18 SULPHATE OF SODA-AMMONIA. 



5. SULPHATE OF SODA AND AMMONIA.* 

 NaO, S0 3 ; NH 4 O, S0 3 + 4HO. 



To determine the amount of soda, a weighed portion 

 of the salt dried at 50 is gradually and carefully 

 heated to redness in a platinum crucible, a fragment 

 of carbonate of ammonia being held in the latter, at 

 the end of the operation, to complete the removal of 

 the excess of sulphuric acid. From the weight of sul- 

 phate of soda obtained, that of the soda is calculated. 



The sulphuric acid is determined in another weighed 

 portion of the salt, which is dissolved in warm water 

 and precipitated by chloride of barium. From the 

 weight of the sulphate of baryta, after filtering, wash- 

 ing and igniting, the amount of sulphuric acid is cal- 

 culated. 



The quantity of the ammonia may be estimated ac- 

 cording to two different methods. 



a. The weighed salt is dissolved in the smallest pos- 

 sible quantity of water, and the soluion mixed with 

 excess of an alcoholic solution of bichloride of platinum, 

 which precipitates the ammonia in the form of ammo- 

 mo-chloride of platinum. When the precipitate is 

 completely separated, it is filtered off', washed with 

 alcohol, dried, and carefully ignited (see No. 1). From 

 the weight of the residual platinum, that of the ammo- 

 nia is calculated. 100 parts of platinum correspond 

 to 26.37 of ammonia. In order to ascertain that the 

 platinum does not contain any sulphate of soda or 

 chloride of sodium which may have been precipitated 

 by the alcohol, it is washed with water and again 

 weighed. 



* To prepare this salt, .two equal portions of dilute sulphuric 

 acid are taken, the one neutralized with carbonate of soda, then 

 mixed with the other, ammonia added to neutralization, and the 

 solution evaporated to the crystallizing point. 



