1210 
At the temperature 7’x of fig. 4, therefore at the upper sublimation 
point of the compound /’, the vapour has the composition # and 
the liquid which can be in equilibrium with that vapour the com- 
position A’ of fig. 1. At the temperature Tp of fig. 4, therefore at 
the minimum melting point, the vapour has the composition D and 
the liquid the composition / of fig. 1. Whereas the compound / 
proceeds in the P,7-diagram of fig. 4 along the three-phase line 
EK the liquid in fig. 1 proceeds along a curve from A towards 
and the vapour along a curve from / towards D; we will call 
these curves the curves AF and FD. 
We now imagine drawn in fig. 1 some more boiling point lines 
of the solutions saturated with / among which also those passing 
through the point A; on each of these a maximum and a minimum 
temperature occurs. The curve AF now intersects each of the boiling 
point lines situated between A and /’ in the point with the maximum 
temperature, or in other words the curve KF is the geometrical 
place of the points with a maximum temperature on the boiling 
point lines situated between A and F. 
The liquid and vapour-of the three-phase line K/ of fig. 4 being 
formed from the solid substance /’, the three points #, L, and Gin 
fig. 1 must always lie on a straight line. 
This means that the temperature along the boiling point line of 
such a liquid is a maximum or a minimum one. 
From a consideration of fig. 1 it follows that here the temperature 
in this case is a maximum, from which follows at once what has 
been said above as to the course of the curve AE’. 
In the same manner we find that the curve FD also intersects 
each of the vapour lines conjugated with the boiling point lines in 
the point with the maximum temperature. 
In fig. 1 we might also have drawn instead of the boiling point 
lines the saturation lines of / under their own vapour pressure. 
We then should have found that the curve AF intersects each of 
these lines in the point with the minimum vapour pressure. 
We now turn the line ZFZ, of fig. 1 until it intersects the curve 
AF of this figure; the corresponding P,7-curve in fig. 4 must then 
meet the three-phase curve A in a point. For in the point of intersection 
of the line ZFZ, and the curve AF in fig. 1 the pressure and tem- 
perature for both curves is namely the same; as, however, the curve 
KF passes through the points with maximum temperature of the 
boiling point lines in fig. 1 and as this is not the case with the 
line ZZ, a higher temperature (the pressure being equal) is found 
1 
on curve KF than on the line ZFZ,. The P,7-curve of the line 
