( 690 ) 
RELATION BETWEEN PRESSURE, COMPOSITION AND TEMPERATURE 
FOR COEXISTING PHASES OF A TERNARY SYSTEM. 
I have deduced the differential equation, which represents the 
relation between and dp, de), dy, and dT for the coexisting phases 
of a ternary system (Arch. Néerl. Série IT, Tome II, pag. 74). This 
equation has ba following form: 
92 92 
vn dp = Wace + (On ty) = + (241) say (de al 
0% A5 | 
Fed +o 55 fda ss 
This equation may be derived from the differential equation of the 
coexistence surface (equation 1 of our previous communication) when 
we substitute in it the value of dv, derived from: 
dw dw dw dp 
in ey Ee te st ( jar 
P dv,2 Cal =F Ow, dv v1 AE Oy, Ov, OT Sr oT ne 
Substituting this we get as factor of dp. 
a a SA of 
dw 
dv? 
d 
and as factor of re : 
Den oy 
(v2—?}) du, + (%2—2}) En + (Y2—Y1) dy; Ov, 
(E)o + L (a. 
dey? 
If we disregard the sign we may write the factor of dp as follows: 
dv, dv, 
ea) — ee) (7) — ved, de 
In the same way as we have done for a pee mixture (Cont. 
II, pag. 109), we may show also for a ternary mixture, that this 
quantity represents the amount with which the volume decreases 
per molecule of the second phasis if we mix a quantity of the second 
phasis with the first and afterwards reduce pressure and temperature 
to their original value, provided we take the limiting value of this 
decrease of volume for the case that the quantity of the second 
phasis is infinitely small compared with that of the first. The sign 
Vg, represents this limiting value. 
fi : 
The factor of 7 may be written as follows: 
Gn nd 
