8. Tar
Synonyms Chair Tar; Pine Tar; Stockholm Tar.
Biological Source Tar is a bituminous liquid obtained from the wood of various species of the natural order Pinaceae, such as: Pinus longifolia Roxb. [Pinus roxburghii Sargent. It is also present in Pinus elliotth (Engelm.) belonging to family Abietaceae (Slash Pine).
Preparation It is usually obtained by the destructive distillation of the wood cuttings from the various species of Pinus as stated above.
Characteristic Features It is dark brown or sometimes black viscous liquid, but its very thin layer on a clean glass plate is almost transparent. It possesses a very strong to moderate specific naphthalene-like odour and has a bitter and pungent taste. It is practically insoluble in water, partially soluble in ethanol, whereas completely soluble in ether, chloroform, volatile oils and fixed oils. It has been observed that when tar is stored for a longer duration, it separates into a layer which is granular in nature by virtue of the fact that minute and critical crystallization of resin acids and catechol take place. Tar is found to be acidic in reaction.
Chemical Constituents Tar contains a good number of chemical constituents in various proportions depending upon the particular species of Pinus and its geographic location, such as: hydrocarbons, resin acid, resinous matter, and includes phenols, phenolic ethers, cresols, catechol, methyl cresols, guaiacol, benzene, toluene, xylene and styrene.
Chemical Tests
1. Shake 1g of drug in 20 ml of water and filter:
(a) To a portion of the filtrate dip a blue-litmus paper which turns red showing acidic reaction.
(b) To another portion of the filtrate add 2-3 drops ferric chloride solutions (0.1%) a red colouration is obtained.
Uses
1. It serves as an expectorant when used in the form of a syrup.
2. Pine tar is frequently employed as antipruritic and antibacterial.
3. It is used largely in ointments externally for the treatment of chronic skin diseases and eczema.
Note This ‘Pine Tar’ distinctly differs from the ‘Coal Tar’ in the following aspects, namely:
(a) Coal tar is obtained by the destructive distillation of bituminous coal at a temperature less than 1000°C.
(b) Coal tar mostly contains, benzone, naphthalene, phenols and pyridine.
(c) It is alkaline to litmus paper.
(d) It has more disinfectant and irritating properties to pine tar.
(e) It becomes more viscous on exposure to air.
