101 



A Simple Method of Measlirinc; IIydroiasis. 



George A. Abbott. 



Several nu^hoils of iiieasnrin,!; the degree of hydrolysis of dissolved 

 salts have been proposed from time to time; e. g., the measureineut of the 

 rate at whieh the solution saponifies an ester, such as ethyl acetate ; the 

 rate of hydration of milk sugar; and the measurement of the partial pr^'S- 

 sure of ammonia gas over solutions of its hydrolysed salts ; but none of 

 these methods is precise, and even under the most favorable conditions, 

 they are far from satisfactory. The first is based upon the bold assmup- 

 tion that the rate of saponification is proportional to the concentration of the 

 hydroxyl ions, and that it is unaffeced by the presence of other molecular 

 aggregates; the second method iuAolves a similar assumption; while the 

 last is of little if any ])ractic-al value, owing to experimental difficulties. 



The method al)oiit to be described was developed in the course of an 

 extended research on the dissociation relations of Ortho and Pyro Phos- 

 phoric Acids and their salts, which will be published in detail elsewhere. 

 It is sibiple and convenient, and should be capable of a fairly wide appli- 

 cation to the ammonium salts of other weak acids ; therefore it has seemed 

 sufficiently interesting to justify a brief description at this time. 



When an aqueous solution of ammonia is shaken up with chloroform, 

 the ammonia distributes itself between the two uon-miscible solvents, and 

 the distribution ratio is eonstaut at a given temperature. Fortunately this 

 ratio is of a magnitude which makes it possible to determine the concen- 

 tration of the ammonia in the aqueous solution by simply titrating a meas- 

 ured volume of the chloroform witli which the solution is in equilibrium. 

 It is obvious that we may take advantage of this fact to determine the con- 

 centration of the free ammonia in a solution of its hydrolysed salt, and thus 

 determine the degree of hydrolysis. It is free from assumptions and is as 

 direct as a chemical analysis itself. 



But, simple in principle as the method appears, its successful applica- 

 tion requires attention to certain experimental details. The chief difficulty 

 arises from the fact that the ammoniacal solutions form emulsions with the 

 chloroform layer which remain turbid even after standing several hours in 



