198 



CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



the temperature coefficients of fluidity themselves are greatest in the 25 per 

 cent mixture. 



Tables 84, 85, and 86 (fig. 99) show that potassium sulphocyanate, in 

 mixtures of ethyl alcohol and water, exhibits a decided minimum in fluidity 

 in the 50 per cent mixture. Here, also, there is the negative viscosity coeffi- 

 cient in the aqueous mixtures, up to a mixture intermediate between the 50 

 per cent and 75 per cent mixtures; from this point on it is positive. The 

 difference in viscosity between the solutions and pure solvent is much greater 

 in the pure ethyl alcohol than it is in pure water; and it will also be noted 

 that the difference between the viscosity of the solution and the pure solvent, 

 in the case of ethyl alcohol, is greater at 25 than at 0. A study of the tem- 

 perature coefficients of fluidity shows that in all the mixtures they are greater 



Curve I, fluidities of mixtures 

 of ethyl alcohol and water at 0. 



Curve II, fluidities of N/10 

 potassium sulphocyajnate in mix- 

 tures of ethyl alcohol and water 

 at 0. 



Curve III, fluidities of the 

 above solvent mixtures at 25. 



Curve IV, fluidities of N/10 

 potassium sulphocyanate in the 

 above solvent mixtures at 25. 



Percentage of Ethyl Alcohol 

 FIG. 99. 



100 



for the pure solvent than they are for the solution. The temperature 

 coefficients of fluidity are greatest in the 50 per cent mixture. 



The temperature coefficients of fluidity decrease with increase in dilution in 

 the per cent, 25 per cent, and 100 per cent mixtures, and increase with 

 increase in dilution in the 50 per cent and 75 per cent mixtures, which are the 

 mixtures in which the maximum fluidity is shown. 



Tables 84, 85,. and 86 (fig. 100) show that potassium sulphocyanate, in 

 mixtures of acetone and water, exhibits a minimum in the fluidity curves 

 in the 50 per cent mixtures at both and 25. Here, again, we have the 

 negative viscosity coefficient in the aqueous solutions and in the 25 per cent 

 mixtures. This negative coefficient becomes zero at some point intermediate 

 between the 25 per cent and the 50 per cent mixtures ; and is positive from 

 that point on throughout the remaining mixtures. We must also call at- 

 tention to the fact that the increase in viscosity with increase in dilution is 



