DISCUSSION OF EVIDENCE. 



151 



substance and a part of the solvent present. In a word, combination 

 of solvent with dissolved substance solvation seems to be a more or 

 less general phenomenon. The original hydrate theory thus becomes 

 the solvate theory of solution. 



TEMPERATURE COEFFICIENTS OF CONDUCTIVITY AND HYDRATION. 



A fairly elaborate investigation on the conductivities, dissociation, 

 and temperature coefficients of conductivity and dissociation of aque- 

 ous solutions was begun in my laboratory about 15 years ago and is 

 still in progress. The work, as a whole, has been recently published 

 by the Carnegie Institution of Washington. 1 The monograph in 

 question contains the investigations of Clover, 2 Hosford, 3 Howard, 4 

 Jacobson, 5 Kreider, 6 Shaeffer, 7 Smith, 8 Springer, 9 West, 10 Wight, 11 

 Wightman, 12 and Winston. 13 The results published in this monograph 

 are for about 110 salts, which were studied from zero to 65, and from 

 the most concentrated solution that could be used to the dilution 

 in most cases of complete dissociation. The temperature coefficients 

 of conductivity were calculated both in conductivity units and in 

 percentage. 



Similar data were obtained for about 90 of the more common organic 

 acids, and the constants for the weaker acids were calculated from the 

 Ostwald dilution law. The dissociations of the salts and acids at the 

 different temperatures were, whenever possible, also calculated. 



The temperature coefficients of conductivity were calculated both 

 in percentage and in conductivity units. A study of the temperature 

 coefficients of conductivity, expressed in conductivity units, brought 

 out a relation which had a very direct bearing on the question of 

 hydration in aqueous solution. This is so important that it will be 

 discussed here in some detail. 



The conductivity of a solution is conditioned by the number of ions 

 present and the velocities with which they move. Rise in temperature 

 not only does not increase the number of ions present, but, as is well- 

 known, diminishes dissociation. The effect of rise in temperature 

 increasing the conductivity of solutions is, then, due to an increase in 

 the velocities with which the ions move. If the ion is driven by a 

 constant force, its velocity would be determined chiefly by the viscosity 

 of the solvent and by the mass and size of the ion. With rise in 

 temperature the driving force would be increased. Rise in tempera- 

 ture w r ould also decrease the viscosity of the solvent. The effect of 



Carnegie Inst. Wash. Pub. No. 170. 



2 Amer. Chem. Journ., 43, 187 (1910). 



3 Ibid., 46, 240 (1911). 



*Ibid., 48, 500 (1912). 



*Ibid., 40, 355 (1908). 



6 Ibid., 45, 282 (1911). 



Ubid., 49, 207 (1913). 



*Ibid., 50, 1 (1913). 



9 Ibid.,48, 411 (1912). 



l Ibid., 44, 508 (1910). 



ll lbid., 42, 520 (1909); 44, 159 (1910). 



I2 lbid., 46, 56 (1911); 48, 320 (1912). 



K Ibid., 46, 368 (1911). 



