W.A.lEARY&CO.'S CHEAP nooi^yroRE, No. 138 North & St., 10 doors bflovv Now, PhHaila University of California. FROM THK 1.115KAKY < >F DR. FRANCIS LIEBKR, 1'rofcsHor <>f History and Law in Columbia Colloge, New York. THK GT1-'T OF MICHAEL REESE Of Sasi Francisco. '" ELEMENTARY CHEMISTRY. ELEMENTARY CHEMISTRY, THEORETICAL AND PRACTICAL BY GEORGE FOWNES, F.R.S., PROFESSOR OP PRACTICAL CHEMISTRY IN UNIVERSITY COLLEGE, LONDON. EDITED, WITH ADDITIONS, BY ROBERT BRIDGES, M.D., PROFESSOR OF CHEMISTRY IN THE PHILADELPHIA COLLEGE OF PHARMACY, ETC. ETC. THIRD AMERICAN, FROM A LATE LONDON EDITION. WITH NUMEROUS WOOD-ENG-RAVING-S. PHILADELPHIA: LEA AND BLANCHARD. 1850. (f ENTERED according to Act of Congress, in the year one thousand eight hundred and fifty, by LEA AND BLANCHARD, In the Clerk's Office of the District Court of the Eastern District of Pennsyl- PHILADELPHIA : T. K. AND P. G. COLLINS, PRINTERS. PREFACE TO THE THIRD AMERICAN EDITION THE approbation with which the former editions of this Manual of Chemistry have been received by teachers and students will, it is hoped, be extended to the present. Having been carefully revised by its author but a short time before his death, and published under the superintendence of his friend, Dr. Bence Jones, it is full and complete up to the date of publication. The task of the American editor has been to add such new matter as may have since appeared, and to adapt it to the wants of the American student by appending, in the form of notes, such points of interest as would be calculated to retain the position the original has justly attained, and to main- tain it on an equality with the advance of chemical science. The notes of the editor are distinguished by his initials. PHILADELPHIA, September, 1850. 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 endeavor, as seen in his manuscript, were to render it as perfect and as minutely accurate as possible. When he hjid finished the most important part of the Organic Chemistry, where the most additions were required, he told me he should " do no more," he had " finished his work/' At his request, I have corrected the press throughout, and made a few alterations that appeared desirable in the only part which he had left unaltered the Animal Chemistry. The Index and the press have also been corrected throughout by his friend, Mr. Robert Murray. H. BENCE JONES, M.D. 30 'GROSVENOR-STREET, Jan. 1850. PREFACE. THH 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 his- tory of the more important among the very numerous bodies which Chemical investigations have made known to us. The woife has no pretensions to be considered a complete treatise on the subject, but is intended to serve as an introduction to the larger and more com- prehensive systematic works in our own language and in those of the Continent, and especially to prepare the student for the perusal of original memoirs, which, in conjunction with practical instruction in the laboratory, can alone afford a real acquaintance with the spirit of research and the resources of Chemical Science. It has been my aim throughout to render the book as practical as possible, by detailing, at as great length as the general plan permit- ted, 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 X PREFACE. subject of the general philosophy of Chemical Science, and even be- fore describing the principle of the equivalent quantities, or explain- ing the use of the written symbolical language now universal among chemists. For the benefit of those to whom these matters are already familiar, and to render the history of the compound bodies described in the earlier part of the work more complete, I have added in foot- notes the view adopted of their Chemical constitution, expressed in symbols. I hsffve devoted as much ^pace as could be afforded to the very important subject of Organfe Chemistry; and it will, I believe, be found ihat th&re are feut few Substances of any general interest which have been altogether omitted, although the very great number of bodies to be described in a limited number of pages rendered it necessary to use as much brevity as possible. GEO. FOWNES. UNIVERSITY COLLEGE, LONDON, October 5, 1847. TABLE OF CONTENTS. PAGE INTRODUCTION ... . .25 PART I. PHYSICS. OF DENSITY 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 OF THE ATMOSPHERE, AND OP 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 DanielFs pyrometer ...... 45 Expansion of liquids and gases. Ventilation. Movements of the atmosphere ...... 46 Conduction of heat ...... 52 Change of state. Latent heat . . . .52 Ebullition: steam . 54 Xll CONTENTS. PAGE Distillation . . . . . . .58 Evaporation at low temperatures . . . .59 Vapor 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 LIGHT. Eeflexion, refraction, and polarization of light . . 70 Chemical rays . . . . ... 75 Radiation, reflexion, absorption, and transmission of heat . 78 MAGNETISM. Magnetic polarity ; natural and artificial magnets . . 85 Terrestrial magnetism . . . . .87' ELECTRICITY. Electrical excitation ; machines . . . .89 Principle of induction ; accumulation of electricity . 90 Voltaic electricity . . . . V . 94 Thermo-electricity. Animal electricity . i'*> .-, .;, 96 Electro-magnetism ; magneto-electricity - . . . 96 Electricity of steam . >-g .- iy , u - n :.'. .-,, 100 PART II. CHEMISTRY OF THE ELEMENTARY BODIES, NON-METALLIC ELEMENTS, Oxygen . . . . .102 Hydrogen ; water ; peroxide of hydrogen . . . -, " 107 Nitrogen ; atmospheric air ; compounds of nitrogen and oxygen . . ,j._ . . 117 Carbon ; carbonic oxide ; carbonic acid 124 CONTENTS. Xlll PAGE Sulphur; compounds of sulphur and oxygen . . 128 Selenium ....... 133 Phosphorus ; compounds of phosphorus and oxygen . 134 Chlorine ; hydrochloric acid. Compounds of chlorine and oxygen . . . . . . . 137 Iodine . v ...... 143 Bromine ....... 145 Fluorine ....... 146 Silicon . . . . . . .147 Boron . , . . . . . . .149 COMPOUNDS FORMED BY THE UNION or THE NON-METALLIC ELE- MENTS AMONG THEMSELVES. Compounds of carbon and hydrogen. Light carburetted hydrogen; olefiant gas; coal and oil-gases. Combus- tion, and the structure of flame .... 150 Nitrogen and hydrogen ; ammonia .... 159 Sulphur, selenium, and phosphorus, with hydrogen . 160 Nitrogen, with chlorine and iodine ; chloride of nitrogen . 164 Chlorine, with sulphur and phosphorus . . . 165 Other compounds of non-metallic elements . . . 165 ON THE GENERAL PRINCIPLES OF CHEMICAL PHILOSOPHY. Nomenclature ....... 167 Law* of combination by weight .... 169 By volume Y . . . . . . . 174 Chemical symbols . . . . . . ^ 177 The atomic theory ...... 179 Chemical affinity ...... 180 Electro-chemical decomposition; chemistry of the voltaic pile . . . 184 METALS. General properties of the metals . . . 194 Chemical relations of the metals ; constitution of salts . 197 Crystallography ..'.... 200 Isomorphism . . . . . . . 207 Polybasic acids ...... 209 2 XIV CONTENTS. PAGE Binary theory of the constitution of salts . . . 211 Potassium ..... . 213 Sodium .... . 220 Ammonium ..... . 227 Lithium . . ... . . 230 Barium . . . . . ... . . 232 Strontium . . .... ... . . 234 Calcium . ,'.'..,. . . .234 Magnesium . . . .... . . . 239 Aluminium . . ... . . . 243 Glucinum . . . . . . 245 Yttrium, cerium, lanthanium, and didymium . . 246 Zirconium. Thorinum ..... 247 Manufacture of glass, porcelain, and earthenware . . 247 Manganese . . . . . . .251 Iron . . 254 Chromium . . jj . . . . .261 Nickel . . ,,..{>< 264 Cobalt ........ 266 Zinc . ..... 267 Cadmium . - . . . . . 268 Bismuth . . . . . . J . 269 Uranium .. . . c . . . 270 Copper . . . . . . . 271 Lead . . . . . . .273 Tin .277 Tungsten ....... 279 Molybdenum ....... 279 Vanadium ....... 280 Columbium (Tantalum) ..... 281 Niobium and Pelopium ..... 281 Titanium . . . . . . "T 282 Antimony .... . ' . 282 Tellurium . . . . . J. . 284 Arsenic ....... 285 Silver ........ 290 Gold . 293 Mercury . 295 Platinum ...... 301 Palladium. 304 CONTENTS. XV PAGE Rhodium ....... 305 Iridium ....... 306 Ruthenium ....... 307 Osmium 308 PART III. ORGANIC CHEMISTRY. INTRODUCTION ....... 310 LAW OF SUBSTITUTION ...... 311 THE ULTIMATE ANALYSIS OF ORGANIC BODIES . . . 315 EMPIRICAL AND RATIONAL FORMULA . . . . 323 DETERMINATION OF THE DENSITY OF THE VAPORS OF VOLATILE LIQUIDS ....... 324 SACCHARINE AND AMYLACEOUS SUBSTANCES, AND THE PRODUCTS OF THEIR ALTERATION ...... 327 Cane and grape-sugars ; sugar of the eucalyptus ; sugar from ergot of rye ; sugar of diabetes insipidus j liquorice- sugar ; milk-sugar ; mannite .... 327 Starch : dextrine ; starch from Iceland moss ; inuline ; gum; pectine; lignine . -. . . .331 Oxalic and saccharic acids ..... 336 Xyloidine ; pyroxyline ; mucic acid ; suberic ; mellitic acid 338 Rhodizonic, and croconic acids .... 339 Fermentation of sugar. Alcohol . . . . 339 Lactic acid . . . . - . . 343 Viscous fermentation ...... 344 Ether, and ethyle-compounds .... 345 Sulphovinic, phosphovinic, and oxalovinio acids . . 350 Heavy oil of wine ... . . . . . 354 Olefiant gas ; Dutch-liquid ; chlorides of carbon . . 355 Ethionic and isethionic acids 358 XVI CONTENTS. PAGE Chloral, &c. . . . . . . .359 Mercaptan ; xanthic acid ..... 360 Aldehyde ; aldehydic acid ; acetal .... 361 Acetic acid ....... 364 Chloracetic acid . . . . . .367 Acetone . ... . . .368 Kakodyle . . . . . .369 SUBSTANCES MORE OR LESS ALLIED TO ALCOHOL. Wood-spirit; methyle compounds .... 373 Sulphomethylic acid ...... 375 Formic acid ; chloroform ..... 376 Formomethylal ; methyl mercaptasn .... 378 Potato-oil and its derivatives . . . . 378 Sulphamilio acid ; valerianic acid .... 380 Chlorovalerisic and chlorovalerosic acids . . . 381 Fusel-oil from grain-spirit . . . . .382 Bitter-almond oil and its products ; benzoyle-compounds . 382 Benzoic acid ; sulphobenzoic acid ; benzone and benzine . 383 Sulphobenzide and hyposulphobenzic acid . . . 385 Nitrobenzide, azobenzide, &c. .... 385 Mandelic acid ; hydrobenzamide ; benzoine ; benzile ; ben- zilic acid ; benzimide, &c. ..... 386 Hippuric acid . . ' . .... 388 Salicine ; salicyle and its compounds ; chlorosamide . 388 Saligenine. Phloridzine. Coumarine . . . 391 Cinnamyle and its compounds ; cinnamic acid ; chloro-cin- nose . . . . . . . .391 VEGETABLE ACIDS. Tartaric acid ....... 394 Racemic acid . . . . . . .397 Citric acid 397 Aconitic or equisetic aci'd . . . . . 398 Malic acid 398 Fumaric and maleic acids ..... 399 Tannic and gallic acids . . . '.'"'" 399 AZOTIZED ORGANIC PRINCIPLES OF SIMPLE CONSTITUTION. Cyanogen ; paracyanogen ; hydrocyanic acid . ' . 403 CONTENTS. XV11 PAGE Amygdaline ; amygdalinic acid .... 406 Metallic cyanides . . . . . 407 Cyanic, cyanuric, and fulminic acids . . . 409 Chlorides, &c. of cyanogen ..... 412 Ferro, and ferridcyanogen, and their compounds ; Prussian blue . . 413 Cobaltocyanogen ...... 416 Sulphocyanogen, and its compounds ; melam ; melamine ; ammeline ; ammelide ..... 416 Urea, and uric acid ...... 418 Allan toin ; alloxan ; alloxanic acid ; mesoxalic acid ; myko- melinic acid ; parabanic acid ; oxaluric acid ; thionuric acid ; uramile ; alloxantine ; murexide ; murexan . 420 Xanthic and cystic oxides ..... 425 THE YEGETO-ALKALIS, AND ALLIED BODIES. Morphia, and its salts ..... 426 Narcotine ; opianic and hemipinic acids ; cotarnine . 427 Codeine ; thebaine ; pseudomorphine ; narceine ; meconine 428 Meconic acid ....... 428 Cinchonia and quina ; quinoidine .... 429 Kinic acid ; chinone ; hydrochinone .... 430 Strychnia and brucia ...... 430 Veratria; conicine ; nicotine ; harmalina ; hyoBcyamine ; daturine ; atropine ; solanine ; delphinine ; emetine ; cu- rarine "'' ...... 431 Gentianine ; populine ; daphnine ; hesperidine ; elaterine ; piperine ; antiarine ; picrotoxine ; asparagine ; caffeine or theine ; theobromine ..... 432 ORGANIC BASES OP ARTIFICIAL ORIGIN. Furfurine . . . . . .433 Benzoline. Thiosinnamine. Toluidine . . . 434 Cumidine. Naphthalidam ..... 435 Thialdine ....... 435 Aniline, and its products. Chinoleine . . . 436 Kyanol Leukol. Picoline . . . . .437 ORGANIC COLORING PRINCIPLES. Indigo ; white indigo ; sulphindylic acid . . . 439 2* XV111 CONTENTS. PAGE Isatine ; anilic and picric acids ; chrysanilic and anthranilic acids . . . .;'.:. .440 Litmus lecanorine ; orcine ; orceine, &c. . . . 442 Cochineal, madder, dye-woods, &c. .... 444 Chrysammic, chfysolepic, and styphnic acids . . 445 OlLS AND FATS. Fixed oils ; margarine, stearine, and oleine ; saponification, and its products ; glycerine .... 446 Palm and cocoa-oils. Elaidine and elaidio acid . . 449 Suberic, succinie, and sebacic acids .... 450 Butter. Butyric, caproic, caprylic, and capric acids . 451 Wax; spermaceti; cholesterine ; oantharidine . ./ 451 Acroleine; acrylic acid * . *-'^ ?* ,^ > - *- 452 Products of action of acids on fats . ^ , * . % 453 Volatile oils. Oils of turpentine, lemons, aniseed, cummin, cedar, gaultheria, valerian . . . . 454 Camphor ; camphoric acid , , . . . '. 456 Oils of peppermint, lavender, rosemary, orange-flowers, rose- petals ....... 457 Oils of mustard, garlic, onions, &c. . . . . 1 457 Resins. Caoutchouc . . . T .'" 458 . Balsams. Benzoene; styrole . "'. "V , 459 COMPONENTS OP THE ANIMAL BODY. Albumen, fibrine, and caseine ; proteine . . . 461 Gelatine and chondrine ..... 466 Kreatine and kreatinine *\ . . . 467 Composition of the blood; respiration ; animal heat . 468 Chyle; lymph; mucus; pus . . . ;'; - <* 473 Milk ; bile ; urine ; urinary calculi . . . -.,. , 474 Nervous substance ; membranous tissue ; bones . , . ,, 481 The function of nutrition in the vegetable and animal king- doms . v . . ' . % . . 483 PRODUCTS OF THE DESTRUCTIVE DISTILLATION, AND SLOW PUTRE- FACTIVE CHANGE OF ORGANIC MATTER. Substances obtained from tar. Paraffine ; eupion ; pica- mar ; kajr .mor ; cedriret ; pittakal ; kreosote ; chrysen and pyren . . . . . . . 489 CONTENTS. XIX PAGE Coal-oil. Kyanol and leukol. Carbolic acid (hydrate of phenyle) ....... 491 Naphthaline and paranaphthaline .... 492 Petroleum, naphtha, and other allied substances . . 493 APPENDIX. On the equivalent numbers. Hydrometer tables. Table of the tension of the vapor of water at different tempera- tures. Table of the proportion of real alcohol in spirits of different densities. Analyses of the mineral waters of Germany. Table of weights and measures . . 496 LIST OF ILLUSTKATIONS BY WOOD-CUTS. FlG. 1 Specific gravity bottle 2 3 4 5 6 ' beads 7 Hydrometer . 8 Urinometer . 9 Specific gravity 10 Elasticity of gases 11 Single air-pump 12 Double " 13 Improved " 14 " " 15 Barometer 16 17 . 18 Expansion of solids 19 " liquids 20 " gases 21 Differential thermometer 22 23 Difference of expansion in metals . 24 Gridiron pendulum 25 Mercury " 26 Compensation balance 27 Daniell's pyrometer 28 Expansion of liquids 29 Atmospheric currents 30 31 " " 32 Boiling paradox 33 Steam-bath . 34 Steam-engine 35 Distillation . PAGE Fi< j. PAGE 28 36 Liebig's condenser 59 29 37 Tension of vapor . 59 29 38 tt 60 29 39 "Wet-bulb hygrometer 62 30 40 Condensation of gases 63 31 41 Thilorier's apparatus 64 32 42 Cold by evaporation 65 32 43 "Wollaston's cryophorus 65 33 44 DanielFs hygrometer 65 34 35 45 46 Reflection of light Refraction of light 70 70 36 47 tt a 71 36 48 it tt 72 37 49 Spectrum 73 38 50 73 39 51 Polarization of light 74 40 52 tt 74 41 53 it 74 41 ^54 Reflection of heat . 78 41 55 79 r 43 56 Effects of electrical cur 43 rent on the magnetic i needle 81 44 57 it tt tt 82 44 58 Current produced by hea t 82 45 59 Mellonis's instrument foi 45 measuring transmitte( 45 heat . 82 47 60 Magnetic polarity 86 50 61 tt it 86 50 62 Electric repulsion 89 51 63 Electroscope . 89 55 57 64 65 Electric polarity Electrical machine 90 92 57 66 " plate 92 58 67 Ley den jar 93 XXII LIST OF ILLUSTRATIONS. FlG. PAGE 68 Electrophorus . . 94 69 Volta's pile ... 95 70 Crown of cups . .. 95 71 Cruikshank's trough . 96 72 Effect of electrical cur- rent on the magnetic needle . * . .97 73 Astatic needle . . 98 74 Magnetism developed by the electrical current 98 75 " " " 98 76 Electro-magnet . . 99 77 Apparatus for oxygen 102 78 Hydro-pneumatic trough 103 79 Transferring gases . 104 80 Pepy's hydro-pneumatic apparatus . . 104 81 Apparatus for hydrogen 107 82 Levity of hydrogen . 108 83 Diffusion of gases . 109 84 Hemming' s safety jet . 110 85 Musical sounds by hy- drogen . . Ill 86 Catalytic effect of pla- tinum . . .112 87 Decomposition of water 113 88 Eudiometer of Cavendish 113 89 Analysis of water . 114 90 Preparation of nitrogen 117 91 Analysis of air . . 118 92 Ure's eudiometer < ; 119 93 Preparation of nitric acid 120 94 " protoxide of nitrogen 122 95 Crystalline form of car- bon . . . . 124 96 " " " 124 97 " " " 124 98 " " " 124 99 Preparation of carbonic acid . . . .126 100 Mode of forming caout- chouc connecting tubes 126 101 Crystalline form of sul- phur . . .128 102 Crystals of sulphur . 128 103 Crystalline form of sul- phur . . .128 104 Preparation of phosphorus 134 105 " chlorine 137 FIG. PAGE 106 Preparation of hydro- chloric acid . . 139 107 Safety tube . . .140 108 Combustion under water 142 109 Preparation of hydriodic acid .... 144 110 " silica . 147 111 Blastfurnace . . 154 112 Reverberatory furnace 154 113 Structure of flame . 155 114 Mouth blowpipe . . 155 115 Structure of blowpipe flame . . .156 116 Argand spirit-lamp . 156 117 Common " . 156 118 Mitchell's " . 157 119 Gas " . 157 120 Davy's safety " . 158 121 Hemming's safety-jet . 158 122 Effect of metallic coil . 158 123 Apparatus for sul- phuretted hydrogen . 161 124 Multiple proportions . 180 125 Water in its usual state 186 126 " undergoing elec- trolysis . . 186 127 Voltameter ^ . ; . 187 128 Decomposition without contact of metals . 188 129 Wollaston's voltaic bat- tery .... 190 130 Daniell's constant " 191 131 Grove's " " 191 132 Electrotype . . .192 133 Lead-tree . . .192 134 Wire-drawing . . 196 135 Wollaston's goniometer 201 136 Reflecting " 201 137 principles of . . 202 138 Crystals, regular system 203 139 " square prisma- tic system . 204 140 " right prisma- tic system . 204 141 " oblique pris- matic system 205 142 " doubly oblique prismatic system . 205 LIST OF ILLUSTRATIONS. XX111 FlG. PAGE 143 Crystals, rhonibohedral system . 206 144 " passage of cube to octahedron 206 145 " " octahedron to tetrahedron 207 146 Alkalimeter . . 224 147 Apparatus for determin- ing carbonic acid . 225 148 Iron manufacture. Blast furnace . . . 259 149 Crystals of arsenious acid^. . . .287 150 Subliming tube for arsenic 288 151 Marsh's test . . 289 152 Weighing tube . . 315 153 Combustion . . 316 154 Chauffer . . .316 155 Water tube . . .316 156 Carbonic acid bulbs . 316 157 Apparatus complete . 317 158 Bulbs for liquids . .318 159 Comparative determina- tion of nitrogen . 319 160 Pipette . . .319 FIG. PAGE 161 Absolute estimation of nitrogen . . . 320 162 Varrentrap's and Will's method . . . 322 163 Determination of the density of vapors . 325 164 Starch granules . . 332 165 Preparation of ether . 353 166 " olefiantgas 355 167 " Dutch liquid 356 168 Catalysis . . .363 169 Preparation of kakodyle 371 170 " benzoic acid 383 171 " tannic acid 400 172 Uric acid crystals . 420 173 Blood globules . . 469 174 Pus " . . 473 175 Milk " ' . . 474 176 Trommer's test . . 479 177 Uric acid calculus . 480 178 Urate of ammonia cal- culus . . . 480 179 Fusible calculus . . 480 180 Mulberry calculus 481 MANUAL OF CHEMISTRY. INTRODUCTION. THE Science of Chemistry has for its object the study of the nature and properties of all the materials which enter into the composition or structure of the earth, the sea, and the air, arid of the various organized or living beings which inhabit these latter. Every object accessible to man, or which may be handled and examined, is thus embraced by the wide circle of Chemical Science. The highest efforts of Chemistry are constantly directed to the discovery of the general laws or rules which regulate the formation of chemical com- pounds, and determine the action of one substance upon another. These laws are deduced from careful observation and comparison of the properties and relations of vast numbers of individual substances; and by this method alone. The science is entirely experimental, and all its conclusions the results of skillful and systematic experimental investigation. The applications of the discoveries of chemistry to the arts of life, and to the relief of human suffering in disease, are in the present state of the science both very numerous and very important, and encourage the hope of still greater benefits from more extended knowledge than that now enjoyed. In ordinary scientific speech the term chemical is applied to changes which permanently affect the properties or characters of bodies, in opposition to effects termed physical, which are not attended by such consequences. Changes of decomposition or combination are thus easily distinguished from those temporarily brought about by heat, electricity, magnetism, and the at- tractive forces, whose laws and effects iie within the province of Physics or Natural Philosophy. Nearly all the objects presented by the visible world are of a compound nature, being chemical compounds, or variously disposed mixtures of chemi- cal compounds, capable of being resolved into simpler forms of matter. Thus, 26 INTRODUCTION. a piece of limestone or marble by the application of a red-heat is decomposed into quicklime and a gaseous body, carbonic acid. Both lime and carbonic acids are in their turn susceptible of decomposition, the first into a metal, calcium and oxygen, and the second into carbon and oxygen. For this pur- pose, 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 elements; riot 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 commence- ment of the present volume. 27 PART I. -PHYSICS. OF DENSITY AND SPECIFIC GRAVITY. IT is of great importance in the outset to understand clearly what is meant by the terms density and specific gravity. By the density of a body is meant its wiass, 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. 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 expression 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 -794 at 60, we mean that equal bulks of these two liquids and of distilled water possess weights in the proportion of the numbers 1-85, -794, and 1 ; or 1850, 794, and 1000. It is necessary to be particular about the temperature; for, as will be hereafter shown, liquids are extremely expansible by heat; otherwise, a con- stant bulk of the same liquid will not retain a constant weight. It will be proper to begin with the description of the mode in which the specific gravity of liquids is determined ; this is the simplest case, and the one which best illustrates the general principle. In order to obtain at pleasure the specific gravity of any particular liquid compared with that of water, it is only requisite to weigh equal bulks at the standard temperature, and then divide the weight of the liquid by the weight of the water; the quotient will of course be greater or less than unity, as the liquid experimented on is heavier or lighter than water. Now, to weigh equal bulks of two fluids, the simplest and best method is clearly to weigh them in succession in the .same vessel, taking care that it is equally full on both occasions, a condition very easy of fulfillment. A thin glass bottle, or flask, with a narrow neck, is procured, of the figure represented in the margin (p. 28), and of such capacity as to contain when filled to about half-way up the neck, exactly 1000 grains of distilled water at 60. Such a flask is easily procured from any one of the Italian artificers, to be found in every large town, who manufacture cheap thermometers for sale. A counterpoise of the exact weight of the empty bottle is made from a bit of brass, an old weight, or something of the kind, and carefully adjusted by * In other words, density means comparative mass, and specific gravity compara- tive weight. These expressions, although really relating to distinct things, are often used quite indifferently in chemical writings, and without practical inconvenience, since mass and weight are directly proportional to each other. 28 DENSITY AND SPECIFIC GRAVITY. Fig. 1. filing: an easy task. The bottle is then graduated, by introducing water at 60, until it exactly ba- lances the 1000-grain weight and counterpoise in the opposite scale; the height at which the water stands in the neck is marked by a scratch, and the instrument is complete for use. The liquid to be examined is brought to the temperature of 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 di- rectly ascertained. A watery liquid in a narrow glass tube always presents a curved surface from the molecular action of the glass, the concavity being upwards. It is better, on this account, in graduating the bottle, to make two scratches, as represented in the drawing, 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 which, also, it may be observed, answers perfectly well for writing upon glass, in the absence of a proper diamond-pencil. The specific gravity bottle above described differs from those commonly made for sale by the instrument-makers. These latter are constructed with a perforated stopper, so arranged that when the bottle is quite filled, the stopper put in its place, and the excess of liquid which flows through the hole wiped from the outside, a constant measure is always had. There are incon- veniences attending the use of the stopper which lead to a preference of the open bottle with merely a mark on the neck, even when very volatile liquids are experimented with. It will be quite obvious that the adoption of a flask holding exactly 1000 grains of water has no other object than to save the trouble of a very trifling calculation ; any other quantity would answer just as well, and, in fact, the experimental chemist is often compelled to use a bottle of much smaller di- mensions, from scarcity of the liquid to be examined. The shape is also in reality of little moment ; any light phial with a narrow neck may be em- ployed, not quite so conveniently, perhaps, as a specific gravity bottle. The determination of the specific gravity of a solid is also an operation of great facility, although the principle is not so obvious. As it would be im- possible to put in practice a direct method like that indicated for liquids, re- course is had to another plan. The celebrated theorem of Archimedes affords a solution of the difficulty. The theorem may be thus expressed : When a solid is immersed in a fluid, it loses a portion of its weight; and this portion is equal to the weight of the fluid which it displaces; that is, to the weight of its own bulk of that fluid. It is easy to give experimental proof of this very important proposition, as well as to establish it by reasoning. The drawing (fig. 2) represents a little apparatus for the former purpose. This'consists of a thin cylindrical vessel of brass, into the interior of which fits very accurately a solid cylinder of the same metal, thus exactly filling it. When the cylinder is suspended beneath the bucket, as seen in the sketch, the whole hung from the arm of a balance and counterpoised, and then the cylinder itself immersed in water, it will be found to have lost a certain weight ; and that this loss is precisely equal to the weight of an equal bulk of water, may then be proved by filling the bucket to the brim, whereupon the equilibrium will be restored. The consideration of the great hydrostatic law of fluid pressure easily DENSITY AND SPECIFIC GRAVITY. 29 proves the truth of the principle laid down. Let the reader figure to himself a vessel of water, having im- mersed 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 heightof the column. It is independent of the form and lateral dimensions of the vessel or immersed body. Moreover, owing to the peculiar physical constitution of fluids, this pressure is exerted equally in every direction, up- wards, downwards, and laterally, with equal force. The floating body is in a state of equilibrium ; therefore the pressure downwards caused by its gravitation must be exactly compensated by the upward transmitted pressure of the column of water a, 6. 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 reason- ing may be applied to a body of irregular form; be- sides, a solid of any figure may be divided by the imagination 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 de- termining 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 completely in pure water at 60, 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 re- quired than to find, by division, how many times the latter number is contained in the former; the quotient will Ije the density, water being taken =1. For example : Fig. 2. Fig. 3. ...I Fig. 4. 30 DENSITY AND SPECIFIC GRAVITY. The quartz-crystals weigh in air . . . 293.7 grains. When immersed in water, they weigh . . .180.1 Difference, being the weight of an equal volume of water 113.6 293 7 = 2.58, the specific gravity required. The arbitrary rule is generally thus written: "Divide the weight in air by the loss of weight in water, and the quotient will be the specific gravity." In reality, it is not the weight in air which is required, but the weight the tody would have in empty space : the error introduced, namely, Fig. 5. the weight of an equal bulk of air, is so trifling that it is usually neglected. Sometimes the body to be examined is lighter than water, and floats. In this case, it is first weighed and afterwards attached to a piece of metal, heavy enough to sink it, and suspended from the balance. The whole is then exactly weighed, immersed in water, and again weighed. The dif- ference between the two weighings gives the weight of a quantity of water equal in bulk to both together. The light substance is then detached, and the same operation of weigh- ing in air, and again in water, repeated on the piece of metal. These data give the means of finding the specific gravity, as will be at once seen by the following example : Light substance (a piece of wax) weighs in air ' ." 133.7 grains. Attached to a piece of brass, the whole now weighs . 183.7 Immersed in water, the system weighs . , 38.8 Weight of water equal in bulk to brass and wax 144.9 Weight of brass in air . . . . . 50.0 Weight of brass in water jvv--- . -. --;--- 44.4 Weight of equal bulk of water . . % . . 5.G 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 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-bub- bles; otherwise a false result will be obtained. Other cases require mention in which these operations must be modified to meet particular difficulties. One of these happens when the substance is dissolved or acted upon by water. This difficulty is easily conquered by sub- stituting some other liquid of known density which experience shows is with- out action. Alcohol or oil of turpentine may generally be used when water is inadmissible. Suppose, for instance, the specific gravity of crystalized sugar is required, we proceed in the following way : The specific gravity of the oil of turpentine is first carefully determined ; let it be .87 ; the sugar is next weighed in the air, then suspended by a horse-hair, and weighed in DENSITY AND SPECIFIC GRAVITY. 31 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 w eight 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 perfectly 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 - - =3.333 specific gravity. oU 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 com- mon 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 the body, inasmuch as its whole weight is counterpoised by a Fig. 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, 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 specific gravity of a fluid. In this manner little glass beads of known specific gravities are sometimes employed in the arts to ascertain in a rude manner the specific gravity of liquids; the one DENSITY AND SPECIFIC GRAVITY. Fig. 7. that floats indifferently beneath the surface, without either sinking or rising, has of course the same specific gravity as the liquid itself; this is pointed out by the number marked upon the bead. The hydrometer in general use consists of a floating vessel of thin metal or glass, having a weight beneath to maintain it in an upright posi- tion, 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 hydro- meter float, because a smaller displacement of fluid will counterbalance its weight. For the same rea- son, 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 differ- ent names, according to the kind of liquid for which they are intended; but the principle is the same in all. The graduation is very commonly arbitrary, two or three different scales being unfortunately used. These may be sometimes reduced, however, to the true numbers expressing the specific gravity by the aid of tables of comparison drawn up for the purpose. A very convenient and useful instrument in the shape of a small hydrometer 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.f The determination of the specific gravity of gases and vapors of volatile liquids is a problem of very great practical importance to the chemist ; the theory of the operation is as simple as when liquids themselves are concerned, but the processes are much more delicate, and involve besides cer- tain corrections for differences of temperature and pressure, founded on principles yet to be discussed. It will be proper to defer the consideration of these matters for the present. The method of determin- ing the specific gravity of a gas will be found de- Fig. 8. * This and other instruments described or figured in the course of the work, may be had of Mr. Newman, 122 Regent street, upon the excellence of whose workman- ship reliance may be safely placed. j- 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 represent the density of the liquid. If, for example, the surface of the liquid coincide with 13 on the scale, the specific gravity will be 1013, about the average density of healthy urine. R. B. DENSITY AND SPECIFIC GRAVITY. 33 scribed under the head of " Oxygen," and that of the vapor of a volatile liquid in the Introduction to Organic Chemistry.* * The mode of determining the specific gravity of a liquid by means of Fig. 9. 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 weight sustained in each case will give the relative weights of equal bulks of the liquids, and on dividing the weight of the liquid by the weight of the water, the quotient will be the specific gravity of the liquid experimented on. For 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 stopper. Now wipe the glass dry, and having removed the additional weights, immerse it in the other liquid, and restore the equipoise as before; this latter weight is the weight of a bulk of the liquid equal to that of the water. The latter divided by the former gives the specific gravity. For example : The glass stopper loses by immersion in water . . 171 grains. The glass stopper loses by immersion in alcohol . . 143 143 = .836 the specific gravity required. R. B. 34 PHYSICAL CONSTITUTION OF THE PHYSICAL CONSTITUTION OF THE ATMOSPHERE, AND OF GASES IN GENERAL. IT requires some little abstraction of mind to realize completely the singu- lar condition in which all things at the surface of the earth exist. We live at the bottom of an immense ocean of gaseous matter, which envelops every- thing, and presses upon everything with a force which appears, at first sight, perfectly incredible, but -whose actual amount admits of easy proof. Gravity being, so far as is known, common to all matter, it is natural to expect that gases, being material substances, should be acted upon by the earth's attraction, as well as solids and liquids. This is really the case, and the result is the weight or pressure of the atmosphere, which is 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 constitution of gases, upon which depends the principle of an extremely valuable instru- ment, the air-pump. Gases are in the highest degree elastic; the volume or space which a gas occupies depends upon the pressure exerted upon it. Let the reader imagine a cylinder, a, closed at the bottom, in which Fi - 10 - moves a piston, air-tight, so that no air can escape between the piston and the cylinder. Suppose now the piston be pressed down- wards with a certain force ; the air beneath it will be compressed into a smaller bulk, the amount of this compression depending on the force applied ; if the power be sufficient, the bulk of the gas may be thus diminished to one hundredth part or less. When the pressure is removed, the elasticity or tension, as it is called, of the included air or gas, will imme- diately force up the piston until it arrives at its first position. Again, take fig. b, and suppose the piston to stand about the middle of the cylinder, hav- ing air beneath in its usual state. If the piston be now drawn upwards, the air below will expand, so as to fill completely the enclosed space, and this to an apparently unlimited ex- tent. A volume of air which under ordinary circumstances ocupices 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 iu a state of extreme tenuity. This power of expansion which gases possess may have, and probably has, in reality, a limit; but the limit is never OE THE ATMOSPHERE. 35 reached in practice. We are quite safe in the assumption, that, for all pur- poses of experiment, however refined, gases are 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: mat- ter is under the influence of two opposite forces, one of which tends to draw the particles together, the other to separate them. By the preponderance of one or other of these forces, we have the three states called solid, liquid, and gaseous. When the particles of matter are immovably bound together by the attractive force, a solid substance results; when the forces are nearly balanced, we have a liquid, the particles of which are free to move, but yet to a certain extent held together ; and, lastly, when the attractive power seems to be completely overcome by its antagonist, we have a gas or vapor. Various names are applied to these forces, and various ideas entertained 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 the 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 cylinder, the space left beneath it must be void of air, since the piston-valve opens only in one direction; the air within the receiver having on that side nothing to oppose its elastic power but the weight of the little valve, lifts the latter, and escapes into the cylinder. So soon as the piston begins to -descend, the lower valve closes, by its own weight, or by the transmitted pressure from above, and communication with the receiver is cut off. As the descent of the piston continues, the air included within the cylinder becomes compressed, its elasticity is increased, and at length it forces open the upper valve, and escapes into the atmosphere. In this manner, a cylinder full of air is at every 36 PHYSICAL CONSTITUTION stroke of the pump removed from the receiver. During the descent of the piston, the upper valve remains open, and the lower closed, and the reverse during the opposite movement In practice, it is very convenient to have two such barrels or cylinders, ar- ranged side by side, the piston-rods of which are formed into racks, having a pinion, or small toothed wheel, between them, moved by a winch. By this Fig. 12. Fig. 13. contrivance the operation of exhaustion is much facilitated and the labor lessened. The arrangement is shown in fig. 12. A simpler and far superior form of air-pump is thus con- structed : the cylinder, which may be of large dimensions, is furnished with an accurately fitted solid piston, the rod of which moves, air-tight, through a contrivance called a stuffing-box, at the top of the cylinder, where also the only valve essential to the apparatus is to be found ; this 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 ex- hausted is made by a tube which enters the cylinder a lit- tle 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 , all communication is stopped between the air above the piston and the vessel to be exhausted; the enclosed air suf- fers compression, until it acquires sufficient elasticity to lift the metal valve and escape by bubbling through the oil. When the piston makes its descent, and this valve closes, a vacuum is left in the upper part of the cylinder, into which the air of the receiver rushes so soon as the piston has passed below the orifice of the connecting tube. In the silk valved air-pump exhaustion ceases when the elasticity of the air in the receiver becomes too feeble to OF THE ATMOSPHERE. 37 raise the valve ; in that last described, the exhaustion may, on the contrary, be carried to an indefinite extent, without, however, under the most favora- ble circumstances, becoming 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 dis- places 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 the drawing below. To return to the atmosphere. Air possesses weight : a light flask or globe of glass, furnished with a stop-cock and ex- hausted by the air-pump, weighs con- siderably 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 securely tying a piece of bladder over the mouth of an open glass receiver, and then exhausting the air from beneath it ; the bladder will become more and more con- cave, until it suddenly breaks. A thin square glass bottle, or a large air-tight tin box, may be crushed by withdrawing the support of th air in the inside. Steam- boilers have been often destroyed in this manner by collapse, in consequence of the accidental formation of a partial vacuum within. After what has been said on the subject of fluid pressure, it will scarcely be neces- sary 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 generated by their gravity. The sides and bottom of an exhausted vessel are pressed upon with as much force as the top. If a glass tube of considerable length could be perfectly exhausted of air, and then held in an upright position, with one of its ends dipping into a vessel of liquid, the latter, on being allowed access to the tube, would rise in its interior until the weight of the column balanced the 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 Fig. 14. I PHYSICAL CONSTITUTION Fig. 15. the column measured, means would be furnished for exactly estimating the amount of pressure exerted by the atmosphere. Such an instrument is the barometer : a straight glass tube is taken, about 36 inches in length, and sealed by the blow-pipe flame at one extremity ; it is then filled with clean, dry mer- cury, care being taken to displace all air bubbles, the open end stopped with a finger, and the tube inverted 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 atmospheric pressure, the space above the mercury in the tube being of necessity empty. The pressure of the atmosphere is thus seen to be capable of sustaining a column of mercury thirty 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 construction was attended with great difficulties, and it has been found impossible 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 pres- sure made upon it, and which is thus expressed : The volume of a gas is inversely as the pressure; the density and elastic force are directly as the pressure, and inversely as the volume. For instance. 100 cubic inches of gas under a pressure of 30 inches of mercury would expand to 200 cubic inches were the pressure reduced to one- half, and shrink, on the contrary, to 50 cubic inches if the original pressure were doubled. The change of density must necessarily be in the inverse proportion to that of the volume, and the elastic force follows the same rule. This, which is usually called the law of Mariotte, is easily demonstrable by direct experiment. A glass tube, about 7 feet in length, is closed at one end, and bent into the form represented, the open limb of the siphon being the longest. It is next attached to a board furnished with a movable scale of inches, and enough mercury is introduced to fill the bencl, the level being evenly adjusted, and marked upon the board. Mercury is now poured into the tube until it is found that the inclosed air has been reduced to one half of its former volume; and on applying the scale, it will be found that the level of the mercury in the open part of the tube stands very nearly 30 inches above that in the closed portion. The pressure of an additional "atmos- phere" has consequently reduced the bulk of the contained air to one-half. If the experiment be still continued until the volume of air is reduced to a OF THE ATMOSPHERE. 39 third, it will be found that the column measures 60 Fig. 16. inches, and so in like proportion as far as the experi- ment 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 vapors of volatile liquids, when remote from their points of liquefaction.* It is a matter of the greatest importance in practical chemistry, since it gives the means of making corrections for pressure, or deter- mining by calculation the change of volume which a gas would suffer by any given change of external pressure. Let it be required, for example, to solve the follow- ing problem: We have 100 cubic inches of gas in a graduated jar, the barometer standing at 29 inches ; how many cubic inches will it occupy when the column rises to 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 accom- panied 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 pressure at different elevations above the sea-level, but that, on the contrary, these must dimin- ish with the altitude, and very rapidly. The lower strata of air have to bear the weight of those above them ; they become in consequence denser and more compressed than the upper portions. The following table, which is taken from Mr. 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. in inches. . . . .1 . . .30 2.705. ... 2 ... 15 5-41 . . .4 . . .7.5 8.115. ... 8 ... 3.75 10-82 . . .16 . . . 1.875 13.525. . . 32 . . . .9375 16-23 . . .64 . . . .46875 * When near the liquefying point the law no longer holds ; the volume diminishes more rapidly than the theory indicates, a smaller amount of pressure being then sufficient. 40 PHYSICAL CONSTITUTION OF THE ATMOSPHERE. Fig. 17. The numbers in the first column form an arithmetical series, by the constant addition of 2.705; those in the second column an increasing geometrical series, each being the double of its pre- decessor; and those in the third, a decreasing geometrical series, in which each number is the half of that standing above it. In ascending into the air in a balloon, these effects are well observed ; the expansion of the gas within the machine, and the fall of the mercury in the barometer, soon indicate to the voyager the fact of his having left below him a considerable part of the whole atmosphere. The invention of the barometer, which took place in the year 1643, by Torricelli, a pupil of the celebrated Galileo, speedily led to the observation that the atmospheric pressure at the same level is not constant, but possesses, on the contrary, a small range of variation, seldom exceeding in Europe 2 or 2.5 inches, and within the tropics usually confined within much narrower limits. Two kinds of variations are distinguished ; regular or horary, and irregular or accidental. It has been ob- served, 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 sum- mer 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 men- tioned. The barometer is applied with great advantage to the measurement 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 fail 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 state of the pressure of the atmosphere. The marginal draw- ing represents a very convenient and economical siphon ba- rometer 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 represented. Pure and warm mercury is next introduced by successive portions until the tube is completely filled, and the latter being held in an upright position, the level of the metal in the lower and open limb is conveniently adjusted by displacing a portion 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 observation is to be taken, the lower extremity or zero of the scale is placed exactly even with the mercury in the short limb, and then the height of the column at once read off. HEAT. 41 HEAT. IT will be convenient to consider the subject of Heat under several sections, and in the following order : 1. Expansion of bodies, or effects of variations of temperature in altering their dimensions. 2. Conduction, or transmission of heat. 3. Change of state. 4. Capacity of bodies for heat. The phenomena of radiation must be deferred until a sketch has been given of the science of light. EXPANSION. If a bar of metal be taken, of such magnitude as to fit accurately to a gauge when cold, heated considerably, and again applied to the gauge, it will be found to have become enlarged in all its dimensions. When cold, it will once more enter the gauge. Again, if a quantity of liquid contained in a glass bulb, furnished with a narrow neck, be plunged into hot water, or exposed to any other source of Fig. 18. Fig. 19. Fig. 20. ' "'""IIHIHIHIIIIIIi 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, 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 princi- ple, 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 4* 42 HEAT. closed and expanded into a bulb, by the aid of the blowpipe flame, and the 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 vapor, 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 temperatures at the point required. This being satisfactorily adjusted, the heat is once more applied, until the column rises quite to the top ; and then the extremity of the tube is hermetically sealed by the blowpipe. The retraction of the mercury on cooling now leaves an empty space in the upper part of the tube, which is essential to the perfection of the instrument. The thermometer has yet to be graduated; and to make its indications comparable with those of other instruments, a scale, having certain fixed points, at the least two in number, must be adapted to it. It has been observed, that the temperature of melting ice, that is to say, of a mixture of ice and water, is always constant; a thermometer, already graduated, plunged into such a mixture, always marks the same degree of temperature, and a simple tube filled in the manner described, and so treated, exhibits the same effect in the unchanged height of the little mercurial column, when tried from day to day. The freezing point of water, or melting- point of ice, constitutes then one of the invariable temperatures demanded. Another is to be found in the boiling-point of water, which is always the same under similar circumstances. A clean metallic vessel is taken, into which pure water is put and made to boil; a thermometer placed in the boiling liquid invariably marks the same degree of temperature so long as the height of the barometer remains 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 France, and throughout the greater part of Germany, the scale called centi- grade is employed; 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 everywhere 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 the north of Germany and 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 labor which now so frequently has to be performed of translating the language of one scale into that of another. To effect this, presents, however, no great diffi- culty. Let it be required, for example, to know the degree on Fahrenheit's scale, which corresponds to 60 centigrade. 100 cent. = 180 Fahr., or 5 cent. = 9 Fahr. Consequently 5 : 9 : : GO : 108. HEAT. 43 But, then, as Fahrenheit's scale commences with 32 instead of 0, that num- ber must be added to the result, making 60 cent. = 140 Fahrenheit. 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 regu- larity 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 em- ployed 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 modifi- cations 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, be- cause the air in the upper and lower reservoir, being equally affected by such changes, no alteration in the height of the fluid column can occur. Accord- ingly, such instruments are called differential thermometers, since they serve to measure differences of temperatures between the two portions of air, while changes affecting both alike are not indicated. Fig. 22 shows another form of the same instrument. Fig. 21. 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 nrtifically 44 HEAT. 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. This is a general rule ; an exception is nevertheless to be found in certain curious liquids, which result from the condensation of gases, whose expansibility ex- ceeds that of the gases themselves. 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 nu- merous 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 correspond- ing curvature. Brass is more dilatable than iron ; if the bar be heated, there- fore, the former expands more than the latter, and forces the straight bar into a curve, whose convex side is the brass; if it be artificially cooled, the brass contracts more than the iron, and the reverse of this effect is produced. Fig. 23. Fig. 24. This fact has received a most valuable application. It is not necessary to insist on the importance of possessing instruments for the accurate measure- ment of time; such are absolutely indispensable to the suc- cessful cultivation of astronomical science, and not less useful to the navigator, from the assistance they give him in finding the longitude at sea. For a long time, notwithstanding the perfection of finish and adjustment 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 ma- chine were subject by alterations of temperature. A clock may be defined as an instrument for registering the number of beats made by a pendulum: now the time of oscillation of a pendu- lum depends principally upon its length ; any alteration in this condition will seriously affect the rate of the clock. The ma- terial of which the rod of the pendulum is composed is subject to expansion and contraction by changes of temperature; so that a pendulum adjusted to vibrate seconds at 60, would go too slow when the temperature rose to 70, from its elonga- tion, and too fast when the temperature fell to 50, 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 opposite direction HEAT. 45 Fig. 26. of the brass or zinc, it is possible to maintain under all circum- -Fig. 25. stances of temperature an invariable distance between the points of suspension and of oscillation. This is often called the gridiron pendulum ; fig. 24 will clearly illustrate its principle ; the shaded bars are supposed to be iron and the others brass. A still simpler compensation pendulum is thus constructed. The weight or bob, instead of being made of a disc of metal, con- sists 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 pen- dulum 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 the draw- ing. When the watch is exposed to a high tem- perature, 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 completely compensated. Many other beautiful applications of the same prin- ciple might be pointed out; the metallic thermome- ter 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 lengthening which the bar had undergone. It remains, there- fore, to measure the amount of this dis- placement, which must be very small, even when the heat has been exceedingly intense. This is effected by the con- trivance, shown in the drawing in which the motion of the longer arm of the lever carrying the vernier of the scale is mul- tiplied by 10, in consequence of its supe- rior length. The scale itself is made Fig. 27. 46 HEAT. comparable with that of the ordinary thermometer, by plunging the instru- ment into a bath of mercury near its point of congelation, and afterwards into another of the same metal in a boiling state, and marking off the interval. By this instrument the melting point of cast iron was fixed at 2786 Fahrenheit, and the greatest heat of a good wind-furnace at about 3300. The actual amount of expansion which different solids undergo by the same increase of heat, has been carefully investigated. The following are some of the results obtained by MM. Lavoisier and Laplace. The fraction indicates the amount of expansion in length suffered by rods of the under- mentioned bodies in passing from 32 to 212. Soft iron Gold .... Copper .... Brass .... Silver . Lead English flint glass . Common French glass TTIT Glass without lead . Another specimen . Steel untempered . Tempered steel . . From the linear expansion, the cubic expansion (or increase of volume) may be easily calculated. When an approximation only is wanted, it will be sufficient to triple the fraction expressing the increase in one dimension. Metals appear to expand pretty miiformly for equal increments of heat within the limits stated, but above the boiling-point of water the rate of ex- pansion 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 indispen- sable 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 filling 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 result being evidently the difference of the two. Liquids vary exceedingly in this particular. The following table is taken from Peclet's Elemens de Physique. Apparent dilatation in glass between 32 and 212. Water . . . ." ^ Hydrochloric acid, sp.gr. 1.137 .... Nitric acid, sp. gr. 1.4 Sulphuric acid, sp. gr. 1.85 . . . . iV Ether Jj Olive oil . . . . . . . . iV Alcohol Mercury ......... -fa The expansion is, for the most part, uniform between these temperatures; but beyond 212 it becomes irregular and increasing. This is well seen in the case of mercury. HEAT. 47 Absolute expansion of mercury for 180 Between 32 and 212 . . . . Between 212 and 392 Between 392 and 572 The absolute amount of expansion of mercury is, for many reasons, a point of great importance ; it has been very carefully determined by a method inde- pendent of the expansion of the containing vessel. The apparatus employed for this purpose by MM. Dulong and Petit is shown in fig. 28, divested, how- ever, of many of its subordinate parts. It consists of two upright glass tubes, connected at their bases by a horizontal tube of much smaller dimensions. Since a free communication exists between the two tubes, mercury poured into the one will rise to the same level in the other, provided its temperature is the same in both tubes; when this is not the case, the hottest column will be the tallest, because the expansion of the metal diminishes its specfic gravity, and the law of hydrostatic equilibrium requires that the heights of such columns should be inversely as their densities. By the aid of the outer cylinders, one of the tubes is maintained constantly at 32, 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 be 6 inches high, and that at 212 6.108 inches, the in- crease in 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 tempera- ture of the air, and then artificially cooled. The liquid will be observed to * Below 4000 Fahrenheit the error may be neglected ; at 500^ it is about IP ; at G300 63. Renault. 48 HEAT. contract regularly, until the temperature falls to about 40, or 8 above the freezing-point. After this, a further reduction of temperature causes expan- sion instead of contraction in the volume of the water, and this expansion continues until the liquid arrives at its point of congelation, when so sudden and violent an enlargement takes place, that the vessel is almost invariably broken. At the temperature of 40, or more correctly, perhaps, 39-5, water is at its maximum density; increase or diminution of heat produces upon it, for a short time, the same effect. A beautiful experiment by Dr. Hope illustrates the same fact. If a tall jar filled with water at 50 or 60, and having in it two small thermometers, one at the bottom and the other near the surfuce, 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, after which it will remain stationary. At length the upper thermometer will also mark 40, but still continue to sink as rapidly as before, while that at the bottom remains stationary. It is easy to explain these effects : the water in the upper part of the jar is rapidly cooled by con- tact with the air; it becomes denser in consequence, and falls to the bottom, its place being supplied by the lighter and warmer liquid, which in its turn suffers the same change ; and this circulation goes on until the whole mass of water has acquired its condition of maximum density, that is, until the temperature has fallen to 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 behavior of water is attended by the most beneficial consequences, in shielding the inhabitants of the waters from exces- sive 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. Ice, how- ever, of great thickness forms over the shallow portions, and on the rivers, and accumulates in mounds upon the beaches where the waves are driven up by the winds. Sea-water has a maximum density at the same temperature as fresh water. The depths of the Polar Seas exhibit this temperature throughout the year, while the surface-water is in summer much above, and in winter much below, 40; in both cases being specifically lighter than water at that temperature. This gradual expansion of water cooled below 40, must be carefully distin- guished from the great and sudden increase of volume it exhibits in the act of freezing, and in which respect it resembles 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 morning split in fragments. The freezing of water in the joints and crevices of rocks is a most potent agent in their dis- integration. 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 vapors, when remote from their condensing-points, follow the same law. 2. The rate of expansion is not altered by a change in the state of com- pression, or elastic force of the gas itself. 3. The rate of expansion is uniform for all degrees of heat. HEAT. 49 4. The actual amount of expansion is equal to l-460th part of the volume of the gas at Fahrenheit, for each degree of the same scale.* It will be unnecessary to enter into any description of the methods of inves- tigation by which these results have been obtained ; the advanced student will find in Pouillet's Elemens de Physique, and in the papers of MM. Magnusf and RegnaultJ 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 example, to find the volume which 100 cubic inches of any gas at 50 would become on the temperature rising to 60. The rate of expansion is ? ^th of the volume at for each degree; or 460 measures at become 461 at 1, 462 at 2, . . 460 + 50 = 510 at 50, and 460 + 60 = 520 at 60. Hence Meas. at 50. Meas. at 60. Meas. at 50. Meas. at 60. 510 : 520 :: 100 : 101.96. This, and the correction for pressure, are operations of very frequent occur- rence 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 experi- ments 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 ex- hibited 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 distant from their points of condensation, there is reason to believe that the law would be strictly fulfilled. The experiments of MM. Dulong and Petit give for the rate of expansion 55glh of the volume at : this is no doubt too high. Those of Rudburg give ^ySt part; of Magnus ^^th; and of Regnault ^^th : the fraction 5^$th is adopted in the text as a convenient number, sufficiently near the mean of the three preceding, to answer all purposes. The ready expansibility of air by heat gives rise to the phenomena of winds; in the temperate regions of the earth these are very variable and uncertain, * Or the amount of expansion is equal to l-492d part of the volume which the gas occupies at 32 F , for each degree of Fahrenheit's scale. R. B. f Poggendorf's Annalen, Iv. 1. I Ann. Chim. et Phys., 3d series, iv. 5, and v. 52. 5 50 HEAT. Fig. 29. but within and near the tropics a much greater regularity prevails; of this the trade-winds furnish a beautiful example. The smaller degree of obliquity with which the sun's rays fall in the locali- ties mentioned, occasions the broad belt thus stretching around the earth to be- come more heated than any other part of the surface. The heat thus acquired by absorption is imparted to the lower stratum of air, which, becoming expanded, rises, and gives place to another, and in this manner an ascending current is established the colder and heavier air streaming in laterally from the more temperate regions, north and south, to supply the partial vacuum thus occasioned. A circulation so commenced will be completed in obedience to the laws of hydrostatics, by the establishment of counter-currents in the higher parts of the atmosphere, having direc- tions the reverse of those on the surface. Such is the effect produced by the unequal heating of the equatorial parts, or, more cor- rectly, 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 equa- torial parts must have a motion of 1000 miles per hour; this velocity di- minishes 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 supply the place of that raised aloft by its diminished density, brings with it the degree of momentum 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 im- mediately 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 com- bined effects of the unequal heating and of the movement of rotation is to generate in the northern hemisphere a constant northeast wind, and in the southern hemisphere an equally constant south-east wind. In the same manner the upper or return current is subject to a change of direction in the reverse order; the rapidly-moving wind of the tropics, transferred laterally towards the poles, is soon found to travel faster than the earth beneath it, producing the effect of a westerly wind, which modifies the primary current. The regularity of the trade-winds is much interfered with by the neighbor- hood of large continents, which produce local effects upon a scale sufficiently great to modify deeply the direction and force of the wind. This is the case in the Indian Ocean. They usually extend from about the 28th degree of latitude in both hemispheres, to within 8 of the equator, but are subject to some variations in this respect. Between them, and also beyond their bound- HEAT. 51 aries, lie belts <^f calms and light variable winds, and beyond these latter extending into higher latitudes in both hemispheres, westerly winds usually prevail. The general direction of the trade-wind of the Northern hemisphere is E.N.E., and that of the Southern hemisphere E.S.E. The trade-winds, it may be remarked, furnish an admirable physical proof of the reality of the earth's movement of rotation. The theory of the action of chimneys, and of natural and artificial ventila- tion, 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 pressure upwards of the column of water, ac, 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 water, then the latter force has the ascendency, and the body sinks. All things so described exist in a common chimney; the solid body, of the same density as that of the fluid in which it floats, is represented by the air in the chimney-funnel; the space ab represents 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 pres- sure 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 jjiay be often noticed in the sum- mer time by the smoke from neighboring 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^ and more recently it has been applied to dwelling-houses and assembly-rooms < c 52 HEAT. 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 traverse every part of the mine, and sweep before it the noxious gases, but too frequently present. CONDUCTION OF HEAT. Different bodies possess very different conducting powers with respect to heat : if two similar rods, the one of iron 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 esta- blished a numerical comparison of the conducting powers of many bodies; the following may be taken as a specimen: Gold . . .1000 Silver ... 973 Copper . . . 898 Iron ... 374 Zinc 363 Tin ... 304 Lead . . . 179 Marble . . . 23.6 Porcelain . . 12.2 Fire-clay . . 11.4 As a class, the metals are by very far the best conductors, although much difference exists between them; stones, dense woods, and charcoal, follow next in order; then liquids in general, and gases, whose conducting power is almost inappreciable. Under favorable circumstances, nevertheless, both liquids and gases may become rapidly heated; heat applied to the bottom of the containing vessel is very speedily communicated to its contents ; this, however, is not so much by conduction as by convection, or carrying. A complete 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 watef 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 uninter- mitting circulation of the liquid takes place as long as heat is applied. CHAKGE OF STATE. If equal weights of water at 32 and water at 174 be mixed, the tempe- rature of the mixture will be the mean of the two temperatures, or 103. If the same experiment be repeated with snow, or finely powdered ice, at 32, and water at 174, the temperature of the whole will be still only 32, but the ice will have been melted. 1 Ib. of water at 32 > ~ OQ 1 Ib. of water at 174 J = 2 Ib " water at 103 ' lib. of ice at 32 > 2 lb . water at 32. 1 lb. of water at 174 HEAT. 53 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. The heat, thus become insensible to the thermometer in effecting the lique- faction of the ice, is called latent heat, or, better, heat of fluidity. Again, let a perfectly uniform source of heat be imagined, of such intensity that a pound of water placed over it would have its temperature raised 10 per minute. Starting with water at 32, in rather more than 14 minutes its temperature would have risen to 174; but the same quantity of ice at 32, 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 communi- cated 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 ; 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. This curious condition of instable equilibrium shown by the very cold water in the preceding experiment, may be reproduced with a variety of solutions which tend to crystallize or solidify, but in which that change is for a while suspended. Thus, a solution of crystallized sulphate of soda in its own weight of warm water, left to cool in an open vessel, deposits a large quantity of the salt in crystals. If the warm solution, however, be filtered into a clean flask, which when full is securely corked and set aside to cool undisturbed, no crystals will be deposited, even after many days, until the cork is withdrawn and the contents of the flask violently shaken. Crystal- lization then rapidly takes place in a very beautiful manner, and the whole becomes perceptibly warm. The law thus illustrated in the case of water is perfectly general. When- ever a solid becomes a liquid, a certain fixed and definite amount of heat disappears, or becomes latent; and conversely, whenever a liquid becomes a solid, heat to a corresponding extent is given out. The amount of latent heat varies much with different substances, as will be seen by the table : Water* . 142 Sulphur . . 145 Lead 162 Zinc . . 493 Tin . . 500 Bismuth 550 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, 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 in chemical experi- ments to cool receivers and condense the vapors of volatile liquids. Pow- dered crystallized chloride of calcium and snow produce cold enough to freeze mercury. Even powdered nitrate of potash, or sal-ammoniac, dissolved in water, occasions a very notable depression of temperature ; in every case, in short, in which solution is unaccompanied by energetic chemical action, cold is produced. * MM. De la Provostaye and Regnault, Ann. Chim. et Phys., 3d series, via. 1. 5* 54 HEAT. No relation is to be traced between the actual melting-point of a substance, 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 accompanied by absorption of sensible heat, and the reverse by its disengagement. The latent heat of steam and other vapors may be ascertained by a similar mode of investigation to that employed in the case of water. When water at 32 is mixed with an equal weight of water at 212, the whole is found to possess the mean of the two temperatures, or 122; on the other hand, 1 part by weight of steam at 212 when condensed into cold water, is found to be capable of raising 5.6 parts of the latter from the free/ing to the boiling-point, or through a range of 180. Now 180 X 5 - G = 1008; that is to say, steam at 212 in becoming water at 212 parts with enough heat to raise a weight of water equal to its own (if it were possible) 1008 of the thermometer. When water passes into steam, the same quantity of sen- sible heat becomes latent. The vapors 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. Vapor of water 967 " alcohol 442 " ether ...... 302 " petroleum 178 " oil of turpentine .... 178 " nitric acid ..... 532 " liquor ammonias .... 837 " vinegar 875 Ebullition is occasioned by the formation of bubbles of vapor within the body of the evaporating liquid, which rise to the surface and there break like bubbles of permanent gas. This occurs in different liquids at very different temperatures; under the same circumstances, the boiling-point is quite con- stant, and often becomes a physical character of great importance in distin- guishing liquids which much resemble each other. A few cases may be cited in illustration : Substance. Boiling-point. Ether 96 Sulphuret of carbon . . . . . 115 Alcohol 177 Water 212 Nitric acid, strong 248 Oil of turpentine 312 Sulphuric acid ...... 620 Mercury . ' . . . . . 662 For ebullition to take place, it is necessary that the elasticity of the vapor should be able to overcome the cohesion of the liquid and the 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; in a partially exhausted receiver or on a mountain top it boils at a much lower temperature; and in the best vacuum of an excellent air-pump, over oil of vitriol, which absorbs the vapor, it will often enter into violent ebullition while ice is in the act of formkig upon the surface. On the other hand, water confined in a very strong metallic vessel may be restrained from boiling by the pressure of its own vapor to an almost unlimited HEAT. 55 extent ; a temperature of 350 or 400 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 illus- trative of the effect of diminished pressure in depressing Fig. 32. the boiling-point of a liquid. A little water is made to boil for a few minutes in a flask or retort placed over a lamp, until the air has been chased out, and the steam issues freely from the neck. A tightly fitting cork is then inserted, and the lamp at the same moment withdrawn. When the ebullition ceases it may be renewed at pleasure for a considerable time by the affusion of cold water, which, by condensing the vapor within, occasions a partial vacuum. The nature of the vessel, or rather, the state of its 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, while in the second it will often rise to 221, or even higher; a momentary burst of vapor then ensues, and the thermometer sinks a few degrees, after which it rises again. In this state the introduction of a few metallic filings, or angular fragments of any kind, occasions a lively disengagement of vapor, while the temperature sinks to 212, and there remains stationary. These remarkable effects must be attributed to an attraction between the surface of the vessel and the liquid.f A cubic inch of water in becoming steam under the ordinary pressure of the atmosphere expands into 1696 cubic inches, or nearly a cubic foot. Steam, not in contact with water, is affected by heat in precisely the same * Marcet, Ann. China, et Phys., 3d series, v. 449. f A remarkable modification of the relation between the temperature of liquids and the vessel containing them, results where the repulsive action predominates. When a small quantity of water is thrown into a red-hot platinum crucible, it assumes a spheroidal form, presents no appearance of ebullition, but only a rotary motion, and evaporates very slowly ; but when the temperature falls to 300, this spheroidal con- dition 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 vapor which is formed and surrounds the globule, but on the fall in temperature, the tension lessens and with it the repulsive action, contact takes place and the heat is rapidly communicated to the liquid, which at once is converted into steam. So slight is the influence of the caloric of the vessel on the contained liquid in this condition, that 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 another heated nearly to ebullition and whose boiling-point is high, the spheroidal state is likewise assumed, as \vater 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 sensation of heat. When wet with water it may be dipped into melted lead without injury or strong sensation of heat, and still less is perceived if alcohol or ether be used. A similar experiment has been performed with melted cast iron as it runs from the furnace, and the 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. 56 HEAT. 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 pro- portion. This elastic force of steam in contact with water, at different temperatures, has been very carefully determined by MM. Arago and Dulong. The force is expressed in atmospheres; the absolute pressure upon any given surface can be easily calculated, allowing 14.6 Ibs. to each atmosphere. The experi- ments were carried to twenty-five atmospheres, at which point the difficulties and danger became so great as to put a stop to the inquiry ; the rest of the table is the result of calculations founded on the data so obtained. Pressure of steam in atmospheres. 1 * . 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 9 10 11 12 Corresponding temp. Fahr. 212 234 251 264 275 285 294 300 308 314 320 326 332 337 342 351 359 367 374 Pressure of steam in atmospheres. 13 14 15 16 17 18 19 20 21 22 23 24 25 30 35 40 45 50 Corresponding ternp. Fahr. 381 387 393 398 404 409 414 418 423 427 431 436 439 457 473 487 491 511 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, and that of the other 350 or 400. 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 tempera- ture 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.* The economical applications of steam are numerous and extremely valuable ; they may be divided into two classes; those in which the heating power is employed, and those in which its elastic force is brought into use. The value of steam as a source of heat depends upon the facility with which it may be conveyed to distant points, and upon the large amount of * The proposition in the text, of the sum of the latent and sensible, heat of steam being a constant quantity, is known by the name of Watt's law, having been deduced by that illustrious man from experiments of his own. It has always agreed well with the rough practical results obtained by engineers, and has lately been confirmed to a great extent, although not completely, by a series of elaborate experiments by M. Regnault. HEAT. 57 Fig. 33. Fig. 34. latent heat it contains, which is disengaged in the act of condensation. An invariable temperature of 2 1 2, 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-ba'ths of various forms are used in the arts with great convenience, and also by the scientific chemist for drying filters and other objects where excessive heat would be hurtful; a very good instrument of the kind was contrived by Mr. Everitt. It is merely a small kettle, surmounted by a double box or jacket, into which the substance to be dried is put, and loosely covered by a card. The apparatus is placed over a lamp, and may be left without attention for many hours. A little hole in the side of the jacket gives vent to the excess of steam. The principle of the steam-engine may be de- scribed in a few words : its mechanical details do not belong to the design of the present volume. The machine consists essentially of a cylinder of metal a, 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 con- nected with the machinery to be put in motion, directly, or by the intervention of an oscillating beam. A pipe communicates with the interior of the cylinder, and also with a vessel surrounded with cold water, called the condenser, 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 con- denser, in such a manner that while the steam is allowed to press with all its force upon one side of the piston, the other, open to the condenser, is necessarily vacuous. The valve is shifted by the engine itself at the proper moment, so that the piston is alternately driven by the steam up and down against a vacuum. A large air-pump, not shown in the engraving, is connected with the condenser, and serves to remove any air that may enter the cylinder, and also the water produced by condensation, together with that which may have been injected. Such is the vacuum or condensing steam- engine. In what is called the high-pressure engine the condenser and air-purnp 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 over- come 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 com- pensated by the absence of the air-pump and the increased simplicity of the 58 HEAT. whole machine. Large engines, both on shore and in stearn-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 Ibs. 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 ^th or even y^th of the stroke. The process of distillation, which may now be noticed, is very simple; its object is either to separate substances which rise in vapor at different tem- peratures, or to part a volatile liquid from a substance incapable of volatiliza- tion. The same process applied to bodies which pass directly from the solid Fig. 35. to the gaseous condition, and the reverse, is called sublimation. Every distil- latory apparatus consists essentially of a boiler, in which the vapor is raised, and of a condenser, in which it returns to the liquid or solid condition. In the still employed for manufacturing purposes, the latter is usually a spiral metal tube immersed in a tub of water. The common retort awd receiver constitute the simplest and most generally useful arrangement for distillation on the small scale ; the retort is heated by a lamp or a charcoal fire, and the receiver is kept cool, if necessary, by a wet cloth, or.it may be surrounded with ice. (Fig. 35.) The condenser of Professor Liebig is a very valuable instrument in the laboratory; it consists of a glass tube tapering from end to end, fixed by per- forated corks in the centre of a metal pipe, provided with tubes so arranged HEAT. 59 hat 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, and extremely volatile liquids condensed. Fig. 36. Liquids evaporated 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 increased with the temperature ; such an idea is incorrect. If a barometer-tube be carefully filled with mercury and in- verted 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 tempera- ture. 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 vapor which instantaneously rises from the water into the vacuum; and that this effect is really due to the elasticity or tension of the aqueous vapor, is easily proved by exposing the barometer to a heat of 212, when the depression of the mercury will be complete, and it will stand at the same level within and without the tube, indi- cating that at that temperature the elasticity of the vapor is equal to that of the atmosphere a fact which the phenomenon of ebullition has already shown. By placing over the barometer a wide open tube dipping into the mercury below, and then filling this tube with water at dif- ferent temperatures, the tension of the aqueous vapor 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 doivn one inch against the pressure of the atmosphere, would of course elevate a column of mercury to the Fig. 37. 60 HEAT. same height against a vacuum, and in this way the tension may be very con- veniently expressed. The following table was drawn up by Dr. Dalton, to whom we owe the method of investigation. Temp. 32 40 50 60 70 80 90 100 110 120 Tension in inches of mercury. .200 .263 .375 - . , : .524 y.- .721 v ' 1.000 1.360 1.860 2.530 3.330 Temp. 130 140 150 160 170 180 190 200 212 Tension in inches of mercury. 4.34 5.74 . : - 7.42 X 9.46 X" 12.13 15.15 />:.' 19.00 23.64 30.00 Fig. 38. Other liquids tried in this manner are found to emit vapors of greater or less tension, for the same temperature according to their different degrees of volatility : thus, a little ether introduced into the tube depresses the mercury 10 inches or more at the ordinary temperature of the air ; oil of vitriol, on the other hand, does not emit any sensible quantity of vapor until a much greater heat is applied; and that given off by mercury itself in warm summer weather, although it may by very delicate means be detected, is far too little to exercise any effect upon the barometer. In the case of water, the evaporation is quite distinct and perceptible at the lowest temperatures, when frozen to solid ice in the barometer-tube ; snow on the ground, or on a house- top, may often be noticed to vanish, from the same cause, day by day in the depth of winter, when melting is impossible. There exists for each vapor a state of density which it cannot pass without losing its gaseous condition and be- coming liquid ; this point is called the condition of maxi- mum density. When a volatile liquid is introduced in sufficient quantity into a vacuum, this condition is always reached, and then evaporation ceases. Any attempt to increase the density of this vapor by compressing it into a smaller space will be attended by the liquefaction of a portion, the density of the remainder being unchanged. If a little ether be introduced into a barometer, and the latter slowly sunk into a very deep cistern of mercury, 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 ob- served, also, that, as the tube sinks, the little stratum of liquid ether increases in thickness, but no increase of elastic force occurs in the vapor above it, and, conse- quently, no increase of density, for tension and density are always, under ordinary circumstances at least, directly proportionate to each other in the same vapor. The point of maximum density of a vapor is dependent upon the temperature ; it increases rapidly as the tempera- ture rises. This is well shown in the case of water. Thus, taking the specific gravity of atmospheric air at HEAT. 61 212= 1000, that of aqueous vapor in its greatest possible state of com- pression for the temperature will be as follows: Temp. Specific gravity. Weight of 100 cubic inches. 32 5.690 . . .136 grains. 50 10.293 . . .247 60 14.108 . . .338 100 46.500 . . 1.113 150 170.293 . . 4.076 212 625.000 . . 14.962 The last number was experimentally found by M. Gay Lussac; the others e calculated upon that by the aid of Dr. Dalton's table of tensions. Thus, there are two distinct methods by which a vapor may be reduced to the liquid form : pressure, by causing increase of density until the point of maximum density for 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 vapor of water at 100, in the state above described, had its temperature reduced to 50, not less than .89* grain of fluid water would necessarily separate, or very nearly eight-tenths of the whole. Evaporation into a space filled with air or gas follows the same law as evaporation into a vacuum ; as much vapor rises, and the condition of maxi- mum 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%acuum, 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 vapor. The ultimate effect is, however, precisely the same. When to a quantity of perfectly dry gas confined in a vessel closed by mercury, a little water is added, the latter immediately begins to evaporate, and after some time as much vapor will be found to have risen from it as if no gas had been present, the quantity depending entirely on the temperature to which the whole is subjected. The tension of this vapor will add itself to that of the gas and produce an expansion of volume, which will be indi- cated by an alteration of level in the mercury. Vapor of water exists in the atmosphere at all times, and in all situations, and there plays a most important part in the economy of nature. The pro- portion of aqueous vapor present in the air is subject to great variation, and it often becomes exceedingly important to determine its quantity. This is easily done by the aid of the foregoing principles. If the aqueous vapor be in its condition of greatest possible density for the temperature, or, as it is frequently, but most incorrectly expressed, the air be saturated with vapor of water, the slightest reduction of temperature will cause the deposition of a portion in the liquid form. If, on the contrary, as is almost always in reality the case, the vapor of water be below its state of maximum density, that is, in an expanded condition, it is clear that a con- siderable fall of temperature may occur before liquefaction commences. The degree at which this takes place is called the dew-point, and it is determined with great facility by a very simple method. A little cup of thin tin plate or silver, well polished, is filled with water at the temperature of the air, and a # 100 cubic inches aqueous vapors at 100, weighing 1.113 grain, would at 50O be- come reduced to 91.07 cubic inches, weighing .2^3 grain. 6 HEAT. delicate thermometer inserted. The water is then cooled by dropping in frag- ments 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 and the dew-point 50 ; the elasticity of the watery vapor present would correspond to a maxi- mum density proper to 50, and would support a column of mercury .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 .375 inch by the vapor. Now a cubic foot of such a mixture must be looked upon as made up of a cubic foot of dry air, and a cubic foot of watery vapor, occupying the same space, and having tensions indicated by the numbers just mentioned. A cubic foot, or 1728 cubic inches of vapor at 70, would become reduced by contraction, according to the usual law, to 1G62.8 cubic inches at 50; this vapor would be at its maximum density, having the specific gravity pointed out in the table; hence 1662.8 cubic inches would weigh 4.1 1 grains. The weight of the aqueous vapor contained in a cubic foot of air will thus be ascertained. In this country the difference between the temperature of the air and the dew-point seldom reaches 30; but in the Deccan, with a temperature of 90, the dew-point has been seen as low as 29, 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 of a thermometer is covered with muslin, and kept wet wijji water; evapora- Fig. 39. tion produces cold, as will presently be seen, and accordingly the thermometer soon sinks below the actual temperature of the air. When it comes to rest, the degree is noticed, and from a comparison of the two temperatures an approximation to the dew-point can be obtained by the aid of a mathemati- cal formula contrived for the purpose. This is called the wet-bulb hygrometer ; it is often made in the manner shown in the margin, 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 connection with the little water reservoir. The perfect resemblance in every respect which vapors bear to permanent gases, led, very naturally, to the idea that the latter might, by the application of suitable means, be made to assume the liquid condition, and this surmise was, in the hands of Mr. Faraday, to a great 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 vapors 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, with the pressure in atmospheres, and the temperature at which the condensation took place.t * Mr. Daniell, Introduction to Chemical Philosophy, p. 154. f Phil. Trans, for 1823, p. 189. HEAT. 63 Atmospheres. Temp. Sulphurous acid . . 2 45 Sulphuretted hydrogen 17 . . . . . 50 Carbonic acid .. 36 ..... Chlorine ... 4 60 Nitrous oxide . .50 ^ 45 Cyanogen ... 3.6 45 Ammonia . . . 6.5 ..... 50 Hydrochloric acid .40 50 The method of proceeding was very simple ; the materials were sealed up in a strong narrow tube, together with a little pressure-gauge, consisting 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 Fig. 40. 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 tempera- ture, produced by means to be presently described, olefiant gas, hydriodic and hydrobromic acids, phosphuretted hydrogen, and the "gaseous fluorides of silicon and boron, were successively liquefied. Oxygen, hydrogen, nitrogen, nitric oxide, carbonic oxide, and coal gas, refused to liquefy at the temperature of 166 F. while subjected to pressures varying in the different cases from 27 to 58 atmospheres.* Sir Isambard Brunei, and, more recently, M. Thilorier, of Paris, succeeded in obtaining liquid carbonic acid in great abundance. The apparatus of M. Thilorier consists of a pair of extremely strong metallic vessels, 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 precaution 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 con- nected with the retort by a strong copper tube and a pair of union screw- joints ; a tube passes from the stop-cock downwards, and terminates near the bottom of the vessel. The operation is thus conducted : 2j Ib. of bicarbonate of soda, and 6} Ib. of water at 100, are introduced into the generator; oil of vitriol to the amount of 1 Ib. is poured into a copper cylindrical vessel, which is lowered down into the mixture, and set upright; the stop-cock is then screwed in to its place, and forced home by a spanner and mallet. The machine is next tilted up on its trunnions, that the acid may run out of the cylinder and mix with the * Phil. Trans, for 1845, p. 155. 64 HEAT. other contents of the generator; and this mixture is favored by swinging the whole backwards and forwards for a few minutes, after which it may be suffered to remain a little time at rest. Fig 41. 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 lique- fied acid will have accumulated in the receiver. When the receiver thus charged has its stop-cock opened, a stream of the liquid is forcibly driven up the tube by the elasticity of the gas contained in the upper part of the vessel. It will be quite proper to point out to the experimenter the great personal danger he incurs in using this apparatus, unless the greatest care be taken in its management. A dreadful accident has already occurred in Paris by the bursting of one of the iron vessels. The cold produced by evaporation has been already adverted to; it is simply an effect arising from the conversion of sensible heat into latent by the rising vapor, 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. When a little water is put into a watch glass, 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 withdrawn as perfectly as possible, the water is in a few minutes converted into a solid HEAT. 65 mass of ice, and the watch-glass very fre- Fig. 42. quently broken by the expansion of the lower portion of water in the act of freezing, a thick crust first forming on the surface. The ab- sence of the impediment of the air, and the rapid absorption of watery vapor by the oil of vitriol, induce such quick evaporation that the water has its temperature almost immedi- ately 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 figure represented, 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 va- por 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 evaporation of the liquefied carbonic acid, just mentioned. When a jet of that liquid is allowed to issue into the air from a narrow aperture, such an intense degree of cold is produced by the vaporization of a part, that the re- mainder freezes to a solid, and falls in a shower of snow. By suffering this jet of liquid to flow into a metal box provided for the purpose, shown in the drawing of the apparatus, a large quantity of the solid acid may be obtained ; it closely resembles snow in appearance, and when held in the hand occasions a painful sensation of cold, while it gra- dually disappears. Mixed with a little, ether, which seems to dissolve it, and poured upon a mass of mercury, the latter is almost instantly fro- zen, and in this way pounds of the solidified metal may be obtained. The temperature of a mixture of solid carbonic acid and ether in the air, measured by a spirit- thermometer, was found to be 106 F. ; when the same mixture was placed beneath the receiver of an air-pump, and exhaustion rapidly made, the temperature sank to 166 F. This was the method of obtaining extreme cold employed by Mr. Fara- day in his last experiments on the liquefaction of gases. Under such circumstances the liquefied hy- driodic, hydrobromic, and sulphurous acid gases, carbonic acid, nitrous oxide, sulphuretted hydrogen, cyanogen, and ammonia, froze to colorless transpa- rent solids, and alcohol became thick and oily. The principle of the cryophorus has been very happily applied by Mr. Daniell to the'constructioii G* I 66 HEAT. of a dew-point hygrometer. The instrument itself is figured in the preceding page. It consists of a bent glass tube terminated by two bulbs, one of which, 6, is half filled with ether, the whole being vacuous as respects atmospheric air. A delicate thermometer 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 temperature of the air. The upper bulb, a, 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 evaporation a distillation of the contained liquid takes place from one part of the apparatus to the other, by which such a reduction of tem- perature 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 difference of temperature indicated by the two thermometers is then read off. CAPACITY FOB HEAT j 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 in 30 minutes. If, now, the experiment be repeated with equal weights of mer- cury 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 temperature, quantities of heat in the 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, and oil at 40, be agitated toge- ther, the temperature of the whole will be found to be 80, instead of 70, the mean of the two ; and if the temperatures be reversed, that of the mix- ture will be only GO . Thus, I Ib. water at 100 1 Ib. of oil at 40? Loss by the water 20. Gain by the oil 40. 1 Ib. water at 40 ~) . I Ib. oil at 100 5 give a mixture at 6 5 hence Gain of water, 20. Loss of oil, 40. 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 sub- stances may be estimated. The first of these is by observing the quantity of ice melted by a given weight of the substance heated to a particular tempera- ture ; 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 preferred as the most accurate. The determination of the specific heat of different substances has occupied the attention of many experimenters ; among these MM. Dulong and Petit, and recently M. Regnault, deserve especial mention. It appears that each solid and liquid has its own specific heat; and it is probable that this, instead > give a mixture at SO 5 hence HEAT. 67 of being a constant quantity, varies with the temperature. Very little is known respecting the specific heats of gases, the investigation being attended with the greatest difficulties ; one thing, however, is clear, namely, that the specific heat varies with the state of condensation, being greater in propor- tion to the rarefaction of the gas. Thus, when air is expanded, a fall of tem- perature results, and when it is compressed, heat is evolved, which may even reach the temperature of 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 tro- pics, and this is due to increased capacity for heat of the expanded air. MM. Dulong and Petit observed in the course of their investigation a most remarkable circumstance. If the specific heats of bodies be computed upon, equal weights, numbers are obtained, all different, and exhibiting no relations among themselves ; but if, instead of equal weights, quantities be taken in the proportion of the chemical equivalents, an almost perfect coincidence in the numbers will be observed, showing that some exceedingly intimate con- nection 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 discovered far more gene- ral than any with which we are yet acquainted. The following table is extracted from the memoirs of M. Regnault, with whose results most of the experiments of Dulong and Petit closely coincide. Specific heat of Specific heat of Substances. equal weights. equivalent weights. Water .... 1 -00000 Oil of Turpentine . . '42593 Glass .... 19768 Iron . .... -11379 . . . S'0928 Zinc -09555 . . . 3.0872 Copper 09515 . . . 3.0172 Lead 03140 . . . 3.2581 Tin 05623 . . . 3.3121 Nickel 10863 . . . 3.2176 Cobalt 10696 . . . 3.1628 Platinum . ' .' . . .03243 . . . 3.2054 Sulphur 20259 . . . 3.2657 Mercury 03332 . . . 3.7128 Silver 05701 . . 6.1742 Arsenic 08140 . . . 6.1326 Antimony 05077 . . . 6.5615 Gold 03244 . . . 6.4623 Iodine 05412 . . . 6.8462 Bismuth 03084 . . . 2.1917 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. llegnault 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. 68 HEAT. 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 com- ponents. 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. 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 for every 45 feet, or 117 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."f" According to this idea, the earth must be looked upon as an intensely heated, fluid spheroid, covered with a crust of solid badly-conducting matter, cooled by radiation into space, and bearing somewhat the same proportion in thickness to the ignited liquid within, that the shell of an egg does to its fluid contents. Without venturing to offer any opinion on this theory, it may be sufficient to observe that it is not positively at variance with any known fact ; that the figure of the earth is really such as would be assumed by a fluid mass; and, lastly, that it offers the best explanation we have of the phenomena of hot springs and volcanic eruptions, and agrees with the chemi- cal 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, mechanical motion and chemical combination. To the first must be referred elevation of temperature by friction and blows ; and to the second, the effects of com- bustion 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; 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 in- * Ann. Chem. et Phys. Ixxiii. 5 ; and the same, 3d series, i. 129. f 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 seven years and two months. The temperature of the water, which is exceedingly abundant, is 82 Fahr. ; the mean temperature of Paris is 51 Fahr. ; the difference is 31, which gives a rate of about 1 for 58 feet. HEAT. 69 creased, 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 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 vapor 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 in- quiry. 70 LIGHT. LIGHT. THE subject of light is so little connected with elementary chemistry, that a very slight notice of some of the most important points will suffice. Two views have been entertained respecting the nature of light. Sir Isaac Newton imagined that luminous bodies emitted, or shot out, infinitely small particles in straight lines, which, by penetrating the transparent part of the eye and falling upon the nervous tissue, produced vision. Other phi- losophers drew a parallel between the properties of light and those of sound, and considered, that, as sound is eertainly 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 favor, 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 for the purpose is exactly known. Now, it has been found by accurate observation, that when the earth is at its greatest distance from Jupiter, the passage of any particular satellite into the shadow of the planet takes place 16 minutes and 26 seconds later than when the earth is at the opposite point of its orbit ; that is, in other words, that the ray of light from the satellite requires that interval of time to pass across 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 rivaled by that of the electrical agent. When a ray of light falls on a plane surface it may be disposed of in three ways; it may be absorbed and disappear altogether 5 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 fulls is of the kind called transparent, as glass or water. The law of reflexion is extremely sirn- Fig. 45. pie. If a line be drawn perpendicular to the surface upon which the ray falls, and a > the angle contained between the ray and the perpendicular measured, it will be found that the ray, after reflexion, takes such a course as to make with the per- pendicular an equal angle on the opposite side of the latter. A ray of light, B, falling at the point p, will be reflected in the di- rection PR', making the angle K'PP' equal to the angle UPP' ; or a ray from the point LIGHT. 71 r falling upon the same spot will be reflected to / in virtue of the same law. Further, 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. Paral- lel 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 true 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 language, is said to be refracted. Let r be a ray of light falling upon a plate of some transparent substance with parallel sides, such as a piece of thick plate glass ; and a its Fig. 46. point of contact with the upper surface. The ray, instead of hold- ing a straight course and passing into the glass in the direction a 6, will be bent downwards to c; and on leaving the glass, and issu- ing 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 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 positions, the refrac- tion increases with the obliquity. Let n represent a ray of light falling upon the surface of a mass of plate glass at the point A. From this point let a perpendicular 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 towards the perpendicular ; in the direction AH' 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 ; their length will be in the case supposed in the propor- tion of 3 to 2. These lines are termed the sines of the angles of incidence and refraction, respectively. Now let another ray be taken, such as r it is refracted in the same manner to /, 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 incidence and refrae- Fig. 47. 72 LIGHT. tion be again compared, they will still be found to bear to each other the proportion of 3 to 2. The fact is expressed by saying that the ratio of the sines of the incidence and refraction is constant for the same medium. The plane of refraction coincides moreover with that of incidence. Different bodies possess different refractive powers ; generally speaking, the densest substances refract most. Combustible bodies have been noticed to possess greater refractive power than their density would indicate, and from this observation Sir I. Newton predicted the combustible nature of the dia- mond long before anything was known respecting its chemical composition. 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 refrae.- tion to that of incidence, making the former unity: this is called the index of refraction for the substance. Thus, in the case of glass, the index of refrac- tion 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* . Ice ... Water . . ., . . .*-< Fluor spar . . .-.." Plate glass . , Rock crystal . Crysolite Sulphuret of carbon 1.10 1.30 1.34 1.40 1.50 1.60 1.69 1.70 Substances. Index of refraction. Garnet -, ,,% . 1.80 Glass, with much oxide of lead . *V 1.90 Zircon . .'. . , >. 2.00 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 properties of prisms and lenses depend. To take an example. Let the sketch 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 se- cond 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 sur- face of the lens producing its own independent effect. The light of the sun and celestial bodies in general, as well as that of the electric spark, and of all ordinary flames, is of a compound nature. If a ray of light from any of the sources mentioned be admitted into a dark room by a small hole in a shutter, or otherwise, and suffered to fall upon a glass prism in the manner described above, it will not only be refracted from its straight course, but will be decomposed into a number of colored rays, which may be received upon a white screen placed behind the prism. When solar light is employed the colors are extremely brilliant, and spread into an oblong space of considerable length. The upper part of this image or spectrum will be violet, and the lower red, the intermediate portion, commencing from the A siliceous deposit in the joints of the bamboo. LIGHT. 73 violet, being indigo, blue, green, yellow, and orange, all graduating imper- ceptibly into each other. This is the celebrated experiment of Sir I. Newton, and from it he drew the inference that white light is composed of seven Fig. 49. primitive colors, the rays of which are differently refrangible 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 colors 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 superimposed, in a certain definite manner, they produce white light, but when one or two of them are in excess, then an effect of color is perceptible, simple in the first case and compound in the second. There are rays of all refrangibilities of each color, and consequently white light in every part of the spectrum, but then they are unequally distributed; the blue rays are more numerous near the top, the yellow towards the middle, and the red at the bottom, the excess of each color producing its characteristic effect. In the diagram below the intensity of each color is represented by the height of a curve, and the effects of mixture will be intelligible by a little consideration. Fig. 50. BLUE. YELLOW. RED. SOLAR SPECTRUM. Bodies of the same mean refractive power do not always equally disperse or spread out the differently colored rays ; because the principal yellow or red rays, for instance, are equally refracted by two prisms of different mate- rials, 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 as respects the length of the image, and the relative extent of the colored bands. The colors of natural objects are supposed to result from the power which the surfaces of the bodies possess of absorbing some of the colored 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 74 LIGHT. Fig. 51. of the yellow and blue rays composing the white light by which it is illumi- nated. A ray of common light made to pass through certain crystals of a particular order is found to undergo a very remarkable change. It becomes split or divided into two rays, one of which follows the general law of refraction, and the other takes a new and extraordinary course, dependent on the posi- tion of the crystal. This effect, which is called double refraction, is beauti- fully 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 doubled. 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 reflexion will be found to have acquired properties which it did not before possess; for on throwing it, under the same angle, upon a second glass plate, it will be observed that there are two particular positions of the latter in which the ray ceases to be reflected. Light which has suffered this change is said to be polarized. The light which passes through the first or polarizing plate, is also to a certain extent in this peculiar con- dition, and by employing a series of similar plates, held parallel to the first, this effect may be greatly increased ; a bundle of fifteen or twenty such plates may be used with great convenience for the experiment. It is to be remarked, also, that the light polarized by transmission in this manner is in an opposite state to that polarized by reflexion; that is, when examined by a second or analyzing plate held at the angle before mentioned, it will be seen to be reflected when the other disappears, and to be absorbed when the first is reflected. It is not every substance which is capable of polar- izing light in this manner; glass, water, and certain other bodies bring about the change in question, each having a particular polarizing angle at which the effect is greatest. Polished metals, on the contrary, do not exhibit these phenomena, at least in the same manner. 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 reflexion when the other vanishes. With a rhomb of transparent Iceland spar of tolerably large dimensions the two oppositely- polarized rays may be widely separated 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 Fig. 53. polarizes by simple transmission, the ray falling perpendicular to its surface ; a part of the light is absorbed, and the remainder modified in the manner LIGHT. 75 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 the second cut, 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 between polarized light and that which has not undergone the change. Some of the most splendid phenomena of the science of light are exhibited when thin plates of doubly refracting substances are interposed between the polarizing arrangement and the analyzer. The luminous rays of the sun are accompanied, as already mentioned, by others which possess heating powers. If the temperature of the different colored 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 manifest a little beyond the visible red ray. It is inferred from this that the heating rays 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 temperatures 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 opposed to the heating rays in the common spectrum in their degree of refrangibility, 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 tolerably ac- curate representations of objects of a texture partly opaque and partly trans- parent, 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 micro- scope. These pictures, however, required to be kept in the dark, and only examined by candle-light, otherwise they became obliterated by the black- ening of the whole surface from which the salt of silver could not be re- moved. These attempts at light-painting attracted but little notice till the publication of Mr. Fox Talbot'sf 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 sensi- bility 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 HerschelJ proposed to employ solutions of the alkaline hyposulphites for removing the excess of chloride of silver from the paper, and thus preventing the further 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 * Journal of the Royal Institution, i. 170. t Phil. Mag. March, 1839. t Phil. Trans, for 1840, p. 1. 76 LIGHT. to Mr. Talbot,* who, in a more recent 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 exceeding 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 demands a great number of minute precautions, only to be learned by experience, 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 moderate 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 diffuse daylight for one second suffices to make 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 immersion in a solution of hypo-sul- phite 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 peroxide salt of iron becomes capable of re- ceiving impressions of this kind, which may afterwards be made evident by red ferrocyanide of potassium, or chloride of gold. Vegetable colors are also acted upon in a very curious and apparently definite manner by the different parts of the spectrum/I" The Daguerreotype 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 vapor of iodine, and then trans- ported to the camera obscura. In the most improved state of the process, 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 vapor of mercury, which attaches itself in the form of exceedingly 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 hyposulphite of soda to remove the undecomposed iodide of silver, and render it permanent. The images of objects thus produced bear the most minute examina- tion with a magnifying glass, the smallest details being depicted with per- fect fidelity. * Phil. Mag. August, 1841. f Phil. Trans. 1842, p. 1. LIGHT. 77 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 shortened to a very few seconds. When the operation is completed, the color of the plate is much improved by the deposition of an exceedingly thin film of gold, which communicates a warm purplish tint, and removes the previous dull leaden- gray hue, to most persons very offensive. The most extraordinary discovery of all is, perhaps, that announced by Professor Moser,* that bodies of all kinds, separated by a very small interval, seem mutually to impress their images on each other, which become manifest when the surfaces are breathed upon or exposed to any easily condensable vapor. This effect is quite independent of light, and takes place in perfect darkness. An engraving, for example, placed behind a plate of glass in the usual manner, and left for many years, will often be found to have impressed upon the latter an outline of its principal features, rendered distinctly visible by the unequal deposition of the film of minute dust which gradually collects upon glass surfaces. These matters are curious, but it is difficult to give any opinion concerning their nature or cause. The phenomena of circular polarization, and the beautiful relations which Mr. Faraday has shown to exist between light and magnetism, interesting and important as they are, cannot with propriety be discussed in the present work. * See Liebig's Annalen, xliv. 173. 78 RADIATION OF HEAT. RADIATION, REFLEXION, ABSORPTION, AND TRANSMISSION OF HEAT. BADIATIOK 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 resi- due is thrown off from the heated body in straight lines or rays, which pass through air without interruption, and become absorbed by the surfaces of neighboring objects which happen to be presented to their impact. This radiant or radiated heat resembles, in very many respects, ordinary light; it suffers reflexion from polished surfaces according to the same law; it is absorbed by those that are dull or rough ; it moves with extreme velocity ; and, finally, it traverses certain transparent media, undergoing refraction at the same time, in obedience to the laws which regulate that phenomenon in optics. The fact of the reflexion 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 mantel-shelf, 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 reflexion, 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 Fig. 54. 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 proceeds from the point where the tangent touches the curve in a direc- tion 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 curvature in a direction pa- rallel 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 reflexion, become parallel (Fig. 54). If two such mirrors be placed opposite to each other at a considerable distance, and so adjusted that their axis shall be coincident, and a hot body placed in the focus of the one, while a thermometer occupies that of the other, the reflection of the rays of heat will become manifest by their effect upon the instrument. 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 gun-powder may be readily fired by a red-hot ball in the focus of the opposite mirror (Fig. 55). RADIATION OP HEAT. Fig. 55. 79 The power of radiation varies exceedingly with different bodies, as may be easily proved. If two similar vessels of equal capacity be constructed of thin metal, and the surface of one highly polished, while that of the other is covered with lamp-black, and both filled with hot water of the same tem- perature, and their rate of cooling observed from time to time with a ther- mometer, it will be constantly found that the blackened vessel loses heat much faster than the one with bright surfaces ; and since both are put on a footing of equality in other respects, this difference, which will often amount to many degrees, must be ascribed to the superior emissive power of the film of soot. By another arrangement, a numerical comparison can be made of these differences. A cubical metallic vessel is prepared, each of whose sides is in a different condition, one being polished, another rough, a third covered with lamp-black, &c. This vessel is filled with water, kept constantly at 212 by a small steam-pipe. Each of its sides is then presented in succession to a good parabolic mirror, having in its focus one of the bulbs of the differential thermometer before described, the bulb itself being blackened. The effect produced on this instrument is taken as a measure of the comparative ra- diating powers of the different surfaces. The late Sir John Leslie obtained by this method of experiment the following results : Lamp-black Writing-paper Glass Plumbago . Emissive power. 100 98 90 75 Tarnished lead Clean lead Polished iron . Polished silver Emissive power. 45 19* 15 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 lamp-black, which reflects nothing, radi- ates 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 until the * The formerly supposed influence of mere difference of surface has been called in Juestion by M. Melloni, who attributes to other causes the effects observed by Sir phn Leslie and others, among which superficial oxidation and differences of phy- sical condition with respect to hardness and density, are among the most important. With metals not subject to tarnish, scratching the surface increases the emissive power when the plates have been rolled or hammered, i. e. are in a compressed state ; and diminishes it, on the contrary, when the metal has been cast and carefully polished without burnishing. In the case of ivory, marble, and jet, where compression cannot take place, no difference is perceptible in the radiating power of polished and rough surfaces. Ann. Chim. et Phys. Ixx. 435. 80 RADIATION OF HEAT. paper is completely scorched, it will be found that the film of metal has per- fectly defended that portion beneath it. The faculty of absorption seems to be a good deal influenced by color; Dr. Franklin found that when pieces of cloth of various colors were placed on snow exposed to the feeble sunshine of winter, the snow beneath them be- came unequally melted, the effect being always in proportion to the depth of the color ; and Dr. Stark has since obtained a similar result by a different method of experimenting. These facts afford an explanation of two very interesting and important natural phenomena, namely, the origin of dew, and the cause of the land and sea-breezes of tropical countries. While the sun remains above the horizon, the heat radiated by the surface of the earth into space is compensated 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 vapor present speedily reaches its point of maximum density, and then begins to deposit moisture, whose quantity will depend upon the pro- portion of vapor in the atmosphere, and on the extent to which the cooling process has been carried. It is observed that dew is most abundant in a clear calm night, succeeding a hot day; under these circumstances, the quantity of vapor 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, indi- cate a temperature of 10, 15, or even 20 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 reduc- tion of temperature; and the same effect is produced by a screen of the thin- nest 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 afterwards 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 un- equally heated from their different absorbing power ; the land becomes much the warmer. The air over the heated surface of the ground, being expanded 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 cooling of the latter will, however, far exceed that of the former, and its temperature will rapidly fall. The air above be- TRANSMISSION OF HEAT. 81 coming 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 j DIATHERMANCY. Rays of heat, in passing through air, receive no more obstruction than those of light under similar circumstances; but with other transparent media the case is different. If a parabolic mirror be taken and its axis directed towards the sun, the rays both of heat and light will be reflected to the focus, which will exhibit a temperature sufficiently high to fuse a piece of metal, or fire a combustible body. If a plate of glass be now placed between the mirror and the sun, the effect will be but little diminished. Now, let the same experiment be made with the heat and light of a com- mon fire; both will be concentrated by reflection as before; but, on interpos- ing the glass, the heating effect at the focus will be reduced almost to no- thing, while the light will not have undergone perceptible diminution. Thus, the rays of heat coming from the sun traverse glass with facility, which is not the case with those emanating from an ordinary red-hot body. In the year 1833, M. Melloni published the first of a seTies of exceedingly valuable researches on this subject, which are to be found in detail in various volumes of the Jlnnales de Chimie et de Physique.* It will be necessary, in the first instance, to describe the method of operations followed by this phi- losopher. Not long before, two very remarkable facts had been discovered : first, that a current of electricity, however produced, exercises a singular and perfectly definite action on a magnetic needle ; and, secondly, that an electric current may be generated by the unequal effects of heat on different metals in con- tact. 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 mag- netism of the earth will permit. When the wire, for example, is placed directly over the needle, while the Fig. 56. current it carries travels from north to south, the ^ needle is deflected from its ordinary direction and the north pole driven to the eastward. When the current is reversed, the same pole deviates to an equal amount towards the west. Placing the wire below the needle instead of above produces the same effect as reversing the current. When the needle is subjected to the action of two currents in opposite directions, the one above and the other below, they will obviously concur in their ef- fects. The same thing happens when the wire carrying the current is bent upon itself, and the needle placed between the two portions; and, since every time the bending is repeated 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 produce any effect when a simple straight wire is employed, may be made by this contrivance to exhibit a powerful action on the magnet. It is on this * Translated also in Taylor's Scientific Memoirs. 82 TRANSMISSION OF HEAT. Fig. 57. Fig. 58. 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 de- gree 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 im- mediately 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, can deve- lop a current strong enough to deflect a com- pass-needle placed within, and, by arranging a number in a series and heating their alter- nate ends, the intensity of the current may be very much increased. Such an arrangement is called a thermo electric pile. M. Melloni constructed a very small thermo-electric pile of this kind, containing fifry-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 deli- cate multiplier, and found himself in the possession of an instrument 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. A perforated screen, the area of whose aperture equaled that of the face of the pile, 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 experiment. After much preliminary labor for the purpose of testing the capabilities of the apparatus and the value of its indications, an extended series of researches Fig. 59. were undertaken and carried on during a long period with great success: some of the most curious results are given in the subjoined table. TRANSMISSION OP HEAT. 83 Four different sources of heat were employed in these experiments, differ- ing in their degrees of intensity : the naked flame of an oil lamp: a coil of pla- tinum wire heated to redness; blackened copper at 734; and the same heated to 212. Transmission of 100 rays of heat from Substances. ^ (Thickness of plate .1 inch, nearly.) Of "*? c3 "S CS j. || |S &! O o O Rock-salt, transparent and colorless 92 92 92 92 Fluor-spar, colorless Rock-salt, muddy 78 65 69 65 42 65 33 65 Beryl .... 54 23 13 Fluor-spar, greenish . - - 46 38 24 20 Iceland spar 39 28 6 Plate-glass 39 24 6 Rock-crystal ... 38 28 6 Rock-crystal, brown 37 28 6 Tourmaline, dark green - 18 16 3 Citric acid, transparent 11 2 Alum, transparent ... 9 2 Sugar-candy .... 8 Fluor-spar, green, translucent 8 6 4 3 Ice, pure and transparent 6 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; tak- ing, for instance, the oil-lamp as the source of heat, out of a quantity of heat represented by 100 rays falling upon the pile, the proportion intercepted by similar plates of rock salt, glass, and alum, may be expressed by the num- bers, 8, 61, and 91; and yet these bodies are equally transparent with re- spect to light. Generally speaking, color was found to interfere with the transmissive power, but to a very unequal extent ; thus, in fluor-spar, color- less, greenish, and deep green, the quantities transmitted were 78, 46, and 8, while the difference between colorless and brown rock-crystal was only 1. Bodies absolutely opaque, as wood, metals, and black marble, stopped the rays completely, although it was found that the faculty of transmission was possessed to a certain extent by some which were nearly in that condition, as thick plates of brown quartz, black mica, and black glass. When rays of heat had once passed through a plate of any substance, the interposition of a second similar plate occasioned much less loss than the first; the same thing happened when a number were interposed, the rays, after traversing one plate, being but little interrupted by others of a similar nature. The next point to be noticed is the great difference in the properties of the rays from different sources. Out of 100 rays from each source which fell on rock-salt, the same proportion was always transmitted, whether the rays pro- ceeded from the intensely heated flame, the red-hot platinum wire, or the copper at 734 or 212 ; but this is true of no other substance in the list. In 84 TRANSMISSION OF HEAT. the case of plate-glass, we have the numbers 39, 24, 6, and 0, as represent- atives of the comparative quantities of heat transmitted through the plate from each source ; or in the three varieties of fluor-spar, as below stated : Flame. Red-heat. 734. 2120. Colorless 78 69 42 33 Greenish 46 38 24 20 Dark green 8 6 4 3 While one substance, beryl, out of 100 rays from an intensely heated source, suffers 54 to pass, and from the same number, that is, an equal quan- tity of heat, from metal at 212, none at all, another transmits rays from the two sources mentioned in the proportion of 8 to 3. These, and many other curious phenomena, are fully and completely ex- plained on the supposition, that among the invisible rays of heat differences are to be found exactly analogous to those differences between rays of light which we are accustomed to call colors. Rock-salt is the only substance yet known which is truly diathermanous, or equally transparent to all kinds of heat rays ; it is to the latter what white glass or water is to light ; it suf- fers rays of every description to pass with equal facility. All other bodies act like colored glasses, absorbing certain of the rays more abundantly than the rest, and coloring, as it were, the heat which passes through them. These heat tints have no direct relation to ordinary colors; their exist- ence is, nevertheless, almost as clearly made out as that of the colored 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 tempera- ture rises, rays of other heat-colors begin to make their appearance, and transmission of some portion of these rays takes place through a greater number of bodies; while at the temperature of intense ignition we find rays of all colors thrown out, some or other of which will certainly find their way through a great variety of substances. By cutting rock-salt into prisms and lenses, it is easy to show that radiant heat may be refracted 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-re- fracting minerals, in the same manner as light itself.* * Dr. Forbes, Phil. Mag. for 1835; also M. Melloni, Ann. Chim. et Phys. Ixv. 5. MAGNETISM. 85 MAGNETISM. A PAHTICULAR species of iron ore has long been remarkable for its property 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 altogether absent. These attractive points, or centres of greatest force, are denomi- nated poles, and the loadstone itself is said to be endued with magnetic polarity. If one of the poles of a natural loadstone be rubbed in a particular manner 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. Further, 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 magnetized, or to constitute an artificial magnet. When a magnetized 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 at- traction 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 existence 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 neighborhood 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, becoming greater as that interval decreases, and greatest of all when in actttal contact. The iron under these circumstances is said to be magnetized by induction or influence, and the effect, which in an instant reaches its maximum, is at once destroyed by removing the magnet. When steel is substituted for iron in this experiment, the inductive action is hardly at first perceptible, and only becomes manifest after the lapse of a certain time ; in this state the steel bar may be removed from the magnet without loss of polarity. It becomes, indeed, a permanent magnet, similar to the first, and retains its peculiar properties for an indefinite period. 8 86 MAGNETISM. Fig. 60. A particular name is given to this resistance which steel always offers in a greater or less degree both to the development of magnetism and its sub- sequent destruction; it is called specific coercive power. The rule which regulates the induction of magnetic polarity in all cases is exceedingly simple, and most import- ant to be remembered. The pole pro- duced is always of the opposite name to that which produces it, a north pole developing south polarity, and a south pole, north polarity. The north pole of the magnet figured in the sketch induces south polarity in all the nearer extremities of the pieces of iron or steel which surround it, and a state similar to its own in all the more remote extremities. The iron thus magnetized is capable of exerting a similar inductive action on' a second piece, and that upon a third, and so to a great number, the intensity of the force diminishing as the distance from the permanent magnet 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. The only substances known which unequivocally exhibit magnetic effects are iron arid certain of its compounds, nickel, and cobalt. Magnetic attractions and repulsions are not in the slightest degree inter- fered with by the interposition of substances destitute of magnetic properties. Thick plates of glass, shellac, metals, wood, or of any substances except those above mentioned, may be placed between a magnet and a suspended needle, or a piece of iron under its influence, the distance being preserved, 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 acquires an opposite pole, so that both portions of the bar become perfect magnets; arid, if the division be still further carried, if the bar be broken into a hun- dred 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 Fig. 61. N IL-A1LJBLJB ILJILH i m\ ! mr-m forces pass; the large magnet is made up of an immense number of little magnets regularly arranged side by side, all having their north poles looking MAGNETISM. 87 one way, and their south poles the other. The middle portion of such a sys- tem 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 opposite directions and completely neutralize each other's influence. Such will not be the case at the extremities of the bar ; there uncompensated polarity will be found ca- pable 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 molecular 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 certain processes of rubbing or touching with another magnet, which require care, but are not otherwise difficult of execution. When great power is wished for, a number of bars may be screwed together, with their similar ends in contact, and in this way it is easy to construct permanent steel magnets capa- ble of sustaining great weights. To prevent the gradual destruction of mag- netic force, which would otherwise occur, it is usual to arm each pole with a piece of soft iron, or keeper, which, becoming magnetized by induction, serves to sustain the polarity of the bar, and even increase in some 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 varia- tion or declination 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 riot only varies at different places, but at the same place at different periods. Thus, at the commencement of the seventeenth century, the declination was eastward ; in 1660, it was 0; 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 diminishing. 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 position in which it may happen to be placed; if the bar so adjusted be then mag netized, 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 horizontal plane passing through the axis. This is called the efrp, or inclination of the needle, and shows the direction in which the force of terrestrial magnetism is most energetically exerted. The amount of this dip is variable 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, considerably to the west- ward of the geographical pole, in Prince Regent's Inlet, lat. 70 5' N. and lon- gitude 94 46' W.; the dipping-needle has here been seen to point directly downwards, while the horizontal or compass-needle ceased to traverse. The 88 MAGNETISM. position of the south magnetic pole has lately been determined by the obser- vations 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 irregu- larities when compared with the equator itself and the parallels of latitude, the magnetic equator deviating from the terrestrial one as much as 12 at its point of greatest divergence. Like the horizontal declination, the dip is also subject to change at the same place. Observations have not yet been made during sufficient time to determine accurately the law and rate of alteration, 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 strong north polarity, and the upper, the contrary state. On reversing the bar the poles are also reversed. All masses of iron whatever, when examined by a suspended needle, will be found in a state of magnetic polarity by the influence of the earth; iron columns, tools in a smith's shop, fire-irons, and other like objects, are all usually magnetic, and those made of steel permanently so. On board ship, the presence of so many large masses of iron, guns, anchors, water-tanks, &c., thus polarized by the earth, causes a derangement of the compass-needles to a very dangerous extent ; happily, a plan has been devised for determining the amount of this local attraction in 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 the various parts of the world. ELECTRICITY. 89 ELECTRICITY. IF glass, or amber, or sealing-wax be rubbed with a dry cloth, it acquires the power of attracting light bodies, as feathers, dust, or bits of paper ; this is the result of a new and peculiar condition of the body rubbed, called electrical excitation. If a light downy feather be suspended by a thread of white silk, and a dry glass tube, excited by rubbing, be presented to it, the feather will be strongly attracted to the tube, adhere to its surface for a few seconds, and then fall off. If the tube be now excited anew, and presented to the feather, the latter will be strongly repelled. . The same experiment may be repeated with shellac or resin ; the feather in its ordinary state will be drawn towards the excited body, and, after touch- ing, 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 pre- sented to it ; a degree of attraction will be observed far exceeding that ex- hibited 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 employed, which, although originating in some measure in theoretical views of the na- ture 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 electricity depends in some measure upon the nature of the surface ; smooth glass rubbed with silk or woollen becomes positive, but when ground or roughened by sand or emery, it acquires under the same circumstances a negative charge. The repulsion shown by bodies in the same electrical state is taken ad- Fig. 62. Fig. 63. ELECTRICITY. vantage of to construct instruments for indicating electrical excitement and pointing out its kind. Two balls of alder-pith, 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 diverg- ence 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, 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 elec- tricity, they show, by an increased or diminished divergence, the state of an electrified body brought into their neighborhood. 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 electri- city; a body already electrified disturbs or polarizes the particles of all sur- rounding 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 Fig. 64. the manner represented, will each become electric by induction 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 posi- tive 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. Magnetic proper- ties are enjoyed by three metals only, and a very few of their compounds, out of the whole list of substances known : electrical excitation is common to every form of matter, solid, liquid, and gaseous. The magnetic polarity of a piece of steel c,an awaken polarity in a second piece in contact with it by the act of induction, and in so doing loses nothing whatever of its power; this is an effect completely different from the apparent transfer or discharge of elec- tricity constantly witnessed, which in the air and in liquids often gives 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 re- pulsion, and those of induction. But in electricity, 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 communication with the earth by any one of ELECTRICITY. 91 the class of substances called conductors of electricity ; all signs of electrical disturbance then ceasing. These conductors of electricity, which thus permit discharge to take place through their mass, are thus 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 electrical 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 vapor 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 con- ductor very 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 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 san^e; 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 in- equality becomes so great that discharge takes place to the air, and the ex- cited 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 is mounted with its axis in a horizontal position, and pro- vided 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 metallic conducting body, armed with a number of points next the glass, occupies the other; both cushion and conductor are insulated by glass sup- ports, 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 com * 1 part tin, 2 zinc, and 6 mercury. ELECTRICITY. Fig 65. municated by contact to other insulated bodies. The maximum effect is pro- duced 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 conductor discharged. Another form of the electrical machine consists of a circular plate of glass moving upon an axis, and provided with two pairs of cushions or rubbers, Fig. 66. ELECTRICITY. 93 attached to the upper and lower parts of the wooden frame, covered with amalgam, between which the plate moves with considerable friction. An insulated conductor, armed as before with points, discharges the plate as it turns, the rubbers being at the same time connected with the ground by the wood-work of the machine, or by a strip of metal. This modification of the apparatus is preferred in all cases where considerable power is wanted. In the practical management of electrical apparatus, great care must be taken to prevent deposition of moisture from the air upon the surface of the glass supports, which should always be varnished with fine lac dissolved in alcohol; the slightest film of water is sufficient to destroy the power of insu- lation. The rubbers also must be carefully dried before use, and the amal- gam renewed if needful; in damp weather much trouble is often experienced in bringing the machine into powerful action. When a piece of iron is applied to a steel magnet, the polarity of the latter is exalted by the reaction of the newly developed force ; in the same manner the intensity of the electrical charge on the surface of a conductor can be raised by the juxta-position of a second conducting body, the two being sepa- rated by an insulating medium. If a disc of metal be connected with the machine, and a second disc placed opposite, within a few inches, and con- nected with the earth, the positive state of the first will be greatly augmented by the induced negative condition of the second ; the limit is in this case, how- ever, soon reached, because the intervening air easily permits spark-discharge to take place through its substance. With a solid insulating body, as glass or lac, this happens with much greater difficulty, even when the plate of insu- lating matter is very thin. It is on this principle that instruments for the accumulation of electricity depend, among which the Leyden jar is the most important. A thin glass jar is coated on both sides with 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 5 when the outside of the jar is connected with the earth, and the knob put in contact with the conductor of the ma- chine, the inner and outer surfaces of the glass become respectively positive and negative, until a very great de- gree of intensity has been attained. On completing the connection between the two coatings by a metallic wire or rod, discharge occurs in the form of an exceedingly bright spark, accompanied 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 moment 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 combustible substances set on fire, and all the well-known effects of lightning exhibited upon a small scale. The electric spark is .often very conveniently employed in chemical in- quiries 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 maybe resorted to which involves less prepa- ration. This is by the use of the electrophorus. A round tray or dish of tinned plate is prepared, having a stout wire round its upper edge; the width may 94 ELECTRICITY. P Jg- '8. 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 diame- ter, 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 flan- nel, 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 electricity becomes much deranged, clouds near the surface of the earth often appearing in a negative state. The circumstances of a thunder-storm exactly resemble those of the charge and discharge of a coated plate or jar; the cloud and the earth represent the two coatings, and the intervening air the bad conducting body or dielectric. The polarities of the opposed surface and of the 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 conducting freely, the discharge is silent and harmless; but in other cases it often proves highly destructive. These dangerous effects are now in a great measure obviated by the use of lightning-rods attached to buildings, the erection of which, how- ever, 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 ingenious plan for the purpose, which is now adopted, with the most complete success, in the Royal 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, be- comes negative; and the platinum remaining unaltered, assumes the positive condition; and, on making a metallic communication in any way between the two plates, discharge ensues, as when the two surfaces of a coated and charged jar are put into connection. No sooner, however, has this occurred, than the disturbance is repeated ; and, as these successive charges and discharges take place through the fluid and metals with inconceivable rapidity, the result is an apparently continuous action, to which the term electrical current is given. It is necessary to guard against the idea which the term naturally suggests, of an actual bodily transfer of something through the substance of the conductors, like water through a pipe ; the real nature of all these phenomena is entirely unknown, and may, perhaps, remain so; the expression is convenient notwith- standing, and consecrated by long use ; and with this caution, the very dan- gerous error of applying figurative language to describe an effect, and then ELECTRICITY. 95 Fig. 69. I seeking the nature of the effect from the common meaning of words, may be avoided. The intensity of the electrical excitement developed by a single pair of metals and a liquid, is too feeble to affect the most delicate gold-leaf electroscope ; but, by arranging a number of such alternations in a 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 invented by Volta, called the pile and crown of cups, depend upon this principle. Upon a plate of zinc is laid a piece of cloth, rather smaller than itself, steeped in dilute acid, or any liquid capable of exerting chemical action upon the zinc; upon this is placed a plate of copper, silver, or platinum ; then a second piece of zinc, another cloth, and 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 ex- perienced; but, unlike the mom entry 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 enduring spark or stream of fire. The second form of apparatus, or crown of cups, is precisely the same in principle, although different in appearance. A number of cups or glasses are arranged in a row or circle, each containing a piece of active and a piece of inactive metal and a portion of exciting liquid ; zinc, copper, and Fig. 70. 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 be- tween the first and last plates by means of a wire, or otherwise, discharge takes place as before. When any such electrical arrangement consists merely of a single pair of conductors and an interposed liquid, it is called a simple circuit; when two or more alternations are concerned, the term "compound circuit" is applied; they are called also, indifferently, voltaic batteries. In every form of such apparatus, however complex it may appear, the direction of the current may be easily understood and remembered. The polarity or disturbance may be considered to commence at the surface of the metal attacked, and to be pro- 96 ELECTRICITY. pagated through the liquid to the inactive conductor, and thence back again by the connecting wire, these extremities of the battery being always respect- ively negative and positive when the apparatus is insulated. In common par- lance, it is said that the current in every battery in an active state starts from the metal attacked, passes through the liquid to the second metal or conducting body, and returns by the wire or other channel of communication; hence, in the pile and crown of cups just described, the current in the battery is always from the zinc to the copper ; and out of the battery, from the copper to the zinc, as shown by the arrows. In the modification of Volta's original pile, made by Mr. Cruikshank, the zinc and copper plates are soldered together and cemented water-tight into a mahogany trough, which thus becomes divided into a series of cells or com- partments capable of receiving the exciting liquid. This apparatus is well fitted to exhibit effects of tension, to act upon the electroscope and give shocks ; hence its advantageous employment in the application of electricity to medi- Fig. 71. cine, as a very few minutes suffice to prepare it for use. The crown of cups was also put into a much more manageable form by Dr. Babington, and still further improved, as will hereafter be seen, by Dr. Wollaston. Subsequently, various alterations have been made by different experimenters with a view of obviating certain defects in the common batteries, of which a description will be found towards the middle of the volume. The term "galvanism," sometimes applied to this branch of electrical sci- ence, is used in honor of Professor Galvani, of Bologna, who, in 1790, made the very curious observation that convulsions could be produced in the limbs of a dead frog when certain metals were made to touch the nerve and muscle at the same moment. It was Volta, however, who pointed out the electrical origin of these motions, and although the explanation he offered of the source of the electrical disturbance is no longer generally adopted, his name is very properly associated with the invaluable instrument his genius gave to science. In the year 1822, Professor Seebeck, of Berlin, discovered another source of electricity, to which allusion has already been made, namely, inequality of temperature and conducting power in different metals placed in contact, or in the same metal in different states of compression and density. Even with a great number of alternations, the current produced is exceedingly feeble com- pared with that generated by the voltaic pile. Two or three animals of the class of fishes, as the torpedo or electric ray, and the electrical 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 the effects of lightning on the compass-needle ftnd upon 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 ELECTRICITY. 97 Professor (Ersted, of Copenhagen, and shortly afterwards fully developed by M. Ampere. The action which a current of electricity, from whatever source proceeding, 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 cur- rent, 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 motion may even be shown by suspending a magnet in such a way that one only of its poles shall besubjected to the current; a permanent movement of rotation will con- tinue as long as the current is kept up, its direction being changed by altering the pole, or reversing the current. The moveable connections are made by mercury, into which the points of the conducting wires dip. It is often of great practical consequence to be able to predict the direction in which a par- ticular pole shall move by a given current, because in all galvanoscopes, and other instruments involving these principles, the movement of the needle is taken as ah indication of the direction of the circulating 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 ap- paratus may be used if reference is often required ; this is a piece of paste- board, or other suitable material cut into the form of an arrow for indicating Fig. 72. '""iiiinail I 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 sus- pension, a long fibre of silk being used for the purpose. The two needles are of equal size, and magnetized as nearly as possible to the same extent ; they are then immovably fixed together, parallel, and with their poles op- posed, and hung with the lower needle in the coil and the upper one above it. The advantage gained is twofold; the system is astatic, unaffected, or nearly so, by the magnetism of the earth ; and the needles being both acted upon in the same manner by the current, are urged with much greater force than one alone would be, all the actions of every part of the coil being strictly concurrent. A divided circle is placed below the upper needle, by which the angular motion can be measured ; and the whole is enclosed in glass, to 9 98 ELECTRICITY. shield the needles from the agitation of the air. The whole is shown in fig. 73. Fig. 73. Fig. 74. Fig. 75. 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 vici- nity : on completing the circuit the wire will be put in motion, and, if the arrangement 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 all 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 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 magnet held near it in the most perfect manner, as long as the cur- rent circulates. When an electric current is passed at right angles to a piece of iron or steel, the latter acquires magnetic polarity, either temporary or permanent as the case may be, the direction of the current determining the position of the poles. This effect is prodigiously increased by causing the current to ELECTRICITY. 99 circulate a number of times round the bar, which then acquires extraordinary magnetic power. A piece of soft iron, worked into the form of a horse-shoe, and surrounded by a coil of copper wire covered with silk or cotton for the pur- pose of insulation, furnishes an excellent illustration of the inductive energy of the current in this respect; when the ends of the wire are put into communi- cation 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 develope magnetism in a transverse direc- tion to its own; in the same manner, magnetism can call into activity electric currents. If the two extremities of the coil of the electro-magnet above de- scribed be connected with a galvanoscope, and the iron magnetized by the application of a permanent steel horse-shoe magnet to the ends of the bar, a momentary current will be developed in the wire, and pointed out by the movement of the needle. It lasts but a single instant, the needle returning after a few oscillations to a state of rest. On removing the 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 em- ploying 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 produced, of such intensity as to give bright sparks and most powerful shocks, and exhibit all the phenomena of voltaic electricity. Fig. 70 represents a very powerful arrangement of this kind. When two covered wires are twisted together or laid side by side for some distance, and a current transmitted through the one, a momentary electrical wave will be induced in the other in the reverse direction, and on breaking connection with the battery, a second single wave will become evident by the aid of the galvanoscope, in the same direction as that of the primary current. These curious induced currents sometimes acquire a degree of intensity supe- 100 ELECTRICITY. rior to that of the battery-current itself. The effect described may even occur in a single wire. M. Ampere discovered in the course of his investigations a number of extremely interesting phenomena resulting from the action of electrical cur- rents on each other, which become evident when arrangements are made for giving mobility to the conducting-wires. He found, that when two currents flowing in the same direction were made to approach each other, strong attraction took place between them, and when in opposite directions, an equally strong repulsion. These effects, which are not difficult to demonstrate, 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 hypothesis of magnetic actions in general, which explains very clearly the influence of the current upon the needle. The polarity of the earth is now generally supposed to be due to electrical currents circulating within and around it, and which may perhaps be called into existence by the unequal heating of the surface by the rays of the sun. 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 interior of the exit tube. It is very doubtful whether mere evaporation can cause elec- trical 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 constructed of wood or clean metal, but the introduction of the smallest trace of oily matter causes a change of sign. The intensity of the charge is, cceteris paribus, in- creased with the elastic force of the steam ; already effects have been obtained very far surpassing those of the most powerful plate electrical machines ever constructed.* * The student will find, in the Experimental Researches of Mr. Faraday, some time since published in a collected form, an inexhaustible fund of information on many of these curious subjects. The complete revolution which the discoveries there described have effected in the received views of electrical phenomena greatly increases the diffi- culty at the present moment of explaining in a clear and satisfactory manner the ele- mentary parts of the science of statical electricity. The articles Magnetism and Electro-magnetism, by Dr. Roget, in the tracts of the Society for the Diffusion of Useful Knowledge, may be also consulted with advantage. 101 PART II. CHEMISTRY OF ELEMENTARY BODIES. THE term element or elementary substance is applied in chemistry to those forms or modifications of matter which have hitherto resisted all attempts to decompose them. Nothing is ever meant to be affirmed concerning their real nature; they are simply elements to us at the present time; hereafter, by new methods of research, or by new combinations of those already possessed 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 recognized, amount to sixty-two in num- ber ; 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 dis- tinction between metals and non-metallic substances, although very conve- nient 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. Metals. Oxygen Antimony Glucinum Magnesium Hydrogen Chromium Zirconium Zinc Nitrogen Vanadium ,, Norium Cadmium Chlorine Tungsten Thorium Nickel Iodine Molybdenum Yttrium Cobalt Bromine Columbium Cerium Copper Fluorine Niobium Erbium ' Iron Carbon Pelopium Terbium Manganese Silicon Titanium Lantanum Lithium Boron Uranium Didymium Sodium Sulphur Platinum Bismuth. Potassium. Selenium Palladium Tin Phosphorus. Rhodium Mercury Iridium Silver Elements of interme- Ruthenium Lead diate characters. Osmium Barium Arsenic Gold Strontium Tellurium. Aluminum Calcium 102 OXYGEN. OXYGEN. Whatever plan of classification, founded on the natural relations of the ele- ments, be adopted, in the practical study of chemistry, it will always be found most advantageous to commence with the consideration of the great consti- tuents 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 dephlogisticaied 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 direct means exist, however, for separating it from the latter, and, accord- ingly, it is always obtained for purposes of experiment by decomposing cer- tain of its compounds, which are very numerous. The red oxide of mercury, or red precipitate of the old writers, may be em- ployed with this view. In this substance, the attraction which holds together the mercury and the oxygen is so feeble that simple exposure to heat suffices to bring about decomposition. The red precipitate is placed 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 me- tallic 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 appa- ratus. This gas is collected and examined by the aid of the pneumatic trough, which consists of a vessel of water provided with a shelf, upon which stand the jars or bottles destined to receive the gas, filled with water and inverted. By keeping the level of the liquid above the mouth of the jar, the water is retained in the latter by the pressure of the atmosphere, and entrance of air prevented. When brought over the extremity of the gas-delivering tube, the bubbles of gas arising through the water collect in the upper part of the jar and displace the liquid. As soon as one jar is filled, it may be removed, still Fig. 77. * From o|if, acid, and yevvcioo, I give rise to. OXYGEN. 103 keeping its mouth below the water-level, and another 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 portion of the salt called chlorate of potash. A common Florence flask serves per- fectly well, the heat of a spirit lamp being sufficient. The salt melts and decomposes with ebullition, yielding a very large quantity of pure oxygen gas, which may be collected in the way above described. The white saline residue in the flask is chloride of potassium. This plan, which is very easy of execu- tion, is always adopted when very pure gas is required for analytical purposes. A third method, very good when perfect purity is not demanded, is to heat to redness, in an iron retort or gun-barrel, the black oxide of manganese of commerce, which, under these circumstances, suffers decomposition, although not to the extent manifest in the red precipitate. If a little of the black oxide 1 of manganese be finely powdered and mixed with chlorate of potash,* and this mixture heated in a flask or retort by a lamp, oxygen will be disengaged -with the utmost facility, and at a far lower temperature than when the chlorate alone is used. All the oxygen comes from the chlorate, the manganese remaining quite unaltered. The materials should be well dried in a capsule before their introduction into the flask. This experiment affords an instance of an effect by no means rare, in which a body seems to act by its mere presence, without taking any obvious part in the change brought about. Whatever method be chosen and the same remark applies to the collec- tion of all other gases by similar means the first portions of gas must be suffered to escape, or be received apart, as they are contaminated by the atmospheric air of the apparatus. The practical management of gases is a point of great importance to the chemical student, and one with which he must endeavor to familiarize himself. The water-trough just described is one of the most indispensable articles of the laboratory, and by its aid all experi- ments on gases are carried on when the gases themselves are not sensibly acted upon" by water. The trough is best constructed of japanned copper, the form and dimensions being regulated by the magnitude of the jars. It should Fig. 78. have a firm shelf, so arranged as to be always about an inch below the level of the water, and in the shelf a groove should be made about half an inch in width, and the same in depth, to admit the extremity of the delivery-tube * In the proportion of one or two parts of the former to ten of the latter. R. B. 104 OXYGEN. Fig. 79. beneath the jar, which stands securely upon the shelf. When the pneumatic trough is required of tolerably large dimensions, it may, with great advantage, have the form and disposition represented in the cut (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 first filling the vessel into which the gas is to be passed with water, inverting it, carefully retaining its mouth below the water-level, and then bringing beneath it the aperture of the jar containing the gas. On gently inclining the latter, the gas passes by a kind of inverted decantatiori 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 partially filled with gas at the pneumatic trough may be removed by placing beneath it a shallow basin, or even a common plate, so as to carry away enough water to cover the edge of the jar ; and 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 trans- ferring to bladders or caoutchouc bags. When such a vessel is to be filled with water, it may be slowly sunk in an upright position in the well of the pneumatic trough, the stop-cock being open to allow the air to escape, until the water reaches the brass cap. The cock is then to be turned, and the jar lifted upon the shelf and filled with gas in the usual way. If the trough be not deep enough for this 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 com- munication between the two being made by a couple of tubes a 6, furnished with cocks fh, one of which passes nearly to the bottom of the drum, as shown in the sectional sketch. A short wide open tube c is inserted obliquely near the bottom of the vessel, into which a plug may be tightly screwed. A stop-cock g near the top serves to transfer gas to a bladder or tube appa- ratus. A glass water-gauge d e, affixed to the side of the drum, and communicating with both top and bottom, indicates the level of the liquid within. To use the gas-holder, the plug is first to be screwed into the lower opening, and the drum completely filled with water. All three stop-cocks are then to be closed, and the plug removed. The pressure of the atmosphere retains the water in the gas-holder; and if no air-leakage occur, Fig. 80. OXYGEN. 105 the escape of water is inconsiderable. The extremity of the delivery-tube is now to be well pushed through the open aperture into the drum, so that the bubbles of gas rises without hindrance to the upper part, displacing the water, which flows out in the same proportion into a vessel placed for its reception. When the drum is filled, or enough gas has been collected, the tube is with- drawn, and the plug screwed into its place. When a portion of the gas is to be transferred to a jar, the latter is to be filled with water at the pneumatic trough, carried by the help of a basin or plate to the cistern of the gas-holder, and placed over the shorter tube. "* On opening the cock of the neighboring tube, the hydrostatic pressure of the column of water will cause condensation in the gas, and increase its elastic force, so that on gently turning the cock beneath the jar, it will ascend into the latter in a rapid stream of bubbles. The jar, when filled, may again have the plate slipped beneath it, and be removed without difficulty. Oxygen, when free or uncombined, is only known in the gaseous state, all attempts to reduce it to the liquid or solid condition by cold and pressure having completely failed. It is, when pure, colorless, tasteless, and inodorous ; it is the sustaining principle of animal life, and of all the ordinary phenomena of combustion. Bodies which burn in the air burn with greatly increased splendor in oxy- gen gas. If a taper be blown out, and then introduced while the wick re- mains red-hot, it is instantly rekindled: a slip of wood or a match is relighted in the same manner. This effect is highly characteristic of oxygen, there being but one other gas which possesses the same property; and this is easily distinguished by other means. The experiment with the match is also con- stantly 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 the air. When a bit of barky charcoal is affixed to a wire, and plunged with a single point red-hot into a jar of ox} r gen, it burns with great brilliance, throw- ing 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 splendor 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 oxy- gen, and enfeebles its chemical powers. The process of respiration in animals is an effect of the same nature as common combustion. The blood contains substances which slowly burn by the aid of the oxygen thus introduced into the system. When this action ceases, life becomes extinct. Oxygen is, bulk for bulk, a little heavier than atmospheric air, 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, 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 * Dumas, Ann. Chim. et Phys., 3d series, iii. 275. 106 OXYGEN. difficulty, but at the same time of very great importance. There are several methods which may be adopted for this purpose ; the one below described appears, on the whole, to be the simplest and best. It requires, however, the most scrupulous care, and the observance of a number of minute pre- cautions, which are absolutely indispensable to success. The plan of the operation is as follows : A large glass globe is to be filled with the gas to be examined, in a perfectly pure and dry state, having a known temperature, and an elastic force equal to that of the atmosphere at the'time of the experiment. The globe so filled is to be weighed. It is then to be exhausted at the air-pump as far as convenient, and again weighed. Lastly, it is to be filled Avith dry air, the temperature and pres- sure of which are known, and its weight once more determined. On the supposition that the temperature and elasticity are the same in both cases, the specific gravity is at once obtained by dividing the weight of the gas by that of the air. The globe or flask must be made very thin, and fitted with a brass cap, surmounted by a small but excellent stop-cock. A delicate thermometer should be placed in the inside of the globe, secured to the cap. The gas must be generated at the moment, and conducted at once into the previously exhausted vessel, through a long tube filled with fragments of pumice moistened with oil of vitriol, or some other extremely hygroscopic substance, by which it is freed from all moisture. As the gas is necessarily generated under some pressure, the elasticity of that contained in the filled globe will slightly exceed the pressure of the atmosphere ; and this is an advantage, since by opening the stop-cock for a single instant when the globe has at- tained 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 experi- ment. 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, arid to bring both gas and air as nearly as possible to the same temperature to ob- viate the necessity of a correction, or at least to diminish almost to nothing the errors involved by such 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 re- lations potash, soda, or the oxide of silver or of lead; these are denominated alkaline or basic oxides, or sometimes salifiable bases. The oxides'of the se- cond group have properties exactly opposed to those of the bodies mentioned; oil of vitriol and phosphoric acid may be taken as the types or representa- tives of the class : they are called acids, and they tend strongly to unite with the basic oxides. When this happens, what is called a salt is generated as sulphate of potash, or phosphate of silver, each of these substances being 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 has a strongly-marked basic character; to this the term protoxide is given. The compounds next succeeding receive HYDROGEN. 107 the names of deufoxide, tritoxide, &c., from the Greek numerals, the different grades of oxidation being thus indicated. It is usual to call the highest oxide not having distinctly acid characters, peroxide, from the Latin prefix, signi- fying excess. Any compound containing less oxygen than the protoxide, is called a suboxide. Other terms are occasionally used : thus, when two oxides of the same substances occur, if the second contain, as is often the case, twice as much oxygen as the first, the expression binoxide is sometimes used to point out this relation. Superoxide or hyperoxide is a word sometimes applied to the higher neutral oxides, which easily pass into protoxides by losing oxygen. HYDHOGEIT. 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 vapor of water transmitted over the heated metal, a large quantity of permanent gas will be disengaged from the tube, and the iron will be- come 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 that oxygen, is disengaged in the gaseous form. The reaction is represented in the subjoined diagram. Water I 5 oxygen Zinc- Sulphuric acid- -Free. -oxide of zinc ) Sulphate of 5 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 substances 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, perforated by two holes for the reception of a small tube-funnel reach- ing nearly to the bottom of the bottle, and a piece of bent glass tube to con- vey away the disengaged gas. Granu- lated 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 Fig. 81. * Hence the name, from yj^p, water, and ytw/iaa. 108 HYDROGEN. has been discharged 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. A little practice will soon enable the pupil to construct and arrange a variety of useful forms of apparatus, in which bottles and other articles always at hand are made to supersede more costly instruments. Glass tube, purchased by weight of the maker, may be cut by scratching with a file and then apply- ing a little force with both hands. It may be softened and bent, when of small dimensions, by the flame of a spirit-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 ingenious 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 colorless, 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 potash 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 odor 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 properties, it is incapable of sustaining life. In point of specific gravity, hydrogen is the 1 lightest substance known; Dumas and Boussingault place its density between .0691 and .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 pneu- Fig. 82. malic trough. A bottle or narrow jar may be filled with hy- drogen without much admixture of air, by inverting it over the extremity of an upright tube delivering the gas. In a short time, if the supply be copious, the air will be wholly displaced and the vessel filled. It may now be removed, the vertical position being carefully retained, and closed by a stopper or glass plate. If the mouth of the jar be wide, it must be par- tially closed by a piece of cardboard during the operation. This method of collecting gases by displacement is often extremely useful. Hydrogen was formerly 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 tjiat of coal- gas, which may be made very light by employing a high tem- perature in the manufacture. Although far inferior to pure hydrogen in buoyant power, it is found in practice to possess advantages over that substance, while its greater density is easily compensated by increasing the magnitude of the balloon. There is a very remarkable property enjoyed by gases and vapors in general, which is seen in a high degree of intensity in the case of hydrogen ; this is what is called diffusive power. If two bottles containing gases, which do not act chemically upon each other at common temperatures, be connoted by a * Ann. Chim. et Phys., 3d series, viii. 201. HYDROGEN. 109 narrow tube and left for some time, these will be found at the expiration 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 down- wards. 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 po- rous earthenware or dry plaster of Paris, and each half filled with a different 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. Mr. Graham, to whom we are indebted for a very valuable investigation of this interesting subject, has established the existence of a very simple relation between the rapidity of diffusion and the density of the gas, which is expressed by saying that the diffusive power varies inversely as the square root of the density of the gas itself. Thus, in the experiment supposed, if one half of the vessel be filled with hydrogen and the other half with oxygen, the two gases will penetrate the diaphragm at very different rates ; four cubic inches of hydro- gen will pass into the oxygen side, while one cubic inch of oxygen travels iu 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 mem- brane, 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 Mr. Graham's diffusion-tube. This is merely a piece of wide glass tube ten or twelve inches in length, having one of its extremi- ties closed by a plate of plaster of Paris about half an inch thick, and well dried. When the tube is filled by displace- ment 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 at- tains 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 of the great economy of Nature of this very curious law affecting the constitution of gaseous bodies ; it is the principal mean by which the atmosphere is preserved in a uniform state, and the accumulation of poisonous gases and exhalations in towns and other confined localities prevented. A 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 diffusion properly so called. For example, the diffusive power of carbonic acid into atmospheric air is very small, but it passes into the latter through a wet blad- der 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 res- 10 110 HYDROGEN. piration is performed; the aeration of the blood in the lungs, and the disen- gagement of the carbonic acid, are effected through wet membranes; the blood is never brought into actualbontact with the air, but receives its supply of oxygen, and disembarrasses itself of carbonic acid by this kind of spurious diffusion. The high diffusive power of hydrogen against air renders it impossible to retain that gas for any length of time in a bladder or caoutchouc bag ; it is even unsafe to keep it long in a gas-holder, lest it should become mixed with air by slight accidental leakage, and rendered explosive.* 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 further exalted by previously mixing the hy- drogen 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 gun- powder, 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 mix- ture, the introduction of a lighted match or red-hot wire determines in a mo- ment the union of the gases. By certain precautions, a mixture of oxygen and hydrogen can be burned at a jet without communication of fire to the contents of the vessel ; the flame is in this case solid. A little consideration will show that all ordinary flames burning in the air or in pure oxygen are, of necessity, hollow. The act of combustion is nothing more than the energetic union of the substance burned with the surround- ing 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 considera- tion ; the combustible and the oxygen are already mixed, and only require to have their temperature a little raised to cause them to combine in every part. The flame so produced is very different in physical characters from that of a simple jet of hydrogen or any other combustible gas; it is long and pointed, and very remarkable in ap- pearance. The safety-jet of Mr. Hemming, the construction of which involves a principle not yet discussed, may be adapted to a common bladder containing the mix- ture, 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 contained ui 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 peculiar appearance of the true hydro oxygen flame, so as to permit the supply of each gas to be exactly regulated by suitable stop-cocks attached to the jet (fig. 84). A piece of thick platinum wire introduced into the flame of the hydro-oxygen blow-pipe melts with the * Professor Graham has since published a very extensive series of researches on the passage of gases through narrow tubes, which will be found in detail in the Philo- sophical Transactions for 1846, p. 573. Fig. 84. HYDROGEN. Ill greatest ease; a watch-spring or small steel file burns Fig. 85. with the utmost brilliancy, throwing off showers of beautiful sparks ; an incombustible oxidized body, as magnesia or lime, becomes so intensely ignited, as to glow with a light insupportable to the eye, and to be susceptible of employment as a most powerful illu- minator, 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 hydrogen, a series of musical sounds are sometimes produced by the partial extinction and rekindling of the flame by the ascending cur- rent 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 parti- cular circumstances, they unite quietly and without explosion. Some years ago Professor DSbereiner, 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 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 has been cleaned by hot oil of vitriol and thorough washing with distilled water, is thrust into a jar containing a mixture of oxygen and hydrogen standing over water, combination of the two gases immediately begins, and the level of the water rapidly rises, and the platinum becomes so hot, that drops of water accidentally falling upon it enter into ebullition. If the metal be very thin and exceedingly clean, and the gases very pure, then its temperature rises after a time to actual redness, and the residue of the mixture explodes. But this is an effect altogether accidental, and dependent upon the high temperature of the platinum, which high temperature has been produced by the preceding quiet combination of the two bodies. When the platinum is reduced to a state of division, and its surface thereby much ex- tended, 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 con- structed. These, however, only act well when constantly used; the spongy platinum is apt to become damp by absorption of moisture from the air, and its power is then for the time lost. The best explanation that can be given of these curious effects, is to sup- pose that solid bodies in general have, to a greater or less extent, the property 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 112 HYDROGEN. were, within the sphere of their mutual attractions by a temporary increase of density, whereupon combination ensues. Coal-gas and ether or alcohol vapor may be made to exhibit the phenomenon of quiet oxidation under the influence of this remarkable surface-action. A close spiral of slender platinum wire, or a roll of thin foil heated to dull red- ness 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 tem- perature being maintained by the heat disengaged in the act of union. Some- times the metal becomes white-hot, and then the gas takes fire. A very pleasing experiment may be made by attaching such a coil of wire to a card, and suspending it in a glass containing a few Fig. 86. drops of ether, having previously made it red hot in the flame of a spirit-lamp. The wire continues to glow until the oxygen of the air is exhausted, giving rise to the production of an irritating vapor which attacks the eyes. The combustion of the ether is in this case but partial; a portion of its hydrogen is alone removed, and the whole of the carbon left untouched. A coil of thin platinum wire may be placed over the wick of a spirit-lamp, or a ball of spongy platinum sus- tained just above the cotton ; on lighting the lamp, and then blowing it out as soon as the metal appears red-hot, slow combustion of the spirit drawn up by the capil- larity of the wick will take place, accompanied by the pungent vapors just mentioned, which may be modified, and even rendered agreeable, by dissolving in the liquid some sweet-smelling essential oil or resin. Hydrogen forms numerous compounds with other bodies, although it is greatly surpassed in this respect not only by oxygen, but by many of the other elements. The chemical relations of hydrogen tend to place it beside the metals. The great discrepancy in physical properties is perhaps more appa- rent than real. Hydrogen is yet unknown in the solid condition, while, on the other hand, the vapor of the metal mercury is as transparent and colorless as hydrogen itself. This vapor is only about seven times heavier than at- mospheric 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 peroxide of hy- drogen. 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 compound has from time to time to the present day occupied the attention of some of the most distinguished cultivators of chemical science. There are two distinct methods of research in chemistry, the analytical, or that in which the com- pound is resolved into its elements, and the synthetical, in which the elements are made to unite and produce the compound. The first method is of much more general application than the second, but in this particular instance both may be employed, although the results of the synthesis are most valuable. * A claim to the discovery of the composition of water on behalf of Mr. James Watt has been very strongly urged, and supported by such evidence that the reader of the controversy may be led to the conclusion that the discovery was made by both parties, nearly simultaneously, and unknown to each other. HYDROGEN. 113 Fig. 87. Fig. 88. The most elegant example of an analysis of water would probably be found 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 ex- tremities of a voltaic apparatus of mode- rate power, decomposition of the liquid takes place in a very interesting manner ; oxygen, in a state of perfect purity, is evolved from the water in contact with the plate belonging to the copper end of the battery, and hydrogen, equally pure, is disengaged at the plate connected with the zinc extremity, the middle por- tions of liquid remaining apparently un- altered. By placing small graduated jars over the platinum plates, the gases can be collected, and their quantities deter- mined. The figure in the margin will show at a glance the whole arrange- ment; the conducting wires pass through the bottom of the glass cup, and away to the battery. When this experiment has been continued a sufficient time, it will be found that the volume of the hydrogen is a very little above twice that of the oxygen; were it not for the ac- cidental circumstance of oxygen being sensibly more soluble in water than hydrogen, the proportion of two to one by measure would come out exactly. 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. Cavendish. (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 moist- ure, and if the stop-cock be then opened under water, the latter will rush in and fill the vessel, leaving merely a bubble of air, the result of imperfect exhaustion. The process upon which most reliance is placed is that in which pure oxide of copper is reduced at a red heat by hydrogen, and the water so formed collected and weighed. This oxide suffers no change by heat, alone, but the momentary contact of hydrogen, or any common combustible matter at a high temperature, suffices to reduce a corresponding portion to the metallic state. Fig. 89 will serve to convey some idea of the arrangement adopted in researches of this kind. A copious supply of hydrogen is produced by the action of dilute sulphuric acid upon the purest zinc that can be obtained; the gas is made to pass in succession through solutions of silver and strong caustic potash, by which its purification is completed. After this, it is conducted through a 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 10* 114 HYDROGEN. an extraordinary attraction for aqueous vapor, that they dry the gas completely during its transit. The extremity of this tube is shown at a. The dry hydro- Fig. 89. gen thus arrives at the part of the apparatus containing the oxide of copper, represented at 6; 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 decompo- sition proceeds, the water produced 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 vapor by the current 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 effect its completion. When the process is at an end, and the apparatus perfectly cool, the stream of gas is discontinued, dry air is drawn through the whole arrangement, and, lastly, the parts are disconnected and re-weighed. The loss of the oxide of copper gives the oxygen ; the gain of the receiver and its drying-tube indi- cates the water, and the difference between the two. the hydrogen. 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,f with the most scrupulous precision, and the above supposition fully confirmed. The composition of water may therefore be considered as established : it con- tains by weight 8 parts oxygen to 1 part hydrogen, and by measure, 1 volume oxygen to 2 volumes hydrogen. The densities of the gases, as already men- tioned, correspond very closely with these results. The physical properties of water are too well known to need lengthened description ; it is, when pure, colorless and transparent, destitute of taste arid odor, and an exceedingly bad conductor of electricity of low tension. It attains its greatest density towards 40 F., freezes at 32, and boils under the pressure of the atmosphere at or near 212. It evaporates at all temperatures. One cubic inch at 62 F. weighs 252.45 grains. It is 815 times heavier than air; an imperial gallon weighs 70,000 grains or 10 Ib. avoirdupois. To all ordi- * Ann. Chim. et Phys., xv. 386. f Ann. Chim. et Phys., 3d series, viii. 189. HYDROGEN. 115 nary 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-millionths of the whole. Clear water, although colorless in small bulk, is blue like the atmosphere when viewed in mass. This is seen in the deep ultramarine tint of the ocean, and perhaps in a still more beautiful manner in the lakes of Switzer- land and other alpine countries, and in the rivers which issue from them; the slightest admixture of mud or suspended impurity destroying the effect. The same magnificent color is visible in the fissures and caverns found in the ice of the glaciers, which is usually extremely pure and transparent within, although foul upon the surface. Steam, or vapor of water in its state of greatest density at 212, compared with air at the same temperature, and possessing an equal elastic force, has a specific gravity expressed by the fraction .625. In this condition, 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 distilla- tion alone will free the liquid from those that are dissolved. In the prepara- tion of distilled water, which is an article of large consumption in the scien- tific laboratory, it is proper to reject the first portions which pass over, and to avoid carrying the distillation to dryness. The process may be conducted in a metal still furnished with a worm or condenser of silver or tin ; lead must not be used. The ocean is the great recipient of the saline matter carried down by the rivers which drain the land; hence the vast accumulation of salts. The fol- lowing 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 .... .766 Chloride of magnesium .... 3.666 Bromide of magnesium .... .029 Sulphate of magnesia .... 2.296 Sulphate of lime ..... 1.406 Carbonate of lime . .033 J Traces of iodine and ammoniacal salt 1000. Its specific gravity was found to be 1.0274 at 60. 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 * Phil. Mag., July, 1839. 116 HYDROGEN. waters scattered over the whole earth, and to which medicinal virtues are attributed. Some of these hold protoxide of iron in solution, and are effer- vescent from carbonic acid gas; others are alkaline, probably from traversing rocks of volcanic origin ; some contain a very notable Quantity of iodine or bromine. Their temperatures also are as variable as their chemical nature. A tabular notice of some of the most remarkable of these waters will be found in the Appendix. Water enters into direct combination with other bodies, forming a class of compounds called hydrates ; the action is often very energetic, much heat being evolved, as in the case of the slaking of lime, which is really the production of a hydrate of that base. Sometimes the attraction between the water and the second body is so great that the compound is not decomposable by any heat that can be applied; the hydrates of potash and soda, and of phosphoric 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 connection with the geometrical figure of the salt. In this case it is easily driven off by the application of heat. Lastly, the solvent properties of water far exceed those of any other liquid known. Among salts, a very large proportion are soluble to a greater or less extent, the solubility usually increasing with the temperature, so that a hot saturated solution deposits crystals on cooling. There are a few exceptions to this law, one of the most remarkable of which is common salt, the solu- bility 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 F., 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 stalactites 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 temperature in the interior of the earth upon felspathic and other rocks. Something of the sort is manifest in the Geyser springs of Iceland, which deposit siliceous sinter.* Peroxide of hydrogen, sometimes called oxygenated water, is an exceedingly interesting substance, but unfortunately very difficult of preparation. It is formed by dissolving the peroxide of barium in dilute hydrochloric acid, carefully cooled by ice, and then precipitating the baryta by sulphuric acid ; the excess of oxygen of the peroxide, instead of being disengaged as gas, unites with a portion of the water, and converts it into peroxide of hydrogen. This treatment is repeated with the same solution and fresh portions of the peroxide of barium until a considerable quantity of the latter has been con- * Phil. Mag., Oct. 1834. NITROGEN. 117 sunned, and a corresponding amount of peroxide of hydrogen formed. The liquid yet contains hydrochloric acid, to get rid of which it is treated i i suc- cession with sulphate of silver and baryta water. The whole process re- quires the utmost care and attention. The peroxide 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 peroxide of hydrogen may be concen- trated under the air-pump receiver until it acquires the specific gravity of 1.45. In this state it presents the aspect of a colorless, transparent, inodorous liquid, possessing remarkable bleaching powers. It is very prone to decom- position; the least elevation of temperature causes effervescence, due to the escape of oxygen gas; near 212 it is decomposed with explosive violence. Peroxide of hydrogen contains exactly twice as much oxygen as water, or 16 parts to one 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 ex- periment 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. A bell-jar is then inverted over the whole, and suf- Fig- 90. fered to rest on the shelf of the trough, so as to project a little over its edge. At first, the heat causes expan- sion of the air of the jar, and a few bubbles are expelled, after which the level of the water rises considerably. When the phosphorus becomes extin- guished 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 other vessels, and its properties examined. Prepared by the foregoing process, nitrogen is con- taminated by a little vapor of phosphorus, which com- municates its peculiar odor. A preferable method is to fill a porcelain tube with turnings of copper, or, still better, with the spongy metal obtained by 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 progress by the heated copper. If chlorine gas be passed into solution of ammonia, the latter substance, which is a compound of nitrogen with hydrogen, is decomposed ; the chlorine combines with the hydrogen, and the nitrogen is set free with effervescence. In this manner very pure nitrogen can be obtained. In making this experi- ment, 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 forma- tion of an exceedingly dangerous explosive compound formed by the contact of chlorine with an ammoniacal salt. Nitrogen is destitute of color, taste, and smell ; it is a little lighter than air, its density being, according to Dumas, -972. 100 cubic inches, at 60, and 30 inches barometer, will therefore weigh 30.14 grains. Nitrogen is incapable * I. e. Generator of nitre; also called azote, from a, privative, and ?&},, life. 118 NITROGEN. 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 characterized by negative pro- perties. The exact composition of the atmosphere has repeatedly been made the subject of experimental research. Besides nitrogen and oxygen, the air con- tains a little carbonic acid, a very variable proportion of aqueous vapor, a trace of ammonia, and, perhaps, a little carburetted hydrogen. The oxygen and nitrogen are in a state of mixture, not of combination, yet their ratio is always uniform. Air has been brought from lofty Alpine heights, and com- pared with that from the plains of Egypt; it has been brought from an ele- vation 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 proportions of oxygen and nitrogen remain unaltered, the diffusive energy of the gases being adequate to maintain this perfect uniformity of mixture. The carbonic acid, on the contrary, being much influenced by local causes, varies consider- ably. 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. Nitrogen Oxygen Composition of the ^Atmosphere. By weight. . 77 parts. . 23 By measure. . 79.19 . 20.81 100 100 3.7 measures to 6.2 measures, in 10,000 measures of Carbonic acid, from air. Aqueous vapor variable, depending much upon the temperature. Ammonia, a trace. 100 cubic inches of pure and dry air weigh, according to Dr. Prout, 31.0117 grains ; the temperature being 60 F. and the barometer standing at 30 inches. Fig. 91. The analysis of air is best effected by passing it over finely-divided copper contained in a tube of hard glass, carefully weighed, and then heated to redness; the nitro- gen 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 introduc- ing into a graduated tube, standing over water, a known quantity of the air to be examined, and then passing into the latter a stick, of phosphorus affixed to the end of a wire. The whole is left about twenty-four hours, during which the oxygen is slowly but completely absorbed, after which the phosphorus is withdrawn and the residual gas read off. Another plan is to mix the air Math hydrogen and pass an electric spark ; after explosion the volume of gas is read off and compared with that of the air employed. Since the analysis of gaseous bodies by explosion is an operation of NITROGEN. 119 Fig. 92. 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. The most 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 of 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, the in- strument 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 mercury has been made equal on both sides by displacing a portion from the open limb by thrusting down a piece of stick, the volume of air is read off. This done, the open part of the tube is again filled up with mer- cury, closed with the finger, inverted into the liquid metal, and a quantity of pure hydrogen introduced, equal as nearly as can be guessed to about half the volume of the air. The eudiometer is once more brought into an erect position, the level of the mer- cury equalized, and the volume again read off; the quantity of hydrogen added is thus accurately ascer- tained. 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 confined by the thumb in the open part of the tube acts as a spring and moderates the explosive effect. Nothing now remains but to equalize the level of the mercury by pouring a little more into the instru- ment, and then to read off the volume for the last time. What is required to be known from this experiment is the diminution the mix- ture suffers by explosion ; for since the hydrogen is in excess, and since that substance unites with oxygen in the proportion by measure of two to one, one- third part of that diminution must be due to the oxygen contained in the air introduced. As the amount of the latter is known, the proportion of oxygen it contains thus admits of determination. The case supposed will render this clear. Air introduced 100 measures. Air and hydrogen . . . . 150 Volume after explosion ... 87 Diminution 63 63 = 21 ; oxygen in the hundred measures, o The working pupil will do well to acquire dexterity in the use of this valuable instrument, by practicing the transference of gas or liquid from the 120 NITROGEN. one limb to the other, &c. In the analysis of combustible gases by explosion with oxygen, solution of caustic potash is often required to be introduced 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. Composition by weight. Protoxide of nitrogen* Deutoxide, or binoxide of nitrogen^ Hyponitrous acidj . Nitrous acid .... Nitric acid ..... Nitrogen. , 14.08 , 14.06 , 14.06 , 14.06 14.06 Oxygen. 8 16 24 i 32 40 Fig. 93. Nitric or Jlzotic acid. In certain parts of India, and also in other hot dry cli- mates 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 commerce as nitre or saltpetre ; it is a compound of nitric acid and potash. To obtain liquid nitric acid, equal weights of powdered nitre and oil of vitriol are intro- duced 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 disap- pear, but towards the end of the process again becomes 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 potash. The reaction is thus explained. AT . C Nitric acid Nltre Potash Oil of vitriol Water Sulphuric acid .Liquid nitric acid. Bisulphate of potash. In the manufacture of nitric acid on the large scale, the glass retort is re- * Otherwise called nitrous oxide. f Otherwise called nitric oxide, t Called by Mr. Graham nitrous acid. 9 Called by Mr. Graham peroxide of nitrogen. The nomenclature adopted in the text is that employed in Dr. Turner's very valuable treatise. NITROGEN. 121 placed by a cast-iron cylinder and the receiver by a series of earthen con- densing vessels connected by tubes. Nitrate of soda, found native in Peru, is often substituted for nitrate of potash. Liquid nitric acid so obtained has a specific gravity of 1.5 to 1.52 ; it has a golden yellow color, which is due to nitrous or hyponitrous 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. Pure liquid nitric acid, in its most concentrated form, is obtained by mixing the above with about an equal quantity of oil of vitriol, redistilling, 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 pro- duct is as colorless as water; it has the sp. gr. 1.517 at 60 F., boils at 184, and consists of 54.06 parts real acid, and 9 parts water; absolute nitric acid in the separate state is unknown.* 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 refuses to attack iron or tin, and its mode of action upon 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 54.06 parts of the former to 36 parts of the latter. Its sp. gr. at 60 is 1.424, and it boils at 250. An acid weaker than this is concentrated 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.| Nitric acid forms with bases a very extensive and important group of salts, the nitrates, which are remarkable for being all 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 chlorine from common salt in the nitre, and sometimes of sulphate from accidental splashing of the pasty mass in the retort. To discover these impurities, a * Anhydrous nitric acid has been isolated by M. Deyille, by treating nitrate of silver by dry chlorine. In consequence of the strong affinity of chlorine for silver, it dis- places both oxygen and nitric acid from the nitrate. The chlorine is dried by passing over chloride of calcium and then through pumice moistened with sulphuric acid : the nitrate of silver is contained in a U shaped tube, to which a similar tube with a spherical reservoir at the curved portion is united by means of the blowpipe. The tube with the spherical reservoir is cooled by a freezing mixture, the nitrate of silver tube placed in a water bath, heated, and the chlorine transmitted in a slow and con- tinuous stream. At ordinary temperatures, there is no appearance of decomposition ; the nitrate of silver is heated to 203, and then the temperature lowered to between 135 and 155, when crystals commence to form on that portion of the tube not im- mersed in the freezing mixture and a small quantity of liquid collects in the reservoir. To transfer the nitric acid, the liquid must be removed from the reservoir, a bulb attached to the U tube containing the crystals, a stream of dry carbonic acid substituted for the chlorine, and the freezing mixture transferred to the bulb while the tube con- taining the crystals is exposed to ordinary temperatures. After collection, the bulb is to be hermetically sealed. Anhydrous nitric acid is a colorless solid, crystallizing in prisms derived from a right rhombic prism. It fuses at a little above 85 and boils at about 113, at which point it begins to decompose, and even at common temperatures is liable to gradual decomposition, producing explosion by the increased tension of the confined gases. Placed in contact with water, it dissolves with the evolution of much heat. Comptes Rend us, 1849. R.B. tThe two hydrates of nitric acid are thus expressed in symbols: NO S ,HO and NO 6 ,4HO. No compound containing two equivalents of water appears to exist, 11 122 NITROGEN. portion is diluted with four or five times its 'bulk of distilled water, and di- vided between two glasses. Solution of nitrate of silver is dropped into the one, and solution of nitrate of baryta into the other; if no clnnge ensue in either case, the acid is free from the impurities mentioned. Nitric acid has been formed in small quantity by a very curious process, namely, by passing a series of electric sparks through a portion of air, water, or an alkaline solution being present. The amount of acid so formed after many hours is very minute; still it is not impossible that powerful discharges of atmospheric electricity may sometimes occasion a trifling production of nitric acid in the air. Nitric acid is not so easily detected in solution in small quantities as many other acids. Owing to the solubility of all its compounds, no precipitant, can be found for this substance. One of the best tests is its power of bleaching a solution of indigo in sulphuric acid when boiled with that liquid. The absence of chlorine must be insured in this experiment by means whioh will hereafter be obvious, otherwise the result is equivocal. Protoxide of Nitrogen ; Nitrous Oxide; (laughing gas.) When solid nitrate of ammonia is heated in a retort or flask,* 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. Protox. nitrogen 22.06 Protox. nitrogen 22.06 Nitrate of Ammonia 80.12 Nitric acid 54.06 Ammonia 17.06 Water 9 r Nitrogen > Oxygen ) Oxygen ( Oxygen ( Nitrogen ( Hydrogen 14.06^______ 14'.06 ^7^- Fig. 94. Water 9 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 colorless, 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 a 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 Fahrenheit, a pressure of 50 atmospheres. 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 ni- trogen. Every two volumes of the gas must con- sequently contain two volumes of nitrogen and one volume of oxygen, the whole being condensed or contracted one-third; a con- stitution resembling that of vapor of water. * 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 apparatus. 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 edge so as to form a lip, or border. The neck will then bear a tight-fitting cork without risk of splitting. NITROGEN. 123 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 at- mospheric air, for a short time, without danger or inconvenience. The effect is very transient, and is not followed by depression. Deutoxide or Binoxidc of Nitrogen; Nitric Oxide. Clippings or turnings of copper are put into the apparatus employed for preparing hydrogen,* toge- ther with a little water, and nitric acid added by the funnel until brisk effervescence is excited. The gas may be collected over cold water, as it is not sensibly soluble. The reaction is a simple deoxitlation of some of the nitric acid by the copper; the metal is oxidized, and the oxide so formed is dissolved by an- other portion of the acid. Nitric acid is very prone to act thus upon certain metals. The gas obtained in this manner is colorless and transparent; in contact with air or oxygen gas it produces deep red fumes, which are readily ab- sorbed by water ; this character is sufficient to distinguish it from all other gaseous bodies. A lighted taper plunged into the gas is extinguished ; lighted phosphorus, however, burns in it with great brilliancy. The specific gravity of deutoxide of nitrogen is 1.039; 100 cubic inches weigh 32.22 grains. It contains equal measures of oxygen and nitrogen gases united without condensation. When this gas is passed into a solution of protoxide of iron, it is absorbed in large quantity, and a deep brown or nearly black liquid produced, which seems to be a definite compound of the two substances. The compound is again decomposed by boiling. Hyponitrous Acid. Four measures of deutoxide of nitrogen are mixed with one measure of oxygen, and the gases, perfectly dry, exposed to a tempera- ture of 0Fahr. They condense to a thin mobile liquid, which at that de- gree of cold is colorless, but becomes green at the ordinary temperature of the air. Its vapor is orange red. Hyponitrous 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; hyponitrite of lead may, however, be prepared by di- gesting metallic lead in a solution of the nitrate, and many other salts of hyponitrous acid may be obtained by indirect means. Nitrous Acid. The term acid applied to this substance is hardly correct, since it does not seem to possess the power of forming salts ; the expression has, notwithstanding, been long sanctioned by use. It is the vapor of nitrous 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; oxide of lead remains behind, while the acid is resolved into a mixture of oxygen and nitrous acid. By surrounding the re- ceiver with a very powerful freezing mixture, the latter is condensed to the liquid form. It is then nearly colorless, but acquires a yellow, and ultimately a red tint, as the temperature rises. At 82 it boils, giving off its well-known red vapor, the intensity of the color of which is greatly augmented by eleva- tion of temperature. This substance, like the preceding, is decomposed by water, being resolved into deutoxide of nitrogen and nitric acid. Its vapor 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 nitrous gas.f * See page 107. f Much doubt yet hangs over the true nature and relations of these two acids. Ac- 124 CARBON. Nitrogen appears to combine, under favorable 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. Schrcetter has shown that in the case of copper, at least, this effect is caused by the formation and subsequent destruction of an azotide. When ammonia is passed over oxide of copper heated at 570, water is formed, and a soft brown powder produced, which when heated further evolves ni- trogen, and leaves metallic copper. The same effect is produced by the con- tact 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 vegetable : when these latter are exposed to destructive distillation in close vessels, a great part of this carbon remains, 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 curious 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 colorless, but now and then having a shade of yellow, pink, or blue. The origin and true geological position of the diamond are unknown ; it is always found embedded in gravel and transported materials, whose history cannot be traced. The crystalline form of the diamond is that of the regular octahedron or cube, or some figure geometrically connected with these ; many of the octahedral crystals exhibit a very peculiar appear- ance, arising from the faces being curved or rounded, which gives to the crystal an almost spherical figure. Fig. 95. Fig. 96. Fig. 97. Fig. 98. The diamond is infusible and inalterable by a very intense heat, provided air be excluded ; heated to ordinary 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 cording to M. Peligot, the only product of the union of deutoxide of nitrogen and ox- ygen is nitrous acid, which in the total absence of water is a white solid crystalline body, fusible at 16 F. At common temperatures it is an orange-yellow liquid. The same product is obtained by heating perfectly dry nitrate of lead. From these experi- ments it appears that hyponitrous acid in a separate state is unknown. Ann. Chim. et. Phys. 3d series, ii. 58. * Ann. der Pharm. xxxvii. 129. The formula of the copper compound is Cu,N. CARBON. 125 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 particu- lar 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. Graphite, or plumbago, appears to consist essentially of pure carbon, al- though most specimens contain iron, the quantity of which varies from a mere trace up to five per cent. Graphite is a somewhat rare mineral ; the finest, and most valuable for pencils, is brought from Borrowdale, in Cumber- land, where a kind of irregular vein is found traversing the ancient slate- beds of that district. Crystals are not common ; when they occur, they have the figure of a short six-sided prism a form bearing no geometrical 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. Lamp-black, the soot produced by the imperfect combustion of oil or resin, is the best example that can be given of pure carbon in its uncrystallized or amorphous state. To the same class belong the different kinds of charcoal. That prepared from wood, either by distillation in a large iron retort, or by the smothered combustion of a pile of fagots partially covered with earth, is the most valuable as fuel. Coke, the charcoal of pit-coal, is much more impure ; it contains a large quantity of earthy matter, and very often sulphur ; the quality depending very much upon the mode of preparation. Charcoal from bones and animal matters in general is a very valuable substance, on account of the extraordinary power it possesses of removing coloring matters from organic solutions; it is used for this purpose by the sugar refiners to a very great extent, and also by the manufacturing and scientific chemist.* The property in question is possessed by all kinds of charcoal in a small degree. Charcoal made from box, or other dense wood, has the property of condens- ing into its pores gases and vapors; 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 properly in the gas of suffering liquefaction. This effect, as well as that of the de- colorizing power, no doubt depends in some way upon the same peculiar action of surface so remarkable in the case of platinum in a mixture of oxy- gen and hydrogen.f * It removes from solution in water the vegetable bases, bitter principles and astringent substances when employed in excess, requiring from twice to twenty times their weight for total precipitation. A solution of iodine in water, or of iodide of potassium is quickly deprived of color. Metallic salts dissolved in water or diluted alcohol are precipitated, though not entirely, requiring about thirty times their weight of animal charcoal. Arsenious acid is totally carried out of solution. In these cases it acts in three different ways, the salt is absorbed unaltered: the oxide in the salt may be reduced ; or, the salts precipitated in a basic condition, the solution showing an acid reaction as soon as the carbon begins to act. It is in this last case especially that traces of the bases can be detected, the acid set free preventing their total prtcipi- tation. The precipitation may hence be prevented by adding an excess of acid, and the bases after precipitation may be dissolved out by boiling with an acid solution. Warrington, Mem. Chim. Soc. 1845: Garrod, Pharm. Journ. 1845: Weppen, Ann. de Chim. 1845. R.B. f 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 11* 126 CARBON. 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. Carbonic oxide Carbonic acid Carbon. 6 Oxygen. 8 16 Carbonic acid is always produced when charcoal burns in air or oxygen gasj it is most conveniently obtained, however, for study, by decomposing a car- bonate with one of the stronger acids. For this purpose, the apparatus for generating hydrogen may again be employed ; fragments of marble are put into the bottle with enough water to cover the extremity of the funnel-tube, and hydrochloric or nitric acid added by the latter, until the gas is freely dis- engaged. Chalk-powder and dilute sulphuric acid may be used instead. The gas may be collected over water, although with some loss; or very con- veniently, by displacement, if it be required dry, as shown in the figure. The Fig. 99. 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.* red heat and pure oxygen gas. In the form of charcoal, it conducts heat slowly and electricity readily. Carbon is insoluble in water and not liable to be affected by air and moisture. It retards putrefaction. R. B. # In connecting tube-apparatus for conveying gases or cold liquids, not corrosive, little tubes of caoutchouc about an inch long Fig. 100. are inexpressibly useful. These are made by bending a piece of sheet India-rubber loosely round a glass tube or rod, and cutting off the superfluous portion with sharp scissors. The fresh-cut edges of the caoutchouc, pressed strongly together, cohere completely, and the tube is perfect, provided they have not been soiled by touching with the fingers. The con- necters 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. CARBON. 127 Carbonic acid gas is colorless ; it has an agreeable pungent taste and odor, 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 venti- lation, 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. Carbonic acid is sometimes emitted in large quantity from the earth in volcanic districts, and it is con- stantly generated where organic matter is in the act of undergoing fermentive decomposition. The fatal "afterdamp" of the coal-mines contains a large proportion of carbonic acid. 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 nitro- gen, 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. 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, according to Mr. Addams. The liquefied acid is colorless and limpid, lighter than water, and four times more expansible than air; it mixes in all proportions with ether, alcohol, naphtha, oil of turpentine, and bisulphuret of carbon, and is insoluble in water and fat oils.f 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 quantity is but small, b"t absolutely, taking into account the vast extent of the atmo- sphere, 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, retain- ing 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 magnesia. 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 introduce 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 caustic pot- * MM. Dulong and Berzelius. f When relieved of pressure, it immediately boils, and seven parts out of eight assume the gaseous state, the rest becoming solid at 9(P F. (Mitchell). Solid car- bonic acid mixed with ether produces in vacuo a very intense cold (- 165 F. Fara- day), capable of solidifying many gases when aided by pressure. Liquid carbonic acid immersed in this mixture becomes a solid so clear and transparent that its condition cannot be detected until a portion again becomes liquid. R. B. 128 SULPHUR. ash, the first is withdrawn by absorption, while the second remains unchanged. Another, and it may be preferable method, is to heat finely-powdered yellow ferrocyanide of potassium with eight or ten times its weight of concentrated sulphuric acid. The salt is entirely decomposed, yielding a most copious supply of perfectly pure carbonic oxide gas, which may be collected over water in the usual manner.* Carbonic oxide is a combustible gas; it burns with a beautiful pale blue flame, generating carbonic acid. It has never been liquefied. It is colorless, has very little odor, and is extremely poisonous, even worse than carbonic acid. Mixed with oxygen, it explodes by the electric spark, but with some difficulty. Its specific gravity is .973; 100 cubic inches weigh 30.21 grains. The relation by volume of these oxides of carbon may thus be made intel- ligible : carbonic acid contains its own volume of oxygen, that gas suffering no change of bulk by its conversion. One measure of carbonic oxide mixed with half a measure of oxygen and exploded, yields one measure of carbonic acid ; hence carbonic oxide contains half its volume of oxygen. Carbonic oxide unites with chlorine under the influence of light, forming a pungent, suffocating compound, possessing acid properties, called phosgene gas, or chloro-carbonic acid. It is made by mixing equal volumes of carbonic oxide and chlorine, both perfectly dry, and exposing the mixture to sunshine; the gases unite quietly, the color disappears, and the volume becomes reduced to one-half. It is decomposed by water. This is an elementary body of great importance and interest. Sulphur is often found in a free state in connection with deposits of gypsum arid rock- salt; its occurrence in volcanic districts is probably accidental. Sicily furnishes a large proportion of the sulphur employed in Europe. In a state of com- bination 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. Its specific gravity is 1.98; it melts when heated, and distils over unaltered, if air be excluded. The crystals of sulphur exhibit two distinct and incom- patible forms, namely, an octahedron with rhombic base, fig. 101, which is the figure of native sulphur, and that assumed when sulphur separates from solution at common temperatures, as when a solution of sulphur in bisulphuret 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 portion poured out. Fig. 102 shows the result of such an experi- ment. Fig. 101. Fig. 102. Fig. 103. * See a paper by the author in Memoirs of Chem. Soc. of London, i. 251. 1 eg. crystallized ferrocyanide of potassium and 6 eq. oil of vitriol yield 6 eg. carbonic oxide, 2 eg. sulphate of potash, 3 eg. sulphate of ammonia, and 1 eg. protosulphate of iron. SULPHUR. 129 Sulphur melts at 232 Fahrenheit; at this temperature it is of the color of amber, and thin and fluid as water ; when further heated, it begins to thicken, and to acquire a deeper color; and between 430 and 480 it is so tenacious that the vessel in which it is contained may be inverted for a moment with- out 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 be- comes brittle and crystalline. From the temperature last mentioned to the boiling point, about 600, sulphur again becomes thin and liquid. In the preparation of commercial flowers of sulphur, the vapor is conducted into a large cold chamber, where it condenses in minute crystals. The specific gravity of sulphur vapor is 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 bisulphuret of .carbon. In its chemical relations, sulphur bears great resemblance to oxygen; to very many oxides there are corresponding sulphurets, and these sulphurets often unite among themselves, forming crystallizable compounds analogous to salts. Compounds of Sulphur and Oxygen. Composition by weight. Sulphur. Oxygen. Sulphurous acid, 16.09 16 Sulphuric acid,* 16.09 24 Hyposulphurous acid, ...... 32.18 16 Hyposulphuric acid, . . . . 32.18 40 Composition by weight. Sulphur. Oxygen. Sulphuretted hyposulphuric acid, . . . 48.27 40 Bisulphuretted hyposulphuric acid,| . . 64.36 40 Acid from protochloride of sulphur, . . 64.36 40 Acid from perchloride of sulphur, . . 80.45 48 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 * The terminations ous and ic, applied to acids, signify degrees of oxidation, the latter being the highest ; acids ending in ous form salts the names of which are made to end in ite, and those in ic terminate in ate, as sulphurous acid, sulphite of soda, sulphuric acid, sulphate of soda. f 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 numbers given are really the equivalent numbers, but are intended only to show the proportions of sulphur and oxygen, without any reference to other bodies. The following are the quantities required to saturate one equivalent of a base : Sulphurous acid, ........ SO, Sulphuric acid, ....... SO 3 Hyposulphurous acid, ....... S a O a Hyposulphuric acid, ...... S a O, Sulphuretted hyposulphuric acid, ..... S 3 O S Bisulphuretted hyposulphuric acid, .... S 4 O S Acid from protochloride, ...... S 4 O 4 Ditto from perchloride, ...... S 4 O 8 130 SULPHUR. sulphuric acid becomes sulphurous. Sulphurous acid thus obtained is a colorless gas, having the peculiar suffocating odor of burning brimstone; it instantly extinguishes flame, and is quite irrespirable. Its density is 2.21, 100 cubic inches weighing 68.69 grains. At F., under the pressure of the at- mosphere, this gas condenses to a colorless, limpid liquid, very expansible by heat. Cold water dissolves more than thirty times its volume of sulphurous acid. The solution may be kept unchanged so long as air is excluded, but access of oxygen gradually converts the sulphurous into sulphuric acid, in the presence of water, although the dry gases may remain in contact for any length of time without change.* One volume of sulphurous acid gas contains one volume of oxygen and one- sixth of a volume of sulphur vapor, condensed into one volume. Gases which, like the present, are freely soluble in water, must be col- lected by displacement, or by the use of the mercurial pneumatic trough. The manipulation with the latter is exactly the same in principle as with the ordinary water-trough, but rather more troublesome, from the great density of the mercury, and its opacity. The whole apparatus is on a much smaller scale. The trough is best constructed of hard, sound wood, and so contrived as to economize as much as possible the expensive 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 combi- nation. 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 Jlcid. Hydrated sulphuric acid has been known since the fif- teenth 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 at Nordhausen in Saxony ; 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 re- mainder is driven off in vapor, which is condensed by the cold vessel. The product is a brown oily liquid, of about 1.9 specific gravity, fuming in the air, arid very corrosive. It is chiefly made for the purpose of dissolving indigo. The second method, which is perhaps, with the single exception men- tioned, always followed as the more economical, depends upon the fact that, when sulphurous acid, nitrous acid, and water are present in certain propor- tions, the sulphurous acid becomes oxidized at the expense of the nitrous acid, which by the loss of one-half of its oxygen sinks to the condition of deutoxide of nitrogen. The operation is thus conducted : A large and very long chamber is built of sheet-lead supported by timber framing; on the out- side, 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 * Liquid sulphurous acid freezes at 105 F. into a colorless transparent solid (Fara- day). The gas itself when moist is rendered solid by cold, a hydrate being formed containing about 20 per cent, of water. R. B. t It does not bleach by destroying the coloring matter, but by forming with it a colorless combination : hence the color is restored on neutralizing the sulphurous acid by an alkali. R. B. SULPHUR. 131 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 ar- rangements is to cause a constant supply of sulphurous acid, atmospheric air, nitric acid vapor, and water in the state of steam, to be thrown into the chamber, there to mix and react upon each other. The nitric acid imme- diately gives up apart of its oxygen to the sulphurous acid, becoming nitrous; it does not remain in this state, however, but suffers further deoxidation until it becomes reduced to deutoxide of nitrogen. That substance in contact with free oxygen absorbs a portion of the latter, and once more becomes nitrous acid, which is again destined to undergo deoxidation by a fresh quantity of sulphurous acid. A very small portion of nitrous acid, mixed with atmo- spheric 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 be- tween the oxygen of the air and the sulphurous acid. The presence of water is essential to this reaction. We may thus represent the change: AT . ., Nitrous acid 46 06 (Nitrogen 14.06 - __ _*. Deutoxide of nitrogen ^. ____ - Oxygen 16 30.06 (Oxygen 16 Sulphurous acid ( Sulphur 32.18 64.18. Oxygen 32 -~^^^- Hydrated sulphuric acid Water . ' . . .18 -- ^98.18. 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 nitrous acids are introduced by separate tubes, symptoms of chemical action become immediately evident, and after a little time a white crystalline matter is observed to condense on the sides of the vessel. This substance appears to be a compound of sulphuric-acid, hyponitrous acid, and a little water.* When thrown into water, it is resolved into sulphuric acid, deutoxide 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 constant when the operation goes on well, and the nitrous acid is not in excess, may perhaps admit of doubt. The water at the bottom of the chamber thus becomes loaded with sul- phuric acid ; when a certain degree of strength has been reached, it is drawn off and concentrated by evaporation, first in leaden pans, and afterwards in stills of platinum, until it attains a density (when cold) of 1.84, or there- abouts; it is then transferred to carboys, or large glass bottles fitted in baskets, * M.'-Gaultier de Claubry assigned to this curious substance the composition ex- pressed by the formula 4HO,2NO 3 +5SO 3 , and this view has generally been received by recent chemical writers. M. de la Provostaye has since shown that a compound, possessing all the essential properties of the body in question may be formed by bring- ing together, in a sealed glass tube, liquid sulphurous acid and liquid nitrous acid, both free from water. The white crystalline solid soon begins to form, and at the ex- pi nil ion of twenty-rsix hours the reaction appears complete. The new product is accompanied by an exceedingly volatile greenish liquid, having the characters of hy- pniiitious arid. The white substance, on analysis, was found to contain the elements of two equivalents of sulphuric acid and one of hyponitrous acid, or NO 3 -f-2SO 3 . M. de la Provostaye very ingeniously explains the anomalies in the different analyses of the leaden chamber product, by showing that the pure substance forms crystallizable combinations with different proportions of liquid sulphuric acid. (Ann. Chim. et Phys.lxxiii.362). 132 SULPHUR. for sale. In Great Britain, this manufacture is one of great national import- ance, and is carried on to a vast extent. An inferior kind of acid is some- times 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 consumption; it very frequently contains arsenic. The most concentrated sulphuric acid, or oil of vitriol, as it is often called, is a definite combination of 40.09 parts real acid, and 9 parts water. It is a colorless, oily liquid, having a specific gravity of about 1.85, of intensely acid taste and reaction. Organic matter is rapidly charred and destroyed by this substance. At the temperature of 15 it freezes; at 620 it boils, and may be distilled without decomposition. Oil of vitriol has a most energetic attraction for water ; it withdraws aqueous vapors from the air, and when diluted, great heat is evolved, so that the mixture always requires to be made with caution. Oil of vitriol is not the only hydrate of sulphuric acid ; three others are known to exist. When the fuming oil of vitriol of Nordhausen is exposed to a low temperature, a white crystalline substance separates, which is a hydrate containing half as much water as the common liquid acid. Then, again, a mixture of 49 parts strong liquid acid and 9 parts water, congeals or crystallizes at a temperature above 32, and remains solid even at 45. 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 40.09 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 sub- stance distils over in great abundance, which condenses into beautiful, white, silky crystals, resembling those of asbestus ; this bears the name of anhy- drous 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 ammoni- acal gas, quite distinct from ordinary sulphate of ammonia, and which indeed possesses none of the characters of a sulphate. This interesting substance may also be obtained by distilling the most concentrated oil of vitriol with a sufficient quantity of anhydrous phosphoric acid. Sulphuric acid, in all soluble states of combination, may be detected with the greatest ease by solution of nitrate of baryta, or chloride of barium. A white precipitate is produced, which does not dissolve in nitric acid. Hyposulphurous Acid. By digesting sulphur with a solution of sulphite of potash 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 instantly resolved into sulphur, which precipitates, and into sulphurous acid, easily recognized by its odor. 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 con- ferred upon them a considerable share of importance in relation to the art of photogenic drawing. Hyposulphuric Add. This is prepared by suspending finely divided peroxide of manganese in water artificially cooled, and then transmitting a stream of sulphurous acid gas ; the peroxide becomes protoxide, half its oxygen con- verting the sulphurous acid into hyposulphuric. The hyposulphate of manga- nese thus prepared is decomposed by a solution of pure hydrate of baryta, and the barytic salt, in turn, by enough sulphuric 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 further, it decomposes SELENIUM. 133 into sulphuric and sulphurous acids. It has no odor, is very sour, and forms soluble salts with baryta, lime, and oxide of lead. Sulphuretted Hyposulphuric Acid. A substance accidentally formed by M. Langlois,* in the preparation of hyposulphite of potash, by gently heating with sulphur a solution of carbonate of potash, previously saturated with sulphurous acid. The salts bear a great resemblance to those of hyposul- phurous acid, but differ completely in composition, while the acid itself is not quite so prone to change. Bisulphuretted Hyposulphuric Add. This was discovered by MM. Fordos and Gelis.f When iodine is added to a solution of hyposulphite of soda, a large quantity of that substance is dissolved, and a clear colorless solution obtained, which, besides iodide of sodium, contains a salt 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. Acids from the Chlorides of Sulphur. Two new acids of sulphur have been added to the preceding by M. Plessy. They were produced by the action of sulphurous acid in solution upon the protochloride and perchloride of sulphur respectively. They form soluble baryta-salts, and differ in their reactions from the six before known. Much doubt yet hangs over the composition of these bodies.J Add of M. Wackenroder. A ninth acid of sulphur has been announced, formed by the action of sulphuretted hydrogen on sulphurous acid. It is described as colorless and inodorous, of acid and bitter taste, and capable of being concentrated to a considerable extent by cautious evaporation. It is supposed to contain SXX. No definite salts have been obtained. ' 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. M. Fremy has described a series of very extraordinary compounds formed by the action of sulphurous acid upon hyponitrite of potash in presence of excess of alkali. Their reactions are extremely curious, and lead to the con- clusion that they are salts of complex acids containing sulphur, nitrogen, hy- drogen, and oxygen, analogous to organic compounds. SELENIUM. This is a very rare substance, much resembling sulphur in its chemical re- lations, and found in association with that element in some few localities, or replacing it in certain metallic combinations, as in the seleniuret of lead of Claustba), in the Hartz. Selenium is a reddish-brown solid body, somewhat translucent, and having an imperfect metallic lustre. Its specific gravity is 4.3. At 212, or a little above, it melts, and at 650 boils. It is insoluble in water, and exhales, when heated in the air, a peculiar and disagreeable odor, which has been * Ann. Chim. et Phys. 3d series, iv. 77. t Ib. 3d series, vi. 454. t Comptes Rendus, Aug. 25, 1845. $ Ann. Chim. et Phys. 3d series, xv. 408. 134 PHOSPHORUS. compared to that of decaying horseradish. There are three oxides of se- lenium, two of which correspond respectively to sulphurous and sulphuric acids, while the third has no known analogue in the sulphur-series. Composition by weight. Oxide of selenium, Selenious acid, Selenic acid, Selenium. 39.57 39.57 39.57 Oxygen. . 8 . 16 . 24 Oxide. Formed by heating selenium in the air. It is a colorless gas, slightly soluble in water, and has the remarkable odor 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 dis- tinct acid properties, and may be sublimed without decomposition. Sul- phurous acid decomposes it, precipitating the selenium. Selenic Acid. Prepared by fusing nitrate of potash or soda with selenium, precipitating the seleniate so produced by a salt of lead, and then decompos- ing the compound by sulphuretted hydrogen. The hydra ted acid strongly resembles oil of vitriol; but, when very much concentrated, decomposes, by the application of heat, into Selenious acid and oxygen. The seleniates bear the closest analogy to the sulphates in every particular. PHOSPHORUS. Phosphorus in a state of phosphoric acid is contained in the ancient un- stratified rocks, and in the lavas of modern origin. As these disintegrate and crumble down into fertile soil, the phosphates pass into the organism of plants, and ultimately into the bodies of the animals to which these latter serve for food. The earthy phosphates play a very important part in the structure of the animal frame, by communicating stiffness and inflexibility to the bony skeleton. This element was discovered in 1669 by Brandt of Hamburg, who prepared it from urine. The following is an outline of the process now adopted. Thoroughly calcined bones are reduced to powder, and mixed with two thirds of their weight of sulphuric acid, diluted with a considerable quantity of water ; this mixture, after standing some hours, is filtered, and the nearly in- soluble sulphate of lime washed. The liquid is then evaporated to a syrupy consistence, mixed with charcoal powder, arid the desiccation com- pleted in an iron vessel exposed to a high tem- perature. When quite dry, it is transferred to a stone-ware retort, to which a wide bent tube is luted, dipping a little way into the water con- tained in the receiver. A narrow tube serves to give issue to the gases, which are conveyed to a chimney. This manufacture is now con- ducted on a very great scale, the consumption of phosphorus for the apparently trifling article of instantaneous light matches being something pro- digious. Phosphorus, when pure, very much resembles in appearance imperfectly bleached wax, and is soft and flexible at common temperatures. Its Fig. 104. PHOSPHORUS. 135 density is 1.77, and that of its vapor 4.35, air being unity. At 108 it melts, and at 550 .boils. It is insoluble in water, and is usually kept immersed in that liquid, but dissolves in oils and in native naphtha. When set on fire in the air, it burns with a bright flame, generating phosphoric acid. Phosphorus is exceedingly inflammable; it sometimes takes fire by the heat of the hand, and demands great care in its management ; a blow or hard rub will very often kindle it. A stick of phosphorus held, in the air always appears to emit a whitish smoke, which in the dark is luminous.* This effect is due to a slow combustion which the phosphorus undergoes by the oxygen of the air, and upon it depends one of the methods employed for the analysis of the atmosphere, as already described. It is singular that the slow oxida- tion of phosphorus may be entirely prevented by the presence of a small quantity of olefiant gas, or the vapor of ether, or some essential oil ; it may even be distilled in an atmosphere containing vapor of oil of turpentine in considerable quantity. Neither does the action -go on in pure oxygen, at least at the temperature of 60, which is very remarkable ; but if the gas be rare- fied, or diluted with nitrogen, hydrogen, or carbonic acid, oxidation is set up. Compounds of Phosphorus and Oxygen. These are four in number, and have the composition below indicated. Composition by weight. Phosphorus. Oxygen, Oxide of phosphorus 62.76 8 Hypophosphorous acid 31.38 8 Phosphorous acid 31.38 24 Phosphoric acidf - 31.38 40 Oxide of Phosphorus. When phosphorus is melted beneath the surface of hot water, and a stream of oxygen gas forced upon it from a bladder, com- bustion ensues, and the phosphorus is converted in great part into a brick- red powder, which is the substance in question in a very impure state. A better method is to introduce into a large wide-necked flask a quantity of phosphorus cut into small pieces, with enough liquid, chloride of phos- phorus to cover it, and leave the whole exposed to the air for twenty-four hours. Phosphoric acid and oxide of phosphorus are slowly formed, and enter into a kind of combination. The excess of chloride being decanted, the solid matter is detached from the flask and put into water, in which the compound dissolves. By heating this solution to 176 it is decomposed, and the oxide precipitates in the state of hydrate, which may be collected, on a filter, and dried over oil of vitriol. The pure oxide is a red or yellow powder, according to its state of divi- sion. It is decomposed by heat into phosphorus and phosphoric acid.J Hypophosphorous Jlcid. When phosphuret of barium is put into water, that liquid is decomposed, giving rise to phosphuretted hydrogen, phosphoric acid, hypophosphorous acid, and baryta; the first escapes as gas, and the two acids remain in union with the baryta. By filtration, the soluble hypophos- phite is separated from the insoluble phosphate. On adding to the liquid the * An amorphous red variety of phosphorus, which is luminous and inflammable only at a very high temperature, has been described in the Annalen der Chem. et Phar. Ixviii. 247. | In Symbols Oxide of phosphorus .... P 2 O Hypophosphorous acid .... PO Phosphorous acid PO 3 Phosphoric acid PO g . Equivalent of phosphorus, 31.38. J Leverrier, Ann. Chim. et Phys. Ixv. 257. 136 PHOSPHORUS. quantity of sulphuric acid necessary to precipitate the base, the hypophos- phorous acid is obtained in solution. By evaporation, it may be reduced to a syrupy consistence. The acid is a powerful deoxidizing agent. All its salts are soluble in water. Phosphorous Acid. Phosphorous acid is formed by the slow combustion of phosphorus in the atmosphere; or by burning that substance by means of a very limited supply of air, in which case it is anhydrous, and presents the aspect of a white powder. The hydrated acid is more conveniently pre- pared by adding water to the terchloride of phosphorus, when mutual de- composition takes place, the oxygen of the water being transferred to the phosphorus, generating phosphorous acid, and its hydrogen to the chlorine, giving rise to hydrochloric acid. By evaporating the solution to the con- sistence of syrup, the hydrochloric acid is expelled, and the residue on cooling crystallizes. Hydrated phosphorous acid is very deliquescent, and very prone to attract oxygen and pass into phosphoric acid. When heated in a close vessel, it is resolved into hydrated phosphoric acid and pure phosphuretted hydrogen gas. It is composed of 55.38 parts real acid and 27 parts water.* The phosphites are of little importance. Phosphoric Acid. When phosphorus is burned under a bell-jar by the aid of a copious supply of dry air, snow-like anhydrous phosphoric acid is pro- duced in great quantity. This substance exhibits as much attraction for water as anhydrous sulphuric acid ; exposed to the air for a few moments, it deliquesces to a liquid, and when thrown into water, combines with the latter with explosive violence. Once in the state of hydrate, the water cannot again be separated. When nitric acid of moderate strength is heated in a retort to which a receiver is connected, and fragments of phosphorus added singly, taking care to suffer the violence of the action to subside between each addition, the phosphorus is oxidized to its maximum, and converted into phosphoric acid. By distilling off the greater part of the acid, transferring the residue in the retort to a platinum vessel, and then cautiously raising the heat to redness, the hydrated acid may be obtained pure. This is the glacial phosphoric acid of the Pharmacopoeia. A third method consists in taking the acid phosphate of lime produced by the action of sulphuric acid on bone-earth, precipitating it with a slight excess of carbonate of ammonia, separating by a filter the insoluble lime- salt, and then evaporating and igniting in a platinum vessel the mixed phos- phate and sulphate of ammonia. Hydrated phosphoric acid alone remains behind. The acid thus obtained is not remarkable for its purity. Indeed, by far the most advantageous method of preparing phosphoric acid on the large scale in a state of purity is to burn phosphorus in a stream of dry at- mospheric air, by the aid of a proper apparatus, not difficult to contrive, in which the process, may be carried on continuously. The anhydrous acid obtained may be preserved in that state, or converted into hydrate or glacial acid by the addition of water and subsequent fusion in a platinum vessel. The hydrate of phosphoric acid is exceedingly deliquescent, and requires to be kept in a closely-stopped bottle. It contains 71.38 parts real acid, and 9 parts water. Phosphoric acid is a powerful acid ; its solution has an intensely sour taste, and reddens litmus paper ; it is not poisonous. There are few bodies that present a greater degree of interest to the chemist . * Or, 3HO+P0 8 . CHLORINE. 137 than this substance; the extraordinary changes its compounds undergo by the action of heat, ch iefly made known to us by the admirable researches of Mr. Graham, will be found described in connection with the general history of saline compounds. Fig. 105. CHLORINE. This substance is a member of a small natural group containing besides, iodine, bromine, and fluorine. So great a degree of resemblance exists between these bodies in all their chemical relations, that the history of one will almost serve with a few little alterations for that of the rest. Chlorine* is a very abundant substance ; in com- mon salt it exists in combination with sodium. It is most easily prepared by pouring strong liquid hydro- chloric acid upon finely-powdered black oxide of manganese, contained in a retort or flask, and apply- ing a gentle heat ; a heavy yellow gas is disengaged, which is the substance in question. It may be collected over warm water, or by dis- placement; the mercurial trough cannot be employed, as the chlorine rapidly acts upon the metal, and be- comes absorbed. The reaction is very easily explained. Hydrochloric acid is a compound of chlorine and hydrogen; when this is mixed with a metallic protoxide, double inter- change of elements takes place, water and chloride of the metal being produced. But when a peroxide, containing twice as much oxygen as the protoxide, is substituted, an additional effect ensues, namely, the decomposition of a second portion of hydrochloric acid by the oxygen in excess, the hydrogen of which is withdrawn, and the chlorine set free. Hydrochloric ( Chlorine acid ( Hydrogen IS Hydrochloric ( Chlorine acid ( Hydrogen Chlorine. Water. Chloride of manganese. Water. Chlorine was discovered in 1774, by Scheele, but its nature was long mis- understood. It is a yellow, gaseous body, of intolerably suffocating properties, producing very violent cough and irritation when inhaled to an exceedingly small extent. It is soluble to a considerable extent in water, that liquid ab- sorbing at 60 about twice its volume, and acquiring the color and. odor of the gas. When this solution is exposed to light, it is slowly changed by de- composition of water into hydrochloric acid, the oxygen being at the same time liberated. When moist chlorine gas is exposed to a cold of 32, yellow crystals are formed, which consist of a definite compound of chlorine and water, containing 35.4 parts of the former to 90 of the latter. Chlorine has a specific gravity of 2.47, 100 cubic inches weighing 76.0 * Fr Of, yellowish-green, the name given to it by Sir H. Davy. 12* 188 CHLORINE, grains. Exposed to a pressure of about four atmospheres, it condenses to a yellow limpid liquid. This substance has but little attraction for oxygen, its chemical energies being principally exerted towards hydrogen and the metals. When a lighted taper is plunged into the gas, it continues to burn with a dull red light, and emits a large quantity of smoke, the hydrogen of the wax being alone con- sumed, and the carbon separated. If a piece of paper be wetted with oil of turpentine, and thrust into a bottle filled with chlorine, the chemical action of the latter upon the hydrogen is so violent as to cause inflammation, accom- panied by a copious deposit of soot. Although chlorine can, by indirect means, be made to combine with carbon, yet this never occurs under the cir- cumstances described. Phosphorus takes fire spontaneously in chlorine ; it burns with a pale and feebly luminous flame. Several of the metals, as copper-leaf, powdered an- timony, and arsenic, undergo combustion in the same manner. A mixture of equal measures of chlorine and hydrogen explodes with violence on the pas- sage of an electric spark, or on the application of a lighted taper, hydrochloric acid gas being formed. Such a mixture may be retained in the dark for any length of time without change; exposed to diffuse daylight, the two gases slowly unite, while the direct rays of the sun induce instantaneous ex- plosion. The most characteristic property of chlorine is its bleaching power ; the most stable organic coloring principles are instantly decomposed and destroyed by this remarkable agent; indigo, for example, which resists the action of strong oil of vitriol, is converted by chlorine into a brownish substance, to which the blue color cannot be restored. The presence of water is essen- tial to these changes, for the gas in a state of perfect dryness is incapable even of affecting litmus. Chlorine is largely used in the arts for bleaching linen and cotton goods, rags for the manufacture of paper, &c. For these purposes, it is sometimes employed in the state of gas, sometimes in that of solution in water, but more frequently in combination with lime, forming the substance called bleaching- powder. When required in large quantities, it is usually made by pouring slightly diluted oil of vitriol upon a mixture of common salt and oxide of manganese contained in a large leaden vessel. The decomposition which ensues may be thus represented : Chloride of (Chlorine - - Chlorine. sodium. ( Sodium Sulphuric acid - - - ^^III^ :r ~" Sulphate of soda. Peroxide of manganese. manganese _ _ Sulphuric acid - "^^. 5 Sul P hate of I nese. Chlorine is one of the best and most potent substances that can be used for the purpose of disinfection, but its employment requires care. Bleaching- powder mixed with water, and exposed to the air in shallow vessels, becomes slowly decomposed by the carbonic acid of the atmosphere, and the chlorine evolved; if a more rapid disengagement be wished, a little acid of any kind may be added. In the absence of bleaching powder, either of the methods for the production of the gas described may be had recourse to, always taking care to avoid an excess. Chloride of Hydrogen ; Hydrochloric, Chlorohydric, or Muriatic Acid. This sub- stance, in a state of solution in water, has been long known. The gas is CHLORINE. 139 prepared with the utmost ease by heating in a flask, fitted with a cork and bent tube, a mixture of common salt and oil of vitriol, diluted with a small quantity of water ; it must be collected by displacement, or over mercury. It is a colorless gas, which fumes strongly in the air from condensing the at- mospheric moisture ; it has an acid, suffocating odor, but is infinitely less of- fensive than chlorine. Exposed to a pressure of 40 atmospheres, it liquefies. Hydrochloric acid gas has a density of 1.269. It is exceedingly soluble in water, that liquid taking up at the temperature of the air about 418 times its bulk. The gas and solution are powerfully acid. The action of oil of vitriol on common salt, or any analogous substance, is thus easily explained : Chloride of sodium Water Sulphuric acid Chlorine Hydrochloric acid. Sulphate of soda. The composition of this substance may be determined by synthesis ; when a measure of chlorine and a measure of hydrogen are fired by the electric spark, two measures of hydrochloric acid gas result, the combination being unattended by change of volume. By weight it contains 35.41 parts chlorine and 1 part hydrogen. Solution of hydrochloric acid, the liquid acid of commerce, is a very im- portant preparation, and of extensive use in chemical pursuits ; it is best pre- pared by the following arrangement: Fig. 106. 140 CHLORINE. A large glass flask, containing a quantity of common salt, is fitted with a cork and bent tube, in the manner represented ; the latter passes through and below a second short tube into a wide-necked bottle, containing a little water, into which the open tube dips. A bent tube, adapted to another hole in the cork of the wash-bottle, serves to convey the purified gas into a quantity of distilled water, by which it is instantly absorbed. The joints are made air- tight by melting over the corks a little yellow wax. Oil of vitriol, about equal in weight to the salt, is then slowly introduced by the funnel ; the disengaged gas is at first wholly absorbed by the water in the wash-bottle, but when this becomes saturated, it passes into the second vessel and there dissolves. When all the acid has been added, heat may be applied to the flask by a charcoal chauffer, until its contents appear nearly dry, and the evolution of gas almost ceases, when the process may be stopped. As much heat is given out during the condensation of the gas, it is necessary to surround the condensing-vessel with cold water. The simple wash bottle figured in the drawing will be found an exceed- ingly useful contrivance in a great number of chemical operations. It serves in the present, and in many similar cases, to retain any liquid or solid matter mechanically carried over with the gas, and it may be always employed when gas of any kind is to be passed through an alkaline or other solution. The open tube dipping into the liquid prevents the possibility of absorption, by which a partial vacuum would be occasioned and the liquid of the second vessel lost by being driven into the first. The arrangement by which the acid is introduced also deserves a moment's notice. The tube is bent twice upon itself, and a bulb blown in one portion. Liquid poured into the funnel rises upon the opposite side of the Fig. 107. first bend until it reaches the second; it then flows over and runs into the flask. Any quantity can then be got into the latter with- out the introduction of air, and without the escape of gas from the interior. The funnel acts also as a kind of safety-valve, and in both directions ; for if by any chance the delivery tube should be stopped and the issue of gas prevented, its increased elastic force soon drives the little column of liquid out of the tube, the gas escapes, and the vessel is saved. On the other hand, any ab- sorption within is quickly compensated by the entrance of air through the liquid in the bulb. The plan employed on the great scale by the manufacturer is the same in principle as that de- scribed ; he merely substitutes a large iron cylinder for the flask, and vessels of stone-ware for those of glass. Pure solution of hydrochloric acid is transparent and colorless ; when strong, it fumes in the air by disengaging a little gas. It leaves no residue on evaporation, and gives no precipitate or milkiness with solution of chloride of barium. When saturated with the gas, it has a specific gravity of 1.21, and contains about 42 per cent, of real acid. The commercial acid has usually a yel- low color and is very impure, containing salts, sulphuric acid, chloride of iron, and organic matter. It may be rendered sufficiently good for most purposes by diluting it to the density of 1.1, which happens when the strong acid is mixed with its own bulk or rather less of water, and then distilling it in a refjrt furnished with a Liebig's condenser. A mixture of nitric and hydrochloric acids has long been known under the name of aqua regia> from its property of dissolving gold. When these two substances are heated together, they both undergo decomposition, nitrous acid and chlorine being evolved ; it is the chlorine which attacks the metal.* * According to the researches of Baudrimont, aqua regia contains a compound of CHLORINE. 141 The presence of hydrochloric acid, or any other soluble chloride, is easily detected by solution of nitrate of silver. A white curdy precipitate is pro- duced, insoluble in nitric acid, freely soluble in ammonia, and subject to blacken by exposure to light. Compounds of Chlorine and Oxygen. Although these bodies never combine directly, they may be made to unite by circuitous means in four different proportions, as below : Composition by weight. Chlorine. Oxygen. Hypochlorous acid 35.41 Chlorous acid 35.41 32 Chloric acid 35.41 40 Hyperchloric acid* .... 35.41 56 Hypochlorous and chloric acids are generated by the action of chlorine on certain metallic oxides ; the former in the cold, the latter at a high temper- ature. Chlorous and hyperchloric acids result from the decomposition of chloric acid. Hypochlorous Jldd, This is best prepared by the action of chlorine gas upon red oxide of mercury. It is a pale yellow gaseous body, containing, in every two measures, two measures of chlorine and one of oxygen. It is very freely soluble in water, and explodes, although with no great violence, by slight ele- vation of temperature. The odor of this gas is peculiar, and but remotely re- sembles that of chlorine. It bleaches powerfully, and acts upon certain of the metals in a manner which is determined by their respective attractions for oxygen and chlorine. It forms with the alkalis a series of bleaching salts. The preparations called chloride of or chlorinated lime and soda, contain hy- pochlorous acid. A description of these will be found under the head of Salts of Lime. The reaction by which hypochlorous acid is produced may thus be illus- trated : Chlorine ___ > Hypochlorous acid. Oxide of ( Mercury mercury ( Oxygen Chlorine * Chloride of mercury. The chloride of mercury, however, does not remain as such ; it combines with another portion of the oxide, when the latter is in excess, forming a peculiar brown compound, an oxychloride of mercury .f chlorine and nitrous acid, which he calls chloronitric acid (NO 3 C1 2 ). Gay Lussac, by further examination has found that there is produced two compounds, hypochlo- ronitric acid (NO 2 C1 2 ) and chloronitrous ncid (NO^Cl) with free chlorine. These com- pounds are given offas gases at the temperature of boiling water, and are condensible by cold; their relative amounts differ with the difference in proportion of nitric and muriatic acids used. When gold is acted on by aqua regia, it is the free chlorine which enters into combination, while the chloronitric vapors are evolved. R. B. * Hypochlorous acid . . . CIO Chlorous acid .... C1O 4 Chloric acid .... C1O S Hyperchloric acid . . . C1O 7 f A very commodious method of preparing hypochlorous acid has lately been de- scribed by M. Pelouze. Red oxide of mercury, prepared by precipitation and dried by exposure to a strong heat, is introduced into a glass tube, kept cool, and well -washed, dry chlorine gas slowly passed over it. Chloride of mercury and hypochlorous acid are formed ; the latter is collected by displacement. When the flask or bottle in which the gas is received is exposed to artificial cold by the aid of a mixture of ice and salt, the hypochlorous acid condenses to a deep red liquid, slowly soluble in water, and very 142 CHLORINE. Fig. 108. Chlorous Acid ; Peroxide of Chlorine. Chlorate of potash is made into a paste with sulphuric acid, previously diluted with half its weight of water and cooled; this is introduced into a small glass retort, and very cautiously heated by warm water; a deep yellow gas is evolved, which is the body in question ; it may be collected over mercury. Peroxide of chlorine has a powerful odor, quite different from that of the preceding compound, and of chlorine itself. It is exceedingly explosive, being resolved with violence into its elements by a temperature short of the boiling point of water. It is composed by measure of two volumes chlorine and four volumes oxygen, condensed into four volumes.* It may be liquefied by pressure. Water dissolves this gas pretty freely, and the solution bleaches. It is said to form salts with the alkalis.f The euchlorim of Davy, prepared by gently heating chlorate of potash with dilute hydrochloric acid, is probably a mixture of chlorous acid and free chlorine. The production of chlorous acid from chlorate of potash and sulphuric acid depends upon the spontaneous splitting of the chloric acid into chlorous acid and hyperchloric acid, which latter remains in union with the potash.J When a mixture of chlorate of potash and sugar is touched with a drop of oil of vitriol, it is instantly set on fire ; the chlorous acid disengaged being de- composed by the combustible substance with such violence as to cause inflam- mation. If crystals of chlorate of potash be thrown into a glass of water, a few small fragments of phos- phorus added, and then oil of vitriol poured down a narrow funnel reaching to the bottom of the glass, the phosphorus will burn beneath the surface of the water by the assistance of the oxygen of the chlorous acid disengaged. The liquid at the same time be- comes yellow, and acquires the odor of that gas. Chloric acid. This is the most imporant compound of the series. When chlorine is passed to saturation into a moderately strong hot solution of caustic pot- ash, or the carbonate of that base, and the liquid concentrated by evaporation, it furnishes on cooling flat tabular crystals of a colorless salt, consisting of potash combined with chloric acid. The mother liquor con tains chloride of potassium. In this reaction a part of the potash is decomposed; its oxygen com- bines with one portion of chlorine to form chloric acid, while the potassium is taken up by a second portion of the same substance. subject to explosion. It is remarkable that the crystalline oxide of mercury prepared by calcining the nitrate, or by the direct oxidation of the metal, is scarcely acted upon by chlorine under the circumstances described. Ann. Chim. et Phys. 3d series, vii. 179. * In equivalents, as already stated, C1O 4 . This is the composition assigned to it by Davy, Gay Lussac, and Soubeiran. Count fitadion considers it to contain C1O 3 , and this view is followed by some writers. f By pressure it is condensed into a liquid, and the liquid when exposed to the cold produced by solid carbonic acid and ether, concretes into a red solid, hard and trans- parent. It melts at 75 (Faraday). R. B. t 3 equiv. chloric $%'. acid ' ( 7 eq. oxygen. 1 eq. chlorine- 5 eq. chlorine 1 eq. chlorine 6 eq. chlorine 6 eq. potash 5 eq. potassium 5 eq. oxygen 1 eq. potash 2 eq. chlorous acid. 1 eq. hyperchloric acid. .5 eq. chloride potassium. 1 eq. chlorate of potash. IODINE. 143 From chlorate of potash chloric acid may be obtained by boiling the salt with a solution of hydrorluosilicic acid, which forms an almost insoluble salt with potash, decanting the clear liquid, and digesting it with a little silica. Filtration through paper must be avoided. By cautious evaporation, the acid may be so far concentrated as to assume a syrupy consistence; it is then very easily decomposed. It sometimes sets fire to paper, or other dry organic matter, in consequence of the facility with which it is deoxidized by combustible bodies. The chlorates are easily recognized ; they give no precipitate when in so- lution with nitrate of baryta or silver; they evolve pure oxygen when heated, passing thereby into chlorides; and they afford, when treated with sulphuric acid, the characteristic explosive yellow gas already described. The dilute solution of the acid has no bleaching power. Hyperchloric Add, Professor Penny has shown that when powdered chlo- rate of potash is thrown by small portions into hot nitric acid, a change of the same" description as that which happens when sulphuric acid is used takes place, but with this important difference, that the chlorine and oxygen, instead of being evolved in a dangerous state of combination, are emitted in a state of mixture. The result of the reaction is a mixture of nitrate of potasli and hyperchlorate of potash, which may be readily separated by their difference of solubility. By treating the potash-salt in the manner directed for chloric acid, the free acid may be obtained tolerably pure. It may be concentrated by evaporation, and even distilled without change. The solution fumes slightly in the air, and has a specific gravity of 1.65. It is very greedy of moisture, and has no bleaching properties. The hyperchlorates much resemble the chlorates; they give off oxygen when heated to redness. The acid is the most stable of the compounds of chlorine and oxygen.* This remarkable substance was first noticed in 1812 by M. Courtois of Paris. Minute traces are found in combination with sodium or potassium in sea-water, and occasionally a much larger proportion in that of certain mine- ral springs. It seems to be in some way beneficial to many marine plants, as these latter have the power of abstracting it from the surrounding water, and accumulating it in their tissues. It is from this source that all the iodine of commerce is derived. Kelp, or the half vitrified ashes of sea-weeds, prepared by the inhabitants of the Western Islands arid the northern shores of Scotland and Ireland, is treated with water, and the solution filtered. The liquid is then concentrated by evaporation until it is reduced to a very, small volume, the chloride of sodium, carbonate of soda, chloride of potassium, and other salts, being re- moved as they successively crystallize. The dark brown mother-liquor left contains very nearly the whole of the iodine; this is mixed with sulphuric acid and peroxide of manganese, and gently heated in a leaden retort, when the iodine distils over and condenses in the receiver. The theory of the ope- * Chlorous acid of Millon (C1O 3 ). When chlorate of potassa is acted on by nitric acid containing nitric oxide, a yellow gas is liberated of the above composition. This may be most readily procured by mixing chlorate of potassa with nitric and arsenious acid and applying a heat between 113 and 120. The arsenious acid deprives the nitric acid of oxygen, forming nitrous acid which immediately reacts on the chloric acid, t akes away oxygen and converts it into chlorous acid (C1O 3 ). Chlorous acid is a gas of a greenish yellow color, exploding at the temperature of 153, soluble in one-sixth its volume of water, both gas and solution readily decom- posing in sunlight. By cold, the gas condenses into a red liquid. (Millon). R. B. 144 IODINE. ration is exactly analogous to that of the preparation of chlorine ; it requires in practice, however, careful management, otherwise the impurities present in the solution interfere with the general result. The manganese is not really essential; iodide of potassium or sodium, heated with an excess of sulphuric acid, evolves iodine. It is probable that this effect is due to a secondary action between the hydriodic acid first pro- duced, and the residue of the sulphuric acid, in which both suffer decompo- sition, yielding iodine, water, and sulphurous acid. Iodine crystallizes in plates or scales of a bluish black color and imperfect metallic lustre, resembling that of plumbago ; the crystals are sometimes very large and brilliant. Its density is 4.948. At 225 it fuses, and at 347 boils, the vapor having an exceedingly beautiful violet color.* It is slowly volatile, however, at common temperatures, and exhales an odor much resembling that of chlorine. The density of the vapor is 8.716. Iodine requires for so- lution about 7000 parts of water, which nevertheless acquires a brown color ; in alcohol it is much more freely soluble. Solutions of hydriodic acid and the iodides of the alkaline metals also dissolve a large quantity ; these solu- tions are not decomposed by water, which is the case with the alcoholic tincture. This substance stains the skin, but not permanently ; it has a very energetic action upon the animal system, and is much used in medicine. One of the most characteristic properties of iodine is the production of a splendid blue color by contact with the organic principle starch. The iodine for this purpose must be free or uncombined. It is easy, however, to make the test available for the purpose of recognizing the presence of the element in question when a soluble iodide is suspected; it is only necessary to add a very small quantity of chlorine-water, when the iodine, being displaced from combination, becomes capable of acting upon the starch. Hydriodic JLdd. The simplest process for preparing hydriodic acid gas is to introduce into a glass tube, sealed at one extremity, a little iodine, then a small quan- ity of roughly-powdered glass moistened with water, upon this a few little fragments of phosphorus, and lastly more glass; this order of iodine, glass, phosphorus, glass, is repeated until the tube is half or two thirds filled. A cork and narrow bent tube are then fitted, and gentle heat applied. The gas is received over mercury. The experi- ment depends upon the formation of an iodide of phosphorus, and its subsequent decomposition by water, hydrated phospho- rous acid and iodide of hydrogen being produced. The glass merely serves to moderate the violence of the action of the iodine upon the phosphorus. Hydriodic acid gas greatly resembles the corresponding chlorine compound; it is colorless, and highly acid ; it furnes in the air, and is very soluble in water/}" Its density is about 4.4. By weight, it is composed of 126.36 parts iodine and 1 Fig. 109. * Whence the name, ^c, violet-colored f Hydriodic acid by intense cold and pressure has been both liquefied and solidified. Faraday, Lend, Atheneum, Feb. 1845. R. B. BROMINE. 145 part hydrogen ; and by measure, of equal volumes of iodine vapor and hy- drogen united without condensation. Solution of hydriodic acid may be prepared by a process much less trou- blesome than the above. Iodine in fine powder is suspended in water, and a stream of washed sulphuretted hydrogen passed; sulphur is deposited, and the iodine converted into hydriodic acid. When the liquid has become colorless, it is heated to expel the excess of sulphuretted hydrogen, and fil- tered. This solution cannot long be kept, especially if it be strong; the oxy- gen of the air gradually decomposes the hydriodic acid, and iodine is set free, which, dissolving in the remainder, communicates to it a brown color. Compounds of Iodine and Oxygen. The most important of these are the iodic and hyperiodic acids. M. Mil- Ion has described two new oxygen-compounds of iodine, which at present possess but little interest. Composition by weight. Iodine. Oxygen. lodic acid 126-36 40 Hyperiodic acid* .... 126-36 56 Iodic acid may be prepared by the direct oxidation of iodine by nitric acid of specific gravity 1.5; the materials are kept at a boiling temperature for several hours, or until the iodine has disappeared. The solution is then cau- tiously distilled to dryness, and the residue dissolved in water and made to crystallize. Iodic acid is a very soluble substance ; it crystallizes in colorless, six-sided tables, which contain water. It is decomposed by heat, and its solution readily deoxidized by sulphurous acid. The iodates much resemble the chlorates ; that of potash is decomposed by heat into iodide of potassium and oxygen gas. Hyperiodic Acid. When solution of iodate of soda is mixed with caustic soda, and a current of chlorine transmitted through the liquid, two salts are formed, namely, chloride of sodium and a combination of hyperiodate of soda with hydrate of soda, which is sparingly soluble. This is separated, converted into a silver-salt, and dissolved in nitric acid ; the solution yields on evaporation crystals of yellow hyperiodide of silver; from which the acid may be separated by the action of water, which resolves the salt into free acid and insoluble sub-hyperiodate. The acid itself may be obtained in crystals. It is permanent in the air, and capable of being resolved into iodine and oxygen by a high temperature."!" BromineJ dates back to 1826 only, having been discovered by M. Balard of Montpellier. It is found in sea water, and is a frequent constituent of saline springs, chiefly as bromide of magnesium ; a celebrated spring of the kind exists near Kreutznach in Prussia. Bromine may be obtained pure by the following process, which depends upon the fact that ether agitated with an aqueous solution of bromine removes the greater part of that substance. The mother liquor, from which the less soluble salts have separated by * IO , and IO V j Graham, Elements, p. 39'2. :f From f ( of j a noisome smell : a very appropriate term. 13 146 FLUORINE. crystallization, is exposed to a stream of chlorine, and then shaken up with a quantity of ether; the chlorine decomposes the bromide of magnesium, and the ether dissolves the bromine thus set free. On standing, the ethereal solu- tion, having a fine red color, separates, and may be removed by a funnel or pipette. Caustic potash is then added in excess, and heat applied ; bromide of potassium and bromate of potash are formed. The solution is evaporated to dryness, and the" saline matter, after ignition to redness to decompose the bromate of potash, heated in a small retort with oxide of manganese and sulphuric acid diluted with a little water, the neck of the retort being plunged into cold water. The bromine volatilizes in the form of a deep red vapor, which condenses into drops beneath the liquid. Bromine is at common temperature a red thin liquid of an exceedingly in- tense color, and very volatile ; it freezes at a little below 0, and boils at 116. The density of the liquid is 2.96, and that of the vapor 5.393. The odor of bromine is very suffocating and offensive, much resembling that of iodine, but more disagreeable. It is slightly soluble in water, more freely in alcohol, and most abundantly in ether. The aqueous solution bleaches. Hydrobromic Add. This substance bears the closest resemblance in every particular to hydriodic acid ; it has the same constitution by volume, very nearly the same properties, and may be prepared by means exactly similar, substituting the one body for the other. The solution of hydrobrornic acid has also the power of dissolving a large quantity of bromine, thereby ac- quiring a red tint. Hydrobromic acid contains by weight 78.26 parts bro- mine, and 1 part hydrogen. Bromic Acid. Caustic alkalis in presence of bromine undergo the same change as with chlorine, bromide of the metal and bromate of the oxide being produced ; these may often be separated by the inferior solubility of the latter. Bromic acid, obtained from bromate of baryta, closely resembles chloric acid; it is easily decomposed. The bromates when heated lose oxygen and be- come bromides. No other compound of bromine and oxygen has yet been described. FLUORINE. This element has never been isolated, at least in a state fit for examina- tion ; its properties are consequently in great measure unknown ; from the observations made, it is presumed to be gaseous, and to possess color, like chlorine. The compounds containing fluorine can be easily decomposed, and the element transferred from one body to another; but its extraordinary chemical energies towards the metals and towards silicon, a component of glass, have hitherto baffled all attempts to obtain it pure in a separate state. Hydrofluoric Acid. When powdered fluoride of calcium (fluor-spar) is heated with concentrated sulphuric acid in a retort of platinum connected with a carefully cooled receiver of the same metal, a very volatile colorless liquid is obtained, which emits copious white and highly suffocating fumes in the air. This is the acid in an anhydrous state. When hydrofluoric acid is put into water, it unites with the latter with great violence ; the dilute solution attacks glass with great facility. The concentrated acid dropped upon the skin is said to occasion deep and malig- nant ulcers, so that great care is requisite in its management. Hydrofluoric acid contains 18.78 parts fluorine and 1 part hydrogen. In a diluted state, this acid is occasionally used in the analysis of siliceous minerals, when alkali is to be estimated; it is employed also for etching on glass, for which purpose the acid may be prepared in vessels of lead, that metal being but slowly attacked under these circumstances. The vapor of SILICON. 147 the acid is also very advantageously applied to the same object in the follow- ing manner: the glass to be engraved is coated with etching-ground or wax, and the design traced in the usual way with a pointed instrument. A shallow basin made by beating up a piece of sheet lead is then prepared, a little powdered fluor-spar placed in it, and enough sulphuric acid added to form with the latter a thin paste. The glass is placed upon the basin, with the waxed side downwards, and gentle heat applied beneath, which speedily disengages the vapor of hydrofluoric acid. In a very few minutes the operation is complete ; the glass is then removed and cleaned by a little warm oil of turpentine. When the experiment is successful, the lines are very clear and smooth. No combination of fluorine and oxygen has yet been discovered. Silicon, sometimes called silicium, in union with oxygen constituting silica, or the earth of flints, is a very abundant substance, and one of great import- ance. It enters largely into the composition of many of the rocks and mineral masses of which the surface of the earth is composed. The following process yields silicon most readily. The double fluoride of silicon and potassium is heated in a glass tube with nearly its own weight of metallic potassium ; violent reaction ensues, and silicon is set free. When cold, the contents of the tube are put into cold water, which removes the saline matter and any residual potassium, and leaves untouched the silicon. So prepared, silicon is a dark brown powder, destitute of lustre. Heated in the air, it burns, and becomes superficially converted into silica. It is also acted upon by sulphur and by chlorine. When silicon is strongly heated in a covered crucible, its properties are greatly changed ; it becomes darker in color, denser, and in- combustible, refusing to burn even when heated by the flame of the oxy- hydrogen blowpipe. Silica. This is the only known oxide; it contains 22.18 parts silicon, and 24 parts oxygen.* Colorless, transparent rock-crystal consists of silica very nearly in a state of purity; common quartz, agate, calcedony, flint, and several other minerals are also chiefly composed of this substance. The experiment about to be described furnishes silica in a state of com- plete purity, and at the same time exhibits one of the most remarkable proper- ties of silicon, namely, its attraction for fluorine. A mixture is made of equal parts fluor-spar and glass, both finely powdered, and introduced into a glass flask, with a quantity of oil of vitriol. A tolerably wide bent tube, fitted to the flask by a cork, passes to the bottom of a glass jar, into which enough mer- cury is poured to cover the extremity of the tube. The jar is then half filled with water, and heat is applied to the flask. The first effect is the disengagement of hydrofluoric acid; this substance, however, finding itself in contact with the silica of the powdered glass, under- goes decomposition, water and fluoride of silicon being produced. The latter Fig. 110. * Or, SiO 3 . 148 SILICON. is a permanent gas, which escapes from the flask by the bent tube. By con- tact with a large quantity of water, it is in turn decomposed, yielding silica, which separates in a beautiful gelatinous condition, and an acid liquid which is a double fluoride of silicon and hydrogen, commonly called hydrofluosilicic acid.* The silica may be collected on a cloth filter, well washed, dried, and heated to redness, to expel water. The acid liquid is kept as a test for potash, with which it forms a nearly insoluble precipitate, the double fluoride of silicon and potassium, used in the preparation of silicon. The fluoride of silicon, instead of being con- ducted into water, may be collected over mercury; it is a permanent gas, destitute of color, and very heavy. Admitted into the air, it condenses the moisture of the latter, giving rise to a thick white cloud. It is important in the experiment above described to keep the end of the delivery tube from touching the water of the jar, otherwise it almost instantly becomes stopped ; the mercury effects this object. There is another method by which pure silica can be prepared, and which is also very instructive, inasmuch as it is the basis of the proceeding adopted in the analysis of all siliceous minerals. Powdered rock-crystal or fine sand is mixed with about three times its weight of dry carbonate of soda, and the mixture fused in a platinum crucible. When cold, the glassy mass is boiled with water, by which it is softened, and in great part dissolved. An excess of hydrochloric acid is then added, and the whole evaporated to complete dryness. By this treatment, the gelatinous silica thrown down by the acid becomes completely insoluble, and remains behind when the dry saline mass is treated with acidulated water, by which the alkaline salts, alumina, oxide of iron, lime, and many other bodies which may happen to be present, are removed. The silica is washed, dried, and heated red hot. The most prominent characters of silica are the following: it is a very fine, white, tasteless powder, not sensibly soluble in water or dilute acids (with the exception of hydrofluoric) unless recently precipitated. It dissolves, on the contrary, freely in strong alkaline solutions. Its density is about 2.66, and it is only to be fused by the oxy-hydrogen blowpipe. Silica is in reality an acid, and a very powerful one ; insolubility in water prevents the manifestation of acid properties under ordinary circumstances. When heated with bases, especially those which are capable of undergoing fusion, it unites with them and forms true salts, which are sometimes soluble in water, as in the case of the silicates of potash and soda when the propor- tion of base is considerable. Common glass is a mixture of several silicates in which the reverse of this happens, the silica, or as it is more correctly called, silicic acid, being in excess. Even glass, however; is slowly acted upon by water. Finely divided silica is highly useful in the manufacture of porcelain. * (1) Reaction of hydrofluoric acid upon silica : Hydrofluoric ( Fluorine . ^^ -Gaseous fluoride of silicon. acid . \ Hydrogen. ^ Silicon ' \ Oxygen - ^=- Water. (2) Decomposition of fluoride of silicon by water : Fluoride of ( Silicon silicon \ Fluorine WatPT 5 Ox Yg en Water . Hydrogen Fluoride of silicon _ _ ZUl^r^w Hydrofluosilicic acid. BORON. 149 This substance is closely related to silicon ; it is the basis of boracic acid. Boron is prepared by a process very similar to that described in the case of silicon, the double fluoride of boron and potassium being substituted for the other salt, and the operation conducted in a small iron vessel instead of a glass tube. It is a dull, greenish-brown powder, which burns in the air when heated, producing boracic acid. Nitric acid, alkalis in a fused condition, chlo- rine, and other agents, attack it readily. There is but one oxide of boron, namely boracic acid, containing 10.9 parts boron and 24 parts oxygen.* Boracic acid is found in solution in the water of the hot volcanic lagoons of Tuscany, whence a large supply is at present derived. It is also easily made by decomposing with sulphuric acid a hot solution of borax, a salt brought from the East Indies, consisting of boracic acid combined with soda. Boracic acid crystallizes in transparent colorless plates, soluble in about 25 parts of cold water, and in a much smaller quantity at a boiling heat ; the acid has but little taste, and feebly affects vegetable colors. When heated, it loses water, and melts to a glassy transparent mass, which dissolves many metallic oxides with great ease. The crystals contain 34.9 parts real acid, and 27 parts water. They dissolve in alcohol, and the solution burns with a green flame. Glassy boracic acid in a state of fusion requires for its dissipation in vapor a very intense and long-continued heat ; the solution in water can- not, however, be evaporated without very appreciable loss by volatilization ; hence it is probable that the hydrate is far more volatile than the acid itself. By heating in a glass flask or retort one part of the vitrified boracic acid, 2 of fluor-spar, and 12 of oil of vitriol, a gaseous fluoride of boron may be obtained, and received in glass jars standing over mercury. It is a trans- parent gas, very soluble in water, and very heavy; it forms a dense fume in the air like the fluoride of silicon.-]- * BO 3 . f These two bodies are thus constiuted : SiF 3 , and BF 3 . 13' 150 COMPOUNDS OF CARBON AND HYDROGEN. ON CERTAIN IMPORTANT COMPOUNDS FORMED BY THE UNION OF THE PRECEDING ELEMENTS AMONG THEMSELVES. COMPOUNDS OF CARBON AND HYDROGEN. THE compounds of carbon and hydrogen already known are exceedingly numerous; perhaps all, in strictness, belong to the domain of organic chemis- try, as they cannot be formed by the direct union of their elements, but always arise from the decomposition of a complex body of organic origin. It will be found convenient, notwithstanding, to describe two of them in this part of the volume, as they very well illustrate the important subjects of combustion, and the nature of flame. Light Carburetted Hydrogen Marsh-gas; Fire-damp; Gas of the Acetates. This gas is but too often found to be abundantly disengaged in coal-mines from the fresh cut surface of the coal, and from remarkable apertures or "blowers," which emit, for a great length of time, a copious stream or jet of gas, which probably existed in a state of compression, pent up in the coal. The mud at the bottom of pools in which water-plants grow, on being stirred, suffers bubbles of gas to escape, which may be easily collected. This, on examination, is found to be chiefly a mixture of light carburetter] hydrogen and carbonic acid ; the latter is easily absorbed by lime water or caustic potash. Until recently, no method was known by which the gas in question could be produced in a state approaching to purity by artificial means; the various illuminating gases from pit-coal and oil, and that obtained by passing the vapor of alcohol through a red-hot tube, contain large quantities of light carburetted hydrogen, associated, however, with other substances which hardly admit of separation. M. Dumas was so fortunate as to discover a method by which that gas can be produced at will, perfectly pure, and in any quantity. A mixture is made of 40 parts crystallized acetate of soda, 40 parts solid hydrate of potash, and sixty parts quicklime in powder. This mixture is transferred to a flask or retort, and strongly heated ; the gas is disengaged in great abundance, and may be received over water.* Light carburetted hydrogen is a colorless and nearly inodorous gas, which does not affect vegetable colors. It burns with a yellow flame, generating carbonic acid and water. It is not poisonous, and may be respired to a great extent without apparent injury. The density of this compound is about .559, 100 cubic inches weighing 17.41 grains; and it contains carbon and hydrogen associated in the proportion of 6 parts by weight of the former to 2 of the latter.j- * Ann. Chim. et Phys. Ixxiii. 93. The reaction consists in the conversion of the acetic acid, by the aid of the elements of water, into carbonic acid and light carbu- retted hydrogen ; the instability of the organic acid at a high temperature, and the attraction of the potash for carbonic acid, being the determining causes. The lime prevents the hydrate of potash from fusing and attacking the glass vessels. All these decompositions are best understood by putting them in the shape of an equation. Acetic acid C 4 H 3 O 3 ) _ ( Carbonic acid. 2 eq. C 3 O 4 . Water HO f } Marsh-gas, 2 eq. C 2 H 4 C 4 H 4 4 C 4 H 4 4 . f The two carburets of hydrogen here described are thus represented in equiva- lents: Light carburetted hydrogen C H a defiant gas - - C ? H, COMPOUNDS OF CARBON AND HYDROGEN. 151 When 100 measures of this gas are mixed with 200 of pure oxygen in the eudiometer, and the mixture exploded by the electric spark, 100 measures of a gas remain, which is entirely absorbable by a little solution of caustic potash. Now carbonic acid contains its own volume of oxygen ; one-half the oxygen added, that is, 100 measures, must have been consumed in uniting with the hydrogen. Consequently, the gas must contain twice its own measure of hydrogen, and enough carbon to produce, when completely burned, an equal quantity of carbonic acid. When chlorine is mixed with light carburetted hydrogen over water, no change follows, provided light be excluded. The presence of light, however, brings about decomposition, hydrochloric acid, carbonic acid, and sometimes carbonic oxide being produced. It is important to remember that the gas is not acted upon by chlorine in the dark. Olefiant Gas. Strong spirit of wine is mixed with five or six times its weight of oil of vitriol in a gas flask, the tube of which passes into a wash- bottle containing caustic potash. A second wash-bottle, partly filled with oil of vitriol, is connected to the first, and furnished with a tube dipping into the water of the pneumatic trough. On the first application of heat to the contents of the flask, alcohol, and afterwards ether, make their appearance ; but, as the temperature rises, and the mixture blackens, the ether vapor diminishes in quantity, and its place becomes in great part supplied by a permanent in- flammable gas; carbonic acid and sulphurous acid are also generated at the same time, besides traces of other products. The two last-mentioned gases are absorbed by the alkali in the first bottle, and the ether- vapor by the acid in the second, so that the olefiant gas is delivered tolerably pure. The reaction is too complex to be discussed at the present moment; it will be found fully described in another part of the volume. Olefiant gas thus produced is color- less, neutral, and but slightly soluble in water.* Alcohol, ether, oil of tur- pentine, and even olive oil, as Mr. Faraday has observed, dissolve it to a considerable extent. It has a faint odor of garlic. On the approach of a kindled taper it takes fire, and burns with a splendid white light, far surpass- ing in brilliancy that produced by light carburetted hydrogen. This gas, when mixed with oxygen and fired, explodes with extreme violence. Its density is .981; 100 cubic inches weigh 30.57 grains. By the use of the eudiometer, as already described, it has been found that each measure of olefiant gas requires for complete combustion exactly three of oxygen, and produces under these circumstances two measures of carbonic acid. Whence it is evident that it contains twice its own volume of hydro- gen, combined with twice as much carbon as in marsh-gas. By weight, these proportions will be 12 parts carbon, and 2 parts hydrogen. Olefiant gas is decomposed by passing through a tube heated to bright red- ness; a deposit of charcoal takes place, and the gas becomes converted into light carburetted hydrogen, or even into free hydrogen, if the temperature be very high. This latter change is of course attended by increase of volume. Chlorine acts upon olefiant gas in a very remarkable manner. When the two bodies are mixed, even in the dark, they combine in equal measures, and give rise to a heavy oily liquid, of sweetish taste and ethereal odor, to which the name chloride of hydrocarbon, or Dutch liquid, is given. It is from this peculiarity that the term olefiant is derived. A pleasing and instructive experiment may also be made by mixing in a tall jar two measures of chlorine and one of olefiant gas, and then quickly * Olefiant gas, by pressure and intense cold produced by the evaporation in a vacuum of solid carbonic acid and ether, is condensed into a colorless transparent liquid, but not frozen. (Faraday.) R. B. 152 COMPOUNDS OP CARBON ANT) HYDROGEN. applying a light to the mouth of the vessel. The chlorine- and hydrogen unite with flame, which passes quickly down the jar, while the whole of the carbon is set free in the form of a thick black smoke. Coal and Oil Gases. The manufacture of coal-gas is at the present moment a branch of industry of great interest and importance in several points of view. The process is one of great simplicity of principle, but requires, in practice, some delicacy of management to yield a good result. When pit-coal is subjected to destructive distillation, a variety of products show themselves; permanent gases, steam, and vapors of tar and volatile oils, besides a not inconsiderable quantity of ammonia from the nitrogen always present in the coal. These substances vary very much in their pro- portions with the temperature at which the process is conducted, the perma- nent gases becoming more abundant with increased heat, but at the same time losing much of their value for the purposes of illumination. The coal is distilled in cast-iron retorts, maintained at a bright red heat, and the volatilized products conducted into a long horizontal pipe of large dimensions, always half filled with liquid, into which dips the extremity of each separate tube; this is called the hydraulic main. The gas and its ac- companying vapors are next made to traverse a refrigerator, usually a series of iron pipes, cooled on the outside by a stream of water ; here the condensa- tion of the tar and ammoniacal liquid becomes complete, and the gas pro- ceeds onwards to another part of the apparatus, in which it is to be deprived of the sulphuretted hydrogen and carbonic acid gases always present in the crude product. This is effected by hydrate of lime, which readily absorbs the compounds in question. The purifiers are large iron vessels, partly filled with a mixture of hydrate of lime and water, in which a churning machine or agitator is kept in constant motion to prevent the subsidence of the lime. The gas is admitted at the bottom of the vessel by a great number of minute apertures, and is thus made to present a large surface of contact to the puri- fying liquid. The last part of the operation, which indeed is often omitted, consists in passing the gas through dilute sulphuric acid, in order to remove ammonia. The quantity thus separated is very small, relatively to the bulk of the gas, but in an extensive work becomes an object of importance. Coal-gas -thus manufactured and purified is preserved for use in immense cylindrical receivers, close at the top, suspended in tanks of water by chains to which counterpoises are attached, so that the gas-holders rise and sink in the liquid as they become filled from the purifiers or emptied by the mains. These latter are made of large diameter, to diminish as much as possible the resistance experienced by the gas in passing through such a length of pipe. The joints of these mains are yet made in such an imperfect manner that immense loss is experienced by leakage when the pressure upon the gas at the works exceeds that exerted by a column of water an inch in height.* Coal-gas varies very much in composition, judging from its variable density and illuminating power, and from the imperfect analyses which have been made. The difficulties of such investigations are very great, and the results merely approximative. The purified gas is believed to contain the following substances, of which the first is most abundant, and the second most valuable. * It may give some idea of the extent of this species of manufacture, to mention that in the year 1838, for lighting London and the suburbs alone, there were eighteen public gas-works, and 2,800.000 invested in pipes and apparatus. The yearly reve- nue amounted to 450.000. and the consumption of coal in the same period to 180,000 tons, 1460 millions of cubic feet of gas being made in the year. There \vere 134,300 private lights, and 30,400 street lamps. 890 tons of coal were used in the retorts in the space of twenty-four hours at midwinter, and 7,120,000 cubic feet of gas consumed in the longest, night. Dr. tire, Dictionary of Arts and Manufactures. COMBUSTION, AND THE STRUCTURE OF FLAME. 153 Light carburetted hydrogen. Olefiant gas. Hydrogen. Carbonic oxide. Nitrogen. Vapors of volatile liquid carburets of hydrogen.* Vapor of bisulphuret of carbon. Separated by Condensation and by the Purifiers. Tar and volatile oils. Sulphate of ammonia, chloride and sulphuret of ammonium. Sulphuretted hydrogen. Carbonic acid. Hydrocyanic acid, or cyanide of ammonia. A very far better illuminating gas may be prepared from oil by dropping it into a red-hot iron retort filled with coke; the liquid is in great part decom- posed and converted into permanent gas, which requires no purification, as it is quite free from the amrnoniacal and sulphur compounds which vitiate the gas from coal. A few years ago this article was prepared in London ; it was compressed for the use of the consumer into strong iron vessels, to the extent of 30 atmospheres; these were furnished with a screw-valve of peculiar construction, and exchanged for others when exhausted. The comparative high price of the material, and other circumstances, led to the abandonment of the undertaking. COMBUSTION, AND THE STRUCTURE OF FLAME. When any solid substance, capable of bearing the fire, is heated to a certain point, it emits light, the character of which depends upon the temperature. Thus, a bar of platinum or a piece of porcelain raised to a particular tempe- rature becomes what is called red-hot, or emissive of red light; at a higher degree of heat this light becomes whiter and more intense, and when urged to the utmost, as in the case of a piece of lime placed in the flame of the oxy-hydrogen blowpipe, the light becomes exceedingly powerful, and acquires a tint of violet. Bodies in these states are said to be incandescent or ignited. Again, if the same experiment be made on a piece of charcoal, similar effects will be observed, but something in addition ; for whereas the platinum or porcelain, when removed, from the fire, or the lime from the blowpipe flame, begin immediately to cool, and emit less and less light, until they be- come completely obscure, the charcoal maintains to a great extent its high temperature. Unlike the other bodies, too, which suffer no change whatever either of weight or substance, the charcoal gradually wastes away until it disappears. This is what is called combustion in 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 combustion, by heating the body to such an extent that it becomes luminous. In all ordinary cases of combustion, the action lies between the burn- ing 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 sub- * These bodies increase the illuminating power, and confer on the gas its peculiar odor. 154 COMBUSTION, AND stance conjoined with a certain proportion of hydrogen and oxygen, all com- mon 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 refractory metals, and to bring about certain desired effects of chemical decomposition. If the rate of consumption of the fuel can be increased by a more rapid in- troduction of air into the burning mass, the intensity of the heat will of ne- cessity rise in the same ratio, there being reason to believe that the quantity of heat evolved is fixed and definite for the same constant quantity of chemical action. This increased supply of air may be effected by two dis- tinct methods; it may be forced into the fire by bellows or blowing machines, as in the common forge, and in the blast and cupola-furnaces of the iron- worker; or it may be drawn through the burning materials by the help of a tall chimney, the fire-place being closed on all sides, and no entrance 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 represented arranged in the fire for an operation of the kind mentioned. (Fig. 111.) The " reverberatory" furnace is one very much used in the arts when sub- stances are to be exposed to heat without contact with the fuel. The fire- chamber a b is "separated from the bed or hearth d d of the furnace by a low wall or bridge c. 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 obtained 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. Fig. 111. Fig. 112. THE STRUCTURE OF FLAME. 155 Fig 113. C _V\..B 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 vapor in this condition constitutes flame, the actual temperature of which always far 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 off is almost infinitely greater. Flames burning in the air, and not supplied with oxygen from another source, are, as already stated, hollow ; the chemical action is necessarily confined to the spot where the two bodies unite. That of a lamp or candle, when carefully examined, is seen to consist of three separate portions. The dark oentral part, easily rendered evident by depressing upon the flame a piece of fine wire-gauze, consists of combustible matter drawn up by the capillarity of the wick, and volatilized by the heat. This is surrounded by a highly luminous cone or envelop, which, on contact with a cold body, deposits soot. On the outside a second cone is to be traced, feeble in its light-giving power, but having an exceedingly high temperature. The explanation of these appearances is easy : carbon and hydro- gen 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 carbon. Now this happens in the case under consideration at some little distance within the outer surface of the flame, namely, in the luminous portion ; the little oxygen which has penetrated thus far 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 white- ness marks a very elevated temperature. In the ex- terior and scarcely visible cone, these particles of car- bon 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 disap- pears. 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 figured in the margin. The flame so produced is very peculiar. Fig. 114. 156 COMBUSTION, AND Fig. 115. Instead of the double envelope just described, two long poiuted cones are observed, which, when the blowpipe is good, and the aperture smooth and round, are very well defined, the outer cone being yellowish, and the inner blue. A double combustion is, in fact, going on, by the blast in the inside, and by the external air. The space between the inner and outer cones is filled with exceedingly hot combustible matter, possessing strong reducing or deoxid- izing powers, while the highly heated air just beyond the point of the exterior cone oxidizes with great facility. A small portion of matter, supported on a piece of charcoal, or fixed in a ring at the end of a fine platinum wire, can thus in an instant be exposed to a very high degree of heat under these contrasted circum- stances, and observations of great value made in a very short time. The use of the instrument requires an even and un- interrupted 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 bum 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. Fig. 117. The accompanying drawing exhibits, in section, an excellent lamp of this kind for burning alcohol or wood-spirit. It is constructed of thin copper, and furnished with ground caps to the wick-holder and aperture* by which the spirit is introduced, in order to prevent loss when the lamp is not in use. Glass spirit-lamps, fitted with caps to prevent evaporation are very conve- nient for occasional use, being always ready and in order/f * When in use, this aperture must always be open, otherwise an accident is sure to happen ; the heat expands the air in the lamp, and the spirit is forced out in a state of inflammation. f The spirit lamp represented in the cut is one contrived by Dr. Mitchell. " It THE STRUCTURE OP FLAME. 157 Fig. 119. 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, cap- sules, and other vessels can be thus exposed to an easily regulated 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, consisting of a common Argand gas-burner fixed on a heavy and low foot, and connected with a flexible tube of caoutchouc or other material, leaves nothing to desire. The kindling-point, or temperature at which com- bustion commences, is very different with different substances ; phosphorus will sometimes take fire in the hand ; sulphur requires a temperature exceeding that of boiling water, charcoal must be heated to redness. Among gaseous bodies, the same fact is observed : hydrogen is inflamed by a red hot wire; carburetted hydrogen re- quires a white heat to effect the same thing. When flame is cooled by any means below the temperature at which the rapid oxidation of the combus- tible 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 carburetted 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 gas and air occupying the extensive galleries and workings of a mine. Sir H. Davy undertook an investigation with a view to discover some remedy for this constantly occurring calamity ; his labors resulted in some exceed- ingly 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 diminution of length ; and to such an extent can this be carried that is made of tinned iron. The alcohol is poured out by means of the hollow- handle, and is admitted to the cylindri- cal burner by two or three tubes which are placed at the very bottom of the fountain. By such an arrangement of parts, the alcohol may be added as it is consumed, and the flame kept uni- form ; and as the pipes which pass to the burner are so remote from the flame, the alcohol never becomes heated so as to fly off through the vent-hole, and thus to cause greater waste and danger of ex- plosion." A cylindrical chimney is an advantageous addition for many pur- poses. It may be made of tin-plate or copper. R B. 14 Fig. 118. 158 COMBUSTION, AND THE STRUCTURE OP FLAME, Fig. 120. Fig. 121. metallic gauze, which may be looked upon as a series of very short, square tubes arranged side by side, arrests in the most complete manner the passage of flame in explosive mixtures, when of sufficient degree of fineness, depending upon the inflammability of the gas. Most providentially, the fire-damp mixture has an exceedingly high kindling point; a red heat does not cause inflammation; conse- quently, a gauze will be safe for this substance, when flame would pass in almost any other case. The miner's safe-lamp is merely an ordinary oil lamp, the flame of which is inclosed in a cage of wire-gauze, made double at the upper part, containing about 400 apertures to the square inch. The tube for supplying oil to the reser- voir reaches nearly to the bottom of the latter, while the wick admits of being trimmed by a bent wire passing with friction through a small tube in the body of the lamp; the flame can thus be kept burning for any length of time, without the necessity of unscrewing the cage. "When this lamp is taken into an explosive atmosphere, although the fire-damp may burn within the cage with such energy as sometimes to heat the metallic tissue to dull redness, the flame is never communicated to the mixture on the out- side. These effects may be conveniently studied by suspending the lamp in a large glass jar, and gradually admitting coal- gas below. The oil flame is at first elongated, and then, as the proportion of gas increases, extinguished, while the interior 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 appearances are so remarkable that the lamp becomes an admirable indicator of the state of the air in different parts of the mine.* The same great principle has been ingeniously applied by Mr. Hemming to the construction of the oxy-hydrogen safety-jet formerly mentioned. This is a tube of brass about four inches long, filled with straight pieces of fine bi'ass wire, the whole being tightly wedged together by a pointed rod, forcibly driven into the centre of the bundle. 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 possibility of Fig. 122. the passage of flame, even with oxygen and hydrogen. The jet may be used, as before mentioned, with a common bladder, without a chance of * This is the true use of the lamp, namely, to permit the viewer or superintendent, without risk to himself, to examine the state of the air in every part of the mine ; not to enable workmen to continue their labors in an atmosphere habitually explosive, which must be unfit for human respiration, although the evil effects may be slow to appear. Owners of coal-mines should be compelled either to adopt efficient means of ventilation, or to close workings of this dangerous character altogether. NITROGEN AND HYDROGEN; AMMONIA. 159 explosion. The fundamental fact of flame being extinguished by contact with a cold body may be elegantly shown by twisting a copper wire into a short spiral, Fig. 122, about .1 inch in diameter, and then passing it cold over the flame of a wax candle; the latter is extinguished. If the spiral be now heated to redness by a spirit-lamp ; and the experiment repeated, no such effect follows.* NITROGEN AND HYDROGEN; AMMONIA. When powdered sal-ammoniac is mixed with moist hydrate of lime, and gently heated in a gas-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 colorless; it has a very powerful, pungent odor, and a strong alkaline reaction to test-paper, by which it may be at once distinguished from all other bodies possessing the same physical characters. Under a pressure of 6.5 atmospheres at 60, ammonia condenses to the liquid form.f 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 ammonicR: 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 .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 azo- tized principles of the animal and vegetable kingdoms, which, when left to putrefactive change or subjected to destructive distillation, almost invariably 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 be- comes doubled. On examination, the tube is found to contain a mixture of 3 measures hydrogen gas and 1 measure nitrogen. Every two volumes of the ammonia, therefore, contained three volumes of hydrogen and one of nitrogen, the whole being condensed to the extent of one-half. The weight of the two constituents will be in the proportion of 3 parts hydrogen to 14.06 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. * Where coal-gas is to be had, it may be advantageously used as a source of heat, by taking advantage of the above-mentioned fact. On passing a current of gas through a wide vertical tube, open at the bottom to afford a free mixture with atmospheric air, but closed at the top by wire gauze, and then kindling the mixture after its escape through the meshes, it will burn with feeble illuminating power, but no loss of heat. When the proportion of the gas to the atmospheric air is such as not to allow the flame to become yellow, the combustion will be complete, and no carbonaceous de- posit will be formed on cold bodies held over the flames. The length and diameter of the cylinder are determined by the amount of gas to be burnt, and the length may be much decreased by interposing a second diaphragm of wire gauze about mid-length of the cylinder, the current of gas being introduced below this, by which means a more thorough and rapid mixture is made with the atmospheric air. Sir John Robinson, K. H., &c., Ed. New Phil. Journal, 1840. R. B. f At the temperature of 103? F., liquid ammonia freezes into a colorless solid, heavier than the liquid itself. (Faradny.) R. B, 160 SULPHUR, SELENIUM, AND Equal weights of sal-ammoniac and quicklime are taken; the lime is slacked in a covered basin, and the salt reduced to powder. These are mixed, and introduced into the flask employed in preparing solution of hydrochloric acid, together with just enough water to damp the mixture, and cause it to aggregate into lumps ; the rest of the apparatus is arranged exactly as in the former case, with an ounce or two of water in the wash-bottle, or enough to cover the ends of the tubes, and the gas conducted afterwards into pure distilled water, artificially cooled, as before. The cork-joints are made tight with wax, a little water is put into the safety-funnel, heat cautiously applied to the flask, and the whole left to itself. The disengagement of ammonia is very regular and uniform. Chloride of calcium, with excess of hydrate of lime, remains in the flask.* The decomposition of the salt is usually represented in the manner shown by the subjoined diagram. Ammonia. .Ammonia. Sal-ammoniac ^ Hydrochloric C Hydrogen _ -, Water. acid . (_ Chlorine. Lime ' ' J Calcium ^Chloride of calcium. Solution of ammonia should be perfectly colorless, leave no residue on evaporation, and when supersaturated by nitric acid, give no cloud or muddi- ness with nitrate of silver. Its density diminishes with its strength, that of the most concentrated being about .875; the value in alkali of any sample of liquor ammonise 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 mariner the corresponding compounds of potash and soda ; these are best discussed in connection 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 potash or soda. SULPHUR, SELENIUM:, AND PHOSPHORUS WITH HYDROGEN. Sulphuretted Hydrogen; Hydro sulphuric Jldd*\ There are two methods by which this important compound can be readily prepared, namely, by the action of dilute sulphuric acid upon sulphuret of iron, and by the decompo- sition of sulphuret of antimony by hydrochloric acid. The first method yields it most easily, and the second in the purest state. Protosulphuret 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 col- lected over tepid water. The reaction is thus explained : Sulphuret of iron { ~ Sulphuretted hydrogen. Water ( Hydrogen^ \ Oxygen Sulphuric acid ~^ Sulphate of oxide of iron. By the other plan, finely powdered sulphuret of antimony is put into a flask, * See fig. 106, p. 139. | Sulphydric acid. PHOSPHORUS WITH HYDROGEN. 161 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 interchange occurs between the bodies present, sulphuretted hydrogen being formed, and chloride of antimony. The action only lasts while the heat is maintained. Hydrochloric acid Sulphuret of anti- mony . Chlorin Sulphur Antimony . ^ Sulphuretted hydrogen. .Chloride of antimony. Fig. 123. Sulphuretted hydrogen is a colorless gas, having the odor of putrid eggs; it is most offensive when in small quantity, when a mere trace is present in the air. It is not irritating, but, on the contrary, powerfully narcotic. 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 oxy- gen is deficient. Mixed with chlorine, it is instantly decomposed, with sepa- ration 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 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, how- ever, 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, to which a bit of bent tube is fitted by a cork, is supplied with a little sulphuret of iron and water; when re- quired for use, a few drops of oil of vitriol are added, and the gas is at once evolved. The experiment com- pleted, 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 sulphuret, while pure hydrogen remains equal in volume to the original gas. Taking this fact into ac- count, and comparing the density of the gas with those of hydrogen and sulphur-vapor, it appears that every volume of sulphuretted hydrogen contains one volume of hydrogen, and |th of a volume of sulphur- vapor, the whole condensed into one volume. This corresponds very nearly with its composition by weight, determined by other means, namely, 16.09 parts sulphur to 1 part hydrogen. 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, and 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, as at Harrowgate, and elsewhere. When accidentally present in the atmo- sphere of an apartment.it maybe instantaneously destroyed by a small quan- tity 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 * Liquid sulphydric acid is solidified at the temperature of 1223, forming a color- less, translucent solid, of greater density than the liquid (Faraday). R. B. 14* 162 SULPHUR, SELENIUM, AND 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 in- soluble sulphurets, formed by the mutual decomposition of the metallic oxides or chlorides and sulphuretted hydrogen, water or hydrochloric acid being pro- duced at the same time. All the metals are, in fact, precipitated whose sul- phurets are insoluble in water and in dilute acids. Sulphuretted hydrogen possesses itself the properties of an acid ; its solu- tion 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. Persulphuret of Hydrogen. This substance corresponds in constitution and instability to the peroxide 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-colored solution is pro- duced, containing among other things persulphuret of calcium. This is fil- tered, and slowly added to an excess of dilute sulphuric acid, with constant agitation. A white precipitate of separated sulphur and sulphate of lime makes its appearance, together with a quantity of yellow oily-looking matter, which collects at the bottom of the vessel ; this is persulphuret of hydrogen.* If the experiment be conducted by pouring the acid into the solution of sulphuret, then nothing but finely-divided precipitated sulphur is obtained. The persulphuret is a yellow, viscid, insoluble liquid, exhaling the odor 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 ; Sekniuretted Hydrogen. This substance is produced by the action of dilute sulphuric acid upon seleniuret of potassium or iron it very much resembles sulphuretted hydrogen, being a colorless gas, freely soluble in water, and decomposing metallic solutions like that substance; in- soluble seleniurets are thus produced. This gas is said to act very power- fully upon the lining membrane of the nose, exciting catarrhal symptoms, and * The reaction which ensues when hydrate of lime, sulphur and water are boiled together, is rather complex, deutosulphuret and pentasulphuret of calcium being formed, together -with hyposulphite of lime, arising from the transfer of the oxygen of the decomposed lime to another portion of sulphur. 2 eq. lime 2 eq. deutosulphuret of calcium. 4 eq. sulphur 2 eq. sulphur ^==-.1 eq. hyposulphurous acid. The deutosulphuret of calcium decomposed by an acid under favorable circumstances yields a salt of lime and deutosulphuret (persulphuret) of hydrogen, 1 eq. deutosulp. (2 eq. sulphur ^^^ 1 e< 3- deutosulphuret of hydrogen. calcium \ 1 eq. calcium, 1 eq. water C 1 eq. hydrogen i 1 eq. oxygen- Sulphuric acid =^*- 1 eq. sulphate of lime. When the acid is poured into the sulphuret, sulphuretted hydrogen, water, and sul- phate 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 substance, hydrochloric acid must be used in place of sul- phuric. PHOSPHORUS WITH HYDROGEN. 168 destroying the sense of smell. It contains 39.57 parts selenium, and 1 part hydrogen. Phosphorus and Hydrogen; Phosphuretted Hydrogen. This body bears a slight analogy in some of its chemical relations to ammoniacal gas ; it is, however, destitute of alkaline properties. Phosphuretted hydrogen may be obtained in a state of purity by heating in a small retort hydrated phosphorous acid, which is by such treatment decom- posed into phosphuretted hydrogen and hydrated phosphoric acid.* Thus obtained, the gas has a density of 1.24. It contains 31.38 parts phosphorus, and 3 parts hydrogen, and is so constituted that every two volumes contain 3 volumes of hydrogen and half a volume of phosphorus vapor, condensed into two volumes. It possesses a highly disagreeable odor of garlic, is slightly soluble in water, and burns with a brilliant white flame, forming water and phosphoric acid. Phosphuretted hydrogen may also be produced by boiling together in a retort of small dimensions caustic potash or hydrate of lime, water, and phos- phorus; the vessel should be filled to the neck, and the extremity of the latter made to dip into the water of the pneumatic trough. In the reaction which ensues, the water is decomposed, and both its elements combine with the phosphorus. The alkali acts by its presence determining the decomposition of the water, in the same manner as sulphuric acid determines the decom- position of water when in contact with zinc. w C Hydrogen . ___ ^ Phosphuretted hydrogen. I Oxygen Phosphorus Phosphorus Lime "~ 7:::s=i ^'Hypophosphite of lime. The phosphuretted hydrogen prepared by the latter process has the singular property of spontaneous inflammability when admitted into the air or into oxygen gas; with the latter, the experiment is very beautiful, but requires caution ; the bubbles should be singly admitted. When kept over water for sometime, the gas loses this property, without otherwise suffering any appre- ciable change; but if dried by chloride of calcium, it may be kept unaltered for a much longer period. M. Paul Thenard has shown that the spontaneous combustibility of the gas arises from the presence of the vapor of a liquid phosphuret of hydrogen, which can be procured in considerable quantity by conveying the gas produced by the action of water on phosphuret of calcium through a tube cooled by a freezing mixture. This substance forms a colorless liquid of high refractive power and very great volatility. It does not freeze at F. In contact with air it inflames instantly, and its vapor in very small quantity communicates spontaneous inflammability to pure phosphuretted hydrogen, and to all other combustible gases. It is decomposed by light into gaseous phosphuretted hydrogen, and a solid phosphuret which is often seen on the inside of jars containing gas which has lost the property of spontaneous inflammability by exposure to light. Strong acids occasion its instantaneous decomposition. Its instability is equal to that of peroxide of hydrogen. It is * Decomposition of hydrated phosphorous acid by heat : [. phosph. . . ^^^- e( l- phosphuretted hydrogen, PH 3 . 4eq. hy- ' drate phos- phorous acid. 12 eq. water. La eq. oxygen 3 eq. hydrog. 9 eq. hydrog. 3 eq. oxygen 9 eq. oxygen 2^3 eq. phos. ac. ) Hydrated ^^9 eq. water } phosphoric acid. 164 NITROGEN WITH CHLORINE AND IODINE. to be observed that the pure phosphuretted hydrogen gas itself becomes spontaneously inflammable if heated to the temperature of boiling water.* Phosphuretted hydrogen decomposes several metallic solutions, giving rise to precipitates of insoluble phosphurets. With hydriodic acid, it forms a crystalline compound somewhat resembling sal ammoniac. Nitrogen with Chlorine and Iodine Chloride of Nitrogen. When sal-ammoniac or nitrate of ammonia is dissolved in water, and ajar of chlorine gas inverted into the solution, the gas is absorbed, and a deep yellow oily liquid is observed to collect upon the surface of the solution, which ultimately sinks in globules to the bottom. This is chloride of nitrogen, the most dangerously-explosive substance known. The following is the safest method of conducting the experiment : A somewhat dilute and tepid solution of pure sal ammoniac in distilled water is poured into a clean basin, and a bottle of chlorine, the neck of which is quite free from grease, inverted into it. A shallow and heavy leaden cup is placed beneath the mouth of the bottle to collect the product. When enough has been obtained, the leaden vessel may be withdrawn with its dangerous contents, the chloride remaining covered with a stratum of water. The operator should protect his face with a strong wire-gauze mask when experimenting upon this substance. The change is explained by the following diagram : Chlorine : ^- Chloride of nitrogen. Chlorine . .. ^""^^-^ Hydrochloric acid. ( ( Nitrogen * Sal-ammoniac < ( Hydrogen ( Hydrochloric acid Hydrochloric acid. Chloride of nitrogen is very volatile, and its vapor is exceedingly irritating to the eyes. It has a specific gravity of 1.653. " It may be distilled at 160, although the experiment is attended with great danger. Between 200 and 212 it explodes with the most fearful violence. Contact with almost any combustible matter, as oil or fat of any kind, determines the explosion at com- mon temperatures ; a vessel of porcelain, glass, or even of cast iron, is broken to pieces, and the leaden cup receives a deep indentation. This body has usually been supposed to contain nitrogen and chlorine in the proportion of 14.06 parts of the former to 106.23 parts of the latter ; but recent experi- ments upon the corresponding iodine compound induce a belief that it contains hydrogen.t Iodide of Nitrogen. When finely-powdered iodine is put into caustic am- monia it is in part dissolved, giving a deep brown solution, and the residue is converted into a black powder, which is the substance in question. The brown liquid consists of hydriodic acid holding iodine in solution, and is easily separated from the solid product by a filter. The latter, while still wet, is distributed in small quantities upon separate pieces of bibulous paper, and left to dry in the air. Iodide of nitrogen is a black, insoluble powder, which, when 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- pound last described, and is attended with the production of violet fumes of iodine. * Ann. Chim. et Phys., 3d series, xiv. 5. According to M. Thenard, the new liquid phosphuret of hydrogen contains PH a and the solid P a H. The gas is represented by the formula PH 3 . | Instead of NC1 3 , it may in reality be NH 2 4-C1, or chloride of amidogen . OTHER COMPOUNDS OF NON-METALLIC ELEMENTS. 165 OTHER COMPOUNDS OF NON-METALLIC ELEMENTS. Chlorine with Sulphur and Phosphorus. Chlorides of Sulphur. The protochlo- 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 arrange- ment. The chloride distils over as a deep orange yellow mobile liquid, of peculiar and disagreeable odor, which boils at 280. As this substance dis- solves both sulphur and chlorine, it is not easy to obtain it in a pure and definite state. It contains 32.18 parts sulphur and 35.41 chlorine.* Chloride of sulphur is instantly decomposed by water; hydrochloric and hyposulphurous acids are formed, and sulphur separated. The hyposul- phurous acid in its turn decomposes into sulphur and sulphurous acid. Per- chloride of sulphur is formed by exposing the above compound for a consider- able time to the action of chlorine, and then distilling it in a stream of the gas. It has a deep red color, is heavier than water, boils at 147, and contains twice as much chlorine as the protochloride. Chlorides of Phosphorus. Ter chloride.^ This is prepared in the same man- ner as chloride of sulphur, by gently heating phosphorus in dry chlorine gas, the phosphorus being in excess. Or, by passing the vapor of phosphorus over fragments of calomel (sub-chloride of mercury) contained in a glass tube and strongly heated. It is a colorless, thin liquid, which fumes in the air, and possesses a powerful and offensive odor. Its specific gravity is 1.45. Thrown into water, it sinks to the bottom of that liquid, and becomes slowly decom- posed, yielding phosphorous acid and hydrochloric acid. This compound con- tains 31.38 parts phosphorus, and 106.23 parts chlorine. Perchloride 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 perchloride. It rnay be obtained in larger quantity by passing a stream of dry chlorine gas into the preceding liquid chloride, which becomes gradually converted into a solid, crystalline mass. Perchloride of phosphorus is de- composed by water, yielding phosphoric and hydrochloric acids. Two bromides of phosphorus are known, closely corresponding in properties and constitution with the chlorides. Several compounds of iodine and phos- phorus appear to exist; but their characters are less definite. Chlorine and Carbon. Three or four 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. Iodine with Sulphur and Phosphorus. These compounds are formed by gently heating together the materials, in vessels from which the air is excluded. They present few points of interest. The iodides of phosphorus, prepared in this manner, are fusible, crystalline substances, which decompose by contact with water, and yield hydriodic acid and phosphorous, or phosphoric acid. Chlorine with Iodine Iodine readily absorbs chlorine gas, forming, when the chlorine is in excess, a solid, yellow compound, and when the iodine pre- ponderates, a brown liquid. The solid iodide is decomposed by water, yielding hydrochloric and iodic acids. Another definite compound is formed by heating in a retort a mixture of 1 part iodine and 4 parts chlorate of potash ; oxygen gas and chloride of iodine *S 9 C1. fPCl 3 . Hence it doubtless contains 1 eq. iodine, and 5 eq. chlorine, or Id,' 166 OTHER COMPOUNDS OF NON-METALLTC ELEMENTS. are disengaged, and the latter may be condensed by suitable -means. lodate and hyperchlorate of potash remain in the retort. This chloride of iodine is a yellow, oily liquid, of suffocating smell and astringent taste; it is soluble in water and alcohol without decomposition. Tt probably consists of 126.36 parts iodine, and 35.41 parts chlorine.* Carbon and Sulphur. Bisulphuret of Carbon. A wide porcelain tube is filled with pieces of charcoal which have been recently heated to redness in a covered crucible, and fixed across a furnace in a slightly inclined position. Into the lower extremity a tolerably wide tube is secured by the aid of a cork ; this tube bends 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 bright redness, fragments of sulphur are thrown into the open end, which is immediately afterwards stopped by a cork. The sulphur melts, and becomes converted into vapor, which, at that high temperature, combines with the carbon, forming an exceedingly volatile compound, which is con- densed 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 con- denser. Bisulphuret of carbon is a transparent colorless liquid of great re- fractive and dispersive power. Its density is 1.272. It boils at 110 F., and emits vapor of considerable elasticity at common temperatures. The odor 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 vapor is mixed with oxygen it becomes explosive. It freely dissolves sulphur, and by spontaneous evaporation deposits the latter in beautiful crystals. Chlorides of Silicon and Boron. Both silicon and boron combine directly with chlorine. The chloride of silicon 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 con- nected with the porcelain tube. The product is a colorless and very volatile liquid, boiling at 122, of pungent, suffocating odor. In contact with water it yields hydrochloric acid and gelatinous silica. This substance contains 22.18 parts silicon, and 106.23 chlorine.! Bromide of silicon maybe obtained by a similar proceeding, the vapor 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 charcoal. It resembles in constitution chloride of silicon. * Or single equivalents, t Or > SiCl 3 , GENERAL PRINCIPLES OF CHEMICAL PHILOSOPHY. 167 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 info'r- 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 con- stant references to examples of combinations, the elements and products of which have been already described so much more difficult is it to gain a clear and distinct idea of any proposition of great generality from a simple enunciation, than to understand the bearing of the same law when illustrated by a single good and familiar instance. Before proceeding further, however, it is absolutely necessary that these matters should be discussed ; the metallic compounds are so numerous 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, further, 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 che- mistry it cannot be dispensed with. It will be proper to commence with a notice of the principles which regu- late the modern nomenclature in use in chemical writings. NOMENCLATURE. In the early days of chemistry, the arbitrary and fanciful names which were conferred by each experimenter on the new compounds he discovered sufficed to distinguish these from each other, and to render intelligible the description given of their production. Such terms as oil of vitriol, spirit of salt, oil of tartar, butter of antimony, sugar of lead, flowers of zinc, sal enixum, sal mirabile, &c., were then quite admissible. In process of time, however, when the number of known substances became vastly increased, the confusion of lan- guage produced by the want of a more systematic kind of nomenclature be- came quite intolerable, and the evil was still further increased by the fre- quent use of numerous synonyms to designate the same substance. In the year 1787, Lavoisier and his colleagues published the plan of the remarkable system of nomenclature, which, with some important extensions since rendered necessary, has up to the present time to a great extent satisfied 168 GENERAL PRINCIPLES OF the wants of the Science. It is in Organic Chemistry that the deficiencies of this plan are chiefly felt, and that something like a return to the old method has been rendered inevitable. Organic Chemistry is an entirely new science which has sprung up since the death of these eminent men, and has to deal with bodies of a constitution or type differing completely from that of the in- organic acids, bases and salts which formed the subjects of the chemical studies of that period. The rapid progress of discovery by which new com- pounds, and new classes of compounds, often of the most unexpected nature, are continually brought to light, sufficiently proves that the time to attempt the construction of a permanent systematic plan of naming organic bodies has not yet arrived. The principle of the nomenclature in use may be thus explained : Ele- mentary substances still receive arbitrary names, generally, but not always, referring to some marked peculiarity of the body; a uniformity in the termi- nation 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 or uret, the choice being one of euphony. Thus we have oxides, chlorides, iodides, bromides, &c., of hydrogen and of the several metals; oxides of chlorine, chlorides of iodine and sulphur; sulphurets and phosplmrets of hydrogen and the metals. The nomenclature of oxides has been already described (p. 106). 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 CMS. When more members of the same group came to be known, recourse was had to a prefix, hypo, or hyper, signifying deficiency or excess. Thus, the two earliest known acids of sulphur were named respectively sulphurous and sulphuric acids; subsequently 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 hyposulphurous and hyposulphuric acids. The names of the new acids of sulphur of still more recent discovery are not yet perma- nently 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 hypophospho- rous, phosphorous and phosphoric acid ; hypochlorous, chlorous, chloric and hyper- chloric acids ; hyponitrous, nitrous and nitric acids, &c. The nomenclature of salts is derived from that of the acid they contain. If the name of the acid terminate in ic, that of the salt is made to end in ate ; if in QMS, that of the saline compound ends in ite. Thus, sulphuric acid forms sulphates of the various bases; sulphurous acid, sulphites; hyposulphurous acid, hyposulphites; hyposulphuric acid, hyposulphates, &c. The rule is here very simple and obvious. The want of uniformity in the application of the systematic nomenclature is chiefly felt in the case of oxides not possessing acid characters, arid in that of some analogous compounds. The old rule was to apply the word protoxide CHEMICAL PHILOSOPHY. 169 to the oxide containing least oxygen, to call the next in order deutoxide, the third trtioxide, &c., after the Greek numerals. 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 ex- ample is to be found in the two oxides of copper ; that which was once called deutoxide is now protoxide, being the most basic of the two, while the former protoxide is degraded into suboxide. The Latin prefix per, or rarely hyper, is used to indicate the highest oxide of a series destitute of acidity, as peroxide of iron, chromium, manganese, lead, &c. Other Latin prefixes, as sesqui, bi or bin, and quad, applied to the names of binary compounds or salts have reference to the constitution of these latter expressed in chemical equivalents.* Thus, an oxide in which the proportions of oxygen and metal are in equivalents, as 1.5 to 1, or 3 to 2, is often called a sesquioxide; if in the proportions of 2 to 1, a binoxide, &c. The same terms are applied to salts ; thus we have neutral sulphate of potash, sesquisulphate of potash, and bisulphate of potash ; the first containing 1 equiva- lent of acid to 1 of base, the second 1.5 of acid to 1 of base, arid the third 2 equivalents of acid to I equivalent of base. In like manner we have neutral oxalate, binoxalate and quadroxalate of potash, the latter 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 often loosely applied, as when a Latin numeral prefix is substituted for one of Greek origin. We speak of tersulphuret instead of tritosulphuret of antimony, and pentasulphuret of antimony. These and other small irregularities are not found in practice to cause serious confusion. THE LAWS OF COMBINATION BT WEIGHT. The great general laws which regulate all chemical combinations admit of being laid down in a manner at once simple and concise. They are four in number, and to the following effect : 1. All chemical compounds are definite in their nature, the ratio of the 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 inva- riably contains the same elements united in unvarying proportions, is a pro- position almost axiomatic; it is involved in the very idea of identity itself. The converse, however, is very far from being true; the same elements combining 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 chemistry; few well-established and undoubted examples being 'known in the inorganic or mineral division of the science. (2.) Multiple Proportions. Illustrations of this simple and beautiful law * See a few pages forward. 15 170 GENERAL PRINCIPLES OP abound on every side; let the reader take for example thf 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 . . . -.: -W ' '; 14.06 8 Deutoxide . . ; <-'-; ,.' : ~ .' 14.06 16 Hyponitrous acid . -. . ...-.'% 14.06 24 Nitrous acid >?. -* . \'.- ' -'-J^ % . 14.06 32 Nitric acid . . -v .- 7-,' '- . 14.06 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 deutoxide, hyponitrous acid, nitrous acid, and lastly, nitric acid. Again, carbonic acid contains exactly twice as much oxygen in proportion to the other constituent as carbonic oxide; the peroxide of hydrogen is twice as rich in oxygen as water ; the corresponding sulphurets exhibit the same phenomena, while the metallic compounds offer one continued series of illustrations of the law, although the ratio is not always so simple as that of 1 to 2. It often happens that one or more members of a series are yet deficient : the oxides of chlorine afford a good example. Chlorine. Oxygen. Hypochlorous acid . ' .- V r ... '; ; . 35.41 8 Chlorous acid "' V?' .s*^-Y^'' /Y**'*'* 7 -"' 35.41 32 Chloric acid .'y/ ';" ' -.-,<'"'* 35 - 41 40 Hy perchloric acid . '^'- r;'r '-"'".; ;*'"'>> 35.41 56 Here the quantities of oxygen progress in the following order: 8, 8x4, 8X5) 8x7 ; gaps are manifest between the first and second substances, and between the third and fourth; these remain to be filled up by future re- searches. 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. 129, 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 intermediate combinations, we may arrange the four direct compounds in such a manner that the sulphur shall remain a constant quantity. Sulphur. Oxygen. Hyposulphurous acid . . . : . . . 32.18 16 Sulphurous acid ".. -.- '.-' V*-,vi' ; - -'-,:' . 32.18 32 Hyposulphuric acid . . . -.-.- '' / 32.18 40 Sulphuric acid ;-; V . . . . 32.18 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 potash and soda : the second contains twice as much acid in relation to the alkaline base as the first. There are three oxalates of potash, namely, the simple oxalate, the binoxalate, and the quadroxalate ; the second has equally twice as much acid as the first; and the third twice as much as the second. Many other cases might be cited, but the student, once in pos- session of the principle, will easily notice them as he proceeds. CHEMICAL PHILOSOPHY. 171 (3.) Laic of Equivalents.' It is highly important that the subject now to be discussed should be completely understood. Let a substance be chosen whose range of affinity and powers of combi- nation are very great, and whose compounds are susceptible of rigid and exact analysis; such a body is found in oxygen, which is known to unite with all the elementary substances, with the single exception of fluorine. Now, let a series of exact experiments be made to determine the proportions in which the different elements combine with one and the same constant quantity of oxygen, which, for reasons hereafter to be explained, may be assumed to be 8 parts by weight; and let these numbers be arranged in a column opposite the names of the substances. The result is a table or list like the following, but of course much more extensive when complete: Oxygen 8 Hydrogen .... 1 Nitrogen . . . . 14.06 Carbon 6 Sulphur ..... 16.09 Phosphorus . . . . 31 38 Chlorine 35.41 Iodine 126.36 Potassium . . . . 39.19 Iron 28 Copper 31.65 Lead 103.56 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 propor- tions in which they unite among themselves, or at any rate bear some exceedingly simple ratio to these proportions. Thus, hydrogen and chlorine combine invariably in the proportions 1 and 35.41; hydrogen and sulphur, 1 to 16.09; chlorine and silver, 35.41 to 108; iodine and potassium, 126.36 parts of the former to 39.19 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, 39.19 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 sulphur and 3 equivalents of oxygen ; that is, a quantity of the latter represented by three times the combining number of oxygen; phosphoric acid is made up of I equivalent of phosphorus and 5 of oxygen; the red oxide of iron con- tains, as will be seen hereafter, 3 equivalents of oxygen to every 2 equivalents of metal, &c. It is an expression which will henceforward be freely and constantly employed ; it is hoped, therefore, that it will be understood. The nature of the law will easily show that the choice of the body des- 17*2 GENERAL PRINCIPLES OF tined to serve for a point of departure is perfectly arbitrary, and regulated by considerations 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 rnay rest assured that, if an oxide be ever discovered, its elements will be associated in the ratio of 8 to 18.7, or in numbers which are either multiples or sub- multiples of these. The number assigned to the starting substance is also equally arbitrary; if, in the table given, oxygen instead of S were made 10, or 100, or even a frac- tional number, it is quite obvious that, although the other numbers would all be different, the ratio, or proportion among the whole, would remain un- changed, and the law would still be maintained in all its integrity. There are in fact two such tables in use among chemists; one in "which oxygen is made = 8, and a second in which it is made = 100; the former is generally used in this country, and the latter on the Continent. The only reason for giving, as in the present 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 an eminent English chemist, and recently, to appearance, substantiated in some remarkable instances by very elaborate investigation, that the equivalents of all bodies are multiples of that of hydrogen; and, consequently, by making the latter unity, the numbers would be all integers. The question must be considered as altogether unsettled. A great obstacle to such a view is presented by the case of chlorine, which certainly seems to be a fractional number; and one single well established exception will be fatal to the hypothesis. As all experimental investigations are attended with a certain amount of error, the results contained in the following table must be looked upon merely as good approximations to the truth. For the same reason, small differences are often observed in the determination of the equivalents of the same bodies l>y different experimenters, of which some notice will be found in the Appendix. CHEMICAL PHILOSOPHY. 173 TABLE OF ELEMENTARY SUBSTANCES, WITH THEIR EQUIVALENTS. Oxy. = 8. Oxy. = 100 Oxy. = 8 Oxy.= 100 Aluminum 13.69 Antimony 129.04 Arsenic . 75.21 171.17 1612.90 940.08 Molybdenum 47.88 Nickel . 29.59 Niobium 598.52 369.68 Barium . 68.55 Bismuth . 70.95 856.88 886.97 Nitrogen . 14.06 Norium 175.75 Boron . 10.90 136.20 Osmium . 99.56 1244.49 Bromine . 78.26 Cadmium. 55.74 978.31 696.77 Oxygen . 8. Palladium 53.27 100. 665.90 Calcium . 20. Carton . 6. Cerium . 45.98 250. 75. 574.70 Pelopium Phosphorus 31.38 Platinum 98.68 392.28 1233.50 Chlorine . 35.41 442.65 Potassium 39.1 9 489.92 Chromium 28.14 351.82 Rhodium 52.11 .651.39 Cobalt . 29.52 368.99 Ruthenium Columbium 184.59 2307.43 Selenium 39.57 494.58 Copper . 31.65 Didymiurn Erbium 395.70 Silicon . 22.18 Silver . 108. Sodium . 23.27 277.31 1350. 290.90 Fluorine . 18.70 233.80 Strontium 43.78 547.29 Glucinum . 26.50 Gold . 99.44 331.26 1243. Sulphur . 16.09 Tellurium 64.14 201.17 801.76 Hydrogen . 1. Iodine . 126.36 12.5 1579.50 Terbium Thorium . 59 59 744.90 Indium . 98.68 1233.50 Tin . 58.82 735.29 Iron . 28. 350. Titanium 24.29 303.66 Latnauum Lead . 103.56 1294.50 Tungsten 94.64 Vanadium 68.55 1183. 856.89 Lithium . 6.43 80.33 Uranium . 60. 750. Magnesium 12.67 Manganese 27 67 Mercury . 100. 158.35 34589 1250. Yttrium . 32.20 Zinc . 33. Zirconium 33.62 402.51 412.50 420.20 (4.) Combining Numbers of Compounds. The law states that the equiva- lent or combining number of a compound is always the sum of the equiva- lents of its components. This is also a great fundamental truth, which it is necessary to place in a clear and conspicuous light. It is a separate and independent law, established by direct experimental evidence, and not deduci- ble 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 no wise different. The example of the acids and alkalis maybe 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 47.19 parts of pot- ash, or 116 parts of oxide of silver, there are required 15* 174 GENERAL PRINCIPLES OP 40.09 parts sulphuric acid, 54.06 " nitric acid, 75.41 " chloric acid, 166.36 " 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 potash, 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 determined by direct experiment, will always be found equal to the sum of the equivalents of the different components of the acid itself. 39.19 = equivalent of potassium. 8. = " oxygen. 47.19 = assumed equivalent of potash. 47.19 parts of potash are found to be exactly neutralized by 40.09 parts of real sulphuric acid, or by 54.06 parts of real nitric acid. These quantities are evidently made up by adding together the equivalents of their con- stituents : 1 equiv. sulphur = 16.09 1 equiv. nitrogen = 14.06 3 " oxygen = 24. 5 " oxygen = 40. 1 " sulphuric acid = 40.09 1 " nitric acid = 54.06 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 numbers of its components, however complex the substance may be. Even among such bodies as the vegeto-alkalis of organic chemistry, the same universal rule holds good. When salts combine, which is a thing of very common occurrence, as will hereafter be seen, it is always in the ratio of the equiva- lent numbers. Apart from hypothetical considerations, no a 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 neutral salts, which decompose each other when mixed, be brought in contact, the new compounds resulting from their mutual decomposition will also be neu- tral. For example, when solution of nitrate of baryta and sulphate of pot- ash are mingled, they both suffer decomposition, sulphate of baryta and nitrate of potash 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 54.06 parts of nitric acid set free by the decomposition of the barytic salt, 47.19 parts of potash are abandoned by the 40.09 parts of sulphuric acid with which they were previously in combination, now trans- ferred to the baryta. But 54.06 and 47.19 are the representatives of com- bining quantities; hence the new compound must be neutral. COMBINATION BY VOLUME. Many years ago, M. Gay Lussac made the very important and interesting discovery that when gases combine chemically union invariably takes place CHEMICAL PHILOSOPHY. 175 either between equal volumes, or between volumes which bear a simple re- lation to each other. This is riot only true of elementary gases, but of com- pound bodies of this description, as it is invariably observed that the contrac- tion 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 vapors 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 themselves. The ultimate reason of the law in question is to be found in the very re- markable 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 word s7 quantities by weight which combine./ occupy under similar circumstances of pressure and temperature either equal volumes, or volumes bearing a simple proportion to each other. In the ex- ample cited betow, equivalent weights of hydrogen, chlorine and iodine vapor occupy equal volumes, while the equivalent of oxygen occupies exactly half that measure. 8.00 grains of oxygen occupy at 60 and 30 in. barom. 23.3 cubic in. LOO grain of hydrogen . . * . 46.7 35.41 grains of chlorine . . . 46.2 126.36 grains of iodine vapor (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 (tke specific gravity) is contained in the weight of one chemical equivalent of the substance. In other words, the equivalent volume is found by dividing the chemical equivalent by the specific gravity. The following table exhibits the relations of specific gravity, equivalent weight and equivalent volume of the principal elementary substances. Sp. gravity. Equiv. weight. Equiv. volume. Hydrogen . . . .0693 . . 1.00 . . 14.43 or Nitrogen . . . .972 . . 14.00 . . 14.40 " Chlorine .... . 2.470 .. 35.42 .. 14.33 " Bromine vapor . . 5.395 . . 78.26 . . 14.51 " Iodine vapor . ,', . 8.716 . . 126.36 . . 14.50 " Carbon vapor* . . .418 ' '. i; 6.00 .. 14.34 " Mercury vapor , . 7.000 .'. . 100.00 .. 14.29 " Oxygen . . . 1.106 . . 8.00 . . 7.23 " Phosphorus vapor . 4.350 . . 31.38 . . 7.21 " | Arsenic vapor . . 10.420 .. 75.21 .. 7.21 Sulphur vapor . . 6.654 .. 16.09 .. 2.418" $ Thus it appears that hydrogen, nitrogen, chlorine, bromine, iodine, carbon, and mercury in the gaseous state have the same equivalent volume; oxygen, phosphorus, and arsenic, one half of this; and sulphur one-sixth. The slight 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: Sp. gravity. Equiv. weight. Equiv. volume. Water vapor . . . .625 . . 9.00 . . 14.40 or 1 Protoxide of nitrogen . 1.525 .. 22.00 .. 14.43 "1 * See further on. 17U GENERAL PRINCIPLES OF Sp. gravity. Eqniv. weight. Equiv. volume. Sulphuretted hydrogen . 1.171 .. 17.09 .. 14.59 " 1 Sulphurous acid . .2.210 .. 32.09 .. 14.52 " 1 Carbonic oxide . . .973 .. 14.00 .. 14.39 " 1 Carbonic acid . . 1.524 . . 22.00 . . 14.43 " 1 Light carburetted hydrogen .559 .. 8.00 .. 14.31 " 1 Olefiant gas . . . .981 . . 14.00 . . 14.27 " 1 Binoxide of nitrogen . 1.039 . . 30.00 . . 28.87 " 2 Hydrochloric acid . . 1.269 . . 36.42 . . 28.70 " 2 Phosphuretted hydrogen 1.240 . . 34.38 . . 27.72 2 Ammonia . . . .589 . . 17.00 . . 28.86 " 2 Ether vapor . . . 2.586 . . 37.00 . . 14.31 " 1 Acetone vapor . . 2.022 . . 29.00 . . 14.34 " 1 Benzol vapor . . 2.738 . . 78.00 . . 28.49 " 2 Alcohol vapor . . 1.613 .. 46.00 .. 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 representing 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 i,t be adhered to throughout. The law of volumes often serves in practice to check and corroborate the results of experimental investigation, and is often of great service in this respect. "There is an expression sometimes made use of in chemical writings which it is necessary to explain, namely, the meaning of the words hypothetical density of vapor, applied to a substance which has never been volatilized, such as carbon, whose real specific gravity in that state must of course be unknown; it is easy to understand the origin of this term. Carbonic acid contains 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 .4183 On the supposition that carbonic acid contains equal volumes of oxygen and this vapor of carbon, condensed to one-half, the latter will have the spe- cific gravity represented by .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 contained in the prediction that, should the specific gravity of the vapor 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 combina- tion by volume, the combining or equivalent volumes of the bodies in question being determined by the method pursued in the case of gases, namely, by dividing the chemical equivalent by the specific gravity. The numbers obtained in this manner representing the combining volumes of the various solid and liquid elementary substances, present far more cases of dis- CHEMICAL PHILOSOPHY. 177 crepancy than of agreement. The latter are, however, sufficiently numerous 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 labors of very many illustrious men ; they are the ex- pression of fact, and are totally independent of all hypotheses or theories whatsoever. CHEMICAL NOTATION J STMBOLS. 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, recourse 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. Further, by a most ingenious idea, the symbol is made to represent not the substance in the abstract, but one equivalent of that substance. Table of Symbols of the Elementary Bodies. Aluminum . , Antimony (Stibium) Arsenic . -. ' ^. "' Barium r , ' ." . Bismuth . , Boron Bromine Cadmium Calcium Carbon Cerium . . Chlorine . Chromium . Cobalt Columbium . Copper (Cuprum) . Didymium Erbium . Fluorine Glucinum Al Gold (Aurum) . Au Sb Hydrogen H As Iodine .... I Ba Iridium .... Ir Bi Iron (Ferrum) Fe B Lantanum Ln Br Lead (Plumbum) Pb Cd Lithium L Ca Magnesium . . Mg C Manganese . . Mn Ce Cl Mercury (Hydrargyrum) Molybdenum Hg Mo Cr Nickel .... Ni Co Niobium Nb Cm Nitrogen .... N Cu Norium .... No Dy Osmium .... Os Er Oxygen .... F Palladium .... Pd G Pelopium Pe 178 GENERAL PRINCIPLES OF Phosphorus . Platinum Potassium (Kalium) Rhodium Ruthenium Selenium Silicon Silver (Argentum) , Sodium (Natrium) Strontium Sulphur P Pt K R Ru Se Si Ag Na Sr S Tellurium Te Terbium . . . Tb Thorium .... Th Tin (Stannum) . . Sn Titanium ... Ti Tungsten (Wolframium) . W Vanadium ... V Uranium U Yttrium .... Y Zinc . . %- V . . Zn Zirconium , N - . Zr Combination between bodies in the ratio of the equivalents is expressed by mere juxtaposition of the symbols, or sometimes by interposing the sign of addition. For example : Water HO, or H-f-O Hydrochloric acid HCl, or H+Cl Protoxide of iron FeO, or Fe-f-0. When more than one equivalent is intended, a suitable number is added, sometimes being placed before the symbol, like a co-efficient in algebra, some- times appended after the manner of an exponent, but more commonly placed a little below on the right. Peroxide of hydrogen H-fSO, or HO 3 , or H0 2 Sulphuric acid S+30, or SQ3, or S0 3 Hyposulphuric acid 2S+5O, or S 7 O 5 , or S 2 O 5 Combination between bodies themselves compound is indicated by the sign of addition or by a comma. When both are used in the same formula, the latter may be very convenient^- 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 ex- amples will serve to illustrate these several points. Sulphate of soda Nitrate of potash NaO-f S0 3 , or NaO , SO 3 K0+N0 5 , or KO , NO 5 . The base being always placed first. Double sulphate of copper and potash CuO , S0 3 -f-KO , S0 3 The same in a crystallized state CuO , S0 3 -f-KO , SO 3 -f 6HO. Common crystallized alum, or double sulphate of alumina and potash, is thus written : Al a O 3 , 3S0 3 +KO , S0 3 , 24HO. In expressing organic compounds, where three or more elements exist, the same plan is used. Sugar C ia H tt O u Alcohol C 4 H 6 O 3 Acetic acid C 4 H 3 O 3 Morphia C 35 H 20 N O 6 Acetate of morphia C 35 H 20 N O 6 , C 4 H g O 3 Acetate of soda NaO , C 4 H 3 3 . CHEMICAL PHILOSOPHY. 170 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, Peroxide of iron FeO 3 , or FeO 3 , or Fe, instead of Fe 2 O 3 Bisulphuret of Carbon C, instead of CS 2 Crystallized alum as before Al S 3 4-KS+24H. THE ATOMIC THEORT. That no attempt should have been made to explain the reason of the very remarkable manner in which combination occurs in the production of chemical 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 ingenious and successful one it is, has been made, namely, the atomic hypothesis of Dr. Dalton. From very ancient times, the question of the constitution of matter with respect to divisibility has been debated, some adopting the opinion that this divisibility is infinite, and others that when the particles become reduced to a certain degree of tenuity, far indeed beyond any state that can be reached by mechanical means, they cease to be further diminished in magnitude; they become, in short, atoms.* Now, however, the imagination may succeed in figuring to itself the condition of matter on either view, it is hardly necessary to mention that we have absolutely no means at our 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 per- haps that of the sages of Egypt and Hindostan long before them. Dr. Dalton's hypothesis sets out by assuming the existence of such atoms or indivisible particles, and states that compounds are formed by the union of atoms of different bodies one to one, one to tw r o, &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, further, 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 pro- duce the same substance, for they may be differently arranged ; and much depends upon this circumstance. Again, the law of multiple proportions is perfectly well explained; an atom of nitrogen unites with one of oxygen to form laughing gas; with two, to form binoxide of nitrogen; with three, to produce hyponitrous 180 GENERAL PRINCIPLES OP acid; with four, nitrous acid; and with five, nitric acid perhaps something after the manner below represented, in which the circle with a cross repre- sents the atom of nitrogen, and the plain circle that of oxygen. Fig. 124. Protoxide. Deutoxide. H ^ r US ^ c 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 ex- planation. The difficulties in the general application of the atomic hypothesis are chiefly felt in attempting to establish some wide and universal relation be- tween combining number and combining volume, among gases and vapors, 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 favor of this or some similar molecular hypothesis. But even here serious discrepancies exist; we may not take liberties with equivalent numbers determined by exact chemical research, and, in addition, all simple relation is found to bo wanting between the capacity for heat of the compound and that of its ele- ments. The theory in question has tendered great service to chemical science; it has excited a vast amount of inquiry and investigation, which have contributed 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 bodies, in such a way as to give rise to a new substance, having for the most part properties completely in discordance with those of its components. * The 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, perhaps, better avoided. CHEMICAL PHILOSOPHY. 181 The attraction thus exerted between different kinds of matter is to be distinguished from other modifications of attractive force which are exerted indiscriminately between all descriptions of substances, sometimes at enormous distances, and sometimes at intervals quite inappreciable. Examples of the latter are to be seen in cases of what is called cohesion, when the particles of solid bodies are immovably bound together into a mass. Then there are- other effects of, if possible, a still more obscure kind; such as the various actions of surface, the adhesion of certain liquids to glass, the repulsion of others, the ascent of water in narrow tubes, and a multitude of curious phe- nomena which are described in works on Natural Philosophy, under the head of molecular actions. From all these, true chemical attraction may be at once distinguished by the deep and complete change of characters which follows its exertion; we might define affinity to be a force by which new substances are generated. It seems to be a general law that bodies most opposed to each other in chemical properties evince the greatest tendency to enter into combination, and, conversely, bodies between which strong analogies and resemblances can be traced, manifest a much smaller amount of mutual attraction. For example, hydrogen and the metals tend very strongly indeed to combine with oxygen, chlorine, and iodine ; the attraction between the different members of these two groups is incomparably more feeble. Sulphur and phosphorus stand, as it were, midway; 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 them- selves 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 dissolved 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 tempe- rature falls, the heat of combination being lost and overpowered by the effects of change of state. The force of chemical attraction thus varies greatly with the nature of the substances between which it is exerted; it is influenced, moreover, to a very large extent by external or adventitious circumstances. An idea formerly prevailed that the relations of affinity were fixed and constant between the same substances, and great pains were taken in the preparation of tables ex- hibiting what was called the precedence of affinities. The order pointed out in these lists is now r acknowledged to represent the order of precedence for the circumstances under which the experiments \vere 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 in- tensity that it is seldom possible to predict the consequences of any yet un- tried 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 displaces the acid from sulphate of magnesia, &c. The salts are-supposed to be dis- solved in water. The second table exhibits the order of affinity for oxygen of several metals, mercury reducing a solution of silver, copper one of mer- cury, &c. tfl 182 GENERAL PRINCIPLES OF Sulphuric acid. Oxygen. Baryta, Lime, Strontia, Magnesia, Potash, Ammonia, Soda, Zinc, Mercury, Lead, Silver. Copper, Jt 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 di- rect and original effects of the specific attractive force. Alteration of temperature may be reckoned among these. When metallic mercury is heated nearly to its boiling point, and in that state exposed for a lengthened period to the air, it absorbs oxygen, and becomes converted into a dark red crystalline powder. This very same substance, when raised to a still higher temperature, spontaneously separates into metallic mercury and oxygen gas. It may be said, and probably with truth, that the latter change is greatly aided by the tendency of the metal to assume the vaporous state 5 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 temperature rises to whiteness. Insolubility and the power of vaporization are, perhaps, beyond all other disturbing causes, the most potent; they interfere in almost every reaction which takes place, and very frequently turn the scale when the opposed forces do not greatly differ in energy. It is easy to give examples. When a solu- tion of lime in hydrochloric acid is mixed with a solution of carbonate of am- monia, double interchange ensues, carbonate of lime and hydrochlorate of am- monia being generated. Here the action can be shown to be in a great mea- sure 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 new ammoniacal salt which chiefly determines the kind of decomposition. When iron-filings are heated to redness in a porcelain tube, and vapor of water passed over them, the water undergoes decomposition with the utmost facility, hydrogen 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 vapor of water, carried forward by the current of gas, es- capes 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 sufficient to settle the point. An atmosphere of steam offers little resistance to the escape of hydro gen; 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 vapor of water by white hot platinum, quite re- cently pointed out by Mr. Grove, will probably be referred in great part to this influence of atmosphere, the steam offering great facilities for the assump- tion of the elastic condition by the oxygen and hydrogen. The decomposition ceases as soon as these gases amount to about 50 Vo ta of the bulk of the mix- ture, and can only be renewed by their withdrawal. The attraction of oxy- gen for hydrogen is probably much weakened by the very high temperature. The recombination of the gases by the heated metal is rendered impossible by their state of dilution. What is called the nascent state is one very favorable to chemical com- bination. Thus, carbon and nitrogen refuse to combine with gaseous hydro- CHEMICAL PHILOSOPHY. 183 gen ; yet when these substances are simultaneously liberated from some pre- vious 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 affinity. The preparation of hydrogen from zinc and sulphuric acid is one of the most fami- liar. A piece of polished zinc or iron, put into pure water, manifests no power of decomposing the latter to the smallest extent; it remains perfectly bright for any length of time. On the addition, however, of a little sulphuric acid, hydrogen is at once freely disengaged, and the metal becomes oxidized and dissolved. Now, the only intelligible function of the acid is to dissolve off the oxide as fast as it is produced. But why is the oxide produced when acid is present, and not otherwise ? The question is very difficult to answer. Great numbers of examples of this curious indirect action might be ad- duced. 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 yel- low transparent glass or silicate of silver. Platinum is attacked by fused hy- drate of potash ; hydrogen is probably disengaged while the metal is oxi- dized ; this is an effect which never happens to silver under the same cir- cumstances, although silver is a much more oxidable substance than platinum. The fact is that potash forms with the oxide of the last-named metal a kind of saline combination, in which the oxide of platinum acts as an acid ; and hence its formation under the disposing influence of the powerful base. In the remarkable decompositions suffered by various organic bodies when heated in contact with caustic alkali or lime, we have other examples of the same fact. Products are generated which are never formed in the absence of the base ; the reaction is invariably less complicated, and its results fewer in number and more definite than in the event of simple destruction by a graduated heat. The preparation of light carburetted hydrogen by the new artificial process, already described, is an excellent example. There is yet a still more obscure class of phenomena, in which effects are brought about by the mere presence of a substance, which itself undergoes no change whatever; the experiment mentioned in the article on oxygen, in which that gas is obtained, with the greatest facility, by heatiug a mixture of chlorate of potash and peroxide of manganese, is an excellent case in point. The salt is decomposed at a very far lower temperature than would other- wise 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 admissi- ble, as it suggests no explanation. It is proper to remark that the contact-decompositions alluded to are some- times mixed up with other effects, which are, in reality, much more intelligi- ble, as the action of finely-divided platinum upon certain gaseous mixtures, in which the solid really seems to have the power of condensing the gas upon its greatly extended surface, and thereby inducing combination by bringing the particles within the sphere of their mutual attractions. 184 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 being 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 perfect uni- formity and constancy at one or the other, according to their chemical cha- racter, 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 sur- face in connection with the zinc or negative extremity of the arrangement. The terminations of the battery itself, usually, but by no means necessarily, of metal, are designated as 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 proportions of one measure of the former to two of the latter nearly. This experiment has be- fore 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 then becoming bleached. Iodide of potassium dissolved in water is decomposed in a similar manner, and with still greater ease; the free iodine at the positive side can be recog- nized by its brown color, 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 equivalents of their components, the latter being strongly opposed to each other in their chemical relations, and held together by very powerful affinities. The amount of power required to effect decomposition varies greatly; so- # From n\e)npov, and o'So?, a way. f From JjMJtTpov, and Xuo>, I loose, j Page 113. CHEMISTRY OP THE VOLTAIC PILE. 185 lution of iodide of potassium, melted chloride of lead, solution of hydrochlo- ric acid, water mixed with a little oil of vitriol and pure water, demand in this respect very different degrees of electrical force, the resistance to decom- position increasing from the first mentioned substance to the last. One of the most important and indispensable conditions of electrolysis is fluidity ; todies which when reduced to the liquid condition freely conduct and as freely suffer decomposition, become absolute insulators to the electricity of the battery when they become solid. Chloride of lead offers a good illus- tration of this fact; when fused in a little porcelain crucible it gives up its elements with the utmost ease, and a galvanometer interposed somewhere in the circuit is strongly affected. But when the source of heat is withdrawn, and the salt suffered to solidify, all signs of decomposition cease, and at the same moment the magnetic needle reassumes its natural position. In the same manner, the thinnest film of ice completely arrests the current of a powerful voltaic apparatus; the instant the ice is liquefied at any one point, so that water-communication may be restored between the electrodes, the current again passes, and decomposition occurs. Fusion by heat, and solu- tion 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 physical 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 decomposi- tion in the manner described. These currents may be conveyed through ex- tensive masses of liquids; the latter seem, under these circumstances, to con- duct 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 symp- tom of a tendency to accumulate around them; a single element is altogether unaffected, directly at least; severance from previous combination is re- quired, 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 disturb- ance 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 traveling in one direction, and the oxygen in the other. The neighboring 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 par- ticle of hydrogen may be made to travel in one direction, by becoming suc- cessively united to each particle of oxygen between itself and the negative electrode; when it reaches the latter, finding no disengaged particle of oxy- gen for its reception, it is rejected as it were from the series, and thrown off in a separate state. The same thing happens to each particle of oxygen, which 16* 186 ELECTRO-CHEMICAL DECOMPOSITION. at the same time passes continually in the opposite direction, by combining successively with each particle of hydrogen, that moment separated, with Fig. 125. MIrII @ Water in usual state. 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 corre- sponding succession of particles of oxygen at the other. The power of the current is exerted with equal energy in every part of the liquid con- ductor, although its effects only become manifest at the very extremities. The action is one of a purely molecular or internal nature, and the me- tal terminations of the battery 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 regarding them in any other light than that of a somewhat figurative mode of representing the curious phenomena described. The circles are intended to indicate the elements, and are distinguished by their respective symbols. Fig. 126. ^"^ ^""^ Water undergoing electrolysis. A distinction is to be carefully drawn between true and regular electroly- sis. 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 simplicity, 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, peroxide of lead, at the positive : the latter substance is the result of a secondary action ; it proceeds, in fact, from the nascent oxygen at the mo- ment of its liberation reacting upon the protoxide of lead present in the salt, and converting it into peroxide, which is insoluble in the dilute acid. There is every reason to believe that when sulphuric- and nitric acids seem to be decomposed by the current, the effect is really due to the water they contain becoming decomposed, and reacting by its hydrogen upon the acid, for these bodies do not belong to the class of electrolytes, as already specified, and would probably refuse to conduct could they be examined in an anhydrous condition. It has generally been thought that the deposition of metal by the current CHEMISTRY OF THE VOLTAIC PILE. 187 must be considered as the consequence of a secondary action, as when a so- lution of sulphate of copper is electrolyzed,and copper reduced upon the sur- face of the negative electrode. This has been considered to arise from the water and sulphate of the oxide being simultaneously decomposed, and the subsequent action of the hydrogen upon the oxide of copper, by which the latter became reduced to the metallic state ; but although this explanation has been rendered very doubtful by recent investigation, and a great number of cases of supposed secondary action thus referred to direct electrolysis, many indubitable examples of the phenomenon referred to yet remain. If a number of different electrolytes, such as acidulated water, iodide of potassium, fused chloride of lead, &c., be arranged in a 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 ascer- tained, 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 165 parts of iodide of potassium, 139 parts of chloride of lead, &c. _Hence the very important conclusion: The action of the current is perfectly definite in its nature, producing a fixed and constant amount of decomposition, expressed in each electrolyte by the value of its chemical equivalent. From a very extended series of experiments, based on this and other me- thods of research, Mr. Faraday was enabled to draw the general inference that effects of chemical decomposition were always proportionate to the quan- tity of circulating electricity, and might be taken as an accurate and trust- worthy measure of the latter. Guided by this highly important principle, he constructed his voltameter, an instrument which has rendered the greatest 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 placing such an instrument in any part of the circuit, the quantity of electric force neces- sary to produce any given effect can be at once estimated ; or, on the other hand, any required amount of the latter can be, as it were, mea- sured out and adjusted to the object in view. The voltameter has received many different forms; one of the most extensively useful is that figured, in which the platinum plates are separated by a very small interval, and the gas is collected in a graduated jar standing on the shelf of the pneumatic trough, the tube of the instrument, which is filled to the neck with dilute sulphuric acid, being passed beneath the jar. The decompositions of the* voltaic battery can be effected by the electricity of the common machine, by that developed by magnetic action, and by that of animal origin, but to an extent incomparably more minute. This arises from the very small quantity of electricity set in motion by the machine, although its tension, that is, power of overcoming obstacles, and passing through imperfect conductors, is exceedingly great. A pair of small wires of zinc and platinum, dipping into a single drop of dilute acid, develop far more electricity, to judge from the chemical effects of such an arrangement, than very many turns of a large plate electrical machine in high action. Never- Fig. 188 ELECTRO-CHEMICAL DECOMPOSITION. theless, polar or electrolytic decomposition can be distinctly and satisfactorily effected by the latter, although on a minute scale. With a knowledge of the principles laid down, the study of the voltaic battery may be resumed and completed. In the first place, two very differ- ent 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 between one pair of metals and that succeeding. Proof was supposed to be given of the fundamental position by an experiment in which discs of zinc and cop- per attached to insulating handles, after being brought into close contact, were found, by the aid of a very delicate gold-leaf electroscope, to be in opposite electrical states. It appears, however, that the more carefully this experiment is made, the smaller is the effect observed; and hence it is judged highly probable that the whole may be due to accidental causes, against which it is almost impossible to guard. On the other hand, the observation was soon made that the power of the battery always 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 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 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 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 carefully riveting, and the latter bent into an arch. A piece of folded filter paper is wetted with solution of iodide of potassium, and placed upon the zinc; the platinum plate is arranged bpposite to the latter, with the end of its wire resting upon the paper, and then the pair plunged into a glass of dilute sulphuric acid, mixed with a few drops of nitric. A brown spot of iodine becomes in a moment evi- dent beneath the extremity of the platinum wire; that is, at the positive side of the arrangement. A strong argument in favor of the chemical view is founded on the easily proved fact, that the direction of the current is determined by the kind of action upon the metals, the one least attacked being 1 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- phuret. 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. CHEMISTRY OF THE VOLTAIC PILE. 189 The metals employed in the practical construction of voltaic batteries are zinc for the active metal, and copper, silver, or, still better, platinum for the inactive one; the greater the difference of oxidability, the better the arrange- ment. The liquid is either dilute sulphuric acid, sometimes mixed with a little nitric, or occasionally, where very slow and long-continued action is wanted, salt and water. To obtain the maximum effect of the apparatus with the least expenditure of zinc, that metal must be employed in a pure state, or its surface must be covered by an amalgam of 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 forwards with increased energy, its intensity is augmented, but the actual amount of electrical force thrown into the current formed is not increased. The quantity, estimated by its decomposing power, is, in fact, determined by that of the smallest and least active pair of plates, the quantity of electricity, in every part or section of the circuit, being exactly equal. Hence, large and small plates, batteries strongly and weakly charged, can never be connected without great loss of power. When a battery, either simple or compound, constructed with pure or with amalgamated zinc, is charged with dilute sulphuric acid, a number of highly interesting phenomena may be observed. While the circuit remains broken the zinc is perfectly inactive, no 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 c^Dsed circuit, which are witnessed in a portion of water undergoing electrolysis ; the oxygen appears at the positive side, with respect to the current, and the hydrogen at the negative; but with this difference, that the oxygen, instead of being set free, combines with the zinc. It is, in fact, a real case of electrolysis, and electrolytes alone are available as exciting liquids. Common zinc is very readily attacked and dissolved by dilute sulphuric acid ; and this is usually supposed to arise from the formation of a multitude of little voltaic circles, by the aid of particles of foreign metals or plumbago, partially embedded in the zinc. This gives rise in the battery to what is called local action, by which, in the common forms of apparatus, three-fourths or more of the metal are often consumed, without contributing in the least to the general effect, but, on the contrary, injuring the latter to some extent. This evil is got rid of by amalgamating the surface. From experiments very carefully made with a " dissected" battery of pe- culiar 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 J grain of hydrogen from the latter, 33 grains of zinc must be oxidized and its equiva- lent 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 equiva- lent of water, or any other electrolyte, out of it. This is an exceedingly important discovery ; it serves to show, in the most striking mariner, the intimate nature of the connection between chemical and electrical forces, amf their remarkable quantitative or equivalent relations. It 190 ELECTRO-CHEMICAL DECOMPOSITION. 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 mariner. In short, we are in such a position that either may be assumed as cause or effect ; it may be that electricity is merely a form or modification of ordinary chemical affinity; or, on the other hand, that all chemical action is a manifestation of electrical force. One of the most useful forms of the common voltaic battery is that con- trived by Dr. Wollaston. The copper is made completely to encircle the zinc plate, except at the edges, the two metals being kept apart by pieces of cork or wood. Each zinc is soldered to the preceding copper, and the whole screwed to a bar of dry mahogany, so that the plates can be lifted into or out of the acid, which is contained in an earthenware trough, divided into separate cells. The liquid consists of a mixture of 100 parts water, 2 parts oil of vitriol, and 2 parts commercial nitric acid, all by 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. Fig. 129. There are many serious evils felt even in this, the best of the old forms of voltaic apparatus; the local action is very great, and the diminution of power extremely rapid, the effects of first emersion being sometimes ten times greater than those observed when the battery has been a little time in use. There are several causes which concur in producing this disagreeable result, such as the adhesion of hydrogen, in bubbles, to the surface of the copper ; the pre- cipitation of metallic zinc upon the latter, and others perhaps less obvious. An instrument of immense value for 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. Each cell of this "constant" battery consists of a copper cylinder 3$ inches in diameter, and of CHEMISTRY OF THE VOLTAIC PILE. 191 1 Fig. 131. a height varying from G to 18 inches. The zinc is Fig. 130. employed in the form of a rod of an inch in dia- meter, carefully amalgamated, and suspended in the centre of the cylinder. A second cell of porous earth- enware or animal membrane intervenes between the zinc and the copper; this is tilled with a mixture of 1 part by measure of oil of vitriol and 8 of water, and the exterior space with the same liquid, saturated with 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 the strength of the solu- tion may remain unimpaired. When a communication is made by a wire between the rod arid the cylinder, a powerful current is produced, which may be exalted in intensity to almost any amount by connecting a suffi- cient number of such cells into a series, on the principle of the crown of cups, the copper of the first being at- tached 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. The interior of the cylinder be- comes covered with a compact deposit of reduced cop- per ; no gas is disengaged, and there is no local action on the zinc. The battery of Professor Grove is another very beau- tiful combination, in which a principle of considerable importance is called prominently into play, namely, the diminution of resistance to the passage of the current in the electrolyte by the affinity of one of the elements of the latter, or of some associated substance, for the liber- ated hydrogen. One of the cells in this battery is represented in the margin, in section. The zinc plate is bent round, so as to present a double surface, and well amalgamated 5 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 Wol- laston'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 char- coal points, &c., can be exhibited with great brilliancy, while the battery itself is very compact and portable, and to a great extent, constant in its action. The zinc, as in the case of Professor DanielTs battery, is only consumed while the current passes, so that the apparatus may be arranged an hour or two before it is required for use, which is often a matter of great convenience. The nitric acid suppresses the whole of the hydrogen, becoming thereby slowly deoxidized and converted into nitrous acid, which at first remains dissolved, but after some time begins to be disengaged from the porous cells in dense red fumes ; this constitutes the only serious drawback to this excellent instrument. Professor Bunsen has modified the Grove battery by substituting for the pla- tinum dense charcoal or coke, which is an excellent conductor of electricity. It is probable that no economy or advantage is gained by this alteration. Mr. Since has contrived an ingenious battery, in which silver covered with 192 ELECTRO-CHEMICAL DECOMPOSITION. 11 a thin coating of finely-divided metallic platinum in 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 ap- plications of voltaic electricity have been made, which may be slightly 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. By using this in its turn as a mould or matrix, an absolutely Fig". 132. perfect fac-simile of the plate or medal is obtained. In the ^^ former case, the impressions taken on paper are quite indis- tinguishable from those directly derived from the work of the artist; and as there is no limit to the number of electrotype plates which can be thus produced, engravings of the most beautiful description may be multiplied indefinitely. The copper is very tough, and bears the action of the press perfectly well. The apparatus used in this and many similar processes is of the simplest possible kind. A trough or cell of wood 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 thinnest 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 products 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 dependent on electrochemical action. When a piece of zinc is suspended in a solution of acetate of lead, the first effect is the decomposition of a portion of the latter, and the deposition of metallic lead upon the surface of the zinc; it is simply a displacement of a metal by a more ox- idable one. The change does not, however, stop here; metallic lead is still deposited in large and beautiful plates Fig. 133. * Traite tie I'Klfof ric-ite el, chi Magnetisme. iii. CHEMISTRY OF THE VOLTAIC PILE. 193 upon that first thrown down, until the solution becomes exhausted, or the zinc entirely disappears. The first portions of lead form with the zinc a voltaic arrangement of sufficient power to decompose the salt, under the peculiar circumstances in which the latter is placed, the metal is precipitated upon the negative 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 electrical current, of sufficient intensity to decompose water, is produced by the reaction of oxygen upon hydrogen. Each element of this interesting apparatus consists of a pair of glass tubes to contain the gases, dipping into a vessel of acidulated water. Both tubes contain platinum plates, covered with a rough deposit of finely- divided platinum, and furnished with conducting wires, which pass through the tops or sides of the tubes, and are hermetically sealed into the latter. When the tubes are charged with oxygen on the one side and. hydrogen on the other, and the wires connected with a galvanoscope, the needle of the instrument becomes instantly affected; and when ten or more are combined in a series, the oxygen-tube of the one with the hydrogen-tube of the next, &c., while the terminal wires dip into acidulated water, a rapid stream of minute bubbles from either wire indicates the decomposition of the liquid ; arid when the experiment is made with a small voltameter, it is found that the oxygen and hydrogen disengaged exactly equal in amount tfie quantities absorbed by the act of combination in each tube of the battery. 17 194 CHEMISTRY OF THE METALS. THE metals constitute the second and larger group of elementary bodies. A great number of these are of very rare occurrence, being found only in a few scarce minerals ; 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 progress of civilization. If arsenic and tellurium be included, the metals amount to forty-nine in number. Physical Properties. One of the most remarkable and striking characters possessed by the metals is their peculiar lustre ; this is so characteristic, that the expression metallic lustre has passed into common speech. This property is no doubt connected with the extraordinary degree of opacity which the metals present in every instance. The thinnest leaves or plates, the edges of crystalline laminae, arrest the passage of light in the most complete man- ner. An exception to this rule is usually made in favor of gold-leaf, which when held up to the day exhibits a greenish color, as if it were really en- dued 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 color, the metals present a certain degree of uniformity ; with three exceptions, viz : copper and titanium, which are red, and gold, which is yellow, all these bodies are included between the pure white of silver, and the bluish-gray tint of lead ; bismuth, it is true, has a pinkish color, 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. CHEMISTRY OF THE METALS. 195 Table of the specific gravities of metals at CO F.* Platinum . . 20.98 Gold . 19.26 Tungsten . . 17.00 Mercury . . 13.57 Palladium . 11. 30 to 11.8 Lead . 11.35 Silver . 10.47 Bismuth . 9.82 Uranium . . . . 9.00 Copper . 8.89 Cadmium . 8.60 Cobalt 8.54 Nickel 8.28 Iron 7.79 Molybdenum . . 7.40 Tin 7.29 Zinc 6.86 to 7.1 Manganese . 6.85 Antimony 6.70 Tellurium . 6.11 Arsenic . 5.88 Titanium . 5.30 Aluminum . 2.60f Magnesium . 1.70 Sodium .972 Potassium .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 mallea- bility. The specific gravity of malleable metals is usually very sensibly increased by pressure or blows, and the metals themselves rendered much harder, with a tendency to brittleness. This condition is destroyed and the former soft state restored by the operation of annealing, which consists in heating the metal to redness out of contact with air (if it will bear that temperature without fusion) and cooling it quickly or slowly according to the circum- stances of the case. After this operation it is found to possess its original specific gravity. Ductility is a property distinct from the last, inasmuch as it involves the principle of tenacity, or power of resisting tension. The art of wire-drawing is one of great antiquity ; it consists in drawing rods of metal through a sue- * Dr. Turner's Elements, p. 446. f Wohler. 196 CHEMISTRY OF THE METALS. Fig. 134. \J cession of trumpet-shaped holes in a steel plate, each being a little smaller than its predecessor, until the requisite de- gree of fineness is attained. The metal often becomes very hard and rigid in this process, and is then liable to break ; this is remedied by annealing. The order of tenacity among the metals susceptible of being easily drawn into wire is the following: it is determined by observing the weights re- quired to break asunder wires drawn through the same orifice of the plate. Iron Copper Platinum Silver Gold Zinc Tin Lead Metals differ as much in fusibility as in density; the following table, ex- 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 de- scribed : Melting points, Fahrenheit. 'Mercury 39 136 Sodium 190 Tin 442 Fusible below a red^ Cadmium Bismuth (about) 442 . . . . 497 heat 1 Lead 612 1 Tellurium rather less fusible than lead I Arsenic unknown 1 Zinc . 773 (^Antimony just below redness ^Silver 1873 Copper Gold . 1996 2016 Cast iron 2786 Pure iron ~| Nickel Cobalt ^ Manganese Palladium J Fusible only in an excellent wind -furnace. Infusible below a < red heat Molybdenum "^ Uranium I Tungsten Chromium Imperfectly melted in - wind-furnace. Titanium 1 Cerium Osmium Iridium ^ Rhodium Infusible in furnace ; fusible by oxy-hydrogen blowpipe. Platinum Columbium CHEMISTRY OP THE METALS. 197 Some metals acquire a pasty or adhesive state before becoming fluid; tins 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 vapor when heated to bright redness; arsenic and tellurium are volatile. CHEMICAL RELATIONS OF THE METALS J 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 mercury is concerned, amalgams, and those generated by combination with the non- metallic elements, as oxides, chlorides, sulphurets, &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 constituent rnetals; 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 equiva- lents of the former to three of the latter ; the peroxides or neutral compounds are still richer in oxygen, and, lastly, the metallic acids contain the maximum proportion of that element. The gradual change of properties by increasing proportions of oxygen is well illustrated by the case of manganese. Metal. Oxygen. Symbols. Characters. Protoxide 1 eq. 1 eq. MnO Strongly basic. Deutoxide 2 eq. 3 eq. Mn 2 O 3 Feebly basic. Peroxide 1 eq. 2 eq. MnO 2 Neutral. Manganic acid 1 eq. 3 eq. Mn0 3 > Strongly Hypermanganic acid 2 eq. 7 eq. Mn 2 O ? $ acid. The oxides of iron and chromium present similar, but less numerous gra- dations. When a powerful oxygen-acid and a powerful metallic base are united in such proportions that they exactly destroy each other's properties, the result- ing 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 remarka- ble 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 follow- ing manner : To form a neutral combination, as many equivalents of acids 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 colors 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. Protosul- phate of iron offers an example ; when a solution of this substance is exposed 17* 198 CHEMISTRY OF THE METALS. to the air, it absorbs oxygen, and a yellow insoluble sub-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 neutral and one equivalent basic persulphate, as indicated by the diagonal zigzag line of division. 1 eq. iron -f- 1 eq. oxygen . . . . 1 eq. sulphuric acid. 1 eq. iron -j- 1 e 1- oxygen . . . . 1 eq. sulphuric acid. | -f- 1 eq. oxygen from air. 1 eq. iron -f- 1 eq. oxygen . . . | 1 eq. sulphuric acid. 1 eq. iron -}- 1 eq. oxygen . . . . 1 eq. sulphuric acid, -j- 1 eq. oxygen from air. Such sub salts are very frequently insoluble. The combinations of chlorine, iodine, bromine, and fluorine with the metals possess in a very high degree the saline character. If, however, the defini- tion formerly given of a salt be rigidly adhered to, these bodies must be ex- cluded from the class, and with them the very substance from which the name is 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 com- mon salt, which contain a metal and a salt-radical, as chlorine, iodine, &c.; and in the second, those which, like sulphate of soda and nitrate of potash, are generally supposed to be combinations of an acid with an oxide. The names haloid* salts, and oxygen-acid, or oxy-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 5 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 hy- drogen-acid is poured upon a metallic oxide, we may rather suppose that both are decomposed, water and a haloid salt of the metal being produced. Take hydrochloric acid and potash by way of example. Hydrochloric $ Chlorine ^^. Chloride potassium. acid . \ Hydrogen- -n . , ( Potassium- Potash . ^ Qxygen ^ Water. On evaporating the solution, the chloride of potassium crystallizes out. When hydrochloric acid and ammoniacal gases are mixed, they combine with some energy and form a white solid salt, sal ammoniac. Now this sub- stance bears such a strong resemblance in many important particulars to chlo- ride of potassium and common salt, that the ascription to it of a similar con- stitution is well warranted. If chloride of potassium, therefore, contain chlorine and metal, sal ammoniac may also contain chlorine in combination with a substance having the chemi- cal relations of a metal, formed by the addition of the hydrogen of the acid to the elements of the ammonia. Hydrochloric $ 1 eq. Chlorine Chlorine acid . . 5 3 eq. **: I 1 eq. ( 1 eq. Chlorine Chlorine ^ I ] eq. Hydrogen C 2 PH H I u ^"^ f Sal-ammoniac. Nitrogen ^^^ Ammonium J * Af, sea-salt, and liJof, form. CHEMISTRY OF THE METALS. 199 The term ammonium is given to this hypothetical body, NH 4 ; it is supposed to exist in all the ammonical salts. Thus we have chloride of ammonium, sulphate of the oxide of ammonium, &c. This view is very strongly sup- ported by the peculiarities of the salts themselves, as will hereafter be seen. Many of the sulphurets also possess the saline character and are soluble in water, as those of potassium and sodium. Sometimes a pair of sulphurets 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 monosulphuret of an alkaline metal, and a higher sulphuret of a non-metal- lic substance or of a metal which has little tendency to form a basic oxide, the two sulphurets having exactly the same relation to each other as the oxide and acid of an ordinary salt. Hence the expressions, sulphur-salt, sul- phur-acid, and sulphur-base, which Berzelius applies to such compounds; they contain sulphur in the place of oxygen. Thus, bisulphuret of carbon is a sulphur-acid; it forms a crystallizable compound with simple sulphuret of potassium, which is a sulphur-base. Were oxygen substituted for the sul- phur in this product, we should have carbonate of potash. KS -f-CS 2 sulphur-salt. KO-fCO 2 oxygen-salt. These remarkable compounds are very numerous and interesting ; they have been studied by Berzelius with great care. Salts often combine together, and form what are called double salts, in which the same acid is in combination with two different bases. When sul- phate of copper and sulphate of potash, or chloride of zinc and sal-ammoniac, are mixed in the ratio of the equivalents, dissolved in water, and the solu- tion 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 potash, 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 colors; hydrogen, in fact, very much resembles a metal in its chemical relations. Bisulphate of potash will, therefore, be a double sulphate of potash and water, while oil of vitriol must be assimilated to neutral sulphate of potash. K0+S0 3 and H0+S0 3 . Water is a weak base ; it is for the most part easily displaced by a metal- lic 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 a few acid salts which contain no water; as the bichromate of potash, and a new anhydrous sulphate of potash discovered by M. Jacque- 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 combination with a salt, or other compound body, from which it can be dis- engaged by the mere application of heat, or by exposure to a dry atmos- phere. Salts which contain water of crystallization have their crystalline form greatly influenced by the proportion of the latter. Green sulphate of iron crystallizes in two different forms, and with two different proportions *= Ann. Chim. et Pliys. Ixx. 311. 200 CHEMISTRY OP THE METALS. 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 a part or the whole of their water of crystallization ; while in a moist atmosphere they may be preserved unchanged. The op- posite 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 existing in the solid state, assumes, under favorable circumstances, a distinct geometrical form or figure, usually bounded by plane surfaces, and having angles of fixed and constant value. The faculty of crystallization seems to be denied only to a few bodies, chiefly highly com- plex organic principles, which stand, as it were, upon the very edge of or- ganization, and which, when in a solid state, are frequently characterized by a kind of beady or globular appearance, well known to microscopical ob- servers. 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 other soluble substances, which have been slowly and quietly deposited, always surpass in size and regularity those of more rapid formation. Solution in water or some other liquid is one very frequent method of effecting crystallization. If the substance be more soluble at a high than at a lower temperature, then a hot and saturated solution by slow cooling will generally be found to furnish crystals ; this is a very common case with salts and various organic principles. If it be equally soluble, or nearly so, at all temperatures, then slow spontaneous evaporation in the air, or over a surface of oil of vitriol, often proves very effective. Fusion and slow cooling may be employed in many cases; that of sulphur is a good example; the metals usually afford traces of crystalline figure when thus treated, which sometimes becomes very beautiful and distinct, as with bismuth. A third condition under which crystals very often form is in pass- ing from a gaseous to a solid state, of which iodine affords a good instance. When by any of these means time is allowed for the symmetrical arrange- ment 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 attend- ing 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 lias 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 CHEMISTRY OF THE METALS. 201 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 colors, offering as great a contrast as those of diamond aud plumbago. The angles of crystals are measured by means of instruments called gonio- meters, of which there are two kinds in use, namely, the old or common goniometer, and the reflective goniometer of Dr. Wollaston. Fig. 135. 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 divided 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 being correct within a fraction of a degree; it is applicable also to the Fig. 136. 202 CHEMISTRY OF THE METALS. measurement of the angles of crystals of very small size, the only condition required being that their planes be smooth and brilliant. The subjoined sketch will convey an idea of its nature and mode of use. a (fig. 1 36) is a divided circle or disc of brass, the axis of which passes stiffly and without shake through the support b. This axis is itself pierced to admit the passage of a round rod or wire, terminated by the milled-edged head c, and destined to carry the crystal to be measured by means of the jointed arm d. A vernier, e, immovably fixed to the upright support, serves to measure 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 ne- cessity of moving the disc. The principle upon which the measurement of the angle rests is very simple. If the two adjacent planes of a crystal be successively brought into the same position, the angle through which the crystal will have moved will be the supplement to that contained between the two planes. This will be easily intelligible by reference to the subjoined diagram, 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. Fig. 137. The lines a c, b c are perpendicular to the respective faces of the crystal, consequently the internal angles d g c, d h c, are right angles. Now, since the sum of the internal angles of a four-sided rectilineal figure, as d g c h, equal four right angles, or 360, the angle g d h (or e df) must of necessity be the supplement to the angle gcft, 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 goniometer effects. One method of using the instrument is the following : The goniometer is placed at a convenient height upon a steady table in front of a well-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 two easily- visible black lines, perfectly parallel. The crystal to be examined is attached to the arm of the goniometer at f by a little wax, and adjusted in such a manner that the edge joining the two planes whose inclination is to be measured shall nearly coincide with, or be parallel to, the axis of the 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 triangular prism has been chosen for the sake of simplicity ; but a moment's consideration will show that the rule applies equally well to any other figure. CHEMISTRY OF THE METALS. 203 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 reflection approaches and overlaps the lower black line seen directly by another portion of the pupil. It is obvious, that if the plane of the crystal be quite parallel to the axis of the instrument (the latter being horizontal), the two lines will coincide completely. If, however, this should not be the case, the crystal must be moved upon the wax until the two lines fall in one when super- posed. 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 oc- cupied 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 di- vision upon the circle itself is very often made backwards, so that the angle of motion is not obtained, but its supplement, or the angle of the crystal required. It may be necessary to remark, that, although the principle of the operation described is in the highest degree simple, its successful practice requires con- siderable skill and experience. If a crystal of tolerably simple form be attentively considered, it will become evident that certain directions can be pointed out in which straight lines may be imagined to be drawn, passing through the central point of the crystal from side to side, from end to end, or from one angle to that opposed to it, &c., about which lines the particles of matter composing the crystal may be conceived to be symmetrically built up. Such linesjor 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 sys' terns ; 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 (I), the regular octahedron (2), and the rhombic dodecahedron (3). The letters a a show the terminations of the three axes, placed as stated . 204 CHEMISTRY OF THE METALS. 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, bisulphuret 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 lateral axes terminate in the central point of each side (1); a second right square prism, in which the axes terminate in the edges (2) ; a corresponding pair of right, square-based octahedra (3 and 4). Fig. 139. Z. a a. Principal, or vertical axis. b b. Secondary, or lateral axes. Examples of these forms are to be found in zircon, native oxide 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). a a. Principal axis. b b } c c. Secondary axes. The system is exemplified in sulphur crystallized at a low temperature, arsenical iron pyrites, nitrate and sulphate of potash, 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- CHEMISTRY OF THE METALS. 205 pendicular to the other. To this system may be referred the four following forms: The oblique rectangular prism (1), the oblique rhombic prism (2), the oblique rectangular-based octahedron (3), the oblique rhombic-based octahedron (4). a a. Principal axis. b b, c c. Secondary axes. Such forms are taken by sulphur crystallized by fusion and cooling, realgar, sulphate, carbonate, and phosphate of soda, borax, green vitriol, and many other salts. 5. The Doubly-oblique Prismatic System. The crystalline forms compre- hended in this division are, from their great apparent irregularity, exceed- ingly difficult to study and understand. In them are traced three axes, which maybe all unequal in length, and all are 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). a a. Principal axis, as before. b &, c c. Secondary axes. Sulphate of copper, nitrate of bismuth, and quadroxalate of potash afford illustrations of these forms. 6. The Rhombohedral System. This is very important and extensive ; it is characterized by the presence of four axes, three of which are equal, in the same plane, and inclined to each other at angles of 60, while the fourth or principal axis is perpendicular to all. The regular six-sided prism (1), the quartz dodecahedron (2), the rhombohedron (3), and a second dodecahedron, whose faces are scalene triangles (4), belong to the system in question. 18 206 CHEMISTRY OF THE METALS. Fig. 143. a a. Principal axis. b b, c c. Secondary axes. 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 un- equally, 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 regu- lar omission of successive rows of particles of matter in a certain order be made at each solid angle, while the crystal continues to increase elsewhere, the result will be the production of small triangular planes, which, as the process advances, gradually usurp the whole of the surface of the crystal, and convert the cube into an octahedron. The new planes are called second- ary, and their production is said to take place by regular decrements upon the solid angles. The same thing may happen on the edges of the cube; a new figure, the rhombic dodecahedron, is then generated. The modifications which can thus be produced of the original or primary figure (all of which are subject to exact geometrical laws) are very numerous. Several distinct modifications may be present at the same time, and thus render the form exceedingly complex. 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.fre- CHEMISTRY OF THE METALS. 207 quently constitutes an excellent guide to the discovery of the primary form itself. Crystals often cleave parallel to all the planes of the primary figure, as in calcareous spar, which offers a good illustration of this perfect cleavage. Sometimes one or two of these planes have a kind of preference over the rest in this respect, the crystal splitting readily in these directions only. A very curious modification of the figure sometimes occurs by the exces- sive growth of each alternate plane of the crystal ; the rest become at length obliterated, and the crystal assumes the character called hemihedral or half- sided. This is well seen in the production of the tetrahedron from the regular octahedron, 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 pro- perty of exactly replacing each other in crystallized, compounds without alteration of the characteristic geometrical figure. Such bodies are said to be isomorphous.* For example, magnesia, oxide of zinc, oxide of copper, protoxide of iron, and oxide of nickel, are allied by isomorphic relations of the most inti- mate 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 color, 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 potash 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 peroxide of iron replace each other con- tinually without change of crystalline figure ; the same remark may be made of potash, soda, and ammonia with an equivalent of water, or oxide of am- monium, these bodies being strictly isomorphous. The alumina in common alum may be replaced by peroxide of iron ; the potash by ammonia, or by soda, and still the figure of the crystal remain unchanged. These replace- ments may be partial only; we may have an alum containing both potash and ammonia, or alumina and oxide 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 protosulphate of iron, and sulphate of copper, isomorphous salt?, yields on evaporation crystals containing both iron and copper. But if before * From Irssi equal, and (*of$n, shape, or form. 208 CHEMISTRY OF THE METALS. evaporation the protoxide of iron be peroxidized by chlorine or other means then the crystals obtained are free from iron, except that of the mother-liquor which wets them. The peroxide salt 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, when- ever they can be observed, in the most perfect manner ; hence the elements themselves are believed to be also isomorphous. Unfortunately, for obvious reasons it is very difficult to observe the crystalline figure of most of the elementary bodies, and this difficulty is increased by the frequent dimorphism 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 re- spects show the closest isomorphic relations. This should occasion no sur- prise, as there are reasons why such variations might be expected, the chief perhaps being the unequal effects of expansion by heat, by which the angles of the same crystal are changed by alteration of temperature. A good ex- ample is found in the case of the carbonates of lime, magnesia, manganese, 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 ex- amined by the more accurate instrument of Dr. Wollaston. These com- pounds are isomorphous, and the measurements of the obtuse angles of their rhombohedra as follows : 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 measure explained by these discoveries. Specimens of the same mineral from different localities were found to afford very discordant results on analysis. But the proof once given of the extent to which substitution of isomorphous bodies may go without 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 peroxide 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 CHEMISTRY OF THE METALS. 209 because it is isomorphous with magnesia and zinc, both undoubted prot- oxides. 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 interest- ing subject. Isomorphous Groups. (1.) (3.) (6.) Chlorine Phosphorus Magnesium Iodine Arsenic Manganese Bromine Antimony. Iron Fluorine. (4.) Cobalt (2.) Barium Nickel Sulphur Strontium Zinc Selenium Lead. Copper Tellurium. (5.) Cadmium Silver Aluminum Sodium Chromium Potassium Calcium Ammonium. Hydrogen. 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 family. Sulphate of copper or of zinc may unite in this manner with sul- phate of soda or potash, but not with sulphate of iron or cobalt; chloride of magnesium 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 Jlcids. There is a particular class of acids in which a departure occurs from the law of neutrality formerly described ; these are acids requir- ing 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 modifi- cations, forming three separate classes of salts which differ completely in properties and constitution. They are distinguished by the names tribasic, bibasic, and monobasic acids, according to the number of equivalents of base required to form neutral salts. Tribasic or Common Phosphoric Acid. When commercial phosphate of soda is dissolved in water and the solution mixed with acetate of lead, an abundant white precipitate of phosphate of lead falls, which may be collected on a filter, and well washed. While still moist, this compound is suspended in distilled water, and an excess of sulphuretted hydrogen gas passed. The oxide of lead is converted into sulphuret, 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 hy- drogen, yields sulphuret of lead and a hydrate of the acid containing three equivalents of water in intimate combination. 18* 210 CHEMISTRY OF THE METALS. f 2 eq. soda Phosphate j 1 " water of soda j 1 " phos- (^ phoric acid 3 eq. acetate (2 eq. acetic acid of lead ) acetic acid oxide of lead 1 eq. tribasic phos- phate of lead 3 eq. sulphuretted hydrogen 3 eq. lead 3 u oxygen 1 " phos- ) phoric acid $ 3 eq. sulphur 3 " hydrogen 2 eq. acetate of soda. 1 " hydrated acetic acid. 1 eq. tribasic phosphate of lead. 3 eq. sulphuret of lead. 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 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 oxide of silver. Bibasic Phosphoric Acid, otherwise called Pyrophosphoric Add. When com- mon phosphate of soda, containing 2NaO,HO,P0 5 +24HO, is gently heated, the 24 equivalents of water of crystallization are expelled, and the salt becomes anhydrous; but if the heat be raised to a higher point, the basic water is also driven off, and the acid passes into the second or bibasic modification. If the altered salt be now dissolved in water, this new com- pound, 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 bibasic hydrate. This solution may be preserved without change at common tem- peratures, but when heated an equivalent of water is taken up, and the sub- stance passes back again into the tribasic modification. Crystals of this hydrate have also been observed by M. Peligot. Their production was accidental. The bibasic phosphates, soluble in water, give a white precipitate with solution of silver. Monobasic, or Metaphosphoric Acid. When common tribasic phosphate of soda is mixed with solution of tribasic hydrate of phosphoric acid, and ex- posed, after proper concentration, to a low temperature, prismatic crystals are obtained, which consist of a phosphate of soda having two equivalents of basic water. NaO,2HO,P0 5 +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 acetate of lead, and the lead salt as before decomposed by sulphuretted hydrogen. * Peligot, Ann. Chem. et Phys. Ixxiii 286. CHEMISTRY OF THE METALS. 211 The solution of the monobasic hydrate is decomposed rapidly by heat, be- coming converted into tribasic hydrate. It possesses the property of coagulat- ing albumen, which, is not enjoyed by either of the preceding modifications. Monobasic alkaline phosphates precipitate nitrate of silver white. The glacial phosphoric acid of pharmacy is, when pure, hydrate of mono- basic phosphoric acid : it contains HO , P0 5 . Anhydrous phosphoric acid, prepared by burning phosphorus in dry air, when thrown into water, forms a variable mixture of the three hydrates. When heated, a solution of the tribasic hydrate alone remains.* Binary Theory of Salts. The great resemblance in properties between the two classes of saline compounds, the haloid and oxy-salts, has very na- turally led to the supposition that both might possibly be alike constituted, and that the latter, instead of being considered compounds of an oxide and an acid, might with greater propriety be considered to contain a metal in union with a compound salt radical, having the chemical relations of chlorine and iodine. On this supposition, sulphate and nitrate of potash will be constituted in the same manner as chloride of potassium, the compound radical replacing the simple one. Old view. New view. KO+SO, K+S0 4 KO+NO. K + NO 6 Hydrated sulphuric acid will be, like hydrochloric acid, a hydruret of salt- radical. H+S0 4 . When the latter acts upon metallic zinc, the hydrogen is simply displaced, and the metal substituted ; no decomposition of water is supposed to occur, and, consequently, the difficulty of the old hypothesis is at an end. When the acid is poured upon a metallic oxide, the same reaction occurs as in the case of hydrochloric acid, water and a haloid salt are produced. All acids must be, in fact, hydrogen acids, and all salts haloid salts, with either simple or compound radicals. This simple and beautiful theory is not by any means new ; it was sug- gested by Davy, who proposed to consider hydrogen as the acidifying prin- ciple in the common acids. It is supported by a good deal of evidence derived from various sources, and has lately 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-isolable compounds is often urged as an objection to the new view ; but the same objection applies to the old mode of considering the subject; a com- pound of 1 eq. nitrogen and 5 eq. oxygen, is as hypothetical as one contain- ing 6 eq. of oxygen. Absolute nitric acid is as yet unknown ;J 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, maybe obtained in a separate state, are destitute of all acid properties so long as the anhydrous condition is retained. * 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 acids travel unaltered, a tribasic salt giving at the positive elec- trode a solution of common phosphoric acid ; a bibasic salt, one of pyrophosphoric acid ; and a monobasic salt, one of metaphosphoric acid. (Professor Daniell and Dr. Miller, Phil. Trans, for 1844, p. 1.) t See Daniell's Introduction to Chemical Philosophy, 2d edit. p. 533. t See p. 121. 212 CHEMISTRY OF THE METALS. The real difficulty in the general application of the binary theory is pre- sented by the three modifications of phosphoric acid. If this could be explained away in a satisfactory manner, there seems no reason to object to its adoption, which would greatly simplify many parts of the science. One great inconvenience would be the change of nomenclature involved. CLASSIFICATION OF METALS. 1. Metals of the Alkalis. Potassium, Lithium, Sodium, Ammonium.* 2. Metals of the Alkaline Earths. Barium, Calcium, Strontium, Magnesium. 3. Metals of the Earths Proper. Aluminum, Norium, Glucinum, Thorium, Yttrium, Cerium, Erbium, Lantanum, Terbium, Didymium. Zirconium, 4. Oxidable 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, Tin, Molybdenum, Antimony, Columbium, Arsenic, Niobium, Tellurium, Pelopium, Osmium. 6. Metals Proper, whose Oxides are reduced by Heat Noble Metals. Gold, Palladium, Mercury, Iridium, Silver, Ruthenium, Platinum, Rhodium. *This hypothetical substance is merely placed with the metals for the sake of convenience, as will be apparent in the sequel. POTASSIUM. 213 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 potash 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 potash 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 wrap round it, and maintain every part at an uni- form 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. Arrangements 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 potash, and preventing its separation from the finely-divided carbonaceous matter. If the potassium be wanted absolutely pure, it must be afterwards re-distil- led in an iron retort, into which some naphtha has been put, that its vapor may expel the air, and prevent oxidation of the metal. Potassium is a brilliant white metal, with a high degree of lustre ; at the common temperature of the air it is soft, and may be easily cut with a knife, but at 32 it is brittle and crystalline. It melts completely at 150, and distils at a low red heat. The density of this remarkable metal is only .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 potash. 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 a jar 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 39.19; and its symbol, K. 214 POTASSIUM. There are two compounds of this metal with oxygen, potash* (potassa) and peroxide of potassium. POTASH (POTASSA) or PROTOXIDE, KO, is produced when potassium is heated in dry air ; the metal burns, and becomes entirely converted into a volatile, fusible, white substance, which is anhydrous potash. Moistened with water, it evolves great heat, and forms the hydrate. HYDRATE OP POTASH (or, OF POTASSA), KO, HO, is a very important sub- stance, and one of great practical utility. It is always prepared for use by decomposing the carbonate by hydrate of lime, as in the following process, which is very convenient : 10 parts of carbonate of potash 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 solution of carbonate, with frequent stirring. When all the lime has been introduced, the mixture is suffered to boil a few minutes, and then re- moved from the fire, and covered up. In the course of a very short time, the solution will have become quite clear, and fit for decantation, the carbonate 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 potash 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 potash, may be concentrated by quick evaporation in the iron or silver vessel to any desired extent; when heated until vapor of water ceases to be disengaged, and then suffered to cool, it furnishes the solid hydrate, containing single equivalents of potash and water. Pure hydrate of potash 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 color to litmus which has been reddened by an acid ; neutralizes completely the most powerful acids ; has a nauseous and peculiar taste, and dissolves the skin, and many other organic matters, when the latter are subjected to its action. It is constantly used by surgeons as a cautery, being moulded into little sticks for that purpose. Hydrate of potash, both in the solid state and in solution, rapidly absorbs carbonic acid from the air ; hence it must be kept in closely stopped bottles. When imperfectly prepared, or partially altered by exposure, it effervesces with an acid. The water in this compound cannot be displaced by heat, the hydrate volatilizing as a whole at a very high temperature. The following table of the densities and value in real alkali of different solutions of hydrate of potash is given on the authority of Dr. Dalton. * It would be an advantage to the young student to adopt the terra potassa instead of potash for the protoxide of potassium. The word potash or potashes is applied commercially to the impurest form of carbonate of potassa, and hence arises some confusion in the mind of the beginner, which if not quickly cleared up, leads to error. For until he has firmly fixed in his mind, the distinctions between bases and salts, and that acids unite with bases only, he may conceive that the name of nitrate or any other salt of potassa, might mean, if called nitrate of potash, a combination of the acid with the potash of commerce. In addition it would promote the uniformity of chemical language, its last syllable being similar to that in soda, &c. R. B. POTASSIUM. 215 Density. Percentage of real alkali. Density. Percentage of real alkali. 1 68 . 51.2 .33 . 26.3 1.60 .... 46.7 .28 234 1.52 . 42.9 .23 . 19.5 1.47 . 39.6 .19 . 16.2 1.44 . 36.8 .15 . 13.0 1.42 . 34.4 1.11 . 9.5 1.39 . 32.4 1.06 . 4.7 1.36 . 29.4 PEROXIDE OF POTASSIUM, K0 3 . 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 potash 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 potash, which unites with the latter, and into oxygen gas. CARBONATE OF POTASH (or OF POTASSA), KO , C0 2 -J-2HO. Salts of potash, containing a vegetable acid, are of constant occurrence in plants, where they perform important, but little understood, functions in the economy of those beings. The potash 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 potash left in the state of carbonate. It is by these indirect means that carbonate, and, in fact, nearly all the salts of potash, 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 diffi- culties 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 favorable to its sub- sequent applications. Potash-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 j 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 commerce, of which very large quantities are obtained from Russia and America. This salt is very impure; it contains silicate and sulphate of potash, chloride of potassium, &c. The purified carbonate of potash 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 potash), and separating the carbonate by solution in water and crystallization, or evaporation to dryness. 216 POTASSIUM. Carbonate of potash is extremely deliquescent, and soluble in less than its own weight of water ; the solution is highly alkaline to test-paper. It is in- soluble 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 POTASH (or OF POTASSA), KO,CO a + HO,CO a . When a stream of carbonic acid gas is passed through a cold solution of carbonate of potash, the gas is rapidly absorbed, and a white, crystalline, and less soluble substance separated, which is the new compound. It is collected, pressed, re-dissolved in warm water, and the solution left to crystallize. Bicarbonate of potash is much less 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. A sesqui-carbonate of potash is also said to exist. NITRATE OF POTASH (or OF POTASSA) ; NITRE; SALTPETRE, KO,NO 5 . This important compound is a natural product, being disengaged by a kind of efflo- rescence from the surface of the soil in certain dry and hot countries. It may also be produced by artificial means, namely, by the oxidation of ammonia in presence of a powerful base. In France, large quantities of artificial nitre are prepared by mixing ani- mal refuse of .all kinds with old mortar or hydrate of lime and earth, and placing the mixture in heaps, protected from the rain by a roof, but freely exposed to the air. From time to time the heaps are watered with putrid urine, and the mass turned over, to expose fresh surfaces to the air. When much salt has been formed, the mixture is lixiviated, and the solution, which contains nitrate of lime, mixed with carbonate of potash ; 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 crys- tallization several times repeated. All the nitre used in this country comes from the East Indies ; it is dis- solved in water, a little carbonate of potash added to precipitate lime, and then the salt purified as above. Nitrate of potash crystallizes in anhydrous six-sided prisms, with dihedral summits; it is soluble in 7 parts of water at 60, and in its own weight of boiling water. Its taste is saline and cooling, and it is without action on vegetable colors. At a temperature below redness it melts, and by a strong heat is completely decomposed. When thrown on the surface of many metals in a state of fusion, or when mixed with combustible matter and heated, rapifl 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. Gurtpowder is made by very intimately mixing together nitrate of potash, charcoal and sulphur, in proportions which approach 1 equiv. 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 : *Dr. M'Culloch, Ency. Brit. POTASSIUM. 217 Theory. Proportions fn practice. Nitrate of potash 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 alder, are also finely ground, after which the materials are weighed out, moistened with water, and thoroughly mixed, by grinding under an edge-mill. The mass is then subjected to great pressure, and the mill-cake thus produced broken in pieces, and placed in sieves made of perforated vellum, moved by machinery, each containing, in addition, a round piece of heavy wood. The grains of pow- der broken off by attrition fall through the holes in the skin, and are easily separated from the dust by sifting. The powder is, lastly, dried by exposure to steam-heat, and sometimes glazed or polished by agitation in a kind of cask mounted on an axis. When gunpowder is fired, the oxygen of the nitrate of potash is transfer- red to the carbon, forming carbonic oxide; the sulphur combines with the potassium, and the nitrogen is set free. The large volume of gas thus pro- duced, and still further expanded by the very exalted temperature, sufficiently accounts for the explosive effects. SULPHATE OF POTASH (or OF POTASSA), KO,SO 3 . The acid residue left in the retort when nitric acid is prepared is dissolved in water, arid neutralized with crude carbonate of potash. 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 potash 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 appear- ance ; 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 POTASH (or OF POTASSA), KO,SO 3 -f-HO,S0 3 . The neutral sulphate in powder is mixed with half its weight of oil of vitriol, and the whole evaporated quite to dryness in a platinum vessel, placed under a chim- ney ; the fused salt is dissolved in hot water, and left to crystallize. The crystals have the figure of flattened rhombic prisms, and are much more so- luble than the neutral salt, requiring only twice their weight of water at 60, and less than half that quantity at 212. The solution has a sour taste and strong acid reaction. BistripHATE OF POTASH (or OF POTASSA), ANHYDROUS, KO,2S0 3 . Equal weights of neutral sulphate of potash and oil of vitriol are dissolved in a small quantity of warm distilled water, and set aside to cool. The anhy- drous sulphate crystallizes out in long delicate needles, which if left several days in the mother-liquor disappear, and give place to crystals of the ordinary hydrated bisulphate above described. This salt is decomposed by a large quantity pf water.* SESQ.UISULPHATE OF POTASH (or OF POTASSA), 2KO,S0 3 +HO,S0 3 . A salt, crystallizing in fine needles resembling those of asbestus, and having the com- * Jacquelain, Ann. Chem. et Phys. vol. vii. p. 311. 19 218 POTASSIUM. position stated, was obtained by Mr. Phillips from the nitric acid residue. M. Jacquelain was unsuccessful in his attempts to reproduce this compound. CHLORATE OF POTASH (or OF POTASSA), KO,Cl0 5 . The theory of the pro- duction of chloric acid, by the action of chlorine gas on a solution of caustic potash, has been already described (p. 142). Chlorine gas is conducted by a wide tube into a strong and warm solution of carbonate of potash, 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 potassium. It may be purified by one or two re-crystallizations. Chlorate of potash is soluble in about 20 parts of cold, and 2 of boiling water; the crystals are anhydrous, flat, and tabular; in taste it somewhat re- sembles nitre. Heated, it disengages oxygen gas from both acid and base, and leaves chloride of potassium. By arresting the decomposition when the evolution of gas begins, and re-dissolving the salt, hyperchlorate of potash 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 explodes with a loud report; hence it cannot be used in the preparation of gunpowder instead of nitrate of potash. Chlorate of potash is now a large article of com- merce, being employed, together with phosphorus, in making instantaneous light matches. HYPERCHLORATE OF POTASH (or of POTASSA), KO,Cl0 7 . This has been already noticed under the head of hyperchloric acid. It is best prepared by projecting powdered chlorate of potash into warm nitric acid, when the chloric acid is resolved into hyperchloric acid, chlorine, and oxygen gases. The salt is separated by crystallization from the nitrate. Hyperchlorate of potash 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 potash. STTLPHURETS OF POTASSIUM. Three distinct compounds of potassium and sulphur are described, containing KS, KS 3 , and KS 5 . Simple or monosulphuret of potassium, is formed by directly combining the metal with sulphur, or by reducing sulphate of potash at a red-heat by hydro- gen or charcoal powder. Another method is to take a strong solution of hy- drate of potash, 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 monosulphuret is a crystalline cinnabar-red mass, very soluble in water The solution has an exceedingly offensive 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 sulphurets of hydrogen, carbon, arsenic, &c., forming crystallizable saline compounds. One of these, KS -j- HS, is produced when hydrate of potash is saturated with sulphuretted hydrogen, as before men- tioned. The higher sulphurets are obtained by fusing the monosulphuret 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 POTASSIUM. 219 potash and sulphur. It is a variable mixture of the two higher sulphurets with hyposulphite and sulphate of potash. When equal parts of sulphur and dry carbonate of potash are melted together at a temperature not exceeding 482 F., 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 color, and the solution is found to contain nothing besides pentasulphuret of potassium and hyposulphite of potash. ( 2 eq. potassium_ ^ 2. eq. pentasulphuret of 3 eq. potash < 2 eq. oxygen^ ^^^"^ potassium. ( 1 eq. potash Zr> sulphate of potash. From both these mixtures the pentasulphuret of potassium maybe extracted by alcohol, in which it dissolves. When the carbonate is fused with half its weight of sulphur only, then the ter- or trito-sulphuret, KS 3 , is produced instead of that above indicated; 3 eq. of potash and 8 eq. of sulphur containing the elements of 2 eq. trito-sulphuret and 1 eq. hyposulphite. The effects described happen in the same manner when hydrate of potash is substituted for the carbonate; and also, when a solution of the hydrate is boiled with sulphur, a mixture of sulphuret and hyposulphite always results.* CHLORIDE OF POTASSIUM, KCl. This salt is obtained in large quantity in the manufacture of chlorate of potash ; 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, assum- ing like that substance the cubic form of crystallization. The crystals dissolve in three parts of cold, and in a much less quantity of boiling water; they are anhydrous, have a simple saline taste, with slight bitterness, and fuse when exposed to a red heat. Chloride of potassium is volatilized by a very high temperature. IODIDE OF POTASSIUM. KI. There are two different methods of preparing this important medicinal compound. (1.) When iodine is added to a strong solution of caustic potash free from carbonate, it is dissolved in large quantity, forming a colorless solution con- taining iodide of potassium and iodate of potash ; the reaction is the same as in the analogous case with chlorine. When the solution begins to be perma- nently colored by the iodine, it is evaporated to dryness, and cautiously heated red-hot; by which, the iodate of potash is entirely converted into * Mitscherlich, Lehrbuch der Chemie, ii. 47. 220 SODIUM. iodide of potassium. The mass is then dissolved in water, and after filtration, 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 colorless. The resulting iodide of iron or zinc is then filtered, and exactly decomposed with solution of pure carbonate of potash, 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 ne - ^ Iodide of ?< Carbonate of > Potash 3 Oxy^n Carbonic acid ^""""^ Carbonate of protoxide of iron. The second method is on the whole to be preferred. Iodide of potassium crystallizes in cubes, which are often, from some un- explained cause, milk-white and opaque ; they are anhydrous, and fuse rea- dily when heated. The salt is very soluble in water, but not deliquescent, when pure, in a moderately dry atmosphere ; it is dissolved by alcohol. Solution of iodide of potassium, like those of all the soluble iodides, dissolve a large quantity of free iodine, forming a deep-brown liquid, not decomposed by water. BROMIDE or POTASSIUM, KBr. This compound may be obtained by pro- cesses exactly similar to those just described, substituting bromine for the iodine. It is a colorless and very soluble salt, quite indistinguishable in ap- pearance and general characters from the iodide. The salts of potash are colorless, when not associated with a colored metal- lic oxide or acid. They are all more or less soluble in water, and may be distinguished by the following characters: (1.) Solution of tartaric acid added to a moderately strong solution of a pot- ash salt, gives after some time a white, crystalline precipitate of cream of tartar ; the effect is greatly promoted by strong agitation. (2.) Solution of chloride of platinum, with a little hydrochloric acid if neces- sary, gives, under similar circumstances, a crystalline yellow precipitate, which is a double salt of chloride of platinum and chloride of potassium. Both this compound and cream of tartar are, however, soluble in about sixty 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 precipitates, when added to a potash-salt. (4.) Salts of potash usually color the outer blowpipe flame purple or violet. This metal was obtained by Davy very shortly after the discovery of potas- sium, and by similar means. It may be prepared in large quantity by decom- posing 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 char- coal in lumps. The whole is then evaporated to dryness, transferred to the iron retort before described, and heated in the same manner to whiteness. A SODIUM. 221 receiver containingjrock-oil is adapted to the tube, and the whole operation carried on hi the same way as when potassium is made. The process, when well conducted, is said to be easy and certain. Sodium is a silver-white metal, greatly resembling potassium in every respect; it is soft at common temperatures, melts at 194, and oxidizes very rapidly in the air. Its specific gravity is .972. Placed upon the surface 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 cool- ing diminished, by adding gum or starch to the water. With hot water it takes fires at once, burning with a bright yellow flame, and giving rise to a solution of soda. The equivalent of sodium is 23'27, and its symbol (Natrium) Na. There are two well-defined compounds of sodium and oxygen ; the prot- oxide, anhydrous soda, NaO, and the peroxide, NaO 2 ,or perhaps, Na0 3 ; they are formed by burning sodium in air or oxygen gas, arid resemble in every respect the corresponding compounds of potassium. HYDRATE OF SODA, NaO, HO. This substance is prepared in practice by 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 potash, and the precautions necessary, apply word for word to that of soda. The solid hydrate is a white, fusible substance, very similar in properties to hydrate of potash. It is deliquescent, but dries up again after a time in consequence of the absorption of carbonic acid. The solution is highly alka- line, and a powerful solvent for animal matter ; it is used in large quantity for making soap. . The strength of a solution of caustic soda may be roughly determined from a knowledge of its density, by the aid of the following table drawn up by Dr. Dalton. Density. 2.00 . 1.85 . 1.72 . 1.63 . 1.55 . 1.50 . 1.47 . 1.44 . CARBONATE OF SODA, NaO,C0 2 -}-l OHO. Carbonate of soda was once ex- clusively obtained from the ashes of sea-weeds, and of plants, such as the Salsola soda, which grew by the sea-side, or, being cultivated in suitable loca- lities for the purpose, were afterwards subjected to incineration. The barilla yet employed in soap-making is thus produced in several places on the coast of Spain, as Alicant, Carthagena, &c. That made in Brittany is called varec. Carbonate of soda is now manufactured on a stupendous scale from com- mon salt, or rather from sulphate of soda, by a process of which the follow- ing is an outline: A charge of 600 Ib. of common salt* is placed upon the hearth of a well- heated reverberatory furnace, and an equal weight of sulphuric acid of sp. gr. 1.6 poured upon it through an opening in the roof, and thoroughly mirx- * Graham, Elements, p. 333. 19* TABLE OF DENSITY. Percentage of real soda. Density. Percentage of real soda. . 77.8 1.40 . . . . 29.0 . 63.6 1.36 . . 26.0 . 53.8 1.32 . . - . . 23.0 . 46.6 1.29 . 19.0 . 41.2 1.23 . . 16.0 . 36.8 1.18 . . 13.0 . 34.0 1.12 . . 9.0 . 31.0 1.06 , . 4.7 222 SODIUM. gled with the salt; hydrochloric acid gas is disengaged, which is usually allowed to escape by the chimney, and the salt is converftd into sulphate of soda. This part of the process takes for completion about four hours, and re- quires much care and skill. The sulphate is next reduced to powder, and mixed with an equal weight of chalk or limestone, and half as much small coal, both ground or crushed. The mixture is thrown into a reverberatory furnace, and heated to fusion, with constant stirring; 2 cwt. is about the quantity operated on at once. When the decomposition is judged complete, the melted matter is raked from the furnace into an iron trough, where it is allowed to cool. When cold, it is broken up into little pieces, and lixiviated with cold or tepid water. The solution is evaporated to dry ness, and the salt calcined with a little saw-dust in a suitable furnace. The product is the soda-ash, or British alkali of com- merce, which, when of good quality, contains from 48 to 52 per cent, of pure soda, partly in the state of carbonate, and partly as hydrate, the remainder being chiefly sulphate of soda and common salt, with occasional traces of sulphite or hyposulphite, and also cyanide of sodium. By dissolving soda-ash in hot water, filtering the solution, and then allowing it to cool slowly, the carbonate is deposited in large transparent crystals. The reaction which takes place in the calcination of the sulphate with chalk and coal-dust seems to consist, first, in the conversion of the sulphate of soda into sulphuret of sodium by the aid of the combustible matter, and, secondly, in the double interchange of elements between that substance and the carbonate of lime. Sulphuret C Sulphur _^. Sulphuret of calcium. of sodium Sodium f~ c Calci Carbonate } Lime 1 Oxygen of lime Carbomc acid ^^ Carbonate of soda. The sulphuret of calcium combines with another proportion of lime to form a peculiar compound, which is insoluble in cold or slightly warm water. Other processes have been proposed, and even carried into execution, but the above is found most advantageous. The ordinary crystals of carbonate of soda contain 10 equivalents of water, but by particular management the same salt may be had with seven equivalents, or sometimes with only one, these differ in figure from the pre- ceding. The common form of the crystal is derived from an oblique rhombic prism ; they effloresce in dry air, and crumble to a white powder. Heated, they fuse in their water of crystallization ; when the latter has been expelled, and the dry salt exposed to a . full red heat, it melts without undergoing change. The common crystals dissolve in two parts of cold, and in less than their own weight of boiling water; the solution has a strong, disagreeable, alkaline taste, and a powerful alkaline reaction. BICARBONATE OF SODA, NaO,CO 2 -f-HO,C0 2 . This salt is prepared by pass- ing carbonic acid gas into a cold solution of the neutral carbonate, or by placing the crystals in an atmosphere of the gas, which is rapidly absorbed, while the crystals lose the greater part of their water, and pass into the new compound. Bicarbonate of soda, prepared by either process, is a crystalline white powder, which cannot be redissolved in warm water without partial decom- position. It requires 10 parts of water at 60 for solution ; the liquid is feebly alkaline to test-paper, and has a much milder taste than that of the SODIUM. 223 simple carbonate. It does not precipitate a solution of magnesia. By ex- posure to heat, the salt is converted into neutral carbonate. A sesquicarbonate of soda containing 2NaO,3CO a -f-4HO has been des- cribed by Mr. Phillips; like the sesquicarbonate of potash, it cannot be formed at pleasure. This salt occurs native on the banks of the soda-lakes of Sa- kena in Africa, whence it is exported under the name of trona. Alkalimetry ; Analysis of Hydrates and Carbonates of the Alkalis. The general principle of these operations consists in ascertaining the quantity of real alkali in a given weight of the substance examined, by finding how much of the latter is required to neutralize a known quantity of an acid, as sulphuric acid. The first step is the preparation of a stock of dilute sulphuric acid of de- terminate strength; containing, for example, 100 grains of real acid in every 1000 grain-measures of liquid:* a large quantity, as a gallon or more, maybe prepared at once by the following means. The oil of vitriol is first examined; if it be good and of the sp. gr. 1.85 or near it, the process is extremely sim- ple; every 49.09 grains of the liquid acid contains 40.09 grains of absolute acid; the quantity of the latter required in the gallon, or 70,000 grain- measures of dilute acid, will be of course 7000 grains. This is equivalent to 8571 grains of the oil of vitriol, for Real acid. Oil of vitriol. 40.09 : 49.09 : : 7000 : 8571. All that is required to be done, therefore, is to weigh out 8571 grains of oil of vitriol, and dilute it with so much water, that the mixture, when cold, shall measure exactly one gallon. It very often happens, however, that the oil of vitriol to be used is not so strong as that above mentioned ; in which case it is necessary to discover its real strength, as estimated from its saturating power. Pure anhydrous car- bonate of soda is prepared by heating to dull redness, without fusion, the bi- carbonate ; of this salt 53.27 grains, or 1 eq., correspond to 31.27 grains of soda, and neutralize 40.09 grains of real sulphuric acid. A convenient quantity is carefully weighed out, and added little by little to a known weight, say 100 grains, of the oil of vitriol to be tried, diluted with four or five times its weight of water, until the liquid, after warming, becomes quite neutral to test-paper. By weighing again the residue of the carbonate, it is at once known how much of the latter has been employed; the amount of real acid in the hundred parts of oil of vitriol is then easily calculated. Thus, suppose the quantity of carbonate of soda used to be 105 grains; then, Carb. soda. Sulph. acid. 53.27 : 40.09 : : 105 : 79; 79 grains of real acid are consequently contained in 100 grains of oil of vitriol ; consequently s 79 : 100 : : 7000 : 8861, the weight in grains of the oil of vitriol required to make one gallon of the dilute acid. The " alkalimeter" is next to be constructed. This is merely a 1000-grain * The capacity of 1000 grains of distilled water at 60. The grain measure of water is often found a very convenient and useful unit of volume in chemical re- searches. Vessels graduated on this plan bear simple comparison with the imperial llon and pint, and frequently also enable the operator to measure out a liquid of wn density instead of weighing it. gall Kno 224 SODIUM. measure, made of a piece of even, cylindrical glass tube, about 15 inches long and .6 inch internal diameter, closed at one extremity, and Fig. 146, moulded into a spout or lip at the other. A strip of paper is pasted on the tube and suffered to dry, after which the instrument is gra- duated by counterpoising it in a nearly upright position in the pan of a balance of moderate delicacy, and weighing into it in succes- sion, 160, 200, 300, &c., grains of distilled water at 60, until the whole quantity, amounting to 1000 grains, has been introduced, the level of the water in the tube being, after each addition, carefully marked with a pen upon the strip of paper, while the tube is held quite upright, and the mark made between the top and bottom of the curve formed by the surface of the water. The smaller divi- sions of the scale, of 10 grains each, may then be made by dividing by compasses each of the spaces into ten equal parts. When the graduation is complete, and the operator is satisfied with its accu- racy, the marks may be transferred to the tube itself by a sharp file, and the paper removed by a little -warm water. The numbers are scratched on the glass with the hard end of the same file. When this alkalimeter is used with the dilute acid described, every divi- sion of the glass will correspond to one grain of real sulphuric acid. Let it be required, by way of example, to test the commercial value of soda-ash, or to examine it for scientific purposes : 50 grains of the sample are weighed out, dissolved in a little warm water, and, if necessary, the solution filtered; the alkalimeter is then filled to the top of the scale with the test-acid, and the latter poured from it into the alkaline solution, which is tried from time to time with red litmus-paper. The addition of acid must of course be made very cautiously as neutralization advances. When the solution, after being heated a few minutes, no longer affects either blue or red test-paper, the measure of liquid employed is read off, and the quantity of soda present in the state of carbonate or hydrate in the 50 grains of salt found by the rule of proportion. Suppose 33 measures, consequently 33 grains of acid, have been taken ; then Sulph. acid. Soda. 40.09 : 31.27 : 33 : 25.G; the sample contains, therefore, 51.2 per cent, of available alkali. It will be easily seen that the principle of the process described admits of very wide application, and that, by the aid of the alkalimeter and carefully prepared test acid, the hydrates and carbonates of potash, soda, and ammonia, both in the solid state and in solution, can be examined with great ease and accuracy. The quantity of real alkali in a solution of caustic ammonia may thus be determined, the equivalent of that substance, and the amount of acid required to neutralize a known weight, being inserted as the second and third terms in the above Rule-of-three statement. The same acid answers for all. It is often desirable, in the analysis of carbonates, to determine directly the proportion of carbonic acid ; the following method leaves nothing to be desired in point of precision: A small, light glass flask of three or four ounces capacity, with lipped edge, is chosen, and a cork fitted to it. A piece of tube, about three inches long, is drawn out at one extremity, and fitted, by means of a small cork and a bit of bent tube, to the cork of the flask. This tube is filled with fragments of chloride of calcium, prevented from escaping by a little cotton at either end; the joints are secured by sealing-wax. A short tube, closed at one SODIUM. 225 extremity, and small enough to go into the flask, is also provided, and the apparatus is complete. Fifty grains of the carbonate to be examined are carefully weighed out and introduced into the flask, together with a little water; the small tube is then filled with oil of vitriol, and placed in the flask in a nearly upright position, and leaning against its side in such a manner that the acid does not escape. The cork and chloride of calcium tube are then adjusted, and the whole apparatus accurately counterpoised on the balance. This done, the flask is slight- ly inclined, so that the oil of vitriol may slowly mix with the other substances and decompose the carbonate, the gas from which escapes in a dry state from the extremity of the tube. When the action has entirely ceased the liquid is heated until it boils, and the steam begins to condense in the drying-tube; it is then left to cool, and weighed, when the loss indicates the quantity of carbonic acid. The acid must be in excess after the experiment. When carbonate of lime is thus analyzed, strong hydrochloric acid must be substituted for the oil of vitriol. SULPHATE OF SODA, GLAUBER SALT, NaO,SO 3 -f- 10HO. This is a by-pro- duct in several chemical operations ; it may of course be prepared directly, if wanted pure, by adding dilute sulphuric acid to saturation to a solution of carbonate of soda. It crystallizes in a figure derived from an oblique rhombic prism; the crystals contain 10 eq. of water, are efflorescent, and undergo watery fusion when heated, like those of the carbonate ; they are soluble in twice their weight of cold water, and rapidly increase in solubility as the temperature of the liquid rises to 91. 5 F., when a maximuni is reached, 100 parts of water dissolving 322 parts of the salt. Heated beyond this point, the solubility diminishes, and a portion of sulphate is deposited. A warm, saturated solution, evaporated at a high temperature, deposits opaque prismatic crystals, which are anhydrous. This salt has a slightly bitter taste, and is pur- gative. Mineral springs sometimes contain it, as at Cheltenham. Bi SULPHATE OF SODA, NaO,SO 3 + HO,SO 3 + 3HO. This is prepared by adding to 10 parts of anhydrous neutral sulphate, 7 of oil of vitriol, evaporating the whole to dryness, and gently igniting. The bisulphate is very soluble in water, and has an acid reaction. It is not deliquescent. When very strongly heated, the fused salt gives up anhydrous sulphuric acid, and becomes simple sulphate ; a change which necessarily supposes the previous formation of a true anhydrous bisulphate, NaO, 2SO 3 . HYPOSULPHITE OF SODA, NaO, S 2 O 2 . There are several modes of procuring this salt, which is now used in considerable quantity for photographic pur- poses. One of the best is to form neutral sulphite of soda, by passing a stream of well washed sulphurous acid gas into a strong solution of carbonate of soda, and then to digest the solution with sulphur, at a gentle heat during several days. By careful evaporation, at a moderate temperature, the salt is obtained in large and regular crystals, which are very soluble in water. NITRATE OF SODA; CUBIC NITRE, NaO,NO 5 . Nitrate of soda occurs native, and in enormous quantity, at Atacama in Peru, where it forms a regu- lar bed, of great extent, covered with clay and alluvial matter. The pure salt commonly crystallizes in rhombohedrons, resembling those of calcareous spar, but is probably dimorphous. It is deliquescent, and very soluble in water. Nitrate of soda is employed for making nitric acid, but cannot be used for gunpowder, as the mixture burns too slowly, and becomes damp in the air. It has been lately used with some success in agriculture as a super- ficial manure or top-dressing. PHOSPHATES OF SODA ; COMMON TRIBASIC PHOSPHATE 2NaO, HO, PO 5 -j- 226 SODIUM. k 24HO. This beautiful salt is prepared by precipitating the acid phosphate of lime obtained by decomposing bone-earth by sulphuric acid, with a slight excess of carbonate of soda. It crystallizes in oblique rhombic prisms, which are efflorescent. The crystals dissolve in 4 parts of cold water, and undergo the aqueous fusion when heated. The salt is bitter and purgative ; it's solu- tion is alkaline to test-paper. Crystals containing 14 equivalents of water, and having a form different from that above mentioned, have been obtained. A second tribasic phosphate, sometimes called sub-phosphate, 3NaO,PO 5 -|- 24HO, is obtained by adding solution of caustic soda to the preceding salt. The crystals are slender six-sided prisms, soluble in 5 parts of cold water. It is decomposed by acids, even carbonic, but suffers no change by heat, except the loss of its water of crystallization. Its solution is strongly alkaline. A third tribasic phosphate, often called super-phosphate or bi-phosphate. NaO, 2HO, P0 5 -j-2HO, may be obtained by adding phosphoric acid to the ordinary phosphate, until it ceases to precipitate chloride of barium, and exposing the concentrated solution to cold. The crystals are prismatic, very soluble, and have an acid reaction. When strongly heated, the salt becomes changed into monobasic phosphate of soda. Tribasic phosphate of soda, ammonia, and water; microcosmic salt, NaO, NH 4 O, HO, PO 5 -|-8HO. Six parts of common phosphate of soda are heated with 2 of water until the whole is liquefied, when 1 part of powdered sal- ammoniac is added ; common salt separates, and may be removed by a filter, and from the solution, duly concentrated, the new salt is deposited in pris- matic crystals, which' may be purified by one or two re-crystallizations. Mi- crocosmic salt is very soluble. When gently heated, it parts with the 8 eq. Of water of crystallization, and, at a higher temperature, that in the base is expelled, together with the ammonia, and a very fusible compound, metaphos- phate of soda, remains, which is valuable as a flux in blowpipe experiments. This salt is said to occur in the urine. *" BIBASIC PHOSPHATE OP SODA ; PIROPHOSPHATE OF SODA, 2NaO, PO.-j- 10HO. Prepared by strongly heating common phosphate of soda, dissolving the residue in water, and re-crystallizing. The crystals are very brilliant, permanent in the air, and less soluble than the original phosphate; their solution is alkaline. A bibasic phosphate, containing an equivalent of basic water, has been obtained; it does not, however, crystallize. MONOBASIC PHOSPHATE OF SODA ; MKTAPHOSPHATE OF SODA, NaO, P0 5 . Obtained by heating either the acid tribasic phosphate, or microcosmic salt, It is a transparent glassy substance, fusible at a dull red-heat, deliquescent, and very soluble in water. It refuses to crystallize, but dries up into a gum- like mass. The tribasic phosphates give a bright yellow precipitate with solution of nitrate of silver ; the bibasic and monobasic phosphates, afford white precipi- tates with the same substance. The salts of the two latter classes, fused with excess of carbonate of soda, yield the tribasic modification of the acid. BIBORATE OF SODA ; BORAX, NaO, 2B0 3 -f-10HO. This compound occurs in the waters of certain lakes in Thibet and Persia ; it is imported" in a crude state from the East Indies under the name of tincal. When purified it con- stitutes the borax of commerce. Much borax is now, however, manufactured from the native boracic acid, of Tuscany. Borax crystallizes in six-sided prisms, which effloresce in dry air, and require 20 parts of cold, and 6 of boiling water for solution. Exposed to heat, the 10 eq. of water of crystalli- zation are expelled, and at a higher temperature the salt fuses, and assumes a glassy appearance on cooling ; in this state it is much used for blowpipe experiments. By particular management, crystals of borax can be obtained with 5 eq. of water; they are very hard, and permanent in the air. Although AMMONIUM. 227 by constitution an acid salt, borax has an alkaline reaction to test-paper. It is used in the arts in soldering metals, and sometimes enters into the composi- tion of the glaze with which stone-ware is covered. Neutral borate of soda may be formed by fusing together borax and car- bonate of soda in equivalent proportions, and then dissolving the mass in water. The crystals are large, and contain NaO, B0 3 -f-8HO. SULPHURET OF SODIUM, NaS. Prepared in the same manner as the mono- sulphnret of potassium ; it separates from a concentrated solution in octahe- dral crystals, which are rapidly decomposed by contact of air into a mixture of hydrate and hyposulphite of soda. It forms double sulphur-salts with sul- phuretted hydrogen, bisulphuret of carbon, and other sulphur-acids. Sulphuret of sodium is supposed to enter into the composition of the beauti- ful pigment ultramarine, prepared from the lapis lazuli, and which is now imitated by artificial means.* CHLORIDE OF SODIUM; COMMON SALT, NaCl. This very important sub- stance is found in many parts of the world in solid beds or irregular strata of immense thickness, as in Cheshire, for example, in Spain, Poland, 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 separates, it is removed from the bottom of the vessels by means of a scoop, pressed while still moist into moulds, and then transferred to the drying-stove. When large crystals are required, as for the coarse grained bay-salt used in curing provisions, the evaporation is slowly conducted. Common salt is apt to be contaminated with chloride of magnesium. When pure, this substance is not deliquescent in moderately dry air. It crystallizes in anhydrous cubes, which are often grouped together into pyra- mids, or steps. It requires about 2^ parts of water at 60 for solution, and its solubility is not sensibly increased by heat; in alcohol it is insoluble. Chloride of sodium fuses at a red heat, and is volatile at a still higher tem- perature. The economical uses of common salt are well known. "j" 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 precipitant for soda, all the salts being soluble; its presence is often determined by purely negative evidence. The yellow color 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 witli those of potash 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 * See Ph;irmacentirnl Journal, ii. 53. j For Chloride of Soda, see Chloride of Lime. I Antimoniate of potassa yields an insoluble white precipitate when added to salta of soda, forming antimoniate of soda. R. B. 228 AMMONIUM. ammonium, capable of playing the part of a metal, and isomorphous 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 pot- ash, and connected with the negative side of a voltaic battery of very mode- rate 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 potash, a soft-solid, metalline mass is also produced, which has been called the ammoniacal amalgam, and considered to contain ammonium in combination with mercury. A still simpler method of preparing this extra- ordinary compound is the following : A little mercury is put into a test-tube with a grain or two of potassium or sodium, and heat applied ; 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 pro- duction of ammoniacal amalgam instantly commences, the mercury increases prodigiously in volume, and becomes quite pasty. The increase of weight is, however, quite trifling: it varies from yg'jj^h. to jj-J^^th part. Left to itself, the amalgam quickly decomposes into fluid mercury, am- monia and hydrogen. It is difficult to offer any opinion concerning the real nature of this com- pound 5 something analogous occurs when pure silver is exposed to a very high temperature, much above its melting-point, in contact with air or oxygen gas; the latter is absorbed in very large quantity, amounting, according to the observation of Gay-Lussac, to 20 times the volume of the silver, and is again disengaged on reduction of the heat. The metal loses none of its lustre, and is not sensibly altered in other respects. The great argument in favor 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 18.06 ; its symbol is NH 4 . CHLORIDE OF AMMONIUM (MURIATE or AMMONIA) ; SAL-AMMONIAC, NH 4 Cl. Sal-ammoniac was formerly obtained from Egypt, being extracted by subli- mation from the soot of camel's 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 free alkali is neutralized, and the carbonate and sulphuret 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 subli- mation 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 favorable circumstances, in distinct cubes or octahedrons; but the crystals are usually small, and aggre- gated together in rays. It has a sharp saline taste, and is soluble in 2f parts of cold, in a much smaller quantity of hot water. By heat, it is sublimed without decomposition. The crystals are anhydrous. SULPHATE OF OXIDE OF AMMONIUM; SULPHATE OF AMMONIA, NH 4 O, SO 3 -|- HO. Prepared by neutralizing carbonate of ammonia by sulphuric acid, or on a large scale, by adding sulphuric acid in excess to the coal gas liquor just mentioned, and purifying the product by suitable means. It is soluble in 2 AMMONIUM. 229 parts of cold water, and crystallizes in long, flattened, six-sided prisms, which lose an equivalent of water when heated. It is entirely decomposed, and driven off by ignition, and, even to a certain extent, by long boiling with water, ammonia being expelled and the liquid rendered acid. CARBONATES OF AMMONIA. These compounds have been carefully ex- amined by Professor Rose, of Berlin,* and appear very numerous. The neu- tral, anhydrous carbonate, NH 3 ,CO, 2 is prepared by the direct union of carbonic acid with ammoniacal gas, both being carefully cooled. The gases combine in the proportions of one measure of the first to two of the second, and give rise to a pungent, and very volatile compound, which condenses in white flocks. It is very soluble in water. The pungent, transparent, carbonate of ammonia of pharmacy which is prepared by subliming a mixture of sal- ammoniac and chalk, always contains less base than that required to form a neutral carbonate. Its composition varies a good deal, but in freshly-prepared specimens approaches that of a sesquicarbonate of oxide of ammonium, 2NH 4 O, 3C0 2 . When heated in a retort, the neck of which dips into mercury, it is decomposed, with disengagement of pure carbonic acid, into neutral hydrated carbonate of ammonia, and several other compounds. Exposed to the air at common temperatures, it disengages neutral carbonate of ammonia, loses its pungency, and crumbles down.to a soft, white powder, which is a bicarbonate containing NH 4 O,C0 2 -|-HO,C0 2 . This is a permanent combination, although still volatile. When a strong solution of the commercial sesquicarbonate is made with tepid water, and filtered, warm, into a close vessel, large and regular crystals of bicarbonate, haying the above composition, 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 potash. NITRATE OF OXIDE OF AMMONIUM ; NITRATE OF AMMONIA, NH 4 0,N0 5 . Easily prepared by adding carbonate of ammonia to slightly diluted nitric acid until neutralization has been reached. By slow evaporation at a mode- rate temperature it crystallizes in six-sided prisms, like those of nitrate of potash ; but, as usually prepared for making nitrous oxide, by quick boiling, until a portion solidifies completely on cooling, it forms a fibrous and indis- tinctly crystalline mass. Nitrate of ammonia dissolves in 2 parts of cold water, is but feebly de- liquescent, and deflagrates like nitre on contact with heated combustible matter. Its decomposition by heat has been already explained.^ SULPHURETS OF AMMONIUM. Several of these compounds exist, and may be formed by distilling with sal-ammoniac the corresponding sulphurets of potassium or sodium. The double sulphuret of ammonium and hydrogen, NH 4 S-|-HS, commonly called hydrosulphate or hydrosulphuret of ammonia, is a compound of great practical utility; it is obtained by saturating a solution of ammonia with well * Annalen der Pharmacie, xxx. 45. t P- 122 - PHOSPHATES OF OXIDE OP AMMONITJM; COMMON TRIBASIC PHOSPHATE, 2NH 4 O, HO,PO S +HO. This salt is formed by precipitating the acid phosphate of lime with an excess of carbonate of ammonia. The solution is allowed to evaporate spontaneously or by a gentle heat. In the latter case ammonia is lost and it becomes necessary to saturate the acid set free, previous to crystallization. It crystallizes in six-sided tables derived from oblique quadrangular prisms. Its crystals are efflorescent, soluble in alcohol, and soluble in four times its weight of cold water. Its solution has an al- kaline, slightly saline taste and alkaline reaction. By heat ammonia is disengaged. The acid tribasic phosphate, NH 4 O,2HO,PO S +4HO, is formed when a solution of the common phosphate is boiled as long as ammonia is given off. It crystallizes in four-sided prisms. Its crystals are permanent, soluble in 5 parts of cold water, acid in taste and reaction. Another tribasic phosphate, 3NH 4 O,PO f subphosphate is formed by adding ammo- nia to either of the above. It falls as a slightly soluble granular precipitate. R. B. 20 230 LITHIUM. washed sulphuretted hydrogen gas, until no more of the latter is absorbed. The solution is nearly colorless at first, but becomes yellow after a time, without, however, suffering material injury, unless it has been exposed to the air. It gives precipitates with most 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. 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 combinations formed not always easily decomposed by heat. The chlorides of copper and silver absorb, in this manner, large quantities of the gas. All these com- pounds must be carefully distinguished from the true ammoniacal salts con- taining ammonium or its oxide. There is supposed to be yet another compound of hydrogen and nitrogen to which the term amidogen has been given, and to which the properties of a salt-radical are ascribed. When potassium is heated in the vapor of water, this substance is decomposed, hydrogen is evolved, and the metal converted into oxide. When the same experiment is made with dry ammoniacal gas, hydrogen is also set free, and an olive-green crystalline compound produced, supposed to contain potassium in union with a new body, NH 2 , having an equivalent of hydrogen less than ammonia. When ammonia is added to a solution of corrosive sublimate, a white pre- cipitate is obtained, which has been long known in pharmacy. Sir R. Kane infers, from his experiments, that this substance should be looked upon as a compound of chloride of mercury with amide of mercury. The latter salt has not been obtained separately ; still less has amidogen itself been isolated. It is thought that ammonia may be considered an amide of hydrogen, ana- logous to water or oxide of hydrogen, capable of entering into combination with salts, and other substances, in a similar manner, yielding instable and easily-decomposed compounds, which offer a great contrast to those of the energetic ^wasi-metal ammonia. The ammoniacal salts are easily recognized ; 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 odor 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 potash 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 LITHIUM. 231 lithia, and then decomposing the amalgam by distillation. It is a white metal like sodium, and very oxidable. The equivalent of lithium is 6.43, 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 following pro- cess: 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 dry ness, acidu- lated 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 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 their quan- tities determined. The hydrate of lithia is much less soluble in water than those of potash and soda; the carbonate and phosphate are also sparingly soluble salts. The chloride crystallizes in anhydrous cubes which are deliquescent. Sulphate of lithia is a very beautiful salt; it crystallizes in lengthened prisms, contain- ing one equivalent of water. The salts of lithia color the outer flame of the blowpipe carmine-red. 232 BARIUM. 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 vapor of potassium is conveyed. The reduced barium is extracted by quicksilver, and the amalgam distilled in a small green glass retort. Barium is a white metal, having the color and lustre of silver; it is mallea- ble, melts below a red heat, decomposes water, and gradually oxidizes in the air. The equivalent of this metal has been fixed at 68.55 ; its symbol is Ba. PROTOXIDE OF BARIUM ; BARYTA, BaO. Baryta,* or barytes, occurs in na- ture in considerable abundance as carbonate and sulphate, forming the vein- stone 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 crys- tallized nitrate by heat in a capacious crucible of porcelain until red vapors are no longer disengaged; the nitric acid is resolved into nitrous acid and oxygen, and the baryta remains behind in the form of a grayish 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 two of boiling water; a hot satu- rated solution deposits crystals on cooling, which contain BaO, HO-|-9HO. Solution of hydrate of baryta is a valuable reagent ; it is highly alkaline to test-paper, and instantly rendered turbid by .the smallest trace of carbonic acid. PEROXIDE OF BARIUM, BaO 2 . 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 peroxide is gray, and forms a white hydrate with water, which is not decomposed by that liquid in the cold, but dissolves in small quantity. The peroxide may also be made by heating pure baryta to redness in a platinum crucible, and then gradually adding an equal weight of chlorate of potash ; peroxide of barium and chloride of potassium are pro- duced. The latter may be extracted by cold water, and the peroxide left in the state of hydrate. It is interesting chiefly in its relation to peroxide of hydrogen. ^ CHLORIDE OF BARIUM, BaCl-{-2HO. This valuable salt is prepared by dis- solving the native carbonate in hydrochloric acid, filtering the solution, and evaporating until a skin begins to form at the surface; the solution on cooling # From <*gi;?, heavy, in allusion to the great specific gravity of the native carbon- ate and sulphate. BARIUM. 233 deposits crystals. When native carbonate cannot be procured, the native sul- phate may be employed in the following manner : The sulphate is reduced to fine powder, and intimately mixed with one-third of its weight of pow- dered coal ^ the mixture is pressed into an earthen crucible to which a cover is fitted, ami exposed for an hour or more to a high red heat, by which the sulphate is converted into sulphuret at the expense of the combustible matter of the coal. The black mass obtained is powdered and boiled in water, by which the sulphuret is dissolved; the solution is filtered hot, and mixed with a slight excess of hydrochloric acid ; chloride of barium and sulphuretted hydrogen are produced, the latter escaping with effervescence. Lastly, the solution is filtered to separate any little insoluble matter, and evaporated to the crystallizing point. The crystals of chloride of barium are flat, four-sided tables, colorlesss and transparent. They contain 2 equivalents of water, easily driven off by heat; 100 parts of water dissolve 43.5 parts at 60, and 78 parts at 220, which is the boiling-point of the saturated solution. NITRATE OF BARYTA, BaO , N0 6 . The nitrate is prepared by methods exactly similar to the above, nitric acid being substituted for the hydrochloric. It crystallizes in transparent colorless octahedrons, which are anhydrous. They require for solution 8 parts of cold, and 3 parts of boiling water. This salt is much less soluble in dilute nitric acid than in pure water ; errors some- times arise from such a precipitate of crystalline nitrate of baryta being mis- taken for sulphate. It disappears on heating, or by large effusion of water. SULPHATE of BARYTA; HEAVY-SPAR; BaO , SO 3 . Found native, often beautifully 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 principally for the purpose of adulterating white-lead; the native salt is ground to fine powder and washed with dilute sulphuric acid, by which its color 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. SULPHURET OF BARIUM, BaS. The protosulphuret of barium is obtained in the manner already described ; the higher sulphurets may be formed by boiling this compound with sulphur. Monosulphuret of barium crystallizes in thin and nearly colorless plates from a hot solution, which contain water, and are not very soluble ; they are rapidly altered by the air. A strong so- lution of sulphuret 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 lead black : the liquid being filtered, yields on cooling crystals of hydrate. In this reaction besides hy- drate of baryta, hyposulphite of that base, and subsulphuret 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,CO a . The natural carbonate is called Withcrite ; the artificial is formed by precipitating the chloride or nitrate with an alkaline carbonate, or carbonate of ammonia. It is a heavy white pow- der, very sparingly soluble in water, and chiefly useful in the preparation of the rarer barytic salts. Solutions of hydrate and nitrate of baryta and of chloride of barium are constantly kept in the laboratory as chemical tests, the first being employed 20* 234 STRONTIUM CALCIUM. to effect the separation of carbonic acid from certain gaseous mixtures, 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 in the air, and capable of decomposing water at common temperatures. The equivalent of strontium is 43.78, 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 hydrate soluble in water. A hot saturated solution deposits crystals on cooling, which contain 12 equivalents of water. The hydrate has a great attraction for car- bonic acid. PEROXIDE OF STRONTIUM, SrO a . The peroxide is prepared in the same manner as peroxide of barium ; it may be substituted for the latter in making peroxide 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 exactly 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 colorless 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 9 equivalents of water, which they lose by heat ; at a higher temperature the chloride fuses. NITRATE OF STRONTIUM, SrO, NO 5 . This salt crystallizes in anhydrous octahedrons, 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 oxidizable metal, obtained with great difficulty by means analogous to those by which barium and strontium are procured. The equivalent of calcium is 20 ; its symbol is Ca. PROTOXIDE OF CALCIUM; LIME; CaO. This extremely important com- pound may be obtained in a state of considerable purity by heating to full redness for some time fragments of the black bituminous marble of Derby- shire or Kilkenny. If required absolutely pure, it must be made by igniting to whiteness, in a platinum crucible, an artificial carbonate of lime, procured by precipitating the nitrate by carbonate of ammonia. Lime in an impure state is prepared for building and agricultural purposes by calcining in a kiln, * RED-FIRE : Grns . Dry nitrate of strontia . 800 Sulphur .... 225 Chlorate of potash . . 200 Lamp-black ... 50 GREEN-FIRE : Grns. Dry nitrate of baryta . 450 Sulphur .... 150 Chlorate of potash . . 100 Lamp-black ... 25 The strontia or baryta-salt, the sulphur, and the lamp-black must be finely powdered and intimately mixed, after which the chlorate of potash may be added in rather coarse powder and mixed without much rubbing with the other ingredients. The red-fire composition has been known to ignite spontaneously. CALCIUM. 235 of suitable construction, the ordinary limestones which abound in many dis- tricts; a red heat, continued for some hours, is sufficient to disengage the whole of the carbonic-acid. In the best contrived lime-kilns the process is carried on continuously, broken limestone and fuel being constantly thrown in at the top, and the burnt lime raked out at intervals from beneath. Some- times,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 infusible, and phosphoresces, or emits a pale light at a high temperature. When moistened with water, it slakes with great violence, evolving heat, and crumb- ling 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 quantity of the compound is taken up. A pint of water at 60 dissolves about 11 grains, while at 212 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 pharmaceu- tical 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 lime- stone may contain potash. The hardening of mortars and cements is in a great measure due to the gradual absorption of carbonic acid ; a very great length of time, however, usually elapses before this conversion into carbonate becomes complete. Mor- tar is known, under favorable circumstances, to acquire extreme hardness with age. Lime-cements which resist the action of water contain oxide of iron, silica, and alumina; they require to be carefully prepared, and the stone not overheated. When ground to powder and mixed with water, solidifica- tion speedily ensues, from causes not 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 probably serves to liberate potash from the insoluble silicate of that base contained in the soil. PEROXIDE OF CALCIUM, Ca0 2 . This is stated to resemble peroxide 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 suit separates from a strong solution in colorless, prismatic, and exceedingly 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 236 CALCIUM. which purpose the latter are slowly transmitted through tubes filled with frag- ments of the salt. Chloride of calcium is also freely soluble in alcohol, which, when anhydrous, forms with it a definite crystallizable compound. SULPHURETS OF CALCIUM. The simple sulphuret is obtained by reducing sulphate of lime, at a high temperature, by charcoal or hydrogen ; it is nearly colorless, 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 bisulphuret, which contain water. When the sulphur is in excess, and the boiling long continued, a pentasulphuret is generated ; hyposulphuric acid is, as usual, formed in these reactions. PHOSPHURET OF CALCIUM. When the vapor of phosphorus is passed over fragments of lime heated to redness in a porcelain tube, a chocolate-brown compound, the so-called phosphuret of lime, is produced. This substance is probably a combination of phosphuret of calcium and phosphate of lime. It yields spontaneously-inflammable phosphuretted hydrogen when put into water. SULPHATE OF LIME ; GYPSUM ; SELENITE ; CaO,S0 3 . Native sulphate of lime in a crystalline condition, containing 2 equivalents of water, is found in considerable abundance in some localities; it is often associated with rock-salt. When regularly crystallized, it is termed selenite. Anhydrous sulphate of lime is also occasionally met with. The salt is formed by precipitation when a moderately concentrated solution of chloride of calcium is mixed with sul- phuric acid. Sulphate of lime is soluble in about 500 parts of cold water, and its solubility is a little increased by heat; the solution is precipitated by alcohol. Gypsum, or native bydrated 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 other applications. It is ex- posed to heat in an oven where the temperature does not exceed 260, 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 colored marbles, or scagliola,are frequently prepared by inserting pieces of natural stone in a soft stucco containing this substance, and polishing the surface when the cement has become hard. Sulphate of lime is one of the most common impurities of spring water. CARBONATE OF LIME; CHALK; LIMESTOXE; MARBLE; CaO,CO a . Car- bonate of lime, often more or less contaminated by oxide 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 they have been subjected since their deposition. The most ancient and highly crystal- line limestones are destitute of visible organic remains, while those of more recent origin are often entirely made up of the shelly exuvise of once living beings. Sometimes these latter are of such a nature as to show that the animals inhabited fresh water; marine species and corals are, however, most abundant. Cavities in limestone and other rocks are very often lined with magnificent crystals of carbonate of lime or calcareous spar, which have evidently been slowly deposited from a watery solution. Carbonate 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, it is freely taken up when carbonic acid happens at the same time to be present. If a little lime-water be poured into a vessel of that gas, the turbidity first pro- duced disappears on agitation, and a transparent solution of carbonate of lime CALCIUM. 237 in excess of carbonic acid is obtained. This solution is decomposed com- pletely by boiling, the carbonic acid being expelled, and the carbonate pre- cipitated. Since all natural waters contain dissolved carbonic acid, it is to be expected that lime in this condition should be of very common occurrence ; and such is really found to be the fact, river, and more especially spring water, almost invariably containing carbonate of lime thus dissolved. In limestone districts, this is often the case to a great extent. Boilers in which such water is heated speedily become lined with a thick, stony incrustation, which is often a source of great inconvenience. The beautiful stalactitic incrustations of limestone caverns, and the deposits of calc-sinter or travertin upon various objects, and upon the ground in many places, are thus explained. Crystallized carbonate of lime exhibits the curious property of dimorphism ; calcareous spar and arragonite, although possessing the same chemical compo- sition, both containing single equivalents of lime and carbonic acid, and nothing besides, have different crystalline forms, different densities, and dif- ferent optical properties. The former occurs very abundantly in crystals derived from an obtuse rhombohedron, whose angles measure 105 5' and 74 55': its density varies from 2.5 to 2.8. The rarer variety, or arragonite, is found in crystals whose primary form is a right rhombic prism ; a figure having no geometrical rela- tion to the preceding ; it is, besides, heavier and harder. PHOSPHATES OF LIME. A number of distinct compounds of lime and phos- phoric acid probably exist. Two tribasic phosphates, 2CaO, HO,P0 5 , and 3CaO , P0 5 , are produced where 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 reprecipitated by that alkali, it is converted into the second. The earth of bones consists principally of what appears to be a combination 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 evapo- rating until the salt separates on cooling in small platy crystals. It is this substance which yields phosphorus, when heated with charcoal, in the ordi- nary process of manufacture, before described. Bibasic and monobasic phos- phates of lime also exist. These phosphates, although insoluble in water, dis- solve readily in dilute acids, even acetic acid. FLUORIDE OF CALCIUM ; FLUOR-SPAR ; CaF. This substance is important as the most abundant natural source of hydrofluoric acid and the other fluorides. It occurs beautifully crystallized, in various colors, 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 varieties, 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 men- tioned.* CHLORIDE OF LIME; BLEACHING POWDER. When hydrate of lime, very slightly moist, is exposed to chlorine gas, the latter is eagerly absorbed, and a compound produced which has attracted a great deal of attention ; this is the bleaching powder of commerce, now manufactured on an immense scale, for bleaching linen and cotton goods. It is requisite, in preparing this substance, to avoid with the greatest care all elevation of temperature, which may be easily done by slowly supplying the chlorine in the first instance. The pro- * Fluoride of calcium exists in the enamel of the teeth, and is also a constituent of fossil bones, and very probably of recent bone, the presence of organic matter render- ing its detection difficult. R. B. 238 CALCIUM. duct, when freshly and well prepared, is a soft, white powder, which attracts moisture from the air, and exhales an odor sensibly different from that of chlorine. It is soluble in about 10 parts of water, merely 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 car- bonated, may by similar means be made to absorb a large quantity of chlo- rine, and give rise to corresponding compounds ; such are the " disinfecting 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 obtained from good bleaching powder, by distilling it with dilute sulphuric or nitric acid, in quantity insufficient to decompose the whole; when the acid is used in excess, chlorine is disengaged.* If this view be correct, chloride of calcium must be formed simultaneously with the hypochlorite, as in the following diagram : Chlorine- =~ Chloride of calcium. Chlorine Lime -~>-.Hypochlorite of lime. When the temperature of the hydrate of lime has risen during the absorp- tion 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- tity, is usually set free. The same change seems to ensue by long keeping, even at the common temperature of the air. In an open vessel it is speedily destroyed by the carbonic acid of the atmosphere. Commercial bleach ing- powder thus constantly varies in value with its age, and with the care origin- ally 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 ; the chlorine or hypochlorous acid thus disengaged in contact with the cloth, causes the destruction of the coloring matter. This process is often repeated, it being unsafe to use strong solutions. White patterns are on this principle imprinted upon colored cloth, the figures being stamped with tartaric acid thickened with gum-water, and then the stuff immersed in the chloride bath, when the parts to which no acid has been applied remain unaltered, while the printed portions are bleached. For purifying an offensive or infectious atmosphere, as an aid toproper ven~ illation, 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 the chloride. An addition of a strong acid causes rapid disengagement of chlorine. The value of any sample of bleachirig-powder may be easily determined * M. Gay-Lussac, Ann. Chim. et Phys. 3d series, v. 296. MAGNESIUM. 239 by the following method, in which the loosely-combined chlorine is estimated by its effect in peroxidizing a proto-salt of iron, of which two equivalents require one of chlorine ; the latter acts by decomposing water and liberating a corresponding quantity of oxygen 78 grains of green sulphate of iron are dissolved in about two ounces of water and acidulated by a few drops of sul- phuric or hydrochloric acid ; this quantity will require for peroxidation ex- actly 10 grains of chlorine. Fifty grains of the chloride of lime to be exam- ined are next rubbed up with a little tepid water, and the whole transferred to the alkalimeter before described, which is then rilled 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 lat- ter has become peroxidized, which may be known by a drop ceasing to give a deep blue precipitate with red ferrocyanide of potassium. The number of grain measures of the chloride solution employed may then be read off, and since these must contain 10 grains of serviceable chlorine, the quantity of the latter in the 50 grains may be easily reckoned. Thus, suppose 72 such mea- sures 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 potash, when free from carbonate, and caustic ammonia, occasion no precipitates in dilute solutions of the earths, especially of the first two, the hydrates being soluble in water. Alkaline carbonates, and carbonate of ammonia, give white precipitates, insoluble in excess of the precipitant, with all three. Sulphuric acid, or a sulphate, added to very dilute solutions of the earths in question, gives an immediate white precipitate with baryta, a similar pre- cipitate after a short interval with strontia, and occasions no change with the lime-salt. The precipitates with baryta and strontia are quite insoluble in nitric acid. Solution of sulphate of lime gives an instantaneous cloud with baryta, and one with strontia after a little time. Sulphate of strontia is itself sufficiently soluble to occasion turbidity when mixed with chloride of barium. Lastly, the soluble oxalates give a white precipitate in the most dilute solu- tions of lime, which is not dissolved by a drop or two of hydrochloric acid. This is an exceedingly characteristic test. The chlorides of strontium and calcium dissolved in alcohol color the flame of the latter red or purple ; salts of baryta communicate to v 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. * Graham's Elements, p. 353. 240 MAGNESIUM. Magnesium is a white, malleable metal, fusible at a red-heat, and not sensibly acted upon by cold 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 12.67, and its symbol Mg. MAGNESIA ; CALCINED MAGNESIA ; MgO. This is prepared with great ease by exposing the magnesia alba of pharmacy to a full red-heat in an earthen or platinum crucible. It forms a soft, white powder, which slowly attracts moisture and carbonic acid from the air, and unites quietly with water to a hydrate which possesses a feeble degree of solubility, requiring about 5,000 parts of water at 60, and 36.000 parts at 212. The alkalinity of magnesia can only be observed by placing a small portion in a moistened state upon test-paper; it neutralizes acids, however, in the most complete manner. It is infusible. CHLORIDE OF MAGNESIUM:, MgCl. When magnesia, or its carbonate, is dis- solved in hydrochloric acid, there can be no doubt respecting the simultaneous production of chloride of magnesium and water; but when this solution comes to be evaporated to dryness, the last portions of water are retained with such obstinacy, that decomposition of the water is brought about by the concurring attractions of magnesium for oxygen, and of chlorine for hydro- gen; 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 por- tions, to neutralize one with magnesia, and the other with ammonia, or car- bonate of ammonia; to mix these solutions, evaporate them to dryness, and then expose the salt to a red-heat in a loosely-covered porcelain crucible. Sal-ammoniac sublimes, and 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 and highly soluble in water, from which it cannot again be recovered by evaporation, for the reasons just mentioned. When long exposed to the air in a melted state, it is converted into magnesia. It is soluble in alcohol. SULPHATE OF MAGNESIA ; EPSOM SALT ; MgO,SO 3 -f-7HO. This salt occurs in sea-water, and in that of many mineral springs, and is now manufactured in large quantities by acting on magnesian lime-stone by diluted sulphuric acid, and separating the sulphate of magnesia from the greater part of the slightly soluble sulphate of lime by the filter. The crystals are derived from a right rhombic prism ; they are soluble in an equal weight of water at 60, and in a still smaller quantity at 212. The salt has a nauseous bitter taste, and like many other neutral salts, purgative properties. When exposed to heat, 6 equivalents of water readily pass off, the seventh being energetically retained. Sulphate of magnesia forms beautiful double salts with the sul- phates of potash and ammonia, which contain 6 equivalents of water of crystallization. CAKBONATE OF MAGNESIA. The neutral carbonate, MgO,C0 2 , occurs native in rhornbohedral 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 prepared by mixing hot solutions of carbonate of potash or soda, and sulphate of mag- MAGNESIUM. 241 nesia, 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, but its composition does not sensibly vary. It contains in 100 parts Magnesia . . . . 41.6 Carbonic acid . . . 30.0 Water 22.4 100. Or, 5 eq. magnesia, 4 eq. carbonic acid, and 6 eq. water. Magnesia alba is slightly soluble in water, especially when cold. PHOSPHATE OF MAGNESIA, 2MgO,HO,PO 5 -f-14HO. This salt separates in small colorless prismatic crystals when solutions of phosphate of soda and sulphate of magnesia are mixed and suffered to stand some time. Mr. Gra- ham states that it is soluble in about 1000 parts of cold water, but Berzelius describes a phosphate which only requires 15 parts of water for solution; this can hardly be the same substance. Phosphate of magnesia exists in the grain of the cereals, and can be detected in considerable quantity in beer. PHOSPHATE OF MAGNESIA AND AMMONIA, 2MgO,NH 4 O,PO 5 -f-12HO. When a soluble phosphate is mixed with salt of magnesia, and ammonia or its car- bonate added, a crystalline precipitate, having the above composition, sub- sides, immediately, if the solutions are concentrated, and after some time, if very dilute; in the latter case, the precipitation is promoted by stirring. This salt is slightly soluble in pure water, but scarcely so in saline liquids. When heated, it is resolved into bibasic phosphate of magnesia, containing 36.68 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 a uri- nary calculus. In practical analysis, magnesia is often separated from solutions by bring- ing it into this state. The liquid, free from lime, alumina, &c., is mixed with phosphate of soda and excess of ammonia, and gently heated for a short time. The precipitate is collected upon a filter and thoroughly washed with water containing a little sal-ammoniac, after which it is dried, ignited to red- ness, and weighed. The proportion of magnesia is then easily calculated. SILICATES OF MAGNESIA. The following natural compounds belong to this class : Steatite or soap-stone, MgO,Si0 3 , a soft, white, or pale-colored, amorphous substance, found in Cornwall and elsewhere; Meerschaum, MgO,SiO 3 -|-HO, from which pipe-bowls are often manufactured; Chrysolite, 3MgO,SiO 3 , a crystallized mineral, sometimes employed for ornamental pur- poses ; a portion of magnesia is commonly replaced by protoxide of iron, which communicates a green color; Serpentine is a combination of silicate and hydrate of magnesia ; Jade, an exceedingly hard stone, brought from New Zealand, contains silicate of magnesia combined with silicate of alu- mina; its green color is due to oxide of chromium; Qugite and hornblende are essentially double salts of silicic acid, magnesia, and lime, in which the magnesia is more or less replaced by its isomovphous substitute, protoxide of iron. The salts of magnesia are strictly isomorphom with those of oxide of zinc, protoxide of iron, oxide of copper, &c.; they are usually colorless, and are easily recognized by the following characters: 21 242 MAGNESIUM. 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 potash and soda, but none with carb. ammonia in the cold. A white crystalline precipitate with soluble phosphates, on the addition of a little ammonia. * Ammonia produces no precipitate in magnesian salts, if a salt of ammonia be present. If the solution be acid, no precipitate falls., for, in this case, the first por- tion of ammonia added, uniting with the excess of acid, forms a salt of ammonia, and the production of a precipitate is prevented. R. B. ALUMINUM OR ALUMINIUM. 243 SECTION in. METALS OF THE EARTHS PROPER. ALUMINUM OB ALUMINIUM. ALUMINA, the only known oxide of this metal, is a substance of very abund- ant occurrence in nature in the state of silicate, as in felspar and its associ- ated 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. Chloride 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 vapors in contact with the melted potassium. The reduction takes place with great disengagement of heat. The metal, separated by cold water from the alka- line chloride, has a tin-white color and perfect lustre. It is obtained in small fused globules by the heat of reduction, which are malleable, and have a specific gravity of 2.6. When heated in the air or in oxygen, it takes fire and burns with brilliancy, producing alumina. Aluminium has for its equivalent the number 13.69; its symbol is AI. ALUMINA, A1 2 O 3 . This substance is inferred to be a sesquioxide, from its isomorphism with the red oxide of iron. It is prepared by mixing solution of alum with excess of ammonia, by which an extremely bulky, white, gela- tinous precipitate of hydrate of alumina is thrown down. This is washed, dried, and ignited to whiteness. Thus obtained, alumina constitutes a white, tasteless, coherent mass, very little acted upon by acid. The hydrate, on the contrary, when simply dried in the air, or by gentle heat, dissolves freely in dilute acid, arid in caustic potash or soda, from which it is precipitated by the addition of sal-ammoniac. Alumina is fusible before the oxyhydrogen blow- pipe. The mineral called corundum, of which the ruby and sapphire are transparent varieties, consists of nearly pure alumina in a crystallized state, with a little coloring 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. CHLOHIDE OF ALUMINIUM, A1 2 C) 3 . The solution of alumina in hydrochloric 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 lamp-black, and the mixture strongly calcined in a covered cruci- ble. It is then transferred to a porcelain tube fixed across a furnace, and heated to redness in a stream of chlorine gas, when the alumina, yielding to the attraction of the chlorine on the one hand, and the carbon on the other, for each of its constituents, suffers decomposition, carbonic oxide being disen- gaged, and chloride of aluminium formed ; the latter sublimes, and condenses in the cool part of the tube. 244 ALUMINUM OR ALUMINIUM. Chloride of aluminium is a crystalline yellowish substance, excessively greedy of moisture, and very soluble. Once dissolved, it cannot be again re- covered. It is said to combine with sulphuretted aud phosphuretted hydrogen, and with ammonia. SULPHATE OF ALUMINA, A1 2 3 , 3SO 3 -f-18HO. Prepared by saturating dilute sulphuric acid with hydrate of alumina, and evaporating. It crystallizes 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 potash, soda, and am- monia, forming double salts of great interest, the alums. Common alum, the source of all the preparations of alumina, contains AI 2 O 3 , 3SO 3 -f-KO, SO 3 -f- 24HO. It is manufactured on a very large scale, from a kind of slaty clay, loaded with bisulphuret of iron, which abounds in certain parts. This is gently roasted, and then exposed to the air in a moistened state ; oxygen is absorbed, the sulphur becomes acidified, sulphate of protoxide of iron and sulphate of alu- mina are produced, and afterwards separated by lixiviation with water. The solution is next concentrated, and mixed with a quantity of chloride of potas- sium, which decomposes the iron salt, forming protochloride of iron and sulphate of potash, 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. Potash alum crystallizes in colorless, 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, and in its own weight of boiling water. Exposed to heat, it is easily rendered anhydrous, and, by a very high temperature, decomposed. The crystals have little tendency to change in the air. Alum is largely used in the arts, in preparing skins, dye- ing, &c.; it is occasionally contaminated with oxide of iron, which interferes with some of its applications. The celebrated Roman alum, made from alum-stone, a felspathic rock, altered by sulphurous vapors, was once much prized on account of its freedom from this impurity. A mixture of dried alum and sugar, carbonized in an open pan, and then heated to redness, out of contact of air, furnishes the pyrophorus of Homberg, which ignites spontaneously on exposure to the atmosphere. The essential ingredient is, in all probability, finely-divided sulphuret of potassium. Soda-alum, in which sulphate of soda replaces sulphate of potash, has a form and constitution similar to that of the salt described; it is, however, much more soluble, and difficult to crystallize. Ammonia alum, containing NH 4 O, S0 3 , instead of KO,S0 3 , very closely re- sembles common potash-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 enter into the composition of a number of crystallized minerals, among which fel- spar 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, suffers complete decomposition, becoming converted into a soft, friable mass of earthy matter. This is the origin of clay; the change itself is seen in great perfection in certain districts of Devonshire and Corn- GLUCINUM. 245 wall, the felspar of the fine white granite of those localities being often dis- integrated to an extraordinary depth, and the rock altered to a substance re- sembling soft mortar. By washing, this finely-divided matter is separated from the quartz and mica, and the milk-like liquid, being collected in tanks and suffered to stand, deposits the suspended clay, which is afterwards dried, first in the air and afterwards in a stove, and employed in the manufacture of porcelain. The composition assigned to unaltered felspar is A1 2 O 3 , 3SiO 3 -j-KO, SiO 3 , or alum, having silicic acid in the place of sulphuric. The exact nature of the change by which it passes into porcelain clay is unknown, although it evidently consists in the abstraction of silica and alkali.* When the decomposing rock contains oxide of iron, the clay produced is colored. The different varieties of shale and slate result from the alteration of ancient clay-beds, apparently in many instances by the infiltration of water holding silica in solution ; the dark appearance of some of these deposits is due to bituminous matter. It is a common mistake to confound clay with alumina; all clays are essentially 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 re- cognized by effervescing with acids. A basic silicate of alumina, 2 A1 2 3 , Si0 3 , 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, albite, containing that alkali in place of potash, 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. Stilbite, heulandite, 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. Peroxide of iron is very often substituted for alumina in these minerals. Alumina when in solution is distinguished without difficulty. Caustic potash 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 re- agent. The alkaline carbonates and carbonate of ammonia precipitate the hydrate, with escape of carbonic acid, no carbonate being known. The precipitates are insoluble in excess. GLT7CINUM. This metal is prepared from the chloride in the same manner as alumi- nium. It is fusible with great difficulty, not acted upon by cold water, and burns when heated in the air, producing glucina. * 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 .24 Water . 12. Alkali and loss 1.76 100. 21* 246 YTTRIUM CERIUM, LANTIIANIUM, AND DIDYMIUM. The equivalent of glucinum is 26.5, and the symbol G. GLUCIBTA, G 2 O & , is a rare earth found in the emerald, beryl, and eudase, from which it may be extracted by a process of tolerable simplicity. It very much resembles alumina, but is distinguished from that substance by its solubility, when freshly precipitated, in a cold solution of carbonate of ammonia, from which it is again thrown down on boiling. The salts of glucina have a sweet taste, whence its name (yXyxyf). 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 already 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 sepa- rated with extreme difficulty. CERIUM, LANTHAITIUM, AND DIDYMIUM. The oxides of these very rare metals are found associated in the Swedish mineral cerite; the metals themselves are almost unknown. M. Vauquelin succeeded in obtaining what was supposed to be metallic cerium, in the form of minute buttons or globules of a hard, white, brittle metal, which resisted the action of nitric acid, but was attacked by aqua regia. The crude oxide of cerium, obtained by precipitating the double sulphate of cerium and potash directly derived from cerite by carbonate of potash, has been shown by Mosander to contain in addition to oxide of cerium, the oxides of two other metals, to which the above names were given. After ignition, it is red-brown. Treated with very dilute nitric acid, oxide of lanthanium is dissolved out, not, however, pure, while the oxides of cerium and didymium remain in great part undissolved. The complete separation of the three bodies is, however, attended with the greatest difficulty, and has indeed been only partially accomplished. The yellow oxide of cerium, obtained by igniting the nitrate, is a mixture of proto- and peroxide, which are extremely difficult to obtain in a separate state. The salts of the former are colorless, and are completely precipitated by sulphate of potash ; the sulphate of the peroxide is yellow, and forms a beautiful double salt with sulphate of potash, which is decomposed by water. Oxide of lanthanium, as pure as it has been obtained, forms a very pale salmon-colored powder, unchanged by ignition in open or close vessels. In contact with water, it gives a snow-white bulky hydrate, which has an alka- line reaction, and decomposes ammoniacal salts by boiling. Its salts are crys- tallizable, colorless, sweet, and astringent, and are precipitated by sulphate of potash. The occasional brown color of crude oxide of cerium is due to oxide of didyrnium. In a pure state, it forms a brown powder, soluble in acids, and generating a series of red crystallizable salts, from which caustic potash pre- cipitates a violet-blue hydrate, quickly changing by exposure to the air. It communicates to glass an amethystine color.* * Annalen der Chemie und Pharmacie, xlviii. 210. ZIRCONIUM THORIUM. 247 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, in the air. The equivalent of zirconium is 33.62, and its symbol Zr. ZIRCONIA, Zr 2 O 3 , is a rare earth, very closely resembling alumina, found in the mineral zircon. The salts are colorless and have an astringent taste. Svanberg has rendered it probable that an undescribed metallic oxide exists in certain varieties of zircon, for the metal of which he proposes the name of norium. THORIUM. The metal of an earth from a very rare mineral, thorite ; it agrees in cha- racter with aluminium, and is obtained by similar means. The equivalent of thorium is 59.59, and its symbol Th. THORINA, ThO, is remarkable for its great specific gravity, and is otherwise distinguished by peculiar properties which separate it from all other sub- stances. 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 processes, where large masses of melted glassy matter are suffered to cool slowly. The alkaline silicates, when in a state of fusion, have the power of dissolving a large quantity of silica. Two principal varieties of glass are met with in commerce, namely, glass composed of silica, alkali, and lime, and glass containing a large proportion of 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 potash or soda, and slaked lime or oxide of lead ; at a high temperature, fusion and combination 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 assumes the peculiar tenacious condition proper for working. The operation of fusion is conducted in large crucibles of refractory fire- clay, which in the case of lead-glass are covered by a dome at the top, and have an opening at the side by which 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 protoxide by the heat, the liberated oxygen serving to destroy any combustible matter which might accidentally find its way into the crucible and stain the glass, by re- ducing a portion of the lead. Potash gives a better glass than soda, although the latter is very generally employed, from its lower price. A certain pro- 248 MANUFACTURE OF GLASS. portion of broken and waste glass of the same kind is always added to the other materials. Articles of blown glass are thus made : The workman begins by collecting a proper quantity of soft, pasty glass at the end of his blowpipe, an iron tube five or six feet in length, terminated by a mouth-piece of wood ; he then com- mences blowing, by which the lump is expanded into a kind of flask, suscep- tible 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-mouth 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 de- tached, and carried to the annealing oven, where it undergoes slow and gradual cooling during many hours, the object of which is to obviate the ex- cessive brittleness always exhibited by glass which has been quickly cooled. The large circular tables of crown-glass are made by a very curious process of this kind; the globular flask at first produced, transferred from the blowpipe to the pontil, is suddenly made to assume the form of a flat disc by the centri- fugal force of the rapid rotatory movement given to the rod. Plate-glass is cast upon a flat metal table, and after very careful annealing, ground true, and polished by suitable machinery. Tubes are made by rapidly drawing out a hollow cylinder; and from these a great variety of useful small apparatus may be constructed with the help of a lamp and blowpipe, or still better, the bellows-table of the barometer-maker. Small tubes may be bent in the flame of a spirit-lamp or gas jet, and cut with great ease by a file, a scratch being made, and the two 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 Potash . . 25 Lime . 12.5 97.5 English flint glass.f Silica . . . 51.93 Potash . . 13.77 Oxide of lead . 33.28 98.98 The difficultly-fusible white Bohemian tube, so invaluable in organic che- mistry, has been found to contain in 100 parts : Silica 72.80 Lime, with trace of alumina . . . 9.68 Magnesia .40 Potash 16.80 Traces of manganese, &c., and loss . . .32 Different colors are often communicated to glass by metal lie oxides. Thus, oxide of cobalt gives deep blue; oxide of manganese, amethyst; suboxide 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 contents of the glass- pot, in which they dissolve, or applied in a particular manner to the surface of the plate or other object, which is then re-heated until fusion of the coloring *Mitscherlich, Lehrbuch, ii. 187. f Faraday, quoted by Turner, Elements, p. 516. PORCELAIN AND EARTHENWARE. 249 matter occurs; such is the practice of enameling 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 potash or soda, and the product treated with water, the greater part dissolves, yielding a so- lution from which acids precipitate gelatinous silica. This is the soluble glass sometimes mentioned by chemical writers ; its solution has been used for ren- dering 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 effusion. The glaze, too, applied for giving a perfectly smooth surface, is closely adhe- rent, and in fact graduates by insensible degrees into the substance of the body. In earthenware, on the contrary, the fracture is open and earthy, and the glaze detachable with greater or less facility. The compact and partly glassy character of porcelain is the result of the 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 in- fusible 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 decom- posed felspar, none of the clays of the secondary strata being pure enough for the purpose; it must be white, and free from oxide of iron. To diminish the retraction which this substance undergoes in the fire, a quantity of finely- divided silica, carefully prepared by crushing and grinding calcined flints or chert, is added, together with a proper proportion of felspar or other fusible material, also reduced to impalpable powder. The utmost pains are taken to effect perfect uniformity of mixture, and to avoid the introduction of par- ticles 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 substance, and the powder remains evenly spread upon its surface ; it is once more dried, and lastly, fired at an exceedingly high temperature. The porcelain-furnace is a circular structure of masonry, having several fire-places, and surmounted by a lofty dome. Dry wood or coal is consumed as fuel, and its flame directed into the interior, and made to circulate around and among the earthen cases, or seggars in which the articles to be fired are packed. Many hours are required for this operation, which requires very careful management. After the lapse of several days, when the furnace has completely cooled, the contents are removed in a finished state, so far as re- gards the ware. The ornamental part, consisting of gilding and paintings in enamel, has yet to be executed, after which the pieces are again heated, in order to flux the colors. This operation has sometimes to be repeated more than once. The manufacture of porcelain in Europe is of modern origin ; the Chinese 250 EARTHENWARE. have possessed the art from the commencement of the seventh century, and their ware is, in some respects, altogether unequaled. The materials em- ployed by them are known to be kaolin, or decomposed felspar; petuntze, or quartz reduced to fine powder ; and the ashes of fern, which contain carbon- ate of potash. STONEWARE. This is a coarse kind of porcelain, made from clay contain- ing oxide of iron and a little lime, to which it owes its partial fusibility. The glazing is performed by throwing common salt into the heated furnace ; this is volatilized, and decomposed by the joint agency of the silica of the ware, and of the vapor of water always present ; hydrochloric acid and soda are produced, the latter forming a silicate, which fuses over the surface of the ware, and gives a thin, but excellent glaze. EARTHENWARE. The finest kind of earthenware is made from a white 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 colors, so common upon plates and household articles, are printed upon paper, in enamel pigment, mixed with oil, and transferred, while still wet, to the unglazed 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 pur- pose ; and powdered coke has been also used with the earth ; such crucibles bear rapid changes of temperature with impunity. MANGANESE. 251 SECTION IY. OXIDABLE METALS PROPER, WHOSE OXIDES FORM POWERFUL BASES. MANGANESE. MANGANESE is tolerably abundant in nature in an oxidized state, forming, or entering into the composition of, several interesting minerals. Traces of this substance are very frequently found in the ashes of plants. Metallic manganese, or perhaps, strictly, carburet 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 Hessian or Cornish crucible with moist charcoal powder, introduced a little at a time, and rammed as hard as possible. A smooth cavity is then scooped in the centre, into which the above-mentioned mixture is compressed, and covered with charcoal -powder. The lid of the crucible is luted down with a little fire-clay, and the whole arranged in a very powerful wind furnace. The heat is slowly raised until the crucible becomes red-hot, after which it is urged to its maximum for an hour or more. When cold, the crucible is broken up, and the metallic button of manganese extracted. Manganese is a grayish-white metal, resembling some varieties of cast iron ; it is hard and brittle, and destitute of magnetic properties. Its specific gravity is about 8. It is fusible with great difficulty, 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 manganese in the cold. Dilute sul- phuric acid dissolves it with great energy, evolving hydrogen. The equivalent of manganese is assumed to be 27.67 ; its symbol is Mn. Oxides of Manganese. Seven different oxides of this metal are described, but two out of the number are, probably, secondary compounds. Protoxide MnO Sesquioxide Mn 2 O 3 Peroxide MnO 2 Red oxide Mn 3 O 4 Varvicite Mn 4 O 7 Manganic acid ...... MnO 3 Hypermanganic acid Mn 2 O 7 PROTOXIDE, MnO. When carbonate of manganese is heated in a stream of hydrogen gas, or of vapor of water, the carbonic acid is disengaged, and a green colored 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 made at a higher temperature, it is probably more stable. This oxide is a very powerful base, 252 MANGANESE. being isomorphus with magnesia and zinc ; it dissolves quietly in dilute acids, neutralizing them completely and forming salts, which have often a beautiful pink color. When alkalis are added to solutions of these compounds the white hydrated oxide first precipitated speedily becomes brown by passing to a higher state of oxidation. SESQJHOXIDE, Mn 2 3 . This compound occurs in nature in the state of hydrate; a very beautiful crystallized variety is found at Ilefeld, in the Hartz. It is produced artificially, by exposing to the air the hydrated protoxide, and forms the principal part of the residue left in the iron retort when oxygen gas is prepared by exposing the native peroxide to a moderate red-heat. The color of the sesquioxide is brown or black, according to its origin or mode of preparation. It is a feeble base, isomorpbous with alumina ; for, when gently heated with diluted sulphuric acid, it dissolves to a red liquid, which, on the addition of sulphate of potash or of ammonia, deposits octahedral crys- tals having the constitution of common alum ; these are, however, decomposed by water. Strong nitric acid resolves this oxide into a mixture of protoxide and peroxide, the former dissolving, and the latter remaining unaltered; while hot oil of vitriol destroys it by forming protosulphate, and liberating oxygen gas. Heated with hydrochloric acid, chlorine is evolved, as with the peroxide, but to a smaller extent. PEROXIDE, MnO 9 . 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. Peroxide of man- ganese has a black color, 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 very large quantity for making chlorine, and as it is subject to great alteration of value from an admixture of the sesquioxide, it becomes desirable to possess means of assaying different samples that may be present- ed, with a view of testing their fitness for the purposes of the manufacturer. One of the best and most convenient methods is the following : 50 grains of the mineral, reduced to very fine powder, are put into the little vessel em- ployed in the analysis of carbonates,* together with about half an ounce of cold water, and 100 grains of strong hydrochloric acid ; 50 grains of crystal- lized oxalic acid are then added, the cork carrying the chloride of calcium tube is fitted, and the whole quickly weighed or counterpoised. The appli- cation of a gentle heat suffices to determine the action: the disengaged chlo- rine converts the oxalic acid into carbonic acid, with the help of the elements of water, two equivalents of carbonic acid representing one of chlorine, and consequently one of peroxide of manganese. Now, the equivalent of the latter substance, 43.67, is so nearly equal to twice that of carbonic acid, 22, that the loss of weight suffered by the apparatus when the reaction has become complete, and the residual gas has been driven off by momentary ebullition, may be taken to represent the quantity of real peroxide in the 50 grains of the sample. RED OXIDE, Mn 3 O 4 , or probably MnO-f-Mn 2 3 . This oxide is also found native, and is produced artificially by heating to whiteness the peroxide or sesquioxide, or by exposing the protoxide or carbonate to a red-heat in an open vessel. It is a reddish-brown substance, incapable of forming salts, and acted upon by acids in the same manner as the two higher oxides already described. Borax and glass in a fused state dissolve this substance, and ac- quire the color of the amethyst. * See page 225. MANGANESE. 253 VARVICITE, Mn 4 7 , or Mn 2 O 3 -|-2MnO 2 .' A natural production, discovered by Mr. Phillips, among certain specimens of manganese-ore from Warwick- shire ; it has also been found at Ilefeld. It much resembles the peroxide, but is harder and more brilliant, and contains water. By a strong heat, var- vicite is converted into red oxide, with disengagement of aqueous vapor 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 peroxide 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 the other salts can be conveniently ob- tained. The liquid referred to consists chiefly of the mixed chlorides of man- ganese 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 peroxide, while the manganese-salt is unaffected. On treating the grayish looking powder thus obtained with water, the chloride of manganese is dissolved out, and may be separated by filtration from the oxide of iron. Should a trace of the latter yet remain, it may be got rid of by boil- ing the liquid for a few minutes with a little carbonate of manganese. The solution of chloride has usually a delicate pink color, which becomes very manifest when the salt is evaporated to dryness. A strong solution deposits rose-colored 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. SESQ.UICHLORIDE, Mn 2 Cl 3 . When precipitated sesquioxide of manganese is put into cold dilute hydrochloric acid, it dissolves quietly, forming a red solu- tion of sesquichloride. Heat disengages chlorine, and occasions the produc- tion of protochloride. SULPHATE op PROTOXIDE OF MANGANESE, MnO,S0 3 -j-7HO. A beautiful rose-colored 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, peroxide 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 persulphate of iron is decom- posed. Water then dissolves out the pure sulphate of manganese, leaving the oxide of iron behind. The salt is used to produce a permanent brown dye, the cloth steeped in the solution being afterwards passed through a solu- tion of bleaching-powder, by which the protoxide is changed to insoluble hy- drate of the peroxide. Sulphate of manganese sometimes crystallizes with five equivalents of water. It forms a double salt with sulphate of potash. CARBONATE OF MANGANESE, MnO,CO 2 . Prepared by precipitating the pro- tochloride by an alkaline carbonate. It is insoluble and buff-colored, or some- times nearly white. Exposed to heat, it loses carbonic acid, and absorbs oxy- gen. MANGANIC ACID, MnO 3 . When an oxide of manganese is fused with an alkali, an additional quantity of oxygen is taken up from the air, and a deep green saline mass results, which contains a salt of the new acid, thus formed under the influence of the base. The addition of nitre, or chlorate of pot- ash, facilitates the production of manganic acid. Water dissolves this com- pound very readily, and the solution, concentrated by evaporation in vacuo, yields green crystals. 22 254 IRON. HYPERMANGANIC ACID, Mn 2 O 7 . When manganate of potash, free from any great excess of alkali, is put into a large quantity of water, it is re- solved into hydrated peroxide of manganese, which subsides, and a deep purple liquid, containing hypermanganate of potash. This effect is accelerated by heat. The changes of color accompanying this decomposition are very remarkable, 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. Hypermanganate of potash is easily prepared on a considerable scale. Equal parts of very finely powdered peroxide of man- ganese and chlorate of potash are mixed with rather more than one part of hydrate of potash 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 color, and are not very soluble in cold water. The manganates and hypermanganates are decomposed by contact with organic matter; the former are said to be isomorphous with the sulphates, and the latter with the hyperchlorates. Salts of the protoxide of manganese are very easily distinguished by re- agents. The caustic alkalis, and ammonia, give white precipitates, insoluble in excess, quickly becoming brown. The carbonates, and carbonate of ammonia, give white precipitates, but little subject to change. Sulphuretted hydrogen gives no precipitate, but sulphuret of ammonium throws down insoluble, flesh-colored sulphuret 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 colorless one in the inner flame. This is by very far the most important member of the group of metals under discussion; 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 Ca- naan, in Connecticut,* forming a vein about two inches thick in mica-slate, and it very frequently 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 ori- gin : these latter contain, in common with the iron of the undoubted meteor- ites, nickel. In an oxidized condition, the presence of iron may be said to be universal; it constitutes great part of the common coloring matter of rocks and soils ; it is contained in plants, and forms an essential component of the blood of the animal body. In the state of bisulphuret it is also very com- mon. Pure iron may be prepared, according to Mitscherlich, by introducing into a Hessian crucible 4 parts of fine iron wire cut small, and 1 part of black oxide of iron. This is covered with a mixture of white sand, lime, and car- * Phillips's Mineralogy, 4th edit. p. 208. IRON. 255 bonate of potash, 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 but- ton of pure metal is thus obtained, the traces of carbon and silicon present in the wire having been removed by the oxygen of the oxide. Pure iron has a white color and perfect lustre; it is extremely soft and tough, and has a specific gravity of 7.8. The crystalline form is probably the cube, to judge from appearances now and then exhibited. In good bar-iron or wire a distinct fibrous texture may always be observed when the metal has been attacked by rusting or by the application of an acid, and upon the perfection of this fibre much of its strength and value depends. Iron is the most tenacious of all the metals, a wire -g^th of an inch in diameter bearing a weight of 601b. It is very difficult of fusion, and before becoming liquid passes through a soft or pasty condition. Pieces of iron pressed or hammered together into this state cohere into a single mass; the operation is termed welding, and is usually performed by sprinkling a little sand over the heated metal, which combines with the superficial film of oxide, forming a fusible silicate, which is subsequently forced out from between the pieces of iron by the pressure applied ; clean surfaces of metal are thus presented to each other, and union takes place without difficulty. Iron does not oxidize in dry air at common temperatures ; heated to red- ness, it becomes covered with a scaly coating of black oxide, and at a high white heat burns brilliantly, producing the same substance ; in oxygen gas the combustion occurs with still greater ease. The finely-divided spongy metal, prepared by reducing the red oxide by hydrogen gas, takes fire spon- taneously 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^noisture speedily leads to the production of rust, which is a hydrate of the peroxide. The rusting of iron is wonderfully promoted by the presence of a little acid vapor.f At a red heat iron decomposes water, evolving Hydrogen, and passing into the black oxide. Dilute sulphuric and hydro- chloric acids dissolve it freely with separation of hydrogen. Iron is strongly magnetic up to a red-heat, when it loses all traces of that remarkable pro- perty. The equivalent of iron is 28, and its symbol Fe. Four compounds of iron and oxygen are described. Protoxide . . . FeO Sesquioxide (peroxide) . Fe 2 O 3 Black oxide . . . Fe 3 O 4 Ferric acid . . . Fe0 3 PROTOXIHE, FeO. This is a very powerful base, neutralizing acids com- pletely, and isomorphous with magnesia, oxide of zinc, &c. It is almost un- known 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 protoxide falls, which becomes nearly black when boiled, possibly from the separation of water. This hydrate, exposed to the air, very rapidly changes, becoming * When obtained at a heat below redness. R. B. f The rusting of iron proceeds with rapidity after it once begins, extending from the point first affected. Iron rust contains ammonia, resulting from the combination of the nascent hydrogen of decomposed water uniting with dissolved nitrogen. This is an important point in medico-legal investigations, as it is considered, that, when stains on a steel instrument yield ammonia by the action of potassa, the presence of organic matter is proved ; but as rust contains ammonia, it becomes necessary to ascertain its absence, or drive it off, previous to operating with potassa. R. B. 256 IRON. green and ultimately red-brown. The soluble salts of protoxide of iron have commonly a delicate, pale green color, and a nauseous metallic taste. PEROXIDE, Fe 2 O 3 . A fe'eble base, isomorphous with alumina. Peroxide of iron occurs native, most beautifully crystallized as specular iron ore in the island of Elba, and elsewhere ; also, as red and brown hamatites, the latter being a hydrate. It is artificially prepared by precipitating a solution of per- sulphate or perchloride of iron by excess of ammonia, and washing, drying, and igniting the yellowish brown hydrate thus produced; fixed alkali must not be used in this operation, as a portion is retained by the oxide. In fine powder, this oxide has a full red color, and is used as a pigment, being pre- pared for the purpose by calcination of the protosulphate ; the tint varies somewhat with the temperature to which it has been exposed. This oxide is unaltered in the fire, although easily reduced at a high temperature by car- bon or hydrogen. It dissolves in acids, with difficulty after strong ignition, forming a series of reddish salts, which have an acid reaction and an as- tringent taste. Peroxide of iron is not acted upon by the magnet.* BLACK OXIDE ; MAGNETIC OXIDE ; LOADSTONE, Fe 3 4 , or probably FeO-{- Fe 2 3 . A natural product, one of the most valuable of the iron ores, often found in regular octahedral crystals, which are magnetic. It may be pre- pared by mixing due proportions of a proto- and a per-salt of iron, precipi- tating them by excess of alkali, and then boiling the mixed hydrates, when the latter unite to a black, sandy substance, consisting of minute crystals of the magnetic oxide. This oxide is the chief product of the oxidation of iron at a high temperature in the air and in aqueous vapor. It is incapable of forming salts. FERRIC ACID, Fe0 3 . A very remarkable compound of recent discovery. The simplest mode of preparing it is to heat to full redness, for an hour, in a covered crucible, a mixture of one part of pure peroxide of iron, and four parts of dry nitre. The brown, porous, deliquescent mass is treated, when cold, with ice cold water, by which a deep, amethystine red solution of ferrate of potash is obtained. This gradually decomposes even in the cold, evolving oxygen gas, and depositing sesquioxide ; by heat the decomposition is very rapid. The solution of ferrate of potash gives no precipitate with salts of lime, magnesia, or strontia; but when mixed with one of baryta, a deep crimson, insoluble compound falls, which is a ferrate of that base, and is very permanent. PROTOCHLORIDE OF IRON, FeCl. Formed by transmitting dry hydrochloric acid gas over red hot metallic iron, or by dissolving iron in hydrochloric acid. The latter solution yields, when duly concentrated, green crystals of the pro- tochloride, containing 4 equivalents of water; they are very soluble and deli- quescent, and rapidly peroxidize in the air. SEsauicHtoRiDE OF IRON, Fe 2 Cl 3 . Usually prepared by dissolving per- oxide in hydrochloric acid. The solution, evaporated to a syrupy consistence, deposits red, hydrated crystals, which are very soluble in water and alcohol. It forms double salts with chloride of potassium and sal-ammoniac. When evaporated to dryness and strongly heated, much of the chloride is decom- posed, yielding peroxide and hydrochloric acid; the remainder sublimes, and afterwards condenses in the form of small, brilliant red crystals, which deli- quesce rapidly. The solution of sesquichloride of iron is capable of dissolv- ing a large excess of recently precipitated hydrate of the peroxide, by which * In the form of hydrate, Fe a O 3 -f3HO, as recently precipitated from the persulphate by ammonia, it constitutes the antidote for arsenious acid. The affinity for water in this case is not strong the hydrate gradually decomposing even when kept under water, its color passing from yellowish brown to red. R. B. IRON. 257 it acquires a much darker color. Anhydrous sesquichloride of iron is also produced by the action of chlorine upon the heated metal. PHOT-IODIDE OF IRON, Fel. This is an important medicinal preparation; it is easily made by digesting iodine with water and metallic iron. The so- lution is pale green, and yields, on evaporation, crystals resembling those of the chloride, which rapidly peroxidize on exposure to air. It is best preserved in solution in contact with excess of iron.* A periodide of iron exists, which is yellowish red and soluble. SULPHURETS OF IRON. Several compounds of iron and sulphur are de- scribed; of these the two most important are the following: Protosulphuret , FeS, is a blackish, brittle substance, attracted by the magnet, formed by heat- ing together iron and sulphur. It is dissolved by dilute acids with evolu- tion of sulphuretted hydrogen gas, and is constantly employed for that purpose in the laboratory, being made by projecting into a red-hot crucible a mixture of 2^ parts of sulphur and 4 parts of iron filings or borings of cast-iron, and excluding the air as much as possible. The same substance is formed when a bar of white hot iron is brought in contact with sulphur. The bisulphuret of iron, FeS a , is a natural product, occurring in rocks of all ages, and evidently formed in many cases by the gradual de-oxidation of sulphate of iron by organic matter. It has a brass-yellow color, is very hard, not attracted by the magnet, and not acted upon by dilute acids. Exposed to heat, sulphur is expelled, and an intermediate sulphuret, the analogue probably of the black oxide, pro- duced. This substance also occurs native, under the name of magnetic pyrites. The bisulphuret is sometimes used in the manufacture of sulphuric acid. Compounds of iron with phosphorus, carbon, and silicon exist, but little is known respecting them in a delinite state. The carburet is contained in cast- iron and in steel, to which it communicates ready fusibility ; the silicon-com- pound is also found in cast-iron. Phosphorus is a very hurtful substance in bar-iron, as it renders it brittle or cold-short. PROTOSULPHATE OF IRON; GREEN VITRIOL, FeO,S0 3 -|-7HO. This beauti- ful and important salt may be obtained by directly dissolving iron in dilute sulphuric acid; it is generally prepared, however, and that on a very large scale, by contact of air and moisture with common iron-pyrites, which, by absorption of oxygen, readily furnishes the substance in question. Heaps of this material are exposed to the air until the decomposition is sufficiently advanced; the salt produced is then dissolved out by water, and the solution made to crystallize. It forms large green crystals, of the composition above stated, which slowly effloresce and peroxidize in the air; it is soluble in about twice its weight of cold water. Crystals containing 4, and also 2 equiva- lents of water, have been obtained. Protosulphate of iron forms double salts with the sulphates of potash and ammonia. PERSULPHATE OF IRON, Fe 2 O 3 3S0 3 . Prepared by adding to a solution of the protosalt exactly one-half as much sulphuric acid as it already contains, raising the liquid to the boiling-point, and then dropping in nitric acid until the solution ceases to blacken by such addition. The red liquid thus obtained furnishes, on evaporation to dryness, a buff colored amorphous mass, which, when put into water, very slowly dissolves. With the sulphates of potash and ammonia, this salt yields compounds having the form and constitution of the alums; the crystals are nearly destitute of color. These latter are de- composed by water, and sometimes by long keeping when in a dry state. They are best prepared by exposing to spontaneous evaporation a solution of * Or protected from the action of oxygen by pure honey, or other saccharine sub- stance, in the proportion of one part to three of the solution. R. B. 22* 258 IRON. persulphate of iron to which sulphate of potash or of ammonia has been added. PROTONITRATE OF IRON, FeO,NO 5 ' When dilute cold nitric acid is made to act to saturation upon protosulphuret of iron, and the solution evaporated in vacuo, pale green and very soluble crystals of protonitrate are obtained, which are very subject to alteration. Pernitrale, Fe 2 3 ,3N0 5 , is readily formed by pouring nitric acid, slightly diluted, upon iron ; it is a deep red liquid, apt to deposit insoluble sub-salt, and is used in dyeing. PROTOCARBOKATE OF IRON", FeO,CO a . The white precipitate obtained by mixing solutions of proto-salt of iron and alkaline carbonate ; it cannot be washed and dried without losing carbonic acid and absorbing oxygen. This substance occurs in nature as spathose iron ore, associated with variable quan- tities of carbonate of lime and of magnesia; and also in the common clay iron-stone, from which nearly all the British iron is made. It is often found in mineral waters, being soluble in excess of carbonic acid ; such waters are known by the rusty matter they deposit. No carbonate of the peroxide is known. The phosphates of iron are all insoluble.* Salts of the protoxide of iron are thus distinguished : Caustic alkalis, and ammonia, give nearly white precipitates, insoluble in excess of the reagent, rapidly becoming green, and ultimately brown, by ex- posure to air. Alkaline carbonates, and carbonate of ammonia, throw down the white carbonate, also very subject to change. Sulphuretted hydrogen gives no precipitate, but sulphuret of ammonium throws down black protosulphuret of iron, soluble in dilute acids. Ferrocyanide of potassium gives a nearly white precipitate, becoming deep blue on exposure to air. Salts of the peroxide are thus characterized : Caustic alkalis, and ammonia, give foxy-red precipitates of hydrated perox- ide, insoluble in excess. The carbonates behave in a similar manner, the carbonic acid escaping. Sulphuretted hydrogen gives a nearly white precipitate of sulphur, and re- duces the peroxide to protoxide. Sulphuret of ammonium gives a black precipitate, slightly soluble in excess. Ferrocyanide of potassium yields Prussian blue. Tincture or infusion of gall-nuts strikes intense bluish-black with the most dilute solutions of persalts of iron. Iron Manufacture. This most important branch of industry consists, as now conducted, of two distinct parts, viz: the production from the ore of a fusible carburet of iron, and the subsequent decomposition of the carburet, and its conversion into pure or malleable iron. * PROTOPHOSPHATE OF IRON, 2FeO, HO,PO 6 , is formed when a solution of common phosphate of soda is added to a solution of protosulphate of iron. It falls as a white precipitate, gradually becoming bluish by the action of the air ; it is soluble in acids, from which ammonia again precipitates it, and re-dissolves the precipitate when added in excess. The blue phosphate contains perphosphate. PERPHOSPHATE OF IRON is formed by adding common phosphate of soda to persul- phate or perchloride of iron ; a white precipitate is produced insoluble in ammonia unless an excess of phosphate of soda be present. Digested with the fixed alkalis or ammonia it becomes brown. R. B. IRON. 259 The clay iron ore is found in association with coal, forming thin beds or nodules; it consists, as already mentioned, of carbonate of iron mixed with clay ; sometimes lime and magnesia are also present. It is broken in pieces, and exposed to heat in a furnace resembling a lime-kiln, by which the water and carbonic acid are expelled, and the ore rendered dark-colored, denser, and also magnetic ; it is then ready for reduction. The furnace in which this operation is performed is usually of very large dimensions, fifty feet or more in height, and constructed of brickwork with great solidity, the interior being lined with excellent fire-bricks ; the figure will be at once understood from the sectional drawing. The furnace is close at the bottom, the fire being maintained by a powerful artificial blast introduced by two or three tuyere- pipes, as shown in the section. The materials, consisting of due proportions Fig. 148. of coke or carbonized coal, roasted ore, and limestone, are constantly sup- plied from the top, the operation proceeding continuously night and day, often for years, or until the furnace is judged to require repair. In the upper part of the furnace, where the temperature is still very high, and where com- bustible gases abound, the iron of the ore is probably reduced to the metallic state, being disseminated through the earthy matter of the ore ; as the whole sinks down and attains a still higher degree of heat, the iron becomes con- verted into carburet by cementation, while the silica and alumina unite with the lime, purposely added, to a kind of glass or slag, nearly free from oxide of iron. The carburet and slag, both in a melted state, reach at last the 260 IRON. bottom of the furnace, where they arrange themselves in the order of their 'densities ; the slag flows out at certain apertures contrived for the purpose, and the iron is discharged from time to time, and suffered to run into rude moulds of sand, by opening an orifice at the bottom of the recipient, previously stopped with clay. Such is the origin of crude or cast-iron, of which there are several varieties, distinguished by differences of color, hardness, and com- position, and known by the names of gray, black and white iron. The first is for most purposes the best, as it admits of being filed and cut with perfect ease. The black and gray kinds probably contain a mechanical admixture of graphite, which separates during solidification. A great improvement has been made in the above described process, by substituting raw coal for coke, and blowing hot air, instead of cold, into the furnace. This is effected by causing the air, on leaving the blowing-machine, to circulate through a system of red-hot iron pipes, until its temperature be- comes high enough to melt lead. This alteration has already effected a pro- digious saving in fuel, without, it appears, any injury to the quality of the product. The conversion of cast into bar-iron, is effected by an operation called puddling; previous to which, however, it commonly undergoes a process the theory of which is not very intelligible. It is re-melted, and suddenly cooled, by which it becomes white, crystalline, and exceedingly hard : in this state it is called yme metal. The puddling process is conducted in an ordinary rever- beratory furnace, into which the charge of fine metal is introduced by a side aperture. This is speedily melted by the flame, and its surface covered with a crust of oxide. The workman then, by the aid of an iron tool, diligently stirs the melted mass, so as intimately to mix the oxide with the metal ; he now and then also throws in a little water, with the view of promoting more rapid oxidation. Small jets of blue flame soon appear upon the surface of the iron, and the latter, after a time, begins to lose its fluidity, and acquires, in succession, a pasty and a granular condition. At this point, the fire is strongly urged, the sandy panicles once more cohere, and the contents of the furnace now admit of being formed into several large balls or masses, which are then withdrawn, and placed under an immense hammer, moved by machinery, by which each becomes quickly fashioned into a rude bar. This is re-heated, and passed between grooved cast iron rollers, and drawn out into a long bar or rod. To make the best iron, the bar is cut into a number of pieces, which are afterwards piled or bound together, again raised to a welding heat, and hammered or rolled into a single bar ; and this process of piling or fagoting is sometimes twice or thrice repeated, the iron becoming greatly improved thereby. The general nature of the change in the puddling furnace is not difficult to explain. Cast-iron consists essentially of iron in combination with carbon and silicon; when strongly heated with oxide of iron, those compounds undergo decomposition, the carbon and silicon becoming oxidized at the ex- pense of the oxygen of the oxide. As this change takes place, the metal gradually loses its fusibility, but retains a certain degree of adhesiveness, so that when at last it comes under the tilt-hammer, or between the rollers, the particles of iron become agglutinated into a solid mass, while the readily fusible silicate of the oxide is squeezed out and separated. All these processes are, in Great Britain, performed with coal or coke, but the iron obtained is, in many respects, inferior to that made in Sweden and Russia from the magnetic oxide, by the use of wood-charcoal, a fuel too dear to be extensively employed in England. Plate-iron is, however, sometimes made with charcoal. Steel. A very remarkable, and most useful substance, prepared by heat- CHROMIUM. 261 ing iron in contact with charcoal. Bars of Swedish iron are embedded in charcoal powder, contained in a large rectangular crucible or chest of some substance capable of resisting the fire, and exposed for many hours to a full red-heat. The iron takes up, under these circumstances,from 1.3 to 1.7 per cent, of carbon, becoming harder, and at the same time fusible, with a certain diminution, however, of malleability. The active agent in this cementation process is probably carbonic oxide ; the oxygen of the air in the crucible com- bines with the carbon, to form that substance, which is afterwards decom- posed by the heated iron, one-half of its carbon being abstracted by the latter. The carbonic acid thus formed takes up an additional close of carbon from the charcoal, and again becomes carbonic oxide, the oxygen, or rather the carbonic acid, acting as a carrier between the charcoal and the metal. The product of this operation is called blistered steel, from the blistered and rough appearance of the bars: the texture is afterwards improved and equalized by welding a number of these bars together, and drawing the whole out under a light tilt-hammer. The most perfect kind of steel is that which has undergone fusion, having been cast into ingot-moulds, and afterwards hammered : of this all fine cut- ting instruments are made; it is difficult to forge, requiring great skill and care on the part of the operator. Steel may also be made directly from some particular varieties of cast-iron, as that from spathose iron ore, containing a little manganese. The metal is retained, in a melted state, in the hearth of a furnace, while a stream of air plays upon it, and causes partial oxidation 5 the oxide produced reacts, as be- fore staled, on the carbon of the iron, and withdraws a portion of that ele- ment. When a proper degree of stiffness or pastiness is observed in the residual metal, it is withdrawn, and hammered or rolled into bars. The wootz, or native steel of India, is probably made in this manner. Annealed cast-iron, sometimes called run steel, is now much employed as a substitute for the more costly products of the forge ; the articles, when cast, are embedded in powdered iron-ore, or some earthy material, and, after being exposed to a moderate red-heat for some time, are allowed slowly to cool, by which a very extraordinary degree of softness and malleability is attained. It is very pos- sible that some little decarbonization may take place during this process. The most remarkable property of steel is that of becoming exceedingly hard when quickly cooled ; when heated to redness, and suddenly quenched in cold water, steel in fact, becomes capable of scratching glass with facility ; if re-heated to redness, and once more left to cool slowly, it again becomes nearly as soft as ordinary iron, and, between these two conditions, any re- quired degree of hardness may be attained. The articles, forged into shape, are first hardened in the mariner described ; they are then tempered, or let down, by exposure to a proper degree of annealing heat, which is often judged of by the color of the thin film of oxide which appears on the polished surface. Thus, a temperature of about 430 F., indicated by a faint straw-color, gives the proper temper for razors: that for scissors, pen-knives, &c., will be com- prised between 470 and 490, and be attended by a full yellow or brown tint. Swords and watch-springs require to be softer and more elastic, and must be heated to 550 or 560, or until the surface becomes deep blue. At- tention to these colors has now become of less importance, as metal baths are often substituted for the open fire in this operation. CHUOM1UM. CHROMIUM is found in the state of oxide,in combination with oxide of iron, in some abundance in the Shetland Islands, and elsewhere ; as chromate of 262 CHROMIUM. lead, it constitutes a very beautiful mineral, from which it was first obtained. The metal itself is got in a half-fused condition by mixing the oxide with th of its weight of charcoal-powder, inclosing the mixture in a crucible lined with charcoal, and -then subjecting it to the very highest heat of a powerful furnace. It is hard, grayish-white, and brittle; of 5.9 specific gravity, and exceedingly difficult of fusion. Chromium is but little oxidable, being scarcely attacked by the most powerful acids ; it forms at least four compounds with oxygen, corresponding to, and probably isomorphous with, those of iron. The equivalent of chromium is 28.14 ;* its symbol is Cr. PROTOXIDE OF CHROMIUM, CrO. When potash is added to a solution of the new protochloride of chromium, a brown precipitate falls, which speedily passes to deep foxy red, with disengagement of hydrogen. The protoxide, in the state of the pale greenish hydrate, is perhaps obtained when ammonia is substituted for potash in the preceding experiment. This substance is a powerful base, forming pale blue salts, which absorb oxygen with extreme avidity. The double sulphate of protoxide of chromium and potash contains 6 eq. of water, like the other members of the same group.f DEUTOXIDE OF CHROMIUM:, CrO-f-Cr 2 O 3 , is the above brownish-red precipi- tate produced by the action of water upon the protoxide. The decomposi- tion is riot complete without boiling. This oxide corresponds with the mag- netic oxide of iron, and is not salifiable. SESQ.UIOXIDE OF CHROMIUM, Cr 2 O 3 . When chromate of mercury, prepared by mixing solutions of subnitrate of mercury and of chromate or bichromate of potash, is exposed to a red-heat, it is decomposed, pure oxide of chromium having a fine green color remaining. In this state the oxide is, like alumina after ignition, insoluble in acids. The hydrate may be had by boiling a somewhat dilute solution of bichromate of potash, strongly acidulated by hy- drochloric acid, with small successive portions of sugar ; carbonic acid escapes and the chromic acid of the salt becomes converted into chloride of chromium, the color of the liquid changing from red to deep green. A slight excess of ammonia precipitates the hydrate from this solution. It has a pale purplish- green color, which becomes full green on ignition ; an extraordinary shrinking of volume and. sudden incandescence is observed when the hydrate is decom- posed by heat. Anhydrous oxide in a beautifully crystalline condition may be prepared by heating to full redness in an earthen crucible bichromate of pot- ash. One-half of the acid suffers decomposition, oxygen being disengaged, and oxide of chromium left. The melted mass is then treated with water, which dissolves out neutral chromate of potash, and the oxide is, lastly, washed and dried. Oxide of chromium communicates a fine green tint to glass, and is used in enamel-painting. This oxide of chromium is a feeble base, resembling, and isomorphous with, peroxide of iron and alumina; the salts it forms have a green or purple color, and are said to be poisonous. The sulphate of sesquioxide of chromium is prepared by dissolving the hydrated oxide in dilute sulphuric acid. It unites with the sulphates of pot- ash and of ammonia, giving rise to magnificent salts which crystallize in regular octahedrons of a deep claret color, and possess a constitution resem- bling that of common alum, the alumina being replaced by oxide of chromium. The finest crystals of chromium alum are obtained by spontaneous evapora- tion, the solution being apt to be decomposed by heat. PROTOCHLORIDE OF CHROMIUM, CrCl. The violet-colored sesquichloride of chromium, contained in a porcelain or glass tube, is heated to redness in a * According to M. Peligot, 26.24. Ann. Chem. et Phys. 3d series, xii. 528. f Id. CHROMIUM. 263 current of perfectly dry and pure hydrogen gas; hydrochloric acid is disen- gaged, and a white foliated mass is obtained, which dissolves in water with great elevation of temperature, yielding a blue solution, which, by exposure to the air, absorbs oxygen with extraordinary energy, acquiring a deep green color, and passing into the state of oxychloride of chromium, Cr 2 Cl 2 -f-0. The protochloride of chromium is one of the most powerful reducing or deoxid- izing agents known. SESQ.UICHLORIDE OP CHROMIUM, Cr 2 Cl 3 . This substance is readily obtained in the anhydrous condition by heating to redness in a porcelain tube a mix- ture of oxide of chromium and charcoal, and passing dry chlorine gas over it. The sesquichloride sublimes, and is deposited in the cool part of the tube, in the form of beautiful crystalline plates of a pale violet-color. According to M. Peligot, it is totally insoluble in water under ordinary circumstances, even at a boiling heat. It dissolves, however, and assumes the deep green hydrated state in water containing an exceedingly minute quantity of the protochloride in solution. The hydration is marked by the evolution of much heat. This remarkable effect must probably be referred tcr the class of actions known at present under the name of katalysis.* The salts of the sesquioxide of chromium are easily recognized. Caustic alkalis precipitate the hydrated oxide, easily soluble in excess. Ammonia, the same, but nearly insoluble. Carbonates of potash, soda, and ammonia throw down a green precipitate of carbonate and hydrate, slightly soluble in a large excess. Sulphuretted hydrogen causes no change. Sulphuret of ammonium precipitates the hydrate of the oxide. CHROMIC ACID, Cr0 3 . 'Whenever oxide of chromium is strongly heated with an alkali, in contact with air, oxygen is absorbed and chromic acid gene- rated. Chromic acid may be obtained nearly pure, and in a state of great beauty, by the following simple process: 100 measures of a cold saturated solution of bichromate of potash are mixed with 150 measures of oil of vitriol, and the whole suffered to cool; the chromic acid crystallizes in brilliant crim- son-red prisms. The mother-liquor is poured off, and the crystals placed upon a tile to drain, being closely covered by a glass or bell jar. j- Chromic acid is very deliquescent and soluble in water; the solution is instantly reduced by contact with organic matter. Chromate of Potash, KO,Cr0 3 . This is the source of all the preparations of chromium ; it is made directly from the native chrome-iron ore, which is a com- pound of the oxide of chromium and protoxide of iron, analogous to magnetic iron ore, by calcination with nitre, or with carbonate of potash, the stone being reduced to powder, and heated for a long time with the alkali in a reverbe- ratory furnace. The product, when treated with water, yields a yellow solu- tion, which, by evaporation deposits anhydrous crystals of the same color, isomorphous with sulphate of potash. Chromate of potash has a cool, bitter, and disagreeable taste, and dissolves in 2 parts of water at 60. Bichromate of Potash, K0.2Cr0 3 . When sulphuric acid is added to the preceding salt in moderate quantity, one-half of the base is removed, and the neutral chromate converted into bichromate. The new salt, of which im- mense quantities are manufactured for use in the arts, crystallizes by slow evaporation in beautiful red tabular crystals, derived from an oblique rhombic #= See page 1.83. f Mr. Warrington: Proceedings of Chem. Soc. i. 18. 264 NICKEL. prism. It melts when heated, and is soluble in 10 parts of water, and the solution has an acid reaction. Chromate of Lead, Pb(XCrO 3 . On mixing solution of chromate or bichro- mate of potash with nitrate or acetate of lead, a brilliant yellow precipitate falls, which is the compound in question; it is the chrome yellow of the painter. When this compound is boiled with lime-water, one-half of the acid is with- drawn, and a subcbromate of an orange-red color left. The subchromate is also formed by adding chromate of lead to fused nitre, and afterwards dis- solving out the soluble salts by water; the product is crystalline, and rivals vermilion in beauty of tint. The yellow and orange chrome colors are fixed upon cloth by the alternate application of the two solutions, and in the latter case by passing the dyed stuff through a bath of boiling lime-water. Chromate of Silver, AgO,CrO 3 . This salt precipitates as a reddish brown powder when solutions of chromate of potash and nitrate of silver are mixed. It dissolves in hot dilute nitric acid, and separates, on cooling, in small ruby-red platy crystals. The chromates of baryta, zinc, and mercury are insoluble ; the first two are yellow, the last is brick-red. A salt of chromic acid is at once recognized by its behavior with solutions of baryta and lead; and also by its color and capability of furnishing, by deoxidation, the green oxide of chromium. CHLOROCHROMIC ACID, CrO 2 -f-Cj. 3 parts of bichromate of potash and 3J parts of common salt are intimately mixed and introduced into a small glass retort ; 9 parts of oil of vitriol are then added, and heat applied as long as dense red vapors arise. The product is a heavy deep red liquid resem- bling bromine ; it is decomposed by water, with production of chromic and hydrochloric acids. Nickel is found in tolerable abundance in some of the metal-bearing veins of the Hartz mountains, and in a few other localities, chiefly as arseniuret, the kupfernickel of mineralogists, so called from its yellowish-red color; the word nickel is a term of detraction, having been applied by the old German miners to what was looked upon as a kind of false copper ore. The artificial, or perhaps rather merely fused, product, called speiss, is nearly the same substance, and may be employed as a source of the nickel-salts. This metal is found in meteoric iron, as already mentioned. Nickel is easily prepared by exposing the oxalate to a high white heat, in a crucible lined with charcoal. It is a white, malleable metal, having a density of 8.8, a high melting-point, and a less degree of oxidability than iron, since it is but little attacked by dilute acids. Nickel is strongly magnetic, but loses its property when heated to 660. This metal forms two oxides, only one of which is basic. The equivalent of nickel is 29.57 ; its symbol is Ni. PROTOXIDE OF NICKEL, NiO. This compound is prepared by heating to redness the nitrate, or by precipitating a soluble salt with caustic potash, and washing, drying, and igniting the apple green hydrated oxide thrown down. It is an ash-gray powder, freely soluble in acids, which it completely neutralizes, being isomorphous with magnesia, and the other members of the same group. The salts of this substance have usually a beautiful green color. PEROXIDE, or SUPEROXIDE OF NICKEL, Ni 2 O 3 . The peroxide is a black insoluble substance, prepared by passing chlorine through the hydrated oxide NICKEL. 265 suspended in water; chloride of nickel is formed, and the oxygen of the oxide decomposed transferred to a second portion. It is also produced when a salt of nickel is mixed with a solution of bleaching-powder. The peroxide is decomposed by heat, and evolves chlorine when put into hot hydrochloric acid. CHLORIDE OF NICKEL, NiCl. This is easily prepared by dissolving oxide or carbonate of nickel in hydrochloric acid. A green solution is obtained which furnishes crystals of the same color, containing water. When rendered anhydrous by heat, the chloride is yellow, unless it contain cobalt, in which case it has a tint of green. SULPHATE OF NICKEL, NiO,S0 3 -f-VHO. This is the most important of the salts of nickel. It forms green prismatic crystals, containing 7 equivalents of water, which require 3 parts of cold water for solution. Crystals with 6 equivalents of water have also been obtained. It forms with the sul- phates of potash and ammonia, beautiful double salts, NiO,S0 3 -4-KO,S0 3 -f- 6HO and NiO,SO 3 -f-NH 4 O,SO 3 -f-6HO. When a strong solution of oxalic acid is mixed with sulphate of nickel, a pale bluish-green precipitate of oxa- late falls after some time, very little nickel remaining in solution. The oxalate can thus be obtained for preparing the metal. CARBONATE OF NICKEL. When solutions of sulphate or chloride of nickel and of carbonate of soda are mixed, a pale green precipitate falls, which is a combination of carbonate and hydrate of nickel. It is readily decom- posed by heat. Pure salts of nickel are conveniently prepared on the small scale from crude speiss or kupfernickelby the following process : The mineral is broken into small fragments, mixed with from one-fourth to half its weight of iron- filings, and the whole dissolved in aqua regia. The solution is gently evapo- rated to dryness, the residue treated with boiling water, and the insoluble arseniate of iron removed by a filter. The liquid is then acidulated with hydrochloric acid, treated with sulphuretted hydrogen in excess, and, after filtration, boiled with a little nitric acid to bring back the iron to the state of peroxide. To the cold and largely diluted liquid, solution of bicarbonate of soda is gradually added, by which the peroxide of iron may be completely separated without loss of nickel salt. Lastly, the filtered solution, boiled with carbonate of soda in excess, yields an abundant pale green precipitate of car- bonate of nickel, from which all the other compounds may be prepared. The salts of nickel are well characterized by their behavior with reagents. Caustic alkalis give a pale apple-green precipitate of hydrate, insoluble in excess. Ammonia affords a similar precipitate, which is soluble in excess, with deep purplish-blue color. Carbonate of potash and soda give pale green precipitates. Carbonate of ammonia, a similar precipitate, soluble in excess, with blue color. Ferrocyanide of potassium gives a greenish-white precipitate. Sulphuretted hydrogen occasions no change. Sulphuret of ammonium throws down black sulphuret of nickel. The chief use of nickel in the arts is in the preparation of a white alloy, sometimes called German silver, made by melting together 100 parts of cop- per, 60 of zinc, and 40 of nickel. This alloy is very malleable, and takes a high polish. 23 266 COBALT. This substance bears, in many respects, an extraordinary resemblance to the metal last described ; it is often associated with it in nature, and may be obtained from its compounds by similar means. Cobalt is a white, brittle metal, having a specific gravity of 8.5, and a very high melting point. It is unchanged in the air, and but feebly attacked by dilute hydrochloric and sul- phuric acids. It is strongly magnetic. There are two oxides of this rnetal, corresponding in properties and constitution with those of nickel. The equivalent of cobalt is 29.52 ; its symbol is Co. PROTOXIDE OF COBALT, CoO. This is gray powder, very soluble in acids, and is a strong base, isomorphous with magnesia, affording salts of a fine red tint. It is prepared by precipitating sulphate or chloride of cobalt with car- bonate of soda, and washing and drying and igniting the precipitate. When the cobalt solution is mixed with caustic potash a beautiful blue precipitate falls, which when heated becomes violet, and at length dirty red, from a change in the state of hydration. PEROXIDE OF COBALT, Co 2 O 3 . The peroxide is a black, insoluble, neutral powder, obtained by mixing solutions of cobalt and of chloride of lime. CHLORIDE OF COBALT, CoCl. The chloride is easily prepared by dissolving the oxide in hydrochloric acid ; it gives a deep rose-red solution, which, when sufficiently strong, deposits hydrated crystals of the same color. When the liquid is evaporated by heat to a very small bulk, it deposits anhydrous crys- tals which are blue ; these latter by contact with water again dissolve to a red liquid. A dilute solution of chloride of cobalt constitutes the well-known blue sympathetic ink; characters written on paper with this liquid are invisi- ble from their palenessof color until the salt has been rendered anhydrous by exposure to heat, when the letters appear blue. When laid aside, moisture is absorbed, and the writing once more disappears. Green sympathetic ink is a mixture of the chlorides of cobalt and nickel. Chloride of cobalt may be prepared directly from cobalt- glance, the native arseniuret, by a process exactly similar to that described in the case of nickel. SULPHATE OF COBALT, CoO,SO 3 4-7HO. This salt forms deep red crystals, requiring for solution 24 parts of cold water; they are identical in form with those of sulphate of magnesia. It combines with the sulphates of potash and ammonia, forming double salts, which contain as usual six equivalents of water. A solution of oxalic acid added to one of sulphate of cobalt occasions, after some time, the separation of nearly the whole of the base in the state of oxa- late. CARBONATE OF COBALT. The alkaline carbonates produce in solutions of cobalt a pale peach-blossom colored precipitate of combined carbonate and hydrate, containing 3CoO,HO-f 2CoCO 3 +HO. The salts of cobalt have the following characters. Solution of potash gives a blue precipitate, changing by heat to violet and red. Ammonia gives a blue precipitate, soluble with difficulty in excess, with brownish red color. Carbonate of soda affords a pink precipitate. Carbonate of ammonia, a similar compound, soluble in excess. Ferrocyanide of potassium gives a grayish-green precipitate. ZINC. 267 Sulphuretted hydrogen produces no change. Sulphuret of ammonium throws down black sulphuret of cobalt. Oxide of cobalt is remarkable for the magnificent blue color it communi- cates to glass: indeed this is a character by which its presence may be most easily detected, a very small portion of the substance to be examined being fused with borax on a loop of platinum wire before the blowpipe. The sub- stance called smalt, used as a pigment, consists of glass colored by oxide of cobalt; it is thus made : The cobalt ore is roasted until nearly free from ar- senic and then fused with a mixture of carbonate of potash and quartz-sand, free from oxide of iron. Any nickel that may happen to be contained in the ore then subsides to the bottom of the crucible as arseniuret; this is the speiss of which mention has already been made. The glass, when complete, is removed and poured into cold water; it is afterwards ground to powder and elutriated. Cobalt-ultramarine is a fine blue color prepared by mixing 16 parts of freshly-precipitated alumina with 2 parts of phosphate or arseniate of cobalt; this mixture is dried and slowly heated to redness. By daylight the color is pure blue, but by artificial light it is violet. Zaffre is the roasted cobalt ore mixed with a quantity of siliceous sand, and reduced to fine pow- der; it is used in enamel painting. A mixture in due proportions of the oxides of cobalt, manganese, and iron is used for giving a fine black color to glass. Zinc is a somewhat abundant metal; it is found in the state of carbonate and sulphuret, associated with lead ores in many districts, both in Britain and on the continent; large supplies are obtained from Silesia. The native car- bonate, or calamine, is the most valuable of the zinc ores, and is preferred for the extraction of the metal: it is first roasted to expel water and carbonic acid, mixed with fragments of coke or charcoal, and then distilled at a full red-heat in a large earthen retort; carbonic oxide escapes, while the reduced metal volatilizes and is condensed by suitable means. Zinc is a bluish-white metal, which slowly tarnishes in the air; it has a lamellar, crystalline structure, a density varying from 6.8 to 7.2, and is, under ordinary circumstances, brittle. Between 25(J and 300 it is, on the con- trary, malleable, and may be rolled or hammered without danger of fracture, and, what is very remarkable, after such treatment, retains its malleability when cold: the sheet zinc of commerce is thus made. At 400 it is so brittle that it may be reduced to powder. At 773 it rnelta: at a bright red heat it boils and volatilizes, and, if air be admitted, burns with a splendid green light, generating the oxide. Dilute acids dissolve zinc very readily; it is con- stantly employed in this manner in preparing hydrogen gas. The equivalent of zinc has been fixed at 33.; its symbol is Zn. OXIDE OF ZINC, ZnO. Only one oxide of this metal is known to exist; it is a strong base, isomorphous with magnesia; it is prepared either by burn- ing zinc in atmospheric air, or by heating to redness the carbonate. Oxide of zinc is a white, tasteless powder, insoluble in water, but freely dissolved by acids. When heated it is yellow. SULPHATE OF ZINC; WHITE VITHIOL; ZnO, SO 3 + 7HO. This salt is hardly to be distinguished by the eye from sulphate of magnesia; it is pre- pared either by dissolving the metal in dilute sulphuric acid, or, more eco- nomically, by roasting the native sulphuret, or blende, which, by absorption of oxygen becomes in great part converted into sulphate of the oxide. The 268 CADMIUM. altered mineral is thrown hot into water, and the salt obtained by evaporat- ing the clear solution. Sulphate of zinc has an astringent, metallic taste, and is used in medicine as an emetic. The crystals dissolve in 2^ parts of cold, and in a much smaller quantity of hot water. Crystals containing six equiva- lents of water have been observed. Sulphate of zinc forms double salts with the sulphates of potash and ammonia. CARBONATE OF ZINC, ZnO,CO 2 . The neutral carbonate is found native ; the white precipitate obtained by mixing solutions of zinc and of alkaline carbonates is a combination of carbonate and hydrate. When heated to red- ness, it yields pure oxide of zinc. CHLORIDE OP ZINC, ZnCl. The chloride may be prepared by heating metallic zinc in chlorine ; by distilling a mixture of zinc-filings and corrosive sublimate ; or, more easily, by dissolving zinc in hydrochloric acid. It is a nearly white, translucent, fusible substance, very soluble in water and alcohol, and very deliquescent. A strong solution of chloride of zinc is sometimes used as a bath for obtaining a graduated heat above 212. Chloride of zinc unites with sal-ammoniac and chloride of potassium to double salts ; the former of these, made by dissolving an equivalent of zinc in the requisite quantity of hydrochloric acid, and then adding an equivalent of sal-ammoniac, is very useful in tinning and soft-soldering copper and iron. A salt of zinc is easily distinguished by appropriate reagents. Caustic potash and soda give a white precipitate of hydrate, freely soluble in excess of alkali. Ammonia behaves in the same manner ; an excess re-dissolves the precipi- tate instantly. The carbonates of potash and soda give white precipitates, insoluble in excess. Carbonate of ammonia gives also a white precipitate, which is redissolved by an excess. Ferrocyanide of potassium gives a white precipitate. Sulphuretted hydrogen causes no change.* Sulphuret of ammonium throws down white sulphuret of zinc. The applications of metallic zinc to the purposes of roofing, the construction of water-channels, &c., are well known ; it is sufficiently durable, but inferior in this respect to copper. CADMIUM. This metal was discovered in 1817 by Stromeyer ; it accompanies the ores of zinc, and, being more volatile than that substance, rises first in vapor when the calamine is subjected to distillation with charcoal. Cadmium re- sembles tin in color, but is somewhat harder; it is very malleable, has a density of 8.7, melts below 500, and is nearly as volatile as mercury. It tarnishes but little in the air, but, when strongly heated, burns. Dilute sulphuric and hydrochloric acids act but little on this metal in the cold; nitric acid is its best solvent. The equivalent of cadmium is 55.74; its symbol is Cd. * With neutral solutions, or zinc-salts of an organic acid, a white precipitate ensues. BISMUTH. 269 OXIDE OF CADMIUM, CdO. The oxide may be prepared by igniting either the carbonate or the nitrate; in the former case it has a pale brown color, and in the latter a much darker tint, and a crystalline aspect. Oxide of cad- mium is infusible; it dissolves in acids, producing a series of colorless salts. SULPHATE OF CADMIUM, CdO,S0 3 -j-4HO. This is easily obtained by dis- solving the oxide or carbonate in dilute sulphuric acid ; it is very soluble in water, and forms double salts with the sulphates of potash and of ammonia, which contain CdO,S0 3 +KO,SO 3 -f 6HO, and the latter CdO,S0 3 +NH 4 O,S0 3 -f6HO. CHLORIDE OF CADMIUM, CdCl. This is a very soluble salt, crystallizing in small four-sided prisms. SULPHURET OF CADMIUM is a very characteristic compound, of a bright yellow color, fusible at a high temperature. It is obtained bypassing sulphu- retted hydrogen gas through a solution of the sulphate, nitrate, or chloride, The salts of cadmium are thus distinguished: Caustic alkalis give a white precipitate of hydrated oxide, insoluble in excess. Ammonia gives a similar white precipitate, readily soluble in excess. The alkaline carbonates, and carbonate of ammonia, throw down white carbonate of cadmium, insoluble in excess of either precipitant. Sulphuretted hydrogen and sulphuret of ammonium precipitate the yellow sulphuret of cadmium. Bismuth is found chiefly in the metallic state, disseminated through an earthy matrix, from which it is separated by simple exposure to heat. The metal is highly crystalline and very brittle ; it has a reddish-white color, and a density of 9.9. Cubic crystals of great beauty may be obtained by slowly cooling a considerable mass of this substance until solidification has commenced, and then piercing the crust, and pouring out the fluid residue. Bismuth melts at about 500, and volatilizes at a high temperature : it is little oxidized by the air, but burns when strongly heated with a bluish flame. Nitric acid, somewhat diluted, dissolves it freely. The equivalent of bismuth is 70.96 ; its symbol is Bi. OXIDE OF BISMUTH, BiO. This is the base of all the salts. It is a straw- yellow powder, obtained by gently igniting the subnitrate. It is fusible at a high temperature, and in that state acts towards siliceous matter as a power- ful flux. PEROXIDE or SUPEROXIDE OF BISMUTH, Bi 2 3 . The peroxide is a brown powder, obtained by boiling the above described oxide with solution of hypo- chlorite of potash. (Bleaching liquid.) It is decomposed by heat, and does not unite with acids. NITRATE OF BISMUTH, BiO,N0 5 -f-3HO. When bismuth is dissolved in moderately strong nitric acid to saturation, and the whole left to cool, large, colorless, transparent crystals of the neutral nitrate are deposited. Water decomposes these crystals ; an acid solution containing a little bismuth is obtained, and a brilliant white crystalline powder is left, which is a subnitrate containing BiO,NO 5 -J-3BiO ; HO. A solution of nitrate of bismuth, free from any great access of acid, poured into a large quantity of cold water, yields an insoluble subnitrate, very similar in appearance to the above, but contain- ing rather a smaller proportion of oxide of bismuth. This remarkable de- composition illustrates at once the basic property of water, and the feeble 23* 270 URANIUM. affinity of oxide of bismuth for acids, the nitric acid dividing itself between the two bases. The decomposition of a neutral salt by water is by no means an uncommon occurrence in the history of the metals ; a solution of chloride of antimony exhibits the same phenomenon ; certain salts of mercury are affected in a similar manner, and other cases might perhaps be cited, less con- spicuous, where the same change takes place to a smaller extent. Subnitrate of bismuth was once extensively employed as a cosmetic, but is said to injure the skin, rendering it yellow arid leather-like. It has been used in medicine. The other salts of bismuth possess few points of interest. Bismuth is abundantly characterized by the decomposition of the nitrate by water, and by the blackening the subnitrate undergoes when exposed to the action of sulphuretted hydrogen gas. A mixture of 8 parts of bismuth, 5 parts of lead, and 3 of tin, is known under the name of fusible metal, and is employed in taking impressions from dies and for other purposes; it melts below 212. The discrepancies so frequently observed between the properties of alloys and those of their con- stituent metals, plainly show that such substances must be looked upon as true chemical compounds, and not as mere mixtures ; in the present case the proof is complete, for the fusible metal has lately been obtained in crystals.* URANIUM. This metal is found in a few minerals, as pitchblende and uranite, of which the former is the most abundant. It appears from the recent interesting researches of M. Peligot,j- that the substance hitherto taken for metallic uranium, obtained by the action of hydrogen gas upon the black oxide, is not in reality the metal, but a protoxide, capable of uniting directly with acids, and, like the protoxide of manganese, not decomposable by hydrogen at a red- heat. The metal itself can be obtained only by the intervention of potassium, applied in the same manner as in the preparation of magnesium. It is de- scribed as a black coherent powder, or a white malleable metal, according to the state of aggregation, not oxidized by air or water, but eminently com- bustible when exposed to heat. It unites also with great violence with chlo- rine and with sulphur. M. P&igot admits three distinct oxides of uranium, besides two other compounds of the metal and oxygen, which he designates as suboxides. The equivalent of uranium is 60. Its symbol is U. PROTOXIDE OF URANIUM, UO. This is the ancient metal ; it is prepared by several processes, one of which has been already mentioned. It is a brown powder, sometimes highly crystalline. When in minute division it is pyro- phoric, taking fire in the air, and burning to black oxide. It forms with acids a series of green salts. A corresponding chloride exists, which forms dark green octahedral crystals, highly deliquescent and soluble in water. M. Peli- got attributes a very extraordinary double function to this substance, namely, that of acting as a protoxide and forming salts with acids, and that of com- bining with chlorine or oxygen after the fashion of an elementary body. DEUTOXIDE OF URANIUM; BLACK OXIDE ; U 4 5 ,or 2UO-f-U 2 O 3 . The black oxide, formerly considered as protoxide, is produced when both protoxide and peroxide are strongly heated in the air, the former gaining, and the latter * Annalen der Chemie und Pharmacie, xliv. 275. f Ann. Chim. et Phys. 3d series, v. 5. COPPER. 271 losing, a certain quantity of oxygen. It forms no salts, but is resolved by solution in acids into protoxide and peroxide. PEROXIDE OF URANIUM, U 2 O 3 . The peroxide is the best known and most important of the three; it forms a number of extremely beautiful yellow salts. When caustic alkali is added to a solution of pernitrate of uranium, a yellow precipitate of hydrated oxide fells, which retains, however, a portion of the precipitant. The hydrate cannot be exposed to a heat sufficient to expel the water without a commencement of decomposition. A better method of ob- taining the oxide is to heat by means of an oil-bath the powdered and dried crystals of the nitrate to 480 F., until no more nitrous fumes are disengaged. Its color in this state is chamois-yellow. NITRATE OF PEROXIDE OF URANIUM, U 2 O 3 ,N0 5 -f-6HO; or (U 2 O 2 ) O,N0 5 -f- 6HO ; U 2 O 2 being the supposed quasi-metal. The pernitrate is the starting point in the preparation of all the compounds of uranium ; it maybe prepared from pitchblende by dissolving the pulverized mineral in nitric acid, evapo- rating to dryness, adding water and filtering ; the liquid furnishes by due evaporation crystals of nitrate of uranium, which are repurified by a repeti- tion of the process, and, lastly, dissolved in ether. This latter solution yields the pure nitrate. The green salts of uranium are peroxidized by boiling with nitric acid. A yellow precipitate with caustic alkalis, convertible by heat into black oxide; a brown precipitate with sulphuret of ammonium; and none at all with sulphuretted hydrogen gas, sufficiently characterize the salts of peroxide of uranium. A solution suspected to contain protoxide may be boiled with a little nitric acid, and then examined. The only application of uranium is that to enamel-painting and the staining of glass ; the deutoxide giving a fine black color, and the peroxide a delicate yellow. Copper is a metal of great value in the arts of life; it sometimes occurs in the metallic state, crystallized in octahedrons, but is more abundant in the condition of red oxide, and in that of sulphuret combined with sulphuret of iron, or yellow copper ore. Large quantities of the latter substance are an- nually obtained from the Cornish mines and taken to South Wales for reduction, which is effected by a somewhat complex process. The principle of this may, however, be easily made intelligible. The ore is roasted in a reverbe- ratory furnace, by which much of the sulphuret of iron is converted into oxide, while the sulphuret of copper remains unaltered. The product of this operation is then strongly heated with siliceous sand ; the latter combines with the oxide of iron to a fusible slag, and separates from the heavier copper-compound. When the iron has, by a repetition of these processes, been got rid of. the sulphuret of copper begins to decompose in the flame- furnace, losing its sulphur and absorbing oxygen; the temperature is then raised sufficiently to reduce the oxide thus produced, by the aid of carbon- aceous matter. The last part of the operation consists in thrusting into the melted metal a pole of birch-wood, the object of which is probably to reduce a little remaining oxide by the combustible gases thus generated. Large quantities of~extremely valuable ore, chiefly carbonate and red oxide, have lately been obtained from South Australia. 272 COPPER. Copper has a well-known yellowish-red color, a specific gravity of 8.96, and is very malleable and ductile; it is an excellent conductor of heat and electricity; it melts at a bright red-heat, and seems to be a little volatile at a- very high temperature. Copper undergoes no change in dry air; exposed to a moist atmosphere, it becomes covered with a strongly adherent green crust, consisting in a great measure of carbonate. Heated to redness in the air, it is quickly oxidized, becoming covered with a black scale. Dilute sul- phuric and hydrochloric acids scarcely act upon copper; boiling oil of vitriol attacks it with evolution of sulphurous acid; nitric acid, even dilute, dissolves it readily. Two oxides are known which form salts ; a third, or superoxide, is said to exist. The equivalent of copper is 31.65; its symbol Cu. PROTOXIDE OF COPPER ; BLACK OXIDE ; CuO. This is the base of the ordinary blue and green salts. It is prepared by calcining metallic copper at a red-heat, with full exposure to air, or, more conveniently, by heating to red- ness the nitrate, which suffers complete decomposition. When a salt of this oxide is mixed with caustic alkali in excess, a bulky pale blue precipitate of hydrated oxide falls, which, when the whole is raised to the boiling-point, becomes converted into a heavy dark brown powder ; this also is anhydrous oxide of copper, the hydrate suffering decomposition, even in contact with water. The oxide prepared at a high temperature is perfectly black and very dense. Protoxide of copper is soluble in acids, and forms a series of very important salts, being isomorphous with magnesia. SUBOXIDE OF COPPER; RED OXIDE; Cu 2 O. The suboxide may be obtained by heating in a covered crucible a mixture of 5 parts of black oxide and 4 parts of fine copper-filings ; or by adding grape-sugar to a solution of sulphate of copper, and then putting in an excess of caustic potash; the blue solution, heated to ebullition, is reduced by the sugar and deposits suboxide. It often occurs in beautifully transparent ruby-red crystals, associated with other ores of copper, and can be obtained in this state by artificial means. This substance forms colorless salts with acids, which are exceedingly instable, and tend to absorb oxygen. The suboxide communicates to glass a magnificent red tint, while that given by the protoxide is green. SULPHATE OF COPPER ; BLUE VITRIOL ; CuO,S0 3 -f-5HO. This beautiful salt is prepared by dissolving oxide of copper in sulphuric acid, or, at less expense, by oxidizing the sulphuret. It forms large blue crystals, soluble in 4 parts of cold and 2 of boiling water; by heat it is rendered anhydrous and nearly white, and by a very high temperature decomposed. Sulphate of copper combines with the sulphates of potash and of ammonia, forming pale blue salts which contain 6 equivalents of water, and also with ammonia, gen- erating a remarkable compound of deep blue color, capable of crystallizing. NITRATE OF COPPER, CuO,NO 5 -f-3HO. The nitrate is easily made by dis- solving the metal in nitric acid; it forms deep blue crystals, very soluble arid deliquescent. It is highly corrosive. An insoluble subnitrate is known ; it is green. Nitrate of copper also combines with ammonia. CARBONATES OF COPPER. When carbonate of soda is added in excess to a solution of sulphate of copper, the precipitate is at first pale blue and floccu- lent, but by warming it becomes sandy, and assumes a green tint ; in this state it contains CuO,C0 2 -|-CuO,HO. This substance is prepared as a pig- ment. The beautiful mineral malachite has a similar composition. Another natural compound, not yet artificially imitated, occurs in large transparent crystals of the most intense blue ; it contains 2CuO,CO 2 -|-CuO,HO. Verditer, made by decomposing nitrate of copper by chalk, is said, however, to have a somewhat similar composition. CHLORIDE OF COPPER, CuCl-f-2HO. The chloride is most easily prepared LEAD. 273 by dissolving the black oxide in hydrochloric acid, and concentrating the green solution thence resulting. It forms green crystals, very soluble in water and in alcohol ; it colors the flame of the latter green. When gently heated, it parts with its water of crystallization and becomes yellowish-brown; at a high temperature it loses half its chlorine and becomes converted into the subchloride. The latter is a white fusible substance, but little soluble in water, and prone to oxidation ; it is formed when copper-filings or copper-leaf are put into chlorine gas. ARSENITE OF COPPER; SCHEELE'S GREEN. This is prepared by mixing solutions of sulphate of copper and arsenite of potash ; it falls as a bright green insoluble powder. This compound is chiefly interesting in relation to the detection of arsenic. The characters of the proto-salts of copper are well marked. Caustic potash gives a pale blue precipitate of hydrate, becoming blackish- brown on boiling. Ammonia also throws down the hydrate; but, when in excess, re-dissolves it, yielding an intense purplish blue solution. Carbonates of potash and soda give pale plue precipitates, insoluble in excess. Carbonate of ammonia, the same, but soluble with deep blue color. Ferrocyanide of potassium gives a fine red-brown precipitate of ferrocyanide of copper. Sulphuretted hydrogen and sulphuret of ammonium afford black sulphuret of copper. The alloys of copper are of great importance. Brass consists of copper alloyed with from 28 to 34 per cent, of zinc; the latter may be added directly to the melted copper, or granulated copper may be heated with calamine and charcoal powder, as in the old process. -Gun-metal, a most trustworthy and valuable alloy, consists of 90 parts copper and 10 tin. Bell and speculum metal contain a still larger proportion of tin; these are brittle, especially that last named. A good bronze for statues is made of 91 parts copper, 2 parts tin, 6 parts zinc, and 1 part lead. The brass of the ancients is an alloy of copper with tin. This abundant and useful metal is altogether obtained from the native sul- phuret, or galena, no other lead ore being found in quantity. The reduction is effected in a reverberatory furnace, into which the crushed lead ore is introduced and roasted for some time at a dull red-heat, by which much of the sulphuret becomes changed by oxidation to sulphate. The contents of the furnace are then thoroughly mixed, and the temperature raised, when the sulphate and sulphuret react upon each other, producing sulphurous acid and metallic lead.* Lead is a soft bluish metal, possessing very little elasticity; its specific ! Oxide of (Lead Free, lead } Oxygen _^-^ 2 sulphurous acid. Sulphuric ~ acid Sulphuret of lead Free. 274 LEAD. gravity is 11.45. It may be easily rolled out into plates, or drawn into coarse wire, but has a very trifling degree of strength. Lead melts at 600 or a little above, and at a white heat boils and volatilizes. By slow cooling it may be obtained in octahedral crystals. In moist air this metal becomes coated with a film of gray matter, thought to be suboxide, and when exposed to the atmosphere in a melted state it rapidly absorbs oxygen. Dilute acids, wiih the exception of nitric, act but slowly upon lead. Chemists are familiar with four oxides of lead, only one of which possesses basic properties. The equivalent of lead is 103.56 ; its symbol is Pb. PROTOXIDE; LITHARGE; MASSICOT; PbO. This is the product of the direct oxidation of the metal. It is most conveniently prepared by heating the car- bonate to dull redness; common litharge is impure protoxide which has under- gone fusion. Protoxide of lead has a delicate straw-yellow color, is very heavy, and slightly soluble in water, giving an alkaline liquid. At a red-heat it melts, and tends to crystallize on cooling. In a melted state it attacks and dissolves siliceous matter with astonishing facility, often penetrating an earthen crucible in a few minutes. It is easily reduced when heated with organic substances of any kind containing carbon or hydrogen. Protoxide of lead forms a large class of salts, which are colorless, if the acid itself be not colored. RED OXIDE; RED LEAD; Pb 3 O 4 , or 2PbO-f PbO 2 . The composition of this substance is not very constant ; it is prepared by exposing for a long time to the air, at a very faint red-heat, protoxide of lead which has not been fused ; it is a brilliant red and extremely heavy powder, decomposed with evolution of oxygen by a strong heat, and converted into a mixture of protoxide and peroxide by acids. It is used as a cheap substitute for vermilion. PEROXIDE OF LEAD ; PUCE OR BROWN OXIDE; PbO 2 . This compound is obtained without difficulty by digesting red-lead in dilute nitric acid, when nitrate of protoxide is dissolved out and insoluble peroxide left behind in the form of a deep brown powder. The peroxide is decomposed by a red-heat, yielding up one-half of its oxygen. Hydrochloric acid converts it into chloride of lead with disengagement of chlorine; hot oil of vitriol forms with it sul- phate of lead, and liberates oxygen.; and solution of ammonia gives nitrate of lead and water. The peroxide is very useful in separating sulphurous acid from certain gaseous mixtures, sulphate of lead being then produced. SUBOXIDE OF LEAD, Pb 2 O. When oxalateof lead is heated to dull redness in a retort, a gray pulverulent substance is left, which is resolved by acids into protoxide of lead and metal. It absorbs oxygen with great rapidity when heated, and even when simply moistened with water and exposed to the air. NITRATE OF LEAD, PbO,N0 5 . The nitrate may be obtained by dissolving carbonate of lead in nitric acid, or by acting directly upon the metal by the same agent with the aid of heat; it is, as already noticed, a by-product in the preparation of the peroxide. It crystallizes in anhydrous octahedrons, which are usually milk-white and opaque; it dissolves in 7^ parts of cold water, and is decomposed by heat, yielding pure protoxide of lead, nitrous acid, and oxy- gen. When a solution of this salt is boiled with an additional quantity of oxide of lead, a portion of the latter is dissolved, and a basic, or sub-nitrate generated, which may be had in crystals. Carbonic acid separates this excess of oxide in the form of a white compound of carbonate and hydrate of lead. Neutral and basic compounds of oxide of lead with hyponitrous, and the elements of nitrous acid, have been described. These last are probably formed by the combination of a hyponitrite with a nitrate. CARBOXATE OF LEAD ; WHITE LEAD ; PbO,CO 2 . Carbonate of lead is some- times found beautifully crystallized in long white needles, accompanying other metallic ores. It may be prepared artificially by precipitating a solution of the nitrate or acetate by an alkaline carbonate; it is also manufactured to an LEAD. 275 | immense extent by other means for the use of the painter. Pure carbonate of lead is a soft, white powder, of great specific gravity, insoluble in water, but easily dissolved by dilute nitric or acetic acid. Of the many methods put in practice, or proposed, for making white-lead the two following are the most important and interesting : One of these consists in forming subnitrate or subacetate of lead by boiling finely-powdered litharge with the neutral salt. This solution is then brought into contact with carbonic acid gas; all the excess of oxide previously taken up by the neutral salt is at once precipitated as white-lead. The solution strained or pressed from the latter is again boiled with litharge, and treated with carbonic acid, these processes being susceptible of indefinite repetition, when the little loss of neutral salt left in the precipitates is compensated. The second, and by far the more ancient method, is rather more complex, and at first sight not very intelligible. A great number of earthen jars are prepared, into each of which is poured a few ounces of crude vinegar; a roll of sheet-lead is then introduced in such a manner that it shall neither touch the vinegar nor pro- ject above the top of the jar. The vessels are next arranged in a large building, side by side, upon a layer of stable manure, or, still better, spent-tan, and closely covered with boards. A second layer of tan is spread upon the top of the latter, and then a second series of pots ; these are in turn covered with boards and decomposing bark, and in this manner a pile of many alter- nations is constructed. After the lapse of a considerable time the pile is taken down and the sheets of lead removed and carefully unrolled; they are then found to be in great part converted into carbonate, which merely re- quires washing and grinding to be fit for use. The nature of this curious process is generally explained by supposing the vapor of vinegar raised by the high temperature of the fermenting matter merely to act as a carrier be- tween the carbonic acid evolved from the tan, and the oxide of lead formed under the influence of the acid vapor; a neutral acetate, a subacetate, and a carbonate being produced in succession, the action gradually traveling from the surface inwards. The quantity of acetic acid used is, in relation to the lead, quite trifling, and cannot directly contribute to the production of car- bonate. A preference is still given to the product of this ol<^ mode of manu- facture on account of its superiority of opacity, or body, over that obtained by precipitation. Commercial white-lead, however prepared, always contains a certain proportion of hydrate. When clean metallic lead is put into pure water and exposed to the at- mosphere, a white, crystalline, scaly powder begins to show itself in a few hours, and very rapidly increases in quantity. This substance is due to the action of the carbonic acid dissolved in the water; it consists of carbonate in combination with hydrate. When common river or spring water is substi- tuted for the pure liquid, this effect is scarcely observable, the little sulphate, almost invariably present, causing the deposition of a very thin but closely- adherent film of sulphate of lead upon the surface of the metal, which pro- tects it from further action. It is on this account that leaden cisterns are used with impunity, at least in most cases, for holding water; if the latter were pure, it would be speedily contaminated with lead, and the cistern be soon destroyed. Natural water highly charged with carbonic acid cannot, under any circumstances, be kept in lead, or passed through leaden pipes with safety. CHLORIDE OF LEAD, PbCl. This salt is prepared by mixing strong solu- tions of acetate of lead and chloride of sodium ; or by dissolving litharge in boiling dilute hydrochloric acid, and setting aside the filtered solution to cool. Chloride of lead crystallizes in brilliant, colorless needles, which require 135 276 LEAD. parts of cold water for solution. It is anhydrous; it melts when heated, and solidifies on cooling to a horn-like substance. IODIDE OF LEAD, Pbl. The iodide of lead separates as a brilliant yellow precipitate when a soluble salt of lead is mixed with iodide of potassium. This compound dissolves in boiling water, yielding a colorless solution, which deposits the iodide on cooling in splendid golden-yellow scales. The soluble salts of lead thus behave with reagents : Caustic potash and soda precipitate a white hydrate, freely soluble in excess. Ammonia gives a similar white precipitate, not soluble in excess.* The carbonates of potash, soda, and ammonia precipitate carbonate of lead, insoluble in excess. Sulphuric acid or a sulphate causes a white precipitate of sulphate of lead, insoluble in nitric acid. Sulphuretted hydrogen and sulphuret of ammonium throw down black sulphuret of lead. An alloy of two parts of lead and one of tin constitutes plumber's solder these proportions reversed give a more fusible compound called fine solder. The lead employed in the manufacture of shot is combined with a little arsenic. * Ammonia gives no immediate precipitate with the acetate. TIN. 277 SECTION Y. OXIDABLE METALS PROPER, WHOSE OXIDES FORM WEAK BASES OR ACIDS. THIS valuable metal occurs in the state of oxide, and more rarely as sul- phuret ; the principal tin-mines are those of the Ertzgebirge in Saxony and Bohemia, Malacca, and more especially Cornwall. In Cornwall the tin-stone is found as a constituent of metal -bearing veins, associated with copper ore, in granite and slate-rocks; and as an alluvial deposit, mixed with rounded pebbles, in the beds of several small rivers. The first variety is called mine, and the second stream tin. Oxide of tin is also found disseminated through the rock itself in small crystals. To prepare the ore for reduction, it is stamped to powder, washed, to sepa- rate as much as possible of the earthy matter, and roasted to expel sulphur and arsenic; it is then strongly heated with coal, and the metal thus obtained cast into large blocks, which, after being assayed, receive the stamp of the Duchy. Two varieties of commercial tin are known, called grain and bar- tin ; the first is the best ; it is prepared from the stream ore. Pure tin has a white color, approaching to that of silver ; it is soft and malleable, and when bent or twisted emits a peculiar crackling sound ; it has a density of 7.3 and melts at 442 F. Tin is but little acted upon by air and water, even conjointly ; when heated above its melting point, it oxidizes rapidly, becoming converted into a whitish powder, used in the arts for polish- ing, under the name of putty powder. The metal is easily attacked and dis- solved by hydrochloric acid, with evolution of hydrogen; nitric acid acts with great energy, converting it into a white hydrate of the peroxide. There are two well-marked oxides of tin, which act as feeble bases or acids, according to circumstances, and a third, which has been less studied. The equivalent of tin is 58.82 ; its symbol is Sn. PROTOXIDE OF TIN, SnO. When solution of protochloride of tin is mixed with carbonate of potash, a white hydrate of the protoxide falls, the carbonic acid being at the same time extricated. When this is carefully washed', dried, and heated in an atmosphere of carbonic acid, it loses water and changes to a dense black powder, which is permanent in the air, but takes fire on the approach of a red-hot body, and burns like tinder, producing peroxide. The hydrate is freely soluble in caustic potash ; the solution decom- poses by keeping into metallic tin and peroxide. SESQJTIOXIDE OF Tix, Sn 2 O 3 . The sesquioxide is produced by the action of hydrated peroxide of iron upon protochloride of tin ; it is a grayish, slimy substance, soluble in hydrochloric acid, and in ammonia. This oxide has been but little examined. PEROXIDE OF TIN, SnO 2 . This substance is obtained in two different states, having properties altogether dissimilar. When perchloride of tin is 24 278 TIN. precipitated by an alkali, a white bulky hydrate appears, which is freely solu- ble in acids. If, on the other hand, the bichloride be boiled with excess of nitric acid, or if that acid be made to act directly on metallic tin, a white substance is produced, which refuses altogether to dissolve in acids, and possesses properties differing in other respects from those of the first modifi- cation. Both these varieties of peroxide of tin have the same composition, and when ignited, leave the pure peroxide of a pale lemon-yellow tint. Both dissolve in caustic alkali, and are precipitated with unchanged properties by an acid. The two hydrates redden litmus paper. PUOTOCHLORIDE OF TIN", SnCl. The protochloride is easily made by dis- solving metallic tin in hot hydrochloric acid. It crystallizes in needles con- taining 3 equivalents of water, which are freely soluble in a small quantity of water, but are apt to be decomposed in part when put into a large mass, unless hydrochloric acid in excess be present. The anhydrous chloride may be obtained by distilling a mixture of calomel and powdered tin, prepared by agitating the melted metal in a wooden box until it solidifies. The chlo- ride is a gray, resinous looking substance, fusible below redness, and volatile at a high temperature. Solution of protochloride of tin is employed as a de- oxidizing agent ; it reduces the salts of mercury and other metals of the same class. PERCHLORIDE, or BICHLORIDE OP TIN, SnCl 2 . This is an old and very curious compound, formerly called fuming liquor of Libavius. It is made by exposing metallic tin to the action of chlorine, or, more conveniently, by dis- tilling a mixture of 1 part of powdered tin, and 5 parts of corrosive subli- mate. The bichloride is a thin, colorless, mobile liquid; it boils at 248, and yields a colorless invisible vapor. It fumes in the air, and when mixed with a third part of water, solidifies to a crystalline mass. The solution of bichlo- ride is much employed by the dyer as a mordant : it is commonly prepared by dissolving metallic tin in a mixture of hydrochloric and nitric acids, care being taken to avoid too great elevation of temperature. SULPHURETS OF TIN. Protosulphuret, SnS, is prepared by fusing tin with excess of sulphur, and strongly heating the product. It is a lead-gray, brittle substance, fusible by a red-heat, and soluble with evolution of sulphuretted hydrogen in hot hydrochloric acid. A sesqui- sulphur et may be formed by gently heating the above compound with a third of its weight of sulphur ; it is yellowish-gray and easily decomposed by heat. Bisulphuret, SnS 2 , or Mosaic gold, is prepared by exposing to a low red-heat, in a glass flask, a mix- ture of 12 parts of tin, 6 of mercury, 6 of sal-ammoniac, and 7 of flowers of sulphur. Sal-ammoniac, cinnabar, and protochloride of tin sublime, while the bisulphuret remains at the bottom of the vessel in the form of brilliant gold-colored scales; it is used as a substitute for gold-powder. Salts of tin are thus distinguished : Protoxide. Caustic alkalis; white hydrate, soluble in excess. Ammonia ; carbonates of } potash, soda, and am- > White hydrate, insoluble in excess. monia . . j Peroxide. Caustic alkalis ; white hydrate, soluble in excess. Ammonia ; white hydrate, slightly soluble in excess. TUNGSTEN MOLYBDENUM. 279 Alkaline carbonates ; white hydrate, slightly soluble in excess. Carbonate of ammonia ; white hydrate, insoluble. Sulphuretted hydrogen ; yellow precipitate of sulphuret. Sulphuret of ammonium ; the same, soluble in excess. Chloride of gold, added to a dilute solution of protochloride of tin, gives rise to a brownish-purple precipitate, called purple of Cassius, very character- istic, whose nature is not thoroughly understood; it is supposed to be a com- bination of oxide of gold and sesquioxide of tin, in which the latter acts as an acid, or AuO,Sn 2 O 3 . Heat resolves it into a mixture of metallic gold and peroxide 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 adm'ixture of a little antimony, &c. Cooking vessels of copper are usually tinned in the interior. TUNGSTEN. Tungsten is found in the mineral wolfram, tolerably abundant in Cornwall; a native tungstate of lime is also occasionally met with. Metallic tungsten is obtained in the state of a dark gray powder, by strongly heating tungstic acid in a stream of hydrogen, but requires for fusion an exceedingly high tempera- ture. 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 94.64 ; its symbol is W. (wolframium). OXIDE OF TUNGSTEN, WO 2 . 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 oxide forms no salts with acids. TUNGSTIC ACID, W0 3 . 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. Two chlorides and two sulphurets 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 oxidizing, when heated in the air, to molybdic acid. The equivalent of molybdenum is 47.88; its symbol is Mo. PROTOXIDE OF MOLYBDENUM, MoO. Molybclate of potash is mixed with excess 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 potash is then added, which precipitates a black hydrate of the protoxide of molyb- denum, and retains in solution the oxide of zinc. The freshly precipitated 280 VANADIUM. protoxide is soluble in acids and in carbonate of ammonia ; when heated in the air, it burns to binoxide. BINOXIDE OF MOLYBDENUM, Mo0 2 . This is obtained in the anhydrous condition by heating rnolybdate 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 color, and then adding a large excess of ammonia. The anhydrous binoxide is deep brown, and insoluble in acids; the hydrate resembles hydrate of the peroxide of iron, and dissolves in acids, yielding red solutions. It is converted into molybdic acid by strong nitric acid. MOLYBDIC ACID, Mo0 3 . The native sulphuret of molybdenum is roasted, at a red-heat, in an open vessel, and the impure molybdic acid thence result- ing dissolved in ammonia. The filtered solution is evaporated to dryness, the salt taken up by water, and purified by crystallization. It is, lastly, decom- posed by heat, and the ammonia expelled. Molybdic acid is a yellow pow- der, fusible at a red heat, and slightly soluble in water. It is dissolved with ease by the alkalis. Three chlorides, and as many sulphurets of molybdenum, are described. VANADIUM. Vanadium is found, in small quantity, in one of the Swedish iron ores, and also as vanadiate of lead. 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 ammoniacal 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, hydrochlorate of ammonia is volatilized, and metallic vanadium left behind. It is a white brittle substance, with 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 68.55; its symbol is V. PHOTOXIDE OP VANADIUM, VO. This is prepared by heating vanadic acid in contact with charcoal or hydrogen; it has a black color and imperfect me- tallic lustre, conducts electricity, and is very infusible. Heated in the air, it burns to binoxide. Nitric acid produces the same effect, a blue nitrate of the binoxide being generated. It does not form salts. BINOXIDE OF VANADIUM, V0 2 . The binoxide is obtained by heating a mix- ture 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 grayish-white 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, VO 3 . The native vanadiSte 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 blue filtered solution is then evaporated to dryness, and the residue digested in ammonia, which dissolves out the vanadic acid reproduced during evapo- ration. Into this solution a lump of sal-ammoniac is put; as that salt dissolves, vanadiate of ammonia subsides as a white powder, being scarcely soluble in a saturated solution of hydrochlorate of ammonia. By exposure to a tempera- TANTALUM OR COLUMBIUM NIOBIUM AND PELOPIUM. 281 ture below redness in an open crucible, the ammonia is expelled, and vanadic acid left. It has a dark-red color, 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. CHLORIDES 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 sub-salt. The terchloride is a yellow liquid obtained by passing chlorine over a mixture of protoxide of vanadium and charcoal. It is converted by water into hydrochloric and vanadic acids. Two sulphurets, corresponding to the chlorides, exist. TANTALUM OR COLUMBIUM. This is an exceedingly rare substance; it is found in the minerals tantalite and yttro-lantalite, and may be obtained pure by heating with potassium the double fluoride of tantalum and potassium. It is a gray 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 potash. The equivalent of columbium is 184.57; its symbol is T (tantalum). BINOXIDE OF TANTALUM, TO 2 . 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, T0 3 . The powdered ore is fused with three or four times its weight of carbonate of potash, 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 alkalis it yields, on the contrary, crystallizable salts. NIOBIUM AND PELOPIUM. The oxides of these two metals exist in the tantalite of Bodenmais, in Bava- ria. 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 sub- limate is obtained of a yellow, readily fusible, and very volatile substance, the chloride of pebpiwn, and a white, infusible, less volatile body, the chloride of niobium. The true chloride of tantalum, from the Finland tantalite, much resembles chloride of pelopium. The American tantalite contains niobic, 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 red- ness, they exhibit strongly the phenomenon of incandescence. While hot, tantalic acid remains white, pelopic acid is rendered slightly yellowish, arid niobic acid dark yellow. Tantalum, niobium, and pelopium may be obtained in a finely-divided metallic state by the action of ammonia on their respective chlorides at a high temperature. So prepared, they are black, pulverulent, not acted on by water, but burning, when heated in the air, to acids.* * Chera. Gazette, Jan. 15, 1845, and Sept. 15, 1846. 24* 282 TITANIUM ANTIMONY. TITANIUM. Crystallized oxide of titanium is found in nature in the forms of titanite and anatase. The metal itself is met with occasionally in the slag adherent to the bottom ol blast-furnaces in which iron ore is reduced, as small brilliant copper-colored cubes, hard enough to scratch glass, and in the highest degree infusible. They resist the action of acids, but are oxidized when heated with nitre. Metallic titanium in a finely-divided state may be obtained by artificial means. 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 24.29 ; its smybol is Ti. TITANIC ACID, TiO 2 . Titanite, or titaniferous iron ore, is reduced to fine powder and fused with three parts of carbonate of potash ; the product is washed with water to remove all soluble matter, and the residue dissolved in strong hydrochloric acid. On dilution with water and boiling, titanic acid is precipitated. When pure the acid is quite white; it is, when recently pre- cipitated, soluble in acids, but the solutions are decomposed by mere boiling. After ignition it is no longer soluble. 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 colorless, 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. ANTIMONY. This important metal is found chiefly in the state of sulphuret. The ore is freed by fusion from earthy impurities, and is afterwards decomposed by heat- ing with metallic iron or carbonate of potash, which retains the sulphur. Anti- mony has a bluish-white color and strong lustre ; it is extremely brittle, being reduced to powder with the utmost ease. Its specific gravity is 6.8 ; it melts at a temperature just short of redness, and boils and volatilizes at a w lake-heat. This metal has always a distinct crystalline, platy structure, but by particular management it may be obtained in crystals, which are rhombohedral. Anti- mony is not oxidized by the air at common temperatures ; strongly heated, it burns with a white flame, producing oxide, which is often deposited in beau- tiful crystals. It is dissolved by hot hydrochloric acid with evolution of hy- drogen and production of chloride. Nitric acid oxidizes it to antimonic acid, which is insoluble in that menstruum. There are three compounds of anti- mony and oxygen j the first has doubtful basic properties, the two others are acids. The equivalent of antimony is 129.04; its symbol is Sb (stibium). OXIDE OF ANTIMONY, SbO 3 . This compound may be prepared 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 solu- tion of chloride of antimony into water, and digesting the resulting precipitate with a solution of carbonate of soda. The oxide thus produced is anhydrous; it is a pale buff-colored 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 antimonious acid. When boiled with cream of tartar (acid tartrate of potash), it is dissolved, and the solution yields on evaporation crystals of tartar emetic, which is almost the only compound of oxide of anti- mony with an acid which bears admixture with water without decomposition. An impure oxide for this purpose is sometimes prepared by carefully roasting the powdered sulphuret in a reverberatory furnace, and raising the heat at ANTIMONY. 283 the end of the process, so as to fuse the product : it has long been known under the name of glass of antimony. ANTIMONIOUS ACID, SbO 4 . This is the ultimate product of the oxidation of the metal by heat and air; it is a grayish-white powder, infusible, and destitute of volatility ; it is insoluble in water and in acids, except when re- cently precipitated. It combines with alkalis, yielding solutions from which acids precipitate the hydrate; the latter reddens litmus paper. ANTIMONIC ACID, Sb0 5 . When strong nitric acid is made to act upon metallic antimony, the metal is oxidized to its highest point, and antimoriic acid produced, which is insoluble. By exposure to a heat short of redness, it is rendered anhydrous, and then presents the appearance of a pale straw- colored powder, insoluble in water and acids, but dissolving in alkalis, with which it forms definite compounds. These latter, when in solution, are de- corn posec? by acids, a white hydrate of antimonic acid being precipitated. Antimonic acid is decomposed by a red-heat, yielding antimonious acid, with loss of oxygen. TEHCHLORIDE OF ANTIMONY; BUTTER OF ANTIMONY; SbCl 3 . This sub- stance is produced when sulphuretted hydrogen is prepared by the action of strong hydrochloric acid on sulphuret of antimony. The impure and highly acid solution thus obtained is put into a retort and distilled until each drop of the condensed product, on falling into the aqueous liquid of the receiver, produces a copious white precipitate. The receiver is then changed, and the distillation continued. Pure chloride of antimony passes over, and solidifies on cooling to a white and highly crystalline mass, from which the air requires to be carefully excluded. The same compound is formed by distilling metallic antimony in powder with 2 times its weight of corrosive sublimate. Chlo- ride of antimony is very deliquescent; it dissolves in strong hydrochloric acid without decomposition, and the solution poured into water gives rise to a white bulky precipitate, which after a short time becomes highly crystalline, and assumes a pale fawn color. This is the old powder of Jllgaroth; it is a compound of chloride and oxide of antimony. Alkaline solutions extract the chlorine and leave oxide of antimony. Finely powdered antimony thrown into chlorine gas, inflames. A chloride of antimony, corresponding to antimonic acid, is formed by passing a stream of chlorine gas over gently heated metallic antimony ; a mixture of the two chlorides results, which may be separated by distillation. The pentachloride is a colorless volatile liquid, which forms a crystalline com- pound with a small portion of water, but is decomposed by a larger quantity into antimonic and hydrochloric acids. SUIPHURET OF ANTIMONY ; CRUDE ANTIMONY ; SbS 3 . The native sulphu- ret is a lead gray, brittle substance, having a radiated crystalline texture, and is easily fusible. It may be prepared artificially by melting together antimony and sulphur. When a solution of tartar-emetic is precipitated by sulphuretted hydrogen, a brick-red precipitate falls, which is the same substance combined with a little water. If the precipitate be dried and gently heated, the water may be expelled without other change of color than a little darkening, but at a higher temperature it assumes the color and aspect of the native sulphuret. This remarkable change probably indicates a passage from the amorphous to the crystalline condition. When powdered sulphuret of antimony is boiled in a solution of caustic potash, it is dissolved, oxide of antimony and sulphuret of potassium being produced. The latter unites with an additional quantity of sulphuret of antimony to a soluble sulphur salt, in which the sulphuret of potassium is the sulphur base, and the sulphuret of antimony the sulphur acid. 284 TELLURIUM. 3 eq. potash Sulphuret of antimony 3 eq. potassium ~ -^-~- ( 3 eq. sulphuret 3 eq. oxygen 3 eq. sulphur of potassium. 1 eq. antimony ""~ -1 eq. oxide of antimony. The oxide of antimony separates in small crystals from the boiling solution when the latter is concentrated, and the sulphur salt dissolves an extra pro- portion of sulphuret of antimony, which it again deposits on cooling as a red amorphous powder, containing a small admixture of oxide of antimony and sulphuret of potassium. This is the kermes mineral of the old chemists. The filtered solution mixed with an acid gives a salt of potash, sulphuretted hydrogen, and precipitated sulphuret of antimony. Kermes may also be made by fusing a mixture of 5 parts sulphuret of antimony and 3 of dry car- bonate of soda, boiling the mass in 80 parts of water, and filtering while hot; the compound separates on cooling. A Pentasulphuret of Antimony, SbS 5 , formerly called sulphur auratum, also exists; it is a sulphur acid. 18 parts finely powdered sulphuret of antimony, 17 parts dry carbonate of soda, 13 parts lime in the state of hydrate, and 3^- parts sulphur, are boiled for some hours in a quantity of water; carbonate of lime, antimoniate of soda, pentasulphuret of antimony, and sulphuret of sodium are produced. The first is insoluble, and the second partially so; the two last named bodies, on the contrary, unite to a soluble sulphur salt, which may by evaporation be obtained in beautiful crystals. A solution of this sub- stance, mixed with dilute sulphuric acid, furnishes sulphate of soda, sulphu- retted hydrogen, and pentasulphuret of antimony, which falls as a golden yellow flocculent precipitate.* A compound of antimony and hydrogen exists, but has not been isolated ; when zinc is put into a solution of oxide of antimony, and sulphuric acid added, the hydrogen disengaged holds antimony as it were in solution. When the gas is conducted through a red hot glass tube of narrow dimensions, or burned with a limited supply of air, metallic antimony is deposited. The few salts of antimony soluble in water are amply characterized by the orange or brick red precipitate with sulphuretted hydrogen, which is soluble in solution of sulphuret of ammonium, and again precipitated by an acid. Besides its application to medicine, antimony is of great importance in the arts of life, inasmuch as it forms with lead type-metal. This alloy expands at the moment of solidifying, and takes an exceedingly sharp impression of the mould. It is remarkable that both its constituents shrink under similar circum- stances, and make very bad castings. Sulphuret of antimony enters into the composition of the blue signal light, used at sea.f TELLURIUM. This metal, or semi-metal, is of very rare occurrence; it is found in a few scarce minerals in association with silver, lead, and bismuth, apparently re- placing sulphur, and is most easily extracted from the sulpho-telluret of bismuth of Chemmitz, in Hungary. The finely-powdered ore is mixed with an equal weight of dry carbonate of soda, the mixture made into a paste with * Mitscherlich, Lehrbuch, ii. 468. f Blue or Bengal light : Dry nitrate of potash / . 6 parts. Sulphur 2 " Sulphuret of antimony 1 part. All in fins powder, and intimately mixed. ARSENIC. 285 oil, and heated to whiteness in a closely covered crucible. Telluret and sul- phuret of sodium are produced, and metallic bismuth set free. The fused mass is dissolved in water and the solution freely exposed to the air, when the sodium and sulphur oxidize to caustic soda and hyposulphite of soda, while the tellurium separates in the metallic state. Tellurium has the color and lustre of silver ; by fusion and slow cooling it may be made to exhibit the form of rhombohedral crystals similar to those of antimony and arsenic. It is brittle, and a comparatively bad conductor of heat and electricity; it has a density of 6.26, melts at a little below a red-heat, and volatilizes at a higher temperature. Tellurium burns when heated in the air, and is oxidized by nitric acid. Two compounds of this substance with oxygen are known, having acid properties; they much resemble the acids of arsenic. The equivalent of tellurium is 64.14; its symbol is Te. TELLUROUS ACID, TeO 2 . This is obtained by burning tellurium in the air, or by heating it in fine powder with nitric acid of 1.25 specific gravity; a so- lution is rapidly formed, from which white anhydrous octahedral crystals of tellurous acid are deposited on standing. The acid is fusible at a red-heat, and slightly volatile at a higher temperature; it is but feebly soluble in water or acids, easily dissolved by alkalis, and reduced when heated with carbon or hydrogen. A hydrate of tellurous acid is thrown down when tellurite of potash is mixed with a slight excess of nitric acid ; it is a white powder, soluble to a certain extent in water, and reddens litmus. TELLURIC ACID, TeO 3 . Equal parts of tellurous acid and carbonate of soda are fused, and the product dissolved in water ; a little hydrate of soda is added, and a stream of chlorine passed through the solution. The liquid is next saturated with ammonia, and mixed with solution of chloride of barium, by which a white insoluble precipitate of tellurate of baryta is thrown down. This is washed and digested with a quarter of its weight of sulphuric acid, diluted with water. The filtered solution gives, on evaporation in the air, large crystals of telluric acid. Telluric acid is freely, although slowly, soluble in water; it has a metallic taste, and reddens litmus-paper. When the crystals are strongly heated, they lose water, and yield anhydrous acid, which is then insoluble in water, and even in a boiling alkaline liquid. At the temperature of ignition, telluric acid loses oxygen, and passes into tellurous acid. The salts of the alkalis are soluble, but do not crystallize ; those of the earths are nearly, or quite, insoluble. There are two chlorides of tellurium, and also a hydruret, which closely re- sembles sulphuretted hydrogen. Arsenic is sometimes found native ; the largest proportion, however, is de- rived from the roasting of natural- arseniurets of iron, nickel, and cobalt; the operation is conducted in a reverberatory furnace, and the volatile products condensed in a long and nearly horizontal chimney, or in a kind of tower of brickwork, divided into numerous chambers. The crude arsenious acid thus produced is purified by sublimation, and then heated with charcoal in a retort ; the metal is reduced, and readily sublimes. Arsenic has a steel-gray color, and high metallic lustre; it is crystalline and very brittle ; it tarnishes in the air, but may be preserved unchanged in pure water. Its density is 5.7 to 5.9. When heated, it volatilizes without fusion, and, if air be present, oxidizes to arsenious acid. The vapor has the odor of garlic. This substance combines with metals in the same manner as sul- phur and phosphorus, which it resembles, especially the latter, in many 286 ARSENIC. respects. With oxygen it unites in two proportions, giving rise to arsenious and arsenic acids. There is no basic oxide of arsenic. The equivalent of arsenic is 75.21 ; its symbol is As. AHSENIOUS ACID; WHITE OXIDE OF ARSENIC; As0 3 . The origin of this substance is mentioned above. It is commonly met with in the form of a heavy, white, glassy-looking substance, with smooth conchoidal fracture, which has evidently undergone fusion. When freshly prepared, it is often transpa- rent, but by keeping becomes opaque, at the same time slightly diminishing in density, and acquiring a greater degree of solubility in water. 100 parts of that liquid dissolve, at 212, about 11.5 parts of the opaque variety; the largest portion separates, however, on cooling, leaving about 3 parts dissolved ; the solution feebly reddens litmus. Cold water, agitated with powdered arsenious acid, takes up a still smaller quantity. Alkalis dissolve this substance freely, forming arsenites, which do not crystallize; it is also easily soluble in hot hydrochloric acid. The vapor of arsenious acid is colorless and inodor- ous ; it crystallizes on solidifying in brilliant transparent octahedrons, which are very characteristic. The acid itself has a feeble sweetish and astringent taste, and is a most fearful poison.* ARSENIC ACID, AsO 5 . Powdered arsenious acid is dissolved in hot hydro- chloric acid, and peroxidized by the addition of nitric acid, the latter being added as long as red vapors are produced; the whole is then cautiously evaporated to complete dry ness. The acid thus produced is white and an- hydrous. Put into water, it slowly but completely dissolves, giving a highly acid solution, which, on being evaporated to a syrupy consistence, deposits, after a time, hydrated crystals of arsenic acid. When strongly heated, it is decomposed into arsenious acid and oxygen gas. This substance is a very powerful acid, comparable with the phosphoric, which it resembles in the closest manner, forming salts strictly isomorphous with the corresponding phosphates; it is also tribasic. An arseniate of soda, 2NaO,HO,AsO 5 -|-24HO, indistinguishable in appearance from common phos- phate of soda, may be prepared by adding the carbonate to a solution of arsenic acid, until an alkaline reaction is apparent, and then evaporating. This salt also crystallizes with 14 equivalents of water. Another arseniate, 3NaO,AsO 5 -f-24HO, is produced when carbonate of soda in excess is fused with arsenic acid, or when the preceding salt is mixed with caustic soda. A third, NaO,2HO,As0 5 -f-2HO, j s made by substituting an excess of arsenic acid for the solution of alkali. The alkaline arseniates which contain basic water lose the latter at a red-heat, but, unlike the phosphates, recover it when again dissolved/}" The salts of the alkalis are soluble in water ; those of the earths fend "other metallic oxides are insoluble, but are dissolved by acids. The precipitate with nitrate of silver is highly characteristic of arsenic acid ; it is reddish-brown. * The best antidote for arsenious acid is the hydrate of the red oxide of iron. In its recently precipitated gelatinous condition, it is most active. It acts by forming an insoluble arseniate of the protoxide of iron ; for the peroxide is reduced to protoxide by losing oxygen, which, passing to the arsenious acid, forms arsenic acid. This change is represented by the following formula, 2 Fe a O 3 and AsO 3 = 4 FeO+AsO s . The hydrate is incapable of decomposing the arsenites. The red oxide, to act as an antidote to the arsenical salts, requires to be combined -with an acid, which may sepa- rate the base, and then the arsenious acid and red oxide react on each other as above. The acetate of the red oxide is the salt used. Magnesia has also been recommended. In the state of recently precipitated hydrate, it acts on a solution of arsenious acid with nearly the same rapidity as the hydrated peroxide of iron. In the condition usually found in the shops, it cannot be depended on with the same certainty, having been too highly calcined. R. B. f Graham, Elements, p. 435. ARSENIC. 287 Three SULPHURETS OF ARSENIC are known. Realgar, AsS a , occurs native; it is formed artificially, by heating arsenic or arsenious acid with a minimum of sulphur. It is a red, fusible, and volatile substance, employed by the pyro- technist in making white-fire. Orpiment, AsS 3 , which is also a natural product of the mineral kingdom, is made by fusing arsenious acid with excess of sul- phur, or by precipitating a solution of the acid by sulphuretted hydrogen. It is a golden-yellow, crystalline substance, fusible and volatile by heat. Two higher sulphurets are also described, AsS 5 , corresponding to arsenic acid, and, AsS 9 ; the former is produced when sulphuretted hydrogen is transmitted through a solution of arsenic acid. It is a yellow, fusible substance, capable of sublimation. Realgar, orpiment, and pentasulphuret of arsenic are sulphur- acids. Arsenic unites with chlorine, iodine, &c. The terchloride, AsCl 3 , is formed by distilling a mixture of 1 part of arsenic, and 6 parts of corrosive sublimate; it is a colorless, volatile liquid, decomposed by water into arsenious and hydrochloric acids. The same substance is produced, with disengagement of heat and light, when powdered arsenic is thrown into chlorine gas. The iodide, AsI 3 , is formed by heating metallic arsenic with iodine ; it is a deep- red crystalline substance, capable of sublimation. The bromide and fluoride are both liquid. Arsenic also combines with hydrogen, forming a gaseous compound, AsH 3 , the analogue of phosphuretted hydrogen. It is obtained pure* by the action of strong hydrochloric acid on an alloy of equal parts zinc and arsenic, and is produced in greater or less proportion whenever hydrogen is set free in con- tact with arsenious acid. Arseniuretted hydrogen is a colorless gas, of 2.695 specific gravity, slightly soluble in water, and having the smell of garlic. It burns when kindled with a blue flame, generating arsenious acid. It is also decomposed by transmission through a red-hot tube. Many metallic solutions are precipitated by this substance. It is, when inhaled, exceedingly poison- ous, even in very minute quantity. Arsenious acid is distinguished by characters which cannot be misunderstood. Nitrate of silver, mixed with a solution of arsenious acid in water, occasions no precipitate, or merely a faint cloud; but if a little alkali, as a drop of am- monia, be added, a yellow precipitate of arsenite of silver immediately falls. The precipitate is exceedingly soluble in excess of ammonia; that substance must, therefore, be added with great caution. Sulphate of copper gives no precipitate with solution of arsenious acid, until the addition has been made of a little alkali, when a brilliant, yellow-green precipitate (Scheele's green) falls, which also is very soluble in excess of am- monia. Sulphuretted hydrogen passed into a solu- tion of arsenious acid, to which a few drops of hydrochloric or sulphuric acid have been added, occasions the production of a copious, bright yellow precipitate of orpiment, which is dissolved with facility by ammonia, and re-precipitated by acids. Solid arsenious acid, heated by the blow- pipe in a narrow glass tube with small frag- ments of dry charcoal, affords a sublimate of metallic arsenic in the shape of a brilliant steel-gray metallic ring. A portion of this, detached by the point of a knife and heated in a second glass tube, with access of air, 288 ARSENIC, yields, in its turn, a sublimate of colorless, transparent, octahedral crystals of arsenious acid. (Fig. 149, magnified.) All these experiments, which jointly give demonstrative proof of the pre- sence of the substance in question, may be performed, with perfect precision and certainty, upon exceedingly small quantities of material. The detection of arsenious acid in complex mixtures containing organic matter and common salt, as beer, gruel, soup, &c., or the fluid contents of the stomach in cases of poisoning, is a very far more difficult problem, but one which is, unfortunately, often required to be solved. These organic matters interfere completely with the liquid tests, and render their indications worth- less. Sometimes the difficulty may be eluded by a diligent search in the suspected liquid, and in the vessel containing it, for fragments or powder of solid arsenious acid, which from the small degree of solubility and high den- sity of the substance, often escape solution. If anything of the Fig. 150. kind be found, it may be washed by decantation with a little cold water, dried, and then reduced with charcoal. For the latter purpose, a small glass tube is taken, having the figure represented in the margin ; white German glass, free from lead, is to be preferred. The arsenious acid, or what is suspected to be such, is dropped to the bottom, and covered with splinters or little fragments of charcoal, the tube being rilled to the shoulder. The whole is gently heated, to expel any moisture that may be present in the charcoal, and the deposited water wiped from the interior of the tube with bibulous paper. The narrow part of the tube containing the charcoal, from a to 6, is now heated by the blow pipe flame ; when red-hot, the tube is inclined, so that the bottom also may become heated. The arsenious acid, if present, is vaporized, and reduced by the charcoal, and a ring of metallic arsenic deposited on the cool part of the tube. To complete the experiment, the tube may be melted at a by the point of the flame, drawn off, and closed, and the arsenic ox- idized to arsenious acid, by chasing it up and down by the heat of a small spirit lamp. A little water may afterwards be in- troduced, and boiled in the tube, by which the arsenious acid will be dissolved, and to this solution the tests of nitrate of silver and ammo- nia, sulphate of copper and ammonia, and sulphuretted hydrogen, may be applied. When the search for solid arsenious acid fails, the liquid itself must be examined; a tolerably limpid solution must be obtained, from which the arsenic may be precipitated by sulphuretted hydrogen, and the orpiment collected, and reduced to the metallic state. It is in the first part of this operation that the chief difficulty is found ; such organic mixtures refuse to filter, or filter so slowly as to render some method of acceleration indispensable. Boiling with a little caustic potash or acetic acid will sometimes effect this object. The following is an outline of a plan, which has been found successful in a variety of cases, in which a very small quantity of arsenious acid had been purposely added to an organic mixture. Oil of vitriol, itself perfectly free from arsenic, is mixed with the suspected liquid, in the proportion of about a measured ounce to a pint, having been previously diluted with a little water, and the whole is boiled in a flask for half an hour, or until a complete separa- tion of solid and liquid matter becomes manifest. The acid converts any starch that may be present into dextrine and sugar ; it coagulates completely albuminous substances, and caseine, in the case of milk, and brings the whole in a very short time into a state in which filtration is both easy and rapid. Through the filtered solution, when cold, a current of sulphuretted ARSENIC. 289 hydrogen is transmitted, and. the liquid is warmed, to facilitate the deposition of the sulphuret, which falls in combination with a large quantity of organic matter, which often communicates to it a dirty color. This is collected upon a small filter, and washed. It is next transferred to a capsule, and heated with a mixture of nitric and hydrochloric acids, by which the organic impu- rities are in a great measure destroyed, and the arsenic oxidized to arsenic acid. The solution is evaporated to dryness, the soluble part taken up by- dilute hydrochloric acid and then the solution saturated with sulphuretted hydrogen ; after some time, a sulphuret again precipitates. The liquid is warmed, and the precipitate washed by decantation, and dried. It is then mixed with black flux, and heated in a small glass tube, similar to that already described, with similar precautions; a ring of reduced arsenic is obtained, which may be oxidized to arsenious acid, and further examined. The black- flux is a mixture of carbonate of potash and charcoal, obtained by calcining cream of tartar in a close crucible ; the alkali is the effective agent in the reduction, the charcoal serving the purpose of preventing subsequent oxida- tion. A mixture of anhydrous carbonate of soda and charcoal may be sub- stituted with advantage for the common black-flux, as it is less hygroscopic.* Other methods of proceeding, different in principle from the foregoing, have been proposed, as that of the late Mr. Marsh, which is exceedingly delicate. The suspected liquid is acidulated with sulphuric acid and placed in contact with metallic zinc ; the hydrogen reduces and dissolves the arsenic, if any be present. The gas is burned at a jet, and a piece of glass or porce- lain held in the flame, when any admixture of arseniuretted hydrogen is at once known by the production of a brilliant black metallic spot of reduced arsenic on the porcelain. A convenient form of instrument for the purpose is that shown in the drawing ; it consists of a bent tube, having two bulbs blown upon it, fitted with a stop-cock and narrow jet. Slips of zinc are put into the lower bulb, which is afterwards filled with the liquid to be examined. On replacing the stop-cock, closed, the gas collects and forces the fluid into the upper bulb, which then acts by its hydrostatic pres- sure and expels the gas through the jet so soon as the stop-cock is opened. It must be borne in mirtd that common zinc and sulphuric acid often contain traces of arsenic.f A slip of copper foil boiled in the poisoned liquid, previously acidulated with hydrochloric acid, with- draws the arsenic and becomes covered with a white alloy. By heating the metal in a glass tube, the arsenic is expelled, and oxidized to arsenious acid. This test is said to answer well in practice. *See a paper by the author on the detection of arensic, Pharmaceutical Journal, i. 514. f Where th^amount of arsenic present is small, it becomes necessary to take advan- tage of the effects of heat, and cause the gas to pass slowly through a red hot tube until all the zinc is dissolved. The reduced arsenic will be deposited on the cool part of the tube just beyond the heated portion. In all cases of using the above test, it is necessary to ascertain the purity of the zinc and acid by trial, previous to addition of the suspected liquid. R. B. 25 Fig. 151. 290 SILVER. SECTION VI. METALS WHOSE OXIDES ARE REDUCED BY HEAT. SILVER is found in the metallic state, in union with sulphur, and also as chloride and bromide. Among the principal silver mines may be mentioned those of the Hartz mountains in Germany, of Kongsberg in Norway, and, more particularly, of the Andes in both North and South America. The greater part of the silver of commerce is extracted from ores so poor as to render any process of smelting or fusion inapplicable, even where fuel could be obtained, and this is often difficult to be procured. Recourse, therefore, is had to another method, that of amalgamation, founded on the easy solubility of silver and many other metals in metallic mercury. The amalgamation-process, as conducted in Saxony, differs somewhat from that in use in America. The ore is crushed to powder, mixed with a quantity of common salt, and roasted at a low red heat in a suitable furnace, by which treatment any sulphuret of silver it may contain is converted into chloride. The mixture of earthy matter, oxides of iron, copper, soluble salts, chloride of silver, and metallic silver, is sifted and put into large barrels, made to revolve on axes, with a quantity of water and scraps of iron, and the whole agitated together for some time, during which the iron reduces the chloride of silver to the state of metal. A certain proportion of mercury is then introduced, and the agitation repeated; the mercury dissolves out the silver, together with gold, if there be any, metallic copper, and other sub- stances, forming a fluid amalgam easily separable from the thin mud of earthy matter by subsidence and washing. This amalgam is strained through strong linen cloth, and the solid portion exposed to heat in a kind of retort, by which the remaining mercury is volatilized and the silver left be- hind in an impure condition. A considerable quantity of silver is obtained from argentiferous galena ; in fact, almost every specimen of native sulphuret of lead will be found to con- tain traces of this metal. When the proportion rises to a certain amount it becomes worth extracting. The ore is reduced in the usual manner, the whole of the silver remaining with the lead ; the latter is then re-melted in a large vessel, and allowed slowly to cool until solidification commences. The portion which first crystallizes is nearly pure lead, the alloy with silver being more fusible than lead itself; by particular management fltois is drained away, and is found to contain nearly the whole of the silver. This rich mass is next exposed to a red heat on the shallow hearth of a furnace, while a stream of air is allowed to impinge upon its surface ; oxidation takes place with great rapidity, the fused oxide or litharge being constantly swept from the metal by the blast. When the greater part of the lead has been thus removed, the residue is transferred to a cupel or shallow dish made of bone- ashes, and again heated ; the last of the lead is now oxidized, and the oxide SILVER. ' 291 sinks in a melted state into the porous vessel, while the silver, almost chemi- cally pure, and exhibiting a brilliant surface, remains behind. Pure silver may be easily obtained. The metal is dissolved in nitric acid; if it contain copper, the solution will have a blue tint; gold will remain un- dissolved as a black powder. The solution is mixed with hydrochloric acid or with common salt, and the white, insoluble curdy precipitate of chloride of silver washed and dried. This is then mixed with about twice its weight of anhydrous carbonate of soda, and the mixture, placed in an earthen cru- cible, gradually raised to a temperature approaching whiteness, during which the carbonate of soda and the chloride react upon each other, carbonic acid and oxygen escape, while metallic silver and chloride of sodium result ; the former fuses into a button at the bottom of the crucible, and is easily detached. Pure silver has a most perfect white color and a high degree of lustre; it is exceedingly malleable and ductile, and is probably the best conductor both of heat and electricity known. Its specific gravity is 10.5. In hardness it lies between gold and copper. It melts at a bright red-heat, about 1873 F., according to the observations of Mr. Daniell. Silver is unalterable by air and moisture ; it refuses to oxidize at any temperature, but possesses the extraor- dinary faculty, already noticed in an earlier part of the work, of absorbing many times its volume of oxygen when strongly heated in an atmosphere of that gas, or in common air. This oxygen is again disengaged at the mo- ment of solidification, and gives rise to the peculiar arborescent appearance often remarked on the surface of masses or buttons of pure silver. The ad- dition of 2 per cent, of copper is sufficient to prevent this absorption of oxy- gen. Silver oxidizes when heated with fusible siliceous matter, as glass, which it stains yellow or orange, from the formation of a silicate. It is little attacked by hydrochloric acid ; boiling oil of vitriol converts it into sulphate with evolution of sulphurous acid; and nitric acid, even dilute and in the cold, dissolves it readily. The tarnishing of surfaces of silver exposed to the air is due to sulphuretted hydrogen, the metal having a strong attraction for sulphur. There are three oxides of silver, one of which is a powerful base isomorphous with potash, soda, and oxide of ammonium. The equivalent of silver is 108 ; its symbol is Ag (argentum). SUBOXIDE OF SILVER, Ag 2 O. When dry citrate of silver is heated to 212 in a stream of hydrogen gas. it loses oxygen and becomes dark brown. The product, dissolved in water, gives a dark colored solution containing free citric acid and citrate of the suboxide of silver. The suboxide is then precipitated by potash. It is a black powder, very easily decomposed, and soluble in ammonia. The solution of citrate is rendered colorless by heat, being re- solved into a salt of the protoxide and metallic silver. PROTOXIDE OF SILVER, AgO/ Caustic potash added to a solution of nitrate of silver throws down a pale brown precipitate, which consists of protoxide of silver. It is very soluble in ammonia, and is dissolved also to a small ex- tent by pure water; the solution is alkaline. Recently precipitated chloride of silver boiled in a solution of caustic potash of specific gravity 1.25 is con- verted, according to the observation of Dr. Gregory, into oxide of silver, which in this case is black and very dense. The protoxide of silver neutralizes acids completely, and forms for the most part colorless salts. It is decom- posed by a red-heat, with extrication of oxygen, spongy metallic silver being left; the sun's rays also effect its decomposition to a small extent PEROXIDE OF SILVER. This is a black crystalline substance which forms upon the positive electrode of a voltaic arrangement employed to decompose a solution of nitrate of silver. It is reduced by heat, evolves chlorine when acted upon by hydrochloric acid, explodes when mixed with phosphorus and 292 SILVER. struck, and decomposes solution of ammonia with great energy and rapid dis- engagement of nitrogen gas. NITRATE OF SILVER, AgO,NO 5 . The nitrate is prepared by directly dis- solving silver in nitric acid and evaporating the solution to dryness, or until it is strong enough to crystallize on cooling. The crystals are colorless, trans- parent, anhydrous tables, soluble in an equal weight of cold, and in half that quantity of boiling water ; they also dissolve in alcohol. They fuse when heated like those of nitre, and at a higher temperature suffer decomposition; the lunar caustic of the surgeon is nitrate of silver which has been melted and poured into a cylindrical mould. The salt blackens when exposed to light, more particularly if organic matters of any kind be present, and is frequently employed to communicate a dark stain to the hair ; it enters into the composition of the " indelible" ink used for marking linen. The black stain has been thought to be metallic silver; it may possibly be suboxide. Pure nitrate of silver may be prepared from the metal alloyed with copper; the alloy is dissolved in nitric acid, the solution evaporated to dryness, and the mixed nitrates cautiously heated to fusion. A small portion of the melted mass is removed from time to time for examination ; it is dissolved in water, filtered, and ammonia added to it in excess. While any copper-salt remains undecomposed, the liquid will be blue, but when that no longer happens, the nitrate may be suffered to cool, dissolved in water, and filtered from the insoluble black oxide of copper. SULPHATE OF SILVER, AgO,SO 3 . The sulphate may be prepared by boiling together oil of vitriol and metallic silver, or by precipitating nitrate of silver by an alkaline sulphate. It dissolves in 88 parts of boiling water, and sepa- rates in great measure in a crystalline form on cooling, having but a feeble degree of solubility at a low temperature. It forms a crystallizable compound with ammonia, freely soluble in water, containing AgO,SO 3 -j-2NH 3 . Hyposulphate of Silver, AgO,S 2 5 -f-2HO, is a soluble crystallizable salt, permanent in the air. The hyposulphite is insoluble, white, and very prone to decomposition; it combines with the alkaline hyposulphites, forming soluble compounds distinguished by an intensely sweet taste. The alkaline hypo- sulphites dissolve both oxide and chloride of silver, and give rise to similar salts, an oxide or cliloride of the alkaline metal being at the same time formed. Car donate of silver is a white insoluble substance obtained by mixing solutions of nitrate of silver and of carbonate of soda. It is blackened and decomposed by boiling. CHLORIDE OF SILVER, AgCl. This substance is almost invariably produced when a soluble salt of silver and a soluble chloride are mixed. It falls as a white curdy precipitate, quite insoluble in water and nitric acid, and but slightly dissolved by a large quantity of hydrochloric acid or an alkaline chlo- ride. When heated it melts, and on cooling becomes a grayish crystalline mass, which cuts like horn ; it is found native in this condition, constituting the horn-silver of the mineralogist. Chloride of silver is decomposed by light both in a dry and wet state, very slowly if pure, and quickly if organic matter be present: it is reduced also when put into water with metallic zinc or iron. It is soluble with great ease in ammonia and in a solution of cyanide of potas- sium. In practical analysis the proportion of chlorine or hydrochloric acid in a compound is always estimated by precipitation by solution of silver. The liquid is acidulated with nitric acid, and an excess of nitrate of silver added ; the chloride is collected on a filter or by subsidence, washed, dried, and fused; 100 parts correspond to 24.69 of chlorine, or 25.46 of hydrochloric acid. IODIDE OF SILVER, Agl. The iodide is a pale yellow insoluble precipitate produced by adding nitrate of silver to iodide of potassium ; it is insoluble or GOLD. 293 nearly so in ammonia, and forms an exception to the silver-salts in general in this respect. The bromide of silver very closely resembles the chloride. SULPHURET OF SILVER, AgS. This is a soft, gray, and somewhat mallea- ble substance, found native in a crystallized state, and easily produced by melting together its constituents, or by precipitating a solution of silver by sulphuretted hydrogen. It is a strong sulphur-base, and combines with the sulphurets of antimony and arsenic: examples of such compounds are found in the beautiful minerals dark and light red silver ore. AMMONIURET OF SILVER; BERTHOLLET'S FULMINATING SILVER. When precipitated oxide of silver is digested in ammonia, a black substance is pro- duced, possessing exceedingly dangerous explosive properties. It explodes while moist when rubbed with a hard body, but when dry the touch of a feather is sufficient. The ammonia retains some of this substance in solution, and deposits it in small crystals by spontaneous evaporation. A similar com- pound containing oxitie of gold exists. It is easy to understand the reason why these bodies are subject to such violent and sudden decomposition by the slightest cause, on the supposition that they contain an oxide of an easily re- ducible metal and ammonia; the attraction between the two constituents of the substance is very feeble, while that between the oxygen of the one and the hydrogen of the other is very powerful. The explosion is caused by the sudden evolution of nitrogen gas and vapor of water, the metal being set free. A soluble salt of silver is perfectly characterized by the white curdy pre- cipitate of chloride of silver, darkening by exposure to light, arid insoluble in hot nitric acid, which is produced by the addition of any soluble chloride. Lead is the only metal which can be confounded with it in this respect, but chloride of lead is soluble to a great extent in boiling water, and is deposited in brilliant acicular crystals when the solution cools. Solutions of silver are reducedjo the metallic state by iron, copper, mercury, and other metals. The economical uses of silver are many : it is admirable for culinary and other similar purposes, not being attacked in the slightest degree by any of the substances used for food. It is necessary, however, in these cases to di- minish the softness of the metal by a small addition of copper. The standard silver of England contains 222 parts of silver and 18 parts of copper. Gold, in small quantities, is a very widely-diffused metal ; traces are con- stantly found in the iron pyrites of the more ancient rocks. It is always met with in the metallic state, sometimes beautifully crystallized in the cubic form, associated with quartz, oxide of iron, and other substances, in regular mineral veins. The sands of various rivers have long furnished gold derived from this source, and separable by a simple process of washing; such is the gold- dust of commerce. When a veinstone is wrought for gold, it is stamped to powder, and shaken in a suitable apparatus with water and mercury; an amalgam is formed, which is afterwards separated from the mixture and de- composed by distillation. The pure metal is obtained by solution in nitro- hydrochloric acid and pre- cipitation by a salt of protoxide of iron, which, by undergoing peroxidation, reduces the gold. The latter falls as a brown powder, which acquires the metallic lustre by friction. 25* 294 GOLD. Gold is a soft metal, having a beautiful yellow color. It surpasses all other metals in malleability, the thinnest gold-leaf not exceeding, it is said, ofFfitf(j(jth of an inch in thickness, while the gilding on the silver wire used in the manufacture of gold-lace is still thinner. It may also be drawn into very fine wire. Gold has a density of 19.5; it melts at a temperature a little above the fusirig-point of silver. Neither air nor water affect it in the least at any temperature ; the ordinary acids fail to attack it, singly. A mixture of nitric and hydrochloric acids dissolves gold, however, with ease, the active agent being the liberated chlorine. Gold forms two compounds with oxygen, and two corresponding compounds with chlorine, iodine, sulphur, &c. Both oxides refuse to unite with acids. The equivalent of gold is 99.44. Its symbol is Au (aurum). STJBOXIDE OF GOLD, Au 2 O. The suboxide is produced when caustic potash in solution is poured upon the subchloride. It is a green powder, partly soluble in the alkaline liquid ; the solution.rapidly decomposes into metallic gold, which subsides, and into peroxide, which remains dissolved. PEROXIDE OP GOLD; Aumc ACID; Au 2 O 3 . When magnesia is added to the perchloride of gold, and the sparingly soluble aurate of that base well washed and digested with nitric acid, the peroxide is left as an insoluble reddish-yellow powder, which, when dry, becomes chestnut-brown. It is easily reduced by heat, and also by mere exposure to light ; it is slightly soluble in strong acids, but forms with them no definite compounds. Alkalis dissolve it freely; indeed the acid properties of this substance are very strongly marked ; it partially decomposes a solution of chloride of potassium when boiled with that liquid, potash being produced. When digested with ammonia, it furnishes fulminating gold. SUBCHLORIDE OF GOLD, Au 2 Cl. This substance is produced when the per- chloride is evaporated to dryness and exposed to a heat of 440 until chlorine ceases to be exhaled. It forms a yellowish-white mass, insoluble in water. In contact with that liquid it is decomposed slowly in the cold, and rapidly by the aid of heat, into metallic gold and perchloride. PERCHLORIDE OF GOLD, Au 2 Cl 3 . This is the most important compound of the metal; it is always produced when gold is dissolved in nitro-hydrochloric acid. The deep yellow solution thus obtained yields, by evaporation, yellow crystals of the double chloride of gold and hydrogen; when this is cautiously heated, hydrochloric acid is expelled, and the residue, on cooling, solidifies to a red crystalline mass of perchloride of gold, very deliquescent, and soluble in water, alcohol, and ether. The perchloride of gold combines with a number of metallic chlorides, forming a series of double salts, of which the general formula in the anhydrous state is MCl-f-Au 2 Cl 3 , M representing an equivalent of the second metal. These compounds are mostly yellow when in crystals, and red when deprived of water, A mixture of chloride of gold with excess of bicarbonate of potash or soda is used for gilding small ornamental articles of copper; these are cleaned by dilute nitric acid, and then boiled in the mixture for some time, by which means they acquire a thin but perfect coating of reduced gold. The other compounds of gold are of very little importance. The presence of this metal in solution may be known by the brown pre- cipitate with protosulphate of iron, fusible before the blowpipe into a bead of gold ; and by the purple compound formed when the chloride of gold is added to a solution of protochloride of tin. MERCURY, OR QUICKSILVER. 295 Gold intended for coin, and most other purposes, i.s always alloyed with a certain proportion of silver or copper, to increase its hardness and durability ; the first-named metal confers a pale greenish color. English standard gold contains yVth of alloy, now always copper. Gold leaf is made by rolling out plates of pure gold as thin as possible, and then beating them between folds of membrane by a heavy hammer, until the requisite degree of tenuity has been reached. The leaf is made to adhere to wood, &c., by size or varnish. Gilding on copper has very generally been performed by dipping the ar- ticles into a solution of nitrate of mercury, and then shaking them with a small lump of a soft amalgam of gold with that metal, which thus becomes spread over their surfaces ; the articles are subsequently heated to expel the mercury and then burnished. Gilding on steel is done either by applying a solution of perchloride of gold, in ether, or by roughening the surface of the metal, heating it, and applying gold-leaf, with a burnisher. Gilding by elec- trolysis an elegant and simple method, now rapidly superseding many of the others has already been noticed. The solution usually employed is ob- tained by dissolving oxide or cyanide of gold in solution of a cyanide of potassium.* MERCURY, OR Q.UICKSILYER. This very remarkable metal has been known from an early period, and, perhaps more than all others, has excited the attention and curiosity of ex- perimenters, by reason of its peculiar physical properties. Mercury is of great importance in several of the arts, and enters into the composition of many valuable medicaments. Metallic quicksilver is occasionally met with in globules disseminated through the native sulphuret, which is the ordinary ore. This latter substance, some- times called cinnabar, is found in considerable quantity in several localities, of which the most celebrated are Almaden in New Castile, and Idria in Car- niola. The metal is obtained by heating the sulphuret in an iron retort with lime or scraps of iron, or by roasting it in a furnace, and conducting the vapors into a large chamber, where the mercury is condensed, while the sul- phurous acid is allowed to escape. Mercury is imported into this country in bottles of hammered iron, containing sixty or seventy pounds each, and in a state of considerable purity. When purchased in smaller quantities, it is sometimes found adulterated with tin and lead, which metals it dissolves to some extent without much loss of fluidity. Such admixture may be known by the foul surface the mercury exhibits when shaken in a bottle containing air, and by the globules, when made to roll upon the table, having a train or tail. Mercury has a nearly silver white color, and a very high degree of lustre ; it is liquid at all ordinary temperatures, and only solidifies when cooled to 40 F. In this state it is soft and malleable. At 662 it boils, and yields a transparent, colorless vapor, of great density. The metal volatilizes, how- ever, to a sensible extent at all temperatures above G8 or 70; below this point its volatility is imperceptible. The volatility of mercury at the boiling heat is singularly retarded by the presence of minute quantities of lead or /inc. The specific gravity of mercury at 60 is 13.56; that of frozen mercury about 14, great contraction taking place in the act of solidification. Pure quicksilver is quite inalterable in the air at common temperatures, but when heated to near its boiling point it slowly absorbs oxygen, and be- comes converted into a crystalline dark red powder, which is the highest * Messrs. Elkington, Application of Electro-Metallurgy to the Arts. 296 MERCURY, OR QUICKSILVER. oxide. At a dull red heat this oxide is again decomposed into its constituents. Hydrochloric acid has little or no action on mercury, and the same may be said of sulphuric acid in a diluted state; when the latter is concentrated and boiling hot, it oxidizes the metal, converting it into sulphate of the red oxide, with evolution of sulphurous acid. Nitric acid, even dilute, and in the cold, dissolves mercury freely. Mercury combines with oxygen in two proportions, forming a gray and a red oxide, both of which are salifiable. As the salts of the red oxide are the most stable and permanent, that substance may be regarded as the true prot- oxide, instead of the gray oxide, to which the term has usually been applied. Until, however, isomorphous relations connecting mercury with the other metals shall be established, the constitution of the two oxides and that of the corresponding chlorides, iodides, &c., must remain somewhat unsettled.* The equivalent of mercury, on the above supposition, will be 100} its symbol is Hg (hydrargyrum). SUBOXIDE OF MERCURY; GRAY OXIDE; Hg a O. The suboxide is easily prepared by adding caustic potash to the nitrate of this substance, or by digest- ing calomel in solution of caustic alkali. It is a dark gray heavy powder, insoluble in water. It is slowly decomposed by the action of light into metal- lic mercury and red oxide. The preparations known in pharmacy by the names blue pill, gray ointment, mercury with chalk, &c., often supposed to owe their efficacy to this substance, merely contain the finely divided metal. PROTOXIDE OF MERCURY ; RED OXIDE; HgO. There are numerous methods by which this compound may be obtained ; the following may be cited as the most important: (1.) By exposing mercury in a glass flask, with a long narrow neck, for several weeks to a temperature approaching 600; the pro- duct has a dark-red color and is highly crystalline; it is the red precipitate of the old writers. (2.) By cautiously heating any of the nitrates of either oxide to complete decomposition, when the acid is decomposed and expelled, oxid- izing the metal to a maximum, if it happen to be in the condition of sub- oxide. The product is in this case also crystalline and very dense, but has a much paler color than the preceding ; while hot it is nearly black. It is by this method that the oxide is generally prepared; it is apt to contain unde- composed nitrate, which may be discovered by strongly heating a portion in a test-tube : if red fumes are produced, or the odor of nitrous acid exhaled, the oxide has been insufficiently heated in the process of manufacture. (3.) By adding caustic potash in excess to a solution of corrosive sublimate, by which a bright yellow precipitate of oxide is thrown down, which only differs from the foregoing preparations in being destitute of crystalline texture and much more minutely divided. It must be well washed and dried."}" Red oxide of mercury is slightly soluble in water, communicating to the latter an alkaline reaction and metallic taste; it is highly poisonous. When strongly heated, it is decomposed, as before observed, into metallic mercury and oxygen gas. NITRATES OF THE OXIDES OF MERCURY. Nitric acid varies in its action upon mercury, according to the temperature. When cold and somewhat diluted, only salts of the gray oxide are formed, and these are neutral or basic * By referring to cyanogen, it will be perceived that when the equivalent of mer- cury is considered to be 100, the constitution of the cyanide of mercury is analogous to the other metallic cyanides, but when taken at 200, it becomes a bicyanide, and then differs from all others, R. B. f This precipitate is considered by Schauffner to be a hydrate, HgO,3HO, for by exposure to the temperature of 3920, it loses water amounting to over 20 per cent, of its weight. R. 13 MERCURY, OR QUICKSILVER. 297 (i. e. with excess of oxide), as the acid or the metal happens to be in excess. When, on the contrary, the nitric acid is concentrated and hot, the mercury is raised to its highest state of oxidation, and a salt of the red oxide produced. Both classes of salts are apt to be decomposed by a large quantity of water, giving rise to insoluble, or sparingly soluble, compounds containing an excess of base. Neutral Subnitrate, Hg 2 0,NO 6 +2HO, forms large colorless crystals, soluble in a small quantity of water without decomposition; it is made by dissolving mercury in an excess of cold dilute nitric acid. When excess of mercury has been employed, a finely crystallized basic salt is, after some time, deposited, containing 3Hg 2 0,2N0 5 -}-3HO ; this is also decomposed by water. The two salts are easily distinguished when rubbed in a mortar with a little chloride of sodium ; the neutral compound gives ni- trate of soda and calomel; the basic salt, nitrate of soda and a black compound of calomel with oxide of mercury. A black substance, called Hahnemanri's soluble mercury, is produced when ammonia in small quantity is dropped into a solution of sub-nitrate; it contains 3Hg 2 0,NO 5 -fNH 3 , or, according to Sir R. Kane, 2HgO,N0 5 -f-NH 3 . Nitrates of the Protoxide (Red Oxide') of Mercury. By dissolving red oxide of mercury in excess of nitric acid and evaporating gently, a syrupy liquid is ob- tained, which, enclosed in a bell-jar over lirne or sulphuric acid, deposits voluminous crystals and crystalline crusts. The crystals and crusts have the same composition, 2 (HgO,N0 5 )-f-HO. The same substance is deposited from the syrupy liquid as a crystalline powder by dropping it into concentrated nitric acid. The syrupy liquid itself appears a definite compound containing HgO,N0 5 -f-2HO. By saturating hot dilute nitric acid with the red oxide, a salt is obtained on cooling which crystallizes in needles, permanent in the air, containing 2HgO,NO 5 -j-HO. The preceding crystallized salts are decomposed by water, with production of compounds more and more basic as the wash- ing is prolonged or the temperature of the water raised. The nitrates of the protoxide of mercury combine with ammonia. Sulphate of the Suboxide of Mercury, Hg 2 O,S0 3 , falls as a white crystalline powder when sulphuric acid is added to a solution of the subnitrate ; it is but slightly soluble in water. Sulphate of the protoxide, HgO,S0 3 , is readily pre- pared by boiling together oil of vitriol and metallic, mercury until the latter is wholly converted into a heavy white crystalline powder, which is the salt in question ; the excess of acid is then removed by evaporation, carried to per- fect dryness. Equal weights of acid and metal may be conveniently employed. Water decomposes the sulphate, dissolving out an acid salt and leaving an insoluble, yellow, basic compound, formerly called turpeth or turbith mineral, containing, according to Kane's analysis, 3HgO,S0 3 . Long-continued washing with hot water entirely removes the remaining acid, and leaves pure oxide of mercury. STJB CHLORIDE OF MERCURY; CALOMEL; Hg 2 Cl. This very important sub- stance may be easily and well prepared by pouring a solution of the subni- trate into a large excess of dilute solution of common salt. It falls as a dense white precipitate, quite insoluble in water; it must be thoroughly washed with boiling distilled water, and dried. Calomel is generally procured by another and more complex process. Dry sulphate of the red oxide is rubbed in a mortar with as much metallic mercury as it already contains, and a quantity of common salt, until the globules disappear, and an uniform mixture has been produced. This is subjected to sublimation, the vapor of the calomel being carried into an atmosphere of steam, or into a chamber containing air; it is thus condensed in a minutely-divided state, and the laborious process of 298 pulverization of the sublimed mass avoided. The reaction is thus ex- plained :* C 1 eq. mercury. -^Calomel, Hg 2 Cl. 1 eq. sulphate J 1 eq. oxygen of mercury ] 1 eq. sul ^phuricacid 1 eq. metallic mercury 1 eq. common C 1 eq. chlorine- salt 1 eq. sodium ^ Sulphate of soda. Pure calomel is a heavy, white, insoluble, tasteless powder ; it rises in va- por at a temperature below redness, and is obtained by ordinary sublimation as a yellowish-white crystalline mass. It is as insoluble in cold diluted nitric acid as the chloride of silver; boiling-hot strong nitric acid oxidizes and dis- solves it. Calomel is instantly decomposed by an alkali, or by lime-water, with production of sub-oxide. It is sometimes apt to contain a little chloride, which would be a very dangerous contamination in calomel employed for medical purposes. This is easily discovered by boiling with water, filtering the liquid, and adding caustic potash. Any corrosive sublimate is indicated by a yellow precipitate.f CHLORIDE OF MERCURY; CORROSIVE SUBLIMATE ; HgCl. The chloride may be obtained by several different processes. (1.) When metallic mercury is heated in chlorine gas, it takes fire and burns, producing this substance. (2.) It may be made by dissolving the red oxide in hot hydrochloric acid, when crystals of corrosive sublimate separate on cooling. (3.) Or, more economically, by subliming a mixture of equal parts of sulphate of the red oxide of mercury and dry common salt ; and this is the plan generally fol- lowed. The decomposition is thus easily explained :J fl eq. mercury . ^ Corrosive sublimate. 1 eq. sulphate j 1 eq. oxygen, of mercury | 1 eq. sul- > (^ phuric acid ) 1 eq. common ( 1 eq. chlorine salt \ I eq. sodium -^"Sulphate of soda. The sublimated chloride forms a white, transparent, crystalline mass, of great density ; it melts at 509, and boils and volatilizes at a somewhat higher temperature. It is soluble in 16 parts of cold and 3 of boiling water, and crystallizes from a hot solution in long, white prisms. Alcohol and ether also * If the gray oxide be considered as protoxide, the sulphate will be bisulphate of the peroxide, HgO a , 2SO 3 , and the decomposition will stand thus : 1 eq. sulphate ( I J1- m f CU e r /ZH ^^ 6q> Cal me1 ' HgCL of mercury ^ 2 ^ g^g^nc ac ^ 1 eq. metallic mercui 2 eq. common (2 eq. chlorine' salt (2 eq. sodium ^ 2 eq. sulphate of soda. | Ammonia is to be preferred, yielding a white precipitate which has less solubility than the red oxide. R. B. J Or on the other supposition : 1 eq. sulphate of mercury 2 eq. common salt 1 eq. mercury Bichloride of mercury. 2 eq. oxygen .^ 2 eq . sulphuric acir! . 2 eq, chlorine -*"''' 2 eq. sodium ^^.2 eq. sulphate of soda. MERCURY, OR QUICKSILVER. 299 dissolve it with facility ; the latter even withdraws it from a watery solution. Chloride of mercury combines with a great number of other metallic chlo- rides, forming a series of beautiful double salts, of which the ancient sal alem- broth may be taken as a good example: it contains HgCl-f-NH 4 Cl-|--HO. Corrosive sublimate absorbs ammoniacal gas with great avidity, generating a compound supposed to contain 2HgCl-f-NH 3 . When excess of ammonia is added to a solution of corrosive sublimate, a white insoluble substance is thrown down, long known under the name of white precipitate. Sir Robert Kane, who has devoted much attention to the salts of mercury, represents this white precipitate as a double amide and chloride of mercury, or HgCl-4-HgNH a , 2 equivalents of chloride of mercury and 1 of ammonia yielding 1 equivalent of the new body and 1 of hydro- chloric acid. A corresponding black compound, Hg a Cl-[-Hg 2 NH 2 , is produced when ammonia is digested on calomel, which must be carefully distinguished from the sub-oxide. Several compounds of chloride of mercury with oxide of mercury also exist. These are produced by several processes, as when an alkaline carbonate or bicarbonate is added, in varying proportions to a solution of corrosive subli- mate. They differ greatly in color and physical character, and are mostly decomposed by water. Corrosive sublimate forms insoluble compounds with many of the azotized organic principles, as albumen, &c. It is, perhaps, to this property that its great antiseptic virtues are due. Animal and vegetable substances are pre- served by it from decay, as in Mr. Kyan's method of preserving timber and cordage. Albumen is, on this account, an excellent antidote to corrosive sub- limate in cases of poisoning. SUBIODIDE OF MERCURY, Hg 2 I. The subiodide is formed when a solution of iodide of potassium is added to nitrate of the suboxide of mercury; it separates as a dirty yellow, insoluble precipitate, with a cast of green. It may be prepared by rubbing together in a mortar mercury and iodine in the pro- portion of 2 equivalents of the former to 1 of the latter, the mixture being moistened from time to time with a little alcohol. IODIDE OF MERCURY, Hgl. When solution of iodide of potassium is mixed with chloride of mercury, a precipitate falls, which is at first yellow, but in a few moments changes to a most brilliant scarlet, which color is retained on drying. This is the neutral iodide; it maybe made, although of rather duller tint, by triturating single equivalents of iodine and mercury with a little al- cohol. When prepared by precipitation, it is better to weigh out the proper proportions of the two salts, as the iodide is soluble in an excess of either, more especially in excess of iodide of potassium. The iodide of mercury exhibits a very remarkable case of dimorphism, attended with difference of color, the latter being red or yellow according to the figure assumed. Thus, when the iodide is suddenly exposed to a high temperature, it becomes bright yellow throughout, and yields a copious sublimate of minute but brilliant yellow crystals. If in this state it be touched by ft hard body, it instantly becomes red, and the same change happens spontaneously after a certain lapse of time. On the other hand, by a very slow and careful heating a sublimate of red crystals, having a totally different form, may be obtained, which are perma- nent. The same kind of change happens with the freshly precipitated iodide, as Mr. Warington has shown, the yellow crystals first formed breaking up in the course of a few seconds from the passage of the salt to the red modifica- tion.* SUB-SULPHURET OP MERCURY, Hg 2 S. The black precipitate thrown down * Memoirs of Chemical Society of London, i. 85. 300 MERCURY, OR QUICKSILVER. from a solution of subnitrate of mercury by sulphuretted hydrogen, is a sub- sulphuret: it is decomposed by heat into metallic mercury and neutral sul- phuret. SULPHUBET OP MERCURY; ARTIFICIAI. CIJOTABAR; VERMILIOST; HgS. Sulphuretted hydrogen gas causes a precipitate of a white color when passed in small quantity into a solution of corrosive sublimate or nitrate of the red oxide; this is a combination of sulphuret with the salt itself. An excess of the gas converts the whole into sulphuret, the color at the same time changing to black. When this black sulphuret is sublimed, it becomes dark red and crystalline, but undergoes no change of composition; it is then cinnabar. The suFphuret is most easily prepared by subliming an intimate mixture of 6 parts of mercury and 1 of sulphur, and reducing to very fine powder the resulting cinnabar, the beauty of the tint depending much upon the extent to which division is carried. The red or crystalline sulphuret may also be formed directly, without sublimation, by heating the black precipitated substance in a solution of pentasulphuret of potassium ; the sulphuret of mercury is in fact soluble to a certain extent in the alkaline sulphurets, and forms with them crystallizable compounds. When vermilion is heated in the air, it yields metallic mercury and sul- phurous acid ; it resists the action both of caustic alkali in solution, and of strong mineral acids, even nitric, and is only attacked by aqua regia. When protoxide of mercury is put into a large excess of pure caustic ammonia, a compound is obtained the color of which varies with the state of the oxide. If the latter be amorphous, it is pale yellow ; if crystalline, then the action of the ammonia is much less energetic, and the product darker in color. This substance possesses very extraordinary properties, those namely of a most powerful base, and probably belongs to the same class as the com- pound bases containing platinum, described under that metal. The body in question bears a temperature of 260 F. without decomposition, becoming brown and anhydrous by the loss of 3 equivalents of water. In this state it contains Hg 4 H 2 N0 2 O. It is insoluble in water, alcohol, and ammonia ; cold solution of potash has no action on the hydrate, but at a boiling heat some ammonia is disengaged. The anhydrous base is only acted on by hydrate of potash in fusion. It combines directly and energetically with acids, forming well-defined compounds; it absorbs carbonic acid with avidity from the air, like baryta or lime. It even decomposes ammoniacal salts by boiling, ex- pelling the arrimonia and combining with the acid.* The salts of mercury are all volatilized or decomposed by a temperature of ignition ; those which fail to yield the metal by simple heating may in all cases be made to do so by heating in a test-tube with a little dry carbonate of soda. The metal is precipitated from its soluble combinations by a plate of copper, and also by a solution of protochloride of tin, used in excess. The behavior of the chloride and soluble salts of the red oxide with caustic potash and ammonia is also highly characteristic. Alloys of mercury with other metals are termed amalgams ; mercury dis- solves in this manner many of the metals, as gohi, silver, tin, lead, &e. These combinations sometimes take place with considerable violence, as in the case iT . # Ann. Chim. etPhys. 3d series, xviii. 333. PLATINUM. 301 of potassium, where light and heat are produced; besides this, many of the amalgams crystallize after a while, becoming solid. The amalgam of tin used in silvering looking-glasses, and that of silver sometimes employed for stopping hollow teeth, are examples. PLATIKTTM. Platinum, palladium, rhodium, iridium, ruthenium, and osmium form a small group of metals, allied in some cases by properties in common, and still more closely by a natural association. Crude platinum, a native alloy of platinum, palladium, rhodium, and a little iron, occurs in grains and rolled masses, sometimes of tolerably large dimensions, mixed with gravel and transported materials, on the slope of the Ural Mountains in Russia, in Cey- lon, and in a few other places. It has never been seen in the rock, which, however, is judged, from the accompanying minerals, to have been ser- pentine. From this substance platinum is prepared by the following process : The crude metal is acted upon as far as possible by nitro-hydrochloric acid ; to the deep yellowish-red and highly acid solution thus produced sal-ammoniac is added, by which nearly the whole of the platinum is thrown down in the state of ammonio-chloride. This substance is washed with a little cold water, dried and heated to redness; metallic platinum in spongy state is left. Although this metal cannot be fused into a compact mass by any furnace- heat, yet the same object may be accomplished by taking advantage of its property of welding, like iron, at a very high temperature. The spongy pla- tinum is made into a thin uniform paste with water, introduced into a sligh^y conical mould of brass, and subjected to a graduated pressure, by which the water is squeezed out, and the mass rendered at length sufficiently solid to bear handling. It is then dried, very carefully heated to whiteness, and hammered, or subjected to powerful pressure by suitable means. If this operation has been properly conducted, the platinum will now be in a state to bear forging into a bar, which can afterwards be rolled into plates, or drawn into wire, at pleasure. Platinum is in point of color a little whiter than iron ; it is exceedingly malleable and ductile, both hot and cold, and is very infusible, melting only before the oxy-hydrogen blowpipe. It is the heaviest substance known,* its specific gravity being 2]. 5. Neither air, moisture, nor the ordinary acids attack platinum in the slightest degree at any temperature ; hence its high value in the construction of chemical vessels. It is dissolved by aqua regia, and superficially oxidized by fused hydrate of potash, which enters into com- bination with the oxide. The remarkable property of the spongy metal to determine the union of oxygen and hydrogen, has been already noticed. There is a still more curious state in which platinum can be obtained, that of platinum-black, where the division is pushed much further. It is easily prepared by boiling a solution of chloride of platinum to which an excess of carbonate of soda and a quantity of sugar have been added, until the precipitate formed, after a little time, becomes perfectly black, and the supernatant liquid colorless. The black powder is collected on a filter, washed, and dried by gentle heat. This sub- stance appears to possess the property of condensing gases, more especially oxygen, into its pores to a very great extent; when placed in contact with a solution of formic acid, it converts the latter, with copious effervescence, into carbonic acid ; alcohol and ether, dropped upon the platinum-black, become * This is in accordance with the usual statement, but iridium (which see) is still denser. R. B. 26 302 PLATINUM. changed by oxidation to acetic acid, the rise of temperature being often suffi- ciently great to cause inflammation. When exposed to a red-heat, the black substance shrinks in volume, assumes the appearance of common spongy platinum, and loses these peculiarities, which are no doubt the result of its excessively comminuted state. Platinum forms two compounds with oxygen, chlorine, &c. The equivalent of platinum is 98.68. Its symbol is Pt. PROTOXIDE OF PLATINUM:, PtO. When protochloride of platinum is di- gested with caustic potash, a black powder, soluble in excess of alkali, is pro- duced: this is the protoxide. It is soluble in acids with brown color, and the solutions are not precipitated by sal-ammoniac. When peroxide of platinum is heated with solution of oxalic acid, it is reduced to protoxide, which re- mains dissolved,. The liquid has a dark blue color, and deposits fine copper- red needles of oxalate of the protoxide of platinum. PEROXIDE OP PLATINUM, PtO 2 . This is best prepared by adding nitrate of baryta to sulphate of the peroxide of platinum ; sulphate of baryta and nitrate of the oxide are produced. From the latter, caustic soda precipitates one- half of the oxide of platinum. The sulphate is itself obtained by acting with strong nitric acid upon the bisulphuret of platinum, which falls as a black powder when a solution of bichloride is dropped into sulphuret of potassium. The hydrate of the peroxide is a bulky brown powder, which, when gently heated, becomes black and anhydrous. It dissolves in acids, and also com- bines with bases; the salts have a yellow or red tint, and a great disposition to unite with salts of the alkalis and alkaline earths, giving rise to a series of double compounds, which are not precipitated by excess of alkali. A combi- nation of oxide of platinum with ammonia exists, which is explosive. Both oxides of platinum are reduced by ignition. PROTOCHLORIDE OF PLATINUM, PtCl. The protochloride is produced when bichloride of platinum, dried and powdered, is exposed for some time to a heat of 400, by which half of the chlorine is expelled ; also, when sulphu- rous acid is passed into a solution of the bichloride until the latter ceases to give a precipitate with sal-ammoniac. It is a greenish-gray powder, insolu- ble in water, but dissolved by hydrochloric acid. The latter solution, mixed with sal-ammoniac or chloride of potassium, deposits a double salt in fine red prismatic crystals, containing, in the last case, PtCl-f-KCl. The correspond- ing sodium compound is very soluble and difficult to crystallize. The proto- chloride is decomposed by heat into chlorine and metallic platinum. PERCHLORIDE OR BICHLORIDE OF PLATINUM, PtCl 2 . This substance is al- ways formed when platinum is dissolved in nitre-hydrochloric acid. The acid solution yields on evaporation to dry ness a red or brown residue, deli- quescent, and very soluble both in water and alcohol; the aqueous solution has a pure orange-yellow tint. Bichloride of platinum combines to double salts with a great variety of metallic chlorides ; the most important of these compounds are those containing the metals of the alkalis and ammonium. Chloride of platinum and potassium, PtCl 2 -}-KCJ, forms a bright yellow crys- talline precipitate, being produced whenever solutions of the chlorides of pla- tinum and of potassium are mixed, or a salt of potash, mixed with a little hydrochloric acid, added to chloride of platinum. It is feebly soluble in wa- ter, still less soluble in dilute alcohol, and is decomposed with some difficulty by heat. It is readily reduced by hydrogen at a high temperature, furnishing a mixture of chloride of potassium and platinum-black; the latter substance may thus, indeed, be very easily prepared. The sodium-salt, PtCl 2 -}-NaCl-j- 6HO, is very soluble, crystallizing in large, transparent, yellow-red prisms of great beauty. The ammonio-chloride of platinum, PtCl 2 -j-NH 4 Cl, is indistin- guishable, in physical characters, from the potassium salt; it is thrown down as a precipitate of small, transparent, yellow, octahedral crystals when sal- PLATINUM. 303 ammoniac is mixed with chloride of platinum ; it is but feebly soluble in wa- ter, still less so in dilute alcohol, and is decomposed by heat, yielding spongy platinum, while sal-ammoniac, hydrochloric acid, and nitrogen are driven off. Compounds of platinum with iodine, bromine, sulphur, and phosphorus have been formed, but are comparatively unimportant. Some very extraordinary compounds have been derived from the proto- chloride of platinum. When ammonia in excess is added to a hot solution of the protochloride of platinum and ammonium, a green crystalline salt separates after a time, which is quite insoluble in water, and is not affected by hydrochloric or sulphuric acids, ammonia, or even a boiling-hot solution of potash. This substance is known as the green salt of Magnus, and contains the elements of protochloride of platinum and ammonia, or PtCl-|-NH 3 . When the above compound is heated with concentrated nitric acid, it be- comes converted into a white, granular, crystalline powder, which on addition of water dissolves, leaving a residue of metallic platinum. The solution yields on standing small, brilliant, colorless prisms of a substance very soluble in water, containing the elements of protochloride of platinum, ammonia, nitric acid, and an additional equivalent of oxygen: PtCl,N 2 H 6 ,0+N0 5 . The platinum and chlorine in this curious body are insensible to ordinary reagents, and ammonia is evolved from it only on boiling with caustic alkali ; the presence of nitric acid can be detected immediately by gently heating a small portion with copper-filings and oil of vitriol. From this substance a series of salt-like bodies can be obtained, some of which have been carefully studied by M. Gros.* Thus, when treated with hydrochloric acid, the nitric acid is wholly displaced, and a compound formed which crystallizes in small, transparent, yellowish octahedrons, sparingly soluble in boiling water, contain- ing PtCl,N 2 H 6 +Cl. With sulphuric acid it gives a substance which crystal- lizes in small, sparingly-soluble, colorless needles, containing PtCl,N 2 H 6 ,O-}- SO 3 . The oxalic acid compound is white and insoluble; it contains PtCl, N 2 Hg,0-f-C 2 O 3 . Crystallizable compounds containing phosphoric, tartaric, citric, malic, formic, and even carbonic acids, were obtained by similar means. These substances have very much the characters of salts of a compound base or <7iasz-metal containing PtCl 5 N 2 H 6 , and which yet remains unknown in a separate state. MM. Reiset and Peyrone have since described two other basic bodies con- taining platinum in the same remarkable condition ; these differ from the preceding in being free from chlorine.")" Protochloride of platinum put into ammonia becomes rapidly converted into a green powder, which, by boiling, slowly dissolves ; the solution, on evaporation and cooling, furnishes beautiful yellowish crystals of the chlorine compound of one of these bases, compounded of platinum and the elements of ammonia. The crystals contained PtN 2 H 6 ,Cl-]-HO. The equivalent of water is easily expelled by heat, and regained by absorption from the air. The green salt of Magnus, boiled with ammonia, yields the same product. A solution of this substance mixed with nitrate of silver gives chloride of silver and the nitrate of the new base, which crystallizes on evaporation in fine, white, transparent needles, containing PtN 2 H 6 ,0-f-N0 5 . The sulphate, iodide, and bromide are also crystallizable. Two carbonates exist. By adding baryta-water to a solution of the sulphate, and evaporating the filtered liquid in vacuo, a white crystalline, deliquescent mass is obtained, which is * Ann. Chim. et Phys. Ixix. 204. f Ann. Chim. et Phys. 3d series, xi. 417, and xii. 193. 304 PALLADIUM. the hydrate of the base, PtN 2 H 6 ,O-f-HO. It is almost comparable in point of alkalinity with potash itself, absorbing carbonic acid with energy, and de- composing ammoniacal salts. When this hydrate is heated to 230, it aban- dons water and ammonia, and leaves a grayish, porous, insoluble mass con- taining PtNH 3 ,0. This is probably an isomeric modification of the second base, whose salts are mentioned below. When a solution of the iodide, PtN 2 H 6 ,I, is long boiled, it deposits a sparingly soluble yellow powder, the composition of which is expressed by the formula PtNH 3 ,I: this is the iodide-compound of a basic substance, PtNH 3 ; and from it by double decomposition a series of analogous salts can be obtained. The green salt of Magnus has the same composition as the chloride of this new 'base, which is yellow and soluble in boiling water, and may be converted into it. The salts of the first base are generally convert- ible into those of the second by heat, and the converse change may also be often effected by ebullition with ammonia. The bichloride, or a solution of peroxide of platinum, can be at once re- cognized by the yellow precipitate with sal-ammoniac, decomposable by heat, with production of spongy metal. Bichloride of platinum and the sodio-chloride of platinum are employed in analytical investigations to detect the presence of potash, and separate it from soda. For the latter purpose, the alkaline salts are converted in chlorides, and in this condition mixed with four times their weight of sodio-chloride of platinum in crystals, the whole being dissolved in a little water. When the formation of the yellow salt appears complete, alcohol is added, and the pre- cipitate collected on a weighed filter, washed with weak spirit, carefully dried, and weighed. The chloride of potassium is then easily reckoned from the weight of the double salt, and this, subtracted from the weight of the mixed chlorides employed, gives that of the chloride of sodium by difference: 100 parts of potassio-chloride of platinum correspond to 35.06 parts of chlo- ride of potassium. Capsules and crucibles of platinum are of great value to the chemist : the latter are constantly used in mineral analysis for fusing siliceous matter with alkaline carbonates. Tjiey suffer no injury in this operation, although the caustic alkali roughens and corrodes the metal. The experimenter must be particularly careful to avoid introducing any oxide of an easily fusible metal, as that of lead or tin, into a platinum crucible. If reduction should by any means occur, these metals will at once alloy themselves with the platinum, and the vessel will be destroyed. A platinum crucible must never be put naked into the fire, but be always placed within a covered earthen crucible. PALLADIUM. The solution of crude platinum, from which the greater part of that metal has been precipitated by sal-ammoniac, is neutralized by carbonate of soda, and mixed with a solution of cyanide of mercury ; cyanide of palladium sepa- rates as a whitish insoluble substance, which, on being washed, dried, and heated to redness, yields metallic palladium in a spongy state. The palla- dium is then welded into a mass, in the same manner as platinum. Palladium closely corresponds with platinum in color, appearance, and difficult fusibility ; it is also very malleable and ductile. In density it differs very much from that metal, being only 11.8. Palladium is more oxidable than platinum. When heated to redness in the air, especially in the state of RHODIUM. 305 sponge, it acquires a blue or purple superficial film of oxide, which is again reduced at a white heat. This metal is slowly attacked by nitric acid; its best solvent is aqua regia. There are two compounds of palladium and oxygen. The equivalent of palladium is 53.27; its symbol is Pd. PROTOXIDE or PALLADIUM, PdO. This is obtained by evaporating to dry- ness, and cautiously heating, the solution of palladium in nitric acid. It is black, and but little soluble in acids. The hydrate falls as a dark brown preci- pitate when carbonate of soda is added to the above solution. It is decom- posed by a strong heat. PEROXIDE OF PALLADIUM:, PdO a The pure peroxide is very difficult to obtain. When solution of caustic potash is poured, little by little, with con- stant stirring, upon the double chloride of palladium and potassium in a dry state, the latter is converted into a yellowish-brown substance, which is the peroxide, in combination with water and a little alkali. It is but feebly solu- ble in acids. PROTOCHLORIDE OF PALLADIUM, PdCl. The solution of the metal in aqua regia yields this substance when evaporated to dryness. It is a dark brown mass, soluble in water when the heat has not been too great, and forms double salts with many metallic chlorides. The potassio and ammonio-chlorides of palladium are much more soluble than those of platinum ; they have a dirty yellow tint. PERCHLORIDE OF PALLADIUM only exists in solution, and in combination with the alkaline chlorides. It is formed when the protochloride of palladium is digested in aqua regia. The solution has an intense brown color, and is decomposed by evaporation. Mixed with chloride of potassium or sal-ammo- niac, it gives rise to a red crystalline precipitate of double salt, which is but little soluble in water. A sulphuret of palladium, PdS, is formed by fusing the metal with sulphur, or by precipitating a solution of protochloride by sulphuretted hydrogen. A palladium-salt is well marked by the pale yellowish-white precipitate with solution of cyanide of mercury, convertible by heat into the spongy metal. Palladium is readily alloyed with other metals, as copper: one of these compounds has been applied to useful purposes. A native alloy of gold with palladium is found in the Brazils, and imported into England. RHODIUM. The solution from which platinum and palladium have been separated in the manner described is mixed with hydrochloric acid, and evaporated to dry- ness. The residue is treated with alcohol of specific gravity .837, which dissolves everything except the double chloride of rhodium and sodium. This is well washed with spirit, dried, heated to whiteness, and then boiled with water ; chloride of sodium is dissolved out, and metallic rhodium remains. Thus obtained, rhodium is a white, coherent, spongy mass, which is infusible and incapable of being welded. It maybe had, however, in a more compact state by fusing it with arsenic or sulphur, and exposing the compound to a high temperature in contact with air. It then acquires a specific gravity of 1 1. Rhodium is very brittle: reduced to powder and heated in the air, it be- comes oxidized, and the same alteration happens to a greater extent when it is fused with nitrate or bisulphate of potash. None of the acids, singly or 20* 306 IRIDIUM. conjoined, dissolve tins metal, unless it be in the state of alloy, as with plati- num, in which case it is attacked by aqua regia. The equivalent of rhodium is 52.11. Its symbol is R. OXIDE OF RHODIUM, R 2 O 3 . Finely powdered metallic rhodium is heated in a silver crucible with a mixture of hydrate of potash and nitre ; the fused mass boiled with water leaves a dark brown insoluble substance, consisting of oxide of rhodium in union with potash. This is digested with hydrochloric acid, which removes the potash, and leaves a greenish gray hydrate of the oxide of rhodium, insoluble in acids. A soluble modification of the same substance, retaining, however, a portion of alkali, may be had by adding an excess of carbonate of potash to the double chloride of rhodium and potas- sium, and evaporating. Another oxide, containing a smaller proportion of oxygen, is supposed to exist, but has not been obtained in a separate state. CHLORIDE OF RHODIUM, R 2 C1 3 . The pure chloride is prepared by adding hydrofluosilicic acid to the double chloride of rhodium and potassium, evapo- rating the filtered solution to dryness, and dissolving the residue in water. It forms a brownish red deliquescent mass, soluble in water, with a fine red color. It is decomposed by heat into chlorine and metallic rhodium. The chloride of rhodium and potassium, R 2 Ci 3 -f-2KCl-j-2HD, is prepared by heating in a stream of chlorine a mixture of equal parts finely-powdered rhodium and chloride of potassium. This salt has a fine red color, is soluble in water, and crystallizes in 4-sided prisms. Chloride of rhodium and sodium is also a very beautiful red salt, obtained by a similar process; it contains R 2 Cl 3 -j- SNaCl -{- 18HO. The chloride of rhodium and ammonium resembles the potassium compound. SULPHATE OF RHODIUM, R 2 O 3 ,3S0 3 . The sulphuret of rhodium, obtained by precipitating one of the salts by a soluble sulphuret, is oxidized by strong nitric acid. The product is a brown powder, nearly insoluble in nitric acid, but dissolved by water ; it cannot be made to crystallize. Sulphate of rhodium and potassium is produced when metallic rhodium is strongly heated with bisulphate of potash. It is a yellow salt, slowly soluble in cold water. An alloy of steel with a small quantity of rhodium is said to possess ex- tremely valuable properties. When crude platinum is dissolved in aqua regia, a small quantity of a gray, scaly metallic substance usually remains behind, having altogether resisted the action of the acid; this is a native alloy of iridium and osmium. It is reduced to powder, mixed with an equal weight of dry chloride of sodium, and heated to redness in a glass tube, through which a stream of rnoist chlo- rine gas is transmitted. The further extremity of the tube is connected with a receiver containing solution of ammonia. The gas, under these circum- stances, is rapidly absorbed, chloride of iridium and chloride of osmium being produced : the former remains in combination with the chloride of sodium ; the latter, being a volatile substance, is carried forward into the receiver, where it is decomposed by the water into osmic and hydrochloric acids, which combine with the alkali. The contents of the tube, when cold, are treated with water, by which the double chloride of iridium and sodium is dissolved out; this is mixed with an excess of carbonate of soda, and evaporated to dryness. The residue is ignited in a crucible, boiled with water, and dried ; it then consists of a mixture of oxide of iron, and a combination of oxide of iridium with soda ; it is reduced by hydrogen at a high temperature, and RUTHENIUM. 307 treated successively with water and strong hydrochloric acid, by which the alkali and the iron are removed, while metallic iridium is left in a divided state. By strong pressure and exposure to a white heat, a certain degree of compactness may be communicated to the metal. Iridium is a white brittle metal, fusible with great difficulty before the oxy- hydrogen blowpipe.* It is not attacked by any acid, but is oxidized by fusion with nitre, and by ignition to redness in the air. The equivalent of iridium-is 98.68. Its symbol is Ir. OXIDES OF IRIDIUM. Four of these compounds are described. Protoxide of iridium, IrO, is prepared by adding caustic alkali to the protochloride, and digesting the precipitate in an acid. It is a heavy black powder, insoluble in acids. It may be had in the state of hydrate by precipitating the protochloride of iridium and sodium by caustic potash. The hydrate is soluble in acids with dirty green color. Sesquioxide, Ir 2 O 3 , is produced when iridium is heated in the air, or with nitre; it is best prepared by fusing in a silver crucible a mixture of carbonate of potash and the perchloride of iridium and potassium, and boiling the product with water. This oxide is bluish-black, and is quite insoluble in acids. It is reduced by combustible substances with explosion. Binoxide of iridium, IrO a , is unknown in a separate state ; it is supposed to exist in the sulphate, produced when the sulphuret is oxidized by nitric acid. A solution of sulphate heated with excess of alkali evolves oxygen gas, and deposits sesquioxide of indium. Peroxide of iridium, IrO 3 , is produced when carbonate of potash is gently heated with the perchloride of iridium; it forms a grayish -yellow hydrate, which contains alkali. CHLORIDES or IRIDIUM. Protochloride, IrCl, is formed when the metal is brought in contact with chlorine at a dull red-heat; it is a dark olive-green insoluble powder. It is dissolved by hydrochloric acid, and forms double salts with the alkaline chlorides, which have a green color. The sesquichloride, Ir 2 Cl 3 , is prepared by strongly heating iridium with nitre, adding water, and enough nitric acid to saturate the alkali, warming the mixture, and then dis- solving the precipitated hydrate of the sesquioxide in hydrochloric acid. It forms a dark yellowish-brown solution. This substance combines with metal- lic chlorides. Bichloride of iridium is obtained in solution by adding hy- drofluosilicic acid to the bichloride of iridium and potassium, formed when chlorine is passed over a heated mixture of iridium and chloride of potassium. It forms with metallic chlorides a number of double salts, which resemble the platinum compounds of the same order. Perchloride of iridium, IrCl 3 , is unknown in a separate state. Perchloride of iridium and potassium is obtained by heating iridium with nitre, and then dis- solving the whole in aqua regia, and evaporating to dryness. The excess of chloride of potassium may be extracted by a small quantity of water. The crystallized salt has a beautiful red color. The variety of tints exhibited by the different soluble compounds of iridium is very remarkable, and suggested the name of the metal, from the word iris. Platinum, palladium, and iridium combine with carbon when heated in the flame of a spirit-lamp ; they acquire a covering of soot, which, when burned, leaves a kind of skeleton of spongy metal. RUTHENIUM. M. Clausf has described under this name a new metal contained in the residue from crude platinum, insoluble in aqua regia. It closely resembles * It is the heaviest substance known, its specific gravity, according to Professor Hare, being 21.8. Proceedings of the Amer. Phil. Soc. May and June, 1842. R. B. f Annalen der Chemie imd Pharm. lix. 234. 308 OSMIUM. iridium in its general characters, but yet possesses distinctive features of its own. It was obtained in the form of small angular masses, with perfect metallic lustre, very brittle and infusible. Its specific gravity is 8.6. It resists the action of acids, but oxidizes readily when heated in the air. The equivalent of ruthenium is 51.7, and its symbol Ru. OXIDES OF RUTHENIUM. Protoxide of ruthenium, RuO, is a grayish-black metallic-looking powder, obtained by heating bichloride of ruthenium with excess of carbonate of soda in a stream of carbonic acid gas, and then wash- ing away the soluble saline matter. It is insoluble in acids. The sesquioxide, Ru 2 O 3 , in the anhydrous condition, is a bluish-black powder formed by heating the metal in the air. It is also precipitated by alkalis from the sesquichloride as a blackish-brown hydrate, soluble in acids with orange-yellow color. The peroxide, RuO a , is a deep blue powder, procured by roasting the bisulphuret. A hydrate of this oxide is known in an impure condition. An acid of ruthe- nium is also supposed to exist. Sesquichloride of ruthenium, Ru 2 Cl 3 , is an orange-yellow soluble salt of as- tringent taste ; when the solution is heated, it becomes green and finally blue, by reduction, in all probability, to protochloride. Sesquichloride of ruthenium forms double salts with the chlorides of potassium and ammonium. The solution of osmic acid in ammonia, already mentioned, is gently heated for some time in a loosely-stopped vessel ; its original yellow color be- comes darker, and at length a brown precipitate falls, which is a combination of sesquioxide of osmium with ammonia: it results from the reduction of the osmic acid by the hydrogen of the volatile alkali. A little of the precipitate is held in solution by the sal ammoniac, but may be recovered by .heating the clear liquid with caustic potash. The brown substance is dissolved in hv- drochloric acid, a little hydrochlorate of ammonia added, and the whole evaporated to dryness. The residue is strongly heated in a small porcelain retort; the oxygen of the oxide combines with hydrogen from the ammonia, vapor of water, hydrochloric acid, and sal-ammoniac are expelled, and osmium left behind, as a grayish porous mass, having the metallic lustre. In the most compact state in which this metal can be obtained, it has a bluish-white color, and, although somewhat flexible in thin plates, is yet easily reduced to powder. Its specific gravity is 10 ; it is neither fusible nor vola- tile. It burns when heated to redness, yielding osmic acid, which volatilizes. Osmiate of potash is produced when the metal is fused with nitre. When in a finely-divided state, it is oxidized by strong- nitric acid. The equivalent of osmium is 99.56 ; its symbol is Os. OXIDES OF OSMIUM. Four compounds of osmium with oxygen are known. Protoxide, OsO, is obtained, in combination with a little alkali, when caustic potash is added to a solution of protochloride of osmium and potassium. It is a dark green powder, slowly soluble in acids. Sesquioxide, Os 2 O 3 , has al- ready been noticed ; it is generated by the deoxidation of osmiate of ammo- nia ; it is black, and but little soluble in acids. It always contains ammonia, and explodes feebly when heated. Peroxide of osmium, Os0 2 , is prepared by strongly heating in a retort a mixture of carbonate of soda and the perchloride of osmium and potassium, and treating the residue with water, and after- wards with hydrochloric acid. The peroxide is a black powder, insoluble in acids, and burning to osmic acid when heated in the air. Osmic acid, OsO 4 , is by far the most important and interesting of the oxides of this metal. It is prepared by heating osmium in a current of pure oxygen gas ; it condenses in the cool part of the tube in which the experiment is made in colorless transparent crystals. Osmic acid melts and even boils below 212 ; its vapor OSMIUM. 309 has a peculiar offensive odor, and is exceedingly irritating and dangerous. Water slowly dissolves this substance. It has acid properties, and combines with bases. Nearly all the metals precipitate osmium from a solution of osmic acid. CHLORIDES OF OSMIUM. Protochbride, OsCl, is a dark green crystalline substance, formed by gently heating osmium in chlorine gas. It is soluble in a small quantity of water, with green color, but decomposed by a large quan- tity into osmic and hydrochloric acids and metallic osmium. It forms double salts with the metallic chlorides. The sesquichloridej Os 2 Cl 3 , has not been isolated ; it exists in the solution obtained by dissolving the sesquioxide in hydrochloric acid. Perchloride, OsCl 2 , in combination with chloride of pot- assium, is produced when a mixture of equal parts metallic osmium and the last-named salt is strongly heated in chlorine gas. It forms fine red octahe- dral crystals, containing OsCJ 2 -f-KCl. Osmium combines also with sulphur and with phosphorus. 310 PAKT III. ORGANIC CHEMISTRY. ,- INTRODUCTIOIT. ORGANIC substances, whether directly derived from the vegetable or ani- mal kingdom, or produced by the subsequent modification of bodies which thus originate, are remarkable as a class for a degree of complexity of consti- tution far exceeding that observed in any of the compounds yet described. And yet the number of elements which enter into the composition of these substances is extremely limited ; very few, comparatively speaking, contain more than four, viz. carbon, hydrogen, oxygen, and nitrogen ; sulphur and phosphorus are occasionally associated with these in certain natural products, and compounds containing chlorine, iodine, arsenic, &c., have been formed by artificial means. This paucity of elementary bodies is compensated by the very peculiar and extraordinary properties of the four first-mentioned, which possess capabilities of combination to which the remaining elements are strangers. There appears to be absolutely no limit to the number of definite, and often crystallizable, substances which can be thus generated, each marked by a perfect individuality of its own. The mode of association of the elements of organic substances is in general altogether different from that so obvious in the other division of the science. The latter is invariably characterized by what may be termed a binary plan of combination, union taking place between pairs of elements, and the com- pounds so produced again uniting themselves to other compound bodies in the same manner. Thus, copper and oxygen combine to oxide of copper, potassium and oxygen to potash, sulphur and oxygen to sulphuric acid ; sul- phuric acid, in its turn, combines both with oxide of copper and oxide of pot- assium, generating a pair of salts, which are again capable of uniting to form the double compound, CuO,S0 3 +KO,SO 3 . The most complicated products of inorganic chemistry may be thus shown to be built up by this repeated pairing on the part of their constituents. With organic bodies, however, the case is strikingly different ; no such arrangement can here be traced. In sugar, C 24 H 22 22 , or morphia, C 35 H 20 N0 6 , or the supposed radical of bitter almond oil, C ]4 H 5 O 2 , and a multitude of similar cases, the elements concerned are, as it were, bound up together into a single whole, which can enter into combination with other substances, and be thence disengaged with properties unaltered. A curious consequence^ of this peculiarity is to be found in the compara- tively inslabk character of organic compounds,-and their general proneness to decomposition and change, when the balance of opposing forces, to which they owe their existence, becomes deranged by some external cause. INTRODUCTION TO OEGANIC CHEMISTRY. 311 If a complex inorganic substance be attentively considered, it will usually be found that the elements are combined in such a manner as to satisfy the most powerful affinities, and to give rise to a state of very considerable per- manence and durability. But in the case of an organic substance containing 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 op- posing forces remain exactly balanced, the integrity of the compound is pre- served; but the moment one of them, from some accidental cause, acquires preponderance over the rest, equilibrium is destroyed, and the organic princi- ple breaks up into two or more new bodies of simpler and more permanent constitution. The agency of heat produces this effect by exalting the attrac- tion of oxygen for hydrogen and carbon ; hence the almost universal destruc- tibility of organic substances by a high temperature. Mere molecular disturb- ance of any kind may cause destruction when the instability 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 resisting 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 carburets of hydrogen, cyanogen, and oxalic acid, con- nect, 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 ele- ments of the air by processes for the most part totally 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 a repetition of such treatment under perhaps varied circumstances, may be broken up into other and still simpler organic combinations; until at length the binary compounds of inorganic chemistry, or bodies so allied to them that they may be placed indifferently in either group, are by such means reached. Organic Substitution products ; Law of Substitution. The study of the action of chlorine, bromine, and nitric acid upon various organic substances has led to the discovery of a very remarkable law regulating the formation of chlori- nated and other analogous compounds, which, without being of necessity absolute in every case, is yet of sufficient generality and importance to require careful consideration. This peculiar mode of action consists in the replace- ment of the hydrogen of the organic substance by chlorine, bromine, iodine, the elements of nitrous acid, and more rarely other substances 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 hydrobromic 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 ordinary views of the functions of powerful salt-radicals, this loss of hydrogen and assumption of the new ele- 312 INTRODUCTION TO ORGANIC CHEMISTRY. ment do actually occur with a great variety of substances belonging to different groups with comparatively trifling disturbance of physical and chemical pro- perties ; the power of saturation, the density of the vapor, and other pecu- liarities of the original substance remain the same, saving the modification they may suffer from the difference of the equivalent weights of hydrogen and the body 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 unequivocally the stamp of its origin. Although numerous examples of these changes will be found described in detail in the following pages, it will be well perhaps to mention here two or " three cases by way of illustration. Dutchliquid, the compound formed by the union of equal measures of olefi- ant gas and chlorine, containing C 4 H 4 C1 2 , is affected by chlorine in obedience to the law of substitution; one, two, four equivalents of hydrogen being suc- cessively removed by the prolonged action of the gas aided by sunshine, and one, two, or four equivalents of chlorine introduced in place of the hydrogen withdrawn as hydrochloric acid. In the last product, the perchloride of car- bon, C 4 C1 6 , the replacement is total; the intermediate products are volatile liquids not differing very much in general characters from Dutch-liquid itself. A great number of compound ethers of the alcohol and methyle 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 add, containing C 4 Cl 3 3 -j-HO, and in which con- sequently the whole hydrogen of the real acid^is replaced by chlorine. Chlo- racetic 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 acetates. Basic substitution-products have been obtained indirectly: the chloraniline and bromaniline of Hofmann are the most striking examples. These will be found fully described among the indigo-.products. The action of fuming nitric acid upon organic substances very commonly indeed gives rise to substitution-products containing the elements of nitrous acid, NO 4 , in place of hydrogen. The benzoyle-compounds, several of the essential oils, natural and derived from resins, will be found to furnish illus- trations. In formulae representing substitution-compounds yet retaining hydrogen, the practice is often adopted of placing the substituting body beneath this residual hydrogen, and uniting them by a bracket on each side. Thus, the formula of the first two products of the action of chlorine on Dutch-liquid are thus written : And pyroxyline, or gun-cotton, which is supposed to be a substitution-product from lignine, C 24 H 20 20 , having 5 equivalents of hydrogen replaced by the elements of nitric acid, will stand INTRODUCTION TO ORGANIC CHEMISTRY. 313 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 pro- perties is fairly and properly ascribed to difference of constitution, the elements being differently arranged. For instance, formic ether and acetate of methyle are isomeric, both containing C 6 H 6 O 4 ; but then the first is by some supposed to consist of formic acid, C 2 H0 3 , combined with ether, C 4 H 5 O ; while the second is imagined, in accordance with the same views, to be made up of acetic acid, C 4 H 3 O 3 , and the ether of wood-spirit, C 2 H 3 0. And this method of ex- planation is generally sufficient and satisfactory : when it can be shown that a difference of constitution, or even a difference in the equivalent numbers, exists between two or more bodies identical in ultimate composition, the reason of their discordant characters becomes to a certain extent intelligible. Organic bodies may be thus classified : 1. Quasi elementary Substances, and their compounds. These affect the dis- position and characters of the true elements, and like the latter evince a tend- ency 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 salt radicals, and the latter organic salt-basyles. Very 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. These quasi-elements are at present the most important and interesting substances in organic chemistry. 2. Organic Salt-bases, not being the oxides of known radicals. The princi- pal 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 is not strictly correct, as these compounds usually manifest feeble acid properties by combining with metallic oxides. This group comprehends the sugars, the different modifica- tions 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. Carburets of Hydrogen, their oxides and derivatives. 7. Fatty Bodies. 8. Compound Acids, containing the elements of an organic substance in combination with those of a mineral or other acid. These bodies form a large and very interesting class, of which sulphovinic acid may be taken as the type or representative. 9. Coloring Principles, and other substances not referable to either of the preceding classes. The action of heat on organic substances presents many important and in- teresting points, of which a few of the more prominent may be noticed. Bodies of simple constitution and of some permanence, which do not sublime unchanged, as many of the organic acids, yield, when exposed to a high, but regulated temperature, in a retort, new compounds, perfectly definite and often crystallizable, which partake, to a certain extent, of the properties of the original substance ; the numerous pyro acids, of which many examples will 27 314 INTRODUCTION TO ORGANIC CHEMISTRY. occur in the succeeding pages, are thus produced. Carbonic acid and water are often eliminated under these circumstances. If the heat be suddenly 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 and carburetted 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 ammonia, partly left in combination with the carbonaceous matter in the distillatory vessel. The products of dry distillation thus become still more complicated. A much greater degree of regularity is observed in the effects of heat on fixed organic matters, when these are previously mixed with an excess of strong alkaline base, as potash or lime. In such cases an acid, the nature of which is chiefly dependent upon the temperature applied, is produced, and remains in union with the base, the residual element or elements escaping in some volatile form. Thus, benzoic acid distilled with hydrate of lime, at a dull red-heat, yields carbonate of lime and bicarburet of hydrogen, or benzine; woody fibre and caustic potash, heated to a very moderate temperature, yield ulmic acid and free hydrogen ; with a higher degree of heat, oxalic acid ap- pears 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 of the more complicated organic, and, more particularly, azotized, principles are subject, have lately attracted much attention. By the expres- sion decay,* Liebig and his followers understand a decomposition of moist organic matter, freely exposed to the air, by the oxygen of which it is gradu- ally burned and destroyed, without sensible elevation of temperature; the term putrefaction, on the other hand, is limited to changes occurring in and beneath 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 decay; and if the decay or its cause, namely, the absorption of oxygen, be prevented, no putrefaction occurs. The most putrescible substances, as animal flesh in- tended for food, milk, and highly azotized vegetables, are preserved indefinitely, by enclosure in metallic cases, from which the air has been com- pletely 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 Vin- ous Fermentation. These actions are yet very obscure, and require to be discussed with great caution. * Or eremacausis, that is, slow burning. THE ULTIMATE ANALYSIS, ETC. 315 THE ULTIMATE ANALYSIS OF ORGANIC BODIES. As organic substances cannot be produced at will from their elements, the analytical method of research is alone applicable to the investigation of their exact chemical composition ; hence the ultimate analysis of these substances becomes a matter of great practical importance. The operation is always executed by causing complete combustion of a known weight of the body to 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 separate means are resorted to for their estimation. The method to be described for the determination of the carbon and hydro- gen owes its convenience and efficiency to the improvements of Professor Lie- big ; it has superseded all other processes, and is now invariably employed in inquiries of the kind. With proper care, the results obtained are wonderfully correct; and equal, if not surpass in precision, those of the best mineral analyses. The principle upon which the whole depends is the following: When an or- ganic substance is heated with the oxides of copper, lead, and several other metals, it undergoes complete combustion at the expense 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, although unchanged by heat alone, gives up oxygen to combustible matter with extreme facility. When nothing but carbon and hydrogen, or those bodies 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 scrupu- lous 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, exposure 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 Fig. 152. conducted in a narrow open tube, about 2^ or 3 inches long; the tube and substance are weighed together, arid, when the latter has been removed, the tube with any little adherent matter is re-weighed. This weight, subtracted from the former, gives the weight of the substance employed in the experiment. As only 5 or 6 grains are used, the weighings should not involve a greater error than ^ J ft th part of a grain. The oxide of copper is best made from the nitrate by complete ignition in an earthen crucible: it is re- duced 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 .4 or .5 inch, and in length vary- ing from 10 to 14 inches; this kind of glass bears a moderate red-heat with- out becoming soft enough to lose its shape. One end of the tube is drawn out to a point, as shown in Fig. 153, and closed; the other is simply heated to fuse and soften the sharp edges of the glass. The tube is now two-thirds 316 THE ULTIMATE ANALYSIS OP filled with the yet warm oxide of copper, nearly the whole of which is trans- ferred 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 Fig. 153. Oxide copper. Mixture. Oxide copper. 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. The chauffer is placed upon flat bricks or a piece of stone Fig. 154. so that but little air can enter the grating, unless the whole he 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. 155, filled with fragments of spongy chloride of cal- cium, is attached by a perforated cork, thoroughly dried, to the open extremity Fig 155. Fig. 156. of the combustion-tube. The carbonic acid is condensed into a solution of caustic potash, of specific gravity 1.25, which is contained in a small glass apparatus on the principle of a Woulfe's bottle, shown in Fig. 156. The ORGANIC BODIES. 317 connection between the latter and the chloride of calcium tube is completed by a little tube of caoutchouc, secured with silk cord. The whole is shown in Fig. 157, as arranged for use. Both the chloride of calcium tube and the potash apparatus are weighed with the utmost care before the experiment. 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 a little bent tube with a perforated cork : if the difference of level of the liquid in the two limbs of the potash-apparatus be preserved for several minutes, the joints are perfect. Red-hot charcoal is now placed around the anterior portion of the combustion-tube a, containing the pure oxide of copper, and when this is red-hot, the fire is slowly extended towards the further extremity by shifting the movable screen g represented in the drawing. Fig. 157. Drawing of whole arrangement. The experiment must be so conducted, that an uniform stream of carbonic acid shall enter the potash 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 con- trary, bubbles of gas, nitrogen, pass through the potash-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 evi- dent, the coals are removed from the further 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 vapor are secured. The parts are, lastly, detached, and the chloride of calcium tube and potash-apparatus re-weighed. The following account of a real experi- ment will serve as an illustration ; the substance examined was crystallized sugar. Quantity of sugar employed . . . 4.750 grains. Potash apparatus weighed after experiment 781.13 " " before experiment 773.82 Carbonic acid . . . 7.31 Chloride of calcium tube after experiment " before experiment Water . 27' 318 THE ULTIMATE ANALYSIS OP 7.31 gr. carbonic acid = 1.994 gr. carbon: and 2.75 gr. water = .3056 gr. hydrogen; or in 100 parts of sugar,* Carbon ........ 41.98 Hydrogen ...... 6.43 Oxygen, by difference . . . 51.59 100. When the organic substance cannot be mixed with the oxide 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 inclosed in a little glass bulb with a narrow stem, which is Fig. 158. 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 oxide of copper can- not be introduced hot, it must be ignited and cooled out of contact with the atmosphere, to pre- vent absorption of watery vapor. This is most conveniently effected by transferring it, in a heated state, to a large platinum crucible, to which a close fitting cover maybe 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, a file-scratch having been previously made; and, lastly, the tube is filled with the cold and dry oxide of copper. It is arranged in the chauffer, the chloride of calcium-tube and potash-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 vapor, 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. Oxide of copper, which has been used, may be easily restored by moisten- ing with nitric acid, and ignition to redness ; it becomes, in fact, rather im- proved than otherwise, as, after frequent employment, its density is increased, and its troublesome hygroscopic powers diminished. For substances which are very difficult of combustion, from the large proportion of carbon they con- tain, and for compounds into which chlorine enters as a constituent, fused and powdered chromate of lead is very advantageously substituted for the oxide 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 en- sures the perfect combustion of the organic body. Analysis of azotized Substances. The presence of nitrogen in an organic * The theoretical composition of sugar C ^H^O^, reckoned to 100 parts, gives- Carbon - ^^.ii^-;.. .- . . . 42. 11 Hydrogen ........ 6.43 Oxygen . . . , :/ . .. . . . 51.46 100. ORGANIC BODIES. 319 compound is easily ascertained by heating a small portion with solid hydrate of potash in a test tube; the nitrogen, if present, is converted into ammonia, which may be recognized by its odor and alkaline reaction. There are several methods of determining the proportion of nitrogen in azotized organic sub- stances, 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 with spongy metallic copper, made by reducing the oxide by hydrogen; this serves to decompose any nitrous acid or binoxide of nitrogen, which may be formed in the act of combustion. During the experiment, some idea of the abundance or paucity of the nitrogen may be formed from the number of bubbles of in- condensible gas which traverse the solution of potash. In the case of compounds abounding in nitrogen, and readily burned by oxide of copper, a method may be employed which is very easy of execution ; 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 oxide 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 Fig. 159. is filled up with a second and larger portion of pure oxide, and a quantity of spongy, metallic copper. A short bent tube, made move- Fig. 160. able 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. 159.) Fire is first applied to the anterior part of the tube containing the metal and unmixed oxide, and, when this is red-hot, to the extreme end. Combustion of the first portion of the mixture takes place, the gaseous products sweeping before them nearly the whole of the air of the apparatus. When no more gas issues, the tube is slowly heated by half an inch at a time, in the usual manner, and all the gas very carefully collected in a graduated jar, until the operation is at an end. The volume is then read off, and some strong solution of caustic potash thrown up into the jar by a pipette with a curved extremity. 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 differences of level in the mercury, 320 THE ULTIMATE ANALYSIS OF and from these data the exact proportion borne by the nitrogen to the carbon can be at once determined.* If the proportion of nitrogen be but small, the error from the nitrogen of the residual atmospheric air becomes so great as to destroy all confidence in the result of the experiment; and the same thing happens when the substance is incompletely burned by oxide of copper ; other means must then be employed. - Fig. 161.f i * Volumes of the two gases represent equivalents ; for 100 cubic inches carbonic acid weigh 47.26 grains 100 nitrogen " 30.14 47.26 : 30.14 : : 22 : 14.01. The last two terms are the equivalent numbers : one equivalent of carbonic acid con- tains besides one equivalent of carbon. f Fig. 161 represents the principal parts of the arrangement for the absolute estima- tion of nitrogen. The three-necked tube is shown attached to the plate of the air-pump, and the long tube with recurved lower extremity, terminating beneath a graduated jar standing upon the mercurial trough, and partly filled with strong solution of potash ORGANIC BODIES. 321 The absolute method of determination may be had recourse to when the fore- going, or comparative method, fails from the first cause mentioned; it gives excellent results, but is very difficult and troublesome in practice, from the accidents to which it is liable. A tube of good Bohemian glass, 22 inches long, is securely sealed at one end ; into this enough carbonate of copper is put to occupy 3 inches, arid upon the copper-salt a plug of asbestus. A little pure oxide of copper is next intro- duced, and afterwards the mixture of oxide and organic substance, the weight of the latter in a dry state having been correctly determined. The remainder of the tube, amounting to nearly one-half of its length, is then filled up with pure oxide of copper and spongy metal, the two being separated by asbestus, and a round cork, perforated by a piece of narrow tube, is securely adapted to its mouth, and made tight by sealing-wax. The tube is arranged in a trough of hot sand, and put into communication with a powerful and perfect air- pump, by which exhaustion may be made. This is best done by a three- branched tube of brass, furnished with a stop-cock, the third opening being connected with a vertical glass tube, exceeding 30 inches in length, made to dip into a mercurial trough. (Fig. 161.) The joints are formed by caoutchouc con- nectors, which, when carefully tied, resist without leaking, the whole pressure of the atmosphere. Exhaustion is now made as completely as possible: the mer- cury rises in the long tube, and remains stationary if the numerous joints of the apparatus be perfect. The heat of a spirit-lamp is then applied to the further extremity of the combustion-tube, so as to decompose a portion of the carbonate of copper ; the gas depresses the mercurial column, and finally escapes in considerable quantity from the delivery-tube. The next step is to remove the sand-trough, and substitute in its place the chauffer, without dis- turbing the apparatus, now filled with carbonic acid. This done, fire is ap- plied to the tube, commencing at the nearer end, and gradually proceeding to the closed extremity, which yet contains some undecomposed carbonate of copper. This, when the fire at length reaches it, yields up carbonic acid, which chases forward the nitrogen lingering in the tube. During the com- bustion, the extremity of the delivery tube is covered by a graduated jar, partly filled with mercury, and partly with strong solution of caustic potash, by which the carbonic acid is wholly absorbed, and nothing 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 vapor, and its weight deter- mined by calculation. When the operation has been very successful, and all precautions minutely observed, the result still leaves an error in excess, amounting to .3 or .4 per cent., due to the residual air of the apparatus, or that condensed into the pores of the oxide of copper. A most elegant and admirable process for estimating nitrogen in all organic compounds, except those containing ammonia and nitric acid, has lately been put in practice by MM. Will and Varrentrapp. When a non azotized organic substance is heated to redness with a large excess of hydrate of potash 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 alkali, while its hydrogen, together with that of the substance, is disengaged, sometimes in union with a little carbon. The same change happens when nitrogen is present, but with this addition: the whole of the nitrogen thus abandoned combines with a portion of the liberated hydrogen to form ammonia. It is evident, therefore, that if this experiment be made on a weighed quantity of matter, and circumstances allow the collection of the whole of the ammonia thus produced, the propor- tion of nitrogen can be easily calculated. 322 THE ULTIMATE ANALYSIS OF ORGANIC BODIES. 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, facilitates mixture with the organic substance, and prevents fusion and lique- faction. A proper quantity of the substance to be analyzed, from five to ten 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 ordinary combustion-tube, the mortar being rinsed witti a little more of the alkaline mixture, and, lastly, with a small quantity of powdered glass, which com- pletely 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 apparatus of three bulbs containing moderately strong hydrochloric acid, attached by a Fig. 162. cork to the combustion-tube. Matters being thus adjusted, fire is applied to the tube, commencing with the anterior extremity. When ignited through- out its whole length, and when no more combustible 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 with a little alcohol, and then repeatedly with distilled water; an excess of pure chloride 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 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, and weighed ; 100 parts correspond to 6.306 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 14.25 parts of nitrogen. The former plan is to be preferred in most cases. Bodies very rich in nitrogen, as urea, must be mixed with about an equal quantity of pure sugar, to furnish incondensible gas, and thus diminish the violence of the absorption which otherwise occurs ; and the same precaution must be taken, for a different reason, with those which contain little or no hydrogen. Estimation of Sulphur in Organic Compounds. When bodies of this class containing sulphur are burned with oxide of copper, a small tube containing peroxide of lead must be interposed between the chloride of calcium tube and the potash-apparatus to retain any sulphurous acid which may be formed. It is better, however, to use chromate of lead. The proportion of sulphur is determined by oxidizing a known weight of the substance by strong nitric EMPIRICAL AND RATIONAL FORMULA. 323 acid, or by fusion in a silver vessel with ten or twelve times its weight of pure hydrate of potash 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 quan- tity of which is determined by precipitation in combination with peroxide 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 oxide 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 second small weighed bulb of liquid in a combustion-tube, which is afterwards filled with fragments of pure quicklime. The lime is brought to a red-heat, and the vapor of the liquid driven over it, when the chlorine displaces oxygen from the metal, and gives rise to chloride of calcium. When cold, the contents of the tube are dissolved in the dilute nitric acid, and the chlorine precipitated by nitrate of silver. EMPIRICAL AND RATIONAL FORMULAE. A chemical formula is termed empirical when it merely gives the simplest possible expression of the composition of the substance to which it refers. A rational formula, on the contrary, aims at describing the exact composition of one equivalent, or combining proportion of the substance, by stating the absolute number of equivalents of each of its elements essential to that object, as well as the mere relations existing between them. The empirical formula is at once deduced from the analysis of the substance, reckoned to 100 parts ; the rational requires, in addition, a knowledge of its combining quantity, which can only be obtained by direct experiment, by synthesis, or by the careful examination of one or more of its most definite compounds. Further, the rational may either coincide with the empirical formula, or it may be a mul- tiple of the latter. Thus, the composition of acetic acid is expressed by the formula C 4 H 3 O 3 , which exhibits the simplest relations of the three elements, and at the same time expresses the quantities of these, in equivalents, required to make up an equivalent of acetic acid; hence, it is both empirical and rational. On the other hand, the empirical formula of crystallized kinic acid is C 7 H 6 6 , while its rational formula, determined by its capacity of saturation, is double, or Cj 4 H 12 O 12 , otherwise written C^HjjOjj-j-HO. In like manner, the empirical formula of the artificial alkaloids fur/urine and benzoline are respectively C 15 H 6 NO 3 and C 21 H 9 N. The equivalents of these substances, that is to say, the quantities required to form neutral salts with one equivalent of any well- defined monobasic acid, will, however, be expressed by the formulae C 30 H 12 N 2 O 6 and C 42 H 18 N 2 ; 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 in 100 parts Carbon . . . .41.98 Hydrogen . . . 6.43 Oxygen . . . .51.59 100. 324 DETERMINATION OF THE DENSITY OF VAPORS. If each of these quantities be divided by the equivalent of the element, the quotients will express the relations in equivalents 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. 4 _1^ = 6.99; 6.43; 5 _15? = 6.44, or 699 eq. carbon, 643 eq. hydrogen, and 644 eq. oxygen. It will be evident, in the first place, that the hydrogen and oxygen are present in the proportions to form water, or as many equivalents of one as of the other. Again, the equivalents of carbon and hydrogen are nearly in the proportion of 12 : 11, so that the formula C W H U O U appears likely to be cor- rect. 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 analy- sis, and observing whether the difference falls fairly in direction and amount within the limits of error of what may be termed a good experiment, viz. two or three-tenths per cent, deficiency in the carbon, and not more than one- tenth per cent, excess in the hydrogen. Carbon . . . .6x12=72 Hydrogen . . . 11 eq. = 11 Oxygen . . . .8x11 = 88 171 171 : 72 :: 100 : 42.11 171 : 11 : : 100 : 6.43 171 : 88 : : 100 : 51.46 Organic acids and salt-radicals have their proper equivalents most fre- quently determined by an analysis of their lead and silver salts, by burning these latter with suitable precautions in a thin porcelain capsule, and noting the weight of the oxide of lead or metallic silver left behind. If the oxide 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 chlo- ride, and both metals thus estimated. An organic base, on the contrary, 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 VAPORS. The determination of the specific gravity of the vapor of a volatile sub- stance is frequently a point of great importance, inasmuch as it gives the means, in 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, about three inches in diameter, is taken, and its neck softened and drawn out in the blowpipe- flame, as represented in the figure; this is accurately weighed. About one hundred grains of the volatile liquid are then introduced, by gently warming DETERMINATION OP THE DENSITY OF VAPORS. 325 the globe and dipping the point into the liquid, which is Fig. 163, then forced upwards by the pressure 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 vapor, which escapes by the narrow orifice, chasing before it the air of the globe. When the issue of vapor has wholly ceased, and the temperature of the bath, carefully observed, appears pretty uniform, the open extremity of the point is hermetically sealed by a small blowpipe-flame. The globe is removed from the bath, suffered to cool, cleansed, if necessary, and weighed, after which the neck is broken off beneath the surface of water which has been boiled and cooled out of contact of air. The liquid enters the globe, and, if the expulsion of the air by the vapor has been complete, fills it: if otherwise, an air-bubble is left whose volume can be easily ascertained by pouring the liquid from the globe into a jar graduated to cubic inches, and then refilling the globe, and repeating the same observation. The capacity of the vessel is thus at the same time known ; and these are all the data required. An example will render the whole intelligible. Determination of the density of the vapor of Acetone. Capacity of globe Weight of globe filled with dry air at 52 F., and 30.24 inches barometer Weight of globe filled with vapor at 212 (temp, of the bath at the moment of sealing the point), and 30.24 inches barometer .... Residual air, at 45 F., and 30.24 in. bar. 31.61 cubic inches. 2070.88 grains. 2076.81 grains. .60 cubic inches. 31.61 cub. inches of air at 52 and 30.24 in. bar. = 32.36 cub. inches at 60 and 30 inch, bar., weighing ...... 10.035 grains. Hence, weight of empty globe, . . 2070.88 10.035 = 2060.845 grains. .6 c. inch of air at 45 = .8 c. inch, at 212; weight of do. by calculation = .191 grain. 31.01 .8 = 30.81 cubic inches of vapor at 212 and 30.24 in. bar., which, on the supposition that it could bear cooling to 60 without liquefaction, would at that temperature, and under a pressure of 30 inch. bar. become reduced to 24.18 cubic inches. Hence, Weight of globe and vapor 2076.810 grains. " residual air . .191 Weight of globe Weight of the 24.18 cubic inches of vapor 28 15.774 326 DETERMINATION OP THE DENSITY OF VAPORS. Consequently, 100 cubic inches of such vapor must weigh 65.23 grains. 100 cubic inches of air, under similar circumstances, weigh 31.01 65.23 =2.103, the specific gravity of the vapor in question, air ol.Ol being unity. In the foregoing statement a correction has been, for the sake of simplicity, 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 tempera- ture of the bath. The density so obtained will be always on this account a little too high. The error to which the mercurial thermometer is, at high temperatures, liable, tends in the opposite direction. It is easy to compare the actual specific gravity of the vapor found in the manner above described with the theoretical specific gravity deduced from the formula of the substance : The formula of acetone is C 3 H 3 O. In combining volumes (p. 176) this is represented by 3 vols. of the hypothetical vapor of carbon, 3 vols. of hydro- gen, and half a volume of oxygen. Or the weight of the unit of volume of acetone vapor will be equal to three times the specific gravity of carbon vapor, three times that of hydrogen, and one half that of oxygen added together, one volume of the compound vapor containing 6^ volumes of its components : 3 vols. hypothetical vapor of carbon . . . .4183x3=1.2549 3 vols. hydrogen 0693x3 = .2079 ^ vol. oxygen = .5528 Theoretical specific gravity 2.0156 CANE AND GRAPE SUGAR. 327 SECTION I. NON-AZOTIZED BODIES OF THE SACCHARINE AND AMYLACEOUS GROUP. SUGAR, STARCH, GUM, LIGNINE, AND ALLIED SUBSTANCES. THE members of this remarkable and very natural group present several interesting cases of isomerism. They are characterized by their feeble apti- tude to enter into combination, and also by containing, with perhaps one ex- ception, oxygen and hydrogen in the proportions to form water. Table of Saccharine and Amylaceous Substances. Cane-sugar, crystallized C 24 H 22 22 Cane-sugar, in combination . . . C 24 H 18 O 18 Grape-sugar, crystallized .... C 24 H 28 O 28 Grape-sugar, in combination . . . ^24^21^21 Milk-sugar, crystallized .... C 24 H 24 O 24 Milk-sugar, in combination . . . C 24 H 19 O 19 Sugar of eucalyptus, crystallized . . . C 24 H 2% 23 Sugar from secale cornutum . . . C 24 H 26 O 26 Mannite ....... C 6 tf 7 Q 6 Starch, unaltered, dried at 212 . . C 24 H 20 O 20 Amidine, or gelatinous starch . . . C 24 H 20 O 20 Dextrine, or gummy starch . . . C 24 H 20 O 20 Starch from cetraria islandica . . . C 24 H 20 O 2Q Inuline ^ 4 11 2l 2l Gum- Arabic C 24 H 22 O 22 Gum-tragacanth C 24 H 20 20 Lignine, or cellulose C 24 H 20 O 20 CANE-SUGAR ; ORDINARY SUGAR, C 24 H 22 22 . This most useful substance is found in the juice of many of the grasses, in the sap of several forest trees, in the roots of the beet and the mallow, and in several other plants. It is extracted most easily and in greatest abundance from the sugar-cane, cultivated 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 con- centrated, the syrup is transferred to a shallow vessel, and left to crytallize, during which time it is frequently agitated in order to hasten the change and 328 CANE AND GRAPE SUGAR. hinder the formation of large crystals. It is, lastly, drained from the dark uncrystallizable syrup, or molasses, and sent into commerce, under the name of raw or Muscovado sugar. The refining of this crude product 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 enclose and separate from the liquid all mechanically suspended, impurities. The solution is decolorized by filtration through animal charcoal, evaporated to the crystallizing-point, and put into conical earthen moulds, where it solidifies, after some time, to a confusedly-crystal- line 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 al- lowed to take place quietly and slowly, sugar-candy results, 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 to 150 or below, and the injurious action of the heat upon the sugar in great measure prevented. Indeed, the production of molasses in the rude colonial manufacture is chiefly the result of the high and long-continued heat applied to the cane-juice, and might be almost entirely prevented by the use of vacuum-pans, the product of sugar being thereby greatly increased in quantity, and so far improved in quality as to become almost equal to the refined article. In many parts of the continent of Europe, sugar is manufactured on a large scale from beet-root, which contains about 8 per cent, of that substance. The process is far more complicated and troublesome than that just described, and the product much inferior. When refined, however, it is scarcely to be dis- tinguished 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 colorless 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 bar ley -sugar : at a higher temperature it blackens and suffers decomposition; and the same effect is produced, as already remarked, by long-continued boiling on the aqueous solution, which loses its faculty of crystallizing and acquires color. The crystals have a specific gravity of 1.6, and are unchanged in the air. * M. Melsens, of Brussels, recommends an entire new process for the extraction anrl refining of sugar. The canes are rasped and mixed with about one per cent, of bisulphite of lime. They are then pressed and moistened with water containing a little of the same solution, and again expressed. The mixed solutions are heated to the boiling point and evaporated in the ordinary way. The bisulphate coagulates any albuminous matters present, and thus destroys the source of any ferment; the lime neutralizes any acid present, while the sulphurous acid, by its avidity for oxygen, counteracts the tendency to oxidation, and decolorizes the natural coloring matters of the cane. By this means perfectly white sugar may be obtained directly from the juice, and the necessity of rapidity in the different steps of the process is obviated, for so completely unalterable is the syrup said to be, as long as any bisulphate remains, that the evaporation may be conducted spontaneously by solar heat. R. B. CANE AND GRAPE SUGAR. 329 The deep brown soluble substance, called caramel, used for coloring spirits, and other purposes, is a product of the action of heat upon cane-sugar. It contains C 24 H 18 O 18 , and is isomeric with cane sugar in combination. The following is the composition assigned to the principal compounds of cane-sugar by M. Peligot, who has devoted much attention to the subject.* Crystallized cane sugar .... C 24 H, 8 O ]8 -|-4HO Compound of sugar with common salt . . C 24 H 18 0, 8 4-NaCl-|-3HO Compound of sugar with baryta . . . C 24 H ]8 O, 8 4-2BaO4-4HO Compound of sugar with lime . . . C 24 H ]S O, 8 -[-2CaO-j-4HO Compound of sugar with oxide of lead . C 24 H, 8 O ig -f-4PbO 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 de- composed by carbonic acid, crystals of carbonate of lime being occasionally produced. The" combination with oxide of lead is prepared by mixing 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 com- mon salt is crystal lizable, soluble, and deliquescent. GRAPE SUGAR; GLUCOSE; SUGAR OF FRUITS, C 24 H 28 28 . This variety of sugar 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 artifi- cially 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 fatal 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 l parts of the cold liquid for solution. Its mode of crystallization is also completely different ; instead of forming, like cane-sugar, bold, distinct crystals, it sepa- rates 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 black- ening, and gives rise to a peculiar compound acid, whose baryta-salt is soluble. Cane-sugar is, under these circumstances, instantly changed to a black mass resembling charcoal. When solutions of cane and grape-sugar are mixed with two separate por- tions of solution of sulphate of copper, and caustic potash added in excess to each, deep blue liquids are obtained, which, on being heated, exhibit different 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 colorless solution. This is an excellent test for distinguishing the two varieties of sugar, or discovering 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. * Ann. Chim. et Phys. Ixvii 113. 28* 330 CANE AND GRAPE SUGAR. Compounds of Grape-sugar, according to Peligot. Crystalline grape-sugar, dried in the air . . C 24 A 2 ,0 21 -f-7HO The same, dried at 206 C 24 H 21 21 -f-3HO Compound of grape sugar with common salt . C 24 H 2) O 2I -f-NaCl-j-5HO The same, dried at 266 C 24 H 2 ,O 21 -f-NaCl-j-2HO Compound of grape-sugar with baryta . . C 24 H 2 ,0 21 - 3BaO+7HO Compound of grape-sugar with lime . . . C 24 H 2 ,O 21 -|-3CaO+7HO Compound of grape-sugar with oxide of lead . C 24 H 21 21 -|-6PbO Sulphosaccharic Acid, C 24 H 20 O 20 ,SO 3 . Melted grape sugar is cautiously mixed with concentrated sulphuric acid, the product dissolved in water, and neu- tralized with carbonate of baryta ; sulphate of baryta is formed together with a soluble sulphosaccharate of that earth, from which the acid itself may be afterwards eliminated. It is a sweetish liquid, forming a variety of soluble salts, and very prone to decompose into sugar and sulphuric acid. Action of dilute Acids upon Sugar. Cane-sugar dissolved i 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 brown- ish-black 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 Malaguti ulmine, and by Liebig sachulmine, is insoluble in ammonia and alkalis; the second, ulmic acid, the sachulmic acid of Liebig, dissolves freely, yielding dark brown solutions precipitable by acids. By long-continued boiling with water, sach- ulmic acid is converted into sachulmine. Both these substances have the same composition, expressed by the empirical formula C 2 HO. Hydrochloric acid, in a dilute state, produces the same effects."* Action of Alkalis upon Sugar. When lime or baryta is dissolved in a solu- tion of grape sugar, and the whole left to itself several weeks in a close ves- sel, the alkaline reaction will be found to have disappeared from the forma- tion of an acid substance. By mixing this solution with subacetate of lead, a voluminous white precipitate is obtained, which, when decomposed by sul- phuretted hydrogen, yields sulphuret of lead, and the new acid, to which the term kalisaccharic or glunc is applied. Glucic acid is very soluble and deli- quescent, has a sour taste and acid reaction: its salts, with the exception of that containing oxide of lead, are very soluble. It contains C 8 H 5 5 . When grape-sugar is heated in a strong solution of potash, soda, or baryta, the liquid darkens, and at length assumes a nearly black color. The addition of an acid then gives rise to a black flocculent precipitate of a substance called melasinic acid, containing C 24 H, 2 0, . Cane-sugar long boiled with alkalis undergoes the same changes, being probably first converted into grape-sugar. SUGAR OF THE EUCALYPTUS, described by Professor Johnston,"}" closely re- sembles ordinary grape-sugar in many particulars, and has the same compo- sition. SUGAH. FROM ERGOT OF RYE. This variety of sugar, extracted by alcohol from the ergot, crystallizes in transparent colorless prisms, which have a * Under the names ulmine and ulmic acid have been confounded a number of brown or black uncrystallizable substances, produced by the action of powerful chemical agents upon sugar, lignine, &c., or generated by the putrefactive decay of vegetable fibre. Common garden mould, for example, treated with dilute, boiling solution of caustic potash, yields a deep brown solution, from which acids precipitate a floccu- lent, brown substance, having but a slight degree of solubility in water. This is ge- nerally called ulmic or humic acid, and its origin ascribed to the reaction of the alkali on the ulmine or humus of the soil. It is known that these bodies differ exceedingly in composition ; they are too indefinite to admit of ready investigation. f Memoirs of Chemical Society of London, i. 159. MANNITE STARCH. 331 sweet taste, and are very soluble in water. It differs from cane-sugar in not reducing the acetate of copper when boiled with a. solution of that substance. It contains C 24 H 26 O 26 . SUGAR OF DIABETES INSIPIDUS. A substance having the other properties of a sugar, but destitute of sweet taste, has been described by M. Thenard as having been obtained from the above-mentioned source. It was capable of furnishing alcohol by fermentation, and of suffering conversion into grape- sugar by dilute sulphuric acid. Its composition is unknown. LTQ.UORICE-SUGAR; GLYCYRRUIZINE. The root of the common liquorice yields a large quantity of a peculiar sweet substance, which is very soluble in water, but refuses to crystallize; it is remarkable for forming with acids compounds which have but sparing solubility. Glycyrrhizine cannot be made to ferment. SUGAR OF MILK; LACTINE, C 24 H 24 24 . This curious substance is an im- portant constituent of milk ; it is obtained in large quantities by evaporating whey to a syrupy state, and purifying the lactine, which slowly crystallizes out, by animal charcoal. It forms white, translucent, four-sided prisms, of great hardness. It is slow and difficult of solution in cold water, requiring for that purpose five or six 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 compounds with oxides 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; MANNITE, C 6 H 7 O 6 . This is the chief component 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 solution whilst hot; the mannite crystallizes on cooling in tufts of slender colorless 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. 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 retained, while the starch passes through with the liquid, and eventually settles down from the latter as a soft, white, insoluble powder, which may be washed with cold water, and dried with very gentle heat. Potatoes treated in this manner yield a large proportion of starch. Starch from grain may be prepared in the same manner, by mixing the meal with water to a paste, and washing the mass upon a sieve : a nearly white, insoluble substance called gluten re- mains behind, which contains a large proportion of nitrogen. The gluten of wheat-flour is extremely tenacious and elastic. The value of meal as an article of food greatly depends upon this substance. Starch from grain is commonly manufactured on the large scale by steeping the material in water for a 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 * By nitric acid it is converted into mucic acid. R. B. 332 DEXTRINE. 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 insoluble 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 decomposition. 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 crystal- line 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- Fig. 164. ferent plants vary both in magnitude and form; those from the Canna cocdnea, or tons les mois, and potato being largest ; and those from wheat, and the cereals in general, very much smaller. The figure. in the margin will serve to convey an idea of the appearance of the granules of potato-starch, highly magnified. 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 proportions of starch be considerable, a thick gelatinous mass, very slightly opalescent from the shreds of fine membrane, the envelope of each separate granule. By the addition of a large quantity of water, this gelatinous starch, or amidine,ma.y be so far diluted as to pass in great measure through filter-paper. It is very doubt- ful, 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 yellowish, horny substance, like gum, which, when put into water, again softens and swells. Thin gelatinous starch is precipitated by many of the metallic oxides, as lime, baryta, and oxide of lead, and also by a large addition of alcohol. In- fusion of galls throws down a copious yellowish precipitate containing tannic acid, which redissolves when the solution is heated. By far the most charac- teristic 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 colors destroyed by heat, temporarily if the heat be quickly withdrawn, and permanently if the boiling be long continued, in which case the compound is decomposed and the iodine volatilized. Starch in the dry state, put into iodine-water, acquires a purplish-black color. The unaltered and the gelatinous starch, in a dried state, have the same composition, namely, C 24 H 20 O 20 ; a compound of starch and oxide of lead was found to contain, when dried at 212, C 24 H 20 O 20 -f-4PbO. DEXTIUNE. 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 conversion into a soluble substance, resembling gum, called dextrine.* The experiment * From its action on polarized light, twisting the plane of polarization towards the right hand. DEXTRINE. 333 is most conveniently made with sulphuric acid, which may be afterwards withdrawn by saturation with chalk. The liquid filtered from the nearly insoluble gypsum may then be evaporated in a water-bath to dryness. The result is a gum-like mass, destitute of crystalline structure, soluble in cold, water, and precipitable from its solution by alcohol, and capable of combining with oxide of lead. Iodine sometimes produces in a solution of dextrine a purplish-red tint, and sometimes occasions no change. When the ebullition with the dilute acid is continued for a considerable period, the dextrine first formed undergoes a further 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 15 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 bulk. By digestion with animal charcoal and a second filtration much of the color will be removed, after which the solution may be boiled down to a thin syrup and left to crystallize ; in the course of a few days it solidifies to a mass of grape- sugar. There is another method of preparing this substance from starch which deserves particular notice. Germinating seeds, and buds in the act of development, are found to contain a small quantity of a peculiar azotized sub- stance, formed at this particular period from the gluten of vegetable albu- minous matter, to which the name diastase is given. This substance possesses the same curious property of effecting the conversion of starch into dextrine, and ultimately into grape-sugar, and at a much lower temperature than that of ebullition. A little infusion of malt, or germinated barley, in tepid water, mixed with a large quantity of thick gelatinous starch, and the whole main- tained at 160 or thereabouts, occasions complete liquefaction in the space of a few minutes from the production of dextrine, which in its turn becomes, in three or four hours, converted into sugar. If a greater degree of heat be em- ployed, the diastase is coagulated and rendered insoluble and inactive. Very little is known respecting diastase itself; it seems very much to resemble vegetable albumen, but has never been got in a state of purity. The change of starch or dextrine into sugar, whether produced by the action of dilute acid or by diastase, takes place quite independently of the oxygen of the air, and is unaccompanied by any secondary product. The acid takes no direct part in the reaction; it may, if not volatile, be all withdrawn with- out loss after the experiment. The whole affair lies between the starch and the elements of water; a fixation of the latter occurring 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 employed. Dextrine itself has exactly the same composition as the original starch. Dextrine 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, 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 ordi- nary meal with albuminous substances. Arrowroot, and the fecula of the Canna coccinea,are very pure varieties, employed as articles of diet; arrowroot is obtained from the Maranta arundinacea, cultivated in the West Indies; it is with difficulty distinguished from potato-starch. Tapioca is prepared from the root of the latropha manihot, being thoroughly purified from its poisonous juice. Cassava is the same substance modified while moist by heat. Sago 334 INULINE GUM. is made from the soft central portion of the stem of a palm ; and salep from the fleshy root of the Orchis mascula. STAHCH FROM ICELAND Moss. The lichen called Cetraria Islandica, puri- fied by a little cold solution of potash from a bitter principle, yields when boiled in water a slimy and nearly colorless liquid, which gelatinizes on cooling, and dries up to a yellowish amorphous mass, which does not 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, lichen-starch contains C 24 H 20 O 20 . The jelly from cer- tain algce, as that of Ceylon, and the so-called Carragheen moss, closely resem- bles the above. INULINE. This substance, which differs from common starch in some im- portant particulars, is found in the root of the Inula helenium, the Helianthus tuberosus, the dahlia, and several other plants; it maybe easily obtained by washing the rasped root on a sieve, and allowing the inuline to settle down from the liquid; or by cutting the root into thin slices, boiling these in water, and filtering while hot; the inuline 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 alcohol, but not by acetate of lead or infusion of galls. Iodine communicates a brown color. Inuline has been carefully analyzed by Mr. Parnell, who finds it to contain, when dried at 212, C 24 H 21 O 21 . 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 condition, it forms white or slightly yellowish irregular masses, which are destitute of crystalline structure, and break with a smooth conchoidal fracture. It is so- luble in cold water, forming a viscid, adhesive, tasteless solution, from which the pure soluble gummy principle, or arabine, is precipitated by alcohol and by sub acetate of lead, but not by the neutral acetate.* Arabine is composed of C 24 H 22 O 22 , and is consequently isorneric with crystallized cane sugar. Mucilage, so abundant in linseed, in the roots of the mallow, 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 precipitated by neutral acetate of lead. Gum tragacanth is chiefly composed of a substance to which the name bas- sorine has been given, and which refuses to dissolve in water, merely soften- ing and assuming a gelatinous aspect. It is dissolved by caustic alkali. Ce- rasine is the term given to the insoluble portion of the gum of the cherry tree ; it resembles bassorine. The ropiness of white wines and saccharine liquids is due to a substance of this kind, which is formed, under peculiar circum- stances, from sugar. Pedine, or the jelly of fruits, seems to be closely allied to the foregoing bo- dies. It may be extracted from various vegetable juices by precipitation by alcohol. It forms when moist a transparent jelly, soluble in water, and taste- less, which dries up to a translucent mass. It is to this substance that the firm consistence of currant and other fruit jellies is ascribed. In contact with bases, pectine becomes converted into peclic acid, which, except that it pos- sesses feeble acid properties, and is insoluble in water, resembles in the closest manner pectine itself. By long boiling with solution of caustic alkali, a fur- * The precipitate produced by sub-salts of lead is a compound of arabine and oxide of lead, C_ a4 H 22 O, 2a -|-2PbO. By the action of very dilute sulphuric acid arabine is slowly changed into dextrine, and by prolonged contact into glucose. Nitric acid decomposes gum and produces first mucic and ultimately oxalic acid. R. B. LIGNINE. 335 ther change is produced, and a new acid, the metapectic, developed, which does not gelatinize. The salts of these two acids are incapable of crystal- lizing. Much doubt, too, exists respecting the composition of these bodies, although they are probably isomeric, or only differ in the elements of water ; they do not appear, from the analyses yet made, to contain oxygen and hy- drogen in the proportion of the equivalent numbers, and consequently scarcely belong to the starch group. According to M. Fremy pectine contains C 16 H 1216' and P 6Ctic acid C 16 H 1115' LIGNINE; CELLULOSE. 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 eveiy 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 membranous cells, and confer stiffness and inflexibility. Thus woody tissue, even when freed as much as possible from coloring matter and resin by repeated boiling with water and alcohol, yields on analysis a result 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 ter- nary compound of carbon and the elements of water, closely allied in compo- sition to starch, if not actually isomeric with that substance.* The properties of lignine may be conveniently studied in fine linen or cot- ton, which are almost entirely composed of the body in question, the asso- ciated vegetable principles having been removed or destroyed by the variety of treatment to which the fibre has been subjected. Pure lignirie 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 lignine, even at a boiling temperature; strong oil of vitriol converts it, in the cold, into a nearly colorless, adhesive substance, which dissolves in water, and presents the characters of dextrine. This curious and interesting experiment may be conveniently made by very slowly adding concentrated sulphuric acid to half its weight of lint, or linen cut into small shreds, taking care to avoid any rise of temperature, which would be attended with charring or blackening. The mixing is completed by trituration in a mortar, 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 combination with a peculiar acid, composed of the elements of sulphuric or hyposulphuric acid, in union with those of the lig- nine, to which the name sulpholignic acid is given. If the liquid, previous to neutralization, be boiled during three or four hours, and the water replaced as it evaporates, the dextrine becomes entirely changed to grape-sugar. Linen rags may, by these means, be made to furnish more than their own weight of that substance. Lignine is not colored by iodine. * Dumas, Chiraie appliquee aux Arts, vi. 5. 336 OXALIC ACID. PRODUCTS ARISING FHOM THE ALTERATION OF THE PRECEDING SUBSTANCES BT CHEMICAL AGENTS. ACTION OF NITRIC ACID. OXALIC ACID, C 2 3 ,HO-}-2HO. This important compound occurs ready formed in several plants, in combination with potash as an acid salt, or with lime. It is now manufactured in large quantities as an article of commerce, by the action of nitric acid on sugar, starch, and dextrine. With the excep- tion of gum and sugar of milk, which yield another product, all the sub- stances comprehended in the saccharine and starch group furnish oxalic acid, as the chief and characteristic result of the long continued action of mode- rately 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 maybe again applied to the vessel, and the liquid concentrated, by distilling off the superfluous nitric acid, until it deposits crystals on cooling. These are drained, redissolved in a small quantity of hot water, and the solution set aside to cool. The acid separates from a hot solution in colorless, 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 crys- tallized acid, on the contrary, is decomposed by a high temperature into car- bonic and formic acids, and carbonic oxide, without solid residue. The crystals of oxalic acid dissolve in 8 parts of water at 60, and in their own weight, or less of hot water ; they are also soluble in spirit. The aqueous solution has an intensely sour taste and most powerful acid reaction, and is highly poisonous. The proper antidote is chalk or 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 peroxides 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 = C 24 H 18 O 18 ) ( 12 eq. oxalic acid = C 24 O 36 36 eq. oxygen = ' O 36 5 ( 18 eq. water = H 18 O 18 C 24 H 1854 C 24 H 1854 The most important salts of oxalic acid are the following: NEUTRAL OXALATE OF POTASH, KO,C 2 O 3 -}-HO. This is prepared by neu- tralizing oxalic acid by carbonate of potash. It crystallizes in transparent rhombic prisms, which become opaque and anhydrous by heat, and dissolve in 3 parts of water. Oxalate of potash is often produced when a variety of organic substances are cautiously heated with excess of caustic alkali. BINOXALATE OF POTASH, KO,2C 2 O 3 -}-3HO. Sometimes called salt of sorrel, from its occurrence in that plant. This, or the substance next to be men- tioned, is found also in the rumex and Oxalis acetosella, and in the garden rhu- barb, associated with malic acid. It is easily prepared by dividing a solution of oxalic acid, in hot water, into two equal portions, neutralizing one witli SACCHARIC ACID. 337 carbonate of potash, and adding the other; the salt crystallizes, on cooling, in colorless rhombic prisms. The crystals have a sour taste, and require 40 parts of cold, and 6 of boiling water for solution. QUADIIOXALATE or POTASH, KO^CgOg-f-^HO. 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, NaO,C 2 O 3 , has but little solubility; a binoxalate exists. OXALATE OF AMMONIA, NH 4 O,C 2 O 3 -j-HO. This beautiful salt is prepared by neutralizing by carbonate of ammonia a hot solution of oxalic acid. It crystallizes in long, colorless, rhombic prisms, which effloresce in dry air from loss of water of crystallization. They are not very soluble in cold water, but 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 grayish 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 elements of an ammoniacal salt, minus those of water. Oxamide is composed of C 2 H 2 N0 2 , or the ele- ments of 1 eq. amidogen, and 2 eq. carbonic oxide. It is insoluble in water arid 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. Oxamide is the representative of a tolerably large class of bodies having very analogous chemical relations, and apparently a common constitution. Oxamide is obtained purer and more abundantly from oxalic ether ; its preparation will be found described under the head of that sub- stance. The binoxalate of ammonia is still less soluble than the oxalate. When this salt is heated in an oil-bath to 450, among other products an acid called the oxamic is generated, containing C 4 H 2 NO 5 -f-HO. It forms soluble com- pounds with lime and baryta. When heated with alkalis it yields ammonia ; hot oil of vitriol resolves it into carbonic oxide and carbonic acid; and water converts it, at a boiling temperature, into binoxalate of ammonia. OXALATE OF LIME, CaO,C 2 3 -f-2HO. This compound is formed when- ever 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 dilute hydrochloric acid. Nitric acid dissolves it easily. When dried at 212 it retains an equivalent of water, which may be driven off by a rather higher temperature. Exposed to a red-heat in a close vessel, it is converted into 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 peroxide of iron freely soluble. The double oxalate of chromium and potash, made by dissolving in hot water 1 part bichromate of potash, 2 parts binoxalate of potash, and 2 parts crystallized oxalic acid, is one of the most beautiful salts known. The crystals appear black by reflected light from the intensity of their color, which is pure deep blue; they are very soluble. The salt contains 3(KO,C 2 3 )-j-Cr 2 O 3 ,3C 2 3 -j-6HO. A corresponding compound containing peroxide of iron has been formed; it crystallizes freely, and has a beautiful green color. SACCHARIC, OR OXALHYDRIC ACID, C ]2 H 5 O n -j-5HO. 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 29 338 MELLITIC ACID. mother-liquor from which the oxalic acid has crystallized. It may be made by heating together 1 part sugar, 2 parts nitric acid, and 10 parts water. When the reaction 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 colorless 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 ad- dition of ammonia, a white insoluble substance separates, which is reduced by gently warming the whole to metallic silver, the vessel being lined with a smooth and brilliant coating of the metal. Nitric acid converts the sac- charic into oxalic acid. An equivalent of saccharic acid requires for neutral- ization 5 equivalents of a base.* XYLOIDINE and PTROXYLINE. When starch is mixed with nitric acid of specific gravity 1.5, it is converted without disengagement of gas into a trans- parent, colorless jelly, which, when put into water, yields a white, curdy, insoluble substance: this is the new body xyloidine. 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 substances belonging to the same class also yield xyloidine ; paper dipped into the strong- est 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 a few minutes in a mixture of nitric acid of sp. gr. 1.5, and concentrated sulphuric 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 become in the highest degree explosive, taking fire at a temperature not much above 300, and burning without smoke or residue. This is pyroxyline^ the gun-cotton of Professor Schoenbein. It differs from xyloidine in composition, in its mode of combustion, and in resisting the action of certain liquids, as ether containing a little alcohol, which dissolve xyloidine with facility. Both xyloidine and pyroxyline appear to be substitution-compounds, in which the elements of nitric acid replace, to a certain extent, those of water in starch and lignine. The analytical results are not very uniform, but the formula? which best agree with them are, xyloidine C 24 H 17 N 3 O 32 , and pyroxyline C 24 H, 5 N 5 O 40 . Mucic ACID, C 12 H 8 14 -f-2HO. Sugar of milk and gum, heated with nitric acid somewhat diluted, furnish, in addition to a small quantity of oxalic acid, a white and nearly insoluble substance called mucic acid. It may be easily prepared by heating together in 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 colors, and forms salts with bases. It requires for solution 66 parts of boiling water. Oil of vitriol dissolves it with red color. Mucic acid is de- composed by heat, yielding, among other products, a volatile acid, the pyro- mucic, which is soluble in water, and crystallizes in a form resembling that of benzoic acid. Pyromucic acid is monobasic; it contains C 10 H 3 O 5 -J-HO. SUIIEIUC ACID, C g H 6 O 3 -f-HO, is formed by the action of nitric acid on the peculiar ligneous matter of cork, and also on certain fatty bodies; it much re- sembles mucic acid, but is more soluble in water. The following bodies are closely allied in composition to oxalic acid: MEI/LITIC ACID, C 4 O 3 -|-HO. This substance occurs, in combination with * According to M. Heintz, saccharic acid contains C B H 8 O,-fHO, and is conse- quently monobasic. FERMENTATION OP SUGAR. 339 alumina, in a very rare mineral called mellite or honeiistone, found in deposits of imperfect coal, or lignite. It is soluble in water and alcohol, and is crys- tal lizable, forming colorless needles. It combines with bases : the mellitates 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- mide and euchronic acid. The former is a white, amorphous, insoluble sub- stance, containing C 8 HN0 4 , and convertible by boiling with water into acid mellitate of ammonia. The latter forms colorless, sparingly-soluble crystals containing in the anhydrous state C, 2 N0 6 . In contact with metallic zinc and deoxidizing agents in general, euchronic acid yields a very extraordinary 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 inflamma- ble gas, and produces a deep red solution containing the potash salt of a pe- culiar acid, the rhodizonic by adding alcohol to the liquid, the rhodizonate of potash is precipitated. This and the lead salt are the only two compounds which have been fully examined ; the acid itself cannot be isolated. Rhodi- zonate of potash is composed of C 7 Cy-|-3KO; hence the acid is tfibasic. When solution of rhodizonate of potash is boiled, it becomes orange yellow from decomposition of the acid, and is then found to contain oxalate of potash, free potash, 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 C 5 4 -f-HO. THE FERMENTATION OF SUGAR, AND ITS PRODUCTS. The term fermentation is applied in chemistry to a peculiar metamorphosis of a complex organic substance, by a transposition of its elements under the agency of an external disturbing force, different from ordinary chemical at- traction, and more resembling those obscure phenomena of contact already noticed, to which the expression katalysis is sometimes applied. The ex- planation which Liebig has suggested of the cause and nature of the fer- mentative change is a very happy one, although of necessity only hypotheti- cal. It has long been known that one of the most indispensable conditions of that process is the presence in the fermenting liquid of certain azotized substances, called ferments, whose decomposition proceeds simultaneously with that of the body undergoing metamorphosis. They all belong to the class of albuminous principles, bodies which in a moist condition putrefy and decompose spontaneously. It is imagined that when these 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, ia the proper state of decay, the 340 t FERMENTATION OF SUGAR. sugar is converted into alcohol, with escape of carbonic acid. Putrid blood, white of egg, or flour-paste, will effect this ; by far the most potent alcoholic ferment is, however, to be found in the insoluble, yellowish, viscid matter de- posited 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 or 80, 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 examined, 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 effervescence is at an end, and the liquid has become clear, it will yield alcohol by distillation. Such is the origin of this important compound ; it is a product of the meta- morphosis of sugar, under the influence of a ferment. The composition of alcohol is expressed by the formula C 4 H 6 O 2 ; it is pro- duced by the breaking up of an equivalent of grape-sugar, C 24 H 28 28 , 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 ap- parently 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 distillation, 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 .835, and yet contains 13 or 14 per cent, of water. Pure or absolute alcohol may be obtained from this by redistilling it with half its weight of fresh quicklime. The lime is reduced to coarse powder, and put into a retort; the alcohol is added, and the whole mixed by agitation. The neck of the retort is securely stopped with a cork, and the mixture left for several days. The alcohol is distilled off by the heat of a water-bath. Pure alcohol is a colorless, limpid liquid, of pungent and agreeable taste and odor; its specific gravity at 60 is .7938, and that of its vapor 1.613. It is very inflammable, burning with a pale bluish flame, free from smoke, and has never been frozen. Alcohol boils at 177 F. when in 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 ; this takes place not only with pure alcohol, but with rectified spirit. It is rniscible with water in all proportions, and, indeed, has a great attraction for the latter, absorbing its vapor 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 number of saline com- pounds, many organic substances, as the vegeto-alkalis, resins, essential oils, and various other bodies; hence its great use in chemical 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 ex- hibiting the proportions of real alcohol and water in spirits of different densi- ties will be found at the end of the volume. The excise proof spirit has a sp.gr. of .9198 at 60 F., and contains 49 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 ALCOHOL. 341 falls as low as 12 per cent. Strong ale contains about 10 per cent. ; ordinary spirits, as brandy, gin, and whisky, 40 to 50 per cent, or occasionally more. These latter owe their characteristic flavors to certain essential oils, present in very small quantity, either generated in the act of fermentation or 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 albumen of the juice absorbs oxygen from the air, runs into decom- position, and in that state becomes a ferment to the sugar, which is gradually converted into alcohol. If the sugar be in excess, and the azotized matter deficient, the resulting wine remains sweet; but if, on the other hand, the proportion of sugar be small, and that of albumen large, a dry wine is pro- duced. When the fermentation stops, and the liquor becomes clear, it is drawn off from the lees, and transferred to casks, to ripen and improve. The color of red wine is derived from the skins of the grapes, which in such cases are left in the fermenting liquid. Effervescent wines, as cham- pagne, are bottled before the fermentation is complete ; the carbonic acid is disengaged under pressure, and retained in solution in the liquid. 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 potash, with a little tartrate of lime and coloring 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 quan- tity 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 gooseberries or currants is employed as a substitute, the malic and citric acids which these fruits contain cannot be thus withdrawn. There is, then, no other resource but to add sugar in sufficient quantity to mask and conceal the natural acidity of the liquor. Such wines are necessarily acescent, prone to a second fer- mentation, 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 flourish. The operation of malting is performed by steeping the barley in water until the grains become swollen and soft, then piling it in a heap or couch, to favor the elevation of temperature caused by the absorption of oxygen from the air, and afterwards spreading it upon a floor, and turning it over from time to time, to prevent unequal heating. When germination has pro- ceeded far enough, the vitality of the seed is destroyed by kiln-drying. During this process, the curious substance already referred to, diastase, is pro- duced, and a portion of the starch of the grain converted into sugar, and ren- dered soluble. In brewing, the crushed malt is infused in water at about 180, and the mixture left to stand during the space of three hours or more. The easily soluble diastase has thus an opportunity of acting upon the unaltered starch of the grain, and changing the larger portion into dextrine and sugar. The clear liquor, or wort, strained from the exhausted malt, is next pumped up into a copper boiler, and boiled with the requisite quantity of hops, for com- municating a pleasant bitter flavor, and conferring on the beer the property of keeping without injury. The flowers of the hop contain a bitter, resinous principle, called lupuline, 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 29* 342 ALCOHOL. air, in order to avoid an irregular acid fermentation, to which it would other- wise be liable. It is then transferred to the fermenting vessels, which in large breweries are of great capacity, and mixed with a quantity of yeast, the product of a preceding operation, by which the change is speedily induced. This is the most critical part of the whole operation, and one in which the skill and judgment of the brewer are most called into play. The process is in some measure under control by attention to the temperature of the liquid, and the extent to which the change has been carried is easily known by the diminished density, or attenuation, of the wort. The fermentation is never suffered to run its full course, but is always stopped at a particular point, by separating the yeast, and drawing off the beer into casks. A slow and almost insensible fermentation succeeds, which in time renders the beer stronger and less sweet than when new. Highly colored beer is made by adding to the malt a small quantity of strongly dried or charred malt, the sugar of which has been changed to 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 grayish-yellow soft solid, nearly insoluble in water, and dries up to a pale brownish mass, which readily putrefies when moistened, and becomes offensive. Under the microscope it exhibits a kind of organized appearance, being made up of little transparent globules, which sometimes cohere in clusters or strings, like some of the lowest members of the vegetable kingdom. Whatever may be the real nature of the substance, no doubt can exist that it is formed from the soluble azotized portion of the grain during the fermentive process. No yeast is ever produced in liquids free from azotized matter; that added for the purpose of exciting fermenta- tion in pure sugar is destroyed, and rendered inert thereby. When yeast is deprived, by straining and strong pressure, of as much water as possible, it may be kept in a cool place, with unaltered properties, for a long time ; otherwise, it speedily spoils. The distiller, who prepares spirits from grain, makes his wort, or wash, much in the same manner as the brewer ; he uses, however, with the malt a large quantity of raw grain, the starch of which suffers conversion into sugar by the diastase of the malt, which is sufficient for the purpose. He does not boil his infusion with hops, but proceeds at once to the fermentation, which he pushes as far as possible by large and repeated doses of yeast. Alcohol is manufactured in many cases from potatoes ; the potatoes are ground to pulp, mixed with hot water and a little malt, to furnish diastase, made to ferment, and then the fluid portion distilled. The potato-spirit is contaminated by a very offensive volatile oil, again to be mentioned ; the crude product from corn contains a substance of a similar kind. The busi- ness of the rectifier consists in removing or modifying these volatile oils, and in replacing them by others of a more agreeable character. In making bread, the vinous fermentation plays an important part; the yeast added to the dough converts the small portion of sugar the meal natu- rally contains into alcohol and carbonic acid. The gas thus disengaged forces the tough and adhesive material into bubbles, which are still further expanded by the heat of the oven, which at the same time dissipates the alcohol; hence the light and spongy texture of all good bread. 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 acid and carbonate of soda in the dough; if proper proportions be taken, and the whole thoroughly mixed, the operation will no doubt be successful. The use of leaven is one of great an- tiquity ; this is merely dough in a state of incipient putrefaction. When LACTIC ACID. 343 mixed with a large quantity of fresh dough, it excites in the latter the alco- holic fermentation, in the same manner as yeast, but less perfectly ; it is apt to communicate a disagreeable sour taste and odor. LACTIC ACID ; LACTIC ACID FERMENTATION. Azotized albuminous sub- stances, which in a more advanced state of putrefactive change act as alcohol- ferments, often possess, at an earlier period of decay, the property of inducing an acid fermentation in sugar, the consequence of which is the conversion of that substance into lactic add. 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 decom- position it converts, under similar circumstances, the sugar into alcohol. Tiie gluten 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, becomes a true lactic acid ferment; if left a day or two longer, it changes its character, and then acts like eommon yeast. Moist animal membranes, in a slightly decay- ing 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 said to be from milk-sugar. An additional quantity of that substance is dissolved in ordinary milk, which is then set aside in a warm place, until it becomes sour and coagulated. The caseine 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 inso- luble the caseine, and the production of that acid ceases. By carefully neutral- izing, however, the free acid by carbonate of soda, the caseine becomes soluble, and, resuming its activity, changes a fresh quantity of sugar into lactic acid, which may be also neutralized, and by a sufficient number of repetitions of this process all the sugar of milk present may, in time, be acidified. When this has taken place, the liquid is boiled, filtered, and evaporated to dryness in a water-bath. The residue is treated with hot alcohol, which dissolves out the lactate of soda. The alcoholic solution may then be decomposed by the cautious addition of sulphuric acid, which precipitates sulphate of soda, inso- luble in spirit. The free acid may, if needful, be neutralized with lime, and the resulting salt purified by recrystallization and the use of animal charcoal, after which it may be decomposed by oxalic 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, 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 60 to 70 F. 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 recrystallization from water. The lactate of lime may be decomposed by the necessary quantity of pure oxalic acid, the filtered liquid neutralized with carbonate of zinc, and, after a second filtration, evaporated until the zinc-salt crystallizes out on cooling. The latter may, lastly, be redissolved in water, and decomposed by sulphu- retted 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 redissolve and disappear. On examination the liquid will then be found to consist chiefly of a solution of butyrate of lime. Lactic acid may be extracted from a great variety of liquids containing de- composing organic matter, as sauei-kraut, a preparation of white cabbage ; the 344 LACTIC ACID. 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. 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 colorless, syrupy liquid, of sp. gr. 1.215. It has an intensely sour taste and acid reaction; is hygroscopic, and very soluble in water, alcohol, and ether. It forms soluble salts with all the metallic oxides. The syrupy acid contains C 6 H 5 O 5 -|-HO, the water being basic, and susceptible of replacement by a metallic oxide. When syrupy lactic acid is heated in a retort to 266, water containing a little lactic acid distils over, and the residue on cooling forms a yellowish solid fusible mass, very bitter, and nearly insoluble in water. It contains C 6 H 5 O 5 . Long-continued boiling with water converts it into ordinary lactic acid. When this substance is further heated it decomposes, yielding nume- rous products. One of these is lactide, formerly called anhydrous lactic acid, a volatile substance, crystallizing in brilliant 'colorless rhombic plates, which, when put into water, slowly dissolve, with production of common lactic acid. Lactide contains C 6 H 4 O 4 ; it combines with ammonia, forming lactamide, a co- lorless, crystallizable, soluble substance, resembling in its chemical relations oxamide. Another product of the action of heat on lactic acid is lactone, a colorless volatile liquid, boiling at 1 98. Acetone is also formed, and car- bonic oxide and carbonic acid 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. LACTATE OF LIME, CaO,C 6 H 5 O 5 -f- 5HO, 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, melting in its water of crystallization at that tem- perature. LACTATE OF ZINC, ZnO,C 6 H 5 O 5 -{-3HO, is deposited from a hot solution in small brilliant 4-sided prismatic crystals, which require for solution 58 parts of cold and 6 of boiling water. The lactate of protoxide of iron is now used in medicine. When the expressed juice of the beet is exposed to a temperature of 90 or 100 for a considerable time, the sugar it contains suffers a peculiar kind of fermentation, to which the term viscous has been applied. Gases are evolved which contain hydrogen, and when the change appears complete, and the products come to be examined, the sugar is found to have disap- peared. Mere traces of alcohol are produced, but, in place of that substance, a quantity of lactic acid, mannite, and a mucilaginous substance resembling gum-Arabic, and said to be identical with gum in composition. Pure sugar can be converted into this substance; by boiling yeast or the gluten of wheat in water, dissolving sugar in the filtered solution, and ex- posing it to a tolerably high temperature, the viscous fermentation is set up, and a large quantity of the gummy principle generated. A little gas is at the same time disengaged, which is a mixture of carbonic acid and hydrogen.f ' '' ^ '-' * Pelouze, Annalen der Chemie und Pharraacie, liii. 112. f To these several modes of fermentation of sugar must yet be added the very curi- ous one quite recently discovered and described by M. Pelouze, in which butyric acid is produced. This will be found under the head Butyric Acid. ETHER. 345 PRODUCTS OF THE ACTION OF ACIDS ON ALCOHOL. ETHER. When equal weights of rectified spirit and oil of vitriol are mixed in a retort, the latter connected with a good condensing arrangement, arid the liquid heated to ebullition, a colorless and highly volatile liquid, long known under the name of ether, or sulphuric ether, distils over. The process must be stopped as soon as the contents of the retort blacken and froth, otherwise the product will be contaminated with other substances, which then make their appearance. The ether obtained may be mixed with a little caustic potash, and redistilled by a very gentle heat. Pure ether is a colorless, transparent, fragrant liquid, very thin and mobile. Its sp. gr. at 60 is about .720 ; it boils at 96 under the pressure of the atmo- sphere, and bears without freezing the severest cold. When dropped on the hand it occasions a sharp sensation of cold, from its rapid volatilization. Ether is very combustible; it burns with a white flame, generating water and car- bonic acid. Although the substance itself is one of the lightest of liquids, its vapor is very heavy, having a density of 2.586. Mixed with oxygen gas, and fired by the electric spark, or otherwise, it explodes with the utmost vio- lence. Preserved in an imperfectly-stopped vessel, ether absorbs oxygen, and becomes acid from the production of acetic acid; this attraction for oxy- gen is increased by elevation of temperature. It is decomposed by transmis- sion through a red-hot tube into olefiant gas, light carburetted hydrogen, and a substance yet to be described, aldehyde. Ether is miscible Math alcohol in all proportions, but not with water ; it dis- solves to a small extent in that liquid, 10 parts of water taking up 1 part, or thereabouts, of ether. It may be separated from alcohol, provided the quan- tity of the latter be not excessive, by an addition of water, and in this manner samples of commercial ether maybe conveniently examined. Ether is a solvent for oily and fatty substances generally, and phosphorus to a small ex- tent, a few saline compounds and some organic principles, but its powers in this respect are much more limited than those of alcohol or water. Ether is found by analysis to contain C 4 H 5 O ; it therefore differs from alco- hol, C 4 H 6 2 , by the elements of water. Alcohol is often regarded as the hy- drate of ether; but as ether cannot be made to combine with water directly, and as alcohol cannot be converted into ether by the abstraction of water by the aid of substances known to possess a high affinity for that body, such a view must be looked upon as entirely hypothetical. The theory of the pro- duction of ether will be discussed in connection with the history of sulpho- vinic acid. COMPOUND ETHEHS. The so called compound ethers constitute a very large and important class of substances derived from alcohol, and containing either the elements of ether, in combination with those of an oxygen-acid, in- organic or organic, or the elements of olefiant gas in union with those of a hydrogen acid. The relations of these compounds to alcohol and the acids are most simply and clearly illustrated by comparing them with ordinary salts, in which the metal is replaced by a hypothetical salt-basyle termed ethyle,cen- taining C 4 H 5 . This substance may then be supposed to form haloid salts by combining directly with chlorine, iodine, bromine, &c , and its oxide, identi- cal or isomeric with common ether, with oxygen-acids, like basic metallic oxides in general. These views will be found highly useful as aids to the memory ; they are, of course, purely imaginary, ethyle being entirely unknown, 346 COMPOUND ETHERS. and the compound ethers distinguished by important characters from real and undoubted salts.* Table of Ethyk Compounds. Ethyle, symbol Ae C 4 H 5 Oxide of ethyle; ether C 4 H 5 Hydrate of the oxide; alcohol . . . C 4 H 5 O,HO Chloride of ethyle C 4 B 5 ,C1 Bromide of ethyle C 4 H 5 ,Br Iodide of ethyle C 4 H 5 .I Cyanide of ethyle C 4 H 5 ,C 2 N Nitrate of oxide of ethyle .... C 4 H 5 O,N0 5 Hyponitrite of oxide of ethyle . . . C 4 H 5 O,NO 3 Oxalate of oxide of ethyle .... C 4 H 5 O,C 2 O 3 &c. &c. The ethers of many of the acids may be formed by the direct action of these latter upon alcohol at a high temperature, the elements of water being dis- placed by those of the acid; this is chiefly conspicuous with the volatile acids. A more ready general method of forming them, however, is to distil a mix- ture of alcohol, sulphuric acid, and a salt of the acid the ether of which is required. The fatty acids, which in general cannot be distilled without more or less decomposition, yield their ethers with great facility by the action of hydrochloric acid gas upon an alcoholic solution of the acid. The ethers of sulphuric and phosphoric acids are yet in great measure unknown, probably from the remarkable tendency of these acids to combine in a different man- ner with the elements of ether, and to generate the compound acids called sulphovinic and phosphovinic. The compound ethers are mostly volatile aromatic liquids, in a few cases crystallizable solids, without action on vegetable colors, sparingly soluble in water, but dissolved in all proportions by alcohol and ether. They are not acted upon in the cold by alkaline carbonates, but suffer decomposition with more or less difficulty when heated with aqueous solutions of caustic alkali, a salt of the acid of the ether being generated, and alcohol formed and set free. An alcoholic solution of hydrate of potash or soda is more active in this respect. The same kind of decomposition is often brought about by the prolonged contact of boiling water. CHLORIDE op ETHYLE; LIGHT HYDROCHLORIC ETHER; AeCl. Rectified spirit of wine is saturated with dry hydrochloric acid gas, and the product distilled with very gentle heat; or a mixture of 3 parts oil of vitriol and 2 of alcohol is poured upon 4 parts of dry common salt in a retort, and heat ap- plied ; in either case the vapor of the hydrochloric ether should be conducted through a little tepid water in a wash- bottle, and then conveyed into a small receiver surrounded by ice and salt. It is purified from adhering water by contact with a few fragments of fused chloride of calcium. Hydrochloric ether is a thin, colorless, and excessively volatile liquid, of a penetrating, aro- matic, and somewhat alliaceous odor. Its sp. gr. is .874, and it boils at 52; it is soluble in 10 parts of water, is not decomposed by solution of nitrate of sHver, but is quickly resolved into chloride of potassium and alcohol by a hot solution of caustic potash. BROMIDE OF ETHYLE; HYDROBROMIC ETHER; AeBr. This is prepared by distilling a mixture of 8 parts bromine, 1 part phosphorus, and 32 parts * The radicals of the ethers have been isolated by a very simple reaction. When an iodide of ethyle is acted on by metallic zinc, the metal combines with the iodine and ethyle is set free. (Frankland.) R. B. COMPOUND ETHERS. 347 alcohol. It is a very volatile liquid, of penetrating taste and smell, and su- perior in density to water. IODIDE OF ETHYLE; HYDIUODIC ETHER; Ael. Obtained by the action of iodide of phosphorus on alcohol, or by saturating spirit with hydriodic acid gas, and distilling. Iodide of ethyle is a colorless liquid, of penetrating ethereal odor, having a density of 1.92, and boiling at 160. It becomes red by contact with air from a commencement of decomposition. SULPHURET OF ETHYLE, AeS. Formed by the action of chloride of ethyle upon a solution of the monosulphuret of potassium.* It is colorless, has a disagreeable garlic odor, and boils at 163. CYANIDE OF ETHYLE, AeCy. This is produced when a mixture of sul- phovinate of potash and cyanide of potassium, both in a dry state, is slowly heated. It is colorless, has a powerful, offensive alliaceous odor, and a sp. gr. of .7. It boils at 180, resists the action of alkalis, but is decomposed by red oxide of mercury. SULPHITE OF ETHYLE; SULPHUROUS ETHER; AeO.S0 2 . This substance was obtained by adding absolute alcohol in excess to chloride of sulphur. It is a limpid strong smelling liquid, of sp. gr. 1.085, boiling at 320, and slowly decomposed by water. NITRATE OF OXIDE OF ETHYLE; NITRIC ETHER; AeO,NO 5 . The nitrate has only recently been obtained; it is prepared by cautiously distilling a mix- ture of equal weights of alcohol and moderately strong nitric acid, to which a small quantity of nitrate of urea has been added. The action of nitric acid upon alcohol is peculiar : the facility with which that acid is deoxidized by combustible bodies leads, under ordinary circumstances, to the production of nitrous acid o~n the one hand, and an oxidized product of alcohol on the other, a hyponitrite of the oxide of ethyle being generated instead of a nitrate. M. Millon has shown that the addition of urea entirely prevents the formation of that substance, and at the same time preserves the spirit from oxidation by undergoing that change in its place, the sole liquid product being the new ether. The experiment is most safely conducted on a small scale, and the distillation must be stopped when seven-eighths of the whole have passed over : a little water added to the distilled product separates the nitric ether. Nitric ether has a density of 1.112; it is insoluble in water, has an agreeable sweet taste and odor, and is not decomposed by an aqueous solution of caustic potash, although that substance dissolved in alcohol attacks it even in the cold, with production of nitrate of potash. Its vapor is apt to explode when strongly heated/f HYPONITRITE OP THE OXIDE OF ETHYLE; HYPONITROUS OR NITROUS ETHER; AeO,NO s . Pure hyponitrous ether can only be obtained by the direct action of the acid itself upon alcohol. 1 part of potato-starch, and 10 parts of nitric acid, are gently heated in a capacious retort or flask, and the vapor of hyponitrous acid thereby evolved conducted into alcohol mixed with half its weight of water, contained in a two-necked bottle, which is to be plunged into cold water, and connected with a good condensing arrangernent. All elevation of temperature must be carefully avoided. The product of this operation is a pale yellow volatile liquid, possessing an exceedingly agreeable odor of apples; it boils at 62, and has a density of .947. It is decomposed by potash, without darkening, into hyponitrite of the base, and alcohol.J Hyponitrous ether, but contaminated with aldehyde, may be prepared by the following simple method : Into a tall cylindrical bottle or jar are to be introduced successively 9 parts of alcohol of sp. gr. .830, 4 parts of water, * Regnault, Ann. Chim. et Phys. Ixxi. 387. t Ann. Chim. et Phys. 3d series, viii 233. j Liebig ; Geiger's Pharmacie, i. 718. 348 COMPOUND ETHERS. and 8 parts of strong fuming nitric acid ; the two latter are added by means of a long funnel with very narrow orifice, reaching to the bottom of the bottle, so that the contents may form three distinct strata, which slowly mix from the solution of the liquids in each other. The bottle is then loosely stopped and left two or three days in a cool place, after which it is found to contain two layers of liquids, of which the uppermost is the ether. It is purified by rectification. A somewhat similar product may be obtained by carefully distilling a mixture of 3 parts rectified spirits and 2 of nitric acid of 1.28 sp. gr.; the fire must be withdrawn as soon as the liquid boils. The sweet spirits of nitre of pharmacy, prepared by distilling three pounds of alcohol with four ounces of nitric acid, is a solution of hyponitrous ether, aldehyde, and perhaps other substances, in spirit of wine. CARBONATE OF OXIDE OF ETHYLE; CARBONIC ETHER; AeO,CO a . Fragments of potassium or sodium are dropped into oxalic ether as long as gas is disengaged ; the brown pasty product is then mixed with water and distilled. The carbonic ether is found floating upon the surface of the water of the receiver as a colorless, limpid liquid of aromatic odor and burning taste. It boils at 259, and is decomposed by an alcoholic solution of potash into carbonate of that base and alcohol.* SILICIC AND BORACIC ETHERS. A number of these compounds appear to exist, containing different proportions of the acids. Silicic ether containing 3AeO,Si0 3 was obtained by M. Ebelmen by the action of anhydrous alcohol upon chloride of silicon. It is a colorless, limpid, aromatic liquid, of sp. gr. .933, boiling at 329, and decomposed by water with production of silicic acid and alcohol. In contact with rnoist air it is gradually resolved into translucent hydrate of silica, which becomes in the end hard enough to scratch glass. By substituting ordinary spirit for absolute alcohol, other compounds containing a larger portion of silicic acid were obtained. Boracic ether was procured by a similar process, substituting the chloride of boron for chloride of silicon. It formed a thin, limpid liquid of agreeable odor, having the sp. gr. of .885, and boiling at 246. It is decomposed by water. Its alcoholic solution burns with a fine green flame, throwing off a thick smoke of-boracic acid. It contains 3AeO,B0 3 . A second boracic ether in the form of a solid glassy fusible substance, containing AeO2BO 3 , was formed by the action of fused boracic acid upon absolute alcohol. It is vola- tile in the vapor of alcohol only, and is decomposed by water.f Of the ethers of the organic acids, the following are the most important: OXALATE OF THE OXIDE OF ETHYLE ; OXALIC ETHER; AeO,C 2 3 . This compound is most easily obtained by distilling together 4 parts binoxalate of potash, 5 parts oil of vitriol, and 4 parts strong alcohol. The distillation may be pushed nearly to dryness, and the receiver kept warm to dissipate any ordinary ether that may be formed. The product is mixed with water, by which the oxalic ether is separated from the undecomposed spirit; it is re- peatedly washed to remove adhering acid, and re-distilled in a small retort, the first portions being received apart and rejected. Pure oxalic ether is a colorless, oily liquid, of pleasant aromatic odor, and 1.09 sp. gr. It boils at 363, is but little soluble in water, and is readily de- composed by caustic alkalis into an oxalate and alcohol. With solution of ammonia in excess, it yields oxamide and alcohol. This is the best process for preparing oxamide, which is obtained perfectly white and pure. When dry gaseous ammonia is conducted into a vessel containing oxalic ether, the gas is rapidly absorbed, and a white solid substance produced, which is soluble in *Ettling, Annalen der Pharmacie, xix. 17. f Ann. 'China, et Phys. 3d series, xvi. 129, xvii. 54. COMPOUND ETHERS. 349 hot alcohol, and separates, on cooling, in colorless, transparent, scaly crystals. They dissolve in water, and are both fusible and volatile. The name oxame- thane is given to this body; it consists of C 8 H 7 N0 6 . The same substance is formed when ammonia in small quantity is added to a solution of oxalic ether in alcohol. When oxalic ether is treated with dry chlorine in excess in the sunshine, a white, colorless, crystalline, fusible body is produced, insoluble in water and instantly decomposed by alcohol. It contains C 6 C1 5 O 4 , or oxalic ether in which the whole of the hydrogen is replaced by chlorine. By the action of ammo- nia in the dry state and in solution this chloroxalic ether yields two new crystallizable compounds, viz. chloroxamethane, C 8 H 2 C1 5 NO 6 , and the ammonia- salt of a new acid containing C g Cl 5 7 .* ACETATE OP OXIDE OF ETHYLE; ACETIC ETHER; AeO,C 4 H 3 3 . Acetic ether is conveniently made by heating together in a retort 3 parts of acetate of potash, 3 parts of strong alcohol, and 2 of oil of vitriol. The distilled pro- duct is mixed with water, to separate the alcohol, digested first with a little chalk, and afterwards with fused chloride of calcium, and lastly, rectified. The pure ether is an exceedingly fragrant, limpid liquid ; it has a density of .890, and boils at 165. Alkalis decompose it in the usual manner. FORMIATE OF THE OXIDE OF ETHYLE ; FoRMIC ETHER J AeOjCgHOg. A mixture of 7 parts of dry formiate of soda, 10 of oil of vitriol, and 6 of strong alcohol, is to be subjected to distillation. The formic ether, separated by the addition of water to the distilled product, is agitated with a little mag- nesia, and left several days in contact with chloride of calcium. Formic ether is colorless, has an aromatic smell, and density of .915, and boils at 133. Water dissolves this substance to a small extent. The ethers of many of the vegetable acids have been obtained and described. The ethers of cyanic and cyanuric acids have been formed and studied.j" ETHERS OF THE FATTT ACIDS. Normal stearic ether has not yet been ob- tained. By passing hydrochloric acid gas into an alcoholic solution of stearic acid, Redtenbacher succeeded in obtaining the compound AeO,HO,C 68 H 66 O 5 . It resembled white wax, was inodorous and tasteless, melted at 86, and could not be distilled without decomposition. It was readily decomposed by boiling with caustic alkalis.J Margaric ether is prepared by a similar mode of proceeding. When purified from excess of acid by agitation with suc- cessive small quantities of weak spirit, and afterwards made to crystallize slowly from the same menstruum, it forms regular, brilliant, colorless crys- tals, fusible at 70, and distilling without decomposition; when less pure, it is in great part destroyed by this latter process. Margaric ether containsi AeO,C 34 H 33 O 3 . An oleic ether, and corresponding compounds of several other less important fatty acids, have been formed and described. They greatly resemble each other in characters. VALERIANIC AND BUTYRIC ETHERS. The ether-compounds of these acids are easily obtained by the preceding process. They are fragrant volatile liquids, having an odor resembling that of the rind of the pineapple. They are lighter than water, boil at a high temperature, and possess the con- stitution and general character of the class of bodies to which they belong. (EtfANTHic ETHER^ The aroma possessed by certain wines appears due to the presence.of the ether of a peculiar acid called the cenanthic, and which is probably generated during fermentation. When such wines are distilled * Ann. Chim. et Phys. 2d series, Ixxiv. 299. f Anrialen der Chemie und Pharmacie, liv. 370. j Ann. Chim. et Phys. 3d series, ii. 488. $ Annalen der Chem. und Pharm. xlii. 46. 30 350 COMPOUND ACIDS CONTAINING on the large scale, an oily liquid passes over towards the close of the opera- tion, which consists, in great measure, of the crude ether; it may be purified by agitation with solution of carbonate of potash, freed from water by a few fragments of chloride of calcium, and re-distilled. CEnanthic ether is a thin, colorless liquid, having a powerful and almost intoxicating vinous odor ; it has a density of .862, boils at 410, and is but sparingly soluble in water, although, like the compound ethers in general, it dissolves with facility in al- cohol. It contains C 18 H lg O 3 , or AeO,C 14 H 13 O 2 . The density of its vapor is 10.5. A hot solution of caustic potash instantly decomposes cenanthic ether ; al- cohol distils over, and cenanthate of potash remains in the retort ; the latter is readily decomposed by warm dilute sulphuric acid, with liberation of oenanthic acid. Purified by repeated washing with hot water, cenanthic acid presents the appearance of a colorless, inodorous oil, which at 55 becomes a soft solid, like butter. It reddens litmus-paper, and dissolves easily in solu- tions of the alkaline carbonates and in spirit, and very much resembles the fatty acids, to be hereafter described, the products of saponification. The acid thus obtained is a hydrate, composed of C 14 H 13 O 2 -f-HO. By distillation this water is abandoned, and anhydrous acid passes over, containing C 14 H 13 2 . CEnanthic ether may be reproduced by distilling a mixture of 5 parts sul- phovinate of potash, and 1 part hydrated cenanthic acid,* or perhaps better, by the ordinary process for the ethers of the fatty acids. CHLOROCARBONIC ETHER. Although the constitution of this substance is doubtful, it may be here described. Absolute alcohol is introduced into a glass globe containing chlorocarbonic acid (phosgene gas) ; the gas is absorbed in large quantity, and a yellowish liquid produced, from which water sepa- rates the chlorocarbonic ether. When freed from water by chloride of cal- cium, and from adhering acid by rectification from litharge, it forms a thin, colorless, neutral liquid, which burns with a green flame. Its density is 1.133; it boils at 202. The vapor, mixed with a large quantity of air, has an agreeable odor, but when nearly pure is extremely suffocating. It contains C 6 H.ClO 4 . The density of the vapor is 3.82. The action of ammonia, gaseous or liquid, upon this substance, gives rise to a very curious product, called by M. Dumas urethane ; sal-ammoniac is at the same time formed. Urethane is a white, solid, crystallizable body, fusible below 212, and distilling unchanged, when in a dry state, at about 356 : if moisture be present, it is decomposed, with evolution of ammonia. Water dissolves this substance very easily ; the solution is not affected by nitrate of silver, and yields, by spontaneous evaporation, large and distinct crystals. It contains C 6 H 7 N0 4 , or the elements of carbonic ether and urea whence the name.f COMPOUND ACIDS CONTAINING THE ELEMENTS OF ETHER. SCLPHOVINIC ACID, C 4 H 5 O,2S0 3 -j-HO. Strong rectified spirit of wine is mixed with an equal weight of ^concentrated sulphuric acid, as in the ordi- nary preparation of ether; the mixture is heated to its boiling point, and then left to cool. When cold, it is diluted with a large quantity of water, and neutralized with chalk; much sulphate of lime is produced. v The mass is placed upon a cloth filter, drained, and pressed; the clear solution is evapo- * Liebig and Pelouze, Ann. Chem. et Phys. Ixiii. 113. f Ann. Chirh. et Phys. liv. 225. THE ELEMENTS OF ETHER. 351 rated to a small bulk by the heat of a water-bath, filtered from a little sul- phate, and left to crystallize; the product is sulphovinate of lime, in beautiful colorless, transparent crystals, containing CaO-}-C 4 H 5 O,2S0 3 -f-2HO. They dissolve in an equal weight of cold water, and effloresce in a dry atmosphere. A similar salt, containing baryta,BaO-f-C 4 H 5 O,2SO g -f-2HO, equally soluble, and still more beautiful, may be produced by substituting, in the above pro- cess, carbonate of baryta for chalk; from this substance the hydrated acid may be procured by exactly precipitating the base by dilute sulphuric acid, and evaporating the filtered solution, in vacuo, at the temperature of the air. It forms a sour syrupy liquid, in which sulphuric acid cannot be recognized, and is very easily decomposed by heat, and even by long exposure in the vacuum of the air-pump. All the sulphovinates are soluble; the solutions are decomposed by ebullition. The lead salt resembles the barytic com- pound. That of potash, easily made by decomposing sulphovinate of lime by carbonate of potash, is anhydrous; it is permanent in the air, very soluble, and crystallizes well. Sulphovinate of potash, distilled with concentrated sulphuric acid, gives ether ; with dilute sulphuric acid, alcohol ; and with strong acetic acid, acetic ether. Heated with hydrate of lime or baryta, the sulphovinates yield a sul- phate of the base and alcohol. PHOSPHOVINIC ACID, C 4 H 5 O,P0 5 -f-2HO. This acid is bibasic. The baryta- salt is prepared by heating to 180 a mixture of equal weights of strong alcohol and syrupy phosphoric acid, diluting this mixture, after the lapse of 24 hours, with water, and neutralizing by carbonate of baryta. The solution of phos- phovinate, separated by filtration from the insoluble phosphate, is evaporated at a moderate temperature. The salt crystallizes in brilliant hexagonal plates, which have a pearly lustre, and are more soluble in cold than in hot water: it dissolves in 15 parts of water at 68. The crystals contain 2BaO-|-C 4 H 5 0, P0 5 -f-12HO. From this substance the hydrated acid may be obtained by precipitating the baryta by dilute sulphuric acid, and evaporating the filtered liquid in the vacuum of the air-pump; it forms a colorless, syrupy liquid, of intensely sour taste, which sometimes exhibits appearances of crystallization. It is very soluble in water, alcohol, and ether, and easily decomposed by heat when in a concentrated state. The phosphovinates of lime, silver, and lead possess but little solubility ; those of the alkalis, magnesia, and strontia are freely soluble. OXALOVINIC ACID, C 4 H 5 0,2C 2 O 3 -f-HO. Oxalic ether is dissolved in anhy- drous alcohol, and enough alcoholic solution of caustic potash added to neu- tralize one-half of the oxalic acid present, whereupon the potash salt of the new acid precipitates in the form of crystalline scales, insoluble in alcohol, but easily dissolved by water. The free acid is obtained as a sour and ex- ceedingly instable liquid by the addition of hydrofluosilicic acid to a solution of the preceding salt in dilute alcohol. It forms with baryta a very soluble salt. A tartrovinic acid has been described, and probably many other compounds of the same type exist. Another, and a different view, is very frequently taken of the substances just described, and of many analogous compounds. The sulphovinates, phos- phovinates, &c., are supposed to possess a constitution resembling that of or- dinary double salts, one of the bases being a metallic oxide, and the second ether. Thus, anhydrous sulphovinate of baryta is written BaO,SO 3 -f-C 4 H 6 O, SOg, or double sulphate of baryta and ether; hydrated sulphovinic acid is HO,SO 3 -4-C 4 H 5 0,S0 3 , or bisulphate of ether. There are, however, grave 352 COMPOUND ACIDS CONTAINING objections against this mode of viewing the subject : in every true double salt the characters both of acid and bases remain unchanged ; alum gives the reactions of sulphuric acid, of alumina, and of potash; while in sulphovinic acid or a sulphovinate not a trace of sulphuric acid can be detected by any method short of actual decomposition, by heat or otherwise. If sulphovinate of baryta contain sulphate of baryta ready formed, it is very difficult to un- derstand how that salt can be decomposed by an addition of sulphuric acid. The student must, however, bear in mind that all views of the constitution of complex organic compounds must, of necessity, be to a great extent hypo- thetical, and liable to constant alteration with the progress of science. Products of the Decomposition of Sulphovinic jlcid by Heat. A solution of sulphovinic acid, or, what is equivalent to it, a mixture, in due proportions, of oil of vitriol and strong alcohol, undergoes decomposition when heated, yielding products which differ with the temperature to which the liquid is subjected. The cause of the decomposition is to be traced to the instability of the compound itself, and to the basic power of water, and the attraction of the latter for sulphuric acid, 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 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 sulphuric 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 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 and above, the production of ether diminishes, and other substances begin to make their appearance, of which the most remarkable is olefiant gas. The mixture in the retort black- ens, sulphurous acid and carbonic acid are disengaged, a yellow, oily aromatic liquid passes over, and a coaly residue is left, which contains sulphur. The chief and characteristic product is the olefiant gas; the others may be con- sidered the result of secondary actions. The three modes of- decomposition may be thus contrasted : =C4H50+ HOan ,2S0 3 + = C QrJ-HO Acetyle and its protoxide are alike hypothetical. ALDEHYDE, C 4 H 4 O 2 or AcO-J-HO. This substance is formed, as already noticed, among other products, when the vapor of ether or alcohol is trans- 31 362 THE OXIDATION OF ALCOHOL. mitted through a red-hot tube ; also, by the action of chlorine on weak alco- hol. 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 oxide of manganese, 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 pro- cess is interrupted. The distilled product is put into a small retort, with its own weight of chloride of calcium, and redistilled; this 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 crys- talline 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 cal- cium, at a temperature not exceeding 87, it is obtained pure and anhydrous.* Aldehydef is a limpid, colorless liquid, of characteristic ethereal odor, which, when strong, is exceedingly suffocating. It has a density of .790, boils at 72 F., 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 potash, a remarkable brown, resin-like substance is produced, the so called aldehyde-resin. Gently heated with oxide of silver, it reduces the latter with- out evolution of gas, the metal being deposited on the inner surface of the vessel as a brilliant aijd uniform film; the liquid contains aldehytlate of silver. The ammonia-compound above mentioned, forms transparent, colorless crystals, of great beauty ; it has a mixed odor of ammonia and turpentine; it dissolves very easily in water, with less facility in alcohol, and with difficulty in ether; it melts at about 170, and distils unchanged at 212. Acids de- compose it, with production of an ammoniacal salt and separation of alde- hyde. The crystals, which are apt to become yellow, and lose their lustre in the air, contain C 4 H 4 2 -{-NH 3 . When pure aldehyde is long preserved in a closely-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 com- pound. In a specimen kept some weeks at 32, transparent acicular crystals were observed to form in considerable quantity, which, at a temperature little exceeding that of the freezing-point of water, melted to a colorless liquid, miscible with water, alcohol, and ether; a few crystals remained, which sublimed without fusion, and were probably composed of the second sub- stance. This new body received the name elaldehyde ; it was found to be identical in composition with aldehyde, but to differ in properties and in the density of its vapor ; the latter has a sp. gr. of 4.515, while that of aldehyde is only 1,532, or one-third of that number. It refuses to combine with am- monia, is not rendered brown by potash, 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 colorless, transparent, prismatic crystals, which sublime without fusion at a tempera- ture above 212, and are soluble in alcohol and ether, but not in water. * Liebig, Ann. Chim. et Phys. lix. 289. f Alcohol dehydrogenatus. ALDEHYDIC ACID ACETAL. 363 They also were found, by anatysis, to have the same composition as al- dehyde.* ALDEHTDIC ACID, C 4 rI 3 O 2 -f-HO. When solution of aldehydato of silver, obtained by digesting oxide of silver in excess with aldehyde, is precipitated by sulphuretted hydrogen, an acid liquid is obtained, which neutralizes alkalis and combines with the oxides of the metals. It is very easily decomposed. Aldehydate of silver, mixed with baryta-water, gives rise to aldehydate of baryta and oxide of silver : if this precipitate be heated in the liquid, the metal is reduced, and neutral acetate of baryta formed ; whence it is inferred that the new acid contains the elements of acetic acid, minus an equivalent of oxygen.f ACKTAL. This substance is one of the products of the slow oxidation of alcohol-vapor 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 cap- sule, 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 potash, 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 potash, and the alcohol removed by washing with .water, after which the acetal is again digested with fused chloride of calcium, and redistilled. Pure acetal is a thin colorless fluid, of agreeable ethereal odor, of sp. gr. .821 at 72 F., and boiling at 220. 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 alde- hyde, and eventually into acetic acid. Nitric and chromic acids produce a similar effect. Strong boiling solution of potash has no action on this sub- stance. Acetal contains C 6 H 7 O 3 , or the elements of 2 eq. ether and 1 eq. aldehyde.J When a coil of fine platinum wire is heated to red- ness, and plunged into a mixture of ether, or alcohol- Fig. 168. vapor and atmospheric air, it determines upon its surface the partial combustion of the former, and gives rise to an excessively pungent acrid vapor, which may be con- densed to a colorlesss liquid by suitable means. The heat evolved in the act of oxidation is sufficient to main- tain the wire in an incandescent state. The experi- ment may be made by putting a little ether into an ale- glass, 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 vapor, until the ether is exhausted. This is the lamp without flame of Sir H. Davy. A ball of spongy platinum may be * Fehling, Annalen der Pharmacie, xxvii. 419. t Liebig, in Geiger's Pharmacie, p. 739. t Stag, Ann. Chim. et Phys. 3d series, xix. 146. 364 ACETIC ACID. 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, spirit of wine be dropped upon dry platinum-black, the oxygen condensed into the pores of the latter reacts so powerfully upon the alcohol as to cause its instant inflam- mation. When the spirit is mixed with a little water, and slowly dropped upon the finely-divided metal, oxidation still takes place, but with less ener- gy, and vapor of acetic acid is abundantly evolved. It is almost unnecessary to add, that the platinum itself undergoes no change in this experiment. Dilute alcohol, mixed with a little yeast, or almost any azotized organic matter, susceptible of putrefaction, and exposed to the air, speedily becomes oxidized to acetic acid. Acetic acid is thus manufactured in Germany, by suffering such a mixture to flow over wood-shavings, steeped in a little vine- gar, contained in a large cylindrical vessel, through which a current of air is made to pass. The greatly extended surface of the liquid expedites the change, which is completed in a few hours. No carbonic acid is produced in this reaction. The best vinegar is made from wine by spontaneous acidification in a par- tially-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. Such is the plan adopted at Orleans.* In England vinegar of an inferior description is prepared from a kind of beer, made for the purpose. The liquor is exposed to the air in half-empty casks, loosely stopped, until acidification is complete. A little sulphuric acid is af- terwards added, with a view of checking further 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 condensible products of the operation. The distillation is conducted in an iron cylinder of large dimensions, to which a worm or condenser is attached ; a sour watery liquid, a quantity of tar, and much inflammable gas pass over, while charcoal of ex- cellent quality remains in the retort. The acid liquid is subjected to distilla- tion, the first portion being collected apart for the sake of a peculiar volatile body, shortly to be described, which it contains. The remainder is saturated with lime, concentrated by evaporation, and mixed with solution 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 crys- tals are drained as much as possible from the dark, tarry mother-liquor, and deprived by heat of their combined water. The dry salt is then cautiously fused, by which the last portions of tar are decomposed or expelled ; it is then re dissolved in water, and re-crystallized. Pure 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, accidentally 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 * Dumas, Chimie appliquee aux Arts, vi. 537. ACETIC ACID. 365 fluid portion, and tlion suffered to melt. Below 60 this substance forms large, colorless, transparent crystals, which above that temperature fuse to a thin, colorless liquid, of exceedingly pungent and well-Tuiown odor ; it raises blisters on the skin. It is miscible in all proportions with water, alcohol, and ether, and dissolves camphor and several resins. When diluted it has a pleasant acid taste. The hydrate of acetic acid in the liquid condition has a density of 1.063, and boils at 248 ; its vapor 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 hydiate of acetic acid contains C 4 H 3 O 3 -j-HO; it is formed from alco- hol by the substitution of 2 eq. of oxygen for 2 eq. of hydrogen. The water is basic, and can be replaced by metallic oxides ; anhydrous acetic acid, like very many other bodies of the same class, is unknown in a separate state. 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 OP POTASH, KO,C 4 H 3 O 3 . This salt crystallizes with great diffi- culty; it is generally met with as a foliated, white, crystalline mass, obtained by neutralizing carbonate of potash 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 potash is thrown down by a stream of carbonic acid. ACETATE or SODA, NaO,C 4 H 3 3 -f-6HO. The mode of preparation of this salt on the large scale has been already described ; it forms large, transparent, colorless 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, and begins to decompose at 600. ACETATE OF AMMONIA; SPIIUT OF MINDEHEIUTS"; NH 4 0,C 4 H 3 3 . The neutral solution obtained by saturating strong acetic acid by carbonate of am- monia cannot be evaporated without becoming acid from loss of base ; the salt passes off in large quantity with the vapor of water. Solid acetate of ammonia is best prepared by distilling a mixture of equal parts acetate of lime and powdered sal-ammoniac ; chloride of calcium remains in the retort. A saturated solution of the solid salt in hot water, suffered slowly to cool in a close vessel, deposits long slender crystals, which deliquesce in the air. Acetate of ammonia has a sharp and cooling, yet sweet taste; its solution becomes alkaline on keeping, from decomposition of the acid. 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, A1 2 O 3 ,3C 4 H 3 O 3 . This salt is very soluble in water, and dries up in the vacuum of the air-pump to a gummy mass, without trace of crystallization. If foreign salts be present, the solution of the acetate becomes turbid on heating, from the separation of a basic compound, which redissolves as the liquid cools. Acetate of alumina is much employed in calico-printing; it is prepared by mixing solutions of acetate of lead and * Acetic acid increases in density by the addition of water, and reaches its maxi- mum 1.079 when 3'2.5 parts have been mixed with 100 of the strongest acid ; it then decreases in density, and when 112 parts have been added its specific gravity is the same as the hydrate, 1.063. R. B. 31* 366 ACETIC ACID. 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 afcicl, and leaves the alumina in a state capable of entering into combination with the dye-stuff. Acetate of manganese forms colorless, rhombic, prismatic crystals, permanent 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 peroxide of iron is a dark-brownish red, uncrystallizable liquid, of powerful astringent taste. Acetate of cobalt forms a violet colored crystalline, deliques- cent mass. The nickel-salt separates in green crystals, which dissolve in 6 parts of water. ACETATE OF LEAD, PbO,C 4 H 3 O 3 -|-3HO. This important salt is prepared on a large scale by dissolving litharge in acetic acid ; it may be obtained in colorless, transparent, prismatic crystals, but is generally met with in commerce as a confusedly crystalline mass, somewhat resembling loaf sugar. From this circumstance, and from its sweet taste, it is often called sugar of lead. The crystals are soluble in about l part 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 higher 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. SUBACETATES OF LEAD. Sesquibasic 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 evaporated to a syrupy con- sistence in the form of crystalline scales. It contains 3PbO,2C 4 H 3 O 3 . A sub-acetate with 3 eq. of base is obtained by digesting at a moderate heat 7 parts of finely-powdered litharge, 6 parts of acetate of lead, and 30 parts of water. Or, by mixing a cold saturated solution of neutral acetate with a fifth of its volume of caustic ammonia, and leaving the whole some time in a covered vessel ; the salt separates in minute needles, which contain 3PbO,C 4 H 3 3 -f- HO. The solution of sub-acetate prepared by the first method is known in pharmacy under the name of Goulard water. A third sub-acetate exists, formed by adding a great excess of ammonia to a solution of acetate of lead, or by digesting acetate of lead with a large quantity of oxide. It is a white, slightly crystalline substance, insoluble in cold, and but little soluble in boiling water. It contains 6PbO,O 4 H 3 O 3 . The solutions of the sub-acetates of lead have a strong alkaline reaction, and absorb carbonic acid with the greatest avidity, becoming turbid from the precipitation of basic carbonate. ACETATE OF COPPER. The neutral acetate, CuO,C 4 H 3 3 -J-HO, is prepared by dissolving verdigris in hot acetic acid, and leaving the filtered solution to cool. It forms beautiful dark-green crystals, which dissolve in 14 parts of cold and 5 parts of boiling water, and are also soluble in alcohol. A solution of this salt, mixed with sugar and heated, yields sub oxide 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 distil- lation, strong acetic acid, containing acetone, and contaminated with copper. The salt is sometimes called distilled verdigris, and is used as a pigment. SUB-ACETATES OF COPPER. Common verdigris, made by spreading the marc of grapes upon plates of copper exposed to the air during several weeks, or by substituting, with the same view, pieces of cloth dipped in crude acetic acid, is a mixture of several basic acetates of copper which have a green or CHLOE ACETIC ACID. ^ 367 blue color. One of these, 3CuO,2C 4 H 3 O 3 -f-6HO, is obtained by digesting the powdered verdigris in warm water, and leaving the soluble part to sponta- neous evaporation. It forms a blue, crystalline mass, but little soluble in cold water. When boiled, it deposits a brown powder, which is a sub-salt with large excess of base. The green insoluble residue of the verdigris contains 3CuO,C 4 H 3 O 3 +3HO; it may be formed by digesting neutral acetate of copper with the hydrated oxide. By ebullition with water it is resolved into neutral acetate and the brown sub-salt. ACETATE OF SILVER, AgO,C 4 H 3 O s , is obtained by mixing acetate of potash with nitrate of silver, and washing the precipitate with cold water to remove the nitrate of potash. It crystallizes from a warm solution in small colorless needles, which have but little solubility in the cold. Acetate of sub-oxide 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 di- rect solar ray 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 bot- tom contains the same substances, together with the unaltered acetic acid. Hydrochloric and carbonic acid gases are at the same time produced, together with a suffocating vapor, 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, besides capsules containing fragments of caustic potash, 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 to drain upon bibulous paper, and dried in vacuo. Chloracetic acid is also occasionally formed under other circumstances, as by the action of water on chloruretted aldehyde, a body the formation of which accompanies that of perchloruretted ether. It has also been produced from perchloride of carbon. Chloracetic acid is a colorless and extremely deliquescent substance ; it has a faint odor, and a sharp, caustic taste, bleaching the tongue and destroying the skin; the solution is powerfully acid. At 115 it melts to a clear liquid, and at 390 boils and distils unchanged. The density of the fused acid is 1.617 5 that of the vapor, which is very irritating, is probably 5.6. The sub- stance contains, according to the analysis of M. Dumas, C 4 C1 3 3 -J-HO, or the elements of hydrated acetic acid from which 3 eq. of oxygen have been with- drawn, and 3 eq. of chlorine substituted. 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 acids. Chlor- acetate of potash crystallizes in fibrous, silky needles, which are permanent in the air, and contain KO,C 4 Cl 3 3 -f-HO. The ammoniacal salt is also crystal- lizable and neutral; it contains NH 4 O,C 4 C1 3 3 4-5HO. Chloracetate of silver is a soluble compound, crystallizing in small grayish scales, which are easily altered by light; it gives, on analysis, AgO,C 4 Cl 3 3 , and is consequently anhy- drous. When chloracetic acid is boiled with an excess of ammonia, it is decom- posed, with production of chloroform and carbonate of ammonia. C 4 H C1 3 4 =C 2 H C1 3 and C 2 O 4 . 368 ACETONE. With caustic potash, it yields a smaller quantity of chloroform, chloride of potassium, carbonate and formiate of potash. The chloride and the fonniate are secondary products of the reaction of the alkali upon the chloroform.* Normal acetic acid may be reproduced from this curious substitution com- pound. When an amalgam of potassium and mercury is put into a strong aqueous solution of chloracetic acid, chemical action ensues, the temperature of the liquid rises, without disengagement of gas, and the solution is found to contain acetate of potash, chloride of potassium, and some caustic potash. ACETONE; PTROACETIC SPIRIT. When metallic acetates in an anhydrous state are subjected to destructive distillation, they yield, among other products, a peculiar inflammable, volatile liquid, designated by the above names. It is most easily prepared by distilling carefully-dried acetate of lead in a large earthen or coated glass retort, by a heat gradually raised to redness; the. re- tort 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 potash, and afterwards rectified in a water-bath from chloride of calcium. This compound may also be prepared by passing the vapor of strong acetic acid through an iron tube heated to dull redness ; the acid is resolved into acetone, carbonic acid, carbonic oxide, and carburetted hydrogen. Pure acetone is a colorless limpid liquid, of peculiar odor; it has a density of .792, and boils at 132; the density of its vapor, 2.022. Acetone is very inflammable, and burns with a bright flame; it is miscible in all proportions with water, alcohol, and ether. This substance contains C 3 H 3 O, and is pro- duced byihe resolution of acetic acid into acetone and carbonic acid. 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 odor. It is lighter than water, and very inflammable. It contains C 3 H 2 , and is produced by the abstraction of the elements of water from acetone. If perchloride of phosphorus be dropped into carefully-cooled acetone, and the whole mixed with water, a heavy oily liquid separates, which contains C 6 H 5 Cl. When this is dissolved in alcohol, and mixed with caustic potash, a second oily product results. This is lighter than water, has an aromatic odor, and contains C 6 H 5 O. Sir Robert Kane has described a number of other compounds formed by the action of acids, and other chemical agents, on acetone, from which the exist- ence of an organic salt-basyle, containing C 6 H 5 , has been inferred, and to which the name of mesityle has been given. Zeise, on the other hand, has shown that by the action of chloride of platinum upon acetone, a yellow crystallizable com- pound can be obtained, having a composition expressed by the formula C 6 H 5 0+PtCl 2 .t Acetic acid is not the only source of acetone ; it is produced in the destruc- tive distillation of citric acid, and may be procured from sugar, starch, and gum by distillation with 8 times their weight of powdered quicklime. The acetone is, in this case, accompanied by an oily, volatile liquid, separable by water, in which it is insoluble. M. Fremy calls this substance met acetone ; it contains C 6 H 5 0, and is consequently isomeric with Kane's oxide of mesi- tyle.J Metacetone distilled with a mixture of bichromate of potash and sulphuric * M. Dumas, Ann. Chim. et Phys. Ixxiii. 73. t Ann. Chim. et Phys. Ixxii. 113. j Ann. Chim. et Phys. lix. 5. KAKODYLE AND ITS COMPOUNDS. 369 acid yields, among other products, metacetonic acidf, C 6 H 5 O 3 -f-HO, a volatile acid, very closely resembling acetic acid, and chiefly distinguished from that substance by the high degree of solubility of its soda-salt. Metacetonic acid is one of the products of the action of hydrate of potash in a melted state upon sugar, and is also generated by the fermentation of glycerine.* When acetate of potash is heated with a great excess of caustic alkali it is converted, as already remarked,f into carbonic acid and light carburetted hy- drogen, by the reaction of the oxygen of the water of the hydrate upon the carbon of the acid. C 4 H 3 O 3 and HO=C 2 4 and C 2 H 4 . KAKODYLE 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 potash and arsenious acid, has been shown by M. Bunsen to be the oxide of an {soluble organic basyle, capa- ble 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 invest- igation of this difficult subject reflects the highest honor on the patience and skill of the discoverer. Kakodyle, so named from its poisonous and offensive nature, contains three elements, viz. carbon, hydrogen, and arsenic. Table of the most important Kakodyle-compounds. Kakodyle (symbol Kd) . . . C 4 H 6 As. Oxide of kakodyle KdO. Chloride of kakodyle - ... KdCl. ) Chloride of kakodyle and copper . . KdCl-f-Cu 2 Cl. Oxy-ohloride of kakodyle . . . 3KdCl-fKdO. Perchloride of kakodyle .... KdCl g . Bromide of kakodyle . . . . KdBr. Iodide of kakodyle Kdl. Cyanide of kakodyle .... KdCy. Kakodylic acid ' KdO 3 . Kakodylate of silver .... AgO,KdO 3 . Kakodylate of kakodyle . . . . KdO,Kd0 3 . Sulphuret of kakodyle .... KdS. Sulphuret of kakodyle and copper . . KdS+SCuS. Persulphuret of kakodyle . . . KdS 3 . Sulphur salts containing persul- ) KdS,KdS 3 Au 2 S,KdS 3 . phuret of kakodyle . > CuS,KdS 3 PbS,K,dS s . Seleniuret of kakodyle .... KdSe. OXIDE OF KAKODYLE ; CADET'S FUMING LIQ.UID; ALKARSIN ; KdO. Equal weights of acetate of potash and arsenious acid are intimately mixed, and introduced into a glass retort connected with a condenser and tubulated receiver, cooled by ice ; a tube is attached to the receiver to carry away the permanently-gaseous products to some distance from the experimenter. Heat is then applied to the retort, which is gradually increased to redness. At the * Metacetonic acid is also the result of several other reactions. It is formed during the fermentation of tartaric acid ; the oxidation of albumen, fibrin and caserne ; and the action of nitric or oieic acid. R. B. f See page 150. 370 KAKODYLE AND ITS COMPOUNDS. 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 kakodyle in a colored and impure condition; the other chiefly consists of water, acetic acid, and acetone. The gas given off during distillation is principally car- bonic acid. The crude oxide of kakodyle is repeatedly washed by agitation with water, previously freed from air by boiling, and afterwards re-distilled from hydrate of potash in a vessel filled with pure hydrogen gas. All these operations must be conducted in the open air, and the strictest precautions adopted to avoid the accidental inhalation of the smallest quantity of the vapor or its products. Oxide of kakodyle is a colorless, ethereal liquid of great refractive power ; it is much heavier than water, having a density of 1.402. It is very slightly soluble in water ; but easily dissolved by alcohol; its boiling-point approaches 300, and it solidifies to a white crystalline mass at 9. The odor of this substance is extremely offensive, resembling that of arseniuretted 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 kakodyle 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 vapor of this body is about 7.5. Oxide of kakodyle is generated by the reaction of arsenious acid on the elements of acetone, car- bonic acid being at the same time formed ; the accompanying products are accidental : 2 eq. acetone, C 6 H 6 O 2 , and 1 eq. arsenious acid, As0 3 = 1 eq. oxide kako- dyle, C 4 H 6 AsO, and 2 eq. carbonic acid, C 2 4 . CHLORIDE OF KAKODILE, KdCl. A dilute alcoholic solution of oxide of kakodyle 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-f-2HgCl; when this is distilled with con- centrated liquid hydrochloric acid, it yields corrosive sublimate, water, and chloride of kakodyle, 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 colorless liquid, which does not fume in the air, but emits a vapor even more fearful in its effects, and more insupportable in odor 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; its vapor is colorless, is spontaneously inflammable in the air, and has a density of 4.56. Dilute nitric acid dissolves the chloride without change; with the concentrated acid, ignition and explosion occur. Chloride of kakodyle combines with sub-chloride of copper to a white, in- soluble, crystalline double salt, containing KdCl-f-Cu 2 Cl, and also with oxide of kakodyle. KAKODYLE, ix 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 kakodyle is digested for three hours, at a temperature of 212, with slips of clean metallic zinc contained in a bulb blown upon a glass tube, previously filled with carbonic acid gas, and hermetically sealed. The metal dissolves quietly without evolution of gas. When the action is com- plete, 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 kakodyle itself. This is rendered quite pure by distil- lation from a fresh quantity of zinc, the process being conducted in the little KAKODYLE AND ITS COMPOUNDS. 371 apparatus shown in the margin, which is made from a piece of glass tube, and is intended to serve the purpose both of retort and receiver. The zinc is introduced into the upper bulb, and the tube drawn out in the manner represented. The whole is then filled with carbonic acid, and the lower extremity put into communication with a Fig. 169. little hand-syringe. On dipping the point a into the crude kakodyle 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 digestion at 212 or a little above, the pure kakodyle is distilled off into the lower bulb, which is kept cool. It forms a colorless, transparent, thin liquid, much resem- bling the oxide in odor, and surpassing that substance in inflammability. When poured into the air, or into oxygen gas, it ignites instantly; the same thing happens with chlo- rine. With very limited access of air it throws off while fumes, passing into oxide, and eventually into kakodylic acid. Kakodyle boils at 338, and when cooled to 21 F. crystallizes in large, transparent, square prisms. It com- bines directly with sulphur and chlorine, and in fact may readily be made to furnish all the compounds previously derived from the oxide. It constitutes the most perfect type of an organic quasi-metal which chemistry yet possesses. Kakodyle is decomposed by a temperature inferior to redness into metallic arsenic, and a mixture of 2 measures light carburetted hydrogen, and 1 measure olefiant gas. Chloride of kakodyle 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, arid also in other operations, a small quntity of a red amorphous powder is often obtained, called erytrarsin. This is insoluble in water, alcohol, ether, and caustic potash, but is gradually oxidized by ex- posure to the air, with production of arsenious acid. It contains C 4 H 6 O 3 As 3 . IODIDE OF KAKODYLE, Kdl. This is a thin yellowish liquid, of offensive odor, and considerable specific gravity, prepared by distilling 6xide of kako- dile with strong solution of hydriodic acid. A yellow crystalline substance is at the same time formed, which is an oxy-iodide. Bromide and fluoride of kakodyle have likewise been obtained and examined. SuLpHtmET OF KAKODYLE, KdS, is prepared by distilling chloride of kako- dyle with a solution of the double sulphuret of barium and hydrogen. It is a clear, thin, colorless liquid, smelling at once of alkarsin and mercaptan, inso- luble in water, and spontaneously inflammable in the air. Its boiling-point is high, but it distils easily with the vapor of water. This substance dissolves sulphur, and generates persulphuret of kakodyle, KdS 3 , which is a sulphur- acid, and combines with the sulphurets of gold, copper, bismuth, lead, and antimony. CYANIDE OF KAKODYLE, Kd,C 2 N. The cyanide is easily formed by distilling alkarsin with strong hydrocyanic acid, or cyanide of mercury. Above 91 F. it is a colorless, ethereal liquid, but below that temperature it crystallizes in colorless four-sided prisms, of beautiful diamond lustre. It boils at about 284, and is but slightly soluble in water. It requires to be heated before inflam- mation occurs. The vapor of this substance is most fearfully poisonous ; the atmosphere of a room is said to be so far contaminated by the evaporation of a few grains, as to cause instantaneous numbness of the hands and feet, ver; tigo, and even unconsciousness. KAKODYLIC ACID; ALKAIIGEN; KdO r This is the ultimate product of the 372 KAKODYLE AND ITS COMPOUNDS. action of oxygen at a low temperature upon kakodyle 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 odor, and after- wards decomposing any kakodylate of mercury that may have been formed by the cautious addition of more alkarsin. The liquid furnishes, by evapora- tion to dryness and solution in alcohol, crystals of the new acid. The sul- phuret, and other compounds of kakodyle, yield, by exposure to air, the same substance. Kakodylic acid forms brilliant, colorless, brittle crystals, which have the form of a modified square prism ; it is permanent in dry air, but deliquescent in a moist atmosphere. It is very soluble in water and in alco- hol, 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 compounds. It unites with oxide of kakodyle, 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 deoxidized, how- ever, by phosphorous acid and protochloride of tin to oxide of kakodyle. Dry hydriodic acid gas decomposes it, with production of water, iodide of kako- dyle, and free iodine ; hydrochloric acid, under similar circumstances, converts it into a corresponding perchloride, which is solid and crystallizable. Lastly, what is extremely remarkable, this substance is not in the least degree poi- sonous. PAHAKAKODYLIC OXIDE. When air is allowed access to a quantity of al- karsin, 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, fails to induce crystallization of the whole. If in this state water be added, everything dissolves, and a solution results which con- tains kakodylic acid, partly free, and partly in combination with oxide of ka- kodyle. When this liquid is distilled, water, having the odor of alkarsin, passes over, and afterwards an oily liquid, which is the new compound. Im- pure kakodylic acid remains in the retort. Parakakodylic oxide, purified by rectification from caustic baryta, is a color- less, oily liquid, strongly resembling alkarsin itself in odor, relations to sol- vents, and in the great number of its reactions. It neither fumes in the air, however, nor takes fire at common temperatures; its vapor, mixed with air, and heated to 190, explodes with violence. By analysis, it is found to have exactly the same composition as ordinary oxide of kakodyle.* * See Annalen der Chemie und Pharmacie, xxiv. 271 ; xxvii. 148; xxxi. 175; xxxvii. 1; xlii. 14, and xlvi. 1. WOOD-SPIRIT AND ITS DERIVATIVES. 373 SECTION II. SUBSTANCES MORE OR LESS ALLIED TO ALCOHOL. WOOD-SPIRIT AND ITS DERIVATIVES. IN the year 1812, Mr. P. Taylor discovered, among the liquid products of the destructive distillation of dry wood, a peculiar volatile inflammable liquid, much resembling spirit of wine, to which allusion has already been made. This substance has been shown by M. Dumas* 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 hypothetically regarded as a hydrated oxide of a body like ethyle. not yet isolated, containing C 2 H 3 , called methyle.^ A very great number of compound methyle-ethers have been described; they present the most complete parallelism of origin, properties, and constitu- tion with those derived from common alcohol. Wood- spirit Series. Methyle (symbol, M.) .... C 2 H 3 Oxide of methyle ..... . C 2 H 3 , O Chloride of methyle . . . . . C 2 H 3 , Cl Iodide of methyle, &c. . . . . . C 2 H 3 , I . Wood-spirit ...... C 2 H 3 , O+HO Sulphate of oxide of methyle . . , , C 2 H 3 , O -}-S0 3 Nitrate of oxide of methyle, &c. . . . C 2 H 3 , O -f-NO 5 Sulphomethylic acid ..... C 2 H 3 O , 2SO 3 -f-HO Formic acid ...... C 2 H O 3 Chloroform ...... C 2 H Cl 3 HYDRATED OXIDE OF METHYLE; PYROXYLIC SPIRIT; WOOD-SPIRIT; MeO-f-HO. The crude wood-vinegar probably contains about T ^th part of this substance, which is separated from the great bulk of the liquid, by sub - jecting 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 ren- * MM. Dumas and Peligot, Ann. China, et Phys. Iviii. 5. f From 'tQv, wine, and JJxm wood ; the termination ux n , yle, is very frequently employed in the sense of matter, material. 32 374 WOOD-SPIRIT AND ITS DERIVATIVES. dered pure and anhydrous, by careful distillation from quicklime, by the heat of a water-bath. Pure wood-spirit is a colorless, thin liquid, of peculiar odor, quite different from that of alcohol, and burning, disagreeable taste ; it boils at 152 F., and has a density of .798 at 68. The density of its vapor 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 purposes it is prepared on a large scale. It may be burned instead of ordinary spirit, in lamps ; the flame is pale-colored, like that of alcohol, and deposits no soot. Wood-spirit dissolves caustic baryta; the solution deposits, by evaporation in vacuo, acicular crys- tals, containing BaO-|-MeO,HO. Like alcohol, it dissolves chloride of calcium in large quantity, and gives rise to a crystalline compound, resembling that formed by alcohol, and containing, according to Kane, CaCl-f-2MeO,HO. OXIDE OF METHTLE ; 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 so- lution of caustic potash, and collected over mercury. This is the wood-spirit ether, a permanently gaseous substance, which does not liquefy at the tempe- rature of 3 F. It is colorless, has an ethereal odor, and burns with a pale and feebly luminous flame. Its specific gravity is 1.617. Cold water dis- solves about 33 times its volume of this gas, acquiring thereby the character- istic taste and odor of the substance ; when boiled, the gas is again liberated. Alcohol, wood-spirit, and concentrated sulphuric acid dissolve it in still larger quantity. CHLORIDE OF METHTLE, MeCl. This compound is most easily prepared by heating a mixture of 2 parts of common salt, 1 of wood spirit, and 3 of concentrated sulphuric acid; it is a gaseous body, which may be conveniently collected over water, as it is but slightly soluble in that liquid. Chloride of rnethyle is colorless ; it has a peculiar odor and^sweetish taste, and burns, 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 F. The gas is decomposed by transmission through a red-hot tube, with slight deposition of carbon into hydrochloric acid gas and a carburetted hydro- gen, which has been but little examined. IODIDE OF METHTLE, Mel, is a colorless and feebly combustible liquid, ob- tained by distilling together 1 part of phosphorus, 8 of iodine, and 12 or 15 of wood-spirit. It is insoluble in water, has a density of 2.237, and boils at 75. The density of its vapor is 4.883. Compounds of methyle with fluorine, cyanogen, and sulphur have also been obtained. SULPHATE OF OXIDE OF METHTLE, MeO , SO 3 . This interesting substance, is readily 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 oleagi- nous liquid found in the receiver is agitated with water, and purified by rec- tification from powdered caustic baryta. The product, which is the body sought, is a colorless oily liquid, of alliaceous odor, having a density of 1.324, and boiling at 370 F. It is neutral to test-paper, and insoluble in water, but decomposed by that liquid, slowly in the cold, rapidly and with violence at a boiling temperature, into snlphomethylic acid and wood-spirit, which is thus re- produced by hydration of the liberated methylic ether. Anhydrous lime or baryta have no action on this substance ; their hydrates, however, and those o potash and soda, decompose it instantly, with production of a sulpho- methylate of the base, and wood spirit. When neutral sulphate of rnethyle is heated with common salt, it yields sulphate of soda and chloride of me- WOOD-SPIRIT AND ITS DERIVATIVES. 375 thyle; with cyanide of mercury or potassium, it gives a sulphate of the base, and cyanide of methyle ; with dry formiate of soda, sulphate of soda and formiate of methyle. These reactions possess great interest. NITRATE or THE OXIDE OF METHYLE, MeO , NO 5 . One part of nitrate of potash is introduced into a retort, connected with a tubulated receiver, to which is attached a bottle, containing salt and water, cooled by a freezing- mixture ; a second tube serves to carry off the incondensible gases to a chim- ney. A mixture of 1 part of wood-sprit and 2 of oil of vitriol is made, and immediately poured upon the nitre ; reaction commences at once, and re- quires but little aid from external heat. A small quantity of red vapor 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 tubulature. The liquid begins to boil at about 140 ; the temperature soon rises to 150, at which point it remains constant; the product is then collect- ed apart, the first and most volatile portions being contaminated with hydro- cyanic acid and other impurities. Even with these precautions, the nitrate of methyle is not quite pure, as the analytical results show. The properties of the substance, however, remove any doubts respecting its real nature. Nitrate of methyle is colorless, neutral, and of feeble odor : its density is 1.182 ; it boils at 150, and burns, when kindled, with a yellow flarne. Its vapor has a density of 2.64, and is eminently explosive ; when heated in a flask or globe to 300, or a little above, it explodes with fearful violence ; the determination of the density of the vapor is, consequently, an operation of danger. Nitrate of methyle is decomposed by a solution of caustic potash into nitrate of that base and wood-spirit. OXAI.ATE OF OXIDE OF METHTLE,MeO,C 2 3 . This beautiful and interest- ing substance is easily prepared by distilling a mixture of equal weights of oxalic acid, wood-spirit, and oil of vitriol. A spirituous liquid collects in the receiver, which, exposed to the air, quickly evaporates, leaving the oxalic methyle-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 little oxide of lead. The product is colorless, and has the odor of common oxalic ether; it melts at 124, and boils at 322. It dissolves freely in alcohol and wood-spirit, and also in water, which, however, rapidly de- composes it, especially when hot, into oxalic acid and wood -spirit. The al- kaline hydrates effect the same change even more easily. Solution of am- monia converts it into oxamide and wood-spirit. With dry ammoniacal gas it yields a white, solid substance, which crystallizes from alcohol in pearly cubes ; this new body contains C 6 H 5 N0 6 , and is designated oxamethylane. Many other salts of oxide of methyle have been formed and examined. The acetate, MeO,C 4 H 3 3 , is abundantly obtained by distilling 2 parts of wood- spirit with 1 of crystallizable acetic acid, and 1 of oil of vitriol. It much resembles acetic ether, having a density of .919, and boiling at 136; the density of its vapor is 2.563. This compound is isomeric with formic ether. Formiate of Methyle, MeO,C 2 H0 3 , is prepared by heating in a retort equal weights of sulphate of methyle and dry formiate of soda. It is very vola- tile, lighter than water, and is isomeric with hydrate of acetic acid. Chloro- carbonic methyle ether is produced by the action of that gas upon wood-spirit; it is a colorless, thin, heavy, and very volatile liquid, containing C 4 H g ClO 4 . It yields with dry ammonia a solid crystallizable substance, called urethylane. SULPHOMETHYLIC ACID, MeO,2S0 3 -J-HO. Sulphomethylate of baryta is 376 WOOD-SPIRIT AND ITS DERIVATIVES. prepared in the same manner as the sulphovinate ; 1 part of wood-spirit is slowly 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 insoluble sulphate, and evaporated, first in a water-bath, and afterwards in vacuo to the due degree of concentration. The salt crystallizes in beautiful square colorless tables, containing BaO-}-C 2 H 3 0,2SO 3 +2HO, which effloresce in dry air, and are very soluble in water. By exactly precipitating the base from this substance by dilute sulphuric acid, and leaving the filtered liquid to evaporate in the air, hydrated sulphomethylic acid may be procured in the form of a sour, syrupy liquid, or as minute acicular crystals, very soluble in water and alcohol. It is very instable, being decomposed by heat in the same manner as sulphovinic acid. Sulphomethylate of potash crystallizes in small, nacreous, rhombic tables, which are deliquescent ; it contains KO4-C 2 H 3 0,2S0 3 . The lead salt is also very soluble. FORMIC ACID. As alcohol by oxidation under the influence of finely- divided platinum gives rise to acetic acid, so wood-spirit, under similar cir- cumstances, yields a peculiar acid product, produced by the substitution of 2 eq. of oxygen for 2 eq. of hydrogen, to which the term formic is given, from its occurrence 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 access of air; the spirit is gradually converted into formic acid. There is no intermediate product corresponding to aldehyde. Anhydrous formic acid, as in the salts, contains C 2 HO 3 , or the elements of 2 eq. carbonic oxide, and 1 eq. water. Pure hydrate of formic acid, C 2 H0 3 -f-HO, is obtained by the action of sulphuretted hydrogen on dry formiate 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 trans- mitted. It forms a clear, colorless liquid, which fumes slightly in the air, of exceedingly penetrating odor, boiling at about 212, and crystallizing in large brilliant plates when cooled below 32. The sp. gr. of the acid is 1.235 ; it mixes with water in all proportions ; the vapor 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. In its concentrated form this acid is ex- tremely 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 convenient method is the follow- ing: 1 part of sugar, 3 of peroxide of manganese, and 2 of water, are mixed in a very capacious retort, or large metal still; 3 parts of oil of vitriol, diluted with an equal weight of water, are then added, and when the first violent effervescence from the disengagement of carbonic acid has subsided, heat is cautiously applied, and a considerable quantity of liquid distilled over. This is very impure ; it contains a volatile oily matter, and some substance which communicates a pungency not proper to formic acid in that dilute state. The acid liquid is neutralized with carbonate of soda, and the resulting formiate purified by crystallization, and, if needful, by animal charcoal. From this, or any other of its salts, solution of formic acid may be readily obtained by dis- tillation with dilute sulphuric acid. It has an odor and taste much resembling those of acetic acid, reddens litmus strongly, and decomposes the alkaline carbonates with effervescence. 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 WOOD-SPIRIT AND ITS DERIVATIVES. 377 little solution of oxide of silver or mercury; the metal is reduced, and pre- cipitates in a pulverulent state, while carbonic acid is extricated ; this reaction is sufficiently intelligible. The chloride of mercury is reduced, by the aid of the elements of water, to calomel, carbonic and hydrochloric acids being formed. The most important salts of formic acid are the following: Formiate of soda crystallizes in rhombic prisms containing 2 eq. of water; it is very solu- ble, and is decomposed like the rest of the salts by hot oil of vitriol with evo- lution of pure carbonic oxide. Fused Math many metallic oxides, it causes their reduction. Formiate of potash is with difficulty made to crystallize from its great solubility. Formiate 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. The salts of baryta, strontia, lime, and magnesia form small prismatic crystals, soluble without difficulty. Formiate of lead crystallizes in small, diverging, colorless needles, which re- quire for solution 40 parts of cold water. The formiates of manganese, pro- toxide of iron, zinc, nickel, and cobalt are also crystal lizable. That of copper is very beautiful, constituting bright blue, rhombic prisms of considerable mag- nitude. Formiate of silver is white, but slightly soluble, and decomposed by the least elevation of temperature. CHLOROFORM. This substance is produced, as already remarked, when an aqueous solution of caustic alkali is made to act upon chloral. It may be ob- tained with greater facility by distilling alcohol, wood-spirit, or acetone with a solution of chloride of lime. 1 part of hydrate of lime is suspended in 24 parts of cold water, and chlorine passed through the mixture until nearly the whole lime is dissolved. A little more hydrate is then added to restore the alkaline reaction, the clear liquid mixed with 1 part of alcohol or wood-spirit, and, after an interval of 24 hours, cautiously distilled in a very spacious vessel. A watery liquid containing a little spirit and a heavy oil collect in the receiver ; the latter, which is the chloroform, is agitated with water, digested with chloride of calcium, and rectified in a water-bath. It is a thin, colorless liquid of agreeable ethereal odor, much resembling that of Dutch- liquid, and sweetish taste. Its density is 1.48, and it boils at 141; the density of its vapor is 4.116. Chloroform is with difficulty kindled, and burns with a greenish flame. It is nearly insoluble in water, and is not affected by concentrated sulphuric acid. Alcoholic solution of potash quickly decomposes it with production of chloride of potassium arid formiate of potash. Chloroform contains C 2 HCJ 3 ; it 'is changed to formic acid by the substitu- tion of three eq. of oxygen for the three eq. of chlorine removed by the alkaline metal. Chloroform may be prepared on a larger scale by cautiously distilling together good commercial chloride of lime, water, and alcohol. The whole product distils over with the first portions of water, so that the operation may be soon interrupted with advantage. This substance has been called strongly into notice from its remarkable effects upon the animal system in producing temporary insensibility to pain when its vapor is inhaled. Bromoform, C 2 H Br 3 , is a heavy, volatile liquid, prepared by a similar pro- cess, bromine being substituted in the place of chlorine. It is converted by alkali into bromide of potassium and formiate of potash. Jocfo/orm, C 2 H I 3 , is a solid, yellow, crystallizable substance, easily obtained by adding alcoholic solution of potash to tincture of iodine, avoiding excess, evaporating the whole to dryness, and treating the residue with water. lodoform is nearly insoluble 32* 378 POTATO-OIL, in water, but dissolves in alcohol, and is decomposed by alkalis in the same manner as the preceding compounds. FORMOMETHYLAL. This is a product of the distillation of wood-spirit with dilute sulphuric acid and oxide of manganese. The distilled liquid is satu- rated with potash, by which the new substance is separated as a light oily fluid. When purified by rectification, it is colorless, and of agreeable aromatic odor; it has a density of .855, boils at 107, and is completely soluble in three parts of water. It contains C 3 H 4 O 2 . METHYLE-MKRCAPTAST is prepared by a process similar to that recommended for ordinary mercaptan, sulphomethylate of potash being substituted for the sulphovinate of lime. It is a colorless liquid, of powerful alliaceous odor, and lighter than water; it boils at 68, and resembles mercaptan in its action on red oxide of mercury. PRODUCTS OF THE ACTION OF CHLORINE ON THE COMPOUNDS OF METHYLE. Chlorine acts upon the methylic compounds in a manner strictly in obedience to the law of substitution; the carbon invariably remains intact, and every proportion of hydrogen, removed is replaced by an equivalent quantity of chlorine. Methylic ether and chlorine, in a dry and pure condition, yield a volatile liquid product, containing C 2 H 2 C1 O ; the experiment is attended with great danger, as the least elevation of temperature gives rise to a violent ex- plosion. This product in its turn furnishes, by the continued action of the gas, a second liquid, containing C 2 H C1 2 0. The whole of the hydrogen is eventually lost, and a third compound, C 2 C1 3 O, produced. Even the oxygen may, it seems, be displaced, and a new chloride of carbon, C 2 C1 4 , generated. Chloride of rnethyle, C 2 H 3 Cl, in like manner gives rise to three successive products. The first, C 2 H 2 CI 2 , is a new volatile liquid, much resembling chlo- ride of olefiant gas; the second, C 2 HC1 3 , is no other than chloroform ; the third is chloride of carbon, C 2 CI 4> * The acetate of methyle, C 6 H 6 O 4 , gives C 6 H 4 CI 2 O 4 , and C 6 H 3 C1 3 4 ; the other salts 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 is said some- times to contain aldehyde, often acetone, and very frequently a volatile oil, which is precipitated by the addition of water, rendering the whole turbid. A specimen of wood-spirit, from Wattwyl, in Switzerland, was found by Gmelin to contain a volatile liquid, differing in some respects from acetone, to which he gave the term lignone. A very similar substance is described by Schweitzer and Weidmann, under the name of xylite.f Lastly, Mr. Scanlan has obtained from wood-spirit a solid, yelfbw, crystallizable substance, called eblanine. 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, and contains, according to Dr. Gregory, C 21 H 9 4 . POTATO-OIL, AND ITS DERIVATIVES. In the manufacture of potato-brandy the crude spirit is found to be con- taminated with an acrid volatile oil, called fusel oil, which is extremely diffi- cult to separate in a complete manner. Towards the end of the distillation it passes over in considerable quantity; it may be collected apart, agitated with several successive portions of water to withdraw the spirit, with which it is mixed, and redistilled. This substance exhibits properties indicative of a constitution analogous to that of alcohol ; it may be considered as the hy- * Regnault, Ann. China, et Phys. Ixxi. 353. f Annalen der Chemie und Pharmacie, xxxvi. 205. AND ITS DERIVATIVES. 379 C 10 H n * The ether of potato oil, and a variety of other compounds, corresponding in every point to those of ordinary alcohol, have been formed, as will be manifest from an inspection of the following table: Amyle (symbol Ayl) .... C 10 H n Amyle-ether C 10 H n ,0 Potato-oil C 10 H n , 0+HO Chloride of amyle, C io H n > Cl Bromide of amyle C 10 H u ,Br Iodide of amyle ... . . C 10 H U ,I Acetate of amyle C io H n > Q -^ C 4^s3 Sulphamilic acid C 10 H u O,2S0 3 -f HO Amilen ....... C, H 10 Valerianic acid C 10 H 9 O 3 HYDRATED OXIDE OF AMYLE; FUSEL OIL; AylO-f-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 and 280 is collected apart and redistilled in the same manner, until an oil is obtained, having a fixed boiling-point at 268 269 F. Thus purified, it is a thin fluid oil, exhaling a powerful and pecu- liarly suffocating odor, and leaving a burning taste; it inflames with some dif- ficulty, and then burns with a pure blue flame. Its density is .818. It un- dergoes 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. AMYLE-ETHER, AylO, was obtained by M. Balard by exposing to a high temperature, in a glass tube hermetically sealed, a mixture of chloride of amyle and alcoholic solution of potash. It is a colorless liquid, of agreeable odor, boiling at 233.f CHLORIDE OF AMYLE, AylCl. The chloride is procured by subjecting to distillation equal weights of potato oil and perchloride of phosphorus, wash- ing the product repeatedly with alkaline water, and rectifying it from chloride of calcium. It is a colorless liquid, of agreeable aromatic odor, insoluble in water, and neutral to test-paper; it boils at 215, 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 chloruretted chloride of amyle, was obtained in the form of a volatile colorless liquid, smelling like camphor, and containing C 10 H 3 C1 9 ; the whole of the hydrogen could not, however, be removed. BROMIDE OF AMYLE, Ayl Br, is a volatile, colorless liquid, heavier than water ; its odor is penetrating and alliaceous. The bromide is decomposed by an alcoholic solution of potash with production of bromide of the metal. IODIDE OF AMYLE, Ayl I, is procured by distilling a mixture of 15 parts of potato oil, 8 of iodine, and 1 of phosphorus. It is colorless when pure, heavier than water, volatile without decomposition at 248, and resembles in other respects the bromide; it is partly decomposed by exposure to light.J * See Cahours, Ann. Chim. et Phys. Ixx. 81 ; and Ixxv. 193. f Ann. Chim. et Phys. 3d series, xii. 294. J Iodide of amyle in sealed tubes is decomposed with considerable rapidity at 32(K> by an amalgam of zinc, the products being iodide of zinc and a colorless volatile fluid, separable by distillation into three portions. That coming over last, at 311, had the composition of C 10 H U , and is pure amyle. It is colorless and transparent, with an ethereal odor and burning taste, boils at 311, and becomes thick and oily at 22 ; its 380 POTATO OIL, ACETATE OF OXIDE OF AMYLE, Ayl 0,C 4 H S O 3 . This interesting product is easily obtained by submitting to distillation a mixture of 1 part of potato-oil, 2 parts of acetate of potash, 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 colorless, limpid liquid, which is in- soluble in water, soluble in alcohol, boils at 257, and becomes converted by an alcoholic solution of potash into an acetate of the base, with reproduction of the oil. SuJpfturet and cyanide of amyle, amyle mercaptan, and numerous other com- pounds of like nature, have been described. SULPHAMILIC 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 corres- ponding to the sulphovinate. The latter may be obtained in a crystalline state by gentle evaporation, and purified by re-solution and the use of animal charcoal. It forms small, brilliant, pearly plates, very soluble in water and alcohol, containing BaO-f-C 10 H 11 0,2SO 3 -j- HO. The baryta may be precipi- tated from the salt by dilute sulphuric acid, and the hydrated sulphamilic acid concentrated by spontaneous evaporation to a syrupy, or even crystalline state j it has an acid and bitter taste, strongly reddens litmus-paper, and is decomposed by ebullition into potato-oil and sulphuric acid. The potash-salt forms groups of small radiated needles, very soluble in water. The sulpha- milate of lime and oxide of lead are also soluble and crystallizable. AMIIEU-. By the distillation of potato-oil with anhydrous phosphoric acid, a volatile, colorless, oily, liquid is procured, quite different in properties from the original substance. It is lighter than water, boils at 320, or thereabouts, and contains no oxygen. Its com position is represented by the formula C ]0 H, ; consequently it not only corresponds to olefiant gas in the alcohol -series, but is isomeric with that substance. The vapor, however, has a density of 5.06, which is five times that of olefiant gas, every measure containing 10 measures of hydrogen. CHLORAMILAL. This is the product of the action of dry chlorine on puri- fied potato oil; when pure, it is an oily, yellowish liquid, insoluble in water, dissolved by alcohol and ether, and having a taste feeble at first, but which afterwards becomes exceedingly acid. It boils at 350. By analysis this substance is found to contain C 20 H ]7 CI 3 O 4 . VAIERIANIC ACID. M. Dumas has shown that when a mixture of equal parts quicklime and hydrate of potash 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 potash produced is in turn decomposed, yielding carbonate of potash and light carburetted hydrogen. Wood-spirit, by similar treatment, yields hydrogen and formiate of potash, which, as the heat increases, becomes converted into oxalate, and eventually into carbonate, with continued disen- gagement 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 pro- Bpecific gravity is .7704, it is combustible, and burns with a bright, but smoky flame ; it is insoluble in water, but miscible in all proportions with alcohol and ether. The other portions which first distil over, consist of two liquids, valerene, isomeric with amilen, C 10 H 10 , and hydmret of amyle, C 10 H n H. Hydruret of amyle is a color- less, transparent and very mobile liquid, with an agreeable odor of chloroform, very light, haying the specific gravity of 0.6385. It is insoluble in water, boils at 86, and burns with a pure white name. Valerene is a colorless liquid, with a disagreeable odor, and boils at 95. (Frankland, Proceed. Chem Soc. Feb. 1850.) R. B, AND ITS DERIVATIVES. 381 duced is found to be identical with a volatile oily acid distilled from the root of the Valeriana 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 or 400. 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 potash, evaporated nearly to dryness to dissipate any undecomposed potato-oil, and then mixed wtth somewhat diluted sul- phuric acid in excess. The greater part of the valerianic acid then separates as an oily liquid, lighter than water; this is a terhydrate of the acid, contain- ing 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, color- less oil, of the persistent and. characteristic odor of valerian-root. It has a sharp and acid taste, reddens litmus strongly, bleaches the tongue, and burns, when inflamed, with a bright, yet smoky light. Valerianic acid has a density of .937 ; it boils at 347. 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 crys- tallizing. The liquid acid is found by analysis to contain C, H 9 3 -}-HO, and the silver-salt, AgO-f-C 10 H 9 O 3 . The terhydrate is always produced when the acid is liberated from combination in contact with water. A more advantageous mode of preparing valerianic acid is the following : 4 parts of bichromate of potash 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 \vater to moderate the violence of the reaction. When the change appears complete, the deep green liquid is distilled nearly to dryness, the product mixed with excess of caustic potash, and the aqueous solution sepa- rated mechanically from a pungent, colorless, oily liquid which floats upon it, and which may possibly be valerianic aldehyde. The alkaline solution is then evaporated to a small bulk and decomposed by sulphuric acid as already di- rected. 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, animal and vegetable, and is produced in many chemical reactions in which oxidizing agents are employed. If an open-topped jar be set in a plate containing a little water, and hav- ing 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 phos- phoric acid, yields valerianic acid. CHLOROVALERISIC ACID. When dry chlorine is passed for a long time into pure valerianic acid, in the dark, the gas is absorbed in great quantity, and much hydrochloric acid produced ; towards the end of the operation a little heat becomes necessary. The product is a semi fluid transparent substance, heavier than water, odorless, and of acrid, burning taste. It does not con- geal when exposed to a very low temperature, but acquires complete fluidity when heated to 86. It cannot be distilled without decomposition. When put into water it forms a thin, fluid hydrate, which afterwards dissolves to a * Ann. Chira. Phys. Ixxiii. 11.3. 382 BITTER-ALMOND OIL, considerable extent. This body is freely soluble in alkalis, from which it is again precipitated by the addition of an acid. Chlorovalerisic acid contains C 10 H 6 C1,0 3 +HO. CHLOROVALEROSIC ACID. This is the ultimate product of the action of chlorine on the preceding substance, aided by exposure to the sun. It resem- bles chlorovalerisic acid in appearance and properties, being semi-fluid and colorless, destitute of odor, of powerful pungent taste, and heavier than water. It can neither be solidified by cold, nor distilled without decomposi- tion. In contact with water, it forms a hydrate containing 3 eq. of that sub- stance, which is slightly soluble. In alcohol and ether it dissolves with fa- cility. It forms salts with bases, of which -the best defined is that of silver. Chlorovalerosic acid is composed of C, H 5 Cl 4 O 3 -4-HO. FUSEL-OIL OP 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 amyle) mixed with alcohol and water. Sometimes it con- tains in addition more or less of the ether or amyle-compounds of certain fatty acids thought to have been identified with oenanthic and margaric acids. These last-named substances form the principal part of the nearly solid fat produced in this manner in whisky distilleries conducted on the old plan. Mulder has described under the name of corn oil another constituent of the crude fusel-oil of hollands ; it has a very powerful odor resembling that of some of the umbelliferous plants, is unaffected by solution of caustic potash, and contains C 24 H 17 O.* The fusel-oil of marc-brandy of the south of France was found by M, Bal- ard to contain potato oil and oananthic 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 cotemporaneous with that of common alcohol. The substances discussed in the next three sections have but little relation to the alcohols; they may, however, be here most conveniently described. BITTER-ALMOND OIL, AND ITS PRODUCTS. The volatile oil of bitter almonds possesses a very high degree of interest, from its study having, in the hands of MM. Liebig and Wohler,^ led to the first discovery of a compound organic body capable of entering into direct combination with elementary principles, as hydrogen, chlorine, and oxygen, and playing in some degree the part of a metal. The oil is supposed to be the hydruret of a salt basyle, containing C 14 H 5 O 2 , called benzoyle, from its rela- tion to benzoic acid, which radical is to be traced throughout the whole series ; it has not yet been isolated. Table of Benzoyle-Compounds. Benzoyle, symbol Bz , C H^52 Hydruret of benzoyle; bitter-almond oil . . C 14 H 5 O 2 -f-H Oxide of benzoyle; benzoic acid . . C 14 H 5 2 -|-O Chloride of benzoyle . . . ... . C 14 H 5 O 2 +Cl Bromide of benzoyle C 14 H 5 O 2 -f- Br Iodide of benzoyle C, 4 H 5 O 2 4-I Sulphuret of benzoyle C, 4 H 5 O 2 -f-S * Ann. der Chemie und Pharmacie, xxiv. 248, xli. 53, xlv. 67 ; also Pharmaceutical Journal, ii. 601. f Annalen der Pharraacie, iii. 249. AND ITS PRODUCTS. HYDHURET OF BENZOYLE; BITTEH.-ALMOND On; BzH. This substance is prepared 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 amygdaline, aided in a very extra- ordinary manner by the presence of the pulpy albuminous matter of the seed. The crude oil has a yellow color, and contains a very considerable quantity of hydrocyanic acid, whose origin is cotemporaneous 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 distillation; water passes over, accompanied by the now purified essential oil, which is to be left for a short time in contact with a few fragments of fused chloride of calcium to free it from water. Pure hydmret of benzoyle is a thin, colorless liquid, of great refractive power, and peculiar and very agreeable odor; its density is 1.043, and its boiling-point 356: 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 solid hydrate of potash, it disengages hydrogen, and yields ben- zoate of the base. The vapor 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 imparting an agree- able flavor to puddings, custards, &c., and even publicly sold for that pur- pose, is in the highest degree dangerous. OXIDE OF BENZOYLE ; BENZOIC ACID ; BzO. This is the sole product of the oxidation at a moderate temperature of bitter-almond oil ; it is not, how- ever, thus obtained for the purposes of experiment and of pharmacy. Seve- ral of the balsams yield benzoic acid in great abundance, more especially the concrete resinous variety known under the name of gum benzoin. When this substance is exposed to a gentle heat in a subliming vessel, the benzoic acid is volatilized, and may be condensed by a suitable arrangement. The sim- plest and most efficient apparatus for this and all similar operations is the contrivance of Dr. Mohr: it consists of a shallow iron pan, over the bottom of which the substance to be sublimed is thinly spread; a sheet of bibulous paper, pierced with a number of pin- Fig- 170. holes, is then stretched over the vessel, and a cap made of thick, strong drawing or cartridge paper, secured by a string or hoop over the whole. The pan is placed upon a sand-bath and slowly heated to the requisite temperature ; the vapor of the acid condenses in the cap, and the crystals are kept by the thin paper dia- phragm from falling back again into the pan. Ben- zoic acid thus obtained assumes the form of light, feathery, colorless crystals, which exhale a fragrant odor, not belonging to the acid itself, but due to a 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 effected with trifling loss, the acid is obtained perfectly white. 384 BITTER- ALMOND OIL, Benzole acid is inodorous when cold, but acquires a faint smell when gently warmed ; it melts just below 212, and sublimes at a temperature a little above; it boils at 462, and emits a vapor of the density of 4.27. It dissolves in about 200 parts of cold, and 25 parts of boiling water, and with great facility in alcohol. Benzoic acid is not affected by ordinary nitric acid, even at a boiling heat. The crystals obtained by sublimation, or by the cool- ing of a hot aqueous solution, contain an equivalent of water, which is basic, or C 14 H 5 3 +HO. All the benzoates have a greater or less degree of solubility; they are easily formed, either directly or by double decomposition. Benzoates of the alkalis and of ammonia are very soluble, and somewhat difficult to crystallize. Benzoate of lime forms groups of small colorless needles, which require 20 parts of cold water for solution. The salts of baryta and strontia are soluble with difficulty in the cold. Neutral benzoate of the peroxide of iron is a soluble compound ; but the basic salt obtained by neutralizing as nearly as possible by ammonia a solution of peroxide of iron, and then adding benzoate of am- monia, is quite insoluble. Peroxide of iron is sometimes thus separated from other metals in practical analysis. Benzoate and sub-benzoate of lead are freely soluble in the cold. Benzoate of silver crystallizes in thin transparent plates, which blacken on exposure to light. NITROBENZOIC ACID. When benzoic acid is boiled for several hours with 4 fuming nitric acid, until red fumes cease to appear, it yields a new acid body, in which the elements of nitrous acid are substituted for an equivalent of hydrogen of the original benzoic acid. Nitrobenzoic acid greatly resembles benzoic acid in characters, and contains C, 4 H 4 N0 7 ,HO. SULPHOBENZOIC ACID. Benzoic acid is soluble without change in concen- trated oil of vitriol, and is precipitated by the addition of water ; it combines, however, with anhydrous sulphuric acid, generating a compound acid analo- gous to the sulphovinic, but bibasic, forming a neutral and an acid series of salts. The barytic compound is easily prepared by dissolving in water the viscid mass produced by the union of the two bodies, and saturating the solu- tion with carbonate of baryta. On adding hydrochloric acid to the filtered liquid, and allowing the whole to cool, acid sulphobenzoate of baryta crystal- lizes 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 dilute sul- phuric acid ; it forms a white, crystalline, deliquescent mass, very stable and permanent, which probably contains C 14 H 5 O 3 , SO 3 -j-2HO.* When dry benzoate of lime is distilled at a high temperature, it yields ben- zone, which, when pure, is a thick, oily, colorless liquid, of peculiar odor; it boils at 482, or a little above, and contains C 13 H 5 0; carbonate of lime re- mains in the retort ; the reaction is thus perfectly analogous to that by which acetone is produced by the distillation of a dry acetate. CaO , C 14 H 5 3 = C 13 H 6 and CaO , C0 2 . The benzone is, however, always accompanied by secondary products, due to the irregular and excessive temperature, as naphthaline, carbonic oxide, and benzol, a body next to be described.f BEXZOL, 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 rednes in a coated glass or earthen retort, water, and a vola- tile oily liquid, termed benzol, pass over, while carbonate of lime, mixed with * Mitscherlich, Lehrbuch, i. 108. | Peligot, Ann. Chim. et Phys. Ivi AND ITS PRODUCTS. 385 excess of hydrate of lime, remains in the retort. The benzol separated from the water, and rectified, forms a thin, limpid, colorless liquid, of strong but not very disagreeable odor, insoluble in water, but miscible with alcohol, having a density of .885, and boiling at 176 F. ; the sp. gr. of its vapor is 2.738. Cooled to 32, it solidifies to a white, crystalline mass. Benzol con- tains carbon and hydrogen only, in the proportion of 2 eq. of the former to 1 of the latter, or probably C 12 H 6 . It is produced by the resolution of the ben- zoic acid into benzol and carbonic acid, the water taking part in the reaction. C 14 H 6 4 = C 12 H 6 and C 2 4 . Benzol is identical with the bicarburet of hydrogen, several years ago dis- covered by Mr. Faraday in the curious liquid condensed during the com- pression of oil-gas, of which it forms the great bulk, being associated with an excessively volatile hydrocarbon, containing carbon and hydrogen in the ratio of the equivalents, the vapor of which required for condensation a tempera- ture of 0. It received the name elherine from its supposed connection with \alcohol and ether. A copious source of benzol has been lately shown to exist in the lightest and most volatile portions of coal-tar oil, which will be noticed in its place under the head of that substance. SULPHOBENZIDE A^D HrposuLPHOBENZic ACID. Benzol combines di- rectly with anhydrous sulphuric acid, to a thick viscid liquid, soluble in a small quantity of water, but decomposed by a larger portion, with separation of a crystalline matter, the sulphobenzide, which may be washed with water, in which it is nearly insoluble, dissolved in ether, and left to crystallize by spontaneous evaporation. It is a colorless, transparent substance, of great permanence, fusible at 212, bearing distillation without change, and resisting the action of acids and other energetic chemical agents. Sulphobenzide con- tains C 12 H 5 S0 2 . The acid liquid from which the preceding substance has been separated, neutralized by carbonate of baryta and filtered, yields hypo* sulphobenzate of baryta, which is a soluble salt, but crystallizes in an imperfect manner. By double decomposition with sulphate of copper, a compound of the oxide of that metal is obtained, which forms fine, large, regular crystals. The hydrate of hyposulphobenzic acid is prepared by decomposing the copper- salt with sulphuretted hydrogen: a sour liquid is obtained, which furnishes, by evaporation, a crystalline residue, containing C 12 H 5 S 2 O 5 -}-HO. The salts of potash, soda, ammonia, and of the oxides of zinc, iron, and silver, crystallize freely. This compound acid can be prepared by dissolving benzol in Nord- hausen sulphuric acid. NITROBENZIDE. Ordinary nitric acid, even at a boiling temperature, has no action on benzol ; the red fuming acid attacks it, with the aid of heat, with great violence. The product, on dilution, throws down a heavy, oily, yellowish, and intensely sweet liquid, which has an odor resembling that of bitter-almond oil. Its density is 1.209; it boils at 415, and distils unchanged. It is but little affected by acids, alkalis, or chlorine, and is quite insoluble in water. Nitrobenzide contains C 12 FT 5 N0 4 . When nitrobenzicle is heated with an alcoholic solution of caustic potash, and the product subjected to distilla- tion, a red compound passes over, which separates, on cooling, in large red crystals, which are nearly insoluble in water, but dissolve with facility in ether and alcohol. This substance, which is called azobenzide, melts at 149, and boils at 379; it contains C 12 H 5 N.* Benzol and chlorine combine when exposed to the rays of the sun ; the product is a solid, crystalline, fusible substance, insoluble in water, containing * Mitscherlich, Lehrhuch. i. 100. 33 386 BITTER-ALMOND OIL, C 12 H 6 C1 6 , called chlorbenzine. When this substance is distilled, it is decom- posed into hydrochloric acid, and a volatile liquid, chlorbenzide, composed of C 12 H 3 CI 3 . CHLORTDE OF BENZOYLE, BzCl. This compound is prepared by passing dry chlorine gas through pure bitter-almond oil, as long as hydrochloric acid continues to be formed; the excess of chlorine is then expelled by heat. Chloride of benzoyle is a colorless liquid, of peculiar, disagreeable and pun- gent odor. Its density is 1.106. The vapor is inflammable, and burns with a tint of green. It is decomposed slowly by cold, arid quickly by boiling water, into benzoic and hydrochloric acids; with an alkaline hydrate, ben- zoate of the base, and chloride of the metal, are generated. If, in the pre- paration of chloride of benzoyle, the chlorine contain vapor of water, a pe- culiar crystalline substance is produced, containing C 42 H, 8 O g , which seems to be a compound of hydrated benzoic acid and bitter almond oil. When pure chloride of benzoyle and dry arnmoniacal gas are presented to each other, the ammonia is energetically absorbed, and a white, solid sub- stance produced, which is a mixture of sal-ammoniac and a highly interest- ing body, benzamide. The sal ammoniac is removed by washing with cold water, and the benzamide dissolved in boiling water, and left to crystallize. It forms colorless, transparent, prismatic, or platy crystals, fusible at 239, arid volatilizable at a higher temperature. It is but slightly soluble in cold, freely in boiling water, also in alcohol and ether. Benzamide corresponds to oxa- mide, both in composition and properties; it contains C, 4 H 7 NO 2 , or benzoate of oxide of ammonium, minus 2 eq. of water, and it sutlers decomposition by both acid and alkaline solutions, yielding, in the first case, a salt of ammonia, and benzoin acid, and, in the second, free ammonia and a benzoate. IODIDE OF BENZOYLE, Bzl. This is prepared by distilling the chloride of benzoyle with iodide of potassium ; it forms a colorless, crystalline, fusible mass, decomposed by water and alkalis, in the same manner as the chloride. The bromide of benzoyle, BzBr, has very similar properties. The sulpfiuret, BzS, is a yellow oil, of offensive smell, which solidifies, at a low tempera- ture, to a soft, crystalline mass. Cyanide of benzoyle, Bz,C 2 N, obtained by heating the chloride with cyanide of mercury, forms a colorless, oily, inflam- mable liquid, of pungent odor, somewhat resembling that of cinnamon. All these compounds yield benzamide with dry ammonia. MANDELIC ACID. Crude bitter almond oil is dissolved in water, mixed with hydrochloric acid, and evaporated to dryness : the residue is boiled with ether, which dissolves out the new substance, and leaves sal ammoniac. Mandelic acid forms small, indistinct, white crystals, which fuse, arid after- wards suffer decomposition by heat, evolving an odor resembling that of the flowers of the hawthorn, and leaving a bulky residue of charcoal. It is freely soluble in water, alcohol, and ether, has a strong acid taste and reac- tion, and forms a series of crystallizable salts with metallic oxides. This substance contains C J6 H 7 O 5 -f-HO, or the elements of bitter-almond oil, and formic acid: it owes its origin to the peculiar action of strong mineral acids on the hydrocyanic acid of the crude oil, by which that body suffers resolu- tion into formic acid and ammonia. It is decomposed by oxidizing bodies, as peroxide of manganese, nitric acid, and chlorine, into bitter-almond oil and carbonic acid. This substance is sometimes called formobenzoic add. HYDUOBENZAMIDE. Pure bitter-almond oil is digested for some hours at about 120 with a large quantity of strong solution of ammonia; the result- ing white crystalline product is washed with cold ether, and dissolved in al- cohol ; the solution, left to evaporate spontaneously, deposits the hydrobenza- mide in regular, colorless crystals, which have neither taste nor smell. This substance melts at a little above 212, is readily decomposed by heat, dis- AND ITS PRODUCTS. 387 solves with ease in alcohol, but is insoluble in water ; the alcoholic solution is resolved by boiling into ammonia and bitter almond oil ; a similar change happens with hydrochloric acid. Hydrobenzamide contains C 42 H 18 N 2 , or the elements of 3 equivalents of bitter-almond oil, and 2 of ammonia, minus 6 equivalents of water. When impure bitter-almond oil is employed in this experiment, the pro- ducts are different, three other compounds being obtained, called by M. Lau- rent benzhydramide, azobenzoyle, and nitrobenzoyle. The first is isomeric with hydrobenzamide, but differs in properties. BENZOIXE. This substance is found in the residue contained in the retort from which bitter almond oil has been distilled with lime and oxide of iron, to free it from hydrocyanic acid ; it is a product of the action of alkalis and alkaline earths on the crude oil, and is said to be only generated in the pre- sence of that remarkable acid. It is easily extracted from the pasty mass by dissolving out the lime and oxide of iron by hydrochloric acid, arid boiling the residue in alcohol. Benzoine forms colorless, transparent, brilliant pris- matic crystals, tasteless and inodorous 5 it melts at 248, and distils without decomposition. Water, even at a boiling heat, dissolves but a small quantity of this body; boiling alcohol takes it up in larger proportion ; it dissolves in cold oil of vitriol, with violet color. The vapor, transmitted through a red- hot tube, yields an oily liquid, changeable by exposure to air to benzoic acid, and which is, probably, bitter almond oil. is, consequently, an isomeric modification of bitter almond oil. BENZFLE. This curious compound is a product of the action of chlorine on benzoine ; the gas is conducted into the fused benzoine as long as hydro- chloric acid continues to be formed, and the crystalline residue purified by solution in alcohol. It forms large, transparent, sulphur-yellow crystals, fusi- ble at 20U, unaltered by distillation, and quite insoluble in water. It dis- solves freely in alcohol, ether, and concentrated sulphuric acid, from which it is precipitated by water. Benzile is composed of C 14 H 5 2 , and is therefore isomeric with the radical of the benzoyle series* BENZILIC ACID. Benzoine and benzile dissolve with violet tint in an alco- holic solution of caustic potash ; by long boiling the liquid becomes colorless, 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, colorless, trans- parent crystals, slightly soluble in cold, more readily in boiling water ; it melts at 248, and cannot be distilled without decomposition. It dissolves in cold concentrated sulphuric acid with a fine carmine-red color. Benzilic acid contains C 28 H n O 5 -j-HO, or 2 eq. benzile and 1 eq. water. BENZONITRIL. When benzoate of ammonia is exposed to destructive dis- tillation, among other products a yellowish volatile oil makes its appearance, having exactly the odor of bitter almond-oil. It is heavier than water, slightly soluble in that liquid, boils at 376, and contains C, 4 H 5 N. It is iso- meric with Laurent's nitrobenzoyle. Benzoate of copper by dry distillation cautiously conducted gave a residue containing salicylic and benzoic acids, and an oily distilled product which crystallized on cooling. The substance possessed the odor of the geranium, melted below 212, and contained C, 4 H 5 2 , being isomeric with benzile and the hypothetical benzoyle. By heating with hydrate of potash it was in- stantly converted into benzoic acid with disengagement of hydrogen. BENZIMIDE. This is a white, inodorous, shining, crystalline substance * Laurent, Ann. Chira. et Phys. lix. 397; also Liebig, in Geiger's Pharmacia, i. 888 SALICYLE AND ITS COMPOUNDS. 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 color, becoming green by the addition of a little water. This reaction is characteristic. Benzimide contains C 28 H ]] NO 4 . A great number of other compounds derived from bitter-almond oil, di- rectly or indirectly, have been described by M. Laurent and others. Many of these contain sulphur, sulphuretted hydrogen and sulphuret of ammonium being employed in their preparation. HIPPUBIC ACID. This interesting substance is in some measure related to the benzoyle-compounds. It occurs, often in large quantity, in combination with potash or soda, in the urine of horses, cows, and other graminivorous animals. It is best 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. 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 color, and begins to exhale the odor of that substance ; it is then filtered, and left to cool. The still impure acid is icdissolved in water, neutralized with car- bonate of soda, and boiled for a short time with animal charcoal; the hot filtered solution is, lastly, decomposed by hydrochloric acid. Hippuric acid in a pure state crystallizes in long, slender, milk-white, and exceedingly frangible square prisms, which have a slight bitter taste, fuse on the application of heat, and require for solution about 400 parts of cold water; it also dissolves in hot alcohol. It has an acid reaction, and forms salts with bases, many of which are crystallizable. Exposed to a high temperature, hippuric acid undergoes decomposition, yielding benzoic acid, benzoate of ammonia, and a fragrant oily matter, with a coaly residue. With hot oil of vitriol, it gives off benzoic acid ; boiling hydrochloric acid converts it into benzoic acid and gelatinejswgar. Hippuric acid contains Cj 8 H 8 NO 5 -j-HO. If, in the preparation of this substance, 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 secre- tion. Complete putrefaction effects the same change; benzoic acid might be thus procured to almost any extent. When benzoic acid is taken internally, it is rejected from the system in the state of hippuric acid, which is then found in the urine. SALICYLE, AND ITS COMPOUNDS. SALICINE. The leaves and young bark of the poplar, willow, and several other trees contain a peculiar crystallizable, bitter principle, called salicine, which in some respects resembles the vegeto-alkalis cinchona and quina, having febrifuge properties. It differs essentially, however, from these bo- dies in being destitute of nitrogen, and in not forming salts with acids. Sali- cine may be prepared by exhausting the bark with boiling water, concentrat- ing the solution to a small bulk, digesting the liquid with powdered oxide of lead, and then, after freeing the solution from lead by a stream of sulphuret- ted hydrogen gas, evaporating uptil the salicine crystallizes out on cooling. It is purified by treatment with animal charcoal and recrystallization. Salicine forms small, white, silky needles, of intensely bitter taste, which have no alkaline reaction. It melts arid decomposes by heat, burning with a bright flame, and leaving a residue of charcoal. It is soluble in 5.G parts of cold water, and in a much smaller quantity when boiling hot. Oil of vitriol SALICYLE AND ITS COMPOUNDS. 389 colors it deep red. The last experiments of M. Piria give for salicine the formula C 26 H 18 O 14 . When salicine is distilled with a mixture of bichromate of potash and sul- phuric acid, it yields, among other products, a yellow, sweet-scented oil, which is found to be identical ivith the volatile oil distilled from the flowers of the Spircea ulmuria, or common meadow-sweet. This substance appears to be the hydruretof a compound salt radical, salicyle, containing C 14 H 5 O 4 ; it has the properties of a hycjrogen acid.* Table of Salicyle-compounds. Salicyle (symb. Si) C i 4 H 5 4 Hyclrosalicylic acid C 14 H 5 4 -4-H Salicyluret of potassium .... C 14 H.O 4 -|-K Iodide of salicyle C 14 H 5 O 4 -fI Bromide of salicyle C 14 H 5 4 -f-Br Salicylic acid C M H 5 O 4 -[-0 HTDROSALICYLIC ACID; ARTIFICIAL OIL- OF MEADOW-SWEET, SlH. One part of salicine is dissolved in 10 of water, and mixed in a retort with 1 part of powdered bichromate of potash, and 2^ parts of oil of vitriol di- luted with 10 parts of water; gentle heat is applied, and after the cessation of the effervesence first produced, the mixture is distilled. The yellow oily product is separated from the water, and purified by rectification from chlo- ride of calcium. It is thin, colorless, and transparent, but acquires a red tint by exposure to the air. Water dissolves a sensible quantity of this sub- stance, acquiring the fragrant odor of the oil, and the characteristic property of striking a deep violet color with a salt of peroxide of iron, a property how- ever 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 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 analy- sis it is found to contain C H H 6 O 4 , or the same elements as crystallized ben- zoic acid ; and the density of its vapor is also the same, being 4.276. SALICTLURET OF POTASSIUM, KSl. This compound is easily prepared by mixing the oil with a strong solution of caustic potash; it separates, on agi- tation, as a yellow crystalline mass, which may be pressed between folds of blotting paper, and recrystallized 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, insoluble in water, but dissolved by spirit and by solution of alkali, called melanic acid. Acetate of potash is formed at the same time. Melanic acid contains C 10 H 4 O 5 . The crystals of salicyluret of potassium contain water which can- not be expelled without partial decomposition of the salt. SALICTLURET OF AMMONIUM, NH 4 ,S1, crystallizes in yellow needles which are quickly destroyed with production of ammonia and the hydruret. Sail- cyluret of barium, Btt,C 14 H 5 O 4 -|-2HO, forms fine yellow acicular crystals, which are but slightly soluble in the cold. Salicyluret. of copper is a green insoluble powder, containing Cu,C, 4 H 5 4 . Salicyluret of copper by destructive distillation gives, among other pro- ducts, hydruret of salicyle arid a solid body forming colorless prismatic crys- * Piria, Ann. Chim. et Phys. Ixix. 281. 33* 390 SALICYLE AND ITS COMPOUNDS. tals, fusible and volatile. It is insoluble in water, dissolved by alcohol and ether, and is unaffected by fusion with hydrate of potash. Nitric acid con- verts it into picric and anilic acids. It contains C 14 H 5 O 3 , and is isomeric with absolute benzoic acid. SALICYLIC ACID, S10. The oxygen compound is obtained by heating hy- druret of salicyle with excess of solid hydrate of potash : the mixture is at first brown, but afterwards becomes colorless; hydrogen gas is disengaged during the reaction. On dissolving the melted mass in water, and adding a slight excess of hydrochloric acid, the salicylic acid separates in crystals, which are purified by re-solution in hot water. This substance very much resembles benzoic acid ; it is very feebly soluble in cold water, is dissolved in large quantities by alcohol and ether, and may be sublimed with the ut- most ease. It is charred and decomposed by hot oil of vitriol, and attacked with great violence by strong, heated nitric acid. Salicylic acid contains C 14 H 6 B +HO. Salicylic acid can also be prepared with great ease by fusing salicine with excess of hydrate of potash, and also by the action of a concentrated and hot solution of potash upon the volatile oil of Gaultheria procumbens. When sali- cylic acid is mixed with powdered glass or sand and exposed to strong and sudden heat in a retort, it is almost entirely converted into carbonic acid and hydrate of phenyle, and the same change happens to many of its salts with even greater facility. CHLORIDE OF .SALICYLE, SlCl. Chlorine acts very strongly upon the hy- druret of salicyle; the liquid becomes heated and disengages large quantities of hydrochloric acid. The product is a slightly yellowish crystalline mass, which, when dissolved in hot alcohol, yields colorless tabular crystals of pure chloride, having a pearly lustre. Chloride of salicyle is insoluble in water; it dissolves freely in alcohol, ether, and solutions of the fixed alkalis; from the latter it is precipitated unaltered by the addition of an acid, differing much in this respect from chloride of benzoyle. It is not even decomposed by long ebullition with a concentrated solution of caustic potash. Heated in a retort, it melts and volatilizes, condensing in the cool part of the vessel in long, snow- white needles. The odor of this substance is peculiar and by no means agreeable, and its taste is hot and pungent. Chloride of salicyle combines directly with metallic oxides ; with potash it forms small red crystalline scales, very soluble in water. The corresponding compound of baryta, prepared from the foregoing by double decomposition, is an insoluble crystalline, yellow powder, containing C 14 H 5 O 4 ,Cl-}-BaO. BROMIDE OF SALICYLE, SlBr. The bromide is prepared by the direct action of bromine on the hydruret of salicyle ; it crystallizes in small colorless needles, and very closely resembles in properties the chloride. The hydruret of salicyle dissolves a large quantity of iodine, acquiring thereby a brown color, but forming no combination ; the iodide may, however, be procured by distilling iodide of potassium with chloride of salicyle. It sublimes as a blackish-brown fusible mass. CHLOHOSAMIDE. The action of dry ammoniacal gas on pure chloride of salicyle 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 de- tected. 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 chloride of salicyle; with an alkali, on the other hand, it gives free ammonia, while chloride of salicyle remains dis- CINNAMYLE AND ITS COMPOUNDS. 391 solved. Chlorosamide contains C 42 H 15 N 2 O 6 C1 3 ; it is formed by the addition of 2 eq. of ammonia to 3 eq. of chloride of salicyle, and the subsequent se- paration of 6 eq. of water. A corresponding and very similar substance, bromosamide, is formed by the action of ammonia on the bromide of salicyle. SALIGENINE. This curious substance is a product of the decomposition of salicine 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 salicine is resolved into saligenine and grape sugar. Saligenine forms colorless, nacreous scales, freely soluble in water, alcohol, and ether. It melts at 180, and decomposes at a higher temperature. Dilute acids at a boiling heat con- vert it into a resinous-looking substance of doubtful composition, called sail- reline. Many oxidizing agents, as chromic acid and oxide of silver, convert this substance into hydruret of salicyle: even platinum-black produces this effect. Its aqueous solution gives a deep indigo blue color with persalts of iron. Saligenine contains C, 4 H g O 4 . Salicine yields with chlorine substitution-compounds containing that ele- ment, which are susceptible of decomposition by synaptase, with production of bodies termed chloro- and bichlorosaligenine. Chlorosaligenine very closely resembles normal saligenine, and contains C 14 H 7 C1O 4 . Certain products called by M. Piria helicine, helicoidine, and anilotic acid are described to result from the action of dilute nitric acid upon salicine. With strong acid at a high temperature nitrosalicylic acid is produced.* PHLORIDZINE. This is a substance bearing a great likeness to salicine, found in the root-rind of the apple and cherry-tree, and extracted by boiling alcohol. It forms fine, colorless, silky needles, soluble in 1000 parts of cold water, but freely dissolved by that liquid when hot; it is also soluble without difficulty in alcohol. It contains C 32 H 2 ,0 18 . Dilute acids convert phloridzine into grape-sugar and a crystallizable sweet substance called phloretine. COUMARINE. The odoriferous principle of the tonka-bean. It may be often seen forming minute colorless 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 off the greater part of the spirit. The syrupy residue deposits on standing crystals of coumarine, which must be purified by pressure from a fat oil which abounds in the beans, and then crystallized from hot water. So obtained, coumarine forms slender, brilliant, colorless needles, fusible at 122, and distilling without de- composition at a higher temperature. It has a fragrant odor and burning taste ; it is very slightly soluble in cold water, more 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 concen- trated solution of potash into coumaric, and eventually into salicylic acid. Coumarine exists in several other plants, as the Melilotus qffidnalis, the Aspe- rula odorata, and the jlnthoxanthum odoratum. According to M. Bleibtreu, it contains C 18 H 6 O 4 .t CINNAMYLE, 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 tin- narnic, which resembles in the closest manner benzoic acid. The supposed radical bears the name of cinnamyle it has not been isolated. * Ann. Chim. et Phys. 3d series, xiv. 257. f Memoirs of Chem. Society, iii. 205. 392 C1NNAMYLE AND ITS COMPOUNDS. Table of Cinnamyle-compounds. Cinnamyle, symbol Ci C lg H 7 2 Hydruret of cinnarnyle ; oil of cinnamon . C 18 H 7 2 -4-H Oxide of cinnamyle ; cinnamic acid . . C lg H 7 O 2 -f-0 Chloride of cinnamyle C 18 H 7 8 4-Cl. HTDRUIIET or CINIJ AMTLE ; OIL OF CINNAMOX ; CiH. Cinnamon of ex- cellent quality is crushed, infused twelve hours in a saturated solution of common salt, and then the whole subjected to rapid distillation. Water parses over, milky from essential oil, which after a time separates. It is col- lected 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 solubility 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, C 18 H 8 2 . CINN-AMIC ACID, CiO. When pure oil of cinnamon is exposed to the air, or inclosed in a jar of oxygen, it is quickly converted by absorption of the 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 in- timately 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 redissolved 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 hy- drochloric acid being added, the whole is allowed to cool; the pure cinnamic acid separates in small plates or needle formed crystals of perfect whiteness. From the original mother-liquor much benzoic acid can be procured. The crystals of cinnamic acid are smaller and less distinct than those of benzoic acid, which in most respects it very closely resembles. It melts at 248, and enters into ebullition and distils without change at 560; the vapor is pungent and irritating. Cinnamic acid is much less soluble, both in hot and cold water, than benzoic ; a hot saturated solution becomes on cooling a soft- solid mass of small nacreous crystals. It dissolves with perfect ease in alco- hol. Boiling nitric acid decomposes cinnamic acid with great energy, and with production of copious red fumes; a small quantity of a volatile oily liquid, having the odor of bitter almond oil, distils over, and a little 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 potash and oil of vitriol, it is almost instantly converted into benzoic acid, which afterwards distils over with the vapor of water; the odor of bitter almond oil is at the same time very perceptible. The action of chlorine is different; no benzoic acid is formed, but other products, which have been yet imperfectly studied. Cinnamic acid forms with bases a variety of salts which are very similar the benzoates. The crystallized acid contains C 18 H 7 3 -4-HO. CHLOROCIJTNOSE. 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, colorless needles, fusible, and susceptible of volatili- zation without change. It is not affected by boiling oil of vitriol, and may be distilled without decomposition in a current of amrnoniacal gas. Chlorocin- CINNAMYLE AND ITS COMPOUNDS. 393 nose contains C 18 H 4 Cl 4 2 ; it is formed by the substitution in the oil of cinna- mon of 4 eq. of chlorine for 4 eq. of hydrogen. The true chloride of cinna- myle, Ci Cl, seems to be first formed in considerable quantity, and subsequently decomposed by the continued action of the chlorine; it has not been sepa- rated in a pure state : it appears as a very thin, fluid oil, convertible into a crystalline mass by strong solution of potash. When cinnamon oil is treated with hot nitric acid, it undergoes decomposi- tion, being converted into hydruret of benzoyle and benzoic acid. With a boiling solution of chloride of lime the same thing happens, a benzoate of the base being generated. If the oil be heated with solution of caustic potash it remains unaffected ; with the solid hydrate, however, it disengages pure hydrogen, and forms a potash-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 un- equal value, viz., that of China, and that of Ceylon ; the former being con- sidered the best; both are, however, evidently impure. The pure oil maybe extracted from them by an addition of cold, strong nitric acid ; the crystalline matter which forms after the lapse of a few hours, separated and decomposed by water, yields pure hydruret of cinnamyle.* There can be no doubt that the cinnamic acid in Tolu and Peru balsams is gradually formed by the oxidation of an oily matter very closely related to the volatile oil of cinnamon. When these balsams are first imported they are nearly fluid, but gradually acquire consistence by keeping. M. Fremy suc- ceeded in separating from these substances, by the aid of an alcoholic solution of potash, an oil, which could not be distilled without partial decomposition, and which by the action of hydrate of potash became in great part converted into cinnamic acid. This substance, called by Fremy cinnameine, cannot be looked upon as a pure hydruret of cinnamyle, although it probably contains the latter; its composition is very uncertain. Cinnameine, artificially cooled, was sometimes found to deposit a solid crystalline substance, which had ex- actly the composition of pure oil of cinnamon, C 18 H 8 O 2 , and Was converted by caustic potash into cinnamic acid : it received the name of met acinnameine.'} * MM. Dumas and Peligot, Ann. Chim. et Phys. Ivii. 305. f Fremy, Ann Chim. et Phys. Ux 196. 394 VEGETABLE ACIDS. SECTION III. VEGETABLE ACIDS. THE vegetable acids constitute a very natural and important family or group of compounds, many of which enjoy 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 combination 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 in connection with their respective sources. Table of Vegetable Adds. Tartaricacid ... . . . C 8 H 4 10 +2HO Racemicacid ' . . ... C 8 H 4 O 10 -(-2HO Citric acid . . . v. . : ' . . C 12 H 5 O n +3HO Aeon itic, or equise tic acid . ''. ; . .- C 4 U O 3 -j-HO Malic acid . . ; - : r i : . \ . C 8 H 4 O 8 -}-2HO Fumaric acid .' . \,,V. . -^ > . < C 4 H O 3 -|-HO Tannicacid . . V' ' . ' : . . C lg H 5 O 9 -f-3HO. Gallic acid ., . , , ~,\ ,..,,._ C 7 H O 3 +2HO. TAHTAIUC 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 acid potash 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 potash, 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 coloring matter of the wine, and sub- sequent crystallization; it then constitutes cream of tartar, and serves for the preparation of the acid. The salt is dissolved in boiling water, and pow- dered chalk added as long as effervescence is excited, or the liquid exhibits an acid reaction ; tartrate of lime and neutral tartrate of potash result ; the latter is separated from the former, which is insoluble, by filtration. The solution of tartrate of potash 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 withdraw the base and liberate VEGETABLE ACIDS. 395 the organic acid. The filtered solution is cautiously evaporated to a syrupy consistence and placed to crystallize in a warm situation. Tartaric acid forms colorless, 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 red- dens litmus strongly, and lias a pure, clean, acid taste. The aqueous solution is gradually spoiled by keeping. Tartaric acid is bibasic; the crystals con- tain C g H 4 O 10 -[-2HO. This substance is consumed in large quantities by the calico-printer, being employed to evolve chlorine from solution of bleaching- powder in the production of white or discharged patterns upon a colored ground. TARTRATES op POTASH. NEUTRAL TARTRATE ; SOLUBLE TARTAR; 2KO,C 8 H 4 O 10 . 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 potash 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 POTASH; CREAM OF TARTAR; KO,HO,C S H 4 10 . The origin and mode of preparation of this substance have been already de- scribed. It forms small transparent or translucent prismatic crystals, irregu- larly 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 g ' th 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 potash, 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 potash- salt, and the whole agitated. TARTRATES OF SODA. Two compounds of tartaric acid with soda are known: a neutral salt, 2NnO,C 8 H 4 O ]0 4-4HO; and an acid salt, NaO,HO,C g H 4 O ]0 -J-2HO. Both are easily soluble in water, and crystallize. Tartaric acid and bicarbonate of soda form the ordinary effervescing draughts. TARTHATE OF POTASH AND SODA; ROCHELLE OR SEIGNETTE SALT; KO,NaO,C 8 H 4 10 -4-lOHO. This beautiful salt is made by neutralizing with carbonate of soda a hot solution of crearn of tartar, and evaporating to the consistence of thin syrup. It separates in large, transparent, prismatic crys- tals, 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. Rocbelle salt has a mild, saline taste, and is used as a purgative. TARTRATES OF AMMONIA. The neutral tartrate is a soluble and efflores- cent salt, containing 2NH 4 O,C 8 H 4 O 10 4-2HO. The acid tartrate, NH 4 O,HO, C 8 H 4 O 10 , closely resembles ordinary cream of tartar. A salt corresponding to Rochelle salt also exists, having oxide of ammonium 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 POTASH AND PEROXIDE OF IRON. Fe ? O 3 ,KO,C ? H 4 O 10 . This is obtained by dissolving h yd rated peroxide of iron in a boiling solution of cream of tartar. It does not crystallize, but exists as a dark-colored mass, or in garnet-red translucent scales, of a sweetish astringent taste, soluble in 4 parts of water, scarcely soluble in alcohol. The iron exists in this compound in such a condition that it is not precipitated by potash, soda, ammonia in the cold, or by ferrocyanide of potassium, unless an acid be previously added. It is decomposed by heat of 26(P, and at a red heat the iron is revived. R. B. 396 VEGETABLE ACIDS. Tartrate of antimony and potash, or tartar-emetic, is easily made by boiling oxide of antimony in solution of cream of tartar ; it is deposited from a hot and concentrated solution in crystals derived from an octahedron with rhom- bic base, which dissolve without decomposition in 15 parts of cold, and 3 of boiling water, and have an acrid and extremely disagreeable metallic taste. The solution is incompatible with, and decomposed by, both acids and alkalis; the former throw down a mixture of cream of tartar and oxide of antimony, and the latter, the oxide, which is again dissolved by great excess of the re- agent. Sulphuretted hydrogen separates all the antimony in the state of sulphuret. Heated in a dry state on charcoal before the blowpipe, it yields a globule of metallic antimony. The crystals contain KO,Sb0 3 ,C 8 H 4 10 -f- 2HO.* An analogous compound containing arsenious acid (As0 3 ) in place of oxide of antimony has been described. Ii has the same crystalline form as tartar emetic. A solution of tartaric acid dissolves hydrated peroxide 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 precipitated by alkalis, fixed or volatile. Indeed, tartaric acid added in sufficient quantity to a solution of peroxide-salt of iron or alumina, entirely prevents the pre- cipitation of the bases by excess of ammonia. Tartrate and ammoniacal tartrate of iron are used in medicine, these compounds having a less disa- greeable 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 solutions of potash salts has been already noticed. ACTION OF HEAT oir TAHTARIC ACID. When crystallized tartaric acid is exposed to a temperature of 400 or thereabouts, it melts, loses water, and passes through three different modifications, called in succession tartralic, tar- trelic. and anhydrous tartaric acid. The two first are soluble in water, and form salts, which have properties completely different from those of ordinary tartaric acid. The third substance, or anhydrous acid, is a white insoluble powder. All three, in contact with water, slowly pass into common tartaric acid. Their composition is thus expressed : Ordinary tartaric acid C 8 H 4 O 10 -|-2HO Tartralic acid 2C 8 H 4 0, -j-3HO Tartrelic acid . . . . . ."' C 8 H 4 O, -j-HO Anhydrous tartaric acid . . . C 8 H 4 10 . The analogy borne by these bodies to the several modifications of phos- phoric acid will be at once evident.^ PTROTARTARIC 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 * According to Dumas, KO,Sbp ? ,C 8 H 4 O lo: f HO. Dried at 212, an equivalent of water is lost, and at 428 two additional equivalents, leaving the compound KO,SbO 3 CaH 3 O 8 , -which can no longer contain ordinary tartaric acid. Ann. Chim. et Phys. 3d series, v. 353. f Fremy, Ann. Chim. et Phys. Ixviii. 353. VEGETABLE ACIDS. 397 semi-fluid black mass, which, by further heating, gives combustible gases, an empyreumatic oil, and a residue of charcoal. The distilled product exhales a powerful odor of acetic acid, and is with great difficulty purified. Pyro- tartaric acid forms a series of salts, and an ether; it is supposed to contain CgH^Og-f-HO. A second pyro-acid sometimes separates in crystals from the preceding compound, and may be obtained in larger quantity by the destruc- tive distillation of cream of tartar; it is composed of C 5 H 3 5 -f-HO. When tartaric acid is heated to 400 F. with excess of hydrate of potash, it is resolved without charring or secondary decomposition into oxalic and acetic acids, which remain in union with the base, and only undergo decom- position at a much higher temperature. RACEMIC ACID ; PARATAKTAIUC 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 add is given; it is rather less soluble than tartaric acid, and separates first from the solution of that substance. Between these two acids, however, the greatest possible resemblance exists ; they have exactly the same composition, and yield, when exposed to heat, the same products ; the salts of racemic acid correspond also, 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. CITRIC ACID. Citric acid is obtained in large quantity from the juice of limes and lemons; it is found in many other fruits, as in gooseberries, cur- rants, &c., in conjunction with another acid, the malic. In the preparation of this acid, the juice is allowed to ferment a short time, in order that muci- lage and other impurities may separate and subside ; the clear liquor is then carefully saturated with chalk, which forms, with the citric acid, an insoluble compound. This is thoroughly washed, decomposed by the proper quantity of sulphuric acid, diluted with water, and the filtered solution evaporated to a small bulk, and left to crystallize. The product is drained from the mother- liquor, redissolved, digested with animal charcoal, and again concentrated to the crystallizing point. Citric acid forms colorless, prismatic crystals, which have a pure and agreeable acid taste ; they dissolve, with great ease, in both hot and cold water ;' the solution strongly reddens litmus, and, when long kept, is subject to spontaneous change. Citric acid is tribasic; its formula in the gently-dried and anhydrous silver- salt is C, 2 rJ 5 O|j. 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 C, 2 H 5 O n ,3HO -J-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 potash, 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 * The easy resolution of tartaric and citric acids into a mixture of oxalic and acetic acids by the action of heat, aided by the presence of a powerful base, has led to the idea of the possible pre-existence of these last-named bodies in the two vegetable acids, which may thus be compounded of two acids of simpler constitution, forming coupled or conjugate acids, of which several have been supposed to exist. These views, although sometimes useful, are not at present supported by evidence of great importance. 34 398 VEGETABLE ACIDS. oxide, 2 eq. of oxide and 1 eq. of basic water, and 1 eq. oxide and 2 eq. basic water, besides true sub salts, in which the water of crystallization is perhaps replaced by a metallic oxide. The citrates of the alkalis are soluble and crystallizable with greater or less facility; those of baryta, strontia, lime, lead, and silver are insoluble. Citric acid resembles tartaric acid in its relations to peroxide of iron ; it prevents the precipitation of that substance by excess of ammonia. The citrate, obtained by dissolving the hydrated oxide in solution of citric acid, dries up to a pale brown, transparent, amorphous mass, which is not very soluble in water; an addition of ammonia increases the solubility. Citrate and ammonia-citrate of iron are elegant medicinal preparations. Very little is known respecting the composition of these curious compounds; the absence of crystallization is a great bar to inquiry. Citric acid is sometimes adulterated with tartaric ; the fraud is easily de- tected by dissolving the acid in a little cold water, and adding to the solution a small quantity of acetate of potash. If tartaric acid be present, a white, crystalline precipitate of cream of tartar will be produced on agitation. ACONITIC, OR EQ.UISETIC ACID. When crystallized citric acid is heated in a retort until it begins to become colored, 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 Jlconitum napellus and the Equisetum fluviatile. Aconitic acid forms a white, confusedly-crystalline mass, permanent in the air, and very soluble in water, alcohol, and ether ; the solution has an acid and astringent taste. The salts of aconitic acid possess but little interest ; that of baryta forms an insoluble gelatinous mass; aconitate of lime, which has a certain degree of solubility, is found abundantly in the expressed juice of the monkshood, and aconitate of magnesia in that of the equisetum. Hydrated aconitic acid contains C 4 HO 3 -|-HO; it is formed in the artificial process above described, by the breaking up of 1 eq. of hydrated citric acid, C 12 H 8 O 141 into 5 eq. of water and 3 eq. of aconitic acid. MALIC ACID. This is the acid of apples, pears, and various other fruits; it is often associated, as already observed, with citric acid. The best process for preparing the acid in question is that of Mr. Everitt, who has demon- strated its existence, in great quantity, in the juice of the common garden rhubarb ; it is accompanied by acid oxalate of potash. The rhubarb stalks are peeled, and ground or grated to pulp, which is subjected to pressure. The juice is heated to the boiling-point, neutralized with carbonate of potash, and mixed with acetate of lime ; insoluble oxalate of lime falls, which is removed by filtration. To the clear and nearly colorless 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 decom- posed by sulphuretted hydrogen.* The filtered liquid is carefully evaporated to the consistence of a 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. Malic acid is colorless, slightly deliquescent, and very soluble in water ; alcohol also dissolves it. The aqueous solution has an agreeable acid taste ; it becomes mouldy, and spoils by keeping. The acid is bibasic, its formula being C g H 4 O 8 -{-2HO ; it forms a variety of salts, some of which are neutral, others acid. The most characteristic of these are the add malate of ammonia, * If the acid be required pure, crystallized malate of lead must be used, the freshly precipitated salt invariably carrying down a quantity of lime, which cannot be re- moved by simple washing. VEGETABLE ACIDS. 399 NH 4 0,HO,C 8 H 4 8 , 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 of any kind, and separates, on cooling, in brilliant, silvery crystals, which contain water. The acid may, by this feature, be distin- guished. The add malate of lime, CaO,HO,C 8 H 4 O 8 -|-6HO, i s also a very beautiful salt, of free solubility 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. FTJMAHIC 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 recipient. 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 substance, having a smaller degree of solubility, is left behind ; it is called fumaric acid from its identity with an acid extracted from the common fumitory. Fumaric acid forms small, white, crystalline laminae, which dissolve freely in hot water and alcohol, but require for that purpose about 200 parts of cold water; it is unchanged by hot nitric acid. When heated in a current of air it sublimes, but in a retort undergoes decomposition. This is a phenomenon often observed in organic bodies of small volatility. Fumaric acid forms salts, which have been recently examined by M. Rieckher, and an ether, which, by the action of ammonia, yields a white, amorphous, insoluble powder, called fumaride, which corresponds in properties and constitution with oxamide. Hydrated fumaric acid cont^fcs C 4 H0 3 -|-HO; hence it is isomeric with aco- nitic acid. The volatile acid produced simultaneously with the fumaric acid is called maleic acid ; it may be obtained in crystals by evaporation in a warm place. It is very soluble in water, alcohol, and ether; it has a strong acid taste and reaction, and is (Convertible by heat into fumaric acid. Hydrated maleic acid contains C 8 H 2 6 -|-2HO. Maleic and fumaric acids are thus seen to have precisely the same composition ; they are formed by the separation of 2 eq. of water from hydrated malic acid. TANNIC AND GALLIC ACIDS. These are substances in which the acid cha- racter is much less strongly marked than in the preceding bodies; they consti- tute the astringent principles of plants, and are widely diffused, in one form or other, through the vegetable kingdom. It is possible that there may be several distinct modifications of tannic acid, which differ among themselves in some particulars. The astringent principle of oak-bark and nut galls, for example, is found to precipitate per-salts of iron bluish-black, while that from the leaves of the sumach and tea-plant, as well as infusions of the substances known in commerce under the names of kino and catechu, are remarkable for giving, under similar circumstances, precipitates which have a tint of green. The color of a precipitate is, however, too much influenced by external causes to be relied upon as a proof of essential difference. Unfortunately, the tannic acid or acids refuse to crystallize; one most valuable test of individuality is therefore lost. After the reaction with per-salt of iron, the most characteristic 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 gelatine, solid muscular fibre and skin, &c., which then acquire the property of resisting putrefaction; it is on this principle that leather is manufactured. Gallic acid, on the contrary, is useless in the operation of tanning. 400 VEGETABLE ACIDS. Tannic Add of the Oak. This substance may be prepared from nut-galls, which are excrescences produced on the leaves of a species of oak, the Quercus infectoria, by the puncture of an insect, by the elegant Fig. 171. and happy method of M. Pelouze. A glass vessel, having somewhat the figure of that represented in the margin, is loosely stopped at its lower extremity by a bit of cotton wool, and half or two-thirds filled with powdered Aleppo-galls. Ether, prepared in the usual manner by rectification, and con- taining, 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 colorless, is a very strong solution of nearly pure tannic acid in water; the upper consists of ether holding in solution gallic acid, coloring 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 crystallization. It is very soluble in water, less so in alcohol, and very slightly soluble in ether. It reddens litmus, and possesses a pure astringent taste without bitterness. A strong solution of this substance mixed with mineral acids gives rise to precipitates, which consist of combinations of the tannic acid with the acids in question ; these compounds are freely soluble in pure water, but scarcely so in acid solutions. Tannic acid precipitates albumed^gelatine, 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 attracts 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. Proto-salt of iron is un- changed by solution of tannic acid ; per-salt, on the contrary, gives 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. Tannic acid, carefully dried, contains C 18 H 5 9 -f-3HO. 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, crystal- lizes in fine colorless needles, which melt when heated, and dissolve very freely in boiling water, but scarcely at all in the cold. Catechin dissolves also in hot alcohol and ether. The aqueous solution acquires a reel tint by exposure to air, and precipitates acetate of lead and corrosive sublimate white, reduces nitrate of silver on the addition of ammonia, but fails to form insoluble compounds with gelatine, starch, and the vegeto alkalis. It strikes a deep green color with peroxide salt of iron. This body is said to be con- vertible by heat into tannic acid. The formula which has been assigned to catechin is C, 5 H 6 O 6 . Japonic and rubinic 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, soluble in alkalis and precipitated by acids containing C 24 H 8 8 -f- HO; it is perhaps identical with a black substance of acid properties, formed by M. Peligot by heating grape-sugar with hydrate of baryta. Rubinic acid has been but little VEGETABLE ACIDS. 401 studied ; it is said to form red insoluble compounds with the earths and certain oxides of the metals. GALLIC ACID. Gallic acid is not nearly so abundant as tannic acid ; it seems to be 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 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-colored mass pro- duced may then be strongly pressed in a cloth, and the solid portion boiled in a considerable quantity of water. The filtered solution deposits on cooling abundance of gallic acid, which may be drained and pressed, and finally puri- fied by re-crystallization. It forms small, feathery, and nearly colorless crystals, which have a beautiful silky lustre; it requires for solution 100 parts of cold, and only three parts of boiling water ; the solution has an acid and astringent taste, and is gradually decomposed by keeping. Gallic acid does not precipi- tate gelatine; with proto-salt of iron no change is produced, but with per-salt a deep bluish-black precipitate falls, which disappears when the liquid is heated, from the reduction gf the peroxide of iron to protoxide at the expense of the gallic acid. The salts of gallic acid have been but little studied ; 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 color; the gallates of most of the other metallic oxides are insoluble. Gallic acid, dried at 212, contains C 7 H0 3 +2HO; the crystals contain 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 afterwards precipitated by an addition of hydrochloric acid, as a grayish insoluble powder. It contains C 7 H 2 4 , when dried at 248, 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 oxy- gen absorbed ; the oxidizing action must therefore be confined to the carbon, and may perhaps be thus represented : 1 eq. tannic acid C 18 H S O 12 } ( 2 eq. gallic acid C 14 H 6 H 10 > = ? 2 eq. water . H 2 O 2 8 eq. oxygen . O 8 ) C 4 eq. carbonic acid C 4 O 8 C 18 H 820 C 18 H 820 Much of the gallic acid is subsequently destroyed, in all probability only a part of that first produced escaping. The changes which gallic acid suffers when exposed to heat are very in- teresting. Heated in a retort by means of an oil-bath, the temperature of which is steadily maintained at 420, or thereabouts, it is resolved into car- bonic acid, and a new acid which sublimes into the neck of the retort in bril- liant, crystalline plates, of the most perfect whiteness ; an insignificant residue of black matter remains behind. The term pyrogallic add is given to the volatile product. It dissolves with facility in water, but the solution cannot 34* 402 VEGETABLE ACIDS. be evaporated without blackening and decomposition ; it communicates a blackish-blue color to salts of the protoxide of iron, and reduces those of the peroxide to the state of protoxide. The acid characters of this substance are very indistinct. Pyrogallic acid contains C 6 H 3 O 3 . When dry gallic acid is suddenly heated to 480, or above, it is decomposed into carbonic acid, water, and a second new acid, the metagallic,* which re- mains in the retort as a black, shining mass, resembling charcoal ; a few crystals of pyrogallic acid are formed at the same time. Metagallic acid is insoluble in water, but dissolves in alkalis, and is again precipitated as a black powder by the addition of an acid. It combines with the oxides of lead and silver, and is composed of C 6 H 2 O 2 . 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. Mohr's subliming apparatus, already described.f All these changes admit of simple explanation. Dry gallic acid. Pyrogallic acid. Carbonic acid. C 7 H 3 5 = C 6 H 3 3 and Pyrogallic acid. Metagallic acid. f^O ^^^ C 6 H 3 O 3 = C 6 H 2 2 and Tannic acid, 3 eq. 6 eq. gallic acid. 2 eq. pyrogallic acid. These phenomena present admirable illustrations of the production of py rogen-acids by the agency of heat. * Pelouze, Ann. Chim. et Phys. liv. 337. f Mem. Chem. Soc. of London, i. 127. CYANOGEN, ITS COMPOUNDS AND DERIVATIVES. 403 SECTION IV. AZOTIZED ORGANIC PRINCIPLES OF SIMPLE CONSTITUTION. CYANOGEN, ITS COMPOUNDS AND DERIVATIVES. CYANOGEN* forms the most perfect type of a quasi-simple salt radical that chemistry presents, as kakodyle 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 colorless, permanent gas, which must be collected over mercury. It has a pungent and very peculiar odor, remotely resembling that of peach-ker- nels, or hydrocyanic acid; exposed while at the temperature of 45 to a pres- sure of 3.6 atmospheres, it condenses to a thin, colorless, transparent liquid.f Water dissolves 4 or 5 times its volume of this gas, and alcohol a much larger quantity; the solution rapidly decomposes, yielding ammonia, brown insoluble matter, and other products. Cyanogen is inflammable ; it burns with a beautiful purple, or peach-blossom colored flame, generating carbonic acid and liberating nitrogen. The specific gravity of this gas is 1.806; it is composed of carbon and nitrogen in the proportion of 2 equivalents of the former to 1 equivalent of the latter, or C 2 N ; this is easily proved by mixing it with twice its measure of pure oxygen, and firing the mixture in the eudiometer; car- bonic 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 capa- city of quasi-element, is designated by the symbol Cy. PARACTANOGEN. 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 Johnston, 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 discovered 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 arrange- * So called from xuavo?, blue, and ysvvaw, I generate, t This liquid by intense cold is frozen into a cole olid, which melts at 30. (Faraday.) R. B. colorless, transparent, crystalline solid, 404 CYANOGEN, ment for furnishing dry sulphuretted-hydrogen gas, while a narrow tube at- tached 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 suffer decomposition in contact with the gas, sulphuret of mercury and cyanide 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 unde- composed, to avoid contamination of the product by sulphuretted hydrogen. The pure acid is a thin, colorless, and exceedingly volatile liquid, which has a density of .7058 at 45, boils at 79 F., and solidifies when cooled to ; its odor is very powerful and most characteristic, much resembling that of peach-blossoms or bitter almond oil ; it has a very feeble acid reaction, and mixes with water and alcohol in all proportions. In the anhydrous state, this substance constitutes one of the most formidable poisons known, and even when largely diluted with water its effects upon the animal system are exceedingly energetic ; it is employed, however, in medicine in very small doses. The inhalation of the vapor should be carefully avoided in all experiments in which hydrocyanic acid is concerned, as it produces headache, giddiness, and other disagreeable symptoms; ammonia and chlorine are the best antidotes.* The acid in its pure form can 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 probably other products. Light favors 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 hy- drochloric for example, the whole solidifies to a crystalline paste of sal-am- moniac and hydrated formic acid ; a reaction which is explained in a very simple manner, 1 eq. of hydrocyanic acid and 3 eq. water, yielding 1 eq. of ammonia and 1 eq. of formic acid. C 2 N,H and 3HO=NH 3 and C 2 HO 3 . On the other hand, when dry formiate of ammonia is heated to 392, it is almost entirely converted into hydrated hydrocyanic acid.| NH 4 , C 2 H0 3 =C 2 N,H and 4HO. Aqueous solution of hydrocyanic acid may be had 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 potassium by diluted sulphuric acid. For example, 500 grains of the pow- dered ferrocyanide may be dissolved in four or five ounces of warm water, and introduced into a capacious flask or globe capable of being connected by a perforated cork and wide bent tube with a Liebig's condenser well supplied with cold water; 300 grains of oil of vitriol are diluted with three or four times as much water and added to the contents of the flask ; dis- tillation 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 carefully studied by Mr. EverittjJ it is sufficiently complicated. * When swallowed, the freshly precipitated black oxide of iron neutralizes its ac- tion by forming Prussian blue, which is inert. A solution containing ten grains of sulphate of the protoxide of iron and a drachm of the tincture of chloride of iron, de- composed by a solution of twenty grains of carbonate of potassa, would be adequate to neutralize about two grains of the pure acid. R. B. t Pelouze, Ann. Chim. et Phys. Ixviii. 395. t Phil. Magazine. Feb. 1835. ITS COMPOUNDS AND DERIVATIVES. 405 6 eq. carbon __ -- L^^' Insoluble yellow salt. 6 eq. carbon 2 eq. ferro- 3 eq. nitrogen cyanide po--^ 3 eq. nitrogen tassium 1 eq. potassium 3 eq. potassium 2 eq. iron 3 en water \ 3 eq ' h y dr S en ' - ^""^^^ ^3 eq. hydrocyanic 3 eq. oxygen ^"^^ acid. ( 3 eq. oxygen 6 eq. sulphuric acid - - 3 e q. bisulphate of potash. The substance described in the above diagram as insoluble yellow salt re- mains in the flask after the reaction, together with the bisulphate of potash ; it contains the elements of 2 eq. cyanide of iron, and 1 eq. cyanide of potas- sium, but its constitution is unknown. On exposure to the air, it rapidly be- comes 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 5, which will give a close approximation to the truth. It is a common remark, that the hydrocyanic acid made from ferro- cyanide of potassium keeps better than that made by other means. The cause of this is ascribed to the presence of a trace of mineral acid. Mr. Everitt actually 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 elegant and convenient process for the extemporaneous preparation of an acid of definite strength, is to decompose a known quantity of cyanide of potassium 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 sepa- ration of the cream of tartar ; no filtration or other treatment need be em- ployed. 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 rosacea, yield on distillation with water a sweet-smelling liquid, containing hydrocyanic acid. This is probably due in all cases to the decomposition of the amygdaline, pre existent in the organic structure. The change in question is brought about, in a very 'Singular manner, by the presence of a soluble azo- tized substance, called emulsine or synaplase, which forms a large proportion of the white pulp of both bitter and sweet almonds. This substance bears a somewhat similar relation to amygdaline that diastase, which it closely re- 406 CYANOGEN, sembles in many particulars, does to starch. Hydrocyanic acid exists ready- formed to a considerable extent in the juice of the bitter cassava. AMYGDALINE is prepared with facility by the following process: The paste of bitter almonds, from which the fixed oil has been expressed, is ex- hausted with boiling alcohol : this coagulates and renders inactive the synap- tase, while at the same time it dissolves out the amygdaline. 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 amygdaline as a white crystalline powder; the latter is collected on a cloth filter, pressed, redissolved 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 odor of the hawthorn. In water, both hot and cold, amygdaline is very in- soluble : a hot saturated solution deposits, on cooling, brilliant prismatic crys- tals, which contain water.* In cold alcohol it dissolves with great difficulty. Heated with dilute nitric acid, or a mixture of dilute sulphuric acid and per- oxide of manganese, it is resolved into ammonia, bitter-almond oil, benzoic acid, formic acid, and carbonic acid; with hypermanganate of potash, it yields a mixture of cyanate and benzoate of that base. Amygdaline is composed of C 40 H 27 N0 22 . 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 solu- ble in water, and coagulable, like albumen, by heat, in which case it loses its specific property. In solution it very soon becomes turbid, and putrefies. The decomposition of amygdaline 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 odor of the volatile oil immediately becomes apparent, and the liquor yields, on distillation, hydrocyanic acid. The nature of the decomposition may be thus approximately represented : f 1 eq. hydrocyanic acid C 2 H N 2 eq. formic acid . C 4 H 2 O 6 (^ 7 eq. water . ' , : H 7 O 7 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 coagu- lating the synaptase before it has had time to act upon the amygdaline. Al- mond-paste, thrown into boiling water, yields little or no bitter-almond oiLf AMYGDALIIUC ACID. When amygdaline is boiled with an alkali or an alkaline earth, it is decomposed into ammonia, and a new acid called the amygdalinic, which remains in union with the base. This is best prepared by means of baryta-water, the ebullition being continued as long as ammonia continues to be evolved. From the solution thus obtained, the baryta may be precipitated by dilute sulphuric acid; the filtered liquid is evaporated in a water-bath. Amygdalinic acid forms a colorless, transparent, amorphous * Liebig in Geiger's Pharmacie, ii. 681. f The action of synaptaae is also prevented by alcohol and the gastric juice. R. B. ITS COMPOUNDS AND DERIVATIVES. 407 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 bitter- almond-oil, formic, and benzoic acids. The amygdalates are mostly soluble, but have been but little studied ; the acid contains C 40 H 26 24 -j-HO. The presence of hydrocyanic acid is detected with the utmost ease ; its remarkable odor and high degree of volatility almost sufficiently characterize it. With solution of nitrate of silver it gives a dense curdy white precipitate, much resembling the chloride, but differing from that substance in not black- ening so readily by light, in being soluble in boiling nitric acid, and in suffer- ing 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. The production of Prussian blue by " Scheele's test" is an excellent and most decisive experiment, which may be made with a very small quantity of acid. The liquid to be examined is mixed with a few drops of solution of protosulphate of iron and an excess of caustic potash, and the whole exposed to the air for 10 or 15 minutes, with agitation; hydro- chloric acid is then added in excess, which dissolves the oxide of iron, and, had hydrocyanic acid been present, leaves Prussian blue as an insoluble pow- der. The reaction becomes quite intelligible when the production of a ferro- cyanide, described a few pages hence, is understood. 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 vapor of hydrocyanic acid, hydrogen being liberated. If pure nitrogen gas be transmitted through a white-hot tube, containing a mixture of carbonate of potash and charcoal, a considerable quantity of cyanide of potassium 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 potash in a close vessel, a very abundant production of cyanide of potassium results, which cannot however be advantageously 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 maybe prepared for use. It may be made by passing the vapor of hydrocyanic acid into a cold alcoholic solution of potash ; the salt is deposited in a crystalline form, and may be separated -from the liquid, pressed and dried. Ferrocyanide of potassium, heated to whiteness in a nearly close vessel, evolves nitrogen and other gases, and leaves a mixture of charcoal, carburet 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 temperature ultimately raised to white- ness; 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 sepa- rated from the black spongy mass below, and preserved in a well-stopped bottle ; the black substance contains much cyanide, which may be extracted 408 CYANOGEN, 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 lately publishedf a very easy and excellent process for making cyanide of potassium, which does not, however, yield it pure, but mixed with cyanate of potash. For many of the applications of cyanide of potassium, as, for example, electro-plating and gilding, for which a consider- able quantity is now required, this impurity will be of no consequence. Eight parts of ferrocyanide of potassium are rendered anhydrous by gentle heat, and intimately mixed with 3 parts of dry carbonate of potash ; this mixture is thrown into a red hot earthen crucible, and kept in fusion, with occasional stirring, until gas ceases to be evolved, and the fluid portion of the mass be- comes colorless. 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 princi- pally metallic iron in a state of minute division. In this experiment, 2 eq. of ferrocyanide of potassium and 2 eq. carbonate of potash yield 5 eq. cyanide of potassium, 1 eq. cyanate of potash, 2 eq. iron, and 2 eq. carbonic acid. The product may be advantageously used, instead of ferrocyanide of potassium, in the preparation of hydrated hydrocyanic acid, by distillation with diluted oil of vitriol. Cyanide of potassium forms colorless, 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 be- comes cyanate of potash. Its solution always presents an alkaline reaction, and exhales when exposed to the air the smell of hydrocyanic acid ; it is de- composed by the feeblest acids, even the carbonic acid of the atmosphere, and when boiled in a retort is slowly converted into formiate of potash 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 SODIUM, NaCy, is a very soluble salt, corresponding closely with the foregoing, and obtained by similar means. CYANIDE OF AMMONIUM, NH 4 Cy. This is a colorless, crystallizable, and very volatile substance, prepared by distilling a mixture of cyanide of potas sium and sal-ammoniac, or by mingling the vapor of anhydrous hydrocyanic acid with ammoniacal gas, or, lastly, according to the observation of M. Langlois,J 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 ox- idable 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 odor, and yields on evaporation crystals of cyanide of mercury. Cyanide of potassium is in like manner decomposed by red oxide of mercury, hydrate of potash being produced. Cyanide of mercury is generally prepared from common ferrocyanide of potassium ; 2 * Pharmaceutical Journal, ii. 573. f Mem. Chem. Soc. of London, i. 94. | Ann. Chim. et Phys. 3d series, i. Ill, ITS COMPOUNDS AND DERIVATIVES. 409 parts of the salt are dissolved in 15 parts of hot water, and 3 parts of dry sulphate of mercury added; the whole is boiled for 15 minutes, and filtered hot from the oxide of iron, 'which separates. The solution, on cooling, de- posits the new salt in crystals. Cyanide of mercury forms white, translu- cent prisms, much resembling those of corrosive sublimate ; it is soluble in 8 parts of cold water, and in a much smaller quantity at a high temperature, and also in alcohol. The solution has a disagreeable metallic taste, is very poisonous, and is not precipitated by alkalis. Cyanide of mercury is useful 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, prepared by mixing acetate of zinc with hydrocyanic acid. Cyanide of cobalt, CoCy, is obtained by similar means; it is dirty white, and insoluble. Cyanide of palladium forms a pale, whitish precipitate when the chloride of that metal is mixed with a soluble cyanide, including that of mercury. Cyanide of gold, Au 2 Cy 3 , is yellowish-white and insoluble, but freely dissolved by solution of cyanide of potassium. Proto- cyanide 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,Fe 2 Cy 3 was formed by M. Pelouze by passing chlorine 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 potash, or passed into a solution of the alkaline base, the reaction resembling that by which chlorate of potash and chloride of potassium are generated when the oxide and the salt-radical are presented to each other. Cyanate of potash is, moreover, formed when the cyanide is exposed to a high temperature with access of air ; unlike the chlorate, it bears a full red-heat without decomposition. Hydrated Cyqnic Arid, 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 re- ceiver to a limpid, colorless liquid, of exceedingly pungent and penetrating odor, like that of the strongest acetic acid ; it even blisters the skin. When mixed with water, it decomposes almost immediately, giving rise to bicarbo- nate of ammonia. C 2 NO , HO and 2HO = C 2 O 4 and NH 3 . 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 a pungent smell to the carbonic acid evolved. The cyanates may thus be easily distinguished. The pure hydrated cyanic acid cannot be preserved ; shortly after its pre- paration^! 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 insoluble in water, alcohol, ether, and dilute acids ; it dissolves in strong oil of 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 distilla- tion it is again converted into the hydrate of cyanic acid. CYANATE OF POTASH, KO,CyO. The best method of preparing this salt is, according to Liebig, to oxidize cyanide of potassium by means of litharge. 35 410 CYANOGEN, The cyanide, already containing a portion of cyanate, described p. 4,08 is re- melted in an earthen crucible, and finely powdered protoxide of lead added by small portions ; the oxide is instantaneously reduced, and the metal, at first in a state of minute division, ultimately collects to a fused globule at the bottom of the crucible. The salt is poured out, and, when cold, powdered and boiled with alcohol; the hot filtered solution deposits crystals of cyanate of potash on cooling. The great deoxidizing 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 cyanate is to mix dried and finely- powdered, ferrocyanide of potassium with half its weight of equally dry peroxide of manganese ; to heat this mixture in a shallow iron ladle with free exposure to air and frequent stirring until the tinder-like combustion is at an end, and to boil the residue in alcohol, which extracts the cyanate of potash. This salt crystallizes from alcohol, in thin, colorless, transparent plates, which suffer no change in dry air, but on exposure to moisture become gradually converted, without much alteration of appearance, into bicarbonate of potash, ammonia being at the same time disengaged. Water dissolves the cyanate of potash in large quantity: the solution is slowly decomposed in the cold, and rapidly at a boiling heat, into bicarbonate of potash and ammonia. When a concentrated solution is mixed with a small quantity of dilute mineral acid, a precipitate falls, which consists of acid cyanurate of potash. Cyanate of potash is reduced to cyanide of potassium by ignition with charcoal in a covered crucible. Cyanate of potash, mixed with solutions of lead and silver, gives rise to insoluble cyanates of the oxides of those metals, which are white. CYANATE OF AMMONIA; UHEA. When the vapor 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 portion of ammonia is dissipated, and the properties of the compound com- pletely changed. It may now be mixed with acids without the least symptom of decomposition, while cold caustic alkali, on the other hand, fails to disen- gage the smallest trace of ammonia. The result of this curious metamor- phosis 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. The properties of urea, and the most advantageous method of preparing it, will be found described a few pages hence. CTANURIC ACID. The substance called melam, of which further 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 boi ling-point, until a specimen of the liquid, on being tried by ammonia, no longer gives a white precipitate : sev^-al 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 substance melts, boils, disengages ammonia in large quantity, and at length becomes converted into a dirty while, 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 colorless; it is then mixed with water, and suffered to cool, whereupon the cyanuric acid separates. ITS COMPOUNDS AND DERIVATIVES. 411 Cyanuric acid in a pure state forms colorless crystals, seldom of large size, derived from an oblique rhombic prism, which effloresce in a dry atmosphere from loss of water. It is very little soluble in cold water, and requires 24 parts for solution at a boiling heat; it reddens litmus feebly, has no odor, and but little taste. This acid is tribasic; the crystals contain C 6 N 3 3 ,3HO-f- 4HO, and are easily deprived of the 4 eq. of water of crystallization. In point of stability, it offers a most remarkable contrast to its isomer, cyanic acid ; it dissolves, as above indicated, in hot oil of vitriol, and even in strong nitric acid, without decomposition, and in fact crystallizes from the latter in an anhydrous state, containing C 6 N g O 3 ,3HO. 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 ammonia. Cyanuric acid is changed by a very high temperature into hydrated cyanic acid. In the latter reaction, 1 eq. of hydrated cyanuric acid splits into 3 eq. hy- drated cyanic acid. C 6 N 3 3 ,3HO = 3(C 2 NO,HO). FULMINIC ACID. This remarkable compound, which is isomeric both with cyanic and cyanuric acids, originates in the peculiar action exercised by hyponitrous acid upon alcohol in presence of a salt of silver or mercury. Neither absolute fulminic acid nor its hydrate has ever been obtained. Fulminate of silver is prepared by dissolving 40 or 50 grains of silver, which need not be pure, in oz. by measure of nitric acid of sp. gr. 1.37 or thereabouts, by the aid of a little heat; a sixpence answers the purpose very well. To the highly acid solution, while still hot, 2 measured ounces of alcohol are added, and heat applied until reaction commences. The nitric acid oxidizes part of the alcohol to aldehyde and oxalic acid, becoming itself reduced to hyponitrous acid, which in turn acts upon the alcohol in such a manner as to form hyponitrous ether, fulminic acid, and water. 1 eq. hy- ponitrous ether and 1 eq. of hyponitrous acid containing the elements of 1 eq. fulminic acid and 5 eq. water. C 4 H 6 0,N0 3 and NO 3 = C 4 N 2 O 2 and 5HO. 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 ex- ceeding 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 for- mula 2HgO , C 4 N 2 2 . The acid is evidently bibasic; when fulminate of silver is digested with 412 CYANOGEN, caustic potash, one-half of tha oxide is precipitated, and a compound pro- duced containing AgO , KO , C 4 N 2 O 2 , which resembles the neutral silver-salt, and detonates by a blow. Corresponding compounds containing soda and oxide of ammonium exist ; but a pure fulminate of an alkaline metal has never been formed. If fulminate of silver be digested with water and cop- per, or zinc, the silver is entirely displaced, and a fulminate of the new metal produced. The zinc-salt mixed with baryta- water gives rise to a pre- cipitate of oxide of zinc, while fulminate of zinc and baryta, ZnO , BaO , C 4 N 2 O 2 , remains 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 vapor are disengaged, together with a large quantity of nitrous ether and aldehyde ; these are sometimes condensed and collected for sale, but are said to contain hydrocyanic acid. The fulmi- nate of mercury separates from the hot liquid, and after cooling may be puri- fied from an admixture p/ reduced metal by solution in boiling water and recrystallization. It much resembles the silver-salt in appearance, proper- ties, arid degree of solubility, and contains 2Hg 2 O , C 4 N 2 2 . It explodes violently by friction or percussion, but, unlike the silyer-compound, 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 potash are added, and the powder, pressed into the cap, is secured by a drop of varnish. The relations of composition between the three isomeric acids are beauti- fully seen by comparing their silver-salts ; the first acid is monobasic, the second bibasic, and the third tribasic. Cyanate of silver AgO , C 2 NO. Fulminate of silver .... 2AgO , C 4 N 2 O 2 . Cyanurate of silver 3AgO , C 6 N 3 3 . Until quite recently, beyond the accidental one of identity of composition, no relation existed between fulminic acid and its isomers. Mr. Gladstone has, however, shown that, when a solution of fulminate of copper is mixed with excess of ammonia, filtered, treated with sulphuretted hydrogen in excess, and again filtered from the insoluble sulphuret of copper, the liquid obtained is a mixed solution of urea and sulphocyanide of ammonium.* CHLOBIDES OF CYANOGEN.' 'Chlorine forms two compounds with cyanogen, 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. colorless gas at the temperature of the air, of insupportable pungency, and soluble to a very considerable extent in water, alcohol, and ether. At F. it congeals to a mass of colorless crystals, which at 5 melt to a liquid whose boiling-point is 11 F. At the temperature of the air it is condensed to the liquid form under a pressure of four atmospheres, and when long preserved in this condition in hermetically-sealed tubes it gradually passes into the solid modification. Solid chloride of cyanogen is generated when anhydrous hydro- cyanic acid is put into a vessel of chlorine gas, and the whole exposed to the sun ; hydrochloric acid is formed at the same time. It forms long colorless needles, which exhale a powerful and offensive odor, compared by some to * Annalen der Pharm. Ixvi. 1. ITS COMPOUNDS AND DERIVATIVES. 413 that, of the excrements of mice; it melts at 284, and sublimes unchanged at a higher temperature. When heated in contact with water, it is decomposed into cyanuric and hydrochloric acids. This compound may be represented by the formula Cy 3 Cl 3 , or C 6 N S ,C1 3 . 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 colorless, volatile, solid substances, of powerful odor. 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 potash 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 potash. 3KCy, Fe, and = KO and 2K , C 6 N 3 Fe. The new substance is catted 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 potash and the new substance being generated ; the oxygen in this case is derived from the decomposition of water. Sulphuret of iron and cyanide of potassium give rise, under similar circumstances, to sulphuret of potassium and ferro- cyanide of potassium. HYDROFERROCYANIC ACID, Cfy2H. Ferrocyanide of lead or copper, both of which are insoluble, may be suspended in water, and decomposed by a stream of sulphuretted hydrogen gas. The filtered solution evaporated in the vacuum of the air-pump over a surface of oil of vitriol furnishes the acid in a solid form. If the aqueous solution be agitated with ether, nearly the whole of the acid separates in colorless, crystalline laminse ; 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 ether. The crystals may be dissolved in alcohol, and the acid again thrown down by ether, which possesses the remarkable property of precipitating this substance from solution.* Hydroferrocyanic acid differs completely from hydrocyanic acid; its solution in water has a powerfully acid taste arid reaction, and de- composes alkaline carbonates with effervescence; it refuses to dissolve oxide of mercury in the cold, but when heat is applied, undergoes decomposition, forming cyanide of mercury arid 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 dis- covered by Mr. Porrett. FERROCYANIDE OF POTASSIUM, 2KCfy-f-3HO, or 2K,C 6 N 3 Fe+3HO. This most beautiful salt is manufactured on a large scale by the following process, which will be now easily intelligible: Dry refuse animal matter of any kind is fused at a red-heat with impure carbonate of potash and some * Posselt, Ann. der Chemie und Pharmacie, xlii. 163. 35* 414 FERROCYANOGEN, iron filings in a large iron vessel, from which the air should be excluded as much as possible ; cyanide of potassium is generated in large quantity. The melted mass is afterwards treated with hot water, which dissolves out the cyanide and other salts ; the cyanide being quickly converted by the oxide or sulphuret* 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 formiate of potash and ammonia. Ferrocyanide of potassium forms large, transparent, yellow crystals, de- rived 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 difficult 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 potassi- um, carburet of iron, and various gaseous products; if air be admitted, the cyanide becomes cyanate. The ferrocyanides are often described as double salts, in which protocya- nide of iron is combined with other metallic cyanides, or with hydrogen. Thus, hydroferrocyanic acid is written FeCy-}-2HCy, and ferrocyanide of po- tassium FeCy-f-2KCy-|-3HO; the oxygen and hydrogen of the water of crystallization being respectively adequate to convert the metals into protox- ide 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 colors. In most of these compounds, the potassium of the base is simply displaced by the new metal; the beautiful brown ferrocyanide of copper contains, for example, 2Cu-fCfy or 2Cu-fC 6 N 3 Fe, and that of lead, 2Pb-f Cfy. With salt of protoxide of iron it gives a nearly white precipitate, which becomes rapidly blue by exposure to air ; this may very possibly be neutral ferrocyanide of iron, 2Fe-f-Cfy. When a ferrocyanide is added to a solution of peroxide salt of iron, Prus- sian 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 com- pletely solved. This difficulty arises in great measure from the existence of several distinct deep blue compounds formed under different circumstances, and having many properties in common, which have been almost unavoid- ably confounded. The following is a summary of the account given by Ber- zelius, who has paid much attention to this subject. Ordinary Prussian Blue, C 18 N 9 Fe 7 , or 3Cfy-{-4Fe. This is best prepared by adding pernitrate of iron to solution of ferrocyanide of potassium, 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 resem- bling in appearance the best indigo ; the fresh-fractured surfaces have a beau- tiful 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 * The sulphur is derived from the reduced sulphate of the crude pearl-ashes used in this manufacture. . AND ITS COMPOUNDS. 415 exception of oxalic acid, in a solution of which it dissolves ; concentrated oil of vitriol converts it into a white, pasty mass, which again becomes blue on the addition of water. Alkalis destroy the color instantly; they dissolve out a ferrocyariide, and leave oxide of iron. Boiled with water and red oxide of mercury, it yields a cyanide of the metal, and oxide of iron. Heated in the air, Prussian blue burns like tinder, leaving a residue of peroxide of iron. Exposed to a high temperature in a close vessel, it disengages water, cyanide of ammonium, and carbonate of ammonia, and leaves carburet of iron. This substance forms a very beautiful pigment, both an oil and a water color, but has little permanency. The Prussian blue of commerce is always ex- ceedingly impure; it contains alumina and other matters, which greatly diminish the brilliancy of the color. The production of Prussian blue by mixing peroxide-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 C 4 eq. iron 2 eq. pernitrate < 6 eq. oxygen of iron. ( 6 eq. nitric acid "^^ 6 eq. nitrate of potash. 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 protosalt of iron and excess of caustic alkali ; the protoxide of iron quickly converts the alkaline cyanide into ferrocyanide. By exposure for a short time to the air, another portion of the hydrated oxide becomes peroxidized; when excess of acid is added, this is dissolved, together with the unaltered protoxide, and thus presented to the ferrocyanide in a state fitted for the production of Prussian blue. Basic Prussian Blue. 3Cfy,4Fe-f-Fe 2 O 3 . This is a combination of Prus- sian blue with peroxide 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 pernitrate of iron to a large excess of ferrocyanide of potassium, is a mixture of insoluble Prussian blue with a compound containing that substance in union with ferrocyanide of potassium, or 3Cfy,4Fe-f-2K,Cfy. This also dissolves in water as soon as the salts have been removed by washing. The other ferrocyanides may be dispatched in a few words. The soda-salt, 2NaCfy-J-12HO, crystallizes in 'yellow four-sided prisms, which are efflorescent in the air and very soluble. Ferrocyanide of Ammonium, 2NH 4 Cfy-f-3HO, is isomorphous with ferrocy- anide of potassium ; it is easily [soluble, and is decomposed by ebullition. Ferrocyanide of barium, 2BaCfy, 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 bismuth are white and insoluble ; those of nickel and cobalt are pale green, and inso- luble ; and lastly, that of copper has a beautiful reddish-brown tint. 416 SULPHOCYANOGEN, 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, contain- ing K,Ca-}-Cfy, the salt-radical being half saturated with potassium, and half with calcium; many similar compounds have been formed. FEHHI, or FERRiDCYAifOGEN, C 12 N 6 Fe 2 ; or Cfdy. This name is given to a substance, by some thought to be a new salt radical, isomeric with ferrocyano- gen, but differing in capacity of saturation ; it has never been isolated. Ferridcyanide 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 color, and ceases to pre- cipitate a salt of the peroxide of iron. It is then evaporated until a skin begins to form upon the surface, filtered, and left to cool ; the salt is purified by re-crystallization. It forms regular prismatic, or sometimes tabular crys- tals, of a beautiful ruby-red tint, permanent in the air, and soluble in 4 parts of cold water ; the solution has a dark greenish color. The crystals burn when introduced into the flame of a candle, and emit sparks. Ferridcyanide of potassium contains SK-j-Cfdy; hence the radical is tribasic; the salt is formed by the abstraction of an equivalent of potassium from 2 eq. of the yellow ferrocyanide of potassium. It is decomposed by excess of chlorine, and by deoxidizing agents, as sulphuretted-hydrogen. The term red ferroprussiat e of potash is often, but very improperly, given to this substance. Ferridcyanide of hydrogen is obtained in the form of a reddish-brown acid liquid, by decomposing ferridcyanide of lead with sulphuric acid; it is very instable, and is resolved, by boiling, into a hydrated percyanide of iron, an insoluble dark green powder, containing Fe 2 Cy 3 -j- 3 HO, and hydrocyanic acid. The ferridcyanides of sodium, ammonium, and of the alkaline earths are solu- ble; those of most of the other metals are insoluble. Ferridcyanide of potassium, added to a salt of the peroxide of iron, occasions no precipitate, but merely a darkening of the reddish-brown color of the solution ; with protox- ide of iron, on the other hand, it gives a deep blue precipitate, containing 3Fe-|-Cfdy, which, when dry, has a brighter tint than that of Prussian blue ; it is known under the name of TurnbuWs blue. Hence, ferridcyanide of potassium is as excellent a test for protoxide of iron as the yellow ferrocyan- ide is for the peroxide. COBALTOCYABTOGEN. A series of compounds analogous to the preceding, containing cobalt in place of iron, have been formed, and partially studied; a hydrogen -acid has been obtained and a number of salts, which much resem- ble those of ferridcyanogen. It is to be expected that other metals of the same isomorphous family may be found capable of replacing iron in these circumstances. SULPHOCYATiTOGEtf ; ITS COMPOUNDS AND DERIVATIVES. The elements of cyanogen combine with sulphur, forming a very import- ant and well-defined salt radical, called sulphocyanogen, which contains C 2 NS 2 , and is monobasic; it is expressed by the symbol Csy. SutPHOCYAsriDE 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 sulphocyanide of iron, leaving little behind but the excess of sulphur employed in the experiment. This solution, which becomes red on exposure ITS COMPOUNDS AND DERIVATIVES. 417 to the air from the oxidation of the iron, is mixed with carbonate of potash, by which the oxide of iron is precipitated, and potassium substituted ; an ex- cess of the carbonate must be, as far as possible, avoided. The filtered liquid is concentrated, by evaporation over the 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 6 eq. sulphur, yielded 2 eq. of sulphocyanide of potassium, and 1 eq. of sulphocyanide of iron. 2K,Cfy = C 6 N 3 Fe , 2K, and 6S = 2(K,C 2 NS 2 ) and Fe,C 2 NS 2 . The new salt crystallizes in long, slender, colorless prisms, or plates, which are anhydrous; it has a bitter, saline taste, and is destitute of poisonous pro- perties ; it is very soluble in water and alcohol, and deliquesces when exposed to a moist atmosphere. When heated, it fuses to a colorless liquid, at a tem- perature 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, resembling 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 vapor, probably 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; Mr. Parnell, how- ever, invariably found it to contain both oxygen and hydrogen, and assigned to it a formula much more complex than that belonging to the true sulphocy- anogen, namely, C, 2 H 3 N 6 S 12 0. 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 potash 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 sul- phocyanogen evolves sulphur and bi-sulphuret of carbon, and leaves a curious, pale straw-yellow substance, called mellon, which contains C 6 N 4 , and enjoys the properties of a salt-radical, combining with hydrogen, and the metals. Mellon bears a dull red-heat without decomposition, but is resolved by strong ignition into a mixture of cyanogen and nitrogen gases. It is quite insoluble in water, alcohol, and dilute acids. HTDnostTLPHOCYANic ACID, HCsy, is obtained by decomposing sulphocya- nide of lead, suspended in water, by sulphuretted hydrogen. The filtered solution is colorless, very acid, and not poisonous : it is easily decomposed, in a very complex manner, by ebullition ; and by exposure to the air. By neu- tralizing the liquid with ammonia, and evaporating very gently, to dryness, sulphocyanide of ammonium, NH 4 ,Csy, is obtained as a deliquescent, saline mass. The sulphocyanides of sodium, barium, strontium, calcium, manganese, and iron are colorless, and very soluble ; those of lead and silver are white and insoluble. A soluble sulphocyanide, mixed with a salt of the peroxide 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 peroxide. MELAM. Such is the name given by Liebig to a curious buff-colored, inso- luble, amorphous substance, obtained by the distillation at a high temperature 418 UREA; URIC ACID, of sulphocyanide of ammonium. It may be prepared in large quantity by intimately mixing 1 part of perfectly dry sulphocyanide of potassium with 2 parts of powdered sal-ammoniac, and heating the mixture for some time in a retort or flask ; bisulphuret of carbon, sulphuret of ammonium, and sulphu- retted hydrogen are disengaged and volatilized, while a mixture of rnelam, chloride of potassium, and some sal-ammoniac remains; the two latter sub- stances are removed by washing with hot water. Melam contains C 12 H 9 N H ; it dissolves in concentrated sulphuric acid, and gives, by dilution with water and long boiling, cyanuric acid. The same substance is produced with dis- engagement of ammonia when melam is fused with hydrate of potash. When strongly heated, melam is resolved into mellon and ammonia. If melam be boiled for a long time in a moderately strong solution of caus- tic potash, until the whole has dissolved, and the liquid be then concentrated, a crystalline substance separates on cooling, which is called melamine. By re-crystallization it is obtained in colorless 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 deco reposition. It contains C 6 H 6 N 6 , and acts as a base, combining with acids to crystallizable compounds. A second basic substance called ammeline, very similar in properties to melamine, is found in the alkaline mother-liquor from which the melamine has separated ; it is thrown down on neutralizing the liquid with acetic acid. The precipi- tate, dissolved in dilute nitric acid, yields crystals of nitrate of ammeline, from which the pure ammeline may be separated by ammonia. It forms a bril- liant white powder of minute needles, insoluble in water and alcohol, and contains C 6 H 5 N.O 2 . 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, 2 H 9 N 9 O 6 . When long boiled with dilute sulphuric acid, ammeline is converted into cyanuric acid and ammonia. UREAJ URIC ACID AND ITS PRODUCTS. These bodies are closely connected with the cyanogen-compounds, and may be most conveniently discussed in the present place. UREA. 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-colored 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 powdered chalk added until effervescence 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, avoid- ing 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 an addition of hydrochloric acid; oxalic acid then throws down the oxalate in such quantity as to render the whole semi-solid. By artificial means, urea is produced by heating solution of cyanate of am- monia. The following method of proceeding yields it in any quantity that AND ITS PRODUCTS. 419 can be desired Cyanate of potash, prepared by Liebig's process,* is dis- solved ^a 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 tadryness in a water-bath, and the dry residue boiled with strong alco- hol, which dissolves out the urea, leaving the sulphate of potash and the ex- cess of sulphate of ammonia untouched. The filtered solution, concentrated by distilling off a portion of the spirit, deposits the urea in beautiful crystals of considerable magnitude. Urea forms transparent, colorless, 4-sided prisms, which are soluble in an equal weight of cold water, and in a much smaller quantity at a high tem- perature. It is also readily dissolved by alcohol. It is inodorous, has a cool- ing, 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 Devo- lution 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 ; with chlorine it yields hydrochloric acid, nitrogen, and carbonic acid. Crystallized urea is anhydrous; it contains C 2 H 4 N 2 O 2 , or the elements of cyanate of oxide of ammonium. It differs from carbonate of ammonia by the elements of water; hence it might with some propriety be called carbamide, were not this name appropriated to another substance. 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 putrefiable organic matter, as mucus, the case is different. In putrid urine no urea can be found, but enough carbonate of ammonia to cause brisk effervescence with an acid ; and if urine, in a recent state, be long boiled, it gives off ammonia and car- bonic acid from the same source. Urea acts as a salt base; with nitric acid it forms a sparingly soluble com- pound, which crystallizes, when pure, in small, indistinct, colorless plates, containing single equivalents of urea, nitric acid, and water. When colorless nitric acid is added to urine, concentrated to a fourth or a sixth of its volume, and cold, the nitrate crystallizes out in large, brilliant, yellow laminae, which are very insoluble in the acid liquid. The production of this nitrate is highly characteristic of urea. The oxalate, when pure, crystallizes in large, trans- parent, colorless plates, which have an acid reaction, and are sparingly solu- ble; it contains an equivalent of water. The other compounds of urea are more soluble. URIC, OR LITHIC Acin. This is a product of the animal organism, and has never been produced by artificial means. It may be prepared from human urine by concentration, and addition of hydrochloric acid ; it crystal- lizes 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 urine 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 potash ; the liquid, filtered from the insig- nificant residue of feculent matter, and earthy phosphates, is mixed with excess of hydrochloric acid, boiled for a few minutes, and left to cool. The * See page 409. 420 URIC ACID, 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, Fig. 172. snow-white powder, tasteless, inodorous, and very sparingly soluble. It is seen under the microscope to consist of minute, but regular crystals. (Fig. 172.) It dissolves in concentrated sulphuric acid without apparent decomposition, and is precipitated by dilution with water. By destructive distillation, uric acid yields cyanic, hydrocyanic, and carbonic acids, carbonate of ammonia, and a black coaly residue, rich in nitrogen. By fusion with hydrate of potash, it furnishes carbonate and cyanate of the base, and cyanide of the alkaline metal. When treated with nitric acid and with peroxide of lead, it undergoes decomposition in a manner to bo presently described. Uric acid is found by analysis to contain C, H 4 N 4 6 . The only salts of uric acid that have attracted any attention are those of the alkalis. Urate of potash is deposited from a hot, saturated solution of uric acid in the dilute alkali as a white, sparingly soluble concretionary 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 resembles the salt of potash ; it forms the chief constituent of gouty concretions 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 buff-colored or pinkish cloud or muddiness, which disappears by re-solution when the urine is warmed ; the secretion from which this is de- posited has usually a slightly acid reaction. It occurs also as a calculus. The following substances result from the oxidation of uric acid by peroxide of lead and nitric acid ; they are some of the most beautiful and interesting bodies known.* ALLANTOIN. Allantoin occurs ready-formed in the allantoic liquid of the foetal calf. It is produced artificially by boiling together water, uric acid, and pure, freshly-prepared peroxide of lead ; the filtered liquid, duly concentrated 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 bril- liant prismatic crystals, which are transparent and colorless, destitute of taste, and without action on vegetable colors. Allantoin dissolves in 160 parts of cold water, and in a smaller quantity at the boiling temperature. It is de- composed by boiling with nitric acid, and by oil of vitriol when concentrated 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 equiva- lents of water, or C 4 H 3 N 2 O a . The production of allantoin from uric acid and peroxide of lead is also perfectly intelligible; 1 eq. of uric acid, 2 eq. of oxygen from the peroxide * Wohler and Liebig ; Untersuchungen iiber die Natur der Harnsaiire. Annaiten. der Pharmacie, xxvi. 241; also, Ann. Chim. et Phys. Ixviii. 225. AND ITS PRODUCTS. 421 and 3 eq. of water, contain the elements of allantoin, 2 eq. of oxalic acid, and 1 eq. of urea. C 10 H 4 N 4 6 , 20, 7 _ J C 4 H 3 N 2 3 ,C 4 6 and 3H 5 ~" and C 2 H 4 N 2 O 2 . 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 which the crystals of allantoin have separated yields, on further 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 effervescence of carbonic acid and nitrogen, and eventually the whole becomes a mass of white, crystalline, pasty matter. This is left to stand some hours, drained from the acid liquid in a funnel 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 crystal- lization. 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 colorless, 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 effloresce 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 C g H 4 N 2 0, ; its production is thus illustrated: 1 eq. of uric acid, 4 eq. of water, and 1 eq. of nitric acid contain the elements of alloxan, 2 eq. carbonic acid, 2 eq. of free nitrogen, 1 eq. of ammonia, and 1 eq. of water. C 10 H 4 N 4 6 ,4HO > C C 8 H 4 N 2 10 , 2C0 2 , 2N , NH 3 , and NO 5 5 I and HO. When to a solution of alloxan, heated to 140 F., baryta-water is added as long as the precipitate first produced re-dissolves, and the filtered solution is then left to cool, a substance is deposited in small, colorless, pearly crystals, 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 sul- phuric 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 contains in the hydrated state C 4 HNO 4 -j-HO, and results from the decomposition of the alloxan, under the influence of the base, into 2 eq. of alloxanic acid and 2 eq. of water. 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 be heated to ebulli- tion, 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 solu- 36 422 URIC ACID, lion 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 crys- tallizable ; it has a sour taste and powerfully acid reaction, and resists a boil- ing heat ; it forms sparingly soluble salts with baryta and lime, and a yel- lowish insoluble compound with oxide of silver, which is reduced with effer- vescence when gently heated. This remarkable acicl contains as hydrate C 3 O 4 -{-2HO, and is consequently bibasic; it is formed by the resolution of alloxan into urea, and 2 eq. of mesoxalic acid: C 8 H 4 N 2 10 =C 2 H 4 N 2 2 and 2C 3 O 4 . When ammonia in access 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 acid it is but feebly soluble in water, easily dis- solved by alkalis, and forms a yellow compound with oxide of silver. My- komelinic acid contains C 8 H.N 4 O 5 ; 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-liquor and purified by re-crystallization. Parabanic acid forms beautiful colorless, trans- parent, 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 ammonia, and mixed with nitrate of silver, it gives a white precipitate. Crystallized parabanic acid contains C 6 N 2 O 4 -j-2HO ; 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 carbo- nic 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 colorless 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 oxalurate 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 soluble; that of silver crystallizes from the mixed hot solution of nitrate of silver and oxa- lurate of ammonia in long, silky needles. Oxaluric acid is composed of C 6 H 3 N 2 O 7 -|-HO; 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 aeid and oxalate of urea. THIONUHIC ACID. A cold solution of alloxan is mixed with a saturated solution of sulphurous acid in water, in such quantity that the odor 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, tliiouurate of ammonia is deposited in great abundance, forming beautiful colorless, crystalline plates, which by solution in water and re-crystallization acquire a fine pink lint. A solution of this salt gives AND ITS PRODUCTS. 423 with acetate of lead a precipitate of insoluble thiormrate 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 maybe obtained by the aid of sulphuretted hydrogen. It forms a white, crystalline mass, permanent in the air, very soluble in water, of acid taste and reaction, and capable of combining directly with bases. When its solution is heated to the boiling- point it undergoes decomposition, yielding sulphuric acid and a very peculiar and nearly insoluble substance, called uramih. Thionuric acid is bibasic, the hydrate contains C g H 5 N 3 S 2 O 12 -f-2HO ; or the elements of alloxan, an equi- valent of ammonia, and 2 eq. of sulphurous acid. URAMILE. The product of the spontaneous decomposition by heat of hy- drated thionuric 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 urarnile. After cooling, it is collected on a filter, washed with cold water to remove the sulphuric acid, and dried by gentle heat, during which it frequently becomes pinkish. 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 becomes purple in the air. It is decomposed by strong nitric acid, alloxan and nitrate of ammonia being generated. Uramile contains C 8 H 5 N 3 O 6 ; or thionuric acid minus the elements of 2 eq. of sulphuric acid. , When a cold saturated solution of thionurate of ammonia 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, colorless prisms, soluble in 8 parts of cold water. Uramilic acid dissolves in concen- trated sulphuric acid without apparent decomposition; 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 Jess so, and that of the oxide of silver is insoluble. Uramilic acid contains C ]6 H, N 5 O 15 ; 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. ALtoxAimifE. This is the chief product of the action of hot dilute nitric 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-liquor from which the crystals of alloxan have separated answers the purpose perfectly well ; it is diluted with a little water, and a copious stream of the gas transmitted through it. Sulphur is deposited in large quantity, mixed with a white, crys- talline substance, which is the alloxantine. The product is drained upon a filter, slightly washed and then boiled in water; the filtered solution deposits the alloxantine on cooling. Alloxantine forms small, four sided, oblique rhombic prisms, colorless and transparent; it is soluble with difficulty in cold water, but more freely at a boiling temperature. The solution reddens lit- rnus, gives with baryta-water a violet-colored precipitate, which disappears on heating, and when mixed with nitrate of silver produces a black precipi- tate of metallic silver. Heated with chlorine or nitric acid, it is changed by oxidation to alloxan. The crystals become red when exposed to ammoniacal vapors. Alloxantine contains C 8 H 5 N 2 O 10 ; 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 dia- luric is applied. When neutralized by ammonia it yields a salt which crys- 424 URIC ACID, tallizes in colorless, silky needles, which contain NH 4 0,C g N 2 O 4 -|-3HO. They become deep-red when heated to 212 in the air. A hot saturated solution of alloxantine mixed with a neutral salt of ammonia instantly assumes a purple color, which however 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, alloxantine disengages carbonic acid, reduces a portion of the metal, and converts the remainder of the oxide into oxalurate. Boiled with water and peroxide of lead, alloxantine gives urea and carbonate of lead. MUREXIDE ; PUHPURATE OF AMMONIA OF DH. TROUT. 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, eva- porating to a certain point, and then adding to the warm, but not boiling liquid, a very slight excess of ammonia. In this experiment alloxantine 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 ura- mile, 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 impu- rity. A third, and perhaps even still better process is that of Dr. Gregory : 7 parts of alloxan and 4 parts of alloxantine are dissolved in 240 parts of boiling water, and the solution added to about 80 parts of cold, strong solu tion of carbonate of ammonia; the liquid instantly acquires such a depth of color as to become opaque, and gives on cooling a large quantity of murexide ; the operation succeeds best on a small scale. Murexide* crystallizes in small square prisms, which by reflected light exhibit a splendid green metallic lustre, like that of the wing-cases of the rose-beetle and other insects ; by transmitted light they are deep purple red. It is soluble with difficulty in cold water, much more easily at a boiling tem- perature, and is insoluble in alcohol and ether. Mineral acids decompose it with separation of murexan, and caustic potash dissolves it, with production of a most magnificent purple color, which disappears when the solution is boiled. Murexide contains, according to Liebig and Wohler, C 12 H 6 N 5 Og ; its production may be thus explained : 2 eq. of uramil and 3 eq. of oxygen from the oxide of mercury give rise to murexide, 1 eq. of alloxanic acid, and 3 eq. of water. 2C 8 H 5 N 3 O 6 and 30==C 12 H 6 N.O 8 , C 4 HN0 4 and 3HO. Or, on the other hand, 1 eq. of alloxan, 2 eq. of alloxantine, and 4 eq. of ammonia, yield 2 eq. of murexide and 14 eq. of water. C 8 H 4 N 2 10 ,2C 8 H 5 N 2 10 ,> __ C 2C 12 H 6 N 5 O 8 and 4NH 3 $ ~" $ and 14 HO. MUREXAX; PURPURIC ACID OF DR. PROUT. Liebig directs this substance to be prepared by dissolving murexide in caustic potash, heating the liquid until the color disappears, and then adding an excess of dilute sulphuric acid. It separates in colorless or slightly yellowish scales, nearly insoluble in cold water. In ammonia it dissolves, and the solution acquires a purple color by exposure to the air, murexide being then produced. Murexan is said to con- * So called from the Tyrian dye, said to have been prepared from a species of mu- rex, a shell-fish. AND ITS PRODUCTS. 425 tain C 6 H 4 N 4 O 5 . This substance, and its relation to murexide, require re-ex- amination. Connected with uric acid by similarity of origin, but not otherwise, are two curious and exceedingly rare substances, called xanthic oxide and cystic oxide. Xanthic oxide was discovered by Dr. Marcet; it occurs as an urinary cal- culus, of pale brown color, foliated texture, and waxy lustre, and is extracted by boiling the pulverized stone in dilute caustic potash and precipitating by carbonic acid. The xanthic oxide fells as a white precipitate, which on dry- ing 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 ammonia or solution of potash. Xanthic oxide gives on analysis C 5 H 2 N 2 O 2 . Cystic Oxide. Cystic oxide calculi, although very rare, are more frequently met with than those of the preceding substance ; they have a pale color, a concentric structure, and often a waxy external crust. The powdered calcu- lus dissolves in great part without effervescence in dilute acids and alkalis, including ammonia; the ammoniacal solution deposits, by spontaneous evapo- ration, small, but beautifully colorless 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 C 6 H 6 NS 2 4 . /^ Uric acid is perfectly well characterized, even when in very small quantity, by its behavior with nitric acid. A small portion heated with a drop or two of nitric acid in a small porcelain capsule dissolves with copious effervescence. When this solution is cautiously evaporated nearly to dryness, and, after the addition of a little water, mixed with a slight excess of ammonia, the deep red tint of murexide is immediately produced. Impure uric acid, in a remarkable state of decomposition, is now imported, into this country in large quantities, for use as a manure, under the name of guano or huano. It comes from the barren and uninhabited islets of the western coast of South America, and is the production of the countless birds that dwell undisturbed in those regions. The people of Peru have used it for ages. Guano usually appears as a pale brown powder, sometimes with whitish specks; it has an extremely offensive odor, the strength of which, however, varies very much. It is soluble in great part in water, and the solution is found to be extremely rich in oxalate of ammonia, the acid having been generated by a process of oxidation.* Guano also contains a peculiar substance called guanine, which closely corresponds with xanthic oxide. * See Trans, of Chem. Soc. of London, i. 36. 36 1 426 VEGETO-ALKALIS. SECTION V. THE VEGETO-ALKALIS. THE vegeto-alkalis, or alkaloids, constitute a remarkable and most interest- ing group of bodies; they are met with in various plants, always in combi- nation with an acid, which is in many cases of peculiar nature, not occur- ring 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. Two 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. MORPHIA, or MORPHINE. 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 morphia, three or four other alkaloids in very variable quantities, combined with sulphuric acid and an organic acid called the meconic. In addition to these, there are gummy, resinous, and coloring matters, caoutchouc, &c., besides mechanical impurities, as chopped leaves. The opium of Turkey is the most valuable, and contains the largest quantity of morphia ; 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 abund- ant buff-colored or brownish-white precipitate falls, which consists principally of morphia and narcotine, rendered insoluble by the withdrawal of the acid. The product is too impure, however, for use. The chief difficulty in the preparation of these substances is to get rid of the coloring matter, which adheres with great obstinacy, re-dissolving with the precipitates, and being again in part thrown down when the solutions are 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 morphia, now Treed to a considerable extent from color, a stream of sulphuretted hydrogen is passed. The filtered and nearly colorless liquid, from which the lead has thus been 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 VEGETO-ALKALIS. 427 the morphia and narcotine; these may be separated by boiling ether, in which the latter is soluble. The meconate of lead, well washed, suspended in water, and decomposed by sulphuretted hydrogen, yields solution of meconic acid. . Morphia 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 morphia may be made to crystallize, while the narcotine, and other bodies, are left behind. Repeated re-crystallization, 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. Thiboumery, which consists in adding hydrate of lime in ex- cess to an infusion of opium, by which the meconic acid is rendered insolu- ble, while the morphia is taken up with ease by the alkaline earth. By exactly neutralizing the filtered solution with hydrochloric acid, the morphia is precipitated, but in a somewhat colored state. Morphia, when crystallized from alcohol, forms small, but very brilliant prismatic crystals, which are transparent and colorless. It requires at least 1000 parts of water for solution, tastes slightly bitter, and has an alkaline reaction. These effects are much more evident in the alcoholic solution. It dissolves in about 30 parts of boiling alcohol, and with great facility in dilute acids; it is also dissolved by excess of caustic potash or soda, but scarcely by excess of ammonia. When heated in the air, morphia melts, inflames like a resin, and leaves a small quantity of charcoal, which easily burns away. Morphia, in powder, strikes a deep bluish color with neutral persalts of iron, decomposes iodic acid with liberation of iodine, and forms a deep yellow or red compound with nitric acid; these reactions are by some considered characteristic. Crystallized morphia contains C 35 H 20 NO 6 -|-2HO. The most characteristic and best-defined salt of this substance is the hydro- chlorate. It. crystallizes in slender, colorless needles, arranged in tufts or stellated groups, soluble in about 20 parts of cold water, and in its own weight at a boiling temperature. The crystals contain 6 eq. of water. The sulphate, nitrate, and phosphate are crystal lizable salts: the acetate crystallizes with great difficulty, and is usually sold in the state of a dry powder. The artificial meconate is sometimes prepared for medicinal use. NARCOTINE The marc, or insoluble portion of opium, contains much narcotine, which may be extracted by boiling with dilute acetic acid. From the filtered solution the narcotine is precipitated by ammonia, and after- wards purified by solution in boiling alcohol, and filtration through animal charcoal. Narcotine crystallizes in small, colorless, brilliant prisms, which are nearly insoluble in water. The basic powers of narcotine are very fee- ble ; it is destitute of alkaline reaction, and, although freely soluble in acids, refuses, for the most part, to form with them crystallizable compounds. Narcotine contains C 48 H 24 NO, 5 . Narcotine yields some curious products by the action of oxidizing agents, as a mixture of dilute sulphuric acid and oxide of manganese, or a hot solu- tion of bichloride of platinum. The most important of these is opianic acid, a substance forming colorless, 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 con- 428 VEGETO-ALKALIS. tains C 20 H 8 5 ,HO. The ammonia-salt, by evaporation to dryness, yields a nearly white insoluble powder, called opiamrnon, containing C 40 H 17 NO J6 , convertible by strong acids into opianic acid and ammonia. Sulphurous acid yields with opianic acid two products Qorrtaining sulphur. A mixture of peroxide of lead, opianic acid, and sulphuric acid gives rise to a crystal- lizable acid substance termed hemipinic acid, containing C 10 H 4 O 5 ,HO. A basic substance, cotarnine, C 26 H 13 N0 5 , 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 long orange-colored needles, and contained C 36 H 19 NO, .* CODEINE. Hydrochlorate of morphia, 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 morphia is precipitated, and the codeine left in solution. Pure codeine crystallizes, by spontaneous evapora- tion, in colorless transparent octahedrons; it is soluble in 80 parts of cold, and 17 of boiling water, has a strong alkaline reaction, and forms crystal- lizable salts. Codeine is composed of C 35 H 20 NO 5 . THEBAINE or PARAMOB.PHINE. This substance is contained in the precipi- tate formed by hydrate of lime in a strong infusion of opium in Thiboumery's process for morphia. 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 colorless needles like those of narcotine, but sparingly soluble in water, readily soluble in the cold in alcohol and ether. It melts when heated, and decomposes at a high temperature. With dilute acids it forms crystallizable compounds, and when isolated and in solution has a powerful alkaline reaction. The composition of thebaine is yet uncertain. Pseudomorphine, narceine, and meconine are also, at least occasionally, con- tained in opium ; they are of small importance, and 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 morphia-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 the base has been removed, which may be known by the acid being entirely combustible, without residue, when heated in the flame of a spirit-lamp upon platinum foil. It is with the great- est difficulty obtained free from color. Meconic acid crystallizes in little colorless pearly scales, which dissolve in four parts of hot water. It has an acid taste and reaction, forms soluble com- pounds with the alkalis, and insoluble salts with lime, baryta, and the oxides of lead and silver. The most remarkable feature of this substance is its pro- perty of striking a deep blood red color with a salt of the peroxide of iron, exactly resembling that developed under similar circumstances, by a sulpho- cyanide. The meconate of iron may, however, be distinguished from the latter compound, as Mr. Everitt has shown, by an addition of corrosive subli- mate, which bleaches the sulphocyanide, but has little effect upon the meco nate. This is a point of considerable practical importance, as in medico-legal * Annalen der Chem. und Pharm. 1. 29; and Ann. China, et Phys. 3d series, xii. 230. VEGETO-ALKALIS. 429 inquiries, in which evidence of the presence of opium is sought for in com- .plex organic mixtures, the detection of meconic acid is usually the object of the chemist; and since traces of alkaline sulphocyanide are said to be found in the saliva, it becomes very desirable to remove that source of error and ambiguity. Crystallized meconic acid contains C 14 HO n ,3HO-|-6HO. When a solution of mecom'c 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, it is decomposed, yielding a new bibasic acid, the comenic containing C 12 H 2 O fc ,2HO, which much resembles in properties meconic acid. Water and car- bonic acid are at the same time extricated. At a higher temperature comenic acid itself is resolved into a second new acid, the pyromeconic, which sublimes and afterwards condenses in brilliant colorless plates. It is monobasic, and contains C 10 H 3 O 5 ,HO. An acid much resembling the meconic has been extracted from the Chelido- nium majus; it is combined with lime, and associated with malic and fumaric acids. Chelidonic acid is tribasic, 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 colorless needles of considerable solubility, containing C I4 H 2 10 ,3HO-|-2HO. CIXCHONIA AND QUINA. It is to these vegeto-alkalis that the valuable medi- cinal 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. Cinchonia is contained in largest quantity in the pale bark; quina in the yellow bark; the officinal red bark 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 separated by converting them into sulphates ; the salt of quina is the least soluble of the two, and crystallizes first. Pure cinchonia, or cinchonine, crystallizes in small, but beautifully brilliant 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 exces- sively bitter. It is a powerful base, neutralizing acids completely, and form- ing a series of crystallizable salts. Quina, or quinine, much resembles cinchonia ; it does not crystallize so well, however, and is much more soluble in water ; its taste is intensely bitter. Sulphate of quina is manufactured on a very large scale for medicinal, use ; it crystallizes in small white needles, which give a neutral solution. The solubility of this compound is much increased by the addition of a little sulphuric acid. Cinchonia is composed of . C 20 H 12 NO, and Quina of .... C 20 H 12 NO 2 . Chinoidine, quinoidine, or amorphous quinine, is contained in the refuse, or mother-liquors of the quinine manufacturer. In its purest state it forms a yellow or brown resin-like mass, insoluble in water, freely soluble in alcohol and ether. It is easily soluble also in dilute acids, and is thence precipitated by ammonia. Quinoidine is said to possess powerful febrifuge properties, and to be identical in composition with quinine. If such be the case, it may bear to quinine the same relation that uncrystallizable syrup does to ordinary 430 VEGETO-ALKALIS. sugar, being produced from quinine by the heat employed in the prepara- tion.* From CMSCO, or Jlrica-bark, a substance denominated aricine has been ex- tracted ; it closely resembles cinchonine. The Cinchona ovata, or white quinquina of Condamine, contains a crystal- lizable basic substance, termed cinchovatine.^ said to contain C 46 H 27 N<,O 8 . It is useless in medicine. KINIC ACID. Kinate of lime is found in the solution from which the bark- alkalis have been separated by hydrate of lime, and is easily obtained by eva- poration, and purified by animal charcoal. From the lime-salt the acid can be extracted by decomposing it by diluted sulphuric acid. The clear solution evaporated to a syrupy consistence deposits large, distinct crystals, which re- semble those of tartaric acid. It is soluble in 2 parts of water, and contains C 1 .H I1 1U HO. When Idnic acid is heated with a mixture of sulphuric acid and peroxide of manganese, it furnishes a very volatile substance termed chinone, the vapor of which is exceedingly irritating to the eyes. This new body forms crys- tals both by sublimation and by solution in boiling water; it melts with gentle heat, crystallizes on cooling, colors the skin permanently brown, and contains C 25 H 8 8 By destructive distillation, kinic acid yields numerous and interesting pro- ducts, which have been studied by M. Wohler, as benzoic acid, carbolic acid, hydruret of salicyle, benzine, a tarry substance not examined, and a new body, colorless hydrochinone, which possesses very curious relations with the chinone above described. It forms colorless six-sided prismatic crystals ; is neutral, destitute of taste and odor, fusible, and easily soluble both in water and alcohol. With care it may be sublimed unchanged. It contains C 25 H 128- Colorless hydrochinone can be easily and directly produced from chinone by the assimilation of hydrogen, as by addition of hydriodic acid to a solution of the latter, when iodine is set free, or by sulphurous acid, or telluretted hy- drogen. An intermediate product of reduction is green hydrochinone. This is ob- tained by the incomplete action of sulphurous acid upon chinone, or by the action of perchloride of iron, chlorine, nitrate of silver, or chromic acid upon colorless hydrochinone; or by mixing together solutions of chinone and color- less hydrochinone. It forms slender green crystals of the color of the wing- case of the rose-beetle, and of the greatest brilliancy and beauty. It is fusi- ble, has but little odor, and dissolves freely in boiling water, crystallizing out on cooling. This substance contains C 25 H 10 O 8 . Other products were obtained by the action of sulphuretted hydrogen and strong hydrochloric acid upon chinone, which possess less interest than the preceding.^ STRYCHNIA and BRTJCIA are contained in Nux vomica, in St. Ignatius' 1 bean, and in false Jlngustura bark ; they are associated with a peculiar acid, called * Amorphous quinine is a mixture of quina, cinchonia, and a resin. Quina may be obtained from it by dissolving in alcohol, precipitating by protochloride of tin, filter- ing and adding ammonia to the clear liquor. The precipitate well washed and dried, and a second time treated with protochloride of tin and ammonia, yields to alcohol pure quina, which crystallizes on evaporating the alcohol. R. B. f Pelouze and Fremy state that the cinchovatine discovered byManzini is identical with aricine, and give its composition as C^H^NC^. Quina may be distinguished from the other organic bases by acting on the solution by chlorine and then adding ammonia, when a greenish-blue color is produced if quina be present. R. B. J Annalen der Chem. und Pharm. li. 145. VEGETO-ALKALIS. 431 the igasuric. Nux vomica seeds are boiled in dilute sulphuric acid until they become soft; they are then crushed, and the expressed liquid mixed, with ex- cess of hydrate of lime, which throws down the alkalis. The precipitate is boiled in spirit of wine of sp. gr. .850, and filtered hot. Strychnia and brucia are deposited together in a colored and impure state, and may be separated by cold alcohol, in which the latter dissolves readily. Pure strychnia crystallizes under favorable circumstances in small, but ex- ceedingly brilliant octahedral crystals, which are transparent and colorless. It has a very bitter taste, is slightly soluble in water, and is fearfully poison- ous. It dissolves in hot, and somewhat dilute spirit, but neither in absolute alcohol, ether, nor in solution of caustic alkali. Strychnia forms with acids a series of well-defined salts. It is composed of C 44 H 23 N 2 4 . Brucia is easily distinguished from the preceding substance, which it much resembles in many respects, by its ready solubility in alcohol, both hydrate and absolute. It dissolves also in about 500 parts of hot water. The salts of brucia are, for the most part, crystallizable. Brucia contains C 44 H 25 N 2 O 7 . VERATRIA is obtained from the seeds of Veratrum sabadilla. In its purest state it is a white, or yellowish-white powder, which has a sharp burning taste, and is very poisonous. It is remarkable for occasioning violent sneez- ing. It is insoluble in water, but dissolves in hot alcohol, in ether, and in acids ; the solution has an alkaline reaction. Veratria contains nitrogen, but its composition is yet doubtful.* A substance called colchidne, extracted from the Colchicum autumnal^ and formerly confounded with veratria, is now considered distinct; its history is yet imperfect. CONICINE, or CONIA, and NICOTINE differ from the other vegetable bases in physical characters; they are volatile oily liquids. The first is extracted from hemlock, and the second from tobacco. They agree in most of their characters, having high boiling points, very poisonous properties, strong alka- line reaction, and the power of forming with acids crystallizable salts. The formula of nicotine is given by Ortigosa as . . . 17.14 Uric acid 1.00 Sulphates of potash and soda . . . . . 6.87 Phosphate of soda t (V- >.-.-. 2-94 ammonia 1.65 lime and magnesia .... 1.00 Chloride of sodium 4.45 Sal ammoniac 1.50 Silica 0.03 Mucus of bladder . 0.32 1000.00 * All dark- colored, uncrystallizable substances, soluble both in water and alcohol, were confounded by the old chemists under the general name of extractive matter. The progress of modern science constantly tends to extricate from this confused mass one by one the many definite organic principles therein contained in a more or less modified form, and to restrict within narrower limits the application of the term. In the above instance, the coloring matter of the urine, and it may be several other sub- stances, are involved. Professor Liebig states that all his endeavors to obtain direct evidence of the exist- ence of lactic acid in the urine, either in a fresh or putrid state, completely failed. Putrid urine yielded a volatile acid in a notable quantity, which turned out to be acetic acid; a little benzoic 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 decomposition 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 constantly produced by the oxida- tion of the proteine compounds of the food, or rather of the body. Lancet, June, 1844. Still more recently, Liebig has announced the discovery in the urine of kreatine and kreatinine, already described. Putrid urine contains kreatinine only. AND URINE. 479 In certain states of disorder and disease, substances appear in the urine which are never present in the normal secretion; of these the most common is albumen. This is easily detected by the addition of nitric acid in excess, \vhich then causes a white cloud or turbidity, or by corrosive sublimate, the urine being previously acidified by a little acetic acid ; boiling causes muddi- ness or even in extreme cases a coagulum, which is insoluble in nitric acid. Mere turbidity by boiling is no proof of albumen, the earthy phosphates being often thrown down from nearly neutral urine under such circumstances; the phosphatic precipitate is, however, instantly dissolved by a drop of nitric acid. In diabetes, the urine contains grape-sugar, the quantity of which commonly increases with the progress of the disease, until it becomes enormous, the urine acquiring a density of 1.030 and beyond. It does not appear that the urea is deficient abso- Fig. 176. lutely, although more difficult to discover from being mixed with such a mass of syrup. The smallest trace of sugar may be discovered in urine by Trommer's test, formerly mentioned : a few drops of solution of sulphate of copper are added to the urine, and afterwards an excess of caustic potash ; if sugar be present, a deep- blue liquid results which, on boiling, deposits red suboxide of copper. With proper manage- ment, this test is very valuable ; it will even detect sugar in the blood of diabetic patients.* Urine containing sugar, mixed with a little yeast and put in a warm place, readily undergoes vi- nous fermentation, and afterwards yields, on distillation, weak alcohol, contaminated with ammonia. Tlie urine of children is said sometimes to contain benzoic acid; it is pos- sible 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- The deposit of buff colored or pinkish amorphous urate of ammonia, which so frequently occurs in urine upon cooling, after unusual exercise or slight derangements of health, may be at once distinguished from a deposit of am- monio magnesian phosphate by its instant disappearance on the application of heat. The earthy phosphates, besides, are never deposited from urine which has an acid reaction. The nature of the red coloring matter 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 odor, and quickly putrefies. In composition it resembles that of man, and is rich in urea. In birds and serpents, the urine is a white pasty substance, consisting almost entirely of urate of ammonia. In herbivorous animals, it is alkaline and often turbid from earthy carbonates and phosphates; urea is still the characteristic ingredient, while of uric acid there is scarcely a trace ; hippuric acid is usually, if not always, present, * Dr. Bence Jones, Med. Chirur. Trans, vol. xxvi. Great care must be taken in using this test, which depends on the instantaneous reduction of the oxide of copper. By long boiling, very many organic substances produce this reaction. 480 URINARY CALCULI. Fig. 177. sometimes to a very large extent. When the urine putrefies, this hippuric acid, as already noticed, becomes changed to ammonia and benzoic acid. UHINABT CALCULI.- Stony 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 endeavors have been made to find some solvent or solvents for these calculi, and thus supersede the neces- sity of a formidable surgical operation for their removal, success has been but very partial and limited. Urinary calculi are generally composed of concentric layers of crystalline or amorphous matter, 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 have an imperfectly crystalline, distinctly concentric structure, and are tolerably hard. Before the blowpipe, the uric acid calculus burns away, leaving a minute quantity of ash, which is often alkaline. It is insoluble in water, but dissolves with facility in caustic potash, with but little ammoniacal odor ; the solution mixed with acid gives a copious white curdy precipi- tate of uric acid, which speedily becomes dense and crystalline. Cautiously heated with nitric acid, and then mixed with a little ammonia, it gives the characteristic reaction of uric acid, viz., deep purple-red murexide. 2. Urate of Ammonia. Calculi of urate of ammonia much resemble the preceding; they are easily distinguished, however. The pow- der boiled in water dissolves, and the solution gives a precipitate of uric acid when mixed with hydrochloric acid. It dissolves also in hot caustic potash with copious evolution of ammonia. 3. Fusible Calculus ; Phosphate of Lime with Phosphate of Magnesia and Ammonia. This is one of the most common kinds. The stones are usually white or pale-colored, smooth, earthy, and soft; they often attain a large size. Before the blowpipe, this substance blackens from animal matter which 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 litne are very rare, as also those of phosphate of mag- nesia and ammonia; the latter salt is sometimes seen forming small, brilliant crystals in cavities in the fusible calculus. Fig. 178 Fig. 179. NERVOUS SUBSTANCE. 481 4. Oxalale of Lime Calculus; Mulberry Calculus. The latter name is de- rived from the rough, warty character, and dark blood-stained aspect of this variety ; it is perhaps the worst form of calculus. It is exceedingly hard ; the layers are thick and Fig. 180. imperfectly crystalline. Before the blowpipe the oxalate 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 nitric acid. When finely powdered and long boiled in a solution of carbonate of potash, oxalate of pot- ash may be discovered in the filtered liquid, when carefully neutralized by nitric acid, by white pre- cipitates with solutions of lime, lead, and silver. A sediment of oxalate of lime, in very minute, transparent, octahedral crys- tals, only to be seen by the microscope, is of common occurrence in urine in which a tendency to urate of ammonia deposits exists. 5. 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 potash, a drop of solution of acetate of lead added, and the whole boiled, a black precipitate containing sulphuret of lead makes its appearance. By these characters cystic oxide is easily recognized. Xanthic oxide, also a definite organic principle, is distinguished by the peculiar deep-yellow color 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 ammo- nia and oxalate of lime are not unfrequently associated in the same stone. NERVOUS SUBSTANCE; MEMBRANOUS TISSUE; BONES. NERVOUS SUBSTANCE. The brain and nerves consist of a kind of half- coagulated albuminous substance, containing several remarkable fatty princi- ples, capable of being extracted by alcohol and ether, some of which are yet very imperfectly known, and about 80 per cent, of water. Besides choleste- rine, and a little ordinary fat, separated in the manner mentioned, M. Fremy* describes two new bodies, cerebric acid and oleo -phosphoric acid. The first is solid, white, and crystalline, soluble without difficulty in boiling alcohol, and forming with hot water a soft, gelatinous mass. It melts when heated, and decomposes almost immediately afterwards, exhaling a peculiar odor, and leaving a quantity of charcoal which contains free phosphoric acid, and is in consequence very difficult to burn. It combines with the alkalis, but forms insoluble compounds. Cerebric acid contains in 100 parts, Carbon 66.7 Hydrogen 10.6 Nitrogen 2.3 Oxygen 19.5 Phosphorus 0.9 41 100.0 * Ann. Chim. et Phys. 3d series, ii. 463. 482 MEMBRANOUS TISSUES BONES. 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 cebroleine, and phosphoric acid, which dissolves. The oily matter of the brain is sufficient in quantity to form with the albu- minous portion a kind of emulsion, which, when beaten up, remains long suspended in water. MEMBRANOUS TISSUES; SKIN. The composition of the many gelatine- giving tissues of the body is in great measure unknown ; even that of gela- tine 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 51.04 Hydrogen 7.08 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 disengage- ment of ammonia in caustic potash, and the solution, when mixed with acid, deposits a kind of proteine common to the whole. It is useless assigning for- mulas 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 impu- rities, is immersed in a dilute solution of tannic acid, the animal matter gra- dually combines with that substance as it penetrates inwards, forming a per- fectly insoluble compound, which resists putrefaction completely ; 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, however, various con- trivances, some of which show great ingenuity, have been adopted with more or less success, for quickening the operation. All leather is not tanned ; glove- leather is dressed with alum and common salt, and afterwards treated with a 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. BONES. Bones are constructed of a dense cellular tissue of membranous matter, made stiff and rigid by insoluble earthy salts, of which phosphate of lime (PO 5 3CaO) is the most abundant. The proportions of earthy and animal matter vary very much with the kind of bone and with the age of the indi- vidual, as will be seen in the following table, in which the corresponding bones of an adult and of a stillborn child are compared: * Annalen der Chemie und Pharmacie, xl. 50. ANIMAL NUTRITION. 483 -\ r ^^^^fc*^' Inorganic Organic Inorganic Organic matter. matter. matter. matter. Femur . 62.49 . 37.51 . 57.51 . 42.49 Humerus . 63.02 . 36.98 . 58.08 . 41.92 Radius . 60.51 . 39.49 . 56.50 . 43.50 Os temporum 63.50 . 36.50 t . 55.90 . 44.10 Costa . 57.49 . 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 is due to Berzelius : Human bones. Ox-bones. Animal matter soluble by boiling . 32.17 ) ~K o n Vascular substance . . . . 1.13 ( Phosphate of lime, with a little fluoride ) ,-a n* < O r of calcium ... 5 57 ' 3 Carbonate of lime .... 11.30 3.85 Phosphate of magnesia . . . 1.16 2.05 Soda, and a little common salt . . 1.20 3.45 100.00 100.00 The teeth have a very similar composition, but contain less 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, neces- sitates an equally constant repair and renewal of the whole frame by the de- position or organization of matter from the blood, which is thus gradually im- poverished. To supply this deficiency of solid material in the circulating fluid is the office of the food. The striking contrast which at first appears in the nature of the food of the two great classes of animals, the vegetable feeders and the carnivorous races, diminishes greatly on close examination : it will be seen that, so far as the materials of blood, or, in other words, those devoted to the repair and sustenance of the body itself, are concerned, the process is the same. In a flesh-eating animal great simplicity is observed in the construction of the digestive organs; the stomach is a mere enlargement of the short and simple alimentary canal ; and the reason is plain ; the food of the creature, flesh, is absolutely identical in composition with its own blood, and with the body that blood is destined to nourish. In the stomach it undergoes mere so- lution, being brought into a state fitted for absorption by the lacteal vessels, by which it is nearly all taken up, and at once conveyed into the blood; the excrements of such animals are little more than the comminuted, bones, fea- thers, hair, and other matters which refuse to dissolve in the stomach. TMe same condition, that the food employed for the nourishment of the body must have the same or nearly the same chemical composition as the body itself, is really fulfilled in the case of animals that live exclusively on vegetable sub- stances. It has been shown* that certain of the azotized principles of plants, * Liebig, Ann. der Chim. und Pharm. xxxix. 129. 484 ANIMAL NUTRITION. which often abound, and are never altogether absent, have a chemical com- position and assemblage of properties which assimilate them in the closest manner, and it is believed even identify them, with the proteine-giving prin- ciples of the animal body; vegetable albumen, fibrine, and caseine are not to be distinguished from the bodies of the same name extracted from blood and milk. If a portion of wheaten flour be made into a paste with water, and cau- tiously washed on a fine metallic sieve, or in a cloth, a grayish, adhesive, elastic, insoluble substance will be left, called gluten, and a milky liquid will pass through, which by a few hours' rest becomes clear by depositing a quan- tity 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 com- position as animal albumen. The gluten itself is a mixture of true vegetable fibrine and a small quantity of a peculiar azotized matter called gliadine, to which its adhesive properties are due. The gliadine 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 caustic alkali, and also in acetic acid. The fibrine of other grain is unaccompanied by gliadine; barley and oatmeal yield no gluten, but incoherent filaments of nearly pure fibrine. Vegetable albumen 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 at a temperature 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 resemblance to the caseine of milk. When a solution of this substance is heated, no coagulation occurs, but a skin forms on the sur- face, 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 potash with production of a small quantity of alkaline sulphuret; the filtered solutions mixed with excess of acid give precipitates of one and the same substance, proteine. The following is the composition in 100 parts of vegetable albumen and fibrine; it will be seen that they agree very closely with the results before given. Albumen. Fibrine. Carbon ...."-. 55.01 54.60 Hydrogen 7.23 7.30 Nitrogen 15.92 15.81 Oxygen, sulphur, and phosphorus . . 21.84 22.29 100.00 100.00 The composition of vegetable caseine, or legumine, has not been so well made out; so much discrepancy appears in the analyses as to lead to the sup- position 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 sustenance in the manner described : some of these, as vegetable fibre or VEGETABLE NUTRITION. 485 lignine, and waxy matter, pass unaltered through the alimentary canal; others, as starch, sugar, gum, and perhaps vegetable fat, are absorbed into the system, and afterwards disappear entirely: they are supposed to con- tribute 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 fibrine, Vegetable albumen, Vegetable caseine, Animal flesh, Blood. To the latter, Fat, Starch, Gum, Cane sugar, Grape sugar, Milk sugar, Pectine, Alcohol 1 ? In a flesh-eating animal the waste of the tissues is very rapid, the tempe- rature 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 non-azotized substances being consumed in the blood in 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 effects are ascribed to differences in the activity of the respiratory function ; in the first instance, the heat-food is supplied faster than it is consumed, and hence accumulates in the form of fat ; in the second, the conditions are re- versed, and the creature is kept in a state of leanness by its rapid consump- tion. The fat of an animal appears to be a provision of nature for the main- tenance 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 is contended that satisfactory evidence exists of the conversion of starch and saccharine substances into fat, by a separation of carbon and oxygen, the change somewhat resembling that of vinous fermentation : it is argued, on the other side, that oily or fatty matter is invariably present in the food supplied to the domestic animals, and that this fat is merely absorbed arid deposited in the body in a slightly modified state. The question can only be decided by correct and most careful quanti- tative experiments, which are yet wanting. It is not known in what manner digestion, the reduction in the stomach of the 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 or 100, dissolves coagulated albumen, fibrine, &c.; but many hours are re- quired for that purpose. The gastric secretion has been supposed to contain a peculiar organic principle called pepsine, said to have been isolated, to which this solvent power is, in conjunction with the hydrochloric acid, attributed. But an artificial mixture containing pepsine scarcely dissolves fibrine or boiled * Animal Chemistry, p. 96 41* 486 VEGETABLE NUTRITION. white of egg more easily than the dilute acid. The characters of pepsine itself are so indefinite as to lead to great doubt of its individuality.* 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 substances identical in composition with the body it is to nourish, or requiring but little chemical change to become s.o. 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; albumen and fibrine are probably more complex compounds than gelatine 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. The 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 nitro- gen of the atmosphere, the water which falls as rain, or is deposited as dew ; the minute trace of ammoniacal vapor present in the air ; the alkali and saline matter extracted from the soil ; such are the substances which yield to plants the elements of their growth. That green healthy vegetables do possess, under circumstances to be mentioned immediately, the property of decomposing car- bonic acid absorbed by their leaves from the air, or conveyed thither in solu- tion through the medium of their roots, is a fact positively proved by direct experiment, and rendered certain by considerations of a very stringent kind. To effect this very remarkable decomposition, the influence of light is indis- pensable ; the diffuse light of day suffices in some degree, but the direct rays of the sun greatly exalt the activity of the process. The carbon separated in this manner is retained in the plant in union with the elements of water, with which nitrogen is also sometimes associated, while the oxygen is thrown off into the air from the leaves in a pure and gaseous condition. The effect of ammoniacal salts upon the growth of plants is so 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 gwanof of the South Seas, which * Among the substances necessary to the functions of digestion, diastase of animal origin has latterly been made to take a part. The view taken by Mialhe of digestion is, that the essential agents in this process are dilute acid, pepsine, and diastase, the two former being constituents of the gastric juice, the latter derived from the salivary and pancreatic glands. The action of the acid is to swell up and moisten the aliment, rendering it fit to be acted on by the pepsine. Under these circumstances, fibrine, gluten and albumen dissolved in the weak acid exhibit many of the chemical properties of caseine, it is coagulated by pepsine, but the coagulum is immediately dissolved by an excess of this principle and completely changed in character. The pepsine has no in- fluence on amylaceous matters ; these are acted upon by the diastase, and, by conver- sion into dextrine and sugar, become soluble. R. B. f Guano is the partially decomposed dung of birds, found in immense quantity on some of the barren islets of the western coast of South America, as that of Peru. More recently, similar deposits have been found on the coast of Southern Africa. The guano now imported into England from these localities is usually a soft, brown powder, of various shades of color. White specks of bone-earth, and sometimes masses of saline matter, may be found in it. That which is most recent, and probably most valuable as manure, often contains undecomposed uric acid, besides much oxalate or hydro- chlorate of ammonia, and alkaline phosphates, and other salts : it has a most offensive VEGETABLE NUTRITION. 487 usually contains a large proportion of ammoniacal salt, and even of pure sul- phate of ammonia. Some of these manures doubtless owe a part of their value to the phosphates and alkaline salts they contain ; still, the chief effect 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 destined to become the food of animals, and of man. The chemistry of vegetable life is of a very high and mysterious order, and the glimpses occasionally obtained of its general nature are few and rare. One thing, however, is manifest, namely, the wonderful relations between the two orders of organized beings, in virtue of which the rejected and refuse matter of the one is made to con- stitute 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. odor. The specimens taken from older deposits have but little smell, are darker in color, contain no uric acid, and much less ammoniacal salt ; the chief components are bone-earth, a peculiar dark-colored organic matter, and soluble inorganic salts. See also p. 425. 488 SUBSTANCES OBTAINED PROM TAR. SECTION IX. ON CERTAIN PRODUCTS OF THE DESTRUCTIVE DISTILLATION AND SLOW PUTREFACTIVE CHANGE OF ORGANIC MATTER. SUBSTANCES OBTAINED FROM TAB. THERE are three principal varieties of tar: (1.) Tar of the wood-vinegar maker, procured by the destructive distillation of dry hard wood ; (2.) Stock- holm far, 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-timber ; 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 ex- tremely complicated nature, from which a number of curious products, to be presently described, have been procured ; the solid brown or black residue constitutes pitch. Hard-wood tar furnishes the following: PARAFFINE; TAR-OIL STEARINE. 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, paraffine appears in the shape of small colorless needles, fusible at 110 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 insolu- ble in water, slightly soluble in alcohol, freely in ether, and miscible in all pro- portions, when melted, with both fixed and volatile oils. The most energetic chemical reagents, as strong acids, alkalis, 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 parum affinis. Paraffine contains carbon and hydrogen only, and in the same proportions as in olefiant gas,' or CH. M. Leroy, of Copenhagen, makes it C 20 H 21 . The rational formula is of course unknown. EUPIONE.* This is the chief component of the light oil of wood-tar; it 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 oxi- dizes and destroys most of the accompanying substances. In a pure state, it is an exceedingly thin, liquid, colorless liquid, of agreeable aromatic odor, but destitute of taste; it is the lightest known liquid, having a density of .655. At 116 it boils and distils unchanged. Dropped upon paper, it makes a # From ^ good, beautiful, and yrtov, fat- SUBSTANCES OBTAINED FROM TAR. 489 greasy stain, which after a time disappears. Eupione is very inflammable, and burns with a bright luminous flame. In water it is 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 C 5 H 6 . Other volatile oils, having a similar origin, and perhaps a similar composi- tion, but differing from the above in specific gravity and boiling-point, are sometimes confounded with eupione. The study of these substances pre- sents many serious difficulties. It is even doubtful whether the eupione be not formed by the energetic chemical agents employed in its supposed purifi- cation, 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, colorless, oily liquid, of feeble odor, but intensely bitter taste. Its density is 1.095, and it boils at 518. 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 crystalline compounds, which, although decomposed by water, are soluble without change in spirit. The composition of this substance is unknown. KAPNOMOR.! Such is the name given by Dr. Heichenbach to another oily liquid obtained from the same source as the last, by a long and complex pro- cess, in which strong solutions of caustic potash are freely used. It is de- scribed as a colorless volatile oil, of high boiling-point, and rather lighter than water ; it has an odor of ginger, and a taste feeble at first, but afterwards becoming connected with an insupportable sense of suffocation. 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 potash salt of which is crystallizable. Its composition is unknown. CEDRTHET.J The lighter oil of hard-wood tar contains a substance, separa- ble from the eupione, &c., by caustic alkalis, which in contact with oxidizing agents, as persulphate of iron, chromic acid, or even atmospheric air, yields a mass of small, red, reticulated crystals, infusible by heat, and soluble in con- centrated sulphuric acid with deep indigo-blue color. This substance is in- soluble in water, alcohol, and ether ; nothing is known respecting its com- position. PITTAKAI, The name is derived from two Greek words signifying pitch or resin and beautiful; it is found in the heavy oil of wood, but has been very imperfectly described. The characteristic property of pittakal is to form with barytes a compound which assumes in the air a fine purple or blue tint, gradually passing into black. KREOSOTE. 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 extracted by a most tedious and complicated series of operations ; it certainly pre-exists, however, in the original material. The tar is distilled in a metallic vessel, and the different products collected apart; the most volatile portion, which is lighter than water and consists chiefly of eupione, is rejected ; the second portion is denser, and contains the kreosote, and is set aside ; the distillation is stopped when paraffine begins to pass over in quantity. The impure * From piX) and amarus, in allusion to its bitter taste. f From Kctmo;, smoke, ^"pa, part. t From cedrtum, tne old name for acid tar-water, and rete, a net. Derived from xpla?, flesh, and g-obfat, I preserve 490 VOLATILE PRINCIPLES OP COAL TAR. kreosote is first agitated with carbonate of potash to remove adhering 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 caus- tic potash of specific gravity 1.12, and decanted from the insoluble oil which floats on the surface ; this alkaline liquid is boiled and left some time in con- tact with air, by which it acquires a brown color 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 again dissolved in caustic potash, boiled in the air, and the solution decomposed by acid, and this treatment repeated until the product ceases to become colored by the joint influence of oxygen and the alkaline base. When so far purified, it is well washed with water, and distilled from a little hy- drate of potash. The first portion contains water ; that which succeeds is pure kreosote. In this condition, kreosote is a colorless, somewhat viscid oily liquid of great refractive and dispersive power. It is quite neutral to test paper ; it has a penetrating and most peculiar odor, that namely, of smoked meat, and a pungent and almost insupportable taste when placed in very small quantity upon the tongue. The density of this substance is 1.037, and its boiling point 397 F. 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 kreo- sote of commerce becomes, however, under these circumstances, gradually brown. 100 parts of cold water take up about 1^- 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 potash 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 composition is yet uncertain. 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. CHRYSEW 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 color, is a pure yellow, crystalline 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 color. Boiling nitric acid converts it into an insoluble red substance, which has been studied. Chrysen is composed of C 3 H. It has the same composition as idri- aline, the fossil fat of the mercury mines of Idria. Pyren differs from the preceding substance in being colorless, crystal lizable in small, soft, micaceous scales, soluble in boiling alcohol and ether. It is fusible and volatile. Pyren contains C 6 H 2 . HYDRATE OF PHENYLE. 491 Oil of ordinary tar, obtained by distillation alone, or with water, consists in great measure of unaltered oil of turpentine, mixed, however, with empyreu- matic oily products, which give it a powerful odor and a dark color. The residual pitch contains much pine-resin, and thus differs from the solid portion of the hard- wood tar so frequently mentioned. Volatile Principles of Coal Tar. Coal-tar yields on distillation a large quantity of thin, dark-colored, volatile oil, which, when agitated with dilute sulphuric acid to remove ammonia and twice rectified with water, becomes nearly colorless : it is very volatile, much lighter than water, very inflammable, and possesses in a high degree the pro- perty of dissolving caoutchouc, on which account it is very extensively used in the manufacture of waterproof fabrics containing that material. It appears that this coal-oil, or artificial naphtha, is a mixture of a number of hydrocarbons, some of which possess basic properties, and form crystal- lizable compounds with acids ; at least, a variety of different substances have been procured from the liquid in question. The remark formerly made re- specting the doubtful pre-existence of substances thus obtained also applies here. The great bulk of the coal-oil appears to be made up of a neutral volatile oil, resembling eupione ; the basic principles constitute but a small part of the whole. The lightest and most volatile portions consist chiefly of benzine. KYANOL or ANILINE, LEUKOL or CHINOLEINE, and PICOLINE, have been already described. These basic constituents of coal-tar oil are extracted by agitating large successive quantities of the oil with hydrochloric acid, and afterwards distilling the acid watery liquid obtained with excess of hydrate of lime. (See p. 437.) CARBOLIC ACID; HYDRATE OP PHENYLE. These bodies are, in all pro- bability, identical. 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, decomposed by hydro- chloric acid, and the oily product obtained purified by cautious distillation, the first third only being collected. Or, crude coal-oil is subjected to distilla- tion in a retort furnished with a thermometer, and the portion which passes over between the temperatures of 300 400 F. collected apart. This product is then mixed with a hot strong solution of caustic potash, and left to stand ; a whitish, 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 hydrate of phenyle forms long, colorless, prismatic needles, which melt at 95 to an oily liquid, boiling at 370 F., and greatly resembling kreo- sote in many particulars; having a very penetrating odor 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 coagulates albu- men. Sulphur and iodine dissolve in it ; nitric acid, chlorine, and bromine attack it with energy. Hydrate of phenyle forms soluble crystallizable com- pounds with the alkaline bases. It contains C, 2 H 5 O,HO. With sulphuric acid, hydrate of phenyle forms the compound acid sulpho- phenic att6?,C, 2 H 6 0,2SO3,HO, which assumes a syrupy state in the dry vacuum. The baryta-salt crystallizes from alcohol in minute needles. 492 NAPHTHALINE. CHLOROPHENISIC ACID. This is the characteristic and principal product of the action of chlorine on hydrate of phenyle. The pure substance is not necessary for the preparation of this body, those portions of crude coal-oil which boil between 360 400 answering very well. The oil is saturated with chlorine, and distilled in the open air, the first and last portions being rejected; the product is again treated with chlorine until the whole solidifies. The crystals are drained and dissolved in hot dilute solution of ammonia ; on cooling, the sparingly-soluble chlorophenisate of ammonia crystallizes out. This is dissolved in pure water, decomposed by hydrochloric acid, washed, and, lastly, distilled. Chlorophenisic acid forms exceedingly fine, colorless, silky needles, which melt when gently heated; it has a very penetrating, persistent, and charac- teristic odor; 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. Chloro- phenisic acid forms well-defined salts, and contains C 12 H 2 C1 3 0,HO. An intermediate product, chlorophenesic aaW, precedes the formation of this sub- stance. Bromophenisic acid is prepared by analogous means, and possesses a constitution and character greatly resembling those of the chlorine-compound. NITROPHENESIC and NITROPHENISIC ACIDS, These 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 arnmoniacal salt of nitrophenesic acid, which requires several successive crystallizations, after which it is decomposed by nitric acid, and the product crystallized from alcohol. Nitrophenesic acid forms blonde-colored prismatic crystals, very sparingly soluble even in boiling water, but freely soluble in alcohol. It has no odor. Its taste, at first feeble, becomes, after a short time, very bitter. At 219 F. it melts, and on cooling crystallizes. In very small quantity it may be dis- tilled without decomposition, but when briskly heated it often detonates, but not violently. The salts of this acid are yellow or orange, and very beau- tiful : they are mostly soluble in water, and detonate feebly when heated. The acid contains C 12 H 3 N 2 O 9 ,HO. Nitrophenisic acid is identical with picric or carbazotic acid (p. 441). It may be prepared with great economy from impure nitrophenesic acid, or from the brown mass insoluble in dilute am- monia already referred to. It is purified by a process similar to that em- ployed in the case of the preceding substances. Nitrophenisic acid contains C 12 H 2 N 3 13) HO.* Several other substances obtained from coal-oil have been incompletely described. NAPHTHALINE. 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 distilla- tion until the contents of the vessel begin to char ; the naphthaline then con- denses in the solid state, but dark-colored and very impure. By simple sub- limation, once or twice repeated, it is obtained perfectly white. In this state naphthaline forms large, colorless, transparent, brilliant crystalline plates, which exhale a faint and peculiar odor, which has been compared to that of * Ann. Chim. et Phys. 3d series, iii. 195. PETROLEUM, NAPHTHA, AND OTHER ALLIED SUBSTANCES. 493 the narcissus. Naphthaline melts at 176 to a clear, colorless liquid, which crystallizes on cooling; it boils at 413, and evolves a vapor 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 a boiling temperature; alcohol and ether dissolve it easily; a hot saturated alcoholic solution deposits fine iridescent crystals on cooling. Naphthaline is found by analysis to contain C 10 H 4 . Naphthaline 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 sulphovinic acid. One of these, the salpJwnaphthalic acid of Mr. Faraday, crystallizes from a hot aqueous solution in small white scales, which are but sparingly soluble in the cold. The free acid is obtained in the usual manner by decomposing the baryta-salt with sulphuric acid ; it forms a colorless, crystal- line, brittle mass, of acid, metallic taste, very deliquescent, and very soluble in water. The second baryta-salt is still less soluble than the preceding. The composition of these substances is yet very uncertain. Fuming nitric acid at a high temperature attacks naphthaline ; 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 naphthaline. The history of the formation of naphthaline is rather interesting ; it is perhaps the most stable of all the more complex compounds of carbon and hydrogen ; 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 vapor through a red-hot porcelain tube, a certain quantity of naphthaline is almost invariably produced. Hence its presence in coal and other tar is mainly dependent upon the tem- perature at which the destructive distillation of the organic substance has been conducted. Lamp-black very frequently contains naphthaline thus accidentally produced. PAKANAPHTHALINE. This substance occurs in the naphthaline of coal-tar, and is separated by the use of alcohol, in which ordinary naphthaline is freely soluble, but paranaphthaline almost totally insoluble; in other respects, it much resembles naphthaline. The crystals obtained by sublimation are, how- ever, usually smaller and less distinct. It melts at 356, and boils at 570, or above. Its best solvent is oil of turpentine. Paranaphthaline has the same composition as naphthaline itself; the density of its vapor is, however, different, viz. 6.741. Its composition maybe represented by the formula C 15 H 6 . PETBOLETTM, NAPHTHA, AND OTHER ALLIED SUBSTANCES. Pit-coal, lignite or brown coal, jet, bitumens of various kinds, petroleum or rock oil, and naphtha, and a few other allied substances more rarely met with, are looked upon as products of the decomposition of organic matter, espe- cially vegetable matter, beneath the surface of the earth, in situations where the conditions of contact with water, and nearly total exclusion of atmosphe- ric 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 carburetted hydrogen are by-products of the reaction ; hence their frequent disengagement, the first from beds of lig- nite, and the second from the further advanced and more perfect coal. 42 494 PETROLEUM, NAPHTHA, The vegetable origin of coal has been placed beyond doubt by microscopic research ; vegetable structure can be thus detected even in the most massive and perfect varieties of coal when cut into thin slices. In coal of inferior quality, much mixed with earthy matter, it is evident to the eye ; the leaves of ferns, reeds, and other succulent plants, more or less resembling those of the tropics, are found in a compressed state between the layers of shale or slaty clay, preserved in the most beautiful manner, but entirely converted into bituminous coal. The coal-mines of Europe, and particularly those of our own country, furnish an almost complete fossil flora ; a history of many of the now lost species which once decorated the surface of the earth. In the lignites, the woody structure is much more obvious. Beds of this material are found in very many of the newer strata, above the true coal, to which they are consequently posterior. As an article of fuel, brown-coal is of comparatively small value; it resembles peat, giving but little flame, and emitting 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 distillation of those bodies. They are very numerous, and have yet been but imperfectly studied. 1. Mineral pitch, or compact bitumen, \he asphaltum or Jews' pitch of some authors. This substance occurs abundantly in many parts of the world ; as, in the neighborhood 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 burn- ing with a red, smoky flame. It consists principally of a substance called by M. Boussingault asphaltene, composed of C 20 H 16 3 . It is worthy of re- mark, that M. Laurent found paranaphthaline in a native mineral pitch. 2. Mineral tar seems to be essentially a solution of asphaltene in an oily fluid called petroline. This has a pale yellow color and peculiar odor; it is lighter than water, very combustible, and has a high boiling-point. It has the same composition as the oils of turpentine and lemon-peel, namely, C 5 H 4 . Asphaltene contains, consequently, the elements of petrolene, together 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 consider able 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 colorless; 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 vapor 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, AND OTHER ALLIED SUBSTANCES. 495 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 immedi- ately on coal. A petroleum spring exists at Colebrookdale, in Shropshire. The sea near the Cape de Verd 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 may be cited an expe- riment of Dr. Reichenbach, who, by distilling with water about 100 Ibs. 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 color and consistence in different specimens of these bodies certainly depends in great measure upon the presence of pitchy and fatty substances dissolved in the more fluid oil. Dr. Gregory found paraffine in petroleum from Rangoon. The boiling-point of rock-oil varies from about 180 to near 600; a ther- mometer inserted into a retort in which the oil is undergoing distillation, never shows for any length of time a constant temperature. Hence it is inferred to be a mixture of several different substances. Neither do the different varie- ties of naphtha give similar results on analysis ; they are all, however, car- burets 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 potassium and sodium. The following are of rarer occurrence: Retinite, or Retinasphalt, is a kind of fossil resin met with in brown coal ; it has a yellow or reddish color, is fusible and inflammable, and readily dissolved in great part by alcohol. The soluble portion, the retinic acid of Prof. John- ston, contains C 21 H, 4 5 . Hatchetine is a somewhat similar substance met with in mineral coal at Merthyr-Tydvil, arid also near Loch Fyne, in Scotland. Idrialine has been already mentioned ; it is found associated with native cin- nabar, and is extracted from the ore by oil of turpentine, in which it dissolves. It is a white, crystalline substance, scarcely volatile without decomposition, but slightly soluble in alcohol and ether, and composed of C 3 H. 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, and soluble with difficulty in alcohol and ether, but easily in oil of tur- pentine. It appears to contain more than one definite principle. APPENDIX. ON THE EQUIVALENT NUMBERS. THE table of equivalent numbers given in the body of the work at p. 173 is chiefly taken from the tables of the Lehrbuch of Berzelius, being in great measure the results of the inquiries of that distinguished philosopher. The equivalents of arsenic, antimony, phosphorus, and columbium have been doubled, from motives of convenience. The equivalents of a few of the more important substances have been revised by subsequent investigations, and the altered numbers have been adopted in certain cases mentioned be- low. Calcium. Dumas,* and Erdmann and Marchand,f make the equivalent of calcium exactly 20. This diifers somewhat from the most recent determi- nation of Berzelius,J by a different process, viz. 20.15. The former number has been provisionally adopted. Carbon. The equivalent of carbon deduced by Dumas from his experi- ments on the combustion of the diamond is exactly 6. Similar experiments by Erdmann and Marchand|| lead to the like conclusion. The numbers de- duced by MM. Liebig and RedtenbacherlT from the analyses of certain silver salts of organic acids is 6.07, which, after all, does not differ very considerably from the whole number. Baron von Wrede,** again, makes the density of oxygen 1.1052, and that of carbonic acid 1.5204; the difference, .4152, re- ferred to the oxygen, gives the combining number for carbon = 6.01. The whole number has been adopted. Chlorine. It is exceedingly important that the equivalent of chlorine should be well established. The method adopted by Berzelius,tf and which also has been followed by Dr. Turner, JJ Pelouze, and Marignac,|||| consists in de- composing by heat a known weight of pure and dry chlorate of potash, and thus determining the relation between the equivalent of chloride of potassium and that of oxygen, the number 8 being assumed for the latter. The pro- portions in which silver and chlorine unite are then determined by direct * Comptes Rendtis, xiv. 537. !Ann. Chim. et Phys. 3d series, viii. 207. Annalen der Chem. und Pharmacie, xlvi. 241. Ann. Chim. et Phys. 3d series, i. 5. Annalen der Chem. und Pharm. xliv. 210. IT Idem, xxxviii. 113. *# Idem, xliv. 211. ft Lehrbuch, v. 106. Jt Phil. Trans, for 1833, p. 523. 66 Comptes Rendus, xiv. 950. Illl Annalen der Chem. und Pharm. xliv. 11. APPENDIX. 497 experiment; and, lastly, the quantity of chloride of silver produced from a known weight of chloride of potassium is ascertained. Thus, in the experi- ment of Berzelius first referred to, 100 parts chlorate of potash yielded 60.85 parts chloride of potassium, and 39.15 parts oxygen. From chlorate of potash 6 equivalents of oxygen are disengaged by heat ; consequently, or the numbers 6.525 and 60.85 represent the relative weights of equivalents of oxygen and of chloride of potassium. Making the former = 8, we have, by simple proportion, 6.525 : 8 : : 60.85 : 74.6005, the real equivalent of chloride of potassium. Again, 100 parts of pure silver, by solution in nitric acid and precipitation by a soluble chloride, yield 132.75 parts of dry chloride of silver; and, fur- ther, 100 parts of pure chloride of potassium, dissolved in water and preci- pitated by nitrate of silver in excess, furnish 192.4 parts of chloride of silver. Hence, Chlor. silver. Chlorine. Chlor. silver. Chlorine. 132.75 : 32.75 : : 192.4 : 47.465, the quantity of chlorine contained in 100 parts of chloride of potassium. Consequently, Chlor. potass. Chlorine. Eq. of chlor. potass. Eq. of chlorine. 100 : 47.465 : : 74.6005 : 35.41. From the preceding data the equivalents of silver and potassium are also easily determined : 132.75 parts of chloride of silver contain 32.75 parts chlorine and 100 parts silver; consequently, 32.75 : 100 : : 35.41 : 108.12, the equivalent of silver. Also, 100 parts of chloride of potassium = 47.465 parts chlorine and 52.535 parts potassium; hence, 47.465 : 52.535 : : 35.41 : 39.19 Dr. Turner's equivalent of chlorine is 35.42 ; that of Marignac is 35.37 ; and, lastly, the number found by Dr. Penny,* by a somewhat different me- thod, is 35.45. The original equivalent of Berzelius is retained in the table. Nitrogen. The density of nitrogen is, according to Dumas, .972, and that of oxygen 1.1057. In binoxide of nitrogen equal measures of the gases are combined; or, by weight, 1 equivalent nitrogen to 2 equivalents oxygen. Hence, the combining number of nitrogen is ascertained by a simple rule of proportion : 1.1057 : .972 : : 16 : 14.06 Zinc. M. Favref has quite recently re-determined the equivalent of zinc by two different methods of investigation; namely, by analysis of the oxalate, and by observing the quantity of hydrogen, estimated in the state of water * Phil. Trans, for 1839, p. 13. f Ann. Chim. et Phys. 3d series, x. 1G3. 42* 498 APPENDIX. after combustion by ignited oxide of copper, disengaged during the solution in an acid of a known weight of pure zinc. The first experiments gave as a mean the number 33.01 ; and the second set 32.97. The whole number, 33, has, therefore, been taken. Iron. Recent experiments of not less than five different chemists concur in assigning the number 28 as a very close approximation to the equivalent of iron.* Silver. The number adopted is deduced from the experiments of MM. Marignac and Maumene, which very closely agree. Mercury. The whole number 100 was obtained by MM. Erdmann and Marchand, and also by M. Millon.f Uranium. The equivalent of uranium is that of M. Peligot. HYDROMETER TABLES. COMPARISON OF THE DEGREES OF BAUME S HYDROMETER WITH THE REAL SPECIFIC GRAVITIES. 1. For Liquids heavier than Water. Degrees. Specific Gravity. Degrees. Specific Gravity. Degrees. Specific Gravity. 1.000 26 1.206 52 1.520 1 1.007 27 1.216 53 1.535 2 1.013 28 1.225 54 1.551 3 1.020 29 1.235 55 1.567 4 1.027 30 1.245 56 1.583 5 1.034 31 1.256 57 1.600 6 1.041 32 1.267 58 1.617 7 1.048 33 1.277 59 1.634 8 1.056 34 1.288 60 1.652 9 1.063 35 1.299 61 1.670 10 1.070 36 1.310 62 1.689 11 1.078 37 1.321 63 1.708 12 1.085 38 1.333 64 1.727 13 1.094 39 1.345 65 1.747 14 1.101 40 1.357 66 1.767 15 1.109 41 1.369 67 1.788 16 1.118 42 1.381 68 1.809 17 1.126 43 1.395 69 1.831 18 1.134 44 1.407 70 1.854 19 1.143 45 1.420 71 1.877 20 1.152 46 1.434 72 1.900 21 1.160 47 1.448 73 1.924 22 1.169 48 1.462 74 1.949 23 1.178 49 1.476 75 1.974 24 1.188 50 1.490 76 2.000 25 1.197 51 1.495 * Central-Blatt, Jan. 1847. t Ann. Chim. et Phys. 3d series, xviii. 333. APPENDIX. 499 2. Baum&s Hydrometer for Liquids lighter than Water. Degrees. Specific Gravity. Degrees. Specific Gravity. Degrees. Specific Gravity. 10 1.000 27 .896 44 .811 11 .993 28 .890 45 .807 12 .986 29 .885 46 .802 13 .980 30 .880 47 .798 * 14 .973 31 .874 48 .794 15 .967 32 .869 49 .789 16 .960 33 .864 50 .785 17 .954 34 .859 51 .781 18 .948 35 .854 52 .777 19 .942 36 .849 53 .773 20 .936 37 .844 54 .768 21 .930 38 .839 55 .764 22 .924 39 .834 56 .760 23 .918 40 .830 57 .757 24 .913 41 .825 58 .753 25 .907 42 .820 59 .749 26 .901 43 .816 60 .745 These two tables are on the authority of M. Franco3ur: they are taken from the Handworterbuch der Chemie of Liebig and Poggendorff. Baume's hydro- meter is very commonly used on the Continent, especially for liquids heavier than water. For lighter liquids, the hydrometer of Cartier is often employed in France. Cartier's degrees differ but little from those of Baume. In the United Kingdom, Twaddell's hydrometer is a good deal used for dense liquids. This instrument is so graduated that the real sp. gr. can be deduced by an extremely simple method from the degree of the hydrometer, namely, by multiplying the latter by 5, and adding 1000 ; the sum is the 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, Sikes's hydrometer is used. 500 APPENDIX. ABSTRACT OF DR. DALTOSr's TABLE OF THE ELASTIC FORCE OF VAPOR OF WATER AT DIFFERENT TEMPERATURES, EXPRESSED 1ST INCHES OF MERCURY. Temp. Force. Temp. Force. Temp. Force. 32 .200 57 .474 90 1.36 33 .207 58 .490 95 1.58 34 .214 59 .507 100 1.86 35 .221 60 .524 105 2.18 36 .229 61 .542 110 2.53 37 .237 62 .560 115 2.92 38 .245 63 .578 120 3.33 39 .254 64 .597 125 3.75 40 .263 65 .616 130 4.34 41 .273 66 .635 135 5.00 42 .283 67 .665 140 5.74 43 .294 68 .676 145 6.53 44 .305 69 .698 150 7.42 45 .316 70 .721 160 9.46 46 .328 71 .745 170 12.13 47 .339 72 .770 180 15.15 48 .351 73 .796 190 19.00 49 .363 74 .823 200 23.64 50 .375 75 .851 210 28.84 51 .388 76 .880 212 30.00 52 .401 77 .910 220 34.99 53 .415 78 .940 230 41.75 54 .429 79 .971 240 49.67 55 .443 80 1.000 250 58.21 56 .458 85 1.170 300 111.81 APPENDIX. 501 TABLE OF THE PROPORTION BY WEIGHT OF ABSOLUTE OR REAL ALCOHOL IN 100 PARTS OF SPIRITS OF DIFFERENT SPECIFIC GRAVITIES. (fOWNES.) Sp.Gr.at600. Per cent, of real Alcohol. Sp. Gr. at 60. Per cent, of real Alcohol. Sp. Gr. at 600. Per cent, of real Alcohol. .9991 0.5 .9511 34 .8769 68 .9981 1 .9490 35 .8745 69 .9965 2 .9470 36 .8721 70 .9947 3 .9452 37 .8696 71 .9930 4 .9434 38 .8672 72 .9914 5 .9416 39 .8649 73 .9898 6 .9396 40 .8625 74 .9884 7 .9376 41 .8603 75 .9869 8 .9356 42 .8581 76 .9855 9 .9335 43 .8557 77 .9841 10 .9314 44 .8533 78 .9828 11 .9292 45 .8508 79 .9815 12 .9270 46 .8483 80 .9802 13 .9249 47 .8459 81 .9789 14 .9228 48 .8434 82 .9778 15 .9206 49 .8408 83 .9766 16 .9184 50 .8382 84 .9753 17 .9160 51 .8357 85 .9741 18 .9135 52 .8331 86 .9728 19 .9113 53 .8305 87 .9716 20 .9090 54 .8279 88 .9704 21 .9069 55 .8254 89 .9691 22 .9047 56 .8228 90 .9678 23 .9025 57 .8199 91 .9665 24 .9001 58 .8172 92 .9652 25 .8979 59 .8145 93 .9638 26 .8956 60 .8118 94 .9623 27 .8932 61 .8089 95 .9609 28 .8908 62 .8061 96 .9593 29 .8886 63 .8031 97 .9578 30 .8863 64 .8001 98 .9560 31 .8840 65 .7969 99 .9544 32 .8816 66 .7938 100 9528 33 .8793 67 502 APPENDIX. DR. SCHWEITZER'S OF THE PRINCIPAL MINERAL WATERS OF GERMANY Grains of Anhydrous Shclesischer. Ingredients in Carlsbad. Ems. Obersalz- One Pound Troy. Brunnen. Carbonate of soda . 7.2712 8.0625 7.6211 Ditto of lithia 0.0150 0.0405 . Ditto of baryta . . 0.0022 . Ditto of strontia 0.0055 0.0080 0.0170 Ditto of lime 1.7775 0.8555 1.5464 Ditto of magnesia . 1.0275 0.5915 1.5496 Ditto (proto) of manganese 0.0048 0.0028 0.0026 Ditto (proto) of iron 0.0208 0.0120 0.0356 Sub phos. of lime . 0.0012 . Ditto of alumina 0.0019 0.0014 . Sulphate of potassa . 0.4050 0.3160 Ditto of soda . 14.9019 . 2.5106 Ditto of lithia . > Ditto of lime . . . Ditto of strontia . . . Ditto of magnesia . . Nitrate of magnesia Chloride of ammonium . m 0.0164 Ditto of potassium . . 0.0338 . Ditto of sodium 5.9820 5.7255 0.8682 Ditto of lithium t . . Ditto of calcium . . . Ditto of magnesium . . . . Ditto of barium . t f Ditto of strontium . t . Bromide of sodium . . 0.0051 Iodide of sodium e . Fluoride of calcium 0.0184 0.0014 . Alumina t . Silica 0.4329 0.3104 0.2423 Total .... 31.4606 16.0525 14.7309 Carbonic acid gas in 1007 cubic inches . . 5 58 51 98 C Sprud. 165 Temperature (F.) . -j Neub. 138 Miihl. 128 Kess. 117 Kran. 84 58 I Ther. 122 Analyzed by . Berzelius. Struve. Struve. APPENDIX. 503 TABLE OF ANALYSES AND OF THE SARATOGA CONGRESS SPRING OF AMERICA. Saratoga Congress Spring. Kissengen. Ragozi. Marienbad. Kreutzbr. Auschowitz. Ferdinands- Brunnen. Eger. Franzens- Brunnen. 0.8261 5.3499 0.0858 4.5976 0.0507 3.8914 0.0282 0.0672 5.8531 4.1155 0.0202 0.0173 0*1379 OX)592 4.8180 1.3185 0.0121 0.1397 1.2540 0.0028 2.9509 2.0390 2.0288 0.1319 28.5868 0.0040 3.0085 2.2867 0.0692 0.2995 0.0040 16.9022 0.0023 1.3501 0.5040 0.0322 0.1762 0.0172 0.0092 1 8^3785 ' 5.5485 OJ004 0.0326 1.6256 19.6653 0.0364 39.3733 10.1727 6.7472 6.'9229 ; 3.6599 0.1613 0.0046 o'ssiu !.: 0.0069 0.1112 OJ609 0.0023 0.2908 0.5023 0.3548 32.7452 56.7136 51.6417 34.4719 31.6670 114 96 105 146 * 154 50 53 53 49 54 Schweitzer. Struve. Berzelius. Steinmami. Berzelius. 504 APPENDIX. DR. SCHWEITZER'S OF THE PRINCIPAL MINERAL WATERS OF GERMANY AND Grains of Anhydrous Ingredients in One Pound Troy. Pyrmont. Spa Pouhon. Fachingen. Carbonate of soda . . 0.5531 12.3328 Ditto of lithia t t t Ditto of baryta Ditto of strontia - Ditto of lime 4/7781 0.7387 1.8667 Ditto of magnesia . Ditto (proto) of manganese Ditto (proto) of iron Sub-phos. of lime . . .'I Ditto of alumina . ' . ! 0.0364 0.3213 o.'oiio 0.8421 0.0389 0.2813 0.0102 0.0064 1.2283 o!o061 Sulphate of potassa Ditto of soda . 0.0314 1.6092 0.0593 0.0281 OJ267 Ditto of lithia 0.0067 t *. Ditto of lime . .. , | 5.0265 t Ditto of strontia 0.0154 . . Ditto of magnesia . Nitrate of magnesia Chloride of ammonium . 2.3684 Ditto of potassium . . ' Ditto of sodium . ; . - ,. ..' ' , 0.3371 3.2337 Ditto of lithium . -{; _ Ditto of calcium t ( Ditto of magnesium Ditto of barium 0.8450 J . J$v. Ditto of strontium . . . . t Bromide of sodium . j . . Iodide of sodium . . i , , . . Fluoride of calcium . i . , . Alumina t 0.0347 t . 62.3535 69.8145 . . 5.9302 . . 0*2685 * * 0.7287 0.1845 12.9090 . . 54.6917 ' 28.4608 . 0.0562 . . 9.7358 , . > 1.2225 14.7495 . e . . 0.2366 . . f 0.5494 . , . , 0.2304 0.3060 . . 0.0024 0.1500 0.0013 m t 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 58 58 47 58 Struve. Struve. Struve. Struve. Struve. 43 506 APPENDIX. WEIGHTS AND MEASURES. 480. grains Troy = 1 oz. Troy. 437.5 " = 1 oz. Avoirdnpoids. 7000. " =1 Ib. Avoirdupoids. 5760. = 1 Ib. Troy. The imperial gallon contains of water, at 60, 70,000. grains. The pint (fth of gallon) .... 8,750. " The fluidounce (^th of pint) . . . .437.5 " The pint equals 34.66 cubic inches. The French kilogramme = 15,433.6 grains, or 2.679 Ib. Troy, or 2.205 Ib. Avoirdupoids. The gramme = 15.4336 grains. " decigramme = 1.5434 " " centigramme = .1543 " " milligramme = .0154 " The metre of France = 39.37 inches. " decimetre = 3.937 " " centimetre = .394 ' " k< millimetre = .0394 " INDEX, A. Absorption of heat, 79 Acetal, 363 Acetates, 365 Acetone, 368 Acetyle compounds, 361 Acid, acetic, 364 aconitic, or equisetic, 398 acrylic, 454 aldehydie, 363 alloxanic, 421 althionic, 338 amygdalinic, 406 anilic, 441 anilotic, 391 anisic or draconic, 455 anthranilic, 442 antimonic and antimonious, 283 arsenious and arsenic, 286 aspartic, 432 benzilic, 387 benzoic, 383 boracic, 149 bromic, 146 butyric, 450 camphoric and campholic, 456 caproic, capric, and caprylic, 450 carbolic, 491 carbonic, 126 estimation of, 224 liquefaction of, 63, 127 solidification of, 127 cerebric, 481 chelidonic, 429 chloracetic, 367 chloric, 142 chlorocarbonic, 128 chlorochromic, 264 chlorous, 142, 144 chloro- and iodo-sulphuric, 133 chlorophenisic, 492 chlorovalerisic, 381 chlorovalerosic, 382 Acid,choleic and choloidic, 476 cholic, 476 chromic, 263 chrysammic, 445 chrysanilic, 442 chrysolepic, 445 chrysophanic, 444 cinnamic, 392 citric, 397 cocinic, 450 columbic, 281 comenic, 429 courmiric, 391 croconic, 339 cuminic, 456 cyanic, 409 cyanuric, 410 dial uric, 423 elaidic, 450 ellagic, 401 ethalic, 452 ethionic and isethionic, 358 erythric, 444 euchronic, 339 ferric, 456 formic, 376 fulminic, 411 fumaric, 399 gallic, 401 hemipinic, 428 hippuric, 388 hydriodic, 144 hydrobromic, 146 hydrochloric, 138 hydrocyanic, 403 hydroferrocyanic, 413 hydrofluoric, 146 hydrofluosilicic, 148 hydrosalicylic, 389 hydroselenic, 162 hydrosulphocyanic, 417 hydrosulphuric, 160 hyperchloric, 143 hyperiodic, 145 508 INDEX. Acid, hypermanganic, 254 hypochlorous, 141 hyponitrous, 123 hypophosphorons, 135 hyposulphobenzic, 385 hyposulphuric, 132 hyposulphurous, 132 igasuric, 430 indinic, 441 inosinic, 468 iodic, 145 isatinic, 441 isethionic, 358 japonic, 400 kakodylic, 371 kinic, 430 lactic, 343 lecanoric, 443 lithofellinic, 477 trial eic. 399 malic, 398 mandelic, 386 manganic, 253 margaric, 447 meconic, 428 melanic, 3S9 mellitic, 338 mesoxalic, 421 metacetonic, 369 metagallic, 402 metaphosphoric, 210 methonic, 338 molybdic, 280 mucic, 338 muriatic, 138 mykomelinic, 422 myristic, 450 myronic, 459 nitric, 120 nitrous, 123 nitrobenzoic, 384 nitro-muriatic, 140 nitrophenesic and nitrophenisic 492 nitrosalicylic, 391 oenanthic, 350 cenanthylic, 453 oleic, 448 oleophosphoric, 482 opianic, 427 osmic, 308 oxalic, 336 oxalovinic, 351 oxaluric, 422 oxamic, 337 palmitic, 449 parabanic, 422 parellic, 443 pectic and metapectic, 334 phocenic, 451 Acid, phosphoric, 136, 209 phosphorous, 136 phosphovinic, 351 picric, 441 pinic, pimaric, and sylvic, 458 purreic, 445 pyrogallic, 401 pyrophosphoric, 210 pyrotartaric, 396 racemic, 397 retinic, 495 rhodizonic, 339 roccelic, 444 rubinic, 400 saccharic or oxalhydric, 337 salicylic, 390 sebacic, 450 selenic, 134 selenious, 134 silicic, 147 stearic. 447 styphnic, 445 suberic, 338, 450 succinic, 450 sulpharnilic, 380 sulphindylic, 440 sulphobenzoic, 384 sulphoglyceric, 449 sulpholignic, 335 sulphomargaric and sulpholeic, 453 sulphomethylic, 375 sulphonaphthalic, 493 sulphosaccharic, 330 sulphovinic, 350 sulphuric, 130 sulphurous, 129 sulphydric, 160 tannic, 399 tantalic, 281 tartaric, 394 tartralic and tartrelic, 39G tartrovinic, 351 telluric and tellurous, 285 thionuric, 422 titanic, 282 tungstic, 279 ulmic, 330 uramilic, 423 uric or lithic, 419, 480 usneic, 444 valerianic, 330 vanadic, 280 xanthic, 361 Acids, nomenclature of, 129, 1GS of M. Fremy, 133 of sulphur, new, 133 polybasic, 209 pyro-, formation of, 313 vegetable, 394 INDEX. 509 Aconitine, 431 Acroleine, 452 Affinity, chemical, 180 disposing, 183 Air-pump, 35 Air, analysis of, 118 Albite, 245 Albumen, 461 vegetable, 484 Alcohol, 389 Aldehyde, 361 bases from, 435 Alkalimeter, 224 Alkalimetry, 223 Alkarsin, 369 Allantoin,420 Alloxan, 421 Alloxantine, 423 Alumina, inorganic salts of, 244 Aluminum, 243 Amalgam, electrical, 91 Amalgams, 300 Amarine, 434 Amber, 458 Amidine, 332 Amidogen, 230 Amilen, 380 Ammeline and ammelide, 418 Ammonia, 159 inorganic salts of, 228 Ammonium and its compounds, 227 Amygdalirie, 406 Amyle compounds, 379 Analcime, 245 Analyses of carbonates, 224 Analysis of azotized substances, 318 organic bodies, 315 siliceous minerals, 147 Aniline, 436 Anisyle, hydruret of, 455 Antiarine, 432 Antimony and its compounds, 282 . Arabine, 334 Aqua regia, 140 Archimedes, theorem of, 28 Argand lamp, 156 Argol, 341 Aricine, 430 Arrowroot, 333 Arsenic and its compounds, 285 detection of, 288 Asparagine, 432 Asphaltum,494 Atmosphere, cold of, 67 chemical history of, 118 physical constitution of,34 vapor of water in, 61 Atomic theory, 179 Atropine, 431 Augite, 241 Axinite, 245 Azobenzide, 385 Azobenzoyle, 387 Azote or nitrogen, 117 Azotides, metallic, 124 B. Balance-wheel, compound, 45 Balsams, 459 Barium and its compounds, 232 Barometer, 40 Baryta, inorganic salts of, 233 Bases, new, containing mercury, 300 platinum, 303 organic, artificial, 433 natural, 426 Bassorine, 334 Battery, gas, 193 various forms of, 190 voltaic, 95 Beeberine,.432 Beer, 341 Bell metal ,.273 Bengal-light, 284 Benzamide, 386 Benzhydramide, 387 Benzile, 387 Benzimide, 387 Benzine or benzol, 384 Benzoene, 459 Benzoine, 37 Benzoline, 434 Eenzone, 384 Benzonitril, 387 Benzoyle compounds, 382 Berberine, 432 Bile, 475 Binary theory of salts, 211 Bismuth, 269 com pounds of, 269 Bitumen, 494 Bleaching-powder, 238 Blende, 267 Blood, composition of, 468 Blowpipe, mouth, 155 oxy hydrogen, 110 Boiling point of fluids, 54 Bones, composition of, 482 Borneene and borneol, 456 Boron, 149 chloride of, 166 fluoride of, 149 Brass, 273 Brazil-wood, 445 Bread, 312 Breezes, land and sea, 80 Brewing, 341 Bromal, 359 Bromanisal, 455 Bromine, 145 43* 510 INDEX. Bromoform, 359, 377 Bronze metal, 273 Brucia, 430 Butter, 450 C. Cadmium and its compounds, 268 Caffeine, 433 Calamine, 267 Calcium and its compounds, 234 Calculi, biliary, 477 urinary, 4SO Calomel, 297 Camphene and camphylene, 455 Camphogen and campholene, 457 Camphor, 456 artificial, 454 Cantharidine, 452 Caoutchouc, 458 connecting tubes, 126 Carbon, 124 bisulphuret of, 166 chlorides of, 165, 356 Carbonic oxide, 127 Carbyle, sulphate of, 358 Carmine, 444 Carthamine, 445 Caseine, 463 Cassava, 333 Castor oil, 453 Catechin, 400 Catechu, 400 Cedriret, 489 Cellulose, 335 Cement, Roman, 235 Cerasine, 334 Cerium, 246 Charcoal, 125 Chemical philosophy, principles of, 167 Chemistry, Organic, Introduction to, 310 Chimneys, action of, 51 Chinoidine, 429 Chinoleine, 437 Chinone, 430 Chloral, 359 Chloramilal, 380 Chloraniline, 436 Chlorbenzine and chlorbenzide, 386 Chlorindoptene, 441 Chlorine, 137 and nitric oxide, 140 oxygen-compounds of, 141 Chlorocinnose, 392 Chloroform, 359, 377 Chlorosamide, 390 Chloroxarnethane, 349 Cholesterine, 452 Chondrine, 467 Chromium and its compounds, 261 inorganic salts of, 263 Chrysen, 490 Chrysolite, 241 Chyle, 473 Cinchonia, 429 Cinchovatine, 430 Cinnabar, 300 Cinnameine, 393 Cinnamyle-compounds, 392 Clay, chemical history of, 244 Coal-gas manufacture, 152 Coal tar-oil, bases from, 437 tar, volatile principles of, 491 Cobalt and its compounds, 266 inorganic salts of, 266 ultramarine, 267 Cobalto-cyanogen-compounds, 416 Cochineal, 444 Cocoa oil, 450 Codeine, 428 Colchicine, 431 Colophene, 455 Colophony, 458 Colored fires, 234 Columbium, 281 Combination, laws of by weight, 10?" volume, 174 Combining numbers, 173 Combustion, 153 Composition, constancy of, 169 Condensation of gases, 62 Condenser, Liebig's, 58 Conduction of heat, 52 Conicine, 431 Connectors, caoutchouc, 126 Copal, 458 Copper and its compounds, 271 inorganic salts of, 272 Cotarnine, 428 Coumarine, 391 Cryophorus, 65 Crystallography, 200 Cumidine, 435 Cuminol, 456 Curarine, 431 Cyamelide, 409 Cyanite, 245 Cyanogen and its compounds, 403 Cymene, 456 Cynamyle and its compounds, 391 Cystic oxide, 425, 481 D. Daguerreotype, 76 Daphnine, 432 Daturine, 431 Decomposition, electro-chemical, 18,4 Delphinme, 431 Density, of gases, 105 of vapor, hypothetical, 17(j or specific gravity, 27 INDEX. 511 Dew, point, 62 theory of, 80 Dextrine, 332 Diamond, 124 Diastase, 333 animal, 486 Diathermancy, 81 Didymium, 246 Diffusion, gaseous, 109 Digestion, animal, 485 Dimorphism, 201 Distillation, 58 destructive, 313, 373 Dragon's-blood, 458 Dutch liquid, 151, 356 E. Earthenware, manufacture of, 247 Eblanine, 378 Ebullition, 54 Elaidine, 450 Elaterine, 432 Electrical machines, 91 Electricity, from steam, 100 general phenomena of, 89 magneto, 99 voltaic, 94 Electrolysis, 184 Electro-dynamics, 97 magnetism, 98 metallurgy, 192 Electrometers, 90 Electrophorus, 93 Elementary bodies, definition of, 101 table of, 101, 173 Emetine, 431 Empirical and rational formula, 323 Ernulsine, 405 Epsom salt, 240 Equivalents, doctrine of, 171 rectification of, 496 table of, 173 Erbium, 246 Ethal, 452 Ether, 345 heavy muriatic, 359 manufacture of, 352 Etherine, 3S5 and etherole, 255 Ethers, compound, 345 of the fatty acids, 349 Ethyle compounds, 246 Euchrone, 339 Eudiometry, 118 Eupione, 488 Evaporation at low temperatures, 63 Expansion by heat, 41 F. Felspar, 244 Fermentation of sugar, 339 viscous, 344 Ferridcyanogen-compounds, 410 Ferrocyanogen-compounds, 413 Fibrine, 462 vegetable, 484 Fire-damp, 150 Fires, red and green, 234 Flame, 153 Fluids, expansion of, 46 Fluorine, 146 Food, chemistry of, 483 Formomethylal, 378 Formulae, empirical and rational, 323 Freezing-mixtures, 53 Friction, development of heat by, 6S Fulminate of silver, 411 Furfurol and furfurine, 433 Furnaces, 154 iron, 259 Fusel-oil, 379, 382 Fusible metal, 270 Fustic- wood, 445 G. Galvanoscopes, 97 Garnet, 245 Gases, correction of vol. of, for pres- sure, 39 for temperature, 4f expansion of, 48 liquefaction of, 62 manipulation with, 103 physical constitution of, 34 Gas of the acetates, 150 flame, 159 holder, 104 Gelatine, 466 Gentianine, 432 Gilding, 295 Glass, manufacture of, 247 tubes, 126, 24S Glauber salt, 225 Gliadine, 4S4 Glucinum, 245 Glucose, 329 Gluten, 331, 484 Glycerine, 449 Glycocoll, 466 Glycyrrhizine, 331 Gold, 293 Goniometers. 201 Goulard-water, 365 Graphite, 125 Green-fire, 234 Guano, 425, 486 Gum Arabic and tragacanth, 334 512 INDEX. Gum, British, 333 Gun-cotton, 338 Gun-metal, 273 Gunpowder, 216 Gutta percha, 459 H. Harmaline, 431 Hatchetine, 495 Heat, animal, 472 conduction of, 58 internal, of the earth, 58 latent, 52 phenomena of, 41 sources of, 68 specific, 66 radiation, reflexion, and absorp- tion of, 78 transmission and polarization of, 81 Helicine and helicoidine, 391 Hematosine, 469 Hematoxyline, 445 Hemming's safety jet, 158 Hepar sulphuris, 218 Hesperidine, 432 Heulandite, 245 Hornblende, 241 Humus, 330 Hydrates, 116 Hydrobenzamide, 386 Hydrochinone, 430 Hydrogen, L07 arseniuretted, 287 carburetted, light, 150 peroxide of, 1 16 persulphuret of, 162 phosphuretted, 163 sulphuretted and seleniu- retted, 161 Hydrometer, 32 tables, 498 Hydrostatics, law of, 28 Hygrometry, 61 Hygrometer, Daniell's, 66 Mason's, 62 Hyoscyamine, 431 I. Idrialine, 495 Ignition, 153 Indian-yellow, 445 Indigo, 439 Inuline, 334 Iodine, 144 chloride of, 165 lodoform, 377 Iridium, 306 Iron and its compounds, 254 inorganic salts of, 257 Iron manufacture, 258 Isatine, 440 Isomerism, 313 Isomorphism, 207 J. Jade, 241 Jet, 493 Jet-pipe, oxyhydrogen, 110, 158 K. Kakodyle, 369 Kalotype process, 75 Kapnomor, 489 Katalysis, 183 Keip, 144 Kerrnes mineral, 284 Kindling-point of gases, 157 Kino, 399 Kreatine and kreatinine, 467 Kreosote, 489 Kyanol, 437 L. Lac, 458 Lactide and lactamide, 344 Lactine, 331 Lactone, 344 Lakes, 439 Lamp chemical, 156 gas, 159 miner's safety, 158 without flame, 112, 363 Lamp-black, 125 Lanthanium, 246 Laumonite, 245 Law of substitution, 311 Laws of combination, 169 Lead and its compounds, 273 action of water on, 275 inorganic salts of, 274 tree, 192 Lecanorine, 443 Legumine, 484 Leucine, 465 Leukol,437 Leyden-jar, 93 Light, chemical agency of, 75 general phenomena of, 70 reflexion, refraction, and polar- ization of, 70 Light carburetted hydrogen, 150 Lightning-rods, 94 Lignine, 335 Lignite, 493 Lignone, 378 Lime, inorganic salts of, 236 Litharge, 274 Lithium and its compounds, 230 Litmus, 442 INDEX. 513 Loadstone, 456 Logwood, 445 Lunar caustic, 292 Lupuline, 341 Lymph, 473 M. Madder, 444 Magnesia, inorganic salts of, 240 Magnesium and its compounds, 239 Magnetism, general phenomena of, 85 terrestrial, 87 Magneto-electricity, 99 Manganese and its compounds, 251 inorganic salts of, 253 Mannite, 331 Margarine, 447 ' Margarone, 448 Mariotte, law of, 38 Marsh-gas, 150 Massicot, 274 Mastic, 458 Meconine, 428 Meerschaum, 241 Melam, 417 Melamine, 418 Mellon, 417 Membrane, 482 Mercaptan, 360 Mercury and its compounds, 295 inorganic salts of, 296 Mesityle, 368 Mesotype, 245 Metacetone, 369 Metacinnameine, 393 Metal, bell, gun, and speculum, 273 fusible, 270 Metals, alkaline earths of, 232 classification of, 212 general properties of, 194 rale of expansion of, 46 table of specific gravities, 195 Methyle-mercaptan, 378 compounds, 373 Mica, 245 Milk, 474 Molybdenum, 279 Morphia, 426 Mortars and cements, 235 Mosaic gold, 278 Moser, images of, 77 Mucilage, 334 Mucus, 473 Multiple proportions, 170 Murexan, 424 Murexide, 424 N. Naphtha, 494 Naphthalidam, 435 Naphthaline, 492 Narceine, 428 Narcogenine, 428 Narcotine, 427 Nepheline, 245 Nervous substance, 481 Nickel and its compounds, 264 inorganic salts of, 265 Nicotine, 431 Niobium, 281 Nitraniline, 437 Nitrobenzide, 385 Nitrobenzoyle, 387 Nitrogen, 1 17; chloride and iodide of, 164 estimation of, 318 oxides of, 120 Nitrous and nitric oxides, 122 Nomenclature of acids and salts, 129 of oxides, 106 Norium, 247 Notation, chemical, 177 Nutrition, animal and vegetable, 483 0. Oils and fats, 446 Oil, castor, 453 gas, 152 palm and cocoa-nut, 449 Oil of aniseed, 455 assafetida, 458 bergamot, 455 bitter-almonds, 382 capivi, 455 cedar-wood, 456 cinnamon, 391 cubebs, 455 cummin, 456 elemi, 455 fusel, 378, 382 garlic, 457 gas manufacture, 153 gaultheria, 456 hops, 458 Indian grass, 455 juniper, 455 laurel, 455 lavender, 457 lemons, 455 marc-brandy, 382 mustard, 477 onions, 458 orange-flowers, 457 orange-peel, 455 pepper, 455 peppermint, 457 potato and grain-spirit, 378 rosemary, 457 roses, 457 turpentine, 454 514 INDEX. Oil of valerian, 456 wine, heavy and light, 254 Oils, volatile, 453 Olefiant gas, 151, 355 Oleine, 448 Orcine and orceine, 443 Organic bodies classified, 313 decomposition of, 313, 314 ultimate analysis of, 315 chemistry, 310 Osmium, 308 Oxamethane, 349 Oxamide, 337, 348 Oxygen, 102 Oxy-hydrogen safety jet, 110, 158 Ozokerite, 495 P. Palladium, 304 Palm oil, 449 Palmitine, 449 Paracyanogen, 403 Paraffine, 488 Paramide, 339 Paramorphine, 428 Paranaphthaline, 493 Pectine, 334 Pelopium, 281 Pendulum, 44 Pepsine, 485 Petalite, 245 Petroleum, 494 Pewter, 279 Phenyle, hydrate of, 491 Philosophy, chemical, 167 Phloridzine and phloretine, 391 Phosphene gas, 128 Phosphorus, 134 chlorides of, 165 iodides of, 165 oxide of, 135 oxygen-acids of, 135 Photography, 75 Picamar, 489 Picoiine, 438 Picrotoxirie, 432 Pile, chemistry of, 184 voltaic, 95 Piperine, 432 Pit coal, 493 Pittekal, 489 Platinum and its compounds, 301 action of, on gases, 111 black, 301 combustible salts of, 357 Plumbago, 125 Pneumatic trough, 103 Polarity, magnetic, 86 Polarization of light, 74 Populine, 432 Porcelain, manufacture of, 247 Potash-salts, inorganic, 214 Potassium and its compounds, 213 Potato-oil compounds, 378 Prehnite, 245 Proof-spirit, 340 Proteine, 464 Prussian-blue, 414 Pseudomorphine, 428 Purple of Cassius, 279 Pus, 473 Putrefaction and decay, 314 Pyren, 490 Pyrometer, 45 Pyrophorus, 244 Pyroxyline, 338 Q- Quercitron-bark, 445 Quinia, or quinine, 429 Quinoidine, 429 R. Red fire, 234 Resins, 458 Respiration, 471 Retinite, 495 Rhodium, 305 Ruthenium, 307 S. Saccharine and amylaceous substances, 327 Safety tube, 140 jet, 158 Safflower, 444 Saffron, 445 Sago and salep, 334 Sal-ammoniac, 228 i Salicine and Salicyle-compounds, 388 ! Saligenine, 391 i Salts, constitution of, 197 binary theory of, 211 < Saponification, 447 Sarcosine, 468 Scheele's green, 287 Selenite, 236 Selenium, 133 Seleniuretted hydrogen, 162 Serpentine, 241 Silica, 147 I Silicon, 147 chloride and bromide of, 1Gb' fluoride of, 148 : Silver and its compounds, 290 German, 265 inorganic salts of, 292 Sinnamine and sinapoline, 434 , Skin, composition of, 482 INDEX. 515 Smalt, 267 Soda, inorganic salts of, 221 Sodium and its compounds, 220 Solanine, 431 Solder, 276 Specific gravity of solids and liquids, 27 gases, 105 vapors, 324 Speculum metal, 273 Speiss, 265, 267 Spermaceti, 452 Spheroidal state of liquids, 55 Spirit lamp, 156 Spodumene, 245 Starch, 331 State, change of, 54 Steam bath, 57 elastic force of, 56 electricity of, 100 engine, 57 Stearine, 447 Steatite, 241 Steel, 260 Stilbite, 245 Stoneware, 250 Strontia, inorganic salts of, 234 Strontium and its compounds, 234 Structure of flame, 153 Strychnia, 430 Styrole, 459 Sublimate, corrosive, 298 Substitution, law of, 312, 360 Sugar, cane and grape, 327 of diabetes insipidus, 331 ergot, 330 eucalyptus, 330 milk, 331 Sulphobenzide, 385 Sulphocyanogen and its compounds, 416 Sulphur, 128 chlorides of, 165 iodides of, 165 milk of, 162 oxygen-acids of, 129 Sulphuretted hydrogen, 160 Symbols, chemical, 177 Synaptase, 406 T. Tantalum or columbium, 281 Tapioca, 333 Tar, varieties of, 488 Tartar-emetic, 396 Taurine, 476 Tellurium, 284 Tension of vapor, 60 Terbium, 246 Terebene and Terebylene, 454 Thebaine, or paramorphine, 428 Theine, or caffeine, 433 Theobromine, 433 Theory, atomic, 179 electro-chemical, 188 Thermo-electricity, 82, 96 Thermometer, 41 Thialdine, 435 Thiosinnamine, 434 Thorium, 247 Tin, 277 Tinned-plate, 279 Titanium, 282 Tolene and toluol, 459 Toluidine,434 Tube, safety, 140 Tungsten, 279 Turpeth mineral, 297 Type-metal, 284 U. Ulmine, 331 Ultimateanalyses of organic bodies, 315 Ultramarine, 227 Uramile, 423 Uranium, 270 compounds of, 271 Urea, 409, 418 Urethane, 350 Urethylane, 375 Urinary calculi, 480 Urine, composition of, 477 Urinometer, 32 V. Valeronitril, 466 Vanadium, 280 Vapor of water, tension of, 59, 500 Vapors, determination of density of, 324 hypothetical, density of, 176 maximum density of, 60 Ventilation, 51 Veratri;i, 431 Verdigris, 366 Vermilion, 300 Vinegar, 364 Vinous fermentation, 339 Vitriol, blue, 272 green, 257 white, 268 Voltaic pile, 184 chemical theory of, 183 Voltameter, 187 W. Wash bottle, 140 Water, chemical history of, 112 decomposition of, by iron and zinc, 107 by galvanism., 113, 185 516 INDEX. Water, of crystallization, 199 purification of, 115 sea, 115 solvent power at high tempear- ture, 116 Waters, mineral, 115, 502, 504 Wax, 451 Weights and measures, 506 Withe rite, 233 Winds, 70 Wines, manufacture of, 340 proportion of alcohol in, 340 Wood-spirit compounds, 373 Wootz, 261 X. Xanthic acid, 417 Xanthic oxide, 425, 481 Xylite, 378, 481 Xyloidine, 338 Y. Yeast, 342 Yttrium, 246 Zaffre, 267 Zinc and its compounds, 267 inorganic salts of, 267 Zirconium, 247 THE END. CATALOGUE OP BLANCHARD & LEA'S PUBLICATIONS. AUGUST, 1851. CAMPBUL&S CHIEF JUSTICES (JVoto Heady) LIVES OF THE CHIEF JUSTICES OF ENGLAND, From the Norman Conquest to the Death of Lord Mansfield. BY LORD CHIEF JUSTICE CAMPBELL. In two very neat vols., crown 8vo., extra cloth, To match the "Lives of the Chancellors" of the same author. The following eminent men are the subjects of this work: Odo, first Chief Justiciar. William Filz Osborne. William de Warrene. Richard de Ben e fact a. William de Carilefo. Flambard. Roger, Bishop of Salisbury. Ralph Basset. Prince Henry. Richard de Luci. Robert, Earl of Leicester. Ranulphusde Glanville. Hugh Pusar. William Longcharnp. Walter Hubert. Geoffrey Fitz Peter. Peter de Rupibus. Hubert de Burgh. Stephen de Segrave Hugh le Des- pencer. Phillip Basset. Henry de Bracton. Ralph de Hengham. De Wayland. De Thornton. Roger le Brabancon. Henry le Scrope. Henry de Staunton. Sir Robert 1'arnyng- Sir William de Thorpe. Sir William Shareshall. Sir Henry Green. Sir John Kny vet. Sir John de Cavendish. Sir Robert Tresilian. Sir Robert Belknappe. Sir William Thirnyng. Sir William Gascoigne. Sir William Hank- ford Sir John Fortescue. Sir John Markham. Sir Thomas Billing. Sir John Hus- sey. Sir John Fineux. Sir John Fitzjames. Sir Edward Montague. Sir James Dyer Sir Robert Catlyn. Sir Christopher Wray. Sir John Popharn. Sir Thomas Fleming. Sir Edward Coke. Sir Henry Montagu. Sir James Ley. Sir Randolph Crewe. Sir Nicholas Hyde. Sir Thomas Richardson. Sir John Brampston. Sir Robert Heath. Rolle. Glynn. Newdegate. Oliver St. John. Bradshawe. Sir Robert Foster.- Sir Robert Hyde. Sir John Kelynge. Sir Matthew Hale. Sir Richard Raynsford. Scroggs. Sir Francis Pemberton. Sir Edmund Saunders. Jeffreys. Sir Edward Herbert. Sir Robert Wright. Sir John Holt. Sir Thomas Parker. Sir John Pratt. Lord Raymond. Lord Hardwicke. Sir William Lee. Sir Dudley Ryder. Sir John Wyles. Wilmot. LordiMansfield. Although the period of history embraced by these volumes had been previously traversed by the recent work of the noble and learned author, yet in "The Lives of the Chief Justices" there is a fund both of interesting information and valuable matter, which renders the book well worthy of perusal by every one who desires to obtain an acquaintance with the constitutional history of his country, or aspires to the rank of either a statesman or a lawyer. None but lawyers of his experience and ac- quiremenis could have compiled a work combining the same interest as a narration, to the public generally, with the same amount of practical information for professional aspirants more particularly. Britannia. CAMPBELL'S LORD CHANCELLORS. LIVES OF THE LORD CHANCELLORS AXD KEEPERS OF THE GREAT SEAL OF ENGLAND, FROM The earliest times to the reign of King George IV. BY JOHN LORD CAMPBELL, A.M., F.R.S.E. Complete in seven handsome crown octavo volumes, extra cloth. Of the solid merit of the work our judgment may be gathered from what has already been said. We will add, that from its infinite fund of anecdote, and happy variety of style, the book addresses itself with equal claims to the mere general reader, as to the legal or historical inquirer; and while we avoid the stereotyped commonplace of affirming that no library can be complete without it, we feel constrained to afford it a higher tribute by pronouncing it entitled to a distinguished place on the shelves of every scholar who is fortunate enough to possess it. Frazer^s Magazine. A work which will take its place in our libraries as one of the most brilliant and valuable contributions to the literature of the present day. Athenaeum. 1 2 BLANCHARD & LEA'S PUBLICATIONS. (History and Biography.) IMPORTANT NEW WORK- Nearly Ready. HISTORY OF NORMANDY AND OF ENGLAND, BY SIR FRANCIS PALGRAVE, Author of "Rise and Progress of the English Commonwealth," &c. In handsome crown octavo. Nearly Ready, Vol. I. The General Relations of Mediaeval Europe ; the Carlovingian Empire, and the Danish Expeditions in the Gauls, until the es- tablishment ofRollo. Vols. II. and III. are in a state of forward preparation, and will shortly follow. A NEW LIFE OF WILLIAM PENN Now Ready. WILLIAM PENN, AN HISTORICAL BIOGRAPHY, FROM NEW SOURCES; With an extra Chapter on the "Macaulay Charges." BY W. HEPWORTH DIXON, Author of ''John Howard and the Prison World of Europe," &c. In one very neat volume, royal 12mo., extra cloth. The volume before us demands especial notice for two reasons in the first place, it is an elaborate biography of William Penn, exhibiting great research, and bringing together a large amount of curious and original information; in the second, it makes an undeniable exposure of blunders committed by Mr. Macaulay in reference to its hero, which wili go far to compromise his character as a historian. This latter sub- ject is of much interest and importance, as Mr. Dixon discusses Mr. Macaulay's charges against Penn, and reinstates the character of the latter on that moral eleva- tion from which it had been most unjustly and carelessly overthrown. The task is by no means a pleasant one; because, whatever the charm of Mr. Macaulay's narra- tive, much of the credit due to his statements of facts, and of reliance on his exami- nation of authorities, are destroyed by this chapter of Mr. Dixon's work. Af a biography the wortf has claims of no common order. Within the compass of a single volume Mr. Dixon has compressed a great variety of facts, many original, and all skilfully arranged so as to produce an authentic moral portrait of his hero. The literary merits of the volume include great research, and a narrative at once con secutiveand vivid. The author has had access to a variety of unpublished material to the letters of Penn and his immediate family, and to MSS. of mt-moirs of several persons, yielding lights which he wanted. It is a long time since a single volume has been published with such a quantity of matter interesting and important in its character. Mr. Dixon compresses his materials by a species of hydraulic power. Mere book-making might have padded out this work into three or four volumes It is another merit of the book that its subject is always prominent, the writer himself be- ing kept well out of sight. In a word, we can praise the work at once for its earnest spirit, its wealth of recovered material, and the art with which the latter has been dis- posed. The AthencEum. On account of the very wide circulation of Mr. Macaulay's volumes, con- taining his accusations against William Penn, the publishers hare placed this work at a low price, in order that it may reach as many as possible of those who may have been biased by the mistakes and misrepresentations of the historian. THE CpURT AND REIGN OF FRANCIS THE FIRST, KING OF FRANCE. By Miss Pardoe, author of " Louis XIV." &c. In two very neat volumes, royal 12mo., extra cloth. MISS KAVANAGH'S WOMAN IN FRANCE JUST PUBLISHED. WOMAN IN FRANCE IN THE EIGHTEENTH CENTURY. By Julia Kava- nagh, author of " Nathalie," " Madeline," &c. In one very neat volume, royal 12mo. PULSZKY'S HUNGARIAN LADY JUST PUBLISHED. MEMOIRS OF AN HUNGARIAN LADY. By Theresa Puls/ky. With an His- torical Introduction, by Count Francis Pulszky. In one vol., royal 12mo., extra cloth. MIRABEAU; a Life History. In Four Books. In one neat volume, royal 12mo., extra cloth. BLANCHARD & LEA'S PUBLICATIONS. (Msforj/ and Biography.-) 3 STRICKLAND'S QUEENS OF ENGLAND. LIVES OF THE QUEENS OP ENGLAND From the Norman Conquest to the accession of the House of Hanover, With Anecdotes of their Courts, now first published from Official Records, Private ns well as Public. NEW EDITION, WITH ADDITIONS AND CORRECTIONS. BY AGNES STRICKLAND. In six volumes, crown octavo, beautifully printed, and bound in various styles. Copies of the duodecimo edition in twelve volumes may still be had. These volumes have the fascination of a romance united to the integrity of history. Times. A most valuable and entertaining work. Chronicle. This interesting and well-written work, in which the severe truth of history takes almost the wildness of romance, will constitute a valuable addition to our biogra- phical literature. Morning Herald. MRS, MARSH'S ROMANTIC HISTORY OF THE HUGUENOTS Now Ready, HISTORY OF THE PROTESTANT REFORMATION IN FRANCE. BY MRS. MARSH, Author of " Two Old Men's Tales," " Emilia Wyndham," &c. In two handsome volumes, royal 12mo., extra cloth. "The object of this unpretending work has been to relate a domestic story, not to undertake a political history to display the virtues, errors, sufferings, and experi- ences of individual men rather than the affairs of consistories or the intrigues of cabinets consequent upon the great struggle to diffuse the principles of the Reformed Religion in France." AUTHOR'S PREFACE. These two delightful volumes belong to the same class as Miss Pardoe's popular works on Francis I. and Louis XIV., and may be regarded as companions to them, having the same characteristics of extensive research, lively style, and entertaining interest, presenting all the authority and utility of History, without the dryness and dulness which was formerly considered necessary to its dignity. Mrs. Marsh's sub- ject is one which gives full scope to her acknowledged powers, and she has treated her romantic and varying story with all the skill that was to be expected of the author of the "Two Old Men's Tales." HISTORY OF TEN YEARS, 1830-1840, OR FRANCE UNDER LOUIS PHI- LIPPE. By Louis Blanc. In two handsome volumes, crown 8vo., extra cloth. Perhaps no work ever produced a greater or more permanent effect than this. To its influence, direct and indirect, may in agreat measure be attributed the movements which terminated in the Revolution of February 1848. HISTORY OF THE FRENCH REVOLUTION OF 1769. By Louis Blanc. In one volume, crown 8vo., extra cloth. PROFESSOR RANKE'S HISTORICAL WORKS. HISTORY OF THE POPES, THEIR CHURCH AND STATE, IN THE 16TH AND 17TH CENTURIES. Complete in one large 8vo volume. HISTORY OF THE TURKISH AND SPANISH EMPIRES, IN THE 16TH CENTURY, AND BEGINNING OF THE 17TH. Complete in one 8vo. volume, HI P STO r RY Pr o C F 7 THE tS REFORMATION IN GERMANY. Parts I. II. and III. Price 81. HISTORY OF THE HUGUENOTS. A new Edition, continued to the Present Time. By W. S. Browning. In one octavo volume, extra cloth. HISTORY OF THE JESUITS, from the Foundation of their Society to its Sup- pression by Pope Clement XIV. Their Mission? throughout the World; their Edu- cational System and Literature ; with their Revival and Present State. By Andrew Steinmetz, author of "The Novitiate," "Jesuit in the Family/' &c. In two hand- some volumes, ciown 8vo., extra cloth. 4 BLANCHARD & LEA'S PUBLICATIONS. (History and Biography.) CHEAPER. EDITION-LATELY PUBLISHED. MEMOIRS OF THE LIFE OF WILLIAM WIRT, BY JOHN P. KENNEDY. SECOND EDITION, REVISED. In two handsome 12mo. volumes, with a Portrait and fac-simile of a letter from John Adams. Also, A handsome Library Edition, in two beautifully printed octavo volumes. The whole of Mr. Wirt's Papers, Correspondence, Diaries, &c., having been placed in the hands of Mr. Kennedy, to be used in this work, it will be found to contain much that is new and interesting relative to the political history of the times, as well as to the private life of Mr. Wirt. In its present neat and convenient form, the work is eminently fitted to assume the position which it merits as a book for every parlor table and for every fireside where there is an appreciation of the kindliness and manliness, the intellect and the affection, the wit and liveliness which rendered William Wirt at once so emi- nent in the world, so brilliant in society, and so loving and loved in the retirement of his domestic circle. Uniting all these attraciions, it cannot fail to find a place in every private and public library, and in all collections of books for the use of schools and colleges; for the young can have before them no brighter example of what can be accomplished by industry and resolution, than the life of William Wirt, as uncon- sciously related by himself in these volumes. GRAHAME'S UNITED STATES. HISTORY OF THE UNITED STATES FROM THE PLANTATION OF THE BRITISH COLONIES TILL THEIR ASSUMPTION OF INDEPENDENCE. Second American edition, enlarged and amended, with a Memoir by President Quincy, and a Portrait of the Author. In two large octavo volumes, extra cloth. HISTORICAL SKETCH OF THE SECOND WAR BETWEEN THE UNITED STATES OF AMERICA AND GREAT BRITAIN. By Charles J. Ingersoll. Vol. 1., embracing the events of 1812-13 ; Vol. II., the events of 1814. Octavo. HISTORY OF CONGRESS UNDER THE ADMINISTRATION OF GENERAL WASHINGTON. One very large octavo volume. MILL'S HISTORY OF THE 6RUSADES, AND OF CHIVALRY. In one octavo volume, extra cloth. SIBORNE'3 WATERLOO. History of the War in France and Belgium in 1815, containing Minute Details, with Maps and Plans, of the Battles of Quatre-Bras, Ligny, Wavre, and Waterloo. In one large octavo volume, extra cloth, with 11 Maps. WHITE'S ELEMENTS OF UNIVERSAL HISTORY. Edited by J. S. Hart. In one very large volume, royal 12mo., extra clolh. NIEBUHR'S HISTORY OF ROME; being the complete work from the foundation of the city to the death of Constantine. In Iwo large octavo volumes. MEMORANDA OF A RESIDENCE AT TFIE COURT OF LONDON. By the Hon. Richard Rush. In one large 8vo. volume. MEMOIRS OF THE REIGN OF GEORGE II., from his Accession to the death of Queen Caroline. By John Lord Hervey. Edited, from the original MSS., by the Right Hon. John Wilson Croker. In two handsome royal 12mo. volumes, extra cloth. WALPOLE'S MEMOIRS OF THE REIGN OF GEORGE III., now first published from the original MS. In two handsome octavo volumes, extra cloth. WRAXALL'S HISTORICAL MEMOIRS OF HIS OWN TIMES. In one octavo volume, extra cloth. WRAXALL'S POSTHUMOUS MEMOIRS OF HIS OWN TIMES. In one oc- tavo volume, extra cloth. BLANCHARD & LEA'S PUBLICATIONS. (Voyages and Travels.) 5 LYNCH'S DEAD SEA. CONDENSED AND CHEAPER EDITION-NOW READY, NARRATIVE OF THE U, S, EXPEDITION TO THE DEAD SEA AND RIYER JORDAN. BY W. F. LYNCH, U. S. N., Commander of the Expedition. New and Condensed edition, with a Map, from actual Surveys, In one neat royal 12mo. volume, extra cloth. The universal curiosity excited by the interesting narrative of this remarkable expedition, has induced the author to prepare a con- densed edition for popular use, which is now furnished at a very low price. In preparing the former editions, the object was to produce a work worthy in every respect of the national character which it assumed, and no pains or expense was spared in bringing out a vo- lume as handsome as anything of the kind as yet prepared in this country. The great demand, which has rapidly exhausted many large impressions of that edition, notwithstanding its price, is a sufficient proof of the intrinsic value and interest of the work ; and in presenting this new and cheaper edition, the publishers would merely state that it contains all the substance of the former volume, from the time the expedition reached Lake Tiberias till its depart- ure from Jerusalem, embracing all the explorations upon the river Jordan and the Dead Sea. Some matter in the preliminary and concluding chapters has been omitted or condensed, and the two maps of the former edition have been reduced in one, preserv- ing, however, all the more important features of the country de- scribed. In its present form, therefore, afforded at about one-third the price of the more costly issue, in a neat and handsome volume, admirably adapted for parlor or fireside reading, or for district schools, Sabbath schools, and other libraries, the publishers confi- dently anticipate a very extensive demand. Copies may still be had of the FINE EDITION, In one very large and handsome octavo volume, "With Twenty-eight beautiful Plates, and Two Maps. This book, so long and anxiously expected, fully sustains the hopes of the most san- guine and fastidious. It is truly a magnificent work. The type, paper, binding, style, and execution are all of the best and highest character, as are also the maps and en- gravings. It will do more to elevate the character of our national literature than any work that has appeared for years. The intrinsic interest of the subject will give it popularity and immortality at once. It must be read lobe appreciated; audit will be read extensively, and valued, both i n this and other countries. Lady's Book. When, however, he fairly "gets under vvt:igh," every page possesses interest, and we follow him with eagerness in his perilous and tortuous voyage down the Jordan, and his explorations of the mysterious sea, upon which the curse of the Almighty visibly rests. His privations, toils, and dangers were numerous, but were rewarded by success where all others had failed. He has contributed maierially to our know- ledge of Scriptural Geography, particularly in his charts of the Jordan and Dead Sea, which he fully explored. If our readers wish to know all he has done, they must procure and read his book ; we cannot give even an outline of il We can only add that the publishers have done their full du'y in their department, and the maps and plates are all thai could be desired. Presbytenan. 6 BLANCHARD Sc LEA'S PUBLICATIONS. (Voyages and Travels.) NOTES FROM NINEVEH, AND TRAVELS IN MESOPOTAMIA, ASSYRIA, AND SYRIA. By the REV. J. P. FLETCHER. In one neat royal 12mo. volume, extra cloth. TRAVELS IN SIBERIA, INCLUDING EXCURSIONS NORTHWARD DOWN THE OBI TO THE POLAR CIRCLE, AND SOUTHWARD TO THE CHINESE FRONTIER. BY ADOLPH ERMAN. Translated by WILLIAM D. COOLEY. In two handsome volumes, royal 12mo., extra cloth. HUNGARY AND TRANSYLVANIA, WITH REMARKS ON THEIR CONDITION, SOCIAL, MORAL, AND POLITICAL. BY JOHN PAGET, ESQ. In two neat volumes, royal 12mo., extra cloth. TURKEY AND ITS DESTINY; THE RESULT OF JOURNEYS MADE IN 1847 and 1848, TO EXAMINE INTO THE STATE OF THAT COUNTRY. BY CHARLES MACFARLANE, ESQ., Author of " Constantinople in 1S28." In two neat volumes, royal 12mo., extra cloth. IMPRESSIONS AND EXPERIENCES OF THE WEST INDIES AND NORTH AMERICA IN 1849. BY ROBERT BAIRD, A. M. In one neat volume, royal 12mo., extra cloth. THE WESTERN WORLD: OR, TRAVELS IN THE UNITED STATES. Exhibiting them in their latest Development, Social, Political, and Industrial. Including a Chapter on California. BY ALEXAXDER MACKAY, ESQ. In two neat volumes, royal 12mo., extra cloth. SIX MONTHS IN THE GOLD MINES. From a Journal of a Three Years' Residence in Upper and Lower California, during 1847, 1848, and 1849. BY E. GOULD BUFFUM, ESQ., Lieutenant 1st. Regiment New York Volunteers. In one neat volume, royal 12mo., paper, 50 cents, or extra cloth. NARRATIVE OF THE UNITED STATES EXPLORING EXPEDITION. By CHARLES WILKES, U. S. N., Commander of the Expedition. In six large volumes, imperial quarto. With several hundred illustrations on steel and wood, and numerous large maps. Price $60. This is ihe same as the edition printed for Congress. As but few have been exposed for sale, those who desire to possess this magnificent monument of the arts of the Uni'ed Stales, would do well to secure copies without delay. EASTERN LIFE, PRESENT AND PAST. By HARRIET MARTINZAU. In one large and handsome volume, crown octavo, extra cloth. BLANCHARD & LEA'S PUBLICATIONS. (Scitnce.-) 7 LIBRARY OF ILLUSTRATED SCIENTIFIC WORKS. A series of beautifully printed volumes on various branches of science, by the most eminent men in their respective departments. The whole printed in the handsomest style, and profusely embellished in the most efficient manner. OZ7" No expense has been or will be spared to render this series worthy of the sup- port of the scientific public, while at the same lime it is one of the handsomest speci- mens of typographical and artistic execution which has appeared in this country. DE I, A HECHE'S GEOLOGY Just Ready. THE GEOLOGICAL OBSERVER. BY SIR HENRY T. DE LA BECHE, C. B., F. R. S., Director-General of the Geological Survey of Great Britain, &c. In one very large and handsome octavo volume, WITH OVER THREE HUNDRED WOOD-OUTS. We have here presented to us, by one admirably qualified for the task, the most complete compendium ol the science of geology ever produced, in which the differ- ent facts which fall under the cognizance of this branch of natural science are ar- ranged under the different causes by which they are produced. From the style in which the subject is treated, the work is calculated riot only for the use of the profes- sional geologist but for that of the uninitiated reader, who will find in it much curious and interesting information on the changes which the surface of our globe has under- gone, and the history of the various striking appearances which it presents. Volu- minous as the work is, it is not rendered unreadable from its bulk, owing to the judi- cious subdivision of its contents, and the copious index which is appended. John Bull. Thi* ample volume is based upon a former work of the author, called How to Ob- serve in Geology ; which has long been out of print, but in its day gave rise to several other directions for observing The alteration of the tiile is something more than a nominal change; it extends the book from the individual to the general observer, showing what has been scientifically seen in the globe, instead of what an individual tnightzne. It is a survey of geological facts throughout the world, classified accord- ing to their nature. Spectator. Having had such abundant opportunities, no one could be found so capable of di- recting the labors of the young geologist, or to aid by his own experience the studies of those who may not have been able to range so extensively over the earth's surface. We strongly recommend Sir Henry De la Beche's book to those who desire to know what has been done, and to learn something of the wide examination which yet lies waiting for the industrious observer. The Alhenezum. TECHNOLOGY ; or, CHEMISTRY APPLIED TO THE ARTS AND TO MANUFAC- TURES. By Da. F. KNAPP, Professor at the University of Giessen. Edited, with numerous Notes and Additions, by DR. EDMUND RONALDS, and DR. THOMAS RICHARDSON. First American Edition, with Notes and Additions by Prof. WALTER R. JOHNSON. In two handsome octavo volumes, printed and illustrated in the highest style of art, with about 500 wood engravings. The style of excellence in which the first volume was got up is fully preserved in this. The treatises themselves are admirable, and the editingboth by the English and American editors, judicious; so that the work maintains itself as the bestof the series to which it belongs and worthy the attention of all interested in the arts of which it treats. Franklin Institute Journal. ELEMENTS OF CHEMISTRY; including the Application of'fhe Science to the Arts. By Thomns Graham, F. R. S., &c. Edited by Robert Bridges, M. D. Second American, from the second and enlarged London edition. In two parts, large 8vo., with several hundred wood-cuts. (Part 1 in press.) 8 BLANCHARD & LEA'S PUBLICATIONS. (Science.} Library of Illustrated Scientific Works (continued'). CARPENTER'S COMPARATIVE PHYSIOLOGY Now Ready, PRINCIPLES OF GENERAL AND COMPARATIVE PHYSIOIOBY; INTENDED AS AN INTRODUCTION TO THE STUDY OF HUMAN PHYSIOLOGY, And as a Guide to the Philosophical Pursuit of Natural History. BY WILLIAM B. CARPENTER, M. D., F. R. S., Author of " Human Physiology," " Vegetable Physiology," &c. &c. THIRD IMPROVED AND ENLARGED EDITION. In one very large and handsome octavo volume, with several hundred beautiful illustrations. This valuable work will supply a want long felt by the scientific public of this country, who have had no accessible treatise to refer to, presenting in an intelligible form a complete and thorough outline of this interesting branch of Natural Science brought up to the most advanced state of modern investigation. The high reputation of the author, on both sides ofthe Atlantic, is a sufficient guarantee for the completeness and accuracy of any work to which his name is prefixed ; but this volume comes with the additional re- commendation that it is the one on which the author has bestowed the greatest care, and on which he is desirous to rest his reputation. It forms a very large octavo volume, beautifully printed, and most profusely illustrated. PRINCIPLES OF THE MECHANICS OF MACHINERY AND ENGI- NEERING. J3y PROFESSOR JULIUS WEISBACH. Translated and Edited by PROF. GORDON, of Glasgow. First American Edition, with Additions by PROF. WALTER R. JOHNSON. In two octavo volumes, beautifully printed, with 900 illustrations on wood. The most valuable contribution to practical science that has yet appeared in this country. Athenatum. . Unequalled by anything of the kind yet produced in this country the most stand- ard book on mechanics, machinery and engineering now exiant. N. Y. Commercial. In every way worthy of being recommended to our readers Franklin Institute Journal. PRACTICAL PHARMACY: Comprising the Arrangements, Apparatus, and Manipulations of the Pharmaceutical Shop and Laboratory. By FRANCIS MOHR, Ph. D., Assessor Pharmaciae ofthe Royal Prussian College of Medi- cine, Coblentz ; and THEOPHILUS REDWOOD, Professor of Pharmacy in the Pharmaceutical Society of Great Britain. Edited, with extensive Additions, by PROF. WILLIAM PROCTER, ofthe Philadelphia College of Pharmacy. In one handsomely printed octavo volume, of 570 pages, with over 500 en- gravings on wood. PRINCIPLES OF PHYSICS AND METEOROLOGY. By PROFESSOR J. MULLER, M. D. Edited, with Additions, by R. EGLESFELD GRIFFITH, M. D. In one large and handsome octavo volume, with 550 wood-cuts, and two colored plates. The style in which the volume is published is in the highest degree creditable to the enterprise of the publishers. It oon'ains nearly four hundred engravings exe- cuted in a style of extraordinary elegance. We commend the book to general favor. It is the best of Us kind we have ever seen. N. Y. Courier and Enquirer. BLANCHARD & LEA'S PUBLICATIONS. (Science.) 9 BEALE ON HEALTH-JUST READY. THE LAWS OF HEALTH IN RELATION TO MIND AND BODY, A SERIES OF LETTERS FROM AN OLD PRACTITIONER TO A PATIENT. BY LIONEL JOHN BEALE, M. R. C. S., &c. In one handsome volume, royal 12mo., extra cloth. The "Laws of Health," in relation to mind and body, is a book which will convey much instruction to non -professional readers; they may, from these letters, glean the principles upon which young persons should be educated, and derive much useful information, which will apply to the preservation of health at all ages. Med. Times. GREGORY ON SVTAGNETISIVI-lffOW READY. LETTERS TO A CANDID INQUIRER ON ANIMAL MAGNETISM, BY WILLIAM GREGORY, M. D., Professor of Chemistry in (he University of Edinburgh. In one neat volume, royal 12mo., extra cloth. INTRODUCTION TO PRACTICAL CHEMISTRY, including Analysis. By John E. Bowman, M. D. In one neat royal 12mo. volume, extra cloth, with numerous illustrations. DANA ON CORALS. ZOOPHYTES AND CORALS. By James D. Dana. In one volume imperial quarto, extra cloth, with wood-cuts. Also, an Atlas to the above, one volume imperial folio, with sixty-one magnificent plaies, colored after nature. Bound in halt" morocco. These splendid volumes form a portion of the publications of the United States Ex- ploring Expedition. As but very few copies have been prepared for sale, and as these are nearly exhausted, all who are desirous of enriching their libraries with this, the most creditable specimen of American Art and Science as yet issued, will do well to procure copies at once. THE ETHNOGRAPHY AND PHILOLOGY OF THE UNITED STATES EXl'LORIIMG EXPEDITION. By Horatio Hale. In one large imperial quarto volume, beautifully printed, and strongly bound in extra cloth. BARON HUMBOLDT'S LAST WORK. ASPECTS OF NATURE IN DIFFERENT LANDS AND DIFFERENT CLIMATES With Scientific Elucidations. By Alexander Von Humboldt. Translated by Mrs. Sabine. Second American edition. In one handsome volume, large royal 12mo., extra cloth. CHEMISTRY OF THE FOUR SEASONS, SPRING, SUMMER, AUTUMN, AND WINTER. By Thomas Griffith. In one handsome volume, royal 12mo , extra cloth, with numerous illustrations. THE MILLWRIGHT'S GUIDE. THE MILLWRIGHT'S AND MILLER'S GUIDE. By Oliver Evans. Eleventh Edition. With Additions and Corrections by the Professor of Mechan i t s in the Franklin Institute, and a description, of an improved Merchant Flour Mil?. By C. and O. Evans. In one octavo volume, with numerous engravings. 1* 10 BLANCHARD & LEA'S PUBLICATIONS. (Science.) SOMERVII/tE'S PHYSICAL GEOGRAPHY. New Edition, much Improved Just Issued, PHYSICAL GEOGRAPHY. BY MARY SOMERVILLE. Second American from the Second and Xevised JLonAon Edition. WITH AMERICAN NOTES, GLOSSARY, &c. In one neat royal 12mo. vol., extra cloth, of over 550 pages. The great success of this work, and its introduction into many of our higher schools and academies, have induced the publishers to prepare a new and much improved edition. In addition to the corrections and improvements of the author bestowed on the work in its passage through the press a second time in London, notes have been introduced lo adapt it more fully o the physical I geography of this country ; and a comprehensive glossary has been added, rendering the volume more particularly suited lo educational purposes. The amount of these additions may be understood from the fact, that not only has the size of the page been increased, but the volume itself enlarged by over one hundred and fifty pages. Our praise comes lagging in the rear, and is well-nigh superfluous. But we are anxious to recommend to our youth the enlarged method of studying geography which her present work demonstrates to be as captivating as it is insiruclive. U'e hold such presents as Mrs. Sornerville has bestowed upon the public, to be of incalculable value, disseminating more sound information than all the literary and scientific insti- tutions will accomplish in a whole cycle of their existence. Blackwood's Magazine. HUMAN HEALTH ; or, the Influence of Atmosphere and Locality, Change of Air and Climate, Seasons, Food, Clothing, Bathing, Mineral Springs, Exercise. Sleep, Corporal and Mental Pursuits, &c. &c., on Healthy Man, constituting Ele- ments of Hygiene. By Robley Dunglison, M. D. Jn one octavo volume. THE ANCIENT WORLD, OR PICTURESQUE SKETCHES OF CREA- TION. By D. T. Ansted, author of "Elements of Geology," &c. In one neat volume, royal 12mo., with numerous illustrations. A NEW THEORY OF LIFE. By S. T. Coleridge. Now first published from the original MS. In one small 12mo volume, cloth. ZOOLOGICAL RECREATIONS. By W. T. Broderip, F.R. S. From the second London edition. One volume, royal 12rno., extra cloth. AN INTRODUCTION TO ENTOMOLOGY; or, Elements of the Natural History of Insects. By the Rev. AVm. Kirby, and Wrn. 8pence. F. R. S. From the sixth London edition. Jn one large octavo volume, with plates, plain or colored. THE RACES OF MEN, a Fragment. By John Knox. In one royal 12mo. volume, extra cloth. AMERICAN ORNITHOLOGY. By Charles Bonaparte, Prince of Canino. la four folio volumes, half bound, wnh numerous magnificent colored plates. LECTURES ON THE PHYSICAL PHENOMENA OF LIVING BEINGS. By Carlo Matteucci. Edited by Jonathan Tereira, M D. In one royal 12nio, volume, extra cloth, with illustrations. >'orr j PHILOSOPHY IN SPORT MADE SCIENCE IN EARNEST. In one handsome volume, royal ISmo , crimson cloth, with numerous illustrations. ENDLESS AMUSEMENT. A Collection of Four Hundred Entertaining Experiments. In one handsome 'volume, royal 18mo., with illustrations, crimson cloih. BLANCHARD & LEA'S PUBLICATIONS. (Science.) 11 JOHNBTON'S PHYSICAL ATLAS. THE PHYSICAL ATLAS OF NATURAL PHENOMENA, FOR THE USE OF COLLEGES, ACADEMIES AND FAMILIES, BY ALEXANDER KEITH JOHNSTON, F.R.G.S., F.G.S. In one large volume, imperial quarto, handsomely and strongly bound, With Twenty-six Plates, Engraved and Colored in the hest style, Together with 112 pages of Descriptive Letterpress, and a very copious Index. This splendid volume will fill a void long felt in this country, where no work has been attainable presenting the results of the important science of Physical Geography in a distinct and tangible form. The list of plates sub- joined will show both the design of the work and the manner in which its carrying out has been attempted. The reputation of the author, and the universal approbation with which his Atlas has been received, are sufficient guarantees that no care has been spared to render the book complete and trustworthy. The engraving, printing, and coloring will all be found of the best and most accurate description. As but a small edition has been prepared, the publishers request all who may desire to procure copies of the work to send orders through their book- sellers without delay. LIST OF PLATES. GEOLOGY. 1. Geological Structure of the Globe. 2. Mountain Chains of Europe and Asia. 3. Mountain Chains of America. 4. Illustration of the Glacier System of the Alps. (Mont Blanc ) 5. Phenomena of Volcanic Action. Palaeontological and Geological Map of the British Islands. (A double sheet.) HYDROGRAPHY. 1. Physical Chart of the Atlantic Ocean. 2. Physical Chart of the Indian Ocean. 3 Physical Chart of the Pacific Ocean or Great Sea. 4. Tidal Chart of the British Seas. 5. The River Systems of Europe and Asia 6. The River Systems of America. Tidal Chart of the World. METEOROLOGY. 1. Humboldt's System of Isothermal Lines. 2. Geographical Distribution of the Cur- rents of Air. 3. Hyetographic or Rain Map of the World. 4. Hyetographic or Rain Map of Europe. NATURAL HISTORY. 1. Geographical Distribution of Plants. 2. Geographical Distribution of the Culti- vated Plants used as Food. 3. Geographical Distribution of Quadru- rnana, Edentata, Marsupialia, and Pachydermata. 4. Geographical Distribution of Carnivorn. 5. Geographical Distribution of Rodentia and Ruminantia. 6. Geographical Distribution of Birds. 7. Geographical Distribution of Reptiles. 8. Ethnographic Mnp of the World. 9. Ethnographic Map of Great Britain and Ireland. The book before us is, in short, a graphic encyclopaedia of the sciences an atlas of human knowledge done into maps. It exemplifies the truth which it expresses that he who runs may read. The Thermal Laws of Leslie it enunciates by a bent line running across a map of Europe: the abstract researches of Gauss it embodies in a few parallel curves winding over a section of the globe; a formula of Laplace it melts down to a little patch of mez/otint shadow; a problem of the transcendental ana- lysis, which covers pages with definite integrals, it makes plain to the eye by a little stippling and hatching on a given degree of longitude! All possible relations of time and space, heat and cold, wet and dry, frost and snow, volcano and storm, cur- rent and tide, plant and beast, race and religion, attraction and repulsion, glacier and avalanche, fossil and mammoth river and mountain, mine and forest, air and cloud, and sea and sky all in the earth, and under the earth, and on the earth, and above the earth, that the heart of man has conceived or his head understood are brought to- gether by a marvellous m'crocosm. and planted on these little sheets of paper thus making themselves clear to every eye. In short, we have a summary of all the cross- questions of Nature for twenty centuries and nil the answers of Nature herself set down and speaking to us voluminous system dans un mot .... Mr. Johnston is well known as a geographer of great accuracy and research ; and it is certain that this work will add to his reputation; for it is beautifully engraved, and accompanied with explanatory and tabular letterpress of great value. London Athf.n&iim. 12 BLANCHARD & LEA'S PUBLICATIONS. (College and School Books.) LARDNER'S HANDBOOKS OF NATURAL SCIENCE. HANDBOOKS OF NATURAL PHILOSOPHY AND ASTRONOMY, BY DIONYSIUS LARDNER, LL.D., ETC. FIRST COURSE, containing Mechanics, Hydrostatics, Hydraulics, Pneumatics, Sound, and Optics, In one large royal 12mo. volume of 750 pages, "With over four hundred Wood-cuts. Also, to be had in three Parts, as follows : Part I. containing MECHANICS, 292 pages, 109 cuts. Part IT. containing HYDROSTATICS, HYDRAULICS, PNEUMATICS, and SOUND, 186 pages, 97 cuts. Part III. containing OPTICS, 270 pages, 154 cuts. THE SECOND COURSE, embracing HEAT, ELECTRICITY, MAGNETISM, AND ASTRONOMY, Of about the same size as the First Course, and illustrated with the same profuseness, is nearly ready, and may shortly be had either in one large volume, or in parts. The reputation which Dr. Lardner has acquired by his numerous scientific works is too widely extended for the publishers to feel it necessary to say anything in praise of the admirable manner in which the principles of Natural Philosophy are popularized and simplified in the present volume. The ob- ject of the author has been to present the numerous and important subjects embraced in his design, in a form suited to the wants of the beginner, ex- plained in clear and simple language, and with references to their practical applications in the arts and sciences. In but very few instances has he pre- supposed a knowledge of mathematics extending to quadratic equations, and this only in cases where the nature of the subject absolutely requires it. To secure the accuracy so necessary to a volume of this kind, the publishers have availed themselves of the services of a gentleman whose scientific ac- quirements enable them, with confidence, to vouch for its correctness. Various errors which had escaped the author's attention have thus been rec- tified, and some omissions supplied ; while a series of questions and exam- ples is appended to each subject, with the view of impressing upon the student the application of the principles laid down in the text, to practical purposes. In order to supply the wants of those who desire to procure separate manuals on the various subjects embraced in this work, it has been arranged for binding either in three parts, or as a whole. The First Part embraces Mechanics; the Second, Hydrostatics, Hydraulics, Pneumatics, and Sound; the Third, Optics. The paging at the head of the pages applies to the sepa- rate parts ; that at the foot, is continuous throughout the volume. It will be seen that the references in the Tables of Contents are designed for the former, and those in the Index for the latter. Either separately or as a whole, it is therefore confidently presented as a complete and reliable, though popular, manual of Natural Philosophy, de- signed either for the use of schools, or for the private student, and fully brought up to the most advanced state of science at the present day. BLANCHARD & LEA'S PUBLICATIONS. (College and School Books.) 13 SCHMITZ & ZUMPT'S CLASSICAL SERIES. Under this title BLANCHARD & LEA are publishing a series of Latin School Books, edited by those distinguished scholars and critics, Leonhard Schmitz and C. G. Zumpt. The object of the series is to present a course of accurate texts, revised in accordance with the latest investigations and MSS., and the most approved principles of modern criticism. These are accompanied with notes and illustrations introduced sparingly, avoiding on the one hand the error of overburdening the work with commentary, and on the other that of leaving the student entirely to his own resources. The main object has been to awaken the scholar's mind to a sense of the beauties and peculiarities of his author, to assist him where assistance is necessary, and to lead him to think and to investigate for himself. For this purpose maps and other en- gravings are given wherever useful, and each author is accompanied with a biographical and critical sketch. The form in which the volumes are printed is neat and convenient, while it admits of their being sold at prices unpre- cedentedly low, thus placing them within the reach of many to whom the cost of classical works has hitherto proved a bar to this department of study. The publishers have received several hundred testimonials of the great value of this series from the most prominent practical teachers of the country. OF THIS SERIES THE FOLLOWING HAVE APPEARED : C^SARIS DE BELLO GALLICO LIBRI IV., 232 pages, with a Map, price 50 cents. P. VIRGILII MARONIS CARMINA, 438 pages, price 75 cents. C. C. SALLUSTII CATILINA ET JUGURTHA, 168 pages, with a Map, price 50 cents. SCHMITZ'S LATIN GRAMMAR, 318 pages, price 60 cents. Q. CURTII RUFI DE ALEXANDRI MAGNI QU.^ SUPERSUNT, 326 pages, with a Map, price 70 cents, M. T. CICERONIS ORATIONES SELECTEE XII., 300 pages, price 60 cents. T. LIVII PATAVINI HISTORIARUM LIBRI I., II., XXL, XXII., 350 pages, with two colored Maps, price 70 cents. KALTSCHMIDT'S SCHOOL LATIN DICTIONARY, in two parts, Latin- English and English-Latin, nearly 900 pages, double columns, price, com- plete, $1 25. Nearly Ready. P. OVIDII NASONIS CARMINA EXCERPTA. In Preparation. SCHMITZ'S INTRODUCTION TO THE LATIN GRAM- MAR ; HORACE; FIRST AND SECOND LATIN READING AND EXERCISE BOOKS; A SCHOOL CLASSICAL DICTIONARY, &c. &c. ** Teachers desirous of examining any of these volumes will be sup- plied with copies or. application to the publishers. If to be sent by mai 1 , stamps should be enclosed to prepay the postage. 14 BLANCHARD & LEA'S PUBLICATIONS. (College and School Books.} Schmitz and ZumpCs Classical Series (continued) THE LAST VOLUME PUBLISHED OF THIS SERIES IS A SCHOOL DICTIONARY OF THE LATIN LAN8UAGE. BY DR. J. II. KALTSCHMIDT. In two parts, Latin-English and English-Latin. Part I, Latin English, 486 pages, strongly bound, price 90 cents. Part II, English Latin, 366 pages, price 75 cents. Or the whole complete in one very thick royal 18mo. volume, of 850 closely printed double columned pages strongly bound in leather, price $1 25. While several valuable and copious Latin Lexicons have within a few years been published in this country, a want has long been felt and acknowledged of a good SCHOOL DICTIONARY, which within reasonable compass and at a moderate price should pre- sent to the student all the information requisite for his purposes, as elucidated by the most recent investigations, and at the same time unincumbered with erudition useful only to the advanced scholar, and increasing the size and cost of the work beyond the reach of a large portion of the community. It is with this view especially that the present work has been prepared, and the names of its distinguished authors are a sufficient guarantee thai this intention has been skillfully and accurately carried out. The present volume has been compiled by Dr. Kaltschmidt, the well-known Ger- man Lexicographer, from the best Latin Dictionaries now in use throughout Europe, and has been carefully revised by Dr. Leonhard Schmitz. It presents as far as possible, the etymology of each word, not only tracing it to its Latin or Greek root, but to roots or kindred forms of words occurring in the cognate languages of the great Indo-Germanic family. This feature, which distinguishes the present Dic- tionary from all others, cannot fail to awaken the learner to the interesting fact of the radical identity of many apparently heterogeneous languages, and prepare him at an early stage for the delightful study of comparative philology. The aim of the publishers has been to carry out the author's views as far as possible by the form and arrangement of the volume. The type, though clear and well printed, is small, and the size of the page such as to present an immense amount of matter in compass of a single handsome ISmo. volume, furnished at a price far below what is usual with such works, and thus placing within the reach of the poorest student a neat, convenient, and complete Lexicon, embodying the investigations of the most distinguished scholars of the age. Although this work has been issued very recently, it has already attracted great 'attention from all interested in education, and it has been introduced into a large number of schools. The publishers subjoin two or three commendatory letters from among a vast number wiih which they have been favored. From Prof J. Forsyt/i, J>., of Princeton University, March 19, 1851 . With the School Dictionary I am greatly pleased. It is so cheap, so convenient, and ia its etymological features so p culiar, aid withal so valuable, that on many a student s table the larger and more costly lexicons will sustain some risk of being superseded. From Prof. G. Harrison. University of Fa., March 17, 1851. I am very much pleased with it. 1 think it will meet an existing want and be very popular with the schoolboys. If the second part be executed as well, 1 shall take great pleasure in recommending the whole work to my friends. From Prof. C. I). ^Cleveland Philadelphia. March 12, 1851. You have done a very great service to the cause of Classical Education in pub- lishing the '-School Dictionary of the Latin Language," by Dr. J. H. Kaltschmidt. We needed something of the kind very much. The larger dici'onaries of Leverett & Andrews are excellent for advanced scholars, but I have found, in my experience, that younger students were confused by the multiplicity of definitions and examples in them, and 1 have therefore long wanted to see a work better adapted to their wants and capacities. This desideratum you have very h:ippily supplied. From J. J. Helm, Esq.. Salem, July 15 1851. If I have been more pleased with any one of -them than the rest, it is the Latin-Eng- lish Dictionary. Ihis is truly a desideratum. We had no small Latin Dictionary that was up to the mark in point of scholarship. This appears to be so. From P. S. Burchan, Esq , Po^keepsie. May 13. 1851. I have had it constantly by me, and therefore know something about it, and I think it the most complete and admirable school dictionary in this country at least. The great fault of manuals of this kind for schools and colleges is, the unwieldy mass of useless quotations from the learned languages, introduced to illustrate, but which generally serves rather to confute the signification of words. This Lexicon defines briefly and lucidly the meaning of the word sought; it shows you how it is used in various authors, by quotations indeed, but by quotations strictly rendered, or introduced as illustrations by implication ; and, what is a merit peculiarly its own. it gives, as far as it is practicable, the etymology of each word Richmond Enquirer. BLANCHARD & LEA'S PUBLICATIONS. (College and School Books.) 15 ELEMENTARY CHEMISTRY; THEORETICAL AND PRACTICAL. By George Fownes, Ph. D., F. R. S., &c. Edited, with Notes and Additions, by Robert Bridges, M.D. Third American from a late London edition. In one large royal 12mo. volume, with numerous illustrations. We know of no treatise so well calculated to aid the student in becoming familiar with the numerous facts in the science on which it treats, or one better calculated as a text-book for those attending Chemical Lectures. * * * * The best text-book on Che- mistry that has issued from our press. American Med. Journal. We know of none within the same limits, wliich has higher claims to our confidence as a college class-book, both for accuracy of detail and scientific arrangement. Augusta Med. Journal. OUTLINES OF ASTRONOMY. By Sir John F. W. Herschel, F. R. S., &c. In one neat volume, crown Svo., with six plates and numerous wood-cuts. We now take leave of this remarkable work, which we hold 1o be, beyond a doubt, the greatest and most remarkable of the works in which the laws of astrono- my and the appearance of the heavens are described to those who are not mathema- ticians nor observers, and recalled to those who are. It is the reward of men who can descend from the ail vancement of knowledge to care for its diffusion, that their works are essential to all, that they become the manuals of the proficient as well as the text-books of the learner. AthtntRum. Probably no book ever written upon any science, embraces within so small a com- pass an entire epitome of everything known within all its various departments, practical, theoretical, and physical. Examiner. ELEMENTS OF NATURAL PHILOSOPHY; Being an Experimental Introduction to the Physical Sciences. Illustrated with over three hundred wood-cuts. By Golding Bird, M. D., Assistant Physician to Guy's Hospital. From the third London edition. In one neat volume, royal 12mo. We are astonished to find that there is room in so small a book for even the bare recital of so many subjects. Where everything is treated succintly, great judgment and much time are needed in making a selection and winnowing the wheat from the chaff Dr. Bird has no need to plead the peculiarity of his position as a shield against criticism, so long as his book continues to be the best epitome in the English lan- guage of this wide range of physical subjects. North American Review, April, 1851. ELEMENTS OF PHYSICS ; or Natural Philosophy, General and Medical. Written for universal use, in plain, or non-technical language By Neil! Arnolt, M. D. A new edition, by Isaac Hays, M. D. Complete in one octavo volume, with about two hundred illustrations. ELEMENTS OF OPTICS, by Sir David Brewster. With Notes and Additions by A. D. Bache, LL. D. In one 12mo. volume, half bound, with numerous wood- cuts. A TREATISE ON ASTRONOMY. By Sir John F. W. Herschel. Edited by S. C. Walker, Esq. In one 12mo. volume, with numerous plates and cuts. AN ATLAS OF ANCIENT GEOGRAPHY. By Samuel Butler, D. D., late Lord Bishop of Lincoln. In one octavo volume, half bound, containing twenty-one colored Maps and an accentuated Index. GEOGRAPHICA CLASSICA ; or, the Application of Ancient Geography to the Classics. By Samuel Butler, D D.,