When an aqueous solution of uranyl nitrate (20 grams) and hydroxylamine hydrochloride (10 grams) is treated with 100 c.c. of 7 per cent, ammonia solution, the ammonium diuranate first formed redissolves, and a canary yellow crystalline powder of composition (NH3OH)2UO4.2NH3 is obtained on allowing to crystallise. This compound is stable at ordinary temperatures, begins to lose ammonia when heated above 70° C., and if heated cautiously to 120° C. yields uranic acid, H2UO4. If allowed to remain in contact with cold water for some hours, or if treated with hot water, it yields hydroxylamine uranate, (NH3OH)2UO4.H2O. The latter is also formed when the ammonio compound is heated at 100° C. with glycerol, or treated with acetic acid (2 molecules), excess being avoided; or when freshly precipitated alkali diuranates are acted upon by hydroxylamine hydrochloride.
Hydroxylamine uranate forms well-defined yellowish-green crystals, which, when slowly heated at 125° C., lose water and ammonia and leave a residue of uranic acid containing, according to Kohlschiitter and Vogdt, nitrogen and nitrous oxide in solution, these gases escaping when the residue is dissolved in dilute acids. Friedheim, however, suggests that the residue consists of uranic acid and what may be considered as an anhydride of the uranate, UO2(NH3O)2O, which on treating with acid yields ammonia, nitrogen, and nitrous oxide. The uranate readily reduces Fehling's solution. |