Anthracene (C14 H10), formerly called para-naphthaline, a solid hydrocarbon which accompanies naphthaline in the last stages of the distillation of coal tar, and which has acquired great importance as the material from which artificial alizarine is now manufactured. In an experiment made on a large scale it was found that 100 tons of tar yielded 0.63 ton of anthracene, or one ton of anthracene can be obtained from the distillation of about 2,000 tons of coal, not reckoning the quantity of anthracene contained in the pitch. The preparation of anthracene is conducted as follows: The semi-fluid product of the fractional distillation of coal tar, commonly called green grease, is placed in a centrifugal machine in order to expel mechanically as much as possible of the oil, and the residue is pressed between hot plates. The crude material is carefully distilled, rejecting the portion which comes over between 340° and 350° C, and the portion remaining in the retort is exhausted with rectified petroleum at a boiling heat, filtered, and cooled. The crystalline mass is expressed and the entire operation repeated several times. On recrystallization from alcohol, the nearly pure anthracene is obtained in rhomboidal plates. If these be carefully sublimed, a chemically pure product is obtained.
Pure anthracene occurs in bluish-white foliated crystals, having a beautiful violet fluorescence. These crystals are rhomboidal tables. A little above 200° C. it melts to a limpid liquid, which becomes rapidly dark-colored. It is not perceptibly volatile at 100° 0., but between 210° and 220° C. it sublimes easily, yielding a fetid and irritating vapor. Distilled at 350° C, it is partially altered. It is quite soluble in boiling alcohol, and in light naphthas, from which it crystallizes out on cooling. Heated slightly with fuming sulphuric acid, it dissolves gradually, giving a greenish solution of the sulphanthracene acid. The green color appears to be due to a trace of nitrous compounds of the acid. Nitric acid attacks anthracene violently, and chlorine and bromine act upon it, yielding substitution products. Anthracene has been made artificially from toluole and from benzole. - The chief use of anthracene is in the artificial production of alizarine. Several patents have been taken out for this purpose by Grabe and Liebermann, who were the original discoverers in 1869 of the methods of its manufacture. (See Alizaeine.)