780 



thing about the change uf pressure starting tVoni ,s along the curves 

 m and sc {Cig. 6). In communication V we have deduced the following 

 rule. When the equilibrium solid -|- ^ c^" be converted with increase 

 of volume into solid -{- L' -f- G' (in which L' differs extremely little 

 from L) then of a threephasetriangle solid — liquid — gas the side 

 solid — liquid turns on increase of pressure towards the vapourpoint 

 and it turns away from the vapourpoint on decrease of pressure. 



When we assume now that .y (tig. 6) is not situated in the vicinity 

 of B or F (the equilibrium B -\- L and F -\- L converts itself into 

 B -\- L' -\- G' and F -\- L' -{- G' with increase of volume) we can 

 apply the above-mentioned rule. We distinguish now according as 

 the vapour is represented by .Vj, s^ or .v.,, three cases. 



1. The vapour is represented by s^. 



First we consider the threephasetriangle Fss^. When the side Fs 

 turns towards c, then conse(piently it turns towards its vapourpoint 

 ó\ ; the vapourpressure increases, therefore, starting from s along sc 

 towards c. 



Let us consider now the threephasetriangle Bss.^. When the side 

 Bs turns towards a, it turns, therefore, away from its vapourpoint 

 .s'l ; coJisequently the vai)Ourpressure decreases starting from 0' along 

 sa towards a. 



Consequently we tin' I that the vapourpressure starting from .v 

 increases along sc and that it decreases along sa. It is evident that 

 this is oidy true for poinis in the vicinity of .y ; the occiwreiice at 

 a greater distance of s of a point of nuiximumpressure on sc and a 

 point of miniinumpressure on sa, is viz. not excluded. 



2. The vapour is i-epresented by s.^. 



It follows from a consideration of the threephasetriangies Fss^ 

 and Bss^ that the vapourpi-essure starting from s increases as well 

 along sc as along sa. 



3. The vapour is i-epresented by .^3. 



It follows from a consideration of threephasetriangies Fss^ and 

 ii.y.s'g that the vapourpressure starting from s decreases along sc and 

 increases along sa. 



We can obtain the previous results also in the following way. 

 Between the four phases of the equilibrium i^ -f i'^-f- Z5 -f- vapour 

 (.y,, .y, or ,yj a phasereaction occurs on change of volume. We choose 

 this reaction in such a direction that vapour is formed, we call the 

 change of volume A V. 



The point s (fig. 6) is a point of the quadruplecurve B -^ F -\- 

 -\-L-^G; A F is positive for each point of this curve. When, 

 however, a point of maxim umtemperature H. occurs on this curve, 



