Hydrogen
A gaseous element, colorless, combustible, and the lightest of ed with a pneumatic trough. The gun-barrel ponderable bodies, its specific gravity being must now be heated to redness, and the water only .06935. It is a constituent part (about in the retort brought into a state of brisk 12 per cent. by weight, and 67 per cent. by ebullition, when the vapor will be decomposvolume) of water. According to Dumas, "it ed, the oxygen being absorbed by the iron, is a gaseous metal, as mercury is a liquid met- and the hydrogen escaping into the gas real." It forms an ingredient in all bodies that ceiver. The gas evolved may be purified, if possess the power of burning with flame; it desired, by passing it through alcohol, &c. burns with a pale blue flame, and, in combi- (See No. 4042.) nation with carbon, constitutes the illuminat- 4047. Tests For Hydrogen. Hydroing gas in general use. In contact with spongy platinum it inflames spontaneously; and, from its extreme lightness, is the best means employed for inflating balloons. It is one of the most useful elements in the material world. Hydrogen forms, with other bodies, a class of acids called hydrogen acids or hydracids. (See No. 3853.)