174 



For the satiirationciirve uiuler a constant pressure of i^, consequently 

 for curve pq, we find: 



2_,, ?^ + (,i.-„) ^-^ - C = (12) 



x y 



or after substitution of the value of Z from (7): 



[XT + [y-^) s + RT] civ + [x.^ + 0/ -ii) t] dy = . . (13) 



When we call rl' the angle which forms the tangent in p or q 

 with the side BC (taken in the direction from B towards Cj 

 we 11 nd ; 



iy—i^) s + RT 



Let us now consider these two tangents in the point /; of tig. 1. 

 In this point ?/— .? < and y—y, > 0. 



The denominators of (11) and (14) have, therefore, either opposite 

 sign or they are both positive, so that we may distinguish three 

 cases. In each of these cases we find q<^i^^; the liquidcurve of the 

 region L-G and the saturationcurve of F under a constant pressure 

 are, therefore, situated in the vicinity of point p with respect to 

 one another in the same way as the curves pf and pq in fig, 1. 



Curve pf can also no more intersect curve pq in its further 

 course; we may see this also in the following way. 



At decrease of P the two curves must touch one another under 

 a definite pressure P/, somewhere in a point h within the component- 

 triangle; 'therefore imagining the liquidcurve of this pressure 7^/, 

 to be represented by ed (fig. 1), we must imagine ed to be drawn 



dy 

 in such a way that it touches pq in h. For this point h — from (9) 



dv 

 must be equal to — from (13) ; then holds : 

 ax 



r + {y-y^)^ 4- RT _xr + {y—/>)s + RT 



(15) 



xs-\r{y-y^)t ^s-^{y—/^)t 



or 



y, = /i (16) 



As y, indicates the vapour conjugated with liquid h, (16) means: 

 the liquid-curve of the region L—G and the saturationcurve under 

 a constant pressure of F touch one another in a point h, when the 

 vapour belonging to this liquid h is represented by the point F. 



As all vapours belonging to curxe ed (fig. 1) are represented by 



