NITEOGENOUS MANUEES. 



235 



of ammonia, but as the acid heats considerably, the steam traverses 

 it without combining with it. The solution of sulphate of ammonia 

 is not, however, concentrated enough to crystallize on cooling, that 

 is why it is evaporated in flat becks of lead, iron, or wood heated by 

 ■s, closed coil. This operation must be done with care. Under the 

 action of heat the organic matter contained in the solution exercises 

 a reducing action on the sulphate of ammonia ; ammonium sulphite' 

 hyposulphite and sulphide of ammonium are formed, two substances 

 which strongly attack the metal of the apparatus ; as, moreover, this 

 reduction gives rise to a great loss of ammonia in the form of am'- 

 monium sulphide which is very volatile, the workman ought to 

 moderate the heating as soon as he perceives the smell (of rotten 

 eggs) of this latter product. Evolution of (NH^)oS or H.,S infringes 

 the alkali act. When the solution is sufficiently concentrated it 

 is run into iron tanks, where the ammonium sulphate is deposited 

 as it cools. The mother liquor which flows from the crystals 

 still contains an important proportion of ammonia. Sulphuric 

 acid is added to it and it is again distilled ; finally it also can 

 be evaporated and recrystallized. The mother liquor from this 



D 



Fig. 41. — Details of Pipe commuuicatiiig with the two Stills of Fio-. 40. 



second evaporation contains too many impurities again to yield sul- 

 phate of ammonia by crystallization. However, it still contains a 

 notable proportion of ammonia in different bodies derived therefrom, 

 that is why it is run into the boiler B to extract the ammonia by 

 distillation after adding milk of lime. 



Mallet's Still. — This still is shown in Figs. 42 (front view) and 

 43 (longitudinal section of one of the batteries). It consists of two 

 batteries of stills AB, BB, CC, DD, which work parallel and impart 

 to it, as will be seen further on, great capacity of production. The 

 stills A and B are fitted with a perforated double bottom, in which 

 the ammoniacal liquor, to which milk of lime has been added, is 

 brought to the boil. They are fitted with an agitator to keep the 

 liquor in motion, to prevent it from adhering to the bottom. The 

 ammoniacal vapours given oft' from these stills pass into the stills 

 C and D, likewise filled with ammoniacal liquor, where they are 

 washed to deprive them of their elements more volatile than 

 ammonia. From the still D they pass into a coil 25 m. (82 ft.) long, 

 the spirals of which are contained in the receiver F, where they are 



