16 Preparation of Substances 



NOTES 



The time of the student is such an impor- 

 tant factor that considerable more than the 

 required amount of ammonia is recommended 

 for use. This obviates waiting for all the 

 ammonia to be driven off and also saves 

 evaporation of the increased amount of water 

 which would distil over. Of com^se a waste 

 of ammonia results. Industrially such a 

 waste of ammonia would not be allowd. 



If the evaporation procedes beyond a cer- 

 tain point the mass upon cooling will be solid 

 salt. In this case filtering and drying are 

 unnecessary. The danger in using this 

 quicker method of drying lies in the fact that 

 the solution of ammonium sulfate in water 

 upon being heated to dryness passes over into 

 a clear molten anhydrous mass so quickly that 

 the change may not be noticed. Heating this 

 molten anhydrous mass results in the decom- 

 position of the salt as explaind in a previous 

 paragraf. 



In the manufacture of coal gas, by heating 

 soft coal much of the nitrogen present is 

 combined with hydrogen forming ammonia. 

 Some of the oxygen that enters the retorts as 

 they are charged combines with the carbon 

 forming carbon dioxid. This weak acid, 

 carbonic acid, unites with the weak base 



