877 
31) the figure 4(I) or S(D: we first choose Ty in such a manner 
that on lowering the pressure, the vapour saturation line has not 
yet disappeared when the vapour line of the heterogeneous region 
passes through the point /. So as to be in harmony with fig. 3, 
Ts has been chosen lower than the minimum melting point and 
higher than the upper sublimation point of the compound £. In conse- 
quence of this, fig. 3 (1) is converted into fig. 4 (1) on reduction of 
pressure, and afterwards at a definite pressure into fig. 5 (I). At 
this pressure the as yet solid compound / melts with formation of 
the vapour m, and the liquid m; hence in fig. 3 we proceed from 
the solid region to a point of the three-phase line A /. 
On further decrease of pressure # is resolved into liquid and gas; 
in fig. 3 we, therefore, proceed from the line A /’ to the liquidum 
gas region. On further reduction of pressure the vapour curve e, d, 
of fig. 5([) passes, at a definite. pressure through the point /’; this 
means that a vapour of the composition /” can be in equilibrium 
with a liquid. The compound F' then passes, in fig. 3, from the 
liquidum-gas region to the line A. On further decrease of pressure 
is now formed fig. 6 (DD), the point / lies now in the vapour region 
so that the compound #’ can only still occur in the state of 
vapour. 
In fig. 3 we, therefore, proceed from the line A/ to the gas region. 
Between fig. 3(1), in which we assume the metastable part ab 
of the liquidum line dade to pass through the point /, and fig. 
5 (1), in which we assume the vapour line d,v, to pass through #, 
there must, of course, lie another one where the theoretical liquidum 
vapour line passes through point /. This means that, in fig. 3, we 
must find, at the temperature 7’g, between the curves ef’ and Af 
a point of the curve g'Sy. If this theoretical vapour curve already 
passes through the point /’ before fig. 5 (I) is formed through reduc- 
tion of pressure, the point of intersection of y'Sg with the vertical 
line then lies in the point B of fig. 3 above the three-phase line; 
if, however, this theoretical line passes through the point £’ when, 
through reduction of pressure, fig. 5 has formed, the above point of 
intersection in fig. 3 lies below the three-phase line. These results, 
as follows from fig. 3, are in harmony with this figure. 
The situation of the metastable sublimation line ASS and of the 
metastable melting point line #S may be found in this manner. 
Here, we will just determine the situation of the triple point S. In 
this point there exists an equilibrium between solid /’ + liquid 
F+ vapour F. 
The equilibrium liquid 4 + vapour / requires that the theore- 
