706 
very perceptibly to the right, which means that the unary mixed 
crystal becomes richer in the @-pseudo component on rise of tem- 
perature. At the moment that the mercury iodide melts, it lies in 
composition between that of the yellow and of the red modification 
at the transition temperature. 
The liquid Z formed is very rich in the 3-component, which is 
in harmony with the fact that the liquid is dark red. The internal 
equilibrium in the liquid phase above the melting point is indicated 
by the line ZL, What direction this line has cannot be ascertained 
with any certainty. 
The possibility of the occurrence of red mixed crystals above the 
transition point by sudden cooling of Hgl, from e.g. 240° to 130° 
is also immediately to be seen from this figure, just as the direct 
formation of the red modification by sudden cooling of molten 
Hel, in a mixture of carbon dioxide and alcohol. 
This is sufficient to show that this figure perfectly accounts for 
the observed phenomena. To be able also to explain tie phenomena 
that can present themselves in the presence of gaseous Hel,, we 
should also indicate the 7’,-projection of the threephase regions of 
the pseudo-system, and then the somewhat unusual situation of the 
system Hel, is apparent. 
The vapour coexisting in the triple point with the orange solid 
phase and the dark red liquid, has a light yellow colour. The 
vapour is, therefore, richest in the pseudo component aHgl,; conse- 
quently the vapour lines in the pseudo system lie as they are 
indicated in fig. 2. This is, indeed, an unusual situation, which 
however, will undoubtedly occur now and then. The vapour lines 
of the unary system are, just as the lines for the solid phases and 
those for the liquid, indicated by thick lines. What the direction is 
of the vapour lines and of the liquid line in the unary system, 
cannot be stated with certainty as yet, but it is of very little 
importance here *). 
If we knew that Hel, is a polymer of aHgl,, the line for the 
internal equilibrium in the vapour would run towards higher tem- 
perature to the left, but that this case should present itself does not 
seem very probable, because, at has been said, the liquid at the 
triple point temperature is richer in the g-eomponent than the 
coexisting solid phase. The assumption of isomerism, therefore, seems 
1) The vapour lines ag and bg of the pseudo system must intersect in g in 
such a way that the metastable prolongations do not lie inside each other, as is 
drawn here, but outside each other. In this case the point G’ will also lie exactly 
on the prolongation of the line GG. 
