ANTHRACENE (from anthrax, or an thrac-, "coal"), a hydrocarbon having the chem ical formula CI4H., and the molecular structure It is obtained by the distillation of coal-tar, oc curring in that portion of the distillate which passes over at temperatures above 500° F. The "anthracene oil," as this part of the crude dis tillate is called, is allowed to stand in the cold for a week or so, until the greater part of the anthracene has crystallized out. The solidified portion when freed from the mother-liquor by pressure or by a centrifugal separator is ground up and washed with petroleum spirit to remove as much as practicable of the paraffin and other impurities. Anthracene so obtained is then sub limed and placed on the market as a50 per cent anthracene," although it may contain as much as 65 per cent of the pure substance. Its precise strength is best determined by treating a known weight with boiling glacial acetic acid and chromium trioxide, and observing the quantity of anthra-quinone that is formed. The crude
anthracene of commerce may be further purified by distillation with caustic potash to which a little caustic lime has been added. Most of the impurities are removed in this way, and the product is further improved by subsequent washing with petroleum spirit, or with carbon disulphide, and finally by recrystallization from a hot mixture of benzene and aniline. Pure anthracene crystallizes in white, monoclinic tab lets melting at 415° F., and boiling at about 680°. It is insoluble in water and dissolves but slightly in other common solvents. It is sol uble, however, in boiling glacial acetic acid, and also in hot benzene. It is used in large quanti ties for the manufacture of alizarin (q.v.) Anthracene is changed, by the action of sun light, into an isomeric substance known as para anthracene (or paranthracene), which melts at F., and is reconverted into anthracene by fusion. See also CQAL-TAR COLORS.