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Harvard College 

By Exchange 

3 2044 097 020 333 

\ \N >- ■ ^ 





GEORGE FOWliraiS, F.R.S., 


un raorEssoE or PBioncu ohhiistrt at xnwnatar vniam, uaaoa, 










rEB 2/ 1932 

Entered, according to Act of Congress, in the year 1853, by 


in the Clerk's Office of the District Court of the United States for tha 

Eastern District of Pennsylvania. 

P tin ted by T. K Sc P Q Collius . 




The lamented death of the Author has caused the reyiBion of this 
edition to fall into the hands of others^ who have fully sustained its 
reputation by the additions which they have made^ more especially 
in the portion devoted to Organic Chemistry^ as set forth in their 
preface. This labour has been so thoroughly performed^ that 
the American Editor has found but little to add, his notes con- 
sisting chiefly of such matters as the rapid advance of the science 
has rendered necessary^ or of investigations which had apparently 
been overlooked by the Author's friends. These additions will be 
found distinguished by his initials. 

The volume is therefore again presented as an exponent of the 
most advanced state of Chemical Science, and as not unworthy a con- 
tinuation of the marked favour which it has received as an elementary 


October, 1853. 

!• (T) 


The design of the present.yolume is to offer to the student com- 
mencing the subject of Chemistry^ in a compact and inexpensive 
form; an outline of the general principles of that science^ and a history 
of the more important among the very numerous bodies which Che 
mica! Investigations have made known to us. The work has no pre-, 
tensions to be considered a complete treatise on the subject; but is 
intended to serve as an introduction to the larger and moi^ compre- 
hensive systematic works in our own language and in those of the 
Continent^ and especially to "prepare the student for the perusal of 
original memoirs^ which; in conjunction with practical instruction in 
the laboratory; can alone afford a real acquaintance with the spirit of 
research and the resources of Chemical Science. 

It has been my aim throughout to render the book as practical as 
possible; by detailing; at as great length as the general plan permitted; 
many of the working processes of the scientific laboratory, and by 
exhibiting; by the aid of numerous wood-engravings, the most useful 
forms of apparatus; with their adjustments and methods of use. 

As one principal object was the production of a convenient and 
useful class-book for pupils attending my own lectures, I have been 
induced to adopt in the book the plan of arrangement followed in 
the lectures themselves; and to describe the non-metallic elements 
and some of their most important compounds before discussing the 
subject of the general philosophy of Chemical Science, and even 



before describing the principle of the equivalent quantities^ or ex- 
plaining tbe use of the written symbolical language now universal 
among chemists. For the benefit of those to whom these matters 
are already familiar, and to render the history of the compound bodies 
described in the earlier part of the work more complete, I have added 
in foot-notes the view adopted of their Chemical constitution, ex- 
pressed in symbols. 

I have devoted as much space as could be afforded to the very im- 
portant subject of Organic Chemistry; and it will, I believe, be found 
that there are but few substances of any general interest which have 
been altogether omitted, although the very great number of bodies to 
be described in a limited number of pages rendered it necessary to 
use as much brevity as possible. 


Univebsitt College, London, 
Odi^er 5, 1847. 





The correctioii of this Edition for the press v^ the daily occapa- 
tion of Professor Fownes^ until a few hours previous to his death in 
January, 1849. -► 

His wish and his endeayour, aB seen in his manuscript, were to 
render it as perfect and as minutely accurate as possible. 

When lie had finished the most important part of the Organic 
Chemistry, where the most additions were required, he told me he 
should "do no more,'* — ^he had "finished his worL*' 

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 haye also been corrected throughout by 
his friend Mr. Robert Murray. 

H. Benoe Jones, M.D. 

80, GaosyxNoa Stbixt, 
Jan.f I860. 


- \ .. -- .. 


»> 1KB 



It has heen the endeayour of the Editors to include in the present 
edition of the Manual the progress of Chemistry since the Author's 

The foundation which he laid^ and the form which he gaye to the 
work; remain untouched. But time has rendered it necessaiy that 
each portion should be revised ; and a few repairs^ and some consider- 
able additions; especially in Organic Chemistry, have been made. 
ThuS; several of the chapters on the Alcohols, the Organic Bases, 
Colouring Matters, &c., have been almost re-written. 

Still, such changes only have been made as the Editors believed 
the Author himself would have desired, if his life had been spared 
to Science. 

H: Bence Jones. 

London, September, 1852. 






Op deksitt ahd specific gravity. 

Methods of determining the specific gravities of fluids and solids 27 

. Constmction and application of the hydrometer , 82 

Or THE physical constitution of the atvosphbbe, and of gases in 


Elasticity of gases. — Constmction 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. 88 


Expansion. — Thermometers 41 

Different rates of expansion among metals; compensation-pendulum 44 

Daniell's pyrometer 45 

Expansion of liquids and gases. — ^Ventilation. — Movements of the atmo- 
sphere 46 

Conduction of heat 52 

Change of state. — Latent heat ^ 52 

Ebullition; steam 54 

Distillation .". 58 

Evaporation at low temperatures 59 

Vapour of the atmosphere; hygrometry 61 

Xiquefaction of permanent gases ». 62 

Production of cold by evaporation 64 

Capacity for heat. — Specific heat 66 

Sources of heat 68 

2 (xiii) 




Befleotion, refractioni and polarization of liglit 71 

Chemical rays 77 

Badiation, reflection, absorption, and transmission of heat 79 


Magnetic polarity; natural and artificial magnets 86 

Terrestrial magnetism 88 


Electrical excitation; machines 92 

Principle of induction ; accumulation of electricity 93 

Voltaic electricity 97 

Thermo-electricity. — Animal electricity 99 

Electro-magnetism; magneto-electricity 100 

Electricity of steam 103 




Oxygen 105 

Hydrogen; water; binoxide of hydrogen , 110 

Nitrogen; atmospheric air ; compounds of nitrogen and oxygen 120 

Carbon; carbonic oxide ; carbonic acid 127 

Sulphur; compounds of sulphur and oxygen , 131 

Selenium.... 136 

Phosphorus; compounds of phosphorus and oxygen..; 137 

Chlorine; hydrochloric acid. — Compounds of chlorine and oxygen 139 

Iodine 143 

Bromine „ 148 

Fluorine 149 

Silicium , , 150 

Boron 151 

Compounds formed bt the union of the non-metallic elements among 

Compounds of carbon and hydrogen. — Light carbonetted hydrogen ; defiant 

gas; coal and oil-gases. — Combustion, and the structure of flame • 153 

Nitrogen and hydrogen; ammonia 162 



Snlplinr, selenmm, and pliosphoms, with hydrogen , -..,. 163 

NitrogeB; with chlorine and iodine; chloride of nitrogen 167 

Other compounds of non-metallio elements 168 

Chlorine, with snlphur and phosphorus 168 

Dn the general pbinciples of chemical philosophy. 

Nomenclature 170 

Laws of combination by weight , 172 

By Tolume , , « 177 

Chemical symbds 180 

The atomic th^Bory 182 

Chemical affinity 183 

Electro-chemical decomposition; chemistry of the voltaic pile 187 


General properties of the metals 197 

Crystallography 202 

Isomorphism , 209 

Polybasic acids ^ , 212 

Binary theory of the constitution of salts 213 

Potassium 217 

Sodium 224 

Ammonium ., 232 

Lithium 235 

Barium 237 

Strontium 239 

Calcium ^ 239 

Magnesium 245 

Aluminium... 248 

Beryllium (glucinum) « 250 

Yttrium, cerium, lanthanium, and didymium 251 

Zirconium. — Thorium 252 

Manufacture of glass, porcelain, and earthenware 252 

Manganese.. 256 

Iron .'. 259 

Aridium 266 

Chromium .^..... 267 

Nickel 269 

Cobalt ^ 271 

Zinc r. 272 

Cadmium 274 

Bismuth 274 

Uranium 276 

Copper 277 

liead 279 

Tin 282 



Tangsten 284 

Molybdenum 284 

Vanadium 285 

Tantalum (columbium) 286 

KioLlum and pelopium 286 

Titanium 287 

Antimony 287 

Tellurium 290 

Arsenic 291 

Silver 296 

Gold .., 299 

Mercury SOI 

Platinum 307 

Palladium 311 

Bhodium 312 

Iridium 312 

Buthenium 314 

Osmium 314 



Intkoduction *. /.... 31C 

Law of substitution 317 

The uLTmATE analysis of organic bodies 320 

Empirical and rational formulae 329 

Determination of the density of the vapours of volatile liquids .... 330 
Saccharine and amylaceous substances, and the products of their 

alteration 333 

Cane and grape-sugars ; sugar from ergot of rye ; sugar of diabetes insipi- 
dus; liquorice-sugar; milk-sugar; mannite 333 

Starch ; dextrin ; starch from Iceland-moss ; inulin ; gum ; pectin ; lignin .. 337 

Oxalic and saccharic acids 341 

Xyloidin; pyroxylin; mucic acid 344 

Suberic, mellitic, rhodizonic, and croconic acids 345 

Fermentation of sugar. — Alcohol 345 

Lactic acid 349 

Ether, and ethyl-compounds 351 

Salphovinic, phosphovinic, and oxalorinic acids 358 

Heavy oil of wine 362 

defiant gas; Dutch liquid; chlorides of carbon 362 


Etbionio and isethionio acids , , 365 

Chloral, Ac : 366 

MercaptAn; xanthic acid , 367 

Aldehyde; aldehydio acid ; acetal 369 

Acetic acid 371 

Chloracetic acid 375 

Acetone 376 

Kakodyl 377 

Substances kobb or less allied to alcohol. 

Wood-spirit; methyl-componnds , ,. 381 

Bolphomethylio acid 384 

Formic acid; chloroform 385 

Formomeih jlal ; methyl-mercaptan , 387 

Potato-oil and its derivatiTes 388 

Sulphamylic acid; yalerianic acid 390 

Chloroyalerisic and chlororalerosic acids 393 

Fusel-oil from grain-spirit; general view of the alcohols ,. 393 

Bitter-almond-oil and its products; benzoyl-cOmpounds 396 

Benzoic-acid ; snlphobenzoic acid ; benzene and benzol 396 

Solphobenzide and hjposnlphobenzic acid 398 

Nitrobenzol, azobenzol, <fcc 399 

Formobenzoio acid; hydrobenzamide ; benzoin; benzile; benzilio acid; 

benzimide, &c 400 

Hippnric acid .' 402 

Homolognes of benzoyl-series 403 

Salicin; salicyl and its compounds 403 

Chlorosamide. — Phloridzin. — Cumarin..... 405 

Cinnamyl and its compounds ; cinnamie acid ; chloro-cinnose 407 

Vegetable acids. 

Tartaric acid..... 410 

Bacemio acid 413 

Citric acid ^ 413 

Aconitic or equisetic acid t 414 

Italic acid 414 

Famaric and maleio acids 416 

Tannic and gallic acids 416 


Cyanogen; paracyanogen ; hydrocyanic acid 420 

Amygdalin; amygdalic acid 423 

Metallic cyanides 424 

Cyanic,, cyanuric, and fulminic acids •.... 426 

Chlorides, Ac, of cyanogen 429 




Ferro- and ARricjanogen, and their compounds; Prussian blue 430 

Cobaltocyanogdn ; nitroprassidos : 433 

Sulphocyanogen, and its compounds ; selenocyanogen ; melam ; melamine ; 

ammeline; ammelide < 434 

Ureay and uric acid ', 436 

AUantoin; alloxan; alloxanio acid; mesoxalic acid; mjkomelinic acid; 

parabanio acid; oxalurio acid; thionuric acid; uramile; alloxantin; 

murexide; murexan 438 

Xanthio and cystic oxides 443 

Thb txgbto-alkalis, and allied bodibs. 

Morpbine, and its salts..... 444 

Narcotine; opianio and hemipinic acids ; cotamine 445 

Codeine; thobaine; pseudo-morphine; naroeine; meconine 446 

Meconic acid * 446 

Cinchonine and quinine; quinoidine 447 

Einio acid; kinone; l^drokinone 448 

Strychnine and brucine; veratrine 449 

Conicine; nicotine; sparteine; harmaline; harmine; caffeine or theine; 

theobromine; berberine; piperine; hyoscyamine; atropine; solanine; 

aconitine; delphinine; emetine; curarine 450 

Gentianin; populin; daphnin; hesperidin; elaterin; antiarin; picrotoxin; 

asparagin; santonin , 451 


Bases of the ethyl-series. — Ethylamine ; biethylamine ; triethylamine ; 

oxide of tetrethyl-ammonium 455 

Bases of the methyl- series. — Methylamine; bimethylamine ; trimethyla- 

mine; oxide of tetram ethyl-ammonium 457 

Bases of the amyl-series. — Amylamine ; biamylamine ; triamylamine ; 

oxide of tetramy] -ammonium 458 

Bases of the phenyl-series. — Aniline; chloraniline; nitraniiine; cyaniline; 

melaniline 459 

Bases homologous to aniline. — Toluidine; xylidine; cumidiue. Naphthali- 

dine; chloronicine 462 

Mixed bases. — Ethylaniline; biethylaniline ; oxide of triethylamyl-ammo- 

nium ; biethylamylamine ; oxide of methylobiethylamyl-ammonium ; 

methylethylamylamine ; ethylamylaniline ; oxide of methyl-ethyl-amylo- 

phenyl-ammonium 463 

Bases op uncertain constitution. 

Chinoline , , 464 

Kyanol; leucol; picoline 405 

Petlnine 465 

• Furfurine •. 465 



Fucusine; amarine; thiosinnamine 466 

Thialdinc; alanine , 467 

Phosphorus-bases 468 

Antimony-bases 469 

Organic colouring principles. 

Indigo; white indigo; sulphindjlic acid 470 

Isatin; anilic and picrio acids ; chrysanilio and anthranilic acids 471 

Litmas — lecanorin; orcin; orcein, &c, ; 474 

Cochineal, madder, dye-woods, ^c 477 

Chrysammic, chrysolepic, and styphnic acids 479 

Oils and pats. 

Fixed oils ; margarin, stearin, and olein ; saponification, and its prodncts ; 

glycerin 480 

Palm and cocoa-oils. — Elaidin and elaidio acid 483 

Suberic, succinic, and sebacic acids.... 484 

Butter, — Butyric, caproic, caprylic, and caprio acids 485 

Wax; spermaceti; cholesterin; cantharidin 486 

Acrolein; acrylic acid 487 

Products of the action of ^cids on fats 487 

Castor-oil; caprylic alcohol 488 

Volatile oils. — Oils of turpentin, lemons, aniseed, cumin, cedar, gaultheria, 

valerian, peppermint, lavender, rosemary, orange-flowers, rose-petals 488 

Camphor; camphoric acid * 492 

Oils of mustard, garlic, onions, <fcc 492 

Kesins. — Caoutchouc 493 

Balsams. — Toluol, styrol 494 

Components op the animal body. 

Albumin, fibrin, and casein; protein 496 

Gelatin and chondrin 500 

Kreatin and kreatinine 602 

Composition of the blood ; respiration; animal heat 503 

Chyle; lymph; mucus; pus 507 

Milk; bile; urine; urinary calculi ^ 508 

Nervous substance ; membranpus tissue ; bones 510 

The function of nutrition in the vegetable and animal kingdoms 518 

Products op the destructive distillation, and slow putrefactive 

CHANGE op organic MATTER^ 

tSubstances obtained from tar. — Paraffin; eupione; picamar; kapnomor; 
cedriret; kreosote; ehrysen and pyren ' , 623 



Coal-oil. — Carbolic acid (hydrate of oxide of phenyl) 626 

Naphthalin and paranaphthalin 529 

Petroleum, naphtha, and other allied substances 530 


: Hydrometer tables. — Table of the tension of the vapour of water at differ- 
ent temperatures. — Table of the proportion of real alcohol in spirits 

of diflferent densities. — Analyses of the mineral waters of Germany. 

Table of weights and measures ^ 533 


Fig. Pago 

1 Specific-grayity botUo 28 

2 " " , ,„ 29 

3 " « 29 

4 " " 29 

6 " « 30 

6 " " beads : 31 

7 Hydrometer «. 32 

8 Urinometer 32 

■ 9 Specific gravity 33 

10 Elasticity of gases «... 34 

11 Single air-pump 35 

12 Double " 36 

13 Improyed" 36 

14 " " ■ 37 

15 Barometer 88 

16 " 39 

17 « 40 

18 Expansion of solids .' * - 41 

19 " Uquids 41 

20 " gases 41 

21 Differential thermometer 43 

22 " " 43 

23 Difference of expansion in metals 44 

24 Gridiron pendulum ,....• 44 

25 Mercury ** 45 

26 Compensation balance 45 

27 Daniell's pyrometer 45 

2S Expansion of mercury 47 

29 AtmoEpberio currents 50 

SO " " 50 

31 " « 51 

32 Boiling paradox ^ • 55 

ZZ Steam-bath .«. 57 

34 Steam-engine 57 

35 Distillation 58 

36 liiebig's condenser 50 

37 Tension of vapour 59 

3S " " 60 

S9 Wet-bulb hygrometer 62 

(xxi) . 


Fig. Pag« 

40 Condensation of gases « 63 

41 Thilorier's apparatus ^ ^ 64 

42 Cold by evaporation 65 

43 WoUaston's cryophoms ', 65 

44 Daniell's hygrometer 65 

46 Reflection of light 72 

46 Refraction of light 72 

47 " « 72 

48 « « 73 

49 Speotmm , 74 

60 " 74 

61 PolarixatioB of light 75 

62 " <* 76 

63 " '« 76 

54 Reflection of heat 79 

65 " " 80 

66 Effects of electrical current on the magnetic needle 82 

67 " " «* «* 82 

68 Current prodnoed by heat 83 

69 Helloni's instniment for measaring transmitted heat 83 

60 Magnetic polarity 87 

61 'f " 87 

62 Electro repnlsion , 93 

63 Electroscope 93 

64 Electric polarity 93 

65 Slectrioal machine 95 

66 « " plate 95 

67 Leyden jar 96 

68 Electrophoras .' 97 

69 Volta*spile 98 

^ 70 Crown of cups 98 

71 Cruikshank's trough 99 

72 Effect of electrical current on the magnetic needle 100 

73 Astatic needle 101 

74 Magnetism developed by the electrical current > 101 

75 « <* « " 102 

76 Electro>magnet 102 

77 Apparatus for oxygen 105 

78 Hydro-pneumatic trough 106 

79 Transferring gases 107* 

80 Pepy's hydro-pneumatic apparatus lOT 

81 Apparatus for hydrogen Ill 

82 Levity of hydrogen Ill 

83 Diffusion of gases 112 

84 Daniell's safety-jet 1 13 

85 Musical sounds by hydrogen 114 

86 CatalyVo effect of platinum 115 


tig. Pag» 

87 Decomposition of water 116 

88 Eudiometer of Cavendish 116 

89 Analysis of water ,•.......• 116 

90 Preparation of nitrogen 120 

91 Analysis of air ;.... 121 

92 Ure's eudiometer 123 

93 Preparation of nitrio acid ^„ 123 

94 " protoxide of nitrogen ...*.... 125 

95 Crystalline form of carbon... 127 

96 " " " 127 

97 w " « 127 

98 « " *' - 127 

99 Preparation of carbonic acid , 129 

100 Mode of forming caoutchouc connecting-tubes « 129 

101 Crystalline form of sulphur 131 

102 Crystals of sulphur 131 

103 Crystalline form of sulphur 131 

104 Preparation of phosphorus 137 

105 '' chlorine 139 

106 " hydrochloric acid 142 

107 Safety-tube : 143 

108 Combustible under water 145 

109/ Preparation of hydriodic acid 147 

110 « sUica « 150 

111 Blast furnace 157 

112 Keverberatory furnace 157 

113 Structure of flame 153 

114 Mouth blowpipe 159 

115 Structure of blowpipe flame • 159 

116 Argand spirit-lamp 159 

117 Common " 159 

118 Mitchell's " 16C 

119 Gas " 16C 

120 Davy's safe " 161 

121 Hemming's safety-jet , 161 

122 ESectof metallic coil 161 

123 Apparatus for sulphuretted hydrogen , 16i 

124 Multiple proportions , 18ii 

125 Water in its usual state 180 

126 " undergoing electrolysis 189 

327 Voltameter 190 

12S Decomposition without contact of metals 191 

129 Wollaston's voltaic battery 193 

130 Paniell's constant " 193 

131 Grove's *' " 194 

132 Electrotype 195 

133 Le&d-tree :9& 


Pig. Pftgo 

134 Wire-drawing 198 

135 WoUaston's goniometer 203 

136 Reflecting " 204 

137 " " principles of 205 

138 Crystals, regular system '. 206 

139 ** regular prismatic system 206 

140 '< right prismatic system 207 

141 '' oblique prismatic system 207 

142 " doubly oblique prismatic system 203 

143 Crystals, rhombohedral system 208 

144 " passage of cube to octahedron 209 

145 " " " octahedron to tetrahedron 209 

146 Alkalimeter 227 

147 Apparatus fo\ determining carbonic aeid 228 

148 ** " " " " 229 

149 Iron manufacture. Blast-furnace 264 

150 Crystals of arsenious acid .*. 293 

151 Subliming tube for arsenic 294 

152 Marsh's test 295 

153 Weighing tube 321 

154 Combustion 321 

155 Chauffer ., 322 

156 Water tube 322 

157 Carbonic acid bulbs 322 

158 Apparatus complete 323 

159 Bulb for liquids .' 324 

160 Comparative determination of nitrogen 325 

161 Pipette 325 

162 Absolute estimation of nitrogen 326 

163 Varentrap's and Will's method 327 

164 Determination of the density of vapours 330 

165 Starch granules 338 

166 Preparation of ether , 361 

167 " defiant gas 363 

168 " Dutch liquid 363 

169 Catalysis 371 

170 Preparation of kakodyle 379 

171 " benzoic acid 397 

172 « tannic acid 417 

173 Uric acid crystals 438 

174 Blood globules 504 

j;r6 Pus " 608 

176 MUk " 608 

177 Trommer's test 614 

178 Uric acid calculus » 516 

179 Urate of ammonia calculus 515 

180 Fusible calculus 516 

181 Mulberry calculus 516 



Thb Science of Chemistry has for its object the study of the nature and 
properties of all the materials which enter into the composition or stmcture. 
of the earth, the sea, and the air, and of the yarious organized or liTing be- 
ings which inhabit these latter. Eyery 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 discoyery 
of the general laws or roles which regulate the formation of chemical com- 
pounds, and determine the action of one substance upon another. These 
laws are deduced from careful obseryation and comparison of the propertied 
and relations of yast numbers of indiyidual substances; — andbytliis method 
alone. The science is entirely experimental, and all its conclusions the re- 
sults of skilful and systematic experimental inyestigation. 

The applications of the discoyeries 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 yery numerous and yery important, and encourage the hope 
of still greater benefits from more extended knowledge than that now 

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 
attractiye forces, whose laws and effects lie within the proyince of Physics 
or Natural Philoi^ophy. 

Nearly aU the objects presented by the yisible world are of a compound 
flatare, being chemical compounds, or yariously disposed mixtures of chem- 
« (26) 


ioal compounds, capable of t)6mg resoWed into simpler forms of matter. 
Thus, a piece of limestone or marble by the application of a red-beat is de- 
composed into quicklime and a gaseous body, carbonic acid. Both lime 
and carbonic acid are in their turn susceptible of decomposition, the first 
into a metal, calcium, and oxygen, and the second into carbon and oxygen. 
Por this purpose, however, simple heat does not suffice, the resolution of 
these substances into their components demanding the exertion of a high 
degree of chemical energy. Beyond this second step of decomposition the 
efforts of Chemistry have hitherto been found to fail, and the three bodies, 
calcium, xsarbon, and oxygen, haying resisted all attempts to resolye them 
into simpler forms of matter, are accordingly admitted into the list of eU- 
menU; — ^not from any belief in their real oneness of nature, but from the 
absence of any eyidence that they contain more than one description of 

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 neyer omitted in the usual courses of oral instruction. A 
sketch of these subjects is, in accordance with these yiews, placed at the 
oommenoement of the present yolume. 



It is of great importance in the outset to understand clearljirhat is meant 
Ij the terms density and specific gravHy, By the density of a body is meant 
its mass, or quantity of matter^ compared with the mass or quantity of matter 
of an eqtud 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. ri5°'5C). Anything else might haye 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 orduiary ex- 
pression of specific weight, therefore, is a number expressing how many 
times the weight of an equal bulk of water is contained in the weight of 
the substance spoken of. If, for example, we say that concentrated oil of 
vitriol has a specific gravity equal to 1*85, or that perfectly pure alcohol has 
a density of 0*794 at 60°, we mean that equal bulks of these two liquids 
and of distilled water possess weights in the proportion of the num- 
bers 1-85, 0794, and 1 ; or 1850, 794, and 1000. It is necessary to be par- 
ticular about the temperature ; for, as will be hereafter shown, liquids are 
extremely expansible by heat ; otherwise, a constant bulk of the same liquid 
will not retain a constant weight It will be proper to begin with the de- 
scription of the mode in which the specific gravity of liquids is determined; 
this is the simplest case, and the one which best illustrates the general 

In order to obtain at pleasure the specific gravity of any particular liquid 
compared with that of water, it is only requisite to weigh equal bulks at the 
standard temperature, and then divide the weight of the liquid by the weight 
of the water ; the quotient will of course be greater or less than unity, as 
the liquor experimented on is heavier or lighter than water. Now, to weigh 
equal bulks of two fluids, the simplest and best method is clearly to weigh 
them in succession in the same vessel, taking care that it is equally full on 
both occasions, a condition very easy of fulfilment. 

A thin glass bottle, or flask, with a narrow neck, is procured, of the figuro 
represented on the next page, (fig. 1), and of such capacity as to contain, 
when filled to about half-way up the neck, exactly 1000 grains of distilled 
water at 60<> (16<>'5C). Such a flask is readily procured from any one of the 
Italian artificers^ to be found in every large town, who manufacture cheap 
thermometers for sale. A counterpoise of the exact weight of the empty 

* In other wordg, density means oomparatlTe mastt and speciflo grarlty oomparatiye vxiahL 
These expressions, although really relating to distinct things, are often useid quite indifTe- 
rently in chemical writings, and without practical inconvenience, since man and weight are 
tfieetly pxoportiona>l to each other. 





bottle is made from a bit of brass, an old weight, 
or something of the kind, and carefully adjusted 
by filing : an easy task. The bottle is then grad- 
uated, by introducing water at 60°, until it ex- 
actly balances the lOOO-grain weight and counter- 
poise in the opposite scale ; the height at which 
the water stands in the neck is marked by a 
scratch, and the instrument is complete for use. 
The liquid to be examined is brought to the tem- 
perature of 60°, and with it the bottle is filled up 
to^the mark before mentioned ; it is then weighed, 
the counterpoise being used as before, and the 
specific gravity directly ascertained. 

A watery liquid in a narrow glass tube always 
presents a curved surface from the molecular ac- 
tion of the glass, the concavity being upwards. It 
is better, on this account, in graduating the bottle, 
to make two scratches as represented in the draw- 
ing, one at the top and the other at the bottom of 
the curve: this prevents any future mistake. The 
Marks are easily made by a fine, sharp, three-sq^uare file, the hard point of 
nhich, also, it may be observed, answers perfectly well for writing upon 
glass, in the absence of a proper diamond-pencil. 

The specific-gravity bottle above described differs from those commonly 
made for sale by the instrument-makers. These latter are constructed with 
a perforated stopper, so arranged that when the bottle is quite filled, the 
stopper put in its place, and the excess of liquid which flows through the 
hole wiped from the outside, a constant measure is always had. There are 
inconveniences attending the use of the stopper which lead to a preference 
of the open bottle with merely a mark on the neck, even when very volatile 
liquids are experimented with. 

It will be quite obvious that the adoption of a flask holding exactly 1000 
grains of water has no other object than to save the trouble of a very trifling 
calculation ; any other quantity would answer just as well, and, in fact, the 
experimental chemist is often compelled to use a bottle of much smaller di- 
mensions, from scarcity of the liquid to be examined. The shape is also in 
reality of little moment ; any light phial with a narrow neck may be em- 
ployed, not quite so conveniently perhaps, as a specific-gravity bottle. 

The determination of the specific gravity of a solid is also an operation of 
great facility, although the principle is not so obvious. As it would be 
Impossible to put in practice a direct method like that indicated for liquids 
recourse is had to another plan. The celebrated theorem of Archimedes 

affords a solution of the diflSculty. This theorem may be thus expressed : 

When a solid is immersed in a fluid, it loses a portion of its weight ; 

and this portion is equal to the weight of the fluid which it displaces ; 

that is, to the weight of its own bulk of that fluid. 

It is easy to give experimental proof of this very important proposition, 

as well as to establish it by reasoning. The drawing (fig. 2) represents a 

little apparatus for the former purpose. This consists of a thin cylindrical 

vessel of brass, into the interior of which fits very accurately a solid cylindei^ 

of the same metal, thus exactly filling it. When the cylinder is suspendeu 

beneath the bucket, as seen in the sketch, the whole hung from the arm of 

a balance and counterpoised, and then the cylinder itself immersed in water, 

it will be found to have lost a certain weight ; and that this loss is precisely 

equal to the weight of an equal bulk of water, may then be proved by filling 


' he backet to the bnm, whereapon the equilibrium 
trill be restored. 

The coDsideratioii of the great hydrostatic lair of 
fluid pressure easily proyes the truth of the principle 
laid down. Let the reader figure to himself a yessel 
of water, having immersed in it a solid cylindrical or 
rectangular body, and so adjusted with respect to 
density, that it shall float indifferently in any part 
beneath the surface (fig. 8). 

Now the law of fluid pressure is to this effect : — 
The pressure exerted by a fluid upon the containing 
Tcssel, or upon anything plunged beneath its surface, 
depends, first, upon the density of that fluid, and, 
secondly, upon tiie perpendicular height of the col- 
umn. It is independent of the form and lateral 
dimensions of the yessel or immersed body. More- 
oyer, owing to the pl^culiar physical constitution of 
fluids, this pressure is exerted equally in eyery di- 
rection, upwards, downwards, and laterally, with 
equal force. 

The floating body is in a state of equilibrium; 
therefore the pressure downwards caused by its gravi- 
tation must be exactly compensated by the upward 
transmitted pressure of the column of water a, b. 

But this pressure downwards is obviously equal to 
the weight of an equal quantity of water, since the 
body of necessity displaces its own bulk — 

Hence, the weight lost, or supported by the water, 
5s the weight of a volume of water equed 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 

A little reflection will show that the same reasoning 
may be applied to a body of irregular form ; besides, 
a solid of any figure may be divided by the imagina- 
tion, into a multitude of little perpendicular prisms, 
or cylinders, to each of which the argument may be 
applied. What is true of each individually, must 
necessarily be true of the whole together. 

This is the fundamental principle ; its application 
is made in the following manner : — Let it be required, 
for example, to know the specific gravity of a body 
of extremely irregular form, as a small group of rock- 
crystals : the first part of the operation consists in 
determining its absolute weight, or, more correctly 
speaking, its weight in air ; it is next suspended from 
the balance-pan by a fine horse-hair, immersed com- 
pletely (fig. 4) in pure water at 60® rl6®'6C), and 
again weighed. It now weighs less, tne difference 
being the weight of the water it displaces, that is, the 
weight of an equal bulk. This being known, nothing 
more is required than to find, by division, how many 
8* / 





times the latter number is contained in the former ; the quotient will be the 
density, water being taken =s 1. For example: — 

The quartz-crystals weigh in air 293*7 grains. 

When immersed in water, they wejgh 180*1 

Difference being the weight of an equal Yolume of *water ... 113*6 
YYgTg = 2*58, the specific gravity required. 

The arbitrary rule is generally thus written : "Divide the weight in air 
by the loss of weight in water, and the quotient will be the specific gravity." 
In reality, it is not the weight in air which is required, but the weight the 
body would have in empty space: the error introduced, 
^S- 6. namely, the weight of an equal bulk of air, is so trifling that 

"^ it is usually neglected. 

Sometimes the body to be examined is lighter than water, 
^ and floats. In this case it is first weighed and afterwards 
attached to a piece of metal (fig. 5), heavy enough to sink 
it, and suspended from the balance. The whole is then ex- 
actly weighed, immersed in water, and again weighed. The 
difference between the two weighings gives the weight of a 
quantity of water equal in bulk to both together. The light 
substance is then detached, and the same operation of weigh- 
ing in air, and again in water, repeated on the piece of metal. 
These data give the means of finding the specific gravity, as 
will be at once seen by the following example : — 

Light substance (a piece of wax) weighs in air 133*7 grains. 

Attached to a piece of brass, the whole now weighs 183*7 

Immersed in water, the system weighs 88*8 

Weight of water equal in bulk to brass and wax 144*9 

Weight of brass in air 60*0 

Weight of brass in water 44*4 

Weight of equal bulk of water ...^ 5*6 

Bulk of water equal to wax and brass 144*9 

Bulk of water equal to brass alone 6*6 

Bulk of water equal to wax alone 139*3 


139*3 "= ^'9598. 

In all such experiments, it is necessary to pay attention to the temperature 
and purity of the water, and to remove with great care all adhering air- 
bubbles ; otherwise a false result will be obtained. 

Other cases require mention in which these operations must be modified 
to meet particular difiSculties. One of these happens when the substance la 
dissolved or acted upon by water. ■ This difficulty is easily conquered by 
substituting some other liquid of known density which experience shows is 
without action. Alcohol or oil of turpentine may generally be used when 
water is inadmissible. Suppose, for instance, the specific gravity of crya« 
tallized sugar is required, we proceed in the following way : — The specifiQ 
gravity of the oil of turpentine is first carefully determined ; let it be 0-87 ; 


(he ffagar is next weighed in the air, then suspended by a horse-hair, and 
weighed in the oil ; the diiference is the weight of an equal bulk of the latter ; 
a simple calculation gives the weight of a corresponding yolume of watez : 

Weight of sugar in air « 400 grains. 

Weight of sugar in oil of turpentine 182-6 

Weight of equal bulk of oil of turpentine 217-6 

87 : 100 = 217-6 : 250, 
the weight of an equal bulk of water: hence the specific gravity of the sugar, 


The substance to be examined may be in small fragments, or powder. 
Here the operation is also very simple. A bottie holding a known weight 
of water is taken ; the specific-gravity bottle already described answers per- 
fectly well. A convenient quantity of the substance is next carefully weighed 
out, and introduced into the bottle, which is then filled up to the mark on 
the neck with distilled water. It is clear that the vessel now contains less 
water by a quantity equal to the bulk of the powder than if it were filled in 
the usual manner. It is, lastly, weighed. In the subjoined experiment 
emery powder was tried. 

The bottle held, of water 1000 grains. 

The substance introduced weighed 100 

Weight of the whole, had no water been displaced 1100 

The observed weight is, however, only 1070 

Hence water displaced, equal in bulk to the powder 30 


g^ = 3-333 specific gravity. 

By this method the specific gravities of metals in powder, metallic oxides, 
and other compounds, and salts of all descriptions, may be determined with 
great ease. Oil of turpentine may be used with most soluble salts. The 
crystals should be crushed or roughly powdered to avoid errors arising from 
cavities iu their substance. 

The theorem of Archimedes affords the key to the general doctrine of the 
equilibrium of floating bpdies, of which an applicatioo is made in the common 
hydrometer, — an instrument for finding the specific gravities of liquids in a 
very easy and expeditious manner. 

When a solid body is placed upon the surface of a fluid specifically heavier 
than itself, it sinks down until it displaces a quantity of fluid equal to its 
own weight, at which point it floats. Thus, in the case of a substance floating 
in water, whose specific weight is one-half that of the fluid, the position of 
equilibrium will involve the immersion of exactly one-half of 
the body, inasmuch as its whole weight is counterpoised by a ^^s* ^ 

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, / o«^ " 
if such could be found, then it would sink beneath the surface, ' 
and remain indifferently in any part. A floating body of known 
specific gravity may thus be used as an indicator of the spe- 
cific gravity of a fluid. In this manner little glass beads (fig. 0) 
of known specific gravities are sometimes employed in the arts 
to ascertain in a rude manner the specific gravity of liquids ; 



Kg. 7. 

the one that floats indifferently beneath the sarface, without either sinking 
or rising, has of coarse the same specific gravity as the liquid itself; this ia 
pointed out by the number marked upon the bead. 

The hydrometer (fig. 7) in general use consists 
of a floating yessel of thin metal or glass, haying 
a weight beneath to maintain it in an uprigM 
position, and a stem above bearing a divided 
scale. The use of the instrument is Tery simple. 
The liquid to be tried is put into a small narrow 
jar, and the instrument floated in it It is obvious 
that the denser the liquid, the higher will the 
hydrometer float, because a smaller displacement 
of fluid will counterbalance its weight. For the 
same reason, in a liquid of less density, it sinks 
deeper. The hydrometer comes to rest almost 
immediately, and then the mark on the stem at the 
fluid-level may be read off. 

Very extensive use is made of instruments of 
this kind in the arts; these sometimes bear dif- 
ferent names, according to the kind of liquid for 
which they are intended ; but the principle is the 
same in all. The graduation is very commonly 
arbitrary, two or three different scales being un- 
fortunately used. These may be sometimes re- 
duced, however, to the true numbers expressing 
the specific gravity by the aid of tables of com- 
parison drawn up for the purpose. 

A very convenient and useful instrument in the 
shape of a small hydrometer (fig. 8) for taking the 
specific gravity of urine, has lately been put into 
the hands of the physician ;* it may be packed into 
a pocket-case, with a little jar and a thermometer, 
and is always ready for use.* 

The determination of the specific gravity of 
gases and vapours of volatile liquids is a problem 
of very great practical importance to the chemist ; 
the theory of the operation is as simple as when 
liquids themselves are concerned, but the pro- 
cesses are much more delicate, and involve be- 
sides certain corrections for differences of tem- 
perature and pressure, founded on principles yet 
to be discussed. It will be proper to defer the 
consideration of these matters for the present. 
The method of determining the specific gravity 
of a gas will be found described under the head of 


* This and other instruments described or figured in the oonrse of the work, may be had 
of Mr. Newman, 122 Kegent Street, upon the exoellenoe of whose workmanship reliance may 
be safely placed. 

^The gradnation of the nrinometer is such that each degree represents 1-1000, thus 
giving the actual specific gravity without calculation, for the number of d^rees on the 
9cale cut by the surfi&oe of the liquid when this instrument is at rest, added to 1000 will 
epresent the density of the liquid. I^ for example, the surface of the liquid coincide with 
23 on the scale, the specific gravity will be 1023, about the average density of healthy 
arine.-~L B, 


*> O^gen,'' and that of the yapottr of a yolatile liquid in the Introduction 
to Organic Chemistry.* 

* The mode of determining? the spedfle graritj of a liquid by means of a Fig. 9. 

solid haa been omitted in the text. It resalts from the theorem of Ar- 
chimedes, tliat if any solid be immersed in water and then in any other 
liquid, the loss of weight sustained in each case will give the relattre 
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 gla^us is suspended, the amount will give the loss of weight by 
immersion or the weight of a bulk of water equal to that of the rod. 
Now wipe the glass dry, and having removed the additional weights, 
immerse it in the other liquid, and restore the equipoise as before; this 
latter weight is the weight of » bulk of the liquid equal to that of the 
water. The latter divided by the former gives the spedflc gravity. For 
example: — 

The glass rod loses by immersion in water 171 grains. 

The glass rod loses by immersion in alcohol 143 

^»*836 the specific gravity required. —B. B. 




Fig. 10. 

It requires some little abstraction of mind to realize completely the singn- 
lar condition in which all things at the surface of the earth exist. We live 
at the bottom of an immense ocean of gaseous matter, which envelopes 
everything, and presses upon everything with a foree which appears, at first 
sight, peifectly 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 llq^uids. 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 
18 necessary to notice one very remarkable feature in the physical constitu- 
tion of gases, upon which depends the principle of an extremely valuable 
instrument, the air-pump. 

Gases are in the highest degree elastic ; the volume or space which a gas 
occupies depends upon the pressure exerted upon it. Let the reader imagine 
a cylinder, a, fig. 10, closed at the bottom, in 
which moves a piston, air-tight, so that no air 
can escape between the piston and the cylinder. 
Suppose now the piston be pressed downwards 
with a certain force ; the air beneath it will be 
compressed into a smaller bulk, the amount of 
this compression depending on the force ap- 
'plied^ if the power be sufficient, the bulk of 
the gas may be thus diminished to one hun- 
dredth part or less. When the pressure is re- 
moved, the elasticity or tension^ as it is called, 
of the included air or gas, will immediately 
force up the piston until it arrives at its first 

Again, take 5, fig. 10, and suppose the piston to 
stand about the middle of the cylinder, having 
air beneath in its usual state. If the piston 
be now drawn upwards, the air below will ex- 
pand, so as to fill completely the enclosed 
space, and this to an apparently unlimited ex- 
tent. A volume of air which under ordinary circumstances Occupies the 
bulk of a cubic inch, might, by the removal of the pressure upon it, be 
made to expand to the c^pacitv 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 difi'used through the whole space, an equal quantity 
being present in every part; the vessel isfull, although the gas is in a state 
of extreme tenuity. This power of expansion which air possesses may have, 
and probably has, in reality, a limit; but the limit is never reached in 




practice. We are quite 6afe in the assamption, that, for all purposes of 
experiment, however refined, air is perfectly elastic. 

It is usual to assign a reason for this indefinite expansibility by ascribing 
to the particles of material bodies, when in a gaseous state, a self^repulsiTO 
energy. This statement is commonly made somewhat in this manner: 
matter is under the influence of two opposite forces, one of which tends to 
draw the particles together, the other to separate them. By the preponde- 
rance of one or other of these forces, we have the three states caUed solid, 
liquid, and gaseous. When the particles of matter, in consequence of the 
direction and strength of their mutual attractions, possess only a yery slight 
power of motion, a Solid substance results; when the forces are nearly 
balanced, we have a liquid, the particles of which in the interior of the 
mass are free to moye, but yet to a certain extent are held together ; and, 
lastly, when the attractive power seems to be completely overcome by its 
antagonist, we have a gas or vapour. 

Various names are applied to these forces, and various ideas entertained 
concerning them ; the attractive forces bear the name of cohesion when they 
are exerted l\etween 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 


The ordinary air-pump, shown in section in fig. 11, consists essentially of 
a metal cylinder, in which moves a tightly-fitting piston, by the aid of its 
rod. The bottom of the cylinder communicates with the vessel to be ex- 
hausted, and is furnished with a valve opening upwards. A similar valve, 
also opening upwards, is fitted to the piston ; these valves are made with 
slips of oiled silk. When the piston is raised fh)m the bottom of the cy • 
tinder, 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 sido 
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 be- 



oomes oompressed, its elasticity is inpreased, and at length it forces open 
the upper valve, and escapes into the atmosphere. In this manner, a cy- 
linder full of air is at every stroke of the pump removed from the receiver. 
During the descent of the piston, the upper valve remains open, and the 
lower closed, and the reverse during the opposite movement 

Pig. 12. 

In practice, it is very convenient to have two such barrels or cylinders, 
arranged side by side, the piston-rods of which are formed 
Ig-lS. into racks, having a pinion, or small-toothed wheel, be- 

rk tween them, moved by a winch. By this contrivance the 

I operation of exhaustion is much facilitated and the labour 

,[ lessened. The arrangement is shown in fig. 12. 

A simpler and far superior form of air-pump is thus 
constructed : the cylinder, which may be of large dimen- 
sions, is furnished with an accurately-fitted solid piston, 
the rod of which moves, air-tight, through a contrivance 
called a stuffing-box, at the top of the cylmder, where also 
the only valve essential to the apparatus is to be found ; the 
latter is a solid conical plug of metal, shown at a in the 
figure, kept tight by the oil contained in the chamber into 
which it opens. The communication with the vessel to be 
exhausted is made by a tube which enters the cylinder a 
little above the bottom. The action is the following : let 
i[lll|||,"j| 'Y the piston be supposed in the act of rising from the bottom 

| |l|lllilJI'il| of the cylinder ; as soon as it passes the mouth of the tube 

tf all communication is stopped between the air above the 
piston and the vessel to be exhausted ; the enclosed air 
suffers compression, until it acquires sufficient elasticity 
to lift the metal valve and escape by bubbling through the 
oil. When the piston makes its descent| and this valve 




doses, a Tacnum is left in ihe upper part, of the cylinder, into iHilcli the lir 
of the receiyer rashes bo soon as the piston has passed below the oxifioe cf 
the connecting tabe. 

In the silk-yalyed air-pnmp, exhaustion ceases when the elasticity of the 
air in the receiver becomes too feeble to raise the yalve; in that last 
described, the exhaustion may, on the contrary, be carried to an indefinite 
extent, without, however, under the most favourable circumstances, be- 
coming complete. The conical valve is made to project a little below the 
cover of the cylinder, so as to be forced up by the piston when the latter 
reaches the top of the cylinder ; the oil then enters and displaces any air 
that may be larking in the cavity. 

It is a great improvement to the machine to supply the piston with a 
reHrf-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 plstdn descends. 
The pomp is worked by a lever in the 
nuumer represented in fig. 14. 

To return to the atmosphere. Air pos- 
sesses weight : a light flask or globe of 
glass, furnished with a stop-cock and ex- 
hausted by the air-pump, weighs consi- 
derably less than when full of air. If the 
capacity of the vessel be equal to 100 
cubic inches, this difference may amount 
to nearly 80 grains. 

The mere fact of the pressure of the 
atmosphere may be demonstrated by se- 
curely tying a piece of bladder over the 
month of an open glass receiver, and then 
exhausting the air f^om beneath it ; the 
bladder will become more and more con- 
cave, until it suddenly breaks. A thin 
square glass bottle, or a large air-tight 
tin box, may be crushed by withdrawing 
the support of the air in the inside. 
Steam-boilers have been often destroyed 
in this manner by collapse, in conse- 
quence of the accidental formation of a 
partial vacuum within. 

After what has been said on the subject 
of fluid pressure, it will scarcely be ne- 
cessary to observe that the law of equality 
of pressure in all directions also holds 
good in the case of the atmosphere. The 
perfect mobility of the particles of air 
permits the transmission of the force ge- 
nerated by their gravity. The sides and 
bottom of an exhausted vessel are pressed 
iipon with as much force as the top. 

If a glass tube of considerable lengtn 

could be perfectly exhausted of air, and 

then held in an upright position, with one 

of its ends dipping into a vessel of liquid, 




Fig .ifi. the latter, on being allowed accese to the tube, would rise in 
its interior until the weight of the column balanced the pres- 
sure of the VkiT upon the 8i:g*face of the liquid. Now if the 
density of this liquid were known, and the height and area 
of the column measured, means would be furnished for ex- 
actly estimating the amount of pressure exerted by the atmo- 
sphere. Such an instrument is the barometer: a straight 
glass tube is taken, about 86 inches in length, and sealed by 
the blow-pipe flame at one extremity ; it is then filled with 
clean, dry mercury, care being taken to displace all air^ 
bubbles, the open end stopped with a finger, and the tube in- 
Terted in a basin of mercury. On remoYing the finger, the 
fluid sinks away from the top of the tube, until it stands at 
the height of about 80 inches abore the leyel of that in the 
basin. Here it remains supported by, and balancing the at- 
mospheric pressure, the space above the mercury in the tube 
I being 6f necessity empty. 

The pressure of the atmosphere is thus seen to be capable 
of sustaining a column of mercury 80 inches in height, or 
thereabouts ; now such a column, haying an area pf one inch, 
weighs between 14 and 15 pound|i, consequently such most 
be the amount of the pressure exerted upon erery square 
inch of the surface of the earth, and of the objects situated 
thereon, at least near the leyel of the sea. This enormous 
force is borne without inconyenience by the animal frame, by 
reason of its perfect uniformity in eyery direotioii, and it may 
be doubled, or eyen tripled without injury. 

A barometer may be constructed with other liquids besides 
merouiy ; but, as Uie height of the column must always bear 
an inyerse proportion to Uie 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 Koyal Society of London possess a water- 
barometer at their apartments at Somerset House. Its con- 
struction was attended with great difficulties^ and it has been found impos- 
sible to keep it in repair. 

It will now be necessary to consider a most important law which connects 
the volume occupied by a gas with the pressure made upon it, and which is 
thus expressed : -— 

The volume of a gas is 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 80 inches of 
mercury would expand to 200 cubic inches were the pressure reduced to 
one-half, and shrink, on the contrary, to 50 cubic inches if the original pres- 
sure were doubled. The change of density must necessarily be in the 
inverse proportion to that of the volume, and the elastic force follows the 
same rule. 

This, which is usually called the law of Mariotte, is easily demonstrable 
by direct experiment. A glass tube, about 7 feet in length, is closed at one end, 
and bent into the form shown in fig. 16^ the open limb of the siphon being 
the longest It is next attached to a board furnished with a moveable scale 
of inches, and enough mercury is introduced to fill the bend, the level being 
evenly adjusted, and marked upon the board. Mercury is now poured into 
the tube until it is found that the inclosed air has been reduced to one-half 
of its former volume ; and on applying the scale it will be found that the level 




of the mercury in the open part of the tnbe stands 'te- 1^. 

very nearly 30 inches above that in the closed portion. 
?rhe pressure of ,an additional " atmosphere" has con- 
sequently reduced the bulk of the contained air to 
one-half. If the experiment be still continued until 
the volume of air is reduced to a third, it will be found 
that the column measures 60 inches, and so in like 
proportion as far as the experiment is carried. 

The above instrument is better adapted for illustra- 
tion of the principle than for furnishing rigorous proof 
of the law ; this has, however, been done. MM. Arago 
and I>ulong published, in the year 1830, an account of 
certain experiments made by them in Paris, in which 
the law in question had been verified to the extent of 
27 atmospheres. 

All gases are alike subject to this law, and all va« 
pours of volatile liquids, when remote from their points 
of liquefaction.' It is a matter of the greatest im- 
portance in practical chemistry, since it gives the 
means of making corrections for pressure, or deter- 
mining by calculation the change of volume which a gas 
would suffer by any given change of external pressure. 

Let it be required, for example, to solve the fol- 
lowing problem : — ^We have 100 cubic inches of gas in 
a graduated jar, the barometer standing at 29 inches ; 
how many cubic inches will it occupy when the column 
rises to 30 inches ? — Now the volume must be inversely 
as the pressure ; consequently a change of pressure in 
the proportion of 29 to 80 must be accompanied by 
a change of volume in the proportion of 80 t6 29 ; 80 
cubic inches of gas contracting to 29 cubic inches 
under the conditions imagined. Hence the answer : 

30 : 29 = 100 : 96-67 cubic inches. 
The reverse of the operation will be obvious. The 
practical pupil will do well to familiarize himself with 
these simple calculations of correction for pressure. 

From what has been said respecting the easy com- 
pressibility of gases, it will be at once seen that the 
atmosphere cannot have the same density, and cannot 
exert equal pressures at different elevations above the 
sea-level, but that, on the contrary, these must diminish 
with the altitude, and very rapidly. The lower strata 
of air have to bear the weight of those above them ; 
they become, in consequence, deeper and more com- 
pressed than the upper portions. The following table, 
which is taken from Prof. Graham's work, shows in a very simple manner 
the rule followed in this respect. 

Height alwye the 

Bea, in miles. Yolume of air. 


2-705 2 

5-41 4 

8- 115 8 

10-82 16 

13-626 32 


Height of barometer, 
in inches. 






0-9375 • 

64 0-46876 

* When near the liquefying point the law no longer holds; the volnme diminishes* 
rapidly than the theory indicates, a smaller amount of pressure being then suffldent. 


Fig. 17. The numbers in the first column form an arithmeiieal series, 

by the constant addition of 2-705 ; those in the second column an 
increasing geometrical series, each being the double of its prede- 
cessor ; and those in the third, a decreasing geometrical series, 
in which each number is the half of that standing aboTe it. In 
ascending in the air in a balloon, these effects are well ob- 
served ; the expansion of the gas within the machine, and the 
fall of the mercury in the barometer, soon indicate to the voya- 
Ijg ger the fact of his haying left below him a considerable part of 
f H Uie whole atmosphere. 

nH The inyention of the barometer, which took place in the year 

1648, by Torricelli, a pupil of the celebrated Galileo, speedily 
led to the observation that the atmospheric pressure at the 
same level is not constant, but possesses, on the contrary, a 
small range of variation, seldom exceeding in Europe 2 or 2*5 
inches, and within the tropics usually confined within much 
narrower limits. Two kinds of variations are distinguished ; 
regular or horary, and irregular or accidental. It has been 
observed, that in Europe the height of the barometer is greatest 
at two periods in the twenty-four hours, depending upon the 
season. In winter, the first maximum takes place about 9 a. m., 
the first minimum at 3 p.m., after which the mercury again 
rises and attains its greatest elevation at 9 in the evening; in 
summer these hours of the aerial tides are somewhat altered. 
The accidental variations are much greater in amount, and 
render it extremely difficult to trace the regular changes above 

The barometer is applied with great advantage to the mea- 
surement of accessible heights, and it is also in daily use for 
foretelling the state of the weather ; its indications are in this 
respect extremely deceptive, except in the case of sudden and 
violent storms, -^hich are almost always preceded by a rapid 
fall in the mercurial column. It is often extremely useful in 
this respect at sea. 

To the practical chemist, a moderately good barometer is an 
indispensable article, since in all experiments in which volumes 
of gases are to be estimated, an account must be taken of the 
pressure of the atmosphere. The marginal drawing represents 
a very convenient and economical siphon barometer for this 
purpose. A piece of new and stout tube, of about one-third of 
an inch in internal diameter, is procured at the glass-house, 
sealed at one extremity, and bent into the siphon form, as repre- 
sented. Pure and warm mercury is next introduced by successive portions 
until the tube is completely filled, and the latter being held in an upright 
position, the level of the metal in the lower and open limb is conveniently 
acliusted by displacing a portion by a stick or glass rod. The barometer is, 
lastly, attached to a board, and furnished with a long scale, made to slide, 
which may be of box-wood, with a slip of ivory at each end. When an ob- 
servation is to be taken, the lower extremity or zero of the scale is placed 
exactly even with the mercury in the short limb, and then the height of the 
column at once read off. 

HEAT. 4l 


It fnO. be conyenient to consider the subject of Heat under eevend see- 

tions, and in the following order : — 

h Expansion of bodies, or effects of Tariations of temperature in altering 
their dimensions. 

2. Condnction, 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. 


If a bar of metal (fig. 18) be taken, of such magnitude as to fit accurately 
to a gauge when cold, heated considerably, and again applied to the guage, |t 
will be found to haye become enlarged in all its dimensions. When cold, it 
will once more enter the gauge. 

Again, if a quantity of liquid contained in a glass bulb (fig. 19), furnished 
with a narrow neck, be plunged into hot water, or exposed t& any other 

Fig. 18. Fig. 10. Fig. 20. 

source of heat, the liquid will mount in the stem, showing that its Tolumo 
has been increased. 

Or, if a portion of air be confined in any yessel (fig. 20), the application of 
a slight degree of heat will suffice to make it occupy a space sensibly larger. 

This most general of all the effects of heat furnishes in the outset a prin- 
ciple, by the aid of which an instrument can be constructed capable of taking 
cognizance of changes of temperature in a manner equally accurate and con- 
yenient : such an instrument is the thermometer. 

A capillary glass tube is chosen, of uniform diameter •■ one extremity ia 
closed and expanded into a bulb, by the aid of the blowpipe flame, and tho 

42 HEAT. 

other somewhat drawn out, and left open. The bulb is now cautiously heated 
bj a spirit lamp, and the open extremity planged into a Tessel of mercury, 
a portion of which rises into the bulb when the latter cools, replacing the 
air which had been expanded and driven out by the heat. By again applying 
the flame, and causing this mercury to boil, the remainder of the air is easily 
expelled, and the whole space filled with mercurial vapour, on the condensa- 
tion of which the metal is forced into the instrument by the pressure of the 
air, until it becomes completely filled. The thermometer thus filled is now 
to be heated until so much mercury has been driven out by the expansion 
of the remainder, that its level in the tube shall stand at common tempera- 
tures at the point required. This being satisfactorily ac^usted, the heat is 
once more applied, until the column rises quite to the top ; and then the 
extremity of tiie 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 
eame under similar circumstances. A clean metallic vessel is taken, into 
which pure water is put and made to boil ; a thermometer placed in the 
boiling liquid just so deep as is necessary to cover the bulb, invariably marks 
the same degree of temperature so long as the height of the barometer re- 
mains unchanged. 

The tube having been carefully marked with a file at these two points, it 
remains to divide the interval into degrees ; this is entirely arbitrary. In 
the greater part of Europe and in America, the scale called centigrade is em- 
ployed ; the space in question being divided into 100 parts, the zero being 
placed at the freezing point of water. The scale is continued above and 
below these points, numbers below being distinguished by the negative 

In England the very inconvenient division of Fahrenheit is still in use ; 
the above space is divided into 180 degrees, but. the zero, instead of starting 
firom the freezing-point of water, is placed 32 degrees below it, so that the 
temperature of ebullition is expressed by the number 212°. 

The plan of Reaumur is nearly confined to a few places in the north of 
Oermany and to Russia ; in this scale the freezing-point of water is made 
0^ and the boiling-point 80®. 

It is unfortunate that an uniform system has not been generally adopted 
in graduating thermometers ; this would render unnecessary the labour which 
now so frequently has to be performed of translating the language of one 
scale into that of another. To effect this, presents, however, no great diffi- 
culty. Let it be required, for example, to know the degree of Fahrenheit's 
scale which corresponds to 60° centigrade. 

100° C. = 180O F., or S® C. = 9° F. 


5 : 9 » 60 : 108. 

HEAT. 43^ 

Bat, tlien, as Fahrenheit's scale commences with 32^ instead of 0^, that 
number must be added to the result, making 60° C. ^ 140° F. 

The rule then will be the following : — To convert centigrade degrees into 
Fahrenheit degrees, multiply by 9, divide the product by 5, and add 82 ; to 
convert Fahrenheit degrees into centigrade degrees, subtract 82, multiply 
by 5, and divide by 9. 

The reduction of negative degrees, or those below zero of either scale, 
presents rather more apparent difficulty; a little consideration, however, 
will render the method obvious, the interval between the two zero-points 
being borne in mind. 

Mercury is usually chosen for making thermometers, on account of its 
regularity of expansion Within certain limits, and because it is easy to have 
the scale of great extent, from the large interval between the freezing and 
boiling-points of the metal. Other substances are sometimes used ; alcohol 
is employed for estimating very low temperatures. 

Air-thermometers are also used for some few particular purposes ; indeed, 
the first thermometer ever made was of this kind. There are two modifica- 
tions of this instrument ; in the first, the liquid into which the tube dips is 
open to the air, and in the second (fig. 21), the atmosphere is completely 
excluded. The effects of expansion are in the one case complicated with 
those arising from changes of pressure, and in the other cease to be visible 
at all when the whole instrument is subjected to alterations of temperature, 
because the air in the upper and lower reservoir, being equally affected by 
such changes, no alteration in the height of the fluid column can occur. 
Accordingly, such instruments are called differential thermometers, since 
they serve to measure differences of temperatures between the two portions 
of air, while changes affecting both alike are. not indicated. Fig. 22 shows 
another form of the same instrument. 

Fig. 21. 

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 
hent 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 enlarge4 in their dimensions by the application of heat, 
and reduced by its abstraction, or, in other words, contract on being artlfi- 



cially cooled ; this effect takes place to a comparatively small extent with 
solids, to a larger amount in liquids, and most of all in the case of gases. 

Each solid and liquid has a rate of expansion peculiar to itself; gases, on 
the contrary, all expand alike for the same increase of heat. 

The difference of expansibility among solids is very easily illustrated by 
the following arrangement : a thin straight bar of iron is firmly fixed by 
numerous rivets, to a similar bar of brass ; so long as the temperature at 
which the two metals were united remains unchanged, the compound bar 
preserves its straight figure ; but any alteration of temperature gives rise to 
a corresponding curvature. Brass is more dilatable than iron ; if the bar 
be heated, therefore, the former expands more than the latter, and forces 
the straight bar into a curve, whose convex side i^ the brass ; if it be arti- 
ficially cooled, the brass contracts more than the iron, and the reverse of 
this effect is produced. 

Fig. 23. 

r ■ ■ 


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 mea- 
surement of time ; such are absolutely indispensable to the 
successful cultivation of astronomical science, and not less use- ^ 
ful to the navigator, from the assistance they give him in find- 
ing the longitude at sea. For a long time, notwithstanding the 
perfection of finish and adjustment bestowed upon clocks and 
watches, an apparently insurmountable obstacle presented 
itself to their uniform and regular movement ; this obstacle 
was the change of dimensions to which the regulating parts of 
the machine were subject by alterations of temperature. A 
clock may be defined as an instrument for registering the num- 
ber of beats made by a pendulum : now the time of oscillation 
of a pendulum depends ;?nwcipaWy upon its length; any altera- 
tion in this condition will seriously affect the rate of the clock. 
The material of which the rod of the pendulum is composed is 
subject to expansion and contraction by changes of tempera- 
ture ; so that a pendulum adjusted to vibrate seconds at 60° 
(15°-5C) would go too slow when the temperature rose to 70® 
(210'1C), from its elongation, and too fast when the tempera- 
ture fell to 50° (10°C), from the opposite cause. 
I j || This great difficulty has been overcome ; by making the rod 

»■ rl i^-^ of a number of bars of iron and brass, or iron and zinc, 
metals whose rates of expansion are different, and arranging 
these bars in such a manner that the expansion in one direction 
of the iron shall be exactly compensated by that in the oppo- 
site direction of the brass or zinc, it is possible to maintain 
under all circumstances of temperature an invariable distance between the 
points of suspension and of oscilUtion. This is often called the ffridvroU 



pendtdum ; fig. 24 will olearlj illostrate its principle ; the shftded Us* 2ft. 
bars are supposed to be iron and the others brass. 

A still simpler compensation pendulum (fig. 25) is thus con- 
structed. The weight or bob, instead of being made of a disc 
of metal, consists of a cylindrical glass jar containing mercnry, 
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 Tolume of the mercury to enlarge, and its leyel to rise 
in the jar ; the centre of gravity is thus elevated, and by properly 
adjusting the quantity of mercury in the glass, the yirtual length 
of the pendulum may be made constant 

In watches, the governing power is a horisontal 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 Uie 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 di£ferent rates of expansion, 
fast soldered together, the most expansible being/>n the outside. 
The compound rim is also cut through in two or more places, as 
represented in fig. 26. When the watch is exposed to a high tempera- 
ture, and the diameter of the wheel becomes enlarged by expansion, each 
segment is made, by the same agency, to assume a 
sharper curve, whereby its centre of gravity is Fig. 26, 

thrown inwards, and the expansive e£fect com- 
pletely compensated. Many other beautiful appli- 
cations of the same principle might be pointed 
oat; the metallic thermometer of M. Br^guet 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 
fiye inches long, is dropped into a tube of black- 
lead ware ; a little cylinder of baked porcelain is 
pat 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 Fig. 27. 

forward the cylinder, which moves with a 
certain degree of friction, and shows, by rjV 
the extent of its displacement, the length- ^"^ 
ening which the bar had undergone. It 
remains, therefore, to measure the amount 
of this displacement, which must be very 
small, even when the heat has been ex- 
ceedingly intense. This is effected by the 
contriyance shown in fig. 27, in which 
the motion of the Icmger arm of the 
lever carrying the vernier of the scale is 
multipled by 10, in consequence of its 
superior length. The scale itself is made 
comparable with that of the ordinary 
thermometer, by plunging the instrument 
into a bath of mercury near its point of 
congelation, and afterwards into another of the same metal in a boiling 
state, and marking off the interval. By this instrument the melting-point 

46 HEAT. 

of cast iroQ wfts fixed at 2786<> Fahrenheit (1530^0), and the greatest heat 
of a good wind-furnace at about 8300° (1815°C). 
The actual amount of expansion which different solids undergo by the 
' same increase of heat, has been carefully inyestigated. 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 82° (0°C) to 212« (lOO^C). 

English flint glass . y^Vv 

Common French glass j-^y 

Glass without lea!d . y^Vi 

Another specimea . y^Vv 

Steel untempered . -^ 

Tempered steel . -^fj 

Soft iron . . . ,|y- 




Brass . . . -g^^ 

Silver - • - . yjr 

Lead ... |j- 

From the UnMr expansion, the eubie expansion (or ioerease of Tolnme) 
may be easily calculated. When an approximation only is wanted, it will be 
sufficient to triple the fraction expressing the increase in one dimension. 

Metals appear to expand pretty uniformly for equal increments of heat 
within the limits stated, but above the boiUng-point of water the rate of 
expansion becomes irregular and more rapid. 

The force exerted in the act of expansion is rery great ; in laying do^wn 
railways, building iron bridges, erecting long ranges of steam-pipes, and in 
executing all works of the kind in which metal is largely need, it is indis- 
pensable to make provision for these changes of dimensions. 

A very useful little application of expansion by heat is that to the cutting 
of glass by a hot iron ; this is constantly practised in the laboratory for a 
great variety of purposes. The glass to be cut is marked with ink in the 
wished-for direction, and then a crack commenced by any convenient method, 
at some distance from the desired line of fracture, may be led by the point 
of a heated iron rod along the latter. with the greatest precision. 

JST^ansion of Fluids. — The dilatation of a fluid may be determined by fill- 
ing with it a thermometer, in which the relation between the capacity of the 
ball and that of the stem is exactly known, and observing the height of the 
column at different temperatures. It is necessary in this experiment to take 
into account the effects of the expansion of the glass itself, the observed re- 
sult being evidently, the difference of the two. 

Liquids vary exceedingly in this particular. The following table is taken 
from P^clet's EUmens de Physique, 

Apparent DUatation in Glass between 32*» (0°C) and !}12*» (lOO^O). 

; Water 5*5 

Hydroxjhloric acid, sp. gr. 1*137 . . . • -si 

Nitric acid, sp. gr. 1*4 ^ 

Sulphuric acid, sp. gr. 1*86 -j^ 

Ether tV 

Olive oil . ^ "i^ 

Alcohol .....'...• T 

Mercury -n 

Most of these numbers must be taken as representing mean results. For 
there are few fluids which, like mercury, expand regularly between these 
temperatures. Even mercury above 212® (lOQoC) expands irregularly, as 
the following table shows. 



Abtolfde Expaimon of Mercury for 180^. 

Between 32*^ (0°C) and 212° (100°C) 
Between 212° (100°C) and 392° (200°C) . 
Between 392° (200°C) and 672° (300°C) 


The absolute amoant of expansion of mercury is, for many reasona, a 
point of great importance ; it has been very carefully determined by a me- 
thod independent of the expansion of the containing TesseL The apparatus 
employed for this purpose by MM. Dulong and Petit is shown in fig. 28, di- 
vested, howerer, of many of its subordinate parts. It consists of two up- 
right glass tubes, connected at their bases by a horizontal tube of much 
smaller dimensions. Since a free communication exists between the two 
tubes, mercury poured into the one will rise to the same le^el in the other, 
proTided its temperature is the same in both tubes ; when this is not the 
case, the hottest column will be the tallest, because the expansion of the 
metal diminishes its specific-gravity, and the law of hydrostatic equilibrium 
requires that the heights of such columns should be inrersely as their den- 
sities. By the aid of the outer cylinders, one of the tubes is maintained. 
constantly at 32° (0°C), while the other is raised, by means of heated water 
or oil, to any required temperature. The perpendicular heights of the 
columns may then be read off by a horizontal micrometer telescope, mofing 
on a Yertical divided scale. 

These heights represent volumes of equal weight, because Yolumea of 
equal weight hear an inverse proportion ta the densities of the liquids, so 
that the amount of expansion admits of being very easily calculated. Thus, 
let the column at 32° (QoG) be 6 inches high, and that at 212<> (100°€) 6-108 
inches, the increase of height, 108 on 6,000, or ^.^ part of the whole, must 
represent the absolute cubical expansion. 

The indications of the mercurial thermometer are inaccurate when very 
high ranges of temperature are concerned, from the increased expansibility 
of the metal ; on tMs 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 tiie case 
of water; it is so remarkable, and its consequences so important, that it is 
necessary to advert to it particularly. 

I<et a large tiiermometer-tube be filled with water at the common tempe- 

J Below 40(F Fahi«nheit (204O-4C) the error may be ntgleetod; at 500° (200%) it to about 
l**; al 630O (332P-6C) eP.— EWnaalt 

48 HEAT. 

rature of the air, and then artificially cooled. The liquid will be obserred 
to contract regularly, until the temperature falls to about 40° (4°4C), or S° 
above the freezing-point. After this, a farther reduction of temperature 
causes expansion instead of contraction in the volume of the water, and this 
expansion continjaes until the liquid arrives at its point of congelation, when 
BO sudden and violent an enlargement takes place, that the vessel is almost 
invariably broken. At the temperature of 4^ (4<''4C), or more correctly, 
perhaps, 89° '5 (4°'1C), water is at its maximum density; increase or dimi- 
nution of heat produces upon it, for a short time, the same effect. 

A beautiful experiment of Br. Hope illustrates the same fact. If a tall 
Jar filled with water at 60° (10°C) or 60° (16°-5C) and having in it two 
small thermometers, one at the bottom and the other near the surface, be 
placed at rest in a very cold room, the following changes will be observed. 
The thermometer at the bottom will fall more rapidly than that at the top, 
until it has attained the temperature of 40° (4°*4C) aftw which it will re- 
main stationary. At length the upper thermometer will also mark 40° 
(4°*40) but still continue to sink as rapidly as before, while that at the bot- 
tom remains stationary. It is easy to explain these effects : the water in 
the upper part of the jar is rapidly cooled by contact with the air ; it be- 
comes denser in consequence, and falls to the bottom, its place being sup- 
plied by the lighter and warmer liquid, which in its turn suffers the same 
change ; and this circulation goes on until the whole mass of water has ac- 
quired its condition of maximum density, that is, until the temperature has 
fallen to 40° (4° '40). Beyond this, loss of heat occasions expansion instead 
of contraction, so that the very cold water on the surface has no tendency 
to sink, but rather the reverse. 

This singular anomaly in the behaviour of water is attended by the most 
beneficial consequences, in shielding the inhabitants of the waters from ex- 
cessive cold. The deep lakes of the North American Continent never freeze, 
the intense and prolonged cold of the winters of those regions being insufii- 
cient to reduce the temperature of such masses of water to 40° (4°*4C). 
Ice, however, of great thickness forms over the shallow portions, and the 
rivers, and accumulates in niounds upon the beaches. Where the waves are 
driven up by the winds. 

Sea-water has a maximum density at the same temperature as fresh 
water. The depths of the Polar Seas exhibit this temperature throughout 
the year, while the surface-water is in summer much above, and in winter 
much below, 40° (4° •40) ; in both cases being specifically lighter than water 
at that temperature. This gradual expansion of water cooled below 40° 
(4° '40) must be carefully distinguished from the great and sudden increase 
of volume it exhibits in the act of freezing, and in which respect it resem- 
bles many other bodies which expand on solidifying. It may be observed 
that the force thus exerted by freezing water is enormous. Thick iron shells 
quite filled with water, and exposed with their fuse-holes securely plugged, 
to the cold of a Canadian winter night, have been found the following morn- 
ing split in fragments. The freezing of water in the joints and crevices of 
rocks is a most potent agent in their disintegration. 

Expansion of Gases. — This is a point of gireat practical importance to the 
chemist, and happily we have very excellent evidence upon the subject. The 
following four propositions exhibit, at a single view, the principal facts of 
the case: — 

1. All gases expand alike for equal increments of heat ; and all vapours, 

when remote from their condensing-points, follow the'same law. 

2. The rate of expansion is not altered by a change in the state of com • 

pression, or elastic force of, the gag itself. 

HBAT. m 

8. Tlk« nte of expiiiim<m is mifbtn for til d ty e w of ImmL 
4. The aetaal amount of ezpansioii is equal to A* part of tlie voliiiM of 
the gas at (K> Fahrenheit, for each degree of ttle easie aeale.* 

It will be mmecessary to enter into any deseripticHi of tho methods 9i in- ' 
vesligatioa by which these results hare been obtained ; the adTanced Btadenl 
will find in Pooillet's UlSmens de Ph^ngue, and in the p»p«ra of MM. Macnoa* 
and Begnanlt' all the information he may require. 

' In the practical manipulation of gases, it Tory often beeonea ne c e ssa iy to 
make a correction for temperatore, or to discoTer how much the Tolume of 
a gas would be increased or diminished by a particular change of tempera- 
ture; this can be effected with great facility. Let it be required, for ex* 
ample, to find tiie volume which 100 cubio inches of any gas at 60^ (IC^C) 
voald become on the temperature rising to 60<> (15<>-5C). 

The rate of expansion is ^^ of the Tolnme at 0« for eaoh degree ; or 4M 
measures at 0° become 461 at 1^, 462 at 2^ •• 460 + 60 a 610 al §0*', and 
460 -f 60 = 520 at 60°. Hence 

]lMS.«t50O. Meas.aiqOO. Mn&aiSOO. M«i.stO0P. 

610 ; 620 » 100 : 101-96. 

If this calculation is required to be madd on the centigrade scale, it must 
be remembered that the aero of that scale is the melting point of ice. AboT* 
this temperature the expansion for eaoh degree of the oendgrade scale' ii 
^^ of the original Tolnme. 

This, and the correction for pressure, are operations of very firequent oo« 
corrence in chemical iuTestigations, 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 qaite recently been shown to be true within certain limits only ; and 
the third, although in the highest degree probable, would be Tory diflicult to 
demonstrate rigidly ; in fact, the equal rate of expansion of air is assumed 
in all experiments on other substances, and becomes the standard by which 
the results are measured. 

The rate of expansion for the different gases is not absolutely the same, 
bat the difference is so small, that for most purposes it may with perfect 
safety be neglected. Neither is the state of elasticity altogether incUnerent, 
the expansion being sensibly greater for ah equal rise of temperature when 
the gas is in a compressed state. 

It is important to notice, that the greatest deriations from the rule are exhi- 
bited by those gases which, as will hereafter be seen, are most easily lique- 
fied, such as carbonic acid, cyanogen, and sulphurous acid, and that the dis- 
crepancies become smaller and smaller as the elastic force is lessened ; so 
that, if means existed for comparing the different gases in states equaUy die~ 
lofU from their points of condensation, there is reason to believe that the 
Ian would be strictly fulfilled. 

The experiments of MM. Dulong and Petit give for the rate of expansion 
trt of the volume at 0^ : this is no doubt too high. Those of Rudburg give 
lijl of Magnus ^j*; and of Regnault fi^s the fraction ^^ is adopted in 
the test as a convenient number, sufiGioienUy near the mean of the three pre- 
ceding, to answer all purposes. 

'Or the araount of expansion is equal to l-492d part of Che volnme the gae ooeaplea at 
«2op. for each degree of Fahxenheit'e scale. On the centigrade scale the expansion H 
I-JM part of the hulk at 09C. — R.-B. 

"IVigsendartrB AmialeDi It. 1. • Ann. Cblm. el Fhya, 8rd series^ iv 8» and v. ML 




fig. 29. 

The reftdy expansibility of air by heat gives rise to the phenomena of 
irinds. In the temperate regions of the earth these are yery variable and 
uncertain, but within and near the tropics a much greater regularity pre- 
vails ; of this the trade-tvinds furnish a beautiful example. 

The smaller degree of obliquity with which the sun's rays fall in the 
localities mentioned, occasions the broad belt thus stretching round the earth 
to become more heated than any other part of the surface. The heat thus 
acquired by absorption is imparted to the low- ' 
est stratum of air, which, becoming expanded, 
rises, and gives place to another, and in this 
manner an ascending current is established, — 
the colder and heavier air streaming in late- 
rally from the more temperate regions, north 
and south, to supply the partial vacuum thus 
occasioned. A circulation so commenced will 
be completed in obedience to the laws of hydro- 
statics, by the establishment of counter-car- 
rents in the higher parts of the atmosphere, 
having directions the reverse of those on the 
surface. (Fig. 29.) 
Such is the effect produced by the unequal 
heating of the equatorial parts, or, more correctly, such would be the effect 
were it not greatiy modified by the earth's movement of rotation. 

As the circumference of the earth is, in round numbers, about 24,000 
miles, and since it rotates on its axis, from west to east, once in 24 hours, 
the equatorial parts must have a motion of 1000 miles per hour; this velo* 
city diminishes rapidly towards each pole, where it is reduced to nothing. 

The earth in its rotation carries with it the atmosphere, whose velocity 
of movement corresponds, in the absence of disturbing causes, with that 
part of the surface immediately below it. The 
air which rushes towards the equator, to sup- 
ply the place of that raised aloft by its dimin- 
ished density, brings with it the degree of mo- 
mentum belonging to that portion of the 
earth's surface from which it set out, and as 
this momentum is less than that of the earth, 
under its new position, the earth itself travels 
■ faster than the air immediately over it, thus 
producing the effect of a wind blowing in a 
contrary direction to that of its own motion. 
The original north and south winds are thus 
deviated from their primitive directions, and 
made to blow more or less fro,(n the eastward, 
so that the combined effects of the unequal 
heating and of the movement of rotation is to generate in the northern hemi- 
sphere a constant north-east wind, and in the southern hemisphere an equally 
constant south-east wind. (Fig. 80.) 

• In the same manner the upper or return current is subject to a change of 
direction in the reverse order ; the rapidly-moving wind of the tropics, trans- 
ferred laterally towards the poles, is soon found to travel faster than the 
earth beneath it, producing the effect of a westerly wind, which modifies the 
primary current 

The regularity of the trade-winds is much interfered with by the neigh- 
bourhood of large continents, which produce local effects upon a scale suf- 
ficiently great to modify deeply the (Erection and force of the wind.' This 
is the case in the Indian Ocean. They usually extend from about the 28th 


- 51 


decree of latitade in both hemfsplieres, to within 8<* of the e<{iiator, bat are 
sabject to some Tariations in this respect. Between them, and also beyond 
their boundaries, lie belts of calms and light Tariable winds, and beyond 
these latter, extending into higher latitudes in both hemispheres, westerly 
winds usually prevail. The general direction of the trade-wind of the North- 
em hemisphere is E.N.E., and that of the Southern hemisphere E.S.E. 

The trade-winds, it may be remarked, furnish an admirable physical proof 
of the reality of the earth's movement of rotation. 

The theory of the action of chimneys, and of natural and artificial ven- 
tilation, belongs to the same subject 

Let the reader turn to the demonstration given of the Archimedean hydro- 
static theorem ; let him once more imagine a body immersed in water, and 
having a density equal to that of the water ; it will remain in equilibrium in 
any part beneath the surface, and for these reasons: — The force which 
presses it downwards is the weight of the body added to the weight of the 
colamn of water above it ; the force which presses it upwards is the weight 
of a column of water equal to the height of both coigoined ; — the density of 
the body is that of wator, that is, it weighs as much as an equal bulk of that 
liquid ; consequently, the downward and upward forces are equally balanced, 
and the body remains at rest. 

Next, let the circumstances be altered ; let the 
body be lighter than an equal bulk of water ; the 
pressure upwards of the column of water, a c, fig. 81, 
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 con^ary, the 
body be specifically heavier than the water, then 
the latter force has the ascendancy, and the body 

All things so described exist in a common chim- 
ney; the solid body, of the same density as that 
of the fluid in which it floats, is represented by 
the air in the chimney-funnel ; the space a b repre- 
sents the whole atmosphere above it. When the air inside and outside the 
chimney is at the same temperature, equilibrium takes place, because the 
downward tendency of the air within is counteracted by the upward pressure 
of that without. 

Now, let the chimney be heated ; the air suffers expansion, and a portion 
is expelled ; the chimney therefore contains a smaller weight of air than it 
did before ; the external and internal columns no longer balance each other, 
and the warmer and lighter air is forced upwards from below, and its place 
sapplie'd by cold air. If the brick-work, or other material of which the 
chimney is constructed, retain its temperature, this second portion of air is 
disposed of like the first, and the ascending current continues, so long as 
the sides of the chimney are hotter than the surrounding air. 

Sometimes, owing to sudden changes of temperature in the atmosphere, 
the chimney may happen to be colder than the air about it. The column 
within forthwith suffers contraction of volume ; the deficiency is filled up 
from without, and the column becomes heavier than one of similar height on 
the outside ; the result is, that it falls out of the chimney, just as the heavy 
body sinks in the water, and has its place occupied by air from above. A 
descending current is thus produced, which may be often noticed in summer 
time by the smoke from neighbouring chimneys finding its way into rooms^ 
which have been, for a considjerable period, without fire. 
The ventilation of mine.s has long been conducted upon the same principle 

52 HBAT. 

wd mere rMmfly it hM been applied to dwellisg-hoiisee snd aasemblj^ 
rooms. The mine is furniahed witii two sh&fte, or with one ehaft^ divided 
throughout by a diaphragm of boards; and these are so arranged, that air 
foroed down the one shall traverse the whole extent of the workings before 
it escapes by the other, A fire kept up in one of these shafts, by rarefying 
the air within, and causing an ascending current, occasions fresh air to tra- 
terse every part of the pune, and sweep before it the noxious gases, but to<t 
frequently present 


Different bodies possess very different eonducting powers with reepect te 
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 

Experiments made by analogous, but more accurate methods, have estaV 
lished a numerical comparison of the conducting powers of many bodies ; 
the f<dlowi|ig may be taken as a specimen :-^ 


. 1000 


. 804 

Silver . 


Lead . 


Copper . 

. 898 

Marble . 

. 23-6 

Iron . 


Porcelain ^. 



. 863 


. 11-4 

M a class, the metals are by very far the best conductors, although much 
difference exists between them ; stones, dense woods, and charcoal, follow 
next in order ; then liquids in general, and gases, whose conducting power 
is almost inappreciable. 

Under favourable circumstances, nevertheless, both liquids and gases may 
become rapidly heated ; heat appUed 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 organio 
fabrics, as wool, silk, feathers, and porous bodies in general, the cavities of 
which are full of air, exhibit such feeble powers of conduction. 

The circulation of heated water through pipes is now extensively applied 
to the warming of buildings and conservatories, and in chemical works a 
serpentine metal tube containing hot oil is often used for heating stills and 
evaporating pans ; the two extremities of the tube are connected with the 
ends of another spiral built into a small furnace at a lower level, and an 
unintermitting circulation of the liquid takes place as long as heat is 


. If equal weights of water at 32° (OoC) and water at 174*> (78°-8C) be 
l^ixed, the temperature of the mixture will be the mean of the two Icraper- 
atures, or lOS*' (89°*4C). If the same experiment be repeated with snow, 
or finely powdered ice, at 32° (QoC) and water at 174® (78° 8C), the tem- 
perature of the whole will be still only 32° (O^C), but the ia tnU have beak 

HEAT. 53 

i lb. of water at B2^ (0®C) 1 o lu * * inoo /onn An\ 
1 lb. of water at 174o (780-80) } = ^ lb. water at lOS- (39o.4C) 

1 lb. of ice at 82° (0«>C) 1 o iv * x oo« ,A„n> 

1 lb. of water at 174o (780-80) } = 2 lb. water at 32o (O^O) 

In the last experiment, therefore, as^ much beat has been apparently lost 
as would have raised a quantity of water equal to that of the ice through a 
range of 1420 (78o-8C). 

The heat, thus become insensible to the thermometer in effecting the lique- 
faction of the ice, is called latent heat, or, better, head of fluidity. 

Again, let a perfectly uniform source of heat be imagined, of such inten- 
sity that a pound of water placed over it would have its temperature raised 
10° (5° -50) per minute. Starting with water at 82o (O^O), in rather more 
than 14 minutes its temperature would have risen 142° (78® -8) ; but the 
same quantity of ice at 32® (0°C), exposed for the same interval of time, 
would not have its temperature raised a single degree. But, then, it would 
have become water ; the heat received would have been exclusively employed 
in effecting the change of state. 

This heat is not lost, for when the water freezes it is again evolved. If a 
tall jar of water, covered to exclude dust, be placed in a situation where it 
shall be quite undisturbed, and at the same time exposed to great cold, tho 
temperature of the water- may be reduced 10° or more below its freezing- 
point without the formation of ice ; but then, if a little agitation be com- 
manicated to the jar, or a grain of sand dropped into the water, a portion 
instantly solidifies, and the temperature of the whole rises to 32° (0°0) ; 
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° (6°-5C). 

This curious condition of instable equilibrium shown by the very cold 
water in the preceding experiment, may be reproduced with a variety of 
solutions which tend to crystallize or solidify, but in which that change is 
for a while suspended. Thus, a solution of crystallized sulphate of soda in 
its own weight of warm water, left to cool in an open vessel, deposits a large 
quantity of the salt in crystals. If the warm solution, however, be filtered 
into a clean flask, which when full is securely corked and set aside to cool 
undisturbed, no crystals will be deposited, even after many days, until the 
cork is withdrawn and the contents of the flask violently shaken. Crystal- 
lization then rapidly takes place in a very beautiful manner, and the whole 
becomes perceptibly warm. 

The law thus illustrated in the case of water is perfectly general. When- 
ever a solid becomes a liquid, a certain fixed and definite amount of heat 
(iisappears, 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 : — 

Sulphur . 
Lead . 

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*^ 
(— n^-TC), while the whole, after a short period, becomes fluid by the 
attraction between the water and the salt ; such a mixture is very often used 

* MM. De la Provostayc and Regnault, Ann. Chim. et Phys., 3d perieb, vlii. 1. 

. 142° (780-8C) 

Zinc . 

. 4930 (2780-80) 

H5 (80 -60) 


. 500 (277 -70) 

. 162 (90 -50) 

Bismuth . 

. 550 (305 -50) 


in chemical emrxments to cool receWers and oondense the Yapoura of Tola« 
tile liqtdds. Powdered crystallized chloride of calcium and snow produce 
cold enough to freeze mercury. Etch powdered nitrate of potassa, or sal- 
ammoniac, dissolved in water, occasions a very notable depression of tem- 
perature ; in every case, in short, in which solution is unaccompanied by 
energetic chemical action, cold is produced. 

Ko relation is to be traced between the actual melting-point of a suV 
stance, and its latent heat when in a fused state. 

A law of exactly the same kind as that described affects uidversaDy the 
gaseous condition ; diange of state from solid or liquid to gas is accompa- 
nied by absorption of sensible heat, and the reverse by its disengagement. 
The latent heat of steam and other vapours may be ascertained by a similar 
mode of investigation to that employd in the case of water. 
, When water at 82® (0^) is mixed with an equal weight of water at 212« 
(lOO^O), the whole is found to possess the mean of the two temperatures, or 
1220 (60oC) ; on the oth^r hand, 1 part by weight of steam at 212o (IWQ) 
when condensed into cold water, is found to be capable of raising 6*6 parts 
of the latter from the freezing to the boiling-point, or through a range of 
180<> (100<»€). Now 180 X 6-6 = 1008; that is to say, steam at 212o 
(100^) in becoming water at 212®, parts with enough heat to raise a weight 
of water equal to its own (if it were possible) 1008« (560®C) of the ther- 
mometer. When water passes into steam, the same quantity of sensible 
heat becomes latent 

The vapours of other liquids seem to have less latent heat than that of 
water; the following table is by Dr. Ure, and serves weU to illustrate this 
point : — 

Vapour of water 967*» (537«»-2C) 

" alcohol 442 (246 -60) 

" ether 802 (167 -70) 

" petroleum 178 (98 -80) 

" oil of turpentine 7. 178 (98 -80) 

" nitric acid 532 (295 -60) 

" liquor ammoniaB 837 (145 -OC 

vinegar 875 

(145 -OC) 
(486 -IC) 

Ebullition is occasioned by the formation of bubbles of vapour within the 
l^ody of the evi^orating liquid, which rise to the surface like bubbles of 
permanent gas. This occurs in different liquids at rery different tempera* 
tores; under the same circumstances, the boiling-point is quite constant, 
and often becomes a physical character of great importance in distinguishing 
liquids which nrach resemble each other. A few cases may be cited in 
illustration : — > 

Substanoe. Boiling-point. 

Ether 96o (35o-5C) 

Bisulphide of carbon 116 (46 -IC) 

Alcohol 177 (80 -60) 

Water 212 (100 C) 

Nitric acid, strong 248 (120 C) 

Oil of turpentine / 312 (155 -50 

Sulphuric acid 620 (826 -20 

Mercury 662 (350 C) 

For ebullition to take place, it is necessary that the elasticity of the vapour 
should be able to overcome the cohesion of the liquid and the pressure 'upon 
Its surface ; hence the extent to which the boiling-point may be modified. 

Water^ under the usual pressure of the atmosphere, boils at 212° (lOO^'C) ; 


in a partially ^ihansted receiver or on a mountain-top it boOfi at a nraeh 
lower temperature ; and in the best yacuum of an excellent air-pnmp, over 
oU of vitriol, which absorbs the vapour, it will often enter into violent 
ebullition while ice is in the act of forming upon the surface. 

On the other hand, water confined in a very strong metallic vessel may be 
restrained from boiling by the pressure of its own vaponr to an almost na- 
limited extent ; a temperature of 350° (177^6) or 400° (204oC) is very easily 
obtained ; and, in fact, it is said that it may be made red-hot, and yet retain 
its fluidity. 

There is a very simple and beautiful experiment illustra- 
tive of the eflfect of diminished pressure in depressing the Kg. 82l 
boiling point of a liquid. A little water is made to boil for 
a few minutes in a flask or retort (fig. 32) placed over a lamp, 
until the air has been chased out, and the steam issues freely 
from the neck. A tightly fitting cork is then inserted, and 
the lamp at the same moment withdrawn. When the 
ebullition ceases it may be renewed at pleasure for a con- 
siderable time by the affusion of cold water, which, by con- 
densing the vapour within, occasions a partial vacuum. 

The nature of the vessel, or rather, the state of its sur- 
face, exercises an influence upon the boiling-point, and this 
to a much greater extent than was formerly supposed. -It 
has long been noticed that in a metallic vessel water boils, under the same 
circumstances of pressure, at a temperature one or two degrees below that 
at which ebullition takes place in glass ; but it has lately been shown * that 
by particular management a much greater difference can be observed. If 
two similar glass flasks be taken, the one coated in the inside with a film of 
shellac, and the other completely cleansed by hot sulphuric acid, water 
heated over a lamp in the first will boil at 211° (99° -40), while in the second 
it will often rise to 221° (105°C) or even higher ; a momentary burst of 
vapour then ensues, and the thermometer sinks a few degrees, after which 
it rises again. In this State the introduction of a few metallic filings, or 
angular fragments of any kind, occasions a lively disengagement of vapour, 
while the temperature sinks to 212° (100°C), and there remains stationary. 
These remarkable effects must be attributed to an attraction between the 
surface of the vessel and the liquid.* 

» Maroet, Ann. Chim. et Phys., 3d series, t. 449. 

* A remarkable modification of the relation between th« temperatxure of Uqutds and th« 
vessel eontaining them, results where the repnleive action predominates. When a small 
quantity of water is thrown into a red-hot platinum crucible, it asflumes a spheroidal form, 
presents no appearance of ebullition, but only a rotary motion, and evaporates very slowly; 
but when the temperature falls to 300°, this spheroidal condition is lost, the liquid, boils and 
i-i soon dissipated. In the spheroidal state there is no contact between the water and metal, 
in ooncequence of the high tension of the small quantity of vapour which is formed and 
surrounds the globule, but on the fall in temperature, the tension lessens and with it the 
repulPive action, contact takes place and the heat is rapidly communicated to the liquid, 
which at onoe is converted into steam. So siij^ht is the influence of the caloric of the vessel 
on the contained liquid in this condition, titat if liquid sulphurous acid be poured on the 
globule, the water is by the sudden evaporation of the acid conyerted into ice at the bottom 
of the red-hot crucible. When a liquid which boils at a low temperature, is thrown on an- 
other heated nearly to ebullition and whose boilinjr-point is high, the ' wpheroidal state is 
likewise assumed, as water on oil, spirits of turpentine, sulphuric acid, &c., and ether ou 
water, Ac. 

As connected with this phenomenon, it ha* been observed that perfect immunity from the 
caloric of highly heated liquids may be obtained by previously moistening the part to which 
the application is made with some fluid which evaporates at a low temperature. Thus the 
hand, while moistened with ether, may be plunged into boiling-water without even the sen- 
sation of heat. When wet with wjiter 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 similai 
experiment has been performed with incited cast-iron as it runs from the fUnuuiB, and tfa» 



A enbio iooli of water in becoming steam under the ordinary pressnre of 
the atmosphere expands into 1696 cubic inches, or nearly a cubic foot. 

Steam, not in contact vith water, is affected by heat in precisely the same 
manner as the permanent gases ; its rate of expansion and increase of elastic 
force are the same. When water is present, howeyer, this is no longer the 
case, but on the contrary, the elastic force' increases in a far more rapid 

This elastic force of steam in contact with water, at different temperatures, 
has been very carefully determined by MM. Arago and Dulong, and very 
lately by M. Regnault The force is expressed in atmospheres ; the abso- 
lute pressure upon any given surface can be easily calculated, allowing 
14*6 lb. to each atmosphere. The experiments were carried to twenty-fiye 
atmospheres, at which point the difficulties and danger became so great as 
to put a stop to the inquiry ; the rest of the table is the result of calcula- 
tions founded on the data so obtained. 

Pressure of steam 
in atmospheres. 

P C 

1 212° 100° 

1-6 234 112 -2 

2 251 121 -2 

2-6 264 128 -8 

8 275 185 

8-5 285 140 -6 

4 294 145-6 

4-5 300 148 -8 

5 308 153 -1 

6-5 314 156 -2 

6 320 160 

6-5 326 163 -1 

7 332 166 -2 

7-5 337 169 

8 342 172 

9 351 177 -2 

10 369 181 -2 

11 367 186 -1 

12 874 190 

Pressure of steam Ciorresponding 

in atmospheres. temperature. 

13 3810 194° 

14 387 197 -7 

15 398 200 -5 

16 398 203 

17 404 206 

18 409 209 

19 414 212 

20 418 214 

21 423 217 

22 427 219 

23 431 221 

24 436 224 

' 26 439 226 

457 236 

473 245 

40 487 252 



491 265 
611 266 

It is a very remarkable fact, that the latent heat of steam diminishes as 
fVe temperature of the st«am 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° (lOO^G), and that of the other 
860O (176®-2C) or 400° (204o-4C). This also appears true with temperatures 
below the boiling-point ; so that it seems, to evaporate a given quantity of 
water the same absolute amount of heat is required, whether it be performed 
slowly at the temperature of the air, in a manner presently to be noticed, or 
whether it be boiled off under the pr^sure of twenty atmospheres. It is 
for this reason that the process of distillation in vacuo at a temperature 
which the hand can bear, so advantageous in other respects, can effect no 
direct saving in fuel.* 

dry parts sulgected to the radiant caloric have been fbund more affected than that exposed 
to (Jie melted metal. 

Vie immunity in the case of usin;; vater as the moistening a.?ent arises from the fiict that 
tb« temperature of the globule in the spheroidal state is much below the boiling-point of the 
liqwd.— R. B. 

^ The proposition in the text, of the sum of the latent and sensible heats of steam being a 
•MMta&t quantity^ is known by the name of WiMs Vxw^ having been deduced by that illus- 



Fig. 33. 

Fig. 31. 

Tke eoonomiMl ftppUeatioiiB of ttMUB tare mmieMras and eztmnely tsIv- 
ftble; they may be divided into two clmsses: those in which the heating 
power is employed, and those in which its elastic force is brought into use. 

The Talae of steam as a source of heat depends 
upon the facility with which it may be conyeyed to 
distant points, and upon the large amount of latent 
heat it contains, which is disengaged in the act of 
condensation. An invariable temperature of 212° 
(lOO^G), or higher, may be kept up in the pipes or 
other vessels in which the steam is contained by 
the expenditure of a very small quantity of the 
latter. Steam-baths of various forms are used in 
the arts with great convenience, and also by the 
scientific chemist for drying filtefs and other ob- 
jects where excessive heat would be hurtfid; a 
very good instrument of the kind was contrived 
by Mr. Everitt. It is merely a small kettle (fig. 
83), surmounted by a double box or jacket, into 

which the substance to be 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 litUe hole in the side of the jacket 
gives vent to the excess of steam. 

The principle of the steam-engine may 
be described in a few words; its mechanicid 
details do not belong to the design of the 
present volume. The machine consists es- 
sentially of a cylinder of metal, a (fig. 34), 
in which works a closely-fitting solid piston, 
the rod of which passes, air-tight, through 
a staffing-box at the top of tiie cylinder, 
and is connected with the machinery to be 
put in motion, directly, or by the interven- 
tion of an oscillating beam. A pipe commu- 
nicates with the interior of the cylinder, and 
also with a vessel surrounded with cold 
water, called the condenser, marked b in the 
sketch, and into which a jet of cold water 
can at pleasure be introduced. A sliding- 
valve arrangement, shown at c, serves to 
open a communication between the boiler 
and the cylinder, and the cylinder and the 
condenser, in such a manner that while the 
steam is allowed to press with all its force 
upon one side of the piston, the other, open 
to the condenser, is necessarily vacuous. 
The valve is shifted by the engine itself at 
the proper moment, so that the piston is al- 
ternately driven by the steam up . and down 
against a vacuum. A large air-pump, not 
shown in the engraving, is connected with the 
condenser, and serves to remove any air that may enter the cylinder, and 
also the water produced by condensation, together with that which may have . 
been injected. 

Such is the vacuum or condensing steam-engine. In what is called the 

triouB man from expeiiments of his own. It hafl always agreed well with the rough practical 
Ksolts obtained by engineers, and has lately been confirmed to a great extent, although not 
completely, by a aeries of elaborate experiments by M. Regnault. 



bigb-pressnre engine, the condenser and alr-pnmp are suppressed, and tbe 
steam is allowed to escape at once from the cylinder into the atmosphere. 
It is obvious that in this arrangement the steam has to OTercome the whole 
pressure of the air, and a much greater elastic force is required to produce 
the same effect ; but this is to a very great extent compensated by the absence 
of the air-pump and the increased simplicity of the whole machine. Large 
engines, both on shore and in steam-ships, are usually constructed on the 
condensing principle, the pressure seldom exceeding six or seyen pounds per 
square inch above that of the atmosphere ; for small engines the high-pressure 
plan is, perhaps, preferable. Locomotive engines are of this kind. 

A peculiar modification of the steam-engine, employed in Cornwall for 
draining the deep mines of that country, is now getting into use elsewhere 
for other purposes. In this machine economy of fuel is carried to a most 
extraordinary extent, engines having been known to perform the duty of 
raising more than 100,000,000 lb. of water one foot high by the consumption 
of a single bushel of coals. The engines are single-acting ; the down-stroke, 
which is made against a vacuum, being the effective one, and employed to 
lift the enormous weight of the pump-rods in the shaft of the mine. When 
the piston reaches the bottom, the communication both with the boiler and 
the condenser is cut off, while an egtUHbrium-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 engines 
is worked expansively, as it is termed, steam of high tension being employed, 
which is cut off at one-eighth or even one-tenth of the stroke. 

The process of distillation, which may now be noticed, is very simple ; its 
object is either to separate substances which rise in vapour at different tem- 
peratures, or to part a volatile liquid from a substance incapable of volatili- 
sation. The same process applied to bodies which pass directly fi:'om the 
solid to the gaseous condition, and the reverse, is called sublimation. Every 
distillatory apparatus consists essentially of a boiler, in which the vapour is 
raised, and of a condenser, in which it returns to the liquid or solid con- 
dition. In the still employed for manufacturing purposes, the latter is 
usually a spiral metal tube immersed in a tub of water. The common retort 
and receiver constitute the simplest and most generally useful arrangement 
for distillation on the small scale ; the retort is heated by a lamp or a char- 

Kg. 86. ' 



wal fire, and th« reeetver is kept oool, if necessary, by a wet eloth, or it may 

be Burroimded with ice. (Fig. 35.) 



The condenser of Professor Liebig is a very valuable instra- 
ment in the laboratory; it consists of a glass tube (fig. 36), 
tapering from end to end, fixed by perforated corks in the centre 
of a metal pipe, provided with tubes so arranged that a current 
of cold water may circulate through the apparatus. By putting 
a few pieces of ice into the little cistern, the temperature of this 
water may be kept at 32° (0®C), and extremely volatile liquids 

Liquids evaporate at temperatures below their boiling-points ; 
in this case the evaporation takes place solely from the surface. 
Water, or alcohol, exposed in an open vessel at the temperature 
of the air, gradually dries up and disappears ; the more rapidly, 
the warmer and drier the air above it. 

This fact was formerly explained by supposing that air and 
gases in general had the power of dissolving and holding in 
solution certain quantities of liquids, and that this power in- 
creased with the temperature ; such an idea is incorrect. 

If a barometer-tube (fig. 37) be carefully filled with mercury 
and inverted in the usual manner, and then a few drops of water 
passed up the tube into the vacuum above^a very remarkable 
effect will be observed; — the mercury will be depressed to a 
small extent, and this depression will increase with increase of 
temperature. Now, as the space above the mercury is void of 
air, and the weight of the few drops of water quite inadequate 
to account for this depression, it must of necessity be imputed 
to the vapour which instantaneously rises from the water into 
the vacuum ; and that this effect is really due to the elasticity 
or tension of the aqueous vapour, is easily proved by exposing 
the barometer to a heat of 212° (100°C), when the depression 
of the mercury will be complete, and it will stand at the same 
level within and without the tube, indicating that at that temper- 
ature the elasticity ,of the vapour is equal to that of the atmo- 
sphere, — a fact which the phenomenon of ebullition has already 

By placing over the barometer a wide open tube dipping into the meroury 
below, and then filling this tube with water at different temperatures, the 



tendob of tha aqueoaB vftponr for each degtt9 of the thermometer may be 
ftccurately determined by its depressing effect upon the mercurial column } 
the same power which forces the latter doitmone inch against the pressure 
of the atmosphere, would of course elevate a column of mercury to the same 
height against a vacuum, and in this way the tension may be very conve- 
niently expressed. The following table was drawn up by Dr. Dalton, to 
whom we owe the method of investigation. 

Tension in inches 
of mercury. 













4-4 .... 

.... 0-268 



15-5 .... 

.... 0-524 

2M .... 

.... 0-721 

26-6 .... 

.... 1000 

32-2 .... 


87-7 .... 

.... 1-860 

43-8 .... 

.... 2-630 

48-8 .... 

.... 8-380 

Fig. 38. 


" C. 



Tension in inches 
of mercury. 






. 54-4 .. 

. 60 ... 

. 65-6 .., 

. 71-1 .., 

. 76-6 .. 

. 82-2 1615 

. 87-7 1900 

. 98-8 23-64 

•100 80-QO 

Other liquids tried in this manner are found to emit 
vapours of greater or less tension, for the same temper- 
ature, according to their different degrees of volatility: 
thus, a little ether introduced into the tube depresses the 
mercury 10 inches or more at the ordinary temperature 
of the air ; oil of vitriol, on the other hand, does not 
emit any sensible quantity of vapour until a much greater 
heat is applied ; and that given off by mercury itself in 
warm summer weather, although it may by very delicate 
means be detected, is far too little to exercise any effect 
upon the barometer. In the case of water, the evapora- 
tion is quite distinct and perceptible at the lowest tem- 
peratures, when frozen to solid ice in the barometer-tube ; 
snow on the ground, or on a house-top, may often be 
noticed to vanish, from the same cause, day by day in the 
depth of winter, when melting was impossible. 

There exists for each vapour « state of density which 
it cannot pass without losing its gaseous condition, and 
becoming liquid; this point is called the condition of 
maximum density. When a volatile liquid is introduced 
in sufficient quantity into a vacuum, this condition is 
always reached, and then evaporation ceases. Any at- 
tempt to increase the density of this vapour by com- 
pressing it into a smaller space will be attended by the 
liquefaction of a portion, the density of the remainder 
being unchanged. If a little ether be introduced into a 
barometer (fig. 38), and the latter slowly sunk into a very 
deep cistern of mercury, it will be found that the height 
of tihe column of mercury in the tube above that in the 
cistern remains \unaltered until the upper extremity of. 
the barometer approaches the surface of the metal in the 
reservoir. It will be observed also, that, as the tube 
sinks, the little stratum of liquid ether increases in thick- 
ness, but no increase of elastic force occurs in the vapour 
above it, and, consequently, no increase of density ; for 
tension and density are always, under ordinary circum- 
stances at least, directly proportionate to each other la 
the same vapour. 

HKAT. 61 

The point of maximnin density of a Taponr is dependent vpon the ten- 
penture ; it inereases rapidly as the temperature rises. This is well shown 
Id the ease of water. Thus, taking the specific gravity of atmospheric air 
at 212^ (lOQoC) =: 1000, that of aqueous vapour in its greatest possible 
state of compression for the temperature will be as follows :— 

Temperatttre. Specific grayity. Weight of 100 enbie inchei. 

P. 0. 

820 0° 5-690 0186 grains. 

50 10- 10293 0-247 

60 16-5 14108 0-338 

100 87-7 46-500 M13 

150 65-6 170-293 4076 

212 100 625000 14-962 

The last number was experimentally found by M. Qay-Lussao ; the othera 
are ealculated upon that by the aid of Dr. Dalton's table of tensions. 

Thus, there are two distinct methods by which a vapour may be reduced 
to the liquid form ; pretsure, by causing increase of density untU the point 
of maximum density for the particular temperature is reached; and cold, by 
which the point of maximum density is itself lowered. The most powerful 
effects are of course produced when both are conjoined. 

For example, if 100 cubic inches of perfectly transparent and gaseous 
vapour of water at 100<> (37°'7G), in the state above described, had its tem« 
perature reduced to 50^ (10°G), not less than 0-87 * grain of fluid water 
would necessarily separate, or very nearly eight-tenths of the whole. 

Evaporation into a space filled with air or gas follows the same law as 
evaporation into a vacuum ; as much vapour rises, and the condition of max- 
imam density is assumed in the same manner as if the space were perfectly 
empty; the sole difference lies in the length of time required. When a 
liquid evaporates into a vacuum, the point of greatest density is attained at 
once, while in the other case some time elapses before this happens ; the 
particles of air appear to oppose a sort of mechanical resistance to the rise 
of the vapour. The ultimate effect is, however, precisely the same. 

When to a quantity of perfectly dry gas confined in a vessel closed by 
mercury, a little water is added, the latter immediately begins to evaporate, 
and after some time as much vapour will be found to have risen from it as 
if no gas had been present, the quantity depending^ entirely on the temper- 
ature to which the whole is subjected. The tension of this vapour will add 
itself to that of the gas, and produce an expansion of volume, which will be 
mdicated by an alteration of level in the mercury. 

^ Vapour of water exists in the atmosphere at all times, and in all situa- 
tions, and there plays a most important part in the economy of natui^. The 
proportion of aqueous vapour present in the air is subject to great variation, 
and it often becomes exceedingly important to determine its quantity. This 
is easily done by the aid of the foregoing principles. 

If the aqueous.vapour be in its condition of greatest possible density for 
the temperature, or, as it is frequently, but most incorrectly expressed, the 
sir be saturated witli vapour of water, the slightest reduction of tempera- 
ture will cause the deposition of a portion in the liquid form. If, on the 
contrary, as is almost always in reality the case, the vapour of water be 
below its state of maximum density^ that is, in an expanded condition, it is 
dear that a considerable fall of temperature may occur before liquefaction 
commences. The degree at which this takes place is called the dew-point, 

Moo cable inches aqneoos vapours at WP (37<'-70), weighing 1-113 grain, wculd at 60^ 
(^OPC), beo9me reduced to 10-29 cubic inches, weighing 0*217 grain. 



and it is determined with great facility by a Tery simple method., A little 
oup of thin tin-plate or silver, well polished, is filled with water at the tem- 
perature of the air, and a delicate thermometer inserted. Xhe water is then 
cooled by dropping in fragments of ice, or dissolving in it powdered sal- 
ammoniac, until a deposition of moisture begins to make its appearance oa 
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° (2lo-lC), and the 
dew-point 50** (10°C) ; the elasticity of the watery vapour present would 
correspond to a maximum density proper to 50° (10°C), and would support 
a column of mercury 0-375 inch high. If the barometer on the spot stood 
at 30 inches, therefore, 29-625 inches would be supported by the pressure 
of the dry air, and the remaining 0-375 inch by the vapour. Now a cubic 
foot of such a mixture must be looked upon as made up of a cubic foot of 
dry air, and a cubic foot of watery vapour, occupying the same space, and 
having tensions indicated by the numbers just mentioned. A cubic foot, or 
1728 cubic inches of vapour at 70° (21°-1C), would become reduced by con- 
traction, according to the usual law, to 1662-8 cubic inches at 50° (10°C) ; 
this vapour would be at its maximum density, having the specific gravity 
pointed out in the table; hence 1662-8 cubic inches would weigh 4-11 grains. 
The weight of the aqueous vapour contained in a cubic foot of air will thus 
be ascertained. In England the difference between the temperature of 
the air and the dew-point seldom reaches 80° ( — 1°-2C) ; but in the Deccan, 
with a temperature of 90° (32° -20), the dew-point has been seen as low as 
29° ( — 1°-6C) making the degree of dryness 61°.* 

Another method of finding the proportion of moisture present in the air 
is to observe the rapidity with which evaporation takes place, and which is 
always in some relation to the degree of dryness; The bulb 
Fig. 39. of a thermometer is covered with muslin, and kept wet with 

water ; evaporation produces cold, as will presently be seen, 
and accordingly the thermometer soon sinks below the ac- 
tual temperature of the air. When it comes to rest, the 
degree is noticed, and from a comparison of the two tempe- 
ratures an approximation to the dew-point can be obtained 
by the aid of a mathematical formula contrived for the pur- 
pose. . This is called the wet-bulb hygrometer ; it is often 
made in the manner shown in fig. 39, where one thermometer 
serves to indicate the temperature of the air, and the other 
to show the rate of evaporation, being kept wet by tho 
thread'in connexion with the little water reservoir. 

The perfect resemblance in every respect which vapours 
bear to permanent gases, led, very naturally, to the idea 
that the latter might, by the application of suitable means, 
be made to assume the liquid condition, and this surmise 
was, in the hands of Mr. Faraday, to a great extent verified. 
Out of the small number of such substances tried, not less 
than eight gave way ; and it is quite fair to infer, that, had 
means of sufficient power been at hand, the rest would have 
shared the same fate, and proved to be nothing more thau 
the vapours of volatile liquids in a state very far removed 
from that of their maximum density. The subjoined table 
represents the results of Mr. Faraday's first investigations. 


^ Mr. Daniell, Introduction to Chemloal Philosophy, p. 154. 

HBAT. 63 

wxtb the pressnre in atmosplieres, and the tempentnre at frhich the ooih 
iens&tion took place.* 


Solphnroos acid 2 

Sulphuretted hydrogen 17 

Carbonic acid 86 

Chlorine 4 , 

Nitrons oxide 50 

Qyanogen 3-6 

Ammonia • 6*5 ............ 

Hydrochloric add 40 









15 -5 


7 -2 


7 -2 





The method of proceeding was very simple ; the materials were sealed np 
\h a strong narrow tube (fig. 40), together with a little pressore-gaage, con- 
Fig. 4a 

sisting of a slender tube closed at one end, and' haying within it, near the 
open extremity, a globule of mercury. The gas being disengaged by the 
application of heat, or otherwise, accnmnlated in the tube, and by its own 
pressure brought about condensation. The force required for this purpose 
was judged of by the diminution of volume of the air in the gauge. 

Mr. Faraday has since resumed, with the happiest results, the subject of 
the liquefaction of the permanent gases. By using narrow green glass tubes 
of great strength, powerful condensing syringes, and an extremely low tem- 
perature, produced by means to be presently described, defiant gas, hydri- 
odic and hydrobromic acids, phosphoretted hydrogen, and the gaseous 
fluorides of silicon and boron, were successively liquefied. Oxygen, hydro- 
gen, nitrogen, nitric oxide, carbonic oxide, and coal-gas, refused to liquefy 
at the temperature of — 166° ( — 74° '40) while subjected to pressures vary* 
ing in the different cases from 27 to 58 atmospheres.* 

Sir Isambard Brunei, and, more recently, M. Thilorier, of Paris, suc- 
ceeded in obtaining liquid carbonic acid in great abundance. The apparatus 
of M. Thilorier (fig. 41) consists of a pair of extremely strong metallic ves- 
sels, one of which is destined to serve the purpose of a retort, and the other 
that of a receiver. They are made either of thick cast-iron or gun-metal, 
or, still better, of the best and heaviest boiler-plate, and are furnished with 
Btop-cocks of a peculiar kind, the workmanship of which must be excellent^ 
The generating vessel or retort has a pair of trunnions upon which it swings 
in an iron frame. The joints are secured by collars of lead, and every pre- 
caution taken to prevent leakage under the enormous pressure the vessel 
has to bear. The receiver resembles the retort in every respect ; it has a 
similar stop-cock, and is connected with the retort by a strong copper tube 
and a pair of union screw-joints ; a tube passes from the stop-cock down- 
wards, and terminates near the bottom of the vessel. 

The operation is thus conducted : 2| lb. of bicarbonate of soda, and 6^ 
lb. of water at 100° (87**-7C), are introduced into the generator ; oil of vitriol 

* PhU. Trans. Ibr 1823, p. 189. 

* Phil. Trans, for 1845, p. 165. 


to the amount of 1 J lb. is poured into a copper cylindrical vessel, which is 
lowered down into the mixture, and set upright; the stop-cock is then 
screwed into its place, and forced home by a spanner and mallet. The ma- 
chine is next tilted up on its trunnions, that the acid may run out of the 
cylinder and mix with the other contents of the generator ; and this mixture 
is favoured by swinging the whole backwards and forW&rds for a few mi- 
nutes, after which it may be suffered to remain a little time at rest. 

The receiver, surrounded with ice, is next connected to the generator, and 
both cocks opened ; the liquefied carbonic acid distils over into the colder 
vessel, and there again in part condenses. The cocks are now closed, the 
vessels disconnected, the cock of the generator opened to allow the contained 
gas to escape ; and, lastly, when the issue of gas has quite ceased, the stop- 
cock itself unscrewed, and the sulphate of soda turned out. This operation 
must be repeated five or six times before any very considerable quantity of 
liquefied acid will have accumulated in the receiver. When the receiver 
thus charged has its stop-cock opened, a stream of the liquid is forcibly 
driven up the tube by the elasticity of the gas contained in the upper part 
of the vessel. 

It will be quite proper to point out to the experimenter the great personal 
danger he incurs in using this apparatus, unless the greatest care bo taken 
in it« management. A dreadful accident has already occurred in Pari 9 by 
the bursting of one of the iron vessels. 

The cold produced by evaporation has been already adverted to ; it is 
simply an effect arising from the conversion of sensible heat into latent by 
the rising vapour, and it may be illustrated in a variety of ways. A little 
ether dropped on the hand thus produces the sensation of great cold, and 
water contained in a thin glass tube, surrounded by a bit of rag, is speedily 
frozen when the rag is kept wetted with ether. 



Kg. 42. 

Wlien a little water is put into a watcli-glas?, 
(fig. 42), supported by a triangle of wire oyer 
a shallow glass dish of sulphuric acid placed 
on the plate of a' good air-pump, the whole 
covered with a low receiver, and the air with- 
drawn as perfectly as possible, the water is in 
a few minutes converted into a solid mass of ice, 
^nd the watch-glass very frequently broken by 
the expansion of the lower portion of water in 
the act of freezing, a thick crust first forming on the surface. The absence 
of the impediment of the air, and the rapid absorption of watery vapour by 
the oil of vitriol, induce such quick evaporation that the water has its tem- 
perature almost immediately reduced to the freesrtng-point. 

The same fact is shown by a beautiful instrument contrived by Dr. Wol- 
laston, called a eryophoruSj or frost-carrier. It is made of glass, of the form 
represented in fig. 48, and contains a small quantity of water, the rest of 
the space being vacuous. When all the water is turned into the bulb, and 
the empty extremity plunged into a mixture of ice and salt, the solidification 
of the vapour gives rise to such a quick evaporation from the surface of the 
Water, that the latter freezes. 

Fig. 43. 

Fig. 44 


AU means of producing artificial cold yield to that derived from the eva- 
poration of the liquefied carbonic acid, just mentioned. When a jet of that 
liquid is allowed to issue into the air from a nar- 
row aperture, such an intense degree of cold is 
produced by the vaporization of a part, that the 
remainder freezes to a solid, and falls in a shower 
of snowj . By suffering this jet of liquid to flow into 
a metal box provided for the purpose, shown in the 
drawing of the apparatus (fig. 44), a large quantity 
of the solid acid may be obtained ; it closely re- 
sembles snow in appearance, and when held in the 
hand occasions a painful sensation of cold, while 
it gradually disappears. Mixed with a little ether, 
and poured upon a mass of mercury, the latter 
is almost instantly fi>ozen, and in this way pounds 
of the solidified metal may be obtained. The addi- 
tion of the ether facilitates the contact of the car- 
bonic acid with the mercury. 

The temperature of a mixture of solid carbonic 
acid and ether in the air, measured by a spirit- 
thermometer, was found to be —106° ( — 76° CC) ; 
when the same mixture was placed beneath the 
receiver of an air-pump, and exhaustion rapidly 
Bade, the temperature sank to — 166° ( — 1-10°C). 
This was the method of obtaining extreme cold 
employed by Mr. Faraday in his last experiments 
(m*tbe'liq«i^action of gases. Under such circum- 


36 HBAT. 

Btanoes, the liquefied hydriodic, bydrobromic, aad Bulplraroiis acid gaies, 
carbonic acid, nitrous oxide, sulphuretted hydrogen, cyanogen, and ammo 
nia, froze to colourless transparent aoUdSy and alcohol became thick and oily. 
The principle of the cryophorus has been very happily applied by Mr. 
Baniell to the construction of a dew-point hygrometer ; fig. 44. It consists 
of a bent glass tube terminated by two bulbs, one of which is half filled with 
etiier, the whole being yacaous as respects atmospheric air. A delicate ther- 
mometer is contained in the longer limb, the bulb of which dips into the 
ether ; a second thermometer on the stand serres to show the actual tempe- 
.rature of the air. The upper bulb is covered with a bit of muslin. When 
an obseryation is to be made, the liquid is all transferred to the lower bulb, 
and ether dropped upon the upper one, until by the cooling effects of evapo- 
ration a distillation of the contained liquid takes place from one part of the 
apparatus to the other, by which such a reduction of temperature of the 
ether is brought about, that dew is deposited on the outside of the bulb, which 
is made of black glass in order that it may be more easily seen. The differ* 
ence of temperature indicated by the two thermometers is then read off. 


Let the reader renew a supposition made when the doctrine of latent heat 
was under consideration ; let him imagiae the existence of an uniform source 
of heat,, and its intensity such as to raise a .given weight of water 10° 
(6° -50 in 30 minutes. If, now, the experiment be repeated with equal 
weights of mercury and oil, it will be found, that instead of 30 minutes, 1 
minute will suffice in the former case, and 15 minutes in the latter. 

This experiment serves to point out the very important fact, that different 
bodies have different capacities for heat ; that equal weights of water, oil, 
and mercury, require, in order to rise through the same range of tempera- 
ture, quantities of heat in proportion of the numbers 30, 15, and 1. This 
is often expressed by saying that the specific heat of water is 30 times as 
great as that of mercury, and the specific heat of oil 15 times as great. 

Again, if equal weights of water at lOO® (37°-7C), and oil at 40® (4o-4C), 
be agitated together, Uie temperature of the whole will be found to be 80^ 
(26°-6C), instead of 70° (21°-1C), the mean of the two ; and if the tempera- 
tures be reversed, that of the mixture will be only 60° (16° 'SC). Thus, 

1 lb. Zn'Z "' 'To ^tl"-lc) } «i- a mixture at 80- (26-6C) , hence 
Loss by the water, 20° (11°-]C). 
Gain by the oil, 40° (22°-2C). 

\ lb.' df at ""* 100° (37°.'7c! } ^^^ * °^^*^« ^* ^^^ (l^^'^C) ; hence 
Gain of water, 20° (11°1C). 
Loss of oil, 40° (22° -20). 

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 
substances 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 tem* 
perature ; the second is by noting the time which the heated body requires 
to cool down through a certain number of degrees ; and the third is the 
method of mixture, on the principle illustrated ; this latter method is pre- 
ferred as the most accurate. 

The determination of the specific heat of different substances has occupied 
the attention of many experimenters ; among these MM. Dulong and Petit, 
and recently M. Regnault, deserve especial mention. It appears that each 
solid and liquid has its own specific heat ; and it is probable that this, in- 

HBAT. 67 

fitttd of being a eiMusUnt quantity, Taries with tke temperatnre. The de- 
tenniaation of the specific heat of gases is attended with peculiar difficulties 
on account of the comparatively large Tolume of small weights of gases. 
Satisfactory results have however been obtained by the method of mixing for 
the following gases. 

Of equal rolamea. Of equal weigtata. 

Air = l Water=:l 

Atmospheric air 1 1 0*2669 

Oxygen 1 0-8848 0-2361 

Hydrogen 1 12-8401 3-2936 

Nitrogen 1 10318 0-2754 

Carbonic oxide 1 1-0806 0-2884 

Protoxide of pitrogen ... 1-227 0-8878 0-2369 

Carbonic acid 1-249 ....* 0-8280 0-2210 

defiant gas 1-754 1-6763 0-4207 

Aqueous vapour 1-960 3-1360 0-8470* 

For the comparison of the specific heat of atmospheric air with that of 
water, we are indebted to Count Rumford ; for the comparison of the specifio 
heat of the varieus gases, to Delaroche and Berard. 

Whenever a gas expands, heat becomes thereby latent Hence the amount 
of heat required to raise a gas to a certain temperature increases the more 
ve allow it to expand. Dulong has found that if the amount of heat re- 
qaired to raise the temperature of a volume of gas (observed at the melting 
point of ice, and at the pressure of 30 inches) to a given height without its 
Tolame undergoing any change, be represented by 1, then if the gas is al- 
lowed to expand until ihe pressure is reduced again to 30 inches whilst the 
high temperature is kept up, the additional amount of heat which is required 
for this purpose is, for oxygen, hydrogen, or nitrogen 0,421 ; for carbonio 
acid 0,423 ; for binoxide of nitrogen 0,343 ; and for olefiant gas 0,240. 

If there be no source of heat from which this additional quantity can be 
obtained, then the gas is cooled during expansion, a portion of "the free heat 
becoming latent. On the other hand, if a gas be compressed, this latent 
heat becomes free, and causes an elevation of temperature, which, under 
faivourable circumstances, may be raised to ignition; syringes by which 
tinder is kindled are constructed on this principle. lu the upper regions of 
the atmosphere the cold is intense ; snow covers the highest mountain-tops 
even within the tropics, and this is due to the increased capacity for heat'of 
the expanded air. 

MM. Dulong and Petit observed in the course of ^eir investigation a most 
remarkable circumstance. If the specific heats of bodies be computed upon 
equal weights, numbers are obtained, all different, and exhibiting no simple 
relations among themselves ; but if, instead of equal weights, quantities be 
taken in the proportion of the chemical equivalents, an alm\)st perfect coin- 
cidence in the numbers will be observed, showing that some exceedingly in- 
timate connexion must exist between the relations of bodies to heat and 
tbeir chemical nature ; and when the circumstance is taken into view, that 
relations of even a still closer kind link together chemical and electrical 
pheaomcna, it is not too much to expect that ere long some law may be dis- 
coyered far more general than any with which we are yet acquainted. 

•The later determinations of Eegnault vary from the above: thus in equal '^eightfl. 
Water»=l; Atmospheric air he gives w 0-2377; Oxygen, 0-2182; Nitrogen, 0-2440; and 
Vapour of Water, 0-4750; and contrary to the results of Oay-Lussao, the specific heat of ais 
ioos not vary with the tcmperatare.—B. B. 

68 HSAr. 

The following table is extracted from the membinl of M. Regnavlt, vlflk 
irhose results most of the experiments of Dolong and Petit closely coincide. 

Subetancee. Spedflc beat of Bpedfie heat of 

equal weights. equiTaleat weights. 

Water 100000 

Oil of Turpentine 0-42598 

Glass ; 0-19768 

Iron. 0-11379 3-0928 

Zinc 009666 80872 

Copper 0-09516 3-0172 

Lead 0-03140 :.....:... 8-2681 

Tin 0-05628 ....:.......,. 8-3121 

Nickel 010868 8-2176 

Cobalt 0-10696 3-1628 

Platinum 003243 3-2054 

Sulphur 0-20259 3-2657 

Mercury 003332 3-7128 

Silver 005701 61742 

Arsenic 008140 6-1326 

Antimony 005077 * 6-5616 

Gold 03244 6-4623 

Iodine 0-05412 6-8462 

Bismuth 0-03084 2-1877 

Of the numbers in the second column, the first ten approximate far toe 
closely to each other to be the result of mere accidental coincidence ; the five 
that follow are very nearly twice as great; and the last is one-third less.' 

Independently of experimental errors, there are many circumstances 
which tend to show, that, if all modifying causes could be compensated, or 
their effects allowed for, the law might be rigorously true. 

The observations thus made upon elementary substances have been ex- 
tended by M. Regnault to a long series of compounds, and the same curious 
law found, with the above limitations, to prevail throughout, save in a few 
isolated cases, of which an explanation can perhaps be given. 

Except in the case of certain metallic alloys, where the specific heats were 
the mean of those of their constituent metals, no obvious relation can be 
traced between the specific heat of th% compound body and of its compo- 
nents. The most general expression of the facts that can be given ia 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 suhmulty^le of the latter. — 
Simple as well as compound bodies will be comprehended in this law.^ 


The first and greatest source of heat, compared with which all others are 
totally insignificant, is the sun. The luminous rays are accompanied by 
rays of a heating nature, which, striking against the surface of the earth, 
elevate its temperature ; this heat is communicated to the air by convection, 
as already described, air and gases in general not being sensibly heated by 
the passage of the rays. 

• The equivalent of Bismuth being assumed as 71, but adopting 213, the number given 
under the head of bismuth, the specific heat of an equiyalent weight will'be 6-6688, or ooii^- 
Cldo with the five preceding, — R. B. ■ ? • > - 

*Aim. Chjun. etPhys. Uiiii. 5;-andthe8ame, 3rdseri«S;i*12dr ~ 

HKAT. f»f 

A second sonroe of^heat is supposed to exist in the interior of the earth. 
It has been obserredy^that in sinlung mine-Bhafts, boring for water, &o., the 
temperature rises in descending, at the rate, it is said, of about 1 ^ (|^C) for 
eyerj 45 feet, or 117^ (65^C) per mile. On the supposition that the rise 
coDtinaed at the same rate, at the depth of less than two miles the earth 
would have the temperature of boiling water ; at nine miles it would be red 
hot ; and at 30 or 40 miles depth, all known substances would be in a state 
of fusion.* 

According to this idea, the earth must be looked upon as an intenselj- 
heated, fluid spheroid, covered with a crust of solid badly-conducting mat- 
ter, cooled by radiation into space, and bearing somewhat the same propor- 
tion in thickness to the ignited liquid within, that the shell of an egg does 
to its fluid contents. Without Tentoring to offer any opinion on this theory, 
it may be sufficient to obserye that it is not positively at variance with any 
known fact; that the figure of the earth is really such as would be assumed 
by a fluid mass ; and, lastly, that it offers the best explanation we have of 
the phenomena of hot springs and volcanic eruptions, and agrees with the 
chemical nature of their products. 

The smaller, and what may be called secondary, sources of heat, are very 
numerous; they may be dirided, for the present, into two groups, me- 
chanical motion and chemical combination. To the first must be referred ele- 
vation of temperature by friction and blows ; and to the second, the effects of 
combustion and animal respiration. With regard to the heat developed by 
friction, it appears to be indefinite in amount, and principally dependent 
upon the nature of the rubbing surfaces. An experiment of Count Rumford 
is on record, in which the heat developed by the boring of a brass cannon 
was sufficient to bring to the boiling-point two and a half gallons of water, 
while the dust or shavings of metal, cut by the borer, weighed a few ounces 
only. Sir H. Davy melted two pieces of ice by rubbing them together in 
vacuo at 82^ (O^C) ; and uncivilized men, in various parts of the world, have 
long been known to obtain fire by rubbing together two pieces of dry wood. 
The origin of the heat in these cases is by no means intelligible. 

Malleable metals, as iron and copper, which become heated by hammering 
or powerful pressure, are found thereby to have their density sensibly 
increased and their capacity for heat diminished ; the rise of temperature is 
thus in some measure explained. A soh iron nail may be made red-hot by 
a few dexterous blows on an anril ; 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 aU probability fixed and definite ; its intensity is dependent upon 
the time over which the action is extended. Science has already been en- 
riched by many admirable, although yet incomplete, researches on this im- 
portant but most difficult subject. 

It is not improbable that many of the phenomena of heat, classed at present 
under different heads, may hereafter be referred to one common cause, 
namely, alterations in the capacity for heat of the same body under different 

* The new Artesian well at Grenelle, near Paris, has a depth of 1794*5 English feet: it ia 
bored through the. chalk hasin to the sand heneatb ; the work occupied seven years and two 
months. The temperature of the water, which is exceedingly abundant, is 820 (270-7C) ; thA 
mean temperature of Paris is 51o (10O-6C); the difference ia 31o (170*2C), which giyea a rate 
•f about 10 ( joG) for 58 feet. 

70 HBA». 

physical conditions.' For example, the definite absorption and eyolntion of 
sensible heat attending change of state may be simply dne to the increased 
capacity for heat, to a fixed and definite amount, of the liquid over the solid, 
and the vapour over the liquid. The experimental proof of the facts is yet 
generally wanting ; in the very important case of water, however, the deci- 
dedly inferior capacity for heat of ice compared with that of liquid water 
seems fully proved from experiments on record. 

-The heat of combination might perhaps, in like manner, be traced to con- 
densation of volume, and the diminution of capacity for heat which almost 
invariably attends condensation. The proof of the proposition in numerous 
coses would be within the reach of comparatively easy experimental inquiry. 

L^aHT* It 


The subject of light is so little connected with elementary chemistry, that 
a very slight notice of some of the most important points will snffice. 

Two yiews have been entertained respecting the nature of light. Sir 
Isaac Newton imagined that luminous bodies emitted, or shot out, infinitely 
small particles in straight lines, which, by penetrating the transparent part 
of the eye and falling upon the nervous tissue, produced vision. Other phi- 
losophers drew a parallel between the properties of light and those of sound, 
and considered, that as sound is certainly the effect of undulations, or little 
waves, propagated through elastic bodies in all directions, so light might be 
nothing more than the consequence of similar undulations transmitted with 
inconceivable velocity through a highly elastic medium, of excessive tenuity, 
filling all space, and occupying the intervals between the particles of mate- 
rial sabstances, to which they gave the name of ether. The wave-hypothesis 
of light is at present most in favour, as it serves to explain certain singular 
phenomena, discovered since the time of Newton, with greater facility than 
the other. 

A ray of light emitted from a luminous body proceeds in a straight line, 
and with eiLtreme velocity. Certain astronomical observations afford the 
means of approximating to a knowledge of this velocity. The satellites of 
Japiter revolve about the planet in the same manner as the moon about the 
earth, and the time required by each satellite for the purpose, is exactly 
known from its periodical entry into or exit from the shadow of the planet. 
The time required by one is only 42 hours. Aomer, the astronomer, at* 
Copenhagen, found that this period appeared to be longer when the earth, ia 
its passage round the sun, was most distant from the planet Jupiter, and, 
on the contrary, he observed that the periodic time appeared to be shorter 
when the earth was nearest to Jupiter. The difference, though very small, 
for a single revolution of the satellite, by the addition of many, so increases, 
during the passage of the earth from its nearest to its greatest distance 
from Jupiter, that is, in about half a year, that it amounts to 16 minutes 
and 16 seconds.*' Bomer concluded from .this, that the light of the sun 
reflected from the satellite, required that time to pass through a distance 
equal to the diameter of the orbit of the earth, and since this space is little 
short of 200 millions of miles, the velocity of light cannot be less than 200,000 
miles in a second of time. It will be seen hereafter that this rapidity of 
transmission is rivalled by that of the electrical agent. 

When a ray of light falls on a plane surface it may be disposed of in three 
ways ; it may be absorbed and disappear altogether ; it may be reflected, or 
thrown off, according to a particular law ; or it may be partly absorbed, 
partly reflected, and partly transmitted. The first happens when the surface 
is perfectly black and destitute of lustre ; the second, when a polished surface 
of any kind is employed; and the third, when the body upon which the light 
falls is of the kind called transparent, as glass or water. 

The law of reflection is extremely simple. If a line be drawn perpendi- 
cular to the surface upon which the ray falls, and the angle contained 
between the ray and the perpendicular measured, it will bo found that the 
lay, after reflection, takes sueh a course as to make with the perpendioulax 



an equal angle on the opposite of the latter^ A ray of light, a, fig. 46, 

falling at the point p, will be reflected in 
the direction pr^, making the angle b^pp^ 
equal to the angle bpp^ ; or a ray from 
the point r falling upon the same spot will 
be reflected to P in Tirtue of the seme 
law. Farther, it is to be observed, that 
the incident and reflected rays are always 
contained in the same vertical plane. 

The same rule holds good if the mirror 
be curved, as a portion of a sphere, the 
curve being considered as made up of a 
multitude of little planes. Parallel rays 
become permanently altered in direction when reflected from curved surfaces, 
becoming divergent or convergent according to the kind of curvature. 

It has just been stated that light passes in straight lines ; but this is only 
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 
Mg- *fl. into a new one, or, in optical lan- 

guage, is said to be refracted. 

Let r, fig. 46, be a ray of light 
falling upon a plate of some trans- 
parent substance with parallel sides, 
such as a piece of thick plate glass ; 
and a its point of contact with the 
upper surface. The ray, instead 
of holding a straight course and 
passing into the glass in the direc- 
tion a bf will be bent downwards 
to c ; and, on leaving the glass, and issuing into the air on the other side, 
It will ag^in be bent, but in the opposite direction, so as to make it parallel 
to the continuation of its former track. The general law is thus expressed : 
— ^When the ray passes from a rare to a denser medium, it is usually refracted 
towards a line perpendicular to the surface of the latter ; and conversely, 
when it leaves a dense medium for a rarer one, it is refracted from a line 
perpendicular to the surface of the denser substance : in the former case 
the angle of incidence is said to be greater than that of refraction ; in the 
latter, it is said to be less. 
The amount of refraction, for the same medium, varies with the obliquity 
with which the ray strikes the surface. When 
perpendicular to the latter, it passes without 
change of direction at all ; and in other posi- 
tions, the refraction increases with the obli- 

Let B, fig. 47, represent a ray of light fall- 
ing upon the surface of a mass of plate glass 
at the point a. From this point let a perpen- 
dicular be raised and continued into the new 
medium, and around the same point, as a 
centre, let a circle be drawn. According to 
the law just stated, the refraction must be to- 
wards the perpendicular ; in the direction ar' 
for example. Let the lines a — a, a^ — a^, at 
right angles to the perpendicular, be drawn, 
tad their length compared by means of a scale of equal parts, and noted ; 

Kg. 47. 



their lengtii will be in the case snp^sM in the proportion of 8 to 2. These 
lines ure termed the sines of the angles of incidence and refiraction, re- 

Now let snothet* itey be taken, snch as r ; it is refracted In the same man« 
ner to r% the binding being greater from the increased-^bliqnity of the ray ; 
bat what is yety remat'kable, if the sines of the t^o new angles of inci- 
dence and refraction be again compared thej iHll still be fonnd to bear to 
each other the proportion of 8 to 2. The fact is expressed by saying, that 
the ratio of the nnea of the incidence and refraction ia conetant for the oamt 

The pfane of refraction coincides moreover with that of incidence. 

Diiferenl bodies possess diifereiit l^fractive powers ; generttUy speaking, 
the densest Substances refhict most. Oombnstible bodies have been noticed 
to possess greater refractive power than their densitv would indicate, an4 
from this observation Sit I. Newton predicted the combustible nature of the 
diatoond long before anything was known respecting its chemical nature. 

The method adopted fbr describing the comparative refractive powers of 
differeat bodies is to fttate the ratio borne by the sine of the an^le of refrac- 
tion to tiiat of incidence, making the former unity : this is called the indei 
xf tefraetioH for the substance. Thus, iu the case of glass, the ifadei of re- 
fraction will be 1'5. When this is Once known for any particular trahsparent 
body, the effect of the latter upon a ray of light entering it, ili aiiy position, 
can be calculated by the aid of the law of sines. 

Index of refraBtlon. 

Tabasheer' 110 

Ice 1-80 

Water .*. 1-84 

Pluor spar 1-40 

Plate glass 1-50 

Rock crystal 1-60 

Crysolite ....«.i. .......;* 1-69 

Bisulphide of Mrbotlt..;^; VTQ 


Garnet ; 1-80 

Olass, with much oxide 

of lead 1'90 

85ircon 200 

Phosphot-ns 2-20 

Diamond 2-50 

Chromaie of lead 800 

Fig. 48. 

When a luminous ray enters a mass of sttbstattee diffeiihg iii vefraetittt 
|N>ver from tiie air, and Whose suHkees tJfe liot pfl.r8ttel) it beeothes perma^ 
nenUy deflected from its eonrse and altered in its 
direction. It is upon this principle that the pro- 
perties of prisms and lenses depend. To take 
an example. — rLet fig. 48 represent a triangnlsr 
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 suiiace, 
and again, from a line perpendicular to the 

second surface on emerging into the air. ^he result wHl be a total change 
in the direction of the ray. 

A convex lens is thus enabled to cohverge rays of light falling upon it, 
and a concave lens to separate them more widely ; eabh Separate part of the 
surface of the lens producing its own independent effect. 

The light of the snii and celestial bodies in general^ M Well is thttt Of ^he 
electric spark, and of all ordinary flames, is of a oompound tkature. If a tif 
of light from any of tiie sources mentioned be admitted iute a dark room by ft 
iBiall hole in the shutter, or otherwise (figv 49), and eiif%r«d to fall t:poti « 

» A SiUOTow depofltt !b the joints «f tM iMaMUM. 


glass prism in the manner described above, it will not only be refracted from 
its straight course, but will be decomposed into a number of coloured rajs, 
which may be receiyed upon a white screen placed behind the prism. When 
fiolar light is employed, the colours are extremely brilliant, and spread into 
an oblong space of considerable length. The upper part of this image or 
spectrum will be violet, and the lower red, the intermediate portion, com- 
mencing from the violet, being indigo, blue, green, yellow, and orange, all 
graduating imperceptibly into each other. This is the celebrated experiment 
of Sir I. Newton, and from it he drew the inference that white light is com- 
posed of seven primitive colours, the rays of which are differently refran- 
gible by the same medium, and hence capable of being thus separated. The 
violet rays are most refrangible, and the red rays least. 

Sir D. Brewster is disposed to think, that out of Newton's seven primitive 
colours four are really compound, and formed by the superposition of the 
three remaining, namely, blue, yellow, and red, which alone deserve the 
name of primitive. When these three kinds of'.rays. are mixed, or super- 
imposed, in % certain definite manner, they prodi^^e white' light, but when 
one or two of them are in excess, then an effect of colour is perceptible, 
simple in the first case, and compound in the second. There are, according 
to tills hypothesis, rays of all refrangibilities of each colour, and conse- 
quently white light in every part of the spectrum, but then they are une- 
qually distributed ; the blue rays are more numerous near the top, the yel- 
low towards the middle, and the red at the bottom, the excess of each colour 
producing its characteristio effect. In the diagram below (fig: 50) the inten- 
sity of each colour is represented by the height of a curve, and the effects 
of mixture will be intelligible by a little consideration. 

Fig. 60. 


> Bodies of tiie same mean refractive power do not always equally disperse 
or spread out the differently coloured rays ; because the principal yellow or 
red rays, for instance, are equally refracted by two prisms of different ma- 
terials, it does not follow that the blue or the violet shall be similarly 
affected. Hence, prisms of different varieties of glass, or other transparent 
vubstances^ give, under umilar cirQumstanceSi very different spectra, both 

, LIGHT. 76 

as respects the length of the image, and the relative extent of the coloured 

The colours of natural objects are supposed to resnlt from the power 
which tbe surfaces of the bodies possess of absorbing some of the coloured 
rays, while they reflect or transmit, as the case may be, the remainder. 
Thus, an object appears red because it absorbs, or causes to disappear, a 
portion of the yellow and blue rays composing the white light by which it is 

A ray of common light made to pass through certaia crystals of a par- 
ticular order is found to undergo a very remarkable change. It becomes 
split or divided into two rays, one of which follows the general law of refrao- 
tion, and the other takes a new and extraordinary course, dependent on the 
position of the crystal. This effect, which is called double refraction, is 
beautifully illustrated in the case of Iceland spar, or crystallized carbonate 
of lime. On placing a rhomb of this substance on a piece of white paper, 
on which a mark or line has been made, the object will be seen double. 

Again, if a ray of light be suffered to fall upon a plate of glass at an angle 
of 5ti® 46', the portion of the ray which suffers reflection will be found to 
have acquired properties which it did not before possess ; for on throwing 
it, under the same angle, upon a second glass plate, it will be observed that 
there are two particular positions of the latter in which the ray ceases to 
be reflected. Light which has suffered this change is said to he polarized. 

The light which passes through the first or polarizipg . 
plate, is also to a certain extent in this peculiar condi- 
tion, and by employing a series of similar plates (fig. 51), 
held parallel to the first, this effect may be greatly in- 
creased ; a bundle of fifteen or twenty such plates may 
be used with great convenience for the experiment. It is 
to be remarked, also, that the light polarized by trans- 
mission in this manner is in an opposite state to that 
polarized by reflection; that is, when examined by a 
second or analyzing plate, held at the angle before men- 
tioned, it will be seen to be reflected when the other dis- 
appears, and to be absorbed when the first is reflected. 

It is not every substance which is capable of polarizing 
light in this manner ; glass, water, and certain other bo- 
dies, bring about the change in question, each having a 
particular polarizing angle at which the effect is greatest. The metals also 
can, by reflection, polarize the light, but they do so very imperfectly. The 
two rays into which a pencil of common light divides itself in passing 
Ibrough a doubly-refracting crystal are found on examination to be polarized 
in a very complete manner, and also transversely, the one being capable of 
reflection when the other vanishes. It is said that both rays are polarized 
in opposite directions. With a rhomb of transparent Iceland spar of toler- 
ably large dimensions the two oppositely-polarized rays may be widely sepa- 
rated and examined apart. 

There is yet another method of polarization, by the employment of plates 
of the mineral tourmaline cut parallel to the axis of the crystal. This body 
polarizes by simple transmission, the ray falling perpendicular to its surface ; 
a part of the light is absorbed, and the remainder modified in the manner 
described. When two such plates are held with their axes parallel, as in 
H' 52, light traverses them both freely ; but when one of them is turned 
round in the manner shown in fig. 63, so as to make the axes cross at right 
wgles, the light is almost wholly stopped, if the tourmalines be good. A 
plate of the mineral thus becomes an excellent test for discriminating be- 
tween the polarized light and that which has not undergone the change. 

^me of the most splendid phenomena of the science of light ar« exhibltetf 




wig. 69. 

vh^n thin plates of doubly-refracting substances i^re interposed between the 
polarizing arrangement and the analyzer. 

Instead of the tourmalins plate, which is always coloured, frequent use 
is made of two Nichol's prisms, or conjoined prisms of carbonate of lime, 
i^hich, in consequence of a peculiar cutting and combination, possess the 
property of allowing only one of the oppositely polarized rays to pass. If 
the two Nichol's prisms are placed one behind the other in precisely si^iilar 
positions, the light polarized by the one goes through the other unaltered. 
But when one prism is slightly turned round in its setting, a cloudiness is 
produced^ and by continuing to turn the prism this increases until perfect 
darkness ensues. This happens, as with the tourmaline plates, when the 
two prisms cross one another- The phenomenon is the same with colourless 
as with coloured light. 

Supposing that polarized light, coloured, for example, by goivg through a 
plate of red glass, passed through the first Nicholas prism and was a.ltogether 
obstructed in consequence of the position of the second prism, then if be- 
tween the two prisms a plate of rock crystal, formed by a section at right 
angles to the principal axis of the crystal, is interposed, the light polarized 
by the first prism by passing through the plate of quartz is enabled par- 
tially to pass through the second Nichol's prism. Its passage through the 
Beoond prism can then again be interrupted by turning the second prism 
round to a tjertain extent. The rotation required Taries with the thickness 
of the plate of rock crystal, and also with the colour of the light that is 
employed. It increases from red in the following order, green, yellow, blue, 

ThiA property of rock crystal was discoyered by Araga The kind of 
polarization has been called circular polarization. No other crystals are 
known to produce the same effect. The direction of the rotation is with 
many plates towards the right hand ; in other plates it is towards the left. 
The one class is said to possess ri^ht-handed polarization ; the other class 
left-handed polarization. 

Biot observed that mai^y solutions of organic substances exhibit the pro- 

?erty of circular polarization, though to a far less extent than rock crystal, 
hus, solution of cane-sugar and tartaric acid possess right-handed polari- 
zation, whilst albumen, grape-sugar, and oil of turpentine, are left-handed. 
In all these sol^tion8 the amount of circular polarization increases with the 
concentration of the fluid and the thickness of the column of liquid through 
which the light passes. Hence circular polarization is an important auxiliary 
in chemical analysis. In order to determine the amount of polarization 
which any fluid exhibits, the liquid is put into a glass tube not less than 
from ten to twelve inches long, which is closed with glass plates, one of 
which should be coloured, red for example. This is then placed between 
the two Nichol's prisms, which have previously been so arranged with regard 
to eAch other that no light could pass through. An apparatus of this de- 
scription, the saccharometer, is chiefly used for determining the concentra- 
t|Q]) of solutions of sugar. 

LIGHT. 77 

Faraday has made tlie remarkable discovery, that if a very strong electric 
current is passed round a substance which possesses the property of circular 
polarization, the amount of rotation is altered to a considerable degree. 

The laminous rays of the sun are accompanied, as already mentioned, by 
others which possess heating powers. If the temperature of the different 
coloured spaces in the spectrum be tried with a delicate thermometer, it 
will be found to increase from the violet to the red extremity, and when the 
prism is of some particular kinds of glass, the greatest effect will be mani- 
fest a little beyond the visible red ray. It is inferred from this that the 
chief mass of the heating rays of the sun are among the least refrangible 
components of the solar beam. 

Again, it has long been known that chemical changes both of combination 
and of decomposition, but more particularly the latter, could be effected by 
the action of light. Chlorine and hydrogen combine at common tempera- 
tures only under the influence of light, and parallel cases occur in gpreat 
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 (he ray which effects these changes ; they 
are produced by certain invisible rays accompanying the others, and which 
are found most abundantly in and beyond the violet part of the spectrum. 
It is there that the chemical effects are most marked, although the intensity 
of the light is exceedingly feeble. The chemical rays are thus directly op- 
posed to the heating rays in the common spectrum in their degree of refran* 
gibility, since they exceed all the otliers in this respect. 

In the year 1802/ Mr. Thomas Wedgwood proposed a method of copying 
paintings on glass by placing behind them white paper or leather moistened 
with a solution of nitrate of silver, which became decomposed and blackened 
by the transmitted light in proportion to the intensity of the latter; and 
Davy, in repeating these experiments, found that he could thus obtain tole- 
rably accurate representations of objects of a texture partly opaque and 
partly transparent, such as leaves and the wings of insects, and even copy 
with a certain degree of success the images of small objects obtained by the 
solar microscope. These pictures, however, required to be kept in the dark, 
and only examined by candle-light, otherwise they became obliterated by 
the blackening of the whole surface from which the salt of silver could not 
be removed. These attempts at light-painting attracted but little notice till 
the publication of Mr. Fox Talbot's* papers, read before the Royal Society, 
in January and February, 1839, m which he detailed two methods of fixing 
the pictures produced by the action of light on paper impregnated witU 
chloride of silver, and at the same time described a plan by which the sen- 
sibility of the prepared paper may be increased to the extent required for 
receiving impressions from the images of the camera obscura. 

Very shortly afterwards. Sir John Herschel' proposed to employ solutions 
of the alkaline hyposulphites for removing the excess of chloride of silver 
from the paper, and thus preventing the farther action of light, and this 
plan has been found exceedingly successful. The greatest improvement, 
however, which the curious art of photogenic drawing has received, is due 
to .Mr. Talbot,* who, in a communication to the Royal Society, described a 
method by which paper of such sensibility could be prepared as to permit 
its application to the taking of portraits of living persona by the aid of a 
good camera obscura, the time required for a perfect impression never ex-, 
ceeding a few minutes. The portraits executed in this manner by Mr. 
Collen and others are beautiful in the highest degree, and leave little room 
for improvement in any respect. The process itself is rather complex, anU 

* Journal of the Royal Institution, i. 170. * Phil. Rtajr. March, 1839 

■ Phil. Trans, for 1840, p. 1. * Phil. Mag. August, VOX, 


7a- naKT.r 

dflD^mcU a gre$t niunber of mmute pi^eavtioQa, only to be leaTnod by exiie- 
i^euce, but which are indispensable to perfect BUccesB. The general plan is 
the following: — 

Writing-paper of good quality is washed on one side with a moderately 
dilute solution of nitrate of silver, and left to dry spontaneously in a darlf 
room ; when dry, it is dipped into a solution of iodide of potassium, and 
again dried. These operations should bo performed by candle-light. When 
required for use, the paper thus coated with yellow iodide of silv^er is brushed 
over with a solution containing nitrate of silver, acetic acid, and galUo acid, 
and once more carefully dried by gentle w:armtb. This kalotyipe paper is so 
sensitive, that exposure to diffused daylight for one second sufiGices to make 
an impression upon it, and even the Ught 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 b^g re'versed ; 
to obtain positive copies nothing more is necessary than to place a piece of 
ordinary photographic paper prepared with chloride of silver beneath the 
kalotype impression, cover them with a glass plate, and expose the whole to 
the light of the sun for a short time. Before this can be done, the kalotype 
must however be fixed, otherwise it will blacken, and this is effected by im- 
mersion in a solution of hyposulphite of soda, and well washing with water. 

Sir John Herschel has shown that a great number of other substances can 
be employed in these photographic processes by taking advantage of the 
fiingular deoxidizing effects of certain portions of the solar rays. Paper 
washed with a solution of a salt of sesquioxide of iron becomes capable of 
receiving impressions of this kind, which may afterwards be made evident 
by ferrioyanide of potassium, or terchloride of gold. Vegetable colours are 
also acted upon in a very curious and apparently definite manner by the 
(different parts of the spectrum.* 

The Daguerreotype, the announcement of which was first made in the 
summer of 1839 by M. Daguerre, who had been occupied with this subject 
from 1826, if not earlier, is another remarkable inst'uice of the decomposing 
effects of the solar rays. A clean and highly-polished plate of sUvered 
copper is exposed for a certain period to tiie vapour of iodine, and then 
transported to the camera obscura. In the most improved state of the pro- 
cess, a very short time suffices for effecting the necessary change in the film 
of iodide of silver. Tile picture, however, only becomes visible by exposing 
it to the vapour of mercury, which attaches itself, in the form of exceed- 
ingly minute globules, to those parts which have been most acted upon, that 
is to say, to the lights, the shadows being formed by the dark polish of the 
metallic plate. Lastly, the drawing is washed with a solution of hyposul- 
phite of soda to remove the undecomposed iodide of silver, and render it 

The images of objects thus produced bear the most minute examination -wltU 
a magnifying glass, the smaUest details being depicted with perfect fidelity. 

Great improvements have been necessarily made in the application of tliis 
beautiful art to taking portraits. By the joint use of bromine and iodine 
the plates are rendered far more sensitive, and the time of sitting is short- 
ened to a very few seconds. When the operation is completed the colour of 
the plate is much improved by the deposition of an exceedingly thin film of 
gold, wliich communicates a warm purplish tint, and removes the provioua 
dull leaden-grey hue, to most persons very offensive. 

> PhU. Trans. 1842, p. 1. 




If a red-hot bait be placed upon a metallio 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 convectiye power of the air; 
and the residue is thrown off from the heated body in straight lines or rays, 
which pass thnough air without interruption, and become absorbed by the 
sarfaces of neighbouring objects which happen to be presented to their 

This radiant or radiated heat resembles, in very many respects, ordinary 
light; it suffers reflection from polished surfaces according to the same law; 
it is absorbed by those that are dull or rough ; it moves with extreme velo- 
city ; and, finally, it traverses certain transparent media, undergoing refrac- 
tion at the same time, in obedience to the laws which regulate that pheno- 
menon in optics. 

The fact of the reflection of heat may be very easily proved. If a person 
stand before a fire in such a position that his face may be screened by the 
mantelshelf, and if he then take a bright piece of metil, as a sheet of tinned 
plate, and hold it in such a manner that the fire may be seen by reflection, 
at the same moment a distinct sensation of heat will be felt. 

The apparatus best fitted for studying these facts consists of a pair of con- 
cave metallic mirrors of the form called parabolic. The parabola is a curve 
possessing very peculiar properties, one of the most prominent being the 
following: — A tangent drawn to any part of the curve 
makes equal angles with two lines, one of which pro^ Tig, 64. 

ceeds from the point where the tangent touches the 
curve in a direction parallel to what is called the axis 
of the parabola, and the other from the same spot 
through a point in front of the curve, called the focus. 
It results from this that parallel Kiys, either of light 
or heat, falling upon a mirror of this particular curva- 
ture in a direction parallel to the axis of the parabola, 
will be all reflected to a single point at the focus ; and 
rays diverging from this focus, and impinging upon the 
mirror, will, after reflection, become parallel (fig. 54). 

If two such mirrors be placed opposite to each other 
at a considerable distance, and so adjusted that thoir 
axes shall be coincident, and a hot body placed in the 
focus of the one, while a thermometer occupies that of the other, the reflec- 
tion of the rays of heat will become manifest by their effect upon the instru- 
ment. In this manner, with a pair of by no means very perfect mirrors, 1» 
inchea in diameter, separated by an interval of 20 feet or more, amadou or. 



gnnpowdcr ma/ be readily fired by a red-hot ball in the focus of the oppo- 
site mirror (fig. 66). , 

Fig. 65. 

The power of radiation yaries exceedingly with different bodies, as may 
be easily proved. If two similar vessels of equal capacity be constructed 
of thin metal, and the surface of one highly polished, while that of the 
other is covered with lampblack, and both filled with hot water of the same 
temperature, and their rate of cooling observed from time to time with a 
thermometer, it will be constantly found that the blackened vessel loses heat 
much faster than the one with bright surfaces ; and since bot^ are put on a 
footing of equality in other respects, this difference, which will often amount 
to many degrees, must be ascribed to the superior emissive power of the film 
of soot. 

By another arrangement, a numerical comparison can be made of these 
differences. A cubical metallic vessel is prepared, each of whose sides is in 
a different condition, one being polished/ another rough, a third covered 
with lampblack, &c. This vessel is filled with water, kept constantly at 
212° (100°C) by a small steam-pipe. Each of its sides is then presented in 
succession to a good parabolic mirror, having in its focus one of the bulbs 
of the differential thermometer before described (fig. 22), the bulb itself 
being blackened. The effect produced on this instrument is taken as a 
measure of the comparative radiating powers of the different surfaces. 
The late Sir John Leslie obtained by this method of experiment the follow- 
ing results : — 

Smissive power. 

Lampblack 100 

Writing-paper 98 

Glass ^0 

Plumbago 76 

Emlssiye irawer. 

Tarnished lead 45 

Clean lead 19 

Polished iron 15 

Polished silver 12 

The best reflecting surfaces are always the worst radiators; polished 
metal reflects nearly all the heat that falls upon it, while its radiating power 
is the feeblest of any substance tried, an^ lampblack, which reflects nothing, 
radiates most perfectly. 

The power of absorbing heat is in direct proportion to the power of emis- 
sion. The polished metal mirror, in the experiment with the red-hot ball, 
remains quite cold, although only a few inches from the latter ; or, again, 
if a piece of gold leaf be laid upon paper, and a heated iron held over it 

* The formerly supposed influence of mere difTerence of surface has been called in questioa 
by M. Melloni, who attributes to other causes the eflPects observed by Sir John Leslie and 
others, among which superficial oxidation and difference of physical condition with respect 
to hardness and density, are among the most important. With motals not subject to tarnish, 
scratching the surface increases the emissive power when the plates have been rolled or 
hammered, t. 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 difEerence is perceptible in the 
wuiiating power of polished and rough surfaces. — Ann. Chim. et l»hy8. Ixx. 438. 

^ BA9IATI6H OF H9AT. 81 

mill tiiep^per is floiiipletely Boerche^ itinll b« foand fliat lli« fibn «r metal 

lias perfectly defead^d that portion beneath it. 
The faculty of absorption seems to be a good deal influenced by colour; 

Br. Franklin found that when pieces of cloth of yarious colours were placed 

on snow exposed to the feeble sunshine of winter, the snow beneath them 
became unequally melted, the effect being always in proportion to the depth 
of the colour; and Dr. Stark has since obtained a similar result by a dif>- 
ferent method of experimenting. According to the late researches of Mel- 
loni, this effect depends less on the colour than on the nature of the colourr 
ing matter which covers the surface of the cloth. 

These facts afford an explanation of two Tory interesting and important 
natural phen<M|iemt, 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 eempen- 
sated by the absorption of the solar beams ; but when the sun sets, and this 
supply ceases, while the emission of heat goes on as actively as before, the 
surface become cooled until its temperature sinks below that of the air. 
The air in contact with the e%rth of course pilirticipates in this reduction of 
temperature ; ;the aqueous vapour present speedily reaches, its point of max- 
imum density, and then begins to deposit moisture, whose quantity will de« 
pend upon the proportion of vapour in the atmosphere, and on the extent to 
vhich the coolixig process has l^en carried. 

It is observed that dew is most abundant in a dear ealm night, succeeding 
a hot day ; under the^e ciroumstances the quantity of vapour in the air is 
usually very great, and at the same time, radiation proceeds with most 
facility. At such times a thermometer laid on the ground will, after some 
time, indicate a temperature of 10° (S^-SC), IS® (80.8C), or even 2G« (11°1C) 
Wow that of the air a few feet higher. Clouds hinder the formation of dew, 
bjr reflecting back to the earth the heat radiated from its surface, and thus 
pre?enting the necessary reduction of temperature ; and the same effect is 
produced by a screen of the thinnest material. stretched at a little height 
above the ground. In this manner gardeners often preserve delicate plants 
from destruction by the frosts of spring and autumn. The piercing cold felt 
just before and at sunrise, even in the height of summer, is the consequence 
of tHU refrigeration having reached its maximum. 

Wiud^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 
(ooiad in the morning covered with dew, while the latter remains dry. 

Land and aea-breezes ^re certain periodical winds common to most seu'^ 
coabts 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 empires near sunset. Shortly after, a wind arises in 
exactly t^e oppostite direction, namely, from the land towards the sea, la&ts 
the whole of the night, Siud only ceases with the reappearance of the sun. 

It is easy to give an explanation of these effects. When the sun shines 
at once upon the surface of the earth and that of the sea, the two become 
unequally heated from their different absorbing power ; the land becomes 
niuch the warmer. The air over the heated surface of the ground, being ex- 
panded by heat, rises, and has its place supplied by colder air flowing from 
the 8ea» producing the ^a-breeze. When the sun sets, both sea and land 
begin to eeol by radiaticm ; the rate of the cooling of the latter will, how- 


iever, far exceed that of the former, and its temperature will rapidly fait 
The air above beconiing 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 
Buch 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. 


Rays of heat, in passing through air, receive no more obstruction than 
those of light under similar circumstances ; but with other transparent media 
the case is different. If a parabolic mirror be taken and its axis directed 
towards the sun, the rays both of heat and light will be reflected to the focus, 
which will exhibit a temperature sufficiently high to fuse a piece of metal, 
or fire a combustible body. If a plate of glass be now placed between the 
mirror and the sun, the effect'will be but little diminished. 

Now, let the same experiment be made with the heat of a kettle filled with 
boiling water ; the heat will be concentrated by reflection as before, but, on 
interposing the glas4, the heating effect at ihe focus will be reduced to 
nothing. Thus, the rays of heat coming from the sun traverse glass with 
facility, which is not the case with those emanating from the boiling water. 

In the year 1888, M. Melloni published the first of a series of exceedingly 
valuable researches on this subject, which are to be found in detail in various 
volumes of the Annales de Chemie et de Physique.* It will be necessary, in the 
first instance, to describe the method of operation followed by this philosopher. 
Not long before, two very remarkable facts had been 
Fig. 56. discovered: Oersted, in Copenhagen, showed that a 

current of electricity, however produced, exercises a 
singular and perfectly definite action on a magnetic 
needle ; and Seebeck, in Berlin, found that an electric 
current may be generated by the unequal effects of heat 
on different metals in contact. If a wire conveying an 
electrical current be brought near a magnetic needle, 
the latter will immediately alter its position and*assume 
a new one, as nearly perpendicular to the wire as the 
mode of suspension and the magnetism of the earth 
will permit.* When the wire, for example, is placed 
directly over the needle (fig. 56), while the current it carries travel^ 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 wiite below 
the needle instead of above produces the same effect as reversing the current. 
When the needle is subjected to the action of two currents in opposite 
directions, the one above and the other below. 
Fig. 67. they will obviously concur in their effects. 

The same thing happens when the wire carry- 
ing the current is bent upon itself (fig. 67), 
and the needle placed between the two por- 
tions ; and since every time the bending is re- 
peated, a fresh portiou of the current is made 
to act in the same manner upon the needle, it 
is easy to see how a current too feeble to pro- 
duce any effect when a simple straight wire is 

' Translated also in Tayloi's Scientific Memoirs. 





employed, may be inade bj this contriTance to exhibit a powerful action on 

the magnet. It is on this principle that instmments called galvanometerM, 
ffalvanoscopeSf or multipliers, are constrncted ; thej serre, not only to indicate 
the existence of electrical currents, but to show by the effect upon the needle 
the direction in which they are moving. By using a very long coil of wire, 
and two needles, immovably connected, and hung by a fine filament of silk, 
almost any degree of sensibility may be communicated to the apparatus. 

When two pieces of different metals, connected together at each end, have 
one of their joints more heated than the other, an electric current is imme- 
diately set up. Of all the metals tried, bismuth and antimony form the 
most powerful combination. A single pair of bars, having one of their juno- 
tions heated in the manner shown in fig. 58, can 
develop a current strong enough to deflect a 
compass-needle placed within, and, by ar- 
ranging a number in a series and heating their 
alternate ends, the intensity of the current may 
be very much increased. Such an arrangement 
is called a thermo-electric pile. M. Melloni 
constructed a thermo-electric pile of this kind, 
containing fifty-five slender bars of bismuth 
^ and antimony, laid side by side and soldered 
together at their alternate ends. He connected 
this pile with an exceedingly delicate multiplier, 

and found himself in the possession of an in- ' ^ 

strument for measuring small variations of temperature far surpassing in 
delicacy the air- thermometer in its most sensitive form, and having great 
advantages in other respects over that instrument when employed for the 
purposes to which he devoted it. 

The substances whose powers of transmission were to be examijied were 
cut into plates of a determinate thickness, and, after being well polished, 
arranged in succession in front of the little pile, the extremity of which was 
blackened to promote the absorption of the rays. (Fig. 69.) A perforated 

Fig. 59. 

screen, the area of whose aperture equalled that of the face of the piH' 
was placed between the source of heat and the body under trial, while a 
second screen served to intercept all radiation until the moment of the ex- 

After much preliminary labour for the purpose of testing the capabilitiefl 
of the apparatus and the value of its indications, an extended series of re- 
searches was undertaken and carried on during a long period with great 
success : some of the most curious results are given in the subjoined table. 

Four different sources of heat were employed in these experiments, dif- 
fering in their degrees of intensity : the naked flame of an oU-lamp ; a ooU 


¥BAN8MtS8IOll 09 HEAT. 

:DrpliKtiinmiHi« Rented to tedntMM; blAoktnfed «;opp«r «t 784« (890«C); aari 
ih« soiiM heated to 212<» (lOOoC).* 

(thickxiflas of plate 0*1 Inoh^ nearly.) 

TiraJiflttaUidiMi Of KX) n^ tff 


Bock-salt« transparent and colourless. 

Fluor*spar, colourless 

Bock-salt, mudd5' 


Fluor-spar, greenish 

Iceland-spat ,...„ , 

Plate-glass , 

Bock-crystal i... 

Bock-crystal, brown 

Toutmaline, dark green 

Citric acid, transparent 

Alum, transparent 


Fluor-spar, green, translucent ....^ 

Ice, pure and transparent '.... 














































On examining this remarkable table, which is an abstract of one much 
hiore extensive, the first thing that strikes the eye is the want of connection 
4>etween the power of transmitting heat and that of transmitting light; 
taking, for instance, the oil-lamp as the source of heat, out of a quantity of 
^eat represented by 100 rays falling upon the pile, the proportion intercepted 
by similar plates of rock-salt, glass, and alum, may be expressed by the 
numbers, 8, 61, and 91 ; and yet these bodies are equally transparent with 
respect to li^iit. Generally speaking, colour w^s found to interfere with the 
transmissive pother, but to a very unequal extent ; thus, in fluot'-spar, colour- 
less, greenisl^ and deep-greeti, the quantities transmitted were 78, 46, and 
8, while the diflference between colourless and brown rock-crystal was only 1. 
Bodies absolutely opaque, as wood, metals, and black marble, stopped the 
rays completely, although it was found that the faculty of transmission was 
possessed to a certain extent by some which were nearly in that condition, 
as thick plates of brown quartz, black mica, and black glass. 

When rays of heat had once passed through a plate of any substance, the 
interposition of a second similar plate occasioned much less loss than the 
first ; the same thing happened when a number were interposed ; the raya» 
after trayersing one plate, being but little interrupted by otiiers of a similar 

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 
iell on rock-salt^ the same proportion was always transmitted, whether the 
rays proceeded from the intensely heated flame, the red-hot platinum wire, 
oi^the copper at 734° {390°C) or 212° (100°C) j but this is true of no other 
Hubstance in the list In the case of plate-glass, we have the numbers 39, 
$4^ (i, oad 0^ as rc^resentatiTes of the comparati?e quantities of heat traas;- 


nitted through the pltfte from eaeh sooree ; or in the three Tarieties of flnor- 

Bpar, as below stated : — 

Flame. Bed-heat 784O(390°O- 212O(100°C>. 

Colourless 78 69 42 83 

Greenish 46 88 24 20 

Dark green 8 6 4 8 

TVhile one substance, beryl, ont of 100 rajs from an intensely heated 
eonrce, suffers 54 to pass, and from the same number (that is, an equal 
quantity of heat) from metal at 212^ (100<>G), none at all ; another, fluor- 
spar, transmits rays from the two sources mentioned, in the proportion of 
8 to 3. 

These, and many other curious phenomena, . are fully and completely 
explained on the supposition, that among the invisible rays of heat differ- 
ences are to be found exactly analogous to those differences between the 
rays of light which we are accustomed to call colours. Rock-salt and air are 
the only substances yet known which are truly diaihermanoua, or equally 
. transparent to all kinds of heat-rays ; they are to the latter what white glass 
or water is to light ; they suffer rays of every description to pass with equal 
facility. All other bod^s act like coloured glasses, absorbing certain of the 
. rays more abundantly than the rest, and colouring, as it were, the heat which 
passes through them. 

These heat-tints have no direct relation to ordinary colours ; their exist- 
ence is, nevertheless, almost as clearly made out as that of the coloured 
rays of the spectrum. Bodies at a comparatively low temperature emit rays 
of such a tint only as to be transmissible by a few substances ; as the tem- 
perature rises, rays of other heat-colours begin to make their appearance, 
and transmission of some portion of these rays takes place through a greater 
number of bodies ; while at the temperature of intense ignition we find rays . 
of an colours thrown out, some or other of which will certainly find their 
way through a great variety of substances. 

By cutting rock-salt into prisms and lenses, it is easy to show that radiant 
heat may be reflected like ordinary light, and its beams made to converge 
or diverge at pleasure ; and, lastly, to complete the analogy, it has been 
Bhown to be susceptible of polarization by transmission through plates of 
doubly-refracting minerals, in the same manner as light itself.^ 

* Dr. Vorbes, PhiL Hag. for 1835; also M. Melloni, Ann. Chem. et Pbys. Izv. 6. 

'93 M'A^NE1?ISM. 


A PASTicvxAB species of iron ore has long been nemtokable for its pro- 
perty of attracting small pieces of iron, and causing them to adhere to its 
surface : it is called loadstone, or magnetic iron ore. 

If a piece of this loadstone be carefully examined, it will be found that 
the attractive force for particles of iron is greatest at cei^tain particular 
points of its surface, while elsewhere it is much diminished, o^ -even alto- 
gether absent. These attractive points, or centres of ^greatest force, are 
denominated poles, and ike loadstone itself is said to be endued with mag- 
netic polarity. 

If one of the poles of a natural loadstone be rubbedjn a paftieular man- 
ner over a bar of steel, its characteristic properties will be communicated 
to the bar, which will then be found to attract iron-filings like the loadstone 
itself. Farther, the attractive force will be greatest at two points -'situated 
very near the extremities of the bar, and least of all towards the middle. 
The bar of steel so treated is said to be magnetised, or to constitute an arti- 
ficial naagnet. 

When a magnetised bar or natural magnet is suspended at it& 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 witii 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 distingui^ed as the north pole of the bar, ahd that which 
points southward, as t^be south pole. A suspended magnet, either natural 
or artificial, of symmetrical form, serves to exhibit certain phenomena of 
attraction and repulsion in the presence of a second magnet, which deserve 
particular attention. When a north pole is presented to a south pole, or a 
south pole to a north, attraction ensues betwe^i them ; the ends of the bars 
approach each other, and, if permitted, adhere with considereble force; 
when, on the other hand, a north pole is brought near a second north pole, 
or a south pole near another south pole, mutual repulsion is observed, and 
the ends of the bars recede from each other as far as possible. Poles of an 
opposite name attract, and of a similar name repel each other. Thus, a small 
bar or needle of steel, properly magnetized and suspended, and having its 
poles marked, becomes an instrument fitted not only to discover the exist- 
ence of magnetic power in other bodies, but to estimate the kind of polarity 
affected by their different parts. 

A piece of iron brought into the neighbourhood of a magnet acquires itself 
magnetic properties; the intensity of the power thus conferred depends 
upon that of the magnet and upon the interval which divides the two ; be- 
coming greater as that interval decreases, and greatest of all when in actual 
contact. The iron under these circumstances is said to be magnetized by 
induction or influence, and the effect, which in an instant reaches its maxi- 
mum, is at once destroyed by removing the magnet. 

When steel is substituted for iron in this experiment, the inductive action 
is hardly perceptible at first, and only becomes manifest after the lapse of a 
oertaioi time ; in this condition, when the steel bar is removed from the mag- 




net, it rotahn & portion of the iodiio^d polAiity. It becomwi indeed, & pe»- 
maDent magnet, similar to the first, and retains its peculiar properties foe 
ftn indefinite period. 

A particular name is given to this resistance which steel always offers in 
a greater or less degree both to the development of magnetism a^d ita sub* 
seqnent destruction ; it is called apedjic coercive power^ 

The rule which regulates the induction of magnetic polarity in all oasee 
is exceedingly simple, and most important to be remembered. The pole pro- 
duced is always of the opposite name 
to that which produced it^ a north pole Is- 00. 

deyeloping south polarity, and a south 
pole north polarity. The north pole of 
the magnet, shown in'fig. 60, induces 
south polarity in all the nearer extrcr 
mities of the pieces of iron or steel 
which surround it, and a state similar 
to its own in all the more remote extre- 
mities. The iron thus magnetized is 
capable of exerting a similar inductive 
action on a second piece, and that upon 
a third, and so to a great number, the 
intensity of the force diminishing as 
the distance from the permanent mag- 
net increases. It is in this way that a 
magnet is enabled to hold up a number 
of small pieces of. iron, or a bunch of 
filings, each separate piece becoming a 
magnet for the time by induction. 

Magnetic polaiity, similar to that which iron presents, has been fbund 
only in some of the compounds of iron, in nickel, and in cobalt. 

Magnetio attractions and repulsions are not in the slightest degree inter- 
fered with by the interposition of substances destitute of magnetic proper- 
ties. Thick plates of glass, shellac, metals, wood, or of any substances 
except those above mentioned, may be placed between a magnet and a sus- 
pended needle, or a piece of iron under its influence, the distance being pre- 
served, without the least perceptible alteration in its attractive power, or 
force of induction. 

One kind of polarity cannot be exhibited without the other. In other 
words, a magnetic pole cannot be insulated. If a magnetized bar of steel 
be broken at its neutral point, or in the middle, each of the broken ends ac- 
quires an opposite pole, so that both portions of the bar become perfect 
magnets ; and, if the division be carried still farther, if the bar be broken 
into a hundred pieces, each fragment will be a complete magnet, having its 
own north and south poles. 

This experiment serves to show very clearly that the apparent polarity of 
the bar is the consequence of the polarity of each individual particle, the 
poles of the bar being merely points through which the resultants of all 
these forces pass ; the large magnet is made up of an immense number of 
little magnets regularly arranged side by side (fig. 61), all havihg their north 

Pig. 61. 


poles looldBg one way, and their south poles the other. The middle portion 
of such a system cannot possibly exhibit attractive or repnlsiye 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 foi^ces will be exerted in op- 
posite directions and neutralize each other's influence. Such will not be the 
case at the extremities of the bar ; there uncompensated polarity will be 
found capable of exerting its specific power. 

This idea of regular polarization of particles of matter in virtue of a pair 
of opposite and equal forces, is not confined to magnetic phenomena ; it is 
the leading principle in electrical science, and is constantly reproduced in 
some form or other in every discussion involving the consideration of mole- 
cular forces. 

Artificial steel magnets are made in a great variety of forms ; such as 
small light needles, mounted with an agate cap for suspension upon a fine 
point ; straight bars of various kinds ; bars curved into the shape of a horse- 
shoe, &.C. All these have regular polarity communicated to them- by cer- 
tain processes of rubbing or touching with another magnet, which require 
care, but are not otherwise difficult of execution. When great power is 
wished for, a number of bars may be screwed together, with their similar 
ends in contact, and in this way it is easy to construct permanent steel mag- 
nets capable of sustaining great weights. To prevent the gradual destruc- 
tion of magnetic force, which would otherwise occur, it is usual to arm eacli 
pole with a piece of soft iron or keeper, which, becoming magnetized by in* 
duction, serves to sustain the polarity of the bar, and even increases in some 
oases its energy. 

The direction spontaneously assumed by a suspended needle indicates that 
the earth itself has the properties of an enormous magnet, whose south pole 
is in the northern hemisphere. A line joining the two poles of such a 
needle or bar indicates the direction of the magnetic meridian of the place, 
which is a vertical plane coincident with the direction of the needle. 

The magnetic meridian of a place is not usually coincident with its geo~ 
graphical meridian, but makes with the latter a certain angle called the de^ 
clination of the needle ; in other words, the magnetic poles are not situated 
within the line of the axis of rotation. 

The amount of this declination of the needle from the true north and 
south not only varies at different places, but in the same place is subject to 
daily, yearly, and secular fluctuations, which are called the variations of 
declination. Thus, at the commencement of the 17th century, the declina- 
tion was eastward ; in 1660, it was ; that is, the needle pointed due north 
and south. Afterwards it^became westerly, slowly increasing until the year 
1818, when it reached 24° 30'', since which time it has been slowly di- 

If a steel bar be supported on a horizontal axis passing exactly through 
its centre of gravity, it will of course remain equally balanced in any posi- 
tion in which it may happen to be placed ; if the bar so adjusted be thea 
magnetized, it will be found to take a permanent direction, the north pole 
being downwards, and the bar making an angle of about 70^, with a hori- 
zontal plane passing through the axis. This is called the dip^ or inclination 
of the needle, and shows the direction in which the force of terrestrial mag- 
netism is most energetically exerted. The amount of this dip is different in 
different latitudes ; near the equator it is very small, the needle remaining 
nearly or quite horizontal ; as the latitude increases the dip becomes more 
decided ; and over the magnetic pole the bar becomes completely vertical. 
Such a situation is in fact^to be found iu the northern hemisphere, consider- 
ably to the westward of the geographical pole, in Prince Regent's Inlet, 
lat. 70^ 5^ N. and longitude 96° 46^ W. ; the dipping-needle has here been 


sees to pomt direetfy ia mn w nr da, iridle tii« korixontiil or eonpan-needl* 
ceued to tnTerse. The position of the south magoetio pole has lately bees 
determined, by the obeerratioBS of Captain Boss, to be abont lat. 7$« S. and 

long. }3QPE. 

By obeerfing a great nmaber of points near the equator in whieh 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 tides, a number 
of smaller circles, called lines of equal dip. These lines present great irreg- 
nlaritifls when compared with the equator itself and the parallels of lati- 
tude, the magnetie equator doriating from the terrestrial one as much as 12* 
at its point of greatest divergence. Like the horizontal decfinatton, the dip 
is also subject to change at the same place. Obserrations have not yet been 
made during sufEicient time to determine accurately the law and rate of alte- 
ration, and great practical difficulties erist also in the construction of the 
instroments. In the year 1778 it was about 7tiP ; at the present time it is 
near 69° 5^ in London. 

The induetiTe power of the magnetism of the earth may be shown by 
holding in a rertical position a bar of very soft iron ; the lower end will be 
foand to possess north polarity, and the upper, the contrary state. On re- 
versing the bar the poles are also reversed. All masses of iron whatever, 
when examined by a suspended needle, will be found in a state of mngnetio 
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-tanlra, &c., thus polarized by the eartib, 
eaases a derangement of the compass-needles to a very dangerous extent ; 
happily, a plan has been devised for determining the amount of this local 
attraction in different positions of the ship, and making suitable corrections. 

The mariner's compass, which is nothing more than a suspended needle 
attached to a circular card marked with the points, was not in general use 
in Europe before the year 1300, although the Chinese have had it from very 
early antiquity. Its value to the navigator is now very much increased by 
correct observations of the exact amount of the declination in various parts 
of the world. 

Probably every substance in the world contributes something to the mag- 
netic action of the earth ; for, according to the latest discoveries of Mr. 
Faraday, magnetism is not peculiar to those substances which have moro 
especially been called magnetic, such as iron, nickel, cobalt, but it is the 
property of all matter, though to a much smaller degree. Very powerful 
magnets are required to show this remarkable fact. Large horse-shoe mag- 
nets, made by the action of the electric current, are most proper. The 
magnetic action on different substances which are capable of being easily 
moved, differs not only according to the size, but also according to the nature 
of the substance. In consequence of this, Faraday divides all bodies into 
two classes. He calls the one magnetic, or, better, paramagnetic, and the 
other diamagnetic. 

The matter of which a paramagnetic (magnetic) body consists is attracted 
by both poles of the horse-shoe magnet ; on the contrary, the matter of a 
diamagnetic body is repelled. When a small iron bar is hung by untwisted 
Bilk between the poles of the magnet, so that its long diameter can easily 
move in a horizontal plane, it arranges itself axially, that is, parallel to the 
straight line which joins the poles, or to the magnetic axis of the poles ; 
assuming at the end which is nearest the north pole, a south pole, and at 
the end nearest the south pole, a north pole. Whenever the little bar is 
removed from this position, after a few oscillations, it returns again to its 
Kerious position. The irhole class of paramagnetic bodies behave in a pr€- 


elMly rinilttr way under itoflar ciiemnsteiieefl ; obIj in the intenrity «f Oe 
effects great differences oocnr. 

On the contrary, diamagnetic bodies hare their long diameters placed 
equatorialljr, that is, at right angles to the magnetic axis. They behare, as 
if at the end opposite to each pole of the magnet, the same kind of polarity 

In the first class of substances, besides iron, which is the best represents* 
tive of the class, we hare nickel, cobalt, manganese, chromium, cerium, 
titanium, palladium, platinum, osmium, aluminium, oxygen, and also most 
of the compounds of these bodies ; most of them, eren when in solution. 
According to Faraday, the following substances are also feebly paramagnetie 
(magnetic) ; paper, sealing-wax, indian-ink, porcelain, asbestos, fluor-spar, 
minium, cinnabar, binoxide of lead, sulphate of sine, tourmaline, graphite, 
And charcoal. 

In the second class are placed bismuth, antimony, sine, tin, cadmium, 
sodium, mercury, lead, silver, copper, gold, arsenic, uranium, rhodium, 
iridium, tungsten, phosphorus, iodine, sulphur, chlorine, hydrogen, and many 
of their compounds. Also, glass free from iron, water, alcohol, ether, nitrio 
acid, hydrochloric acid, resin, wax, olive oil, oil of turpentine, caoutchouc, 
sugar, starch, gum, and wood. These are diamagnetic. 

If diamagnetic and paramagnetic bodies are combined, their peculiar pro- 
perties are destroyed. In most of these compounds, occasionally, in conse- 
quence of the presence of the smallest quantity of iron, the peculiar mag- 
netic power remains more or less in excess. Thus green bottle glass and many 
varieties of crown glass are magnetic in consequence of the iron in ihem. 

In order to examine the magnetic properties of fluids they are placed in 
very thin glass tubes, the ends of which are closed by melting, they 
are then hung horizontally between the poles of the magnet. Under the 
influence of poles sufficiently powerful, they begin to swing, and accord- 
ing as the fluid contents are paramagnetic (magnetic), or diamagnetic, they 
assume an axial or equatorial position. 

Under certain circumstances substances which belong to the paramagnetic 
class behave as if they were diamagnetic. This happens in consequence of 
a differential action. Thus, for example, when a glass tube full of a dilute 
solution of sulphate of iron is allowed to swing in a concentrated solution 
^f sulphate of iron, instead of in the air, it assumes an equatorial position. 
The air, in consequence of the oxygen in it, is itself paramagnetic (magnetic). 
Hence such bodies as appear to possess feeble diamagnetic properties, can 
only show their true properties when hung in a vacuum. 

Faraday has tried the magnetic condition of gases in different ways. One 
way consisted in making soap bubbles with the gas which he wished to in- 
vestigate, and bringing Siese near the poles. Soap and water alone is feebly 
diamagnetic. A bubble filled with oxygen was strongly attracted by the 
magnet. All other gases in the air are diamagnetic, that is, they are re- 
pelled. But, as Faraday has shown, in a different way, this partly arises 
from the paramagnetic (magnetic) property of the air. Thus he found that 
nitrogen, when this cUnerential action was eliminated, was perfectly indif- 
ferent, whether it was condensed or xarified, whether cooled or heated. 
IrYhen the temperature is raised, the diamagnetic property of gases in the 
air is increased. Hence the flame of a candle or of hydrogen is strongly 
repelled by the magnet. Even warm air is diamagnetic in cold air. 

For some time it has been believed that bodies in a crystalline form had a 
special and peculiar behaviour when placed between the poles of a magnet. 
It appeared as though the magnetic directing power of the crystal had some 
peculiar relation to the position of. its optic axis ; so that, independently of 
the magnetic property of the substance of the crystal, if 4he crystal i 


pontitely optiesi, it posMSted Oe power of plftdiig its optio uia psranel 
irith the line which joined the poles of the mag;net, while optically negative 
crystals tried to arrange their axes at right angles to this line. This sappo- 
sitioD is disproved by Uie excellent investigation of Knoblauch and TyndalL 
It follows fh>m their observations that the peenliaritj in regard to crystals 
is dependent on their internal state of cohesion, that is, on unequal com* 
preasion in different directions. If crystalline, or even nncrystalline sab- 
Btanoes are nneqnally compressed in clifferait directions, they are found to 
possess a preponderating directive force in the direction in which they aro 
most strongly compressed, so that when this direction does not coincide with 
the long diameter of the body, magnetic bodies will even anango themielvM 
eqnstoiiaUy, and diamagnetic bodies aziaUy. 



If glass, amber, or sealing-wax, be mbbed with a dry c1o€h, 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 nibbed, called elec- 
trical excitation. 

If a light downy feather be suspended' by a thread of white silk, and a 
dry glass tube, excited by rubbing, be presented to it, the feather will be 
strongly attracted to the tube, adhere to its surface for a few seconds, and 
then fall off. If the tube be now excited anew, and presented to the feather, 
the latter will be strongly repelled. 

The same experiment may be repeated with shellac or resin ; the feather 
in its ordinary state will be drawn towards the excited body, and after 
touching, again driTen from it with a certain degree of force. 

Now, let the feather be brought into contact with the excited glass, so as 
to be repelled by that substance, and let a piece of excited sealing-wax be 
presented to it ; a degree of attraction will be obserred far exceeding that 
exhibited when the feather is in its ordinary state. Or, again, let the feather 
be made repulsiyc for sealing-wax, and then the excited glass be presented ; 
strong attraction will ensue. 

The reader will at once see tlie perfect parallelism between the effects 
described and some of the phenomena of magnetism ; the electrical excite- 
ment haying 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 exciteii glass and resin being to each other as the north and south poles 
of a pair of magnetized bars. 

To distinguish these two different forms of excitement, terms are em- 
ployed, which, although originating in some measure in theoretical yiews of 
the nature of the electrical disturbance, may be understood by the student 
as purely arbitrary and distinctiye ; it is customary to call the electricity 
manifested by glass positive or vitreous, and that deyeloped in the case of 
shellac, and bodies of the same class, negative or resinous. The kind of elec- 
tricity depends in some measure upon the nature of the surface ; smooth 
glass rubbed with silk or wool becomes ordinarily positiye, 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 adyan- 
tage of to construct instruments for indicating electrical excitement and 
pointing out its kind. Two balls of alder-pith (fig. 62), hung by threads or 
ycry fine metal wires, serye this purpose in many cases ; they open out when 
excited, in yirtue of their mutual repulsion, and show by the degree of diyer- 
gencc the extent to which the excitement has been carried. A pair of gold 
leaves suspended beneath a bell jar, and communicating with a metal cap 
above (fig. 63), constitute a much more delicate arrangeipent, and one of 
great value in all electrical investigations. These instruments are called 
electroscopes or electrometers; when excited by the communication of a 
known kind of electricity, they show, by an increased or diminished diver- 
gence, the state of an electrified body brought into their neighbourhood. 


Tig. 62. Fig. 63. 


o iL b 

One kind of electricity can no more be deyeloped without the other than 
one kind of magnetism; the rubber and the body rubbed always assume 
opposite states, and the positiTe 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 eleo* 
tricity ; a body already electrified disturbs or polarizes the particles of all 
surrounding substances in the same manner and according to the same law, 
inducing a state opposite to its own in the nearer portions, and a similar 
state in the more remote parts. A series of globes suspended by silk threads, 
in the manner represented in fig. 64, will each become electric by induction 

Kg. 64. 

. Q -Q* Q*- -Q+ -Q* 

when a charged body is brought near the end of the series, like so many 
pieces of iron in the vicinity of a magnet, the positive half of each globe 
looking in one and the same direction, and the negative half in the opposite 
one. The positive and negative signs are intended to represent the states. 

The intensity of the induced electrical disturbance diminishes with the 
distance from the charged body ; if this be removed or discharged, all the 
effects cease at once. 

So far, the greatest resemblance may be traced between these two sets of 
phe&omena ; but here it seems in great measure to cease. The magnetic 
polarity of a piece of steel can awaken polarity in a second piece in contact 
with it by the act of induction, and in so doing loses nothing whatever of 
its power ; this is an effect completely different from the apparent transfer 
or discharge of electricity constantly witnessed, which in the air and in 
tiqnids often give rise to the appearance of a bright spark of fire. Indeed, 
ordinary magnetic effects comprise two groups of phenomena only, those 
namely of attraction and repulsion, and those of induction. But in elec- 
tricity, in addition to phenomena very closely resembling these, we have the 
effects of disekarffe, to which there is nothing analogous in magnetism, and 
which takes place in an instant when any electrified body is put in oommu- 

nication with the earth by any one of the class of substances called con- 
ductors of electricity ; all signs of electrical disturbance then ceasing. 

These condactors of electricity, which thus permit discharge to take place 
through their mass, are contrasted with another class of substances called 
non-conductors or insulators. The difference, however, is only one of degree, 
not of kind ; the very best conductors offer a certain resistance to the elec- 
trical discharge, and the most perfect insulators permit it to a small extent 
The metals are by far the best conductors ; glass, silk, shellac, and dry gas, 
or vapour of any sort, the very worst ; and between these there are bodies 
of all degrees of conducting power. 

Electrical discharges take place silently and without disturbance in good 
conductors of sufficient size. But if the charge be very intense, and the 
conductor very small or imperfect from its nature, it is often destroyed with 

When a break is made in a conductor employed in effecting the discharge 
of a highly-excited body, disruptive or spark-discharge, so well known, takes 
place across the intervening air, provided the ends of the conductor be not 
too distant. The electrical spark itself presents many points of interest in 
the modifications to which it is liable. 

The time of transit of the electrical wave through a chain of good conduct- 
ing bodies of great length is so minute as to be altogether inappreciable to 
ordinary means of observation. Professor Wheatstone's very ingenious ex- 
periments on the subject give, in the instance of motion through a copper 
wire, a velocity approaching that of light. 

Electrical excitation is apparent only upon the surfaces of bodies, or those 
portions directed towards other objects capable of assuming the opposite 
state. An insulated ball charged with positive electricity, and placed in the 
centre of the room, is maintained in that state by the inductive action of the 
walls of the apartment, which immediately become negatively electrified ; in 
the interior of the ball there is absolutely no electricity to be found, althongh 
it may be constructed of open metal gauze, with meshes half an inch wide. 
Even on the surface the distribution of electrical force will not always be the 
same ; it will depend upon the figure of the body itself, and its position with 
regard to surrounding objects. The polarity will always be highest in the 
projecting extremities of the same conducting l&ass« and greatest of all when 
' these are attenuated to points, in which case the inequality becomes so great 
that discharge takes place to the air, and the excited condition cannot be 

The construction and use of th^ common electrical maehine, and other 
pieces of apparatus of great practical utility, will, by the aid of these pdn- 
iiples, become intelligible. 

A glass cylinder (fig. 65) is mounted with its axis in a horizontal poBi^aoiiy 
and provided with a handle or winch by which it may be turned. A leather 
cushion is made to press by a spring against one side of the cylinder, while 
a large metal conducting body, armetF with a number of points next the 
glass, occupies the other ; both cushion and conductor are insulated by glass 
supports, and to the upper edge of the former a piece of silk is attached 
long enough to reach half round the cylinder. Upon the Guahion is spread 
a quantity of a soft amalgam of tin, zinc, and mercury/ mixed up vrith & 
little grease; this substance is found by experience to excite glass most 
powerfully. The cylinder, as it turns, thus becomes charged by friction 
against the rubber, and as quickly discharged by the row of points attached 
to the great conductor ; and as the latter is also completely insulated, its 
surface speedily acquires a charge of positive electricity^ which may be 

1 Part tin, 2 line^ and 6 mareaix. 



eommanicated liy-contactio other iosalated bodies. The maximum effect ifl 
produced when the rubber is connected by a chain or wire with the earth. 
If negatixe electricity, be wanted, the rubber must be insulated and the con- 
ductor dischnrged. 

Another form of the electrical machine consists of a circular plate of glass 
(fig. 66)BU>¥ing ^pon an^axis, and provided with two pairs of cushions or 


or rabben, attaehed to the upper »nd lower perta of the wooden frame, 
covered with amalgam, between whieh the plate moves with considerable 
friction. An insolated conductor, armed as before with points, discbarges 
the plate as it tnms, the rubbers being at the same time connected with Uie 
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 vamished with' fine lac dissolved in 
alcohol ; the slightest film of water is sufficieat to destroy the power of insu- 
lation. The rubbers also must be carefully dried before use, and the amal- 
gam renewed if needful ; in damp weather much trouble is often experienced 
in bringing the machine into powerful action. 

When the conductor of the machine is charged with electricity, it acts 
indirectly on, and accumulates the contrary electricity to its own, at the sur- 
face of all the surrounding conductors. It produces the greatest effect on 
the conductor that b nearest to it, and which is in the best connection with 
the ground, whereby the electrici^ of the same kind as that of the machine 
may pass to the earth. As the inducing electricity attracts the induced 
electricity of an opposite kind ; so, on the other hand, is the former attracted 
by the latter. Hence the fluid which the conductor receives from the ma- 
chine must especially accumulate at that spot to which another good con- 
ductor of electricity is opposed. If a metal disc is in connection with the 
conductor of a machine, and if another similar disc, which is in good con- 
nection with the earth, is placed opposite to it, we have an arrangement by 
which tolerably large and good conducting surfaces can be brought close to 
one another; thus the positive condition of the first disc, as well as the nega- 
tive condition of the other, must be increased to a very considerable degree ; 
the limit is in this case, however, soon reached, because the intervening air 
easily permits spark-discharge to take place through its substance. With a 
solid insulating body, as glass or lac, this happens with 
Fig. 07. much greater difficulty, even when the plate of insulating 

matter is very thin. It is on this principle that instru- 
ments for the accumulation of electricity depend, among 
which the Ley den jar is the most important. 

A thin glass jar (fig. 67) is coated on both sides with tin- 
foil, care being taken to leave several inches of the upper 
part uncovered ; a wire, terminating in a metallic knob, 
communicates with the internal coating ; when the outside 
of the jar is connected with the earth, and the knob put 
in contact with the conductor of the machine, the inner 
and outer surfaces of the glass become respectively posi- 
tive and negative, until a very great degree of intensity 
has been attained. On completing the connection between 
the two boatings by a metallic wire or rod, discharge oc- 
curs in the form of an exceedingly bright spark, accom- 
panied by a loud snap ; and if the body be interposed in the circuit, the 
peculiar and disagreeable sensation of the electric shock is felt at the mo- 
ment of its completion. 

By enlarging the dimensions of the jar, or by connecting together a number 
in such a manner that all may be charged and discharged simultaneously, 
the power of the apparatus may be greatly augmented. Thin wires of metal 
may be fused and dissipated ; pieces of wood may be shattered, many com- 
bustible Bubstatices set on fire, and all the well-known effects of lightning 
exhibited upon a small scale. 

StlOtBIOITTr ' 97 

The eleetrle ipai^lt is oftett rery conteftfcntlf efinployvd in diemieiU iiiqid- 
ries for firing gaseous mixtnres in close yessels. A small Leyden jar charged 
by the machine is the most effeotlTe coatriranoe for this purpose, but, not 
unfireqneatly, a method may be resorted to whieh UToWee lew preparation. 
This is by the use of the eleetrophoms. 
A roond trsy or dish of tinned plate is 1^ M. 

prepared (fig. 68), having a stout wire 
rmind its upper edge ; the iridth may be 
aboot twelve tnehes, and the depth half 
•D inch. This tray is filled with melted 
iheQao, and the surfaee rendered as even 
as possible. A brass dise, with rounded 
edge, of aboat nine inohes diameter, is 
tlflo provided, and fitted with an insulating 
hancQe. When a spark is wanted, the 
tesinotis plate is ezeited by striking with 

a dry, warm piece of fur, or a silk handkerchief; the cover is placed npon 
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 bri|^t 
spuk; and, aa the resin is not discharged by the cover, which 'merely 
tonchee 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 mazi- 
nam at a particular period of the day. In cloudy and stormy weather the 
diBtribution of the atmospheric electricity becomes much deranged, clouds 
near the surface of the earth often appearing in a negative state. 

The circumstances of a thunder-storm exactly resemble those of the 
charge and discharge of a coated plate or jar ; the cloud and the earth repre- 
lent the two coatings, and the intervening air the bad-conducting body or 
dieUetrie, The polarities of the opposed surface and of the insulating medium 
between them become raised by mutual induction, until violent ^eruptive 
disehuge takes place through the air itself, or through any other bodies 
which may happen to be in the interval. When these are capable of con- 
ductiog freely, the discharge is silent and harmless ; but in other cases it 
often proves highly destructive. These dangerous effects are now in a great 
meanore obviated by the use of lightning-rods attached to buildings, the 
erection of which, however, demands a number of precautions not always 
understood or attended to. The masts of ships may be guarded in like 
maimer by metal conductors ; Sir W. Snow Harris has devised a most inge- 
nious plan for the purpose, which is now adopted, with the most complete 
BQccess, in the British Navy. 

When two solid conducting bodies are plunged into a liquid which acts 
npon them unequally, the electric equilibrium is also disturbed, the one ac- 
quiring the positive condition, and the other the negative. Thus, pieces of 
line and platinum put into dilute sulphuric acid, constitute an arrangement 
capable of generating electrical force ; the zinc being the metal attacked, 
becomes negative ; and the platinum remaining unaltered, assumes the posi* 
tive condition ; and on making a metallic communioation 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 nndMlischarges take place through the fluid 
and metals with inconceivable rapidity, the resuUis anapparentiy continuous 
action, to which the term electrical current is given. 

U is necessary to gioavd against the idea which th* teno-Balnnilly 0iiggtst% 



Fig. 60. 

of an actual -bodily transfer of something through the substance of the con- 
ductors, like water through a pipe ; the real nature of all these phenomena 
is entirely unknown, and may perhaps remain so ; the expression is couTe- 
uient notwithstanding, and consecrated by long use ; and with this- caution, 
the very dangerous error of applying figurative language to describe an 
effect, and then seeking the nature of the effect from the common meaning 
of words, may be avoided. 

The intensity of the electrical excitement developed by a single pair of 
metals and a liquid, is too feeble to affect the most delicate gold-leaf elec- 
troscope ; but, by arranging a number of such alternations 
in a connected series, in such a manner, that the direction 

^ of the current shall be the same in each, the intensity 

f ^ \. may be very greatly exalted. The two instruments in- 
■" * vented by Volta, called the pile, and crown of cups, depend 

upon this principle. 

Upon a plate of zinc (fig. 69) is laid a piece of cloth, 
rather smaller than itself, steeped in dilute acid, or any 
liquid capable of exerting chemical action upon the zinc ; 
upon this is placed a plate of copper, silver, or platinum ; 
then a second piece of zinc, another cloth, and plate of 
inactive metal, until a pile of about twenty alternations 
has been built up. If the two terminal plates be now 
touched with wet hands, the sensation of the electric 
shock will be experienced; but, unlike the momentary 
effect produced by the discharge of a jar, the sensation 
will be prolonged and continuous, and with a pile of one hundred such pairs, 
excited by dilute acid, it will be nearly insupportable. When such a pile is 
insulated, the two extremities exhibit strong positive and negative states, and 
when connection is made between them by wires armed with points of hard 
charcoal or plumbago, the discharge takes place in the form of a bright en> 
during spark or stream of fire. 

The second form of apparatus, or crown of cups, is precisely the same in 
principle, although different in appearance. A number of cups or glasses 
(fig. 70) are arranged in a row or circle, each containing a piece of active and 


a piece of inactive metal, and a portion of exciting liquid ; zinc, copper, and 
dilute sulphuric acid, for example. The copper of the first cup is connected 
with the zinc of the second, the copper of the second with the zinc of the 
third, and so to the end of the series. On establishing a communication 
between the first and last plates by means of a wire, or otherwise, discharge 
takes place as before. 

When any such electrical arrangement consists merely of a single pair of 
conductors and an interposed liquid, it is called a simple circuit; when two 
or more alternations are concerned, the term " compound circuit " is applied ; 
they arc called also, indifferently, voltaic batteries. In every form of such 


apiiaratos, however e<»nplex it may appear, the durection of the emrent may 
be easily understood and remembered. The polarity or disturbance may be 
considered to commence at the surface of the metal attacked, and to be pro- 
pagated through the liquid to the inactive conductor, and thence back again* 
by the connecting wire, these extremities of the battery being always re- 
£pecti?ely negative and positive when the apparatus is insulated. In common 
parlance, it is said that the current in every battery in an active state starts 
from the metal attacked, passes through the liquid to the second metal or 
conducting body, and returns by the wire or other channel of communica- 
tion; hence, in the pile and crown of cups just described, the current in the 
battery is always from the zinc to the copper ; and out of the battery, from ' 
the copper to the zinc, as shown by the arrows. 

In tiie modification of Volta's original pile, made by Mr. Cruikshank, the 
zioo and copper plates are soldered together and cemented water-tight into 
.a mahogany trough (fig. 71), which thua becomes divided into a series of 

Pig. 71. 

cells or compartments capable of receiving the exciting liquid. This appa- 
ntiis is well fitted to exlubit effects of tension^ to act upon the electroscope 
and give shocks ; hence its advantageous employment in the application of 
electricity to medicine, as a very few minutes suffices to prepare it for use. 
The crown of cups was also put into a much more manageable form by Dr. 
Babington, and still farther improved, as will hereafter be seen, by Br. 
Wollaston. Subsequently, various alterations have been made by different 
experimenters with a view of obviating certain defects in the common bat- 
teries, of which a description will be found towards the middle of this 

The term "galvanism," sometimes applied to this branch of electrical 
science, is used in honour of Professor (}alvani, 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 Yolta, however, who pointed out the 
electrical origin of these motions, and although the explanation he offered 
of the source of the electrical disturbance is no longer generally adopted, 
his name is very properly associated with the invaluable instrument his 
genius gave to science. 

In the year 1822, Professor Seebeck, of Berlin, discovered another source 
of electricity, to which allusion has already been made, namely, inequality 
of temperature and conducting power in different metals placed in contact, 
or in the same metal in different states of compression and density. Even 
with a great number of alternations, the current produced is exceedingly 
feeble compared with that generated by the voltaic pile. 

Two or Uiree animals of the class of fishes, as the torpedo, or eUetrie ray, 
and the eleetrie eel of South America, are furnished with a special organ or 
apparatus for developing electrical force, which is employed in defence, or 
in die pursuit of prey. Electricity is here seen to be closely connected with 
nervous power ; the shock is given at the wUl 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 


ik9 effSeeto «f figliteng on flie oorapwn-oeedle and upofi smaM sImA «rtte1«f, 
as kniveB and forks, to whieh polarity has suddenly been given by the stroke, 
it was not nntil 1819 that the laws of these phenomena were discovered by 
Professor CErsted, of Copenhagen, and shortly afterwards fully developed by 
M. Ampere. 

The action which a current of electricity, from whatever source proceed- 
ing, exerts upon a magnetized needle is quite peculiar. The poles or centres 
of magnetic force are neither attracted nor repelled by the wire carrying the 
current, but made to move around the latter, by a force which may be 
termed tangmUalj and which is exerted in a direction perpendicular at once 
to that of the current, and to the line joining the pole and the wire. Both 
poles of the magnet being thus acted upon at the same time, and in contrary 
directions, the needle is forced to arrange itself across the current, so that 
Its axis, or the line joining the poles, may be perpendicular to the wire ; and 
this is always the position which the needle will assume when^the influence 
of terrestrial magnetism is in any way removed. This curious angular mo« 
tion may even be shown by suspending a magnet in such a way that one only 
of its poles shall be subjected to the current ; a permanent movement of 
rotation will continue as long as the current is kept up, its direction being 
changed by altering the pole, or reversing the current. The moveable con- 
nections are made by mercury, into which the points of the conducting-wires 
dip. It is often of great practical consequence to be able to predict the 
direction in which a particular pole shall move by a given current, because 
in all galvanoscopes, and other instruments involvi^ig these principles, the 
movement of the needle is taken as an indication of Uie direction of the cir- 
culating current. And this is easily done by a simple mechanical aid to the 
memory : — Let the current be 'supposed to pass through a watch from the 
face to the back ; the motion of the north pole will be in the direction of the 
hands. Or a little piece of apparatus (fig. 72) may be used if referenoe is 

7%. 78. 


'""nijiisi^ fs , "''j""iiin|mBp 

i h 

often required ; this is a piece of pasteboard, or other suitable material, eut 
into the form of an arrow for indicating the current, crossed by a magnet 
having its poles marked, and arranged in the true position with respect to 
the current. The direction of the latter in the wire of the galvanosoope can 
at once be known by placing the representative magnet in the direction 
assumed by the needle itself. 

The common galvanoscope, consisting of a coil of wire having a compass- 
needle suspended on a point within it, is greatly improved by the addition 
of a second needle, as already in part described, and by a better mode of 
suspension, a long fibre of silk being used for the purpose. The two needles 
are of equal size, and magnetized as nearly as possible to the same extent ; 
they are then immovably fixed together, parallel, and with their poles op- 
posed, and hang with the lower needle in the coil and the upper one above 
it. The advantage gained is twofold ; the system is cutatie, unnffeoted, or 
nearly so, by the magnetism of the earth ; and the needles being both acted 
ppos in th« Bamd manner by the current, are urged with much greater force. 



thao line alone would be, all the fietions of every p«rt of the coil htmg 
strictly oonctirrent. A divided circle is placed below the upper needle, by 
which the angular motion can be measured ; and the whole is enclosed in 
glass, to shield the needles from the agitation of the air. The arrangement 
is shown in fig. 78. 

Hg. 73. 

Kg. 74. 

The action between the pole and thfe- wire is mutual, as may be shown by 
rendering the wire itself moveable and placing a magnet in its vicinity : on 
completing the circuit, the wire will be put in motion, and, if the arrange- 
ment permits, rotate around the magnetic pole. 

A little consideration will show, that, from the 
peculiar nature of the electro-dynamic force, a 
wire carrying a current, bent into a spiral or 
helix, must possess the properties of an ordinary 
magnetized bar, its extremities being attracted 
and repelled by the poles of a magnet. Such is 
really found to be the case, as may be proved by a 
Tariety of arrangements, among which it will be 
sufficient to cite the beautiful little apparatus of 
Professor de la Hive. — A short wide glass tube 
(fig. 74) is fixed into a cork ring of considerable 
sizd ; a little voltaic battery, consisting of a single 
pair of copper and zinc plates, is fitted to the tube, and to these the ends 
of the spiral are soldered. On filling the tube with dilute acid and floating 
the whole in a large basin of water, the helix will be observed to arrange 
itself in the magnetic meridian, and on trial it will be found to obey a mag- 
net held near it in the most perfect manner, as long as the current circu • i 

When an electric current is passed at right angles to a piece of iron or 
steel, the latter acquires magnetic polarity, either temporary or permanent 
as the case may be, the direction of the current determining the position of 
the poles. This effect is prodigiously increased by causing the current to 
circulate a number of times round the bar, which then acquires extraordi- 
nary magnetic power. Apiece of soft iron, worked into the form of a horsO' 
shoe (fig. 76), and surrounded by'a coil of copper wire covered with silk or 
cotton for the purpose of insulation, furnishes an excellent Illustration of 
the inductive energy of the current in this respect ; when the ends of t!k9 



Vig. 7^ 

irire ftr* ]rat itttd eommHiieatioii with » small Toltaic battery of a single pidr 
of plates, the iron instantly becomes so highly magnetic 
as to be capable of sustaining a very heavy weight. 

A current of electricity can thus develop magnetism 
in a transverse direction to its own ; in the same man- 
ner, magnetism can call into activity electric currents. 
If the two extremities of the coil of the electro-magnet 
above described be connected with a galvanoscope, and 
the iron magnetized by the application of a permanent 
steel horse-shoe magnet to the ends of the bar, a mo- 
mentary current wUl be developed in the wire, and 
pointed out by the movement of the needle. It lasts 
bat a single instant, the needle returning after a few os- 
cillations to a state of rest. On removing the magnet, 
whereby the polarity of the iron is at once destroyed, a 
second current or wave will become apparent, but in the 
opposite direction to that of the first. By employing a 
very powerful steel magnet* surrounding its iron keeper 
or armature with a very long coil of wire, and then 
making the armature itself rotate in A*ont of the faces 
of the magnet, so that its induced polarity shall be 
rapidly reversed, magneto-electric currents may be pro- 
duced, of such intensity as to give bright sparks and most powerful shocks, 
and exhibit all the phenomena of voltaic electricity. Fig. 76 represents a 
Tery powerful arrangement of this kind. 

Fig. 76. 

^ When two oovereu wires are twisted together or laid side by side for somo 
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 
oonnezion with the battery, a second single wave will become evident by the 
aid of the.galvanoscope, in the same direction as that of the primary cur- 
rent ^ In the same way, when a current of electricity passes throi^h one 
tam in » coil of irire, it induoes two secondary currents in all tho other 


turns of the coil ; when the eiremt is closed, the first is moving in the oppo> 
Bite direction to the primary current ; the second, when the cireait is broken, 
has a motion in the same lUrection as the primary carrent. The effect of 
the latter is added to that of the primary current Hence, if a wire coil be 
made part of the conducting wire of a weak electric pile, and if the primary 
current, by means of an appropriate arrangement, is made and broken in 
rapid saccession, we can increase in a remarkable manner the effects which 
are produced at the moment of breaking the circuit either at the place of 
interruption — such as the spark-discharges; or in secondary closing-con- 
doctors, such as the action on the nenres or the decomposition of water. 

M. Ampere discoTcred 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 CTident 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 iHien in opposite directions, aa 
equally strong repulsion. — These effects, iHiich are not difficult to demon- 
strate, have absolutely no relation that can be traced to ordinary electrical 
attractions and repulsions, from which they must be carefully distinguished ; 
they are purely dynamkj hsving to do with electricity in motion. M. 
Ampere founded upon this discovery a most beautiful and ingenious hyp6* 
thesis of magnetic actions in general, which expluns very clearly the influ- 
ence of the current upon the needle. 

The eleetricity 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 fHction, not of 
the pure steam itself, but of particles of condensed water, against the inte- 
rior of the exit-tube. It is very doubtful whether fnere evaporation can cause 
electrical disturbance, and the hope first entertained that these phenomena 
would throw light upon the cause of electrical excitement in the atmosphere^ 
is now abandoned. The steam is usually positive, if the jet-pipe be con- 
structed of wood or clean metal, but the introduction of the smallest trace 
of oily matter causes a change of sign. The intensity of the charge is, 
taterit paribus, increased with the elastic force of the steam. By this means, 
effects have been obtained very far surpassing those of the most powerful 
plate electrical machines ever constructed. 



Thb term element or dementary subttanee is applied in chemistry to those 
forms or modificatioQS of matter which have hitherto resisted all attempts to 
decompose them. Nothing is ever meant to be affirmed concerning their 
real nature ; they are simply elements to us at the present time ; hereafter, 
by new methods of research, or by new combinations of those already pos- 
sessed by science, many of the substances which now figure as elements may 
possibly be shown to be compounds; this has already happened, and majT" 
again take place. 

The elementary bodies, at present recognised, amount to sixty-two in 
number ; of these, about forty-seven belong to the class of metals. Several 
of these are of reoent discovery and as yet very imperfectly known. The 
distinction between metals and non-metallic substances, although very con- 
venient for purposes of description, is entirely arbitrary, since the two classes 
graduate into each other in the most complete manner. 

It will be proper to commence with the latter and least numerous division. 
The elements are named as in the subjoined table, which, however, does not 
indicate the order in which they will be discussed. 

















(or Glucinum) 



(or Wolfram) 











. Carbon 

(or Columbium) 


























Klementfi of interm«- 



diate ehaneien. 













Whaierer plan of classification, founded on ihe natoral relations of the 
elements, be adopted, in the practical study of chemistry, it will always be 
foand most advantageous to commence witJi the consideration of the great 
constituents of the ocean and the atmosphere. 

Oxygen was discovered in the year 1774, by Scheele, in Sweden, and Dr. 
Priestley, in England, independently of each other, and described under the 
terms empyreal air and dephlogitticated air. The name oxygen* was given to 
it by Lavoisier some time afterwards. Oxygen exists in a free and uncom- 
bioed state in the atmosphere, mingled with another gaseous body, nitrogen : 
no good direct means exist, however, for separating it from the latter, and, 
accordingly, it is always obtained for purposes of experiment by decom- 
posing certain of its compounds, which are very numerous. 

The red oxide of mercury, or red precipitate of the old writers, may be 
employed with this view. In this substance, the attraction which holds to- 
gether the mercury and the oxygen is so feeble, that simple exposure to heat 
Boffiees to bring about decomposition. The' red precipitate is placed in a 
short tube of hwrd 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- 
l&mp being applied to the substance, decomposition speedily commences, 
globules of metallic merqury collect in the cool part of the wide tube, which 
answers the purpose of a retort, while gas issues in considerable quantity from 
the apparatus. This gas is collected and examined by the aid of the pneu- 
matic trough, which consists of a vessel of water provided with a shelf, upon 
which stand the jars or bottles destined to receive the gas, filled with water 
sod inverted. By keeping the level of the liquid above the mouth of the jar, 
the water is retained in the latter by the pressure of the atmosphere, and 
entrance of air is prevented. When brought over the extremity of the gas- 
delivering tube, the bubbles of gas rising through the water collect in the 
npper part of the jar and displace the liquid. As soon as one jar is filled. 

Fig. 77. 

* From d^bs, Mid, and ysvvdto, I give rise to. 



it mny be remoTed, Btill keeping its moath below the water-level, and an- 
other substituted. The whole arrangement is shown in fig. 77. 

The experiment described is more instructiTe as an excellent ease of the 
resolution by simple means of a compound body into its constituents, than 
Taluable as a source of oxygen gas. A better and more economical method 
is to expose to heat in a retort, or flask furnished with a bent tube, a por- 
tion of the salt called chlorate of potassa. A common Florence flask serves 
perfectly well, the heat of a spirit-lamp being sufficient. The salt melts 
and decomposes with ebullition, yielding a very large quantity of oxygen 
gas, which may be collected in the way above described. The first portion 
of the gas often contains a little chlorine. The white saline residue in the 
flask is chloride of potassium. This plan, which is very easy of execution, 
. is always adopted when very pure gas is required for analytical purpose. 

A third method, very good when perfect purity is not demanded, is to heat 
to redness, in an iron retort or gun-barrel, the black oxide of manganese of 
commerce, which under these circumstances suffers decomposition, althongh 
not to the extent manifest in the red precipitate. 

If a little of the black oxide of manganese be finely powdered and mixed 
with chlorate of potassa, and this mixture heated in a flask or retort by a 
lamp, oxygen will be disengaged with the utmost facility, and at a far lower 
temperature than when the chlorate alone is used. All the oxygen comes 
from the chlorate, the manganese remaining quite unaltered. The materials 
should be well dried in a capsule before tiieir 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 contaminate by the at- 
mospheric air of the apparatus. The practical management of gases is a 
point of great importance to the chemical student, and one with which he 
must endeavour to familiarize himself. The water-trough just described is 
one of the most indispensable articles of the laboratory, and by its aid all 
experiments on gases are carried on when the gases themselves are not sen- 
sibly acted upon by water. The trough is best constructed of japanned 
copper, the form and dimensions being regulated by the magnitude of the 
jars. It should have a firm shelf, so arranged as to be always about an inch 
below the level of the water, and in the shelf a groove should be made 
about half an inch in width, and the same in depth, to admit the extremity 
df the delivery-tube beneath the jar, which stands securely upon the shelf. 

Fig. 78. 




Wken the pneomfttie tron^ is required of tolerablj large dfrnenfflons, it may 
with great adTantage hare the form and disposition represented in the cot 
(fig. 78) ; one end of the groofe spoken of, whieh crosses the riielf or shallow 
portion, ifl shown at a. 

Gases are transferred from jar to jar with the utmost facflitj, by first 
filling the vessel into which the gas is to be passed with water, inyerting it, 
esrefully retaining its month below the water-loTel, and then bringing be- 
oesth it the aperture of the jar omtaining the gas. On gently inclining the 
bitter, the gas passes by a kind of inyerted decantation into the second 
TesseL When tiie latter is narrow, a funnel may be placed loosely in its 
neck, by which loss of gas will be found to be prerented. 

Ajar wholly or partially filled with gas at the pneumatic trough may b. 
remoTed by placing beneath it a shallow basin, 
or even a common plate (fig. 79), so as to 
cany away enough water to coTor tiie edge of 
the jar; and gas, especially oxygen, may be 
80 preserred for many hours without material 

Gas-jars are often capped at the top, and 
fitted with a stojKGock for transferring to blad- 
ders or caoutchouc bags. When such a yessel 
is to be filled with water, it may be slowly 
Bunk in an upright position in the well of the 
pneamatic trough, Uie stopcock being open to 
allow the air to escape, until the water reaches 
the brass cap. The oock 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 manoeuyre, 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 

Sir. 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 
eopper (fig. 80), surmounted by a shallow 
trough or cistern, the communication be- 
tween the two being made by a couple of 
tabes, a 6, furnished with cocks, /A, one of 
which passes nearly to the bottom of the 
drom, as shown in the sectional sketch. A 
short wide open tube, c, is inserted obliquely 
near the bottom of the vessel, into which a 
ping may be t^htly screwed. A stop-cook, 
Sy near the top, serves to transfer gas to a 
bladder or tube apparatus. A glass water- 
gnage, dty affixed to the side of the drum, 
and communicating with both top and bot- 
tom, indicates the level of the liquid within. 
To use the gas-holder, the plug is first to 
be screwed into the lower opening, and the 
dram 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 
gu-holder, and if so air-leakage occur, the escape of water is inconslder* 

Kg. 80. 

106 OXTGEN. 

ftble; The eitremity of tli« deUTery-tal>e is now to \M wett ptmhed ^ftmgk 
ike open aperture into the drum, eo that the bubbles of gas rise without hin- 
drance to the upper part, displacing the water, which flows out in the same 
proportion into a vessel placed for its reception. When the drum is filled, or 
cnongh gas has been collected, the tube is withdrawn, and the plug screwed 
into its place. 

When a portion of the gas is to l)e transferred to a jar, the latter is 
filled with water at the pneumatic trough, carried by the help of a basin or 
plate to the oistem of the gas-holder, and placed oyer the shorter tube. On 
opening the cock of the nei^boitting tube, the bydrostatio pressure of the 
column of water will cause condensation of the gas, and increase its elastic 
fwce, 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 difficidty. 

Oxygen, when free or uncombined, is only known in the gaseous state, aU 
attempts to reduce it to the liquid or solid condition by cold snd pressure 
having completely failed. It is, when pure, colourless, tasteless, and in- 
odorous ; it is the sustaining principle of animal life, and of all the ordinary 
phenomena of combustion 

Bodies which bum in the air bum with greatly increased splendour in 
oxygen gas. If a taper be blown out, and then in^oduced while the wick 
remains red-hot, it is instantly rekindled : a slip of wood or a match is re- 
lighted in the same manner. This effect is highly characteristic of oxygen, 
there being but one other gas which possesses the same property ; and this 
is easily distinguished by other means. The experiment with the match is 
also constantly used as a rude test of the goodness of the gas when it is about 
to be collected from the retort, or when it has stood some time in contact 
with water exposed to air. 

When a bit of charcoal is affixed to a wire, and plunged with a single 
point red-hot into a jar of oxygen, it bums with great brilliancy, throwing 
off beautiful scintillations, until, if the oxygen be in excess, it is completely 
consumed. An iron wire, or, still better, a steel watch-spring, armed at its 
extremity with a bit of lighted amadou, and introduced into a vessel of good 
gas, exhibits a most beautiful appearance of combustion. If the experiment 
be made in a jar standing on a plate, the fused globules of black oxide of 
iron fix themselves in the glaze of the latter, after falling' through a Btratum 
of water half an inch in depth. Kindled sulphur bums with great beauty 
in oxygen, and phosphorus, under similar circumstances, exhibits a splendour 
which the eye is unable to support. 

In these and many other similar cases which might be mentioned, the same 
ultimate effect is produced as in atmospheric air ; the action is, however, 
more energetic from the absence of the gas which in the air dilutes the 
oxygen, and enfeebles its chemical powers. The process of respiAtiOn in ani- 
mals is an effect of the same nature as common combustion. The*blood con- 
tains substances which slowly bum by the aid of the oxygen thus introduced 
into the system. When this action ceases, life becomes extinct. 

Oxygen is, bulk for bulk, a ^ittle heavier than atmospheric air, which ia 
usaally taken as the standard of unity of specific grarity among gases. Its 
specific gravity is expressed by the number 1*1057; * 100 cubic inches at GO*' 
(15^'5G). and under th'e mean pressure of the atmosphere, that is, SO inches 
of mercury, weigh 34*29 grains. 

It has been already remarked, that to determine with the last degree of 
accuracy the specific gravity of a gas, is an operation of very great practical 
difficulty, but at the same time of very great importance. There are several 

<"»• ' ' " ■ I II 1 III , 

» ))u«uu^, Ann. Chim. ot Phj a., 34 oedw, iiji. 27|i. 


meiliods which may be Adopted for thie purpose ; liie one below desoribed 
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* 
caatioDS, 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 
know9 temperature, and an elastic f^roe equal to tiiat of the atmosphere at 
the time of the experiment. The glebe so filled is to be weighed. It is 
then to be exhausted at the air-pomp as far as convenient, and again 
weighed. Lastly, it is to be filled with dry air, the temperature and pres- 
sure of which are known, and its weight (mce more determined. On the 
supposition that the temperature and elasticity are the same in both oases, 
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, 
«armoanted by a small but excellent stop-cock. A delicate thermometer 
should be placed in the inside of the globe, secured to the cap. The gae 
must be generated at the moment, and conducted at once into the previously 
exhausted vessel, through a long tube filled with fragments of pumice moist- 
ened with oil of vitriol, or some other extremely hygroscopic substance, by 
which it is freed from all moisture. As the gas is necessarily generated 
QDder some pressure, the elasticity of that contained in the filled globe will 
slightly exceed the pressure of .the atmosphere; and this is an advantage, 
since by opening the stop-cock for a single instant when the globe has 
attained an equilibrium of temperature, the tension becomes exactly that of 
the air, so that all barometrical correction is avoided, unless the pressure of 
the atmosphere should sensibly vary during the time occupied by the expe- 
riment It is hardly necessary to remark, that the greatest care must aJso 
be taken to purify and dry the air used as the standard of comparison, and 
to bring bol^ gas and air as nearly as possible to the same temperature, to 
obviate the necessity of a correction, or at least to diminish almost to nothing 
the errors involved by such a process. 

. The compounds formed by the direct union of oxygen with other bodies, 
bear the general name of oxides^ these are very numerous and important. 
They are conveniently divided into three principal groups or classes. The 
first division contains all those oxides which resemble in their chemical rela- 
tions, potassa, soda, or the oxide of silver or of lead ; these are denominated 
alkaline or baaie oxides, or sometimes salifiable bases. The oxides of the 
second group have properties exactly opposed to those of the bodies men- 
tioned ; oil of vitriol and phosphoric acid may be taken as the types or repre- 
sentatives of the class: they are called euids, and tend strongly to unite 
with the basic oxides. When this happens, what is called a 8(dt is generated 
as sulphate of potassa, or phosphate of silver, each of these substances be- 
ing compounded of a. pair of oxides, one of which is highly basic and the 
other highly acid. 

Then there remains a third group of what may be termed neutral oxides, 
from their little disposition to enter into combination. The black oxide of 
manganese, already mentioned, is an excellent example. 

It very frequently happens that a body is capable of uniting with oxygen 
in several proportions, forming a series of oxides, to which it is necessary 
to give distinguishing names. The rule in such cases is very simple, at least 
when the oxides af the metals are concerned. In such a series it is always 
found that one out of the number has a strongly-marked basic character ; to 
this the term protoxide is given. The compounds next succeeding receive 
the names of binoxide or deutoxide, teroxide or tritoxidey &o., from the Latin or 
Oreek numerals, the different grades of oxidation being thus indicated. If 
10 . 


there be a compound between the protoxide and binoxide, the name sesqui' 
oxide i^ usually applied. So it is usual to call the highest oxide, not having 
distinctly acid characters, peroxide^ from the Latin prefix, signifying excess. 
Any compound containing less oxygen than the protoxide, is called a sub- 
oxide. Superoxide or hyperoxide are words sometimes used instead of per- 

Ozone, — It has long been known that dry oxygen, or atmospheric air, 
when exposed to the passage of a series of electric sparks, emits a peculiar 
and somewhat metallic odour. The same odour may be imparted to moist 
oxygen, by allowing phosphorus to remain for some time in it. A more 
accurate examination of this odorous air has shown that, in addition to the 
smell, it assumes several properties not exhibited by pure oxygen. One of 
its most curious effects is the liberation of iodine from iodide of potassium. 
The oxygen thus altered has been the subject of many researches lately, 
particularly by Prof. Schoenbein, of Basel, who proposed the name of ozone* 
for it The true nature of ozone, however, is still unknown, most probably 
it is a peculiar modification of oxygen. 


Hydrogen is always obtained for experimental purposes by deoxidizing 
water, of which it forms the characteristic component." 

If a tube of iron or porcelain, containing a quantity of filings or turnings 
of iron, be fixed across a furnace, and its middle portion be made red-hot, 
and then the vapour of water transmitted over the heated metal, a large 
quantity of permanent gas will be disengaged from the tube, and the iron 
will become converted into oxide, and acquire an increase in weight. The 
gas is hydrogen ; it may be collected over water and examined. 

When zinc is put into water, chemical action of the liquid upon the met-al 
is imperceptible ; but if a little sulphuric acid be added, decomposition of 
the water ensues, the oxygen unites with the zinc, forming oxide of zinc, 
which is instantly dissolved by the acid, while the hydrogen, previously in 
union with the oxygen, is disengaged in the gaseous form. The reaction is 
represented in the subjoined diagram. 

Water /Hydrogen Free. 

I Oxygen ^ 

Zinc oxide of zinc -i Sulphate of 

Sulphuric acid r, / oxide of zinc 

It is not easy to explain the fact of the ready decomposition of water by 
zinc, in presence of an acid or other substance which can unite with the 
oxide so produced ; it is, however, a kind of reaction of very common oc- 
currence in chemistry. 

The simplest method of preparing the gas is the following. — A wide-necked 
bottle is chosen, and fitted with a sound cork (fig. 81), perforated by two 
holes for the reception of a small tube-funnel reaching nearly to the bottom 
of the bottle, and a piece of bent glass tube to convey away the disengaged 
gas. Granulated zinc, or scraps of the malleable metal, are put into the 
bottle, together with a little water, and sulphuric acid slowly added by the 
funnel, the point of which should dip into the liquid. The evolution of gag 
is easily regulated by the supply of acid, and when enough has been dis- 
charged to expel the air of the vessel, it may be collected over water into a 
jar, or passed into a gas-holder. In the absence of zinc, filings of iron or 
Hmall nails may be used, but with less advantage. 

« From 8^w, I gmell. 

^ Henoe the mane, from 6d<»p, water, and }<'tyydw. 



Fig. 81. 

A little practice will soon enable the 
pupil to construct and arrange a variety 
of useful forms of apparatus, in whicli 
bottles" and other articles always at 
hand, are made to supersede more 
costly instruments. Glass tube, pur- 
chased by weight of the maker, may be 
cut by scratching with a file, and then 
applying a little force with both hands. 
It may be softened and bent, when of 
small dimensions, by the flame of a 
gpirit-lamp, or even a candle or gas-jet. 
Corks may be perforated by a heated 
wire, and the hole rendered smooth and 
cylindrical by a round file, or the in- 
genious cork-borer of Dr. Mohr, now 
to be had of most instrument makers, 
may be used instead. Lastly, in the 
erent of bad fitting, or unsoundness in 
the cork itself, a little yellow wax 
melted over the surface, or even a little grease applied with the finger, 
renders it sound and air-tight, when not exposed to heat. 

Hydrogen is colourless, tasteless, and inodorous, when quite pure. To 
obtain it in this condition, it must be prepared from the purest zinc that can 
be obtained, and passed in succession through solutions of potassa and nitrate 
of silver. When prepared from commercial 2inc, it has a slight smell, which 
is due to impurity, and when iron, has been used, the odour becomes very 
strong and disagreeable. It is inflammable, burning when kindled with a 
pale yellowish flame, and evolving much heat, but very little light. The 
result of the combustion is water. It is even less soluble in water than 
oiygeo, and has never been liquefied. Although destitute of poisonous pro- 
perties, it is incapable of sustaining life. 

In point of specific gravity, hydrogen is the lightest substance known; 
Dumas and Boassingault place its density between 0-0691 and 
00695;* hence 100 cubic inches will weigh, under ordinary 
circumstances of pressure and temperature, 2-14 grains. 

When a gas is much lighter or much heavier than atmospheric 
air, it may often be collected and examined without the aid of 
the pneumatic trough. A bottle or narrow jar may be filled 
with hydrogen without much admixture of air, by inverting it 
over the extremity of an upright tube delivering the gas (fig. 
82). In a short time, if the supply be copious, the air will 
be wholly displaced and the vessel filled. It may now be 
removed, the vertical position being carefully retained, and 
closed by a stopper or glass plate. If the mouth of the jar be 
wide, it must be partially closed by a piece of card-board 
daring the operation. 'This method of collecting ga^es by 
displacement is often extremely useful. Hydrogen was for- 
merly used for filling air-balloons, being made for the purpose 
on the spot from zinc or iron and dilute sulphuric acid. Its use 
is now superseded by that of coal-gas, which may be made very light by 
employing a high temperature in the manufacture. Although far inferior 
to pure hydrogen in buoyant power, it is found in practice to possess advan* 
tages over that substance, while its greater density is easily compensated 
by increasing the magnitude of the balloon. 

* Ann. Chim. et Phys. Sd. series, viiL ZOI. 

Kg. 82. 

112 fiTDftoasH. 

There is a very remiurkable property enjoyed by gases and yaponrs in 
general, which is seen in a high degree of intensity in the case of hydrogen , 
this is what is called diffusive power. If two bottles, containing gases which 
do not act chemically upon each other at common temperatures, be connected 
by a narrow tube and left for some time, these will be found, at the expira- 
tion of a certain period, depending much upon the narrowness of the tube 
and its length, uniformly mixed, even though the gases differ greatly in 
density, and the system has been arranged in a vertical position, with the 
heaviest gas downwards. Oxygen and hydrogen can thus be made to mix, 
in a few hours, against the action of gravity, through a tube a yard in length, 
and not more than one-quarter of an inch in diameter ; and the fact is true 
of all other gases which are destitute of direct action upon each other. 

If a vessel be divided into two portions by a diaphragny or partition of 
porous earthenware or dry plaster of Paris, and each half filled with a dif- 
ferent gas, diffusion will immediately commence through the pores of the 
dividing substance, and will continue until perfect mixture has taken place. 
All gases, however, do not permeate the same porous body, or, in other 
Words, do not pass through narrow orifices with the same degree of facility. 
Professor Graham, to whom we are indebted for a very valuable 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 
Jig. 88. other half with oxygen, the two gases will penetrate the 

diaphragm at very different rates ; four cubic inches of hy- 
drogen will pass into the oxygen side, while one cubic inch 
of oxygen travels in the opposite direction. The densities 
of the two gases are to each other in the proportion of 1 to 
16 ; their relative rates of diffusion will be inversely as the 
square roots of these numbers, or 4 to 1. 

By making the diaphragm of some flexible material, as 
a piece of membrane, the accumulation of the lighter gas 
on the side of the heavier may be rendered evident by the 
bulging of the membrane. The simplest and most striking 
method of making the experiment is by the nse of Profes- 
sor Graham's diffusion-tube (fig. 88). This is merely a 
piece of wide glass tube ten or twelve inches in length, 
having one of its extremities closed by a plate of piaster 
of Paris about half an inch thick, and well dried. When 
the tube is filled by displacement with hydrogen, and then 
set upright in a glass of water, the level of the liquid rises 
in the tube so rapidly, that its movement is apparent to the eye, and speedily 
attains a height of several inches above the water in the glass. The gas is 
actually rarefied by its superior diffusive power over that of the external 

It is impossible to over-estimate the importance in the great economy of 
Nature, of this very curious law affecting the constitution of gaseous bodies; 
it is the principal means by which the atmosphere is preserved in an uniform 
litate, 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 smnll 
apertures, and the apparently similar passage of gas through wet or moist 
fnembranes and other substances, which is really due to temporary liquefac- 
tion or solution of the gas, and is an effect completely different from diffu- 
sion, properly so called. For example, the diffusive power of carbonic acid 



into atmospheric air is yery small, but it passes into the latter througb a wet 
bladder with the fitmost ease, in virtue of its solubility in the water with 
which the membrane is moistened. It is by such a process that the function 
of respiration is performed ; the aeration of the blood in the lungs, and the 
disengagement of the carbonic acid, are effected through wet membranes ; 
the Mood is never brought into actual contact with the air, but receires its 
sapply 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 
au- by slight accidental leakage, and be rendered explosive.* 

It has been stated, that, although the light emitted by the flame of pure 
hydrogen is exceedingly feeble, yet the temperature of the flame is very 
high. This temperature may be still farther exalted by previously mixing 
the hydrogen with as much oxygen as it requires for combination, that is, 
as will presently be seen, exactly half its volume. Such a mixture bums 
hke gunpowder, independently of the external air. When raised to the 
requisite temperature for combination, the two gases unite with explosive 
Tiolence. If a strong bottle, holding not more than half a pint, be filled 
vith such a mixture, the introduction of a lighted match or red-hot wire 
determines in a moment the union of the gases. By certain precautions, a 
mixture of oxygen and hydrogen can be burned at a jet without communi- 
cation of fire to the contents of the vessel ; the flame is in this case solid. 

A little consideration will show, that all ordinary flames burning in the 
air or in pure oxygen are, of necessity, hollow. The act of combustion is 
nothing more than the energetic union of the substance burned with the 
surrounding oxygen ; ancl this union can only take place at the surface of 
the burning body. Such is not the case, however, with the flame now under 
consideration ; the combustible and the oxygen are already mixed, and only 
require to have their temperature a little raised to cause them to combine in 
every part. The flame so produced is very different in phy- 
sical characters from that of a simple jet of hydrogen or any 
other combustible gas ; it is long and pointed, and very re- 
markable in appearance. 

The safety-jet of Mr. Hemming, the construction of which 
myoWes a principle not yet discussed, may be adapted to a com- 
mon bladder containing the mixture, and held under the arm, 
and the gas forced through the jet by a little pressure. 
Although the jet, properly constructed, is believed to be safe, 
it is best to use nothing stronger than a bladder, for fear of 
injury in the event of an explosion. The gases are often con- 
tained in separate reservoirs, a pair of large gas-holders, for 
example, and only suffered to mix in the jet itself, as in the 
contrivance of Professor Daniell ; in • this way all danger is 
avoided. The eye speedily becomes accustomed to the pecu- 
liar appearance of the true hydro- oxygen flame, so as to 
permit the supply of each gas to be exactly regulated by 
auitable stop-cocks attached to the jet (fig. 84). 

A piece of thick platinum wire introduced into the flame 
of the hydro-oxygen blowpipe melts with the greatest ease ; 
a watch-spring or small steel file burns with the utmost 
brilliancy, throwing off showers of beautiful sparks ; an in- 

* ProfoMor Graham hrs since published a very extensive series of researches on the pa9< 
•^e of ga^es through narrow tubes, which will be found in detail in the Philosophi'*al Tr«n». 
•ctjons for 1846, p. 678. 

Fig. 84. 


ooiDbu8tibl<» oxidized body, as inagn«na or lime, becomes fio intessely ig- 
nited, as to glow with a light insupportable to the eye, agd to be susceptible 
of employment as a most powerful illuminator, as a substitute for the sun's 
rays in the solar microscope, and for night-signals in trigonometrical surreys. 
If a long glass tube, open at both ends, be held over a jet of hydro- 
rig. 85. gen (fig. 86), a series of musical sounds are sometimes produced by 
Ql the partial extinction and rekindlilig of the flame by the ascending 
^^ current of air. These little explosions succeed each other at regular 
intervals, and so rapidly as to give rise to a musical note, the pitch 
depending chiefly upon the length and diameter of the tube. 

Although oxygen and hydrogen may be kept mixed at common 
temperatures for any length of time without combination taking 
place, yet, under particular circumstances, they unite quietly and 
without explosion. Some years ago. Professor Dobereiner, of Jena, 
made the curious observation, that finely-divided platinum possessed 
the power of determining the union of the gases ; and, more recently, 
Mr. Faraday has shown that the state of minute division is by no 
means indispensable, since rolled plates of the metal had the same 
property, provided their surfaces were absolutely clean. Neither is 
the efi'ect strictly confined to platinum ; other metals, as palladium 
and gold, and even stones and glass, enjoy the same property, 
although to a far inferior degree, since they often require to be aided 
by a little heat. When a piece of platinum foil, which has been 
cleaned by hot oil of vitriol and thorough washing with distilled 
water, is thrust into a jar containing a mixture of oxygen and hydro- 
gen standing over water, combination of the two gases immediately 
begins, and the level of the water rapidly rises, the platinum 
becoming so hot, that drops, of water accidentally falling upon it 
enter into ebullition. If the metal be very thin and exceedingly clean, and 
the gases very pure, then its tenfperature rises after a time to actual redness, 
and the residue of the mixture explodes. But this is an effect altogether 
accidental, and dependent upon the high temperature of the platinum, which 
high temperature has been produced by the preceding quiet combination of 
the two bodies.. When the platinum is reduced to a state of division, and 
its surface thereby much extended, it becomes immediately red-hot in a 
mixture of hydrogen and oxygen, or hydrogen and air ; a jet of hydrogen 
thrown upon a little of the , spongy metal, contained in a glass or capsule, 
becomes at once kindled, and on this principle machines for the production 
of instantaneous light have been constructed. These, however, only act 
well when constantly used ; the spongy platinum is apt to become damp by 
absorption of moisture from the air, and its power is then for the time lost 
The best explanation that can be given of these curious effects, is to sup- 
pose that solid bodies in general have, to a greater or less extent, the pro- 
perty of condensing gases upon their surfaces, and that this faculty is 
enjoyed pre-eminently by certain of the non-oxidizable metals, as platinum 
and gold. Oxygen and hydrogen may thus, under these circumstances, be 
brought, as it were, within the sphere of their mutual attractions by a tem- 
porary increase of density, whereupon combination ensues. 

Coal-gas and ether or alcohol vapour may be made to exhibit the phenome- 
non of quiet oxidation under the influence of this remarkable surface-action. 
A close spiral of slender platinum wire, a roll of thin foil, or even a common 
platinum crucible, heated to dull redness, and then held in a jet of coal-gas, 
becomes strongly ignited, and remains in that state as long as the supply of 
mixed gas and air is kept up, the temperature being maintained by the heat 
iliseogaged in the act of union. Sometimes the metal becomes white-bot, 
snd then the gas takes fire. 


A rery pleasing experiment may be made by attaching such a coil ot wire 
to a card, and suspending it in a glass containing a few drops of ether 
(fig. 86), having previously made it red-hot in the flame 
of a spirit-lamp. The wire continues to glow until the 'ig- 86. 

oxygen of the air is, exhausted, giving rise to the pro- 
duction of an irritating vapour which attacks the eyes. 
The combustion of the ether is in this case but partial ; 
a portion of its hydrogen is alone removed, • and the 
whole of the carbon left untouched. 

A coil of thin platinum wire may be placed over the 
wick of a spirit-lamp, or a ball of spongy platinum sus- 
tained just above the cotton ; on lighting the lamp, and 
then blowing it out as soon as the metal appears red-hot, 
slow combustion of the spirit drawn up by the capillarity 
of the wick will take place, accompanied by the pungent 
Tapours just mentioned, which may be modified, and 
even rendered agreeable, by dissolving in the liquid some 
Bweet-smelling essential oil or resin. 

Hydrogen forms numerous compounds with other bodies, although it ifl 
greatly surpassed in this respect not only by oxygen, but by many of the 
other elements. The chemical relations of hydrogen tend to place it beside 
the metals. The great discrepancy in physical properties is perhaps more 
apparent than real. Hydrogen is yet unknown in the solid condition, while, 
on the other band, the vapour of the metal mercury is as transparent and 
colourless as hydrogen itself. This vapour is only about seven times heavier 
than atmospheric air, so that the diflFerence in this respect is not nearly so 
great as that in the other direction between air and hydrogen. 

There are two oxides of hydrogen, namely, water, and a very peculiar 
substance, discovered in the year 1818, by M. Thenard, called binoxide of 

It appears that the composition of water was first demonstrated in the 
year 1781, by Mr. Cavendish,* but the discovery of the exact proportions in 
which oxygen and hydrogen unite in generating that most important com- 
pound has from time to time to the present day occupied the attention of 
some of the most distinguished cultivators of chemical science. There are 
two distinct methods of research in chemistry : the analytical, or that in which 
the compound is resolved into its elements, and the synthetical, in which the 
elements are made to unite and produce the compound. The first method 
is of much more general application than the second, but in this particular 
instance both may be employed, although the results of the synthesis are 
most valuable. 

The most elegant example of analysis of water would probably be 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 extremities of a voltaic apparatus of moderate 
power, decomposition of the liquid takes place in a very interesting 
manner ; oxygen, in a state of perfect purity, is evolved from the water in 
contact with the plate belonging to the copper end of the battery, and 
hydrogen, equally pure, is disengaged at the plate connected with the zinc 
extremity, the middle portions of Mquid remaining apparently unaltered 
By placing small graduated jars over the platinum plates, the gases can b© 

* A claim to the discovery of the composition of water on behalf of Mr. James Watt, has 
Ifcen very stroDf^Iy urged, and supported by such evidence that the reader of the controversy 
n&S^be led to the conclusion tiiat the di. covery was made by both parties nearly iimult«f 
^ >osly} and anknown to eaclLi>ther. ' 



Fig. 87. 

Fig. 88. 

collected, and their quantities determined. 
Fig. 87 will show at a glance the whole 
arrangement; the conducting wires pass 
through the bottom of the glass cup, and 
thence to the battery. 

When this experiment has been con- 
tiifued a sufficient time, it will be found 
that the volume of the hydrogen is a very 
little above twice that of the oxygen; 
were it not for the accidental circumstance 
of oxygen being sensibly more soluble in 
water than hydrogen, the proportion of 
two to one by measure would come out 

Water, as Mr. Grove has lately shown, 
is likewise decomposed into its constituents 
by heat. The efiect is produced by intro- 
ducing platinum balls, ignited by electricity or other means, 
into water or steam. The two gases are, however, obtained 
in very small quantities at a time. 

When oxygen and hydrogen, both as pure as possible, are 
mixed in the proportions mentioned, passed into a strong glass 
tube filled with mercury, and exploded by the electric spark, 
all the mixture disappears, and the mercury is forced up into 
the tube, filling it completely. The same experiment may be 
made with the explosion-vessel or eudiometer of Mr. Caven- 
dish. (Fig. 88.) The instrument is exhausted at the air- 
pump, and then filled from a capped jar with the mixed 
gases ; on passing an electric spark by the wires shown at a, 
explosion ensues, and the glass becomes bedewed with 
moisture, and if the stop-cock be then opened under water, 
the latter will rush in and fill the vessel, leaving merely a 
bubble of air, the result of an imperfect exhaustion. 

The process upon which most reliance is placed is that in 
which pure oxide of copper is reduced at a red heat by hy- 
drogen, and the water so formed collected and weighed. This 
oxide suffers no change by heat alone, but the momentary - 
contact of hydrogen, or any common combustible matter at a high tem- 
perature, suffices to reduce a corresponding portion to the metallic state. 
Fig. 89 will serve to convey some idea of the arrangement adopted in re 
searches of this kind. 

Fig. 89. 

W^ — ■ 

A copious supply of hydrogen is procured by the action of dilute sul- 
phuric acid upon the purest zinc that can be obtained ; the gas is made to 
pass in succession through solutions of silver and strong caustic pota8sa,«by 
which its purification is completed. After this^ it is conducted through a 


fnbe fbree or fonr feet in length, filled with fragments of pumice-stone 
steeped in concentrated oil of vitriol, or with anhydrous phosphoric acid. 
These substances have such an extraordinary attraction for aqueous vapour, 
that they dry the gas completely during its transit. The extremity of this 
tube is shown at «. The dry hydrogen thus arrives at the part of the appa- 
ratas containing the oxide of copper, represented at b ; this consists of a 
tvo-necked flask of very hard white glass, maintained at a red heat by a 
spirit-lamp placed beneath. As the decomposition proceeds, the water pro- 
duced by the reduction of the oxide begins to condense in the second neck 
of the flask, whence it drops into the receiver e, provided for the purpose. 
A second desiccating tube prevents the loss of aqueous vapour by the cur- 
rent of gas which passes in excess. 

Before the experiment can be commenced, the oxide of copper, the purity 
of which is well ascertained, must be heated to redness for some time in a 
current of dry air ; it is then suffered to cool, and very carefully weighed 
with the flask. The empty receiver and second drying tube are also weighed, 
the disengagement of gas set up, and when the air has been displaced, heat 
slowly applied to the oxide. The action is at first very energetic ; the oxide 
often exhibits the appearance of ignition ; as the decomposition proceeds, it 
becomes more sluggish, and requires the application of a good deal of heat 
to effect its completion. 

When the process is at an end, and the apparatus perfectly cool, the 
stream of gas is discontinued, dry air is drawn through the whole arrange- 
ment, and, lastly, the parts are disconnected and re-weighed. The loss of 
the oxide of copper gives the oxygen ; the gain of the receiver and its dry- 
ing-tube indicates the water, and the difference between the two, the hy- 

A set of experiments, made in Paris in the year 1820,' by MM. Bulong 
and Berzelius, gave as a mean result for the composition of water by weight, 
8*009 parts oxygen to 1 part hydrogen ; numbers so nearly in the proportion 
of 8 to 1, that the latter have usually been assumed to be true. 

Quite recently the subject has been re-investigated by M. Dumas,* with 
the most scrupulous precision, and the above supposition fully confirmed. 
The composition of water may therefore be considered as established: it 
contains by weight 8 parts oxygen to 1 part hydrogen, and by measure, 1 
volume oxygen to 2 volumes hydrogen. The densities of the gases, as al- 
ready mentioned, correspond very closely with these results. 

The physical properties of water are too well known to need lengthened 
description ; it is, when pure, colourless and transparent, destitute of taste 
and odour, and an exceedingly bad conductor of electricity of low tension. 
It attains its greatest density towards 40° (4°'5C>, freezes at 32° (OoC), and 
boils under the pressure of the atmosphere at or near 212° (100°C). It 
evaporates at all temperatures. One cubic inch at 62° (16°'7C) weighs 
252-45 grains. It is 815 times heavier than air; an imperial gallon weighs 
70,000 grains or 10 lb. avoirdupois. To all ordinary observation, water is 
incompressible ; very accurate experiments have nevertheless shown that it 
does yield to a small extent when the power employed is very great ; the 
diminution of volume for each atmosphere of pressure being about 51-mU- 
lionths of the whole. 

Clear water, although colourless in small bulk, is blue like the atmosphere 
when viewed in mass. This is seen in the deep ultramarine tint of the ocean, 
and perhaps in a still more beautiful manner in the lakes of Switzerland 
and other Alpine countries, and in the rivers which issue from them ;. ihe 
(lightest admixture of mud or suspended impurity destroying the effect. 

» Ann. Chim. et Pbys. xv. 886. ' * Ann. Chim. et Phys. 8rd series, viii. IPd. 


The same magnificeiit colour is yisible in the fissures and caverns found ia 
the ice of the glaciers, which is usually extremely pure and transparent 
within, although foul upon the surface. 

Steam, or vapour of water, in its state of greatest density at 212° (100°C), 
compared with air at the same temperature, and possessing an equal elastic 
force, has a specific gravity expressed by the fraction of 0-625. In this con- 
dition, it may be represented as containing, in every two volumes, two 
volumes of hydrogen, and one volume of oxygen. 

Water seldom or never occurs in nature in a state of perfect purity ; even 
the rain which falls in the open pountry, contains a trace of ammoniacal salt, 
while rivers and springs are invariably contaminated to a greater or less 
extent with soluble matters, saline and organic. Simple filtration through a 
porous stone or a bed of sand will separate suspended impurities, but dis- 
tillation alone will free the liquid from those that are dissolved. In the pre- 
paration of distilled water, which is an article of large consumption in the 
scientific laboratory, it is proper to reject the first portions which pass over, 
and to avoid carrying the distillation to dryness. The process may be con- 
ducted in a metal still furnished with a worm or condenser of silver or tin ; 
lead must not be used. 

The ocean is the great recipient of the saline matter carried down by the 
rivers which drain the land; hence the vast accumulation of salts. The 
following table will serve to convey an idea of the ordinary composition of 
sea-water ; the analysis is by Dr. Schweitzer/ of Brighton, the water being 
that of the Channel : — 

1000 grains contained 

Water 964-746 

Chloride of sodium .• 27-059 

Chloride of potassium 0-766 

Chloride of magnesium 8-666 

Bromide of magnesium 0-029 

Sulphate of magnesia 2-296 

Sulphate of lime 1-406 

Carbonate of lime 0033 

Traces of iodine and ammoniacal salt 


Its specific gravity was found to be 1-0274 at 60® (IS^-SC). 

Sea-water is liable to variations of density and composition by the influence 
of local causes, such as the proximity of large rivers or masses of melting 
ice, and other circumstances. 

Natural springs are often impregnated to a great extent with soluble sub- 
stances derived from the rocks they traverse ; such are the various mineral 
waters scattered over the whole earth, and to which medicinal virtues are 
attributed. Some of these hold protoxide of iron in solution, and are effer- 
vescent from carbonic acid gas ; others are alkaline, probably from traver- 
sing rocks of volcanic origin ; some contain a very notable quantity of iodine 
or bromine. Their temperatures also are as variable as their chemical 
nature. A tabular notice of some of the most remarkable of these waters 
will be found in the Appendix. 

Water enters into direct combination with other bodies, forming a class 
of compounds called hydrates; the action is often very energetic, much heat 
being evolved, as in the case of the slaking of lime, which is really the pro- 
duction of a hydrate of that base. Sometimes the attraction between the 

> Phil. Mag. July, 1839. 


water and the second body is so great that the compound is not decomposable 
bj any heat that can be applied ; the hydrates of potassa and soda; and of 
phosphoric acid, furnish examples. Oil of yitriol is a hydrate of snlphnric 
acid, from which the water cannot be thus separated. 

Water very frequently combines with saline substances in a less intimate 
manner than that above described, constituting what is called water of crys- 
tallization, from its connexion with the geometrical figure of the salt In 
this case it is easily driven off by the application of heat. 

Lastly, the solvent properties of water far exceed those of any other liquid 
known. Among salts, a very large proportion are soluble to a greater or 
less extent, the solubility usually increasing with the temperature, so that a 
hot saturated solution deposits crystals on cooling. There are a few excep- 
tions to this law, one of the most remarkable of which is common salt, the 
solubility of which is nearly the same at all temperatures ; the hydrate and 
certain organic salts of lime, also, dissolve more freely in oold than in hot 

Water dissolyes gases, but in yery unequal quantities ; some, as hydrogen, 
oxygen, and atmospheric air, are but little acted upon ; others, as ammonia 
and hydrochloric acid, are absorbed to an enormons extent ; and between 
these extremes -there are various intermediate degrees. Generally, the colder 
the water, the more gas does it dissolve ; a boiling heat disengages the whole, 
if the gas be not very soluble. 

When water is heated in a strong vessel to a temperature above that of 
the ordinary boiling-point, its solvent powers are still further increased. 
Dr. Turner inclosed in the upper part of a high-pressure steam-boiler, worked 
at 300° (149°C), pieces of plate and crown glass. At the expiration of four 
months the glass was found completely corroded by the action of the water ; 
what remained was a white mass of silica, destitute of alkali, while stalac- 
tites of siliceous matter, above an inch in length, depended from the little 
wire cage which inclosed the glass. This experiment tends to illustrate the 
changes which may be produced by the action of water at a high tempe- 
rature in the interior of the earth upon felspathic and other rocks. Some- 
thing of the sort is manifest in the Geyser springs of Iceland, which deposit 
siliceous sinter.* > 

Bmoxide of hydrogen, sometimes called oxygenated watery is an exceedingly 
interesting substance, but unfortunately very difficult of preparation. It is 
formed by dissolving the binoxide of barium in dilute hydrochloric acid, 
carefully cooled by ice, and then precipitating the baryta by sulphuric acid ; 
the excess of oxygen of the binoxide, instead of being disengaged as gas, 
Tmites with a portion of the water, and converts it into binoxide of hydrogen. 
This treatment is repeated with the same solution and fresh portions of the 
binoxide of barium until a considerable quantity of the latter has been con- 
Bumed, and a corresponding amount of binoxide of hydrogen formed. The 
liquid yet contains hydrochloric acid, to get rid of which it is treated in suc- 
cession with sulphate of silver and baryta-water. The whole process re- 
quires the utmost care and attention. The binoxide of barium itself is pre- 
pared by exposing pure baryta, contained in a red-hot porcelain tube, to a 
stream of oxygen. The solution of binoxide of hydrogen may be concen- 
trated under the air-pump receiver until it acquires the specific gravity of 
1'46. In this state it presents the aspect of a colourless, transparent, ino- 
dorous liquid, possessing remarkable bleaching powers. It is very prone to 
decomposition ; the least elevation of temperature causes effervescence, due 
to the escape of oxygen gas ; near 212° (lOO^C) it is decomposed with ex/. 

« Phil. Mag. Oct 1834. 



Fig. 90. 

plosire violenoe. Binozide of hydrogen contains ezaoUy imw fts mii«k 
ttygen as water, or 16 parts to 1 part of hydrogen. 


Nitrogen' constitutes about four-fifths of the atmosphere) and enters into 
a great variety of combinations. It may be prepared for the purpose of expe- 
riment by several methods. One of the simplest of these is to burn out the 
oxygen from a confined portion of air, by phosphorus, or by a jet of hy- 
A small porcelain capsule is floated on the water of the pneumatic trough, 
and a piece of phosphorus placed in it and set on fire. 
(Fig. 90.) A bell-jar is then inverted over the whole, 
and suffered to rest on the shelf of the trough, so as 
to project a little over its edge. At first, the heat 
causes expansion of the air of the jar, and a few bub- 
bles are expelled, after which the level of the water 
rises considerably. When the phosphorus becomes 
extinguished by exhaustion of the oxygen, and time 
has been given for the subsidence of the cloud of finely- 
divided, snow-like phosphoric acid, which floats in the 
residual gas, the nitrogen may be decanted into ano- 
ther vessel, and its properties examined. 

Prepared by the foregoing process, nitrogen is con- 
taminated by a little vapour of phosphorus, which 
communicates its peculiar odour. A preferable me- 
thod is to fill a porcelain tube with turnings of copper, 
or, still better, with the spongy metal obtained by reducing Sie oxide by 
hydrogen ; to heat this tube to redness, and then pass through it a stream 
of atmospheric air, the oxygen of which is entirely removed during its pro- 
gress by the heated copper. 

If chlorine gas be passed into solution of ammonia, the latter substance, 
which is a compound of nitrogen with hydrogen, is decomposed ; the chlo- 
rine combines with the hydrogen, and the nitrogen is set free with efferves- 
cence. In this manner very pure nitrogen can be obtained. In making this 
experiment, it is necessary to stop short of saturating or decomposing the 
whole of the ammonia, otherwise there will be great risk of accident from 
the formation of an exceedingly dangerous explosive compound formed by 
the contact of chlorine with an ammoniacal salt. 

Nitrogen is destitute of colour, taste, and smell ; it is a little lighter than 
ur, its density being, according to Dumas, 0-972. 100 cubic inches, at 60° 
(15°'5C), and 30 inches barometer, will therefore weigh 30-14 grains. Nitro- 
gen is incapable of sustaining combustion or animal existence, although, like 
hydrogen, it has no positive poisonous properties ; neither Is it soluble to 
any notable extent in water or in caustic alkali ; it is, in fact, best charac- 
terixed by negative properties. 

The exact composition of the atmosphere has repeatedly been made the 
subject of experimental research. Besides nitrogen and oxygen, the air 
contains a little carbonic acid, a very variable proportion of aqueous vapour, 
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 heists, and 
compared with that from the plains of Egypt ; it has been brought from an 
elevation of 21,000 feet by the aid of a balloon ; it has been collected and 
examined in London and Paris, and many other districts ; still the propor^ 

' t. e. Qnuenlbn of nitre; aim called aiote, fitom «, privative^ awl ^w^ lift. 



Urns of oxygen sod mtrogoi remain maltertd, ilie diiliimTe mergy of tlie 
gases being adequate to maintain this perfect mufonnitj of mixture. The 
Mrbome acid, on the contrary, being much influenced by local causes, Taries 
considerably. In the following table the proportion of oxygen and nitrogen 
are giren on the authority of M. Dumas, and the carbonic acid on that of 
BerSaossure; the ammonia, the discoTery of which is due to liebig, is too 
onaU in quantity for direct estimatioh. 

CanqtotUion of ike Atmo^here. 
By weight. 

Nitrogen... 77 parts 

Oxygen 23 «• 


.. 7919 
.. 20-81 




Carbonic acid, from 8*7 measures to 6*2 measures, in 10,000 
* Aqueous yaponr Tariable, 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 OO^ F. (15o-6C) and tiie baro- 
meter standing at 30 Inches. 

The analysis of air is very well effected by passing it 
orer findy-divided copper contained in a tube of hard glass, 
esrefolly weighed, and then heated to redness; the ni- 
trogen is suffered to flow into an exhausted glass globe, 
also previously weighed. The increase of weight after 
the experiment gives the information sought. 

An easier, but less accurate method, consists in intro- 
docing into a graduated tube, standing over water (fig. 91), 
1 known quantity of the air to be examined, and then 
passing into the latter a stick of phosphorus affixed to 
the end of a wire. The whole is left about twenty-four 
hours, during which the oxygen is slowly but completely 
absorbed, after which the phosphorus is withdrawn and the 
residual gas read off. 

Professor Liebig has lately proposed to use an alkaline 
solution of pyro-gallic acid, (a substance which will be 
described in the department of organic chemistry,) for the 
absorption of oxygen. The absorptive power of such a 
solution, which turns deep black on coming in contact with 
the oxygen, is very considerable. Liebig*s method combines great accuracy 
with unusual rapidity and facility of execution. 

Another plan is to mix the air with hydrogen and pass an electric spark ; 
after the explosion the volume of gas is read off and compared with that of 
the air employed. Since the analysis of gaseous bodies by explosion is an 
operation of great importance in practical chemistry, it may be worth while 
describing the process in detail, as it is applicable, with certain obvious 
variations, to a number of analogous cases. 

A convenient form of apparatus for the purpose is the siphon eudiometer 
of Dr. Ure ; this consists of a stout glass tube, having an internal diameter 
if 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 
•park. The closed limb is carefully graduated. When required for use, the 




iBBtnilBeiit 18 filled with mituij and inToted into 4 
Teasel of the same fluid. A quantity of the air to be 
ezamined is then introdnoed, the manipulation being 
precisely the same as with experiments oTer water ; 
the open end is stopped with a finger, and the air 
transferred to the eloeed extremity. The instrument 
is next held upright, and after the level of the mer- 
cury has been made equal on both sides by displacing 
a portion from the open limb by thrusting down a 
piece of stick, the Tolume of air is read off. This 
done, the open part of the tube is again filled up with 
mercai^, closed with the finger, interted into the 
liquid metal, and a qulmtity of pure hydrogen intro- 
duced, equal, as ne«^y as 'can be guessed, to aboat 
half the yolume of the air. The eudiometer is once 
more brought into an erect posttton, the leytA. of tiie 
mercury equalized, and the Yolume again read off; 
the quantity of hydrogen added is thus aeeurately 
ascertained. All is now ready for the explosion ; the 
instrument is held in the way represented, the open 
end being firmly closed by the thumb, while the knuckle of the fore-finger 
touches the nearer platinum wire ; the spark is then passed by the aid of a 
charged jar or a good electrophoms, and explosion ensues. The air con- 
fined by the thumb in the open part of the tube acts as a spring and mode- 
rates Ihe explosive effect Nothing now remains but to equalise the lerel 
of the mercury by pouring a little more into the instrument, and then to 
read off the volume for the last time. 

What is required to be known from this experiment is the dimmutian the 
mixture suffers by explosion ; for since the hydrogen is in excess, and since 
that substance unites with oxygen in the proportion by measure of two to 
one, one-third' part of that diminution must be due to the oxygen contained 
in the air introduced. As the amount of the latter is known, the proportion 
uf oxygen it contains thus admits of determination. The ease supposed 
will render this clear. 

Air introduced 100 measures. 

Air and hydrogen .'. 160 

Volume after explosion 87 

Diminution 68 

-— SB 21 ; oxygen in the hundred measures. 

The working pupil will do well to acquire dexterity in the use of this val- 
uable instrument, by practising the transference of gas or liquid from the 
one limb to the other, &c. In the analysis of combustible gases by explo- 
sion with oxygen, solution of caustic potassa is often required to be intro- 
duced into the closed part 

Compounda of Nitrogen and Oxygen, 

There are not less than five distinct compounds of nitrogen and oxygen, 
thus named and constituted : — 

NfTiioGsir. ' 129 

OompMltton bf va^lit 

Nitrogen. Oxygen. 

Protoxide of nitrogen » , 14 8 

Binoxide of nitrogen^ 14 16 

Nitrous acid 14 24 

H^onitric acid* 14 82 

Nitric acid 14 ;.... 40 

Nifxifi or Azotic Acid. — lA certain parts of India, aod alao in other hot dr^ 
elimates where rain is rare, the surface of the soil is occasionally covereU 
bj a saline efflorescence, lih^ that sometimes apparent on newly-plastered 
walb ; this substance collected, dissolved in hot water, the solution filtered 
sod made to crystallize, furnishes the highly important salt known in com- 
iseree as nitre or saltpetre ; it is a compound of nitric acid and potaesa. 
To obtain liquid nitric acid, equal weights of powdered nitre and oii of 
Titrid are introduced into a glass retort, and heat applied by means of an 
Argand gas-lamp or charcoal chauffer. A flask, cooled by a wet cloth, \b 
adapted to the retort, to serve for a receiver. No luting of any kind must 
be used. 

is the distillation advances, the red fumes which first arise disappear, but 
towards the end of the process again become manifest. When this happens, 
and very little liquid passes over, while the greater part of the saline matter 
of the retort is in a state of tranquil fusion, the operation may be stopped ; 
and when the retort is quite cold, water may be introduced to dissolve out 
the bisolphate of potassa. The reaction is thus explained. 

m f ** 'fti i Water .-^'''^^'""^^,^^^ 

KM 01 Timoi ^ g^iph^ic acid _:::-=^Bi8ulphate of potassa. 

In the manufaeture of nitric acid on t^e large scale, the glass i^tort is 
replaced by a cast-iron cylinder, and the receiver by a series of earthen con- 
densing vessels connected by tubes. (Fig. 93.) Nitrate of soda, found native 
in Peru, is often substituted for nitrate of potassa. 

rig. 93. 

Liquid nitric acid so obtained has a specific gravity of 1*5 to 1-62 ; it has a 
golden yellow colour, which is due to nitrous or hyponitric acid held in solu- 
tion, and which, when the acid is diluted with water, gives rise by its decom- 
position to a disengagement of nitric oxide. It is exceedingly corrosive, 
Btaining the skin deep yellow, and causing total disorganization. Poured 
opoQ 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. 

» OtherwUie called nitrous oxide. • OtherwiM called nitric oxide. 

* Called by Profeteor Graham peroxide of nitrogen. 


Pure liquid nitric acid, in its most concentrated form, is obtained by mix* 
ing the above with about an equal quantity of oil (»f vitriol, re-distilling, 
collecting apart the first portion which comes over, and exposing it in a 
vessel slightly warmed, and sheltered from the light, to a current of dry 
air, made to bubble through it, which completely removes the nitrous acid. 
In this state the product is as colourless as water; it has the sp. gr. 1-517 
at 60° (15°-5C), boils at 184° (84° -SC), and consists of 54 parts real acid, 
and 9 parts water. Although nitric acid in a more dilute form acts very 
violently upon many metals, and upon organic substances generally, this is 
not the case with the compound in question ; even at a boiling heat it re- 
fuses to attack iron or tin, and its mode of action on lignin, starch, and 
similar substances, is quite peculiar, and very much less energetic than that 
of an acid containing more water. 

A second definite compound of real nitric acid and water exists, containing 
64 parts of the former to 36 parts of the latter. Its sp. gr. at 60o (15o-5C) 
is 1-424, and it boils at 250^ (121 <>C). An acid weaker than this is concea- 
trated to this point by evaporation ; and one stronger, reduced to the same 
amount by loss of nitric acid and water in the form of the first hydrate.* 

Absolute nitric acid, in the separate state, was unknown up to 1849, when 
M. Deville succeeded in obtaining this remarkable substance by exposing 
nitrate of silver, which is a combination of nitric acid, silver, and oxygen, 
to the action of chlorine gas. Chlorine and silver combine, forming chloride 
of silver, which remains in the apparatus, whilst oxygen and anhydrous 
nitric acid separate. The latter is a colourless substance, crystallizing in 
six-sided columns, which fuse at SQ^ (80°C), and boil between 113° and 
122° (45° and 50°C), when they commence to be decomposed. Anhydrous 
nitric acid has been found to explode sometimes spontaneously. It dissolves 
in water with evolution of much heat, forming hydrated nitric acid. It con- 
sists of 14 parts of nitrogen and 40 parts of oxygen. 

Nitric acid forms with bases a very extensive and important group of salts, 
the nitrates, which are remarkable for all being soluble in water. The 
hydrated acid is of great use in the laboratory, and also in many branches 
of industry. 

The acid prepared in the way described is apt to contain traces of chlo- 
rine from common salt in the nitre, and sometimes of sulphate from acci- 
dental splashing of the pasty mass in the retort. To discover these impuri- 
ties, a portion is diluted with four or five times its bulk of distilled water, 
and divided between two glasses. Solution of nitrate of silver is dropped 
into the one, and solution of nitrate of baryta into the other ; if no change 
ensue in either case, the acid is free from the impiirities mentioned. 

Nitric acid has been formed in small quantity by a very curious process, 
namely, by passing a series of electric sparks through a portion of air, 
water, or an alkaline solution being present. The amount of acid so formed 
after many hours is very minute ; still it is not impossible that powerful 
discharges of atmospheric electricity may sometimes occasion a trifling pro- 
duction of nitric acid in the air. A very minute quantity of nitric acid is 
also produced by the combustion of hydrogen and other substances in the 
atmosphere ;. it is also formed by the oxidation of ammonia. 

Nitric acid is not so easily detected in solution in small quantities as many 
other acids. Owing to the solubility of all its compounds, no precipitant can 
be found for this substance. One of the best tests is its power of bleaching 
a solution of indigo in sulphuric acid when boiled with that liquid. The 

• The two hydrates of nitric acid are thus expressed hy symbols : — ^NOb, HO and NO*, 4II0. 
No compound containlDg two equiyalentg of water appears to e^iist. 



ftbsenee of eUorine must be ensiired in this experiment by means irhich wiH 
hereafter be obvious, otherwise the result is equivocal. 

Protoxide of Nitrogen ; Nitrous Oxide ; (laughing gas.) — When solici 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 decompoBition will be understood from the subjoined diagram. 


Nitric acid 


' Nitrogen 

Brotoz. nitrogen 22 

Protoz. nitrogan 22 
Water 27 

-Water ». 

Fig. 94. 

No particular precautian i» required in the ope- 
ration, save due regulation of the heat, and the 
aroidance of tumultuous disengagement of the gas. 

Protoxide of nitrogen is a colourless, transparent, 
and almost inodorous gas, of distinctly sweet taste. 
Its specific gravity is 1*525; 100 cubic inches 
weigh 47*29 grains. It supports the combustion 
of a taper or piece of phosphorus with almost as 
-much energy as pure oxygen; it is easily distin- 
galshed, 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 46** 
(7°'2C) a pressure of 50 atmospheres ; the liquid 
when exposed under the bell-glass of the air-pump 
is rapidly converted into a snow-like solid. Whei^. 
mixed with an equal volume of hydrogen, and fired 
by the electric spark in the eudiometer, it explodes 
with violence, and liberates its own measure of nitrogen. Every two vol- 
umes of the gas must consequently contain two volumes of nitrogen and one 
volume of oxygen, the whole being condensed or contracted one-third; a 
constitution resembling that of vapour-of water." 

The most remarkable feature in this gas is its intoxicating power upon the 
animal system. It may be respired, if quite pure, or merely mixed with 
atmospheric air, for a short time, without danger or inconvenience. The 
effect is very transient, and is not followed by depression. 

Binexide of Nitrogen ; Nitric Oxide, — Clippings or turnings of copper are 
pQt into the apparatus, employed for preparing hydrogen," together with & 
little w^ter, and nitric acid add'ed by the funnel until brisk effervescence is 
excited. The gas may be collected over cold water, as it is not sensibly 

The reaction is a simple deoxidation of some of the nitric acid by the 
copper ; the metal is oxidized, and the oxide so formed is dissolved by an- 

' Florence oil-flasks, which may he purchased at a very trifling sum, constitute exceedingly 
uefal TtttselB for chemical purpoi^es, and often supersede retorts or other expensive appa- 
nitM. They are rendered atill 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 
CO as to form a lip, or border. The neck will then bear a tight-fitting cork without risk of 

*8oepageU8. •See page 111. 


126 NITRO0SN. 

other portion of tbo aoid. Nitric acid is Tcry prone to act thus upon certain 


The gas obtained in this manner is colonrless and transparent ; in contact 
with air or oxygen gas it produces deep red fumes, which are readily ab- 
sorbed by water ; this character is sufiScient to distinguish it from all other 
gaseous bodies. A lighted taper plunged into the gas is extinguished ; lighted 
phosphorus, however, burns in it with great brilliancy. 

The specific gravity of binoxide of nitrogen is 1-039; 100 cubic inches 
weigh 82*22 grains. It contains equal measures of oxygen and nitrogen 
gases united without condensation. When this gas is passed into a solution 
of protoxide of iron it is absorbed in large quantity, and a deep brown or 
nearly black liquid produced, which seems to be a definite compound of the 
two substances. The compound is again decomposed by boiling. 

Nitrous Acid. — Four measures of binoxide of nitrogen are mixed with one 
measure of oxygen, and the gases, perfectly dry, exposed to a temperature 
of 0® ( — 170-8C). They condense to a thin mobile green liquid. Its vapour 
is orange-red. 

Nitrous acid is decomposed by water, being converted into nitric acid and 
binoxide of nitrogen. For this reason it cannot be made to unite directly 
with metallic oxides ; nitrite of potassa may, however, be prepared by fusing 
nitrate of potassa, when part of its oxygen is evolved; and many other salts 
of nitrous acid may be obtained by indirect means. 

Hyponitric Acid. — It has been doubted whether the term acid applied to 
this substance be correct, since it seems to possess the power of forming salts 
only in a very limited degree; the expression has, notwithstanding, been 
long sanctioned by use. Moreover, a beautiful crystalline lead-salt of this 
substance has been discovered by M. P^ligot. It is formed by digesting 
nitrate of lead ,with metallic lead. 

It is chiefly the vapour of hyponitric acid which forms the deep red fumes 
always produced when binoxide of nitrogen escapes into the air. 

When carefully dried nitrate of lead is exposed to heat in a retort of hard 
glass, it is decomposed ; protoxide of lead remains behind, while the acid is 
resolved' into a mixture of oxygen and hyponitric acid. By surrounding the 
receiver with a very powerful freezing mixture, the latter is condensed to 
the liquid form. It is then nearly colourless, but acquires a yellow, and ul- 
timately a red tint, as the temperature rises. At 82® (27° -SC) it boils, 
giving off its well-known red vapour, the intensity of the colour of which is 
greatly augmented by elevation of temperature. 

This substance, like the preceding, is decomposed by water, being resolved 
into binoxide of nitrogen and nitric acid. Its vapour is absorbed by strong 
nitric acid, which thereby acquires a yellow or red tint, passing into green, 
then into blue, and afterwards disappearing altogether on the addition of 
successive portions of water. The deep red fuming acid of commerce, called 
nitrous acid, is simply nitric acid impregnated with hyponitric gas.* 

Nitrogen appears to combine, under favourable circumstances, with metals 
When iron and copper are heated to redness in an atmosphere of ammonia^ 
they become brittle and crystalline, but without sensible alteration of weight. 
M. Schrotter has shown that in the case of copper, at least, this effect is 

* Much doubt yet hangs over the true nature and relations of these two adds. AooordiDg 
to M. Pfiligot, the only product of the union of binoxide of nitrogen and oxygon is hyponitric 
acid, which in the total absence of water is a white Folid crystalllDe body, fusible at 16"^ 

U8*dCy. At common temperatures it la an orange-yellow liquid. The same product is ob- 
led by heating perfectly dry nitrate of lead. From these experiments it would appear~ 
that nitrous acid in a separate state is unknown. Ann. Cbim, et Phys. 3d series, \\. 58, 



caused by ihe fbmatioa ftiid snbseqiieiit defltroction of a nitride, that is, a 

compound of nitrogen with eopper. When ammonia is passed over protoxide 
of copper heated to 670° (298®-9C), water is formed, and a soft brown 
powder produced, which when heated farther evolvt^s nitrogen, and leaves 
metallic copper. The same effect is produced by the contact of strong acids. 
A similar compound of chromium with nitrogen appears to exist. 

This substance occurs in a state of purity, and crystallized, in two distinct 
and very dissimilar forms, namely, as diamond, and as graphite or plumbago. 
It constitutes a large proportion of all organic structures, animal and vege- 
table : when these latter are exposed to destructive distillation in close ves- 
sels, a great part of this carbon remains, obstinately retaining some of the 
hydrogen and oxygen, and associated with the earthy and alkaline matter of 
the tissue, giving rise to the many varieties of charcoal, coke, &c. 

The diamond is one of the most remarkable substances known ; long prized 
on account of its brilliancy as an ornamental gem, the discovery of its curi- 
oas chemical nature confers upon it a high degree of scientific interest. 
Several localities in India, the island of Borneo, and more especially Brazil, 
furnish this beautiful substance. It is always distinctly crystallized, often 
quite transparent and colourless, but now and then having a shade of yellow, 
pink, or blue. The origin and true geological position of the diamond are 
unknown ; it is always found embedded in gravel and transported materials, 
whose history cannot be traced. The crystalline form of the diamond is 
that of the regular octahedron or cube, or some figure geometrically con- 
nected with these; many of the octahedral crystals exhibit a Very peculiar 
appearance, arising from the faces being curved or rounded, which gives to 
the crystal an almost spherical figure. 

FSg. 95. 

Fig. 96. 

Fig. 97. 

Fig. 98. 


The diamond is infusible and inalterable by a very intense heat, provided 
air be excluded : but when heated, thus protected, between the poles of a 
Btrong galvanic battery, it is converted into coke or graphite ; heated to or- 
dinary redness in a vessel of oxygen, it bums with facility, yielding carbonic 
acid gas. 

This is the hardest substance known ; it admits of being split or cleaved 
without difl&culty in certain particular directions, but can only be cut or 
abraded by a second portion of the same material ; the powder rubbed off 
in this process serves for polishing the new faces, and is also highly useful 
to the lapidary and seal-engraver. One very curious and useful application 
qf 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 
eryiial of diamond having the rounded octahedral figure spoken of, held in 
one particular position on the glass, namely, with an edge formed by the 
meeting of two adjacent faces presented to the surface, and then drawn 
along with gentle pressure, causes a deep split or cut, which penetrates to 
a considerable depth into the glass, and determines its fracture with perfect 

128 CAHBON. 

Graphite, or plumbago, appears to consist essentially of pure carbon, al* 
though most specimens contain iron, the quantity of which varies from a 
mere trace up to five per cent. Graphite is a somewhat rare mineral ; the 
finest, and most valuable for pencils, is brought from Borrowdale, in Cum- 
berland, where a kind of irregular vein is found traversing the ancient slate- 
beds of that district. Crystals are not conmion ; when they occur, they 
have the figure of a short six-sided prism ; — a form bearing no geometrio 
relation to that of the diamond. 

Graphite is often formed artificially in certain metallurgic operations ; the 
brilliant scales which sometimes separate from melted cast iron on cooling, 
called by the workmen " kish," consist of graphite. 

Lampblack, the soot produced by the imperfect combustion of oil or resin, 
is the best example that can be given of carbon in its uncrystaUized 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, 
18 the most valuable as fuel. Coke, the charcoal of pit-coal, is much more 
impure ; it contains a large quantity of earthy matter, and very often sul- 
phur; the quality dependiDg very much upon the mode of preparation. 
Charcoal from bones and animal matters in general is a very valuable sub- 
stance, on account of the extraordinary power it possesses of removing 
colouring matters from organic solutions ; it is used for this purpose by the 
sugar-refiners to a very great extent, and also by the manufacturing and 
scientific chemist.* The property in question is possessed by ^1 kinds of 
charcoal in a small degree. 

Charcoal made from box, or other dense wood, has a property of con- 
densing into its pores gases and vapours ; of ammoniacal gas it is said to 
absorb not less than ninety times its volume, while of hydrogen it takes up 
less than twice its own bulk, the quantity being apparently connected with 
the property in the gas of sufiFering liquefaction. This eflfect, as well as 
that of the decolorizing power, no doubt depends in some way upon the 
same peculiar action of surface so remarkable in the case of platinum in a 
mixture of o lygen and hydrogen." 

Compounds of Carbon and Oxygen, 
There are two direct inorganic compounds of carbon and oxygen, called 
carbonic oxide and carbonic acid ; their composition may be thus stated : — 

CkiBiposiiion by weight. 

Carbon. Oxygen. 

Carbonic oxide .• 6 8 

Carbonic acid 6 16 

* It removes from aolution in vater the vegetable bases, bitter prindples and astringent 
aubstances, when employed in excess, requiring from twice to twenty times their weight for 
total precipitation. A solution of iodine in water, or iodide of potassium, is qoiclcly de< 
prived of colour. Metallic salts dissolved in water or diluted alcohol are precipitated, though 
not entirely, requiring about thirty times their weight of animal charcoal. Arsenious acid 
U totally carried out of solution. In these cases it acts in three different ways: the salt is 
Absorbed unaltered; the oxide in the salt may be reduced; or, the salts precipitated in a 
liasic condition, the solution showing an acid reaction as soon as the carbon b^ns to act. It 
is in this last case especially that traces of the bases can be detected, the acid set firee pre- 
venting their total precipitation. The precipitation may hence be prevented by adding an 
excess of acid, and the ba^s after precipitation may be dissolved out by boiling with an add 
solution. — Warrington, Mem. Chim. Soc. 1S45; Oarrod, Pharm. Joum. 1845; Weppen, Ann. 
deCbim. 1845. — K. B. 

> Carbon is a combustible uniting with oxygen and producing carbonic add. Its different 
forms exhibit much difference in this respect; in the very porous condition of charcoal it 
burns readily, while in its most dense form, the diamond, it requires a bright red heat and 

Eure oxygen. In the form of charcoal it conducts heat slowly and electridty readily. Oar< 
on is insoluble in water and not liable to be affected by air and moisture. It retards putre> 
fitoUon.— ft.B. 



Carhonie Acid is always produced when charcoal bums in air or in oxygen 
gas; it is most oonveniently obtained, however, for study, by decomposing 
i carbonate with one of the stronger acids. For this purpose, the apparatus^ 
for generating hydrogen may be again employed ; fragments of marble are 
put into the bottie, with enough water to coyer the extremity of the funnel- 
tube, and hydrochloric or nitric acid added by the latter, until the gas is 
freely disengaged. Chalk-powder and dilute sulphuric acid may be used 
instead. The gas may be collected over water, although with some loss ; or"" 

Kg. 99. 

Tery conTcniently, by displacement, if it be required dry, as shown in fig. 
99. The long drying-tube is filled with fragments of chloride of calciufn, 
and the heavy gas is conducted to the bottom of the vessel in which it is to 
be received, the mouth of the latter being lightly closed.* 

Carbonic acid gas is colourless ; it has an agreeable pungent taste and 
odour, but cannot be respired for a moment without insensibility following. 
Its specific gravity is 1-624,* 100 cubic inches weighing 47-26 grains. 

This gas is very hurtful to animal life, even when largely diluted with air ; 
it acts as a narcotic poison. Hence the danger arising from imperfect ven- 
tilation, the use of fire-places and stoves of all kinds unprovided with proper 
chimneys, and the crowding together of many individuals in houses and 
ships without efiScieut means for renewing the air ; for carbonic acid is con- 
stantly disengaged during the process of respiration, which, as we have seen, 
(page 108,) is nothing but a process' of slow combustion. This gas is some- 
times emitted in large quantity from the earth in volcanic districts, and it is 
constantly generated where organic matter is in the act of undergoing fer- 
mentive decomposition. The fatal ** after-damp" of the coal-mines contains 
a large proportion of carbonic acid. 

' In oonnocting tabe-apparatus for conTeying gases or oold liquids, not oorrosiye, littlti 
tcbes of caoutchouc about an inch long, arc inr 
expresnUy uf>efuL The^e are made by bending 
a piece of sheet India-rubber, a, fig. 100, loosely 
round a glass tube or rod, o, and cutting off the 
superfluous portion with sharp scissors. The 
fr«9b-cut edges of the caoutchouc pros>~ed strongly 
to;;etber, cohere completely, provided they have 
■ot been soiled by touching vrith the fingers, and 
tbe tube is perfect. The connectors are secured 
by two or three turns of tliin silk cord. The 
glass tubes are sold by weight, and are easily 
bent in the flame of a spirit-lamp, and, when 
Meessary, cnt by scratching with a file, and 
Weaking asunder. 

* MM. Dalong and Berzeliui. 

Fig. 100. 


A lifted taper pltm^d into catbonic acid is iDstantly extinguished, even 
to the red-hot snuff. When diluted with three times its volume of air, it 
Btill has the power of extinguishing a light. The gas is easily known from 
nitrogen, which is also incapable of supporting combustion, by its rapid 
absorption by caustic alkali or by lime-water ; the turbidity communicated 
to tlie latter from the production of insoluble carbonate of lime is very 

Cold water dissolyee about its own yolume of carbonic acid, whatever bo 
the density of the gas with which it is In contact ; the solution temporarily 
reddens litmus paper. In common soda-water, and also in effervescent 
wines, examples may be seen of this solubility of the gas. Even boiling 
water absorbs a perceptible quantity. 

Some of the interesting phenomena attending the liquefaction of carbonio 
acid have been already described ; it requires for the purpose a pressure of 
between 27 and 28 atmospheres at 32° (0°C), according to Mr. Addams. 
The liquefied acid is colourless aad limpid, lighter than water, and four 
times more expansible than air; it mixes in all proportions with ether, 
alcohol, naphtha, oil of turpentine, and bisulphide of carbon, and is insoluble 
in water and fat oils. It is probably destitute when in this condition of all 
properties of an acid.* 

Carbonic acid exists, as already mentioned, in the air ; relatively, its quan- 
tity is but small, but absolutely, taking into account the vast extent of the 
atmosphere, it is very great, and fully adequate to the purpose for which it 
is designed, namely, to supply to plants their carbon, these latter having 
the power, by the aid of their green leaves, of decomposing carbonic acid, 
retaining the carbon, and expelling the oxygen. The presence of light is 
essential to this extraordinary effect^ but of the manner of ita execution we 
are yet ignorant 

The carbonates form a very large and important group of salts, wme of 
which occur in nature in great quantities, as the carbonates of Hmeand mag- 

Carbonic Oxide. — When carbonic acid is passed over red-hot charcoal or 
metallic iron, one-half of its oxygen is removed, and it becomes converted 
into carbonic oxide. A very good method of preparing this gas is to intro- 
duce into a flask fitted with a bent tube some crystallized oxalic acid, or salt 
of sorrel, and pour upon it five or &ix times as much strong oil of vitriol. 
On heating the mixture the organic acid is resolved into water, carbonic acid, 
and carbonic oxide ; by passing the gases through a strong solution of caus- 
tic potassa, the first is withdrawn by absorption, while the second remains 
unchanged. Another, and it may be preferable method, is to heat finely- 
powdered yellow ferrocyanide of potassium with eight or ten times its weight 
of concentrated sulphuric acid. The salt is entirely decomposed, yielding a 
most copious supply of perfectly pure carbonic oxide gas, which may be col- 
lected over water in the usual manner.^ 

Carbonic. oxide is a combustible gas; it burns with a beautiful pale blue 
flame, generating carbonic acid. It has never been liquefied. It is colour- 
less, has very little odour, and is extremely poisonous, even worse than 
carbonic acid. Mixed with oxygen, it explodes by the electric spark, but 

* When relieved of pressure it immediately boils, and seven parts out of eight af>sume the 
gaseous state, the rest becoming solid at —90° (670*7C) (Mitchell). Solid carbonic acid mixed 
■with ether produces in vacuo a very intense cold ( — 165° [109°'4C] Faraday), capable of 
solidifying; many gases when aided by pressure. Liquid carbonic acid immersed in this mix- 
ture becomes a solid so clear and transparent that its condition cannot be detected until a 
portion again becomes liquid. — R. B. 

9 See a paper by the author, in Memoirs of Chem. Soc. of London, i. 251. 1 eq. crystal- 
lized ferrocyanide of potassium, and 6 eq. oil of vitriol, yield 6 eq. carbonic oxide, 2 eq. sol 
phate of potassa, 8 eq. sulphate of ammonia, and 1 eq. protosulphate of iron. 


with some difficulty. Its specific grayitj is 0*978 ; 100 cnbio inc^M weigli 
80-21 grains. 

The relation by Tolame of these oxides of carbon may thns be made in- 
telligible : — carbonic acid contains its own volame of oxygen, that gas suffer-^ 
iog no change of bnlk by its eonyersion. One measure of carbonic oxide^ 
mixed with half a measure of oxygen and exploded, yields one measure ofj 
CArbonic acid ; hence carbonic oxide contains half its Tolome of oxygen. f 

Carbonic oxide unites with chlorine under the influence of light, forming 
8 pungent, suffocating compound, possessing acid properties, called phosgene 
gas, or chloro-carbonic acid. It is made- by mixing equal Tolumes of car- 
bonic oxide and chlorine, both perfectly dry, and exposing the mixture to 
sunshine; the gases unite quietly, the colour disappears, and the volume 
becomes reduced to one-half. It is decomposed by water. 

This is an elementary body of gr^at importance and interest. Sulphur 
is often found in a fVee dttkte in connection with deposits of gypsum and rock- 
salt; its occurrence in volcafiici districts is probably accidentaL Sicily fur- 
nishw a large proportidn of th6 bUlphur employed in Europe. In a state of 
combination with iron and other metals, and as sulphuric acid, united to 
lime and magnesia, it is Also Abundant. 

Pure sulphur is a pale yellow brittle solid, of well-known appearance. It 
melts' when heated, and distils over unaltered, if air be excluded. The crys- 
tals of sulphur exhibit two distinct and incompatible forms, namely, an oc- 
tahedron with rhombic base (fig. 101), which is the figure of native sulphur, 
and that assumed when sulphur separates from solution at common tempe- 
ratures, as when a solution of sulphur in bisulphide of carbon is exposed to 
slow eraporation in the air; and a lengthened prism (fig. 108), having no 
relation to the preceding ; this happens when a mass of sulphur is melted, 
and, after partial cooling, the crust at the surface broken, and the fluid por 
tion poured out. Fig. 102 shows the result of such an experiment 

Pig. 101. Fig. 102. Fig. 103. 

The specific gravity of sulphur varies according to the form in which it is 
CTystallized. The octahedral variety has a specific gravity 2-046 ; the pris- 
matic variety a specific gravity 1 '982. 

Sulphur melts at 232° (lllO'lC) ; at this temperature it is of the colour 
of amber, and thin and fluid as water ; when farther heated, it begins to 
thicken, and to acquire a deeper colour: and between 480^^ (221 '^C) and 480^ 
j249oC), it is so tenacious that the vessel in which it is contained may be 
mrerted for a moment without the loss of its contents. If in this state it be 
poured into water, it retains for many hours its remarkable soft and flexible 
condition, which should be looked upon as the amorphous state of sulphur. 
After a while it again becomes brittle and crystalline. I^rom the tempera- 
ture last mentioned to the boiling-point, about 792o (400<^C), sulphur again 


becomes thin and liquid. In the prepsration of commercial flowers of snl- 
phiir, the vapour is conducted into a large cold chamber, "where it condenses 
in minute crystals. The specific gravity of sulphur-vapour is 6*664. 

Sulphur is insoluble in water and alcohol ; oil of turpentine and the fat 
oils dissolve it, hut the best substance for the purpose is bisulphide of car- 
bon. In its chemical relations sulphur bears great resemblance to oxygen ; 
to very many oxides there are corresponding sulphides, and these sulphides 
often unite among themselves, forming crystalUzable compounds analogous 
to salts. 

Compounds of Sulphur and Oxygen, 

Oompoeitioii "by weight 

Sulphur. Oxygen. 

Sulphurous acid 16 16 

Sulphuric acid* ..'. 16 24 

Hyposulphurous acid 82 16 

Hyposulphuric acid ' 32 40 

Sulphuretted hyposulphuric acid 48 40 

Bisulphuretted hyposulphuric acid* 64 ,. 40 

Trisulphuretted hyposulphuric acid 80 40- 

Sulphurout Add. — This is the only product of the combustion of sulphur 
in dry air or oxygen gas. It is most conveniently prepared by heating oil 
of vitriol with metallic mercury or copper clippings ; a portion of the acid 
is decomposed, one-third of its oxygen being transferred to the metal, while 
the sulphuric acid becomes sulphurous. Sulphurous acid thus obtained is a 
colourless gas, having the peculiar suffocating odour of burning brimstone ; 
it instantly extinguishes flame, and is quite irrespirable. Its density is 2-21, 
100 cubic inches weighing 68*69 grains. At 0® (— 17**-8C), under the pres- 
sure of the atmosphere, this gas condenses to a colourless, limpid liquid, 
very expansible by heat. Cold water dissolves more than thirty times its 
volume of sulphurous acid. The solution may be kept unchanged so long 
as air is excluded, but access of oxygen gradually converts the sulphurous 
into sulphuric acid, in the presence of water, although the dry gases may 
remain in contact for any length of time without change. When sulphurous 
acid and aqueous vapour are passed into a yessel cooled to below 17° or 21° 
( — 6° or — -8°C), a crystalline body forms, which contains about 24-2 acid to 
76-8 water. 

One volume of sulphurous acid gas contains one volume of oxygen, and 
J^th of a volume of sulphur-vapour, condensed into one volume. 

Gases which, like the present, are freely soluble in water, must be col- 
lected by displacement, or by the use of the mercurial pneumatic trough. 

* The terminations out and tc, applied to adds, fdgnify degrees of oxidation, the latter heing 
the highest; adds ending in oui form salts the names of which are made to end In iUi and 
those in ifi terminate in attf as gulphurom add, stdphite of soda, tulphurie add, nUj^^cUe of 

* The more advanced student will he glad to see these stated in equiyalents hy the use of 
gymhols, hereafter to be explained, their relations becoming thereby much mote evident The 
numbers given are really the equivalent numbers, but are intended only to show the pro- 
portions of sulphur and oxygen, without any reference to other bodies. The following are 
the quantities required to saturate one equivalent of a base: 

Sulphurous add SOa 

Sulphuric add SOs 

Hyposulphurous add S3O1 

Hyposulphuric add, Dithionic add ^ SsO» 

Sulphuretted hyposulphuric add, Trithionic acid SsO» 

Bisulphuretted hyposulphuric add, Teirathionic add S4O1 

Trisulphuretted hyposulphuric add, Fisntathionus add SsOs 

SUIiPHUB. 188 

The manipulation with the latter is exactly the eame in principle as iriih the 
ordinary water-trough, hut rather more trouhlesome, 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 
cootriTed as to economise as much as possible the expensive floid it is to 

Sulphurous acid has bleaching properties ; it is used in the arts for bleach- 
ing wcoUen goods and straw-plait. A piece of blue litmne-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 ciystallizable ; they are easily formed by direct com- 
bination. Sulphites of baryta, strontia, and lime, are insoluble in water, 
bat soluble in hydrochloric acid. The strong acids decompose them ; nitrio 
add converts them into sulphates. 

Sulphuric Acid. — Hydrated sulphuric acid has been known since the 
fifteenth century. There are two distinct processes by which it is at the 
present time prepared, namely, by the distillation of green sulphate of iron, 
and by the oxidation of sulphurous acid by nitrous acid. 

The first process is still carried on in some parts of Germany, especially 
in the neighbourhood of Nordhausen in Prussia ; the sulphate of iron, derived 
from the oxidation of iron pyrites, is deprived by heat of the greater part 
of its water of crystallization, and subjected to a high red heat in earthen 
retorts, to which receivers are fitted as soon as the acid begins to distil over. 
A part gets decomposed by the very high temperature ; the remainder is 
driven off in vapour, which is condensed by the cold vessel. The product is 
a brown oily liquid, of about 1-9 specific gravity, fuming in the air, and very 
corrosive. It is chiefly made for the purpose of dissolving indigo. 

The second method, which is perhaps, with the single exception mentioned, 
always followed as the more economical, depends upon the fact, that, when 
snlpharous acid, hyponitric acid, and water are present in certain propoiv 
tions, the sulphurous acid becomes oxidized at the expense of the hyponitric 
acid, which by the loss of one-half of its oxygen sinks to the condition ol 
binoxide of nitrogen. The operation is thus conducted : — A large and very 
long chamber is built of sheet-lead supported by timber framing ; on the 
ontside, at one extremity, a small furnace or oven is constructed, having a 
wide tube leading into the chamber. In this sulphur is kept burning, tiie 
flame of which heats a crucible containing a mixture of nitre and oil of 
vitriol. A shallow stratum of water occupies the floor of the chamber, 
and sometimes a jet of steam is also introduced. Lastly, an exit is provided 
at the remote end of the chamber for the spent and useless gases. The 
effect of these arrangements is to cause a constant supply of sulphurous 
acid, atmospheric air, nitric acid vapour, and water in the state of steam, 
to be thrown into the chamber, there to mix and react upon each other. 
The nitric acid immediately gives up a part of its oxygen to the sulphurous 
acid, becoming hyponitric ; it does not remain in this state, however, but 
snffers farther deoxidation until it is reduced to binoxide of nitrogen. That 
Bnbstance in contact with free oxygen absorbs a portion of the latter, and 
once more becomes hyponitric acid, which is again destined to undergo de- 
oxidation by a fresh quantity of sulphurous acid. A very small portion of 
hyponitric acid, mixed with atmospheric air and sulphurous acid, may thus 
in time convert an indefinite amount lOf the latter into sulphuric acid, by 
acting as a kind of carrier between the oxygen of the air and the sulphurous 
add. The presence of water is essential to this reaction. 

We may represent the change by the diagram on the succeeding page : •— 

r Nitrogen 14 ^ Binoxide of nitrogen < 

Hypoiutrie add 46 -j Oxygen 16 . 
(Oxygen 16^ 

Water 18 "^^ ^ Hydrated sulphuric acid 98 

Such is the simplest view that can be taken of the production of salphprie 
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 th« 
air within, and sulphurous and hyponitric acids are introduced by separate 
tubes, symptoms of ohem oal action become immediately evident, and after 
a little time a white crystalline matter is observed to condense on the sides 
of the vessel. This substance appears to be a compound of sulphuric acid, 
nitrous acid, and a little water.* When thrown into water, it is resolved into 
aulphuric acid, binoxide of nitrogen, and nitric acid. This curious body is 
certainly very often produced in large quantity in the leaden chambers ; but 
that its production is indispensable to the success of the process, and con- 
stant when the operation goes on well, and the hyponitric acid is not in 
excess, may perhaps admit of doubt. 

The water at the bottom of the chamber thus becomes loaded with sul- 
phuric acid ; when a certain degree of strength has been reached, it is drawn 
off and concentrated by evaporation, first in leaden pans, and afterwards in 
stills of platinum, until it attains a density (when cold) of 1*84, or there- 
abouts; it is then transferred to carboys, or large glass bottles fitted in bas- 
kets, for sale. In Great Britain this manufacture is one of great national 
importance, and is carried on to a vast extent. An inferior kind of acid is 
sometimes made by burning iron pyrites, or poor copper ore, as a substitute 
for Sicilian sulphur; this is chiefly used by the makers for their own con« 
sumption ; it very frequently contains arsenic. 

The most concentrated sulphuric acid, or oil of vitriol^ as it is often called, 
is a definite combination of 40 parts real acid, and 9 parts water. It is a 
colourless, oily liquid, having a specific gravity of about 1*85, of intensely 
acid taste and reaction. Organic matter is rapidly charred and destroyed 
by this substance. At the temperature of — 16° ( — 26o*lC) it freezes; at 
620° (826o*6C) it boils, and may be distilled without decomposition. Oil of 
vitriol has a most energetic attraction for water; it withdraws aqueous 
vapours from the air, and when diluted, great heat is evolved, so that the 
mixture always requires to be made with caution. Oil of vitriol is not the 
only hydrate of sulphuric acid ; three others are known to exist. When the 
fuming oil of vitriol of Nordhausen is exposed to a low temperature, a white 
.crystalline substance separates, which is a hydrate containing half as much 
water as the common liquid acid. Then, again, a mixture of 49 parts strong 
liquid acid and 9 parts water, congeals or crystallizes at a tempet^ture above 

* H. Gaultier de daubry atwlgiied to this oarious BtibBtanee the oomposition expreraed ^J 
the formula 4H0, 'iNOs+dSOs, and this view has generally been received by recent chemical 
writers. M. de la Provdstaye has since sliown that a compound, poatjessing all the essential 
properties of the body in question, may be formed by bringing together, in a sealed glass 
tube, liquid sulpharons wid and liquid hyponitric add, both teee from water. The white 
crystalline solid soon begins to form, and at the expiration of twenty-six hours the reaction 
appears complete. The new product is accompanied by an exceedingly volatile greenish 
liqtdd having the characters of nitrous acid. The white substance, on analysis, was found 
to contain the elements of two equivalents of sulphuric add and one of uitroos iKdd, or 
>rOs+2SOs. M. de la Provostaye very ingeniously explains the anomalies in the diff<a«n^ 
analyses of the leaden chamber product, by sho^ring that the pure substance forms crystal- 
Usable oomMnttttou with difforent ptoportioms of Uquld sulphuric add. (Ann. ddin. et 
Phyg. IxxiiL 302.) 


320 (0OCJ, and i^emtins solid even at 46*> (7o-2C>. LnstiTV wlwo awiy 

dilate acid is concentrated by evaporation in vacuo over a Biurfiaoe of oil of 
vitriol, the evaporation stops ^hen the real acid and water bear to each 
other the proportion of 40 to 27. 

When good Nordhausen oil of vitriol is exposed in a retort to a gentle 
heat, and a receiver cooled by a freezing mixture fitted to it, a volatile 
substance distils over in great abundance, wliich condenses into beautifol, 
white, silky crystals," resembling those of asbestos ; this bears the name of 
aohydrons sulphuric acid. When put into water it hisses like a hot iron, 
from the violence with which combination occurs ; exposed to the air even 
for a few moments, it liquefies by absorption of moisture, forming common 
liquid sulphuric acid. It forms an exceedingly curious compound with dry 
ammoniacal gas, quite distinct from ordinary sulphate of ammonia, and 
which indeed possesses none of the characters of a sulphate. This interest- 
ing substance may also be obtained by distilling the most gonceatrated 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. 

Hypotulphurout Acid. — By digesting sulphur with a solution of sulphite 
of potassa or soda, a portion of that substance is dissolved, and the liquid, 
by slow evaporation, furnishes crystals of the new salt. The acid cannot be 
isolated; when hydrochloric acid is added to a solution of a hyposulphite, 
the acid of the latter is alihost instantly resolved into sulphur, which pre- 
cipitates, and into sulphurous acid, easily recognized by its odour. The 
most remarkable feature of the alkaline hyposulphites is their property of 
dissolving certain insoluble salts of silver, as the chloride — ^a property which 
has lately conferred upon them a con8ideral)le share of importance in rela- 
tion to the' art of photogenic drawing. 

Hyposulphuric Acid, IHikionic Acid. — This is prepared by suspending 
finely divided binoxide of manganese in water artificially cooled, and then 
transmitting a stream of sulphurous acid gas ; the binoxide becomes pro- 
toxide, half its oxygen converting the sulphurous acid into hyposulphui-io. 
The hyposulphate of manganese thus prepared is decomposed by a solution 
of pure hydrate of baryta, and the barytic salt, in turn, by enough sul- 
phnric acid to precipitate the base. The solution of hyposulphuric acid 
may be concentrated by evaporation in vacuo, until it acquires a density of 
1*347: pushed farther, it decomposes into sulphuric and sulphurous acids. 
It has no odour, is very sour, and forms soluble salts with baryta, lime, and 
protoxide of lead. 

Stdphuretted hyposulphuric Add, IVithionic Acid. — A substance accidentally 
formeid by M. Langlois,* in the preparation of hyposulphite of potassa, by 
gently heating with sulphur a solution of carbonate of potassa, saturated 
with sulphurous acid. The salts bear a great resemblance to those of hypo- 
snlphurous acid, but differ completely in composition, while the acid itself 
is not quite so prone to change. It is obtained by decomposing the potassa 
salt by hydrofluosilicio acid ; it may be concentrated under the receiver of 
the air-pump, but it is gradually decomposed into sulphur, sulphurous and 
Bolphnric acids. 

Bittdphureited hyposidphuric Acid, Tetrathionic Acid. — This was discovered 
by MM. Fordos and G^lis.* When iodine is added to a solution of hyposul- 
phite of soda, a large quantity of that substance is dissolved, and a clear, 
f^Diiess solution obtained, which, besides iodide of sodium, contains a salt 

« Ann. Cbim. et Phys. 3d series, iv. 77. 
•Jd.Sd aeries, vi. 454 



'of a peculiar acid, richer in snlphur than the preceding. By suitable means, 
the new substance can be eliminated, and obtained in a state of solution. 
It yery closely resembles fayposulphuric acid. The same acid is produced by 
the action of sulphurous acid on subchloride of sulphur. * 

Trwdphwetted hyposulphuric Acid, Pentathionic Acid, — Another acid of 
sulphur has been announced by M. Wackenroder, who formed it 1)y the 
action of sulphuretted hydrogen on sulphurous acid. It is described as 
colourless and inodorous, of acid and bitter taste, and capable of being con- 
centrated to a considerable extent by cautious evaporation. It contains S5O5 ; 
under the influence of heat, it is decomposed into sulphur, sulphurous and 
sulphuric acid and sulphuretted hydrogen. The salts of pentathionic acids 
are nearly all soluble. The baryta salt crystallizes from alcohol in square 
prisms. The acid is also formed when hyposulphate of lead is decomposed 
by sulphuretted hydrogen, and when protochloride of sulphur is heated with 
sulphurous acid. 

Sulphurous acid unites, under peculiar circumstances, with chlorine, and 
also with iodine, forming compounds, which have been called chloro- and 
iodo-sulphuric acids. They are decomposed by water. It ^Iso combines 
with dry ammoniacal gas, giving rise to a remarkable compound ; and with 
nitric oxide also, in presence of an alkali. 


This is a very rare substance, much resembling sulphur in its chemical 
relations, and found in association with that element in some few localities, 
or replacing it in certain metallic combinations, as in the selenide of lead of 
Clausthal, in the Hart^. 

Selenium is a reddish-brown solid body, somewhat translucent^ and having 
an imperfect metallic lustre. Its specific gravity, when rapidly cooled after 
fusion, is 4-3. At 212° (1C0°C), or a little above, it melts, and at 650° 
(348®-8C) boils. It is insoluble in water, and exhales, when heated in the 
air, a peculiar and disagreeable odour, which has been compared to that of 
decaying horseradish. There are three oxides of selenium, two of which 
correspond respectively to sulphurous and sulphuric acids, while the third 
has no known analogue in the sulphur series. 

Composition by weight. 

Seleuium. Osygen. 

Oxide of selenium 39-5 8 

Selenious acid 39-5 16 

Selenic acid 39*5 24 

Oxide. — Formed by heating selenium in the air. It Is a colourless gas, 
slightly soluble in water, and has the remarkable odour above described. It 
has no acid properties. 

Selenious Acid. — This is obtained by dissolving seleninm in nitric acid, and 
evaporating to dryness. It is a white, soluble, deliquescent substance, of 
distinct acid properties, and may be sublimed without decomposition. Sul- 
phurous acid decomposes it, precipitating the selenium. 
. Selenic Acid. — Prepared by fusing nitrate of potassa or soda with selenium, 
precipitating the seleniate so produced by a salt of lead, and then decom- 
posing the compound by sulphuretted hydrogen. The hydrated acid strongly 
resembles oil of vitriol ; but, when very much concentrated, decomposes, by 
the application of heat, into selenious acid and oxygen. The seleniates bear 
the closest analogy to the sulphates in every particular. 



Fig. 104. 


Phosphorus in a state of phosphoric acid is contained in the ancient un- 
itratified rocks, and in the lavas of modern origin. As these disintegrate and 
cnimble 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 
struetore of the animal frame, by communicating stiffness and inflexibility 
to the bony skeleton. 

This element was discovered in 1669 by Brandt, of Hamburg, who pre- 
pared it from urine. The following is an outline of the process now adopted. 
Thoroughly calcined bones are reduced to powder, and mixed with two- 
thirds of their weight of sulphuric acid, diluted with a considerable quantity 
of water ; this mixture, after standing some hours, is filtered, and the nearly 
insoluble sulphate of lime washed. The liquid is then evaporated to a 
syrupy consistence, mixed with charcoal powder, and the desiccation com- 
pleted in an iron vessel exposed to a high temperature. When quite dry, 
it is transferred to a stoneware retort, to which a wide bent tube is luted, 
dipping a little way into the water contained in the receiver. A narrow tube 
^rves to give issue to the gases^ which are con- 
veyed to a chimney. (Fig. 104.) This manufac- 
ture is now conducted on a very great scale, the 
consumption of phosphorus, for the apparently 
trifling article of instantaneous light matches, 
being something prodigious. 

Phosphorus, when pure, very much resembles 
in appearance imperfectly bleached wax, and is 
soft and flexible at common temperatures. Its 
density is 1-77, and that of its vapour 4-35, air 
being unity. At 108° (42°-2C) it melts, and at 
550° (287° -70) boils. It is insoluble in water, 
and is usually kept immersed in that liquid, btLt 
dissolves in oils, in native naphtha, and especially 
in bisulphide of carbon. When set on fire in 
the air, it burns with a bright flame, generating 
phosphoric acid. Phosphorus is exceedingly in- 
flammable ; it sometimes takes fire by the heat 
of the hand, and demands great care in its management ; a blow or hard 
rub will very often kindle it. A stick of phosphorus held in the air always 
appears to emit a whitish smoke, which in the dark is luminous. This efi'ect 
18 chiefly due to a slow combustion which the phosphorus undergoes by the 
oxygen of the air, and upon it depends one of the methods employed for the 
analysis of the atmosphere, as already described. It is singular that the 
slow oxidation of phosphorus may be entirely prevented by the presence of 
a small quantity of defiant gas, or the vapour of ether, or some essential 
oil ; it may even be distilled in an atmosphere containing vapour of oil of 
turpentine in considerable quantity. Neither does the action go on in pure 
oxygen, at least at the temperature of 60° (16°-6C), which is very remark- 
able; but if the gas be rarefied, or diluted with nitrogen, hydrogen, or car* 
bonic acid, oxidation is set up. According to the researches of Marchand, 
evaporation of phosphorus causes a luminosity, even when there is no oxida- 

A very remarkable modification of this element is known by the name of 

amorphous phosphorus. It was discovered by Schrotter, and may be made 

by exposing for fifty hours common phosphorus to a temperature of about 

404° to 482° (240° to 250°C) in an atmosphere vjhich is unable to act chemi- 



cally upon it. At this temperature it beoomes red and opaque, and iosolable 
in bisulphide of carbon, whereby it may be separated from ordinary phos- 
phorus. It m^y be obtained in compact masses when common phosphorus 
is kept for eight days at a constant high temperature. It is a coherent^ 
reddish-brown, infusible substance, of specific gravity between 2*089 and 
2-106. It does not become luminous in the dark until its temperature is 
raised to about 392° (200°C), nor has it any tendency to combine with the 
oxygen of the air. When heated to 600° (260°C), it is reconverted into 
ordinary phosphorus. 

Compounds of Phoaphorut and Oxygen, — These are four in number, and 
have the composition indicated below. 

Composition by weight 

Phosphorus. Oxygen. 

Oxide of phosphorus 64 8 

Hypophosphorous acid 32 8 

Phosphorous acid 32 24 

Phosphoric acid * , 32 40 

Ovidt of Pho9phoru8. — When phosphorus is melted beneath the surface of 
hot water, and a stream of oxygen gas forced upon it from a bladder, com- 
bustion ensues, and the phosphorus is converted in great part into a brick- 
red powder, which is the substance in question. It is decomposed by heat 
into phosphorus and phosphoric acid. 

Hypophosphorous Add. — When phosphide of barium is put into hot water, 
that liquid is decomposed, giving rise to phosphoretted hydrogen, phos- 
phoric acid, hypophosphorous acid, and baryta ; the first escapes as gas, and 
the two acids remain in union with the baryta. By filtration the soluble 
hypophosphite is separated from the insoluble phosphate. On adding to the 
liquid the quantity of sulphuric acid necessary to precipitate the base, the 
hypophosphorous acid is obtained in solution. By evaporation it may be 
reduced to a syrupy consistence. 

The acid is very prone to absorb more oxygen, and is therefore a powerful 
deoxidizing agent. All its salts are soluble in water. 

Phosphorous Acid. — Phosphorous acid is formed by the slow combustion 
of phosphorus in the atmosphere ; or by burning that substance by means 
of a very limited supply of air, in which case it is anhydrous, and presents 
the aspect of a white powder. The hydrated acid is more conveniently 
prepared by adding water to the terchloride of phosphorus, when mutual 
decomposition takes place, the oxygen of the water being transferred to the 
phosphorus, generating phosphorous acid, and its hydrogen to the chlorine, 
giving rise to hydrochloric acid. By evaporating the solution to the con- 
sistence of syrup, the hydrochloric acid is expelled, and the residue on 
cooling crystallizes. 

Hydrated phosphorous acid is very deliquescent and very prone to attract 
oxygen and pass into phosphoric acid. When heated in a close vessel, it is 
resolved into hydrated phosphoric acid and pure phosphoretted hydrogen gas. 
It IS composed of 66 parts real acid and 27 parts water. * 

The phosphites are of little importance. 

Phosphoric Add. — ^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- 

« In ^mbols— Oxide of phosphorns P»0 

Hypophospliorous acid ~ P O 

Ptiosphorous acid P 0» 

Phosplioric acid ..'. P Ob 

Equivalent of phosphorus, <)2 

»0r, 3H0, P0». 



daced in great quantity. This subetance exhibits as rnneli attraction for 
water as anhydrous salphuric acid ; exposed to the air for a few moments, 
it deliquesces to a liquid, and when thrown into water, combines with the 
latter with explosiye yiolence. 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 
reoeirer is connected, and fragments of phosphorus added singly, taking 
care to snflfer the yiolence of the action to subside between each addition, 
the phosphorus is oxidized to its maximum, and conyerted into phosphorio 
acid. By distilling off the greater part of the acid, transferring the residue 
In the retort to a platinum yessel, and then cautiously raising the heat to 
redness, the hydrated acid may be obtained pure. This is the glacial phot- 
pkorie 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 eyaporating and igniting in a platinum yessel the mixed 
phosphate and sulphate of ammonia. Hydrated phosphoric acid alone remains 
behind. The acid thus obtained is not remarkable for its purity. One of 
the most advantageous methods of preparing phosphoric acid on the large 
scale in a state of purity, is to burn phosphorus in a stream of dry atmo- 
spheric air, by the aid of a proper apparatus, not difficult to contriye, in 
which the process may be carried on continuously. The anhydrous acid 
obtained may be preserved in that state, or conyerted into hydrate or glacial 
acid, by the addition of water and subsequent fusion in a platinum yessel. 
The hydrate of phosphoric acid is exceedingly deliquescent, and requires to 
be kept in a closely stopped bottle. It contains 72 parts real acid, and 9 
parts water. 

Phosphorio 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 
chemiat than this substance ; the extraordinary changes 
it8 compounds undergo by the action of heat, chiefly *"**• ^^^' 

made known to us by the admirable researches of 
Prof. Graham, will be found described in connection 
with the general history of saline compounds. 


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 alberations, 
for that of the rest. 

Chlorine * is a very abundant substance ; in common 
salt it exists in combination with sodium. It is most 
easily prepared by pouring strong liquid hydrochloric 
acid upon finely-powdered black oxide of manganese, 
contained in a retort or flask, and applying a gentle 
heat; a heavy yellow gas is disenguged, which is the 
rabslance in question. (Fig 105.) 

It may be collected over warm water, or by displace- 
ment; the mercurial trough cannot be employed, as 
tlic chlorine rapidly acts upon the metal, and becomes 

* Vrom YXu»f»df , ycUovrish-greoa, the name given to it by Sir II. Davy. 


The reatttioii is very earity expluiied. Hydroelilmio neid in a eempofind 
of chlorine and hydrogen ; whoi this is mixed with a metallic protoxide, 
double interchange of elements takes place, water and chloride of the metal 
being produced. But when some of the hinoxida are substituted, an addi- 
tional effect ensues, namely, the decomposition of a second portion of hydro- 
chloric acid by the oxygen in excess, the hydrogen of which is withdraws, 
and the chlorine set free. 

Hydrochloric f Chlorine Chlorine. 

acid \ Hydrogen ^ — ^ Water. 

Binoxide of ( Man|ane8e — ^=^ Chloride of manganese. 

manganese [oxy|en ^^^ 

Hydrochlorio f Chlorine - 

acid \ Hydrogen ""-^-^ Water. 

Chlorine was discoTcred in 1774, by Scheele, but its nature was long mis- 
understood. It is a yellow gaseous body, of intolerably suffocating proper- 
ties, producing very violent cough and irritation when inhaled even in ex- 
ceedingly small quantity. It is soluble to a considerable extent in water, 
that liquid absorbing at 60° (15°*5C) about twice its volume, and acquiring 
the colour and odour of the gas. When this solution is exposed to light, it 
is slowly changed by decomposition of water into hydrochloric acid, the 
oxygen being at the same time liberated. When moist chlorine gas is 
exposed to a cold of 32«' (0°C), yellow crystals are formed which consist of 
A definite compound of chlorine and water containing 85*5 parts of the 
former to 90 of the latter. 

Chlorine has a specific gravity of 2-47, 100 cubic inches weighing 76-6 
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 bum 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, 
accompanied by a copious deposit of soot. Although chlorine can, by indi- 
rect means, be made to combine with carbon, yet this never occurs under 
the circumstances described. 

Phosphorus'takes fire spontaneously in chlorine ; it bums with a pale and 
feebly luminous flame. Several of the metals, as copper-leaf, powdered 
• antimony, and arsenic, undergo combustion in the same manner. A mixture 
of equal measures chlorine and hydrogen explodes with violence on the pas- 
sage of an electric spark, or on the application of a lighted taper, hydro- 
chloric 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 

The most characteristic property of chlorine is its bleaching power; the 
most stable organic cplouring principles are instantly decomposed and de- 
stroyed by this remarkable agent ; indigo, for example, which resists the ac- 
tion of strong oil of vitriol, is converted by chlorine into a brownish sub- 
stance, to which the blue colour cannot be restored. The presence of water 
i^ essential to these changes, for the gas in a state of perfect dryness is in- 
capable even of affecting litmus. 



Chlorine is largely used in the arts for bleaching linen and cotton goods, 
i«g8 for the manufac'tiire of paper, &o. 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 often made by 
pouring slightly diluted oil of yitriol 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 

Salphuric acid 

Binoxideof fSx"d,of 

manganese |^ manganese 

Sulphuric acid 

Sulphate of soda. 

! Sulphate of man- 
ganese ' 

Chlorine is one of the best and most potent substances that can be used 
for the purpose of (fislnfection, but its employment requires care. Bleach- 
ing-powder mixed with water, and exposed to the air in shallow Tossels, be- 
comes 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; Hydrochlorie, Chlorhydrie or Muriatic Acid. — This 
substance in a state of solution in water, has been long known. The gas is 
prepared with the utmost ease by heating in a flask, fitted with a cork and 
bent tube, a mixture of common salt and oil of vitriol, diluted with a small 
quantity of water ; it must be collected by displacement, or over mercury. 
It is a colourless gas, which fumes strongly in the air from condensing the 
atmospheric moisture ; it has an acid, suffocating odour, but is infinitely less 
offensive than chlorine. Exposed to a pressure of 40 atmospheres, it 

Hydrochloric acid gas has a density 1-269. It is exceedingly soluble ia 
water, that liquid taking up at the temperature of the air about 418 times 
its hulk. The gas and solution are powerfully acid. 

The action of oil of vitriol on common salt, or any analogous substance, if 
thus easily explained : — 


Sttlphorio add 

Hydrochlorio add. 

Sulphate of soda. 

The composition of this substance maybe determined by synthesis: when 
a measure of chlorine and a measure of hydrogen are fired by the electric 
Bpark, two measures of hydrochloric acid gas result, the combination being 
unattended by change of volume. By weight it contains 35-6 parts chlorine 
and 1 part hydrogen. 

Solution of hydrochloric acid, the liquid acid of commerce, is a very im- 
portant preparation, and of extensive use in chemical pursuits ; it is best 
prepared by the following arrangement : . 

A large glass flask, containing a quantity of common salt, is fitted with a 



oork and' bent tobe, in the aiiMBer represented in fig. 106 ; tlfe lM/t«t pMSes 
through and below a second short tube into a wide-necked bottle, contumnfp 

Pig. loe 

a little water, into which the open tube dips. A bent tube is adapted to an- 
other hole in the cork of the wash-bottle, so as to convey the purified g:aa 
into a quantity of distilled water, by which it is instantly absorbed. The 
joints are madB air-tight by melting over the corks a little yellow wax. 

Oil of Titricl, 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 chauflFer, 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 gi*eat 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 bein^ driven into the first. 

The arrangement by which the acid is introduced, also deserves a moment's 
notice. The tube is bent twice upon itself, and a bulb blown in one portion. 
(Fig. 107.) Liquid poured into Uie funnel rises upo9 the opposite side of 

cuhouinm* III 

ih« tot Bend vlitil it roMihes the sewmd; it ilMi il(r»8 (fwr iadnuit 1M» 

the flask. Any quantity can then be got into the latter without the 
introduction of air, and without the escape of gas from the inte- ^* 107* 
rior. The funnel acts also as a kind of safety-valTe, and in both c:^ 
directions ; for if by any chance the deli¥ery-tube shoidd be stopped 
and the issue of gas prevented, its increased elastic force soon drives 
the little column of liquid out of the tube, the gas escapes, and the 
vessel is saved. On the other hand, any absorption within is quickly 
compensated by the entrance of air through the liquid in the bulb. 
The plan employed on the great scale by the manufacturer is the 
same in principle as that described ; he merely substitutes a large 
iron cylinder for the flttsk, and vessels of stone-ware for those of 

Pare solution of hydrochloric acid is transparent and colourless ; 
when strong, it fumes in the air by disengaging a little gas. It 
leaves no residue on evaporation, and gives no precipitate or milki- 
ness with solution of chloride of barium. When saturated with the 
gas, it has a ^eeific gravity of 1*21, and-contains about 42 per cent, 
of real acid. The commercial acid has usually a yellow colour, and 
is very impure, contaimng salts, sulphuric acid, chloride of iron, and 
organic matter. R may be tendered 'Sufficiently good for most pur^ 
poses by diluting it to the density of 1*1, which happens when the strong 
acid IB mixed witii its own bulk or rather less of water, and then distilling it 
in a retort furnished with a Liebig's condenser. 

A mixture of nitric and hydrochloric acids has long been known under the 
Dafoe of aqtta regia, from its property of dissolving gold. When these two 
substances are heated together, they both undergo decomposition, hyponitrid 
add and chlorine being evolved. This at least appears to be the final result 
of the action ; at a oertain stage, however, two peculiar substances, coft- 
sisting of nitrogen, oxygen, and chlorine, (chlorohypomtric aoid* and chlo- 
ro&itrous acid,') appear to be formed. It is chiefly the chlorine which 
attacks the metil. 

The presence of hydrochloric aoid, or any other soluble chloride, is easily 
detect^ by solution of nitrate of silver. A white curdy precipitate is pre*' 
daced, insoluble in nitric acid, freely soluble in vnmonia) sad subject td 
blacken by exposure to light 

Odmpounek of {/hlorme and Oxygen, 
Although these bodies never combine directly, they may be made to unit^ 
by circuitous means in five different proportions, as below i — 

Oomposition liy weigbt. 
Chlorine. Oxygen. 

Hypochlorous acid 35*5 8 

Chlorous add 36-6 24 

Hypochloric acid 35*5 •...,. 32 

Chloric acid... 35-5 40 

Perchloric acid' 36-6 56 

Hypochloroas and chhnrlc acids are generated by the action of chlorib^ on 
certain metallic oxides ; tiie former in the cold, the latter at a high tempe^ 

* N0» Cl* « NOad. 

* Hypochlorons add CIO 

Chlorous add ClOt 

Hypochloric add ; CIO4 

Chloric add ClOs 

Ferchlorio add. ^^ G10> > 


xatnre. Chlorous, hjrpoclilorio, and perchloric acids resiilt tnm the decom- 
position of chloric acids. 

Hypochlorous Acid. — This is best prepared by the action of chlorine gas 
upon red oxide of mercury. It is a pale yellow gaseous body, containing, 
in every two measures, two measures of chlorine and one of oxygen. It is 
very freely soluble in water, and explodes, although with no great violence, 
by slight elevation of temperature. The odour of this gas is peculiar, and 
but remotely resembles that of chlorine. It bleaches powerfully, and acts 
upon certain of the metals in a manner which is determined by their re- 
spective attractions for oxygen and chlorine. It forms with the alkalis a 
series of bleaching salts. 

The preparations called chloride of^ or chlorinated lime and soda, contain 
hypochlorous acid. A description of these will be found under the head of 
Salts of Lime. 

The recK^tion by which hypochlorous acid is produced may thus be illus- 
trated : — 

Chlorine ——^^^s-^ Hypochlorous acid. 

Oxide of f 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 oxy chloride of mercury.* 

Chlorotu Acid. — This substance is prepared by heating in a flask filled to 
the neck, a mixture of 4 parts of chlorate of potassa and 8 parts of arsenious 
acid with 12 parts of nitric acid previously diluted by 4 parts of water. 
During the operation, which must be performed in a water-bath, a greenish 
yellow gas is evolved, which is sparingly soluble in water, and cannot be 
condensed by exposure to a freezing mixture. It slowly combines with 
bases, producing a class of salts called chlorites. The process which gives 
rise to chloroi^s acid is rather complicated. The arsenious acid deprives the 
nitric acid of part of its oxygen, reducing it into pitrous acid, which is 
oxidized again at the expense of Uie chloric acid. This, by the loss of two- 
fifths of ita oxygen, becomes chlorous acid. 

ffppochlorie Acid; Peroxide of Chlorine. — Chlorate of potassa is made into 
t^ paste with concentrated sulphuric acid, and cooled ; this is introduced into 
a small glass retort, and very cautiously heated by warm water ; a deep 
yellow gas is evolved, which is the body in question; it can be collected only 
by displacement, since mercury decomposes, and water absorbs the gas. 

Hypochloric acid has a powerful odour, quite different from that of the 
preceding compounds, and of chlorine itself. It is exceedingly explosive, 
being resolved with violence into its elements by a temperature short of the 
boiling point of water. Its preparation is, therefore, always attended by 
danger, and should be performed only on a small scale. It is composed 
by measure of one volume of chlorine and two volumes of oxygen, con- 

* A very oommodiotis method of preparing hypochlorous acid has lately heen described 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, and dry chlorine gas is 
alowly 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, aod very subject to explosion. It is remarkable that 
tiie cryOalUne oxide of mercury prepared by JSalcinlng the nitrate, or by the direct oxidation 
of the metal, is scarcely acted upon by chlorine under the drcumstanoefl described, — Ann. 
CShim. et Phys. 3d series, viL 179- 




4tiisQd into two TolvmeaL* It ma^p b» Uqoefisd lij oold, %h^ solntiea of |b% 
gas in wat^r bleaches. Salts of this acid haye not yet iMen obtained. 

The euchlorine of Davy, prepared bj gently beating eUorate of potaawk 
with dilute hydrochloric acid, is probab^ a noj^t^are of oU^rouf acid and 
free cl^loidne. 

The production of chlorous acid from chlorate of potassa and anlpliiurla 
acid, dej^enda upon the spontaneous spUttiiig of the ehlori^ aeid into ehloroua 
acid and percUorie. acid, which latter fomaina in union with the potoaa*.^ 

When a mixture of chlorate of potassa and sugar is touobed with a drop 
of oil of vitriol, it is instantly set on fir« ; the hypochlori^ Md duengagod 
being decomposed by the combustible substance with 
such Tiolence as to cause infiammation. If crystals, 
of chlorate of potassa be thrown into a. glass of water^ 
a few small fragments of phosphorus added, and 
then oil of Titriol poured down a narrow funnel 
reaching to the bottom of the glass, the phosphorua 
will burn beneath the surface of the water by the as-, 
sistapoe of the pxygen of the hypochloric acid disen- 
gaged. Fig. 1Q8. The liquid at the same time 
becomes yellow, and acquires the odour of that gas. 

Chlotic Acid, — This is the most important com- 
pound of the series. When chlorine is passed to 
saturation into a moderately strong hot solution of 
caustic potassa, or the carbonate of that base, and 
the liquid concentrated by eyaporatlon, it furnishes, 
on coolingi flat tubqlar crystals of a colourless salt, 
consisting of potassa combined with chloric acid. 
The mother-liquor contains chloride of potassium. In this reaction a part 
of the potassa is decomposed; its oxygen combines with one portion of 
chlorine to form chloric acid, while the potassium is taken up by a second 
portion of the same substance.' 

From chlorate of potassa, chloric acid may be obtained by boiling the 
salt with a solution of hydrofluosilicio acid, which forms an almost insohible 
salt with potassa, decanting the clear liquid, and digesting it with a little 
silica, which removes the excess of the hydrofluo^cio a^id. Filtration 
through paper must be avoided. 

By cautious evaporation, the acid may be so far concentrated aa to assume 
a syrupy consistence ; it is then very easily decomposed. It sometimes seta, 
fire to paper, or other dry organic matter, in consequence of the fisunlity with 
which it is deoxidized by combustible bodies. 

The chlorates are easily recognized ; they give no precipitate when in 
solution with nitrate of baryta or silver ; they evolve pure oxygen when 
heated, passing thereby into chlorides ; and they afford, when treated with 
sulphuric acid, the characteristic explosive yellow gas already described. 
The dilute solution of the acid has no bleaching powers 

Perchloric Add, — Prof. Penny has shown that when powdered ohlorate of 
potassa is thrown by small portions into, hot nitric acid» a change of the 

< In equivalents, aB aUreadj stated, CIO4. 

r 2 eq. chlorine 
* 3 equiv. chloric add< 8 eq. oxygen 

(. 7 eq. oxygen - 
1 eq. chlorine 

6eq. potaifa 

r 5 eq. potassium 
k < 6 eq. oxygen 
(. 1 eq. potaaea 

2 eq. hypochloric acid. 

-1 eq. perchlovio add. 
5 eq. chloride potassium. 

1 eq. chlorate 

146 IODINE. 

Bame descrfptioii as that whicli happens when SQlphuiic acid is used takes 
place, but with this important difference, that the chlorine and oxygen, 
instead of being evoWed in a dangerous state of combination, are emitted in 
a state of mixture. The result of the reaction is a mixture of nitrate of 
potassa and perchlorate of potassa, which jnay be readily separated by their 
difference of solubility. 

By treating the potassa palt in the manner directed for chloric acid, the 
free acid may be obtained tolerably pure. It may be concentrated by evapo- 
ration, and even distilled without change. The solution fumes slightly in 
the air, and has a specific gravity of 1-66. It is very greedy of moisture, 
and has no bleaching properties. The perchlorates much resemble the chlo- 
rates ; they give off oxygen when heated to redness. The acid is the most 
stable of the compounds of chlorine and oxygen. 


This remarkable substance was first noticed in 1812 by M. Courtois of 
Paris. Minute traces are found in combination with sodium or potassium 
in sea-water, and occasionally a much larger proportion in /that of certain 
mineral springs. It seems to be in some way beneficial to many marine 
plants, as these latter have the power of abstracting it from the surrounding 
water, and accumulating it in their tissues. It is from this source that all 
the iodine of commerce is derived. It has lately been found in minute 
quantity in some aluminous slates of Sweden, and in several varieties of 
coal and turf. 

Kelp, or the half-vitrified ashes of sea-weeds, prepared by the inhabitants 
of the Western Islands and the northern shores of Scotland and Ireland, 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 
removed as they successively crystallize. The dark brown mother-liquor 
left contains very nearly the whole of the iodine ; this is mixed with sul- 
phuric acid and binoxide of manganese, and gently heated in a leaden retort, 
when the iodine distils over and condenses in the receiver. The theory of 
the operation is exactly analogous to that of the preparation of chlorine ; 
it requires in practice, however, careful management, otherwise the impari- 
ties present in the solution interfere with the general result. 

The manganese is not really essential ; iodide of potassium or sodium, 
heated with an excess of sulphuric acid, evolves iodine. This effect is due 
to a secondary action between the hydriodic acid first produced, and the 
excess of the sulphuric acid, in which both suffer decomposition, yielding 
iodine, water, and sulphurous acid. • 

Iodine crystallizes in plates or scales of a bluish-black colour and imper- 
fect metallic lustre, resembling that of plumbago ; the crystals are sometimes 
very large and brilliant. Its density is 4-948. At 225° (107° -20) it fuses, 
and at 347° (175°C) boils, the vapour having an exceedingly beautiful violet 
colour.* It is slowly volatile, however, at common temperatures, and exhales 
an odour much resembling that of chlorine. The density of the vapour is 
8*716. Iodine requires for solution about 7QD0 parts of water, which never- 
theless acquires a brown colour ; in alcohol it is much more freely soluble. 
Solutions of hydriodic acid and the iodides of the alkaline metals also dis- 
solve a large quantity. ; these solutions are not decomposed by water, which 
is the case with the alcoholic tincture. 

. This substance stains the skin, but not permanently ; it has a. very ener- 
getic action upon the animal system, and is much used in medicine. 

* Whence the name, luS^Sf TioletHX>loured. 



Rg. 109. 

One of the most cbaraeteristic properties of iodine is tlie produciioii of a 
splendid blue colour by contact with the organic principle starch. The iodine 
for this purpose must be free or uncombined. It is easy, however, to make the 
test available for the purpose of recognizing the presence of the element in 
question when a soluble iodide is suspected ; 
it is only necessary to add a very small quan- 
tity of chlorine- water, when the iodine, being 
displaced from combination, becomes capable 
of acting upon the starch. 

Hydriodic Acid. — The simplest process for 
preparing hydriodic acid gas is to introduce 
into a glass tube (fig. 109), sealed at one 
extremity, a little iodine, then A small quan-. 
tity of roughly-powdered glass moistened 
with water, upon this a few little fragments 
of phosphorus, and lastly more glass ; this 
order of iodine, glass, phosphorus, glass, is 
repeated until the tube is half or two-thirds 
filled. A cork and narrow bent tube are 
then fitted, and gentle heat applied. The 
gas is received over mercury. The experi- 
ment depends upon the formation of an 
iodide of phosphorus, and. its subsequent 
decomposition by water, hydrated phospho- 
rous acid and iodide of hydrogen being produced. The glass merely serves 
to moderate the violence of the action of the iodine upon the phosphorus. 

Hydriodic acid gas greatly resembles the corresponding chlorine compound ; 
it is colourless, and highly acid ; it fumes in the air, and is very soluble in 
water. Its density is about 4-4. By weight it is composed of 127 parts iodine 
and 1 part hydrogen ; and by measure, of equal volumes of iodine-vapour 
and hydrogen united without condensation. 

Solution of hydriodic acid may be prepared by a process much less trou- 
blesome than the above. Iodine in fine powder is suspended in water, and 
a stream of washed sulphuretted hydrogen passed through the mixture ; 
Bnlphur is deposited, and the iodine converted into hydriodic acid. When 
the liquid has become colourless, it is heated to expel the excess of sulphu- 
retted hydrogen, and filtered. This solution cannot long be kept, especially 
if it be strong ; the oxygen of the air gradually decomposes the hydriodic 
acid, and iodine is set free, which, dissolving in ^q remainder, communicates 
to it a brown colour. 

Compounds of Iodine and Oxygen, 

The most important of these are the iodic and periodic acids. 

Composition by weight 

Iodine. Oxygen. 

Iodic acid 127 40 

Periodic acid* *. 127 56 

Iodic Acid may be prepared by the direct oxidation of iodine by nitric acid 
of specific gravity 1-6; 6 parts of dry iodine with 200 parts of nitric acid 
are kept at a boiling temperature for several hours, or until the iodine has 
disappeared. The solution is then cautiously distilled to dryness, and the 
residue dissolved in water and made to crystallize. 

* IDs, and lOr. 

148 Bat)MiNE. 

Idditt M&A IsftVetyEotablB fiabstaMO©; it wyfttftiliifes ill cbMatfesS, Vix- 
0!ded tables, irhich contain water. It is decomposed by heat, and iis solHtion 
readily deoicidized by sulphurous acid. The iodates much resemble the 
chlorates ; that of potassa is decomposed by heat into iodide of potassmm 
and oxygen gas. 

Periodic Add. — ^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 pcrlodate of soda 
with hydrate of soda, which is sparingly soluble, l^his is separated, con- 
Terted into a* silver-salt, and dissolved in nitric acid ; the solution yields on 
evaporation crystals of yellow periodate of silver ; from which the acid may 
be separated by the action of water, which resolves thB salt into free acid 
and insoluble basic periodate. - 

The acid itself may be obtained in crystals. It Is permanent in the aii*, 
and capable of being resolved into iodine and oxygen by a high temperature. 

Bromine * dates back to 1826 only, having been discovered by M. Balard of 
Montpelier. It is found in sea- water, and is a frequent constituetat of saline 
springs, chiefly as bromide of magnesium ; — a celebrated «|)ring of the kind 
exists near Ereuznach in Prussia. Bromine may be obtained pure by the 
following process, which depends upon the fact, that ether agitated with 
^n aqueous solution of bromine, removes the greater part of that substance. 

The mother-liquor, from which the less soluble salts have separated by 
crystallization, is exposed to a stream of chlorine, and then shakea up wi^ 
a quantity of ether; the chlorine decomposes the bromide of ma^nesi^m, 
and the ether dissolves the bromine thus set free. On -standing, the ethereal 
solution, htiving a fine red colour, separates, and may be removed by a funnel 
or pipette. Caustic potassa is then added in excess, and heat apt)lied; 
bromide of potassium and bromate of potassa are fosmed. The solution is 
evaporated to dryness, and the saline matter, after ignition to redness to 
decompose the bromate of potassa, heated in a small retort with binoxide 
of manganese and sulphuric acid dilated with a little water., the neck of the 
retort being plunged into cold water. The bromine volatilizes in the foi'm 
of a deep red vapour, which condenses into drops l>eneath the liquid* 

Bromine is at common temperatures a red thin liquid of an exceedingly 
Intense colour, and very volatile; it freezes at about 19° .( — 7°-2C), and 
boils at 1460-4 (63°C). The density of the liquid is 2-976, and that of the 
vapour 6-39. The odour of brotaine 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. 

Hydrohromic Acid. — ^Thi's 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 hydrohromic acid 
has also the power of dissolving a large quantity of bromine, thereby acquir- 
ing a red tint. Hydrobromic acid contains by weight 80 parts bromine, 
%tnd 1 part hydrogen. 

Bromic Acid. — ^Caustic alkalis in presence of broiinine nndergo "the same 
change as with chlorine, bromide of the metal and bromate of tli^ oxide 
being proiJuced; thcBe may often be eepariited by the inferior solubility of 

* From Bp&uoSi ^ noieoiDe smell : a vory appropriate term. 

TLUOBINX — 811.10 in M. 14» 

the latter. Bromie add, obtained from bromate of baryta* closely raaembles 

chloric acid; it is easily decomposed. The bromates when heated lose 
oxygen and become bromides. 
No other compound of bromine and oxygen has yet been described. 

This element has never been isolated, at least in a state fit for examination ; 
its properties are consequently in great measure unknown ; from the obser- 
TBtions made, it is presumed to be gaseous, and to possess colour, like 
chloriae. The compounds containing fluorine can be easily decomposed, and 
the element transferred from one body to another; but its extraordhiary 
chemical energies towards the metals and towards silicium, a component of 
glass, have hitherto baffled all attempts to obtain it pure in a separate state. 
As fluoride of calcium it exists in small quantities in many animal substances ; 
SQch as bones. Several chemists have endeavoured to obtain it by decom- 
posing fluoride of silver by means of chlorine in vessels of fluor-spar, but 
even these experiments have not led to a decisive result. 

Hydrofluoric Acid. — When, powdered fluoride of calcium (fluor-spar) is 
heated with concentrated sulphuric acid in a retort of platinum or lead con- 
nected with a carefully cooled receiver of the same metal, a very volatile 
colourless liquid is obtained, which emits copious white and highly suflToca- 
tiDg fumes in the air. This was formerly believed to be the acid in an 
anhydrous state. M. Louyet, however, states that it still contains water, 
and that hydrofluoric acid, like hydrochloric acid, when anhydrous, is a gas. 

When hydrofluoric acid is put into water, it unites with the latter with 
great violence ; the dilute solution attacks glass with great facility. The 
concentrated acid dropped upon the skin occasions deep and malignant ulcers, 
so that great care is requisite in its management Hydrofluoric acid contains 
19 parts fluorine and 1 part hydrogen. * 

In a diluted state, this acid is occasionally used in the analysis of siliceous 
minerals, when alkali is to be estimated ; it is employed also for etching on 
glass, for which purpose the acid may be prepared in vessels of lead, that 
metal being but slowly attacked under these circumstances. The vapour of 
the acid is also very advantageously applied to the~Bame object in the fol- 
lowmg manner : the glass to be engraved is coated with etching-ground or 
wax, and the design traced in tlie usual way with a pointed instrument. A 
shallow basin made by beating up a piece of sheet lead is then prepared, a 
little powdered fluor-spar placed in it, and enough sulphuric acid added to 
form with the latter a thin paste. The glass is placed upon the basin, with 
the waxed side downwards, and gentle heat applied beneath, which speedily 
disengages the vapour of hydrofluoric acid. In a very few minutes the ope- 
ration is complete ; the glass is then removed and cleaned by a little warm 
oil of turpentine. When the experiment is successful, the lines are very 
clear and smooth. 

No combination of fluorine and oxygen has yet been discovered. 


Silicium, sometimes called silicon, in union with oxygen constituting silica, 
or the earth of flints, is a very abundant substance, and one of great im- 
portance. It enters largely into the composition of many of the rocks and 
mineral masses of which the^surface of the earth is composed. The following 
process yields silicium most readily. The double fluoride of silicium and 
potassium is heated in a glass tube with nearly its own weight of metallic 
potassium; violent reaction ensues, and silicium is set free. When cold, 
tb^ contents of the tube are put into cold water, which removes the saline 



Kg. 110 

prepared, tiliciam is a dark brown powder, disstitute of la^re. Heated in 
the air, it burns, and becomes superficially conyert^d into silica. It is also 
acted upon by sulphur and by chlorine. When silicium is strongly heated in 
a coyered crucible, its properties are greatly changed ; it becomes darker in 
colour, denser, and incombustible, refusing to burn even when heated by the 
flame of the oxy-hydrogen blowpipe. 

Silica. — This is tihe only known oxide ; it contains 21*3 parts silicium, and 
"24 parts oxygen.* Colourless transpar^it rock-crystal consists of silica very 
tiearly in a state of purity; common quartz, agate, calcedony, flint, and 
'BCTeral other minerals, are also chiefly composed of this substance. 

The experiment about to be described, furnishes silica in a state of com- 
plete purity, and at the same time ex- 
hibits one of the most remarkable pro- 
perties of silicium, namely, its attraction 
for fluorine. A mixture is made of equal 
parts fluor-spar and glass, both finely 
powdered, and introduced into a glass 
flask, with'^a quantity of oil of yitriol. A 
tolerably wide bent tube, fitted to the 
flask by a cork, passes to the bottom of a 
glass jar, into which enough mercury is 
poured to cover the extremity of the 
tube. The jar is then half filled with 
water, and heat is applied to the flask. 
(Fig. 110.) 

The first cflfect is the disengagement 
of hydrofluoric acid ; this substance, how- 
ever, finding itself in contact with the 
silica of the powdered glass, undergoes 
decomposition, water and flouride of silicium being produced. The latter is 
a permanent gas, which escapes from the flask by the bent tube. By con- 
tact with a large quantity of water, it is in turn decomposed, yielding silica, 
which separates in a beautif al gelatinous condition, and an acid liquid which 
is a double fluoride of silicium and hydrogen, commonly called hydroflao- 
silicic 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 baryta and potassa^ with which it 
forms nearly insoluble precipitates, the double fluoride of silicium and potas- 
sium being used, as was stated, in the preparation of silicium. The fluoride 
of silicium, instead of being conducted into water, may be collected over 
mercury ; it is a permanent gas, destitute of colour, and very heavy. Ad- 
mitted into the air, it condenses the moisture of the latter, giving rise to a 

* Or, SiOs. 

* (1) Beaction of hydrofluoric add upon silica: — 

Hydrofluoric «m{«^;J^«„-- 
gm^ f Silidum - 

^^ (Oxygen 

-Gaseous fluoride of sUlciuin. 


2) Decomposition of fluoride of silidum 1^ water :>- 
Pluoridoof rilWo«(|nj^™ ^811i«. 

Fluoride of siUdiun j ^::=:=^»-Hydrofluodlidc add. 

BOBON. 1^1 

tiiick white cloud. It ia knportatit in the ezperiment labove tfesdHbeil to 
keep the end of the delivery-tube from touching the water of the jar, other- 
wise it almost instantly becomes stopped ; the mercury effects this object. 

There i§, another method by which pure silica can be prepared, and which 
is also Tery 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 softenecl, and almost entirely Resolved. An excess 
of hydrochloric acid is then added to the filtered liquid, and the idiole eva- 
porated to complete dryness. By this treatment the gelatinous silica thrown 
down by the acid becomes completely insoluble, and remains behind when 
the dry saline mass is treated with acidulated water, by which the alkaline 
salts, alumina, sesquioxide of iron, lime, and many other bodies which may 
happen to be present, are removed. The silica is washed^ dried, and heated 

The most prominent characters of silica are the following : it is a very 
fine, white, tasteless powder, not sensibly soluble in water or dilute acids 
(with the exception of hydrofluoric) unless recently precipitated. It dis- 
solves, on the contrary, freely in strong alkaline solutions. Its density is 
about 2-66, and it is only to be fused by the oxy-hydrogen blowpipe. 

Silica is in reality an acid, and a very powerful one ; insolubility in water 
prevents the manifestation of acid properties under ordinary circumstances. 
When heated -with bases, especially those which are capable of undergoing 
fusion, it unites with them and forms true salts, which are sometimes solu- 
ble in water, as in the case of the silicates of potassa and soda when the 
proportion of base is considerable. Common glass is a mixture of several 
silicates in which the reverse of this happens, the silica, or as it is more cor- 
rectly called, silicic acid, being in excess. Even glass, however, is slowly 
acted upon by water. 

Finely-divided silica is highly useful in the manufacture of porcelain. 

This substance is closely related to silicium ; it is the basis of boracio 

Boron is prepared by a process very similar to that described in the case 
of silicium, the double fluoride of boron and potassium being substituted for 
the other salt, and the operation conducted in a small iron vessel instead of 
a glass tube. It is a dull greenish-brown powder, which burns in the air 
when, heated, producing boracic acid. Nitric acid, alkalis in a fused condi- 
tion, chlorine, and other agents, attack it readily. 

There is but one oxide of boron, namely, boracic acid, containing 10 9 parts 
boron and 24 parts oxygen.^ 

Boracic acid is found in solution in the water of the hot volcanic lagoons 
of Tuscany, whence a large supply is at present derived. It is also easily 
made by decomposing with sulphuric acid a hot solution of borax, a salt 
brought from the East Indies, consisting of boracic acid combined with soda. 

Boracic acid crystallizes in transparent colourless plates, soluble in about 
25 parts of cold water, and in a much smaller quantity at a boiling heat ; 
the acid has but little taste, and feebly affects vegetable colours. When 
heated, it loses water, and melts to a glassy transparent mass, which dis- 
solves many metallic oxides with great ease. The crystals contain 34-9 
parts real acid, and 27 parts water. They dissolve in alcohol, and the solu- 
tion boms with a green flame. 


152 BO BON. 

Glassy boraoic aoid in a state of fusion requires for its dissipation in 
yapour a very intense and long-continued heat ; the solution in water cannot, 
however, be evaporated without very appreciable loss by volatilization; 
henoe it is probable that the hydrate is far more volatile than the^acid itself. 

By heating in a glass flask or retort one part of the vitrified boracic acid, 
2 of fluor-spar, and 12 of oil of vitriol, a gaseous fluoride of boron may be 
obtained, and received in glass jars standing over mercury. It is a trans- 
parent gas, very soluble in water, and very heavy ; it forms a dense fume in 
the air like the fluoride of silicium.^ 

* These two bodies are thus constituted:— SilVi'uid BVf 

COMPOUNDS <0^ iCkllBbil A^^D HTDBOOSN. 168 



The compounds of carbon and hydrogen already known are exceedingly 
numerous ; perhaps all, in strictness, belong to the domain of organic che- 
mistry^ as they cannot be formed by the direct union of their elements, but 
always arise from the decomposition of a complex body of organic origin. 
It will be found convenient, notwithstanding, to describe two of them ib this 
part of the volume, as they very well illustrate the important subjects of 
combustion, and the nature of flame. 

Light Carbonetted or Carbur cited Hydrogen ; Marth-gca ; Fire-damp; &a9 of 
the Acetates, — This gas is but too often found to be abundantly disengaged in 
coal-mines from the fresh-cut surface of the coal, and from remarkable aper- 
tures or << blowers," which emit for a great length of time a copious stream 
or jet of gas, which probably existed in a state of compression, pent up in 
the coal. 

The mud at the bottom of pools in which water^planis grow, on being 
stirred, suffers bubbles of gas to escape, whioh may be easily collected. 
This, on examination, is found to be chiefly a mixture of light carbonetted 
hydrogen and carbonic acid ; the latter is easily absorbed by lime-water or 
caustic potassa. 

Until recently, no method was known by which the gas ib question could 
be produced in a state approaching to purity by artificial means ; the various 
illuminating gases from pit-coal and oil, and that obtained by passing the 
vapour of alcohol through a red-hot tube, contain large quantities of light 
carbonetted hydrogen, associated, however, with other substances which 
hardly admit of separation. M. Dumas was so fortunate as to discover a 
method by which that gas can be produced at will, perfectly pure, and in 
any quantity. 

A mixture is made of 40 parts crystallized acetate of soda, 40 parts solid 
hydrate of potassa^ and 60 parts quicklime in powder. This mixture is 
transferred to a flask or retort, and strongly heated ; the gas is disengaged 
in great abundance, and may be received over water. ^ 

Ijght carbonetted hydrogen is a colourless and nearly inodorous gas, which 
does not affect vegetable colours. It burns with a yellow flame, generating 

* Ann. Chim. et Fhys. Ixxiii. 93. The reaction consists in the oonversion of the aoetio acid^ 
V the aid of tbe elements of water, into carbonic acid and light carbonetted hydrogen ; the 
instobiUty of tbe orfsmae acid at « high temperature, and the attraction of the potassa for 
earbonic acid, heing the determining causes. The lime prevents the hydrate of potassa from 
fusing iaad attacking the glass vessels. This decomposition is best understood by putting it 
in the shape of an equation. 

Acetic add C4H3O8 \^( Carbonic acid, 2 eq. C9 O4. 
Water HO/ (. Marsh-gas, 2 eq. C9H4 

C4H«0«. C4H4O4. 


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 
0*559, 100 cubic inches weighing 17*41 gridns; and it contains carbon and 
hydrogen associated in the proportion of 6 parts by weight of the former to 
2 of the latter.* 

When 100 measures of this gas are mixed with 200 of pure oxygen in the 
eudiometer, and . the mixture exploded by the electric spark, 100 measures 
of a gas remain which is entirely absorbable by a little solution of caustic 
potassa. Now carbonic acid contains its own volume of oxygen ; hence ooe- 
half of the oxygen added, that is, 100 measures, must have been consumed 
in uniting with the hydrogen. Consequently, the gas must contain twice its 
own measure of hydrogen, and enough carbon to produce, when completely 
burned, an equal quantity of carbonic acid. 

When chlorine is mixed with light carbonetted hydrogen oyer water, no 
change follows, provided light be excluded. The presence of light, however, 
brings about decomposition, hydrochloric acid, carbonic acid, and sometimes 
other products being produced. It is important to remember that the gas 
is not acted upon by chlorine in the dark. 

OUfiant Uas. — Strong spirit of wine is mixed with five or six times its 
weight of oil of vitriol in a glass-flask, the tube of which passes into a wash- 
bottle containing caustic potassa. A second wash-bottle, partly filled with 
oil of vitriol, is connected to the first, and furnished with a tube dipping into 
the water of the pneumatic trough. On the first application of heat to the 
contents of the flask, alcohol, and afterwards ether, make their appearance ; 
but, as the temperature rises, and the mixture blackens, the ether-vapour 
diminishes in quantity, and its place becomes in great part supplied by a 
permanent inflammable gas ; carbonic acid and sulphurous acid are also 
generated at the same time, besides traces of other products. The two last- 
mentioned gases are absorbed by thealkali in the first bottle, and the ether 
vapour by fiie acid in the second, so that the defiant gas is delivered tole- 
rably pure. The reaction is too complex to be discussed at the present mo- 
ment ; it will be found fully described in another part of the volume. Ole- 
fiant gas thus produced is colourless, neutral, and but slightly soluble in 
water. Alcohol, ether, oil of turpentine, and even olive oil, as Mr. Faraday 
has observed, dissolve it to a considerable extent' It has a faint odour of 
garlic. On the approach of a kindled taper it takes fire, and bums wit^ a 
splendid white light, far surpassing in brilliancy that produced by light car- 
bonetted hydrogen. This gas, when mixed with oxygen and fired, explodes 
with extreme violence. Its density is 0-981 ; 100 cubic inches weigh 30-57 

By the use of the eudiometer, as already described, it has been found that 
each measure of' defiant gas requires for Complete combustion exactly three 
of oxygen, and produces under these circumstances two measures of car- 
bonic acid. Whence it is evident that it contains twice its own volume of 
hydrogen, combined with twice as much carbon as in marsh-gas. 

By weight, these proportions will be 12 parts carbon, and 2 parts 

Olefiant gas is decomposed by passing through a tube heated to bright 
redness ; a deposit of charcoal takes place, and the gas becomes converted 

^ The two carbides of hydrogen here described are thus represented ia equiyalents:— 
Light carbonetted hydrogen Clla 

Olefiant gas CaHa 

* Olefiant gas, \iy pressure and intense cold, produced by the eTaporation in a yacuum of 
solid carbonic acid and ether, is condensed into a colourless transparent liquidj but not iroien. 
(laraday.)— R B, 


into light Cliirbonetted hydrogen, or eren into free hjdrogen, if the temper- 
atare be yery high. This latter change is of coarse attended by increase of 

Chlorine acts npon defiant gas in a yery remarkable manner. When the 
tvo bodies are mixed, eyen in the dark, they combine in equal measures, and 
gi?e rise to a heayy oily liquid, of sweetish taste and ethereal odour, to 
which the name chloride of hydrocarbon, or Dutch liquid, is giyen. It is 
from this peculiarity that the term olefiant is deriyed. 

A pleasing and instructiye experiment may also be made by mixing in a 
tall jar two measures of chlorine and one of olefiant gas, and then quickly 
applying a light to the mouth of the yessel. 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 Oases, — The manufacture qf coal-gas is at the present mo- 
ment a branch . of industry of great interest and importance in seyeral 
points of yiew. 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 destructiye distillation, ayariety of products 
show themselyes ; permanent gases, steam, and yolatile oils, besides a not 
inconsiderable quantity of ammonia from the nitrogen always present in the 
coaL These substances yary yery much in their proportions with the tem- 
peratare at which the process is conducted, the permanent gases becoming 
more abundant with increased heat, but at the same time losing much of 
their yalue for the purposes of illumination. 

The coal is distilled in cast-iron retorts, maintained at a bright red heat, 
and the yolatilized 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 yapours are next made to trayerse a refrigerator, usually a 
series of iron pipes, cooled on the outride by a stream of water ; here the 
condensation of the tar and ammoniacal liquid becomes complete, and the 
gas proceeds onwards to another part of the apparatus, in which it is to be 
depriyed of the sulphuretted hydrogen and carbonic acid gases always present 
in the crude product. This is generally effected by hydrate of lime, which 
readily absorbs the compounds in question. The purifiers are large iron 
Teasels, partly filled with a mixture of hydrate of lime and water, in which 
a chnming machine or agitator is kept in constant motion to preyent the 
sobsidence of the lime. The gas is admitted at the bottom of the yessel by 
a great number of minute apertures, and is thus made to present a large 
snrface of contact to the purifying liquid. The last part of the operation, 
which indeed is often omitted, consists in passing the gas through dilute 
Bulphuric acid, in order to remoye ammonia. The quantity thus separated 
is very small, relaliyely to the bulk of the gas, but in an extensiye work be- 
comes an object of importance. 

Coal-gas tiius manufactured and purified is preseryed for use in immense 
cylindrical receiyers, 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. * 

'It may give some idea of the extent of this species of manufacture, to mention, that in- 
tks year 1888, for lighting London and the suburhs alone, there were eighteen public gas 
wwkc, amd £2,800,000 inyMt«d in pipes and apparatus. The yearly revenae amounted to 

\^ qQMB|¥|»TXO>Njk ▲M9 

Goftl^as Tories v^xtsk ia o«i9f ositioD, jud^g from ite^ vanaUe density 
^T^d illaminating power,, and frpm the ans^ysea which have been n^^de. The 
difficulties of such investigations are very great, apd unless particular pre- 
oaut^ be tal^ea, the resuHs are merely approximaUve. The purified gas is 
l>eUeve4 to ooatain the foUowuiig sul^stances,. of ^hich the j^&t i^ ^^st aj^w^r 
4ant, an4 the second m^ost valuable. 

Light carboQjetted hydrogen. 

Olefiapt gas. ^ 


Carbonic oxide^ 


Vapours of volatile Ifqtuid, carbides of hydrogen.* 

Vapour of bisulphide of carbon. 

Separated hyi CondeMotion and hy the Purifiers, 

Tar an4 Toljatile oils. 

Sujphate of ammonia, ohlonde and sulphide. Okf ^mnwninT^. 

Sulphuretted hydrogen. 

Garbonio aoid. 

Hydrocyanic acid, or cyajB^d^ of apmif^junnij. 

A very ftir better illuminating gas may be. prepared ftrom oil, by dropping 
it into a red-hot iTon retort filled with coke ; the liquid is in great part de- 
compjosed and converted into permanent gas, which requires no purification, 
as it is quite free from the ammoniacal and sulphur compounds which vitiate 
the gas from coal. A few years ago this article was prepared in London ; it 
was compressed for the use of the consumer into strong iron vessels, to the 
extent of 30 atmospheres ; these were furnished with a screw-valve of pecu- 
liar construction, and exchanged for others when exhausted. The comparative 
high price of the material, and other circumstances, led to the abandonment 
of the undertaking. 


When any solid substance^ capable of bearing the fire, is heated to a. certain, 
point, it emits light, the chareoter of which depends upon the temperature. 
Thus, a bar of pUtinum or a piece of porcelain raised to a particular temper 
rature, become what is called red-hot, or emissive of red light ; at a higher 
degree of heat this light becomes, whiter and more intense, and when urge4 
to the utmost, a9 iry the ease of a piece of lime placed in the flame of the oxy- 
hydrogen blowpipe, the light becomes exceedingly powerful and acquires sk 
tint of violet. Bodies in these states are said to be incasidescent or ignUed. 

Again,, if the same experiment be made on a pieee of charcoal, similar 
effects will>e observed, but something in addition; for whereas the platinum 
or porcelain, wh^ removed from the fire, or the lime from the blow-pipe 
flame, begin immediately to eool, and emit less and less light, until they 
become completely obscure, the eharceal maintains to a great extent its high 
temperature. UnUke the other bodies too,, which suffer no change whatever 
either of weight or substance, the charcoal gradi^^lly -pastes away until it 

j&450,000, and the oonsumptiop of oo^ in the same period to 180,000 tons, l,ieo mHUoni of 
cubic feet of gas being made in the year. There were 134,300 private lights, and 30,400 stieet 
lamps. 890 tons of coal were used in the retorts in the space of twenty-four hours at mid- 
winter, and 7,1^)000 cubic feet of gas consumed in the longest night. — Dr. Ure, IMctionary 
of Arts and Manufactures. Since that time the production of gas has been Tery oonsidfirably 
•t xhoM l)odies i«crea«« thp illuminating power, and cosfi^i; 04 th« g«A it# pecuUitr odour. 



dissppears. TMs is whAt is called tomhugUm im oontMvdiKt&ictloti to mere 
ignition ; the charcoal bums, and its temperature is kept up by the heat 
eroWed 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 whatsoeyer, 
if its energy rise sufficiently high, may produce the phenomenon of com- 
bustion, by heatinff ike body to euch an acUnt that it becomes lummoue. 

In all ordinary cases of combustion, the action lies between the burning 
body and the oxygen of the air ; and since the materials employed for the 
economical production of heat and light consist of carbon chiefly, or that 
substance conjoined with a certain proportion of hydrogen and oxygen, all 
common effects of this nature are cases of tlie rapid and violent oxidation 
of carbon and hydrogen by the aid of the free oxygen of the air. The heat 
must be referred to &e act of chemical union, and the light to the elevated 

By this principle it is easy to understand the means which must be adopted 
to inerlease the heat of ordinary fires to the point necessary to melt refrac- 
tory metals, and to bring about certain desired effects of chemical decom- 
position. If the rate of consumption of the fuel can be increased by a more 
rapid introduction of air into tiie burning mass, the intensity of the heat 
will of necessity rise in the same ratio, there being reason to believe that the 
quantity of beat evolved is fixed and definite for the same constant quantity 
of chemical action. This increased supply of air may be effected by two 
distinct methods; it may be forced into the fire by bellows or blowing- 
machines, as in the common forge, and in the blast and cupola-furnaces of 
the iron-worker, or it may be drawn through the burning materials by the 
help of a tall chimney, the fire-place being closed on all ades, and kH> en- 
trance of air allowed, save between the bars of the grate. Such is the kind 
of fomace generally employed by the scientific chemist in assaying and in 
the reduction of metallic oxides by charcoal ; the principle will be at once 
onderstood by the aid of the sectional drawing, in which a crucible is repre- 
sented, arranged in the fire for an operation of the kind mentioned. 
(Fig. 111.) 

Fig.m. Fig. 112 


The "reverberatory" furnftoe (fig. 112) is one very mncli used in the arts 
when substances are to be exposed to heat without contact with the fuel. 
The fire-chamber is separated from the bed or hearth of the furnace by a 
low wall or bridge of brick-work, and the flame and heated air are reflected 
downwards by the arched form of the roof. Any degree of heat can be ob- 
tained in a furnace of this kind, from the temperature of dull redness, to 
that required to melt very large quantities of cast-iron. The fire is urged 
by a chimney provided with a sliding-plate or damper \o regulate the draught. 
Solids and liquids, as melted metal, enjoy, when sufficiently heated, the 
faculty of emitting light; the same power is possessed by gaseous bodies, 
bu% the temperature required to render a gas luminous is incomparably 
higher than in the cases already described. Gas or vapour in this condition 
constitutes flame., the actual temperature of which generally exceeds that of 
the white heat of solid bodies. 

The light emitted from pure flame is exceedingly feeble; illuminating 
power is almost entirely dependent upon the presence of solid matter. The 
flame of hydrogen, or of the mixed gases, is scarcely visible in full daylight ; 
in a dusty atmosphere, however, it becomes much more luminous by igniting 
to intense whiteness the floating particles with which it comes in contact. The 
piece of lime in the blowpipe flame cannot have a higher temperature than 
that of the flame itself; yet the light it throws off is infinitely greater. 

Flames burning in the air, and not supplied with oxygen 
Fig. 113. from another source, are, as already stated, hollow ; the che- 

mical action is necessarily confined to the spot where the two 
bodies unite. That of a lamp or candle, when carefully ex- 
-V-— C amined, is seen to consist of three separate portions. The 
- dark central part, a, fig. 113, easily rendered evident by de- 
— -B pressing upon the flame a piece of fine wire-gauze^ consists of 
combustible matter drawn up by the capillarity of the wick, 
\-'—JL and volatilized by the heat. This is surrounded by a highly 
luminous cone or envelope, b, which, in contact with a cold 
body, deposits soot. On the outside a second cone, c, is to 
be traced, feeble in its light-giving power, but having an 
exceedingly high temperature. The explanation of these ap- 
pearances is easy : carbon and hydrogen are very unequal in 
their attraction for oxygen, the latter greatly exceeding the former in this 
respect; consequently, when both are present, and the supply of oxygen 
limited, the hydrogen takes all, to the exclusion of a great part of the car- 
bon. Now this happens in the case under consideration, at some little dis- 
tance within the outer surface of the flame, namely, in the luminous portion ; 
the little oxygen which has penetrated thus far inwards is entirely consumed 
by the hydrogen, and the particles of deposited charcoal, which would, were 
they cooler, form smoke, become intensely ignited by the burning hydrogen, 
and evolve a light whose whiteness marks a very elevated temperature. In 
the exterior and scarcely visible cone, these particles of carbon undergo 

A jet of coal-gas exhibits these phenomena ; but, if the gas be previously 
mingled with air, or if air be forcibly mixed with, or driven into the flame, 
no such separation of carbon occurs, the hydrogen and carbon burn together^ 
and the illuminating power almost disappears. 

The common mouth blowpipe is a little instrument of high utility ; it is 
merely a brass tube, fitted with an ivory mouth-piece, and terminated by a 
jet, having a small aperture by which a current of air is driven across the 
flame of a candle. The best form is perhaps that contrived by Mr. Pepys, 
and shown in fig. 114. The flame so produced is very peculiar. 
Instead of the double envelope just described, two long pointed cones are 



obserred, which, idien the blowpipe is good, end 
the aperture Bmooth and round, are very well de- 
fined, the outer one being yellowish, and the inner 
blue. Fig. 115. A doable combustion is, in fact, 
going on, bj the blast in the inside, and by the 
external air. The space between the inner and 
outer cones is filled with exceedingly hot com- 
bustible matter, possessing strong reducing or 
deoxidizing powers, while the highly heated air 
just beyond the point of the exterior cone ox- 
idizes with great facility. A small portion of 
matter, supported on a piece of charcoal, or 
fixed in a ring at the end of a fine platinum 
wire, can thus in an instant be exposed to a very 
high degree of heat under these contrasted cir- 
cumstances, and observations of great value made 
in a very short time. The use of the instrument 
requires an even and uninterrupted blast of 
some duration, by a method easily acquired with 
a little patience ; it consists in employing for 
the purpose the muscles of the cheeks idone, 
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 exhibits, in sec- 
tion, an excellent lamp of thisrkind for burning 
alcohol or wood-spirit. It is constructed of thin 
copper, and furnished with ground caps to the 
wick-holder and aperture * by which the spirit is 
introduced, in order to prevent loss when the 
lamp is not in use. Glass spirit-lamps, fitted 

Fig. 116. 


Fig. lift. 

Fig. 117. 

* When in use this aperture must always he open, otherwise an accident is sure to happen, 
Uw heat expands the air in the lamp, and the spirit is foroed out in a state of inflammation. 



Kg. 119. 

with caps (figk 1 17) to prevent evaporation, are very e«iiTentent fbr occa- 
Bional use, being always ready and in order.* 

In London, and other large towns where coal-gas is to be had, that sub- 
stancQris constantly used wit,h the greatest economy and advantage in every 
respect as a source of heat. Retorts, flasks, capsules, 
^and other vessels, can be thus exposed to an easily re- 
gulated and invariable temp^ature for many succes^ve 
hours. Small platinum orucibles may be ignited to 
redness by placing them over the flame on a little wire 
triangle. The arrangement shown in flg. 119, consist- 
ing of a common Argand gas-burner fixed on a heavy 
and low foot, and connected with a flexible tube of 
caoutchouc or other material, leaves nothing to desire. 

The kindling-point, or temperature at wMch combus- 
tion commences, is very different with different substan- 
ces ; phosphorus will sometimes take fire in the hand ; 
sulphur requires a temperature exceeding that of boil- 
ing water ; charcoal must be heated to redness. Among 
gaseous bodies the same fact is observed : hydrogen is 
inflamed by a red-hot wire; carbonetted hydrogen re- 
quires a white heat to effect t^e same thing. When flame 
is cooled by any means below the temperature at which the rapid oxidation 
of the combustible gas occurs, it is at once extinguished. Upon this depends 
the principle of Sir H. Davy's invaluable safe-lamp. 

Mention has already been made 'of the frequent disengagement of great 
quantities of light carbonetted hydrogen gas in coal-mines. This gas, mixed 
with seven or eight times its volume of atmospheric air, becomes highly ex- 
plosive, taking fire at a light, and burning with a pale blue flame ; and many 
fearful accidents have occurred from the ignition of large quantities of 
mxKed air and gas occupying the extensive galleries and workings of a 
mine. Sir H. Davy undertook an investigation with a view to discover some 
remedy for this constantly-occurring calamity ; his labours resulted in some 
exceedingly important discoveries respecting flame, of which the substance 
has been given, and which led to the construction of the lamp wMch. 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 othei- 
wise, the flame is not communicated to the otlier, provided the diameter of 
the tube, its length, and the conducting power for heat of its material, bear 
a certain proportion to each other ; the flame is extinguished by cooling, and 
its transmission rendered impossible. 

In this experiment, high conducting power and diminished diameter com- 
pensate for diminution of length ; and to such an extent can this be carried, 

Fig. 118. 

» The ppirit-lamp represented in flg. 118, is 
one contrived hy Dr. MitchelL ** It is made 
of tinned iron. The alcohol is poured ont hy 
means of the hollow handle, and is admitted 
to the cylindrical hurner by two or three 
tubes which are placed at the very bottom of 
the fountain. By such an arrangement of 
parts, the alcohol may be added as it is con- 
sumed, and the flame kept uniform; and as 
the pipes which pass to the burner are so re* 
mote from the flame, the alcohol never be* 
comes heated so as to fly off through the 
vent-hole, and thus to cause greater waste 
and danger of explosion." 

A <^lindrical chimney is an advantageous 
addition fbr maiiy purposes. It may be Blade 
of tin-plate or eopper. — R. B. 




fhat metallic gauze, which may be looked upon as a series of rery 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 proyidentially, the fire-damp mixture has an ex- 
ceedingly lugh kindling point ; a red heat does not cause in- 
flammation ; consequently, the gauze will be safe for this 
substance, when flame would pass in almost any other case. 

The miner's safe-lamp (fig. 120) is merely an ordinary oil- 
lamp, the flame of which is enclosed in a cage of wire gauze ; 
made double at the upper part, containing about 400 aper- 
tures to the square inch. The tube for supplying oil to the 
reservoir reaches nearly to the bottom of the latter, while the 
wick admits of being trimmed by a bent wire passing with 
friction through a small tube in the body of the lamp ; the 
flame can thus be kept burning for any length of time, with- 
out the necessity of unscrewing the cage. When this lamp is 
taken into an explosive atmosphere, although the fire-damp 
may bum within the cage with such energy as sometimes 
to heat the metallic tissue to dull redness, the flame is not 
communicated to the mixture on the outside. 

These effects may be conveniently studied by suspending 
the lamp in a large glass jar, and gradually admitting coal- 
gas below. The oil-flame is at first elongated, and then, as 
the proportion of gas increases, extinguished, while the in- 
terior of the gauze cylinder becomes filled with the burn- 
iog mixture of gas and air. ^ As the atmosphere becpmes 
purer, the wick is once more relighted. These appear- . 
ances are so remarkable, that the lamp becomes an admi- 
rable indicator of the state of the air in different parts of 
the mine.' 

The same great principle has been ingeniously applied 
by Mr. Hemming to the construction of the oxy-hydrogen 
safety-jet formerly mentioned. This is a tube of brass 
about four inches long, filled with straight pieces of fine 
brass wire, the whole being tightly wedged together by a 
pointed rod, forcibly driven into the centre of the bundle. 
Fig. 121. The arrangement thus presents a series of 
metal tubes, very long in proportion to their diameter, the 
cooling powers of which are so great as to prevent the pos- 
Bihility of the passage of flame, even vrith oxygen and hy- 
drogen. The jet may be used, as before mentioned, with 
a common bladder, without a chance of explosion. The 
fundamental fact of flame being extinguished by contact 
with a cold body, may be elegantly shown by twisting a 
copper wire (fig. 122) into a short spiral, about 0*1 inch 

Fig. 122. 


' This is the true uae of the lamp, namely, to permit the viewer or Buperintendent, with 
out risk to himself, to examiue the state of the air in every part of the mine; not to enable 
workmen to continue their labours in an atmosphere habitually explosive, which must he 
unfit for human respiration, although the evil effects may he slow to appear. Owners of 
coal-mines should be compelled either to adopt efficient means of ventilation, or to doM 
workings of thiu dangerous character altogether. 


ki dkiMter, and tben pttenng it eM over the flame of a wax eaadle ; tlr 
latter is extingaished. If the spiral be now heated to redness bj a spirit 
lamp, and the experiment repeated, no such effect follows/ 


When powdered sal-ammoniac is mixed with moist hjdrat« of lime, and 
gently heated in a glass flask, a large quantity of gaseous matter is disengaged, 
which must be collected ever mercozy, or by displacement, advantage b^g 
taken of its low specific gra-vity. 

Ammoniacal gas thus obtained is colonrless; it has a very powerful pun- 
gent odour, and a strong alkaline reaction to test-paper, by which it may be 
at once distinguidied from nearly all other bodies possessing the same pin- 
eal characters. Under a pressure of 6*5 atmospheres at ^^ (15<>*50), am- 
monia condenses to the liquid form.* Water dissolves about 700 times its 
Tolume of this remarkable gas, forming a solution which in a more dilute 
state has long been known under the name of Uguor ammofiicB ; by heat, i 
great part is again expelled. The solution is decomposed by chlorine, sal- 
ammoniac being formed, and nitrogen set free. 

Ammonia has a density of 0*589 ; 100 cubic inches weigh 18*26 grains 
It cannot be formed by the direct union of its elements, although it is soi 
times produced under rather remarkable circumstances by the deoxidati* 
of nitric acid. The great sources of ammonia are the feebly-compounded^ 
azotized principles of the animal and Tegetable kingdoms, which, when left 
to putrefactive change, or suljected to destructive distillation, almost inva- 
riably give rise to an abundant production of this substance. 

The analysis of ammoniaoal gas is easily effected. When a portion is ocm^ 
fined in a graduated tube over mercniy, and electric sparks passed through 
it for a considerate time, the volume of the gas gradually increases until it 
becomes doubled. On examination, the tube is found to contain a mixture 
of 8 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 8 parts hydrogen to 14 
parts nitrogen. 

Ammonia may also be decomposed into its elements by^ transmission 
through a red-hot tube. 

Solution of ammonia is a very valuable reagent, and is employed in a great 
number of ebemical operations, for some of which it is necessary to have it 
perfectly puSre. Tlve best mode of preparation is the following : — 

Equal weights of sal-ammoniac and quicklime are taken ; the lime is slaked 
in a covered basin, and the salt reduced to powder. These are mixed, and 
introduced into the flask employed in preparing solution of hydrochlorio 
acid, together with just enough water to damp the mixture, and cause it to 
aggregate into lumps ; the rest of the apparatus is arranged exactly as in 

* Where ooal'gas is to be bad, )t may be advantageously used as a source of beat, by taking 
■dyantage of the aboye-mentioned fact. On passing a current of gas through a wide verti<!cl 
tube, open at the bottom to afford a free mixture with atmospheric air, but closed at toe top 
by wire gause, and then kindling the mixture after its escape through the meshes, it will 
bum with feeble illuminating power, but no loss of heat When the proportion of the Kas 
to the atmospheric air is such as not to allow the flame to become yellow, the oombustJon 
will be complete, and no carbonaceous deposit will be formed on cold bodies hold over the 
fiames. The length and diameter of the cylinder are determined by the amount of gas to be 
burnt, and the length may be much decreased by interposing a second diaphragm of wire 
gauze about mid-length of the cylinder, the current of gas being introduced below thin, bj 
which means a more thorough and rapid mixture is made with the atmoapheiio air. — ^jr 
John Kobinson, K. H. Aa, Ed. New Phil. Journal, 1840.— K. B. 

• AX the temperature of — 103P (— 75<K)), liqriid ammonia freeies into a oolourleM tolfd* 
liMrter than the Uquid it8elC-<Faraday.>- R. B. 


tbe fonner case, with an oxme% or two of water in the waeh-bottle, or enough 
to coTcy the ends of the tabes, and the gas conducted afterwards into pure 
distilled water, artificially cooled, as before. The cork-joints are made tight 
▼ith wax, a little water is put into the safety-funnel, heat oantionsly 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. 

f Ammonia— Ammonia. 

Sal-ammoniac 'j Hydrochloric ^Hydrogen-. ^^-^ Water. 

( acid / Chlorine^ 

""»• { C^fc^ ^ ^""^Chloride of 


Solution of ammonia should be perfectly colourless, leaye no residue on 
eyaporation, and when supersaturated by nitric acid, give no cloud or roud- 
diness with nitrate of silver. Its density diminishes with its strength, that 
of the most concentrated being about 0*875 ; the value in alkali of any 
fianrple ef liquor ammonisd |s 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 tlds experiment will be found described under 

When solution of ammonia is mixed with acids of various kinds, salts are 
generated, wbich resemble in the most complete manner the corresponding 
compounds of potassa and soda ; these are best discussed in connexion with 
the latter. Any ammoniacal salt can at once be recognized by the evolution 
of ammonia when it is heated with hydrate of lime, or solution of carbonate 
of potassa or soda. 


A combination of nitrogen with boron was first obtained by Balmain. 
Woehler prepared it by mixing one part of pure dry borat with two parts of 
dry sal-ammoniac, heating to redness, boiling with water and hydrochloric 
acid, filtering and washing with hot water, when the compound remained in 
the form of a white powder. As yet it has not been obtained quite free 
from oxygen. 


Sulphuretted Hydrogen ; Hydrosulphurie Add, — There are two methods by 
which this important compound can be readily prepared, namely, by the 
action of dilute sulphuric acid upon sulphide of iron, and by the decomposi- 
tion of sulphide of antimony by hydrochloric acid. The first method yields 
it most easily, and the second in the purest state. 

Protosulphide of iron is put into the apparatus for hydrogen, already 
ieveral 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 tp 
be collected 0T«r tepid water. The reaction is thus explained : — 

* See Fig. 106, p. 142. 



Sulphide of Iron jf^j''" 

^^^ {Z^. 

Snlphurie arid 

Snlpharetted hydrogen. 

Sulphate of protoxide of iron. 

By the other plan, finely-powdered snlphide of antimony is put into a flask, 
to which a cork and bent tube can be adapted, and strong liquid hydro- 
chloric acid poured upon it. On the application of heat, a double inter- 
change occurs between the bodies present, sulphuretted hydrogen being 
formed, and chloride of antimony. The action only lasts while the heat is 

Hydrochloric acid { chlorif^ 

Sulphide of antimony { ^^^^^^ 

Sulphuretted hydrogen. 

Chloride of antimony. 

Fig. 123. 

Sulphuretted hydrogen is a colourless gas, having the odour of putrid 
®ggs ; it is most offensiTe when in small quantity, when a mere trace is pre- 
sent in the air. It is not irritating, but, on the contrary, powerfully narcotic. 
When set on fire, it burns with a blue flame, producing water and sulphuroas 
acid when the supply of air is abundant ; and depositing sulphur when the 
oxygen is deficient. Mixed with chlorine, it is instantly decomposed, with 
separation of the whole of the sulphur. 

This gas has a specific gravity of 1-171 ; 100 cubic inches weigh 86-33 

A pressure of 17 atmospheres at 50° (10®C) reduces 
it to the liquid form. Cold water dissolves its own 
volume of sulphuretted hydrogen, and the solution 
is often directed to be kept as a test ; it is so prone 
to decomposition, however, by the oxygen of the air, 
that it speedily spoils. A much better plan is to keep 
a little apparatus for generating the gas always at 
hand, and ready for use at a moment's notice. A small 
bottle or flask (fig. 128), to which a bit of bent tube ia 
fitted by a cork, is supplied with a little sulphide of 
iron and water; when required for use, a few drops 
of oil of vitriol are added, and the gas is at once 
evolved. The experiment completed, the liquid is 
poured from the bottle, replaced by a little clean water, 
and the instrument is again ready for use. 

When potassium is heated in sulphuretted hydrogen, the metal burns with 
great energy, becoming converted into sulphide, while pure hydrogen remains, 
equal in volume to the original gas. Taking this fact into account, and 
comparing the density of the gas with those of hydrogen and sulphur-vapour, 
it appears that every volume of sulphuretted hydrogen contains one volume 
of hydrogen and one-sixth of a volume of sulphur-vapour, the whole con- 
densed into one volume. This corresponds very nearly with its composition 
by weighty determined by other means, namely, 16 parts sulphur and 1 part 

When a mixture is made of 100 measures of sulphuretted hydrogen and 
160 measures of pure oxygen, and exploded by the electric spark, complete 
combustion ensues, ana 100 measures of sulphurous acid gas restdt 

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- 


Bplen of an apAvtment, it maj be iastaotuMwIy dtiteo^ed by ft 

quantity of chlorine gas. 

There are few reagents of greater yalne to the pntetioal ohemitt than this 
iDbBtanee ; when brought in contact with manj metallio solutioi^ it giTes 
rifle to precipitates, which are often exceedingly characteristic in appevrance, 
ind it n^uently affords the means also of sepacatiiig metals from each other 
vith the greatest precision and certainty. The precipitates spoken of ar# 
insolable sulphides, formed by the mutual deebmposition of the BMtallio 
oxides or chlorides and sulphuretted hydrog^, water or hydrochloric acid 
bemg prodneed at the same time. All the metals are, iq fact, precipitated 
whose sulphides are insoluble in water and ii| dilute acids. 

Sulphuretted hydrogen possesses itself the properties of an add; its 
lolution in water reddens litmus paper. 

The best teat for the presence of this compound is paper w^ted wttii 
eolation of acetate of lead. This salt is blackened by the smallest trace of 
the gas. 

FefnUphide of Hydrogen. — This substance conrespox|da in constitntiom 
ind instability to the binozide of hydrogen ; it is prepared by the following 
means: — 

Squai weights of daked lime and towem of sulphuv are boiled with 6 ov 
6 parts of water for half an hour, when a de^ orangensoloured solution ia 
produced, containing among other things persnlphide of calcium. This is 
filtered, and slowly Mided to an excess of dilute sulphuric acid, wUh eonstaat 
agitation. A white precipitate of separated sulphur and sulphate of lime 
makes its appearance, together with a quantity of yellow oily-*loofciBg 
matter, which collects at l£e bottom of the vessel ; thii ia persnlphide of 

If the experiment be conducted by pouring the «ai into the solution of 
sulphide, then nothing but finely-divided precipitated sulphur is obtained. 

The persnlphide is a yellow, viscid, insoluble liquid, exhaling the odour 
Q^ snlphurett'ed hydrogen ; its specific gravity is 1*769. It is slowly decom- 
posed even in the cold into sulphur and sulphuretted hydroge^t f^nd instantly 
by a higher temperaturOf or by coptact with many metallic o<i4«a. ThU 
compound probf^bly contains twice as mucb sulphur Ia relation to th9 oth^ 
elements, as solphuretted hydrogen. 

Hydrogen and Selenium i Seienieihd Hydrogen, — This subfjkauce 'm prodoo^ 
by the action of dilute sulphuric acid upou Qeleuide of potassium or iron ; 
it very much rt^sembles sulphuretted by^og^o, b^ng a oorofi?le88 gi>f , freely 

' Hie reaction which ensuea wbeu hydrate of lime, snlpbor, and vater, fjra boiled together, 
ii rather complex; bisulphide or pentapulpbide of c^cium betn|[ formed, together with hypo 
ralphite of lime, aridbog firom the transfer of the oxy^ejx of the decomposed Uime to another 
pfniioa of mlphar. 

4 ^ y*^^ S 3 «<!• cal<^m :=7^ 2eq. MsolpUde of oaldom. 

2eq.mne^ 2eq. oxygen ^^ — ' 

4 eq. anlphur- 

2 eq. ^aipho r ^'-^ 1 eq. hnwsuliA vKnia add. 

Ae bisnlphifde of calduoi) decomposed by aa add nndev ftvonnbla dpoomstaaieefl^ yieUf a 
nit of Ume' and biaolphide (persolphidp) of hydcogen. 


'-^-^^ •••• 1 J:5:S?sri^^^^ 

Sulphuric add =^^ ^ ^' ?«lPh»*« rf lime- 
When the acid ia poured into the sulphide, sulphuretted hydrogen, water, and 8nl]Aiaie 9f 
lime, ai« pnxivioed. while the excess of sulphur is thrown down as a fine wjiite powder, 1M 
"pradpftat^ enlphur" of the Pharmacopoeia. When the object is to propara the latter tn^ 
■Uaoa^ hydrochloric add moat be used In the place of sulphuric. 


soluble in irater, and decomposing metallic solutions like that snbtance ; in- 
soluble selenides are thus produced. This gas is said to act very powerfully 
upon the lining membrane of the nose, exciting, catarrhal symptoms, and 
destroying the sense of smell. It contains 89*5 parts selenium, and I pari 

Photpkonu and Hydrogen ; Phoapkoretted Hydrogen, — This body bears a 
slight analogy in some of its chemical relations to ammoniacal gas ; it is, 
howcTer, destitute of alkaline properties. 

Phosphoretted hydrogen may be obtained in a state of purity by heating^ 
in a small retort hydrated phosphorous acid, which is by such treatment de- 
composed into phosphoretted hydrogen and hydrated phosphoric acid.* 

Thus obtained, the gas has a density of 1 '24. It contains 82 parts phos- 
phorus, and 8 parts hydrogen, and is so constituted that every two volumes 
contain 8 volumes of hydrogen and half a volume of phosphorus-vapour« 
condensed into two volumes. It possesses a highly disagreeable odour of 
garlic, is slightly soluble in water, and burns with a brilliant white flame, 
ibrming water and phosphoric acid. 

Phosphoretted hydrogen may also be produced by boiling together in a 
retort of small dimensions caustic potassa or hydrate of lime, water, and 
phosphorus ; the vessel should be filled to the neck, and the extremity of 
the latter made to dip into the water of the pneumatic trough. In the reaction 
which ensues the water is decomposed, and both its elements combine with 
the phosphorus^. The alkali acts by its presence determining the decomposition 
of the water, in the same manner as sulphuric acid determines the decompo- 
sition of water when in contact with zinc. 

Water / ^^^^^8®^ ■ ^^„^^'^ '' Phosphoretted hydrogen. 

"•\ Oxygen^ ^ 

Phosphorus - 

Pho8phorus____ _^^^ 

Lime ^^-.v^ i Hypophosphite of lime. 

The phosphoretted hydrogen prepared by the latter process has the sin- 
gular property of spontaneous inflammability when admitted into the air or 
into oxygen gas ; with the latter, the experiment is very beautiful, but re- 
quires caution ; the bubbles should be singly admitted. When kept over 
water for some time, the gas loses this property, without otherwise suffering 
any appreciable change : but if dried by chloride of calcium, it may be kept 
unaltered for a much longer period. M. Paul Th^nard has shown that the 
spontaneous combustibility of the gas arises from the presence of the vapour 
of a liquid phosphide of hydrogen, which can be procured in small quantity, 
by conveying the gas produced by the action of the water on phosphide of 
calcium through a tube cooled by a freezing mixture. This substance forms 
a colourless liquid of high refractive power and very great volatility. It does 
not freeze at 0° ( — 17°-8C). In contact with air it inflames instantly, and 
its vapour in very small quantity communicates spontaneous inflammability 
to pure phosphoretted hydrogen, and to all other combustible gases. It is 
decomposed by light into gaseous phosphoretted hydrogen, and a solid phos- 
phide which is often seen on the inside of jars containing gas which has lost 

^ Beoompoflitioii of hydrated phosphorouB add by heat: >- 

r 4eq. ^ 
real add 1 

i eq. hydrated 

12 eq. 

1 eq. phoRph. --p-^ ®4- phosphoretted hydrogen, PBU 

S eq. phospb. < 
12 eq. oxygen 
^ 3 eq. hydrog.-' 

9 eq. bydrog. -->.^^<::-s, 13 eq. phos-) TTvrtr.f,-l «l.«^ 
3 eq. oxygen -T:^:^^,^ 1 phoric ac. ^^Sf^i'lff**^ 
9 eq. oxygen -^^ b eq. i^ater. J ^^"^^ ***• 


the property of spontaneous inflammation by exposore to light. Strong 
acids occasion its instantaneous decomposition. Its instabilitj is equal to 
that of binoxide of hydrogen. It is to be obeerred that the pure phospho- 
retted hydrogen gas itself becomes spontaneously inflammable if heated to 
the temperature of boiling water.* 

Phosphoretted hydrogen decomposes seyeral metallic solutions, giving rise 
to precipitates of insoluble phosphides. With hydriodic aoid it forms a crys- 
talhne compound somewhat resembling sal-ammoniac. 


Chloride of Nitrogen, — When sal-ammoniac or nitrate of ammonia is dis~ 
solved in water, and a jar of chlorine gas inverted into the solution, the gas 
is absorbed, and a deep yellow oily liquid is observed to collect upon the 
surface of the solution, which ultimately sinks in globules to the bottom. 
This is chloride of nitrogen, the most dangerously-explosive substance known. 
The following is the safest method of conducting the experiment : — 

A somewhat dilute and tepid solution of pure sal-ammoniac in distilled 
water is poured into a clean basin, and a bottle of chlorine, the neck of 
which is quite free from grease, inverted into it. A shallow and heavy leaden 
exxp is placed beneath the mouth of the bottle to collect the product When 
enough has been obtained, the leaden vessel may be withdrawn with its dan- 
gerous contents, the chloride remaining covered with a stratum of water. 
The operator should protect his face with a strong wire-gauze mask when 
experimenting upon this substance. 
The change is explained by the following diagram :- 

Chlorine ^^^^^ Chloride of nitrogen. 

Chlorine ^ ^ ■ ""^^^^^^^ ■ Hydrochloric acid 

( J Nitrogen ^^^"^^^^^^^^-^""^ 
Sal-ammoniac -j i Hydrogen ^ 

( Hydrochloric acid Hydrochloric acid. 

Chloride of nitrogen is very volatile, and its vapour is exceedingly irrita- 
ting to the eyes. It has a specific gravity of 1-653. It may be distilled at 
160° (71°*1C), although the experiment is attended with great danger. 
Between 200° (93°-8C) and 212° (100°C) it explodes with the most fearful 
violence. Contact with almost any combustible matter, as oil or fat of any 
kind, determines the explosion at common temperatures ; a vessel of porce- 
lain, glass, or even of cast-iron, is broken to pieces, and the leaden cup 
receives a deep indentation. This body has usually been supposed to contain 
nitrogen and chlorine in the proportion of 14 parts of the former to 106*6 
parts of the latter, but recent experiments upon the corresponding iodine- 
compound induce a belief that it contains hydrogen.* 

Iodide of Nitrogen. — When finely-powdered iodine is put into caustic am- 
monia it is in part dissolved, giving a deep, brown solution, and the residue 
is converted into a 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- 

* Ann. Chim. et Phys. Srd series, zir. 6. According to M. Th6nard, the new liquid phosphide 
of hydrogen oontains PHs and the solid PsH. The gas is represented hy the ibrmola PHs. 

* Instead of NCls, it may in reality he NH Cls. 

168 ot&slt odM^ouffBs ol* 

pon)aA Ust desbiibed, abd li atte6d6d IHtb tliie prodaetion of yioleiit Tdmed 
of iodine. Dr. Gladstone hoei proted that this sabstance contains hydrogen, 
and that it may be yiewed as ammonia, in Vrhich two-thirds of the hydrogen 
are replaced by iodine. 


CMorme vjUK Sulphmr and Phoaphonu,^— Chloride of Sulphur, — ^The snbehlo^ 
lide is easily prepared by passing dry chlorine oyer the surface ^ stQphui^ 
l^ept melted in a small glass retort connected with a good condensing ar- 
rangement. The chl<:»tid^ distils oter as a deep orange-yellow mobile Hqnid, 
of peculiar and disagreeable odour, which boils at 280^ (137^*80. As this 
substance dissolves both sulphur and chlorine, it is not easy to obtain it in a 
pure and definite state. It contains 82 parts sulphur and d5-5 chlorine.* 

Subchloride of sulphur is instantly decomposed by water ; ~ hydrochloric 
and hyposulphurous acids are formed, and sulphur separated, the hypo- 
snlphurous acid in its turn decomposes into sulphur and sulphurous acid. 

Protocbioride of sulphur is formed by exposing the aboye compound for a 
eonsiderable time to the action of chlorine, and Sien distilling it in a stream 
of the gas. It has a deep red colour, is heavier than water, boils at 147<> 
(63^-9'C), and contains twice as much chlorine as the subchloride.* 

Cfhloridet of Phosphorut. — Terchloride,* — This is prepared in the same man- 
ner as subchloride of sulphur, by gently heating phosphprAs in dry chlorine 
gas, the phosphorus being in excess. Or, by passing the vapour of plios* 
phorus over fragments of calomel (subchloride of mercury) contained in a 
glass tube and strongly heated. It is a colourless, thin liquid, which fumes 
in the air, and possesses a powerful and offensive odour. Its specific gravity 
is 1*46. Thrown into Water) it sinks to the bottom of that liquid, and be- 
comes slowly decomposed, yielding phosphoyoxis acid atid hydrochloric acid. 
This compound contains 82 parts phosphorus, and 106 '5 parts chlorine. 

Pentaehloride of Phosphonu.* — 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 ara introduced ; the retort is then emanated, and 
filled with dry chlorine gas. The phosphorus takes fire, and bums with a 
pale flame, fidrming a white» volatile, crystalline stbiimate, which is the pen- - 
tachloride. It may be obtained in larger quantity by passing a stream of 
chlorine gas into the preceding liquid terchloride, which become^ gradually 
converted into a solid, crystalline mass. Pentaehloride of phoaphoras is 
decomposed by. water, yielding phosphoric and hydrochloric acids. 

Two bromides of phosphorus are known, closely corresponding in proper- 
ties and constitution with the chlorides. Several compounds of iodine and 
phosphorus appear to exist : they are fusible crystalline sttbstances, which 
decompose by contact with water, and yield hycb:iodic and phosjAorons, or 
phosphoric acid. 

Chlorine dnd Carbon, — Several compounds of chlorine and carbon are 
known. They are obtained indirectly by the action of chlorine upon certain 
organic compounds, and are described in connection with the history of 
Alcohol, &c. 

Iodine Hfiih Sulphur and Pho^horue, — These compounds are formed by 
gently heating together the materials in vessels fh>m which the air is ex- 
cluded. They preseiit few points of interest. 

Chlorine with Iodine, — Iodine readily absorbs chlorine gas, forming, when 
the enlorine is in excess, a solid, yellow compound, and when the iodine pre- 
ponderates, a brown liquid. The solid iodide is decomposed by water, yield- 
ing hydrochloric and iodic acids.' 

*S«C1. *SCl. »PCh. •PCU. 

* Heno0 it doubtlesfl contains 1 eq. iodine^ and 6 eq. chlorine or ICla. 



Another definite compoiind is formed by heating in a retort a mixture of 
1 part iodine and 4 parts chlorate of potassa ; oxygen-gas and chloride of 
iodine are disengaged, and the latter may be condensed by suitable means, 
lodate and perchlorate of potassa remain in the retort I 

This chloride of iodine is a yellow, oily liquid, of suffocating smell and ; 

astringent taste ; it is soluble in water and alcohol without decomposition. 
It probably consists of 127 parts iodine, and 35*5 parts chlorine.* 

Carbon and Sulphur. — Bisulphide of Carbon. — A wide porcelain tube is ' 

nlled with pieces of charcoal, which have been recently heated to redness in a ' 

?oyered crucible, and fixed across a furnace in a slightly inclined position. i 

Into the lower extremity a tolerably wide tube is secured by the aid of a 
cork ; this tube bends downwards, and passes nearly to the bottom of a bottle 
filled with fragments of ice and a little water. The porcelain tube being 
heated to a bright redness, fragments of sulphur are thrown into the open 
end, which is immediately afterwards stopped by a cork. The sulphur 
melts, and becomes conrerted into vapour, which, at that high temperature, 
eombines with the carbon, forming an exceedingly volatile compound, which 
IS condensed by the ice and collects at the bottom of the vessel. This is 
collected and re-distilled with very gentle heat in a retort connected with a 
good condenser. Bisulphide of carbon is a transparent colourless liquid of 
great refractive and dispersive power. Its density is 1*272. It boils at 110^ 
(43°'3G), and emits vapour of considerable elasticity at common temper- 
atues. The odour of this substance is very repulsive. When set on fire in 
the air it bums with a blue flame, forming carbonic acid and sulphurous 
•eid gases ; and when its vapour is mixed with oxygen it becomes explosive. 

It freely dissolves sulphur, and by spontaneous evaporation deposits the 
latter in beautiful crystals ; it also dissolves phosphorus 

Chlorides of SiKeium and Boron. — Both silicium and boron combine directly 
with chlorine. The chloride of silicium is most easily obtained by mixing 
finely-iyvided riliea with charcoal-powder and oil, strongly heating the mix* 
tore in a covered crucible, and then exposing the mass so obtained in a por- 
eelain tube, heated to full redness, to the action of perfectly dry chlorine 
gas. A good condensing arrangement, supplied with ice-cold water, must 
be couected with the porcelain tube. The product is a colourless and very 
volatile liquid, boiling at 122o (50oC), of pungent, suffocating odour. In 
contact with water it yields hydrochloric acid and gelatinous silica. This 
tabstance contains 21*8 parts silicium, and 106-5 chlorine.' 

Bromide of Silieiwn may be obtained by a similar proceeding, the vapour 
of bromine being substituted for chlorine ; it resembles the chloride, but is 
less volatile. 

Chloride of Boron is a permanent gas, decomposed by water with produc- 
tion of boracio 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 teniperature an intimate mixture of glassy boracio acid and char* 
coal. It resembles in constitution chloride of silicium. 

* Or siogle equivalentB. *0r SiCls. 




The study of the non-metallic elements can be pushed to a very consider 
able extent, and a large amount of precise and exceedingly important infor- 
mation acquired, without much direct reference to the great fundamental 
laws of chemical union ; the subject cannot be discussed in this manner com- 
pletely, as will be obvious from occasional cases of anticipation in many of 
the foregoing foot-notes ; still, much may be done by this simple method of 
proceeding. The bodies themselves, in their combinations, furnish admirable 
illustrations of the general laws refterred to, but the study of their leading 
characters and relations does not of necessity involve a previous knowledge 
of these laws themselves. 

It is thought that by such an arrangement the comprehension of these 
very important general principles may become in some measure facilitated 
by constant references to examples of combinations, the elements and pro- 
ducts of which have been already described. So much more 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 farther, however, it is absolutely necessary that these 
matters should be discussed ; the metallic compounds are so numerous and 
complicated, that the establishment of some general principle, some con- 
necting link, becomes indispensable. The doctrine of equivalents, and the 
laws which regulate the formation of saline compounds, supply this defi- 

In the organic department of the science, the most interesting perhaps of 
all, a knowledge of these principles, and, farther, an acquaintance or even 
familiarity with the beautiful system of chemical notation now in use, are 
absolutely required. This latter is found of very great service in the study 
of salts and other complex inorganic compounds, but in that of organic 
chemistry it cannot be dispensed with. 

It will be proper to commence with a notice of the principles which regu- 
late the modem nomenclature in use in chemical writings. 


In the early days of chemistry the arbitrary and fanciful names which 
were conferrea by each experimenter on the new compounds he discovered 
suiBced to distinguish these from each other, and to render intelligible the 
description given of their production. Such terms as oil of vitriol, spirit of 
salty oil of tartar, butter of antimony, sugar of lead, flowers of zinc, sal enixum, 
salmirabile, &c., were then quite admissible. In process of time, however, 
when the niynber of known substances became vastly increased, the confu- 
sion of language produced by the want of a more systematic kind of nomen- 
clature became quite intolerable, and the evil was still farther increased by 
the frequent use of numerous synonyms to designate the same substance. 

In the year 1787, Lavoisier and his colleagues published the plan of the 


remarkable sjstem of nomenclattire, which, with some important extensions 
siDce rendered necessary, has np to the present time to a great extent satisfied 
the wants of the science. It is in organic chemistry that the deficiencies of 
this plan are chiefly felt, and that something like a retnm to the old method 
has been rendered inevitable. Organic chemistry is an entirely new science 
which has sprung up since the death of these eminent men, and has to deal 
with bodies of a constitution or type differing completely from that of the 
inorganic acids, bases and salts which formed the subjects of the chemical 
fltndies of that period. The rapid progress of discovery, by which new com- 
pounds, and new classes of compounds, often of the most unexpected nature, 
are continually brought to light, sufficiently proves that the time to attempt 
the construction of a permanent systematic plan of naming organic bodies 
has not yet arrived. 

The principle of the nomenclature in use may be thus explained : — ^Ele- 
mentary substances still receive arbitrary names, generally, but not always, 
referring to some marked peculiarity of the body ; an uniformity in the ter- 
mination of the word has generally been observed, as in the case of new 
metals whose names are made to end in turn. 

Compounds formed by the union of non-metnllic elements with metals, or 
with other non-metallic elements, are collected into groups having a kind of 
generic name derived from the non-metallic element, or that most opposed 
in characters to a metal, and made to terminate in ide.*^ Thus we have 
oxides, chlorides, iodides, bromides, &c., of hydrogen and of the several 
metals ; oxides of chlorine ; chlorides of iodine and sulphur ; sulphides and 
phosphides of hydrogen and the metals. 

The nomenclature of oxides has been already described (p. 109). They 
are divided into three classes, namely, alkaline or basic oxides, neutral 
oxides, and oxides possessing acid characters. In practice the term oxide 
is usually restricted to bodies belonging to the first two groups, those of the 
third being simply called acids. Generally speaking, these acids are derived 
from the non-metallic elements, which yield no basic oxides ; many of the 
metals, however, yield acids of a more or less energetic description. 

The same element in combining with oxygen in more than one proportion 
may yield more than one acid ; in this case it has been usual to apply to the 
acid containing most oxygen the termination tc, and to the one containing 
the lesser quantity the termination ous. When more members of the same 
group came to be known, recourse was had to a prefix, hypo or hyper, (or 
per,) signifying deficiency or excess. Thus, the two earliest known acids 
of sulphur were named respectively wlphurotu and ntlphuric acids ; subse- 
qaently 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 hypomlphurous and hypoeulphuric 
acids. The names of the new acids of sulphur of still more recent discovery 
are not yet permanently fixed ; Lavoisier's system, even in its extended form, 
fails to furnish names for such a lengthened series. Other examples of the 
nomenclature of acids with increasing proportions of oxygen are easily found ; 
as hypophoifphorotis, phosphorous and phosphoric acids ; hypochlorous, chlorous, 
hypoehloric, chloric, and perchloric acids ; nitrous, hyponitric, and nitric acids, &c. 
The nomenclature of salts is derived from that of the acid they contain; 
if the name of the acid terminate in ic, that of the salt is made to end in ate: 
if in ous, that of the saline compounds ends in ite. Thus, sulphuric acid forms 
sulphates of the various bases ; sulphurous acid, sulphites ; hyposulphurous 
acid, hyposulphites ; hyposulphuric acid, hyposulphates, &c. The rule here ia 
rery simple and obvious. 

1 Formerly the termination uret was likewise frequently used. 



The Want of ubifornftlty in the amplication of the systenfttic nomenclature 
is chieflj felt in the clase of oxides not possessing acid characters, and in 
that of some analogous compounds. The old rule was to apply the irord 
protoxide to the oxide containing least oxygen, to call the next in order hva- 
oxidej the third tritosude^ or teroxide ;. Ac. 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 tuboxide. An 
example is to be found in the two oxides of copper ; that which was once 
called binonde ie now protoxide, being the most basic of the two, while the 
Isomer protoxide is degraded into snboxide. 

The Latin ptefix per, or rarely kyper, is sometimes nsed to indicate the 
highest oxide of a series destitute of acidity^ as peroxide of iron, chromium, 
manganese, lead, &c. Other Latin prefixes, as seȤui. In or bin, and quad, 
applied to the name of binary compounds or salts, have reference to the eon- 
stitution of these latter expressed in chemical equivalents/ Thus, aa oxide 
Sn which the proportion of oxygen and metal are in equivalents, as 1*5 to 1, or 
8 to 2, is often called a sesquioxide ; if in the proportion of 2 to 1, a blnonde, 
ftc. The same terms are applied to salts ; thus we have neutral sulphate of 
potassa, setquieutphate of potassa, and bieulphaie of potassa ; the first con- 
taining 1 equivalent of acid to 1 of base, the second 1*5 of add to 1 of base, 
and the third 2 equivalents of acid to 1 equivalent of base. In like manner 
we have neutral oxalate, binoxalcUe, and quadroxalate of potassa, 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 termlphide instead of tritosulphide of antimony. 
These and other small irregularities are not found in practice to cause seri- 
ous confusion. 


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. yfhm any body is capable of uniting with a second in several pro- 
portions, these proportions bear a simple relation to each other. 

8. If a body. A, unite with other bodies, B, C, D, the quantities of 
B, C, D, which unite with A, represent the relations in which they unite 
among themselves, in the event of union taking place. 

4. The combining quantity of a compound is the sum of the combining 
quantities of its components. 

(1.) Constancy of Composition, — That the same chemical compound invari- 
ably contains the same elements united in unvarying proportions, in a propo- 
sition almost axiomatic; it is involved in the very idea of identity itself. 
The converse, however, is very far from being true ; the same elements com- 
bining in the same proportions do not of necessity generate the same 

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 organio 

* See a few paged fimraid. 


chemistry ; only a few well-established and undoubted examples being known 
in tho organic or mineral division of the science. 

(2.) Multiple Proportions. — Illustrations of this simple and beautifdl law 
abound on every side ; let the reader take for example the compounds of 
nitrogen and oxygen, five in number, containing the proportions of the two 
elements so described that the quantity of one of them shall remain con- 

Nitrogen. Oxygnn. 

Protoxide 14 8 

Binoxide 14 16 

Nitrous acid 14 24 

Hyponitric acid 14 32 

Nitric acid 14 40 

It will be seen at a glance, that while the nitrogen remains the same, the 
qaantities 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, ^^^ 8x.3» gi^® respectively the oxygen in the protoxide, the binoxide, 
ni^us acid, hyp<mitric acid, and lastly, nitric acid. Again, carbonic acid 
contains exactly twice as much oxygen in proportion to the other constituent 
as carbonic oxide ; the binoxide of hydrogen is twice as rich in oxygen aa 
water ; the correspok;ding sulphides exhibit the same phenomena, while the! 
metallic compounds ofier one continued series of illustrations of the law, 
although the ratio is not always so simple as that of 1 to 2. 

It often happens that one or more members of a series are yet deficient : 
the oxides of chlorine afford an example 

' Chlorine. Oxygen. 

Hypochlorous acid 35-5 8 

Chlorous acid 35-6 ...... 24 

Hypochloric acid 35-5 32 

Chloric acid 35 5 40 

Perchloric acid 35-5 66 

Here the quantities of oxygen progress in the following order: — 8, 8x3, 
8x4, 8x6,' 8x7 ; a gap is manifest between the first and second substances; 
this remains to be filled up by future researches. The existence of a simple 
relfttion among the numbers in the second column is however not the less 
evident. Even when difficulties seem to occur in applying this principle, 
they are only apparent, and vanish when closely examined. In the highly 
complex sulphur series, given at p. 132, the numbers placed in each column 
are multiples of the lowest amongst them ; and, by making the assumption, 
which is not at all extravagant, that certain of the last-named bodies are in- 
termediate combinations, we may arrange the four direct compounds in such 
\ manner that the sulphur shall remain a constant quantity. 

Sulphur. Oxygen. 

Hyposulphurous acid .\ 32 16 

Sulphurous acid ,....> 32 82 

Hyposulphuric acid 82 40 

Sulphuric acid 32 48 

Compound bodies of all kinds are also subject to tho law of multiples 
when they unite among themselves, or with elementary substances. There 
are two sulphates of potassa and soda : the second contain^ twice as much 
acid in relation to the alkaline base as the first. There are three oxalates 
of potassa, namely, the simple oxalate, t^e binoxalate, and the quadroxalattf ;, 
15 « 



tilM second has equallir twice as much acid as the first; and the third tirioe 
as much as the second. Many other cases might be cited, but the student^ 
once in possession of the principle, will easily notice them as he proceeds. 

(3.) Law of Equivatentt, — 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 suscepSble 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 tlie substances. The result is a table or list 
like the following, but of coarse much more extensive when complete. 

Oxygen 8 

Hydrogen. 1 

Nitrogen 14 

I Carbon 6 

Snlphnr 16 

Phosphorus 32 

Chlorine 85'6 

Iodine 127 

Potassium 89 

Iron , 28 

Copper , 81-7 

Lead 103-7 

Silver 108 

&c. &c. 

Now the law in question is to this effect : — If such nnmbers represent 
the proportions in which the different elements combine with the arbitrarily- 
flxed quantity of the starting snbstance, the oxygen, they also represent the 
proportions in which they unite among themaelvea, or at any riate bear some ex- 
ceedingly simple ratio to these proportions. 

Thns, hydrogen and chlorine combine invariably in the proportions 1 and 
85*6; hydrogen and sulphur, 1 to 16; chlorine and silver, 86-5 to 108; 
iodine and potassium, 127 parts of the former to 39 of the latter, &o. This 
rule is nerer departed from in any one instance. 

The term equivalent is applied to these numbers for a reason which will 
now be perfectly intelligible ; they represent quantities capable of exactly 
replacing each other in combination : 1 part of hydrogen goes as far in com- 
bining with or saturating a certain amount of oxygen as 28 parts of iron, 39 
of potassium, or 108 of silver ; for the same reasons, the numbers are said 
to represent combining quantitiee, or proportionale. 

Nothing is more common than to speak of so many equivalents of this or 
that substance being united to one or more equivalents of a second ; by this 
expression, quantities are meant just so many times greater than these rela- 
tive numbers. Thus, sulphuric acid is said to contain 1 equivalent of sul- 
phur and 8 equivalents of oxygen ; that is, a quantity of the latter repre- 
sented by three times the combining number of oxygen ; phospho!ric acid is 
made up of 1 equivalent of phosphorus and 5 of oxygen ; the red oxide of 
iron contains, as will be seen hereafter, 8 equivalents of oxygen to every 2 
^uivalents of metal, &c. It is an expression which will henceforward be 


freely and constaQtIy employed ; it is hoped, therefore, that it will be nnder- 

The nature of the law will easily show that the choice of the body destined 
to serve for a point of departure is perfectly arbitrary, and reg^nlated by con- 
siderations of convenience alone. 

A body might be chosen which refuses to unite with a considerable som- 
ber of the elements, and yet the equiTalents 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 egui" 
valmt quantity of hydrogen or calcium, already known. We may rest as- 
sured that if an oxide of fluorine be ever discovered, its elements will be 
associated in the ratio of 8 to 19, or in numbers which are either multiples 
or submultiples of these. 

The number assigned to the starting-substance is also equally arbitrary ; 
if, in the table given, oxygen instead of 8 were made 10, or 100, or even a 
fractional number, it is quite obviouft that although the other numbers would 
all be different, the ratiOf 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 sb 8, and a second in which it is made ss 100 ; the former 
b generally used in this country and England, and the latter still to a 
certain extent on the Continent. The only reason for giving, as in the pre- 
sent volume, a preference to the first is, that the numbers are smaller and 
more easily remembered. 

The number 8 has been chosen in this table to represent oxygen, from an 
opinion long held by the late Dr. Front, and recently to appearance substan- 
tiated in some remarkable instances by very elaborate investigation, that the 
equivalents of all bodies are multiplies of that of hydrogen ; and, conse- 
queatly, 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 
^^iS$^a^3 are often observed in the determination of the equivalents of the 
eam^^^ies by different experimenters. 




Oxy. — 8. 

Aluminium.... 18*7 

Antimony 129 

Arsenic 76 

Barium 68-5 

Beryllium 6-9 

Bismuth , 213 

Boron 10-9 

Bromine 80 

Cadmium 66 

Calcium 20 

Carbon 6 

Cerium 47 (?) 

Chlorine 36-5 

Chromium 26*7 

Cobalt 29-5 

Copper 31-7 

Didymium 50 (?) 


Fluorine 19 

Gold 197 

Hydrogen 1 

Iodine 127 

Iridium 99 

Iron 28 

Lanthanum ... 47 (?) 

Lead.. 108-7 

Lithium 6-5 

Magnesium ... 12 
Manganese.... 27*6 

Mercury 100 

Molybdenum.. 46 

Oxy — 100. 


Oxy.— 100. 



... 29-6 • 






... 14 






... 99-6 




... 8 



Palladium .. 

... 63-8 






... 82 




... 98-7 



Potassium .. 

... 89 



' Rhodium ... 

... 62-2 



Ruthenium . 

... 62-2 



Selenium ... 

... 39-5 




... 21-8 




. 108 




... 23 



... 43-8 




... 16 



Tantalum ... 





... 64-2 






... 59-6 




... 68 



Titanium ... 

... 26 




... 92 




... 60 



Vanadium .. 

... 68-6 






... 82-6 




... 33-6 


(4.) Combining Numbers of Compounds. — The law states that the equivalent 
or combining number of a compound is always the sum of the equivalents 
of its components. This is also a great -fundamental truth, which it is neces- 
sary to place, in a clear and conspicuous light. It is a separate and inde- 
pendent law, established by direct experimental evidence, and not deducible 
from either of the preceding. 

The method of investigation by which the equivalent of a simple body is 
determined, has been already explained ; that employed in the case of a com- 
pound is in nowise different. The example of the acids and alkalis may be 
taken as the most explicit, and at the same time most important. An aciiL 
itnd a base, combined in certain definite proportions, neutralize, or mask each. 
other's properties completely, and the result is a salt ; these proportions are 
called the equivalents of the bodies, and they are very variable. Some acids 
have very high capacities of saturation, of others a much larger quantity 
must be employed to neutralize the same amount of base; the bases them- 
selves present also similar phenomena. Thus, to saturate 47 parts of potassa, 
or 116 parts of oxide of silver, there are required 


4D purts flttlpknrio Mid, 
64 <* nitric acid, ^ 

76 -6 ♦* ohlorio acid, 
167 ** iodic acid, 
61 *' acetic acid. 

Numbers very different, but representing quantities which replace each 
other in combination. Now» if a quantity of some base, such as potassa, be 
taken, which is represented bj the sum of the equiyalents of potassium and 
oxygen, then the quantity of any acid requisite for its neutralisation, as de- 
termined b;y direct experiment, will always be found equal to the Bum of th« 
equivalents of the different components of the acid itself. 

89«B>eqiiind«iit of potassiam. 
8a= « oxygen. 

47 3s=M»amed equivalent of potassa. 

47 parts of potassa are found to be exactly neutralised by 40 parts of real 
salpkorio JMsid, or by 64 parts of real nitric acid. These qnanttttes are 
evidently made up by addi«g together the equivalents ef their eeastitwenfti :— 

1 eqtdvalent of sulphur = 16 1 equivalent of nitrogen iss 14 

8 " oxygen = 24 5 ** oxygen = 40 

1 « sulphuric acid = 40 1 « nitric acid = 64 

And the aawe is true if any acid be taken, and the <|iiantitiee ef different 
htses required for its neuti»lisation detennined; the eeimbini&f Aumber 
of the compound will always be found to be the sum of the eombining nimip 
bers ef its components, however complex the attbatanoe may be. iSvea 
among such bodiea as the veigeto-aUt^alis of organic chemistij, the sane ui&* 
venal role holds good. When salts conhine, which is a thing of veiy com* 
mon occurrence, as will hereafter be men, it is always in t£e ratio ef the 
equivalent numbers. Apart from hypothetical consideration, no d priori 
leason can be shown why such should be. the case ; it is, as before remarked, 
an independent law, estahUshed like the rest, by experiment 

A curious ob s erv a t i on was very early made to this effect :-^lf two neutra . 
salts -^ich decompose each other when mixed, be broup^t in contact, the 
new compounds resulting from their mutual decomposition will also be neutraL 
For example, when solution of nitrate baryta and sulphate of potassa are 
mingled, they both suffer decomposition, sulphate of baryta ajftd nitrate of 
potassa being simultaneously formed, both of which are perfectiy netftral. 
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 64 parts of nitric acid set free by tiie decompositioB 
of the barytic salt, 47 parts of potassa are abandoned by the 40 parts of 
Bulj^uric acid vrith which they were previously in comblaalien, hew trans- 
ferred to the baryta. But 64 and 47 «re tiie r>^>resentativee of oombiniBg 
quantities ; hence the new compound must be neutral 


Many years ago, M. Gay-Lussac made the very important and interesting 
discovery that when gases combine chemically, union invariably takes place 
either between equal volumes, or between volumes which bear a simple rela- 
tion to each other. This is not only true of elementary gases, but of oom-j 


pound bodies of this description, as it is inyariably observed that the con- 
traction of bulk which so frequently follows combination itself also bears a 
simple relation to the volumes of the combining gases. The consequence 
of this is, that compound gases and the vapours of complex volatile liquids 
(which are truly gases to all intents and purposes) follow the same law as 
elementary bodies, when they unite with these latter or combine among them- 

The ultimate reason of the law in question is to be found in the very 
remarkable relation established .by the hand of Nature between the specifio 
gravity of a body in the gaseous state and its chemical equivalent ; — a rela- 
tion of such a kind that quantities by weight of the various gases expressed 
by their equivalents, or in other words, quantities by weight which combine; 
occupy under similar circumstances of pressure and temperature either equal 
volumes, or volumes bearing. a similar proportion, to each other. In the 
example cited below, equivalent weights of hydrogen,, chlorine, and iodine- 
vapour, occupy equal volumes, while the equivalent of oxygen occupies 
exactly half that measure. 

. CabiQ indkeK 
- 8-0 grains of oxygen occupy at 60* (160'5C)t«id 30 inches barom. 23-3 - 

I'O grain of hydrogen X. • ^6*7 

85*5 grains of chlorine.., ., 46-2 

127*0 grains of iodine-vapour (would measure) 46*7 

If both the specifio gravity and the chemical equivalent of a gas be knoi^, 
its equivalent or combining volume can be easily determined, since it will be 
represented by the number of times the weight of an unit of volume (the 
specific gravity) is contained in the weight of one chemical equivalent of the 
substance. In other words, the equivalent volume is found by dividing the 
chemical equivalent by the specific gravity. The following table exhibits 
the relations of specific gravity, equivalent weight, and equivalent volume 
of the principal elementary substances. 

Sp. grayitj. Equiv. weight Equiv. Tolmne. 

Hydrogen 00693 10 14'4aorl 

Nitrogen , 0-972 140 14-87 " 1 

Chlorine 2-470 85-6 14-33 " 1 

Bromine-vopour 5-395 800 14-82 « 1 

Iodine-vapour > 8-716 1270 14-57 " 1 

Carbon- vapour* 0-418 6-0 .-.. 14-34 " 1 

Mercury-vapour 7000 1000 14-29 " 1 

Oxygen 1-106 80 7-23 " J 

Phosphorus- vapour 4-350 320^ 735"} 

Arsenic-vapour 10-420 750 719 ♦* i 

Sulphur-vapour 6-654 16 2-40 " ^ 

. Thus it appears that hydrogen, nitrogen, chlorine, bromine, iodine, carbon, 
and mercury, in the gaseous state, have the same equivalent volume ; oxygen, 
phosphorus, and arsenic, one-half of this; and sulphur one-sixth. The 
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 : — 

' See fjEurther on. 


8p. gnvitj. Kqnlr. welgltt Kqnlr. Tolniiie.* 

Water-vapour 0-626 .... 9-0 .... 14-40 op 1 

Protoxide of nitrogen 1-625 .... 220 .... 14-43 «« 1 

Sulphuretted hydrogen 1-171 .... 17-0 .... 14-61 "1 

Sulphurous acid 2-210 .... 820 .... 14-62 " 1 

Carbonic oxide 0-973 .... 14-0 ... 14-39 ** 1 

Carbonic acid 1-624 .... 22-0 .... 14-43 " 1 

light carbonetted hydrogen 0-659 .'... 80 .... 14-31 <* 1 

defiant gas 0-981 .... 14-0 .... 14-27 " 1 

Binoxide of nitrogen 1-089 .... 800 .... 28-87 " 2 

%drochlorio acid 1^1-269 .... 36-6 .... 28-70 «* 2 

Jhosphoretted hydrogen 1-240 .... 36-0 .... 28-22 " 2 

Ammonia 0-689 .... 17-0 .... 28-86 " 2 

Bther-vapoup '. 2-586 .... 87-0 .... 14-31 " 1 

Acetone-yapour 2022 .... 290 .... 14-34 " 1 

BcMol-vapour 2-738 .... 78-0 .... 28-49 «* 2 

Alcohol-yapour , 1-613 .... 460 .... 28-62 " 2 

Hi the preceding tables the ordinary standard of specific gravity for gases, 
atmospheric air, has been taken. It is, however, a matter of perfect indif- 
ference what substance be chosen for this purpose ; the numbers represent- 
ing the combining volumes will change with the divisor, but the proportions 
they bear to each other will remain unaltered. And the same remark 
applies to the equivalent weights ; either of the scales in use may be taken, 
provided that it be adhered to throughout. 

The law of volumes often serves in practice to check and corroborate the 
resolta of experimental investigation, and is often of great service in this 

There is an expression sometimes made use of in chemical writings which 
it is necessary to explain, namely, the meaning of the words hypothetical dm- 
iUif of vapoury applied to a substance which has never been volatilized, such 
as carbon, whose real specific gravity in that state must of course be un- 
known; it is easy to understand the origin of this term. Carbonic acid con- 
tains a volume of oxygen equal to its own; consequently, if the specific 
gravity of the latter be subtracted from that of the former gas, the residue 
will express the proportion borne -by the weight of the carbon, certainly 
then in a vaporous state, to that of the two gases. 

The specific gravity of carbonic acid is 1-6240 

That of oxygen is 1'1067 


On the supposition that carbonic acid contains equal volumes of oxygen 
and this vapour of carbon, condensed to one-half, the latter will have the 
specific gravity represented by 0-4183 and the combining volume given in the 
table. But Uhis is merely a supposition, a guess ; no proof can be given 
that carbonic acid gas is so constituted. All that can be safely said is con- 
tained in the prediction, that, should the specific gravity of the vapour of 
carbon ever be determined, it will be found to coincide with this number, or 
to bear some simple and obvious relation to it. 

For many years past, attempts have been made to extend to solids and 
liquids the results of Gay-Lussac's discovery of the law of gaseous combi- 
nation by volume, the combining or equivalent volumes of the bodies in 
question being determined by the method pursued in the case of gases, 
namely, by dividing the chemical equivalent by the specific gravity. The 



BWiib^Tg obiauMd ia ikU maaiMir rej^senting the combining Tolmnes of the 
Tarions 8olid and liquid elementary substances, present far more cases of 
discrepancy than of agreement. The latter are, howeyer, sufficiently nvk- 
merouB to excite great interest in the inyestigation. 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 i?ith many 
great difficulties, chiefly arising from the unequal expansion of solids and 
Squids 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 gOTemed and related ; and it cannot be too often re- 
peated, that tho discoYery of these beautiful laws has been the result of 
pure experimental inquiry. They have been established on this firm and 
stable foundation by the joint labours of very many illustrious men ; they 
are the expression of fact, and are totally independent of all hypotheses or 
theories whatsoever. 


For eoBYonienee in eommunioating ideaa respecting the comporitioii, aoid 
supposed eonstitation, of chemical compounds, and explaining in a clear and 
simple manner, the results of changes they may happen to undergo, re- 
oourae 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 be«n 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 coi^oined with a seoond small one, the 
most characteristic in the word, as the names of many bodies be^ alike. 
The single letter is usually confined to the earliest discovered, or most im- 
portant element. Farther, by a most ingenious idea, the symbol is made to 
represent not the substance in the abstract, but one eguivalerU of tkat nil* 

Table of Symbols of the Elementary Bodiee. 

Aluminium Al 

Antimony (Stibium).. ., Sb 

Arsetidc As 

Barium Ba 

Beryllium Be 

Bismuth Bi 

Boron « Bo 

Bromine Br 

Cadmium Cd 

Galinum Ca 

CarbOA C 

Cerium Ce 

Chlorine CI 

Chromium Cr 

Cobalt Co 

Copper (Cuprum) Cu 

Pidymium Dy 

Erbium £r 

Fluorine F 

Gold (Aurum) An 

Hydrogen H 

Iodine I 

Iridium , Ir 

Iron (Ferrum) Fe 

Lantanum Ln 

Lead (Plumbum) Pb 

Lithium L 

Magnesium Mg 

Manganese Mn 

Mercury (Hydrargyrum).,.. Kg 

Molybdenum Mo 

Nickel Ni 

Niobium , Nb 

Nitrogen N 

NoriuDl No 

Osmium « Os 

Oxygen Q 

Palladium Pd 



piiim. Pe 

Phosphoras P 

Platinum ^ Pt 

PotBseium (Kalium) K 

Rhodinm R 

Eathenium Ra 

Selenium Se 

Silicium Si 

Silver (Argentum^ Ag 

Sodium (Natrium) Na 

Strontium Sr 

Sulphur S 

Tantalum Tft 

Tellurinm ; Te 

Terbium Tb 

Thorium Th 

Tin(Stannum) Sn 

Titanium Ti 

Tungstea (Wolframium) W 

-Vanadium V 

Uranium IT 

Yttrium Y 

Zinc Zn 

Zirconium Zr 

.Combination between bodies in the ratio of the equivalents is expressed 
by mere juxtaposition of the symbols, or sometimes by interposing the sign 
of addition. For example : — 

Water HO, or H-f-O 

Hydrochloric acid HCl, or tf + Cl 
Protoxide of iron FeO, or Fe-f-0 

When more than one equivalent is intended, a suitable number is addeij, 
sometimes being placed before the symbol, like a co-efficient in algebra, 
sometimes appended after the manner of an exponent, but more commonly 
placed a little below on the right. 

Binoxide of hydrogen H -f- 20, or HO", or HOj 

Sulphuric acid S -j- 30, or SO*, or SO, 

Hyposulphuric acid.. 2S4-60, or SH)» or SjOj 

Combination between bodies themselves compound is indicated by the sign 
of addition, or by a comma. When both are used in the same formula, the 
latter may be very conveniently applied, as Professor .Graham has suggested, 
to indicate the closest and most intimate union. A number standing before 
symbols, inclosed within a bracket, signifies that the whole of the latter are 
to be multiplied by that number. Occasionally the bracket is omitted, when 
the number affects all the symbols between itself and the next sign. A few 
examples will serve to illustrate these several points. 

Sulphate of soda NaO-f SO, , or NaO , SO, 
Nitrate of potassa KO-f NOg , or KO , NOj 

The base being always placed first. 

Double sulphate of copper and potassa CuO , SO, + EO , SO, 

The same in a crystalUzed state t CuO , SOj-f KO , SO,<f 6H0 

Common crystallized alum, or double sulphate of alumina and potassa, is 
thus written : — 

A1,0, , 3S0,-f KO , 80,4- 24HO 

In expressing organic oompounds, where three or more elements exist, the 
9ame plan is used. 

Sugar , CjgH./On 

Alcohol C^HgOj 

Acetic acid HO , C.H3O, 

Morphine C34H,,N 0, 

Acetate of morphine C,4H,gN Og , C4H,0, 

Acetate of soda NaO , C.H.O. 



"By sucli a RyBtem, the eye is enabled to embrace the whole at a glanbe, 
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- 
eyer, are btr no means generally adopted. Thus, two equivalents of a sub- 
stance are indicated by the symbol with a short line drawn through or below 
it ; an equivalent of oxygen is .signified by a dot, and one of sulphur by a 
comma. These alterations are sometimes convenient for abbreviating a long 
formula^ but easily liable to mistakes. Thus, 

Sesquioxide of iron FeO', or FeO*, or Fe, instead of Fe, 0, 

Bisulphide of carbon C, instead of OSa 

Crystallized alum as before A1S,4.KS4.24H. 


That no attempt should have been made to explain the reason of the very 
remarkable manner in which combination occurs in the production of che- 
mical compounds, and to point out the nature of the relations between the 
different modifications of matter which fix and determine these peculiar and 
definite changes, would have been unlikely, and in contradiction with the 
speculative tendency of the human mind. Such an attempt, and a very inge- 
nious and successful one it is, has been made, namely, the atomic hypothesis 
of Dr. 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 farther diminished in magnitude ; 
they become, in short, atoms.* Now, however the imagination may succeed 
in figuring to itself the condition of matter on cither view, it is hardly neces- 
sary to mention that we have absolutely no means at our disposal for deciding 
such a question, which remains at the present day in the same state as when 
it first engaged the attention of the Greek philosophers, or perhaps that of 
the sages of Egypt and Hin(jlostan long before them. ^ 

Dr. Dalton's hypothesis sets out by assuming the existence of such atoms 
or indivisible particles, and states, that compounds are formed by the union 
of atoms of different bodies, one to one, one to two, &c. The compound atom 
joins itself in the same manner to a compound atom of another kind, and a 
combination of the second order results. Let it be granted, farther, that the 
relative weights of the atoms are in the proportions of the equivalent numbers, 
and the hypothesis becomes capable of rendering consistent and satisfactory 
reasons for all the consequences of those beautiful laws of combiDation lately 

Chemical compounds mus^ always be definite; they must always contain 
the same number of atoms, of the same kind, arranged in a similar manner. 
The same kind and number of atoms need not, however, of necessity produce 
the same substance, for they may be differently arranged ; and much depends 
upon this circumstance. 

Again, the law of multiple proportions is perfectly well explained ; an atom 

* *^oj» that which cannot Ije cat 


of nitrogetl iinif es with one of oxygen to form langhing g%0 ; nHfh two, to 
form binoxide of nitrogen'; with three, to produce nitrons acid ; with four, 
hjponitric acid ; and with five, nitric acid, — perhaps something after the 
manner represented in fig. 124, in which the circle with a cross represents 
the atom of nitrogen, and the plain circle that of oxygen. 

Fig. 124. 
Protoxide. Binoxide. 


• Two atoms of one substance may unite themselves with three or even with 
seven of another, as in the case of one of the acids of manganese ; but such 
combinations are rare. 

The mode in which bodies replace, or may be substituted for, each other, 
is also perfectly intelligible, as a little consideration will show. 

Finally, the law which fixes the equivalent of a compound at the sum of 
the equivalents of the components, receives an equally satisfactory expla- 

The difficulties in the general application of the atomic hypothesis are 
chiefly felt in attempting to establish some wide and universal relation be- 
tween combining number and combining volume, among gases and vapours, 
and in the case of the highly complex products of organic chemistry. These 
obstacles have grown up in comparatively recent times. On the other hand, 
the remarkable observations of the specific capacities for heat of equivalent 
quantities of the solid elementary substances, might be urged in favour of 
this or some similar molecular hypothesis. But even here serious discrep- 
ancies exist ; we may not take liberties with equivalent numbers determined 
by exact chemical research, and, in addition, a simple relation is generally 
found to be wanting between the capacity for heat of the compound and that 
of its elements. 

The theory in question has rendered great service to chemical science ; it 
has excited a vast amount of inquiry and investigation, which have contribu- 
ted very 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 
bat 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 
tery intimate and permanent nature, takes place between two or more 

* The expresrion atomic weight is very often substituted for that of equivalent weight, and 
bb in fad, in almost every case to be understood as such: it is, perhaps, better avoided. 


bodies, in such a way as to give rise to a new substance, haTing, for the most 
part,' properties completely in discordance with those of its components. 

The attraction thus exerted between different kinds of matter is to be dis- 
tinguished from other modifications of attractive force which are exerted 
incUscriminately between all descriptions of substances, sometimes at enor- 
mous distances, and sometimes at intervals quite inappreciable. Examples 
of the latter are to be seen in cases of what is called cohesion, when the par- 
ticles of solid bodies are immovably bound together into a mass. Then 
there are other effects of, if possible, a still more obscure kind ; such ns the 
various actions of surface, the adhesion of certain liquids to glass, the re- 
pulsion of others, the ascent of water in narrow tubes, and a multitude of 
curious phenomena which are described in works on Natural Philosophy, 
under the head of molecular actions. From all these, true chemical attraction 
may be at once distinguished by the deep and complete change of characters 
which follows its exertion ; we might define affinity to be a force by which 
new substances are generated. 

It seems to be a general law that bodies most opposed to each other in 
chemical properties evince the greatest tendency to enter into combination, 
and, conversely, bodies between which strong analogies and resemblances 
can be traced, manifest a much smaller amount of mutual attraction. For 
example, hydrogen and the metals tend very strongly indeed to combine -with 
oxygen, chlorine, and iodine ; the attraction between the different members 
of these two groups is incomparably more feeble. Sulphur and phosphorus 
stand, as it were, mid-way ; they combine with substances of one and the 
other class, their properties separating them sufficiently from both. Acids 
are drawn towards alkalis, and alkalis towards acids, while union among 
themselves rarely, if ever, takes place. 

Nevertheless, chemical combination graduates so imperceptibly into mere 
mechanical mixture, that it is^ often impossible to mark the limit. Solution 
is the result of a weak kind of affinity existing between the substance dis- 
solved and the solvent ; an affinity so feeble as completely to lose one of its 
most prominent features when in- a more exalted condition, namely, power of 
causing elevation of temperature ; for in the act of mere solution the tem- 
perature falls, the heat of combination being lost and overpowered by the 
effects of change of state. 

The force of chemical attraction thus varies greatly with the nature of 
the substances between which it is exerted ; it is influenced, moreover, to a 
very large extent by external or adventitious circumstances. An idea for- 
merly prevailed that the relations of affinity were fixed and constant between 
the same substances, and great pains were taken in the preparation of tables 
exhibiting what was called the precedence of affinities. The order pointed 
out in these lists is now acknowledged to represent the order of precedence 
for the circumstances under which the experiments were made, but nothing 
more; so soon as these circumstances become changed, the order is disturbed. 
The ultimate effect, indeed, is not the result of the exercise of one single 
force, but rather the joint effect of a number, so complicated and so variable 
in intensity, that it is but seldom possible to predict the consequences of any 
yet untried experiment. The following may serve as examples of the tables 
alluded to ; the first illustrates the relative affinities of a number of bases 
for sulphuric acid, each decomposing the combination of the acid with the 
base below it ; thus, magnesia decomposes sulphate of ammonia ; lime dis- 
places the acid from sulphate of magnesia, &c. The salts are supposed to 
be dissolved in water. The second table exhibits the order of affinity for 
oxygen of several metals, mercury reducing a solution of silver, copper ono 
of mercury, &c. 



Silllflivrie icM. 
Bftrytft, Lime, 

Strontia, Magnesia, 

Potassa, Ammonia. 


Zinc, Mewnry, 

Lead, Silter. 


It will be proper to examine shortly some of these extraneous oaiises to 
vhich allasion has been made, which modify to so great an extent the direct 
and original effects of the specific attractive force. 

Alteration of temperature may be reckoned among these. When metallie 
merciuy is heated nearly to its boiling point, and in that state exposed for a 
lengthened period to the air, it absorbs oxygen, and becomes conyerted 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 Taporous 
state ; but, precisely the same fact is observed with another metal, palladium, 
which is not volatile at all, but which oxidates superficially at a red>heat^ 
and again becomes reduced when the temperature rises to whiteness. 

Insolubility and the power of vaporisation are perhaps, beyond all other 
disturbing causes, the most potent ; they interfere in almost every reaction 
which takes place, and very frequently turn the scale when the opposed forces 
do not greatly differ in energy. It is easy to give examples. When a solu- 
tion of lime in hydrochloric acid is mixed with a solution of carbonate of 
ammonia, double interchange ensues, carbonate of lime and hydrochlorate 
of ammonia being generated. Here the action can be shown to be in a great 
measure determined by the insolubility of the carbonate of lime. Again, 
dry carbonate of lime, powdered and mixed with hydrochlorate of ammonia, 
and the whole heated in a retort, gives a sublimate of carbonate of ammonia, . 
Trhile chloride of calcium remains behind. In this instance, it is no doubt 
the great volatility of the ammoniacal salt which chiefly determines the kind 
of decomposition. 

When iron-filings are heated to redness in a porcelain tube, and vapour of 
water passed over them, the water undergoes decomposition with the utmost 
facility, hydrogen is rapidly disengaged, and the iron converted into oxide. 
On the other hand, oxide of iron heated in a tube through which a stream 
of dry hydrogen is passed, suffers almost instantaneous reduction to tht 
metallic state, while the vapour of water, carried forward by the current of 
gas, escapes as a jet of steam from the extremity of the tube. In these 
experiments, the affiuities between the iron and oxygen, and the hydrogen 
and oxygen, are so nearly balanced, that the ditference of atmosphere is suf- 
ficient to settle the point. An atmosphere of steam offers little resistance 
to the escape of hydrogen ; one of hydrogen bears the same relation to steam ; 
and this apparently tritliug difference of circumstances is quite enough for 
the purpose. 

The decomposition of vapour of water by white-hot platinum, pointed out 
by Mr. Qrove, will probably be referred in great part to this influence of 
atmosphere, the steam offering great facilities for the assumption of the 
elastic condition by the oxygen and hydrogen. The decomposition ceases 
as soon as these gases amount to about l-3000th of the bulk of the mixture, 
and can only be renewed by their withdrawal. The attraction of uxygen 
for hydrogen is probably much weakened by the very high temperature. The 
recombination of the gases by the heated metal is rendered impossible by 
their state of dilution. 

What is called the nascent state is one very favourable to chemical com- 
Dination. Thus carbon and nitrogen refuse to combine with gaseous hy- 


drogen ; yet when these substances are simultaneously liberated from soma 
previous combination, they unite with great ease, as when organic matters 
are destroyed by heat, or by spontaneous putrefactive change. There is a 
strange and extraordinary, and at the same time very extensive class of 
actions, grouped together under the general title of cases of disposing affin- 
ity. The preparation of hydrogen from zinc and sulphuric acid is one. of 
the most familiar. A piece of polished zinc or iron, put into pure water, 
manifests no power of decomposing thg. latter to the smallest extent ; it 
remains perfectly bright for any length of time. On the addition, however, 
of a little sulphuric acid, hydrogen is at once freely disengaged, and the 
metal becomes oxidized and dissolved. Now, the only intelligible function 
of the acid is to dissolve off the oxide as fast as it is produced ; but why is 
the oxide produced when acid is present, and not otherwise ? The question 
is very difficult to answer. 

Great numbers of examples of this curious indirect action might be 
adduced. Metallic silver does not oxidize at any temperature ; nay more, 
its oxide is easily decomposed by simple heat ; yet if the finely-divided metal 
be mixed with siliceous matter and alkali, and ignited, the whole fuses to a 
yellow transparent glass or silicate of silver. Platinum is attacked by fused 
hydrate of potassa; hydrogen is probably disengaged while the metal is 
oxidized ; this is an effect which never happens to silver under the same cir- 
cumstances, although silver is a much more oxidable substance than plati- 
num. The fact is, that potassa forms with the oxide of the last-named 
metal a kind of saline combination, in which the oxide of platinum acts as 
an acid ; and hence its formation under the dupoting influence of the power- 
ful base. 

In the remarkable decomposition suffered by various organic bodies when 
heated in contact with caustic alkali or lime, we have other examples of the 
same fact. Products are generated which are never formed in the absence 
of the base ; the reaction is invariably less complicated, and its results fewer 
in number and more definite, than in the event of simple destruction by a 
graduated heat. The preparation of light carbonetted hydrogen by the new 
artificial process, already described, is an excellent example. 

There is yet a still more obscure claiss of phenomena, in which etfects are 
brought about by the mere presence of a substance, which itself undergoes 
no change whatever ; the experiment mentioned in the article on oxygen, 
in which that gas is obtained, with the greatest facility, by heating a mix- 
ture of chlorate of potassa and binoxide of manganese, is an excellent case 
in point. The salt is decomposed at a very far lower temperature than 
would otherwise be required. The oxide of manganese, however, is not in 
the slightest degree altered ; it is found, after the experiment, in the same 
state as before. The name katalyais is sometimes given to these peculiar 
actions of contact ; the expression is not significant, and may be for that 
reason the more admissible, as it suggests no explanation. 

It is proper to remark, that the contact-decompositions alluded to are 
sometimes mixed up with other effects, which are, in reality, much more in- 
telligible, as the action of finely-divided platinum upon certain gaseous mix- 
tures, in which the solid really seems to have the power of condensing the 
gas upon its greatly extended surface, and thereby inducing combination by 
bringing the particles within the sphere of their mutual attractions. 



When a Toltaic current of considerable power is made to traverse Tarions 
compound liquids, a separation of the elements of these liquids ensues ; pro- 
vided that the liquid be capable of conducting a current of a certain degree 
of energy, its decomposition almost always follows. 

The elements are disengaged solely at the limiting surfaces of the liquid; 
where, according to the common mode of speech, the current enters and 
leaves the latter, all the intermediate portions appearing perfectly quiescent. 
Id addition, the elements are not separated indifferently and at random at 
these two surfaces, but, on the contrary, make their appearance with per- 
fect uniformity and constancy at one or the other, according to their che- 
mical character, namely, oxygen, chlorine, iodine, acids, &c., at the surface 
connected with the copper or positive end of the battery ; hydrogen, the 
metals, &c., at the surface in connection with the zinc or negative extremity 
of the arrangement 

The termination of the battery itself, usually, but by no means necessa- 
rily, of metal, are designated poles or electrodejij^ 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 etectrolym^^ and the liquids, which, 
when thus treated, yield up their elements, are denominated electrolytes. 

When a pair of platinum plates are plunged into a glass of water to which 
a few drops of oil of vitriol have been added, and the plates connected by 
wires with the extremities of an active battery, oxygen is disengaged at the 
positive electrode, and hydrogen at the negative, in the proportion of one 
measure of the former to two of the latter nearly. This experiment has 
before been described.* 

A solution of hydrochloric acid mixed with a little Saxon blue (indigo), 
and treated in the same manner, yields hydrogen on the negative side, and 
chlorine on the positive, the indigo there becoming bleached. 

Iodide of potassium dissolved in water is decomposed in a similar man- 
ner, and with still greater ease ; the free iodine at the positive side can be 
recognized by its brown colour, or by the addition of a little gelatinous 

Every liquid is not an electrolyte ; many refuse to conduct, and no decom- 
position can then occur ; alcohol, ether, numerous essential oils, and othei 
products of organic chemistry, besides a few saline inorganic compounds, act 
in this manner, and completely arrest the current of a very powerful battery. 
It is a very curious fact, and well deserves attention, that very nearly, if not 
all the substances acknowledged to be susceptible of electrolytic decomposi- 
tion, belong to one class ; they are all binary compound s, containing single 

* From ^\tKTpovy and hcb^, a way. 

• From i^\tKrpov, and A«5w, I loose. 
» Page 116. 


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; 
solution of iodide of potassium, melted chloride of lead, solution of hydro- 
chloric acid, water mixed with a little oil of vitriol, and pure water, demand 
in this respect very different degrees of electrical force, the resistance to 
decomposition increasing from the first-mentioned substance to the last. 

One of the most important and indispensable conditions of electrolysie is 
fluidity ; bodies which when reduced to the liquid condition freely conduct 
and as freely suffer decomposition, become absolute insulators to the elec- 
tricity of the battery when they become solid. Chloride of lead offers a good 
illustration of this fact ; when fused in a little porcelain crucible it gives up 
its elements with the utmost ease, and a galvanometer, interposed somewhere 
in the circuit, is strongly affected. But when the source of heat is withdrawn, 
and the salt suffered to solidify, all signs of decomposition cease, and at the 
same moment the magnetic needle reassumes its natural position. In the 
same manner the thinnest film of ice completely arrests the current of a pow- 
erful voltaic apparatus ; the instant the ice is liquefied at any one point, so 
that water-communication may be restored between the electrodes, the cur- 
rent again passes, and decomposition occurs. Fusion by heat, and solution 
in aqueous liquids, answer the purpose equally well. A fluid substance may 
conduct a strong current of electricity without being decomposed ; there are 
a few examples already known* ; the electrolysis of a solid is, from its physi- 
cal properties, of course out of the question. 

Liquids often exhibit the property of conduction for currents strong enough 
to be indicated by the galvanometer, but yet incapable of causing decompo- 
sition in the manner described. These currents may be conveyed through 
extensive masses of liquids ; the latter seem, under these circumstances, to 
conduct after the manner of metals, without perceptible molecular change. 

The metallic terminations of the battery, the poles or electrodes, have, in 
themselves, nothing in the shape of attractive or repulsive power for the 
elements so often separated at their surfaces. Finely-divided metal suspended 
in water, or chlorine held in solution in that liquid, shows not the least 
symptom of a tendency to accumulate around them ; a single element is alto- 
gether unaffected, directly at least ; severance from that previous combination 
is required, in order that this appearance should be exhibit-ed. 

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 decomposif ion is rapidly proceeding, the intervening water be 
examined by a beam of light, or by other means, not the slightest disturbance 
or movement of any kind will be perceived, nothing like currents in the liquid 
or bodily transfer of gas from one part to another can be detected, and yet 
two portions of water, separated perhaps by aii interval of four or five inches, 
may be respectively evolving pure oxygen and pure hydrogen. 

There is, it would seem, but one mode of explaining this and all similar 
cases of regular electrolytic decomposition ; this is by assuming that all the 
particles of water between the electrodes, and by which the current is con- 
veyed, simultaneously suffer decomposition, the hydrogen travelling in one 
direction and the oxygen in the other. The neighbouring elements, thus 
'brought into close proximity, unite and reproduce water, again destined to 
be decomposed by a^ repetition of the same change. In this manner each 
particle of hydrogen may be made to travel in one direction, by becoming 
successively united to each particle of oxygen between itself and the negative 
electrode ; when it reaches the latter, finding no disengaged particle of oxygen 



for ite reception, it is rejected as it were from the series, and thrown oiF in 
a separate state. The same thing happens to each particle of oxygen, which 
at the same time passes continually in the opposite direction, by combining 
successively with each particle of hydrogen that moment separated, with 
which it meets, until at length it arrives at the positive plate or wire, and is 
disengaged. A succession of particles of hydrogen are thus continually 
thrown off from the decomposing mass at one extremity, and a corresponding 
succession of particles of oxygen at the other. The power of the current is 
exerted with equal energy in every part of the liquid conductor, although its 
effeeia only become manifest at the Tery extremities. The action is one of a 

Fig. 125. 


Water in usual state. ^ 

purely molecular or internal nature, and the metal terminations of the bat- 
tery merely serve the purpose of completing the connection between the 
latter and the liquid to be decomposed. The figures 125 and 126 are intended 
to assist the imagination of the reader, who must at the same time avoid re- 
garding them in any other light than that of a somewhat figurative mode of 
representingthe curious phenomena described. The circles are intended to 
indicate the elements, and are distinguished by their respective symbols. 

Kg. 126. 

Water undergoing electrolysis. 

A distinction is to be carefully drawn between true and regular electro- 
lysis, and what is called secondary decomposition, brought about by the 
reaction of the bodies so eliminated upon the surrounding fluid, or upon the 
substance of the electrodes ; hence the advantage of platinum for the latter 
purpose when electrolytic actions are to be studied in their greatest sim- 
plicity, that metal being scarcely attacked by any ordinary agents. When, 
for example, a solution of nitrate or acetate of lead is decomposed by the 
current between platinum plates, metallic lead is deposited at the negative 
side,. and a brown powder, binoxide of lead, at the positive: the latter sub- 
stance is the result of a secondary action; it proceeds, in fact, from the 
nascent oxygen at the moment of its liberation reacting upon the protoxide 
of lead present in the salt, and converting it into binoxide, which is insoluble 
in the dilute acid. There is every reason to believe that when sulphuric 
and nitric acids seem to be decomposed by the current, the efl'ect is really 
due to the water they contain becoming decomposed, and reacting by its 
hydrogen upon the acid ; for these bodies do not belong to the class of elec- 
trolytes, as already specified, and would probably refuse to conduct could 
they be examined in an anhydrous condition. 

If a number of different electrolytes, such as acidulated water, sulphate 
of copper, iodide of potassium, fused chloride of lead, &c.y be arranged in a 

190 £LB01*BO-CH£MICAL 0£CO]f 9001^1^11; 

series, *bA the ssme current be made to trftyefse th6 whole, all will suffer 
decomposition at tbe same time, but by. no means to the same amount. If 
arraogements be made by which the quantities of the eliminated elements 
can be accurately ascertained, it will be found, when the decomposition has 
proceeded to some extent, that these latter will have been disengaged exactly 
in the ratio of the chemical equivalents. The same current which decomposes 
9 parts of water will separate into their elements 166 parts of iodide of po- 
tassium, 189-2 parts of chloride of lead, &c. Hence the very important 
conclusion : The action of the current is perfectly definite in its nature, pro^ 
ducing a fixed and constant amount of decomposition, expressed in each 
electrolyte by the value of its chemical equivalent. 

From a very extended series of experiments, based on this and other me- 
thods of research, Mr. Faraday was enabled to draw the general inference that 
effects of chemical decomposition were always, proportionate to the quantity 
of circulating electricity, and might be taken as an accurate and trustworthy 
measure of the latter. Guided by this highly 
Fig. 127. important principle, he constructed his vollame- 

^, ,-^ ^ ter, an instrument which has rendered the great- 

n "X est service to electrical science. This is merely 

JL A an arrangement by which a little acidulat^ 

7^ \ water is decomposed by the current, the gas 

^ evolved being collected and measured. By plac- 

\ ing such an instrument in any part of the circuit, 

^ the quantity of electric force necessary to pro- 

^ duce any given effect can be at once estimated ; 

\ or, on the other hand, any required aniount of 

\ the latter can be, as it were, measured out and 

\ adjusted to tlie object in view. The voltameter 
^=* has received many different forms ; one of the 
^y^J3 most extensively useful is that shown in fig. 127, 

in which the platinum plates are separated by a 
very small interval, and the gas is collected in a graduated jar standing on 
the shelf of the pneumatic trough, the tube of the instrument, which is filled 
to the neck with dilute sulphuric acid, being passed beneath the jar. 

The decompositions of the voltaic battery can be effected by the electricity 
of the common machine, by that developed by magnetic action, and by that 
of animal origin, but to an extent incomparably more minute. This arises 
from the very small quantify 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, develbpe far • 
more electricity, to judge from the chemical effects of such an arrangement, 
than very many turns of a large plate electrical machine in high action. 
Nevertheless, polar or electrolytic decomposition can be distinctiy and satis- 
factorily effected by the latter, although on a minute scale. 

With a knowledge of the principles laid down, the study of the voltaie 
battery may be resumed and completed. In the first place, two very different 
views have been held concerning the source of the electrical disturbance in 
that apparatus. Volta himself ascribed it to mere contact of dissimilar 
metals ; to what was denominated an electro-motive force, called into being 
by such contact ; the liquid merely serving the purpose of a conductor be- 
tween one pair of metals and that succeeding. Proof was supposed to be 
given of the fundamental position by an experiment in which discs of zino 
and copper attached to insulating handles, after being brought into close 
contact, were found,. by the aid of a very delicate gold-leaf electroscope, to 
^ in opposite electrical states. It appears, however, that the more f^mfoUy 


this experiment is ms4% the emaller is th« 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 obsenration was soon made that the power of the 
battery always bore some kind of proportion to the chemical action upon the 
line; that, for instance, when pure water was used the effect was extremely 
feeble ; with a soliition 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 exi>eriment8 of Mr. Faraday and Professor Daniell have given very 
great support to the chemical theory, by showing that contact of dissimiUr 
metals is not necessary in order to call into being powerful electrical currents, 
and that the development of electrical force is not only in 
some way connected with the chemical action of the liquid of Fig. 128. 
the battery, but that it is always in direct proportion to the 
latter. One very beautiful experiment, in which decompo- 
sition of iodide of potassium by real electrolysis is performed 
by a current generated without any contact of dissimilar 
metals, can be thus made: — A plate of sine (fig. 128) is 
bent at a right angle, and cleaned by rubbing with sand- 
paper. A plate of platinum has a wire of the same metal 
attached to it by careful rivetting, and the latter bent into 
an arch. A piece of folded filter-paper is wetted with a so- 
lution of iodide of potassium, and placed upon the zinc ; the 
platinum plate is arranged opposite to the latter, with the 
Old of its wire restiog upon the paper, and then the pair 
plunged into a glass of dilute sulphuric acid, mixed with a 
few drops of nitric. A brown spot of iodine becomes in a moment evident 
beneath the extremity of the platinunl wire ; that is, at the positive side of 
the arrangement. 

A strong argument in favour of the chemical view is founded on the easily- 
proved fact, that the direction of the current is determined by the kind of 
action upon the metals, the one least attacked being always positive. Let 
two polished plates, the one iron and the other copper, be connected by wires 
with a galvanometer, and then immersed in a solution of an alkaline sul- 
phide. The needle in a moment indicates a powerful current, passing from 
the copper, through the liquid, to the iron, and back again through the wire. 
Let the plates be now removed, cleaned, and plunged into dilute acid ; the 
needle is again driven round, but in the opposite (Erection, the current now 
passing from the iron, through the liquid, to the copper. In the first. instance 
the copper is acted upon, and not the iron ; in the second, these conditions 
are reversed, and with them the direction of the current 

The metals employed in the practical construction of voltaic batteries are 
sine for the active metal, and copper, silver, or, still better, platinum for the 
inactive one ; the greater the difference of oxidability, the better the arrange- 
ment The liquid is either dilute sulphuric acid, sometimes mixed with a 
little nitric, or occasionally, where very slow and long-continued action is 
wanted, salt and water. To obtain the maximum effect of the apparatus 
with the least expenditure of zinc, that metal must be employed in a pure 
state, or its surface must be covered by or amalgamated with mercury, whicl| 
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 
robbing 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 urgea 
forwards with inereMed energy, its intensity is augmented, but the actual 


amouiit of electrical force thrown into the cnrrent form is not increased. 
The ' quantity, estimated by its decomposing power, is, in fact, determined 
hy that of the smallest and least active pair of plates, the quantity of elec- 
tricity in every part or section of the circuit being exactly equal. Hence 
large and small plates, batteries strongly and weakly charged, can never be 
connected without great loss of power. 

When a battery, either simple or compound, constructed with pure or with 
amalgamated zinc, is charged with dilute sulphuric acid, a number of highly 
interesting phenomena may be observed. While the circuit remains broken 
the zinc is perfectly inactive, no water is decomposed, no hydrogen liberated ; 
but the moment the connection is completed, torrents of hydrogen arise, 
not from the zinc, but from the copper or platinum surfaces alone, while the 
zinc undergoes tranquil and imperceptible oxidation and solution. Thus, 
exactly the same effects are seen to occur in every active cell of a closed 
circuit, which are witnessed in a portion of water undergoing electrolysis ; 
the oxygen appears at the positive side, with respect to the current, and the 
hydrogen at the negative ; but with this difference, that the oxygen, instead 
of being set free, combines with the zinc. It is, in fact, a real case of elec- 
trolysis, and electrolytes alone are available as exciting liquids. 

Common zinc is very readily attacked and dissolved by dilute sulphurio 
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 iLree-fourths 
or more of the metal are often consumed, without contributing in the least 
to the general effect, but, on the contrary, injuring the latter to some extent. 
This evil is got rid of by amalgamating the surface. 

From experiments very carefully made with a "dissected" battery of 
peculiar construction, in which local action was completely avoided, it has 
been distinctly proved that the quantity of electricity set in motion by the 
battery varies exactly with the zinc dissolved. Coupling this fact with that 
of the definite action of the current, it will be seen, tiiat when a perfect 
battery of this kind is employed to decompose water, in order to evolve 1 
grain of hydrogen from the latter, 83 grains of zinc must be oxidized and its 
equivalent quantity of hydrogen disengaged in each active cell of the battery. 
That is to say, that the electrical force generated by the oxidation of an 
equivalent of zinc in the battery, is capable of effecting the decomposition 
of an equivalent of water, or any other electrolyte out of it. 

This is an exceedingly important discovery ; it serves to show in the most 
striking manner, the intimate nature of the /connection between chemical and 
electrical forces, and their remarkable quantitative or equivalent relations. 
It almost seems, to use an expression of Mr. Faraday, as if a transfer of 
chemical force took place through the substance of solid metallic conductors ; 
that chemical actions, called into play in one portion of the circuit, could be 
made at pleasure to exhibit their effects without loss or diminution in any 
other. There is an hypothesis, not of recent date, long countenanced and 
supported by the illustrious Berzelius, which refers all chemical phenomena 
to electrical forces ; which supposes that bodies combine because they are in 
opposite electrical states ; even the heat and light accompanying chemical 
union may be, to a certain extent, accounted for in this manner. In short, 
we are in such a position, that either may be assumed as cause or effect ; it 
may be that electricity is merely a form or modification of ordinary chemical 
affinity ; or, on the other hand, that all chemical action is a manifestation 
of electrical force. 

One of the most useful forms of the common voltaic batteiy is that con- 
trived by Pr. Wollaston (fig. 129). The copper is made completely to enoirele 

-OfllMl^TftT Of TiHJI ^0<i«9lJ<3 ^l|b«. 


«g. i». 


fk« zmo plftte, except at the edges, the two metftls being kept apart by pieces 
of cork or wood. Each sine is soldered to the preceding copper, and the 
whole BCiewed to a bar of dry mahogany, so that the {dates can be lifted 
into er out of the acid, which is contained in an earthenware trough, divided 
into separate ceils. The liquid consists of a mixture of 100 parts water, 2( 
parts oil of Titriol, and 2 parts commercial nitric acid, all by measure. A 
namber of such batteries are easily connected together by straps of sheet 
eopper, and admit of being put into action with great ease. 

The great objection to this and to all tiie older forms of the Toltaic battery 
is, that the power rapidly decreases, so that after a short tinre scarcely the 
tenth part of Ute original action remiUns. This loss of po^er depends partly 
on the gradoal change of the-sulphuric acid into sulphate of cinq, but etiU 
mmre on the coaiting ef hjrdrogen, and at a later stage, on tbe pifecipitatiAD 
of metallic ziiic on the copper plates. It is self-erident 
that if the copper prlate in the fluid became covered 
with sine, it would electrically, act like a tine plate. 
This is precisdy the action of the hydrogen, whereby 
a decrease of electrical power is produced. This effect, 
ptodttoed by tiie eubstances separated fix)m the liquid, 
is commonly called polarization. 

An instrument of immense value fbr the purposes of 
electro-chemical research, in which it is desired to 
maintain powerful and equable currents for many suc- 
cesslre hours, has been contrived by Professor Daniell 
(fig. 130). Each cell of this ** constant" battery con- 
sists of a copper cylinder B^ inches in diameter, and 
of a height varying from 6 to 18 inches. The tine is 
employed in the form of a rod f of an inch in diameter, 
carefully amalgamated, and suspended in the centre of 
the cylinder. A second cell of porous earthenware or 
animal memlntuie intervenes between the zinc and the 
copper ; this is filled with a mixture of 1 part by mea- 
sure of oil of vitriol and 8 of water, and the exterior 
space with the same liquid, saturated with sulphate of 
copper. A sort of little colander is fitted to the top of 
the cell, in ^i^oh crystalf of the sulphate of ooi^per avs pl«oe4, so tet 4i« 


strength of the solution may remain unimpaired. When a commnnication is 
made by a wire between the rod and the cylinder, a powerful current is pro- 
duced, the power of which may be increased to any extent, by connecting a 
sufficient number of such cells into a series, on the principle of the crown 
of cups, the copper of the first being attached to the zinc of the second. 
Ten such alternations constitute a very powerful apparatus, which has the 
great advantage of retaining its energy undiminished for a lengthened period. 
For the copper plates become covered with a compact precipitate of copper 
without the evolution of any hydrogen, so long as the solution of sulphate 
of copper remains saturated. By this most excellent arrangement the sur- 
faces of the copper plates retain their original chemical properties unchanged. 
The polarization is avoided, and the chief cause of the gradual loss of power 
is removed. 

Mr. Grove, on precisely the same principles, succeeded afterwards in form- 
ing a zinc and platinum battery, the action of which is con- 
Fig. 131. stant. To hinder the evolution of hydrogen on the plati- 
num plates he employed the oxidizing action of nitric acid. 
One of the cells in this battery is represented in the 
margin, in section (fig. 181). The zinc plate is bent round, 
so as to preseirt a double surface, and well amalgamated ; 
within it stands a thin flat cell of porous earthenware, filled 
with strong nitric acid, and the whole is immersed in a 
mixture of 1 part by measure of oil of vitriol and 6 of 
' water, contained either in one of the cells of WoUaston's 
trough, or in a separate cell of glazed porcelain, made for 
the purpose. The apparatus is completed by a plate of 
platinum foil which dips into the nitric acid, and forms the 
positive side of the arrangement. With ten such pairs, 
experiments of decomposition, ignition of wires, the light 
between charcoal points, &c., can be exhibited with great 
brilliancy, while the battery itself is very compact and 
portable, and, to a great extent, constant in its action. The zinc, as in the 
•case of Professor Daniell's battery, is only consumed while the current 
passes, so that the apparatus may be arranged an hour or two before it is 
required for use, which is often a matter of great convenience. The nitric 
acid suppresses the whole of the hydrogen, becoming thereby slowly deoxi- 
dized and converted into nitrous acid, which at first remains dissolved, but 
after some time begins to be disengaged from the porous cells in dense red 
ftimes ; this constitutes the only serious drawback to this excellent instru- 

Professor Bunsen has modified the Grove battery by substituting for the 
platinum, dense charcoal or coke, which is an excellent conductor of elec- 
tricity. By this alteration, at a very small expense, a battery may be made 
as powerful and useful as that of Grove. On account of its cheapness, any 
one may put together one hundred or more of Bunsen's cells ; by which the 
most magnificent phenomena of heat and light may be obtained. 

Mr. Smee has contrived an ingenious battery, in which silver covered with 
a thin coating of finely-divided metallic platinum is employed in association 
with amalgamated zinc and dilute sulphuric acid. The rough surface appears 
to permit the ready disengagement of the bubbles of hydrogen. 

Within the last nine or ten years, several very beautiful and successful 
applications of voltaic electricity have been made, which may be 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 reyersei a most faiUifid representation of the latter. 



Fig. 132. 

Bj oaing this in its tam as a moiild or matrix, an absolutely perfect /oe* 
nmile of the plate or medal is obtained. In the former case, 
the impressions taken on paper are quite indistinguishable from 
those directly derived from the work of the artist ; and as there 
is DO 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 tou^, and bears 
the action of the press perfectly welL 

The apparatus used in this and many similar processes is 
of the simplest possible kind. A trough or cell of wood (fig. 
132) is divided by a porous diaphragm, made of a very thin 
piece of sycamore, into two parts ; dilute sulphuric acid is put 
on one side, and a saturated solution of sulphate of copper, 
sometimes mixed with a little acid, on the other. A plate of 
zinc is soldered to a wire or strap of copper, the other end of 
which is secured by similar means to the engraved copper 
plate. The latter is then immersed in the solution of sulphate, 
and the zinc in the acid. To prevent deposition of copper on the back of 
the copper plate, that portion is covered with varnish. For medals and 
small works a porous earthenware cell, placed in a jelly-jar, may be used. 

Other metals may be precipitated in the same manner, in a smooth and 
compact form, by the use of certain precautions which have been gathered 
by experience. Electro-gilding and plating are now carried on very largely 
and in great perfection by Messrs. Elkington and others. Even non-conduct- 
ing bodies, as sealing-wax and plaster of Paris, may be coated with metal ; 
it is only necessary, as Mr. Murray has shown, to rub over them the thin- 
nest possible film of plumbago. Seals may thus be copied in a very few 
hours with unerring truth. 

M. Becquerel, several years ago, published an exceedingly interesting ac- 
count of certain experiments, in which crystallized metals, oxides, and other 
insoluble substances had been produced by the slow and continuous action 
of feeble electrical currents, kept up for months, or even years. These pro- 
ducts exactly resembled natural minerals, and, indeed, the experiments 
threw great light on the formation of the latter within the earth.* 

The common but very pleasing experiment of the lead tree is greatly de- 
pendent on electro-chemical action. When a piece of zinc is 
suspended in a solution of acetate of lead, the first effect is 
the decomposition of a portion of the latter, and the deposi- 
tion of metallic lead upon the surface of the zinc ; *it is simply 
a displacement of a metal by a more oxidable one. The 
change does not, however, stop here ; metallic lead is still 
deposited in large and beautiful plates upon that first thrown 
down, until the solution becomes exhausted, or the zinc en- 
tirely disappears. (Fig. 133.) The first portions of lead form 
with the zinc a voltaic arrangement of sufficient power to de- 
compose the salt, under the peculiar circumstances in which 
the latter is placed, the metal is precipitated upon the nega- 
tive portion, that is, the lead, while the oxygen and acid are 
taken up by the zinc. 

Professor Grove has contrived a battery, in which an elec- 
trical current, of sufficient intensity to decompose water, is produced by the 
reaction of oxygen upon hydrogen. Each element of this interesting appa- 
ratus consists of a pair of glass tubes to contain the gases, dipping into a 
▼essel of acidulated water. Both tubes contain platinum plates, covered 

Fig. 133. 

* Traits de I'Eleotricitd et du Magn6ti8me, Ui. 280. 


j^dSk »R>ih;1i diepocit of ibi«l]F-dMded'pIftlllsiiiDj and ftiniislied with eondndanst 
wires, which pass tfarovg|h the tops- or sides of the tubes, and are hermeti- 
cally sealed into the latter. Wfa«a the tubes are charged with oxygen on the 
one side and hydrogen on the other, and the wires connected with a galvano- 
scope, the needle of the instrument becomes instantly affected ; and when 
ten or more are combined in a series, the oxygen-tube of the one with the 
hydrogen-tabe of the next, &o<, while the terminal wires dip into acidulated 
water, a rapid stream of minute bubbles from either wire indicates the de- 
composition of the liquid ; and when the experiment is made with a small 
voltameter, it is found- that the oxygen and hydrogen disengaged, exactly 
equal in amount the quantities absorbed by the act of combination in each 
tube of the battery. 



Thi metals constitate the second and larger group of elementary bodiefl 
A great number of these are of Tery 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, tlie metals themselves being almost unknown. Many are 
used in medicine and in the arts, and are essentially connected with the pro- 
gress of civilization. 

If arsenic and tellurium be included, the metals amount to forty-nine in 

Physical Properties, — One of the most remarkable and striking characters 
possessed by the metals is their peculiar lustre ; this is so characteristic, that 
the expression metallic lustre has passed into common speech. This pro- 
perty is no doubt connected with the extraordinary degree of opacity which 
the metals present in every instance. The thinnest leaves or plates, the edges, 
of crystalline laminae, arrest the passage of light in the most complete man- 
ner. An exception to this rule is usually made in favour of gold-leaf, which 
when held up to the daylight exhibits a greenish colour, as if it were really 
endued with a certain degree of translucency ; the metallic film is, however, 
always so imperfect, that it becomes difficult to say whether the observed 
effect may not be in some measure due to multitudes of little holes, many of 
which are visible to the naked eye. 

In point of colour, the metals present a certain degree of uniformity ; with 
two exceptions, viz. copper, which is red, and gold, which is yellow, all these 
bodies are included between 4he pure white of silver, and the bluish-grey 
tint of lead ; bismuth, it is true, has a pinkish colour, but it is very feeble. 

The differences of specific gravity are very wide, passing from potassium 
and sodium, which are lighter than water, to platinum, which is nearly 
twenty-one times heavier than an equal bulk of that fluid. 

Table of the Specific Gravities of Metals at 60° (15o-5C).' 

Platinum „ 20-98 

Gold 19-26 

Tungsten 17-60 

Mercury '. 13-67 

Palladium 11-80 to 11-8 

Lead 11-35 

Silver 10-47 

Bismuth 9-82 

Uranium 9*00 

Copper 8-89 

Cadmium , 8-60 

- I I I ■ , .1 Ilia 

* Dr. Turner's Elements, eSghih edition, p. 845. 



Cobalt 8-54 

Nickel 8-28 

Iron 8-79 

Molybdenum 740 

Tin 7-29 

Zinc 7-86 to 71 

Manganese 6*85 

Antimony 6-70 

Tellurium 6-11 

Arsenic r 5*88 

Aluminium 2*60* 

Magnesium 1*70 

Sodium 0-972 

Potassium 0-865 

The property of malleability, or power of extension under the hammer 
or between the rollers of the flatting-mill, is enjoyed by certain of the 
inetals to a. rery 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 siWer wire used in the manufacture of gold lace is even thinner, 
imd 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, idiich are altogether destitute 
of malleability. 

The specific gravity of malleable metals is usually very sensibly increased 
by pressure or blows, and the metals themselves rendered much harder, with 
a tend^icy to brittleness. This condition is destroyed and the former soft 
state restored by the operation of annealingy 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 re- 
sisting tension. The art of wire-drawing is ofne of great 
antiquity ; it consists in drawing rods of metal through a 
succession of trumpet-shaped holes in a steel plate (fig. 
184), each being a Uttle smaller than its predecessor, until 
the requisite degree of fineness is attained. The metal 
often becomes very hard and rigid in this process, and ia 
then liable to break ; this is remedied by annealing. The 
order of tenacity among the metals susceptible of being 
easily drawn into wire is the following : it is determined 
by observing the weights required to break asunder wires 
drawn througli tae same orifice of the plate : 

Tig. 184. 








Metals differ as mueh in fusibility as in density ; the following table, ex- 

• WbWw. 



Fusible below 
a red heat 

triieted from £be late Dr. Turner's excellent work, will girft an idea of tbeir 
relations to heat. The melting-points of the metals which only fnse at a 
temperature above ignition, and that of zinc, are on the authority of Mr. 
Daniell, having been observed by the help of the pyrometer before described : 

Melting points. 
P. C. 

'Mercury —390 —390.44 

Potassium 136 67-77 

Sodium 194 90 

Tin 442 227 -77 

Cadmium (about) 442 277-77 

Bismuth 497 258-33 

Lead 612 322-77 

Tellurium — rather less fusible than lead 

Arsenic — unknown 

Zinc „ 773 411-66 

^ Antimony — just below redness 

Silver 1873 1022-77 

Copper ^ 1996 1091-11 

Gold 2016 1102-22 

Cast iron 2786 1530 

Pure iron.... 



Manganese. . 
Palladium .. 
Molybdenum . ^ 


Titanium .... 





Infiisible below « 
a red heat 

Fusible only in an excellent wind- 

Imperfectly melted in wind-furnace. 

Infusible in furnace ; fusible by oxy- 
hydrogen blowpipe. 

Some metftls acquire a pasty or adhesive state before becoming fluid ; this 
is the case with iron and platinum, and also with the metals of the alkalis. 
It is this peculiarity which confers the very valuable property of welding, 
by which pieces of iron and steel are united without solder, and the finely- 
divided metallic sponge of platinum converted into a solid and compact bar. 

Volatility is possessed by certain members of this class, and perhaps by 
all, could temperatures sufficiently elevated be obtained. Mercury boils and 
distils below a red heat; potassium, sodium, zinc, and cadmium, rise in 
vapour when heated to a bright redness ; arsenic and tellurium are volatile. 


Metallic combinations are of two kinds ; namely, those formed by the 
union of metals among themselves, which are called alloys, or where mer- 
cury is concerned, amalgams, and those generated by combination with the 
non-metallic elements, as oxides, chlorides, sulphides, &c. In this latter 
case the metallic characters are^very frequently lost. The alloys themselves 
are really true chemical compounds, and not mere mixtures of the consti- 


tuent metals ; their properties often differ completely from those of tho 

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 c&mbine with either acids or alkalis, and those 
which have distinct acid properties. The strong bases are all protoxides ; 
they contain single equivalents of metal and oxygen ; the weaker bases are 
usually sesquioxides, containing metal and oxygen in the proportion of two 
equivalents of the former to three of the latter; the peroxides or neutral 
compounds are still richer in oxygen, and, lastly, the metallic acids contain 
the maximum proportion of that element. 

The gradual change of properties by increasing proportions of oxygen is 
yreVL illustrated by the case of manganese. 

Metal. Oxygen. Symbols. Charactert. 

Protoxide 1 eq. ... 1 eq. ... MnO ... Strongly basic. 

Sesquioxide 2 eq. ... 3 eq. ... MdjOj .:. Feebly basic. 

Binoxide 1 eq. ... 2 eq. ... MnO, ... Neutral. 

Manganic acid.... 1 eq. ... 3 eq. ... MnO, | strongly acid. 

Permanganic acid 2 eq. ... 7 eq. ... MujO, j ^-^ 

The oxides of iron and chromium present similar, but less numerous gra- 

When a powerful oxygen-acid and a powerful metallic base are united in 
such proportions that they exactly destroy each other's properties, the re- 
sulting salt is said to be neutral;, it is incapable of affecting yegetable 
colours. Now, in all these well-characterized neutral salts, a constant and 
very remarkable relation is observed to exist between the quantity of oxygen 
in the base, and the quantity of acid in the *salt This relation is expressed 
in the following manner : — To form a neutral combination, as many equiva- 
lents of acid must be present in the salt as there are of oxygen in the base 
itself. In fact, this has become the very definition of neutrality, as the 
action on vegetable colours is sometimes an unsafe guide. 

It is easy to see the application of this law. When a base is a protoxide, 
a single equivalent of acid suffices to neutralize it ; when a scsquioxide, not 
less than three are required. Hence, if by any chance, the base of a salt 
should pass by oxidation from the one state to the other, the acid will be in- 
sufficient in quantity by one-half to form a neutral combination. Sulphate 
of the protoxide of iron offers an example ; when a solution of this substance 
is exposed to the air, it absorbs oxygen, and a yellow insoluble sub-salt^ or 
, b'w'c-saUt is produced, which contains an excess of base. Four equivalents 
of the green compound absorb from the air two equivalents of oxygen, and 
give rise to one equivalent of neutral and one equivalent of basic sulphate 
of the sesquioxide, as indicated by the diagonal zigzag line of division. 

1 eq. iron + 1 eq. oxygen 1 eq. sulphuric acid. 

1 eq. iron -j- 1 eq. oxygen 1 eq. sulphuric acid. 

I -)- 1 eq. oxygen from air 

1 eq. iron -4- 1 eg. oxygen 1 1 eg. sulphuric acid. 

1 eq. iron -j- ^ cq. oxygen 1 eq. sulphuric acid. 

4" 1 eq. oxygen from air. 

Such sub-salts or basic salts are very frequently insoluble. 

The combinations of chlorine, iodine, bromine, and fluorine with the metals 
possciss in a very high degree the saline character. If, however, the definition 
formerly given of a salt be rigidly adhered to, these bodies must be excluded 
from the class, and with them the very substance from which the name is 

CffSMISTB'T or TffB MXTiiLfi^. 201 

derived, that is, common ult, ithUsh. is a cfil<»nde of sodinm. To obviate 
this anomaly, it has been found necessary to create two classes of salts ; in 
the first division will stand those constituted after the type of common salt, 
which contain a metal and b, aak-radical, as chlorine, iodine, &c. ; and in the 
second, those which, like sulphate of soda and nitrate of potassa, are gene- 
rally supposed to be combinations of an acid with an oxide. The names 
haloid^ salts, and oxygen-acid, or oxy-sdlU, 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 
yalae: it is much more probable, indeed, that no truly saline compounds of 
hydrogen-acids exist, at any rate in inorganic chemistry. When a solution 
of any hydrogen-acid is poured upon a metallic oxide, we may. rather suppose 
that both are decomposed, water and a haloid salt of the metal being pro* 
doeed. Take hydrochloric acid and potassa by way of example. 

B^ochlorio f Chlorine - ^.^ Chloride of potassium. 

I add \ Hydrogen-- ^""^ 

I Potossa /Potassium- 

u»»» ^ Oxygen r^=*i. Water. 

. On evaponbtmg tiie solution, the chloride of potassium orystalllxes out 

When hydr(>chloric acid and ammoniacal gases are mixed, they combine 
with some energy and form a white solid salt, sal-ammoniac. Now this sub- 
stance bears such a strong resemblance in many important particulars to 
chloride of potassium and common salt, that the ascription to it of a similar 
constitution is well warranted. 

If chloride of potassium, therefore, contain chlorine and metal, sal-ammo- 
niac may also contain chlorine in conibination with a substance having the 
chemical relations* of a metal, formed by the addition of the hydrogen of the 
add to the elements of the ammonia. 

Hydrodiloric r 1 eq. Chlorine Chlorine ...1 

acid \l eq. Hydrogen I gal- 

Ammonia ... I ? ^^- S.y^^Sen^:::-;^ \ ammoniac. 

"^ * \ 1 eq. Nitrogen — ^^"^^ Ammonium J 

The term ammornum is given to this hypothetical body, NH^ ; it is sup- 
posed to exist in all the anmioniacal salts. Thus- we have chloride of 
ammonium, sulphate of the oxide of ammonium, &o. This view is very 
strongly supported by the peculiarities of the salts themselves, and by the 
existence of a series of substances intimately related to these salts in organio 
chemistry, as will hereafter be seen. 

Many of the sulphides also possess the saline character and are soluble in 
water, as those of potassium and sodium. Sometimes a pair of sulphides 
will anite in definite proportions, and form a crystallizable compound. Such 
bodies bear a very close resemblance to oxygen-acid salts; they usually 
contain a protosulphide of an alkaline metal, and a higher sulphide of a nou'- 
metallic subsfance or of a metal which has little tendency to form a basic 
ozide, the two sulphides having exactly the same relation to each other as 
the oxide and acid of an ordinary salt. Hence the expressions sulphur-mft, 
*ulphur-acid, and sulphur-base, which Berzelius applies to such compoundB ; 
they contain sulphur in the place of oxygen. Thus, bisulphide of carbon is 
a sulphur-acid f it forms a crystallizable compound with protosulphide of 
potassium, which is a sulphur-base. Were oxygen substituted for the sulphur 
in this product,, we should have carbonate of potassa. 

' SXf, searsalt, and tiSast form. 


KS+CSj sulphur-salt. 
KO -f CO2 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 saltt, in 
which the same acid is in combination with two different bases. When sul- 
phate of copper and sulphate of potassa, or chloride of zinc and sal-ammoniac, 
are mixed in the ratio of the equivalents, dissolved in water, and the solution 
made to crystallize, double salts are obtained. These latter are often more 
beautiful, and crystallize better than their constituent salts. 

Many of the compounds called super , or add salts, such as bisulphate of 
potassa, which have a sour taste and acid reaction to test-paper, ought 
strictly to be considered in the light of double salts, in which one of the 
bases is water. Strange as it may at first sight appear, water possesses 
coDsiderable basic powers, although it is unable to mask acid reaction on 
vegetable colours ; hydrogen, in fact, very much resembles a metal in its 
chemical relations. Bisulphate of potassa will, therefore, be a double sul- 
phate of potassa and water, while oil of vitriol must be assimilated to neutral 
sulphate of potassa. 

KO-f SO, and HO+SO,. 

Water is a weak base ; it is for the most part easily displaced by a metallic 
oxide; yet cases occur now and then in which the reverse happens, and 
water is seen to decompose a salt, in virtue of its basic power. 

There are few acid salts which contain no water ; as the bichromate of 
potassa, and a new anhydrous sulphate of potassa discovered by M. Jaque- 
lain.» It will be necessary, of course, to adopt some other view in these 
cases. The simplest will be to. consider them as really containing two equi- 
valents of acid to one of base. 

By water of crystaUizaiion is meant water in a somewhat loose state of com- 
bination with a salt, or other compound body, from which it can be disen- 
gaged by the mere application of heat, or by exposure to a dry atmosphere. 
Salts which contain water of crystallization have their crystalline form greatly 
influenced by the proportion of the latter. Green sulphate of iron crystal- 
lizes in two different forms, and with two different proportions of water, 
according to the temperature at which the salt separates from the solution. 

Many salts containing water effloresce in a dry atmosphere, crumbling to 
powder, and losing part or the whole of their water of crystallization ; while 
in a moist atmosphere they may be preserved unchanged. The opposite 
effect to this, or deliquescence, results from a strong attraction of the salt for 
water, in virtue of which it absorbs the latter from the air, often to the 
extent of liquefaction. 

Crystallization; CrystaUine Forms. — Almost every substance, simple and 
compound, capable of existence in the solid state, assumes, under favourable 
circumstances, a distinct geometrical form or figure, usually bounded by 
plane surfaces, and having angles of fixed and constant value. The faculty 
of crystallization seems to be denied only to a few bodies, chiefly highly 
complex organic principles, which stand, as it were, upon the very edge of 
organization, and which, when in a solid state, are frequently characterized 
by a kind of beady or globular appearance, well known to microscopical 

The most beautiful examples of crystallization are to be found among 
natural minerals, the result of exceedingly slow changes constantly occurring 
within the earth ; it is invariably found that artificial crystals of salts, and 

*■ Ann. Chim. et Pbys. Ixz. 311. 



other soluble sabstances, which have been slowly and qnietly deposited, 
always surpass in size and regularitj those of more rapid formation. 

Solution in water or some other liquid is one very frequent method of 
effecting crystallization. If the substance be more soluble at a high than at 
a lower temperature, then a hot and saturated solution by slow cooling will 
generally be found to furnish crystals ; this is a very common case with salts 
and various organic principles. If it be equally soluble, or nearly so, at all 
temperatures, then slow spontaneous evaporation in the air, or over a sur- 
face of oil of vitriol, often proves very effective. 

Fusion and slow cooling may be employed in many cases ; that of sulphur 
is a good example; the metals usually afford traces of crystalline figure 
when thus treated, which sometimes become very beautiful and distinct, as 
with bismuth. A third condition under which crystals very often form is in 
passing from a gaseous to a solid state, of which iodine affords h good in* 
stance. When by any of these means time is allowed for the symmetrical 
arrangement of the particles of matter at the moment of solidification, 
crystals, are produced. 

That crystals owe their figure to a certain regularity of internal structure, 
is shown both by their mode of formation and also by the peculiarities at- 
tending their fracture. A crystal placed in a slowly-evaporating Saturated 
solution of the same substance grows or increases by a continued deposition 
of fresh matter upon its sides in such a manner that the angles formed by 
the meeting of the latter remain unaltered. 

The tendency of most crystals to split in particular directions, called by 
mineralogist? cleavage^ is a certain indication of regular structure, while the 
curious optical properties of many among them, and their remarkable mode 
of expansion by heat, point to the same conclusion. 

It may be laid down as a general rule that every substance has its own 
crystalline form, by which it may very frequently be recognized at once ; 
not that each substance has a different figure, although very great diversity 
in this respect is to be found. Some forms are much more common than 
others, as the cube and six-sided prism, which are very frequently assumed 
by a number of bodies, not in any way related. 

The same substance may have, under different sets of circumstances, as 
high and low temperatures, two different crystalline forms, in which case it 
is said to be dimorphous. Sulphur and carbon furnish, as already noticed, 
examples of this curious fact ; another case is presented by carbonate of 
lime in the two modifications of calcareous spar and arragonite, both chemi- 
cally the same, but physically different. A fourth example might be given 
in the iodide of mercury, which also has two distinct forms, and even two 
distinct colours, offering as great a contrast as those of diamond^and plum- 

Fig. 135. 



Tbe -angles of crysiak are measttred by means of instniments called fftmi- 
cmeters, of which there are two kinds in use, namely, the old or common 
goniometer, and the refleotiTe goniometer of Dr. WollastoD. 

The common goniometer consiets of a pair of steel blades moYing with 
friction up<m a centre, as shown in the cut (fig. 135). The edges a a are 
carefully a€|)usted to the faces of the crystal, whose inclination to each other 
it is required to ascertain, and then the instrument being applied to the di- 
Tided 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 indieations be- 
ing correct within a fraction of a degree; it is applicable also to the mea- 
surement of the angles of crystals of very smaU size, the only condition 
, required being that their planes be smooth and brilliant. The subjoined 
sketch (fig. 136) will convey an idea of its nature and mode of use. 

Fig. 138. 

a is a divided circle or disc of brass, the axis of which passes stiffly and 
without shake through the support b. This axis is itself pierced to admit 
the passage of a round rod or wire, terminated by the milled-edged head e, 
and destined to carry the crystal to be measured by means of the jointed 
arm d. A vernier, c, immovably fixed to the upright support, serves to mea- 
sure with great accuracy the angular motion of the divided circle. The 
crystal at / can thus be turped round, or ac^usted in any desired position, 
without the necessity of moving the disc. 

The principle upon which the measurement ef the angle rests is very 
simple. If the two adjacent planes of a crystal be successively brought into 
the same position, the angle through which the crystal will have moved will 
be the supplement to that contained between the two planes. This will be easily 
intelligible by reference to fig. 137, in which a crystal having the form of a 
triangular prism' is shown in the two positions, the angle to be measured 
being that indicated by the letters e df. 

The lines ac, be, are perpendicular to the respective faces of the crystal. 

* The triangular prism has been choeen for the sake of eimplidtj; bat a momenVs oou- 
iideration will show that the rule applies equally well to anj other figure. 


Fig. 137. 


eonseqnenfly the internal angles dgc, dhc, are right angles. Now, sinoe 
the sum of the internal angles of a fonr-sided rectilineal figure, as ef^e A, 
equal four right angles, or 860^', the angle gdh{pT e df) must of necessitj 
be the supplement to the angle gehy or that throngh which the crystal 
moTes. iUl that is required to be done, therefore, is to measure the latter 
angle with accuracy, and subtract its value from 180<' ; and this the gonio- 
meter effects. 

One method of using the instrument is the following : — The goniometer is 
placed at a oonyenient 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 
Bimilar ribbon, acljusted parallel to the first, is fixed beneath the window, a 
foot or eighteen inches above the floor. The object is to obtain too easily- 
Tisible black lines, perfectly parallel. The crystal to be examined is attached 
to the arm of the goniometer at / by a little wax, and ac^tisted in such a 
manner that the edge joining the two planes whose inclination is to be mea- 
Bured 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. 186) until 
the eye placed near it perceives the image of the upp^ black l^e reflected 
from the surface of one of the planes in question. Following this image, 
the crystal is still cautiously turned until the upper black line seen by re- 
flection approaches and overlaps the lower black line seen direetJy by another 
portion of the pupil. It is obvious, that if the plane of the crystal be quite 
paraUel 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 
erystal must be moved upon the wax until the two lines fall in one when su- 
perposed. The second face of the crystal must then be adjusted in the same 
manner, oare 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 bnng 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, 
28 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 preyiously 
occupied by the first. Nothing then remains but to read off by the vernier 
the angle through which the circle has been moyed in this operation. The 
dlTision upon the circle itself is very often made backwardt, so that tho 



angle of motion is not obtained, but its supplement, or the angle of the 
crystal required. 

It may be necessary to remark, that, although the principle of the opera- 
tion described is in the highest degree simple, its successful practice requires 
considerable skill and experience. 

If a crystal of tolerably simple form be attentively considered, it will be- 
come evident that certain directions can be pointed out in which straight 
lines may be imagined to be drawn, passing through the central point of the 
crystal from side to side, from end to end, or from one angle to that opposed 
to it, &c., about which lines the particles of matter composljig the crystal 
may be conceived to be symmetrically built up. Such lines or axet 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 
iyatetM ; these are as follows : — 

1. Th§ rtgular tystem, — The crystals of this division have three equal axes, 
all placed at right angles to each other. The most important forms are the 
cube (1), tiie reffular octahedron (2), and the rhombic dodecahedron (3). 

The letters a — a show the terminations of the three axes, placed as stated. 

Very many substances, both simple and compound, assume these forms, as 
most of the metals, carbon in the state of diamond, common salt, iodide of 
potassium, the alums, fluor-spar, bisulphide of iron, garnet, spinelle, &c. 

2. The square prismaHe system, — Three axes are here also observed, at 
iright-angles to each other. Of these, however, two only are of equal length, 
the diird being usually longer or shorter. The most important forms are : 
a riyhi square prismy in which the latter axes terminate in the central point 

Fig. 130. 

/I ^ ■ 





Or-a. Principal, or vertical axi& 
-b— ^ SMOBdary, q| lataral axis. 

<$M]t^MCl»t&t OI* 9ffS lUftAtffir 


of 6ac1i side (1 ) ; ik ^econtf right square prism, in irhiolk the sxeb termini^ ki 
the edges (2) ; a correspondug pair of riffht aquare^Mued otUihidra (S and 4). 

Examples of these forms are to be found in zircon, natiye biaozide of ti% 
apophyllite, yellow ferrocjanide 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 
prim (1), the right rhombic prism (2), the right rectangular-bcued octahedron^ 
(3), and the right rhombic-based octahedron (4). 


a-^a. Prindpal «zli. 
h—b, e—c Secondary axes. 

The system is exemplified >n sulphur crystallized at a low temperature, 
arsenical iron pyrites, nitrate and sulphate of potassa, sulphate of baryta, &c 

4. The oblique prismatic system. — ^Crystals belonging to this group have also 
three axes which may be all unequal, two of these (the secondary) are placed 
at right angles, the third being so inclined as to be oblique to one and per- 
pen(Ucular to the other. To thid system may be referred the four following 

Principal axis. 
h^-b, e c. Secondary axes. 

forms: — The oblique rectangular prism (1), the oblique rhombic prism (2), the 
obUque reetangtUar-based octahedron (8), the oblique rhombic-based octahe* 
dron (4). 

Such forms are taken by sulphur crystallized by fusion and cooling, real- 
gar, sulphate, carbonate and phosphate of soda, borax, green vitriol, and 
many oUier salts. 

6. The doubl/y-^blique prismatic system. — The crystalline forms comprehended 
in this diTision are, from their great apparent irregularity, exceedingly dif- 
fififilt to study and understand. In them are traced three axes, which ma/ 


be all unequal in lengtih, and are all oblique to each other, as in the two 
doublp'ObUque prmu (1 and 2), and in the correspondmg^ doubly-oblique ocia* 
kedront (8 and 4). 

Jig. 142. 
12 8 4 

. Principal axis, as before. 
b—b, o—c. Secondary axes. 

Sulphate of oopper, nitrate of bismuth, and quadroxalate of potassa, a£ford 
illustrations of these forms. 

6. The rhombohedral system. — This is very important and extensive : it is 
characterized hy the presence of four axes, three of which are equal, in the 
same plane, and inclined to each other at angles of 60*^, while the fourth or 


Fig. 143. 

<* 8 

a— a. Principal axis. 
h — b. Secondary axes. 

principal axis is perpendicular to all. The regular eix-sided prism (l),^thb 
quartz-dodecahedron (2), the rhombohedron (3), and a second dodecahedron, 
whose faces are scalene triangles (4), belong to the system in question. 

Examples are readily found ; as in ice, calcareous spar, nitrate of soda, 
beryl, quartz or rock crystal, and the semi-metals, arsenic, antimony, and 

If a crystal increase in magnitude by equal additions on every part, it is 
quite clear that its figure must remain unaltered ; but, if from some cause 
this increase should be partial, the newly-deposited matter being distributed 
unequally, but still in obedience to certain definite laws, then alterations of 
form are produced, giving rise to figures which have a direct geometrical 
connection with that from which they are derived. If, for example, in the 
cnih% a regular omission of successive rows of particles of matter in a cer- 
tam order be made at each solid angle, while the crystal continues to increase 
elsewhere, the result will be the production of small triangular pianos. 



Wtueh, AS tli« process adyances, grftcFoally ntsnrp tlie ivliole of t)ie tfttrTaee of 
flie cTystal, and conTert tire cube into an octahedron. The new planes are 
c«dled secondary f and their production is said to take ]>laoe by regular deere* 
mmtt upon the solid angles. The same thing may happen on the edges of 
the cube ; a new figure, the rhombic dodecahedron, is then generated. Fig. 
144. The modifications which can thus be produced of the original or 
primary figure (all of which are subject to exact geometrical laws) are totj 
sumerous. Several distinct modifications may be present at the sune time, 
iod 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 belongmg to the same natural group or 
crystaUographical system as the primary form, and having their axes comadeni 
tptth those of the latter. The crystals of each system are thus subject to a 
peculiar and distiuct set of modifications, the observation of which very 
frequently constitutes an excellent guide to the discovery of the primary 
form itself. ^ 

Crystals often cleave parallel to all the planes of the primary figure, as in 
calcareous spar, which ofi'ers 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 Tery curious modification of the figure sometimes occurs by the exces- 
siTe growth of each alternate plane of £e crystal ; the rest become at length 
obliterated, and the crystal assumes the character called hemihedral or half- 
sided. This is^well seen in the production of the tetrahedron from the regular 
octahedron (fig. 145), and of the rhombohedric form by a similar change 
from the quartz-dodecahedron already figured. 

Fig. 145. 

Passage of octahedron to tetrahedron. 

JRdatums of form and constitution; Isomorphism. — Certain substances to 
irhich a similar chemical constitution is ascribed, possess the remarkable 
property of exactly replacing each other in crystallized compounds without- 
alteration of the characteristic geometrical figure. Such bodies are said to 
be isomorphotis.^ 

18 « 

* From hof, equal, and ft^pfnt >hape or form. 


For example, magnesia, oxide of zino, oxide of copper, protoxide of Sr&H/ 
and oxide of nickel, are allied by isomorphic relations of the most intimate 
nature. The salts formed by these substances with the same acid and 
similar proportions of water of crystallization, are identical in their form, 
and, when of the same colour, cannot be distinguished by the eye ; the sul- 
phates of magnesia and zinc may be thus confounded. The sulphates, too, 
all combine with sulphate of potassa and sulphate of ammonia, giving rise 
to double salts, whose figure is the same, but quite different from that of the 
simple sulphates. Indeed, this connection between identity of form and 
parallelism of constitution runs through all their combinations. 

In the same manner, alumina and sesquioxide of iron replace each other 
continually without change of crystalline figure ; the same remark may be 
made of potassa, soda, and ammonia, with an equivalent of water, or oude 
of ammonium, these bodies being strictly isomorphous. The alumina in 
in common alum may be replaced by sesquioxide of iron ; the potassa by 
ammonia, or by soda, and still the figure of the crystal remains unchanged. 
These replacements may be partial only ; we may have an alum containing 
both potassa and ammonia, or alumina and sesquioxide of chromium. By 
artificial management, namely, by transferring the crystal successively te^ 
different solutions, we may have these isomorphous and mutually replacing 
compounds distnbuted in different layers upon the same crystal. 

For these reasons, mixtures of isomorphous salts can never be separated 
by crystallization, unless their difference of solubility is very great. A 
mixed solution of sulphate of protoxide of iron and sulphate of copper, iso- 
morphous salts, yields on evaporation crystals containing both iron and 
copper. But if before evaporation the protoxide of iron be converted into 
sesquioxide by chlorine or other means, then the crystals obtained are free 
from iron, except that of the mother-liquor which wets them. The salt of 
sesquioxide of iron is no longer isomorphous with the copper salt, and easily 
separates from the latter. 

When compounds are thus found to correspond, it is inferred that, the ele- 
ments composing them are also isomorphous. Thus, the metals magnesium, 
zinc, iron, and copper are presumed to be isomorphous ; arsenic and phos- 
phorus should present the same crystalline form, because arsenic and phos- 
phoric acids give rise to combinations which agree most completely in figure 
and constitution. The chlorides, iodides, bromides, and fluorides, agree, 
whenever they can be observed, in the most perfect manner ; hence the ele- 
ments themselves are believed to be also isomorphous. Unfortunately, for 
obvious reasons, it is very difficult to observe the crystalline figure of most 
of the elementary bodies, and this difficulty is increased by the frequent di- 
morphism they exhibit. 

Absolute identity of value in the angles of crystals is not always exhibited 
by isomorphous substances. In other words, small variations often occur 
in the magnitude of the angles of crystals of compounds which in all other 
respects show the closest isomorphic relations. This should occasion no 
surprise, as there are reasons why such variations may be expected, the 
chief perhaps being the unequal effects of expansion by heat, by which the 
angles of the same crystals are changed by alteration of temperature. A 
good example is found in the case of the carbonates of lime, magnesia, man- 
ganese, iron, and zinc, which are found native crystallized in the form of 
obtuse rhombohedra (fig. 143, 3) not distinguishable from each other by the 
eye, or even by the common goniometer, but showing small diflferences when 
examined by the more accurate instrument of Dr. Wollaston. These com- 
pounds are isomorphous, and the measurements of the obtuse angles of theix 
V rhombohedra as follows : — 



Carbonate of lime lOe^* 5^ 

" magnesia 107 » 26^ 

" protox. manganese 107° 2(K 

" " iron 107° 

" zinc 107040^ 

Anomalies in the composition of yarioas earthy minerals which formerly 
threw much obscurity upon their chemical nature, have been in great mea- 
Bore expluned by these discoyeries. 

Specimens of the same mineral from different localities were found to 
afford Tery discordant results on analysis. But the proof once ^ven of the 
extent to which substitution of isomorphous bodies may go without destruc- 
tion of what may be called the primitiye type of the compound, these diffi- 
enlties yaoish. 

Another benefit conferred on science by the discoyeries in question, is 
tli&t 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 ail the elementary bodies become known, — at present 
ooly a certaia number have been traced. 

Decision of a doubtM point concerning the constitution^ of a compound 
may now and then be yery satisfactorily made by a reference to this same 
law of isomorphism. Thus, alumina, the only known oxide of alumioium, 
is judged to be a sesquioxide of the metal from its relation to sesquioxide 
of iron, which is certainly so ; the black oxide of copper is inferred to be 
really the protoxide, although it contains twice as much oxygen as the red 
oxide, because it is isomorphous with magnesia and zinc, both undoubted 

The subjoined table will serve to convey some idea of the most important 
families of isomorphous elements ; it is taken from Professor Graham's sys- 
tematic work,* to which the pupil is referred for fuller details on this inte- 
resting subject. 

Isomorphoua Oroups. 

(1.) (8.) (7.) 

Sulphur Barium Sodium 

Selenium Strontium Silver 

Tellurium. Lead. Gold 

(2.) (4.) Potassium 

Magnesium Tin Ammonium, 

Calcium Titanium. (8.) 

Manganese (6.) Chlorine 

Iron Platinum Iodine 

Cobalt Iridium Bromine 

Nickel Osmium. Fluorine 

Zinc (6.) Cyanogen, 

Cadmium Tungsten (9.) 

Copper Molybdenum Phosphorus 

Chromium TantaluuL Arsenic 

Aluminium Antimony 

Beryllium Bismuth. , 


There is a law concerning the formation of double salts which may now 
be mentioned ; the two bases are never taken from the same isomorphous 

* Second edition, p. 149. 


family. Sulphate of copper or of zinc may unite in this manner with sulphate 
of soda or potassa, but not with sulphate of iron or cobalt ; chloride of mag- 
nesium may combine with chloride of ammonium, but not with chloride of 
zinc or nickel, &c. It will be seen hereafter that this is a matter of some 
importance in the theory of the organic acids. 

Polybasic Adds. — There is a particular class of acids in which a departure 
occurs from the law of neutrality formerly described ; these are aeids re- 
quiring two or more equiyalents 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 yery frequently occur. 

Phosphoric acid is capable of existing in three different states or modifica- 
tions, forming three separate classes of salts which differ eompletely in pro- 
perties and constitution. They are distinguished by the names trihamj 
biba^iCf 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 
lilter, and well washed. While still moist, this compound is suspended in 
distilled water, and an excess of sulphuretted hydrogen gas passed into it. 
The protoxide of lead is converted into sulphide, which subsides as a black 
insoluble precipitate, while phosphoric acid remains in solution, and is easily 
deprived of the residual sulphuretted hydrogen by a gentle heat. 

The soda-salt employed in this experiment contains the tribasic modifica- 
tion of phosphoric acid ; of the three equivalents of base, two consist of soda 
and one of water ; when mixed with solution of lead, a tribasic phosphate of 
the oxide of that metal falls, which when decomposed by sulphuretted hydro- 
gen, yields sulphide of lead and a hydrate of the acid containing three 
equivalents of water in intimate combination. 

r 2 eq. soda — -7- 2 eq. acetate of soda. 

Phosphate J 1 »» water ~7y^ " hydrated acetic acid. 

Of soda I 1 ,, phos-\ 

phoricacid / ^ 
3 eq. acetate f2eq.a.etica^^ 

^^ ^^^^ 1 3 ;; oxide of lead ^^ 1 eq tribasic phosphate 

eq. tribasic phos- J 8 „ oxygen 
phate of lead 1 ^ »» phos- ) 

of lead. 
3 eq. lead -7 8 eq. sulphide of lead. 

3 eq. snlphuiltted \ 3 eq. sulphur^ ""**v^v 

hydrogen 1 8 „ hydrogen -^ 1 eq. tribasic hydrate of 

phosphoric acid. 

The solution of tribasic hydrate may be concentrated by evaporation w 
vacuo over sulphuric acid until it crystallizes in thin deliquescent plates. 
The same compound in beautiful crystals, resembling those of «ugar-candy, 
has been accidentally formed.* It undergoes no change by boiling with 
water, but when heated alone to 400° (204°-4C) loses some of its combined 
water, and becomes converted into a mixture of the bibasic and monobasic 
hydrates. At a red heat it becomes entirely changed to monohydrate, whichi 
at a still higher temperature, sublimes. 

Tribasic phosphoric acid is characterized by the yellow insoluble salt it 
forms with protoxide of silver. 

/ P61igot, Ann. China, et Phys. IxxiU. 280. 


Bibasie Fhotphoric Add, or Pyrcphotphoric Aad. — When oommon phos- 
phate of soda, containing 

2NaO, HO, PO5+24HO, 
is gently heated, the 24 equiyalents 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 
bibasie modification. If the altered salt be now dissolved in water, this new 
compound, the bibasie phosphate of soda, crystallizes out When mixed with 
Bolution of acetate of lead, bibasie pfaosphate of lead is thrown down, which, 
decomposed by sulphuretted hydrogen, furnishes a solution of the bibasio 
hydrate. This solution may be preserved without change at common tem- 
peratures, but when heated, an equivalent of water is taken up, and tho 
substance passes back again into the tribasic modification. 

Crystals of this hydrate have also been observed by M. P^ligot. Their 
production wa.s accidental. The bibasie phosphates soluble in water give a 
vhite precipitate with solution of silver. 

Monobasic, or Metaphosphorie Acid. — When common tribasic phosphate of 
Boda is mixed with solution of tribasic hydrate of phosphoric acid, and ex- 
posed, after proper concentration, to a low temperature, prismatic crystals 
are obtained, ^hich consist of a phosphate of soda having two equivalents of 
basic water. 

NaO, 2H0, P0,-|-2H0. 

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 eold water, precipitated with ace- 
tate of lead, and the lead-salt, as before, decomposed by sulphuretted hy- 

The solutioii of the monobasic hydrate is decomposed rapidly by heat, 
becoming conTerted into tribasic hydrate. It possesses the property of co- 
agnlating albumen, which is not ei^oyed by either of the preceding modifi- 
cations. MoDobasic alkaline phosphates precipitate nitrate of silver white. 

The gladid phosphoric acid of pharmacy is, when pure, hydrate of mono- 
basic phosphoric acid : it contains HO, PO^ . 

Anhydrous phosphoric acid, prepared by burning phosphorus in dry air, 
when thrown into water, forms a variable mixture of the three hydrates. 
When heated, a solution of the tribasic hydrate alone remains.* See also 
phosphates of soda. 

Binary Theory of SalU. — ^The great resemblance in properties between the 
two classes of saline compounds, theu haloid and oxy-salts, has very naturally 
led to the supposition that both might possibly be alike constituted, and that 
the latter, instead of being considered compounds of an oxide and an acid, 
mrght with greater propriety be considered to contain a metal in union with 
a compound salt-radical, having the chemical relations of chlorine and 
iodine. ^ 

On this supposition sulphate and nitrate of potassa will be constituted in 
the same manner as chloride of potassium, the compound radical replacing 
the simple one. 

Old vievr. New view. 


KO-l-NOfi K-f.NO« 

* The three modifications of phosphoric acid possess properties so dissimilar that thej 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 adds 
travd wudtered, a tribaflic salt giving at the posittve electrode a solution of common pho»> 
pfaorie add; a bibasie salt, one of pyrophosphoric acid ; and a monobasic salt, one of met»> 
phosphoric acid (Professor Daniell and Dr. Miller, Phil. Trans, for ISU, p. 1). 


Hydrated salphuric acid will be, like hydrocMoric aoid, a b^Khnde of a salt- 

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 
ease of hydrochloric acid, water and a haloid salt are pi'bduced. All acids 
must be, in fact, hydrogen acids, and all salts haloid salts, with either simple 
or compound radicals. 

This simple and beautiful theory is not by any means new ; it was sug- 
gested by Davy, who proposed to consider hydrogen as the acidifying prin- 
ciple in the common acids, and lately reyived and very happily illustrated by 
liebig. It is supported by a good deal of evidence derived from various 
sources, and has received great help from a series of exceedingly interesting 
experiments on the electrolysis of saline solutions, by the late Professor 
Daniell.* The necessity of creating a great number of non-insoluble com- 
pounds is often urged as an objection to the new view ; but the same objec- 
tion applies to the old mode of considering the subject Hyposulphurous 
acid and hyposulphurio add are unknown in their tree states. The com- 
pounds SgOg and S2O4 are as hypothetical as the substances S^O, and S.O,. 
The same remark applies to almost every one of the organic acias ; and, what 
is well worthy of notice, those acids which, like BUlphiiric, phosphoric, and 
carbonic acids, may be obtained in a separate state, are desUtvie of all acid 
properties so long a* the anhydrous condition is retained. 

Some very interesting observations have been published lately by M. Gep- 
hardt,* which are likely to hasten a change in the notation of acids generally. 

It has been pointed out that sulphuric and nitric acid, which, according 
to the theory of oxygen acids, are considered as compounds respectively of 
teroxide of sulphur and pentoxide of nitrogen with water, S03,H0, and NOg, 
HO, may be considered likewise as hydrogen acids, analogoua to hydro- 
chloric and hydrocyanic add. 

Hydrochloric acid HCl 

Hydrocyanic acid HCvN 

Sulphuric acid ") HSO 

Hydrosulphanic acid / ' "' * 

Nitric acid "^ ^ HNO«. 

Hydronitranic acid.. / " 

Among the many facts which have been adduced in favour of the theory 
of oxygen acids, the preparation of the so-called anhydrous acids SO, and 
N0» (see pages 124 end 136) has always been considered as powerful props. 
On the other hand, the followers of the tlieory of hydrogen acids have inva- 
riably called attention to the scarcity of the so-called anhydrous acids, and 
especially to the fact that, with a few exceptions, they are entirely wanting 
in Organic Chemistry. The researches of M. Gerhardt just referred to, 
have furnished the means of making the anhydrous organic aoids ; but the 
circumstances under which they are produced exhibit these substances in a 
perfectly new light, and prove that they stand in a very different relation to 
the hydrated acids from what is generally assumed. 

If dry benzoate of soda be heated with chloride of benzoyl (see page 399) 
to a temperature of 266° (130oC), a limpid liquid is formed, which is de- 

* See Danieirs Introduction to Chemical Pliilosophy, 2d edition, p. 538. 

* Cbem. Soc. Quar. Jour. v. 127. 


composed with depositioa of chloride of sodium wlien heated a few degrees 
higher; there is formed, at the same time, a white crystaUine product, 
which has exactly the composition of anhydrous benzoic add, for it contains 
CitEfi, or BsO, if we represent Ci«HkOi by Bz. The decomposition which 
takes place is represented by the following equation :— 

The new substance crystallizes in beautiful oblique prisms, fusible at 90<'*4 
(33°C), and volatile without decomposition. It is insoluble in water, but 
readily dissolves in alcohol and ether ; these eolutiona are perfectly neutral to 
test-paper. Cold water has not the slightest effect upon this body ; by boil- 
ing water it is gradually converted into benzoic add. This change immedi- 
ately occurs with boiling solutions of the alkalis. Boiling alcohol converts 
it into benzoate of ethyl. From the mode of formation, it is evident that 
the substance in question cannot be regarded as anhydrous benzoic acid, al- 
tkoagh it agrees with that substance in composition. It is obviously a sort 
of a salt, benzoate of benzoyl, or benzoic acid in which one equivalent of hy- 
drogen is replaced by benzoyl. 

Benzoic acid BzO,HO 

New compound BzO,BzO. 

If an additional support for this view was required, it would be found in 
the circumstance that chloride of benzoyl acts in exactly the same manner 
upon cumate, cinnamate, and salicylate of soda, a series of compounds be- 
ing produced which are perfectly analogous to the preceding substance, but 
contain in the place of benzoyl cuminyl, CaoHuOsssCm ; cinnamyl, CuHfO'zs 
Ci; or talicyl, Ct4H804=sSl. 

Benzoic add BzO,HO 

Benzoate of benzoyl BzO,BzO 

Benzoate of cuminyl BzO,CmO 

Benzoate of dnnamyl BzO,CiO 

Benzoate of salicyl BzO,S10. 

These substances are for the most part fusible, odourless solids, or oils 
heatier than water. With the alkalis they yield a mixture of the acids from 
which they have, been produced. Several are not volatile without decompo- 

A perfectly similar series of substances has been obtained with acetic acid. 
The acetic chloride, ClCfHsOa, corresponding to chloride of benzoyl, is formed 
in a most interesting process, namely, by the action of pentachloride of 
phosphorus (see page 168) upon acetate of soda, when chloride of sodium, 
ozichloride of phosphorus, PClaO„ and chloride of acetetyl^ are formed. 


The action of chloride of acetetyl upon dry acetate of soda gives rise to 

the formation of an oily liquid, which has the composition of anhydrous 

acetic add, C*H,0„ but which in reality is acetate of ltcetetyl=C4H30j, 

C^O^O." This liquid boils at 278°-6 (137®C) ; it is not miscible at once 

* Aeeie^l in order to dirtlngviah it from aoeijl, G^Hs. 

* This formula requires an equivalent of oxygen to produce two equivalents of anhydnua 


In the leaetlon beiwveii aoetate of soda and chloride of acetyle, an equivalent of oxygen from 
fbe sods eonverta the acetyl into anhydrous acetic add with the ibrmaUon of dUoride of 
ndiuffi. _ 


Awtetyla here spoken o^ is firom its composition acetous or aldehydie add. — B. B. ; 


irith cold water, but only after oontinued agitation. Hot water dissolves it 
at once with formation of acetic acid. 

The application to inorganic compounds of the method, by means of which 
these substances are produced, promises in fHiture very important materials 
for the elaboration of several of the most interesting questions with which 
chemists are engaged at the present moment. 

The general application of the binary theory still presents a few difficul- 
ties. But it is very probable that the progress of discovery will ultimately 
lead to its universal adoption, which would greatly simplify many parts of 
the science. One great inconvenience will be the change of nomenclature 


MadU of the Alkalis. 
Potassium, Lithium, 

Sodium, Ammonium. 1 

Metals of the Alkaline Earths, 
Barium, Calcium, 

Strontium, Magnesium. 

Metals of the Earths Proper, 
Aluminium, Korium, 

Beryllium, Thorium, 

Yttrium, Cerium, 

Erbium, Lantanum, 

Terbium, Didymium. 


OxtdabU Metals proper, whose (hcides form powerfid Eases, 
Manganese, Zinc, 

Iron, Cadmium, 

Chromium, Bismuth, 

Nickel, Lead, 

Cobalt, . Uranium. 


Ozidable Metals Proper, whose Oxides form weak Eases, or Adds, 
Vanadium, Titanium, 

Tungsten, Tin, 

Molybdenum, Antimony, 

Tantalum, Arsenic, 

Niobium, Tellurium, 

Pelopium, Osmium. 

Metals Proper, whose Oxides are reduced by Heat; Noble Metals. 
Gold, Palladium, 
Mercury, Iridium, 
Silver, Ruthenium, 
Platinum, Rhodium. 
— . ^ _^ 

• This hypothetical Bubstance is merely placed with the metals for the sake of ooavenlenoe. 
•■ will he apparent in the sequeL ^ 




Potassium was discovered by Sir H. Davy in 1807, who obtained it la 
Tery small quantity by exposing a piece of moistened hydrate of potassa to 
the action of a powerful voltaic battery, the alkali being placed between a 
pair of platinum plates put into connection with the apparatus. Processes 
hftTO since been devised for obtaining this curious metal in almost any 
qiuntity that can be desired. 

An intimate mixture of carbonate of potassa and charcoal is prepared by 
calcining, in a covered iron pot, the crude tartar of commerce ; when cold, 
it is rubbed to powder, mixed with one-tenth part of charcoal in small lumps, 
and quickly transferred to a retort of stout hammered iron ; the latter may 
be one of ihe iron bottles in which mercury is imported, a short and some- 
iriiat 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 
nniform degree of heat, approaching to whiteness. A copper receiver, 
divided in the centre by a diaphragm, is connected to the iron pipe, and kept 
cool by the application of ice, while the receiver itself is partly filled with 
naphtha or rock-oil, in which the potassium is to be preserved. Arrange- 
ments being thus completed, the fire is gradually raised until the requisite 
temperature is reached, when decomposition of the alkali by the charcoal 
commences, carbonic oxide gas is abundantly disengaged, and potassium 
distils over, and falls in large melted drops into the liquid. The pieces of 
charcoal are introduced for the purpose of absorbing the melted carbonate 
of potassa, and preventing its separation from the finely divided carbonaceous 

If the potassium be wanted absolutely pure, it must be afterwards re-dis- 
tilled in an iron retort, into which some naphtha has been put, that its 
Tapoor may expel the air, and prevent the oxidation of the metal. 

Potassium is a brilliant white metal, with a high degree of lustre ; at the 
common temperature of the air it is soft, and may be easily cut with a knife, 
but at 32° (0°C) it is brittle and crystalline. It melts completely at ISG® 
(57° -770), and distils at a low red heat. The density of this remarkable 
metal is only 0-866, water being unity. 

Exposed to the air, potassium oxidizes instantly, a tarnish covering the 
surface of the metal, which quickly thickens to a crust of caustic potassa. 
Thrown upon water, it takes fire spontaneously, and burns with a beautiful 
purple flame, yielding an alkaline solution. When brought into contact with 
a little water in 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 89 ; and its symbol^ K. 

There are two compounds of this metal with oxygen, — potassa and teroiide 
of potassium. 

Potassa, Potash, or Pbotoxipb of Potassium, KO, is produced when 
potassium is heated in dry air ; the metal burns, and becomes entirely con- « 
yerted into a volatile, fusible, white substance, which is anhydrous potassa. 
Moistened with water, it evoWes great heat, and forms the hydrate. 

The hydrate of potassa, EO, HO, is a very important substance, 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 con- 
venient : — 10 parts of carbonate of potassa are dissolved in 100 parts of 
water, and heated to ebullition in a clean untinned iron, or still better, alver 
vessel ; 8 parts of good quicklime are meanwhile slaked in a covered basiD, 
and the resulting hydrate of lime added, little by little, to the boiling solu- 
tion of carbonate, with frequent stirring. When all the lime has been in- 
troduced, the mixture is suffered to boil a few minutes, and then remoyed 
from the fire, and covered up. In the course of a very short Ume, the solu- 
tion 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 potassa be 
dilute, otherwise the decomposition becomes imperfect; the proportion of 
lime recommended is much greater than that required by theory, but it is 
always proper to have an excess. 

The solution of hydrate, or, as it is commonly called, caustic potassa, may 
be concentrated by quick evaporation in the iron or silver vessel to any 
desired extent ; when heated until vapour of water ceases to be disengaged, 
and then suffered to cool, it furnishes the solid hydrate, containing single 
equivalents of potassa and water. 

Pure hydrate of potassa is a white solid substance, very deliquescent and 
soluble in water; alcohol also dissolves it freely, which is the case with com^ 
paratively few of the compounds of this base ; the solid hydrate of com- 
merce, which is very impure, may thus be purified. The solution of this 
substance possesses, in the very highest degree, the properties termed alka- 
line ; it restores the blue colour to litmus which has been reddened by an 
acid; neutralizes completely the most powerful acids; has a naseous and 
peculiar taste, and dissolves the skin, and many other organic matters, when 
the latter are subjected to its action. It is constantly used by surgeons as a 
cautery, being moulded into little sticks for that purpose. 

Hydrate of potassa, both in the solid state and in solution, rapidly absorbs 
carbonic acid from the air ; hence it must be kept in closely stopped bditles. 
"When imperfectly prepared, or partially altered by exposure, it efferroscea 
with an acid. 

The water in this compound cannot be displaced by heat, the hydrate vo- 
latilizing as a whole at a very high temperature. 

The following table of the densities and value in real alkali of different 
solutions of hydrate of potassa is given on the authority of Dr. Dalton. 


tage of • 



Percentagi ■)f 
real alk^ L 








119 7.... 













Teroxide 09 POTASBitTM, KO3. — This is ka orangd-yellow fosible sabstance, 
geoerated when potassiam is burned in excess of dry oxygen gas, and also 
formed, to a small extent, when hydrate of potassa is long exposed, in a 
meltM state, to the air. When nitre is decomposed by a strong heat, per- 
oxide of potassium is also produced. It is decomposed by water into potassa, 
Thich imites with the latter, and into oxygen gas. 

Carbonate of potassa, KO, CO^+^HO. — Salts of potassa containing a 
vegetable acid are of constant occurrence in plants, where they perform im- 
portant, but not yet perfectly understood, functions in the economy of those 
beings. The potassa is derived from the soil, which, when capable of sup- 
porting vegetable life, always contains that substance. When plants are 
burned, the organic acids are destroyed, and the potassa left in the state of 

It is by these ipdirect means that carbonate, and, in fact, nearly all the 
salts of potassa, are obtained ; the great natural depository of the alkali is 
the felspar of granitic and other unstratified. rocks, where it is combined 
irith silica, and in an insoluble state. Its extraction thence is attended with 
too many difficulties to be attempted on the large scale ; but when these 
rocks disintegrate into soils, and the alkali acquires solubility, it is gradually 
taken np by plants, and accumulates in their substance in a condition highly 
favourable to its subsequent applications. 

Potassa-salts are always most abundant in the green and tender parts of 
plants, as may be expected, since from these evaporation of nearly pure 
water takes place to a large extent ; the solid timber of forest trees contains 
comparatively little. 

In preparing the salt on an extensive scale, the ashes are subjected to a 
process called lixiviation ; they are put into a large cask or tun, having an 
aperture near the bottom, stopped by a plug, and a quantity of water is 
added. After some hours the Uquid is drawn off, and more water added, 
that the whole of the soluble matter may be removed. The weakest solutions 
are poared upon fresh quantities of ash, in place of water. The solutions 
are ihen evaporated to dryness, and the residue calcined, to remove a little 
brown orgauio matter ; the product is the crude potash or pearlash of com- 
merce, of which very large quantities are obtained from Bussia and America. 
This salt is very impure; it contains silicate and sulphate of potassa, 
chloride of potassium, &c. 

■ The purified carbonate of potassa of pharmacy is prepared from the crude 
article, by adding nn equal weight Qf cold water, agitating, and filtering; 
most of the foreign salts are, from their inferior degree of solubility, left 
behind. The solution is then boiled down to a very small bulk, and suffered 
to cool, when the carbonate separates in small crystals containing 2 equiv. 
of water, which are drained from the mother-liquor, and then dried in a stove. 
A still purer salt may be obtained by exposing to a red-heat purified 
cream of tartar (acid tartrate of potassa), and separating the carbonate by 
solution in water and crystallization, or evaporation to dryness. 

Carbonate of potassa is extremely deliquescent, and soluble in less than 
its own weight of water ; the solution is highly alkaline to test-paper. It is 
insoluble in alcohol. By heat the water of crystallization is driven off, and 
by a temperature of full ignition the salt is fused, but not otherwise changed. 
This substance is largely used in the arts, and is a ^compound of great im- 

Bicarbonate op potassa, KO, CO2-4-HO, CO,. — When a stream of car- 
bonic acid gas is passed through a cola solution of carbonate of potassa, the 
gas is rapidly absorbed, and a white, crystalline, and less soluble substance 
separated, which is the new compound. It is collected, pressed, re-dissolved 
in warm water, and the solution left to crystallize. 


' Bicarbonate of potassa is muoh 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, deriye their form from a right rhombic prism ; they are decomposed 
by heat, water and carbonic acid being extricated, and simple carbonate left 

NiTEATB OP potassa; nit&b; saltpbtek, KO, NO5. — This important 
compound is a natural product, being disengaged by a kind of efflorescence 
from the surface of the soil in certain dry and hot countries, v It may also be 
produced by artificial means, namely, by the oxidation of ammonia in pres- 
ence of a powerful base. 

In France, large quantities of artificial nitre are prepared by mixing animal 
refuse of all kinds with 0' t mortar or hydrate of Ibne and earth, and placing 
the mixture in heaps, pr/'iCcted ft-om the rain by a roof, but freely exposed 
to the air. From time to time the heaps are watered with putrid urine, and 
the mass turned over, to expose fresh surfaces to the air. When much salt 
has been formed, the mixture is lixiviated, and the solution, which contains 
nitrate of lime, mixed with carbonate of potassa ; carbonate of lime is formed, 
and the nitric acid transferred to the alkali. The filtered solution is then 
made to crystallize, and the crystals purified by re-solution and crystalliza- 
tion seyeral times repeated. 

All the nitre used in this country comes from the East Indies ; it is dis- 
solved in water, a little carbonate of potassa added to precipitate lime, and 
then the salt purified as above. 

Nitrate of potassa crystallizes in anhydrous six-sided prisms, with dihedral 
summits; it is soluble in 7 parts of water at 60® (15® 'SC), and in its own 
weight of boiling water. Its taste is saline and cooling, and it is withoojb 
action on vegetable colours. At a temperature below redness it melts, and 
by a strong heat is completely decomposed. 

' When thrown on the surface of many metals in a state of fusion, or when 
mixed with combustible matter and heated, rapid oxidation ensues, at the 
expense of the i oxygen of the nitric acid. Examples of such mixtures are 
found in common gunpowder, and in nearly all pyrotechnic oompositions, 
which burn in this manner independently of the oxygen of the air, and even 
under water. Gunpowder is made by very intimately mixing together nitrate 
of potassa, charcoal, and sulphur, in proportions which approach 1 eq. nitre, 
8 eq. carbon, and 1 eq. sulphur. 

These quantities give, reckoned to 100 parts, and compared with the pro- 
portions used in the manufacture of the English government powder,^ the 
following results :— 

Theory. Proportions in praotkw. 

Nitrate of potassa 74-8 75 

Charcoal 13-3 15 

Sulphur 11-9 10 

100- 100 

The nitre is rendered very pure by the means already mentioned, freed 
from water by fusion, and ground to fine powder : the sulphur and charcoal, 
the latter being made from light wood, as dogwood or elder, are also finely 
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, 

> Dr. M'CuUocb, Ency. Brtt. 


and placed in Bteres made of perforated Yellnxn, moyed by machineiT; each 
containing, in addition, a round piece of heavy wood. The grains of powder 
broken off by attrition fall through the holes in the skin, and are easily sepa- 
rated from the dust by sifting. The powder is, lastly, dried by exposure t<» 
Bteam-heat, and sometimes glazed or polished by agitation in a kind of cask 
mounted on an axis. 

When gunpowder is fired, the oxygen of the nitrate of potassa is trans 
fcrred to the carbon, forming carbonic acid ; the sulphur combines with the 
potassium, and t^e nitrogen is set free. The large volume of gas thus pro* 
diiced, and still farther expanded by the very exalted temperature, suffi« 
oiently accounts for the explosive effects. 

Sulphate of potassa, KO,SOs. — The acid residue left in the retort when 
nitric acid is prepared is dissolved in water, and neutralized with crude car- 
bonate of potassa. The solution furnishes, on cooling, hard transparent 
crystals of the neutral sulphate, which may be re-dissolved in boiling water, 
and re-crystallized. 

Sulphate of potassa is soluble in about 10 parts of cold, a&d in a much 
smaller quantity of boiling water ; it has a bitter taste, and is neutral to 
test-paper. The crystals much resemble those of quartz in figure and ap 
pearaace^ they are anhydrous, and decrepitate when suddenly heated, 
whieh is often the case with salts containing no water of crystallization. 
They are quite insoluble in alcohol. 

BisuLPHATS OF POTASSA, KOjSO, -f- H0,S03. The neutral sulphate in 
powder is mixed 'With half its weight of oil of vitriol, and the whole evapo- 
rated quite to dryness in a platinum vessel, placed under a chimney ; the 
fused salt is dissolved in hot water, and left to crystallize. The crystals 
have the figure of flattened rhombic prisms, and are much more soluble than 
the neutral salt, requiring only twice their weight of water at 60° (16° -SC), 
and less than half that quantity at 212° (100°C). The solution has a sour 
taste and strong acid reaction. 

BrsiTLPHATB OF POTASSA, ANHYDROUS, K0,2S0g. — Equal weights of neutral 
solphate of potassa and oil of vitriol are dissolved in a small quantity of 
warm distilled water, and set aside to cool. The anhydrous sulphate ciys- 
tallizes out in long delicate needles, which if left several days in the mother- 
liquor disappear, and give place to crystals of the ordinary hydrated bisul- 
phate above described. This salt is decomposed by a large quantity of 

Sbsquisitlphatb of. POTASSA, 2(KO,S03) -f- HCSOy — ^A salt, crytallizing 
in fine needles resembling those of asbestos, and having the compositiou 
stated, was obtained by Mr. Phillips from the nitric acid residue. M. Jacque- 
Lain was unsucoessfulin his attempts to reproduce ^his compound. 

Chlorate of potassa, KOjClOg. — The theory of the production of chlorio 
acid, by the action of chlorine gas on a solution of caustic potassa, has been 
already described (p. 145). 

Cl))orine gas is conducted by a wide tube into a strong and warm solution 
of carbonate of potassa, until absorption of the gas ceases. The liquid is, 
if necessary, evaporated, and then allowed to cool, in order that the slightly 
soluble chlorate may crystallize out. The mother-liquid affords a second 
crop of crystals, but they are much more contaminated by chloride of potaa- 
sium. It may be purified by one or two re-crystallizations. 

Chlorate of potassa is soluble in about 20 parts of cold, and 2 of boilinjr 
water ; the crystals are anhydrous, flat, and tabular ; in taste it somewhat 
resembles nitre. Heated, it disengages oxygen gas from both acid and base^ 
and leaves chloride of potassium. By arresting the decomposition when the 

« Jacqaelain, Ann. Chimr et Phys. vol. vii. p. 311. 


eroliitioii of gas begins, and re-dissoWing the salt, perohloiite of potassa 
and chloride of potassium may be obtained. 

This salt deflagrates yiolently with combustible matter, explosion often 
occarring by friction or blows. When about one grain weight of chlorate 
and an equal quantity of sulphur are rubbed in a mortar, tiie mixture ex- 
plodes with a loud report ; hence it cannot be used in the preparation of gun- 
powder instead of nitrate of potassa. Chlorate of potassa is now a large 
article of commerce, being employed, together with phosphorus, in making 
instantaneous tight matches. 

Pbbohlosats of potassa, EOjClOy. — This has been already noticed 
under the head of perchloric acid. It is best prepared by projecting 
powdered chlorate of potassa into warm nitric acid, when the chloric acid is 
resoWed into perchloric acid, chlorine, and oxygen gases. The salt is 
separated by crystallization from the nitrate. Perchlorate of potassa is a 
very feebly soluble salt; it requires 56 parts of cold water, but is more freely 
taken up at a boiling heat. The crystals are small, and have the figure of 
an octahedron, with square base. It is decomposed by heat, in. the same 
manner as chlorate of potassa. 

Sulphides or potassium. — There are not less than fiye or six distinct 
compounds of potassium and sulphur, of which, howeyer, only three are of 
eu£Scient importance to be noticed here ; these are the compounds, contain- 
ing KS, ES,, and ESg. 

Simple or protontfphide of potassium, is formed by directly combining the 
metal with sulphur, or by reducing sulphate of potassa at a red-heat by hy- 
drogen or charcoal powder. Another method is to. take a strong solution of 
hydrate of potassa, and after dividing it into two equal portions, saturate 
the one with sulphuretted hydrogen gas, and then add the remainder. The 
whole is then evaporated to dryness in a retort, and the residue fused. 

The protosulphide is a crystalline cinnabar-red mass, very soluble in water. 
The solution has an exceedingly 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 sulphides of hydrogen, carbon, arsenic, &c., forming 
orystalliiable saline compounds. One of these, ES-f-HS, is produced whea 
hydrate of potassa is saturated with sulphuretted hydrogen, as before men- 

The higher sulphides are obtained by fusing the protosulphide with dif- 
ferent proportions of sulphur. They are soluble in water, and decomposed 
by acids, in the same manner as the foregoing compound, with this addition, 
that the excess of sulphur is precipitated as a fine white powder. 

Hepar sulpkuris is a name given to a brownish substance, sometimes used 
in medicine, made by fusing together different proportions of carbonate of 
potassa and sulphur. It is a variable mixture of ^e two higher sulphides 
with hyposulphite and sulphate of potassa. 

When equal parts of sulphur and dry carbonate of potassa are melted to- 
gether at a temperature not exceeding 482o (250<'C.), the decomposition of 
the salt is quite complete, and all the carbonic acid is expelled. The fused 
mass dissolves in water, with the exception of a little mechanically-mixed 
sulphur, with dark brown colour, and the solution is found to contain nothing 
besides pentasulphide of potassium and hyposulphite of potassa. 

r 2 eq. potassium 2 eq. of pentasulphide of po- 

8 eq. potassa -j 2 eq. oxygen^^ ^^^^"""^ slum, 
. potassa^ 


eq. hyposulphite of po* 


When the mixture haa been expoaed to a temperature appreMhlng that 
of ignition, it is fonnd on the contrary to contain sulphate oi potassa, arising 
from the decomposition of the hyposulphite which then occurs. 

4 cq. hyposul- 
phite of po- - 

4 eq. 

4 eq. hy- 
posulph. - 

1 eq. potassium 
1 eq. oxygen 
3 eq. potassa^ 
5 eq. sulphur 
3 eq. sulphur. 
8 eq. oxygen 

1 eq. pentasulphide 
of potassium. 

8 eq. sulphate of 

. From hoth these mixtures the pentasulphide of~potassium may be ex- 
tracted by alcohol, in which it dissolves. 

When the carbonate is fused with half its weight of sulphur only, then the 
tersalphide, ESg, is produced instead of that above indicated ; 8 eq. of po- 
tassa and 8 eq. of sulphur containing the elements of 2 eq. sulphide and 1 
eq. hyposulphite. 

The effects described happen in the same manner when hydrate of potassa 
is substituted for the carbonate ; and also, when a solution of the hydrate is 
boiled with sulphur, a mixture of sulphide and hyposulphite always results. 

Cetloridb of potassium, KCl. — This salt is obtained in large quantity in 
the manufacture of chlorate of potassa ; it is easily purified from any portions 
of the latter by exposure to a dull red-heat. It is also contained in kelp, 
and is separated for the use of the alum-maker. 

Chloride of potassium closely resembles common salt in appearance, as- 
suming, like that substance, the cubic form of crystallization. The crystals 
dissolve in three parts of cold, and in a much less quantity of boiling water ; 
they are anhydrous, have a simple saline taste, with slight bitterness, and 
fuse when exiposed to a red-heat. Chloride of potassium is volatilized by a 
very high temperature. 

Iodide op potassium, KI. — There are two different methods of preparing 
this important medicinal compound. 

(1.) When iodine is added to a strong solution of caustic potassa free from 
carbonate, it is dissolved in large quantity, forming a colourless solution 
containing iodide of potassium and iodate of potassa ; the reaction is the 
same as in tlie analogous case with (Chlorine. When the solution begins to 
he permanently coloured by the iodine, it is evaporated to dryness, and cau- 
tiously heated red-hot, by which the iodate of potassa is entirely converted 
into iodide of potassium. The mass is then dissolved in water, and after fil- 
tration, made to crystallize. 

(2.) Iodine, water, and iron-filings or scraps of zinc, are placed in a warm 
situation until the combination is complete, and the solution colourless. The 
resulting iodide of iron or zinc is then filtered, and exactly decomposed with 
solution of pure carbonate of potassa, great care being taken to avoid excess 
of the latter. Iodide of potassium and carbonate of protoxide of iron, or 
zinc, are obtained; the former is separated by filtration, and evaporated 
until the solution is suflSciently concentrated to crystallize on cooling, the 
washings of the filter being added to avoid loss. 

( Iodine ■ --^ Iodide of potassium. 

' \ Iron- 

Iodide of iron . 

f Potassium 

Carbonate of potassa J ^°**^** 1 Oxygen 
( Carbonic acid- 

Carbonate of protoxide 
of iron. 

The second method is, on the whole, to be preferred. 

224 BODIUM. 

Iodide of potassium crystalliaes in cubes, irhicli are often, from 'some un- 
explained cause, milk-white and opaque; they are anhydrous, and fuse 
readily when heated. The salt is very soluble in water, but not deliquescent, 
when pure, in a moderately dry atmosphere ; it is dissolved by alcohol. 

Solution of iodide of potassium, like those of all the soluble iodides, dis- 
solves a large quantity of free iodine, forming a deep brown liquid, not de- 
composed by water. ^ 

Bromide of potassium, KBr. — This compound may be obtained by pro- 
oessea exactly similar to those Just described, substituting bromine for the 
iodine. It is a colourless and very soluble salt, quite indistinguishable in 
appearance and general characters from the iodide. 

The salts of potassa are colourless, when not associated with a coloured 
metallic oxide or acid. They are 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 
potassa-salt, gives, after some time, a white, crystalline precipitate of cream 
of tartar ; the effect is greatly promoted by strong agitation. 

(2.) Solution of bichloride of platinum, with a little hydrochloric acid, if 
necessary, gives, under similar circumstances, a crystalline yellow precipi- 
tate, which is a double salt of bichloride of platinum and chloride of potas- 
sium. Both this compound and cream of tartar are, however, soluble in 
about 60 parts of cold water. An addition of alcohol increases the delicacy 
of both tests. 

(3.) Perchloric acid, and hydrofluosilicic acid, give rise to slightly-soluble 
wlute precipitates when added to a potassa-salt. 

(4.) Salts of potassa usually colour the outer blowpipe flame purple or 
violet ; this reaction is clearly perceptible only when the potassa-salts are 


This metal was obtained by Davy very shortly after the discovery of po- 
tassium, and by similar means. It may be prepared in large quantity by 
decomposing carbonate of soda by charcoal at a high temperature. 

Six parts of anhydrous carbonate of soda are dissolved in a little hot 
water, and mixed with two parts of finely-powdered charcoal and one part 
of charcoal in lumps. The whole is then evaporated to dryness, transferred 
to the iron retort before described, and heated in the same manner to white- 
ness. A receiver containing rock-oil is adapted to the tube, and the whole 
operation carried on in the same way as when potassium is made. The pro- 
cess, when well conducted, is easier and more certain than that of making 

Sodium is a silver-white metal, greatly resembling potassium in every re- 
spect ; it is soft at common temperatures, melts at; 194° (90°C), and oxidizes 
very rapidly in the air. Its specific gravity is 0-972. Placed upon the sur- 
face of cold water, sodium decomposes that liquid with great violence, but 
seldom takes fire unless the motions of the fragment be restrained, and its 
rapid cooling diminished, by adding gum or starch to the water. With hot 
water it takes fire at once, burning with a bright yellow flame, and giving 
rise to a solution of soda. 

The equivalent of sodium is 23, and its symbol (Natrium) Na. 

There are two well-defined compounds of sodium and oxygen ; the pro- 
toxide, anhydrous soda, NaO, and the binoxide, NaOg, or perhaps, teroxide 
NaOg ; they are formed by burning sodium in air or oxygen gas, and resem- 
ble in every respect the corresponding compounds of potassium. 

Hyobats or SODA, NaO, HO. — This substance is prepared in practice by 



deoompoBing a somewhat dilute solution of carbonate of soda by hydrate of 
lime ; the description of the process employed in the case of hydrate of po- 
tassa, and the precautions necessary, apply word for word to that of soda. 

The solid hydrate is a white, fusible substance, Tory similar in properties 
to hydrate of potassa. It is deliquescent, but dries up again after a time in 
consequence of the absorption of carbonic acid. The solution is highly al- 
kaline, and a powerful solvent for animal matter; it is used in large quan- 
tity for making soap. 

The strength of a solution of caustio soda may be roughly determined 
from a knowledge of its density, by the aid of the following table drawn up 
by Dr. Dalton. 




Poroentaffo of 









r. 23-0 





















Cabbonatx of soda, NaCCOj+lOH^* — Carbonate of soda was once ex- 
clnsiyely obt^iined from the ashes of sea-weeds, and of plants, such as the 
Salsola toda, which grew by the sea-side, or, being cultivated in suitable lo- 
calities for the purpose, were afterwards subjected to incineration. The 
barilla^ yet employed to a small extent in soap-making, is thus produced in 
several places on the coast of Spain, as Alicant, Carthagena, &c. That 
made in Brittany is called varee. 

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 foUow- 
ing is an outline ; — 

A charge of 6001b. 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 min- 
gled with the salt ; hydrochloric acid gas is disengaged, which is either 
allowed to escape by the chimney, or condensed by suitable apparatus; and 
the salt is converted into sulphate of soda. This part of the process takes 
for completion about four hours, and requires much care and skill. 

The sulphate is next reduced to powder, and mixed with an equal weight 
of chalk or limestone, and half as much small coal, both ground or crushed. 
The mixture is thrown into a reverberatory furnace, and heated to fusion, 
▼ith constant stirring ; 2 cwt. is about the quantity operated on at once. 
When the decomposition is judged complete, the melted matter is raked from 
the surface into an iron trough, where it is allowed to cool. When cold, it 
is broken up into little pieces, and lixiviated with cold or tepid water. The 
solution is evaporated to dryness, and the salt calcined with a little saw-dust 
in a suitable furnace. The product is the soda-ash, or British'alkali of com- 
merce, which, when of good quality, contains from 48 to 62 per cent, of 
pare soda, partly in the state of carbonate, and partly as hydrate, the re- 
mainder being chiefly sulphate of soda and common salt, with occasiona) 
traces of sulphite or hyposulphite, and also cyanide of sodium. By dissolving 

* Graham, Elements, p. 303, voL !. 

S29 flODIUM. 

«oda-Mh !b hot wa^er, fiitering tiie solntioii, 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 
ohalk and coal-dust seems to consist, first, in the conversion of the sulphate 
ot soda into salphide of sodium by the aid of the combustible matter, and, 
secondly, in the doable interchfuige of elements between that substance and 
the carbonfite of lime. 

eulphide of sodium { ^^?^^^ ■ ^^ Sulphide of calcium. 

{Lime / Calcium ^^*<C^7 
\ Oxygen -..^^^^^^^^v.,^^^ 
Carbonic acid ' ^-^^^^ Carbonate of soda. 

The sulphide of calcium combines with another proportion of lime to form 
a peculiar compound, which is insoluble in cold or slightly warm water. 

Other processes have been proposed, and even carried into execution, but 
the above, which was originally proposed by M. Leblanc, is found most ad- 

The ordinary crystals of carbonate of soda contain ten equivalents of water, 
but by particular management the same salt may be had with fifteen, nine, 
seven, equivalents, or sometimes with only one. The common form of the 
crystal is derived from an oblique rhombic prism ; they effloresce in dry air, 
and crumble to a white powder. Heated, they fuse in their water of crys- 
tallization ; when the latter has been expelled, and the dry salt exposed to 
a full red-heat, it melts without undergoing change. The common crystals 
dissolve in two parts of cold, and in less than their own weight of boiling 
water ; the solution has a strong, disagreeable, alkaline taste, and a power- 
ful alkaline reaction. 

BiCAEBONATB OP SODA, NaO,COj -|- H0,C02. — This salt is prepared by 
passing carbonic acid gas into a cola solution of the neutral carbonate, or 
by placing the crystals in an atmosphere of the gas, which is rapidly ab- 
sorbed, while the crystals lose the greater part of their water, and pass into 
the new compound. 

Bicarbonate of soda, prepared by either process, is a crystalline white 
powder, which cannot bo re-dissolved in warm water without partial decom- 
position. It requires 10 parts of water at 60° (16° -60) for solution; the 
liquid is feebly alkaline to test-paper, and has a much milder taste than that 
of the simple carbonate. It does not precipitate a solution of magnesia. 
By exposure to heat, the salt is converted into neutral carbonate. 

A sesquicarbonate of soda containing 2NaO,3C02-f-4HO has been described 
by Mr. Phillips ; like the sesquicarbonate of potassa, it is formed at plea- 
sure only with diflBiculty. This salt occurs native on the banks of the soda- 
lakes of Sokena in Africa, whence it is exported under the name of trona. 

Alkalimetry; Analysis of Hydrates and Carbonates of the Alkalis. — The 
general principle of these operations consists in ascertaining the quantity 
of real alkali in a given weight of the substance examined, by finding how 
much of the latter is required to neutralize a known quantity of an acid, as 
sulphuric acia. 

The first step is the preparation of a stock of dilute sulpburio acid of 
determinate strength; containing, for example, 100 grains of real acid in 
every 1,000 grain-measures of liquid : ' a large quantity, as a gallon or more, 

» The capadty of 1,000 grains of distilled water at 60° (1505C). The iprain-measure of water 
li often foand a very convenient and useful unit of volume' in chemical researcheii. Yemiela 
graduated on thig plan bear simple comparison with the imperial gallon and pint, and fre- 
quently also enable tLe operator to measure out a liquid of known density *"ft^(i of weigli- 

dOBitiH. 1227 

may be prepared at once by the following means. The oil of vitriol Is first 
examined ; if it be good and of the sp. gr. 1-85 or near it, the process is ex- 
tremely simple ; every 49 grains of the liquid acid contains 40 grains of 
absolute acid ; the quantity of the latter required in the gallon, or 70,000 
grain-measures of dilute acid, will be of course 7,000 grains. This is eqni 
Talent to 8,571 grains of the oil of vitriol, for 

Beal add. Oil of TiirioL 
40 : 49' » 7000 : 8575 

All that is required to be done, therefore, is to weigh out 8,575 grains of 
oil of vitriol, and dilute it with so much water, that the mixture, when cold, 
ihaU, measure exactly one gallon. 

It, very often happens, however, that the oil of vitriol to be used is not so 
strong as that above mentioned ; in which case it is necessary to discover its 
real strength, as estimated from its saturating power. Pure anhydrous car- 
bonate of soda is prepared by heating to dull redness, without fusion,- the 
bicarbonate ; of this salt 58 grains, or 1 eq., correspond to 31 grains of sod% 
and neu^alize 40 grains of real sulphuric acid. / 

A convenient quantity is carefully weighed out, and added, little by little, 
to a known weight, say 100 grains, of the oil of vitriol to be tried, diluted 
with four or five times its weight of water, until the liquid, after warming, 
becomes quite neutral to teat-paper. By weighing again the residue of the 
carbonate, it is at once known how much of the latter has been employed ; 
the amount of real acid in the hundred parts of the oil of vitriol is then 
easily calculated. Thus, suppose the quantity of carbonate of soda used to 
be 105 grains ; then, 

Carb. soda. Sulph. add. 

53 : 40 = 105 : 79-24; 

79-24 grains of real acid are consequently contained in 100 grains Kg- 148. 
of oil of vitriol ; consequently, 

79-24 : 100 = 7000 : 8833-82 

the weight in grains of the oil of vitriol required to make one 
gallon of the dilute acid. 

The " alkalimeter" is next to be constructed. This is merely a 
lOOO-grain naeasure, made of a piece of even, cylindrical glass tube, 
about 15 inctes long and 0*6 inch internal diameter, closed at one 
extremity, and moulded into a spout or lip at the other, yig. 146,' 
A strip of paper is pasted on the tube and suffered to dry, after 
which the instrument is graduated by counterpoising it in a nearly 
upright position in the pan of a balance of moderate delicacy, and 
weighing into it, in succession, 100, 200, 300, Ac, grains of dis- 
tilled water at 60° (16°-5C), until the whole quantity, amounting 
to 1,000 grains, has been introduced, the level of the water in the 
tube being, after each addition, carefully marked with a pen upon 
the strip of paper, while the tube is held quite upright, and the 
mark made between the top and the bottom of the curve formed by 
the surface of the water. The smaller divisions of the scale, of 10 
grains each, may then be made by dividing, by compasses each of 
the spaces into ten equal parts. When the graduation is complete, 
and the operator is satisfied with its accuracy, the marks may be 
transferred to the tube itself by a sharp file, and the paper removed 
by a little warm water. The numbers are scratched on the glass with the 
hard end of the same file, or inth a diamond. When this alkalimeter is nsed 

228 SODIUM. 

^tfa the dUute add described, eveiy division of the glass will eorrespond to 
one grain of real sulphuric acid. 

Let it be required, by way of example, to t^st the commercial value of 
soda-ash, or to examine it for scientific purposes : 60 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 litnius-paper. The addition of acid must 
of course be made Tery 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 60 grains of salt 
found by the rule of proportion. Suppose 88 measures, consequently 33 
grains of acid, have been taken ; then 
Sulph. add. Soda. 

40 : 81 = 88 : 25-57; 

the sample contains, therefore, 51-2 per cent, of available alkali. 

It will be easily seen that the principle of the process described admits of 
yery wide application, and that^ by the aid of the alkalimeter and carefully 
prepared test-acid, the hydrates and carbonates of pbtassa, soda, and am- 
monia, both in the solid state and in solution, can be examined with great 
ease aud accuracy. The quantity of real alkali in a solution of caustic am- 
monia may thus be determined, the equivalent of that substance, and the 
amount of acid required to neutralize a known weight, being inserted as the 
second and third terms in the above rule-of-three statement. The same acid 
answers for all. ^ 

It is often desirable, in the analysis of carbonates, to determine directly 
the proportion of carbonic acid ; the following methods leave nothing to be 
desired in point of precision : — ' 

A small light glass flask (fig. 147) of three or four 
Fig. 147. ounces capacity, with lipped edge, is chosen, and a cork 

fitted to it. A piece of tube about three inches long is 
drawn out at one extremity, and fitted by means of a 
small cork and a bit of bent tube, to the cork of the 
flask. This tube is filled with fragments of chloride of 
calcium, prevented from escaping by a little cotton at 
either end ; the joints are secured by sealing-wax. A 
short tube, closed at one extremity, and small enough to 
go into the. flask, is also provided, and the apparatus is 
complete. Fifty grains of the carbonate to be examined 
are carefully weighed out and introduced into the flask, 
together with a little water, the small tube is then filled with oil of vitriol, 
and placed in the flask in a nearly upright position, and leaning against its 
side in such a manner that the acid does not escape. The cork and chloride 
of calcium tube are then adjusted, and the whole apparatus accurately 
counterpoised on the balance. This done, the flask is* slightly inclined, so 
that the oil of vitriol may slowly mix with the other substances and 
decompose the carbonate, the gas from which escapes in a dry state from 
the extremity of the tube. When the action has entirely ceased the liquid 
is heated until it boils, and the steam begins to condense in the drying-tube ; 
it is then left to cool, and weighed, when the loss indicates the quantity of 
carbonic acid. The acid must be in excess after the experiment. When 
carbonate of lime is thus analyzed, strong hydrochloric acid must be substi- 
tuted for the oil of vitriol. 
Instead of the above apparatus, a neat arrangement may be used which 

▼as first suggested by Will and FresexdiM. It eonsists ef two snukH iflass 
flasks, A and B, fig. 148, the latter being somewhat smaller than the former. 
Both the flasks are provided with a donbly perforated cork. A tabe, open at 
both ends, bnt closed at the npper extremity by means ef a small qnantttj af 
wax, passes through the cork of A, to the very 
bottom of the flask, whilst a second tube reach- Is. Ma 

ing to tbe bettom of B, establishes a oommuni- 
eation between the two flasks. T^e oork of B 
is proTided, moreoyer, with a short tube, d. In 
order to analyse a carbonate, a suitable quan- 
tity (fifty grains) is put into A, together with 
some water. B is half filled with ooncentrated 
Bulphurio Boid, the apparatus tightly fitted and 
weighed. A small quantity of air is now 
sucked out of flask B by means of the tube d, 
whereby the air in A is likewise rarified. Im- 
mediately a portion of sulphuric acid ascends 
in the tube c, and flows over into flask A, 
causing « disengagement of carbonic acid, 
winch escapes at d, after having been perfectly 
dried by passing through the bottle B. This 
operation is repeated until the whole of the carbonate is decomposed, and 
the process terminated by opening the wax stopper and drawing a quantity 
of air through the apparatus. The apparatus is now re- weighed. The dif- 
ference of the two weighings expresses the quantity of carbonic acid in the 
compound analysed.^ 

Sulphate op soda, Glaubbb's salts, NaO, SO, -flOHO. — This is a by- 
product in seyeral 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 deriyed from an 
oblique rhombic prism ; the crystals contain 10 eq. of water, are efflores- 
cent, and undergo watery fusion when heated, like those of the carbonate ; 
they are soluble in twice their weight of cold water, and rapidly increase in 
solubility as the temperature of the liquid rises to 91^ 'b (83®CJ, when a 
maximum is reached, 100 parts of water dissolying 822 parts of the salt. 
Heated beyond this point, the solubility diminishes, and « portion of sul- 
phate is deposited. A warm saturated solution, eyaporated at a high tempe- 
rature, deposits opaque prismatic crystals, which are anhydrous. This salt 
has a slightly bitter taste, and is purgatiye. Mineral springs sometimes con- 
tain it, as at Cheltenham. 

BisuLPHATE OF SODA, NaO, SO, + HO, SO, + 8H0. — This is prepared by 
adding to 10 parts of anhydrous neutral sulphate, 7 of oil of yitriol, eyapo- 
rating the whole to dryness, and gently igniting. The bisulphate is yery 
soluble in water, and has an acid reaction. It is not deliquescent. When 
yery strongly heated, the fused salt giyes up anhydrous sulphuric acid, and 
becomes simple sulphate ; a change which necessarily supposes the preyious 
formation of a true anhydrous bisulphate, NaO,2SO,. 

Htfosulphitb of soda, NaO, Sj^O,. — There are seyeral modes of procu- 
ring this salt, which is now used m considerable quantity for photographic 
purposes. One of the best is to form neutral sti^hiie of soda, by passing a 
stream of well washed sulphurous acid gas into a strong solution of carbo- 
nate of soda, and then to digest the solution with sulphur at a gentle heat 
during seyeral days. By careful eyaporation at a modern temperature, the 
salt is obtained in large and regular crystals, which are yery soluble in water. 

* A oonTenient modification of this has been made by Dr. WeiheriU| (Joura. Frank. insUt 
«Dd amxher ^ Sebaflber. (Ghem. OaMtte, Jan. 15, IMS.— B. B.) 

ffSO frODlUM. 

lfiTR4T8 or BODA ; otuio KiTEB, NaO, NOg. — ^Nitrftte of soda oecunnfttiTe, 
. and in enormous quantity, at Atacama, in Peru, where it forms a regular 
bed, of great extent, covered with clay and alluvial matter. The pure salt 
.commonly crystallizes in rhombohedrons, resembling those of calcareous 
spar, but is probably dimorphous. It is deliquescent, and very soluble in 
water. Nitrate of soda is employed for making nitric acid, but cannot be 
used for gunpowder, as the mixture bums too slowly, and becomes damp in 
the air. It has been lately used with some success in agriculture as a su- 
perficial manure or top-dressing. 

Phosphates op soda ; common tbibasio phosphate, 2NaO, HO, PO5+24 
HO. — This beautiful salt is prepared by precipitating the acid phosphate of 
lime obtained by decomposing bone-earth by sulphuric acid, with a slight 
excess of carbonate of soda. It crystallizes in oblique rhombic prisms, 
which are efflorescent. The crystals dissolve in 4 parts of cold water, and 
undergo the aqueous fusion when heated. The salt is bitter and purgative; 
its solution is alkaline to test-paper. Crystals containing 14 equivalents of 
water, and having a form different from that above mentioned, have been 

A second tribasic phosphate, sometimes called subphosphate, 3NaO, 
PO5+24HO, is obtained by adding a solution of caustic soda to the prece- 
ding salt. The crystals are slender six-sided prisms, soluble in 6 parts of 
cold water. It is decomposed by acids, even carbonic, but suffers no change 
by heat, except the loss of its water of crystfillizntion. Its solution is strongly 
alkaline. A third tribasic phosphiite, often called superphosphate or biphos- 
phate, NaO,2HO,P05-|-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, 
NH40,HO,P05-f.8HO. — Six parts of common phosphate of soda are heated 
with 2 of water until the whole is liquefied, when 1 part of powdered sal- 
ammoniac is added ; common salt separates, and may be removed by a filter, 
and from the solution, duly concentrated, the new salt is deposited in pris- 
matic crystals, which may be purified by one or two re-crystallizations. 
Microcosmic salt is very soluble. When gently heated, it parts with the 8 
- eq. of water crystallization, and, at a higher temperature, the water acting 
as base is expelled, together with the ammonia, and a very fusible compound, 

• metaphosphate of soda, remains, which is valuable as a flux in blowpipe ex- 
periments. This salt is said to occur in the urine. 


Prepared by strongly heating common phosphate of soda, dissolving the 

residue in water, and re-crystallizing. The crystals are very brilliant, per- 
manent in the air, and less soluble than the original phosphate ; their solution 
is alkaline. A bibasic phosphate, containing an equivalent of basic water, 
has been obtained ; it does not, however, crystallize. 

Monobasic PHOSPHATE op soda; metaphosphate op soda, NaCPOg. — 
Obtained by heating either the acid tribasic phosphate, or microcosmic salt. 
It is a transparent glassy sub'Btance, fusible at a dull red-heat, deliquescent, 
and very soluble in water. It refuses to crystallize, but dries up into a 
gum-like mass. 

If this glassy phosphate be cooled very slowly a beautifully cryBtalline 

mass IS obtained. It may be separated by means of boiling water from the 

Titreous metaphosphate which will not crystallize. Another metaphosphate 

has been obtained by adding sulphate of soda to an excess of phosphoric acid, 

'Evaporating and heating to upwards of 600° (315<''6G). Possibly these 

SODIUM. ' 281 

lerertl metamMipliAtAS may be represented by the formtihe NaO^PO.? 
2XaO,2P05; SNaCSPOg. 

The tribasic phosphates give a bright yellow precipitate with gelation 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 
irith excess of carbonate of soda, yield the tribasic modification of the acid. 

Pkoiphates intermediate between the monobane and bibtuie pkoaphates of soda, 
SNaO,2P05, and GNaCSPOg. — The first is produced by fusing 100 parts of 
anhydrous pyrophosphate of soda, and 76-87 parts of metaphosphate of soda* 
The white crystalline mass is reduced to powder, and quickly exhausted with 
water. The solution, on exposure to the atmosphere, yields small plates which 
are very soluble in water. 

The second is produced by fusing 100 parts of pyrophosphate of soda, and 
807-5 of metaphosphate ; it crystaJJiizes with more difficulty than the prece- 
ding compound. 

MM. Fleitmann and Henneberg, the discoyerers of these new phosphates, 
represent the different phosphates thus : — ^ 

Common phosphate 6NaO,2P05 

Pyrophosphate 6NaO,3POj 

New phosphates jeNaOisPO* 

Metaphosphate eNaO.GPO, 

In each of which six equivalents of the base are combined with a different 
polymeric acid. 

BiBosATE OF soda; bo&az, NaO,2BO3-4<'10HO. — This compound occurs 
in the waters of certain lakes in Thibet ana Persia ; it is imported in a crude 
BUte from the East Indies under the name of tincal When purified, it con- 
Btitntes the borax of commerce. Much borax is now, however, manufactured 
from the native boracio acid of Tuscany. Borax crystallizes in six-sided 
prisms, which effloresce in dry air, and require 20 parts of cold, and 6 of 
boiling water for solution. Exposed to heat, the 10 eq. of water of crystal- 
lization are expelled, and at a higher temperature the salt fuses, and assumes 
« glassy appearance on cooling ; in this state it is much used for blowpipe 
experiments, the metallic oxides dissolving in it to transparent beads, many 
of which are distinguished by characteristic colours. By particular manage- 
ment, crystals of borax can be obtained with 6 eq. of water ; they are very 
hard, and permanent in the air. Although by constitution an acid salt, 
horax has an alkaline reaction to test-paper. It is used in the arts for sol- 
dering metals, its action consisting in rendering the surfaces to be joined 
nietallic, by dissolving the oxides, and sometimes enters into the composition 
of the glaze with which stoneware is covered. 

j^eutral 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,B03-f 8H0. 

Sulphide op sodium, NaS. — Prepared in the same manner as the proto- 
wilphide 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 
Bolphuretted hydrogen, bisulphide of carbon, and other sulphur-acids. 

Sulphide of sodium is supposed to enter into the composition of the beau- 
tiful pigment tdtramarine, prepared from the lapis lazuli, and which is noTf 
imitated by artificial means.* 
Chloridb of sodium ; ooMMOir SALT, NaCl. — This very important sub» 

* See PharmaoeuticalJoumal, iL 58. 


wkaAce is t<miA' in mnaxy pmrts of tira irof Id in 9oKd beds* or ivregidiir 'etraCa 
of immense thickness,' as in Cheshire, for example, in Spain, Qalicia, and 
many other localities. An inezhanstible supply exists also in the waters of 
the ocean, and large quantities are annually obtained from saline springs. 

The ro«k-salt is almost always too impure for use ; if no natural brine- 
Bpring exist, an artificial one is formed by sinking a shaft into the rock-salt^ 
and, il necessary, introducing water. This, when saturated, is pumped up, 
ftnd evaporated more or less rapidly in large iron pans. As the salt sepa- 
rates, it is remoyed 'from the bottom of the yessels by means of a scoop, 
pressed while still moist into moulds, and Uien transferred to the dryings 
Btove. When large crystals are required, as for the ooarse'grained bai^»aU 
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. Ifc 
crystallizes in anhydrous cubes, which are often grouped together into pyra- 
mids, or steps. It requires about 2} parts of water at 60° (15^*50) for solu- 
tion, and its solubility is not sensibly increased by heat; it dissolves to some 
extent in spirits, but is nearly insoluble in absolute alcohol. -Chloride of 
sodium fuses at a red-heat, and is volatile at a still higher temperature. The 
economical uses of common salt are well known. 

!the iodide and bromide of sodium much resemble the corresponding potas- 
sium-compounds : they crystallize in cubes which are anhydrous, and are 
very soluble in water. 

There is no good precipitant for soda, all the salts being very soluble with 
the exception of antimonate of soda, the use of which is attended with diffi- 
culties ; its presence is often determined by purely negative evidence. The 
yellow colour imx>arted by soda-salt to the outer flame of the blowpipe, and 
to combustiUe matter, ia a character of some importance. 


In connection with the compounds of potassium and sodium, those formed 
by ammonia are most conveniently studied. Ammoniacal salts correspond 
in every respect in constitution with those of potassa and soda ; in all cases 
the substance which replaces those alkalis is hydrate of ammonia, or, as it 
IS now almost generally considered, the oxide of a hypothetical substance 
called ammonium, capable of playing the part of a metal, and ismorphous 
with potassium and sodium^ All attempts to isolate this substance have 
failed, apparently from its tendency to separate into ammonia and hydrogen 
gas. ^ 

When a globule of mercury is placed on a piece- of moistened caustic po- 
tassa, and connected with the negative side of a voltaic battery of very, 
moderate power, while the circuit is completed through the platinum- plats 
upon which rests the alkali, decomposition of the latter takes place, and an 
amalgam of potassium is rapidly formed. 

If this experiment be now repeated with a piece of sal-ammoniac instead 
of hydrate of potassa, a soft solid, metalline mass ia also produced, which 
has been called the ammoniacal amalffamt and considered to oontain ammo- 
nium in combination with mercury. A still simpler method of preparing 
this extraordinary compound is the following : — A little mercury ia put into 
a test-tube with a grain or two of potassium or sodium, and gentle heat ap- 
plied; combination ensues, attended by heat and light. When cold, the 
fluid amalgam is put into a capsule, and covered with a strong solution of 
sal-ammoniac. The production of Rmmonlacal amalgam instantly com« 
mences, the mercury increases prodigiously in volume, and becomes quite 


ptstf. The inoreasci of tr^gbt is, hoireTer, quite trifliiig; ItTaries from' 

mijtl* to T^J^th part. 

Left to itself, the amalgam quickly deoomposes into fluid mercury, ammo- 
via, and hydrogen. 

It is difficult to offer any opinion concerning the real nature of this com« 
poond: something analogous occurs when pure nlyer is exposed to a yery 
high temperature, much above its melting-point, in contact with air or oxy- 
gen gas ; the latter is absorbed in very large quantity, amounting, accord- 
ing to the observation of Gay-Lussac, to 20 times the volume of tiie silver, 
and is again disengaged on lessening the heat. The metal loses none of its 
lustre, and is not sensibly altered in other respects. 

The great argument in favour of the existenc%of ammonium is founded 
on the perfect comparison which the ammoniacal salts bear with those of 
the alkaline metals. 
The equivalent of ammonium is 18; its symbol is NH4. 
Chloride of ammonium ; (Mubiatb op Ammonia ;) sal-ammoittac, NH^Ct 
— Sal«ammoDiac was formerly obtained from Egypt, being extracted by sub- 
limation from the soot of camels' dung; it is now largely manufactured from 
the ammoniacal liquid of the gas-works, and from the condensed products 
of the distillation of bones, and other animal refuse, in the preparatioa of 
animAl charcoal. 

These impure and highly offensive solutions are treated with slight excess 
of hydrochloric acid, by which the alkali is neutralized, and the carbonate 
and salphide decomposed with evolution of carbonic acid and sulphuretted 
hjdrogen gases. The liquid is evaporated to dryness, and the salt carefully 
heated, to expel or decompose the tarry matter ; it is then purified by 8ul>- 
limation in large iron vessels lined with clay, surmounted with domes of lead. 
Sublimed sal-ammoniac has a fibrous texture, it is tough, and difficult to 

When crystallized from water it separates under favourable circumstances, 
In distinct cubes or octahedrons ; but the crystals are usually small, and ag- 
gregated together in rays. It has a sharp saline taste, and is soluble in 2} 
parts of cold, in a much smaller quantity of hot water. By heat, it is sub- 
limed without decomposition. The crystals are anhydrous. Chloride of 
ammonium forms 'double salts with chloride of magnesium, nickel, cobalt, 
manganese, zinc, and copper. >^ 

Sulphate op oxide of ammonium; sulphate op ammonia, NH^O, 
SOj-j-HO. — Prepared by neutralizing carbonate of ammonia by sulphurio 
acid, or on a large scale, by adding sulphuric acid in excess to the coal-gas 
liquor Just mentioned, and purifying the product by suitable means. It is 
soluble in 2 parts of cold water, and crystallizes in long, flattened, six-sided 
prisms, which lose an equivalent of water when heated. It is entirely de- 
composed, and driven off by ignition, and, even to a certain extent, by long 
boiling with water, ammonia being expelled and the liquid rendered acid. 

Carbonates op ammonia. — These compounds have been carefully exam- 
ined by Professor Rose, of Berlin,* and appear very numerous. The neutral, 
anhydrous carbonatey NIIj.COj, is prepared by the direct union of carbonio 
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 pre- 

' Annalen der Pharmade, xxz. 45 


paved 8pe<»]nen& approaches tbaiof aBeaqmcarboaatti of oxMe of ammooiikiB,' 
2 NH^OjSCOj. — ^When heated in a retort, the neck of which dips into mer- 
cury, it is decomposed, -with disengagement of pure carbonic acid, into 
neutral hjdrated carbonate of ammonia, and several other compounds. Ex- 
posed to the air at common temperatures, it (Hsengages neutral carbonate 
of ammonia, loses its pungency, and crumbles down to a soft, white powder, 
vhich is a bicarbonate, containing NH4O,0O2-f-HO,CO2. This is a permanent 
combination, although still volatile. When a strong solution of the commer- 
cial sesquicarbonate is made with tepid water, and filtered, warm^ into a 
close vessel, large and regular crystals of bicarbonate, having the above com- 
position, are sometimes deposited after a few days. These are inodorous, 
t|uite permanent in the air, and resemble, in the closest manner, crystals of 
bicarbonate of potassa. 

Nitrate or oxide op Ammonium; niteatb of ammonia, NH40,N05.— 
Easily prepared by adding carbonate of ammonia to slightly diluted nitric 
aeid until neutralization has been reached. By slow evaporation at a mode- 
rate temperature it crystallizes in six-sided prisms, like those of nitrate of 
potassa ; but, as usually prepared for making nitrous oxide, by quick boiling, 
until a portion solidifies completely on cooling, it forms a fibrous and indis- 
tinct crystalline mass. 

Nitrate of ammonia dissolves in 2 parts of cold water, is but feebly deli- 
quescent, and deflagrates like nitre on contact with heated combustible 
matter. Its decomposition by heat has been already explained.' 

Sulphides of Ammonium. — Several of these compounds exist, and may 
be formed by distilling with sal-ammoniac the corresponding sulphides of 
potassium or sodium. 

The double sulphide of ammonium and hydrogen, NH^S-f-HS, commonly 
called hydrosulphate of ammonia, or, more correctly, hydrosulphate of sul- 
fide of ammonium, is a compound of great practical utility ; it is obtained 
by saturating a solution of ammonia with well-washed sulphuretted hydrogen 
gas, until no more of the latter is absorbed. The solution is nearly colourless 
at first, but becomes yellow after a time, without, however, suffering material 
injury, unless it has been exposed to the air. It gives precipitates with most 
metallic solutions, which are very often characteristic, and is of great service 
in analytical chemistry .<* 

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 ia 
a yellow soluble substanee, altogether distinct from sulphite of ammonia. 

» Page 125. 

'Phosphates of Ozidx op AiofONitiM; Common Tribasic Phosphate, 2 NIl4O,HO,PO6+H0.— 
This salt is forixMd by precipitating tho 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 add set free, previoas 
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 on alkaline, slightly saline taste and alkaline reaction. Bj 
heat ammonia is disengaged. 

The add tribasic phosphata, NIl40,2HO,P06+4HO, is formed when a solution of the common 
phosphate is boiled as long as ammonia is given off. It crystallizes in fbur-sided prisms. Its 
crystals are permanent, soluble in 5 parts of cold water, add in taste and reaction. 

Another tribasic phosphate, 3NH40,PO» subphosphate is fbrmed by adding ammonia to 
either of the abov* It falls as a slightly soluble granular predpitate.— B. B, 

Dry carbonic acid satl sMinonui also «mt» to form a T<^atil6 wldta powder^ 
as already mentioned. 

When certain salts, especially chloridea in an anhydrous state, are exposed 
to ammooiAcal gas, the latter is absorbed with great energy, and the combi- 
nations formed are not always easily decomposed by heat. The chlorides of 
copper and silver absorb, in this manner, large quantities of the gas. All 
these compoonds must be carefully distinguished from the true ammoniacal 
Balis containing ammonium or its oxide. 

There is supposed to be yet another compound of hydrogen and nitrogen 
to which the term amidogen has been given. When potassium is heated in 
the vapour of water, this substance is decomposed, hydrogen is evolved, and 
the metal converted into oxide. When the same experiment is made with 
dry ammoniacal gas, hydrogen is also set free, and an olive-green crystalline 
compound produced, supposed to contain potassium in union with a new body, 
NHj. having an equivalent of hydrogen less than ammonia. 

When ammonia is added to a solution of corrosive sublimate, a white pre- 
cipitate is obtained, which has been long known in pharmacy. Sir R. Kane 
infers, from his experiments, that this substance should be looked upon as a 
compound of chloride of mercury with amide of mercury. The latter salt 
has not been obtained separately ; still less has amidogen itself been isolated. 

It has been thought that ammonia may be considered an amide of hydrogen, 
analogous to water or oxide of hydrogen, capable of ente^ng into combina- 
tion with salts, and other substances, in a similar manner, yielding unstable 
and easily decomposed compounds, which offer a great contrast to those of 
the energetic quasi-rsietoX ammonium ; the views of chemists upon this sub- 
ject are, however, still divided. 

The ammoniacal salts are easily recognised ; they are all decomposed or 
volatilized by a high temperature ; and when heated with hydrate of lime, 
or solution of alkaline carbonate, evolve ammonia, which may be known by 
its odour and alkaline reaction. The salts are all more or less soluble, the 
acid tartrate of ammonia and the double chloride of ammonium and platinum 
being among the least so ; hence the salts of ammonia cannot be distinguished 
from those of potassa by the tests of tartaric acid and platinum-solution. 

A connecting link between this class of metals and the next succeeding. 
Lithium Is obtained by electrolyzing, in contact with mercury, the hydrate 
of lithia, and then decomposing the amalgam by distillation. It is a white 
metal like sodium, and very oxidable. Jhe eciuivaleut of lithium is 6-6, and 
its symbol L. 

The oxide, lithia, LO, is found in pctalitc, spodumene, lepidolite, and a 
few other minerals, and sometimes occurs in minute quantities in mineral 
springs. From petalite it may be obtained, on the small scale, by the fol- 
lowing process : — The mineral is reduced to an exceedingly fine powder, 
mixed with five or six times its weight of pure carbonate of lime, and the 
mixture heated to < whiteness, in a platinum crucible, placed within a well- 
covered earthen one, for twenty minutes or half an hour. The shrunken 
coherent mass is digested in dilutfe hydrochloric acid, the whole evaporated 
to dryness, acidulated water added, and the silica separated by a filter. The 
solution is then mixed with carbonate of ammonia in excess, boiled and 
filtered ; the clear liquid is evaporated to dryness, and gently heated in a 

23S lithium; 

platinnm crndble, to expel the sal-ammoniao. The residue is then wetted 
with oil of vitriol, gently evapprated once more to dryness, and ignited; 
pure fused sulphate of lithia remains.' 

This process will serve to give a good idea of the general natnre of the 
operation by which alkalis are extracted in mineral analysis, and theii 
quantities determined. 

The hydrate of lithia is much less soluble in water than those of potsssa 
and soda; the carbonate and phosphate are also sparingly soluble salts. 
The chloride crystallizes in anhydrous cubes which are deliquescent Sul- 
phate of lithia is a very beautiful salt ; it crystallizes in lengthened prisms 
containing one equivalent of water. It gives no double salt with sulphate 
of alumina. 

The salts of lithia colour the outer flame of the blowpipe carmine-red. 

B^ABIWH. 23% 


Babittx was obtained by Sir H. Dayj by means similar to those mentioned 
in the oase of lithhtm ; it is procured more advantageously, by strongly heat- 
ing baryta in an iron tube, through whioh the vapour of potassium is con- 
veyed. The reduced barium is extracted by quicksilver, and the amalgam 
distilled in a. small green glass retort. 

Barium is a white metal, having the colour and lustre of silver ; it is mal- 
leable, melts below a red heat, decomposes water, and gradually oxidizes in 
the air. . 

The equivalent of this metal has been fixed at 68*6 ; its symbol is Ba. 

Pbotoxidb of barium; babyta, BaO. — Baryta,* or barytes, occurs in 
nature in considerable abundance as carbonate and sulphate, forming the 
veinstone in many lead-mines ; from both these sources it may be extracted 
ivith facility. The best method of preparing pure baryta is to decompose 
the crystallized nitrate by heat in a capacious crucible of porcelain until red 
vapours are no longer disengaged ; the nitric acid is resolved into nitrous 
acid and <^xygen, and the baryta remains behind in the form of a greyish 
spongy mass, fusible at a high degree of heat. When moistened with water, 
it combines to a hydrate with great elevation of temperature. 

The hydrate is a white, soft powder, having a great attraction for carbonic 
acid, and soluble in 20 parts of cold and 2 of boiling water ; a hot saturated 
solution deposits crystals on cooling, which contain BaO, HO-f 9H0. Solu- 
tion of hydrate of baryta is a valuable re-agent; it is highly alkaline to 
test-paper, and instantly rendered turbid by the smallest trace of carbonic 

BiNoxiDE o9 BABiuM, BaOj. — This may be formed, as already mentioned, 
by exposing baryta, heated to full redness in a porcelain tube, to a current 
of pure oxygen gas. The binoxide is grey, and forms a white hydrate with 
water, which is not decomposed by that liquid in the cold, but dissolves in 
small quantity. The binoxide may also be made by heating pure baryta to 
redness in a platinum crucible, and then gradually adding an equal weight 
of chlorate of potassa; binoxide of barium and chloride of potassium are 
produced. The latter may be extracted by cold water, and the binoxide 
left in the state of hydrate. It is interesting chiefly in its relation to bin- 
oxide of hydrogen. When dissolved in dilute acid, it is decomposed by 
bichromate of potassa, oxide of silver, chloride of silver, sulphate and car 
bonate of silver. 

Chloride of barium, BaCl-f-2H0. — This valuable salt is prepared by 
dissolving the native carbonate in hydrochloric acid, filtering the solution, 

^ From Paf6Sf heavy, in oIIubIob to the great spedflc gravity of the native c4rl)onate an4 


find eyaporating until a skin begins to form at ih6 Burface; the eolation on 
cooling deposits crystals. When native carbonate cannot be procured, the 
native sulphate may be employed in the following manner: — The sulphate is 
reduced to fine powder, and intimately mixed with one-third of its weight 
of powdered coal ; the mixture is pressed into an earthen crucible to which 
a cover is fitted, and exposed for an hour or more to a high red-heat, by 
which the sulpha/te is converted into sulphide at the expense of the com- 
bustible matter of the coal. The black mass obtained is powdered and boiled 
in water, by which the sulphide is dissolved ; the solution is filtered hot, and 
mixed with a slight excess of hydrochloric acid ; chloride of barium and sul- 
phuretted hydrogen are produced ; the latter escaping with effervescence. 
Lastly, the solution is filtered to separate any little insoluble matter, and eva- 
porated to the crystallizing point. 

The crystals of chloride of barium are flat, four-sided tables, colourless 
and transparent. They contain 2 equivalents of water, easily driven off by 
heat; 100 parts of water dissolve 48-5 parts at CO*' (16<>-6C), and 78 parts 
at 223" (106° -50, which is the boiling-point of the saturated solution. 

Nitrate of baryta, BaO, NOj. — The nitrate is prepared by methods 
exactly similar to the above, nitrio acid being substituted for the hydro- 
chloric. It crystallizes in transparent colourless octahedrons, which are 
anhydrous. They require for solution 8 parts of cold, and 8 parts of boil- 
ing water. This salt is much less soluble in dilute nitric acid than in pure 
water ; errors sometimes arise from such a precipitate of crystalline nitrate 
of baryta being mistaken for sulphate. It disappears on heating, or by large 
affusion of water. 

Sulphatb of baryta; hbavy-spab; BaO, SO,. — Found native, often beau- 
tifully crystallized. This compound is always produced when sulphuric acid 
or a soluble sulphate is mixed with a solution of a barytic salt. It is not 
sensibly soluble in water or in any dilute acid, even nitric ; hot oil of vitrid 
dissolves a little, but the greater part separates again on cooling. Sulphate 
of baryta is used as a pigment, but often for the purpose of adulterating 
white-lead ; the native salt is ground to fine powder and washed with dilute 
sulphuric acid, by which its colour is improved, and a little oxide of iron 
probably dissolved out. The specific gravity of the natural sulphate is as 
high as 4-4 to 4-8. 

Sulphide of barium, BaS. — The protosulphide of barium is obtained in 
the manner already described ; the higher sulphides may be formed by boil- 
ing this compound with sulphur. Protosulphide of barium crystallizes in 
thin and nearly colourless plates from a hot solution, which contain water, 
and are not very soluble ; they are rapidly altered by the air. A strong 
solution of sulphide may be employed in the preparation of hydrate of baryta, 
by boiling it with small successive portions of black oxide of copper, until a 
drop of the liquid ceases to precipitate a salt of the lead black ; the liquid 
being filtered, yields, on cooling, crystals of hydrate. In this reaction, besides 
hydrate of baryta, hyposulphite of that base, and sulphide of copper are 
produced ; the latter is insoluble, and is removed by the filter, while most 
of the hyposulphite remains in the mother^liquor. 

Carbonate or baryta, BaO, COj. — The natural carbonate is called withe- 
rife; the artificial is formed by precipitating the chloride or nitrate with an 
alkaline carbonate, or carbonate of ammonia. It is a heavy, white powder, 
very sparingly soluble in water, and chiefly useful in the preparation of the 
rarer baryta-salts. 

Solutions of hydrate and nitrate of baryta and of the chloride of barium 
fffe constantly kept in the laboratory as chemical tests, the first being em- 


•plojrBd to effeot tlie sepantioii of oarbonie add tnm oertoin gaseous toix* 
tures, and the two latter to preoipitate solphnrio acid from solation. 

The soluble salts of baryta are poisonous, which is not the case with 
those of the base next to be described. 


The metal strontium may be obt^ned from its oxide by means similar to 
those described in the case of barium ; it is a white metal, heayy, oxidizable 
in the air, and capable of decomposing water at common temperatures. 

The equivalent of strontium is 43-8, and its symbol is Sr. 

Peotoxidb op strontium ; stkontia ; 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 by- 
drate, soluble in water. A hot saturated solution deposits crystals on cool- 
ing, which contain 10 equiyalents of water. The hydrate has a great at- 
traction for carbonic acid. 

BiNoxiDB OP STRONTIUM, SrOj. — The binoxide is prepared in the same 
manner as binoxide of barium ; it may be substituted for the latter in mak- 
ing binoxide of hydrogen. 

The native carbonate and sulphate of strontia, met with in lead-mines and 
other localities, serve for the preparation of the various salts by means ex- 
actly similar to those already described in the case of baryta ; they have a 
very feeble degree of solubility in water. 

Chloride op strontium, SrCl. — The chloride crystallizes in colourless 
needles or prisms, which are slightly deliquescent, and soluble in 2 parts of 
cold and still less of boiling water ; they are also soluble in alcohol, and the 
solution, when kindled, burns with a crimson flame. The crystals contain 6 
equivalents of water, which they lose by heat ; at a higher temperature the 
chloride fuses. 

Nitrate op strontia, SrOjNOg. — This salt crystallizes in anhydrous oc- 
tahedrons, which require for solution 5 parts of cold, and about half their 
weight of boiling water. It is principally of value to the pyrotechnist, who 
employs it in the composition of the well-known ** red-fire." * 

This is a silver^white and extremely pxidable metal, obtained with great 
difficulty by means analogous to those by which barium and strontium are 

The equivalent of calcium is 20 ; its symbol is Ca. 

Protoxide op calcium; lime; CaO. — This extremely important com- 
pound may be obtained in a state of considerable purity by heating to full 
redness, for some time, fragments of the black bituminous marble of Derby« 
shire or Kilkenny. If required absolutely pure, it must be made by ignit- 
ing to whiteness, in a platinum crucible, an artificial carbonate of lime, pro- 
cured by precipitating the nitrate by carbonate of ammonia. Lime in an 
impure state is prepared for building and agricultural purposes by calcining 

Dry nitrate of slxontia 800 

Bulphur 225 

Chlorate of potassa 200 

Lampblatdc 60 

OREEir-FiEE:-:- Orns. 

Dry nitrate of baryta 450 

Sulphur 160 

Chlorate of potassa 100 

Lampblack 25 

The strontia or baryta-ealt, the sulphur, and the lampblack, must be finely powdered and 
httlmstely mixed, after which the chlorate of potassa should be added in rather coarse pow- 
der, and mixed without much rubbing with the other iogredientfl. The red-fire oompositiQn 
has been known to ignite spontaoeoufdy. 

n0 CASiT^lOafi. 

4n % kiln of sriitlribliB tXNiiteiiotidB, tkB ordimrf ttmntoiite ^Mi^idMiiiid'bi 
many distriots ; a red-heat^ coBtiinied for some hours, is sufficient to disen- 
gage tiiD whole of the carbonic aoid. In the best contrived lime^kihis the 
process is carried on continuously, Inroken limeBtone and fuel being con- 
stantly thrown in at the top, and the burned lime raked out at intervals from 
beneath.. Sometimes, when the iimestoaes contain silica, and the heat has 
been very high, the lime refuses to slake, and is said to be over-lmrnedf in 
this case a portion of silicate has been formed. 

Pure lime is white, and often of considerable hardness ; it is quite infusi- 
ble, and phosphoresces, or emits a pale light at a high temperature. When 
moistened with water, it slakes with great violence, evolving heat, and 
crumbling to a soft, white, bulky powder, which is a hydrate containing a 
single equivalent of water ; the latter can be again expelled by a red-heat. 
This hydrate is soluble in water, but far less so than either the hydrate of 
baryta or of strontia, and what is very remarkable, the colder the water, the 
larger the quantity of the compound whict is taken up. A pint of water at 
60° (160-6C) dissolves about 11 grains, whUe at 212° (lOOoC) only 7 grains 
are retained in solution. The hydrate has been obtained in thin delicate 
crystals by slow evaporation under the air-pump. Lime-water is always 
prepared for chemical and pharmaceutical purposes by agitatiug 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, aiid also in medicine. Lime- 
water prepared from some varieties of limestone may contain potassa. 

The hardening of mortars and cements is in a great measure due to the 
gradual absorption of carbonic acid ; but even after a very great length of 
time, this conversion into carbonate is not complete. Mortar is known, 
under favourable circumstances, to acquire extreme hardness witii age. 
Lime-cements which resist the action of water, contain the oxides of iron, 
silica, and alumina ; they require to be careifuUy prepared, and the stone not 
over-lxeated. When ground to powder and mixed with water, solidification 
speedily ensues, from causes not yet thoroughly understood, and the cement, 
once in this condition, is unaffected by wet. Parker's or Roman cement is 
made in this manner from the nodular masses of calcareo-argillaceous iron- 
stone found in the London clay. Lime is of great importance in agrieultore; 
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 oljects, as the destruction of eertain hurtful eompoonds 
of iron in marsh and peat-land, is often attained. The addition of lime pro- 
bably serves likewise to liberate potassa from tite insoluble ediicate of that 
base contained in the soil. 

BiNoxiDB OF CALciuif, CaOg. -^ This is stated to resemble binoxide of 
barium, and to be obtainable by a similar process. 

Chloride of calcium, CaCl. — Usually prepared by dissolving marble in 
hydrochloric acid ; also a by-product in several chemical manufactures.. The 
salt separates from a strong solution in colourless, prismatic, and exceed- 
ingly deliquescent crystals, which contain 6 equivalents of water. By heat 
this water is expelled, and by a temperature of strong ignition the salt is 
fused. The crystals reduced to powder are employed in the production of 
artificial cold by being mixed with snow or powdered ice ; and the chloride, 
strongly dried or in a fused condition, is of great practical use in desiccating 
gases, for which purpose the latter are slowly transmitted throi^ tubes 

filed.inth finfippDM^ts of ihfi Afik. Cbloidie of oatdiim is ftlio fte«iy tfolnbito 
is alcohol, wMcfa, when anhyd|^o^B, forms with It a definite ory«taUizsbl« 

SuLPHipjs Of CAtciUM. — The simple sulphide is obtained by redaoing 
sulphate of lime at a hig^ temperature by oharcoal or hydrogen ; it is nearly 
coloorlessy and bat llttje soluble in water. — By boiling together hydrate of 
lime, water, and fiow«rs of sulphur, a red solution is obtained, which on 
cooling deposits crystals of bisulphide, which contain water. When the 
sulphur is tp. excess, ^d the boiling long contimied, a pentasulphide is 
generated ; hyposulphurous acid is, as usual, formed in these reactions. 

PHOsppins or CALOiuji.t— Wh€»n the ▼spoor of phosphorus is passed ever 
fira^ents qf lin^ h<^ftted to redness in a poreelain tube, a chocolate-brown 
compound, tl^e ao-cailed phosphide of Ume, is produoed. This substance is 
probably a mecbanical mixture of phosphide of calcium, and phoBj^ate of 
lime. It yields apontaneoxMsly inflammable phosphoretted hydrogen when 
pat into water.* 

SuLPHATfi OF like; qypsuh ; ^blksitb; CaO, SO,. — Katiye sulphate of 
lime in a crystalline condition, containing 2 equivalents of water, is found ia 
considerable abundance i|i some localities ; it is often associated with rock- 
salt When regularly ^crystaJlijsed, it is termed selemte. Anhydrous sulfriiate 
of Ui{ie is also occasipnally met with. The salt is formed by precipitation 
when a moderately concentrated aolatlon of chloride of calcium is mixed 
with sulphuric acid. Siulphate of lime is soluble in about 500 parte of cold 
water, and its s<dubiUty is a little increased by heat. It is metre soluble in 
water containing chlpride of ammonium or nitrate of potassa. The solution 
is precipitated by alcohol. Oypsum, or natim bydrated sulphate, is largely 
employed for the purpose of making casts of statues and medals, and also 
for moulds in the porcelain and eartiienware manufactures, imd for other 
applications. It is exposed to heat in an oven where the temperature does 
not exceed 260° (126<=>'60), 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^forokation of .the same hydrate ; but this effect 
does not happen if the gypsum has been oTor^heated. It is often called 
plaster of Paris. Ant^ial coloured marbles, or 9eagl%ola, 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 oi the most common impurities of spring water. 

The peculiar prqperty water acquires by the presence in it of lime, is 
termed hardne^. It manifests itself by the effect such waters have upon 
the palate, and particularly by its peculiar behaviour with soap. Hard 
waters yield a lather with soap only after the whole of the liihe-salts have 
been thrown down .from the water in the form of an insoluble lime-soap. 
Upon this principle. Prof. Clark's soap-test for the hardness of waters is 
based.* The hardness produced by sulphate of lime is called permanent hard- 
nea, since it cannot be remedied. 

Ca&bonate or hiUM ; chalk ; limestone ; marble ; OaO, OO^. — Carbo- 
nate of lime, often more or less contaminated by protoxide of ircm, 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 

^ Aeooiding to M. Paul Tbenard, the phosphide of calciutai existing in this mixture, has 
the oompo^itions PCas. Br coming in contact with water, it yields liquid phosphoretted 
hydrogen, PGaa+ 2U0 — 26aO + PUi— (Page 166). 

The greater portion of tbe liquid phosphide Is immediately decomposed into aolid auA 
gaseoua pbosphoretted hydrogen.— 5 FHs»8PHs + P"H* 

■ Journal of the Pliann^oaatioal Society, toI. tL p. £96. 

242 * cAtiOiv^: 

tbey hare been subjeoied since tfreir deposition. The most ancient and 
bi^ly crystalline limestones are destitute of visible organic remains, while 
those of more recent origin are often entirely made np of the shelly exnvisB 
of once living beings. Sometimes these latter are of snch 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 ycry 
often lined with magnificent crystals of carbonate of lime or calcareous spar, 
which have evidently been slowly deposited from a watery solution. Carbo- 
nate of lime is always precipitated when an alkaline carbonate is mixed with 
a solution of that base. 

Although this substance is not sensibly soluble in pure water, is is freely 
taken up when carbonic acid happens at the same time to be present. If a 
little lime-water be poured into a vessel of that gas, the turbidity first pro- 
duced disappears on agitation, and a transparent solution of carbonate of 
lime in excess of carbonic acid is obtained. This solution is decomposed 
completely by boiling, the carbonic aCid being expelled, and the carbonate 
precipitated. Since all natural waters contain dissolved carbonic acid, it is 
to be expected that lime in this condition should be of very common occur- 
rence ; and such is really found to be the fact ; river, and more especially 
spring water, almost invariably containing carbonate of lime thus dissolved. 
In limestone districts, this is often the case to a great extent. The hardnesi 
of water, which is owing to the presence of carbonate of lime, is called fm- 
ywaryy since it is diminished to a very considerable extent by boiling, and 
may be nearly removed by mixing the hard water with lime-water, when both 
the dissolved carbonate and the dissolved lime, which becomes thus carbo- 
nated, are precipitated. Upon this principle, Prof. Clark's process of soft- 
ening water is Imsed. This process is of considerable importance, since a 
supply of hard water to towns is in many respects a source of great inconve- 
nience. As has been already mentioned, the use of such water, for the pur- 
poses of washing, is attended with a great loss of soap. Boilers in which 
such water is heated, speedily become lined with a thick stony incrustation.* 
The beautiful stalactitic incrustations of lime-stone caverns, and the deposits 
of calc-sinter or travertin upon various objects, and upon the ground in many 
places, are thus explained by the solubility of carbonate of lime in water 
containing carbonic acid. 

Crystallized carbonate of lime exhibits the curious property of dimorphism; 
calcareous spar and arragonite, although possessing the same chemical com- 
position, both containing single equivalents of lime and carbonic acid, and 
nothing besides, have different crystalline forms, different densities, and dif- 
ferent optical properties. 

The former occurs very abundantly in crystals derived from an obtuse 
rhomboid, whose angles measure 105° 6' and 74° 55^ : its density varies from 
2-5 to 2-8. The rarer variety, or arragonite, is found in crystals whose pri- 
mary form is a right rhombic prism ; a figure having no geometrical relation 
to the preceding; it is, besides, heavier and harder. 

Phosphates of limb. — A number of distinct compounds of lime and phos- 
phoric acid probably exist. Two tnbasic phosphates, 2CaO,llO,P05, and 
3CaOPOg, are produced when the correspon<£ng soda-salts are added in so- 
lution to chloride of calcium ; the first is slightly crystalline, and the second 
gelatinous. When the first phosphate is digested with ammonia, or dissolved 
in acid and re-precipitated by that alkali, it is converted into the second. 

' Many proposals have been made to prevent the formation of boile^depooits. The most 
efBdent appears 40 be the method of Dr. Ritterband, which confcists in throwing into the 
boiler a small quantity of sal-ammoniac, when carbonate of ammonia is formed, which is 
Volatilized with the steam, chioride of calcium remaining in solution. It need scarcely be 
sientioned that this plan is inapplicable in the caBe of permanently hard waters. 


Tiie earth of bones consists prtndpallj of what appears to be a combi- 
nation of these two salts. Another phosphate, containing 2 equiTalents 
of basic water, has been described, which completes the series ; it is formed, 
by dissolviog either of the preceding in phosphoric, hydrochloric, or nitrio 
acid, and evaporating until the salt separates on cooling in small platj crys- 
tals. It is this substance which yields phosphorus, when heated with char- 
coal, in the ordinary process of manufacture before described. Bibask and 
moHobtuic phQsphatee of lime also exist. These phosphates, although inso- 
lable in water, dissolye readily in dilute acids, eyen acetic acid. 

FLuaniDE OF calcium ; flvob-spar ; GaF. — This substance is important 
as the most abundant natural source of hydrofluoric acid and the other 
fluondes. It occurs beautifully crystallized, in yarious colours, in lead-yeias, 
the crystals having commonly the cubic,' but sometimes the octahedral form, 
parallel to the faces of which latter figure they always cleave. Some varie- 
ties, when heated, emit a greenish phosphorescent light. The fluoride is 
quite insoluble in water, and is decomposed by oil of vitriol in the manner 
already mentined, vide p. 149. 

Chloride op limb ; BLBAOHiNO-POWDBtt. — 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 bleach ing-powder of commerce, now manufactured on an immense scale, 
for bleaching linen and cotton goods. It is requisite, in preparing this sub- 
stance, to avoid with the, greatest care all eleyation of temperature, which 
may be easily done by slowly supplying the chlorine in the first instance. 
The product, when freshly and well prepared, is a soft, white powder, which 
attracts moisture from the air, and exhales an odour sensibly dififerent from 
that of chlorine. It is soluble in about 10 parts of water, the unaltered hy- 
drate being left behind ; the solution is highly alkaline, and bleaches feebly. 
"When hydrate of lime is suspended in cold water, and chlorine gas trans- 
mitted through the mixture,- the lime is gradually dissoWed, and the same 
peculiar bleaching eompound produced ; the alkalis also, either caustic or 
carbonated, may by similar means be made to absorb a large quantity of 
chlorine, and give rise to corresponding compounds ; such are the " disinfect* 
log solutions" of M. Labarraque. 

The most consistent view of the constitntion of these curious compounds 
is that which supposes them to contain salts of hypochlorons acid, a substance 
as remarkable for bleaching powers as chloriae itself; and this opinion seems 
borne out by a careful comparison of the properties of the bleaching-salts 
with those of the true hypochlorites. Hypochlorous acid can be actually ob- 
tained from good bleaching-powder, by distilling it with dilute sulphuric or 
nitric acid, in quantity insuflicient to decompose the whble ; 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. 

\ Calcium - 
Chlorine - 
Lime ^ • ^ ^'^ ■Hypochlorite of lime. 

When the temperature of the hydrate of lime has risen during the absorption 
of the chlorine, or when the compound has been subsequently exposed to 
heat, its bleaching properties are impaired or altogether destroyed ; it then 
contains chlorate of lime and chloride of calcium ; oxygen, in variable quan* 

* M. eay-Lnasae, Ann. CfaJm. et Phys. 3rd series, v. 206 


tity, ir Qtfibilly M free. Thff nDie chan^ seeiqB to ensue by loBg keeping, 
even at the common temperature of the air. In an open vessel it is speedily 
destroyed by llie carbonic acid of the atmosphere. Commercial bleaching- 
]^wder thus constantly varies in value with its age, and with the care origi- 
nally bestowed upon its preparation ; the best may contain about 30 per cent 
of available chlorine, easily liberated by an acid, which is, however, far short 
of the theoretical qpiantity. 

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 
6t lime and then transferred to a vat containing dilute sulphuric acid. De- 
eomposition ensues ; both the lime of the hypochlorite and the calcium of 
the chloride are converted into sulphate of lime, while the free hypochloroos 
and hydrochloric acids yield water and free chlorine. 

The chlorine thuit disengaged in contact with the cloth, causes the destrac- 
lion of the colouring matter. This process is often repeated, it being unsafe 
to use strong solutions. White patterns are on this principle imprinted upon 
coloured cloth, the figures beiog stamped with tartaric acid thickened with 
gum-water, and tiien the stuff immersed in the chloride bath, when the 
jparts to which no acid has been applied remain unaltered, while the printed 
j^ortions are bleached. 

For purifying an offensive or infectious atmosphere, as an aid to proper 
venHiatiofif the bleaching-powder is very convenient. The solution is exposed 
in riiallow vessels, or cloths steeped in it are suspended in the apartment, 
when the carbonic add of the air slowly decomposes it in the manner above 
described. An addition of a strong acid clauses rapid disengagement of 

The TaTue of any sample of bleaching-powder tnay be easily determined by 
the following me^od, in which the loosely combined chlorine is estimated 
by ittf effect in peroiidizing a protosalt of iron, of which two equivalents re- 
quire one of cbJorine ; the latter acts by decomposing water and liberating 
a corresponding quantity of oxygen — 78 (more correctly 78-16) grains of 
green sulphate of iron acre disetolved in about two ounces of water, and acidu- 
lated by a fsw drops of sulphuric or hydrochloric acid ; this quantity will 
require for peroxidation 10 grains of chlorine. Fifty grains of the chloride 
of lime to be examined are next rubbed up with a little tepid water, and the 
whole transferred to the alkalimeter * before described, which is then filled 
up to with water, after which the contents are well mixed by agitation. 
The liquid is next gradually poured into the solution of iron, with constant 
stirring until the latter has become peroxidized, which may be known by a 
drop ceasing to give a deep blue precipitate with ferricyanide of potassium. 
The number of grain^measures of the chloride solution employed may then 
be read off, since these must contain 10 grains of serviceable chlorine, the 
quantity of the latter in the 50 grains may be easily reckoned. Thus, sup- 
pose 72 such measures have been taken, then 

Measures. Ors. chlorine. Measures. Gnu cblorina. 

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, 
ftnd from each other. 

Caustic potassa, 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. 

* Vid« p. 227. * Graham's Slements, toI. t. p. 414. 


Alkaline carbonates, and carbonate of ammonia, give white predpitatee, 
insoluble in excess of the precipitant, with all three. 

Sulphuric acid, or a sulphate, added to Tery dilute eolations of the earths 
in qaestion, gives an immediate white precipitate with baryta, a similar pre- 
cipitate after a short interval with strontia, and occasions no change with 
the lime-salt. The precipitates with baryta and strontia are quite insoluble 
in nitric acid. 

Solution of sulphate of lime gives an instantaneous cloud with baryta, 
and one with strontia after a little time. Sulphate of strontia is itself suffi- 
ciently soluble to occasion turbidity when mixed with chloride of barium. 

Lastly, the soluble oxalates give a white precipitate in the most dilute so- 
lutions of lime, which is not dissolved by a drop or two of hydrochloric nor 
by an excess of acetic acid. This is an exceedingly characteristic test. 

The chlorides of strontium and calcium dissolved in alcohol colour the 
flame of the latter red or purple ; salts of baryta eommnnicate to the flame 
a pale green tint. 


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 met^ilUe magnesium set free. When the tube 
and its contents are completely cold, it is broken up, and the fragment)^ put 
into cold water, by which the metal is separated from the salt. 

Magnesium is a white, malleable metal, fusible at a red-heat, and not sen- 
sibly acted upon by cold water ; it is oxidized by hot water. Heated in the 
air, it burns and produces magnesia, which is the only oxide. Sulphuric 
and hydrochloric acids dissolve it readily, evolving hydrogen. 

The equivalent of this metal is 12, and its symbol Mg. 

Magnesia; calcined magnesia; MgO. — This is prepared with great ease 
by exposing the magnesia alba of pharmacy to a full red-heat in an earthen 
or platinum crucible. It forms a soft, white powder, which slowly attracts 
moisture and carbonic acid from the air, and unites quietly with water to a 
hydrate which possesses a feeble degree of solubility, requiring about 5,000 
parts of water at 60° (15°-5C) and 36,000 parts at 212° (lOO^C). The al- 
kalinity of magnesia can only be observed by placing a small portion in a 
moistened state upon test-paper; it neutralizes acids, however, in the most 
complete manner. It is infusible. 

Chloride of magnesium, MgCl. — When magnesia, or its carbonate, is 
dissolved in hydrochloric acid, there can be no doubt respecting the simul- 
taneous production of chloride of magnesium and -water; but when this so- 
lution comes to be evaporated to dryness, the last portions of water are 
retained with such obstinacy, that decomposition of the water is brought 
about by the concurring attractions of magnesium for oxygen, and of chlo- 
rine for hydrogen; hydrochloric acid is expelled, and magnesia remains. 
If, however, sal-ammoniac or chloride of potassium happen to be present, a 
double salt is produced, which is easily rendered anhydrous. The best mode 
of preparing the chloride is to divide a quantity of hydrochloric acid into 
two equal portions, to neutralize one with magnesia, and the other with am- 
monia, or carbonate of ammonia; to mix these solutions, evaporate them to 
drynesti, and then expose the salt to a red-heat in a loosely covered porce- 
lain crucible. Sal-ammoniac sublimes, and chloride of magnesium in a fused 
state remains ; the latter is poured out upon a clean stone, and when cold, 
transferred to a well-stopped bottle. 

The chloride so obtained is white and crystalline. It is very deliquescent 

i46 MAGNESIU«t. 

ididl Mf^ly solnbltf in water, front Irhieh it oandot again be reco?erecl by 
eyaporation, for tbe reasoDS jast mentioned. When long exposed to tbe air 
in A malted state, it is conTerted into magnesia. It is soluble in alcohol 

Sulphate of magnesia Epsom salt; MgO,SOj4-7HO. — This salt occurs 
in sea-water, and in that of many mineral springs, and is now manufactured 
in large qnantities by acting on magnesian lime-stone by diluted sulphuric 
acid, and separating the sulphate of magnesia from the greater part of the 
slighOy 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« (160-6C), and in a still smaller quantity at 212° (100°C). 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 oif, 
the seventh being energetically retained. Sulphate of magnesia forms beau- 
tifbl double salts with ihe sulphates of potassa and ammonia, which contain 
6 equivalents of water of crystallization. 

Cabbonate of magnesia. — The neutral carbonate, MgO,COg, occurs native 
in rhombohedral crystals, resembling those of calcareous spar, embedded in 
talc-slate : a soft earthy variety is sometimes met with. 

When magnesia alba is dissolved in carbonic acid water, and the solution 
left to evaporate spontaneously, small prismatic crystals are deposited, 
which consist of carbonate of magnesia, with 8 equivalents of water. 

The magnesia alba itself, although often called carbonate of magnesia, is 
iiot so in reality ; it is a compound of carbonate With hydrate. It is pre- 
pared by mixing hot solutions of carbonate of potassa or soda, and sulphate 
of magnesia, the latter being kept in slight excess, boiling the whole a few 
minutes, during which time much carbonic acid is disengaged, and then well 
washing the precipitate so produced. If the solution be very dilute, the 
magnesia alba is exceedingly light and bulky; if otherwise, it is denser. 
The composition of this precipitate is not perfectly constant. In most cases 
it contains 4(MgO,COj,) + Mga,HO-|- 6H0. 

Magnesia alba is Slightly soluble in water, especially when cold. 

Phosphate of magnesia, 2MgO,HO,POg-hl4HO. — This salt separates 
in small colourless prismatic crystals when solutions of phosphate of soda 
and sulphate of magnesia are mixed and suflfered to stand some lime. Prof. 
Graham states that it is soluble in about 1,000 parts of cold water, but 
Berzelius describes a phosphate which only requires 15 parts of water for 
solution : this can hardly be the same substance. Phosphate of magnesia 
exists in the grain of the cereals, and can be detected in considerable 
quantity in beer. 

Phosphate of magnesia a»d ammonia, 2MgO,NH^O,P05-f-12HO.— When 
a Soluble phosphate As mixed with a salt of magnesia, and ammonia or its 
carbonate added, a crystalline precipitate, having the above composition, 
subsides immediately, ii the solutions are concentrated, and aft«T 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. 
Whjen heated, it is resolved into bibasic phdsphate (pyrophosphate) of mag- 
nesia, containing 86-71 per cent, of magnesia. At a strong red-heat it fuses 
to a white enamel-like mass. The phosphate of magnesia and ammonia 
sometimes forms an urinary calculus. 

In practical analysis, magnesia is often separated from solutions by 
bringing it into this state. The liquid, free from alumina, lime, &c., ia 
mixed with phosphate of soda and excess of ammonia, and gently heated 
tor a short tiiAe. The precipitate is collected upon a filter and thoroughly 
Washed with water containing a little sal-ammoniac, after which it is dried, 
ignited to redness^ and weighed. The proportion of magnesia ia then easily 

Silicates of magkesia. — The following natnral compounds belong to this 
class: — Steatite or soap-stone^ MgCSiOj, asoft, white, or pale-coloured, amor- 
phons substance, found in Cornwall and elsewhere ; Meerschaum^ MgO,SiOj-l- 
HO, from which pipe-bowls are often manufactured ; — Chrysolite, 3MgO,SiOj, 
& crystallized mineral, sometimes employed for ornamental purposes ; a por- 
tion of magnesia is commonly replaced by protoxide of iron which communi- 
cates a green colour ; — Serpentine is a combination of silicate and hydrate of 
magnesia ; — J'ade, an exceedingly hard stone, brought from New Zealand, con- 
tains silicate of magnesia combined with silicate of alumina ; its green 
coloar is due to sesquioxide of chromium; — Augite and hornblende are 
essentially doable salts of silicic acid, magnesia, and Hrae, in which the 
magnesia is more or less replaced by its isomorphous substitute, protoxide 
of iron. 

The salts of magnesia are strictly isomorphous with those of the protox- 
ides of zinc, of iron, of copper, &o. ; they are usually colourless, and are 
easily recognised by the following characters i — 

A gelatinous white precipitate with caustic alkalis, including ammonia, 
insoluble in excess, but soluble in solution of sal-ammoniac. 

A white precipitate with the carbonates of potassa and soda, but nans 
with carbonate of ammonia in the cold. 

A white crystalline precipitate with soluble phosphates, on the addition 
of a little ammonia. 




Alumina, the only known oxide of this metal, is a substance of very aban- 
dant occurrence in nature in the state of silicate, as in felspar and its asso- 
ciated minerals, and in the various modifications of clay thence derived. 
Aluminium is prepared in the same manner as magnesium, but with rather 
more difficulty ; a platinum or iron tube closed at one extremity may be em- 
ployed. Sesquichloride of aluminium is first introduced, and upon that 
about an equal bulk of potassium loosely wrapped in platinum foil. The 
lower part of the tube is then heated so as to sublime the chloride and bring 
its vapours in contact with the melted potassium. The reduction takes place 
with great disengagement of heat. The metal, separated by cold water from 
the alkaline chloride, has a tin-white colour and perfect lustre. It is oly- 
tained in small fused globules by the heat of reduction, which are malleable, 
and have a specific gravity of 2-6. When heated in the air or in oxygen, it ■ 
takes fire and burns with brilliancy, producing alumina. 

Aluminium has for its equivalent the number 13*7 ; its symbol is Al. 

Alumina, Al^O,. — This substance is inferred to be a sesquioxide, from its 
isomorphism with the red oxide of iron. It is prepared by mixing solution 
of alum with excess of ammonia, by which an extremely bulky, white, gela- 
tinous precipitate of hydrate of alumina is thrown down. This is washed, 
dried, and ignited to whiteness. Thus obtained, alumina constitutes a white, 
tasteless, coherent mass, very little acted upon by acids. The hydrate, on 
the contrary, when simply dried in the air, or by gentle heat, dissolves freely 
in dilute acid, and in caustic potassa or soda, from which it is precipitated 
by the addition of sal-ammoniac. Alumina is fusible before the oxyhydro- 
gen blowpipe. The mineral called corundum^ of which the ruby and sap- 
phire are transparent varieties, consists of nearly pure alamina in a crystal- 
lized state, with a little colouring oxide ; emery, used for polishing glass and 
metals, is a coarse variety of corundum. Alumina is a very feeble base, 
and its salts have often an acid reaction. 

Sesquichloride of aluminium, AljClg. — The solution of alumina in hydro- 
chloric acid behaves, when evaporated to dryness, like that of magnesia, the 
chloride being decomposed by the water, and alumina and hydrochloric acid 
produced. The chloride may be thus prepared : — Pure precipitated alumiua 
is dried and mixed with lampblack, and the mixture strongly calcined in a 
covered crucible. It is then transferred to a porcelain tube fixed across a 
furnace, and heated to redness in a stream of chlorine gas, when the alu- 
mina, yielding to the attraction of the chlorine on the one haud, and the 
carbon on the other, for each of its constituents, suffers decomposition, car- 
bonic oxide being disengaged, and sesquichloride of aluminium formed ; the 
latter sublimes, and condenses in the cool part of the tube. 

^ A^IiUMINIUM. 249 

S^si^aii^lbride of almniniiim is a ei7Blsl£A« ydlloirah mAMdam^, exe^y- 
meij greedy of moisture, and yery soluble. Once dissolved, it cannot be 
again recoyered. It is said to combine with sidrphnretted and phospfaoretted 
liydrogen, and witii ammonia. 

Sulphate of alumina, AlgOg^SSOg-f-l^HO* — Prepared by saturating 
dilute sulphuric acid with hydrate of alumina, and evaporating. It crystal- 
lizes in thin, pearly plates, soluble in^ 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 aiiso described, one of which is insoluble in water. 

Sulphate of alumina combines with the sulphates of potassa, soda, and 
ammonia,' forming double salts of great interest, the alumg. Common alum, 
the soui^ce of all the preparations of alumina, contains AljO-^SSO^-I^KOySOy 
4-24HO. It is manufactured, on a very large scale, from a kind of slaty clay, 
loaded with bisulphide of iron, which abounds in certain parts. This is 
gently roasted, and then exposed to the air in a moistened state ; oxygen ia 
absorised, I3ie sulphur becoJies acidified, sulphate of protoxide of iron and 
sulphate of alumina are produced, and afterwards separated by lixiviation 
with water. The solution ia next concentrated, and mixed with a qnantLty 
of chloride of potassium, which decomposes the iron-salt, forming proton 
chloride of iron and sulphate of potassa, which latter con^bines, with tho 
sulphate of alumina, to alum. By crystallization, the alum is separated 
from the highly soluble cUoride of iron, aitd afterwards eadily purified by a 
repetition of that process. Other methods of alum-iiiaking exist, and vr^ 
BometimeB employed. Potassa-alum crystallizes in colourless, transparent 
octahedrons, which often exhibit ^e faces of the cube. It has a sweetish 
and astringent taste, reddens litmus paper, and dissolves in IS parts of water 
at 60° (15® '50), and in its own weight of boiling water. Exposed to heat, 
it is easily rendered anhydrous, and, by a very high temperature, decom«- 
posed. The crystals have little tendency to change in the air. Alum is 
largely used in the arts, in preparing skins, dyeing, &c. ; it is occasionally 
contaminated with oxide of iron, which interferes with some of its applica- 
tions. The celebrated Roman alum, made from alum-stonef a felspathic rock, 
altered by sulphurous vapours, was once much prized on account of its free- 
dom from this impurity. 

A mixture of dried alum and sugar, carbonized in an ope'n pan, and then 
heated to redness, out of contact of air, furnishes iht pyrophortis of Homherg^ 
which ignites spontaneously on exposure to the atmosphere. The essential 
ingredient is, in all probability, finely divided sulphide of potassium. 

Soda-alufh, in which sulphate of soda replaces sulphate of pfotassa, has a 
form and constitution similar to that of the salt described ; it is, however, 
much more soluble, and difficult to crystallize. 

Ammonia-alumy containing l!fH40,S03, instead of KO,SO-, very closely re- 
sembles common potassa-alum, having the same figure, and appearance, and 
constitution, and nearly the same degree of solubility as that substance It 
is sometimes manufactured foi* commercial use. When heated to redness, it 
yields pure alumina. 

Few of the other salts of alumina, except th& silicates, present points of 
interest ; these latter are of great importance. Silicates of alumina eniei 
into the composition of a number of crystallized minerals, among which 
felspar occupies, by reason of its abundant occurrence, a prominent place. 
Granite, porphyry, trachyte, and other ancient unstratified rocks, consist iu 
great part of this mineral, which, under peculiar circumstances, by no means 
well understood, and particularly by the action of the carbonic acid of the 
air, suffers complete decomposition, becoming converted into a soft, friable 
mass of earthy matter. This is the origin of clay ; the change itself is seen 


in great perfection in certain districts of Deyonshire and Cornwall, the felspar 
of the fine white granite of those localities being often disintegrated to an 
extraordinary depth, and th,e rock altered to a substance resembling soft 
mortar. By washing, this finely divided matter is separated from the quart* 
and mien, 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 porcelam. 
The composition assigned to unaltered felspar is AljOj,, dSiOs+KO.SiOj, or 
alum, having silicic acid in the place of sulphuric. The exact nature of the 
change by which it passes into porcelain clay is unknown, although it evi- 
dently consists in the abstraction of silica and alkali/ 

TVhen the decomposing rock contains oxide of iron, the clay produced is 
coloured. The different varieties of shale and slate result from the alteration 
of ancient clay-beds, apparently in many instances by the infiltration of water 
holding silica in solution ; the dark appearance of some of these deposits is 
due to bituminous matter. 

It is a common mistake to confound clay with alumina ; all clays are es* 
eentially 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 marU, and 
are recognized by effervescing with acids. 

A basic silicate of alumina, 2AI2OS, SiO,, is found crystallized, constitu'ting 
the beautiful mineral called cyanite. The compounds formed by the union 
of the silicates of alumina with other silicates are almost innumerable; a 
8oda-felspar, aUnte, containing that alkali in place of potassa, is known, and 
theve are two somewhat similar lithia-compounds apodumene and petaUte. 
The zeolites belong to this class: analdvie^ nephelme. mesotypcy &c., are do'uble 
silicates of soda and alumina, with water of crystallization. Siilbitej heulan" 
dile, laumonite, prehniUt &o., consist of silicate of lime, cotnbined with silicate 
of alumina. The garnets, axiniie, mica^ &c., have a similar composition, bnt 
are anhydrous. Sesquioxide of iron is very often substituted for alumina 
in these minerals. 

Alumina, when in solution, is distinguished without difficulty. 

Caustic potassa and soda occasion white gelatinous precipitates of hydrate 
of alumina, freely soluble in excess of the alkali. ^ 

Ammonia produces a similar precipitate, insoluble in excess of the reagent 

The alkaline carbonates and carbonate of ammonia precipftate the hydrate, 
with escape of carbonic acid. The precipitates are insoluble in excess. 


This metal is prepared from the chloride in the same manner as aluminium. 
It is fusible with great difficulty, not acted upon by cold water and burns 
when heated in the air, producing berylla. 

The equivalent of beryllium is 6-9, and the symbol Be. 

*■ A specimen of white porcelain clay from Dartmoor, Devon, gave the author ihe following 
result on analysis :— 

Silica 47-20 

Alumina, with trace of iron and manganese ..... S8*S0 

Lime 0-24 

Water 12O0 

AlkaU and loss : 1-76 



BsftTLLA, BejOg, is a rare earth found ip the emerald, beryl, and eudaee^ 
from which it may be extracted by a tolerably simple process. It very much 
resembles alamina, but is distinguished from that substance by its solubility, 
when freshly precipitated, in a cold solution of carbonate of ammonia, from 
which it is again thrown down on boiling. The salts of berylla haye a sweet 
taste, whence its former name glucina {y^vKis)' 

The metal of a very rare earth, ytiria, contained in a few scarce minerals. 
The name is derived from Ytterby, a place in Sweden, where one of these, 
gadoUniU^ 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 yery powerful base, the two others are weak ones. They are 
separated with extreme difficulty. 


The oxides of these very rare metals are found associated in the Swedish 
mineral eerite; the equivalent of cerium is about 47, and its symbol Ce. 
This metal forms a protoxide CeO, and a sesquioxide CcjO,. 

The crude sesquioxide of cerium obtained by precipitating the double 
sulphate of cerium and potassa directly derived from eerite by carbonate of 
potassa, has been shown by Mosander to contain in addition to sesquioxide 
of cerium, the oxides of two other metals, to which the above names were 
given. After ignition it is red-brown. The complete separation of these 
three bodies is attended with the greatest difficulty, and has indeed been 
only partially accomplished.^ Oxide of cerium may be obtained pure by 
beating the mixture of the three oxides first with diluted and afterwards 
with concentrated nitric acid, which gradually removes the whole of the 
oxides of lathanium- and didymium. 

The yellow oxide of cerium, obtained by igniting the nitrate, is a mixture 
of pro to- and sesquioxide, which are extremely difficult to obtain in a sepa- 
rate state. The salts of the former are colourless, and are completely pre- 
cipitated by sulphate of potassa ; the sulphate of the sesquioxide is yellow, 
and forms a beautiful double salt with sulphate of potassa, which is decom- 
posed by water. The metal cerium has been obtained from the chloride by 
the action of sodium. 

Oxide of lanthanium, as pure as it has been obtained, forms a very pale 
salmon-coloured powder, unchanged by ignition in open or close vessels. In 
contact with water it gives a snow-white bulky hydrate which has an alkaline 
reaction, and decomposes ammoniacal salts by boiling. Its salts are 
crystallizable, colourless, sweet, and astringent, and are precipitated by 
sulphate of potassa. 

A tolerably pure lanthanium-salt may be obtained by slowly crystallizing 
an acid solution containing the sulphates of lanthanium and didymium, 
picking out the rose-coloured crystals ^containing didymium), and the viole* 
ones (containing lanthanium and didymium), adding the solution of the lattei 
to the mother-liquor^ and repeating the process. In this manner the whole 
of the didymium-salt may be finally separated by crystallization. MetalUo 
lanthanium is prepared like cerium. 

The occasional brown colour of crude oxide of cerium is due to oxide of 

* A Rynopsls of the various methods for the separation of cerium, lanthanium, and didy 
miom has been given by Mr. H. Watts. Chem. Soc Quar. Jour, it 140. 

252 gUliCONIUM — TQOHIUA^ — aL^ii9. 

di^ymiuni. Jn & pore state, it formfl a brown powder, soluble \n Aoids, And 
generating a seri^ of red 4;ry«tallizable salts, from which caustic potasju 
prec^itates a Tiolet- blue liydrate, quickly ohanging by exposure to tiie air. 
It oommuaicates to glass an amethystine colour.' 


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 bu^iished. It takes fire when heated in 
.the air. 

The equiyalent of zirconium is 33 <6, aud its symbol Zr. 

ZiitcoNiA, Zr.Og, 13 a rare earth, very closely resembling Alumina, fonnd 
together with ewGikf in the mineral zircon. The 3aLt8 are colourless and have 
.an astringent taste. 

gvanberg has rendered it probable that an undescribed vietaUic oxide 
exists in certain varieties pf zircon, for the metal of which he proposes the 
name of norium, 


The metal of an earth from a very rare mineral, thorite; it agrees in 
character with aluminium, and is obtained by similar means. 

The equivalent of thorium is 59-6, and its symbol Th. 

Thobia, ThQ, is remarkable for its great specific gravity, and is otherwise 
distinguished by peculiar properties which separate it from all other 

Manufaoture of Okus, PoreeUnnj and Earikenware, 

GLAi^s.-^^lass is a mixture of various insoluble silicates, with excess of 
silica, -altogether destitute of crystalline structure: the simple silicates, formed 
by fusing the bases with silicic acid in equivalent proportions, very often 
crystallize, which happens also with the greater number of the natural sili- 
cates included among the earthly minerals. Compounds identical with some 
.of these are also occasionally formed in artificial processses, where large 
.masses pf melted glassy matter are suffered to cool slowly. The alkaline 
silicates, when in a §tate of fusion, have the powder 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-gloat belong to the former division ; flint- 
4flat8, and the material of artificial gems to the latter. The lead promotes 
fusibility, and confers also density and lustre. Common ^reen bottle glass 
contains no lead, but much silicate of black oxide of iron, derived from the 
impure materials. The principle of the glass manufacture is very simple. 
Silica, in the shape of sand, is heated with carbonate of potassa or soda, 
and slaked lime or oxide of lead ; at a high temperature, fusion and combi- 
nation occur, and the carbonic acid is expelled. When the melted mass has 
become perfectly dear and free from air-bubbles, it is left to cool until it as- 
sumes the peculiar tenacious condition proper for working. 

The operAtion of fusion is conducted in lArge crucibles of refiractory fire- 
clay, which in the case of lead-glass are covered by a dome at the top, and 
■have an opening at the side by which the materials are introduced and the 
melted glass withdrawn. Great care is exercised in the choice of the sand, 
which must be quite white and free from oxide of iron. Red-lead, one of 
the higher oxides, is preferred to litharge, although immediately reduced to 

* Annalen d»r Gbemie uadPhannade. xlviiL 2}Q. 

GLASS. 9$ft 

prejtoxlde bjr tlfee hent^ the liberated oxygen aemng to deatro]'^ voy eombuar^ 
tlble matter which might accidentally find its w^y into the crucible and stain, 
the glass by reducing a portion of the lead. Potassa gives a better glasa 
than soda» although the latter is very generally employed, from its lower 
price. A certain proportion of broken and waste glass of the same kind ia 
always added to the other materials. 

Articles of blown glass are thus made: — The workman begins by collect- 
ing a proper quantity of soft, pasty glass at the end of his hlow-pipe^ aa 
iron tube, fiye or six feet in length, terminated by a mouth-piece of wood ; 
he then, commences blowing, by which the lump is expanded into a kind of 
flask, susceptible of haying its form modified by the position in which it ia 
held, and the Telocity of rotation continually given to the iron tube. If an 
open-mouthed yessel is to be made, an iron rod, called a pontil or puntil, ia 
dipped into the glass-pot and applied to the bottom of the flask, to which it. 
thus serves as a handle, the blowpipe being removed by the application of a 
cold iron to the neck. The vessel is then re-heated at a hole left for the 
purpose in the wall of the furnace, and the aperture enlarged,' and the vessel 
otherwise altered in figure by the aid of a few simple tools, until completed. 
It is then detached, and carried to the annealing oven, where it undergoea 
slow and gradual cooling during many hours, the object of which is to obvi- 
ate the excessive britUeness always exhibited by glass which has beea 
quickly cooled. The large circular tabl^ of crown-glaiss are made by a very 
curious process of this kind ; the globular flask at first produced, trans- 
ferred from the blowpipe to the pon^ is suddenly made to assume the foroi 
of a flat disc by the centrifugal force of the rapid rotatory movement given 
to the rod. Plate-glass is cast upon a flat metal table, and after very care- 
ful annealing, ground true and polished by suitable machinery. Tubes aro 
made by rapidly drawing out a hollow cylinder ; and from these a great va- 
riety of useful apparatus may be constructed with tke help of a lamp and 
blowpipe, or still better, the bellows-table of the barometer-maker. SmaU 
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 resulta 
on analysis : — 

Bohflmian plftt^iglaai (excellent).* 

Silica 600 

Potassa 250 

lime 12-6 



Silica 61-93 

Potassa 13-77 

Oxide of lead 88-28 


The difficultly-fusible white Bohemian tube, so invaluable ia organio ohe« 
mistry, has been found to contain in 100 parts : — 

SiUca 72-80 

Lime, with trace of alumina 9-68 

Magnesia -40 

Potassa 16-80 

Traces of manganese, &o., and loss -82 

Different colours are often communicated to glass by metallic oxides. 
Thus, oxide of cobalt gives deep blue ; oxide of manganese, amethyst ; sub- 
oxide of copper, ruby-red ; black oxide of copper, green ; the oxides of 
iron, dull green or brown, &c. These are either added to the melted eon 

« MitocherUch» Lebrbuch, ii. 187. > fvOiBf, 



tents of the glass-pot, in which they dissolye, or applied in a particular 
manner to the surface of the plate or other object, which is then re-heated 
until fusion of the colouring matter occurs ; such is the practice of enam- 
elling and glass-painting. An opaque white appearance is given by oxide 
of tin ; the enamel of watch-faces is thus prepared. 

When silica is melted with twice its weight of carbonate of potassa or 
Boda, and the product treated with water, the greater part dissolves, yielding 
a solution from which acids precipitate gelatinous silica. This is the solubk 
glata sometimes mentioned by chemical writers ; its solution has been used 
for rendering muslin and other fabrics of cotton or linen less combustible. 

PoBCELAiN AND EABTHBNWABE. — The plasticity of natural clays, and their 
hardening when exposed to heat, are properties which suggested in very early 
times their application to the making of vessels for the various purposes of 
daily life ; there are few branches of industry of higher antiquity than that 
exercised by the potter. 

True porcelain is distinguished from earthenware by very obvious charac- 
ters. In porcelain the body of the ware is very compact and translucent, 
and breaks with a conchoidal fracture, symptomatic of a commencement of 
fusion. The glaze, too, applied for giving a perfectly smooth surface, is 
closely adherent, and in fact graduates by insensible degrees into the sub- 
stance of the body. In earthenware, on the contrary, the fracture is open 
and earthy, and the glaze detachable with greater or less facility. The com- 
pact and partly glassy character of porcelain is the result of the admixture 
with the^lay of a small portion of some substance, fusible at the temperature 
to which the ware is exposed when baked or fired, and which, absorbed by 
the more infusible portion, binds the whole into a solid mass on cooling ; 
such substances are found in felspar, and in a small admixture of silicate 
of lime, or alkali. The clay employed in porcelain-making is always 
directly derived from the de(5&mposed felspar, none of the clays of the secon- 
dary strata being pure enough for the purpose ; it must be white, and free 
from oxide of iron. To diminish the retraction which this substance under- 
goes in the fire, a qantity of finely divided silica, carefully prepared by 
crushing and grinding calcined flints or chert, is added, together with a 
proper proportion of felspar or other fusible material, also reduced to impal- 
pable powder. The utmost pains are taken to eflfect perfect uniformity of 
mixture, and to avoid the introduction of particles of grit or other foreign 
bodies. The ware itself is fashioned either on the potter's wheel ; — a kind 
of vertical lathe ; — or in moulds of plaster of Paris, and dried, first in the air, 
afterwards by artificial heat, and at length completely hardened by exposure 
to the temperature of ignition. The porous biscuit is now fit to receive its 
glaze, which may be either ground felspar, or a mixture" of gypsum, silica, 
and a little porcelain clay, diflfused through water. The piece is dipped for 
a moment into this mixture, and withdrawn ; the water sinks into its sub- 
stance, and the powder remains evenly spread upon its surface ; it is bnce 
more dried, and lastly, fired at an exceedingly high temperature. 

The porcelain-furnace is a circular structure of masonry, having several 
fire-places, and surmounted by a lofty dome. Dry wood or coal is consumed 
as fuel, and its flame directed into the interior, and made to circulate around 
and among the earthen cases, or seggars in which the articles to be fired are 
packed. Many hours are required for this operation, which must be very 
carefully managed. After the lapse of several days, when the furnace has 
completely cooled, the contents are removed in a finished state, so far as 
regards the ware. 

The ornamental part, consisting of gilding and painting in enamel, has yet 
to be executed, after which the pieces are again heated, in order to flux the 
oolours. This operation has sometimes to be repeated more than once. 

The mannfactare of porcelain in Europe is of modem origin ; tbe Chinefft 
iiave possessed the art from the commencement of the seventh century, and 
their ware is, in some respects, altogether unequalled. The materials em* 
ployed by them are known to be kaoUn^ or decomposed felspar ; petuntzty or 
quartz reduced to fine powder ; and the ashes of fern, which contain carbonate 
of potassa. 

Stoneware. — This is a coarse kind of porcelain, made from clay containing 
oxide of iron and a little lime, to which it owes its partial fusibility. The gla- 
zing is perfprmed by throwing common salt into the heated furnace ; this is vo- 
latilized, and decomposed by the" joint agency of the silica of the ware, and 
of the yapour of water always present ; hydrochloric acid and soda are pro- 
duced, the latter forming a silicate, which fuses over the surface of the ware, 
and gives a thin, but excellent glaze. 

Earthenware. — The finest kind of earthenware is made from a white 
secondary clay, mixed with a considerable quantity of silica. The articles 
are thoronghly dried and fired, after which they are dipped into a readily 
fusible glaze-mixture, of which oxide .of lead is usually an important ingre- 
dient, and, when dry, re-heated to the point of fusion of the latter. The 
whole process is much easier of execution than the making of porcelain, and 
demands less care. The ornamental designs in blue and other colours, so 
common upon plates and household articles, are printed upon paper in enamel 
pigment, mixed with oil, and transferred, while still wet, to the unglazed 
ware. When the ink becomes dry, the paper is washed off, and the glazing 

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 gjound ware of 
the same description. The Hessian and Cornish crucibles are among the 
best. Sometimes a mixture of plumbago and clay is employed for the same 
purpose ; and powdered coke has been also used with the earth ; such cru- 
cibles bear rapid changes of temperature with impunity. 






Makoavxse is tolerably abundant in nature in an oxidized state, forming, 
or entering into the compoBition of» several interesting minerals. Traces of 
this substance are very frequently found in the ashes of plants. 

Metallic manganese, or perhaps, strictly, carbide of manganese, may be 
best prepared by the foUoiriDg process. The carbonate is calcined in an 
open yessel, 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 
«f anhydrous borax. A charcoal crucible is next prepared by filling a Hes- 
viam 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 mixtore is compressed, and 
covered with .charcoal-powder. The lid of the crucible is then fixed, and 
the whole arranged in a rerj powerful wind-furnace. The heat is slowly 
raised until the crucible becomes red-hot, after which it is urged to its maxi- 
-mum for an hour or more. When -cold, the crucible is broken up, and the 
metallic button of manganese extracted. 

Manganese is a greyish-white metal, resembling some varieties of cast- 
iron ; it is hard and brittle, and destitute of magnetic properties. Its spe- 
cific gravity is about 8. It is fusible with great 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 sulphuric acid dissolves it with great energy, evolving hydrogen. 

The equivalent of manganese is assumed to be 27-6; its symbol is Mn. 

Oxides of Manganese. — Seven different oxides of this metal are described, 
but two out of the number are, probably, secondary compounds. 

Protoxide MnO 

Sesquioxide MnjOj 

Binoxide MnO^ 

Proto-sesquioxide (red oxide) , MnjO^ssMnO, MnjO, 

Varvicite Mn407=MnjO32Mn0j 

Manganic acid MnO, 

Permanganic acid Mn^O^ 

Protoxide, MnO. — When carbonate of manganese is heated in a stream 
of hydrogen gas, or of vapour of water, the carbonic acid is disengaged, 
and a green-coloured powder left behind, which is the protoxide. Prepared 
at a dull red-heat only, the protoxide is so prone to absorb oxygen from the 
air, that it cannot be removed from the tube without change ; but when at a 
higher temperature it appears more stable. This oxide is a very powerful 


•base, being isomorplioiis with magnesia and rine ; it diseoWes quietly in 
dilate aoids, neutralizing them completely and forming salts, which have 
often a beautiful pink colour. When alkalis are added to solutions of these 
compounds the white hydrated oxide first precipitated speedily becomes 
brown by passing into a higher state of oxidation. 

SssQuioxiDE, MngOj. — This compound occurs in natnre in the state of 
hydrate; a Tery beautiful crystallized Tariety is found at Uefeld, in the 
Harti. It is produced artificially, by exposing to the air the hydrated prot- 
oxide, and forms the principal part of the residue left in the iron retort when 
oxygen gas is prepared by exposing the native binoxide to a moderate red- 
heat. The colour of the sesquioxide^is brown or black, according to its 
origin or mode of preparation. It is a feeble base, isomorphous with alu- 
mina ; for, when gently heated with diluted sulphuric acid, it dissolves to a 
red liquid, which, on the addition of sulphate of potassa or of ammonia, 
deposits octahedral crystals having the constitution of common alum ; these 
are, however, decomposed by water. Strong nitric acid resolves this oxide 
into a mixture of protoxide and binoxide, the former dissolving, and the 
latter remaining unaltered ; while hot oil of vitriol destroys it by forming 
sulphate of the protoxide, and liberating oxygen gas. Heated with hydro- 
chloric acid,' chlorine is evolved, as with the binoxide, but to a smaller extent. 
Binoxide, MnO,. — The most common ore of manganese ; it is found both 
massive and crysUilUzed. It may be obtained artificially in the anhydrous 
state by gently calcining the nitrate, or in combiaation with water, by adding 
BolutioQ of bleaching-powder to a salt of the protoxide. Binoxide of man- 
ganese has a black colour, is insoluble in water, and refuses to unite with 
acids. It is decomposed by hot hydrochloric acid and by oil of vitriol in the 
same manner as the sesquioxide. 

As this substance is an article of commerce of considerable importance, 
being used in a very large quantity for making chlorine, and as it is subject 
to great alteration of value from au admixture of the sesquioxide and several 
imparities, it becomes desirable to possess means of assaying different sam- 
ples that may be presented, with a view of testing their fitness for the pur- 
poses of the manufacturer. One of the best and most convenient methods 
is the following : — 50 grains of the mineral, reduced to a very fine powder, 
are put into the little vessel employed in the analysis of carbonates,' together 
with about half an ounce of cold water, and 100 grains of strong hydro- 
chloric acid ; 50 grains of crystallixed oxalic acid . are then added, the cork 
carrying the chloride of calcium tube is fitted, and the whole quickly 
weighed or counterpoised. The application of a gentle heat suffices to deter- 
mine the action : the disengaged chlorine converts the oxalic acid into car- 
bonic acid, with the help of the elements of water, two equivalents of car- 
bonic acid representing one of chlorine, and consequently one of binoxide 
of manganese. Now, the equivalent of the latter substance, 43-6, is so 
nearly equal to twice that of carbonic acid, 22, that the loss of weight 
suffered by the apparatus when the reaction has has become complete, and 
the residual gas has been driven off by momentary ebullition, may be taken 
to represent the quantity of real binoxide in the 50 grains of the sample. 
It is obvious that the little apparatus of Will and Fresenius, described at 
page 229, may be used with the same advantage. 

Red oxide, Mn,04, or probably MnO-f-MngOg. — This oxide is also found 
native, and is produced artificially by heating to whiteness the binoxide or 
sesquioxide, or by exposing the protoxide or carbonate to a red-heat in an 
open vessel. It is a reddish-brown substance, incapable of forming salts, 
and acted upon by acids in the same manner as the two higher oxides already 

* See page 228. 

"SSi iSlAN-QANteSB. 

deverib«d. Btrnx. tfHd f^lnis hi a fused state dissdli^e this fmbstance, n&*d 
ikcquire tlito colour of the amethyst. 

Vakvicitb, Mn^O^, or Mn20g-j-2Mn02. — A natural prodnction, discorered 
by Mr, Phillips, among certain specimens of manganese-ore from Warwick- 
shire ; it has also been found at Ilefeld. It much resembles the binoTide, 
but is harder and more brilliant, and contains "water. By a stfoog heat, 
Tarvicite is converted into red oxide, with disengagement of aqueous rapour 
«nd oxygen gas. 

Ghloridb of MA90AVB815, MnCl. — This salt may be prepared in a state 
of purity from the dark brown liquid residue of the preparation of chlorine 
from binoxide of manganese and hydrochloric acid, which often accumulates 
in the laboratory to a considerable extent in the course of inTestigation ; 
from the pure chloride, the carbonate and all other salts can be couTeniently 
obtained. The liquid referred to consists chiefly of the mixed chlorides of 
manganese and iron ; it is filtered, evaporated to perfect dryness; and then 
slowly heated to dull ignition in an earthen vessel, ^with constant stirring. 
The chloride of iron is thus either volatilized or converted by the remaining 
water into insoluble sesquioxide, while the manganese-salt is unaffected. On 
treating the greyish-looking powder thus obtained with water, the chlorido 
of manganese is dissolved out, and may be separated by filtration from the 
sesquioxide of iron. Should a trace of the latter yet remain, it may be got 
rid of by boiling the liquid for a few minutes with a little carbonate of man- 
ganese. The solution of chloride has usually a delicate pink colour, which 
becomes very manifest when the salt is evaporated to dryness. A strong 
solution deposits rose-coloured tabular crystals, which contain 4 equivalents 
of water ; these are very soluble and deliquescent The chloride is fusible 
at a red-heat, is decomposed slightly at that temperature by contact of air, 
and is dissolved by alcohol, with which it forms a crystallizable compound. 

.Sesquiohlobide, Mn^ CI3. — ^When precipitated sesquioxide of manganese 
is put into cold dilute hydrochloric acid, it dissolves quietly, forming a red 
solution of sesquichloride. Heat disengages chlorine, and occasions the pro- 
duction of protochloride. 

Sulphate of peotoxide'Of manganese, MnO,S03-}-7HO. — A beautiful 
rose-coloured and very soluble salt, isomorphous with sulphate of magnesia. 
It is prepared on a large scale for the use of the dyer, by heating, in a close 
vessel, binoxide of manganese and coal, and dissolving the impure protoxide 
thus obtained in sulphuric acid, with the addition of a little hydrochloric 
acid towards the end of the process. The solution is evaporated to dryness, 
and again exposed to a red-heat, by which the sulphate of sesquioxide of 
iron is decomposed. Water then dissolves out the pure sulphate of manga- 
nese, leaving the sesquioxide of iron behind. The salt is used to produce a 
permanent brown dye, the cloth steeped in the solution being aftewards 
passed through a solution of bleaching-powder, by which the protoxide is 
changed to insoluble hydrate of the binoxide. Sulphate of manganese 
sometimes crystallizes with five equivalents of water. It forms a double salt 
with sulphate of potassa. 

Cabbonate of BftANGANSSE. — Prepared by precipitating the protochloride 
'by an alkaline carbonate. It is insoluble and buff-coloured, or sometimes 
nearly white. Exposed to heat, it loses carbonic acid, and absorbs oxygen. 
Maxoanio acid, MnOg. — When an oxide of manganese is fused with an 
alkali, an additional quantity of oxygen is taken up from the air, and a deep 
green saline mass results, which contains a salt of the new acid, thus formed 
under the influence of the base. The addition of nitre, or chlorate of 
potassa, facilitates the production^ of manganic acid. Water dissolves this 
compound very readily, and the solution, concentrated by evaporation m 
vacuo, yields green crystals. 


PsufAHGANic AoiB, Mnfi^. —When mangaiuite of pcrtassa, free Arom any 
great excess of alkali, is put into a large quantity of water, it is resolved 
into hjdrated binoxide of manganese, which subsides, and a deep purple 
liquid, conbilning permanganate of potassa. This effect is accelerated by 
iieat The changes of colour accompanying this decomposition are yery re- 
markable, and have procured for the substance the name mineral chameleon ; 
excess of alkali hinders, in some measure, the reaction, by conferring greater 
stability on the mangaaate. Permanganate of potassa is easily prepared on 
a considerable scale. £qual parts of Tery finely powdered binoxide of man- 
ganese and chlorate of .potassa are mixed with rather more than one part of 
£jdrate of potassa dissolved in a little water, and the whole exposed, after 
evaporation to dryness, to a temperature just short of ignition. The mass 
is treated wi^b 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 Hsool. The crystals have a dark purple colour, and 
are not very soluble in cold water. The manganates and permanganates are 
decomposed by contact with organic matter ; the fbrmer are said to be iso- 
morphous with the sulphates, and the latter with the perchlorates. 

Salts of the protoxide of manganese are very easily distinguished by 

The fixed caustic alkalis, and ammonia, give white precipitates, insoluble 
in excess, quickly becoming brown. 

The carbonates of the fixed alkalis, and carbonate of ammonia, give.white 
precipitates, but little subject to change, and insoluble in excess of carbonate 
of ammonia. 

Sulphuretted hydrogen gives no precipitate, but sulphide of ammonium 
throws down insoluble, flesh-coloured sulphide of manganese, which is very 

Ferrocyanide of potassium gives a white precipitate. 

Manganese is also easily detected by the blowpipe ; it gives with borax an 
amethystine bead in the outer or oxidizing flame, and a colourless one in the 
inner flame. Heated upon platinum foil with carbonate of soda, it yields a 
green mass of manganate of soda. 

This is by very far the most impm'tant member of the group of metals 
under discussion ; there are few subBtances to which it yields in interest, 
vhen it is considered how very intimately the knowledge of the properties 
and uses of iron is connected with human civilization. 

Metallic iron is^ of exceedingly rare occurrence ; it has been found at 
Canaan, in Connecticut,* forming a vein about two inches thick in mica-slate, 
but it invariably enters into the composition of those extraordinary stones 
known to fall from the air, called meteorites. Isolated masses of soft malleable 
iron also, of largo dimensions, lie loose upon the surface^f the earth in South 
America and elsewhere, and are presumed to have had a^similar origin: 
these latter contain, in common with the iron of the undoubted meteorites, 
nickel. In an oxidized condition, the presence of iron may be ,said to be 
universal ; it constitutes great part of the common colouring matter of rocks 
and soils ; it is contained in plants, and forms an essential component of the 
blood of the animal body. In the state of bisulphide it is also very common. 
Pure iron may be prepared, according to Mitscherlich, by introducing into 

» Pbillip's Mineralogy, fourth edit. p. 208. 

260 IRON. 

. a Hessian cmcible 4 parts of fine iron wire cut smull, and 1 part of black 
oxide of iron. This is covered with a mixture of white sand, lime, and car- 
bonate of potassa, in the proportions used for glass-making, and a cover being 
closely applied, the crucible is exposed to a very high degree of heat. A 
button of pure metal is thus obtained, the traces of carbon and silicum pre- 
sent in the wire having been removed by the oxygen of the oxide. 

Pure iron has a white colour and perfect lustre ; it is extremely soft and 
tough, and has a specific gravity of 7*8. The crystalline form is probably 
the cube, to judge from appearances now and then exhibited, in good bar- 
iron or wire a distinct fibrous texture may always be observed when the 
metal has been attacked by rusting or by the application of an acid, and 
upon the perfection of this fibre much of its strength and value depends. 
Iron is the most tenacious of all the metals, a wire g^j^th of an inch in diame- 
ter bearing a weight of 601b. It is very difficult of fusion, and before be- 
coming liquid passes through a' soft or pasty condition. Pieces of iron 
pressed or hammered together in this state cohere into a single mass ; the 
operation is termed welding, and is usually performed by sprinkling a little 
sand over the heated metal, which combines with the superficial film of oxide, 
forming a fusible silicate, which is subsequently forced out from between 
the pieces of iron by the pressure applied ; clean surfaces of metal are thus 
presented to each other, and union takes place without difficulty. 

Iron does not oxidize in dry air at common temperatures ; heated to red- 
ness, it becomes covered with a scaly coating of black oxide, and at a high 
white-heat burns brilliantly, producing the same substance ; in oxygen gas 
the combustion occurs with still greater ease. The finely divided spongy 
metal, prepared by reducing the oxide by hydrogen gas, takes fire spontane- 
ously in the air.* Pure water, free from air and carbonic acid, does not 
tarnish a surface of polished iron, but the combined agency of free oxygen 
and moisture speedily leads to the production of rust, which is a hydrate of 
the sesquioxidc. The rusting of iron is wonderfully promoted by the pre- 
sence of a little acid vapour.* At a red-heat iron decomposes water, evolving 
hydrogen, and passing into the black oxide. Dilute sulphuric and hydro- 
chloric acids dissolve it freely with separation of hydrogen. Iron is strongly 
magnetic up to a red-heat, when it loses all traces of that remarkable pro- 

The equivalent of iron is 28, and its symbol Fe. 

Four compounds of iron and oxygen are described. 

Protoxide FeO 

Sesquioxide (peroxide) FcjOg 

Protosesquioxide (black oxide) Fe304=FeO, FcjOg 

Ferric acid FeOg 

Pbotoxtde, FeO. — This is a very powerful base, neutralizing acids com- 
pletely, and isomorphous with magnesia, oxide of zinc, &c. It is almost 
unknown in a separate state, from its extreme proneness to absorb oxygen 
and pass into the sesquioxide. When a salt of this substance is mixed with 
caustic alkali or ammonia, a bulky whitish precipitate of hydrate of the pro- 
toxide falls, Which becomes nearly black when boiled, the water being sepa- 

* When obtained at a heat below redness. — R. B. 

• The rusting of iron proceeds with rapidity after it once begins, extending from the point 
firtt affected. Iron rust contains ammonia, resulting fh)m the combination of the naHcent 
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 
(»nUiius ammonia, it becomes necessary to ascertain its absence, or drive it o£f, previous to 
opfcTHZing with potassa, — R. B. 

IB ON. 261 

rated. Thi* Tiydwit* «^68ed \o the nir, Teiy rapidly changes, becomiDg 
green and ultimately red-brown. The soluble salts of protoxide of iron have 
commonly a delicate pale green colour, and a nauseous lAeiallic taste. 

Sesquioxidb, Fe^Og. — A feeble base, isomorphous with alumina. Sesqui- 
oxide of iron occurs native, most beautifully crystallized as specular iron ore 
in the island of Elba, and elsewhere ; also as red and brown hoRmatites, the 
latter being a hydrate. It is artificially prepared by precipitating a solution 
of sulphate of the sesquioxide or the sesquichloride of iron by excess of am- 
monia, and washing, drying, and igniting the yellowish-brown hydrate thus 
produced ; fixed alkalt must not be used in this operation, as a portion is re- 
tained ISy the oxide. In fine powder, this oxide has a full red colour, and is 
used as a pigment, being prepared for the purpose by calcination of the sul- 
phate of the protoxide ; the tint varies somewhat with the temperature to 
which it has been exposed. This oxide is unaltered in the fire, although 
easily reduced at a high temperature by carbon or hydrogen. It dissolves 
in acids, with difficulty after strong ignition, forming a series of reddish 
salts, which have an acid reaction and an astringent taste. Sesquioxide of 
iron is not acted upon by the magnet.* 

Black oxide; magnetic oxide ; loadstone, Fe304, or ^probably Fe04- 
Fe,Oj. — A natural product, one of the most valuable of the iron ores, often 
found in regular octahedral crystals, which are magnetic. It may be pre- 
pared by mixing due proportions of salts of the protoxide and sesquioxide 
of iron, precipitating them by excess of alkali, and then boiling the mixed 
hydrates, when the latter unite to a black sandy substance, consisting of 
minute crystals of the magnetic oxide. This oxide is the chief product of 
the oxidation of iron at a high temperature in the air and in aqueous vapour. 
It is incapable of forming salts. 

Fekbio acid, FeOj. — A very remarkable compound of recent discovery. 
The simplest mode of preparing it is to heat to full redness, for an hour, in 
a covered crucible, a mixture of one part of pure sesquioxide of iron, and 
four parts of dry nitre. The brown, porous, deliquescent mass is treated 
when cold with ice-cold water, by which a deep amethystine red solution of 
ferrate of potassa is obtained. This gradually decomposes even in the cold, 
evolving oxygen gas, and depositing sesquioxide ; by heat the decomposition 
is very rapid. The solution of ferrate of potassa gives no precipitate with 
salts of lime, magnesia, or strontia, but when mixed with one of baryta, a 
deep crimson, insoluble compound falls, which is a ferrate of that base, and 
is very permanent. 

PaoTOCHLORiDB OF IRON, FcCl. — Formed by transmitting dry hydrochloric 
acid gas over red-hot metallic iron, or by dissolving iron in hydrochloric acid. 
The latter solution yields, when duly concentrated, green crystals of the pro- 
tochloride, containing 4 equivalents of water; they are very soluble and 
deliquescent, and rapidly oxidize in the air. 

Sesquichloride of iron, FcjClg. — Usually prepared by dissolving sesqui- 
oxide in hydrochloric acid. The solution, evaporated to a syrupy consistence, 
deposits red, hydrated crystals, which are very soluble in water and alcohol. 
It forms double salts with chloride of potassium and sal-ammoniac. When 
evaporated to dryness and strongly heated, much of the chloride is decom- 
posed, yielding sesquioxide and hydrochloric acid ; the remainder sublimes, 
and afterwards condenses in the form of small brilliant red crystals, which 
deliquesce rapidly. ^ The solution of sesquichloride of iron is capable of dis* 
solving a large excess of recently precipitated hydrate of the sesquioxide, by 

•In the fonn of hydrate, FeaOs+SIIO, as recently precipitated from the persulphate by am- 
monia, it oonf(tlt»tes the antidote ibr arsenious acid. The affinity for water in thin case is not. 
Btroog— the hydrate gradually deoom]»osiBg even when kept under water, its colour pajtfiing 
ftom yellowish brown to red.— B. B. 

.'262 IRON. 

. irhicli it acquires a much darker colour. Aohydrotis seaqtaohloride of iron 
is also produced by the action of chlorine upon the heated metal. 

Protiodide of iron,, Fel. — This is an important medicinal preparation; 
it is easily made by digesting iodine mth water and metallic iron. The so- 
lution is pale green, and yields, on evaporation, crystals resembling those of 
the chloride, which rapidly oxidize on exposure to air. It is best preserved 
in solution in contact with excess of iron.* A sesqui-iodide of iron exists, 
which is yellowish-red and soluble. 

Sulphides of iron. — Several compounds of iron and sulphur are de- 
scribed ; of these the two most important are the following. JPrototulphide^ 
FeS, is a blackish, brittle substance, attracted by the magnet, formed by 
heating together iron and sulphur. It is dissolved by dilute acids with evo- 
lution of sulphuretted hydrogen gas, and is constantly employed for that 
purpose in the laboratory, being made by projecting into a red-hot crucible 
a mixture of 2^ parts of sulphur and 4 parts of iron filings or borings of 
cast-iron, and excluding the air as much as possible. The same substance 
is formed when a bar of white hot-iron is brought in contact with sulphur. 
The bisulphide of iron, FeSg, iron pyrites, is a natural product, occurring in 
rocks of all ages, and evidently formed in many cases by the gradual de- 
oxidation of sulphate of iron by organic matter. It has a brass-yellow 
colour, is very hard, not attracted by the magnet, and not acted upon by 
dilute acids. Exposed to heat, sulphur is expelled, and an intermediate sul- 
phide, analogous probably to the black oxide, is produced. This substance 
also occurs native, under the name of magnetic pyrites. The bisulphide is 
sometimes used in the manufacture of sulphuric acid. 

Compounds of iron with phosphorus, carbon, and silicium exist, but little 
is known respecting them in a definite state. The carbide is contained in 
cast-iron and in steel, to which it communicates ready fusibility ; the silioinm- 
compound is also found in cast-iron. Phosphorus is a very hurtful substanoe 
in bar-iron, as it renders it brittle or cold-short. 

Sulphate of protoxide of iron ; qreen vitriol, FeO,S03-f-7HO. — This 
beautiful and important salt may be obtained by directly dissolving iron in 
dilute sulphuric acid ; it is generally prepared, however, and that on a very 
large scale, by contact of air and moisture with common iron pyrites, which, 
by absorption of oxygen, readily furnishes the substance in question. Heaps 
of this material are exposed to the air until the decomposition is sufficiently 
advanced ; the salt produced is then dissolved out by water, and the solution 
made to crystallize. It forms large green crystals, of the composition above 
stated, which slowly effloresce and oxidize in the air ; it is soluble in about 
twice its weight of cold water. Crystals containing 4, and also 2 equiva- 
lents of water, have been obtained. Sulphate of protoxide of iron forms 
double salts with the sulphates of potassa and ammonia. 

Sulphate OF sesquioxidb op ibon, FejOg.SSOj. — Prepared by adding to 
a solution of the protosalt exactly one-half as much sulphuric acid as it 
already contains, raising the liquid to the boiling-point, and then dropping 
in nitric acid until the solution ceases to blacken by such addition. The red 
liquid thus obtained furnishes, on evaporation to dryness, a buff-coloured 
amorphous mass, which, when put into water, very slowly dissolves. With 
the sulphates of potassa and ammonia, this salt yields compounds having 
the form and constitution of the alums ; the crystals are nearly destitute of 
colour. These latter are decomposed by water, and sometimes by long keep- 
ing when in a dry state. They are best prepared by exposing to spontaneous 
evaporation a solution of sulphate of sesquioxide of iron to which sulphate 
of potassa or of ammonia has been added. 

^ Or protev.'ted from tho action of oxygen by pure honey, or other saccharine subBtanoei 
tu the proportion of one part to three of the solution.— U. B. 

IRON. 268 

TTiTBATB OP THE P50T0XIDB OF iBow, FcO^NOg. -^ When dflute cold nitric 
ftcid is made to act to saturation npon protosnlphide of iron^ and the solu- 
tion evaporated in Tacuo, pale green and very soluble crystals of protonitrate 
are obtained, which are very subject to alteration. The nitrate of the ses- 
qoioxide is readily formed by pouring nitric acid, slightly diluted, upon iron ; 
it is a deep red liquid, apt to deposit an insoluble basic salt, and is used in 

Garbokate of protoxide of irow, FeOjCOj. — The white precipitate ob- 
tuned by mixing solutions of protosalt of iron and alkaline carbonate ; it 
cannot be washed and dried without losing carbonic acid and absorbing 
oxygen. This substance occurs in nature as spathote iron i>re, associated with 
▼ariable quantities of carbonate of lime and of magnesia ; and also in the 
common clay iron-atone, from which nearly all the British iron is made. It 
is often found in mineral waters, being soluble in excess of carbonic acid ; 
Buch waters are known by the rusty matter they deposit No carbonate of^ 
the sesquioxide 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 sulphide of ammonium 
throwd down black protosulphide of iron, soluble in dilute acids. 

Ferrocyanide of potassium gives a nearly white precipitate, becoming deep 
blue on exposure to air. 

Salts of the sesquioxide are thus characterized : — 

Caustic alkalis, and ammonia, give foxy-red precipitates of hydrated ses- 
quioxide, insoluble in excess. 

The carbonates behave in a similar manner, the carbonic acid escaping. 

Sulphuretted hydrogen gives a nearly white precipitate of sulphur, and 
reduces the sesquioxide to protoxide. 

Sulphide of ammonium gives a black precipitate, slightly soluble in excess. 

Ferrocyanide of potassium yields Prussian blue. 

Tincture or infusion of gall-nuts strikes intense bluish-black with the 
most dilute solutions of salts of sesquioxide of iron. 

Iron Manufacture. — This most important branch of industry consists, as 
now conducted, of two distinct parts ; viz., the production from the ore of a 
fusible (carbide) of iron, and the subsequent decomposition of the carbide, 
and its conversion into pure or malleable iron. 

The clay iron ore is found in association with coal, forming thin beds or 
nodules r it consists, as already mentioned, of carbonate of iron mixed with 
clay ; sometimes lime and magnesia are also present. It is broken in pieces, 

« Phobphatk of protoxide of Ibow, 2FeO, HO.POs, is formed when a solution of common 
pbosphate of soda is added to a solntion of protosulphate of iron. It falls as a white preci- 
pitate, gradnallj 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 
blae phosphate contains perphosphate. 

PROSPBATB OF SESQUIOXIDE OF Irow is formed by adding common phosphate of soda to per- 
niTphate or perchloride of iron; a white precipitate is produced insoluble in ammonia unlesii 
an excess of phosphate of soda be present. Digested with the fixed alkalis or ammonia A 
becomes brown.— B. B. '' 



i^d exposed to h«at lo » furnaee resembliog a lime-1dln« ^7 vkkh tiie vi^ 
and carbonic acid ara expelled^ and the ore rendered dark-coloured,, denser, 
and also magnetic ; it is then ready for reduction. The furnace in which 
this operation is performed is usually of very large dimensions, fifty feet or 
more in height, and constructed of brick work with great solidity, the 
interior being lined with excellent fire-bricks ; the figure will be at once 
understood from the sectional drawing (fig. 149). The furnace is close i^t 

Fig. 149. 

the bottom, the fire being maintained by a powerful artificial blast introduced 
by two or three tuyere-pipes^ as shown in the section. The materials, con* 
sisting of due proportions of coke or carbonized coal, roasted ore, and lime- 
stone, are constantly supplied from the top, the operation proceeding con^ 
tinuously night and day, often for years, or until the furnace is judged to 
require repair. In the upper part of the furnace, where the temperature is 
still very high, and where combustible gases abound, the iron of the ore is 
probably reduced to the metallic state, being disseminated through the 
earthy matter of the ore ; as the whole sinks down and attains a still higher 
degree of heat, the iron becomes converted into carbide by cementatiotiy 
while the silica and alununa unite with the lime, purposely added, to a kind 
of glass or slag, nearly free from oxide of iron. The carbide and slag, both 
m a melted state, reach at last the bottom of the furnace, where they arrange 
themselves in the order of their densities; the slag flows out at certain 
apertures contrived for the purpose, and the iron is discharged from time te 
tune, and suffered to run into rude moulds of sand by opening an orifice at the 

ixftfom of tiib reeipieut, prerfMisly stopped irl«h ctey. flneii ii the ovigin 
of cmde or or oast-iron, of which there are sereral rarietiea, distingnidied 
by difierences of colour, hardness, and composition, and known by the names 
of greif, blacky and wkiu iron. The first is for most purposes the best, as it 
admits of being filed and cat with perfect ease. The black and grey kinds 
pirobably contain a mechanical adnuxtore of graphite, which separ^ee during 

A great improvement has been made in the above described process, by 
■nbstitating raw coal for coke, and blowkig hot air, instead of cold, into the 
furnace. This is effected by causing the air, on leaving the blowing-machine, 
to drculate through a system of nd-hot iron pipes, until its temperatun 
becomes high enough to melt lead. This alteration has already effected a 
prodigious BiTiBg in taxX, without, U appears, any injury to 'the quality of 
the product. 

The conTersion' of cast into bar^iron is effected by an iteration called 
puddling ; previous to which, however, it commonly undergoes a process the 
theory of which is not perfectly intelligible. It is remelted, and suddenly 
cooled, by which it becomes white, crystalline, and exceedingly haird: in this 
state it is called j&M-m^to/. The puddling process is conducted in an ordi- 
nary reverberatory fumaoe, into which the charge of fine-metal is introduced 
by a nde aperture. This is speedily melted by the flame, and its surface 
cavered withs 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 otide with 
the metal ; he now and then also throws in a little water, wiUi a view of pro- 
moting more rapid oxidation. Small jets of blue flame soon appear upon 
the surface of the iron, and the latter, after a time, begins to lose its fluidity, 
and acquires, in succession, a pasty and a granular condition. At this point, 
the fire is strongly urged, the sandy particles once more cohere^ and the 
contents of the furnace now admit of. being formed into several large balls 
or masses, which are then withdrawn, and placed 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 n single bar ; and this 
process of pUin0 orfetgofting is sometimes twice or thrice repeated, the iron 
becoming greatly improved thereby. 

The general nature of the change in the puddling fiimace is not difficult 
to explain. Cast-iron consists essentially of irofi in combination with carbon 
and silicium ; when strongly heated with oxide of ilrcn, those compounds un- 
dergo decomposition, the carbon and silicium becoming oxidised 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-hamdier, 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 Bngland. Plate-iron is, however, some- 
times made with charcoal. 

Steel. — A very remarkable, and most useful substance, prepared by heat" 
ing iron in contact with charcoal. Bars of Swedish iron are embedded in 
charcoal powder, contained in a large rectangular crucible or chest of some 
substance capable of resisting the fire, and exposed for many hours to a full 
red-heat The iron takes up, under these circumstances, from 1*8 to 1-7 

266 A&XDIUM. 

pef cent: of cilrboii, becoming harder, and at the same time fusible, m^ a 
certain diminution, however, of malleability. The active agent in this ce- 
mentation process is probably carbonic oxide ; the oxygen of the air in the 
ci'ucible combines with the carbon, to form that substance, which is after- 
wards decomposed by the heated iron, one half of its carbon being abstracted 
by the latter. The carbonic acid thus formed takes up an additional dose 
of carbon from the charcoal, and again becomes carbonic oxide, the oxygeB, 
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 blis- 
tered 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 ; the oxide pro- 
duced reacts, as before stated, on the carbon of the iron, and withdraws a 
portion of that element. When a proper degree of stiffness or pastiness id 
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 thi'^ manner. 
Annealed cast-iron, sometimes called run-steel, is now much employed as a 
substitute for the more costly products of the forge; the articles, when cast, 
are embedded in powdered iron ore, or some earthy material, and, after be- 
ing exposed to a moderate red-heat for some time, are allowed slowly to 
cool, by which a very extraordinary degree of softness and malleability is 
attained. It is very possible that some little decarbonization may take place 
during this process. 

The most remarkable property of steel is that of becoming exceedingly 
hard when quickly cooled ; when heated to redness, and suddenly quenched 
in cold water, steel, in fact, becomes capable of scratching glass with fa- 
cility ; if re-heated to redness, and once more left to cool slowly, it again 
becomes nearly as soft as ordinary iron, and, between these two conditions, 
any required degree of hardness may be attained. The articles, forged into 
shape, are first hardened in the manner described ; they are then tempered, 
or let dovm, by exposure to a proper degree of annealing heat, which is often 
judged of by the colour of the thin film of oxide which appears on the 
polished surface. Thus, a temperature of about 430^ (22 PC), indicated by 
a faint straw-colour, gives the proper temper for razors ; that for scissors, 
pen-knives, &c., will be comprised between 470<> (243°C) and 490° (254oC), 
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 660° (288°C) or 
560° (293^0), or until the surface becomes deep blue. Attention to tiiese 
colours has now become of less importance, as metal baths are often sub- 
stituted for the open fire in this operation. 

Aridium (from 'Apiyj, Mars, and tUos, appearance) from the resemblance 
of its oxide to oxide of iron. Ulgren considers this as a new metal. He 
found it in the chrome iron from Roros, and in iron ore from Oemstolso. 
There are stir doubts hanging over the existence of this metal. 



Chromium is found in the state of oxide, in combination with oxide of 
iron, in some abundance in the Shetland Islands, and elsewhere ; as chro- 
mftte of lead, it constitutes a very beautiful mineral, from which it was first 
obtained. The metal itself is got in a half-fused condition by mixing the 
oxide with one-fifth of its weight of charcoal-powder, inclosing the mixture 
in a crucible lined with charcoal, and then subjecting it to the very highest 
beat of a powerful furnace. It is hard, greyish- white, and brittle ; of 6'9 
specific grayity, and exceedingly difficult of fusion. Chromium is but little 
oxidable, being scarcely attacked by the most powerful acids ; it forms at 
least four compounds with oxygen, corresponding to, and probably ismor- 
phous with, those of iron. 

The equivalent of chromium is 26 '8 ; its symbol is Cr. 

Peotoxidb of CHROMiiTM, CrO. — When potassa is added to a solution of 
the protochloride of chromium, a brown precipitate falls, which speedily 
passes to deep foxy red, with disengagement of hydrogen. The protoxide, 
in the state of the pale greenish hydrate, is perhaps obtained when ammonia 
is substituted for potassa in the preceding experiment. This substance is a 
powerful base, forming pale blue salts, which absorb oxygen with extreme 
avidity. The double sulphate of protoxide of chromium and potassa con^ 
tains 6 eq. of water, like the other members of the same group. 

Pbotosesquioxide op chromium, CrO-j-CrgOg, is the above brownish-red 
precipitate produced by the action of water, upon the protoxide. The de- 
composition ie not complete without boiling. This oxide corresponds with 
the magnetic oxide of iron, and is not salifiable. 

Sesquioxide of chromium, CrgO,. — ^When chromate of mercury, prepared 
by mixing solutions of the nitrate of suboxide of mercury and of chromate 
or bichromate of potassa, is exposed to a red-heat, it is decomposed, pure 
Besquioxide of chromium having a fine green .colour, remaining. In this 
state the oxide is, like alumina after ignition, insoluble in acids. From a 
solution of sesquioxide of chromium in potassa or soda, green gelatinous 
bydrated sesquioxide of chromium is separated on standing. When finely 
powdered and dried over sulphuric acid, its formula is CrjOj+6HO. A hy- 
drate may also be had by boiling a somewhat dilute solution of bichromate 
of potassa, strongly acidulated by hydrochloric acid, with small successive 
portions of sugar or alcohol ; in the former case, carbonic acid escapes ; in 
the latter a substance called aldehyde and acetic acid are formed, substances 
with which we shall become acquainted in organic chemistry, and the chromic 
acid of the salt becomes converted into scsquichloride of chromium, the 
colour of the liquid changiog from red to deep green. A slight excess of 
ammonia precipitates the hydrate from this solution. It has a pale purplish- 
green colour, which becomes full green on ignition ; an extraordinary shrink- 
ing of volume and sudden incandescence is observed when the hydrate is 
decomposed by heat. Anhydrous sesquioxide in a beautifully crystalline 
condition may be prepared by heating to full redness in an earthen crucible 
bichromate of potassa. One-half of the acid suffers decomposition, oxygen 
being disengaged, and oxide of chromium left The melted mass is then 
treated with water, which dissolves out neutral chromate of potassa, and 
the oxide is, lastly, washed and dried. Sesquioxide of chromium commu- 
nicates a fine green tint to glass, and is used in enamel-painting. 

The sesquioxide of chromium is a feeble base, resembling, and isomor- 
phous with, sesquioxide of iron and alumina; the salts it forms have a green' 
or purple colour, and a're said to be poisonous. 

The sulphate of sesquioxide of chromium is prepared by dissolving the 
hydrated oxide in dilate sulphuric acid. It unites with the sulphates of po* 

268 CttEOMIUM. 

tftMa and of ammoniA, giying rise to magnificent salts which crystalliie m 
regular octahedrons of a deep claret colour, and possess a constitution re> 
sembling that of common alum, the alumina being replaced by sesquiozide 
of chromium. The finest crystals of chromium-alum are obtained by spon- 
taneous eyaporation, the solution being apt to be decomposed by heat 

Protochlobids or chbohivm, CrCl. — The yiolet-coloured sesquiehloride 
of chromium, contained in a porcelain or glass tube, is heated to redness in 
a current of perfectly dry and pure hydrogen gas ; hydrochloric acid is dis- 
engaged, and a white foliated mass is obtained, which dissolves in water 
with great elevation of temperature, yielding a blue solution, which, by ez- 

Sosure to the air, absorbs oxygen with extraordinary energy, acquiring a 
eep green colour, and passing into the state of oxychloride of chromium, 
2CtJCI^ CrgO,. The protochloride of chromium is one of the most powerful 
reducing or deoxidizing agents known. 

Seiquichix)]udi ofchbomiun, CrgClj. — This substance is' readily obtuned 
in the anhydrous condition by heating to redness in a porcelain tube a mix- 
ture of sesquioxide of chromium and charcoal, and passing dry chlorine gas 
over it. The sesquiehloride sublimes, and is deposited in the cool part of 
the tube, in the form of beautiful crystalline plates of a pale violet colour. 
According to M. P^ligot, it is totally insoluble in water under ordinary cir- 
cumstances, even at a boiling heat. It dissolves, however, and assumes the 
deep green hydrated state in water containing an exceedingly minute quan- 
tity of the protochloride in solution. The hydration is marked by the evo- 
lution of much heat. This Vemarkable,,effect must probably be referred to 
the class of actions known at present under the name of katalysls/ 

The salts of the sesquioxide of chromium are easily recognized. 

Caustic alkalis precipitate the hydrated oxide, easily soluble in excess. 

Ammonia, the same, but nearly insoluble. 

Carbonates of potassa, soda, and ammonia, throw down a green precipitate 
of carbonate and hydrate, slightly soluble in a large excess. 

Sulphuretted hydrogen causes no change. 
• Sulphide of ammonium precipitates the hydrate of the sesquioxide. 

Chromic acid, CrO,. — Whenever sesquioxide of chromium is strongly 
heated with an alkali, in contact with the air, oxygen is absorbed and 
chromic acid generated. Chromic acid may be obtained nearly pure, and in 
a state of great beauty, by the following simple process : — 100 measures of 
a cold saturated solution of bichromate of potassa are mixed with 150 
measures of oil of vitriol, and the whole suffered to cool ; the chromic acid 
crystallizes in brilliant crimson-red prisms. The mother-liquor is poured 
off, and the crystals placed upon a tile to drain, being closely covered by a 
glass or bell-jar.' Chromic acid is very deliquescent and soluble in water ; 
the solution is instantly reduced by contact with organic matter. 

Chromate of Potasta, KOjCrO,. — This is the source of all the preparations 
of chromium ; it is made directly from the native chrome-iron ore, which is a 
compound of the sesquioxide of chromium and protoxide of iron, analogous 
to magnetic iron ore, by calcination with nitre or with carbonate of potassa, 
*he stone being reduced to powder, and heated for a long time with the 
alkali in a reverberatory furnace. The product, when treated with water, 
yields a yellow solution, which by evaporation deposits anhydrous crystals 
of the same colour, isomorphous with sulphate of potassa. Chromate of 
potassa has a cool, bitter, and disagreeable taste, and dissolves in 2 parts of 
water at 60*^ (IS^-SC). 

* See pa«e 186. 

" Mr. Warrington; Proceedings of Chen. Soe. L !& 

NICKEL. 269* 

Bkhfomaie of Pot^isa, K0,2Cr03, — When snlpliTiric acid is added to the 
preceding salt in moderate quantity, one-bal|' of the base is removed, and 
the neatral chromate converted into bichromate. The new salt, of 'vrhich 
immense quantities are manufactured for use in the arts, crystallizes by slow 
eraporation in beautiful red tabular crystals, derived from an oblique rhombic ' 
prism. It melts when heated, and is soluble in 10 parts of water, and the 
Bolutitfn has an acid reaction. 

Chromate of Lead^ PbO,CrO,. — On mixing solution of chromate or bichro- 
mate of potassa with nitrate or acetate of lead, a brilliant yellow precipitate 
falls, which is the compound in question; it is the ehrome-yellow of the 
painter. When this compound is boiled with lime-water, one-half of the 
acid is withdrawn, and a subchromate of an orange-red colour lefL The 
sabchromate is also formed by adding chromate of lead to fused nitre, and 
afterwards dissolving out the soluble salts by water ; the product is crystal- 
line, and rivals vermilion in beauty of tint. The yellow and orange chrome- 
colours are fixed upon cloth by the alternate application of the two solutions, 
and in the latter case by passing the dyed stu£f through a bath of boiling 

Chrcmate of Silver, AgOyOrO,! — This salt precipitates as a reddish brown 
powder when solutions of cliromate of potassa and nitrate of silver are 
mixed. It dissolves in hot dilute nitric acid, and separates, on cooling, in 
small ruby-red platy crystals. The chromates of baryta, zinc, and mercury 
are insoluble ; the first two are yellow, the last is brick-red. 

Penkromie Acid is obtained, according to Barreswill, by mixing chromic 
acid irtth dilute binoxide of hydrogen or bichromate of potassa with a dilute 
but very acid solution of binoxide of barium in hydrochloric acid, when a 
liquid is fornaed of a blue colour, which is removed from the aqueous 
Bolation by ether. The composition of this very unstable compound is per- 
haps OgOy. 

A salt of chromic acid is at once recognised by its behaviour with solu- 
tions of baryta and lead ; and also by its colour and capability of furnishing, 
by deoxidation, the green sesquioxide of chromium. 

Ghlobochbomic acid, CrO,-^-Cl.* — 3 parts of bichromate of potassa and 
8^ parts of common salt are intimately mixed and introduced into a small 
glass retort ; 9 parts of oil of vitriol are then added, and heat applied as 
long as dense red vapours arise. The product is a heavy deep red liquid 
resembling bromine ; it is decomposed by water, with production of chromic 
and hydrochloric acids. 

Nickel. ^ 

Nickel is found in tolerable abundance in some of the metal-bearing veins 
of the Hartz mountains, and in a few other localities, chiefly as arsenide, the 
kupfemickd of mineralogists, so called from its yellowish-red colour; the 
irord nickel is a term of detraction, having been applied by the old German 
biners to what was looked upon as a kind of false copper ore. 

The artificial, or perhaps rather merely fused, product, called speiss, i» 
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 

' If this formula be trebled, we obtain Cr806Cla=2Cr08,CrCl8, and the substance becomes a 
compound of 2 eq. of chromic acid and 1 eq. of terchloride of cliromiuw. The terchlorid« of, 
cUxomium is not known in the free state. 

270 NICKEL. 

a crncible Ik^^d with -cbori^oal. It is a white, malleable metal, bamg a den- 
sity of 8*8, a high meltiDg point, and a less degree of oxidability than iron, , 
'since it is but little attacked by dilute acids. Nickel is strongly magnetic, 
but loses this property When heated to 660<' (349°C). This metal forms two 
oxides, only one of which is basic. The equivalent of nickel is 29-6; its 
symbol is Ni. 

Protoxide or nickel, NiO. — This compound is prepared by heating to 
redness the nitrate, or by precipitating a soluble salt with caustic pota8Sf^ 
and washing, drying, and igniting the apple-green hydrated oxide thrown 
down. It is an ash-grey powder, freely soluble in acids, which it completely 
Beutralizes, being isomorphous with magnesia, and the other members of the 
same group. The salts of this substance, when hydrated, have usually a 
beautiful green oolonr; in the anhydrous state they are yellow. 

Sesquioxidb, o& peroxide of nickel, NigOy — This oxide is a black in- 
soluble substance, prepared by passing chlorine through the hydrated oxide 
suspended in water ; chloride of nickel is formed, and the oxygen of the 
oxide decomposed transferred to a second portion. It is also produced when 
a salt of nickel is mixed with a solution of bleaching-powder. The sesqui- 
oxide is decomposed by heat, and evolves chlorine when put into hot hydro- 
chloric acid. 

Chloride of nickel, NiCL — This is easily prepared by dissolvmg oxide 
or carbonate of nickel in hydrochloric acid. A green solution is obtained 
which furnishes crystals of the same colour, containing water. When ren- 
dered anhydrous by heat, the chloride is yellow, unless it contain cobalt, in 
which case it has a tint of green. 

Sulphate of nickel, NiO,SO,+7HO.— 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 sulphates 
of potassa and ammonia beautiful double salts, NiO, SO- -f KO.SOj -f- 6H0 
and NiO, SO. -f NH^O, SO3+6HO. When a strong solution of oxalic acid 
is mixed with sulphate of nickel, a pale bluish-gi'een precipitate of oxalate 
falls after some time, very little nickel remaining in solution. The oxalate 
can thus be obtained for. preparing' the metal. 

Carbonate of nickel. — When solutions of sulphate or chloride of nickel 
and of carbonate of soda are mixed, a pale green precipitate falls, which is 
a combioation of carbonate and hydrate of nickel. It is readily decomposed 
by heat 

Pure salta of nickel are conveniently prepared on the small scale from 
omde speiss or kupfemickel by the following process ijr- The mineral is 
broken into small fragments, mixed with from one-fourth to half its weight 
of iron-filings, and the whole dissolved in aqua regia. The solution is gently 
evaporated to dryness, the residue treated with boiling water, and the inso- 
luble arsenate of iron removed by a filter. The liquid is then acidal^ted 
with hydrochloric acid, treated with sulphuretted hydrogen in excess, which 
precipitates the copper, and, after filtration, boiled with a little nitric acid to 
bring back the iron to the state of sesquioxide. To the cold and largely 
diluted liquid, solution of bicarbonate of soda is gradually added, by which 
the sesquioxide of iron may be completely separated without loss of nickel- 
salt Lastly, the filtered solution, boiled with carbonate of soda in excess, 
yields an abundant pale green precipitate of carbonate of nickel,* firom which 
all the other compounds may be prepared. 

« This precipitate may still oontain cobalt, which can only be separated from it by yvrt 
aomi^loated procemes, Ite which the more advanced student is referred to *' Liebig and Kot^p's 
ilaaiua Report," ii. 884. 

cobaAt. 271 

The salts of nickel are well characterized by th«ir bebaTlonr with re- 

Gaastte alkalis giye a pale apple-green precipitate of hydrate, insoluble in 

Ammonia affords a similar precipitate, which is solable in excess, with 
deep purplish-bloe- colour. 

Carbonate of potassa and soda give pale green precipitates. 

Carbonate of ammonia, a similar precipitate, soluble in excess, with blue 

Ferrocjanide of potassium gives a greenish-white precipitate. 

Cyanide of potassium produces a green precipitate, which dissolves in an 
excess of the precipitant to an amber-coloured liquid which is re-precipitated 
by addition of hydrochloric acid, . 

Sulphuretted hydrogen occasions no change, if the nickel be in combina- 
tion with a strong acid. 

Sulphide of ammonium throws down black sulphide of nickel. 

The chief use of nickel in the arts is in the preparation of a white alloy, 
sometimes called German silver, made by melting together 100 parts of 
copper, GO of zinc, and 40 of nickel. This alloy is very malleable, and takes 
a high polish. 

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 hodrocbloria 
and sulphuric acids. It is strongly magnetic. There are two oxides of 
this metal, corresponding in properties and constitution with those of 
nickel. •» 

The equivalent of cobalt is 29-55 : its symbol is Co. 

P&OTOXiDE OF COBALT, CoO. — This is a grey powder, very soluble in acids, 
and is a strong base, isomorphous with magnesia, affording salts of a fine 
red tint. It is prepared by precipitating sulphate or chloride of cobalt with 
carbonate of soda, and washing and drying and igniting the precipitate. 
When the cobalt>solution is mixed with caustic potassa a beautiful blue pre 
cipitate falls, which when heated becomes violet, and at length dirty red, 
from absorption of oxygen and a change in the state of hydration. 

Sbsquioxioe of cobalt, COgOg. — The sesquioxide is a black, insoluble, 
neutral powder, obtained by mixing solutions of cobalt and of chloride of 

Ohlobidb of cobalt, CoCl. — The chloride is easily prepared by dissolving 
the oxide in hydrochloric acid; it gives a deep rose-red solution, which, 
when sufficiently strong, deposits hydrated crystals of the same colour. 
When the liquid is evaporated by heat to a very small bulk, it deposits anhy- 
drous crystals which are blue; these latter by contact with water agaiu 
dissolve to a red liquid. A dilute solution of chloride of cobalt constitutes 
the well-known bltie sympathetic ink ; characters written on paper with this 
liquid are invisible from their paleness of colour until the suit has been 
rendered anhydrous by exposure to heat, when the letters appear blue. 
When laid aside, moisture is absorbed, and the writing ouce more dis- 
appears. Green sympathetic ink is a mixture of the chlorides of cobalt and 

272 ZTNC. 

Chloride of cobalt may be prepared directly from cobaU-glancf., the natiTO 
arsenide, by a process exnctly similar to that described in the case of luckel. 

Sulphate op cobalt, CoO,S03-f-7HO. — This salt forms deep red crystals, 
requiring for solution 24 parts of cold water; they are identical in form 
-with those of sulphate of magnesia. It combines with the sulphates of po- 
tassa and ammonia, forming double salts, which contain as usual six equiva- 
lents of water. 

A solution of oxalic aci4 added to one of sulphate of cobalt occasions, 
after some time, the separation of nearly the whole of the base in the state 
of oxalate. 

Carbonate of cobalt. — The alkaline carbonates produce in solution of 
cobalt a pale peach-blossom coloured precipitate of combined carbonate and 
hydrate, containing^3(CoO,HO)-f 2(CoOCO,). 

The salts of cobalt have the following characters: — 

Solution of potassa gives a blue precipitate, changing by heat to violet 
and red. 

Ammonia gives a blue precipitate, soluble with difficulty in excess, with 
brownish red colour. 

Carbonate of soda affords a pink precipitate. 

Carbon9,te of ammonia, a similar compound, soluble in excess. 

Ferrocyanide of potassium gives a greyish-green precipitate. 

Cyanide of potassium affords a yellowish-brown precipitate, which dissolves 
in an excess of the precipitant. The clear solutions; after boiling, may be 
mixed with hydrochloric acid without giving a precipitate. 

Sulphuretted hydrogen produces no change, if the cobalt be in combination 
with a strong acid. 

Sulphide of ammonium throws down black sulphide of cobalt. 

Oxide of cobalt is remarkable for the magnificent blue colour it communi- 
cates to glass : indeed this is a character by which its presence may be most 
easily detected, a very small portion of the substance to be examined being 
fused with borax on a loop of platinum wire before the blowpipe. The sub* 
stance called smalts used as a pigment, consists of glass coloured by oxide of 
cobalt ; it is thus made : — The cobalt ore is roasted until nearly free from 
arsenic, and then fused with a mixture of carbonate of potassa and quartz- 
sand, free from oxide of iron. Any nickel that may happen to be contained 
in the ore then subsides to the bottom of the crucible as arsenide ; this is 
the speisa of which mention has already been made. The glass, when com- 
plete, is removed and poured into cold water ; it is afterwards ground to 
powder and elutriated. Cobalt-ultramarine is a fine blue colour prepared by 
mixing 16 parts of freshly precipitated alumina with 2 parts of phosphate or 
arsenate of cobalt : this mixture is dried and slowly heated to redness. By 
daylight the colour is jfure blue, but by artificial light it is violet. Zaffer is 
the ;*oasted cobalt ore mixed with a quantity of siliceous sand, and reduced 
to fine powder ; it is used in enamel-painting. A mixture in due proportions 
of the oxides of cobalt, manganese, and ir\)n is used for giving a fine black 
colour to glass. 

Zinc is a somewhat abundant metal ; it is found in the state of carbonate 
and sulphide associated with lead ores in many districts, both iii Britain and 

ziNd. iii 

on tbt €oBii]i»Lt ; lavge snppHet are obtaiaed tkom Sflcflja. The natire ear- 

boDste, or calamine, is the most TaluaWe 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 fall 
red-heat in a large earthen retort ; carbonic oxide escapes, while the reduced 
metal yolatilizes and is condensed by suitable means, generally with minute 
quantities of arsenic. 

Zinc is a bluish-white metal, which slowly tarnishes in the air ; it has a 
lamellar, crystalline structure, a density varying from 6-8 to 7*2, and is, 
under ordinary drcumstaaces, brittle. Between 250*' (12PC) and 800<' 
(149°C) it is, on the contrary, malleable, and may be rolled or hammered 
without danger of fracture, and, what is very remarkable, after such treat- 
ment, retains it malleability when cold : the sheet-zinc of commerce is thua 
made. At 400° (204° -40) it is so. brittle that it may be reduced to powder, 
it 773° (411® -60) it melts : at a bright red-heat it boils and yolatilizes, and, 
if air, be admitted, bums with a splendid green light, generating the oxide. 
Dilute acids dissolve zinc very readily; it is constantly employed in this 
manner in preparing hydrogen gas. 
Tke equivalent of zinc has been fixed at 32G ; its symbol is Zn. 
Pbotoxide or zinc, ZnO. — Only one oxide of this metal is known to 
eidst; it is a strong base, isomorphous with magnesia; it is prepared either 
by burning zinc in atmospheric air, or by heating to redness the carbonate. 
Oxide of zinc is a white tasteless powder, Insoluble in water, but freely dis- 
solyed by acids. When heated it is yellow, but turns white again on cooling. 
Sulphate or zinc ; white yitbiol ; ZnO, S0,-)-7H0. This salt is hardly 
to be distinguished by the eye from the sulphate of magnesia ; it is pre- 
pared by dissolving the metal in dilute sulphuric acid, or, more economically, 
by roasting the native sulphide, or blende, which by absorption of oxygen 
becomes in great part converted into sulphate of the oxide. The altered 
mineral is thrown hot into water, and the salt obtained by evaporating the. 
clear solution. Sulphate of zinc has an astringent metallic taste, and is 
used in medicine as an emetic. The crystals dissolve in 2 J parts of cold,, 
and in a much smaller quantity of hot water. Crystals containing 6 equiva- 
lents of water have been observed. Sulphate of zinc forms double salts, 
vith the sulphates of potassa and ammonia. 

Cabbonate of zinc, ZnO,C02. — The neutral carbonate is found native ; 
the white precipitate obtained by mixing solutions of zinc and of alkaline 
carbonates is a combination of carbonate and hydrate. When heated to 
redness, it yields pure oxide of zinc. 

CuLOBiDE 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^' 
(100°C). Chloride of zinc unites with sal-ammoniac and chloride of potas- 
sium to double salts ; the former of these, made by dissolving an equivalent 
of zinc in the requisite quantity of hydrochloric acid, and then adding an 
equivalent of sal-ammoniac, * is very usaful in tinning and soft-soMering 
copper and iron. 

A salt of zinc is easily distinguished by appropriate reagents. 

Caustic potassa and soda give a white precipitate of hydrate, freely soluble 
in excess of alkali* 

Ammonia behaves in the same manner ; an excess re-dissolves the precipi 
ute instantly. 


The carbonates of potassa and soda give white precipitates, insoloble io 


Carbonate of ammonia gives also a white precipitate, which is re-dissolTed 
hy an excess. 

Ferrocyauide of potassium gives a white precipitate. 

Sulphuretted hydrogen causes no change/ 

Sulphide of ammonium throws down white sulphide of zinc. 

The applications of metallic zinc to the purposes of roofing, the constrac- 
tion of water-channels, &c., are well known ; it is sufficiently durable, but 
inferior in this respect to copper. 


This metal was discovered in 1817 by Stromeyer; it accompanies the ores 
of zinc, and, being more volatile than that substance, rises first in vapour 
when the calamine is subjected to distillation with charcoal. Cadmium 
resembles tin in colour, but is somewhat harder ; it is very malleable, has 
a density of 8*7, melts below 500° (260°C), and is nearly as volatile as mer- 
cnry. It tarnishes but little in the air, but, when strongly heated, burns. 
Dilute sulphuric and hydrochloric acids act but little on this metal in the 
cold ; nitric acid is its best solvent. 

The equivalent of cadmium is 56 ; its symbol is Cd. 

Protoxide of cadmium, CdO. — The oxide may be prepared by igniting 

' either the carbonate or the nitrate ; in the former case it has a pale brown 

colour, and in the latter a much darker tint and a crystalline aspect. Oxide 

of cadmium is infusible ; it dissolves in acids, producing a series of colourless 


Sulphate op cadmium, CdO,S08+4HO. — This is easily obtained by dis- 
solving the oxide or carbonate in dilute sulphuric acid ; it is very soluble in 
water, and forms double salts with the sulphates of potassa and of ammonia, 
which contain CdCSOg-fKCSOa+eHO, and CdO.S034 NH4O,SO,-|-6H0. 

Chloride of cadmium, CdCl. — This is a very soluble salt, crystallizing in 
small four-sided prisms. 

Sulphide of cadmium is a very characteristic compound, of a bright yellow 
colour, fusible at a high temperature. It is obtained by passing sulphuretted 
hydrogen gas through a solution of the sulphate, nitrate, or cMoride. 

The salts of cadmium are thus distinguished : — 

Fixed caustic alkalis give a white precipitate of hydrated oxide, insoluble 
in excess. 

Ammonia gives a similar white precipitate, readily soluble in excess. 

The alkaline carbonates, and carbonate of ammonia* throw down white 
carbonate of cadmium, insoluble in excess of either precipitant. 

Sulphuretted hydrogen and sulphide of ammonium precipitate the yellow 
sulphide of cadmium. 

Bismuth 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 crj'stalline and very brittle; it has a reddish-white colour, 
and a density of 9-9. Cubic crystals of great beauty may be obtained by 

* With neutral solutions, or zincHsalts of on organic acid, a white precipitate ensues. 


Blowfly cooling » considerable mass of this substance until solidification has 
coiamenced, and then piercing the crust, and pouring out the fluid residue. 
Bismuth melts at about 500o (260oC}, and volatilizes at a high temperature : 
it is little oudized by the air, but bums when strongly heated with a bluish 
flame. Nitric acid, somewhat diluted, dissolves it freely. 
The equivalent of bismuth is 213, its symbol is Bi. 

T£BoxiDB OF BISMUTH, BiO,. — This is the base of all the salts. It is a 
straw-yellow powder, obtained by gently igniting the neutral or basic nitrate. 
It is fusible at a high temperature, and in that state acts towards siliceous 
matter as a powerful flux. 

BisMUTHio ACID, BiOj. — If teroxide of bismuth be suspended in a strong 
solution of potassa, and chlorine be passed through this liquid, decomposition 
of water ensues ; hydrochloric acid being formed and the teroxide converted 
into the pentoxide. To separate any teroxide which may have escaped oxi- 
dation, the powder is treated with dilute nitric acid, when the bismuthio 
acid is left as a reddish powder, which is insoluble in water. This substanoe 
combin43S with bases, but the compo^unds are not very well known. When 
heated it loses oxygen, an intermediate oxide Bi04 ^^^S formed, which may 
be considered as bismuthate of bismuth, 2Bi04SBBiO,,BiOf. 
NrrBATE OF BISMUTH, BiOg^NOs+QHO. — When bismuth is dissolved in 
X moderately strong nitric acid to saturation, and the whole left to cool, large, 
colourless, transparent crystals of the neutral nitrate are deposited. Water 
decomposes these crystals; and an acid solution confining a littie bismnth 
is obtained, and a brilliant white crystalline powder is left, which varies to 
a certain extent in composition according to the temperature and the quan- 
tity of water employed, but which frequently consists of a basio nitrate of 
the teroxide Bi03,3N05-f-2HO. A solution of nitrate of bismuth, free from 
any great excess of acid, poured into a large quantity of cold water, yields 
an insoluble basic nitrate, very similar in appearance to the above, but con- 
taining rather a larger proportion of teroxide of bismuth. This remarkable 
decomposition illustrates at once the basic property of water, and the feeble 
affinity of teroxide of bismuth for acids, the nitric acid dividing itself between 
the two bases. The decomposition of a neutral salt by water is by no means 
an uncommon occurrence in the history of the metals ; a solution of terchlo- 
ride of antimony exhibits the same phenomenon ; certain salts of mercury 
are affected in a similar manner, and other cases might perhaps be cited, less 
conspicuous, where the same change takes place to a smaller extent 

The basic nitrate of teroxide of bismuth was once extensively employed as 
a cosmetic, but is said to injure the skin, rendering it yellow and leather-like. 
It has been used in medicine. 
The other salts of bismuth possess few point^i of interest. 

Bismuth is sufficiently characterized by the decomposition of the nitrate 
by water, and by the blackening the nitrate undergoes when exposed to the 
action of sulphuretted hydrogen gas. 

A mixture of 8 parts of bismuth, 5 parts of lead, and 3 of tin, is known 
under the name of fusible metal, and is employed in taking impressions from 
dies and for other purposes ; it melts below 212° (lOO^C). The discrepan- 
cies so frequently observed between the properties of alloys and those of 
their constituent metals, plainly show that such substances must be lookea 
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 

Xl^ 9BA.NIUM. 

This metnl is found m a few minerals, m pitchblende and uranite, af irhich 
. the former is the most abundant. It appears fV*om the recent interesting re- 
searches of M. P61igot, that the substance hitherto taken for metallic ura- 
nium, obtained by the action of hydrogen gas upon the black oxide, is noi 
in reality the metal, but a protoxide, capable of uniting directly irith acids, 
.«nd, like the protoxide of manganese, not decomposable by hydrogen at a 

• rvd-heat The metal itself can be obtained only by the interrention of po- 
tassium, applied in the same manner as in the preparation of magnesiam. 

' It is described as a black coherent powder, or a white malleable metal, ac- 
cording to the state of aggregation, not oxidized by air or water, but emi- 
nently combustible when exposed to heat. It unites also with great yiolenee 
with chlorine and with sulphur. M. P^ligot admits three distinct oxides of 
uranium, besides two other compounds of the metal aAd oxygen, which he 
designates as suboxides. 

The equiyalent of uranium is 60. Its symbol is U. 

Pbotqxidb of uaAmuH, 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 
pyropfaorio, 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 . P^ligot attributes a Tery extraordinary double function to this substance, 
namely, that of acting as a protoxide and forming salts with acids, and that 
of combining with chlorine or oxygen after the fashion of an elementary 

Pbotosbsquioxidb 01 tTBABiTTM; BLACK OXIDE; XT4O5, or 2U0-f TIjOg.— 
The black oxide, formerly considered as protoxide, is produced when both 
protoxide and sesquioxide are strongly heated in the air, the former gaining, 
and the latter losing, a certain quantity of oxygen. It forms no salts, but 
is resolved by solution in acids into protoxide and sesquioxide. 

Sbsquioxide of uranium, U2O3. — The sesquioxide is the best known and 

• most important of the three ; it forms a number of extremely beautiful yel- 
low salts. When caustic alkali is added to a solution of nitrate of sesqui- 

. oxide of uranium, a yellow precipitate of hydrated oxide falls, which, re- 
tains, however, a portion of the precipitant. The hydrate cannot be exposed 
to a heat sufficient to expel the water without a commencement of decompo- 

.sition. A better method of obtaining the sesquioxide is to heat by means 
of an oil-bath the powdered and dried crystals of the nitrate to 480*' (249^0), 
until no more nitrous fumes are disengaged. Its colour in this state is 

Nitrate of sesquioxide of uranium, U203,N05-|-6H0; or (UjOj) 0, NOg 
-f-6H0; UgOj being the supposed ^U6ui-me^a/. — This nitrate is the starting 
point in the preparation of all the compounds of uranium; it majr be pre- 
pared from pitchblende by dissolving the pulverized mineral in nitric acid, 
evaporating to dryness, adding water and filtering ; the liquid furnishes, by 
due evaporation, crystals of nitrate of uranium, which are purified by a 
repetition of the process, and, lastly, dissolved in ether. This latter solu- 
tion yields the pure nitrate. 

The green salts of uranium are peroxidized by boiling with nitric acid. 

A yellow precipitate with caustic alkalis, convertible by heat into black 
oxide ; a brown precipitate with sulphide oi^ ammonium ; and none at aU 
with pulnhuietted hydrogen gas, sufficiently characterize the salts of sesqui- 

ooppBB. 27T 

oxide of nnuiiam. A solution suspected to eontun protoxide may be belled 
vith a little nitrio acid, and then examined. 

The only application of uranium is that to enamel-painting and the stain- 
ing of glass ; the protoxide giving a fine black colour, and the sesquioxide 
a delicate yellow. 


Copper is a metal of great yalue 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 sulphide combined inth sulphide 
of iron, or yeilow 'copper ore. Large quantities of the latter substance are 
annually obtained from the Cornish mines and taken to South Wales for re- 
duction, which is effected by a somewhat complex process. The principle 
of this may, howcTer, be easily made intelligible. The ore is roasted in a 
reverberatory furnace, by which much of the sulphide of iron is conyerted 
into oxide, while the sulphide of copper remains unaltered. The product 
of this operation is then strongly heated with siliceous sand ; the latter 
combines with the oxide of iron to a fusible elaffy and separates tirom the 
heavier copper-compound. When the iron has, by a repetition of these pro- 
cesses been got rid of, the shlphide of copper begins to decompose in the 
flame-furnace, losing its sulphur and absorbing oxygen ; the temperature is 
then raised sufficiently to reduce the oxide thus produced, by the aid of car- 
bonaceous matter. The last part of the operation consists in thrusting into 
the melted metal a pole of birch-wood, the object of which is probably to 
reduce a little remaining oxide by the combustible gases thus generated. 
Large quantities of extremely valuable ore, chiefly carbonate and red oxide, 
have lately been obtained from South Australia. 

Copper has a well-known yellowish-red colour, a specific gravity of 8*96, 
and is very malleable and ductile ; it is an excellent conductor of heat and 
electricity ; it melts at a bright red-heat, and seems to be a little volatile at 
a very high temperature. Copper undergoes no change in dry air; exposed 
to a moist atmosphere, it becomes covered with a strongly adherent green 
crust, consisting in a great measure' of carbonate. Heated to redness in 
the air, it is quickly oxidized, becoming covered with a black scale. Dilute 
sulphuric and hydrochloric acids scarcely act upon copper; boiling oil of 
vitriol attacks it with evolution of sulphurous acid ; nitric acid, even dilute, 
dissolvea it readily with evolution of binoxide of nitrogen. Two oxides are 
known which form salts ; a third, or peroxide, is said to exist. 
The equivalent of copper is 31*7 ; its symbol Cu. 

Protoxide of copper; black oxide; CuO. — This is the base of the 
ordinary blue and green salts. It is prepared by calcining metallic copper 
at a red-heat, with full exposure to air, or, more conveniently, by heating to 
redness the nitrate, which sufi^ers complete decomposition. When a salt of 
this oxide is mixed with caustic alkali in excess, a bulky pale blue precipi- 
tate of hydrated oxide falls, which, when the whole is raised to the boiling- 
point, becomes converted into a heavy dark brown powder ; this also is an- 
hydrous oxide of copper, the hydrate suffering decomposition, even in 
contact with water. The oxide prepared at a high temperature is perfectly 
black and very dense. Protoxide of copper is soluble in acids, and forms a 
series of very important salts, being isomorphous with magnesia. . 

Suboxide of copper ; bed oxide ; CujO. — The suboxide may be obtained 
by heating in a covered crucible a mixture of 6 parts of black oxide and 4 
parts of fine copper-filings ; or by adding grape-sugar to a solution of sul« 
phate of copper, and then putting in an excess of caustic potassa ; the blue 
solution, heated to ebullition, is reduced by the sugar and depositis suboxide 

Q78 ooppxB. 

ft offteii (HMran 3ii beaotifdUy transparent raby-red erjstftls, aasoeiated with 
other ores of copper, and can be obtained in this state by artificial means. 
This Bubstancd forms colourless salts with acids, which are exceedingly 
instable, and tend to absorb oxygen. The suboxide oommunicates to glass a 
magnificent red tint, while that given by the protoxide is green. 

Sulphate of copper; blue vitriol; CuO,SO,-)-6HO. — This beautiful 
salt is prepared by dissolving oxide of copper in sulphuric acid, or, at less 
expense, by oxidizing the sulphide. It forms large blue crystals, soluble in 
4 parts of cold and 2 of boiling water ; by heat it is rendered anhydrous and 
nearly white, and a very high temperature decomposed. Sulphate of copper 
combines with the sulphates of potassa and of ammonia, forming pale blue 
salts which contain 6 equivalents of water, and also with (trnmonioj gene- 
rating a remarkable compound of deep blue colour, capable of crystallizing. 

Nitrate of copper, CuO,N05-j- 8H0. — The nitrate is easily made by 
dissolving the metal in nitric acid ; it forms deep blue crystals, very soluble 
and deliquescent. It is highly corrosive. An insoluble subnitrate is known ; 
it is green. Nitrate of copper also combines with ammonia. 

Carbonates of copper. — When carbonate of soda is added in excess to 
a solution of sulphate of copper, the precipitate is at first pale blue and 
floc'culent, but by warming it becomes sandy, and assumes a green tint ; in 
this state it contains CUiO,C03-f CuO,HO-|-HO. This substance is prepared 
as a pigment. The beautiful mineral malachite has a similar composition, 
but contains one equivalent of water less. Another natural compound, not 
yet artificially imitated, occurs in large transparent crystals of the most 
intense blue ; it contains 2(CuO,G02)-)-CuO,HO. Verditer^ made by decom- 
posing nitrate of copper by chalk, is said, however, to have a somewhat 
similar composition. 

Chloride of copper, CuCl-f-2H0. — The chloride is most easily prepared 
by dissolving the black oxide in hydrochloric acid, and concentrating the 
green solution thence resulting. It forms green crystals, very soluble in 
wat«r and in alcohol ; it colours the flame of the latter green. When gently 
heated, it parts with its water of crystallization and becomes yellowish- 
brown ; at a high temperature it loses half its chlorine and becomes con- 
verted into the subchloride. The latter is a white fusible substance, but 
little soluble in water, and prone to oxidation ; it is formed when copper- 
filings or copper-leaf are put into chlorine gas. 

AlisENiTE OF COPPER ; Scheele's GREEN. — TMs is prepared by mixing 
soli]Aions of sulphate of copper and arsenite of potassa ; it falls as a bright 
green insoluble powder. 

The characters of the protosalts of copper are well marked. 

Caustic of potassa gives a pale blue precipitate of hydrate, becoming 
blackish-brown anhydrous protoxide on boiling. 

Ammonia also throws down the hydrate ; but, when in excess, re-dissolves 
it, yielding an intense purplish blue solution. 

Carbonates of potassa and soda give pale blue precipitates, insoluble in 

Carbonate of ammonia, the same, but soluble with deep blue colour. 

Ferrocyanide of potassium gives a fine red-brown precipitate of ferrocya- 
nide of copper. 

Sulphuretted hydrogen and sulphide of ammonium afford black sulphide 
of copper. V 

The alloys of copper are of great importance. Brass consists of copper 
•Uoy«d with firom 28 to 84 per cent of zino ; the latter may be added di- 

LSAD. 279 

rectlj to the melted copper, or grannliited copper may be heated with calft- 
mine and charcoal-powder, as in the old process. Oun-metal^, a most 
trustworthy and yaluable alloy, consists of 90 parts copper and 10 tin. Bell 
and speculum metal contain a still larger proportion of tin ; these are brittle, 
especially the last-named. A good bronze for statues is made of 91 parts 
copper, 2 parts tin, 6 parts zinc, and 1 part lead. The brass of the ancients 
is an alloy of copper with tin. 

This abundant and useful metal is altogether obtained from the native sul- 
phide, or galena, no other lead-ore being found in quantity. The reduction is 
effected in a reverberatory furnace, into which the crashed lead ore is intro- 
duced and roasted for some time at a dull red>heat, by which much of the 
sulphide becomes changed by oxidation to sulphate. The contents of the 
furnace are then thoroughly mixed, and the temperature raised, when the 
sulphate and sulphide react upon each other, producing sulphurous acid and 
metallic lead.* 

Lead is a soft bluish metal, possessing very little elasticity ; its specific, 
gravity is 11*45. It may be easily rolled out into plates, or drawn into coarse 
wire, but has a very trifling degree of strength. Lead melts at 600° (815° -SC) 
er a little above, and at a white-heat boils and volatilizes. By slow cooling 
it may be obtained in octahedral crystals. In moist air this metal becomes 
coated with a film of grey matter, thought to be suboxide, and when exposed 
to the atmosphere in a melted state it rapidly absorbs oxygen. Dilute acids, 
with the exception of nitric, act but slowly upon lead. Chemists are fami- 
liar with four oxides of lead, only one of which possesses basic properties. 

The equivalent of lead is 103-7 ; its symbol is Pb. 

Pbotoxidr; lithakoe; massicot; PbO. — This is the product of the 
direct oxidation of the metal. It is most conveniently prepared by heating 
the carbonate to dull redness ; common litharge is impure protoxide which 
has undergone fusion. Protoxide of lead has a delicate straw-yellow colour, 
is very heavy, and slightly soluble in water, giving an alkaline liquid. At a 
red-beat it melts, and tends to crystallize on cooling. In a melted state it 
attacks and dissolves siliceous matter with astonishing facility, often pene- 
trating an earthen crucible in a few miputes. It is easily reduced when 
heated with organic substances of any kind containing carbon or hydrogen. 
Protoxide of lead forms a large class of salts, which are colourless if the acid 
itself be not coloured. 

Bed oxide; bed-lead; PbjO^, or 2PbO-f-PbOg. — The composition of 
this substance is not very constant ; it is prepared by exposing for a long 
time to the air, at a very faint red-heat, protoxide of lead which has not been 
fused ; it is a brilliant red and extremely heavy powder, decomposed with 
evolution of oxygen by a strong heat, and converted into a mixture of pro- 
toxide and binoxide by acids. It is used as a cheap substitute for vermilion. 

BiNOXiDB OP lead ; PUCE OR BROWN OXIDE ; PbOj- — This compound is 
obtained without difficulty by digesting red-lead in dilute nitric acid, when 
nitrate of protoxide is dissolved out and insoluble binoxide left behind in the 
form of a deep brown powder. The binoxide is decomposed by a red-heat, 
yielding up one-half of its oxygen. Hydrochloric acid converts it into chlo- 
ride of lead with disengagement of chlorine ; hot oil of vitriol forms with it 

{Oxide of fLead Free, 
lead ( Oxygen — ---- 2 Sulphurous add. 
Sulphuric j Sulphur -_,,^-;;5>-' 
acid ( 3 Oxjs^nj^:^^ 
BoJphide of le,«l { ^J^'^^ j^ 

280 LEAD. 

iulpliate of lead, and liberates oxygen. The binoxide is very nseful in sepa- 
rating sulphurous acid from certain gaseous mixtures, sulphate of lead being 
then produced. ~ . 

Suboxide op lead, PbjO. — "When oxalate of lead is heated to dull redness 
in a retort, a grey pulverulent substance is left, which is resolved by acids 
into protoxide of lead and metal. It absorbs oxygen with great rapidity 
when heated, and even when simply moistened with water and exposed to^ 
the air. 

Nitrate op lead, PbO,N05. — The nitrate may be obtained by dissolving 
carbonate of lead in nitric acid, or by acting directly upon the metal by the 
same agent with the aid of heat ; it is, as already noticed, a by-product in 
the preparation of the binoxide. It crystallizes in anhydrous octahedrons, 
which are usually milk-white and opaque ; it dissolves in 7} parts of cold 
"water, and is decomposed by heat, yielding nitrous acid, oxygen, and pro- 
toxide of lead, which obstinately retains traces of nitrogen. 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 nitrate generated, which may be had 
in crystals. Carbonic acid separates this excess of oxide in the form of a 
white compound of carbonate and hydrate of lead. 

Neutral and basic compounds of oxide of lead with nitrous, and the demenU 
of hyponitric acid, have been described. These last are probably formed by 
the combination of a nitrite with a nitrate. 

Cabbonate of lead ; white-lead ; PbOjCOg. — Carbonate of lead is some- 
times found beautifully crystallized in long white needles, accompanying 
other metallic ores. It may be prepared by precipitating in the cold a solu- 
tion of the nitrate or acetate by an alkaline carbonate ; wKen the lead solu- 
tion is boiling, the precipitate is a basic salt, containing 2(PbO,COj) + H0, 
PbO ; it is also manufactured to an immense extent by other means for the use 
of the painter. Pure carbonate of lead is a soft, white powder, of great 
specy&c gravity, insoluble in water, but easily dissolved by dilute nitric or 
acetic acid. 

Of the many methods put in practice, or proposed, for making white-lead, 
the two following are the most important and interesting : — One of these 
consists in forming a basic nitrate or acetate of lead by boiling finely pow- 
dered litharge with the neutral salt'. This solution is then brought into con- 
tact with carbonic acid gas ; all the excess of oxide previously taken up by 
the neutral salt is at once precipitated as while-lead. The solution strained 
or pressed from the latter is again boiled with litharge, and treated with car- 
bonic acid, these processes being susceptible of indefinite repetition, when 
the little loss of neutral salt left in the precipitates is compensated. The 
second, and by far the more ancient method, is rather more complex, and at 
first sight not very intelligible. A great number of earthen jars are pre- 
pared, into each of which is poured a few ounces of crude Tinegar ; a roll 
of sheet-lead is then introduced in such a manner that it shall neither touch 
the vinegar nor project above the top of the jar. The vessels are next ar- 
ranged in a large building, side by side, upon a layer of stable tnanui-e, or, 
still better, spent-tan, and closely cohered with boards. A second layer of 
tan is spread upon the top of the latter, and then a second series of pots ; 
these are in turn covered with boards and decomposing bark, and in this 
manner a pile of many alternations is constructed. After the lapse of a con- 
siderable time the pile is taken down and the sheets of lead removed and 
carefully unrolled ; they are then found to be in great part converted into 
carbonate, which merely requires washing and grinding to be fit for use. 
The nature of this curious process is generally explained by supposing the 
vapour of vinegar raised by the high temperature of the fermenting matter 
merely to act as a carrier between the carbonic acid evolved from the tan. 

LKAD 281 

and tbe oxide of lead formed under the inflaence of the acid rapovr ; a nea- 
tnJ acetate, a basic acetate, and a carbonate being produced io succession, 
the action gradually travelling from the surface inwards. The quantity of 
acetic acid used is, in relation to the lead, quite trifling, and cannot directly 
contribute to the production of the carbonate. A preference is still given 
to the product of this old mode of manufacture on account of its superiority 
of opacity, or body^ over that obtained by precipitation. Commercial white- 
lead, however prepared, always contains a certain proportion of hydrate. 

When clean metallic lead is put into pure water and exposed to the atmo- 
sphere, a white, crystalline, scaly powder begins to show itself in a few 
hours, and very rapidly increases in quantity. This substance may consist 
of hydrated protoxide of lead, formed by the action of the oxygen dissolved 
in the water and from the lead. It is slightly soluble, and may be readily 
detected in the water. In most cases, however, the formation of this deposit . 
is due to the action of the carbonic acid dissolved in the water ; it consists 
of carbonate in combination with hydrate, and is very insoluble in water. 
When common river or spring water is substituted for the pure liquid, this 
effect is less observable, the little sulphate, almost invariably present, causing 
the deposition of a very thin but closely adherent film of sulphate of lead 
upon the surface of the metnl, which protects it from farther action. It is 
on this account that leaden cisterns are used with impunity, at least in most 
cases, for holding water ; if the latter were quite pure, it would be speedily 
contaminated with lead, and the cistern be soon destroyed. Natural water 
highly charged with carbonic acid cannot, under any circumstances, be kept 
in lead, or passed through leaden pipes with safety, the carbonate, though 
Tery insoluble in pure water, being slightly soluble in water containing car- 
bonic acid. 

Chloride of lead, PbCl. — This salt is prepared by mixing strong solu- 
tions of acetate of lead and chloride of sodium ; or by. dissolving litharge in 
boiling dilute hydrochloric acid, and setting aside the filtered solution to 
cool. Chloride of lead crystallizes in brilliant, colourless needles, which 
require 135 parts of cold water for solution. It is anhydrous ; it melts when 
heated, and solidifies on cooling to a horn-like substance. 

loDiDB OF LKAD, Pbl. — The iodidc 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 colourless solution, which 
deposits the iodide on cooling in splendid golden-yellow scales. 

The soluble salts of lead thus behave with reagents: — 

Caustic potassa and soda precipitate a white hydrate, freely soluble in 

Ammonia gives a similar white precipitate, not soluble in excess.' 

The carbonates^ of potassa, soda, and ammonia, precipitate carbonate of 
lead, insoluble in excess. 

Sulphuric acid or a sulphate causes a white precipitate of sulphate of lead,, 
insoluble in nitric acid. 

Sulphuretted hydrogen and sulphide of ammonium throw down black 
salphide of lead. 

An alloy of 2 parts of lead and 1 of tin consiitvitea 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. 
24* ■ 

282 TIN. 



This valuable metal occurs in the state of oxide, and more rarely as sal- 
phide ; the principal tin mines are those of the Erzgebirge in Saxony and 
Bohemia, Malacca, and more especially Cornwall. In Cornwall the tin-stono 
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- 
find the second atream-tin. Oxide of tin is also found disseminated through 
the rock itself in small crystals. 

To prepare the ore for reduction, it is stamped to powder, washed, to 
separate as much as possible of the earthy matter, and roasted to expel 
sulphur and arsenic ; it is then strongly iieated 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 ffrain- and 
bar-tin ; the first is the best ; it is prepared from the stream ore. 

Pure tin has a white colour, approaching to that of silver ; it is soft and 
malleable, and when bent or twisted emits a peculiar crackling sound ; it has 
a density of 7-3 and melts at 442° (2270-77C). Tin is but little acted upon 
by air and water, even conjointly ; when heated above its melting-point it 
oxidizes rapidly, becoming converted into a whitish powder, used in the arts 
for polishing, under the name of putty-powder. The metal is easily attacked 
and dissolved by hydrochloric acid, with evolution of hydrogen ; nitric acid 
acts with great energy, converting it into a white hydrate of the binoxide. 
There are two well-marked oxides of tin, which act as feeble bases or acids, 
according to circumstances, and a third, which has been less studied. 

The equivalent of tin is 58 ; its symbol is Sn. 

Protoxide op tin, SnO. — When solution of protochloride of tin is mixed 
with carbonate of potassa, a white hydrate of the protoxide falls, the car- 
bonic acid being at the same time extricated. When this is carefully washed, 
dried, and heated in an atmosphere of carbonic acid, it loses water, and 
changes to a dense black powder, which is permanent in the air, but takes 
fire on the approach of a red-hot body, and burns like tinder, producing 
binoxide. The hydrate is freely soluble in caustic potassa ; the solution 
decomposes by keeping into metallic tin and binoxide. 

Sesquioxide of tin, SugO,. — The sesquioxide is produced by the action 
of hydra ted sesquioxide of iron upon protochloride of tin ; it is a greyish, 
slimy substance, soluble in hydrochloric acid, and in ammonia, ^bis oxide 
lias been but- little examined. 

Binoxide of tin, SnOj. — This substance is obtained in two different states^ 
having properties altogether dissimilar. When bichloride of tin is precipi- 
tated by an alkali, a white bulky hydrate appears, which is freely soluble in 

TIN. 283 

acids. If, on the other hand, the bichloride be boiled with excess of nitric 
acid, or if that acid be made to act directly on metallic tin, a white sub- 
Btance is produced, which refuses altogether to dissoWe in acids, and pos- 
Besses properties differing in other respects from those of the first modifica- 
tion. BoUi these yarieties of binoxide of tin have the same composition, 
and when ignited, leave the pure binoxide of a pale lemon-yellow tint 
Both dissolye in caustic alkali, and are precipitated with unchanged proper- 
ties by an acid. The two hydrates redden litmus-paper.* 

Protoohloride of tin, SnCl. — The protochloride is easily made by dis- 
BOlring metallic tin in hot hydrochloric acid. It crystallizes in needles con- 
taining 2 equivalents of water, which are freely soluble in a small quantity 
of water, but are apt to be decomposed in part when put into a large mass, 
unless hydrochloric acid in excess be present. The anhydrous chloride may 
be obtained by distilling a mixture of calomel and powdered tin, prepared 
by agitating the melted metal in a wooden box until it solidifies. The chlo- 
ride is a grey, resinous-looking substance, fusible below redness, and volatile 
at a high temperature. Solution of protochloride of tin is employed as a 
deoxidizing agent; it reduces the salts of mercury and other metals of the 
same class. 

Bichloride or perchloride of tin, SnClj. — This is an old and very cu- 
rious compound, formerly called fuming liquor of Libqviua. It is made by 
exposing metallic tin to the action of chlorine, or, more conveniently, by 
distilling a mixture of 1 part of powdered tin, and 6 parts of corrosive sub- 
limate. The bichloride is a thin, colourless, mobile liquid ; it boils at 248^ 
(120OC), and yields a colourless invisible vapour. It fumes in the air, and 
when mixed with a third part of water, solidifies to a crystalline mass. The 
solution of bichloride is much employed by the dyer as a mordant ; it is com- 
monly prepared by dissolving metallic tin in a mixture of hydrochloric and 
nitric acids, care being taken to avoid too great elevation of temperature. 

Sulphides of tin. — Protosulphide, SnS, is prepared by fusing tin with ex- 
cess of sulphur, and strongly heating the product. It is a lead-grey, brittle 
substance, fusible by a red-heat, and soluble with evolution of sulphuretted 
hydrogen in hot hydrochloric acid. A sesquisulphide may be formed by gently 
heating the above compound with a third of its weight of sulphur ; it is yel- 
lowish-gre}', and easily decomposed by heat. Bisulphide^ SnSj, or Mosaic 
goldj is prepared by exposing to a low red-he^t, in a glass flask, a mixture 
of 12 parts of tin, 6 of mercury, 6 of sal-ammoniac, and 7 of flowers of 
sulphur. Sal-ammoniac, cinnabar, and protochloride of tin sublime, while 
the bisulphide remains at the bottom of the vessel in the form of brilliant 
gold-coloured scales; it is used as a substitute for gold-powder. 

Salts of tin are thus distinguished : — 

Caustic alkalis ; white hydrate, soluble in excess. 
Aiomonia; carbonates of potassa, |^^^.j^ ^^^ ^^^, j^^j^^^ . 
soda, and ammonia V excess! 

lulff o?'amlTm'::::::::::::: } ^^-^ p-'p'*-** <>f p-tosuipMde. 

Caustic alkalis ; white hydrate, soluble in excess. 
Ammonia ; white hydrnte, slightly soluble in excess. 

' Fremy has called the first of thone oxides fttannio add SnOsi. The recond he has named 
inctMttannic add SusOio. See alK) U. Koee Pugg. Ann. Ixxv. I, who thinks that there art 
other modificationa of this oxide of tin. 


Alkaline carbonates : white hydrates, slightly solnble in excesi 
Carbonate of ammonia ; white hydrate, insoluble. 
Sulphuretted hydrogen ; yellow precipitate of sulphide. 
Sulphide of ammonium ; the same, soluble in excess. 

Terchloride of gold, added to a dilute solution of protochloride of tin» 
gives rise to a brownish-purple precipitate, called purple of Ccusiut, very 
characteristic, whose nature is not thoroughly understood ; it is supposed to 
be a combination of oxide of gold and sesquioxide of tin, in which the latter 
acts as an acid. Heat resolves it into a mixture of metallic gold and binox- 
ide of tin. Purple of Cassius is employed in enamel-painting. 

The useful applications of tin are very numerous. Tinned-plaie consists 
of iron superficially alloyed with this metal; pewter^ of the best kind, is 
chiefly tin, hardened by the admixture of a little antimony, &c. CooldDg 
vessels of copper are usually tinned in £he interior. 


Tungsten is found, as tungstate of protoxide of iron, in the mineral wolf- 
ram, tolerable abundant in Cornwall ; a native tungstnte of lime is also oc- 
casionally met with. Metallic tungsten is obtained in the state of a dark 
grey powder, by strongly heating tungstic acid in a stream of hydrogen, but 
requires for fusion an exceedingly high temperature. It is a white metal, 
very hard and brittle; it has a density of 17 -4. Heated to redness in the 
air, it takes fire, and reproduces tungstic acid. 

The equivalent of tungsten is 92, its symbol is W (wolframium). 

BiNOXiDE OF TUNGSTEN, WOj- — This is most easily prepared by exposing 
tungstic acid to hydrogen, at a temperature which does not exceed dull red- 
ness. It is a brown powder, sometimes assuming a crystalline appearance 
and an imperfect metallic lustre. It takes fire when heated in the air, and 
burns, like the metal itself, to tungstic acid. < The binoxide forms no salts 
with acids. 

Tungstic acid, WOg. — When tungstnte 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 difiScult. Tungstic acid is a yellow 
powder, insoluble in water, and freely dissolved by caustic alkalis. When 
stroiigly ignited in the open air, it assumes a greenish tint. 

Intermediate or blue oxide of tungsten, W205,=W02,W03. — This sub- 
stance is obtained by heating tungstate of ammonia, or by exposing the 
brown binoxide to the action of hydrogen at a very low temperature. The 
same compound appears to be produced if tungstic acid be separated from 
one of its salts, by hydrochloric acid and the liquid be digested with metallic 
sine, when the solution or the precipitate assumes a beautiful blue colour, 
which is very characteristic of this metal. 

Two chlorides and two sulphides of tungsten are known to exist. 

. Metallic molybdenum is obtained by exposing molybdic acid in a charcoal- 
lined crucible to the most intense heat that can be obtained. It is a white, 
brittle, and exceedingly infusible metal, having a density of 8*6, and oxi- 
dizing, v^hen heated in the air, to molybdic acid. 

The equivalent of molybdenum is 46 ; its symbol is Mo. 

Protoxide of moltbpenum, MoO. — Molybdate of potassa is mixed with 


excMS of hydrochloric acid, by which the molybdic acid first precipitated is 
re-dissolved ; into this acid solutioD zinc is put : a mixture of chloride of 
ziDC and protochloride of molybdenum results. A large quantity of caustio 
potassa is then added, which precipitates a black hydrate of the protoxide 
of molybdenum, and retains in solution the oxide of zinc. The freshly pre- 
cipitated protoxide is soluble in acids and in carbonate 'of ammonia ; when 
heated in the air, it burns to binoxide. 

BiNoxiDE OF MOI.TBDKNUM, MoOg. — This is obtained in the anhydrous con- 
dition by heating molybdate of soda with sal-ammoniac, the molybdic acid 
being reduced to binoxide by the hydrogen of the ammoniacal salt ; or, in a 
hydrated condition, by digesting metallic copper in a solution of molybdic 
acid in hydrochloric acid, until the liquid assumes a red colour, and then 
adding a large excess of ammonia. The anhydrous binoxide is deep brown, 
and insoluble in acids ; the hydrate resembles hydrate of sesquioxide of iron, 
and dissolves in acids, yielding red solutions. It is converted into molybdio 
acid by strong nitric acid. 

MoLTBDic ACID, M0O3. — The native bisulphide of molybdenum is roasted, 
at a red-heat, in an open vessel, and the impure molybdic acid thence re- 
sulting dissolved in ammonia. The filtered solution is evaporated to dryness, 
the salt taken up by water, and purified by crystallization. It is, lastly, 
decomposed by heat, and the ammonia expelled. Molybdic acid is a white 
crystalline powder, fusible at a red-heat, and slightly soluble in water. It 
is dissolved with ease by the alkalis. It forms two series of salts, namely, 
neutral molybdates MOjMoO-, and acid molybdates MO,2Mo03. Three 
chlorides, and as many sulphides of molybdenum, are described. 

Tanadium is found, in small quantity, in one of the Swedish iron ores, 
and also as vanadate of lead. It has also been discovered in the iron slag of 
Staffordshire. 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, chloride of ammonium is volatilized, and 
metallic yanadium left behind. It is a white brittle substance, of perfect 
metallic lustre, and a very high degree of infusibility ; it is neither oxidized 
by air or water, nor attacked by sulphuric, hydrochloric, or even hydrofluoric 
acid ; aqua regia dissolves it, yielding a deep blue solution. 

The equivalent of vanadium is 68*6 ; its symbol is Y. 

Protoxide of vanadium, VO. — This is prepared by heating vanadic acid 
in contact with charcoal or hydrogen ; it has a black colour, and imperfect 
metallic lustre, conducts electricity, and is very infusible. Heated in the 
air, it bums 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«. — The binoxide is obtained by heating a 
mixture of 10 parts protoxide of vanadium, and 12 of vanadic acid in a vessel 
filled with carbonic acid gas ; or by adding a slight excess of carbonate of 
soda to a salt of the binoxide ; in the latter case it falls as a greyish- white 
hydrate, readily becoming brown by absorption of oxygen. The anhydrous 
oxide is a black insoluble powder, convertible by heat and air into vanudio 
acid. It forms a series of blue salts, which have a tendency to become green 
and ultimately red, by the production of vanadic acid. Binoxide of vanadium 
also unites with alkalis. 

Vanadic acid, VO3. — The native vandate of lead is dissolved in nitric 
acid, and the lead and arsenic precipitated by sulphuretted hydrogen, which 
at the same time reduces the vanadic acid to binoxide of vanadium. The 


blue filtered solution is then evaporated to dryness, and the residue digested 
in ammonia, which dissoWes out the yanadic acid reproduced during evapo- 
ratiou. Into this solution a lump of sal-ammoniac is put ; as that salt dis^ 
solves, vanadate of ammonia subsides as a white powder, being scarcely solu- 
ble in a saturated solution of chloride of ammonium. By exposure to a tem- 
perature below redness in an open crucible, the ammonia is expelled, and 
vanadic acid left. It has a dark-red colour, and melts even below a red- 
heat ; water dissolves it sparingly, and acids with greater ease ; the solutions 
easily suffer deoxidation. It unites with bases, forming a series of red or 
yellow salts, of which those of the alkalis are soluble in water. 

Chlobides 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 oxichloride. 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 sulphides, corresponding to the chlorides, exist. 


This is, an exceedingly rare substance ; it is found in the minerals tanialiit 
and yttro-tantalite, and may be obtained pure by heating with potassium the 
double fluoride of tantalum and potassium. It is a grey metal, but little 
acted on by the ordinary acids, and burning to tantalic acid when heated ia 
the air, or when fused with hydrate of potassa. 

The equivalent of tantalum is 184 ; its symbol is T. 

BiNOXiDE OF TANTALUM, TOj. — When tantalic acid is heated to whiteness 
in a crucible lined with charcoal, the greater part is converted into this sub- 
stance. It is a dark-brown powder, insoluble in acids, and easily changed 
by oxidation to tantalic acid. 

Tantalic acid, TO3. — The powdered ore is fused with three or four times 
its weight of carbonate of potassa, and the product digested with water; 
from this solution acids precipitate a white hydrate of the body in question. 
It is soluble in acids, but forms with them no definite compounds ; with al- 
kalis it yields, on the contrary, crystallizable salts. The specific gravity of 
the acid varies 7-03 to 8-26. 


The oxides of these two metals exist in the tantalite of Bodenmais in Ba- 
varia. When the supposed tantalic acid from this source is mixed with dry 
powdered charcoal, and heated to redness in a current of chlorine gad, a 
sublimate is obtained of a yellow, readily fusible, and very volatile substance, 
the chloride of pelopium, and a white, infusible, less volatile body, the chlo- 
ride of niobium. The true chloride of tantalum, from the Finland tantalite, 
much resembles chloride of pelopiura. The American tantalite contains nio- 
bic, pelopic, and tungstic acids, the former in greatest quantity. 

All these chlorides are decomposed by water, with production of hydro- 
chloric acid and the insoluble acids of the metals in the hydrated state. In 
properties these bodies greatly resemble each other. When heated to redness, 
they exhibit strongly the phenomenon of incandescence. While hot, tantalic 
acid remains white, pelopic acid is rendered slightly yellowish and has a spe- 
cific giavity varying from 5-79 to 6 37, and niobic acid becomes dark yellow, 
with a specific gravity between 4-56 and 6"26. 

Tantalum, niobium, and pelopium may be obtained in a finely-divided me- 
tallic state by the action of ammonia on their respective chlorides at a high 


teniperatttre. So prepared, they hre black, pnlYemlent^ not acted on by 
irater, but burning, when heated in the air, to acids. 


Crystallized oxide of titanium is found in nature in the forms of tiianit€ 
and anatoM. Occasionally in the slag adherent to the bottom of blast-furnaces 
in which iron ore is reduced small brilliant copper-coloured cubes, hard 
enough to scratch glass, and in the highest degree infusible are found. This 
substance, of which a single smelting furnace in the Hartz produced as much 
as 80 pounds, was formerly belieyed to be metallic titanium. Recent re- 
searches of Wohler, however, have shown it to be a combination of cyanide 
of titanium with nitride of titanium. When these crystals are powdered, 
mixed with hydrate of potassa and fused, ammonia is eTolved, and titanate 
of potassa is formed. Metallic titanium in a finely divided state may be ob- 
tained by heating fluoride of titanium and potassium with potassium. Thei*e 
are two compounds of this substance with oxygen; viz. an oxide and an 
acid : Yery little is known respecting the former. 

The equivalent of titanium is 25 ; its symbol is Ti. 

Titanic acid, Ti02. — Titanate, or titaniferous iron ore, is reduced to fine 
powder and fused with twice its weight of carbonate of potassa, powdered, 
dissolved in dilute hydrofluoric acid when titanofluoride of titanium and 
jftotassium soon begins to separate. From its hot aqueous solution snow-like 
titanate of ammonia is precipitated by ammonia, which is easily soluble in 
hydrochloric acid, and when ignited gives pure titanic acid. When pure the 
acid is quite white ; it is, when recently precipitated from solutions, soluble 
in acids, but the solutions are decomposed by mere boiling. After ignition 
it is no longer soluble, passing over into metatitanic acid. Titanic acid, on 
the whole, very much resembles silica, and is probably often overlooked and 
confounded with that substance in analytical researches. 

Bichloride of titanium. — This is a colourless, volatile liquid, resembling 
bichloride of tin ; it is obtained by passing chlorine over a mixture of titanic 
acid and charcoal at a high temperature. It unites very violently with 
water. On passing the vapour with hydrogen through a red-hot tube, 
hydrochloric acid and a new compound Ti^Cl, are formed. 


This important metal is found chiefly in the state of sulphide. The ore is 
freed by fusion from earthy impurities, and is afterwards decomposed by 
heating with metallic iron or carbonate of potassa, which retains the sulphur. 
Antimony has a bluish-white colour and strong lustre; it is extremely 
brittle, being reduced to powder with the utmost ease. Its specific gravity 
is 6-8 ; it melts at a temperature just short of redness, and boils and vola- 
tilizes at a white-heat. This metal has always a distinct crystalline, platy 
structure, but by particular management it may be obtained in crystals, 
which are rhombohedral. Antimony is not oxidized by the air at common 
temperatures ; strongly heated, it burns with a white flame, producing ter- 
oxide, which is often deposited in beautiful crystals. It is dissolved by hot 
hydrochloric acid with evolution of hydrogen and production of terchloride. 
Nitric acid oxidizes it to antimonio acid, which is insoluble in that men- 
struum. There are three compounds of antimony and oxygen ; the first has 
doubtful basic properties, the second is indifferent, and the third is an acid. 

The equivalent of antimony is 129. Its symbol is Sb (stibium). 

Teroxidb of antimony, SbOg. — This compound may be prepabed 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 solution of terchloride of antimony into water, and digesting tfat« 


resnltiBg precipitate with a solution of carbonate of soda. The teroilde 
thus produced is anhydrous ; it is a pale buff-coloured powder, fusible at a 
red-heat, and volatile in a close vessel, but in contact with air, it, at a high 
temperature, absorbs oxygen and becomes changed to the intermediate oxide. 
There exists a sulphate, nitrate, and oxalate of teroxide of antimony. )iVhen . 
boiled with cream of tartar (bitartrate of potassa), it is dissolved, and the 
solution yields, on evaporation, crystals of tartar-emetic^ which is almost, the 
only compound of teroxide of antimony with an acid which bears admixture 
with water without decomposition. An impure oxide for this purpose is 
sometimes prepared by carefully roasting the powdered sulphide in a rever- 
beratory furnace, and raising the heat at the end of the process, so as to fuse 
the product ; it has long been known under the name of gluss of antimony. 

Intermediatb oxide, Sb04=Sb03,Sb05. — This is the ultimate product 
of the oxidation of the metal by heat and air ; it is a greyish white powder, 
infusible, and destitute of volatility ; it is insoluble in water and in acids, 
except when recently precipitated. When treated with tartaric acid or 
bitartrate of potassa, teroxide of antimony is dissolved, antimonic acid 
remaining behind ; alkalis, on the other hand, remove antimonic acid, ter- 
oxide of antimony being left. 

Antimonic acid, SbOg. — When strong nitric acid is made to act upon 
metallic antimony, the metal is oxidized to its highest point, and antimonic 
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 strav- 
coloured powder, insoluble in water and acids. It is decomposed by a red- 
heat, yielding the intermediate oxide, with the loss of oxygen. 

Antimonic acid is likewise obtained by decomposing pentachloride of anti- 
mony and an excess of water, when, together with the metallic acid, hydro* 
acid is produced. The hydrated antimonic acid produced by the two pro- 
cesses mentioned, differs in many of its properties, and especially in its 
deportment with bases. The substance produced by nitric acid is monobasic, 
producing salts of the formula MO.SbOg, the other is bibasic, and forms two 
series of salts of the composition 2MO,Sb05 and MOjHOjSbOg. In order to 
distinguish the two modifications, M. Fremy, who first pointed out the bibasic 
nature of the acid obtained from the pentachloride, has proposed to distin- 
guish it as metantimonic acid. Among the salts of the latter, an acid 
metantimonate of potassa KO,HO,Sb05-|-6HO, is to be noticed, which yields 
a precipitate with soda-salts. It ia the only reagent which precipitates soda, 
but must be employed with great care and circumspection. It is obtained 
by fusing antimonic acid with an excess of potassa in a silver crucible, dis- 
solving the fused mass in a small quantity of cold water, and allowing it to 
crystallize in vacuo. The crystals which form are metantimonate of potassa 
2K0, SbOg, which, when dissolved in pure water, are decomposed into free 
potassa and acid metantimonate. 

Terchlobide of antimony ; butter of antimony ; SbClg. — This substance 
is produced when sulphuretted hydrogen is prepared by the action of strong 
hydrochloric acid on tersulphide 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 terchloride of antimony passes over, and soli- 
difies on cooling to a white and highly crystalline mass, from which the air 
requires to be carefully excluded. The same compound is formed by distil- 
ling raf ' allic antimony in powder with 2 J times its weight of corrosive subli- 
mate. Terchloride of antimony is very deliquescent ; it dissolves in strong 
liydrochloric acid without decomposition, and the solution poured into water 
l^ves rise to a white balky precipitate, which, after a short time, becomes 


Idgfaly dTStalline, and assumes a pale fawn colour. This is the old powder 
0/ Algaroth ; it is a compound of terchloride and teroxide of antimony. Al- 
kaline solutions extract the chloride and leave teroxide of antimony. Finely 
powdered antimony thrown into chlorine gas inflames. 

PiNTACHOBiDB OF Antimont, Corresponding to antimonic acid, is fQ(rmed 
by passing a stream of chlorine gas ever gently heated metallic antimony ; a 
mixture of the two chlorides results, which may be separated by distillation. 
The peniaekloride is a colourless volatile liquid, which forms a crystalline 
compound with a small portion of water, but is decomposed by a larger quan- 
tity into antimonic and hydrochloric acids. 

Tbbsulphidb of antimont ; crudb antimony ; SbS,. — The native sulphide 
is a lead-grey, brittle substance, having a radiated crystalline texture, and 
is easily fusible. It may be prepared artificially by melting together anti- 
mony and sulphur. When a solution of tartar-emetic is precipitated by sul- 
phuretted 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 ot£er change of colour than a little dark- 
ening, but at a higher temperature it asstimes the colour and aspect of the 
native sulphide. This remarkable change probably indicates a passage from 
the amorphous to the crystalline condition. 

When powdered tersulphide of antimony is boiled in a solution of caustic 
potassa, it is dissolved, teroxide of antimony and sulphide of potassium being 
produced. The latter unites with an additional quantity of tersulphide of 
antimony to a soluble sulphur-salt, in which the sulphide of potassium is the 
solphur-base, and the tersulphide of antimony is the sulphur-acid. 

f 3 eq. potassium -,,^ - f 8 eq. sulphide of 

3 eq. potassa ... -J ^ — '^ \ potassium. 

( 3 eq. oxygen ---^-^^^g^---^^ 

Tersulphide of f 3 eq. sulphur -^ " ^^„,._ ^ *^^^^iA^ ^# 

The teroxide of antimony separates in small crystals from the boiling solu- 
tion when the latter is concentrated, and the sulphur-salt dissolves an extra 
proportion of tersulphide of antimony, which it again deposits on cooling as 
a red amorphous powder, containing a small admixture of teroxide of anti^- 
mony and sulphide of potassium. This is the kermes mineral of the old 
chemists. The filtered solution mixed with an acid gives a salt of potassa, 
sulphuretted hydrogen, and precipitated tersulphide of antimony. Kermes 
may also be made by fusing a mixture of 6 parts tersplphide of antimony 
and 3 of dry carbonate of soda, boiling the mass in 80 parts of water, and 
filtering while hot ; the compound separates on cooling. 

Pbntasulphidb of antimony, SbSj, formerly called sulphur auratum, also 
exists ; it is a sulphur-acid. 18 parts finely powdered tersulphide of anti- 
mony,' 17 parts dry carbonate of soda, 13 parts lime in the state of hydrate, 
and Bh parts sulphur, are boiled for some hours in a quantity of water; car- 
bonate of lime, antimonate of soda, pentasulphide of antimony, and sulphide 
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, 
whicji may by evaporation be obtained in beautiful crystals. A solution of 
this substance, mixed with dilute sulphuric acid, furnishes sulphate of soda, 
sulphuretted hydrogen, and pentasulphide of antimony, which falls as a 
golden-yellow flocculent precipitate. 

Antimonetted hydrogen. — A compound of antimony and hydrogen exists, 
out has not been isolated ; when zinc is put into a solution of teroxide of 
antimony, and sulphuric acid added, part of the hydrogen combines with the 


^atimonjr. TMs gas burns widi a greenish flame, giving rise to white fumes 
of teroxide of antimony. When the gas is conducted through a red-hot glass 
tube of narrow dimensions, or burned with a limited supply of air, such as 
is the cade when a cold porcelain surface is pressed into the flame, metallio 
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 sulphide of ammonium, and again precipitated by an 

Besides its application to mediciife, 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 
circumstances, and make very bad castings. Tersulphide of antimony enters 
into the comnosition of the blue signal-light, used at sea/ 


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 
replacing sulphur, and is most easily extracted from the sulpho-telluride of 
bismuth of Chemnitz, in Hungary. The finely powdered ore is mixed with 
an equal weight of dry carbonate of soda, the mixture made into a paste 
with oil, and heated to whiteness in a closely covered crucible. Telluride 
and sulphide 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 
Boda, while the tellurium separates in the metallic state. TeUurium has the 
colour and lustre of silver ; by fusion and slow cooling it may be made to 
exhibit the form of rbombohedral crystals similar to those of antimony and 
arsenic. It is brittle, and a comparatively bad conductor of heat and elec- 
tricity ; it has a density of 6*26, melts at a little below red-heat, and vola- 
tilizes at a higher temperature. TelluHum bums 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*2 ; its symbol is Te. 

TsiiLUBOus AOiD, TeOj. — This is obtained by burning tellurium in the air, 
qr by heating it in fine powder with nitric acid of 1-26 specific gravity; a 
solution is rapidly formed, from which white anhydrous octahedral crystals 
of tellurous acid are deposited on standing. iThe 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 potassa is mixed with a slight excess of nitric acid ; it is a white 
powder, soluble to a certain extent in water, and reddens litmus. 

Tbllurio acid, TeO,. — 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 tellurite of baryta is thrown 
down. This is washed and digested with a quarter of its weight of sulphuric 

* Blue or Bengal light:— 

Dry nitrate of potassa 6 parts. 

Sulphur 2 " 

Tersulphide of antimony -. 1 *< 

AU in flue powder and intimately mixML 


acid, diluted Trith water. The filtered solution gives, on evaporation in tiie 
air, large crystals of telluric acid. 

Telluric acid is freely, although slowly, soluble in water; it has a metallio 
taste, and reddens litmus-paper. "When the crystals are strongly heated, 
they lose water, and yield anhydrous acid, which is then insoluble jn water, 
aud 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, 

There are two chlorides of tellurium, and also a hydride, which closely 
resembles sulphuretted hydrogen. 

Arsenic is sometimes found native ; it occurs in considerable qnantity as a 
constituent of many minerals, combined with metals, sulphur and oxygen. 
In the oxidized state it has been found in very minute quantity in a great 
many mineral waters.^ The largest proportion is derived from the roasting 
of natural arsenides of iron, nickel, and cobalt ; the operation is 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 
sablimation, and then heated with charcoal in a retort ; the metal is reduced, 
and readily sublimes. 

Arsenic has a steel-grey colour, 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 vapour has 
the odour of garlic. This substance combines with metals in the same 
manner as sulphur and phosphorus, which it resembles, especially the latter, 
in many respects. With oxygen it unites in two proportions, giving rise tc 
arsenious and arsenic acids. There is no basic oxide of arsenic. 

The equivalent of arsenic is 75 ; it symbol is As. 

Arsenious acid ; white oxide of arssmio ; AsOg. — 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 concfioidal fracture, 
which has evidently undergone fusion. When freshly prepared, it is often 
transparent, but by keeping becomes opaque, at the same time slightly 
diminishing in density, and acquiring a greater degree of solubility in water. 
100 parts of that liquid dissolve at 212<' (lOO^C), 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. 
AlksUis dissolve this substance freely, forming arsenites; also compounds 
with ammonia, baryta, strontia, lime, magnesia, and oxide of manganese, 
have been formed ; it is also easily soluble in hot hydrochloric acid. The 
vapour of arsenious acid is colourless and inodorous ; it crystallizes on solidi- 
fying in brilliant transparent octahedrons. The acid itself has a feeble 
sweetish and astringent taste, and is a most fearful poison.^ 

■ The best ftntidote for arsenious aoid 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 arsenlate 
of tlie protoxide of iron ; for the peroxide is reduced to protoxide by losing oxygen, which, 
pafssing to the arseinioos aoid, forms arsenie acid. This change Is represented by the following 
formula, - 

2 FesOs and AsOs— 4 FeO + AsOs. 

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 separate the base, and 


Absekio acid, ASO5. — Powdered arseniouB acid is dissolved in hot hydro- 
chloric acid, and oxidized by the addition of nitric acid, the latter being 
added as long as red vapours are produced ; the whole is then cautiously 
evaporated to complete dryness. 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 crys^ls of arsenic acid. When strongly heated, it is 
decomposed into arsenious acid and oxygen gas. 

This substance is a very powerful acid, comparable with phosphoric, which 
it resembles in the closest manner, forming salts strictly isomorphous with 
the corresponding phosphates ; it is also tribasio. An arsenate of soda, 
2NaO,HO,As05 -f- 24HO, indistinguishable in appearance from common phos- 
phate of soda, may be prepared by adding the carbonate to a solution of ar- 
senic acid, until an alkaline reaction is apparent, and then evaporating. 
This salt also crystallizes with 14 equivalents of water. Another arsenate, 
8NaO,As05-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,AsOg-f-2HO, is made by substituting an excess of arsenic 
acid for the solution of alkali. The alkaline arsenates which contain basic 
water lose the latter at a red-heat, bj^t unlike the phosphates, recover it 
when again dissolved.^ The salts of the alkalis are soluble in water ; those 
of the earths and other metallic oxides are insoluble, but are dissolved hy 
acids. The precipitate with nitrate of silver is highly characteristic of arse- 
nic acid ; it is reddish-brown. 

Three Sulphides or Absemic are known. Realgar, AsSg, occurs native ; 
it is formed artificially, by heating arsenic acid with the proper proportion 
of sulphur. It is an orange-red, fusible, and volatile substance, employed 
in painting and by the pyrotechnist in making while-fire. Orpiment, AsSg, 
which is also a natural product of the mineral kingdom, is made by fusing 
arsenic acid with excess of sulphur, or by precipitating a solution of the acid 
by sulphuretted hydrogen. It is a golden-yellow crystalline substance, fasi- 
ble and volatile by heat. A higher sulphide, AsSg, corresponding to arsenic 
acid, is produced when sulphuretted hydrogen is transmitted through a solu- 
tion of arsenic acid. The solution of arsenic acid is not immediately pre- 
cipitated, the pentasulphide being deposited only after some hours' stand- 
ing. Its precipitation is considerably accelerated by ebullition. It is a 
yellow fusible substance, capable of sublimation. Realgar, orpiment, and 
pentasulphide of arsenic are sulphur-acids. 

Arsenic unites with chlorine, iodine, &c. The terchloridey AsClg, is formed 
by distilling a mixture of 1 part of arsenic, and 6 parts of corrosive subli- 
mate ; it is a colourless, volatile liquid, decomposed by water into arsenious 
and hydrochloric acids. The same substance is produced, with disengage- 
ment of heat and light, when powdered arsenic is thrown into chlorine gas. 
The iodide, Asl,, 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|, 
analogous to phosphoretted hydrogen. It is obtained pure by the action of 
strong hydrochloric acid on an alloy of equal parts of zinc and arsenic, and 
is produced in greater or less proportion whenever hydrogen is set free in 

then the arsenious acid and red oxide react on each other as ahoye. The acetate of the red 
oxide is the calt used. 

Magnesia has also heen recommended. In the state of recently prerdpitated 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 coimot be depended on wiUx the same 
certainty, haying been too hV:;hly calcined. — R. B. 

* Graham, Elements, p. 436. 


contact with arsenions acid. Arsenetted hydrogen is a colotirlesg gas, of 
2-695 specifia gravity, slightly soluble in water, and having' the smell of gar- 
lic. 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, exceed- 
ingly poisonous, even in very minute quantity. 

Arsenious acid is distinguished by characters which cannot be misunder- 

Nitrate of silver, mixed with a solution of arsenious acid in water, occi^ 
sions no precipitate, or merely a faint cloud ; but if a little alkali, as a drop 
of ammoaia, 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 ; it is likewise very 
soluble in nitric acid. 

Sulphate of copper gives no precipitation with solution of arsenious acid, 
until the addition has been made of a little alkali, when a brilliant yellow- 
green precipitate (Scheele's green) falls, which also is very soluble in excess 
of ammonia. 

Sulphuretted hydrogen passed into a solution 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- ^le- 1^0. 
meats of dry charcoal, affords a sublimate 
of metallic arsenic in the shape of a bril- B <^ 
liant steel-grey metallic ring. A portion of ^i;^^ T^tt 
this, detached by the point of a knife and ^ ^» \^SC^ 
heated in a second glass tube, with access of J^ ^^^ .^^S 
air, yields, in its turn, a sublimate of colour- 
less, transparent, octahedral crystals of ar- 
senious i^cid. (Fig. 150, magnified), ^'^==^Jk^ ^S K ^ 

All these experiments, which /otii/Zy give ^©K ^ ^w^^ L^i 
demonstrative proof of the presence of the ^a ^^fv-dZlA 

substance in question, may be performed, with ^ij^ ^^ ^ 

perfect precision and certainty, upon exceed- >^ ^7 ^ 

ingly small quantities of material. |^ *^. 

The detection of arsenious acid in complex 
mixtares 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 worthless. Sometimes the difficulty may be 
eluded by a diligent search in the suspected liquid, and in the vessel con- 
taining it, for fragments or powder of solid arsenious acid, which, from the 
small degree of. solubility, often escape solution, and from the high density 
of the substance may be found at the bottom of the vessels in which the 
fluids' are contained. If anything of the kind be found, it may be washed 
by decantation with a little cold water, dried, and then reduced with char- 
coal. 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 ha 
preferred. The arsenious acid, or what is suspected to be such, i=3 dropped 
to the bottom, and covered -with splinters or little fragments of charcoal, 


Fig. 151. the tube being filled to tbe Bboiilder. The whole is gently 
heated, to expel any moisture that may be present In the char- 
coal, and the deposited water wiped from the interior of the 
tube with bibulous paper. The narrow part of the tube con- 
taining the charcoal, from a to 6, (fig. 151), is now heated by 
the blowpipe flame ; when red-hot, the tube is inclined, so that 
the bottom also may become heated. The arsenious acid, if 
present, is ▼aporized, and reduced by the charcoal, and a ring 
of metallic arsenic deposited on the cool part of the tube. 
To complete the experiment, the tube may be melted at a by 
the point of the flame, drawn off, and closed, and the arsenic 
oxidized to arsenious acid, by chasing it up and down by the 
heat of a small-spirit-lamp. A little water may afterwards 
be introduced, and boiled in the tube, by which the arsenious 
acid will be dissoWed, and to this solution the tests of nitrate 
of Bilyer and ammonia, 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 diffi- 
culty 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 potassa or acetic acid will sometimes effect this object. The 
following is an outline of a plan, which has been found successful in a 
Tariety of cases, in which a Tery small quantity of arsenious acid had been 
purposely added to an organic mixture. Oil of Titriol, 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 
B little water, and the whole is boiled in a flask for half an hour, or until 
a complete separation of solid and liquid matter becomes manifest. The 
acid converts any starch that may be present into dextrin and sugar; 
it coagulates completely albuminous substances, and casein, in the case of 
milk, and brings the whole in a very short time into a state in which filtra- 
tion is both easy and rapid. Through the filtered solution, when cold, a 
current of sulphuretted hydrogen is transmitted, and the liquid is warmed, 
to facilitate the deposition of the tersulphide, which falls in combination 
with a large quantity of organic matter, which often communicates to it a 
dirty colour. This is collected upon a small filter, and washed. It is next 
transferred to a capsule, and heated with a mixture of nitric and hydro- 
chloric acids, by which the organic impurities are in a great measure de- 
stroyed, and the arsenic oxidized to arsetiic acid. The solution is evaporated 
to dryness, the soluble part taken up by dilute hydrochloric acid, and then 
the solution saturated with sulphurous acid, whereby the arsenic acid is re- 
duced to the state of arsenious acid, the sulphurous being oxidized to sul- 
phuric acid ; the solution of arsenious acid may be precipitated by sulphu- 
retted hydrogen without any difficulty. The liquid is warmed, and the pre- 
cipitate washed by decantation, and dried. It is then mixed- with blaek-fiux, 
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 farther examined. The black-flux is a mix- 
ture of carbonate of potassa and charcoal, obtained by calcining cream of 
tartar in a close crucible ; the alkali transforms the sulphide into arsenious 
acid, the charcoal subsequently effecting the deoxidation. A mixture of 



Fig. 152. 

anhydrous carbonate of soda and charcoal may be substituted irith adTan- 
tage for the common black-flux, as it is 10*83 hygroscopic* 

Other methods of proceeding, different in principle from the foregoing, 
have been proposed, as that of the late Mr. Marsh, which is exceedingly 
delicate. The suspected liquid is acidulated with sulphuric acid and placed 
in contact with metallic zinc ; the hydrogen reduces the arsenious acid and 
combines with the arsenic, if any be present. The gas is burned at a jet, 
and a piece of glass or porcelain held in the flame, when any admixture of 
arsenetted hydrogen is at once known by the production of a brilliant black 
metallic spot of reduced arsenic on the porcelain. 

It has been observed (page 290) that antimonetted hydrogen giyes a simi- 
lar result. In order to distinguish the two substances, the gas may be 
passed into a solution of nitrate of silver. Both gases give rise to a black 
precipitate, which in the case of antimonetted hydrogen consists of antimo- 
uide of silver, Agj Sb, whilst it is pure silver in the case of arsenetted hy- 
drogen, the arsenic being then converted into arsenious acid, which combinet 
with a portion of oxide of silver. The arsenite of 
silver remains dissolved in the nitric acid which is li- 
berated by the precipitation of the silver, and may 
be thrown down with its characteristic yellow colour 
by adding ammonia to the liquid filtered off from the 
black precipitate. 

A convenient form of Marsh's instrument is that 
shown in fig. 152, 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 ex- 
amined. On replacing the stop-cock, closed, the gas 
collects and forces the fluid into the upper bulb, 
which then acts by its hydrostatic pressure and ex- 
pels the gas through the jet as soon as the stop-cock is 
opened. It must be borne in mind that both common 
zinc and sulphuric acid often contain traces of arsenic.^ 

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. 

* See a paper by the author on the detection of arsenic Pharmaceutical Journal, t. 614. 

^ Where the amount of an^enic pre^eut ifl email, it becomes neoessary to take advantage of 
the effects of heat, and cause the gas to pass slowly through a red-hot tube until all the sine 
U dissolved. The roduoed 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 ascertnin the puritj 
of the sine and acid by trial, previous to addition of the suspected liquid. — K. ii. 




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 mountiins in Germany, of Eongsberg 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, there- 
fore, 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 Germany, 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 sulphide 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 bar- 
rels, 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 mer- 
cury is then introduced, and the agitation repeated ;. the mercury dissolves 
out the silver, together with gold, if there be any, metallic copper, and other 
substances, 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 distilled off and the silver left 
behind in an impure condition. 

A considerable quantity of siWer is obtained from argentiferous galena ; 
in fact, almost every specimen of native sulphide of lead will be found to 
contain traces of this metal. When the proportion rises to a certain amount 
it becomes worth extracting. The ore is reduced in the usual manner, the 
whole of the silver remaining with the lead ; the latter is then" re-melted in 
a large vessel, and allowed 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 this is drained 
away, and 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- 
aah^Sy and again heated ; the last of the lead is now oxidized, and the oxide 

SILVER. 297 

Dinks in a melted state into the porous vessel, while the silver, almost che- 
mically pure, and exhibiting a brilliant surface, remains behind. 

Pare silver may be easily obtained. The metal is dissolved in nitric add; 
if it contains copper, the solution will have a blue tint ; gold will remain un*. 
dissolved as a blac]i^ 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 

Pure silver has a most perfect white colour, 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. .Ii( hardness 
it lies between gold and copper. It melts at a bright red-heat, about 1873® 
(1023°C), according to the observations of Mr. Paniell. Silver is inalterable 
by air and moisture ; it refuses to oxidize at any temperature, but possesses 
the extraordinary faculty, already noticed in an earlier part of the work, of 
absorbing many times its volume of oxygen when strongly heated in an at- 
mosphere of that gas, or in common air. This oxygen is again disengaged 
at the moment of solidification, and gives rise to the peculiar arborescent 
appearance o^ten remarked on the surface of masses or buttons of pure 
silver. The addition of 2 per cent, of copper is sufficient to prevent this 
absorption of oxygen. Silver oxidizes when heated with fusible siliceous 
matter, as glass, which it stains yellow or grange, from the formation of a 
ffllicate. It is little attacked by hydrochloric acid ; boUing oil of vitriol con- 
verts 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 potassa, soda, and oxide of am- 

The equivalent of silver is 108 ; its symbol is Ag (argentum). 

Suboxide of silver, Ag^O. — When dry citrate of silver is heated to 212« 
(lOO^C) in a stream of hydrogen . gas, it loses oxygen and becomes dark 
brown. The product dissolved in water, gives a dark-coloured solution con- 
taining free citric acid and citrate of the suboxide of silver. The suboxide 
is then precipitated by potassa. It is a black powder, very easily decom- 
posed, and soluble in ammonia. The solution of citrate is rendered colourless 
by heat, being resolved into a salt of the protoxide and metallic silver. 

Pbotoxide of silver, AgO. — Caustic potassa 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 extent by pure water ; the solution is alkaline. Recently precipitated 
chloride of silver, boiled in a solution of caustic potassa of specific gravity 
1-25, according to the observation of Dr. Gregory, is converted, although 
with difficulty, 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, colourless salts. It is decomposed by a red-heat, with extrication of 
oxygen, spongy metallic silver being left ; the sun's rays also effect its de- 
composition 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 

B08 8iLVt:R. 

teted upon by hydrocMoric aoid, explodes vrheti mixed with pbospliorus and 
struck, and decomposes solution of ammonia with great energy and rapid 
disengagement of nitrogen gas. 

Nitrate of silver, AgOjNO^ — The nitrate is prepared by directly dis- 
BoWing silver in nitric acid and evaporating the solution to dryness, or until 
it is strong enough to crystallize on cooling. The crystals are colourless, 
transparent, anhydrous tables, soluble in an equal weight of cold, and in 
half that quantity of boiling water ; they also dissolve in alcohol. They fuse 
when heated like those of nitre, and at a higher temperature suiFer decom- 
position ; 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 nsed 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 
Tindecomposed, 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 inso- 
luble black oxide of copper. 

^ Sulphate of silver, AgCSOg. — The sulphate may be prepared by boil- 
ing together oil of vitriol and metallic silver, or by precipitating a concen- 
trated solution of nitrate of silver by an alkaline sulphate. It dissolves in 
88^ parts of boiling water, and separates in great measure in a crystalline 
form on cooling, having but a feeble degree of solubility at a low tempera- 
ture. It forms a crystallizable compound with ammonia, freely soluble in 
water, containing AgO,S03+2NH3. 

Hyposulphate of Silver^ AgO,S205-|-HO, 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 solu- 
ble compounds distinguished by an intensely sweet taste. The alkaline hy- 
posulphites dissolve both oxide and chloride of silver, and give rise to similar 
Salts, an oxide or chloride of the alkaline met«l being at the same time 
formed. Carbonate of silver is a white insoluble substance obtained by mix- 
ing 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, but one 
part of chloride of silver is soluble in 200 parts of hydrochloric acid when 
concentrated, and in about 600 parts when diluted with double its weight 
of water. When heated it melts, and on cooling becomes a greyish crystal- 
line mass, which cuts like horn ; it is found native in this condition, consti- 
tuting 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 or- 
ganic matter be present : it is reduced also when put into water with metal- 
lic zinc or iron. It is soluble with great ease in ammonia and in a solution 
of cyanide of potassium. 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 better by 
subsidence, washed, dried, and fused ; 100 parts correspend to 24*7 of chlo- 
rae, or 25*43 of hydrochloric acid. 

GOLD. 899 

Iodide of silvsb, AgL — The iodide is s pale yellow insoluble precipitate 
produced by adding nitrate of silver to iodide of potassium; it is insoluble, 
or nearly so, in ammonia, and forms an exception to the silver-salts in gene- 
ral in this respect' The hromicU of silver very closely resembles th^ 

Sulphide of silver, AgS. — This is a soft, grey, and somewhat malleable 
substance, found native in a crystallized state, and easily produced by melt- 
ing together its constituenjts, or by precipitating a solution of silver by sul- 
phuretted hydrogen. It is a strong sulphur-base, and combines with the 
sulphides of antimony and arsenic : examples of such compounds are found 
in the beautiful minerals dark and light red silver ore. 

Ammonia compound qf silver; Berthollet's fulminating silver.— 
When precipitated oxide of silver is digested in ammonia, a black substance 
is -produced, 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 compound containing oxide of gold exists. It is easy to understand 
the reason why these bodies are subject to such violent and sudden decom- 
position by the slightest cause, on the supposition that they contain an oxide 
of an easily reducible metal and ammonia ; the attraction between the two 
constituents of the substance is very feeble, while that between the oxygen 
of the one and the hydrogen of the other is very powerful. The explosion 
is caused by the sudden evolution of nitrogen gas and vapour 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, and insoluble 
in hot nitric acid,' which is produced by the addition of any soluble chlo- 
ride. Lead is the only metal which can be confounded with it in thiB re- 
spect, 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 reduced to the metallic state by iron, copper, mercury, and other 

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 diminish the softness of the metal by a small addition of copper. The 
standard silver of England contains* 222 parts of silver and 18 parts of 


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 
ffold-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, irbich Acquires the 
metallic lustre by friction. 

Gold is a soft metal, having a beautiful yellow colour. It surpasses all 
other metals in malleability, the thinnest gold-leaf not exceeding, it is said, 
Svirsvn ^^ ^^ ^°^^ ^° thickness, while the gilding on the silver wire used in 
the manufacture of gold-lace is still thinner. It may also be drawn into yerj 
fine wire. Gold has a density of 19-5 ; it melts at a temperature a little 
above the f using-polnt of silver. Neither air nor water affect it in the least 
at any temperature ; the ordinary acids fail to attack it, singly. A mixtare 
of nitric and hydrochloric acids dissolves gold, however, with ease, the ae- 
tive 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 197. Its symbol is Au (aurum). 

Peotoxtdb of gold, AuO. — The protoxide is produced when causUc po- 
tassa in solution is poured upon the protochloride. It is a green powder, 
partly soluble in the alkaline liquid ; the solution rapidly decomposes into 
metallic gold, which subsides, and into teroxide, which remains dissolved. 

Teboxide of gold ; auric acid ; AuO,. — When magnesia is added to the 
terchloride of gold, and the sparingly soluble aurate of that base well washed 
and digested with nitric acid, the teroxide is left as an insoluble reddish- 
yellow powder, which, when dry, becomes chestnut-brown. It is easily re- 
duced by heat, and also by mere exposure to light ; it is insoluble in oxygen 
acids with the exception of strong nitric acid, insoluble in hydrofluoric acid, 
easily dissolved by hydrochloric and hydrobromic acids. 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, potassa being produced. When digested with ammo- 
nia, it furnishes fulminating gold. 

Protochloride of gold, AuCl. — This substance is produced when the 
terchloride is evaporated to dryness and exposed to a heat of 440° (226° -60 
until chlorine ceases to be exhaled. It forms a yellowish-white mass, inso- 
luble in water. In contact with that liquid it is decomposed slowly in the 
cold, and rapidly by the aid of heat, into metaUio gold and terchloride. 

Terchloride of gold, AuCl,. — 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 
hehted, hydrochloric acid is expelled, and the residue, on cooling, solidifies 
to a red crystalline mass of terchloride of gold, very deliquescent, and so- 
luble in water, alcohol, and ether. The terchloride 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 MCI -|- AuCl,, 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 terchloride of gold with excess of bicarbonate of potassa 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 sulphate of protoxide of iron, fusible before the blowpipe into 
a bead of gold ; and by the purple compound formed when the terchloride 
of gold is added to a solution of protochloride of tin. 


^ <}old intended for eoiii, and most other purposes, is always atloyed witli ft 
certain proportion of silTor or copper, to increase its hardness and durability ; 
the first named metal confers a pale greenish colour. English standard gold 
contains j\ 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 arti- 
cles into a solution of nitrate of mercury, and then shaking them with a 
small lump o{ 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 terchloride of gold, in ether, or by roughening the surface of the 
metal, heating it, and applying gold-leaf, with a burnisher. Gilding by 
electrolysis — ^an elegant and simple method, now rapidly superseding many 
of the others — ^has already been noticed. The solution usually employed is 
obtained by dissolving oxide or cyanide of gold in a solution of cyanide of 


This yery remarkable metal has been known from an early period, andf 
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 mercury is occasionally met with in globules disseminated through 
the native sulphide, which is the ordinary ore. This latter substance, 
sometimes called cinnabar, is found in considerable quantity in several 
localities, of which the most celebrated are Alma^en in New Castile and 
Idria in Garniola. Only recently it has been discovered in great abundance, 
and of remarkable purity, in California. The metal is obtained by heating 
the sulphide in an iron retort with lime or scraps of iron, or by roasting it 
in a furnace, and conducting the vapours into a large chamber, where the 
mercury is condensed, while the sulphurous acid is allowed to escape. 
Mercury is imported into this country in bottles of hammered iron, contain- 
ing seventy-five pounds each, and in a state of considerable purity. When 
purchased in smaller quantities, it is sometimes found adulterated with tin 
and leady 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 colour, and a very high degree of lustre ; 
it is liquid at all ordinary temperatures, and only solidifies when cooled to 
*_40o (— 40OC). In this state it is soft and malleable. At 662° (86O0C) it 
boils, and yields a transparent, colourless vapour, of great density. The 
metal volatilizes, however, to a sensible extent at all temperatures above 68^ 
(20°C) or 70° (21 oC) ; below this point its volatility is imperceptible. The 
volatility of mercury at the boiling heat is singularly retarded by the pre- 
sence of minute quantities of lead or zinc. The specific gravity of mercury 
at 60® (15°*5C) is 18-59; 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 

*■ Moens. Blkingtoo, Application of £l«otro-M«tallttrgy to the Art«. 


•xidlk At a dnll re^-heat this oxide is again decomposed into its eoDBtitoeiitfl. 
Hydrochlorlo acid has Utile or no action on mercury, and the same may 'to 
Bald of sulphunc acid in a dilated state ; vhen the latter is conceotrated and 
boiling hot, it oxidises the metal, converting it into sulphate of the red oxide, 
friitk eyoltttion of sulphurous acid. Nitric acid, eyen dilute and in tho cold, 
dissoWes mercury freely, with an evolution of binoxide of nitrogen^ 

Mercury combine» with oxygen in two proportions, forming a grey 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 regargded as the true 
protoxide, instead of the grey oxide, to which the term has formerly been 
appUed. 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 

The equivalent of mercury on the above supposition, will be 100; its 
symbol is Hg (hydrargyrum). 

Suboxide of mebcuby; asisY oxide; Hg^O. — The suboxide is easily 
prepared by adding caustic potassa to the nitrate of this substance, or by 
digesting calomel in solution of caustic alkali. It is a dark grey, nearly 
black, heavy powder, insoluble in water. It is slowly decomposed by the 
action of light into metallic mercury and- red oxide. The preparations known 
in pharmacy by the names blue piU^ grey ointment^ merewry with eha^j &c., 
often supposed to owe their efEicacy to this substance, merely contain the 
finely divided metal. 

PsoTOXiDE OF mehcuby; red oxide; HgO. — There are numerous methods 
by which this method may be obtained ; the following may be cited as the 
most important: — (1) By exposing mercury in a glass flask, with a long 
narr^ neck, for several weeks to a temperature approaching 600° (316°'6C) ; 
the product has a dark red colour and is highly crystalline ; it is the nd 
predpUate of the old writers. (2) By cautiously heating any of the nitrates 
of either oxide to complete decomposition, when the acid is decomposed and 
expelled, oxidizing the metal to a maximum, if it happen to be in the con- 
dition of a suboxide. The product is in this case also crystalline and very 
dense, but has a much paler colour than the preceding ; while hot it is nearly 
black. It is by this method that the oxide is generally prepared ; it is apt 
to contain undecomposed nitrate, which may be discovered by strongly 
boating a portion in a test-tube : if red fumes are produced or the odour of 
nitrous acid exhaled, the oxide has been insufficiently heated in the process 
of manufacture. (3) By adding caustic potassa in excess to a solution of 
corrosive* sublimate, by which a bright yellow precipitate of oxide is thrown 
down, which only dififers from the foregoing preparations in being destitute 
of crystalline texture and much more minutely divided.^ It must be well 
washed and dried. 

Bed 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 grey oxide are formed, and these are neutral or 

' By referrixig to (^anogen, H will be perceived that when the equivalent of mercnrv is 
oonfiidered to be 100, the constitution of the cyanide of meroury la analogoas to the otber 
metallic cyanides, but when talcen at 200, it Lecomes a bicyanide, and then differs firom all 
othem.— R. B. 

• This precipitate is considered by Shanffner to be a hydrate, HgO,3IIO, for by exposure to 
the temperatoN of 882P| it kiw w«ter Mooimtwg to ot«c 20 per eeoL of its wet^bt— B. B. 

^810 (i. '0. i^ith «»W88 of «ddv), ftstbe add or the mettO. faKppens to te in 

excess. When, on the contrary, the nitric acid is concentrated dnd hot, the 
mercury is raised to its highest state of oxidation, and a salt of the red oxide 
prodaced. Both classes of salts are apt to be decomposed by a large 
quantity of water, giving rise to insoluble, or sparingly soluble, compounds 
containing an excess of base. 

Neutral nitrate of the suboxide, IIg20,N05-|-2nO, forms large colourless 
crystals, soluble in a small quantity of water without decomposition ; it is 
made by dissolying mercury in an excess of cold dilate nitric acid. 

When excess of mercury has been employed, a finely crystallized basic 
salt is, after some time, deposited, containing SUgJOt^iiO^-^-'SRO ; this is 
also decomposed by water. The two salts are easily distinguished when 
rubbed in a mortar with a little chloride of sodium ; the neutral compound 
gives' nitrate of soda and calomel ; the basic salt, nitrate of soda and a blnck 
compound of calomel with oxide of mercury. A black substance, called 
HahnemanrC a soluble mercury, is produced when ammonia in small quantity 
is dropped into a solution of the nitrate of the suboxide ; it contains SHgaO, 
NOg-l-NHj, or, according to Sir R. Kano, 2HgO,N064-NHj ; the composition 
of this preparation evidently varies according to the temperature and the 
concentration of the solutions. 

Nitrates of the Protoxide (Red Oxide) of Mercury. — By dissolving red oxide 
of mercury in excess of nitric acid and evaporating gen^, a syrupy liquid 
is obtained, which, enclosed in a bell-jar over lime or sulphuric acid, de- 
posits voluminous crystals and crystalline crusts. The crystals and crusts 
have the same composition, 2(HgO,N05)-|-HO. The same substance is de- 
posited from the syrupy liquid as a crystalline powder by dropping it into 
concentrated nitric acid. The syrupy Uquid itself appears to be a definite 
eompoond containing Hg0,N0g4-2H0. 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,N05-|-HO. The preceding crystal- 
lized salts are decomposed by water, with production of compounds more and 
more basic as the washing is prolonged or the temperature of the water 
raised. The nitrates of the protoxide of mercury combine with ammonia. 

Sulphate of the Suboxide of Mercury, Hg20,S03, falls as a white crystalline 
powder when sulphuric acid is added to a solution of the nitrate of the sub- 
oxide ; it is but slightly soluble in water. Sulphate of the protoxide, HgO, 
jSOy is readily prepared by boiling together oil of vitriol and metallic mer- 
cury until the latter is wholly converted into a heavy white crystalline pow- 
der, which is the salt in question ; the excess of acid is then removed by 
evaporation, carried to perfect dryness. Equal weights of acid atid metal 
may be conveniently employed. Water decomposes the sulphate, dissolving 
oat an acid salt and leaving an insoluble, yellow, basic compound, formerly 
called lurpeth or turbiih mineral, containing, according to Kane's analysis, 
3HgO,SOs. Long-continued washing with hot water entirely removes the 
remaining acid, and leaving pure protoxide of mercury. 

SuBCHLOBiDS OF MBROUBY ; CALOMEL ; HgjCl. — This vcry importont sub- 
ctance may be easily and well prepared by pouring a solution of the nitrate of 
the suboxide into a large excess of dilute solution of common salt. It falls 
as a dense white precipitate, quite insoluble in water ; it must be thoroughly 
washed with boiling distilled water, and dried. Calomel is generally pro- 
cured by another and more complex process. Dry sulphate of the red oxide 
is rubbed in a mortar with as much metallic mercury as it already contains, 
and a quantity of^common salt, until the globules disappear, and an uniform 
mixture has been produced. This is subjected to sublimation, the vapour of 
the calomel being carried into an atmosphere of steam, or into a chamber 
containing air ; it is thus condensed in a minutely-divided «tate, and the la- 


borious proeeta of piilT«rization of the sublimed mass aToid«<L The reaetioit 
is thofl explained :* — 

{1 eq. mercury^.^^ ^Calomel, HggCl. 
1 eq. oxygen "Z^^^ 
1 eq. sul- 
phuric acid. 

1 eq. metallic mercury 
1 eq. common \ 1 eq. chlorine 
salt } l.eq. sodium ^^^ Sulphate of soda. 

Pure calomel is a heavy, white, insoluble, tasteless powder; it rises in 
Tapour at a temperature below redness, and is obtained by ordinary subli- 
mation as a yellowish-white crystalline mass. It is as insoluble in cold di- 
luted nitric acid as the chloride of silver ; boiling-hot strong nitric acid oxi- 
dizes and dissolves it. Calomel is instantly decomposed by an alkali, or by 
lime-water, with production of sub-oxide. It is sometimes apt to contain a 
little chloride, which would be a very dangerous contamination in calomel 
employed for medical purposes. This is easily discovered by boiling with 
water, filtering the liquid, and adding caustic potassa. Any corrosive sub- 
limate is indicated by a yellow precipitate. 

Pbotochlobide of mkbcuby ; cobbosiye subliuatb ; HgCl. — The chlo- 
ride may be obtained by several different processes. (1) When metallio 
mercury is heated in chlorine gas, it takes fire and bums, producing this 
substance. (2) It may be made by dissolving the red oxide in hot hydro- 
ohloric acid, when crystals of corrosive sublimate separate on cooluig. (3) 
Or, more economically, by subliming a mixture of equal parts of sulphate of 
the red oxide of mercury and dry common salt ; and this is the plan gene- 
rally followed. The decomposition is thus easily explained : ' — 

1 eq. sulphate of 

1 eq. mercury ^Corrosive sublimate. 

1 eq. oxygen 
1 eq. sul- 'J 


phuric acid 
1 11. f 1 eq. chlorine ^ ^''""^-^^;::::^^ 
leq.cominon8aU|j^q 3^ji„^ -^-Sulphate of soda. 

The sublimed protochloride forms a white, transparent, crystalline mass, 
of great density ; it melts at 609° (265<»C), and boils and volatilises at a 
somewhat higher temperature. It is soluble in 16 parts of cold and 3 of 
boiling water, and crystallizes from a hot solution in long white prisms. Al- 
cohol and ether also dissolves it with facility ; the latter even withdraws it 
from a watery solution. Chloride of mercury combines with a great number 

» If the grey oxide be considered as protoxide, the sulphate will be sulphate of the binot 
iie, HgOii, 2S08, and the decomposition will stand thus:— 

of mercury \ 2 e?. sulphurlolSr; 

1 eq. metallic mercury ^^ 

2 eq. common \ 2 eq. chlorine 
salt \ 2 eq. sodium ^ — -^ 2 eq. sulphate of soda. 

Or on the other supposition : — 

1 eq. sulphate of Q ^ "^^""^^ — ——^Bichloride of merouiy. 

n*®'®^^ 1 2 eq.* sulphuric add;>^^^ 

29q.common8alt|2 eq. chlorme __^^5^2 eq. sulphate of soda. 


-tfT «fher methllio ^lilortdM, formiiig « rnnm of beanlifol dooble fMlts, of 
^bieh the ancient sal alembroth mxy be taken as a good example : it coBtaina 
HgCl-f> NH4CI4- HO. CorroaiTe sublimate absorbs ammoniaeal gas with great 
avidity, generating a compound supposed to contain 2HgCl-|-NH,. 

When excess of ammonia is added to a solution of corrosiye sublimate, 9 
white insoluble substance is thrown down, long known under the name of 
fohite precipitate. Sir Robert Kane, who has devoted much attention to the 
salts of mercury, represents this white precipitate^ as a doable amide and 
chloride of mercury, or HgCl-f-HgNHj, 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, HggCl-f-HgNU,, is produced 
when ammonia is digested with calomel, which must be carefully distin- 
guished from the suboxide. 

Several compounds of protochloride of mercury with protoxide of mercury 
also exist. These are produced by several processes, as when an alkaline 
carbonate or bicarbonate is added in varying proportions to a solution of 
corrosive sublimate. They diifer greatly in colour and physical character, 
and are mostly decomposed by water. 

Corrosive sublimate forms insoluble compounds with many of the azotized 
organic principles, as albumin, &c. It is perhaps to this property that its 
great antiseptic virtues are due. Animal and vegetable substfmces are pre- 
served by it from decay, as in Mr. Kyan's method of preserving timber and 
cordage. Albumin is on this account an excellent antidote to corrosive sub- 
limate in cases of poisoning. 

SuBToniDE OF MERCiTRT, IfpTjT. — 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 
proportion of 2 equivalents of the former to 1 of the latter, the mixture being 
moistened from time to time with a little alcohol. 

Peotiodidb of mercury, Hgl. — When solution of iodide of potassium is 
mixed with protochloride of mercury, a precipitate falls, which is at first 
yellow, but in a few moments changes to a most brilliant scarlet, which colour 
is retained on drying. This is the neutral iodide ; it may be made, although 
of rather duller tint, by triturating single equivalents of iodine and mercury 
with a little alcohol. When prepared by precipitation, it is better to weigh 
out the proper proportions of the two salts, as the iodide is soluble in an 
excess of either, more especially in excess of iodide of potassium. The iodide 
of mercury exhibits a very remarkable case of dimorphism, attended with 
differencfe of colour, the latter being red or yellow, according to the figure 
assumed. Thus, when the iodide is suddenly exposed to a high temperature, 
it becomes bright yellow throughout, and yields a copious sublimate of minute 
but brilliant yellow crystals. If in this state it be touched by a hard body, 
it instantly becomes red, and the same change happens spontaneously after 
a certain lapse of time. On the other hand, by a very slow and careful heat- 
ing, a sublimate of red crystals, having a totally diflferent form, may bo 
obtained, which are permanent. The same kind of change happens with the 
freshly precipitated iodide, as Mr. Warington has shown the yellow crystals 
first formed breaking up in the course of a few seconds from the passage of 
the salt to the red modification.* 

SuBsuLPHiDE OF MERCURY, HggS. — The black precipitate thrown down 
from a solution of the nitrate of suboxide of mercury by sulphuretted hydro- 
gen, is a subsulphide ; it is decomposed by heat into metiUlic mercury and 
neutral sulphide. 

> Hemoin! of Chomical Society of London, 1. 86. 
26 » 


SiTLPRiDi ov mbboust; abtivioial oiMMABAR ; TSBMiLioir; HgS. -^Sul- 
phuretted hydrogen gas causes a precipitate of a white coloar when passed 
in small quantity into a solution of corrosive sublimate or nitrate of the red 
oxide ; this is a combination of sulphide with the salt itself. An excess of 
the gas converts the whole into sulphide, the colour at the same time chang- 
ing to black. When this black sulphide is sublimed, it becomes dark red 
and crystalline, but undergoes no change of composition ; it is then cinnabar. 
The sulphide is most easily prepared by subliming an intimate mixtare of 6 
parts of mercury and 1 of sulphur, and reducing to a very fine powder the 
resulting cinnabar, the beauty of the tint depending much upon the extent 
to which division is carried. The red or crystalline sulphide may also be 
formed directly, without sublimation, by heating the black precipitated sub- 
stance in a solution of pentasulphide of potassium ; the sulphide of mercury 
is in fact soluble to a certain extent in the alkaline sulphides, and forms vith 
them crystallizable compounds. 

When vermilion is heated in the air, it yields metallic mercury and sul- 
phurous add ; it resists the action both of caustic alkali in solution, and of 
strong mineral acids, even nitric, and is only attacked by aqua regia. 

When protoxide of mercury is put into a large excess of pure caustic 
ammonia, a compound is obtained, the colour of jrhich varies with the stato 
of the oxide. If the latter be amorphous, it is pale yellow ; if crystalline, 
then the action of the ammonia is much less energetic, and the product 
darker in colour. This substance possesses very extraordinary properties, 
those, namely, of a most powerful base, and probably belongs to the sam^ 
class as the compound bases containing platinum, described under that 
metal. The body in question bears a temiierature of 260** (126o-5C), with- 
out decomposition, becoming brown and anhydrous, by the loss of 3 equiva- 
lents of water. In this state it contains NH2Hg^O3==NHjHgjO-|-2Hg0 or 
KHg404-2H0. It is insoluble in water, alcohol, and ammonia; cold solu- 
tion of potassa has no action on the hydrate, but at a boiling heat some 
ammonia is disengaged. The anhydrous base is only acted on by hydrate 
of potAssa in fusion. It combines directly and energetically with acids, form- 
ing well-defined compounds ; it absorbs carbonic acid with avidity frojn the 
air, like baryta or lime. It even decomposes ammoniacal salts by boiling, 
expelling the ammonia 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 behaviour of the protochloride and soluble salts of the red oxide with 
caustic potassa. and ammonia is also highly characteristic. 

Alloys of mercury with other metals are termed amalffams ; mercury dis- ' 
,8oives in this manner many of the metals, as gold, silver, tin, lead, &c. | 
These combinations sometimes take place with considerable violence, as in , 
the case of potassiuin, whete light and heat are produced ; besides this, many 
of the amalgam^ crystallize after a while, becoming solid. The amalgam of 

* Ann. Cbim. et Pbys. 3d series, xvUi. 333. 


tm used in silveriag looking-glasses, and that of silTer sometimes employed 
fur stopping hollow teeth, are examples. 


Platinum, palladium, .rhodium, iridium, ruthenium, and osmium, form a 
email group of metals, allied in some cases by properties in common, and 
Btill more closely by their natural association. Crude platinum, a natire alloy 
of platinum, palladium, rhodium, iridium, and a little iron, occurs in grains 
and rolled masses, sometimes of tolerably large dimensions, mixed with 
gravel and transported materials, on the slope of the Ural Mountains in 
Russia, in Ceylon, and in a few other places. It has neyer been seen in the 
rook, which, however, is judged, from the accompanying minerals, to have 
been serpentine. It is stated to be always present in small quantities with 
native silver. 

From this substance platinum is prepared by ^he following process :-^The 
crude metal is acted upon as far as possible by nitro-hydrocbloric acid,' con* 
taining an excess of hydrochloric acid, and slightly diluted with water, in 
order to dissolve as small a quantity of iridium as possible ; to the deep yel- 
lowish-red and highly acid solution thus produced sal-ammoniac is added, by 
which nearly the whole of the platinum is thrown down in the state of am- 
monio-chloride. This substance is washed with a little cold water, dried 
and heated to redness ; metallic platinum in spongy state is left. Although 
this metal cannot be fused into a compact mass by any furnace-heat, yet the 
same object may be accomplished by taking advantage of its property of 
welding, like iron, at a very high temperature. The spongy platinum is 
made into a thin uniform paste with water, introduced into a slightly conical 
mould of brass, and subjected to a graduated pressure, by which tiio water 
is squees^d out, and tiie mass rendered at length sufficiently solid to bear 
handling. It is then dried, very carefully heated to whiteness, and ham- 
mered, or subjected to powerful pressure by suitable means. If this opera- 
tion has been properly conducted, the platinum will now be in a state to bear 
forging into a bar, which can afterwards be rolled into plates, or drawn into 
wire, at pleasure. 

Platinum is in point of colour a little whiter than iron ; it is exceedingly 
malleable, and ductile, both hot and cold, and is very infusible, melting only 
before the oxy-hydrogen blowpipe. It is the (except Iridium) heaviest suh* 
stance known, its specific gravity being 21-5. Neither air, moisture, nor the 
ordinary acids attack platinum in the slightest degree at any temperature ; 
hence its high value in the construction of chemical vessels. It is dissolved 
by aqua regia, and superficially oxidized by fused hydrate of potassa, which 
enters into combination with the oxide. 

The remarkable property of the spongy metal to determine the union of 
oxygen and hydrogen has been already noticed. There is a still more curious 
state in which platinum can be obtained, that of platinum-black, where the 
division is pushed much farther. It is easily prepared by boiling n solution 
of bichloride of platinum to which an excess of carbonate of soda and a quan- 
tity of sugar have been added, until the precipitate formed after a little time 
becomes perfectly black, and the supernatant liquid colourless. The black 
powder is collected on a filter, washed, and dried by gentle heat. This sub- 
stance appears to possess the property of condensing gases, more especially 
oxygen, into its pores to a very great extent: when placed in contact with a 
solution of formic acid, it converts the latter, with copious effervescence, into 
carbonic acid ; alcohol, dropped on the platinum-black, becomes changed by 
oxidation to acetic acid, the rise of temperature being often sufficiently great 
to cause inflammation. When exposed to a red-heat, the black substance 
shrinks in volume, assumes the appearance of common spongy platinum, and 

'808 PLATTHtJlff. 

loses these peeuHnrittes, Mrhi«h are no doubt tliet«8«iltof Hsiexoesd'v^t^'^dm- 

minuted state. Platinum forms two compounds with oxygen, chlorine, &c. 
The equivalent of platinum is 98*7.* Its symbol is Pt. 

Protoxide of platinum, PtO. — When protochloride of platinum is di- 
gested with caustic potassa, a block powder, soluble in exoess of alkali, is pro- 
duced : this is the protoxide. It is soluble in acids with brown colour, and 
the solutions are not precipitated by sal-ammoniaic. When binoxide of pla^ 
tinum is heated with solution of oxalic aeid, it is reduced to protoxide, which 
remains dissolved. The liquid has a dark blue colour, «nNl deposits fise eop- 
per-red needles of oxidate of the protoxide of platinum. 

Binoxide of platinum, PtOg. — This is best pr^ared by «dding nitrate 
■of baryta to sulphate of the binoxide of platinum ; sulpbate of baryta and 
nitrate of the binoxide are produced. From the latter, caustic soda precipi- 
tates one-half of the binoxide of platinum. The sulphate is itself obtained 
•by acting with strong nitric acid upon the bisulphide of platinum, ^ddeh falls 
as a black powder when a solution of bichloride is dropped into sulphide of 
potassium. The hydrate of the binoxide is a bulky brown powder, which, 
when gently heated, becomes black and anhydrous. It may also be formed 
by boiling bichloride of platinum with a great excess of caustic soda, and 
then adding acetic acid. It dissolves in acids, and also combines with bases; 
the salts have. a yellow or red tint, and a great disposition to unite with salts 
of the alkalis and alkaline earths, giving rise to a series of double compounds, 
which are not precipitated by excess of alkali. A combination of binoxide 
of platinum with ammonia exists, which is explosive. Both oxides of plati- 
num are reduced to the metallic state by ignition. 

Protochloride of platinum, PtCl. — The protochloride is produced whoa 
•biclilovide of platinum, dried and powdered, is exposed for seme time to a 
heat of 400° (204** -50, by which half of the chlorine is expelled ; also, when 
sulphurous acid is passed into a solution of the bichloride until the latter 
ceases to give a precipitate with sal-ammoniac. It is a greenish-grey pow- 
der, insoluble in water, but dissolved by hydrochloric acid. The latter solu- 
tion, mixed with sal- ammoniac ^or chloride of potassium, deposits a double 
salt in fine red prismatic crystals, containing in the last case, PtCJ-f-KCl. 
'The corresponding spdium-compound is very soluble and difficult to crystal- 
lize. The protochloride is decomposed by heat into chlorine ai^jd metallic 

Bichloride or perchloride of Platinum, PtCL. — This substance is al- 
ways formed when platinum is dissolved in nitro-hydrochloric acid. The 
acid solution yields on evaporation to dryness a red or brown residue, deli- 
quescent, and very soluble both in water and alcohol ; the aqueous solution 
has a pure orange-yellow tint. Bichloride of platinum combines to double 
salts with a great variety of metallic chlorides; the most important of these 
compounds are those containing the metals of the alkalis and ammonium. 
■Bichloride of platinum and chloride of potassium, PtClj, KCl, forms a bright yel- 
low crystalline precipitate, being produced whenever solutions of the chlo- 
rides of platinum and of potassium are mixed, or a salt of potassa, mixed 
with a little hydrochloric acid, added to bichloride of platinum. It is feebly 
soluble in water, still less soluble in dilute alcohol, and is decomposed with 
some difficulty by heat. It is readily reduced by hydrogen at a high tem- 
perature, furnishing a mixture of chloride of potassium and platinum-black ; 
the latter substance may thus, indeed, be very easily prepared. The sodium- 
salt, PtClj, NaCl-(-6H0, is very soluble, crystallizing in large, transparent, 
yellow-red prisms of great beauty. The ammonio-chloride of platinum, PtClj, 
l*(Ii^Cl, is indistinguishable, in physical characters, from the potassium-salt; 

* 08*94» Prof. AndMws, Cbem. Qar., Oct 18&2. . 


it is thrown down as a pr^pitate of small, transparent, yellow, octaliednil 
crystals when sal-amraoniac is mixed with chloride of platinum ; it is but 
feebly soluble in water, still less so in dilute alcohol, aud is decomposed by 
heat, yielding spongy platinum, while sal-ammoniac, hydrochloric acid, and 
nitrogen are driven off. Compounds of platinum with iodine, bromine, sul- 
phur, and phosphorus have been formed, but are comparatively unim" 

Some very extraordinary compounds have been derived from the. proto-, 
chloride of platinum. 

When ammonia in excess is added to a hot solution of the protochloride 
of platinum and ammonium, a green crystalline salt separates after a time, 
which is quite insoluble in water, and is not affected by hydrochloric or sul- 
phuric acids, ammonia, or even a boiling-hot solution of potassa. This sub- 
stance is known as the green salt of Magnus, and contains the elements of 
protochloride of platinum and ammonia, or PtCl-j-NHj. 

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, colourless prisms of a substance very so- 
luble in water, containing the elements of protochloride of platinum, ammo- 
nia, nitric acid, and an additional equivalent of oxygen: — 


The platinum and chlorine in this curious body are Insensible to ordinary 
reagents, and ammonia is evolved from it only on boiling with caustic alkali ; 
the presence of nitric acid can be detected immediately by gently heating a 
small portion with copper-filings and oil of vitriol. Prom this substance a 
series of salt-like bodies can be obtained, some of which have been carefully 
studied by M. Gros. Thus, when treated with hydrochloric acid, the nitric 
acid is wholly displaced, and a compound formed which crystallizes in small, 
transparent, yellowish octahedrons, sparingly soluble in boiling water, con- 
taining PtCl.NjHgCl. With sulphuric acid it gives a substance which crys- 
tallizes in small, sparingly soluble, colourless needles, containing PtCl, 
NjHjO-l-SOj. The oxalic acid compound is white and insoluble ; it contains 
PtCl,N2ffQO-|-C20g. Crystallizabie compounds containing phosphoric, tar- 
taric, citric, malic, formic, and even carbonic acids, were obtained by similar 
means. These substances have very much the characters of salts of a com- 
pound base or ^a»-metal containing PtC^NgHg, and which yet remains un- 
known in a separate state. M. Raewsky has repeated and extended the 
observations of M. Gros. 

MM. Keiset and Peyrone have also described two other basic bodies con- 
taining platinum in the same remarkable condition : these differ from the 
preceding in being free from chlorine. 

Protochloride of platinum put into ammonia becomes rapidly converted 
into a green powder, which, by boiling, slowly dissolves; the solution, on 
evaporation and cooling, furnishes beautiful yellowish crystals of the chlorine- 
compound of one of these bases, compounded of platinum and the elements 
of ammonia. The crystals contained PtNjHgCl-f-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 tlie new base, which crystallizes on evaporation 
in fine, white, transparent needles, containing PtNjHgO-f-NOj. The sulphide, 
iodide, and bromide are also crystallizabie. Two carbonates exist. By adding 
baryta-water to a solution of the sulphate, or by treating the chloride with 
protoxide of silver, and evaporating the filtered liquid in vacuo, a whito. 


'erystalKne, denqve^eut mass is obtained, irfaieh is tlx^ Ifydffttb (ft the Ints^, 
PtNgHgO-f-HO. It is almost comparable in point of alkalinity -with potassa 
itself, absorbing carbonic acid with energy, and decomposing ammoniacal 
salts. When this hydrate is heated to 230° (llO^G), it abandons water and 
-ammonia, and leaves a greyish,-porous, insoluble mass containing PtNH,,0. 
This is probably an isomeric modification of the second base, whose salts are 
mentioned below. 

When a solution of the iodide, PtNgHjI, is long boiled, it deposits a spar- 
ingly soluble yellow powder, the composition of which is expressed by the 
formula PtNH,!: this is the iodine-compound of a second basic substance, 
PtNH,; and from it by double decomposition a series of analogous salts can 
be obtained. When the iodine-compound is treated with protoxide of silver, 
the base itself is obtained in the form of a powerfully alkaline solution. The 
green salt of Magnus has the same composition as tiie chloride of this new 
base, which is yellow and soluble in boiling water, and may be conyerted into 
it. The salts of the first base are generally conyertibl^ into those of the 
flecond by heat, and the converse change may also be often effected by ebul- 
lition with ammonia. 

The subject of the platinum-bases appears to be by no means exhausted. 
Only quite recently another remarkable basic compound containing ammonia 
and platinum has been discovered by M. Gerhardt. The chloride of Reiset's 
second base, the compound* PtNHgCl, when treated with chlorine, absorbs 
this element, and becomes converted into a lemon-yellow powder, consisting 
of small octahedrons, and having the composition PtNH.Clg. Boiled with 
nitrate of silver, this substance yields chloride of silver and, according to the 
quantity of nitric acid present, a salt, PtNH302,2N05, or PtNU^O^^NOj-f 
3 HO. On adding ammonia to the latter nitrate, a crystalline precipitate 
takes place, which consists of PtNH302~|-2HO. This substance, which is 
slightly soluble in water, may be viewed as the hydrated base existing in the 
bichloride and in the nitrates previously described 

The bichloride, or a solution of binoxide of platinum, can be at once re- 
cognized by the yellow precipitate with sal-ammoniac, decomposable by heat^ 
with production of spongy metal. 

Bichloride of platinum and the sodio-chloride of platinum are employed 
in analytical investigations to detect tlie presence of potassa, and separate it 
from soda. For the latter purpose, the alkaline salts are cony«rted into 
chlorides, and in this condition mixed with four times their weight of sodio- 
chloride of platinum in crystals, the whole being dissolved in a little water. 
When the formation of the yellow salt appears complete, alcohol is added, 
and the precipitate collected on a weighed filter, washed with weak spirit, 
carefully dried, and weighed. The chloride of potassium is then easily reck- 
oned from the weight of the double salt, and this, subtracted from the weight 
of the mixed chlorides employed, gives that of the chloride of sodium by 
difference ; 100 parts of potasso-chloride of platinum correspond to 35 06 
parts of chloride of potassium. 

Capsules and crucibles of platinum are of great value to the chemist; the 
latter are constantly used in mineral analysis for fusing siliceous matter with 
alkaline carbonates. They suffer no injury in this operation, although the 
caustic alkali roughens and corrodes the metal. The experimenter must be 
particularly careful to avoid introducing any oxide of any easily fusible 
metal, as that of lead or tin, into a platinum crucible. If reduction should 
by any means oceui, these metals will at once allay themselTOS with the phip 


tinum, and the yessel will be destroyed. A platinum cmcible mnst nerer be 
pat naked into the fire, but be always placed within a covered earthen 


The solution of erude 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 
separates as a whitish insoluble substance, which, on being washed, dried, 
and heated to redness, yields metallic palladium in a spongy state. The pal- 
ladium is then welded into a mass, in the same manner as platinum. 

Palladium closely corresponds with platinum in colour, appearance, and 
difficult fosibility ; it is also very malleable and ductile. In density it differs 
very much from that metal, being only 11-8. Palladium is more oxidable 
than platinum. When heated to redness in the air, especially in the state 
of sponge, it acquires a blue or purple superficial film of oxide, which is 
again reduced at a white heat This metal is slowly attacked by nitric acid ; 
its best solvent is agua regia. There are two compounds of palladium and 

The equivalent of palladium is 53-3; its symbol is Pd. 

Pbotoxidb op palladium, PdO. — This is obtained by evaporating to dry- 
ness, and cautiously heating, the solution of palladium in nitric acid. It is 
black, and but little soluble in acids. The hydrate falls as a dark brown 
precipitate when carbonate of soda is added to the above solution. It is 
decomposed by a strong heat 

BiNoxiDE OF PALLADIUM, PdOg. — The pure binoxide is very difficult to 
obtain. When solution of caustic potassa is poured, little by little, with 
constant stirring, upon the double chloride of palladium and potassium in a 
dry state, the latter is converted into a yellowish -brown substance, which is 
the binoxide, in combination with water and a little alkali. It is but feebly 
soluble in acids. 

pROTOGHLORiDE OP PALLADIUM, PdCI. — The solutiou of the metal in aqua 
regia yields this substance when evaporated to drynesss. 'It is a dark brown 
mass, solable in water when the heat has not been too great, and forms 
double salts with many metallic chlorides. The potassio- and ammonio- 
chlorides of palladium are much more soluble than those of platinum ; they 
have a brownish-yellow tint. 

Bichloride op palladium only exists in solution, and in combination with 
the alkaline chlorides. It is formed when the protochloride of palladium is 
digested in aqua regia. The solution has an intense brown colour, and is 
decomposed by evaporation. Mixed with chloride of potassium or sal-ammo- 
niac, it gives rise to a red crystalline precipitate of double salt which is but 
little soluble in water. 

A tulphide of paUadiumy 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 soluUoQ of cyanide of mercury, convertible by heat into ihe spongy 
metaL This precipitate is a double salt, having the formula PdCy,HgCy,HO. 

Palladium is readily alloyed with other metals, as copper : one of thesu 
compounds, namely, the alloy with silver, has been applied to useful pur> 
poses. A native alloy of gold vith palladium is found in the Brazils, and 
imported into England. 


The solution from which platinum and palladium have been separated in 
the manner described is mixed with hydrochloric acid, and eyaporated to 
dryness. The residue is treated with alcohol of specific gravity 0-837, 
which dissolves everything except the double chloride of rhodium and sodium. 
This is well washed with spirit, dried, heated to whiteness, and then boiled 
with water ; chloride of sodium is dissolved out, and metallic rhodium re- 
mains. '^ Thus obtained, rhodium is a white, coherent, spongy mass, which 
is more infusible and less capable of being welded than platinum. Its spe- 
cific gravity varies from 10-6 to 11. 

Rhodium is very brittle : reduced to powder and heated in the air, it be- 
comes oxidized, and the same alteration happens to a greater extent when it 
is fused with nitrate or bisulphate of potassa. None of the acids, singly or 
conjoined, dissolve this metal, unless it be in the state of alloy, as with pla- 
tinum, in which it is attacked by aqua regia. 

The equivalent of rhodium is 52-2 ; its symbol is K. 

Pbotoxidb of rhodium, bo, is obtained by roasting finely divided me- 
tallic rhodium. It is but little known. 

Sesquioxide of rhodium, BgOg. — Finely-powdered metallic rhodium is 
heated in a silver crucible with a mixture of hydrate of potassa and nitre ; 
the fused mass boiled with water leaves a dark brown, insoluble substance, 
consisting of sesquioxidie of rhodium in union with potassa. This is digested 
with hydrochloric acid, which removes the potassa and leaves a greenish- 
grey hydrate of the sesquioxide of rhodium, insoluble in acids. A soluble 
modification of the same substance, retaining, hoWever, a portion of alkali, 
may be had by adding an excess of carbonate of potassa to the double chlo- 
ride of rhodium and potassium, and evaporating. 

Sesquichloeidk of rhodium, RjClj. — The pure sesquichloride is prepared 
by adding hydrofluosilicic acid to the double chloride of rhodium and potas- 
sium, evaporating the filtered solution to dryness, and dissolving the residue 
in water. It forms a brownish-red deliquescent mass, soluble in water, with 
a fine red colour. It is decomposed by heat into chlorine and metallic rho- 
dium. The chloride of rhodium and potassium, K2Cls-f-2KCl-|-2H0, is pre- 
pared by heating in a stream of chlorine a mixture of equal parts finely 
powdered rhodium and chloride of potassium. This salt has a fine red 
colour, is soluble in water, and crystallizes in four-sided prisms. Chioride of 
rhodium and sodium is also a very beautiful redT salt, obtained by a similar 
process; it contains BgClg-f-SNaCl-f-lSHO. The chloride of rhodium end 
ammonium resembles the potassium-compound. 

Sulphate of rhodiuji, B203,3SOj. — The sulphide of rhodium, obtained 
by precipitating one of the salts- by a soluble sulphide, is oxidized by strong 
nitric acid. The product is a brown powder, nearly insoluble in nitric acid, 
but dissolved by water ; it cannot be made to crystallize. Sulphate of rho- 
dium and potassium, is produced when metallic rhodium is strongly heated 
with bisulphate of potassa. It is a yeUow salt, slowly soluble in cold water. 

An alloy of steel with a small quantity of rhodium is sidd to possess ex- 
tremely valuable properties. 


When crude platinum is dissolved in aqua regia, a small quantity of a grey 
scaly metallic substance usually remains behind, having altogether resisted 
the action of the acid ; this is a native alloy of iridium and osmium. It is 
reduced to powder, mixed with an equal weight of dry chloride of sodium, 
Ibnd heated to redness in a glass tube, through which a stream of moist chlo- 


rine gas is transmitted. The fiirtlter extremity ef the tube kr eeniiecled wHfif 
a rcceirer oontainiDg solution of ammonia. The gas, under these eircura- 
Btances, is rapidly aosol^bed, chloride of iridium and chloride of osmium be* 
ing produced : the former remains in eombination with the chloride of so- 
dium; the latter, being a volatile substance, is carried forward into the 
reeeirer, where it is decomposed by the water into osmic and hydroehlorio 
aeids, 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 
eTaporated to dryness. The residue is ignited in a crucible, boiled with 
water, and dried ; it then consists of a mixture of sesquioxide of iron, and 
a combination of oxide of iridium with soda; it is reduced by hydrogen at 
a high temperatuf e, and treated successively with water and strong hydro- 
chloric acid, by which the alkali and the iron are removed, while metallic 
indiQiH is left in a divided state. By strong pressure and exposure to a 
white heat, a certun degree of compactness may be oommunicated to the^ 

Iridium is a white brittle metal, fusible with great dSi&eulty before tiie 
oxy-hydrogen blovrpipe.* It is not attacked by any aoid, but i» oxidised b/ 
fasioQ with nitre, and by ignition to redness in the air. 
The equivalent of iridium is 99. Its symbol is Ir. 

Oxides of iridium.^— Four of these oompouflds are descHbed. Proioxide 
of indium^ IrO, ia prepared by adding caustic alkali to the protoohloride, 
and digesting the precipitate in an acid. It is a heavy black powder, inso- 
luble iu acids. It may be had in the state of hydrate by precipitating the 
protochloride of iridium and sodium by caustic potassa. The hydrate is so- 
luble in acids with dirty green colour. Se»quiaxide, Ir^O,, is produced when 
iridium is heated in the air, or with nitre ; it is best prepared by fusing in 
a silver crucible & mixture of carbonate of potassa and the terchloiide of 
iridium and potassium, and boiling the product with water. This oxide is 
bluittb-blaok, and is quite insoluble in acids. It is reduced by combustible 
stthstances with explosion. Binoxide of iridium^ IrO,* is unknown in a sepa- 
rate state; it is supposed to exist in the sulphate, produced when the sul- 
pbide is oxidized by nitric acid. A solution of sulphate heated with excess 
cf ilkali evolves oxygen gas, and deptosite sesquioxide of iridium. Teroxid^ 
of iridium^ IrO,, is produced when carbonate of potassa is gently heated with 
the terchloride of iridium ; it forms a greyish^-yellow hydrate^ niiieh con- 
taiiis alknli. 

CflLOBiDEs OF iniDiujf . — Protochloride^ IrCl, is formed when the metal if 
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 
saJtd with the alkaline chlorides, which have a green colour. The aesqukhlo' 
ride, IrjClg, is prepared by strongly heating iridium with nitre, adding water, 
and enough nitric acid to saturate the alkali, warming the mixture) and then 
dissolving the precipitated hydrate of the sesquioxide in hydroehlorie acid. 
It forms a dark yellowish-brown solutifon. This substance combines with 
metallic chlorides. Bkhioride of iridium is obtained in solution by adding 
hjdrofluosilloic acid to the bichloride of iridium and potassium, foi^aed 
when chlorine ia 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. Terchloride cf 
iridium, IrClg, is unknown in a separate state. Terchloride of iridium and 
polamum is obtained by heating iridium with nitre, and then dissolving the 

* It is the beavlttHt substance known, its specific gravity, nooording to PnrfeaKNT Uan, Uta^ 
21-4. Pn>oeeding8 of the Amer. Phil. Soc. May and June, 1842. — R. B 



The solution from which platiDum and palladium have been separated in 
the manner described is mixed with hydrochloric acid, and evaporated to 
dryness. The residue is treated with alcohol of specific gravity 0-887, 
which dissolves everything except the double chloride of rhodium and sodinm. 
This is well washed with spirit, dried, heated to whiteness, and then boiled 
with water ; chloride of sodium is dissolved out, and metallic rhodium re- 
mains. "^ Thus obtained, rhodium is a white, coherent, spongy mass, which 
is more infusible and less capable of being welded than platinum. Its spe- 
cific gravity varies from 10-6 to 11. 

Rhodium is very brittle : reduced to powder and heated in the lur, it be- 
comes oxidized, and the same alteration happens to a greater extent when it 
is fused with nitrate or bisulphate of potassa. None of the acids, singly or 
conjoined, dissolve this metal, unless it be in the state of alloy, as with pla- 
tinum, in which it is attacked by aqua regia. 

The equivalent of rhodium is 52-2 ; its symbol is K. 

Protoxide op rhodium, RO, is obtained by roasting finely divided me- 
tallic rhodium. It is but little known. 

Sesqvioxide of rhodium, RjOj. — Finely-powdered metallic rhodium is 
heated in a silver crucible with a mixture of hydrate of potassa and nitre ; 
the fused mass boiled with water leaves a dark brown, insoluble substance, 
consisting of sesquioxide of rhodium in union with potassa. This is digested 
with hydrochloric acid, which removes the potassa and leaves a greenish- 
grey hydrate of the sesquioxide of rhodium, insoluble in acids. A soluble 
modification of the same substance, retaining, hoWever, a portion of alkali, 
may be had by adding an excess of carbonate of potassa to the double chlo- 
ride of rhodium and potassium, and evaporating. 

Sesquichloridb of rhodium, RgClj. — The pure sesquichloride is prepared 
by adding hydrofluosilicic acid to the double chloride of rhodium and potas- 
sium, evaporating the filtered solution to dryness, and dissolving the residue 
in water. It forms a brownish-red deliquescent mass, soluble in water, with 
a fine red colour. It is decomposed by heat into chlorine and metallic rho- 
dium. The chloride of rhodium and potassium^ R2Cl9-|-2ECl-)-2H0, is pre- 
pared by heating in a stream of chlorine a mixture of equal parts finely 
powdered rhodium and chloride of potassium. This salt has a fine red 
colour, is soluble in water, and crystallizes in four-sided prisms. Chloride of 
rhodium, and sodium is also a very beautiful recT salt, obtained by a similar 
process; it contains RgCls-fSNaCl-f-lSHO. The chloride of rhodium and 
ammonium resembles the potassium-compound. 

Sulphate of rhodium, R203,3SOj. — The sulphide of rhodium, obtained 
by precipitating one of the salts- by a soluble sulphide, is oxidized by strooj; 
nitric acid. The product is a brown powder, nearly insoluble in nitric acid, 
but dissolved by water ; it cannot be made to crystallize. Sulphate of rho- 
dium and potassium^ is produced when metallic rhodium is strongly heated 
with bisulphate of potassa. It is a yellow salt, slowly soluble in cold water. 

An alloy of steel with a small quantity of rhodium is said to possess ex- 
tremely valuable properties. 


When crude platinum is dissolved in aqua reffiOy a small quantity of a grey 
scaly metallic substance usually remains behind, having altogether resisted 
the action of the acid ; this is a native alloy of iridium and osmium. It is 
reduced to powder, mixed with an equal weight of dry chloride of sodium, 
amd heated to redness in a glass tube, through which a stream of moist cMo- 

IRiDlVM. ^ S13 

rine gas is transmitted. The ftntlier eztremitj of the tube k eoniiecled tnA' 
a rcceirer oontaining solution of ammonia. The ^s, under tiiese eircnra- 
stances, is rapidly aosd^bed, ohloride of iridium and chloride of osmium be* 
)Dg prodaeed : the former remains In eombination with the ohloride of so- 
dium; the latter, being a yolatile substance, is carried forward into the 
reeeirer, where it is decomposed by the water into osmic and hydrocfalorio 
adds, which combine with the alkali. The contents of the tube when cold 
are treated with water, by which the douMe chloride of iridium and sodium 
18 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 sesqnioxide of iron, and 
a combination of oxide of iridium with soda; it is reduced by hydrogen at 
a high tempecatuire, and treated successively with water and strong hydro- 
ohloric acid, by which Che alkali and the iron are removed, while metallio 
iridium is left in a divided state. By strong pressure and exposure to a 
white heat, a certain degree of compactness may be oommunicated to the^ 

Iridium is a white brittle metal, fusible with great difficulty before tiie 
oxy-hydrogen blowpipe.^ It is not attacked by any acid, but is ozicSxed by^ 
fusion with nitre, and by ignition to redness in the air. 

The equivalent of iridium is 99. Its symbol is Ir. 

OxiDSS 0¥ IRIDIUM.^— Four of these compounds are desoHbed. Freioxuh 
cf iridium, IrO, is prepared by adding caustic alkali to the protoohloride, 
and digesting the precipitate in an acid. It is a heavy black powder, inso- 
luble in acids. It may be had in the state of hydrate by precipitating the 
protochloride of iridium and sodium by caustic potassa. The hydrate is so- 
luble in acids with dirty green colour. Setquiwtide, Ixfi^j is produced when 
iridium is heated in the air, or with nitre ; it is best prepared by fusing in 
a silver crucible a mixture of carbonate of potassa and the terchloride of 
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^ IrOgi is unknown in a sepa- 
rate state; it is supposed to exist In the sulphate, produced when the sul- 
phide is oxidized by nitric acid. A solution oi sulphate heated with excess 
cf rdkali evolves oxygen gas, and deposits sesquioxide of iridium. Teroxidi 
cf iridium, IrO,, is produced when carbonate of potassa is gently heated with 
the terchloride of iridium ; it forms a greyish-yellow hydrate^ niiieh con- 
tains alkali. 

Chlokides of ininiUM. — Proioehloride, IrCl, is formed when the metal if 
brought in contact with chlorine at a dull red>faeat; it is a dark olive-green 
insoluble powder. It is dissolved by hydrochloric acid, and forms double 
salts with the alkaline chlorides, which have a green colour. The aesquiehlo* 
ride, IrgClj, is prepared by strongly heating iridittm with nitre, adding water, 
and enough nitric acid to saturate the alkali, warming the n{xture> and then 
dissolving the precipitated hydrate of the sesquioxide in hydrochloric acid. 
It forms a dark yellowish-brown solutifon. This substance combines with 
metallic chlorides. Bichloride of iridium is obtained in solution by adding 
hydrofluosilicio aci4 to the bichloride of iridium and potassium, formed 
when chlorine is passed over a heated mixture of iridium and chloride 
of potassium. U forms with metallic chlorides a number of double salts, 
which resemble the platinum -compounds of the same oi^er. Terchloride cf 
iridium, IrClg, is unknown in a separate state. TerchloHde of iridium arid 
potassium is obtained by heating iridium with nitre, and then dissolving the 

* It is the heaviuBt Rubstnnre known, it« specific gravity, nocording to PnrfeaKNT Uatn, 
ti'H, pTooeedingg of the Amer. Phil. Soc. May and June, 1842. —R. B 



whole m 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 colour. The variety of tints 'exhibited by the diffe- 
rent soluble compounds of iridium is very remarkable, and suggested the 
name of the metal^ from the word iris. 

Platinum, palladium, and iridium combine with carbon when heated in the 
flame of a spirit-lamp ; they acquire a covering of soot, which, when burned, 
leaves a kind of skdeton of spongy metal. 


M. Olaus has described under this name a new metal contained in the 
residue from crude platinum, insoluble in a^ua regia. It closely resembles 
iridium in its general characters, but yet possesses distinctive features of 
its own. It was obtained in the form of small angular masses, with perfect 
metallic lustre, very brittle and infusible. Its specific gravity is 8*6. It 
resists the action of acids, but oxidizes readily when heated in the air. 

The equivalent of ruthenium is 52-2, and its symbol Bu. 

Oxides op buthbnium. — Protoxide of ruthenium, RuO, is a greyish-black 
metallic-looking powder, obtained by heating bichloride of ruthenium ivith 
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 tesquioxidef 
BugOs, in the anhydrous condition is a bluish-black powder formed by heating 
the metal in the air. It is also precipitated by alkalis from the sesquichlo- 
ride as a blackish-brown hydrate, soluble in acids with orange-yellow colour. 
The binoxide, RuOg, is a deep blue powder, procured by roasting the bisul- 
phide. A hydrate of this oxide is known in an impure condition. An acid 
of ruthenium is also supposed to exist. 

Sesquichloride of ruthenium, RugClj, is an orange-yellow soluble salt of 
astringent taste ; when the solution is heated, it becomes green and finally 
blue, by reduction, in all probability, to protochloride. Sesquichloride of 
ruthenium forms double salts with the chlorides of potassium and ammoniam. 


The solution of osmic acid in ammonia, already mentioned, is gently heated 
for some time in a loosely-stopped vessel ; its original yellow colour becomes 
darker, and at length a brown precipitate falls, which is a combination of 
sesquioxide of osmium with ammonia : it results from' the reduction of the 
osmic acid by the hydrogen of the volatile alkali. A little of the precipitate 
is held in solution by the sal-ammoniac, but may be recovered by heating 
the clear liquid with caustic potassa. The brown substance is dissolved in 
hydrochloric acid, a little chloride of ammonium added, and the whole evapo- 
rated to dryness. The residue is strongly heated in a small porcelain retort; 
the oxygen of the oxide combines with hydrogen from the ammonia, vapour 
of water, hydrochloric acid, and sal-ammoniac are expelled, and osmium left 
behind, as a greyish porous mass, having the metallic lustre. 

In the most compact state in which this metal can be obtained, it has a 
bluish-white colour, and, although somewhat flexible in thin plates, is jet 
easily reduced to powder. Its specific gravity is 10; it is neither fusible 
nor volatile. It burns when heated to redness, yielding osmic acid, which 
volatilizes. Osmate of potassa is produced when the metal is fused with 
nitre. When in a finely divided state,- it is oxidized by strong nitric acid. 

The equivalent of osmium is 99-6 ; its symbol is Os. 

Oxides of osmium. — Five compounds of osmium with oxygen are known. 
Protoxide, OsO, is obtained, in combination with a little alkali, when caustic 
]>otassa is added to a solution of protochloride of osmium and potassium. It 
is a dark green powder, slowly soluble in acids. Sesquioxide^ Os,Og, has 

OSMIUM. 315 

already been noticed ; it is generated by the deoxidaiion of osmate of am- 
monia ; it is black, and but little soluble in acids. It always contains 
ammonia, and explodes feebly when heated. Binoxide of osmium, OsO,, is pre- 
pared by strongly heating in a retort a mixture of carbonate of soda and the 
bichloride of osmium and potassium, and treating the residue with water, and 
afterwards with hydrochloric acid. The binoxide is a black powder, insoluble 
in acids, and burning to osmic acid when heated in the air. Osmious acid 
OsOj is known only in combination. On adding alcohol to a solution of 
osmate of potassa, the alcohol is oxidized at the expense of the osmic acid, 
and a rose-red crystalline powder of osmite of potassa is produced. On at- 
tempting to separate the acid, it is decomposed into the binoxide and osmic 
acid. Osmic acid, OSO4, is by far the most important and interesting of the 
oxides of this metal. It is prepared by heating osmium in a current of pure 
oxygen gas ; it condenses in the cool part of the tube in which the experi- 
ment is made in colourless transparent crystals. Osmic acid melts and even 
boils below 212° (lOO^'C) ; its vapour has a peculiar offensive odour, and is 
exceedingly irritating and dangerous. Water slowly dissolves this substance. 
It has acid properties, and combines with bases. Nearly all the metals pre- 
cipitate osmium from a solution of osmic acid. By the action of ammonia 
on osmic acid, a new acid has been formed, containing osmium, nitrogen, 
and oxygen. It has been called osman-osmic acid or osmamic acid. Some 
doubts are hanging over the formula of this substance. It produces salts 
with many bases. 

Chlorides of osmium. — Protochtoride, OsCl, is a dark green crystalline 
substance, formed by gently heating osmium in chlorine gas. It is soluble 
in a small quantity of water, with green colour, but decomposed by a large 
quantity into osmic and hydrochloric acids and metallic osmium. It forms 
double salts with the metallic chlorides. The sesquichloride, OsgCl,, has not 
been isolated ; it exists in the solution obtained by dissolving the sesquioxide 
in hydrochloric acid. Bichloride, OsClg, in combination with chloride of 
potassium, is produced when a mixture of equal parts metallic osmium and 
the last-named salt is strongly heated in chlorine gas. It forms fine red oc- 
tahedral crystals, containing OsClg^-K^l* 

Osmium combines also with sulphur and with phosphorus. 




Oroaitic substances, whether directly deriyed from the Tegetflble or ani- 
mal kingdom, or produced by the subsequent modilication of bodies which 
thus originate, are remarkable as a class for a degree of complexity of eon* 
Btitution 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 ; yery few, comparatiTely speaking, eontaia 
more than four, riz., carbon, hydrogen, oxygen, and nitrogen ; sulphur and 
phosphorus are occasionally associated with these in certain mineral pro- 
ducts ; and compounds containing chlorine, bromine, iodine, arsenic, anti- 
mony, zinc, &c., haye been formed by artificial means. This pancity of 
elementary bodies is compensated by the yery peculiar and extraordinary 
properties of th6 four first-mentioned, which possess capabilities of combi- 
nation to which the remaining elements are strangers. There appears to \» 
absolutely no limit to the number of definite, and often crystallizable, sab- 
totances which can be thus generated, each marked by a perfect individuality 
of its own. 

Tho mode of association of the elements of organic substances is in gene- 
ral altogether dififerent from that so obrious in the other dirision of the 
science. The latter is invariably characterized by what may be termed » 
binary plan of combination, union taking place between pairs of elements, 
and the compounds so produced again uniting themselves to other compound 
bodies in the same manner. Thus, copper and oxygen combine to oxide of 
copper, potassium and oxygen to potassa, sulphur and oxygen to sulphuric 
acid ; sulphuric acid, in its turn, combines both with oxide of copper and oxide 
of potassium, generating a pair of salts, which are again capable of uniting 
to form the double compound, Cu0,S0j-)-K0,S03. 

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 ^ase is strikingly different ; no such ar- 
rangement can here be traced. In sugar, CjjH.jO,,, or morphine, C34HjgN0g, 
or the radical of bitter almond oil, Cj4Hg02« ana a multitude of similar cases, 
the elements concerned are, as it were, bound up together into a single 
whole, which can enter into combination with other substances, and be thence 
disengaged with properties unaltered. 

A curious consequence of this peculiarity is to be found in the compara- 
tively instable character of organic compounds, and their general proneness 
to decomposition and change, when the balance of opposing forces, to which 
they 0^ their existence, becomes deranged by some external cause. 

If a complex inorganic substance be attentively considered, it will usually 
be found that the elements are combined in such a manner as to satisfy the 
most powerful affinities, and to give rise to a state of very considerable per- 
manence and durability But in the case of an organic substance oontainioe 



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 carbonio 
acid ; the hydrogen and oxygen attract each other in a powerful manner, 
and the nitrogen, if that body be present, also contributes its share to these 
internal sources of weakness by its disposition to generate ammonia. While 
the opposing forces remain exactly balanced, the integrity of the compound 
is preserved; but the moment one of them, from some accidental cause, 
acquires preponderance over the rest, equilibrium is destroyed and the 
~ organic principle breaks up into two or more new bodies of simpler and more 
permanent constitution. The agency of heat produces this e£fect by 
exalting the attraction of oxygen for hydrogen and carbon ; hence the almost 
aniversal destructibility of organic substances by a high temperature. Mere 
molecular disturbance of any kind may cause destruction when the insta- 
bility is very great. 

As a general rule, it may be assumed that those bodies which are most 
complex from the number of elements, and the want of simplicity in their 
equivalent relations, are by constitution weakest, and least capable of resist- 
ing the action of disturbing forces ; and that this susceptibility of change 
diminishes with increased simplicity of structure, until it reaches its minimum 
m those bodies which, like the carbides of hydrogen, like cyanogen, and 
oxalic acid, connect, by imperceptible gradations, the organic and the mineral 
departments of chemical science. 

The definite organic principles of the vegetable and animal kingdoms form 
but a very small proportion of the immense mass of compounds included 
within the domain of organic chemistry: by far the greater number of these 
are produced by modifying by suitable means the bodies furnished by the 
plant or the animal, and which have themselves been formed from the 
elements of the air by processes for the most part unknown, carried on under 
the control of vitality. Unlike these latter, the artificial modifications 
referred to, by oxidation, by the action of other powerful reagents, by the 
influence of heat, and by numerous other sources of disturbance, are, for 
the most part, changes of descent in order of complexity, new products being 
"thus generated more simple in constitution and more stable in character than 
the bodies from which they were derived. These, in turn, by repetition of 
such treatment under perhaps varied circumstances, may be broken 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-producta : Law of Substitution. — The study of the action 
of chlorine, bromine, iodine, and nitric acid upon various organic substances 
has led to the discovery of a very remarkable law regulating the formation 
of chlorinetted and other analogous compounds, which, without being of 
necessity absolute in every case, is yet of sufficient generality and import- 
ance to require careful consideration. This peculiar mode of action consists 
in t