GALLIC ACID, the acidum gallicum of pharmacy, was dis covered by K. W. Scheele. It occurs in sumach, dividivi, Chinese tea, pomegranate, root-bark and gall-nuts, being present in the last of these to the extent of 3%. A paste of powdered gall-nuts and water is allowed to remain exposed to air for several weeks at 20-25° C, the mould on the surface of the material being removed from time to time. The tannins present are slowly decomposed by the moulds (Penicillium glaucum and Aspergillus niger), and a more rapid and quantitative hydrolysis is effected by the use of a pure culture of Aspergillus gallomyces. Finally the paste is boiled with water, and the hot, filtered solution, on cooling, yields crude gallic acid, which is purified by recrystallization from boiling water. The acid is soluble in 10o parts of cold and three parts of boiling water from which it crystallizes in silky needles or prisms containing water (I mol. of crystallization; it loses this water at 120° C and melts at C. When heated to higher temperatures it loses carbon dioxide and yields pyrogallol or pyro gallic acid, the well known photographic developer. It is inodorous but has an astringent and acidic taste. With ferric salts it gives a deep blue colour, and with ferrous salts, on exposure to air it furnishes blue-black f errosof erric gallate. (See INK.) Gallic acid has the formula and is 3.4.5. trihydroxybenzoic acid. It is used in the manufacture of several colouring matters, anthragallol, anthracene brown, gallocyanine, galloflavin, gallamin blue. Methyl gallate (m.p. 202° C) is em ployed in the production of prune. (See DYES, SYNTHETIC.) Basic bismuth gallate, obtained from gallic acid and bismuth nitrate in presence of potassium nitrate and acetic acid, is a crystalline yellow powder, used as an inodorous antiseptic under the name dermatol in substitution for iodoform.
(G. T. M.)