This section is from the book "A Practical Treatise On Friction, Lubrication, Fats And Oils", by Emil F. Dieterichs. Also available from Amazon: A practical treatise on friction, lubrication, fats and oils.
Tar oils are obtained from tar, being the result of the destructive distillation of wood and bituminous coal.
Wood is distilled in iron retorts and in covered heaps or pits to obtain thereby the resulting charcoal. The lighter products of the distillation are wood alcohol, naphtha and pyrolignic acid, the latter being used in the manufacture of acetic acid and other acetate products. The tar obtained by the destructive distillation of wood is re-distilled and wood-tar oil is obtained, from which picric acid is made by treatment of the oil with nitric acid. The oil is also used in the manufacture of leather oils, medicinal soaps and ointments. Creosote, another product obtained by the distillation of wood-tar, is in its chemical composition very different from the carbolic acid, often misnamed creosote, obtained by the distillation of tar from the destructive distillation of bituminous coal at the gas-works.
By the distillation of tar from the gas-works we obtain benzol and coal-tar oil. This benzol is a product of far different chemical composition than the benzine obtained from petroleum, although often confounded with it. Benzol, when treated with nitric acid, is converted into nitro-benzol (or myrbane oil), which has a strong odor, like oil of bitter almonds. This oil is much used in perfumery and for scenting soaps and greases, for lubricating, and for deblooming petroleum oils.
When acted upon with nascent hydrogen this nitro-benzol or myrbane oil is converted into aniline oil, from which the many beautiful aniline colors are made by the use of powerful oxidizing agents. Coal-tar oil, too, contains large amounts of aniline oil, which is separated from it by agitation with strong mineral acids, which combine with the aniline oils.
Coal-tar is also used in the manufacture of coal-tar paints for painting roofs, smokestacks and iron structures. The product left in the still is the well known asphaltum, extensively used in roofing and for paving purposes.