IN MIXTURES OF ACETONE AND WATER. 



115 



For the same salt the coefficients of conductivity, while nearly equal, 

 are somewhat smaller than those of fluidity. As Davis and Jones have 

 pointed out, this is due to "the decrease in association of the solvent 

 with rise in temperature, causing a decrease in the ionization of the 

 solute, and therefore a smaller conductivity." 



In most cases the molecular conductivities of N/800 and N/1600 are 

 practically the same, showing that the dissociation has apparently 

 become nearly constant. If the conductivity depends only upon the 

 velocity of the ions and the number of ions present, then, in the case 

 of a non-hydrated electrolyte, since velocity is proportional to fluidity, 



fj. x in solvent <p of solvent 



in water 



of water 



100 



90 



80 







70 



o 



s. 



50 



40 



200 



10 



7 



100 



90 



.1? 80 



-a 

 g 



70 



60 



50 



40 



"75 62.5 50 37.5 25 12.5 

 Percentage acetone. 



FIG. 50. Conductivity of rubidium 

 chloride in acetone-water at 25. 



_ 

 1600 



75 62.5 50 37.5 25 12.5 

 Percentage acetone. 



FIG. 51. Conductivity of rubidium 

 nitrate in acetone-water at 25. 



This would indicate a value of /*<* = 102 for rubidium bromide at 25 

 in "50 per cent" acetone. The molecular conductivity becomes con- 

 stant at about 80. This indicates either that the equilibrium between 

 ions and molecules becomes constant at a = 80/102 = 78 per cent 

 (where a is the percentage dissociation) ; or that the dissociation is 

 complete at the N/800 dilution, and the molecular conductivity is 

 decreased by a decreasing velocity of the ions. The first alternative 

 seems improbable. The second may seem unlikely in view of the fact 

 that at high concentrations rubidium salts are not appreciably solvated. 

 This, however, is not evidence that there is no solvation at great dilu- 

 tion. And this would seem to be the most probable explanation of the 

 low constant value for z. 



