222 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



The conductivities in mixtures of acetone with water show the minimum 

 previously observed in a number of cases. This minimum is closely connected 

 with the minimum in fluidity observed in these mixtures. 



The conductivities of potassium iodide in mixtures of methyl or ethyl 

 alcohol with acetone, obey the rule of averages, and the conductivity curves 

 are nearly straight lines at all the dilutions. In mixtures of acetone with 

 the alcohols the fluidity curve is nearly a straight line. 



One of the most important facts brought out in this investigation, and one 

 that had not been observed in any of our previous work, is that lithium nitrate 

 and calcium nitrate give a very pronounced maximum in conductivity in mix- 

 tures of acetone with methyl alcohol or ethyl alcohol. It was pointed out that 

 this must be due either to an increase in the dissociation, increasing the number 

 of ions present, or to a diminution in the size of the ionic spheres, causing the 

 ions present to move more rapidly. It was shown to be possible to eliminate 

 one of these. 



The fluidities of mixtures of acetone with the alcohols were shown to obey 

 the rule of averages, which would indicate that there is no increase in the mo- 

 lecular aggregation when the alcohols and acetone are mixed. In terms of the 

 well-established hypothesis of Dutoit and Aston, such a mixture would not dis- 

 sociate to a greater extent than the constituent solvents. Further, direct 

 measurements of dissociation at extreme dilutions have failed to show any 

 great difference between the dissociating power of the mixtures and that of 

 the pure solvents. Further, the maximum moves from the 25 per cent 

 mixture at large concentration to the 75 per cent mixture in the more dilute 

 solutions. This would not be expected if the dissociating power is greatest 

 in a certain mixture. 



We have thus eliminated increase in dissociation as being the cause of the 

 maximum and are compelled to accept the other alternative, that the maxi- 

 mum in conductivity is due to a change in the dimensions of the atmospheres 

 about the ions. 



In dealing with conductivity in single solvents and in mixtures of these 

 with one another, we must take into account not only the effect of each con- 

 stituent of the mixture on the association of all the other constituents, and 

 the viscosity of the individual solvent or solvents, but also the sizes of the 

 spheres of the solvents around the ions, and any changes in the sizes of these 

 spheres in different mixtures of the solvents. 



These ionic spheres, or solvates, have been shown by Jones to exist generally 

 in solutions, and the ions must drag these spheres with them in their move- 

 ments under the action of the current. 



Any change in the size of these spheres would produce a change in the effect- 

 ive mass of the ion, and, consequently, a change in the velocity with which 

 it would move. 



