ALLOXANTIN, a product obtained by the combination of alloxan and dialuric acid. It forms small hard prisms which be come red on exposure to air containing ammonia, owing to the formation of murexide (ammonium purpurate), The formation of murexide is used as a test for the presence of uric acid, which on evaporation with dilute nitric acid gives alloxantin, when by the addition of ammonia to the residue the purple red colour of murexide becomes apparent. Alloxantin, C8H4N407.3H20, may also be obtained by the action of sulphur etted hydrogen on alloxan, and it probably possesses the con stitution one of the three molecules of water being possibly constitutional. The tetra-methyl derivative, amalic acid, C8(CH3)4N407, has been prepared by oxidizing caffeine (see PURINES) with chlorine water, and forms colourless crystals which are only slightly soluble in hot water.