(ii.) Phenols. The extraction of the phenolic constituents of the tar or its distillates is complicated by the fact that resinous and asphaltic substances accompany the phenols in solution in the al kali. These impurities, however, can be eliminated by agitation of the alkaline solution with organic solvents or by saturation with salt. The crude phenols (10-20% of the tar) obtained on acidification as a black oil, can be further purified by extraction with light petroleum, followed by precipitation of the residue from an ethereal solution by fresh petroleum. The petroleum ex tract consists of low-boiling phenols including phenol itself, the cresols and 1 : 2 :4-, 1 :3:5-, 1:3:4-, and 1 :4 : 2- xylenols. Cate chol, fl-naphthol and trimethylphenols have also been identified. The higher phenols of the tar are amorphous solids varying in colour from pale yellow to black.
(iii.) Bases. The crude bases, representing 2-3% of the tar, are also composed of a low mobile fraction and a higher viscous frac tion containing solid, amorphous substances of unknown con stitution. The lower bases consist of pyridine and quinoline with their mono-, di- and tri- methyl derivatives. Only traces of pri
mary bases are present in the tar. There have been identified pyridine, 2-methylpyridine, 2 :4-dimethylpyridine, 2 :4 : 6-trimethyl pyridine, aniline, quinoline and 2-methylquinoline. Stable sul phur compounds are present in all fractions of the tar and are only destroyed by treatment with granular sodium at high temperatures.
Utilization of Low-Temperature Tar Products.—The commer cial possibilities of low-temperature tar have not yet been fully developed, but its application in various directions has been demonstrated. The low-boiling distillates, owing to their "un saturated" nature, form satisfactory fuel possessing certain anti detonating qualities. It has been claimed that the higher frac tions of the neutral oils form an exceptionally good lubricant, whilst the "middle" or "dead" oils are suitable for combustion in the Diesel engine. Special characteristics are also claimed for low-temperature tar pitch, which can be used along with or in place of high-temperature tar pitch.