97. ESTIMATION OF AMMONIA. 



81 



97. Ammonia. 1 A portion of the aqueous extract ( 92) is 

 mixed with two volumes of alcohol and filtered. To the filtrate 

 and washings calcined magnesia is added, and the ammonia 

 distilled off into a receiver containing a measured quantity of 

 normal sulphuric or hydrochloric acid, every precaution being 

 taken to avoid loss of ammonia and spirting of the magnesia 

 mixture into the receiver. The apparatus I use is represented in 

 Fig. 2. The flask A should not be more than half full of magnesia 



mixture, and a plug of glass wool should be inserted in the neck. 

 The small tube e contains glass beads, which are moistened with 

 part of the acid. The distillation is complete when the vapours 

 that issue on opening the clip & are free from alkaline reaction. 

 The estimation may be completed in either of the two following 

 ways : 



(a) The excess of acid in the receiver is determined volumetri- 

 cally and deducted from the quantity taken. From the differ- 



1 Compare also Morgen, Zeitschr. f. anal. Chem. xx. 37 (1881). 



6 



