KAHLENBERG — THEORY OF ELECTROLYTIC DISSOCIATION. 317 



Copper sulphate is also undissociated in 5 per cent, solutions 

 or over (Table 11). When the molecular weight observed 

 equals 163.0, which corresponds to no dissociation, the conduc- 

 tivity indicates about 22 per cent, dissociation. In the most 

 dilute solution tested, the molecular weight found, 115.6, corre- 

 sponds to 38 per cent, dissociation; the conductivity indicates 

 about 32 per cent. 



From the foregoing it is evident that with the exception of 

 a few instances (and these at certain special concentrations) 

 the agreement between the value of the degree of dissociation, 

 as calculated from the freezing-point of the solutions, and that 

 deduced from their conductivity, must in general be pro- 

 nounced poor, even in the case of the most dilute solutions 

 tested ; while in the somewhat stronger solutions there is no 

 agreement at all, many of the cryoscopic determinations show- 

 ing no dissociation, whereas the conductivity indicates quite 

 appreciable dissociation. 



Arrhenius 1 in his original table presents figures from cryo- 

 scopic data indicating no dissociation for MgS0 4 , FeS0 4 , 

 CuS0 4 , ZnS0 4 , and CdS0 4 , whereas the electrical conductivity 

 (he used the results obtained at room temperatures) showed 

 considerable dissociation, which agrees substantially with, the 

 results above recorded for the stronger solutions. Cadmium 

 iodide, as Arrhenius shows, exhibits a similar behavior. Ar- 

 rhenius seeks to explain away the discrepancy in the case of 

 the sulphates mentioned by assuming that the inactive or un- 

 dissociated molecules in the solutions are polymerized; and 

 he seeks to base this assumption on the fact that Hittorf 2 

 found the migration numbers of MgS0 4 and ZnS0 4 to show 

 a considerable variation with the concentration, which was also 

 found to be true — though much more markedly — in the case of 

 Cdl 2 , for which Hittorf assumed double molecules in the so- 

 lution in order to explain the phenomena lie observed. The lat- 

 ter also clearly states that he applies the same explanation 

 to the other salts of the magnesia series, for their migration 



i \. c. 



*Pogg. Ann. 106, 547 (1859). 



