( 281 ) 



MET Mr 



(r,-rj ,lp-= (.r,-.^)J.., ^-- <ri\ 



w, 1 



The properties of the initial direction of the sections normal to the 

 T-axis, normal to the /;-axis and normal to the ,i'-axis are given by this 



equation and they are known when the value of -^ ^ is known. 



If ii'j and ^1 represent the value of x and of the molecular volume 

 of the liquid phase, and in the same wa}' x^ and i\ these quantities 

 for the vapour phase, then the equation : 



{i\—v,} dp = MRT '-- dx^ + — dT 



X, T 



holds for the vapour phase. 



As the difference of the specific volumes of liquid and vapour of 

 a component is generally represented by u, i\ — 1\ = Mu, and this 

 equation might also be written 



.^;„ — X, r 



udp = RT dx, 4- -dT. 



^ x^ ' ^ T 



For the section normal to the ,i'-axis, so for the component itself, 



we find the well-known equation of Clapeyron : 



r dp 



— — T— . 

 u dT 



X 



For this section it is not required to know — , but for the otiier 



sections it is indispensable. 



This relation is found by means of the property which says, that 



I ^— I must have the same value for liquid and vapour phase. 



P'rom : 



V 



Tf? = MRT 1(1- A') I (l-x) + xlx] — fpdv + F{T) 

 we find : 



\OxJoT 1— '^' J 0'^ 



and equating this value for the two phases we get : 



1— '^1 J \OxJoT 1—.^, J \OxJvT 



MRTl'-llzh^fh) ,,, 

 x,l—x^ J \OxJvT 



or 



I"» 



