( 193 ) 



as yet. If it should be possible that — becomes negative, and for 



dT 



the present I do not see any reason to consider this impossible, this 



can only take place in the case of a plaitpoint line descending with the 



temperature. Accordingly the final point of the three phase pressure, 



so the plaitpoint, lies on that part of the section of the surface of 



saturation which lies between minimum pressure and critical point 



of contact, and it is known, that then also the plaitpoint line must 



descend in its p, ^-projection, because it is the envelope of the 



dp 



sections of the surface of saturation. If — is negative at the final 



dT 



point, this value must have passed through 0; this will then require 

 that no heat is released with conversion of the middle phase into 

 the two others, and so that if heat is released with conversion into 

 one of the two extreme phases, the conversion into the other extreme 

 phase is attended by heat-absorption l ). And without further investi- 

 gation this cannot be pronounced as impossible. 



dp 



Finally we point out that — ■ cannot become infinite. For this it 



would be required that the denominator is equal to zero without 

 this being the case with the numerator. Then the area of the three 

 phase triangle must be equal to zero or the 3 points must lie on a 

 straight line. This is the case when two points coincide, but then 

 the numerator is also equal to zero. Now a pAine — for the three 

 points always lie on the same isobar — can indeed be intersected 

 by a straight line in 3 points, but in this case this would have to 

 occur in the same three points with a g-line; this observation will 

 most likely suffice to put down this case as one that does not occur. 

 So we have in the p , ^-projection of the threephase pressure a 

 curve which, at least as a rule, ascends with the temperature; under 

 every point of this line is a point of the plaitpoint line (hidden 

 point) and above every point is a second point of this line (realisable 

 point). This second point is wanting if the plait should not be 

 closed at the bounding volume. 



Shapes of plaitpoint lines {p, T-projection). 



According to the above considerations I shall describe a possible 

 shape of plaitpoint line for the case of two components, for which 



!) The diagrams p. 126 Gont. II, in which the value of % and iv n for coexisting 

 phases has been represented, must be supplemented, when also incomplete 

 miscibility is assumed. 



13* 



