1913] Solutions of Ammonium Citrate 29 



1. Extraction Method. — Ammonia is soluble to a slight extent 

 in chloroform ; citric acid and ammonium citrate are insoluble 

 in chloroform. This fact affords an accurate method of esti- 

 mating the excess of ammonia in an aqueous solution of these 

 substances. The distribution ratio of ammonia between chloro- 

 form and water has been shown by Bell and Feild^ to be about 

 1 :25 at ordinary temperatures ; that is, between equal volumes 

 of water and chloroform, free ammonia will distribute itself 

 about ^/2« in the chloroform layer and "'/^g in the water layer. 



A citric acid solution containing 370 grams per liter Avas pre- 

 pared. To 100 cc. lots of this solution varying amounts of strong 

 ammonia were added and the resulting solutions diluted to200cc. 

 This addition was made through a narrow tube leading into the 

 acid so as to avoid losses of ammonia by volatilization. Of this 

 solution lOOcc. were shaken out with 125cc. of chloroform and 

 50cc. of this chloroform layer to which about 50cc. of water 

 were added was titrated against 0.1 N hydrochloric acid solution 

 using methyl red as indicator. During this titration all the 

 ammonia passed from the chloroform layer to the water layer as 

 it was neutralized by the acid. In these determinations only 

 a part of the total excess of ammonia is estimated, but knowing 

 what fraction is taken, the total excess of ammonia may be esti- 

 mated. For each gram of free ammonia left in 100 cc. of the 

 water layer after shaking out, there is 0.04 gram in 100 cc. of 

 the chloroform layer or 0.05 gram in 125 cc. of the chloroform 

 layer. Hence, of the total excess of ammonia in the sample V» 

 is in the 125 cc. of chloroform. In 50 cc. there are '/^'^ of the 

 portion, shaken out and as only half of the total is shaken out 

 there is Vio5 of the total excess of ammonia actuallv titrated. 



«</. Am. Chem. Soc, 33, 940 (1911j. 



