108 CONDUCTIVITY AND VISCOSITY IN MIXED SOLVENTS. 



where m^ and ra 2 are the amounts of the components, and ^ and < 2 are 

 their respective fluidities. 



This is similar to the conception which we have in electricity, where the 

 conductance of two or more conductors is represented by the sum of their 

 separate conductances. The conductance of a single conductor is expressed 



by the value -^, where c is the specific conductivity, a- the cross-section of 



L 



the conductor, and I the length. The conductance of a pair of conductors of 

 different material, in parallel, is, per unit length, 



fa + <T 2 )C = CjO-j + C 2 (T 2 



Admitting this reasoning, it becomes evident that conductivity and fluidity 

 are strictly comparable. It will be noticed, moreover, that the viscosities are 

 not additive. 



If 77! and 772 represent the viscosities of the two components, then, since vis- 

 cosity is the reciprocal of fluidity, we have from (1) : 



(H+04-+=S 



H 771 772 



By making mi and ra 2 the percentages of the respective components : 



_1_ _m 1 IMI 



H 7/t 772 



Wi = [wiji/2 + (1 - mO^l H 



= KOfe-ifc) + 7i]# (2) 



NOW let W 1 (72-7 1 + 7 1 = W' 1 7 2 -7 1 



then 7/2 t)i 



Substituting this value in (2), 



m\= H - = constant 

 >?2 *7i 



which is the equation of the equilateral hyperbola, the Y-axis of which is the 

 distance ; - to the left of the origin, to which equation (1) is referred. 



Thus, we seem justified in concluding that the hyperbola is the normal curve 

 for viscosities. 



From the above considerations we are led to the belief that inferences 

 drawn from viscosity curves alone may lead to erroneous conclusions. For 

 example, Wijkander 1 reached the conclusion that in no case is the viscosity 

 identical with that calculated by the admixture rule. In the case of mixtures 

 of ether with chloroform, and of ether with carbon disulphide, there were 



1 Beibl. Wied. Ann., 8, 3 (1879). 



