( 18) 



It is also noteworthy about this figure, that when following the 

 P, T-line, starting with the point G resp. with the point D, we 

 first meet with a point, where the tangent is vertical, and (place 

 where X^ = 0) after that with a point where it is horizontal. 



If we now consider a concentration on the ri(/ht of the line of 

 the compound, the F, T-line corresponding with this will cut the 

 other continually ascending branch of the three phase line of the com- 

 pound, and by means of equation (4a) and the scheme for the 

 reversal of sign of A\ and A'^ preceding it, we obtain a curve as 

 indicated by G^ F^ F^ D^. The situation of the loci A'^ ^ and 

 Xj = being different on the fight from that on the left, this 

 P, T-line differs from that just discussed. When now, starting from 

 the point G■^ resp. D.^, we follow the P,7^-line, we meet first with 

 a point, where it is vertical, so we have just the reverse of the 

 preceding case. About the situation of the points P/ and F^ we 

 may point out, that jP/ always lies at lower temperature than F^. 



The loci Xj = and A^ ^ intersecting on the line of the 

 compound, the P, T-line for the concentration of the compound will 

 have to give to a certain extent the transition-case between the two 

 lines discussed. 



What happens when we approach the curve of the compound, we 

 see immediately from fig. 1. The distance between the loci Aj = 

 and Aj = becoming smaller and smaller, the points of contact of 

 the vertical and horizontal tangents will draw nearer and nearer, 

 which prepares us for what happens when we have arrived at the 

 line of the compound. We see from the scheme for the signs of 

 Aj and X^ that when the loci A"j := and A'^ =; have coincided, 

 the signs of A^ and X^ reverse simultaneously, on account of which 



P( — ) retains the same sign, viz. remains positive. Combining this 



with what we know about the course of the P,P-lines somewhat 

 to the right and the left of the curve of the compound we are led 

 to the conclusion, that the P, 7 -line for the concentration of the 

 compound will have two cusps, each formed by two branches with 

 a common tangent. I have not been able to decide whether these 

 points will be cusps of the first or the second kind. The former 

 has been assumed in the diagram. 



It is further noteworthy for this P, 7 -line that, as Van der Waals ') 

 already demonstrated before, both the line of sublimation and the 

 melting-point line must toucii the three-phase line, so that the P,P-line 



1) Verslag 21_April 1897, 482. 



