COAL-TAR

The importance of this substance was realized only when Faraday discovered benzene and Perkin isolated the first aniline dye, mauve. When coal is heated beyond its decomposition point without acce of air (destructive distillation), three products are obtained: (a) dried residue, (b) evolved gases, (c) condensed distillate. The last separates into two layers: (1) holds a small portion of the distillate in solution, and consists of water either previously existing in the coal or produced during the destructive distillation; (2) a viscid, dark-colored oil, sometimes heavier, sometimes lighter than (1). This is coal-tar. Its quality and quantity are influenced by the temperature at which the decomposition is carried on. Atlow temperatures the hydro-carbons produced are mostly fatty, at high temperatures aromatic. The quality of the coal and the shape of the gas retorts are other factors which alter the nature of the products, since if the gas retort is so shaped that the gases are kept. in contact with the hot walls much decomposition results. Coal-tar isa complex mixture yielding on distillation benzene, toluene, phenol, creosote, etc. It is employed as a coating for preserving stone, iron, and timber. Mixed with dry lime and clay, it forms asphalt for paving. The coal-tar industry is cla ified as a ‘key industry,’ for dyes, drugs, explosives, are all made from its primary derivatives. town, Leicestershire, England; coal mines., Pop. 19,000.