At the end of this time, the solution is cooled to room temperature and 240 g. (6 moles) of solid u.s.p. sodium hydroxide is slowly dissolved in it. When solution is complete, the reaction mixture is again heated on the steam bath under a hood. When the temperature reaches 60–70°, evolution of ammonia begins and becomes more vigorous with rise in temperature. Most of the ammonia is evolved in forty-five minutes, but the solution is heated for at least three hours, and the last traces of ammonia are removed by bubbling steam through the hot solution for forty-five to sixty minutes more.