18t> Dr. J. P. Kuenen on the Condensation and Critical 



21. The Tables VII -XL contain the results for the five 

 mixtures ; the diagram (fig. 2) shows the relative position of 

 the vapour-pressure curves for the pure substances, the border- 

 curves for the mixtures, and the plaitpoint curve which 

 envelops the border-curves. Only two of the border-curves, 

 for mixtures 068 and 0'27, have been drawn in order not to 

 make the diagram too complicated. 



The diagram is qualitatively the same as that for nitrous 

 oxide and ethane : quantitatively there is a difference in the 

 circumstance that the mixture of minimum critical tempera- 

 ture and the mixture of maximum vapour-pressure are much 

 nearer to each other than in the other case. Mixture 0'51 

 was about the mixture of maximum pressure (point B), while 

 the minimum critical temperature (point A) occurs for a 

 mixture containing only a little more ethane (a'=0'53 or 054) . 

 The same points B and A were much farther apart for 

 N 2 0-C 2 H 6 , where they belonged to mixtures a 7 = 02 and - 5 

 respectively. 



22. It was stated in my former paper that the critical phe- 

 nomena of the mixtures of N 2 and C 2 H 6 are little marked. 

 Between C and A, and also between C and B, the condensa- 

 tion should be retrograde of the first kind between the two 

 critical temperatures f p and t c ; between A and B the con- 

 densation should be retrograde of the second kind. The 

 latter phenomenon has never yet been observed owing to 

 disturbing circumstances such as gravitation and small im- 

 purities. For C 2 H 2 -C 2 H 6 the chances of observing special 

 critical phenomena between A, B are obviously even smaller 

 than for N 2 0-C 2 H 6 . 



I succeeded this time in observing critical phenomena of 

 the first kind with all five mixtures. This is chiefly owing to 

 the temperatures being more constant than formerly. The 

 phenomena were very marked for the mixtures 068, 061, 

 and 0*51, much less marked with mixtures 041 and 0*27. 

 Though the relative position of P (plaitpoint) and C (critical 

 point) is the same along the curves CxB and C 2 A, this is not 

 the case as regards the point of maximum pressure M. Be- 

 tween B and G 1? M is between P and C ; along AC 2 , P is 

 between M and C. The results with mixtures 0*08, 061, and 

 0*27 are in accordance with this rule ; mixture 041 shows M 

 to be near P but on the wrong side ; mixture 0*51, which is 

 about the mixture of maximum vapour-pressure, should have 

 one critical point ; evidently it contained some other admixture. 

 Moreover, the differences between p b andp e are considerable for 

 this mixture, while they should be very small, not larger than 

 for the components used. Altogether the results show that at 

 least some of the mixtures contained a small admixture of air. 



