130) 
Hence, on inerease of the pressure, the three-phase triangle turns 
in such a manner that the conjugation line solid-vapour gets in 
front; on diminution of the pressure the three-phase triangle turns in 
the opposite direction, but in such a manier that the conjugation 
line solid-liquid precedes. 
On increase in pressure the two three-phase triangles of fig. 3 
(I) with their conjugation line solid-vapour in front, will therefore 
move towards each other; on diminution in pressure they move away 
from each other, with the conjugation line solid-liquid in front, to 
be converted, for instance, into fig. 8 (I). If in fig. 11 (I) we sup- 
pose each liquid to be united with its correlated vapour and the 
solid substance /’ we notice that the three-phase triangle moves in 
conformity with the above mentioned rule. 
It is evident that we must not look upon this rotation of the 
three-phase triangle as if this turns in its entirety without a change 
in form; during this rotation not only the length of the conjugation 
lines solid-liquid and solid-vapour is changed, but also the angle 
formed by the two lines. 
In the case mentioned sub 2 the changes in the volumes have 
the opposite sign to that mentioned in the case sub 1; the three- 
phase triangle then of course will turn in the opposite direction namely 
in such a manner that on increase in pressure the conjugation line 
solid-vapour gets in front. 
A similar case we meet in fig. 12 ([),*if in this we take two 
three-phase triangles, one at each side, and adjacent to the straight 
line Hin m,; the two triangles turn the conjugation line solid-vapour 
towards each other. On lowering the pressure the two triangles must 
move towards each other and on increasing the pressure they must 
part from each other, which is in conformity with fig. 12 (1). 
In the case mentioned sub 3, the two conjugation lines, solid- 
liquid and solid-vapour, of the three-phase triangle will, on increase 
in pressure, move towards each other, and on decrease in pressure 
part from each other; in the case mentioned sub 4 they move in 
opposite directions. 
Let us suppose that the exphased vapour saturation line of /, in 
fig. 13 (1) is situated at the other side of £. We now take a liquid 
close to the point m so that its conjugated vapour is adjacent to 
the point m,. The three-phase triangle then forms in / an angle of 
nearly 180°. As here occurs the case mentioned sub. 3, the two con- 
jugation lines solid-liquid and solid-vapour must draw nearer each other 
on increase in pressure. And this is in-agreement with fig. 13 (I). 
If we take a liquid close to the point M and hence a vapour 
85 
Proceedings Royal Acad. Amsterdam. Vol. XV. 
