Tar is any of a group of thick, oily, dark brown or black liquids. Most tars are by-products of the conversion of such organic matter as coal, petroleum, or wood into useful industrial products.
Coal tar
is condensed from vapors given off during the manufacture of coke from soft coal (see Coke ). A type of coal tar called high-temperature coke-oven tar is the most important industrial tar. This tar is used as a raw material for such products as disinfectants, dyes, perfumes, plastics, roofing and water-proofing materials, and synthetic drugs. See Coal tar .
Coal gasifier tar
is a by-product of certain manufacturing processes that convert coal into a high-energy gas. This gas can be used as a substitute for natural gas. Coal gasifier tar is a source of organic chemicals.
Petroleum tar
is generally a by-product of processes that convert heavier parts of crude oil into gasoline and other fuels. Chemical processes used to prepare ethylene (an organic gas) are another source of petroleum tar. This tar is used to produce asphalt, coke, and pitch.
Wood tar
is a by-product of the destructive distillation of wood in the production of charcoal (see Distillation (Destructive distillation) ). The tar is condensed from vapors given off during the process. It is an important source of acetic acid, methyl alcohol, pine oil, and turpentine.
