34& 



Conductivity of Aqueous Solutions. Part XII. 



Table 145. Internal-energy-increase attending the ionization of water and its ioniza- 

 tion- constant calculated by an empirical equation. 



These values of the ionization-constant at 0, 25, and 100 necessarily 

 agree with the directly determined ones given in table 144. It is of inter- 

 est to note, however, that this is also true of the calculated value at 156, 

 which shows that up to this temperature the assumed equations hold true, 

 and that therefore the values interpolated for the intermediate tempera- 

 tures between and 156 are doubtless substantially correct. Even at 

 218 the difference between the observed and calculated values (461 and 

 512), though doubtless real, is not very large; it lies in such a direction 

 as to indicate that the energy-change &U is decreasing at a more rapid 

 rate at temperatures above 156 than at the temperatures below it. 



This is also shown by the fact that the ionization-constant at 306 

 is much less than at 218, while according to the linear equation the value 

 of At/ should become zero, and therefore that of the ionization-constant 

 K should become a maximum, very near the former temperature, namely, 

 at 302. The real maximum value of the constant seems to lie between 

 250 and 275. Above this temperature AU assumes a negative value; 

 and therefore the neutralization of completely ionized acids and bases 

 would be attended by an absorption of heat. 



It may also be mentioned that at the lower temperatures, the calculated 

 values agree well with the heats of neutralization directly measured by 

 W6rmann,f who found for hydrochloric and nitric acids when neutralized 

 with potassium and sodium hydroxides as mean values 14,710 calories 

 at and 13,410 calories at 25. 



It seems worth while to call attention to a possible theoretical explana- 

 tion of the fact that water, unlike all other substances thus far investi- 

 gated, continues to increase in ionization up to so high a temperature as 

 250 to 275. This phenomenon may well arise from the facts that water 



fDrude's Ann. Phys., 18, 793 (1905). 



