hydrated oxide wf phenyl. With sulphuric acid, hydrate of oxide of phenyl forms the compound acid, mlpliaphenic acid, Ci2H50,2S05,nO=Pyl 0,2S03,HO, which assumes a syrupy A gre.at de.il of the kreosote which occurs in commerce is, in fact, nothiug but moi'e or loss pure carbohc acid. VOLATILE PRINCIPLES OF COAL-TAR. 527 state in the dry vacuum. This acid closely corresponds to sulphovinic acid (see page o58). The baryta-salt crystallizes from alcohol in minute needles. Phonyl-alcohol dissolves potassium with evolution of hydrogen, a com- pound OialljOjKO being produced, which is analogous to the substance formed in a similar manner from common alcohol (see page 347). On heating this potassa-compound Avith iodide of methyl, ethjd, or amyl, a series of double ethers are produced represented by the following formulae : — Oxide of phenyl and methyl PylO,MeO = C,2n50,C2H30 = CiJI^Oj Oxide of phenyl and ethyl PylOjAeO = Ci2H50,C4H30 = C,6H,(,0j Oxide of phenyl and amyl Pyl0,Ay0 = CiglWCjoHiiO = CaallieOg Those substances also described by the names aniiol (because it is likewise produced by th«} distillation of anisic acid (see page 491), phenelol and phe- namylol are evidently analogous to the compounds of oxide of methyl with those of ethyl and amyl, which have been mentioned in pages 382 and 389. A chloride of phenyl, CigHgClrrzPylCl, has been produced by the action of pentachloride of phosphorus upon hydrated oxide of phenyl. This com- pound, however, which is a heavy oil, is but very imperfectly known. Cyanide of phenyl, C,4H5N=C,2ll5C2N=PylCy, has not yet been produced from phenyl-alcohol directly. The substance, however, which has been de- scribed under the name of benzonitrile (page 401), is both by composition and deportment cyanide of phenyl, perfectly analogous to cyanide of ethyl (see page 354). Boiled with potassa it is converted into ammonia and ben- zoic acid, cyanide of ethyl furnishing ammonia and propionic acid. Starting from this decomposition, benzoic acid may be viewed as phenyl-oxalic acid ^i4^^5^3'HO=Ci2H5,C203,HO, just as propionic acid may be regarded as ethyl-oxalic acid (see page 392). Hydrated oxide of phenyl when treated with chloride of benzoyl (see page 400) yields hydrochloric acid and a white fusible crystalline compound which is benzoaie of phenyl €521150,0,411503= PylO,BzO, analogous to benzoate of ethyl; when heated with ammonia, phenyl-alcohol yields aniline G ^2^1^'^ z=z CjallsHgN^PylHgN {phenylamine), the ethylamine of the phenyl-series (see page 4o9). The following table gives a synopstis of the phenyl-compounds, which have been placed iu juxtaposition with the corresponding terms of the ethyl- series : — Phenyl-alcohol PylO,HO AeO,HO Ethyl-alcohol ^""potassl ^^^"^^"}^^^^'^^ AeO,KO Oxide of ethyl-potassa Sulphophenic acid PylO,2S03,HO AeO,2S03,HO Sulphovinic acid AeO Oxide of ethyl Chloride of phenyl PylCl(?) Aecl Chloride of ethyl Cyanide of phenyl | p ,p ^ f Cyanide of ethyl (pro- (benzonitrile) /^ •>'''- J^ ^^^J \ pio nitrile) Benzoate of phenyl PylOjPylCjOa AeO,Ae,C203 Propionate of ethyl Phenyl-amine (aui- 1 x^rr -n 1 attt * t-.xu ^ jj^^ ^ vlSrigPyl NIT^Ae Ethylamine Phenyl-urea C2(n3Pyl)N02 C2(H3Ae)N02 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°-oC) answering verjr 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 witL 528 VOLATILE PRINCIPLES OP 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(li2C]3)0,lIO. By the action of a great excess of chlorine an analogous acid richer in chlo- rine is formed. It is called chlorophcnusic acid, and contains CjjClgOjHO. Brornophenisic 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, Ci2H4N06,HO = Cj2(H4N04)0,HO. Nitrophencsic 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. Nitrophencsic 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° (104°C) 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 Ci2H3N209,HO=C,2H3(N04)20,HO. Nitro- phenisic acid is identical with picric or carbazotic acid (see page 473). It may be prepared with great economy from impure nitrophencsic 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 C,2H2N30i3,HO=Ci2H2(N04)30,HO.' The following table exhibits the relation of these substitution-products; — Phenyl-alcohol CjaHg 0,H0 = Phenol I Chlorophenisic acid 0,2(112013) 0,H0 = Trichlorophenol Nitrophenasic acid C,2(Il4N04) 0,HO = Nitrophenol Nitrophencsic acid C,2(H3[N04]2) 0,HO = Binitrophenor - Nitrophenisic acid C,2(H2[N04]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 408). They are chiefly benzol, toluol, xylol, cumol, and cymol.'' The solid hydrocarbons are naphthalin and para- naphthalin together with several similar substances less perfectly known. * Ann. Chim. et Phys. 3d scries, iii. 195. ' The same hydrocarbons have been lately found by M. Cahours in the oily liquids pre ripitated by water from commercial wood-ppirits (^see page 387). VOLATILE PRINCIPLES OP COAL-TAR. 529 Naphthalin. — 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° (80°C) 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 CyjH^ or C^q^^. 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 C2oH7S205,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 name 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 (C20H8CI4) 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. Phthalic acid is bibasic, and contains CjgH40g,2HO; when heated it loses 2 eq. of water, and becomes Ci6^4^6* Treated with fuming nitric acid it yields a nitro-acid, nitro-phtha- lic acid, Ci6(H3N04) Og, 2H0. When distilled with baryta it is converted into benzol : — C,6^l608-f4BaO = 4(BaOCOj)-fC,2H8 Phthalic 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 J»f one of the chlorine products of naphthalin, of chloronaphthalu acid, both in composition and properties with alizarin. This substance con- tains C2o(H5Cl)06, and may be viewed as chloralizarin : — Alizarin Cgg Hg Og Cloronaphthalic acid C2o(H5Cl)08. 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 ai'c, however, usually smaller and less distinct. It melts at 356° (180°C), and boils at 570° (299°C), 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 CgQHjj. PETROLEUM, NAPHTHA, AND OTHEK ALLIED SUBSTANCES. Pit-coal, lignite or hrotcn coal, jet, bitumen of various "km^s, petroleum or rcck-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- epheric 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- sive 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 Df many of the now lost species which ouce 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 cf comparatively small value ; it resembles peat, giving but little flame and ^mitting 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 w^orld ; 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 Cj^HigOg. 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 CioHg. 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 Vei'de 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 lb. 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 : — Reiiniie, 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 retime 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 04911,40 ; it is generally associated with a hydrocarbon idryl, which contains C42H14. Ozokerite, or fossil wax, is found in Moldavia, in a layer of bituminous shale ; it is brownish and has a somewhat pearly appearance ; it is fusible below 212° (100°C), and soluble with difficulty in alcohol and ether, but easily in oil of turpentin. It appears to contain more than one definite principle. APPENDIX. i5« (688) 534 APPENDIX. HYDROMETER TABLES OOHPARIBON OF THE DEGEEES OF BAUME's HTDEOMETEE WITH THE EEAl SPECIFIC GRAVITIES. 1. For liquids heavier than water. Degrees. Specific Gravity. Degrees. Specific Gravity. Degrees. Specific Gravity. 1000 26 1-206 52 1-520 1 1-007 27 1-216 53 1-535 2 1013 28 1-225 54 1-551 • 3 1-020 29 1-235 55 1-567 4 1-027 30 1-245 56 1-583 5 1-034 31 1-256 57 58 1-600 6 1041 32 ]'24T 1-617 7 1048 83 l-27f 59 1-634 8 1056 34 1-288 60 1-652 9 1063 35 1-299 61 1-670 10 1070 36 1-310 62 1-689 11 1-078 37 1-321 63 1-708 12 1085 38 1-333 64 1-727 13 1-094 39 1-345 65 1-747 14 1-101 40 1-357 66 1-767 16 1-109 41 1 369 67 1-788 16 1-118 42 1-381 68 1-809 17 M26 43 ] -395 69 1-831 18 1-134 44 1 -407 70 1-854 19 1143 45 1 420 71 1-877 20 M52 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 M88 50 1-490 76 2-000 25 1-197 51 1-495 APPENDIX. 58^ 2. Baume's Hydrometer for liquids lighter than water. Degrees. Specific Gravity. Degrees. Specific Gravity. Degrees. Specific Gravity. 10 1000 27 0-896 44 0-811 11 0-993 28 0-890 45 0-807 12 0-986 29 0-885 46 0-802 13 0-980 30 0-880 47 0-798 14 0-973 31 0-874 • 48 0-794 15 0-967 32 0-869 49 0-789 16 0-960 33 0-864 50 0-785 17 0-954 34 0-859 51 0-781 18 0-948 35 0-854 52 0-777 19 0-942 36 0-849 53 0-773 20 0-936 37 0-844 54 0-768 21 0-930 38 0-839 55 0-764 22 0-924 39 0-834 56 0-760 23 0-918 40 0-830 57 0-757 24 0-913 41 0-825 58 0-753 25 0-907 42 0-820 59 0-749 26 0-901 43 0-816 60 0-745 These two tables are on the authority of M. Francoeur ; they are taken from the Handworlerbuch der Chemie of Liebig and Poggendorff. Baum^'a hydrometer is very commonly used on the Continent, especially for liqtiidg heavier than water. For lighter liquids, the hydrometer of Cartier is often employed in France, Cartier's degrees differ but little from those of Baum6. 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 sp. 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 DE. DALTON's TABLE OP THE ELASTIC FORCE OF VAPOUR OF WATER AT DIFFERENT TEMPERATURES, EXPRESSED IN INCHES OF MERCURY. Temperature. Temperature. Temperature. Force. Force. Force. Fah. Cent. Fah. Cent Fah. Cent. 32° Oo-O 0-200 57° 13°-88 0-474 90° 32° -2 1-36 33 0°-55 0-207 58- 140.4 0-490 95 35° 1-58 34 1°-1 0-214 59 15° 0-507 100 870.77 1-86 35 l°-66 0-221 60 15°-5 0-524 105 40° -5 2-18 36 2° -2 0-229 61 16°-1 0-542 110 43°-3 2-53 37 2°-77 0-237 62 j6°-66 0-560 115 46°-l 2-92 38 3°-3 0-245 63 17°-2 0-578 120 48° -88 3-33 39 3°-88 0-254 64 170.77 0-597 125 51°-66 3-75 40 40.4 0-263 65 ]8°-3 0-616 130 54° -4 4-34 41 5° 0-273 66 18°-88 0-635 135 57°-2 5-00 42 5°-55 0-283 67 19°-4 0-665 140 60° 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 1 46 70.77 0-328 71 21°-66 0-745 170 76°-66 12-13 47 8°-3 0-339 72 22°-2 0-770 180 82°-2 15-15 48 8°-88 0-351 73 22°-77 0-796 190 87°-77 1900 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° 3000 52 11°-1 0-401 77 25° 0-910 220 104°-4 34-99 53 110-66 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 OP THE PBOPOETION BY WEIGHT OF ABSOLUTE OR REAL ALCOHOL IN 100 PABT8 OF SPIRITS OP DIFFERENT SPECIFIC GRAVITIES. (FOWNES.) Sp.Gr. at60° (150-5C). Per cent, of real Alcohol. Sp. Gr. at 60° (150-60.) Per cent, of real Alcohol. Sp. Gr. at 60° (150-5C). 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 0-9047 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 69 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 PKINCIPAL MINERAL WATERS OF GERMANS Grains of Anhydrous Ingredients in One Pound Troy. Carlsbad. Ems. Schlesischer. Obersalz- Brunnen. Carbonate of Soda 7-2712 0-0150 0*0655 1-7775 1-0275 0-0048 00208 0-0012 00019 14-9019 6-9820 0-oi84 0-4329 8-0625 0-0405 0-0022 00080 0-8555 0-5915 0-0028 0-0120 0-*66l4 0-4050 0-0338 6-7255 0-'6bl4 0-3 104 7-6211 0-0170 1-5464 1-5496 0-0026 0-0356 0-3160 2-5106 0-01*64 0-'8682 0-"6051 0-'2423 Ditto of Lithia Ditto of Baryta Ditto of Strontia Ditto of Lime Ditto of Magnesia Ditto (proto) of Manganese Ditto (proto) of Iron....... Sub-Phos. of Lime .- Ditto of Alumina ./ Sulphate of Potassa Ditto of Soda Ditto of Lithia Ditto of Lime Ditto of Strontia Ditto of Magnesia Nitr. of Magnesia Chlor. of Ammonium Ditto of Potassium Ditto of Sodium Ditto of Lithium Ditto of Calcium Ditto of Magnesium Ditto of Strontium Bromide of Sodium Iodide of Sodium Fluoride of Calcium Alumina Silica Total Carbonic Acid Gas in 100 cubic inches Temperature - } 31-4606 68 Sprud. 165° (73°-8C) Neub. 138° (58° -8C) Muhl. 128° (53°-3C) Ther. 122° (50°C) Berzelius. 160525 61 Kess. 117° (47° -2C) Kran. 84° (28° -8C) Struve. 14-7809 98 58° (14° 5C) Struve. • Analyzed by APPENDIX, 539 TABLE OF ANALYSES AND OF THE SABATOQA CONGRESS SPRINO OF AMERICA. Saratoga Congress Spring. Kissengen. Ragozi. Marienbad. Kreutbr. Auschowitz. Ferdinands- Brunnen. Eger. Franzens- Brunnen- 0-8261 0-0672 5-8531 4-1155 00202 0-0173 0-1379 0-1004 00326 1-6256 19-6653 0-1613 0-0046 0-0069 0-1112 0-*6592 4-8180 1-3185 00121 0-1397 1-2540 5-5485 0-0364 39-3733 3-6599 0-'3331 0-1609 5-3499 00858 0-*6028 2-9509 2-0390 20288 0-1319 28-5868 ;;;;;; 10-1727 0-6623 0-2908 4-5976 0507 0-6640 3-0085 2-2867 00692 0-2995 0-6640 16-9022 6-7472 0-5023 3-8914 0-0282 0-6623 1-3501 0-5040 00322 01762 0-0172 0-0092 18-3786 6-9229 0-3548 32-7452 114 50° (10°C) Schweitzer. 56-7136 96 53° (11°-6C) Struve. 51-6417 105 53°(11°-6C) 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 4*7781 0-0364 0-3213 o'-ono 0-0314 1-6092 0-0067 5-0265 0-0154 2-3684 0-8450 0-*37'27 0-5531 0-7387 0-8421 00389 0-2813 00102 00064 0-0593 0281 0-3371 0-'3739 12-3328 1-8667 1-2983 0-0061 0-1267 3-2337 0-0657 Ditto of Lithia Ditto of Baryta Ditto of Strontia Ditto of Lime Ditto of Magnesia Ditto (proto) of Manganese Ditto (proto) of Iron Sub-Phos. of Lime Ditto of Alumina Sulphate of Potassa Ditto of Soda Ditto of Lithia Ditto of Lime Ditto of Strontia Ditto of Magnesia Nitr. of Magnesia Chlor. of Ammonium Ditto of Potassium ,. Ditto of Sodium Ditto of Lithium Ditto of Calcium Ditto of Magnesium Ditto of Barium Ditto of Strontium Bromide of Sodium Iodide of Sodium Fluoride of Calcium Alumina Silica Total 15-4221 160 56° (13°-3C) Struve. 3-2691 136 50° (10°C) Struve. 18-9300 135 50° (10°C) Bischoff. Carbonic Acid Gas in 100 \ cubic inches j Temperature (F.) Analyzed bv APPENDIX, 541 TABLE OF ANALYSES AND OF THE SARATOGA CONGRESa SPRING OF AMERICA, Continued. Selters. Sfndschiitz. Pailna. Kreuznacb. Elisen- Brunneu. Adelheids- Quelle. 4-6162 5-2443 0-0902 00014 0-0024 0-0144 0-0387 1-4004 5- 1045 0-5775 0-2058 0-4703 1-5000 0-8235 4-8045 1-1812 0-2980 00032 0-0072 0-OOli 0-0095 0-1495 0-0121 0-0007 00117 0-0026 0-0020 0-0088 0-2978 •••••• 3-6705 17-6220 l'-1287 00347 62-3535 5-9802 3-6000 92-8500 l*-956o 69-8145 0-0066 0-*2685 •••••. 0-7287 0-1845 12-9690 l-'2225 14-7495 54-6917 0562 9-7358 0-2366 28-4608 . .... 0-5494 0-2304 00024 0-3060 0-1500 0-()6i3 0'0086 0-0166 0-2265 0-0900 0-1320 0-2355 0-1922 21-2982 98-0133 188-4806 68-0190 35-4739 126 20 7 12 10 58° (14°-5C) 58° (14°-5C) 58° (14°-5C) 47° (8°-3C) 58° (14°-5C) Struve. Struve. Struve. Struve. Struve. 46 M2 APPENDIX. WEIGHTS AND MEASURES 480-0 grains Troy = 1 oz. Troy. 437*6 ** =1 oz. Avoirdupoida. 7000-0 " = 1 lb. Avoirdupoida. 6760-0 " =1 lb. 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) 437-6 " The pint equals 34-66 cubic inches. The French kilogramme = 16,433-6 grains, or 2-679 lb. Troy, or 2-205 lb. avoirdupoida. The grammme = 15-4836 grains. ** decigramme = 1-5434 " " centigramme = 0-1543 " " milligramme = 0-0154 ** The mitre of France = 39-37 inchei. «' decimltre = 3-937 " " centimltre = 0-394 *« " millimUre = 0394 *• INDEX, Page A BSORPTiox of heat 80 Acer saccharinum 334 Acetal 371 Acftarakle 356 Acetate of acetetyl 215 Acetate of oxide of amyl... 389 Acetates 373 A.etetyl 215 Acetic acid ~ 371, 395 anhydrous 214,215 ether 356 Acetine 483 Acetone 376 Acotonitrile 373 Acetyl 369 Acid, acetic 371, 395 anhydrous 214, 215 aconitic 414 acrylic 487 aldehydic 370 alloxanic 440 alphaorsellic 475 althionic 366 amalic 460 amvgdalic 423 aniiic 406,473 anilotic 406 anisic 490 anthranilic 459, 474 antimonic 288 arsenic 292 arsenious 291 aspartic 416,452 auric 300 azoUc 123 balenic. 395 henzilic 401 benzoic 396 anhydrous 215 betaorsellic 475 biamuthic 275 boracic 151 bromic 148 bromo-hydrosalicylic... 405 bromo-phenisic 528 butyric 393, 485 cainpholic , 492 camphoric 492 capric 394. 485 caproic 394, 4''5 caprylic 394,485 carbazotic 473 carbolic 526 carbonic 129 liquefaction of. 63 carminic 477 cerebric 517 cerc'tic 4&6 Acids — contimied. Page cerotylic 394 cetylic 394, 486 chelidonic 447 chloracetic 318, 375 chlorhydric 141 chloric 145 chlorocarbonic 131 chlorochromic 269 chlorohydrosalicylic 405 chlorohyponitric 143 chloronaphthalic 530 chloroni<*ic 463 chloronitrous 143 chlorophenisic 528 chlorosulphuric... 136, 364 chlorous 144 chlorovalerisic 393 chlorovalerosic 393 cholalic 510 choleic 510 choloidinic 511 chrysammic 479 chrysanilic 459, 473 chrysolepic 479 chrysophanic 477 chromic 268 cinnamic 407 citraconic 414 citric 413 cocinic 484 comenic 447 croconic 345 cumaric 407 cumio 403,491 cyanic 426 cyanuric 426, 427 delphinic 485 dextro-racemic 413 dialuric 442 dithionic 135 draconic 491 elaidic 484 ellagic 418 equisetic 414 erythric 474 ethalic 486 ethionic 366 euchronic 345 euxanthic 479 evernic 475 eTerninic 476 ferric 261 formic 385,394 formobenzoic 400 fulminic 428 fumaric 416 {THllic 416,418 glyco-benzoic 402 Acids — cont. Paob glyco-cholalic 510 glyco-hyo-cholalic 512 glycolic 402,501 glucic .339 hemipinic 4^ hippuric 4(W' huraic 336 hydriodic 147 hydrobromic 148 hydrochloric 141 hydrocyanic 420 hydroferricyanic 433 hydroferrocyanic 430 hydrofluoric 149 hydrofluosilicic 149 hydroleic 487 hydromargaric 487 hydromargaritic 487 hydrosalicylic 404 hydrosulphocyanic 435 hydrosulphuric 103 hyocholalic 512 hyocholic 511 hypochloric 144 hypochlorous 144 hyponitric 126 hypophosphorous 138 hyposulphobenzic 398 hyposulphuric, sulphu- retted 135 hyposulphurous 135 igasuric 449 indinic 472 inosinic 503 itaconic 414 iodic 147 iodo-sulphuric 136 isatinic 472 isethionic 345 japonic 418 kakodyJic 379 kalisaccharic 336 kinie 447,448 lactic 349 lecanoric 475, 476 levo-racemic 413 lithic 433 lithofellinic 512 malamic 415 maleic 416 malic 414 manganic 259 margaric 481 meconic 446 melanic 404 melasiuic. ... 336 raclissic 39* mellitic 3U 544 INDEX. Kcws — cont Page mesoxalic 440 mctacetonic 376 metagallic 419 metamargaric 488 metapectic 340 inetaphoRphoric. 213 methionic 306 metoleic 4R7 mucic 344 muriatic 141 mykomelinic 440 myristic 484 myronic 493 nitric 123 nitrasinic 490 •nitrobenzoic 397 nitrococcusic 477 nitrocumio 403 nitrophenasic 528 nitrophenesic 528 ^.+ nitrophenisic 528 nitrosalicylic 406,4"^' nitrotoluylic 4 nitrous 126 renanthic 257 oenanthylic 395,488 oleic 482 oleophosphoric 517 opianic 445 orsellinic 474,475 oxalic 341 oxalovinic 359 oxaluric 440 oxamic 343 oxalinic 461 palmitic 484 parabanic 440 paratartaric 413 purellic 476 poetic 341 polargonic 357, 395 pnntathionic 136 perchloric 145 perchromic 269 periodic 148 permanganic 259 phoceni- 485 jvhosphethylic: 359 phosphohiethylik. 359 phosphoric 138 anhydrous 213 bibasic 213 glacial 213 monobasic 213 tribasic 212 phosphorous 138 phosphovinic 358 phthalic... 529 picric 473 pimaric 494 pinic 493 propionic , 376,395 prussic 420 Durpuric 443 purreic 479 pyrogallic 419 pyromeconic 447 pyromucic 345 pyrophosphoric 213 pyrotartaric •... 412 racemic 413 retinic 5:>'2 rhodizonir 345 Acins — cont. Page ricinoleic 488 rubiacic 478 ruble 418 saccharic 343 sncchulmic 336 salicylic 406 salicylous 404 sebacic 484 selenic 136 selenious.. 136 stearic 481 styphnic 479 suberic 345,484 succinic 484 sulphamylic 390 sulphindigotic 471 pulphindylic 471 sulphobenzoic 398 Bulphoglyceric 4R3 sulpholeic 487 sulphomargaric 487 sulphomethylic 383, 384 Bulphonaphthalic 529 sulphophenic 526 sulphosaccharic 335 sulphotoluolic 495 eulphovinic 358 sulphuric 133 sulphuric, anhydrous... 135 sulphurous 132 eylvic 493 tannic 416 tartaric 410 tartaric, anhydrous 412 tartralic 412 tartrelic 412 lartrovinic 359 tauro-cholalic 511 tauro-hyo-cholalic 512 telluric 290 tellurous 290 tetrathionic 135 thionuric 441 tnluylic .....' 403 trithionic 135 ulmic 336 uramilic 441 uric 436, 438 usnic 476 valerianic 390, 395 valeric 390, 395, 492 xanthic 368 salts 202 anhydrous 214 bibasic 212 fatty 345 hydrogen- theory of. 214 monobasic 212 notation of. 213 oxygen- theory of 214 polybasic 212 terminology of 132 tribasic 212 vegetable 410 Aconitates 414 Aconitic acid 414 Acouitine 451 Aconituirt, acid of 414 Aconitiim napellus 451 Acrolein 482,487 Acrylic acid 487 Affinity, chemical 183 Aftpr-damp of coal-miner. 12P i'AOI Air-pum; 34, 36 Air, atmospheric 120 Alanine 350, 370, 467 Albite 250 Albumin 495 Albuminous principles.... 496 Alcohol 346 absolute 34(5 butyl- 392, 395 capryl- 395, 488 cerotyl- 395, 486 cetyl- 395, 48(5 ethal- 486 Alcohols, generally 393 Alcohol, melissic 394, 486 table of, in aqueous mix- tures 537 Aldehyde 851, 379 ba.ses from 467 resin" 370 Aldehydic acid 370 Alembruth, sal 305 Algaroth, powder of. 289 Alizarin 477 Alkalimeter 227 Alkalimetry 226 Alkaloids 444 artificial 463 Alkargen 379 Alkarsin 377 Allantoin 438 AUiaria officinalis, oil of.. 493 Alloxan 439 AUoxanin acid 440 Alloxantin 441,451 Alloys 199 of copper 278 Allyl 493 oxide of. 493 sulphide of 493 sulphocyanide of. 493 Almonds, oil of bitter 39P Aloes 479 Alphaorsellic acid 475 Althionic acid 366 Alums 249 Alum, common 249 Roman 249 Alumina 248 .acetate of 373 analytical remarks on.. 25C silicates of 249 sulphate of 249 Aluminium 248 chloride of 248 Alum stone 249 Amalgam, ammoniacal... 2"!2 Amalgam 199, 306 Amalic acid 450 Amarine 401, 466 Amber 484, 494 Amidin ,"^38 Amidogen 235 Amidogen-bases 454 Ammeiide 436 Ammeline 436 Ammonia 162 acetate of. 373 alum 249 analytical remarks on.. 235 benzoate of 397 cyanate of 427 rnalate rf .415 INDEX. 545 Ammoxia — roni. Pagb oxalate of 343 purpurate of 442 tartrate of 411 urate of 438 Ammonium 201,2.32 cyanide of. 425 ferrocyanide of. 433 palicylide of 404 Amnii liquor 508 Amorphous quinine 448 Amy^'dalic acid 423 Amygdalin 396, 423 Amyiaceou.s group 333 Amyl and its compounds 3S8 series, bases of the 458 Amylamine 458 -urea 458 Amvl-ammonia 458 Amylene 390 Amylic ether 389 mercaptan 390 Amylotriethyl - ammo- nium, oxide of 464 Analcime 250 Analy.sis, ultimate, of or- ganic bodies 320 Analysis of carbonates.... 228 Analytical method of che- mical research 115 Anhydrous acids 214 Anil'ic acid 406, 473 Aniline 399,459,463 homologues of 462 -urea ^2 Anilotic acid 406 Animal heat 507 body, components of.... 496 Aniseed, oil of. 490 Anisic acid 490 Anisoin 490 Anisol 491 Auisyl, hydride of. 490 Anthranilic acid 459, 474 Antiarin 452 Antimonic acid 288 Antimony 287 bases 469 crude 289 potassa, tartrate of. 411 Aqua regia 143 Arabin 340 Archil 474 Argand lamp 169 Argol..- 347, 410 Aricine 448 Aridium 266 Arragonite 242 Arrow poison of central America 451 Arrowroot 339 Arsenic acid 292 Arsenic and its com- pounds 291 analytical details 293 detection in organic mixtures 293 Arsenious acid 291 Artemisia 4.52 Arterial blood 503 Assafoetida 479 oil of 493 Asparagin 415, 452 Af^fMAjrus 452 4IalAtes 415 Maleicacid 416 Malic acid 414 Malleability of metals 198 Malting 34S Tagjs Manganese, acetate of. 374 and its compounds 256 assay of. 257 Manna sugar 337 Mannite 3:57 Manures 5'J2 Maple, sugar from 334 Marble 241 artificial coloured 241 ]VTarc-brandy, fusel-oil of.. 393 Margaric acid 481 ether .357 Margarin 480, 4^1 Margarone 482 Marienbad, water of 539 Mariotte's law 38 Marsh gas 153 Marsh mallow 452 Marls 250 Massicot 279 Mastic 494 Meadow-sweet, oil of. 404 Measures 642 Meat 518 Meconic acid 446 Meconine 446 Meerschaum 247 Melam 436 Melamine 436 Melaniline 461 Melanic acid 404 Melasinic acid 336 Melis.sic acid 394 alcohol 394,486 Mellite 345 Mellitic acid 345 Mellon 435 Membranous tissues 516 Membranes, mucous 508 Mercaptan 367 methyl- 387 Mercury ■„... 301 acetates of. 375 analytical remarks on... 306 cyanide of 425 fulminate of 429 its compounds... 302 Meridian, magnetic 88 Me.Mtilol 376 Me.'iityl 376 Mesotype 250 Mesoxalic acid 440 Metacetone 376 Metacetonic acid 376 Metaldehyde 370 Metagallic acid ' 419 Metals 197- classification 216 Metamargaric aeid 487 Metapectin 340 Metapectic acid „. 340 Metaphosphoric acid 213 Metastyrol 495 Meteorites 259 Methionic acid 366 Methyl 381 Methylamine 457 -urea 457 Methyl-ammonia 457 Methvl-compounds... 381.382 Methyl-pther ' 3S2 Methyl-ethyl-amylamino. 4f4 -urea 457 INDEX 551 Page Blethyl - ethyl - amylophe- nvlammonium, oxide of 464 Metbyl-mercaptan 3S7 Methylo-biethyl-amyl-am- monium, oxide of 464 Methyl-salicylateof, oxide of 491 Methyl-series, bases of the 457 Metoleic acid 487 Metre 542 Mica 250 Slicrocosmic salt 230 Milk 508 spirit from 509 Milk-sugar 336 Miudererus, spirit of. 373 Mineral chameleon 259 waters, table of. 638 Molasses 334 Molecular actions 184 Molybdenum 284 Momordica daterium 452 Monobasic acids 212 Mordant 283 Mordants 470 Morphia 444 Morphine 444 Mortar 240 Mosaic gold 283 Mucic acid 344 Mucilage 340 Mucx)us membranes 508 Mucus 508 Mulberry calculus 616 Multiple proportions 173 Multiplier 83 Murexan 443 Murexide 442 caffein 450 Muriatic acid 141 ether, heavy 367 Muscovado sugar 334 Mushroom sugar 337 Must 347 Mustard, oil of 492 bases from the oil of.... 466 Mykomelinic acid 440 Myricin 492 Myristicacid 484 Myi-istica moschata 484 Myronic acid 493 N. Naphtha 531 Naphthalidine 462 Naphthalin 462, 529 Narc«ine 446 Narcogenine 446 Narcotine 445 Kepheline 250 Nervous substance 51 Neutrality of salts 200 Neutralization 176 Nickel 269 acetate of. 374 analytical remarks 271 Nicotine 450, 469 Niobium 286 Nitraniline 460 Nitranisic acid 490 Nitraniside 490 Nitrate of ammonia 234 Nitrate — cont. Page of baryta 238 of bismuth 275 of lead... 280 of oxide of methyl 384 of potassa 220 of soda 230 of silver 298 Nitrates 124 of mercury 302 Nitre 220 cubic 230 sweet spirits of. 355 Nitric acid 123 acid, fuming 126 ether 354 oxide 126 Nitrile-bases 455 Nitro-benzamide 462 Nitro-benzoic acid 397 Nitro-benzol 399,462 Nitro-chlorouicene 463 Nitro-ooccusic acid 477 Nitro-cumic acid 403 Nitro-cumol 462 Nitrogen 120 binoxide of. 126 chloride of. 167 compounds with oxygen 122 estimation in organic bodies 324 iodide of 167 Nitro-naphthalase 462 Nitro-phenasic acid 528 Nitro-phenesic acid 528 Nitro-phenisic acid 528 Nitro-prussides 433 Nitro-salicylamide 492 Nitro-salicylic acid ... 406, 473 Nitro-toluol 402,495 Nitro-toluylic acid 403 Nitrous acid 126 ether 355 oxide 125 Nitro-xylol 462 Nomenclature 170 Norium 352 Notation, chemical 180 Nutgalls 417 Nutrition, plastic ele- ments of 520 0. Octahedron 206 (Enanthic acid. 357 ether 357 CEnanthylicacid 395 Oil gas 155 of alliaria officinalis 493 of aniseed 490 of assafoetida 493 of badian 491 of bergamot 490 of bitter almonds 396 of bitter fennel 491 of capivi 490 of cedar wood 491 of cinnamon 407 of elemi 490 of cubebs 490 of cumin 491 of garlic 493 of gaultheria procum- bens 406, 491 Oih— cont. Paos of Guiana-laurel 490 of hops 490 of horseradish 493 of juniper 490 of lavender 492 of lemons , 490 of meadow-sweet 404 of mustard 492 of onions 49.3 of orange flowers 492 of orange peel 490 of pepper 490 of peppermint 492 of rosemary 492 of rose petals 492 of spiraea nlmaria 404 ofturpentin 489 of valerian 492 of vitriol 134 of wine, heavy and light 362 of wintergreen 491 Oils 480 drying or non-drying... 480 volatile 488 Olefiant gas 154 and its compounds 362 Oleic acid 482 Olein 480, 482 Olive oil 488 Onions, oil of. 493 Opiammon 445 Opianic acid 445 Opianine 446 Opium 444 Orange flowers, oil of 492 oil of -peel 490 Orcein 476 Orcin 474, 476 Organic baijes 444 bases, artificial 453 substances, action of heat on 319 substances, classifica- tion 319 substances, composition elementary 318 substances, decomposi- tion of. 319 substances, ultimate analysis of. 320 Orpiment 292 Orsellinic acid 474,475 Osmium 314 Oxalate of oxide of methyl 384 Oxalates 342 Oxalic acid 341 ether 356 Oxalo-nitrilc.i 4G1 Oxalo-vinic acid 359 Oxaluric acid 440 Oxamethane ••.... 356 Oxamethylane 384 Oxamic acid 343 ether 358 Oxamide 343 Oxanilic acid 461 Oxanilide 461 Oxide, cystic 443 ofallyl *93 of amyl, bydrated 388 of benzoyl 896 of bismuth 275 of copper 227 552 INDEX Oxinn — cont. Page of kakodyl 377 o1 methyl 882 of methyl, hydrated.... 381 xanthic 443 Oxides 109 of antimony 288 of chromium 267 of gold 300 of hydrogen 115 of mercury 302 of platinum 308 of potassium 218 of silver 297 of sodium 224 of zinc 273 Oxygen 105 -adds 201 Oxy-hydrogen, flame and blowpipe 113 safety-jet 161 Oxy-salts 201 Ozone 110 P. Palladium, cyanide of 311, 426 Palmilate of oxide of me- lissyl 486 Palmitin 485 Palmitic acid 485 Palm-oil 484 Papaverine 446 Parabanic acid 440 Paracvanogen 420 Paraffin 623 Parakakodylic oxide Paramagnetic bodies 89 Paramide 345 Paramorphine 446 Paramylene 390 Paranaphthalin 530 Parapectin 340 Paratartaric acid 413 Parellic acid 470 Parmelia parietina 476 Pear, flavour of 389 Pearlash 219 Pectic acid 340 Pectin 340 Pelargonic acid 357, 395 Pelopium 286 Pentathjonic acid 136 Popper, oil of 490 Peppermint, oil of. 492 Pepsin 521 Perclilorato of potassa ... 222 Porch loric acid 145 Pori'USRion-caps 429 I'eriodic acid 148 IVroxide of chlorine 144 I'ersulphide of hydrogen. KiS Peru balsam 408 J'eruvin 408 Pctalite 250 Potinine 405 F'ettcukofer's bile-test 511 Petroleum 531 Petrolene 5ol Petuntze 255 Piienetol 527 I'heuol 491,526 Phenyl 524 alcohol 459, .^27 benzcate-'f 527 PHENTL — COT?/. Pagk chlorid«of. 527 cyanide of 527 hydrated oxide 520 . series, bases of — 459 Phenyl-amine 469 Philosophy, chemical 170 Phloretin 406 Phloridzin 406 Phocenic acid 485 Phorone 492 Phosgene gas 131 Phosphate of lime 241 Phosphate of magnesia... 246 of magnesia and ammo- nia 246 Phosphate of soda 2.30 Phosphethylic acid 359 Phosphide of calcium 241 Phosphobiethylic add 359 Phosphoretted hydrogen. 166 Phosphoric acid 1'58 acid, anhj'drous 213 add, bibasic 213 acid, glacial 213 acid, monobasic 213 acid, tribasio 212 ether 354,3-59 Phosphorous add 138 Phosphorus 137 -bases 468 chloride of 168 compounds of 138 Phosphovinic acid 358 Photography 77 "Phthalic acid 529 Picamar 524 Picoline 465 Picric acid 473, 528 Picro-erythrin 475 Picrotoxin 452 Pimaric add 494 Pinic add 493 Piperine 451 Pitch 623 mineral 531 Pit-coal 530 Plants, supply of carbon to 130 Plaster of Paris 241 Plate glass 252 Platinum and its com- pounds 307 analytical remarks 310 bases 309 Wack 307 surface-action of.... 114, 115 Plumbago 128 Polarity, magnetic 86 Polyba^c acids 212 452 254 250 446 Ponlil or puntil 253 Populin j Porcelain I clay Porphyroxine Potash 21S crude 219 Potassa 218 I acetate of 373 alum 249 analytical remarks on.. 224 I lienzoate of ,. 397 bicarbonate of. 220 I bisulphide of 221 PoTA?sA — ^on^ Paoh carbonate of 219 chlorate of. 221 cyanate of. 426 nitrate of. 220 oxalate of 342 perehlorate of. 222 sulphate of 221 tartrates of. 411 urate of 438 Potassium and its com- pounds 217 bromide of. 224 chloride of 223 cyanide of 424 ferricyanideof. 431 ferrocyauide of. 433 salicylide of. 404 sulphides of 222 sulphocyanide of. 434 Potato-oil 488 Precipitate, white 305 Prehnite 250 Proof-spirit 347 Propione. 376 Propionic acid 376, 395 Proportionals 174 Proportions, multiple 173 Propylene 388 Protein 499 binoxideof. 500 teroxide of 500 Protide 500 Protochloride of tin 283 Protoxide of tin 382 Prussian blue 432,433 Prussiate of potash, red... 433 yellow 431 Prussic acid 420 Pscudo-erythrin 475 Pseudo-morphine 446 Pudding 265 Pii Una, water of. 541 Purple of Cassius 283 Purpurate of ammonia... 442 Purpuric acid 442 Purpurin 478 Purree 479 Purreic acid 479 Purrenone 479 Pus 508 Putrefadion 320 Putty powder 2^2 Pyrites 262 Pyrniont, water of 540 Pyroacetic spirit 376 Pyro-adds 319 Pyrobeuzolin 4li6 Pyrogallic acid 419 Pyrogen acids 419 Pyromeconic acid 447 Pyi'omucic acid 34-') Pyrophorus of Ilomberg.. 249 Pyrophosphoric add 213 Pyrotartaric acid 413 Pyroxy lie spirit 3S1 Pyroxylin 344 Q. Quercitron bark 479 Quicksilver 301 Qnina 447 Quinidine 448 j Quinine 447 INDEX 55a Page Quinine, amorphous 448 Quiaoliue 464 Quinoidine 448 R. Uadiation of heat Kacemlc acid Realgar Red dyes Red fire Red lead -. Reflection of heat of light Refraction, double of light Rennet Resins Respiration « elements of. Retinic acid ~ Retinite Reverberatory furnace.... Rhodium Rhodizonic acid Ricinoleic acid Rocella tinctoria 474, Rocellinin Rochelle salt Rock oil Rock salt Roman alum Rosemary, oil of Rubia tinctorum Rubiacin Rubiacic acid Rubian Rubic acid Rust Ruthenium 79 413 292 477 239 279 79 71 75 72 499 493 506 506 532 532 158 312 345 488 475 475 411 532 232 249 492 477 478 478 478 418 260 314 Saccharic acid 343 Saccharic group a33 Sacchulmic acid 336 Sacchulmin 336 Safety-lamp 161 Safflowcr 478 Saffron 479 Sago 339 Saf-alembroth 305 Sal-ammoniac 233 Salicin 403, 452 Salicyl and its compounds 403 hydride of 452 Salicylate of oxide of me- thyl 491 Salicylic acid 406 Salicylides 404 Salicylous acid 404 Saligenin 405 Saliretin 405 Saliva 521 Salsola soda 225 Salt, definition 109 of sorrel 342 Salts, super or add 202 binary theory of 213 constitution of. 199 double 202 neutral 200 Saltpetre 123, 220 Sandarac 494 Santonin 452 47 Pace Saponification 481 ' Saratoga Congress spring 539 Sarcosine 503 Saturation 176 Schlesischer Obersalz- brunnen 538 Scheele's green 278 Scagliola 241 Sea-water 118 Sebacic acid 484 Seed lac 494 Seggars 254 Seidchutz, water of. 541 Seignette salt 411 Selenic acid 136 Selenietted hydrogen 1C5 Selenious acid 136 Selenite 241 Selenium 136 Seleno-cyanogen 435 Sellers, water of. 541 Serpentine 247 Serum of blood 504 Silica 150 Silicates of alumina 249 of magnesia 247 Silicic ether 355 Silicium 149 chloride of. 169 fluoride of 150 Silver, acetate of. 375 analytical remarks 299 benzoateof 397 cyanide of 426 fulminate of. 428 its compounds 296 standard of England.... 299 Sikes' hydrometer 535 Sinapoline 467 Sinnamine 467 Size 502 Shellac 494 Skin 517 Smce's battery 194 Smalt ; 272 Soap * 481 Soap-stone 247 Soap-test of Dr. Clark 241 Soda, acetate of. 373 alum 249 analytical remarks on... 232 ash 225 ash, testing its value.... 228 bicarbonate of 226 carbonate of. 225 hydrate of. 224 oxalate of 343 tartrates of. 411 urate of. 438 Sodium 224 cyanide of. 424 ferro-cyanide of. 4-33 oxides of. 224 Solanine 450 Solder 281 Solids, expansion of. 44 Sorrel, salt of. 342 Spa Pouhon, water of 540 Spar, calcareous 242 Sparteine 450 Specific gravities of metals 197 gravity of solids and liquid." 27 Page Specific heat 66 Speculum metal 279 Spectrum 74 Speiss 269 Spermaceti 486 Spirit from milk 509 of Mindererus 373 pyroxylic 381 Spirits, table of spec. gr. of 537 Spudomene 250 Springs 118 Starch 3.37 State, change of, by heat.. 62 Steambath 57 Steam engine 57 specific gravity of. nndon edition. In one large and handsome octavo volume, with over three hundred beautiful illustrations. CARPENTER (WILLIAM B^, M.D.— The Microscope and its Revelations. With an Ap- pendix containing the Applications of the Microscope to Clinical Medicine, by F. G. Smith, M.D. With 434 beautiful wood engravings. In one large and very handsome octavo volume of 724 pages, extra cloth or leather. (Now Ready.) CARPENTER (W f LLIAM B.), >r. D.— -Emments (or Manual) or Prtsiologt, iNCLunma Pht- 8I0L0GICAL Anatomy. Second / v*rican, from a new and revised London edition. With one hundred and ninety illustrations. In one very handsome octavo volume. CARPENTER (WILLIAM « \ M. D.— PRiNaPLES op General Physiology, including Organto Chemistry and Histology. With a Gen«ral Sketch of the Vegetable and Animal Kingdom. In one large and handsome octavo volume, with several hundred illustrations. (Preparing.) CARPENTER(WILLIAMB.), M.D.— A Prize Essay on the Use of Alcoholic Liquors m Health and Disease. New edition, with a Preface by D. P. Condie, M. D., and explanatlona of scientific words. In one neat 12mo. volume. \ CHRISTISON (ROBERT), M.D.— A Dispensatory; or, Commentary on the Pharmacopoeias of Great Britain and the United States; comprising the Natural History, Description, Chemistry, Pharmacy, Actions, Uses, and Doses of the Articles of the Materia Medica. Second edition, revised and improved, with a Supplement containing the most important New Remedies. With copious Additions, and two hundred and thirteen large wood- engravings. By R. Eglesfeld Qrifiath, M.D. In one very large and handsome octavo volume, of over 1000 pages. CHELIUS (J. M.), M. D.— A System of Surgery. Translated from the German, and accom- panied with additional Notes and References, by John P. South. Complete in three very large octavo volumes, of nearly 2200 pages, utrongly bound, with raised bandg and double titles. ,