( 197 ) 



sented by the point ƒ/, Avherc llic li(niid curve accj, the va])om 

 curve aeg and the solubility isolherni fceg meet. 



The second three-phase pressure is represented by the curve e c ,s' 

 and lies considerably higher. The coexisting phases have here different 

 concentration, and are denoted by e, c and ,s'. Here e is the saturated 

 liquid phase and e the vapour phase which coexists with the solid 

 phase .9. 



If \ve now start from these three phases, and lower (he })rcssure 

 at constant temperature, we reach the region for solid B -{- vapour, 

 as Fig, 1 represents. So below the three phase pressure ecs and 

 above the triplepoint pressure of B, only vapour can occur by the 

 side of solid B in stable condition, and the curxc representing the 

 vapours which can coexist with solid B is the lowest branch of the 

 continuous solubility isotherm, viz. eg. 



The line a c denotes the unsaturated liquids coexisting with the 

 vapours lying on the line a e. The lines c g and e g represent meta- 

 stable conditions, viz. supersaturated solutions with their coexisting 

 vapours. The curve c f, the upper part of the solubility isotherm 

 represents the liquids coexisting with solid B. 



The second ^;-.i'-diagram, represented in Fig. 2, corresponds with 

 a somewhat higher temperature t^. We are now above the trij)lepoint 

 temperature and the lowest three phase pressure is not a triplepoint 

 pressure now, but perfectly comparaI)le with the highest three phase 

 pressure. A result of this is, that Ave get below the lowest three 

 phase pressure a reflection of what takes place above the highest 

 three phase pressure. The solubility xsoihevwi f\c^e^ e\c\f^ cuts, as 

 it were, a portion out of the region for liquid -|- vapour, on account 

 of which between the two occurring three phase pressures indicated 

 by the curves e^ c^ s^ and e\ c! ^ s\, only solid B can coexist with 

 vapour in stable condition. The line c'l/V, like c^ /i represents now 

 the liquids coexistiiig with solid B, and the portion (^i e\ the \'apours 

 coexisting with solid B. 



As to the whole course of the solubility isotherm it may be observed 

 that this line has now two maxima, two minima and four vertical 

 tangents. For the portion /i Ci ^i the points of contact of the vertical 

 tangents lie in the metastable or the stable region, whereas those 

 for the second piece e\c\f\ arc situated in the unstable region. 



At higher temperatures the three phase pressures draw nearer and 

 nearer to each other and coincide finally, as may be seen from fig. 1. 



When we examine this change in the p-.r-diagram it appears that 

 the points e^ and c^ move downward and at the same time to the 

 right, whereas the points e\ and c\ move upward and to the left. 



