HYDANTOIN crystallizes from water in colourless needles, and melts at 208-220° C. It is constitutionally glycolyl urea, or CI-12 the ureide of glycollic acid, CO , and is obtained by \ NH. CO heating allantoin or alloxan with hydriodic acid, by heating bromo acetylurea with alcoholic ammonia or by the action of urea on dihydroxytartaric acid. When hydrolysed with baryta water, hydantoin yields hydantoic (glycoluric) acid, colourless prisms, m.p. 153-156°, which are readily soluble in hot water.