465. ALKANNA.—ALKANET. The root of Alkan'na tincto'ria Tausch. Habitat: Grecian Archipelago and Southern Europe. Fusiform, about 100 mm. (4 in.) long, from the thickness of a quill to that of the little finger, often crowned with soft, white, hairy root-stocks; the bark is of a dark-purple color, friable; and separates easily in thin, papery layers from the yellowish, twisted ligneous column; the wood is composed of distinct, slender woodfibers cohering together and cleft by purple, friable, medullary rays; in the commercial samples, however, it is generally more or less decayed, loose, and spongy. Odorless and tasteless. Alkanna is employed exclusively for coloring oils, ointments, and plasters, which is accomplished by suspending it, tied up in a rag, into the melted fat. Its coloring principle has been termed alkannin; it is a red, resin-like substance, soluble in alcohol, ether, and fats, but insoluble in water.
Preparation of Alkannin.—Obtained by evaporation of ethereal tincture, or precipitating a weak alkaline aqueous solution of alkanet by an acid.