ALLOX′ANTIN

C 8 H 4 N 4 O 7 .3H 2 O. A crystallisable substance, first obtained by Dr Prout from uric acid. Prep. 1. Uric acid, 1 part; is boiled in water, 32 parts; dilute nitric acid being added until solution is complete; the resulting liquid is evaporated to 2 ⁄ 3 rds its volume, and then set aside for 10 or 12 hours; the crystals, which are deposited, are purified by re-solution and crystallisation. 2. Sulphuretted hydrogen gas is pa ed, in a full stream, through a moderately strong aqueous solution of alloxan, in the cold. The alloxan tin, which is deposited as a crystalline ma , is purified by draining, cautious washing with cold water, re-solution in boiling water, and re-crystallisation. The impure mother-liquor from which crystals of alloxan have separated, if diluted with water, may be used for this purpose. Prop., . Crystals, small colourle , transparent, four-sided, oblique rhombic prisms; scarcely soluble in cold water; solution reddens litmus; with baryta water it gives a characteristic violet-coloured precipitate, which disappears on heating; and with nitrate of silver a black precipitate of that metal; the crystals are reddened by ammoniacal vapours.