COAL GAS, a mixture of gases pro duced by the destructive distillation of coal at regulated temperatures. It is used in lighting streets, houses, etc., and for cooking and heating purposes. Coal gas is colorless and has a disagreeable smell. It is purified from H2S by ferric hydrate, which is moistened with FeSO. and MO, to remove ammonia. The car bon disulphide can be removed by pass ing it through an iron tube filled with iron turnings and heated to redness. Coal gas consists of a mixture of hydro gen, 40 to 50 per cent., carbon-monoxide about 5 per cent., marsh gas (CH.) about 40 per cent., which contribute nothing to the illuminating power of the gas; it depends upon the presence of heavy hydro-carbons, principally C211. ethene, ordinary gas containing about 4 per cent., and cannel gas about 8 per cent. Coal gas also contains small quan tities of acetylene, butylene, etc., and aromatic hydro-carbons, as benzine, etc. The percentage of nitrogen is very vari able. When gas is burned a large quan tity of water is formed, hence, if a gas stove is used to dry a room there must be sufficient ventilation to carry off the aqueous vapor. The escape of coal gas
from pipes into the soil is very injurious to the roots of trees and shrubs. The admixture of a very small quantity of air greatly impairs the illuminating power of coal gas. Three causes are capable of decreasing the luminosity of flame, viz.: (1) withdrawal of heat; (2) dilution; and (3) oxidation of luminous material. See GAS.
Poisoning by coal gas, is known only as an accident. Occasionally sudden fatal consequences ensue among workmen from exposure to a sudden rush of un diluted gas from gasometers and mains. More commonly, slowly fatal cases result from the gas-tap in a bedroom being left open carelessly, from accidental extinc tion of the light, from blowing the gas out, or from leakage of the pipes in a house, or at a distance, the gas gaining entrance to the house in the latter case through cellars, walls, and more especial ly by means of drains and sewer-pipes.