HIPPURIC (hipferik) ACID, an organic acid, CHINH(GI-LCO)COOH, existing in the urine of herbivorous animals, and, in small quantities, in that of human beings. It is in creased by a vegetable diet, and by the disease called diabetes, and may be caused to appear in the human urine in considerable quantities by the administration of benzoic acid with the food. It is most conveniently prepared by boil ing horse urine with milk of lime, filtering, neu tralizing with hydrochloric acid, and evaporat ing to about one eighth of its volume. The con urine is then acidified with hydro chloric acid and allowed to stand, when impure hippuric acid comes down as a yellowish-brown precipitate. To purify the crude product, it is heated to 212° F. with not quite enough water to entirely dissolve it, and chlorine gas is passed through the solution until the unpleasant smell has entirely disappeared. The solution is then filtered while hot, and the crystals which separate upon cooling are isolated and subjected again to the same treatment, the chlorine being passed through the solution, in this second treat ment, until the solution is bright yellow. When
thus prepared, hippuric acid crystallizes from water in the form of large prismatic plates, belonging to the trimetric system. Its crystals are colorless or white, free from odor and have a slightly bitter taste. Hippuric acid has a specific gravity of about 1.308, and melts at 369° F.; it begins to boil at about 465° F., giv ing off benzoic acid and benzonitrile. It is in soluble in benzene, carbon disulphid, and cold chloroform, and is but slightly soluble in ether and in cold water. It is very soluble, however, in boiling water, and in hot alcohol. With bases, hippuric acid forms salts that are remark able for the beauty of their crystalline forms. When boiled with dilute hydrochloric, sulphuric, nitric or oxalic acid, it yields benzoic acid and glycocoll.