308 J. î». KUENEN. 



brum on tlie otlier can iiot l)e denied. An e([iially distinct contrast exists 

 between formation of liquid in a single substance even witb association 

 of molécules, and irréversible polymérisation. At the same time it is 

 possible that there may be some connection between the strong affinity 

 at low and tlie action at liigh températures. 



The chief results arrived at are the following: 



1°. The mixtures hâve a minimum vapour-pressure in accordance 

 with what could be derived from Fijiedel's experimeuts. This minimum 

 exists up to the critical condition. 



2°. Addition of hydrochloric acid raises the critical température of 

 methylether. Eor the reasons explained above the complète relation be- 

 tween crilical température and pressure could uot be obtained. 



The results are represented in the tigure y>'àge 309. The curves were coin- 

 pleted in the part of the diagram where observations were im])ossible by 

 hypothetical pièces. The gênerai character of the diagram seems beyond 

 doubt. It shows how the mixtures as expected combine a maximum 

 critical température (at .-/) with the minimum va])our-])ressure and in 

 what manner the minimum curve meets the plaitpointcurve at B. As 

 was proved by van der Waals ') the two curves touch each other at 

 B, and the plaitpointcurve is continuons at J. According to principles 

 laid down by me before ^) the mixtures will hâve rétrograde condensa- 

 tion of the 1 ^' kind, between Cj and B, of the second kind between B 

 und .-7, and of the P* kind between A and C.,. 



The diagram agrées generally with one obtained a priori for a mixture 

 with minimum vapour-pressure by Hartman "'). It bears to a high degree 

 the internai évidence of correctness and it can hardly be doubted will 

 be confirmed when a difl'erent représentative of the type without chemi- 

 cal action is examined. 



Another peculiarity of the tigure worth noticing is the broadness of 

 some of the condensation loops of which the loop in the figure for a 

 mixture of 7 % ether to 93 % acid shows a striking exaniple. Near the 

 minimum the loops are necessarily very narrow and therefore also be- 

 tween B and C j : this is not the case with the mixtures between />' and 



') Yan der Waals. Kon. Ak. Mei 25 1895. 



') KuENEN. Communications. Leidenn". 13,1894. 



') Hartman. Dissertatie. Leiden 1899. 



