to pass through the wire. As soon as the wire becomes incandescent, it forms around itself an atmosphere of vapour, which it immediately decomposes. Moreover, a natural valve being formed by the conflict of ascending gas and descending water, the bubbles of mixed gas are cut off by an intermittent action; and thus, as their recombination is prevented, a volume of gas collects in the bend of the tube and is ultimately expelled at the orifice. It detonates on the application of a light. If again, a button of platinum wire be fully ignited by the oxyhydrogen blowpipe, and then plunged into water heated nearly to its boiling point, bubbles of mixed gas ascend and may be collected in an inverted tube. Various forms of apparatus have been devised for the purpose of increasing the action and rendering the evolution of gas continuous: they are fully described in the memoir above referred to. The decomposition may also be effected by means of an ignited button of the alloy of iridium and osmium, also by ignited palladium; but the effects are not so striking as with platinum. Silica and other oxides also seemed, in Mr. Grove's experiments, to effect the decomposition; but the results were not satisfactory.

The mode of action in this very remarkable phenomenon is involved in some obscurity. Various explanations have been suggested: some have attributed it to a catalytic action of the platinum. But it is perhaps most probable-as suggested by the discoverer-that the cause of the decomposition is to be found in the rarefaction produced by the heat. Grotthuss has shown that mixtures of oxygen and hydrogen, or chlorine and hydrogen, when much rarefied, will not detonate by the electric spark. We know also that other compounds may be decomposed by mere elevation of temperature: e. g., oxide of chlorine at a very moderate heat, ammonia at a higher, and certain metallic oxides, viz. the oxides of mercury, silver, gold, and the other noble metals, at a still higher temperature; and the decomposition of water in the manner just described appears to form the final term of this series of actions. There appears

indeed to be an extensive series of facts which point to a generalized antagonism between thermic repulsion and chemical affinity, and a consequent establishment of the law of continuity between physical and chemical attraction. (Vid. Phil. Mag. J. 31, 96.) T.

Observation 1. Davy, who doubts the materiality of heat, explains the difference between a hot and a cold body by supposing the atoms of the former to make larger vibrations than those of the latter: hence expansion. The same view is taken by Mohr. (Ann. Pharm. 24, 141.)

Observation 2. Irvine and Dalton make no difference between free and combined heat. When uncombined heat becomes accumulated in a solid body to a certain point, it causes that body to assume the liquid form; and since, according to the opinion of these philosophers, this change of form is accompanied by increased capacity for heat, absorption of heat must take place. They therefore consider all development and absorption of heat in chemical or mechanical changes of ponderable bodies as proceeding from an alteration of capacity for heat. According to these hypotheses they endeavour to find the so-called Zero, the absolute of the scale of temperature, or the absolute quantity of heat contained in bodies. Since, e. g., the specific heat of ice is, according to Kirwan, 0-9 of that of water, and ice in passing to the state of water absorbs 75° of heat, these 75° are equal to one-tenth of the absolute quantity of heat

contained in water; hence the zero of the temperature for water at 0° must be situated at 750° (1318° Fah.). They likewise determine the zero from the heat evolved on mixing two substances, and the specific heat of the resulting mixture. But the widely discrepant results of these calculations, according to the nature of the substances considered,—the zero being situated, according to Dalton's experiments between 6130 and — 2390, and according to an experiment of Lavoisier and Laplace. actually above red heat, are the best arguments against the rejection of the theory of combined heat. If the statement of Delaroche & Bérard, that the specific heat of vapour of water is only 0.8470, should be completely established, the preceding view of the subject would be completely overthrown, since, if there were no such thing as combined heat, the conversion of water into vapour would then be attended with evolution of heat.-Comp. Thomson (System of Chemistry.)

100000

Clement & Desormes place the absolute zero at - 266·6° C. (— 447.9° Fah.) partly with reference to a not very probable hypothesis concerning the heat contained in a vacuum (p. 252), partly from the following considerations. Air at 0° expands for each degree C. of heat superadded by 375 375 or and contracts for each degree of heat abstracted, by If this law be applicable at all temperatures, the limit of diminution of volume must be found at 266-6; below this point there can be no further contraction of volume and therefore no further abstraction of heat. Or:-If 266-6° of heat be imparted to air at 0° its volume becomes doubled; according to the above law, the air, when its volume is dombled, must contain twice the quantity of heat which it contains at 0; consequently at 0° it must contain 2666° more heat than at the absolute zero. [Vid. p. 256.]

CHAPTER III.

ELECTRICITY.

TH. ANDREWS. Thermo-Electricity. Phil. Mag. J. 10, 433; also Pogg. 41, 164.

Conducting power of Flame. Phil. Mag. J. 9, 176; also Pogg. 43, 310.

Armstrong.

Electricity by Expansion of Air and Aqueous Vapour. Phil. Mag. J. 18, 133, 328 and 500; 19, 25; 20, 5; 21, 1; 22, 194; Ann. Chim. Phys. 75, 328; Pogg. 52, 328. Becquerel. Electricity by Pressure. Ann. Chim. Phys. 22, 5; Thermoelectricity, 23, 135 (also Schw. 39, 448); Chemical Electricity, 23, 152; 23, 244 (also Schw. 40, 385); 23, 259 (also Schw. 40, 405); 24, 203; Electricity by Capillarity, 24, 237 (also Schw. 40, 408); Chemical Electricity, 24, 348; 25, 405 (also Schw. 43, 71; also Pogg. 2, 169); 26, 176 (also Schw. 44, 153; also Pogg. 2, 180); 27, 5 (also Pogg. 2, 191); 27, 14 (also Pogg. 2, 201); 28, 19, and 27 (also N. Tr. 11, 1, 236); Thermo-electricity, 31, 371 (also Pogg. 9, 345); Chemical Electricity 34, 153 (also Pogg. 11, 457); 35, 113. Electricity by Cleavage of Crystals, 36, 265 (also Pogg. 12, 147); Electricity by Wire in Flame, 36, 328 (also Pogg. 11, 437); Crystalelectricity, 37, 5, and 355 (also Pogg. 13, 628); Friction-electricity of Metals, 38, 113 (also Pogg. 13, 619); Compounds produced by Electricity, 41, 5 (abstr. Pogg. 16, 306); Thermo-electricity, 41, 353 (also Pogg. 17, 535); Combinations and Decompositions by Galvanic Action, 42, 226 (also Pogg. 18, 143; also Schw. 58, 439); 43, 131 (also Pogg. 18, 147); 43, 380; Thermo-electricity, Frictionelectricity, and Chemical Electricity, 46, 265, and 337; Galvanic Decompositions, 48, 337; Electricity developed in the Cementation of Iron by Charcoal, 49, 131; Platinum with Gold, Peroxide of Manganese, Black Lead, 60, 164; Galvanic Formation of Carbonate of Lime, 60, 173; Galvanic Apparatus with Nitric Acid and Potash, Bibl. univ. 60, 215; also Pogg. 37, 429.-Also Ann. Chim. Phys. 66, 84; also Pogg. 44, 437.-Electric Current, which decomposes, but does not produce Heat. Bibl. univ. 59, 218; also Pogg. 37,

433.

Becquerel (E). Conducting Power of Solids and Liquids. V. Ann. Chim. Phys. 20, 53.

Van Beek. Metals with Sea-water. Pogg. 12, 274; again, Ann. Chim. Phys. 64, 225.

Beetz. Certain Phenomena of Voltaic Decomposition. Pogg. 61, 209.— Rusting of Iron, and its Connection with the Passive State, 92, 234.-Voltaic Polarization of Iron, 63, 283.-Passivity of Iron, 67, 186.

Berzelius & Hisinger. Galvanic Decomposition of Salts. Gilb. 27, 270. Berzelius. Galvanic Action on Coloured Papers. Gilb. 27, 316.—

Theory of the Electric Pile. N. Gehl. 3, 177. Binks. Laws of Galvanism. Phil. Mag. J. 11, 62; 12, 54, 135, 171, and 276.

Voltaic Pile.

G. Bischof.
Metals. Schw. 52, 230.
R. Böttger. Thermo-electricity. Pogg. 50, 41.-Nobili's Rings. J. pr.
Chem. 8, 476.-Electricity produced by Tin with Nitrate of Copper.
Ann. Pharm. 29, 77.-Galvanic Tinning, Gilding, Platinizing, and
Zinking. Ann. Pharm. 34, 84; 35, 221, and 350; 39, 171.-
Electrotype. Ann. Pharm. 35, 216; 39, 180.-Production of pure
Iron in the coherent State by Galvanic Electricity. Pogg. 67, 117.
Brewster. Crystal-Electricity. Edinb. J. of Sc. 1, 208; also Pogg. 2,
297; also Schw. 43, 87.

Kastn. Archiv. 4, 13.-Electric Series of

Buff. Galvanism. Ann. Pharm. 32, 1 and 7; 34, 129 and 241; 35, 1. A. Connel. Galvanic Decompositions. N. Edinb. Phil. J. 19, 163; Phil. Transact. of Edinb. 13; also J. pr. Chim. 5, 167; Phil. Mag.

J. 18, 353. Callan. New Voltaic Battery. Cumming. Thermo-electricity. also Schw. 40, 312 and 317. Daniell. Voltaic Combinations. Phil. Transact. 1836, 1, 107; abstr. Pogg. 42, 262.—Galvanic Decompositions. Phil. Transact. 1838 and 9; abstr. Ann. Pharm. 36, 32.-Electrolysis of Salts. Phil. Mag. J. 22, 461.-Electrolysis of Secondary Compounds. Phil. Mag. J. 24, 463.

Phil. Mag. J. 31, 81.
Ann. Phil. 21, 427; 22, 177 and 321;

Daniell & Miller. Electrolysis of Secondary Compounds. Phil. Mag. J. 25, 175.

J. Davy. Iron with Tin; Galvanism without Chemical Action. N. Edinb. Phil. J. 17, 42 and 46. H. Davy. Galvanic Decompositions. N. Gehl. 5, 1; also Gilb. 28, 1 and 162.-Electricity in vacuo. Phil. Transact. 1822, 64; also Gilb. 72, 357.-Protection of Copper by Iron. Phil. Transact. 1825, 328; also Schw. 56, 434; Ann. Chim. Phys. 33, 319.-Chemical and Electric Actions. Ann. Chim. Phys. 33, 276; also N. Tr. 15, 1, 84.

M. Davy. Experimental Researches on Voltaic Electricity. N. Ann. Chim. Phys. 19, 401. De la Rive. Galvanic Decompositions. Ann. Chim. Phys. 28, 190; 35, 164.-Secondary Currents. Bibl. univ. 35, 92; also Ann. Chim. Phys. 36, 34; also Pogg. 10, 425.-Electric Conduction. Ann. Chim. Phys. 35, 160; Bibl. univ. 40, 196; also Pogg. 15, 523.Direction and Force of the Electric Current. Ann. Chim. Phys. 37, 325; also Pogg. 15, 122.-Chemical Electricity. Mém. de la Soc. de Phys. de Genève, 4, 285; abst. Ann. Chim. Phys. 39, 298; abstr. Pogg. 15, 98.-Development of Heat by the Electric Current. Bibl. univ. 40, 40; also Ann. Chim. Phys. 40, 371; abstr. Pogg. 15, 257.— Zine and Sulphuric Acid. Bibl. univ. 43, 391; also Pogg. 19, 221. -Electric Conduction of Mercury. Ann. Chim. Phys. 40, 408.Chemical Electricity. Compt. rend. 1835, 312.-History of the new Theory of Electricity. Bibl. univ. 52, 225 and 404; 53, 70, 170 and 315.-Electricity by Friction of Metals. Bibl. univ. 59, 13; also Pogg. 37, 506.-Electric Conduction at different Temperatures. Bibl. univ. N. S. 7, 388; also Pogg. 42, 99.-Chemical Electricity. Ann. Chim. Phys. 61, 38; 62, 147; also Pogg. 40, 355 and 515.-Galvanic Oxidation of Platinum. Pogg. 46, 489.-Galvanic Gilding. Ann. Chim. Phys. 72, 398; also J. pr. Chem. 20, 157.-Researches on the Voltaic Arc. Phil. Mag. J. 31, 421.

VOL. I.

X

Donné. Dry Pile. Ann. Chim. Phys. 42, 71; abstr. Schw. 58, 81.—
Electricity in the Human Body. Ann. Chim. Phys. 57, 405.
Erman. Gilb. 7, 485 and 501; 8, 197 and 284; 10, 1 and 326; 11, 89,

143 and 166; 14, 385; 22, 14, 220 and 318; 64, 45; Pogg. 25, 657. Faraday. Experimental Researches in Electricity.-Series 1: Phil. Trans. 1832, I, 125.-Series 2: ib. 1832, I, 163.-Series 3: 1833, I, 23.-Series 4: 1833, II, 507.-Series 5: 1833, II, 675.-Series 6: 1834, I, 1; Series 7: 1834, I, 77.-Series 8: 1834, II, 425.-Series 9: 1835, I, 41.-Series 10: 1835, II, 263.—Series 11: 1838, I, 1.— Series 12: 1838, I, 83.-Series 13: 1838, I, 125.-Series 14: 1838, II, 265.-Series 15: 1839, I, 1.-Series 16: 1840, I, 61.-Series 17: 1840, I, 93.-Series 18: 1843, I, 17.-Series 19: 1846, I, 1.— Series 20: 1846, I, 21.-Series 21: 1846, I, 41.-These researches are likewise published in the Philosophical Magazine.

On Static Electric Induction. Phil. Mag. J. 22, 200.-Comparison between the Chemical Action and Contact Theories of the Voltaic Battery. Phil. Mag. J. 24, 136.-Diamagnetic Conditions of Flame and Gases. Phil. Mag. J. 31, 401.--On Gutta Percha as an Insulator. Phil. Mag. J. 32, 165.

Fechner. Schw. 53, 61, 129 and 429; 55, 223 and 442; 57, 1; 60, 17;

63, 249; Pogg. 41, 225; 42, 481; 43, 432; 44, 37; 48, 1 and 225. N. W. Fischer. Metallic Reduction. Gilb. 72, 289; Pogg. 4, 291. Gahn & Hisinger. Decomposition of Water by the Electric Spark. Gilb. 27, 311.

L. Gmelin. Electro-chemical Theory. Pogg. 44, 1.

Grotthuss. Electro-chemistry. Gill. 61, 60. Decomposition of Water. Ann. Chim. Phys. 58, 54; also in his Physico-chemical Researches, 126.-Galvanic Decomposition through a Glass Plate. Schw. 28, 315. Electricity developed in the Freezing of Water. Ann. Chim. Phys. 27, 111.

Grove. New Battery with Nitric Acid. Phil. Mag. J. 13, 430; 14, 127; 15, 287; also Pogg. 48, 30.-Conducting Power of Water. Pogg. 48, 305.-Amalgamated Zinc. Phil. Mag. J. 15, 81; also J. pr. Chem. 18, 114.-Voltaic Process of Etching a Daguerrotype Plate. Phil. Mag. J. 20, 18.-Experiments on Voltaic Reaction, 23, 443.-Gas Voltaic Battery, 21, 417; 24, 268, 346 and 412.On Grotthuss' Theory of Molecular Decomposition and Recomposition, 27, 348.-Application of Voltaic Electricity to the Lighting of Mines, 27, 348.-On certain Phenomena of Voltaic Ignition, and on the Decomposition of Water by Heat, 30, 20, and 91.

Hankel. Crystal-electricity. Pogg. 49, 493; 50, 237, 471 and 605; 53, 629.

Hare. Calorimotor and Deflagrator. Ann. Phil. 14, 176; also Schw. 26, 313.—Ann. Phil. 17, 329; 2, 328; 4, 119.

Hauy. Electricity by Pressure and Friction. Ann. Chim. Phys. 5. 95; 8, 383; also Schw. 20, 383; 25, 135.-J. Phys. 89, 455. Henkel. Thermo-electricity of Metals and Metallic Minerals. Pogg. 62, 197.-Strength of the Electric Current between Metals. Pogg. 62, 479. Henrici. Galvanism. Pogg. 47, 431; 48, 372; 52, 387; 53, 277; 58, 61 and 232.--Influence of Temperature on the Conducting Power of Liquids for Galvanic Currents. Pogg. 66, 174.-Theory and Application of Electricity. Phil. Mag. J. 27, 164.

Jacobi. Becquerel's Circuit. Pogg. 40, 67.-Chamber Battery, 43, 328,