204 Conductivity of Aqueous Solutions. Part VII. 



not exist in significant quantity even at 306 is shown, however, by the 

 agreement of the ionization-constants for water derived from the experi- 

 ments with salt solutions of very different concentrations, since in these 

 the percentage of acetamide should vary greatly, owing to its being pro- 

 portional to the product of the ammonium and acetate ion concentrations. 

 It was found very difficult to analyze accurately the ammonium acetate 

 solutions left in the bomb. The ammonium content could be determined 

 within 0.2 per cent by making the solution alkaline with sodium hydroxide 

 and distilling off the ammonia into standard sulphuric acid ; but even this 

 accuracy could not be obtained in determining the acetic acid. The proced- 

 ure was therefore changed so as to make the oxidation as small as possible. 

 After the initial 18 measurement, the bomb was set in water at 60, and 

 was kept evacuated for two or three minutes down to a pressure of a few 

 centimeters ; this caused the solution to boil vigorously, so that nearly all 

 the air was carried out of the bomb. Several determinations of the con- 

 ductance at 18 after this treatment, showed an increase of only 0.2 to 0.3 

 per cent caused by evaporation of water. It is probably safe to assume 

 that in the pure ammonium acetate solutions there was no appreciable loss 

 of ammonia from the salt, because the hydrolysis is less than 3 per cent 

 and the vapor pressure of ammonia therefore practically inappreciable, 

 and also because the observed change in conductivity was so small. In 

 the solutions containing an excess of ammonium hydroxide or acetic acid 

 the loss of these substances that probably occurred by vaporization is not 

 important, since the concentration of the excess of acid or base needs to 

 be known only approximately. The oxidation at 218 was thus reduced 

 to 0.5 per cent or less. This change in concentration can be corrected for 

 accurately enough by assuming that the change of concentration of ammo- 

 nium acetate is proportional to the change of specific conductance at 18. 

 In all the experiments at 306 the same procedure was followed, but the 

 loss by oxidation of the salt could not be kept so low. It was necessary, 

 also, to determine the excess of ammonium hydroxide or acetic acid after 

 each experiment, since the addition of one equivalent of base or acid at 

 306 produces a much greater change in the hydrolysis and conductance 

 than at 218. The only practicable method found was to empty and dry 

 the bomb, replace in it a weighed quantity of the solution, weigh in enough 

 acetic acid (or ammonium hydroxide) solution to slightly exceed the free 

 ammonium hydroxide (or acid) present, and determine the conductance 

 of this mixture. Since a small excess of acid or base has no appreciable 

 conductance, the total concentration of the ammonium acetate could be 

 calculated from this conductance ; and by subtracting from this the con- 

 centration of salt at the end of the experiment, as given by the final 

 conductance at 18, there was obtained the concentration of free ammo- 



