(38) 



Beyond the point R, the temperature, and with it also the 

 pressure, decreases, as is to be seen from the succession of the 

 different spinodal curves, so that in the /»,7kliagTam (fig. !«) tlie 

 plaitpoint curve C,R,A shows a cusp at R^, and begins to run back. 



It is known that this case is realized with mixtures of C, Hg and 

 CH3OH, ether and water (Kuenen), etc. It is the principal type I, 

 as I have fully described it in one of my two preceding papers '). 



Remarkable and quite unexpected is the fact that this type may 

 be realized for mixtures of normal substances. It was formerly 

 believed that such deviating plaitpoint curves were only possible 

 when at least one of the two substances is anomalous. This, however, 

 seems not to be the case; more and more the conviction gains ground 

 with me that the anomaly of one or of both components only 

 accentuates the phenomena sharper or brings them into attainable 

 regions of temperature. 



It is also striking in fig. la, that the curve C^ C, has the same 

 appearance, viz. with an inllection in the middle part, as the typical 

 curve as observed by Kuenen for C^Hg -f CH3OH (see fig. 1 of my 

 just cited paper). Only in our case there is not yet a pronounced 

 maximum and minimum, as with the mixtures of C^Hj with the 

 strongly anomalous substance CH3OH. 



The type of fig. 1 occurs for comparatively small values of (p. 

 According to the equation given in § 3 the proportion ^2/^1 = 4 

 corresponds with (p = l. The critical temperatures of the two 

 components must, therefore, lie comparatively far apart. 



As ^i/j-o = — , Tg is considerably higher than T,. If we put 



To^l, as has been done in the figure, then T^ = 0,59 and 1\ = 2,37. 



b. Some mathematical and numerical details. 



The plaitpoint curve C\C, touches the line x=:'/^ in Co, the 

 curve AC\ touches the line .i' = in A. Moreover the curve 0^0^ 

 touches the line x = V^ once more in D, and it does so at 

 to == 7j (^ = 1,5 6). In Ci and C\ no contact takes place. 



When <fi becomes < 1 , and approaches to (^V^; ^^^en becomes 

 larger and larger and approaches to 00), then the curve C\A approaches 

 the straight line .i' = more and more and the curve CqC^ the 

 dotted curve in the figure, which continues to present a clearly 



1) These Proc. VII p. 63G-638, April 22, 1905. 



