347 



When we know that {F,) and (F^) go towards higher tempera- 

 tures, and (i^,) (Ft) and (F^) towards lower pressures, then we find 

 at once, by construing (20) in the inverse direction the isentropical 

 reaction. , 



Firstly we shall apply those considerations to a simple case viz. 

 to the addition of a new substance to the invariant unary equili- 

 brium F {x = 0) = F -\- L -\- G. The P.T-diagram may belong to 

 two types, viz. when the volume decreases, on melting of the solid 

 substance, then fig 1 is true; when the volume increases, then fig 2 

 is valid. The regions in which occur the phases F, L and G are 

 indicated l)y the same letters, but in a circle; the curves are repre- 

 sented by (F), {L) and (G) ; in accordance with our notation is 

 {F)= L-\- (9, etc. 



Wheji we add to F (x = 0) a new substance, wliich occurs only 

 in the liquid, then the monovariant equilibrium F = F -\- L -\- G 

 arises; when we take away from it L, then we keep the equilibrium 

 F+G = iL). 



Curve E coincides therefore in figs 1 and 2 with curve (L) of 

 the invariant unary equilibrium E{x=zO). 



'^v ® .^ ,., 



«"' -; d)^' 



Fig. 1. 



Fig. 2. 



When we add a volatile substance, then we must take away 

 from the monovariant equilibrium the phases L and G, so that we 

 keep F only. Therefore, curve F must be situated in the region F, 

 as f. i. ia, ib and ic in the figs 1 and 2. 



When Ave add a substance, which is not volatile, which gives, 

 however, mixed-crystals with F, then \ve must take away from the 

 equilibrium E the phases F and L, so that the vapour G only 

 remains. Therefore, curve E must be situated in the region G. 



We may obtain also these results by using the qualitative iso- 

 volumetrical and isentropical reaction, which we can deduce easily 



