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,
Coal breaker 19th century and early 20th century led to the use of mechanical devices for separating impurities from coal in coal breakers. Screens and sorters were used for dry coal. Some examples from the beginning of the 20th century are: To handle wet coal, coal jigs were used. Coal jigs separated coal from impurities by using gravity. Since the relative density of uniformly sized pieces of coal, slate, ash, dirt, and sulphur vary, pieces of each element will descend through water at different speeds—allowing them to be separated. Some examples of coal jigs from the beginning of the 20th century include: