234 



CHEMICAL MANUEES. 



to see if they still contain an important proportion of ammonia. 

 If the test shows that the liquor is exhausted it is run into the 

 boiler B, placed at a slightly lower level alongside the boiler A. 

 With this end in view the boiler A communicates on the opposite 

 side with the boiler B by a pipe d (Fig. 41), which is naturally at 

 a level high enough not to be reached by the fire. It suf&ces to 

 open the taps e, f, i, and A-. Milk of lime is added in the boiler B 

 to the water from A. The boiler A is recharged, and the taps i and 

 h being closed, the contents of the two boilers are brought to the 

 boil, whilst the same process goes on as already described in the 

 boiler A ; pure ammonia gas is formed in the boiler B as the result 

 of the decomposition by the caustic lime of the chloride and sulphate 

 of ammonia still contained in the water which had been treated in 

 A. This gas also passes into the vat C ; when a test at the test-tap 



Fig. 40.— Naked Fire Ammonia Still. 



shows that all the ammonia is volatilized, it is presumed that the 

 water in the boiler B is exhausted and is run off. For that purpose 

 the pipe d is fitted with two short pieces m and I closed with 

 wooden plugs. To run off the liquid all that has to be done is to 

 open them as well as the tap A'. Ammonia can also be distilled in 

 a single boiler, taking care to mix the milk of lime with the gas 

 liquor beforehand. As the residual liquid would then contain 

 not only chloride and sulphate of lime, but also carbonate of lime 

 and various other salts, and as the mass of these insoluble salts 

 would greatly hinder distillation, it is better to use two boilers, 

 besides the sides of the boilers would become encrusted with lime 

 salts and rapidly put it out of use. When the sulphuric acid in the 

 vat C is saturated with ammonia it forms a fairly concentrated 

 solution of sulphate of ammonia. In the first phases of the opera- 

 tion this acid is greatlv diluted bv the steam mixed with the vapour 



