Tar is a dark black liquid with high viscosity. According to its source, tar
is classified into the following three categories:
1. Coal Tar
2. Mineral Tar
3. Wood Tar
This variety of tar is prepared by heating coal in closed iron vessels. The escaping gases are allowed to pass through tubes which are kept cool by circulation of water. Coal tar gets deposited in these tubes. It is usually contained as a bye product during the manufacture of coal gas. Coal tar is used for making macadam roads, preserving timber, etc.
This variety of tar is obtained by distilling bituminous shales. It contains less volatile matter.
This variety of tar is obtained by the distillation of pines and similarother resinous trees. It contains creosote oil and hence, it possesses strong preservative property.