HYDROGEN (Gr., °producing waters in reference to the fact that in burnin7 in air or oxygen hydrogen forms water-vapor) a gaseous element, discovered by Paracelsus in the 16th century. In the year 1766, Cavendish, an Eng lish chemist, investigated this gas more thor oughly, and gave it the name of inflammable air, and, by continued investigations, in 1781 proved its elementary character. Lavoisier, finally, gave it the name of hydrogen. Hydro gen is the lightest known substance, and it also has the smallest known atomic weight. Its chemical symbol is H, its molecular formula Hi, and its atomic weight 1.008.
Physical Colorless, tasteless, odorless.
Specific gravity, 0.06949 (air =1).
1 liter at 0° C., 760 mm., 0.089873 g.
1 cubic foot at 32° F., 29.92-inch pres sure, .00561 pounds.
Atomic volume of liquid, 1.4.
Specific heat at 0° C. (gas), 3.410. Specific heat of liquid, 6.00.
Atomic heat, 3.44 (gas) ; 6.05 (liquid). Valence, I.
Thermal conductivity at C. (Ag =1), .000327.
Freezing (and melting) point, — C. Boiling point, — 252.5 C.
Density of liquid hydrogen, 0.070 (lightest liquid known).
Solubility in water, 2.1 volumes of hydro gen to 100 volumes of water.
Obeys Boyle's Law under pressure, with variations according to Van der Wall's equation.
(a — 0.00042) (b— 0.00088).
Coefficient of expansion at constant sure (760 mm.. 0— 100° C.), 0.003661. Coefficient of pressure, at constant volume (520-694 mm., 0-100° C.), 0.0036626.
Chemical Properties.
1. Hydrogen is inflammable. In admixture with oxygen in the presence of moisture and dust and under the influence of sunlight com bustion takes place slowly. With the aid of catalysts, however, e.g., finely divided Pt, Pd, Ir, Os or Au, the reaction between hydrogen and oxygen is rapid. The ignition tempera tures of mixtures of hydrogen and oxygen vary between and 540° C. (electrolytic hydrogen 536° C.) Hydrogen is not poisonous nor toxic.
2. Hydrogen combines directly with fluor ine, even in the dark at room temperature, with explosive violence. With chlorine, it does not combine in dark at room temperature, but does when heated above 400° C. In diffused light combination is slow at room temperature. Under influence of direct sunlight (or other active rays) combination is violent. Combines directly with bromine in dark at 'temperatures above C. and slowly even at 100° in the presence of light.
3. Hydrogen- is very active chemically when occluded in certain finely divided metals, such as Pd or Pt or Os; and also when in contact with finely divided Ni, Co, Fe and Cu. In the presence of nickel many organic compounds can be reduced or saturated by hydrogen (hydro genation of oils.
How Hydrogen may be ob tained by : (1) Decomposition of Water by Metals.—
The alkali and alkaline earth metals react with water and liberate hydrogen; e.g., sodium, potassium or calcium.
Na, plus 2H,0°.'2NaOH plus Fine aluminum turnings (containing 1 — 2 per cent bichloride of mercury and 0.5 per cent potassium cyanide) will decompose water at 70° ; 1 kg. yielding 1,300 liters of hydrogen. (Fr. P. 392,725, 1908. Compt. rend. 1908, 147, 3).
By Metallic Hydrides.— °Hydrolith" is calcium hydride. This reacts very rapidly with water, evolving hydrogen.
CaH, plus 211.0= Ca (OH), plus 2H,. Consult French patent 327,878, 1902. 1 kg yields over I cu. m. of hydrogen.
(2) Decomposition of Acids by Metals.— When dilute sulphuric or muriatic acid is treated with an actd-soluble metal like Zn or Fe, hydrogen is formed, H,SO4 plus Fe = FeSO, plus H2.
This is the usual laboratory method for gen erating hydrogen gas.
(3) Decomposition of Alkali Solutions by Metals.—Aluminum and zinc react with aqueous solutions of the alkalis, liberating hydrogen.
Zn plus 2NaOH =Na:ZnO, plus H.
Very pure hydrogen is obtained in this way. Consult British patent 11,838, 1912.
(4) Electrolysis of Water.— This method which is of great commercial importance will be dealt with later.
Commercial Methods of Manufacture.— (1) Electrolysis of Aqueous .Solution.— When an electric current is passed through water containing an acid or alkali in solution, the water is decomposed, hydrogen gas being liberated at the cathode and oxygen at the anode.
Full description of methods, apparatus and production is given under the heading of OXYGEN. By this method hydrogen is obtained in the largest volume, purest state and at the lowest cost. This method was originally in troduced into this country by a firm of French jewelers, and the manufacture of apparatus for this purpose was initiated and perfected by the International Oxygen Company. The industry has, however, grown so rapidly that there are at the present time several firms manufacturing apparatus of this kind. Consult 'Oxygen - By Electrolysis of Water.> (2) Decomposition of Water by Means of When steam is passed over iron heated to redness, the steam is decomposed, 3Fe plus 4H.0 = Fe.O. plus 4H,.
The iron oxide can be reduced by means of water gas, yielding metallic iron and more hydrogen. The production of hydrogen may be made continuous by alternately passing steam and waters through the furnaces containing the iron.' Consult British patents 10,356, 1903; 17,591, 1909; 11,878, 1910.
For data regarding the physical condition of iron most desirable for this process, consult British patent, 27,735, 1912 usdiaohe co. French " 453,077, 1913 J "