608 



An acute-angled thieei)liasetriangle moves on increase of pressure 

 witli the side solid—gas ahead, on decrease of pressure with the 

 side solid — liquid ahead. 



2. The formation of vapour in the binary system F -[- L -]^ G 

 takes place with decrease of volume (A V <C 0)- 



The triangles move in the opposite direction as sub 1.. 



We see that the position of the threephasetriangles in the figs. 

 2 — 4 are in accordance with these rules. 



In a similar way as we have converted (8) into (14), we may 

 deduce from (9) : 



1 ('-^'^ =_j^,/!iri_i^ .... (15) 



AW represents here (he heat that is required to form 1 quantity 

 of vapour. The same rules as above may be deduced from this, 

 we must then however replace increase of pressure by decrease of 

 T and decrease of pressure by increase of T. 



We should have been able to deduce the rules, deduced above, 

 for the movement of the threephase triangles on change of pressure 

 and temperature, from the rules found in Communication V and VI. 



As a particular case of the above-discussed we may put the 

 question : what intluence has a third substance on the binary equi- 

 librium F -\- L -\- G when tliis is situated in the point of maximum 

 sublimation or in the minimummelting point of the substance F. 



In the point of maximum sublimation the binary vapour^has the 

 same composition as the substance F^; therefore ?/j =('?. The vapour- 

 saturationcurve under its own vapour-pressure goes through the point 

 F (in this transition-case between the figures 2 and 3 fi^ coincides 

 therefore with F). When we put in (8) and (9) yi =: /?, we find : 



— (-] z:.— — '^ d— f-^ = ^ ~' (16) 



RT ' \dx J,^o V,-v' X ^" RT' ' \dx A==o A W ' x' ^ ^ 



Herein V-^ — v is the increase of volume on sublimation, LW the 

 heat of sublimation of the substance F. Therefore, both are positive. 

 From (16) it now follows : 



when the equilibrium F -\- L -\- G is situated in the point of 

 maximum sublimation of the substance F, addition of a third substance 

 will increase the pressure (7^ constant) and decrease the temperature 

 (/-* constant). 



In the minimum-melting point the binary liquid has the same com- 

 position as the substance F, therefore y = /?. The salurationcurve 

 mider its own \a{)Oiii"-pressure goes therefore Ihroiigh point F. (lu 

 this Irausiiion-case between figs. 3 and 4, n, therefore, coincides witii 



