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HYDROGEN [symbol H, atomic weight x-o...

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Originally appearing in Volume V14, Page 114 of the 1911 Encyclopedia Britannica.
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HYDROGEN [See also:symbol H, atomic See also:weight x-oo8 (0=16)] , one of the chemical elements. Its name is derived from Gr. uSwp, See also:water, and ryevvaew, to produce, in allusion to the fact that water is produced when the See also:gas See also:burns in See also:air. Hydrogen appears to have been recognized by See also:Paracelsus in the 16th See also:century; the combustibility of the gas was noticed by Turquet de See also:Mayenne in the 17th century, whilst in 1700 N. See also:Lemery showed that a mixture of hydrogen and air detonated on the application of a See also:light. The first definite experiments concerning the nature of hydrogen were made in 1766 by H. See also:Cavendish, who showed that it was formed when various metals were acted upon by dilute sulphuric or hydrochloric acids. Cavendish called it " in-flammable air," and for some See also:time it was confused with other inflammable gases, all of which were supposed to contain the same inflammable principle, " phlogiston," in See also:combination with varying amounts of other substances. In 1781 Cavendish showed that water was the only substance produced when hydrogen was burned in air or See also:oxygen, it having been thought previously to this date that other substances were formed during the reaction, A. L. See also:Lavoisier making many experiments with the See also:object of finding an See also:acid among the products of See also:combustion. Hydrogen is found in the See also:free See also:state in some volcanic gases, in fumaroles, in the carnallite of the See also:Stassfurt potash mines (H. Precht, Ber., 1886, 19, p.

2326), in some meteorites, in certain stars and nebulae, and also in the envelopes of the See also:

sun. In combination it is found as a constituent of water, of the gases from certain See also:mineral springs, in many minerals, and in most See also:animal and See also:vegetable tissues. It may be prepared by the See also:electrolysis of acidulated water, by the decomposition of water by various metals or metallic hydrides, and by the See also:action of many metals on acids or on bases. The See also:alkali metals and alkaline See also:earth metals decompose water at See also:ordinary temperatures; See also:magnesium begins to react above 7o° C., and See also:zinc at a dull red See also:heat. The decomposition of See also:steam by red hot See also:iron has been studied by H. Sainte-Claire Deville (Comptes rendus, 1870, 70, p. 1105) and by H. Debray (ibid., 1879, 88, p. 1341), who found that at about 1500° C. a See also:condition of See also:equilibrium is reached. H. See also:Moissan (See also:Bull. See also:soc. chim., 1902, 27, p. 1141) has shown that See also:potassium hydride decomposes See also:cold water, with See also:evolution of hydrogen, KH+See also:H2O= KOH -•- H2.

See also:

Calcium hydride or hydrolite, prepared by passing hydrogen over heated calcium, decomposes water similarly, 1 See also:gram giving 1 litre of gas; it has been proposed as a commercial source (Prats Aymerich, Abst. J.C.S., 1907, ii. p. 543), as has also See also:aluminium turnings moistened with potassium See also:cyanide and mercuric chloride, which decomposes water regularly at 70°, I gram giving 1.3 litres of gas (Mauricheau-Beaupre, Comptes rendus, 1908, 147, p. 310). See also:Strontium hydride behaves similarly. In preparing the gas by the action of metals on acids, dilute sulphuric or hydrochloric acid is taken, and the metals commonly used are zinc or iron. So obtained, it contains many impurities, such as See also:carbon dioxide, See also:nitrogen, oxides of nitrogen, phosphoretted hydrogen, arseniuretted hydrogen, &c., the removal of which is a See also:matter of See also:great difficulty (see E. W. See also:Morley, Amer. Chem. Journ., 189o, 12; p. 460).

When prepared by the action of metals on bases, zinc or aluminium and See also:

caustic soda or caustic potash are used. Hydrogen may also be obtained by the action of zinc on ammonium salts (the nitrate excepted) (Lorin, Comptes rendus, 1865, 6o, p. 945) and by See also:heating the alkali formates or oxalates with caustic potash or soda, Na2C204+2NaOH = H2+2Na2CO3. Technically it is prepared by the action of superheated steam on incandescent See also:coke (see F. Hembert and See also:Henry, Comptes rendus, 1885, 1o1, p. 997; A. See also:Naumann and C. Pistor, Ber., 1885, 18, p. 1647), or by the electrolysis of a dilute See also:solution of caustic soda (C. Winssinger, Chem. Zeit., 1898, 22, p. 609; " See also:Die Elektrizitats-Aktiengesellschaft," Zeit. f.

Elektrochem., 1901, 7, p. 857). In the latter method a 15 % solution of caustic soda is used, and the electrodes are made of iron; the See also:

cell is packed in a wooden See also:box, surrounded with See also:sand, so that the temperature is kept at about 7o° C.; the solution is replenished, when necessary, with distilled water. The purity of the gas obtained is about 97%• Pure hydrogen is a tasteless, colourless and odourless gas of specific gravity 0.06947 (air =1) (See also:Lord See also:Rayleigh, Proc. See also:Roy. Soc., 1893, p. 319). It may be liquefied, the liquid boiling at -252.68° C. to -252.84°C., and it has also been solidified, the solid melting at—264° C. (J. See also:Dewar, Comptes rendus, 1899, 129, p. 451; Chem. See also:News, 1901, 84, p.

49; see also LIQUID GASES). The specific heat of gaseous hydrogen (at See also:

constant pressure) is 3.4041 (water =1), and the ratio of the specific heat at constant pressure to the specific heat at constant See also:volume is 1.3852 (W. C. See also:Rontgen, Fogg. See also:Ann., 1873, 148, p. 580). On the spectrum see See also:SPECTROSCOPY. Hydrogen is only very slightly soluble in water. It diffuses very rapidly through a porous membrane, and through some metals at a red heat (T. See also:Graham, Proc. Roy. Soc., 1867, 15, p.

223; H. Sainte-Claire Deville and L. Troost, Comptes rendus, 1863, 56, p. 977). See also:

Palladium and some other metals are capable of absorbing large volumes of hydrogen (especially when the See also:metal is used as a See also:cathode in a water electrolysis apparatus). L. Troost and P. Hautefeuille (Ann. chim. phys., 1874, (5) 2, p. 279) considered that a palladium hydride of See also:composition Pd2H was formed, but the investigations of C. Hoitsema (Zeit. phys. Chem., 1895, 17, p. 1), from the standpoint of the phase See also:rule, do not favour this view, Hoitsema being of the See also:opinion that the occlusion of hydrogen by palladium is a See also:process of continuous absorption.

Hydrogen burns with a See also:

pale See also:blue non-luminous See also:flame, but will not support the combustion of ordinary combustibles. It forms a highly explosive mixture with air or oxygen, especially when in the proportion of two volumes of hydrogen to one volume of oxygen. H. B. See also:Baker (Proc. Chem. Soc., 1902, 18, p. 40) has shown that perfectly dry hydrogen will not unite with perfectly dry oxygen. Hydrogen combines with See also:fluorine, even at very See also:low temperatures, with great violence; it also combines with carbon, at the temperature of the electric arc. The alkali metals when warmed in a current of hydrogen, at about 36o° C., See also:form hydrides of composition RH(R=Na, K, Rb, Cs), (H. Moissan, Bull. soc. chim., 1902, 27, p. 1141); calcium and strontium similarly form hydrides CaH2, SrH2 at a dull red heat (A.

Guntz, Comptes rendus, 1901, 133, p. 1209). Hydrogen is a very powerful reducing See also:

agent; the gas occluded by palladium being very active in this respect, readily reducing ferric salts to ferrous salts, nitrates to nitrites and See also:ammonia, See also:chlorates to chlorides, &c. For determinations of the volume ratio with which hydrogen and oxygen combine, see J. B. See also:Dumas, Ann. chim. phys., 1843 (3), 8, p 189; O. See also:Erdmann [and R. F. Marchand, ibid. p. 212; E. H. Keiser, Ber., 1887, 20, p.

2323; J. P. See also:

Cooke and T. W. See also:Richards, Amer. Chem. Journ., 1888, 10, p. 191; Lord Rayleigh, Chem. News, 1889, 59, p. 147; E. W. Morley, Zeit. phys.

Chem., 189o, 20, p. 417; and S. A. Leduc, Comptes rendus, 1899, 128, p. 1158. Hydrogen combines with oxygen to form two definite compounds, namely, water (q.v.), H2O, and hydrogen peroxide, 11202, whilst the existence of a third See also:

oxide, ozonic acid, has been indicated. Hydrogen peroxide, H2O2, was discovered by L. J. See also:Thenard in 1818 (Ann. chim. phys., 8, p. 306). It occurs in small quantities in the See also:atmosphere. It may be prepared by passing a current of carbon dioxide through See also:ice-cold water, to which small quantities of See also:barium peroxide are added from time to time (F.

Duprey, Comptes rendus, 1862, 55, p. 736; A. J. See also:

Balard, ibid., p. 758), BaO2+See also:CO2+H2O=H202+BaCO3. E. See also:Merck (Abst. J.C.S., 1907, ii., p. 859) showed that barium percarbonate, BaCO4, is formed when the gas is in excess; this substance readily yields the peroxide with an acid. Or barium peroxide may be decomposed by hydrochloric, hydrofluoric, sulphuric or silicofluoric acids (L. Crismer, Bull. soc. chim., 1891 (3), 6, p. 24; •See also:Hanriot, Comptes rendus, 1885, too, pp.

56, 172), the peroxide being added See also:

HYDROGRAPHY- -=HYI ROLYSIS. benzoic and other organic acids are readily oxidized in the presence of ferrous sulphate (H. J. H. See also:Fenton, See also:Jaw. Chem. Soc., 1900, 77, p. 69), and sugars are readily oxidized in the presence of ferric chloride (O. See also:Fischer and M. See also:Busch; Bcr., 1891, 24, p. 1871). It is sought to explain these oxidation processes by assuming that the hydrogen peroxide unites with the See also:compound undergoing oxidation to form an addition compound; which subsequently decomposes (J.

H. Kastle and A. S. Loevenhart, Amer. Chun. Jaurn., 1903, 29, pp. 397, 517)• Hydrogen peroxide can also react as a reducing agent, thus See also:

silver oxide is reduced with a rapid evolution of oxygen. The course of this reaction can scarcely be considered as definitely settled; M. See also:Berthelot considers that a higher oxide of silver is formed, whilst A. See also:Baeyer and V.. Villiger are of opinion that reduced silver is obtained [see Comptes rendus, 1901, 133, p. 555; Ann.

Chim. Phys., 1897 (7), I I, p. 217, and Ber., 19o1, 34, p• 2769]. Potassium' permanganate, in the presence of dilute sulphuric acid, is rapidly reduced by hydrogen peroxide, oxygen being given off, 2KMn04-1-3H,SO4+5IJ2O2 = K2SO4+2MnSO4+8H20+502. See also:

Lead peroxide is reduced to the monoxide. Hypochlorous acid and its salts, together with the corresponding See also:bromine and See also:iodine compounds, liberate oxygen violently from hydrogen peroxide, giving hydrochloric, hydrobromic and hydriodic acids (S. Tanatar, Ber., 1899, 32,p. 1013). On the constitution of hydrogen peroxide see C. F. See also:Schonbein, Jour. See also:peak. Chem., 1858–1868; M.

Traube, Ber., 1882–1889; J. W. Briihl, See also:

Bert; 1895, 28, p. 2847; 1900, 33, p. 1709; S. Tanatar, Ber., 1903, 36, p. 1893. Hydrogen peroxide finds application as a See also:bleaching agent, as an antiseptic, for the removal of the last traces of See also:chlorine and See also:sulphur dioxide employed in bleaching, and for various quantitative separations in See also:analytical See also:chemistry. (P. Jannasch, Ber., 1893, 26, p.2908). It may be estimated by titration with potassium permanganate in acid solution; with potassium ferricyanide, in alkaline solution, 2K,Fe(CN)s+2KOFI+H202 2K4Pe(CN)6+2H20+02;orbyoxidizing arsenious acid in alkaline solution, with the peroxide and back titration of the excess of arsenious acid with See also:standard iodine (B. Grtitzner, See also:Arch. der Pharm., 1899, 237, p.

705). It may be recognized by the See also:

violet coloration it gives when added to a very dilute solution of potassium bichromate in the presence of hydrochloric acid ; by the See also:orange-red See also:colour it gives with a solution ' of See also:titanium dioxide in concentrated sulphuric acid; and by the precipitate. of Prussian blue formed when it is added to a. solution containing ferric chloride and potassium ferricyanide. Ozonic Acid, H204. By the action of See also:ozone on a 4o% •solution of potassium hydroxide, placed in a freezing mixture, an orange-See also:brown substance is obtained, probably K204, which A. Baeyer and V. Villiger (Ber., 1902, 35, p. 3038) think is derived from ozonic acid, produced according to the reaction 03+1120 = H2O4.

End of Article: HYDROGEN [symbol H, atomic weight x-oo8 (0=16)]

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