Hence, as a rule dn, dm and dq are not 0; if, however, we can 
draw through the point zy of the saturation curve under its own 
vapour pressure a tangent passing through the point /’ we find: 
hence dg =0, whereas dn and dm differ from nil. It means that 
no vapour takes part in the reaction so that the system [HL is 
converted into another system /’+ L’ devoid of vapour. 
We have noticed previously that the saturation line of the sub- 
stance / under its own vapour pressure which passes through the 
point # can have a form like the curve Fab of fig. 2 (II). At a 
somewhat lower temperature this curve still possesses about ihis 
form but it becomes cireamphased. In fig. 4 a part 
of this curve has been drawn. So long as the point /” 
is situated sufficiently close to this curve we can draw 
through / four tangents at this curve with the points 
of contact , Rk’, X and XX’. Let us now imagine in 
fig. 4 the saturation line under its own vapour pressure 
to be shifted further towards the left and also its 
correlated vapour line to be drawn. 
We now allow a conjugation line solid-liquid to 
turn from m in such u direction that the pressure 
increases. Let us now proceed from m towards a. On 
the branch mf, the conjugation line /“liquid turns 
towards the vapour point, from A} to #’ away from the vapour 
point and from A’ to a and further on it again turns towards the 
vapour point. The same applies to the branch mAXA’b on which, in 
the points X and A’, the direction of the rotation of the conjugation 
line gets reversed. The conversion of # + L into / + L’ + G then 
takes place on branch mF and 7 XN (andn_X ) with increase in volume, on 
branch RR’ (and AX) with decrease in volume and on branch 
R’a (and A’5) again with increase in volume. In the point of contact 
Rk now appears the case sub 42 and in the point of contact /?’ 
the case cited sub A3. Let us take for instance the two-phase 
complex /’+ liqnid A. We now notice that on increase as well as 
on decrease in pressure the conjugation line F-liquid F gets situated 
within the new three-phase triangle so that /’-+ liquid ? is converted 
into IH LL + G’. 
On an infinitesimal change in pressure, nothing takes place in the 
Fig. 4. 
points Zand 2’ but a solution, or a erystallisation of solid matter. 
As /* melts with inerease in volume and in this case also dissolve 
