Properties of Liquid Mixtures. 



57 



Since, however, the relation between g and s (or between £ 

 and 7)) has not so far been expressed successfully by an 

 equation, it is not possible to integrate the differential equa- 

 tion in order to compare it with experiment. This is true 

 even for the mixtures of benzene and toluene with carbon 

 tetrachloride, since the empirical equations, quoted above, 

 do not extend through the whole range of q, and therefore 

 the arbitrary constant in the integral equation cannot be 

 determined. We are reduced therefore to the very rough 

 process of comparing the differential equation itself with 

 experiment, by measuring the slope of the vapour-pressure 

 curves at various points. The relation log£ = log&-M' log q 

 or log s = log Bk/ A + r log q gives ~d{\og s)/~d(\og q) =r, and 

 hence 



v-e= 



rp 3?' 



The agreement shown between the two sides of this equation 

 Thus : 



is verv rough. 



Carbon tetrachloride and Toluene. 



:. 



0073 



0163 



0-240 



0350 



0-517 



0-708 



n-Z 



0-105 

 0-123 



0-181 

 0-233 



0230 

 0-276 



0247 

 0-311 



0-225 



0-278 



0164 

 0-198 



Carbon tetrachloride and Benzene. 



z. 



0-043 



0197 



0-376 



0-660 



0-830 



r\~l 



0011 

 0010 



0-036 

 0-037 



0-036 

 0-040 



017 

 0-017 



0005 

 0-009 





Whether the disagreement is due to the difficulty of treating 

 the differential equation directly, to errors of experiment, or 

 to the approximations in the theory, I am at present unable 

 to say. 



In the case of the alcohol mixtures Margules's form of the 

 equation was adopted, and the differential coefficients measured 

 from the smoothed curves. The results following show, it will 

 be seen, the kind of agreement that might be expected in the 



, 



