07 



point S the molting- [)oiiit curve Sd", and in llie nuixininin snbli- 

 nuilion [)oint D (he snblinialion cnrve a" D of Ihe complex /'' + F'. 

 These curves are indicated in tig. 4 by the same letters. 



If the system F -{- F' -\- /> -j- G is found in (he minimum melting 

 point S the reaction : 



F+F':^L or F'-^F^L or F:^ F' -\- L 

 takes place (Series A, B or 6')- We always take these and the 

 following reactions in the direction from the left to the right. As 

 we always assume that in these reactions heat must l)e supplied 

 for the formation of liquid from the solid substance, A W for each 

 of these reactions is positive. 



During the fusion or transformation the volume may, however, 

 increase as well as decrease; AV can, therefore, be positive as 

 well as negative. Here, we will call A F positive so that in agreement 



with fig. 4, ~y^ is positive in the point >S' in case ot the tour-phase 



curve as well as of the melting point line Sd" . 



We now consider the e(iuilibriuni F -\- F' -\- L -\- (r in a point 

 X (not drawn in the figure) on branch J^S in (he immediate vicinity 

 of the point S. The equilibrium has thus been shifted in the negative 

 direction. From the reaction series A, B, and C it follows that the 

 reaction 



i/_|_iy^'_|- (-^L or F' J^ G:^F-\- L or F ^ G:^ F ^ L 

 now occurs. These diiFer from the previous three-phase reactions 

 only in so far that in the first term oidy the vapour pliase has 

 been inlroduced. So long as the [)oint .Y lies very close to S, only 

 a very little quantity of vapour will take part in the reaction : 

 LW and A F are, therefore, botii still positive. 



If, however X gets removed from S still further in the negative 



