1302 
adjacent to the point M,, the case mentioned sub 4 oceurs and 
the movement of the conjugation lines is in conformity with the rule 
deduced above. The cases mentioned sub 3 and sub 4 also occur 
in other figures, for instance also in fig. 12 (U). 
In the above considered conversion of / + L we can distinguish 
three special cases. 
1. The case, mentioned above sub A 2 and A 3, which has already 
been discussed in detail, when no vapour is formed at an infini- 
tesimal change in pressure or in volume. 
2. At an infinitesimal change in volume the quantity of the liquid 
does not alter (its composition, of course, changes). 
3. At an infinitesimal change in volume the quantity of solid 
matter does not change. 
In each of these cases one of the sides of the three-phase triangle 
will occupy a special position. We have already noticed previously 
that in the case mentioned sub 1 the conjugation line solid-liquid 
meets the saturation line under its own vapour pressure. 
In the case mentioned sub 2, di in the formula given in the 
previous communication V (p. 1213) must be taken = 0: from that 
it follows that the tangent drawn in the liquidum point to the 
saturation line under its own vapour pressure is parallel to the con- 
jugation line solid-vapour. 
In the case mentioned sub 3 dn in the said formula must be 
taken ==0; this signifies that the conjugation line liquid-vapour touches in 
the liquidum point the saturation line under its own vapour pressure. 
In the saturation curves deduced previously diverse examples of 
these cases are to be found. 
It is evident that in the system £ + G, three corresponding cases 
may be distinguished; these then relate to the direction of the tangent 
in the vapour point of a vapour saturation line under its own vapour 
pressure. 
We will now consider the case already mentioned in the previous 
communication sub B, when a phase reaction between the three 
phases takes place. The three phases are then represented by three 
points of a straight line and the pressure for the system 7+ L 4 G 
is then a maximum or a minimem. 
Let us first take the case mentioned sub B1 when the reaction 
F2L+G occurs; the point / then falls between the points £ 
and G as, for instance, in fig. 4 (I), if in these figures we suppose 
a, to bave coincided with 6, and a with 6. We then obtain fig. 5 (I) 
