In the manufacture of sulphate of ammonia, the gas liquor, containing sulphide, hyposulphite, cyanide, and other compounds of ammonia, is heated first alone and then with slaked lime in an automatic still, and those compounds which are volatile, e.g. sulphide and cyanide, pass over along with the free ammonia through a pipe and bell-shaped exit into a tank containing sulphuric acid. The ammonia is absorbed by the sulphuric acid, leaving sulphuretted hydrogen and hydrocyanic acid free, and it is usual to connect the bell-shaped exit to a purifier, in which the gases are absorbed; if this is done there will be no escape of injurious gases.