perature we must first of all proceed in the direction indicated by 
van derWaals') where he treats of the three-phase equdibna 
of a binary compound with liquid and vapour. 
To the tpM-surface of the liquid and vapour condihon another 
one bas to be added which shows the connection between those 
quantities in the homogeneous solid phase. If we consider the case 
occurring most frequently that the fusion takes place w.th an increase 
in Volume this surface will be found between the liquid-vapour 
surface and the iiw-plane. ,, , . , 
As to the form of this new qiws-surface it should be observe 
that it will practically be a plane with descriptive lines proceeding 
from the ipv-plane for x = 0, to that for x = \. For the mixing of 
two solid substances to a homogeneous solid phase takes place either 
without a change- in volume or with a hardly appt eeiab e one )_ 
If we now wish to know which are the coexisting phases we must 
allow tangent planes to move over these surfaces and thus cause 
the appearance of the derived surfaces and connodal lines ). 
Let us commence by considering a 
surface for a temperature below the triple¬ 
point temperatures of the components. 
The surface for the solid condition will 
then be situated very low, the tangent 
plane will rest both on this surface and 
on the vapour part of vapour-liquid sur¬ 
face. The lines and g x K ^ % 2 
indicate the connodal lines so formed. 
The derived surface thus obtained will be 
situated lower than the derived surface 
which rests on the two parts of the 
vapour-liquid surface and which, there¬ 
fore, does not represent stable conditions, 
but the vapour equilibria of “super¬ 
cooled” liquids. The connodal lines (<?A 
and ej x ) proceeding therefrom are situated 
between the connodal lines of the solid- 
Fig. 2- vapour equilibrium. 
If we proceed to a higher temperature the correlated connodal lines 
i) Verslagen Kon. Akad. V, p. 482, (1897). 
