TAR

'Tar' is a viscous black liquid derived from the destructive distillation of organic matter. Most tar is produced from coal as a byproduct of coke production, but it can also be produced from petroleum, peat or wood.

Contents

Types of tar

General

Coal tar

Wood tar

Uses

See also

Sources

Types of tar

General

The word "tar" is used to describe several distinct substances. Naturally occurring "tar pits" (e.g. the La Brea Tar Pits in Los Angeles) actually contain asphalt, not tar, and are more accurately known as ''asphalt pits''. Tar sand deposits contain various mixtures of sand (or rock) with bitumen or heavy crude oil rather than tar, as does the Tar Tunnel in Shropshire. "Rangoon tar", also known as "Burmese Oil" or "Burmese Naphtha", is actually petroleum. "Tar" and "pitch (resin)" are sometimes used interchangeably; however, pitch is considered more solid while tar is more liquid.

Coal tar

In English and French, "tar" is a substance primarily derived from coal. It was formerly one of the products of a gasworks. Tar made from coal or petroleum, is considered toxic and carcinogenic because of its high benzene contents, however coal tar in low concentrations is used as a topical medicine. Coal and petroleum tar has pungent odor.

Wood tar

In Northern Europe, the word "tar" refers primarily to a substance derived from wood, which is used even as an additive in the flavoring of candy and other foods. Wood tar is microbicidial and has a pleasant odor.
'Production of wood tar'
The heating (dry distilling) of pine wood causes tar and pitch to drip away from the wood and leave behind charcoal. Birchbark is used to make particularly fine tar (''tökötti'').
The by-products of wood tar are turpentine and charcoal. When deciduous tree woods are subjected to destructive distillation the by-products are methanol (wood alcohol) and charcoal.

Uses

Tar is used in treatment of the skin-disease psoriasis, where coal tar is the most effective. Tar is also a general disinfectant. Petroleum tar was also used in ancient Egyptian mummification circa 1000 BC.
Tar was a vital component of the first sealed, or "tarmac", roads. It was also used as seal for roofing shingles and to seal the hulls of ships and boats. For millennia wood tar was used to waterproof sails and boats, but today sails made from inherently waterproof synthetic substances have negated the need for tar. Wood tar is still used to seal traditional wooden boats and the roofs of historical shingle-roofed churches, as well painting exterior walls of log buildings.
In Finland wood tar was once considered a panacea reputed to heal "even those cut in twain through their midriff". A Finnish proverb states that ''if sauna, vodka and tar won't help, the disease is fatal''. The use of wood tar in traditional Finnish medicine is because of its microbicidial properties.
Wood tar is also available diluted as tar water, which has numerous uses:

★ Flavoring for candies (e.g. Terva Leijona) and alcohol (Terva Viina)

★ As a spice for food, like meat

★ Scent for saunas. Tar water is mixed on water that is turned to steam to the air

★ Anti-dandruff agent in shampoo

★ As a component of cosmetics
Mixing tar with linseed oil varnish produces tar paint. It has a translucent brownish hue, and can be used as saturating and toning the wood and protecting it from weather. The tar paint can also be toned with various pigments, producing translucent colours and preserving the wood texture. Because of its paint-like properties, wet tar should not be touched with bare skin, as it can dry to produce a permanent stain, though paint thinner has been known to remove it.
Tar has number 1999 in the United Nations list of Dangerous goods.

See also

★ Bitumen

★ Coal tar

★ Pine tar

★ Pitch (resin)

★ Pitch drop experiment

★ Tarring and feathering

Sources

★ Geotimes - February 2005 - Mummy tar in ancient Egypt

★ [1] - details history and uses of "Rangoon Tar".