Mixtures of Ethane and Nitrous Oxide. 



189 



both sides near the maximum-mixture cover each other in 

 the figure. In a case like this it is much better to add as a 

 third axis of coordination the #-axis, and to draw the p-t- 

 curves for the mixtures each in its own plane. The curves 

 together in this manner form the p-t-x-surface. Sections of 

 the p-t-x-surf&ce perpendicular to the £-axis again give 

 curves having the shape of loops (p-x-curyes) , which may be 

 considered as an extension of Konowalow's curves*: he only 

 gives the upper branches of the p-x-curyes. A complete p-x- 

 curve is given by Prof, van der Waals in his treatise f . 



34. The maximum-curve meets the plaitpoint-curve in B. 

 Fig. 7 shows the manner in which the three curves (the 



Tiff. 7. 



maximum-curve and the two branches of the plaitpoint- 

 curve) meet in B. It will have to be decided theoretically 

 whether, perhaps, the plaitpoint curve has no singular point 

 iu B, in which case the maximum-curve would touch it in B. 

 35. B. Critical Phenomena. — The plaitpoint-curve (fig. 2) 

 consists of three parts, being situated between both the critical 



Fisr. 8. 



points C L and C 2 , and separated by the two points A and B. 

 A is the meeting-point of two branches of the plaitpoint- 



* Wied. Ann. xiv. p. 34. 

 t Arch. Neerl. xxiv. p. 21. 



