542 



Fig. ± 



Tlie iiietastable [)art h.c of curve (!(' mnsl therefore go lliroiigli point 



/' and the niela.stal»le pari .i'J>, of / 



curve d^e-i must go through the point , 



/j. Fig. 2 may also be imagined to '~M, 



have arisen from fig. 1 in that the 



threephasetriangles FF'z, Faa, and 



Fyi/^ move nntil tliey touch along 



one side. 



Of the two solutions ic and ƒ, 



saturated with F -}- F' , the latter 



may be in equilibrium with the 



vapour /i ; at the temperature and 



under the pressure to which fig. 2 



applies, therefore, the fonrphaseecpiilibrium 7''+ i^' + Jiquid ƒ + 



vapour f\ occurs. 



If the pressure decreases still more, a diagram occurs which we 



shall call tigure 2a. We obtain this figure 2a when we leave the 



point ƒ in fig. 2 out of account. The two saturationcurves and 



curve de then go no more through one point ; nor the two 



vapoursaturationcurves and curve d,c\. Only one solution now exists, 



nl. ti, saturated with F-\-F'; the other is metastable and replaced 



by the vapour /\, which may be in equilibrium with the complex 



JP -^ F' . The fourphaseequilibriuni occurring in fig. 2 has vanished 



of course also in fig. 2a. 



We shall now contemplate the diagram, occurring at the mini- 

 mum-melting point of the complex F -\- F\ one of the many pos- 

 sible diagrams is drawn in fig. 3, wherein also are indicated the 

 metastable parts of the two saturationcurves and of the liquid- and 

 vapour-curve of the heterogeneous region. 



Fig. 3 can be imagined to have arisen 

 from fig. 2 in the following way. We 

 change the temperature and the pressure 

 in such a way, that we retain a diagram 

 as fig. 2 ; the fourphase equilibrium 

 F ^ F' -\- liquid ƒ -j- vapour f^ there- 

 fore remains, although ƒ and /^ change 

 of course their composition. A 'similar 

 change of pressure and temperature is 

 always possible when we change these 

 in accordance with the /^, T-curve of the 

 fourphase equilibrium F-^-F' -\-L-\-G. 

 We take this change now in such 



Fig. 3. 



