CHEMICAL THEORY OF SOLUTIONS. PAKT T. 43 



where Ca is the molar fraction of ©a in the gas phase, and the 

 suffixes denote the relation to the chosen temperatures T^ and To. 

 CL can be calculated from the specific volume of the vapour. 

 If we make ^ = one atmosphere, the value of h is known, and 

 jT« and 2ß are the respective boiling points. By equation (27) 

 we can express Cxi and Gxi in terms of D and %. There being 

 thus four equations to evaluate four nnknowai constants, the 

 problem can be solved, and the correctness of the values so 

 obtained can be tested by means of the vapour pressures at other 

 temperatures. In this way it will be possible to determine the 

 degree of association of liquids with tolerable accuracy. But the 

 calculation will be somewhat tedious. 



It has been frequently observed that the vapour is not 

 polymerised to any noticeable degree, while the liquid must be 

 looked upon as highly associated. In such cases n-p is very small 

 in comparison with 7iy_, and equation (27) is reduced to 



P=C^-ß (29) 



In order to evaluate D, %, and T^ in such cases the vapour 

 pressures at three different temperatures must be given besides 

 the value of v. 



Differentiating both sides of equation (29) with respect to 

 T, we get 



dT "" bT "■ iiT \v-{v-V)C^ "■) HT" 



1 — C 

 where ^ — ^\p ^ + qx is the quantity of heat absorbed during 



the production of one mol of the vapour. Now if Teouton's 

 law be valid for all normal liquids under all pressures below a 

 certain value, as indicated in the foregoing chapter, Düheing's 



