;s89 



fig. 2. The points F, F', ƒ and y are situaled in (liis fignre in sucli 

 a way that the}- form the angular points of a quadriUiteral, they 

 may, however, also form a triangle, surrounding the point F ov F' . 

 The same applies to the points F, F' , g^ and J\. 



In addition to the above mentioned instances, the different diagrams 

 may yet still differ from one another with respect to the reactions 

 which may take place in either of the two four-phase systems 

 F-^F' -{-L^G. For the system /^'-f 7^^' + liquid (/ + vapour^,, 

 we distinguish the following cases : 



a. The point g^ is situated within the triangle FF'g. 



Reaction : F -{- F' -^ L:^G. 



h. The points form a quadrilatei-al ; the line Fq^ intersects F'q. 



Reaction -. F' ^ L:^F -^ G. 



c. The points form a quadrilateral; the line F(j intersects F'g^. 

 Reaction -. F -^ L:^F' -{- G. 



d. The point g is situated within the triangle FF'g^. 

 Reaction : L:^F -\- F' -^ G. 



For the system F -\- F' + liquid ƒ + vapour/; we may of conrse 

 distinguish the same cases. 



If we consider the above-mentioned reactions in the direction 

 from left to right, vapour is formed, and, therefore, the volume 

 increases. The three-phase equilibria, which are formed, when the 

 reactions take place from left to right, exist therefore at lower tem- 

 peratures, and those which are formed when the reactions take place 

 from right to left exist, therefore, at higher pressures than the four- 

 phase equilibrium. Hence the following is easily deduced : out of 

 the point of intersection of the two saturation curves under their 

 own vapour pressures, the pressure 



1. decreases along both curves, when reaction a 



2. increases along the one curve and decreases along the other, 

 when reaction b or c 



3. increases along both cnrves, v/hen reaction d takes place in 

 the four-phase equilibrium. 



The same of course applies to both the vapour saturation curves 

 under their own vapour pressures. As follows from the position of 

 the points of intersection in fig. 2, the reaction "a" is there assumed 

 for the equilibrium F -\- F' + liquid ƒ/ -j- vapcur^/j, the reaction 'V/" 

 for the equilibrium F -{- F' -\-\\(\\\\^ f -\^ v'ix\iQ\\Y J\. The pressure 

 changes along the curves in the vicinity of the points of intersection 

 of this figure are in accordance with the previous considerations. 



It is evident that yet many other cases are possible, which can 

 be obtained by combining the reactions a—d^ two at a time. It 



