(557) 
Other cases of similar critical terminating points through the 
meeting of three-phase lines in binary mixtures might be conceived 
when no homogeneous mixing in all concentrations is possible in 
the liquid phase and when, therefore, two liquid layers are possible. 
It was of great importance for the knowledge of the conditions of 
existence of solid phases at high temperatures and pressions to also trace 
the critical terminating points in similar cases. If we indicate the two 
liquid layers by ZL, and Z,, the vapour by G and the one or other 
component in the solid state by S, then besides the three-phase line 
SLG, two other three-phase lines SL,L, and L,L,G will be possible. 
In order to trace the critical terminating points of these lines we 
first consider the line L, L, G. Here 
we first take exclusively the cases 
where the p,z-diagram has the form 
of Fig. 3, in which G, L, and J, 
indicate pressure and concentration of 
coexisting vapour with two liquid 
layers. The three-phase pressure for 
this system lies, therefore, between the 
vapour pressure of liquid A and 5 
Py and B): 
Fig. 3. The p, ¢-line CM for the three-phase 
equilibrium L, L,G is situated accordingly in Fig. 1 between AA, 
and BA. 
On elevation of temperature £, and L, may approach each other, 
or recede. If the first happens and if they still coincide below the 
line A,A,, for instance in J/, then the two layers become identical, 
a case of which many instances have been found by ALExEsEW and 
XOTHMUND. This point has been quite properly called a critical point. 
This critical terminating point of the line for 1,/,G' must of course 
necessarily be a point of intersection with a critical line. The said 
critical line is the line DM in Fig. 1. 
If the liquids Z, and Z, can be made to mix more completely 
by an increase of pressure a mixing point D will be found to exist 
in Fig. 3 at a sufficiently high pressure. If now L, L, approach each 
other at a higher ¢, D will then be situated at a lower pressure 
whilst the concentration in the mixing point may differ. In this way 
is obtained the critical line DM for the phases L,Z,. Its one ter- 
minating point lies at the meeting point J/ where G occurs together 
with £,L, and where consequently the lowest possible pressure is 
1) The other case where the three-phase pressure is higher than those two does 
not lead to materially different results. 
