876 
which is in agreement with fig. 3. This will continue until on further 
reduction of pressure the vapour line of the heterogeneous region 
passes through point £. This means that a vapour # can be in 
equilibrium with a liquid; this again is in harmony with fig. 3; 
therein we proceed from the liquidum gas region to the curve Kf. 
On still further reduction of pressure the gas region of fig. 1 (1) 
moves over the point / so that, in harmony with fig. 3 the com- 
pound F can occur only in the state of vapour. 
Between the liquidum line de and the vapour line d,e, of the 
heterogeneous region JL G of fig. 1 (1) is situated the projection 
of the line of intersection of the liquidum and the vapour side of 
the ¢-surface. This line indicates a series of solutions which each can 
be in equilibrium with a vapour of the same composition; all these 
liquids and vapours, however, are metastable and break up into a 
liquid of the liquidum line and a vapour of the vapour line of the 
heterogeneous region + G. We will call this line of intersection 
the theoretical liquidum-vapour line. 
As this theoretical line passes, at a definite pressure, through the 
point #, there exists at this pressure the equilibrium: liquid / + 
vapour # in a metastable condition; hence, we have a point of the 
theoretical evaporation line Sg of fig. 3 and it is, moreover, evident 
that this must be situated in the liquidum-gas region of fig. 3. 
We now choose a temperature 77 lower than 74; this will 
cause the saturation line of # to disappear at Tp at a lower pres- 
sure than at 74. We now choose 7’g so low that, on lowering the 
pressure the saturation line of / has not yet disappeared when the 
liquidum line of the heterogeneous region passes through the point 
F. Tp is, therefore lower than the minimum melting point of /. 
If we now choose a very high pressure, the corresponding diagram 
will then consist of fig. 1 (1) wherein, however, the gas region and 
the heterogeneous region 1+ G are still wanting. On reducing the 
pressure fig. 1 (I) is formed first, then fig. 2 (D and further fig. 3 (I); 
at these pressures the compound # still occurs in the solid condition 
so that it finds itself in the solid region of fig. 3. At a definite 
pressure the metastable part of the liquidum line dade situated 
between the points a and #/ in fig. 3 (1) will pass through the point 
F; this means that a liquid of the composition /’.may be in equili- 
brium with vapour; this is only possible in the metastable condition 
for in the stable condition F only occurs as a solid. Hence, in fig. 3 
we find ourselves in the solid region on a point of the metastable 
curve ef. 
On further reduction of pressure there is now formed from fig. 
