150 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



that the change in the value of the constant is greater for the weaker 

 electrolyte. 



The ionization constant for water itself is a function of the tem- 

 perature. At ordinary temperature the constant has been variously 

 determined, the values at 18 lying between 0.68 and 0.80, the lower 

 value being probably the more nearly correct. 



In the following table are given values of the ionization constant of 

 water at various temperatures up to 306 . 10 



TABLE LIII. 

 IONIZATION CONSTANT OF WATER AT DIFFERENT TEMPERATURES. 



18 25 100 156 218 306 



K W X 10 14 ... 0.089 0.46 0.82 48. 223. 461. 168. 



The ionization constant of water thus increases very rapidly at lower 

 temperatures and passes through a maximum not far from 218. The 

 large value of the ionization constant of water and the relatively low 

 values of the ionization constants of the acids and bases at higher tem- 

 peratures lead to a relatively large hydrolysis of the salts of anything 

 but the strongest acids and bases, and it is not improbable that even 

 salts of the strong acids and bases ultimately suffer hydrolysis at low 

 concentrations at the highest temperatures. 



The increase in the ionization constant of the weak acids between 

 and 40 may be related to the molecular changes which water under- 

 goes within this temperature interval. Within this interval the density 

 and specific heat of water are abnormal and within this temperature 

 interval, also, the viscosity effects in solution, as well as the viscosity 

 effects under pressure, exhibit abnormal relations, as has already been 

 pointed out. An adequate explanation of these various phenomena, how- 

 ever, appears not to exist. 



The ionization of different electrolytes in water at temperatures from 

 18 to 306 are given in Table LIV at concentrations of 0.01 and 0.08 

 normal. An examination of this table shows that the ionization of all 

 electrolytes decreases markedly with the temperature, the decrease being 

 the greater the higher the temperature and the higher the concentration. 

 The ionization-temperature curves of different binary electrolytes corre- 

 spond closely with one another, with the exception of the strong acids 

 and silver nitrate. In the case of the last named salt, however, the 

 ionization values at the highest temperatures are subject to large errors, 



10 Noyes, loc. cit., p. 346. 



