SULPHATE OF AMMONIA 107 



with caustic soda, and the volatilised ammonia collected 



N 

 in 25 C.C. — sulphuric acid and estimated by back- 



titration in the usual manner. 



As an alternative method^ dispensing with distillation, 



25 C.C. of the solution may be boiled in a conical flask 



N 

 with 50 c.c. of — sodium hydroxide. A small funnel is 



placed in the neck of the flask to prevent loss by 



spirting, and boiling is continued until no more 



ammonia is given off. This may be determined by 



holding a strip of red litmus paper in the issuing steam. 



When the reaction is complete the liquid is cooled 



down and the funnel and neck of the flask are rinsed 



back with distilled water. A drop or two of methyl 



orange is added, and the residual caustic soda is 



. N 



determined by running in — HgSO^ until neutral. 



(NHj2S04 + 2NaOH = Na2S04+2H20 + 2NH3. 



Every 40 grams of NaOH used up during the 

 reaction corresponds to 17 grams of ammonia or 14 

 grams of nitrogen. 



{c) Qualitative Examination. — The sulphate of 

 ammonia solution should meanwhile be examined for 

 the constituents noted above under the Ammoniacal 

 liquor (89 {a), p. 105). If any of these is present in 

 large quantity, which is very unlikely, it should be 

 estimated separately. 



Nitrate of Soda. 



Nitrate of soda is obtained from extensive natural deposits 

 occurring in South America. ' The crude material is known as 

 caliche^ and may contain 20 to 60 per cent, of sodium nitrate. It is 

 purified by recrystallisation, and the finished product contains in 

 the average 96 per cent, sodium nitrate. 



