104 



which we will call A, B, and C, respective)'. It is evident that 

 this only applies so long as the fonr-phase equilibrinm is found in 

 the vicinity of the niinimum melting point. 



If we ascertain what reactions can occur in the four-phase equili- 

 brium F -\- F' -\- L -\- G when the vapour is represented by a point 

 in the vicinity of D^ we find in an .analogous manner as above: 

 if a foLirphase equilibrium F -\- F' -\- L ^ (t moves in a positive 

 direction through the maximum sublimation point of the complex 

 F -\- F' the following reaction series appears: 



^j^F':;tL-{- G F-\-F':^G F+F' -\- L:^G 



or F':^F-]- L-i- G F':^F-^G F' -^ L-^F-^G 



ov F:^F -^L^G F^F'-^G F+L:^F ^G 



which we will call A^, B^, and C^ respectively. We notice that the 



last reaction of series A, B and C agrees with the first reaction of 



series A^, B^ and CV 



The above reaction series, as has been already stated, are only 

 valid so long as the four-phase equilibrium is present in the vici- 

 nity of the minimum melting point or the maximum sublimation 

 point; at a greater distance other reactions may occur besides the 

 above mentioned ones. We will explain this with a single example 

 and choose therefore fig. 1. If the system is found in the maximum subli- 

 mation point, hence the liquid in Z) and the vapour in i)^, the reaction 

 F -\- F' "^ G takes place. If now the system moves in a positive 

 direction, hence the liquid from I) towards c and the vapour from 

 Di towards c^, G gets within the triangle T^i^'L causing the reaction 

 JP j^ JP' -i^ L -^ G to take place. (Also see reaction series A^). 



If now the system moves further in a positive direction, the point 

 G can arrive outside the triangle FF'L; this, for instance, is the 

 case with the system F -\- F' -\- Lc -\- Gc^ . 



The reaction F^ F' -\- L:^G then becomes F' -\- L:^F-\-G; 

 by way of transition the three-phase reaction : F' -\- L'^G occurs. 

 This is the case at the moment that the conjugation line liquid- 

 vapour j)asses through the point F' . 



If the four-phase equilibrium moves still further in a positive 

 direction, the point L can arrive within the triangle FF'G; the 

 reaction L "^ F -\- F' -\- G then takes place. By way of transition, 

 at the moment that the conjugation line liquid-vapour passes through 

 the point F, the three-phase reaction L"^ F -{- G appears. 



On moving the four-phase equilibrium in a positive direction we 

 thus get first the reaction series A and A^ followed by the reactions: 

 F' ■^L:;tG;F'-{-L:^F+G;L:;ï:F^G and L^F-{-F'-^G. 

 This latter reaction is the same as the first reaction in series A, 



