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From Wikipedia, the free encyclopedia

Tar is modified resin produced primarily from the wood and roots of pine by destructive distillation under pyrolysis. It is a viscous black liquid. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden vessels against rot. The largest user was the Royal Navy. Demand for tar declined with the advent of iron and steel ships.

Tar-like products can also be produced from other forms of organic matter such as peat. Mineral products resembling tar can be produced from fossil hydrocarbons including petroleum. Coal tar is produced from coal as a byproduct of coke production.

Contents

Production

Tar kiln at Trollskogen in Öland, Sweden.

In Northern Europe, the word "tar" refers primarily to a substance that is derived from the wood and roots of pine. In earlier times it was often used as a water repellent coating for boats, ships, and roofs. It is still used as an additive in the flavoring of candy, alcohol and other foods. Wood tar is microbicidal and has a pleasant odor — a sweet musky scent much like that of barbecue. Producing tar from wood was known in ancient Greece, and has probably been used in Scandinavia since the iron age. For centuries, dating back at least to the 14th century, tar was among Sweden's most important exports. Sweden exported 13,000 barrels of tar in 1615 and 227,000 barrels in the peak year of 1863. Production nearly stopped in the early 20th century, when other chemicals replaced tar and wooden ships were replaced by steel ships.

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, known as "Russian oil", suitable for leather protection. The by-products of wood tar are turpentine and charcoal. When deciduous tree woods are subjected to destructive distillation the products are methanol (wood alcohol) and charcoal.

Tar kilns (Swedish: tjärdal, Norwegian: tjæremila, Finnish: tervamiilu) are dry distillation ovens, historically used in Scandinavia for producing tar from wood. They were built close to the forest, from limestone or from more primitive holes in the ground. The bottom is sloped into an outlet hole, to allow the tar to pour out. The wood is split to dimensions of a finger and stacked densely, and finally covered tight with dirt and moss. If oxygen can enter, the wood might catch fire, and the production would be ruined. On top of this, a fire is stacked and lit. After a few hours, the tar starts to pour out, and continues to do so for a few days.

Uses

Tar was 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 as painting exterior walls of log buildings. Tar is also a general disinfectant.

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. Wood tar is used in traditional Finnish medicine because of its microbicidial properties.

Wood tar is also available diluted as tar water, which has numerous uses:

  • As a flavoring for candies (e.g. Terva Leijona) and alcohol (Terva Viina)
  • As a spice for food, like meat
  • As a scent for saunas. Tar water is mixed into water which is turned into steam in the sauna
  • As an anti-dandruff agent in shampoo
  • As a component of cosmetics


Mixing tar with linseed oil varnish produces tar paint. Tar paint has a translucent brownish hue, and can be used to saturate and tone wood and protect it from weather. Tar paint can also be toned with various pigments, producing translucent colours and preserving the wood texture.

Other types of tar

A tar-like substance can be produced from corn stalks by heating in a microwave. This process is known as pyrolysis.
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Term misuse

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

Coal

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

Coal tar is listed at number 1999 in the United Nations list of dangerous goods.

See also

References

Sources


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

TAR, a product of the destructive distillation of organic substances. It is a highly complex material, varying in its composition according to the nature of the body from which it is distilled, - different products, moreover, being obtained according to the temperature at which the process of distillation is carried on. As commercial products there are two principal classes of tar in use - (1) wood tar, the product of the special distillation of several varieties of wood, and (2) coal tar, which is primarily a by-product of the distillation of coal during the manufacture of gas for illuminating purposes.. These tars are intimately related to bitumen, asphalt, mineral pitch and petroleum.

Wood Tar. - Wood tar, known also as Stockholm and as Archangel tar, is principally prepared in the great pine forests of central and northern Russia, Finland and Sweden. The material chiefly employed is the resinous stools and roots of the Scotch fir (Pinus sylvestris) and the Siberian larch (Larix sibirica), with other less common fir-tree roots. A large amount of tar is also prepared from the roots of the swamp pine australis) in North and South Carolina, Georgia and Alabama, in the United States. In the distillation of wood a series of products, including gas, tar, pyroligneous acid, acetone, wood spirit (see Methyl Alcohol) and charcoal may be obtained, and any of these may be the primary object of the operation.

The carbonization of wood can be effected in two ways: (I) by stacking and firing as in the manufacture of charcoal: this method is very wasteful as it is impossible to recover the valuable byproducts; and (2) by distilling from retorts, ovens or kilns (after the manner of coke production from coal): this method is more economical as it leads to the isolation of all the by-products. The retorts may be horizontal or vertical and the heating effected by any available fuel, or by the inflammable gases and less valuable grades of tar obtained in previous operations. The condensing plant is also of variable design; a common pattern consists of a connected series of slightly inclined copper pipes contained in a rectangular tank of water (see Coal Tar). After settling the distillate separates into three layers: the lowest consists chiefly of tar and creosote oils with a little acetic acid; the middle layer consists of water, containing pyroligneous acid, wood spirit, acetone with a little tarry matter; whilst the upper consists of light hydrocarbons. The tarry layer is run off by means of a cock near the base of the tank, and is then distilled from retorts resembling coal tar stills. At first, between 110° and 120° C., water and acetic acid comes over; then, between 120° - 230° C., the heavy or creosote oils; the residue in the still is wood pitch, which finds application in making briquettes, artificial asphalts, certain varnishes, &c. The crude tar and pitch are also largely used as protective coatings for woodwork exposed to atmospheric conditions. The heavy oils on further fractional distillation yield more acetic acid, and then mixtures of carbolic acid, creosols, &c.

Wood tar is a semi-fluid substance, of a dark brown or black colour, with a strong pungent odour and a sharp taste. Owing to the presence of acetic acid, it has an acid reaction; it is soluble in that acid, as well as in alcohol and the fixed and essential oils, &c. Some varieties of tar have a granular appearance, from the presence of minute crystals of pyrocatechin, which dissolve and disappear on heating the substance.

See P Dumesny and J. Noyer, Wood Products, Distillates and Extracts (Engl. trans. 1908).

Medicine

Wood tar is used in medicine under the name of Fix liquida. Its preparation unguentum picis liquidae is composed of wood tar and yellow beeswax. Externally tar is a valuable stimulating dressing in scaly skin diseases, such as psoriasis and chronic eczema. Internally wood tar is a popular remedy as an expectorant in subacute and chronic bronchitis. It is usually given as tar water, part of wood tar being stirred into 4 parts of water and filtered. Given internally tar is likely to upset the digestion; taken in large quantities it causes pain and vomiting and dark urine, symptoms similar to carbolic acid poisoning.

Coal tar is used in medicine as Pix liquida preparata. From it is made Liquor picis carbonis, prepared with tincture of quillaia. Coal tar is rarely prescribed for internal use. Its external use is similar to that of wood tar: the Liquor carbons detergens, a proprietary preparation, owes its properties chiefly to the contained phenol. It is used in water as a lotion for skin diseases, and also in an inhaler in the treatment of whooping-cough, croup and bronchitis.


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Simple English

.]]

Tar is a viscous black liquid. It is made by 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

Term misuse

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

Coal

In English, German and French, "tar" is a substance primarily made from coal. It used to be one of the products of gasworks. Tar made from coal or petroleum is considered toxic. It causes cancer because of its high benzene content. In low concentrations, however, coal tar is used as a topical medicine. Coal and petroleum tar has a pungent odor.

Coal tar is listed at number 1999 in the United Nations list of dangerous goods.

Wood

, Sweden.]] In Northern Europe, the word "tar" refers primarily to a substance that is derived from the wood and roots of pine. In earlier times it was often used as a water repellent coating for boats, ships, and roofs. It is still used as an additive in the flavoring of candy, alcohol and other foods. Wood tar is microbicidal and has a pleasant odor. Producing tar from wood was known in ancient Greece, and has probably been used in Scandinavia since the Iron Age. For centuries, dating back at least to the 14th century, tar was among Sweden's most important exports. Sweden exported 13,000 barrels of tar in 1615 and 227,000 barrels in the peak year of 1863. Production nearly stopped in the early 20th century, when other chemicals replaced tar and wooden ships were replaced by steel ships.

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, known as "Russian oil", suitable for leather protection. The by-products of wood tar are turpentine and charcoal. When deciduous tree woods are subjected to destructive distillation the products are methanol (wood alcohol) and charcoal.

Tar kilns (Swedish: tjärdal, Norwegian: tjæremila) are dry destillation ovens, historically used in Scandinavia for producing tar from wood. They were built close to the forest, from limestone or from more primitve holes in the ground. The bottom is sloped into an outlet hole, to allow the tar to pour out. The wood is split to dimensions of a finger and stacked densely, and finally covered tight with dirt and moss. If oxygen can enter, the wood might catch fire, and the production would be ruined. On top of this, a fire is stacked and lit. After a few hours, the tar starts to pour out, and continues to do so for a few days.

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.[1]

Tar was a vital component of the first sealed, or "tarmac", roads. The streets of Baghdad were the first to be paved with tar from the 8th century AD.[1] 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. Wood tar is used in traditional Finnish medicine because of its microbicidial properties.

Wood tar is also available diluted as tar water, which has numerous uses:

  • As a flavoring for candies (e.g. Terva Leijona) and alcohol (Terva Viina)
  • As a spice for food, like meat
  • As a scent for saunas. Tar water is mixed into water that is turned to steam to the air
  • As an anti-dandruff agent in shampoo
  • As a component of cosmetics

Mixing tar with linseed oil varnish produces tar paint. Tar paint has a translucent brownish hue, and can be used to saturate and tone wood and protect it from weather. Tar paint can also be toned with various pigments, producing translucent colours and preserving the wood texture. Because of its paint-like properties, tar should not be touched with bare hands or feet, as it can dry to produce a permanent stain. However, in any case, paint thinner is used to remove it.

References

  1. Dr. Kasem Ajram (1992). The Miracle of Islam Science (2nd Edition ed.). Knowledge House Publishers. ISBN 0-911119-43-4. 

Sources


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