FLUIDITY. 



Ill 



Now let us consider lithium nitrate. In mixtures of acetone with the 

 alcohols, we get a pronounced maximum in conductivity in the 75 per cent 

 mixtures, at high dilutions. Since these solvents gave no such maximum 

 in the case of potassium iodide, the maximum must be connected with the 

 lithium nitrate itself. There are two possible explanations of the phenome- 

 non: (1) Increase in dissociation in the 75 per cent mixture; (2) increase in 

 the mobility of the ions, due to the diminution in the size of the ionic spheres. 

 We shall attempt to decide between these two possibilities. 



We have shown by consideration of the fluidities that the liquids are not 

 more associated in the mixtures than in the pure solvents; hence, if we 

 accept the hypothesis of Dutoit and Aston, that dissociating power increases 

 with the association of the solvent, the maximum can not be due to increase 

 in dissociation in the mixture. For example, calcium nitrate shows a pro- 

 nounced maximum in conductivity in mixtures of alcohol and acetone, even 

 though the dissociation of calcium nitrate in pure acetone is very small. 

 It hardly seems probable that the acetone increases the dissociation of pure 

 alcohol if it does not form complexes with it. We also have the fact, found 

 by Jones and Carroll, that even in the case of alcohol and water, where 

 molecular aggregations are known to be formed, there is not an increase in 

 dissociation larger than the possible experimental error. Furthermore, if 

 the 75 per cent mixture has the highest dissociating power, we should not 

 expect to find the maximum moving from the 25 per cent mixture to beyond 

 the 75 per cent mixture, as the concentration of the dissolved substance 

 decreases. This is the case with lithium nitrate, in mixtures of the alcohols 

 and acetone. Finally, the maximum in conductivity should manifest itself 

 in the most concentrated solutions of potassium iodide, in mixtures of ace- 

 tone with the alcohols. This is contrary to the facts. We, therefore, accept, 

 tentatively, the view that the maximum in conductivity is due, primarily, to a 

 change in the dimensions of the ionic spheres. 



The determination, however, of the dissociation of lithium nitrate in 

 pure alcohol, in pure acetone, and in a 75 per cent mixture of these solvents, 

 would be a very important check. Through the kindness of Mr. L. McMaster 

 this point has been tested for acetone and ethyl alcohol, as shown in 

 table 65. 



TABLE 65. Conductivity of lithium nitrate 



corrected), 



