Tar is a viscous black liquid made of hydrocarbons that can form in multiple ways. Because of this, the chemical composition of tar varies, though it is always made of organic matter of some sort.
It has many uses as a waterproofing and sealing agent. It is also used for many medicinal purposes.
Classified of Tar
Tat is classified on the basis of its sources.
• Coal Tar
• Mineral Tar
• Wood Tar
A heavy, back, and strong-smelling liquid is known as coal tar. In closed iron vessels, the variety of tar is prepared by heating the coal.
The escaping gases are allowed to pass through the tube, which is kept cool by the circulation of water. The coal tax gets deposited in these tubes.
It is usually derived as a byproduct during the manufacture of coal gas. The coal tar is used for making macadam roads, preserving timber, etc.
Distillation of bituminous shales gives us mineral tar. It contains less matter.
Distillation of pipes and resinous wood gives wood tar. In contains, creosote oil which can be obtained by further distillation of wood and hence is possessed stronger preservation property.
However, the wood creosote is not so good as coal tar creosote for the preservation of timber.
Use of Tar
For coating of sleepers, wooden poles, latrine walls, etc.
Bitumen Vs. Tar
||Bitumen Colour Dark with slight reddish time
||And Tar colour Deep dark
||Bitumen carbon content is midium (moderate)
||Tar Bitumen carbon content is very high
||Bitumen usually solid in state.
||Tar viscous liquid sate
||Bitumen effect on heating time bitumen is melt
||Here, Tar effect on heating becomes more fluid when heated.
||Bitumen setting time very less respect to tar
||Tar setting time is more compared to bitumen
||Bitumen adhesive power is high but not more than tar
||Tar adhesive power is very high compared to bitumen
||Bitumen resistance to acid effect is more compared to tar
||Tar resistance to acid effect is less compared to bitumen
||Bitumen is obtained from fractional distillation of crude oil
||Tar is obtained by destructive distillation of coal or wood
||Molecular weight range for road bitumen is 400 to 5000
||Molecular weight range for road tar is 150 to 3000
||Bitumen consists of large amount of aromatic hydrocarbon
||Tar consist of large amount of oily matter with lower molecular weight
||It shows more resistance to weathering action
||It shows less resistance to weathering
||Bitumen normally use as damp proof course and as roofing felt.
||Tar use for preseving timber.
||Less temperature susceptibility
||More temperature susceptibility