POTASSIUM AND SODIUM IODIDES. 



57 



by hydrochloric acid, but data are not at hand for comparison. Jones and 

 Lindsay's values for lithium nitrate are available and have been used (table 

 29). From this table, apparently, the dissociation is greater at the higher 

 temperature. But, as we have said, no final conclusions can be drawn from 

 these data, since we can not be certain that limiting conductivity values were 

 reached by Jones and Lindsay. In the case of hydrochloric acid, however, 

 they were reached in at least one instance. Further investigation will be 

 needed to decide this matter. 



It is interesting at this point to see whether the hypothesis of Dutoit and 

 Aston * is quantitatively true for the cases that have been considered. This 

 hypothesis states that the dissociating power of a solvent is dependent upon 

 its association, as determined by the surface-tension method of Ramsay and 

 Shields. 2 If the hypothesis holds quantitatively, it may be formulated thus : 



a 3/ 



= - , where a and a' are the dissociations of the solutions compared, and x 



Ct & 



and x' the association factors of the solvents. The relation may be put 



into the form - = constant. 

 x 



In comparing solutions in different solvents, there should be the same 

 number of gram-molecules of electrolyte dissolved in the same number of 

 gram-molecules of each solvent. Where solutions in water, methyl alcohol, 

 and ethyl alcohol are to be compared, the volumes will have the ratio 18, 40, 

 and 58 approximately. 



A comparison is made on this basis for potassium and sodium iodides in 

 water and methyl and ethyl alcohols (table 34). For the ethyl alcohol solu- 

 tion the dissociation was calculated from the data of Vollmer. 3 The others 

 were taken from the preceding tables. 



TABLE 34. for potassium and sodium iodides in water and methyl and ethyl 



alcohols at 25. 



Similarly, assuming that Dutoit and Aston's hypothesis holds for 50 per 

 cent methyl alcohol, we may calculate the degree of association. Taking the 



1 Compt. rend., 125, 240 (1897). 



2 Ztschr. phys. Chem., 12, 433 (1893). 



3 Wied. Ann., 62, 328 (1894). 



