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or: 
we Oo (VE Ot) Bees A ee ey 
wherein C and C, are independent of P and 7. When we intro- 
duce the partial vapour-tension : 
Psa, Pa=y,P and Po=(1l—«,—y,) P 
then (2) passes into: 
alog Pa + Blog PB + (1—a—p)log Pp = C . . . . (3) 
Or: 
4 B plas : 
Bas ai 8 fe a= (yt leus CO) 
_ When we keep the temperature constant, it follows from (1) 
(we) 7, -F (y¥,—8)s,] da, + [le ee, + (WB dy, = 
OV, OV, . 
me |" Ph (aw) Ov, + (8—y,) | dP 
We call / the distance from / to a point (x, y,) of the vapour- 
saturationeurve; we take d/ positive in sueh a direction that / 
becomes larger. Then we have: 
dl dz, dy, 
l ea vof 
When we substitute these values of dw, and dy, in (4) and when 
we represent the coefficient of dP by AV,, we find: 
Poe 1. AV,.dP 
(or, + 2 (@,—@) (y,—B) 8, + (B), 
Herein AV, is the increase of volume when 1 mol. solid / 
sublimates into such a large quantity of vapour that the composition 
does not change. It follows from (5): each point of the vapoursatu- 
rationeurve moves on increase of pressure (dP>>0) away from 
F (dl > 0) and on decrease of pressure (dP <0) towards F 
(dl< 0). We may express this also in the following way: on 
increase of pressure the vapoursaturationcurve extends itself, on 
decrease of pressure it contracts. 
In a similar way we find: on increase of pressure the vapour: 
saturationeurve contracts, on decrease of pressure it extends. 
When we keep the temperature constant and when we lower the 
pressure, then the vapoursaturationcurve shall, as it contracts, reduce 
itself under a definite pressure to the point #. The solid substance /’is 
then in equilibrium with a vapour of the composition /’ or in other 
words: the solid substance / sublimates. To every temperature 7’ 
consequently a definite pressure P belongs, under which /’ subli- 
mates. When we draw in a P, 7-diagram the temperatures and the 
(4) 
(5) 
