tar and pitch
tar and pitch, viscous, dark-brown to black substances obtained by the destructive distillation of coal, wood, petroleum, peat, and certain other organic materials. The heating or partial burning of wood to make charcoal yields tar as a byproduct and is an ancient method for the production of both tar and pitch. Coal tar is a residue in the manufacture of coal gas and coke. By the application of heat, tar is separated into several materials, one of which is pitch. The terms tar and pitch are loosely applied to the many varieties of the two substances, sometimes interchangeably. For example, asphalt, which is naturally occurring pitch, is called mineral tar and mineral pitch. Tar is more or less fluid, depending upon its origin and the temperature to which it is exposed. Pitch tends to be more solid. When ships were made of wood, tar had numerous uses, and an available supply of tar was an important factor in maritime growth. Tar made vessels watertight and protected their ropes from deterioration. All but small quantities of the tar now produced is fractionally distilled to yield naphtha, creosote, carbolic oil, and other equally important crude products. Among the substances produced by refining the various crude materials are benzene, toluene, cresol, and phenol. Tar from pine wood is used in making soap and medicinal preparations. Pitch is used in the manufacture of roofing paper, in varnishes, as a lubricant, and as a binder for coal dust in the making of briquettes used as fuel. Coal-tar derivatives are used in the manufacture of dyes, cosmetics, and synthetic flavoring extracts.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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