Coal tar the European Chemicals Agency. The exact mechanism of action is unknown. Coal tar is a complex mixture of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds. It is a keratolytic agent, which reduces the growth rate of skin cells and softens the skin's keratin. Coal tar is produced through thermal destruction (pyrolysis) of coal. Its composition varies with the process and type of coal used – lignite, bituminous or anthracite. Coal tar contains approximately 10,000 chemicals, of which only about 50% have been identified. Components include polycyclic aromatic hydrocarbons (4-rings: chrysene, fluoranthene, pyrene, triphenylene, naphthacene, benzanthracene, 5-rings: picene, benzo[a]pyrene, benzo[e]pyrene,
Pittsburgh coal seam matter (gases expelled when coal is burned), leaving carbon and ash from the coal fused together in the form of coke. They made coke in turf-covered "mounds," in which coal burned slowly and without oxygen to drive off impurities. The adoption of beehive coke ovens in the 1830s spurred the use of Pittsburgh-seam coal in iron furnaces, and these ovens made better-quality coke than mounds. Pittsburgh-seam coal, especially the highest-quality coal found in the Connellsville district, was the best coal in America for making coke. When converted into coke, it was sufficiently strong to withstand the weight of iron ore