Section 86. Ionization of Water. 



233 



calculated directly by the first method or from the weighted mean value 

 of the percentage hydrolysis (100 h) for the salt in the mixture. The 

 mean value calculated from the latter is, however, to be considered the 

 most accurate. It will be seen that this agrees well in all cases with the 

 value given in the last column, which was calculated directly by the 

 second method from the conductance of the salt in pure water. To get 

 the best final value from each group of experiments we have combined 

 these two by assigning to the former a weight of 100 and to the latter 

 a weight equal to the percentage hydrolysis. Table 92 contains the 

 final hydrolysis values so obtained, the ionization values for the salt, the 

 ionization-constant of water calculated from them by the equation 

 Kw = K A KBh 2 /y 2 , and the square root of the constant, which represents 

 the concentration Cb. of the hydrogen (or hydroxide) ion in pure water. 



Table 92. Ionization of zvater at 218 and 306 . 



A comparison of these values of the ionization-constant with those 

 presented in Part VI by Noyes and Kato (48 at 100 and 223 at 156) 

 shows that the constant is considerably greater at 218 than at the lower 

 temperatures, but that it has become much less at 306. From a plot 

 of the values it appears probable that the maximum lies between 250 

 and 275. 



