Coal-tar or gas-tar is a thick black viscous liquid produced by the destructive distillation of coal for the manufacture of illuminating gas, consisting principally of oily hydrocarbons. It passes over with the gas into the condensers along with ammonia liquor, but being heavier than the latter, it is easily separated from it when the whole is allowed to stand. It was formerly of comparatively little use; but ince the 19th century a great number of valuable products have been derived from it by distillation, such as ammonia, naphtha, creasote, carbolic acid, and benzene, while it is also the source of the whole series of aniline colours, and other dyes, of alizarine, salicylic acid, etc. Research Coal-tar
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