1913] Solutions of Ammonium Citkate 33 



Both methods here presented are for the determination of the 

 proportion in which ammonia and citric acid must be mixed to 

 arrive at a neutral solution. These proportions vary of course 

 with the strength of the separate solutions. From the proportion 

 found large quantities of neutral ammonia citrate may be pre- 

 pared, after which the solution may be diluted to the required 

 density. 



SUMMARY 



In this paper two methods are proposed for the determination 

 of the end point in the titration of a weak acid by a weak base, 

 where the ordinary indicators fail. In the first method an index 

 of the excess of ammonia is obtained by shaking out with chloro- 

 form and by titrating the chloroform with a dilute acid. In 

 the second method the rise in temperature due to the heat of 

 neutralization is observed as the titration proceeds, the end 

 point being at the break in the heating curve. Both these me- 

 thods are simpler than the method formerly proposed where the 

 conductivities of solutions must be determined at constant tem- 

 perature. 



Chapel Hill, N. C. 



