It is not, however, generally necessary to resort to so elaborate a process merely to distinguish the class to which tannins belong. The tannin, or its infusion, may be simply boiled with dilute hydrochloric acid for some time, replacing the acid lost by evaporation. The solution is diluted to 50 _c.c._ and allowed to cool. Ellagic acid and phlobaphenes may separate, and must be filtered off. If the precipitate is pale, it is probably ellagic acid, and maybe recognised by the nitric acid test. If red, it probably consists of phlobaphenes, and may be treated with cold alcohol, in which phlobaphenes are freely soluble, but ellagic acid very little. The ellagic acid will therefore be left on the filter if present in any quantity, while the alcoholic solution may be precipitated by the addition of water, and the phlobaphenes further examined by treatment with potash. Gallic Acid.--_Dioxysalicylic acid_, C_{6}H_{2}(OH)_{3}CO.OH, exists ready formed in some plants, and is a product of the fermentation of gallotannic acid under the influence of the nitrogenous ferment, pectase, or of its decomposition by boiling with acids or alkalies. It crystallises in white, or yellowish white needles, containing 1 mol. (9·5 per cent.) of water, which it loses at 212° F. (100° C.). It is soluble in 100 parts of cold or 3 of boiling water, in alcohol or glycerin, and slightly so in ether, by agitation with which it may however be removed from its aqueous solution. Gallic acid fuses at a temperature of about 449° F. (232° C.) (Etti, Chem. Soc. Jour., xxxvi. 160), but at about 410° F. (210° C.) begins to lose carbonic dioxide, and yields a crystalline sublimate of pyrogallol (see p. 66). If the heat be raised suddenly to 482° F. (250° C.) a considerable quantity of black shining metagallic acid is formed.