1159 
RT’ RT « 
ae yr ——— 4, 5 a) 
en 
B AV 
AW 
Hence it follows: 
on addition of a new substance, which does not occur in the 
mixed crystals, the (congruent or incongruent) melting-point of the 
mixed-crystals under constant pressure is lowered. 
We shall briefly consider more in detail the case that a new 
substance is added to the binary invariant (P or 7’) equilibrium; 
E=M, + M,+ L. For this we imagine that in the figs 1—4 the 
points a, a, and a represent the two mixed-crystals M, and M, and 
the liquid Z. In the figs 1 and 3 then a congruent melting takes 
place and in the figs 2 ‘and 4 an incongruent melting. 
When we add at constant 7’ or P a new substance, which occurs 
also in the mixed-crystals, so that ternary mixed-crystals occur, then 
M, and WM, trace the three-phases-curves a, b,c, and a,6,c,; the 
liquid ZL traces the three-phases-curves abc. In figs 1 and 2 the 
three-phases-triangle 6, 6,6 turns its liquid-point 6 away from the 
side YZ of the components-triangle, in figs 3 and + towards this side. 
In a similar-way as with the equilibrium Z, + Z,-+ G we now 
find that also for the equilibrium M, + M,-+ L the sign of (d7’)p 
must be the same as is indicated in the figs 1—4; this is also valid 
for (dAP)r when AV is >0; for AV <0 we must take, however 
the opposite sign for (dP)7. 
Consequently we find the rule: 
when we trace the threephases-curves of the equilibrium M, + 
M,+ L starting from their binary terminating-points, 
then under constant P the temperature decreases, when the three- 
phases-triangle turns its liquid-point away from the side (with the 
binary terminating points) (figs 1 and 2), 
and under constant P the temperature increases, when the three- 
phases-triangle turns its liquid-point towards the side (with the 
binary terminating-points) (figs 3 and 4). 
The reader himself may easely find the rule for the change of 
pressure at constant 7’. 
When the added new substance does not occur in the mixed- 
crystals, so that those rest binary ones, then in the figs 1—4 the 
curves a,b,c, and a,b,c, must coincide with the side YZ. The 
three-phases-triangle 6, 6,6 is then always situated with the angle- 
points 6, and 6, on the side YZ, while the liquid-point 6 is situated 
within the concentration-diagram. Therefore, we imagine in the figs 
