60 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



the viscosity of the mixture is much greater than would be expected 

 from the law of averages. This is best shown graphically by plotting the 

 viscosities as ordinates and the percentage composition of the mixtures as 

 abscissae. The viscosity curve is seen to pass through a maximum. The 

 fluidity of a liquid is the reciprocal of its viscosity. If, therefore, we show 

 graphically the variations in fluidity as the variations in viscosity were shown, 

 the fluidity curve is seen to pass through a minimum. In all cases, of course, 

 the fluidity is less than a proper average. 



The mixtures in which the minimum of conductivity is found to occur are 

 approximately the mixtures in which this minimum of fluidity appears. The 

 explanation of the conductivity minimum which we offer, to supplement that 

 suggested by Jones and Lindsay, is the following : 



The minimum in conductivity is caused primarily by the great decrease of 

 fluidity resulting when the two components of the solvent mixture are brought 

 together. 



From the results of Pagliani and Battelli l and of Traube l we have cal- 

 culated the various fluidities of mixtures of methyl and ethyl alcohols and 

 water, for the temperatures 0, 10, 20, and 30, and have plotted the 

 fluidity curves (figs. 13 and 14) in the manner indicated. 



A consideration of these curves makes it evident that, for mixtures of water 

 and methyl alcohol at 0, the minimum of fluidity occurs in a mixture con- 

 taining 31 per cent methyl alcohol by weight (37 per cent by volume) ; at 

 20 the minimum occurs in a 40 per cent mixture (46 per cent by volume). 

 Further, the drop in fluidity is more pronounced the lower the temperature. 



For mixtures of ethyl alcohol and water, at 0, the minimum occurs in a 

 34 per cent (40 per cent by volume) mixture. At 30 it is found in a 50 per 

 cent (56 per cent by volume) mixture. The minimum is also more pro- 

 nounced at the lower temperature. 



It should be noted that the change in fluidity is very small over a con- 

 siderable range particularly in the case of mixtures of ethyl alcohol and 

 water. At 30 the change of fluidity between 30 per cent and 60 per cent is 

 very slight. 



We have here, then, a satisfactory explanation of the minimum. The two 

 minima, conductivity and fluidity, are parallel throughout. 



The parallelism may be summed up as follows : 



(1) The conductivity minimum is found to be accompanied by a minimum 

 in fluidity. 



(2) Both minima are more pronounced at lower temperatures, and both 

 occur at approximately the same points. 



(3) The effect of increase in temperature is the same upon both minima 



1 Loc. cit. 



