Page:International Library of Technology, Volume 93.djvu/112

 about .45, air being taken as unity. It yields from about 650 to 725 British thermal units per cubic foot. The well-known pungent odor of coal gas is due mainly to the olefiant gas, composed of what are known as the heavy hydrocarbons.

WATER GAS

63. Composition. — Water gas is a mixture of hydrogen and carbon monoxide. It is made commercially by the contact of steam with incandescent carbon in the form of anthracite or coke. The steam is decomposed, the hydrogen being separated from the oxygen. The oxygen takes up carbon from the coal or coke and forms carbon monoxide, along with a small amount of carbon dioxide. The resultant gases from the contact of steam with incandescent carbon are then mainly hydrogen and carbon monoxide, chemically separate but mechanically mixed together. This is what is called blue, or uncarbureted, water gas. It burns with a flame that gives little light, and is consequently useless for lighting purposes except in incandescent lamps of the Welsbach type. In actual practice, this water gas is always enriched with oil gas, which furnishes the hydrocarbons necessary to make a luminous flame. In many of the older forms of apparatus, the oil gas was made separately, but it is now commonly produced in the same machine as that in which the water gas is made.

64. Analysis. — The following is a volumetric analysis of a sample of purified water gas:

Constituents of Gas Per Cent. Hydrocarbon vapors 1.2 Carbon dioxide 3.0 Heavy hydrocarbons 12.6 Oxygen .4 Carbon monoxide 28.0 Hydrogen 31.4 Methane 20.2 Nitrogen 3.2 Total 100.0