863 
In order to find the saturation line, under its own pressure. of a 
definite temperature 7’ we take the vapour- and the liquidum surface 
of this temperature 7’; we then obtain fig. 5 in which the pressure 
axis is taken perpendicularly to the component triangle ABC. The 
liquidum surface is represented by the drawn, the vapour plane by the 
dotted lines. If the vapour contains only two of the components the 
vapour side reduces itself to a curve situated in one of the border 
planes; if it contains but one single component it reduces itself to 
a single point. Like in our former considerations, we further assume, 
provisionally, that in the liquidum side occurs neither a maximum, 
minimum, nor a siationary point. 
We further take, at the assumed temperature 7’ and an arbitrary 
pressure P, a saturation line of the solid substance /. If we alter 
the pressure, 7’ remaining constant, this saturation line changes its 
form. If, to the component triangle, we place perpendicularly the 
P-axis and if on this we place the different saturation lines we get 
an isothermic-polybaric saturation surface of /. This surface may lie 
as in fig. 6 or 7; the component triangle has been omitted from 
both figures, the arrows point in the direction of increasing pressure. 
That both cases are possible is evident from what follows : 
V>v. At the assumed temperature 7’ the substance /’ will 
melt at a definite pressure. Because the substance melts with increase 
of volume the saturation line of / will appear on elevation of 
Zn 
P P 
Ze 
Fig. 6. Fig. 7. 
pressure, so that we obtain a surface like in fig. 6, namely with the 
convex side directed downwards. 
V<v. At the assumed temperature 7’ the solid substance 
will also melt at a definite pressure. Because on melting there is 
now a decrease of volume, the saturation line of / will now appear 
on reduction of pressure. We thus obtain a surface like in fig. 7, 
namely with the concave side. directed downwards. 
The surfaces of figs. 5, 6, and 7 are isothermic-polybaric; they, 
therefore, apply only to a definite temperature; if this is changed 
those surface alter their form and situation. On elevation of tempe- 
rature the liquidum and vapour surfaces of fig. 5 shift upwards likewise 
the surface of fig. 6. On elevation of temperature, the surface of fig. 7 
