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tar and pitch
a black viscous substance obtained after distilling the fuel and oil fractions from petroleum. The yield of tar from various petroleums is 15–30 percent based on the petroleum. The main components of tar are oil not distilled during the fractionation of petroleum, petroleum resins, solid asphaltic substances (asphaltenes. carbenes, and carboids), and substances of an acidic nature (asphaltogenic acids and their anhydrides). Tar has a density of 0.95–1.0g/cm3 and a viscosity of 18°-45° of conventional viscosity at 100° C.
Tar containing a considerable amount of oil fractions is called semitar; its viscosity is 18°-25° of conventional viscosity and its flash point, 140° C. Tar is also the name for concentrated residues of petroleum oil (petroleum tar) that undergo multistage refining processes to obtain high-quality motor oils. The residues obtained after the sulfuric acid refining of petroleum products are called acid tars.
Tar is used to prepare petroleum bitumens and in road construction. Semitar is used to lubricate coarse mechanisms. Oil tars are used as plasticizers in the rubber industry and in construction. Cracking and destructive hydrogenation can be used to convert very viscous tars into gasoline, diesel fuel, and other substances.
REFERENCESNametkin, S. S. Khimiia nefti [3rd ed.]. Moscow. 1955.
Nefteprodukty: Svoislva, kacheslvo, primennie. Spravochnik. Moscow, 1966.
a liquid product of the dry distillation of solid fuels, such as coal and lignite, shales, wood, and peat. The consistency of tar varies from a readily mobile liquid to a mass that flows with difficulty; it is usually dark brown, but it can be almost black. Tar is a complex mixture of organic compounds; its composition depends on the initial material and the method of treatment. The low-temperature (500°-600°C) dry distillation of coal or peat—that is, semicoking—yields so-called primary tar. The coking of coal yields coal tar. The tar formed by heat treating wood is called wood tar.
(1) A plucked stringed instrument used in the Caucasus. The tar has an overall length of approximately 900–1,000 mm. It has three pairs of melody strings (or three pairs and one single string) and two pairs of drone strings.
(2) In Arab countries, a small tambourine.
coal-tar pitch, tar
The resulting archive, a "tar file" (humourously, "tarball") is often compressed, using gzip or some other form of compression (see tar and feather).
There is a GNU version of tar called gnutar with several improvements over the standard versions.
Filename extension: .tar
MIME type: unregistered, but commonly application/x-tar
Unix manual page: tar(1).
Compare shar, zip.