556 
pound is alsa possible when no formation of mixed-crystal takes place 
whatever. The mutual proportions, however, are very different there 
and, as we will notice below, the conditions for the appearance of 
these remarkable points are also different. 
2. The general equation for the three-phase equilibrium in a 
binary system can, as is well-known‘), be written as follows: 
En dP («s— er) Qes — (es — #6) Qrs 
ig al ae E "\ Ir ij ‘ <n yr . - £, ® (1) 
dil (es — ey) Vos — (es — «G) Vis 
or 
vs rr | UG 
Se wag =r ES 
_ Od LS — UL a 
Prati co (2) 
; Ws LG v - 
GINT eras 
Ug: WJ 
in which the symbols with a double phase-index indicate respectively 
the heat and the change in volume when one gram-molecule of 
one phase is dissolved in an infinitely large quantity of the other, 
the external conditions being kept constant. Qgs has, therefore, 
the order of a sublimation heat, Qzs that of a melting heat. Hence 
Qgs is usually a few times greater than Q,s. Likewise Vas is 
always greater than Vs and this in the order of 10+ times greater. 
Let us now consider first a system 
with a continuous series of mixed 
crystals such as the system p Cl,C,H, 
—-p Br,C,H, *), in which the three- 
phase line has a form as in fig. 1 
when sketched as P7- and Tx-projec- 
tion. We remember that for a ina- 
ximum (or minimum) it is necessary 
that the numerator in the equation (2) 
should become zero and that for this 
it is required that 
“S—“, ° Qrs rie i 
1) Compare VAN DER WAALs-KOHNsTAMM, Lehrbuch der Thermodynamik II p. 
521 et seq. (Leipzig 1912). 
2) Comp. my communications I and II in these Proc. 1909, 537 and 1910, 206 
also Zeitschr. f, physik Chem. 79, 657 (1912). 
——_—s 
