Coal Tar
tar produced in the destructive distillation of bituminous coal. It is a thick, sticky, dark-colored substance, and is used in the manufacture of printers' ink, for asphalt pavements, coating ships, etc. The composition of coal tar varies according to the temperature at which the coal is distilled, the higher the temperature the larger being the yield of solid bodies. Coal tar when distilled first gives off gas, then water containing ammoniacal salts salts, then a brown light oil which, when purified, is called coal-naphtha; at higher temperatures a yellow, heavy, fœtid oil called dead-oil, or creosote oil, then naphthalene; afterward the black residue in the retort solidifies on cooling and forms pitch, which is used to form asphalt, and a black varnish to protect iron from rust.
If the distillation is continued, the pitch yields a yellow substance like butter, containing anthracene, phenanthrene, fluorene; afterward, at red heat, a bright orange powder, consisting chiefly of pyrene C16H10 and chrysene C18H12; the residue forms a hard, porous coke. Coal tar colors are dyes prepared from aniline, naphthalene, phenol, and other compounds contained in coal tar. See DYE- ING.
COAL TAR COLORS. See DYEING.