176 Dr. Kuenen on the Critical Phenomena of 



two cases mentioned above. If P is situated beyond R we 

 have r.c. I. (figs. 8, 9) ; if R lies beyond P we have r.c. IL 

 (fig. 10). Keeping in view the connexion between border- 

 curve and plaitpoint-curve, the question whether the second 

 case can be realized comes to the same as whether the plait- 

 point-curve or a part of it may rise, while the border-curves 

 are situated on its left side (fig. 10). Now it appears that 

 there are different cases in which such a situation must occur. 

 If the critical points of some of the mixtures lie outside the 

 critical temperatures of the two substances, a part of the 

 plaitpoint-curve will answer to the above postulate. But this 

 is not a necessary condition. If the substance of the higher 

 critical temperature has at the same time larger vapour- 

 pressures than the substance of the lower critical temperature, 

 the plaitpoint-curve will have the same property. This case 

 is represented in fig. 1. R lies beyond P. Between the 



Fig. 1. 



two temperatures T P and T R the mixture, the border-curve of 

 which is drawn in the figure, must show retrograde conden- 

 sation of the 2nd kind (r.c. II.). Even if the curves are 

 more complicated than is supposed in the figure, the curve 

 CiCg will nevertheless fulfil the condition at least for a part 

 of its course. 



7. There is only a small number of combinations of two 



