210 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



coefficients of fluidity of the pure solvents, which are a minimum in the 75 

 per cent mixture. The methyl alcohol, being much more associated than the 

 pure acetone, a small mass of it would cause a proportionally greater decrease 

 in the association of the acetone, and in about the 75 per cent mixture we 

 should expect to find the condition for molecular combination of these two 

 solvents most favorable. The complex molecule thus formed explains the 

 fluidity maximum, in terms of the view of viscosity and fluidity maxima and 

 minima that we have already suggested. Since the fluidity of the solvent 

 has become much greater, the ionic velocity is increased. 



Thus we conclude that the maximum in conductivity is dependent upon two 

 factors : The cliange in the size of ionic spheres and the change in the fluidity 

 of the solvent. 



Reference to the work of J. J. Thompson, 1 Briihl, 2 Nernst, 3 Ciamician, 4 

 Dutoit and Aston, 5 Ramsay and Shields, 8 Crompton, 7 and Donnan, 8 shows that 

 the prevailing idea concerning the action of dissociating solvents upon dis- 

 solved electrolytes is that the dissociating action of the solvent is mainly a 

 function of the dielectric constant and the degree of association of the solvent. 

 We wish, however, to call attention again to the fact that the dissociating 

 action of the solvent is also dependent largely upon the nature of the dis- 

 solved electrolyte. We have already seen that the conductivity of copper 

 chloride in water is much greater than the corresponding conductivity of 

 potassium sulphocyanate in water. Now if the dissociating action of all 

 solvents were solely a function of the properties of the solvent, we should 

 expect the conductivity of copper chloride in any other solvent to be greater 

 than the corresponding conductivity of potassium sulphocyanate in that 

 solvent. But such is not the case, since we find that in methyl alcohol, for 

 example, the conditions are exactly the reverse of what they are in water, 

 and, further, that potassium sulphocyanate has a much greater conductivity 

 in methyl alcohol than copper chloride has under the same conditions. 



A number of other similar cases have been mentioned in the "General 

 summary of facts established" in this section. These facts show conclusively 

 that the nature of the dissolved salt also plays a large part in determining 

 what the dissociating action of any given solvent will be. The prob- 

 able explanation of the marked difference in the action of dissociating sol- 

 vents towards binary and ternary electrolytes is, in the case of water and 

 methyl alcohol for example, as follows: Water, being a highly associated 

 solvent, has the power of breaking down the ternary electrolytes into the 

 simplest ions, each molecule of the ternary electrolyte yielding three ions. 



'Phil. Mag., 36, 320 (1893). 6 Compt. rend., 125, 240 (1897). 



2 Ztschr. phys. Chem., 13, 531 (1894). 6 Ztschr. phys. Chem., 12, 433 (1893). 



3 Ibid., 18, 514 (1895); 27, 319 (1898); 30, 7 Journ. Chem. Soc., 71, 925. 



1 (1899). 8 Phil. Mag., (6) 15, 305. 



4 Ibid., 6, 403 (1890). 



