i88 



Conductivity of Aqueous Solutions. Part VI. 



Table 69. Hydrolysis of ammonium acetate and ionization-constant of 



water at 156. 



An examination of the values of Kw given in the last column of table 69 

 shows that those derived from the experiments where acetic acid was 

 added agree closely with one another not only in case of the successive 

 additions of the acid but also at the two different concentrations of the 

 salt; while those from the experiments where ammonium hydroxide was 

 added are far less concordant whether considered with respect to the suc- 

 cessive additions (in the second series) or to the different salt-concentra- 

 tions. This fact, taken in conjunction with the experience that the base 

 solutions are far more liable to contamination, justifies the adoption of the 

 value 223 X 10~ 14 derived from the experiments with the acid as the best 

 final value for the ionization-constant of water at 156. It is worthy of 

 note, however, that the mean value 229 X 10~ 14 derived from the experi- 

 ments with the base is less than 3 per cent higher than this. 



Table 70. Ionization of zvater at vari- 

 ous temperatures. 



Finally it is of much interest to compare the values of the ionization- 

 constants of water and the concentration of hydrogen or hydroxide ions in 

 it at 18, 100, and 156. At 18 the constant has been derived from the 

 conductivity measurements of Kohlrausch and Heydweiller with the 

 purest water obtainable, and this value has been roughly confirmed in 

 a variety of other ways.* This we have included with our values at 100 



*See Nernst, Theoretische Chemie, 4 te Auflage, p. 503 (1903). 



