4 Conductivities and Viscosities in Pure and in Mixed Solvents. 



results, interpreted in the light of the work of Dutoit and Aston, point 

 to a lower degree of association in the case of the mixed solvents than 

 in that of the pure solvents themselves. That this is true was shown 

 by Jones and Murray, who carried out cryoscopic measurements with 

 mixtures of water, formic acid, and acetic acid; and showed that the 

 molecular weights of these substances were always less in solution than 

 the molecular weights of the pure solvents themselves, as determined 

 by the method of Ramsay and Shields. 



Jones and Carroll, in extending this investigation, showed that the 

 change in the viscosity of the medium was an important factor condi- 

 tioning the decrease in the conductivity of salts in such binary mixtures 

 of liquids, the decrease in ionization due to changes in association being 

 only one of the factors to be taken into account. 



However, it remained for Jones and Veazey to offer a satisfactory 

 explanation of the increase in viscosity which occurs when two highly 

 associated liquids are mixed, and also to account for the phenomenon 

 of negative viscosity, or the lowering of the viscosity of the solvent by 

 a dissolved substance. They carried out an extensive investigation in 

 mixtures of the alcohols and of acetone with water, and found that the 

 conductivity minima referred to above were more general than had 

 hitherto been supposed, and that this was very closely related to the 

 fluidity minima observed in these same mixtures. 



The work of Thorpe and Rodger having shown that viscosities depend 

 largely upon the frictional surfaces of the physical particles in any 

 solution, it followed that if these surfaces were increased or diminished 

 by any means whatsoever, there would result a corresponding increase 

 or decrease in the fluidity of the medium. The work of Jones and 

 Murray, as already stated, had brought out the fact that on mixing 

 two highly associated liquids a material diminution in the association 

 of both takes place. This would result in an increase in the number of 

 ultimate particles in a given volume, with a corresponding decrease in 

 their size, and therefore an increase in their frictional surfaces which 

 would be exposed to one another. Consequently, the viscosity curves 

 for the various mixtures should pass through a maximum, the position 

 of which would depend upon the relative effects of the solvents upon 

 one another. 



Quite recently Jones and Davis, studying viscosity, tested the results 

 obtained by Jones and Murray, using the same mixtures which they 

 had employed acetic acid and water, formic acid and water, and formic 

 acid and acetic acid. They obtained results, recorded later in this 

 chapter, which were in perfect accord with the earlier work of Jones 

 and Murray. It was shown that the curve for the viscosity of acetic 

 acid and water passes through a well-defined maximum towards the 

 acetic acid end of the curve, showing the large effect of water on the 

 association of acetic acid; while the curve for formic acid and acetic 



