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tar




A black or dark brown, odorous liquid obtained by destructive distillation of coal (see coal tar) or wood, especially from conifers. Tar is a complex mixture of hydrocarbon compounds. Tar from petroleum is a major source of hydrocarbons for the synthesis of pharmaceuticals, pesticides, and plastics; cruder tar compounds such as pitch are used for road surfacing and protecting timber against rot and pests. Wood tar yields creosote and paraffin.


Tarmac

Tarmac is a mixture of tar and gravel and is used mainly to cover roads, drives, and paths. It is hard-wearing, impervious to water and provides an ideal surface for the runner tires of motor vehicles.


Tar sands

Porous, often black, rocks such as limestone, sands, and sandstones that contain deposits of bitumen (asphalt) in the spaces between the grains and commonly have a distinct odor of tar. Extensive deposits are found in North America, primarily in Alberta and Texas. Estimates of the amount of bitumen contained in these deposits are extremely high, but its high viscosity makes extraction difficult.


Related category

   • INDUSTRIAL CHEMISTRY