191 
6th Case. If a binary compound appears as a solid phase, 
different cases may be distinguished, the most interesting of which 
I will discuss here. In the first place we shall suppose that the com- 
ponents B and C do not give critical end-points either with A, nor 
with the compound BC, but that this compound gives critical end- 
points only with the most volatile component A. It is clear that when 
this case occurs, the triple point temperature of the compound BC 
will probably lie far above that of the components B and C. 
If we draw the projection of 
the vapour and the liquid line of 
the three-phase equilibria Sgco + L 
+ G and that of the critical iso- 
therm on the concentration triangle 
corresponding to a temperature 
lying above the critical tem- 
perature of A and a little above 
the highest eutectic temperature 
of the system B—C;, Fig. 7. is 
formed. 
Fig. 7. The isotherm Ak, is convex 
seen from A, as it is supposed 
here that the compound BC'is less 
volatile than the components 5 
and C. When the liquid vapour 
surface in the ternary v-a-figure 
recedes more on rise of tempera- 
ture than the surface of nodes for 
the liquids and vapour coexisting 
with solid BC, the critical isotherm 
will touch this surface of nodes 
at a given temperature; then the 
liquid and the vapour line of this surface of nodes merge continuously 
into each other. At a still somewhat higher temperature a closed 
portion is formed in the surface of nodes, in consequence of 
which two ternary critical end-points have appeared, as fig. 8 shows. 
If we think the temperature as gradually rising, the critical end- 
points will recede from each other in the beginning, and they will 
also move towards the plane BC, but before the triple point tem- 
perature of the compound has been reached the points p, and p, 
will approach each other, and they will coincide, because when we 
approach the triple point temperature, the surface of nodes of the 
liquids and vapours that coexist with solid BC will have to con- 
