Coal Gas

Illuminating gas is made by heating bituminous coal in clay or iron retorts, at a cherry-red heat, and it is purified by pa ing through condensers, in which it deposits coal tar, thence through scrubbers, in which a shower of water absorbs the ammoniacal compounds produced, and finally through purifiers, charged with slaked lime, which removes the sulphur compounds and carbon dioxide. Ferric hydroxide is also used in place of the slaked lime, for economy, but it is not so efficacious with either impurity. 5 to 10 per cent of cannel coal is generally added to the charge to enrich the gas. One ton of coal yields ab. 10,000 cu. ft. of gas, 10 to 15 gals. of coal tar and the equivalent of 22 lbs. ammonium sulphate. The best gas has an illuminosity of 20 to 30 candle power. It consists of a mixture of 50 per cent hydrogen, 25 per cent marsh gas, 10 per cent carbon monoxide, 8 per cent olefiant gas and the balance higher hydrocarbons and impurities, varying very much, depending upon the coal used and the temperature of distillation. See WATER GAS.