DISCUSSION OF EVIDENCE. 167 



The work already discussed in mixed solvents is all recorded in 

 Publication No. 80 of the Carnegie Institution of Washington. The 

 results of the following five investigations are recorded in Publication 

 No. 180 of the Carnegie Institution of Washington. 



The problem of measuring dissociation in non-aqueous solvents is 

 a difficult one. The freezing-point method is frequently not applicable. 

 Many common solvents, such as the alcohols, freeze at temperatures 

 which are too widely removed from the ordinary temperature of the 

 laboratory to measure with sufficient accuracy. The boiling-point 

 method could be used only with fairly concentrated solutions. Dilute 

 solutions produce such a slight rise in the boiling-point that this small 

 quantity can not be measured with a very high degree of accuracy. 

 The boiling-point method has the further disadvantage of being so 

 largely affected by slight changes in the barometer. 



The hope of measuring conductivity in non-aqueous solvents in 

 general seemed to rest in the conductivity method. This method as 

 ordinarily applied would not be satisfactory. The dilution at which 

 complete dissociation would be reached in such solvents is so great 

 that the Kohlrausch method in any such form as he left it could not 

 be applied to the problem. 



The conductivity method was greatly improved by Kreider; 1 the 

 greatest improvement being in the form of cell employed. With the 

 improved method Kreider studied the dissociations of a number of 

 salts in methyl and ethyl alcohols and in mixtures of these solvents 

 with water. He measured the conductivities of solutions as dilute 

 as 100,000 liters. 



, . ... M methyl alcohol 



He found the following relation: - ,, , ; T r~= constant. 



IJL ethyl alcohol 



When a salt is dissociated in each of two solvents, for the same con- 

 centration of the salt there are the same number of ions in the two 

 solutions. Conductivity is a function of the number of the ions and 

 their velocities. When numbers of the ions are constant, as in this 

 case, conductivity is a function of the relative velocities of the ions. 

 The velocity of an ion is conditioned by its mass and volume and by 

 the fluidity of the solvent. If the masses and volumes of the ions in 

 the two solvents are constant, the velocities of the ions should vary 

 as the fluidities of the solvents. The ratio between the values of IJ. M 

 in the two solvents should be the same as the ratio between the fluidities 

 of these solvents. This was, however, found not to be the case. The 

 bearing of this fact on the condition of the ions in the two solvents in 

 question is important. This shows that the mass and probably the 

 volume of the solvated ion must differ in the two solvents. 



The ratio between the values of ^> for a salt in the two solvents, 

 compared with the ratio between the fluidities of the two solvents, 



'Amer. Chem. Journ., 45, 282 (1911). 



