( 7J ) 



ivj q 



but 



still remains positive on tlie left and on the 



right of that point. With somewhat higher degree of 7 



da 



O is 



intersected twice, and two points may be pointed out in the //-line 

 in the unstable branch where it is directed vertically. Between these 



/dp\ 

 '2 points M s negative. But then too the //-line has hut 3 branches 



\dvj 9 

 and so Maxwell's rule can only he applied once ; then we find only 

 two points of the binodal curve, viz. a point indicating a liquid 

 volume lying in the left side of the figure, and a point indicating a 

 vapour volume, lying much more to the right side, but still remaining 

 sufficiently on the left of the double point of the vapour binodal 

 curve. Then the 7-line cuts the binodal curve in no other points on 

 the vapour side. If the value of 7 rises higher, a third special point 

 appears again on the unstable branch of the p-line, i. e. when the 

 7-line begins to have 4 points of intersection in common with the 

 spinodal curve. This will be the case when it passes through the 

 hidden plaitpoint P 2 (see fig. 17). Then it touches the spinodal curve, 



but in such a war that [ has the reversed sign of ( - 



W '/ Wjspin 



The ride that in a plaitpoint the //-line and the 7-line envelop the 



plait is. accordingly, restricted to the realisable plaitpoints. It must 



run exactly the other way about for hidden plaitpoints. So there 



/'<■, /./-V\ (d?v\ /,/-V\ 



— I = I — has the reversed sign ot and of ( 



fay, W) e U-y*» WJo„; 



In this third special point of the unstable branch of the »-curve 



Fig. IS, 



