30 



JOUEISTAL OF THE MiTCHELL SoCIETY 



\_July 



59.5 40.0 



Total cc, ammonia added. 



•Fig. I. 



40.5 



The proportion in which the citric acid and ammonia solu- 

 tions must he mixed to give a solution exactly neutral may be 



found by a graphic method. 

 In Fig. 1 the number of 

 cc. of ammonia added is 

 abscissa and the number 

 of cc. of acid required to 

 neutralize the excess of 

 ammonia in 50 cc. of the 

 chloroform layer is ordi- 

 nate. By extrapolating it 

 is seen that 39.7 cc. of 

 ammonia solution would 

 just neutralize the amount 

 of the citric acid solution 

 employed. 'No trace of 

 free ammonia was found 

 in any of the solutions to 

 which 39.5 cc. or less of the ammonia solution had been added. 

 When as much as 40.0 cc. had been added, the free ammonia 

 could be detected by odor and these solutions showed increasing 

 amounts of ammonia in the titrations. The solution containing 

 39.8 cc. of ammonia contained very little free ammonia, for 50 

 cc. of the chloroform extract required only 0.22 cc. of the acid. It 

 will be seen that this method will indicate the proportions in 

 which the solutions of ammonia and citric acid must be mixed 

 with at least the accuracy which is possible in the ordinary com- 

 parison of an acid and base by buret readings. 



II. Temperature Method. — The second method here present- 

 ed for the preparation of a neutral solution of ammonium 

 citrate, like the conductivity method, is a physical method. Tt 

 was suggested by the fact that, during the addition of the first 

 35 cc. of ammonia to the citric acid in the former method, so 

 much heat was developed that the solution had to be cooled at 

 least twice during the mixing. After the neutral point is reach- 

 ed, there is no appreciable heat effect due to further additions 

 of ammonia. 



