392 



As the three-phase equilibria F -{-. L -\- G and F' -\- L -{- (r are 

 formed here, when the reaction proceeds from left to right, both 

 these equilibria exist under pressures lower than those of the four-phase 

 equilibrium. On both saturation cur\'es under their own vapour 

 pressures, the pressure decreases therefore from the point g outwards. 

 In the system F -\- F' -\- L -\- G the volume increases, of course, 

 with the formation of vapour. 



VI. The temperature is equal to the point of maximum temperature Jiv. 

 The two saturation curves under their own vapour pressures 



touch one another; the same applies to the two vapour saturation 

 curves. The two points of contact are situated on the same side of 

 the line FF'. In fig. ö one of the many possible cases has been 

 drawn. As the point JV is generally situated in the vicinity of the 

 line FF', consequently in the four-phase equilibrium reaction a does 

 usually not take place, but instead one of the reactions b — d 

 takes place. 



^--^ In tig. 5 the curves touch one another 



externally. It is evident that they may 

 also touch one another internally, or that 

 one or more of the four curves may be 

 exphased. 



From our previous considerations it 

 follows that, during a reaction between 

 .the four phases of the system F -\- F' -\- 

 liquid N -\- vapour JSf-^, the volume remains 

 Fig. 5. constant. 



While the point of contact between two saturation curves under 

 a constant pressure is situated on the line FF' (the only exceptions 

 being metastable points of contact, which may be situated on the 

 spinodal line, when the liquids separate into two layers), the point 

 of contact of two saturationcurves under their own vapour pressures 

 is always situated outside the line FF' . 



VII. The temperature is higher than the point of maximum tem- 

 perature 7V. 



The two saturation curves under their- own vapour pressures 

 neither intersect nor touch each other; the one is situated either 

 outside or completely round about the other. The same, of course 

 applies to the two vapour saturation curves under their own vapour 

 pressures. 



For this purpose we have deduced from fig. I, that, at the maxi- 

 mum temperature Tjsf the two saturation curves as well as the two 

 vapour saturationcurves under their own vapour pressui-es touch 



