Summary. 



341 



which have roughly the same ionization at 18, are also not far from 

 equally ionized at much higher temperatures. The decrease in percentage 

 ionization per ten degrees ( 10 3 Ay/At) at the concentration 0.08 normal 

 has for the neutral salts the following average values : 



Thus the rate of decrease in ionization is small between 18 and 100 

 for either type of salt ; but it becomes greater at the higher temperatures, 

 especially in the case of the tri-ionic salts ; and for the highest temperature- 

 interval (281 -306) it is extremely rapid for both types of salt. The 

 decrease in ionization of hydrochloric acid, nitric acid up to 156, and 

 sodium hydroxide is about the same as that of the di-ionic salts ; thus the 

 average value of ( 10 3 Ay/A) at 0.08 normal for hydrochloric and 

 nitric acids is 0.38 between 18 and 100, 0.63 between 100 and 156 ; 

 and for hydrochloric acid 0.76 between 156 and 218. Between 156 and 

 306 nitric acid decreases in ionization much more than the other sub- 

 stances of the same type. 



The physical property of the solvent which is most closely related to its 

 ionizing power is, as has been shown by Thomson and by Nernst, its dielec- 

 tric constant. It is therefore of some interest to compare its variation with 

 the temperature with that of the ionization of salts. Unfortunately, the 

 dielectric constant of water has been determined only between and 76. 

 Drude* has, however, derived for this interval a quadratic equation, from 

 which a value at 100 may be calculated, probably without great error. 

 The values of the dielectric constant obtained from this equation are 81.3 

 at 18 and 58.1 at 100, and the ratio of these is 1.40. 



The question now arises, what function of the ionization should be com- 

 pared with this? It seems clear that, from a theoretical standpoint, it is 



simplest to consider the ratio ^f- ^ of the concentrations of un-ion- 



Ci(l Yi) 



ized salt which prevail in solutions that at the two temperatures (t 2 and r x ) 



have the same concentration of the ions (that is, solutions for which 



C 2 y 2 = C x y x ) ; for in such solutions the electric force between the ions, and 



therefore their tendency to unite to form un-ionized molecules, in so far 



as this has an electrical origin, must be inversely proportional to the dielec- 



*Wied. Ann. Phys., 59, 50 (1896). 



