362 
M vanishes in consequence of the coin- 
cidence of this point with the minimum 
L,, at which moment a point of inflection 
appears with horizontal tangent. At this 
moment the possibility of the existence 
of a metastable unary liquid ceases, so 
that this condition bas already become 
impossible before the critical mixing point 
has been reached in the pseudo-system. 
This consideration is in itself already 
sufficient to indicate in a 7'x-diagram the 
situation of the liquid lines in the unary 
system with respect to those in the pseudo- 
binary one. If we assume that the pseudo- 
system, just as the system nicotine-water, 
presents an upper and a lower critical 
Fig. 3 2. mixing point, fig. 3. is formed. 
The closed line PP, indicates the coexisting liquid phases in the 
pseudo-binary system. Outside the region enclosed within this conti- 
nuous curve, runs the line kk,, on which the stable internal liquid 
equilibria are found, and inside this region lie the metastable internal 
liquid equilibria on the line &', &, 4’). In the points 4’, and 4’ this line 
passes continuously into the locus of the maximum points M of 
0S , 
the ¢-z-lines, and as in these points (=) =), just as for the stable 
av PI 
BN 0°6 
and metastable unary equilibria, but (5 ) <0, we may call the 
BAP 
loeus of the maximum points M the line of the unstable internal 
equilibria. 
The theory of allotropy attributes the phenomena of monotropy 
and enantiotropy to the occurrence of different kinds of molecules 
of one substance, and says that when there exist two or more solid 
states of a substance, the differences in properties are owing to the 
situation of the internal equilibrium which will be different in the 
two solid states. 
Now we saw just now that when a substance occurs in two 
different liquid states, this phenomenon must also be ascribed by the 
theory to the existence of two different internal equilibria between 
different kinds of molecules of the same substance. So according to 
1) The lines of the internal equilibria have here a very peculiar shape, which is 
dependent on the phenomenon of unmixing. | shall return to this subject later on. 
