110 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



If the salt happens to be highly dissociated in water and very little disso- 

 ciated in the other solvent, the curves may be at such an angle with the axis 

 of X that there will be only a sagging of the curve and not an actual minimum. 

 Therefore, the amount of deviation from the normal curve appears to us to be 

 a matter of prime importance, while the finding of a minimum is not. 



If we could make a correction at the different parts of the curve for the 

 different degrees of dissociation in the pure solvents and in the mixtures, we 

 should then have a curve exactly parallel to the fluidity curve, if it is true 

 that fluidity and dissociation are the only factors concerned, as Dutoit and 

 Friderich, and Jones and Carroll supposed. In our case it is almost impos- 

 sible to make the correction with the data at hand, except, possibly, in the 

 case of potassium iodide. The conductivity values for potassium iodide 

 show that it is nearly dissociated in all mixtures, but with the other salts com- 

 plete dissociation is not even approximately reached. Thinking that it 

 might be possible to calculate /too, we have tested Kohlrausch's formula, 



fM 00 fj. v __ T^ 



r l 



U 3 



where C is the concentration and K is a constant. We found that it did not 

 apply except in aqueous solutions. Vollmer 1 has already shown that the 

 Ostwald dilution law does not apply to solutions in ethyl alcohol and methyl 

 alcohol. Solutions of potassium iodide, in mixtures of methyl alcohol and 

 water, were investigated by Zelinsky and Krapiwin and Jones and Lindsay. 

 The conductivity curves resemble the fluidity curves for methyl alcohol and 

 water, as shown by Jones and Carroll. We have found the same similarity 

 in the case of potassium iodide and water. 



If we accept the Kohlrausch and Jones's hypotheses of ionic spheres, it is 

 evident that the atmosphere about the ions remains of the same size through- 

 out all the mixtures ; otherwise the ions would tend to show a maximum in 

 conductivity in those mixtures where the atmosphere is smallest, causing a 

 divergence from the fluidity curves. Difference in dissociation would also 

 cause a divergence between the conductivity and fluidity curves. In the 

 above case, however, the dissociation is large and all the curves are parallel. 



If we pass now to potassium iodide in mixtures of acetone with methyl 

 alcohol and ethyl alcohol, we find, again, that the conductivity curves and 

 fluidity curves are very similar, i. e., nearly straight lines, with a tendency 

 towards a maximum, which is greater in the case of methyl alcohol than in 

 that of ethyl alcohol. Evidently the changes in the size of the ionic spheres 

 and the changes in the dissociation have either counteracted each other or 

 remained zero. 



1 Ann. der Phys., 62, 328 (1894). 



