226 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



due in part to a change in the size of the ionic spheres, but that another factor 

 also comes into play. 



It was found that the maxima in conductivity correspond to the maxima 

 in fluidity of the mixed solvents. These maxima in fluidity are probably due, 

 as has been shown, to an increase in the size of the molecules of the solvent. 

 From the work of Jones and Murray this can not be caused by an increased 

 association of the molecules of the several solvents, since the action of each 

 solvent on the other is to diminish its association. This increase in size of the 

 molecular aggregates of the solvents must be due to the combination of one 

 solvent with the other, forming a molecular complex. This would diminish 

 the viscosity, or increase the fluidity, and, consequently, increase the velocity 

 with which the ions would move through the solvent. This factor must also 

 be taken into account in explaining the conductivity maxima observed in a 

 number of these investigations. 



A reason is suggested to account for the fact that different solvents show 

 different relative dissociating powers in the case of binary and ternary electro- 

 lytes. Weakly dissociated solvents are probably capable of breaking down 

 ternary electrolytes into only two ions; while strongly dissociating solvents 

 can break these molecules down into three ions. This would also explain 

 why ternary electrolytes, showing greater conductivity in water than binary 

 electrolytes, often show much smaller conductivity in the alcohols and in 

 acetone than binary electrolytes. 



The temperature coefficients of conductivity are a maximum in the 25 and 

 50 per cent mixtures of the organic solvents with water. These are about 

 the mixtures in which the solvents show least association the molecules 

 would be in the simplest condition and therefore most favorable for chemical 

 action. The solvents probably combine with the dissolved substance to the 

 greatest extent in such mixtures,, and the effect of rise in temperature, breaking 

 down these complexes, would therefore be a maximum. 



The conductivity of solutions of potassium sulphocyanate in substances 

 like acetone is much greater than in water. This was proved to be due to 

 the greater fluidity of the acetone. Potassium sulphocyanate dissolved in 

 water lowers the viscosity of water, i. e., the solution has a smaller viscosity 

 than water itself. On examining the literature it was found that salts of potas- 

 sium, rubidium, and caesium are practically the only known electrolytes which 

 lower the viscosity of water when dissolved in it. Certain salts of potassium, 

 however, do not lower the viscosity of water, just as might be expected, since 

 viscosity is an additive property of both the ions present in the solution. The 

 anions tend to increase the viscosity of the solution, while certain cations, viz. 

 potassium, rubidium, and caesium, have a tendency to diminish the viscosity 

 of a solution. If the effect of the negative ion more than overcomes that of 

 the positive ion, potassium, rubidium, and caesium, then the solution is 



