( 540) 
In order that (2) 
d 
volume, be equal to 0, (=) must be equal to zero somewhere 
Lt vT ' 
dv, integrated between the liquid and the vapour 
of 
between these two volumes. In consequence the particularity that 
mixtures may be formed, for which 2; = 22 occurs only when a 
locus exists in the av diagram, along which GE) Accordingly 
Quint. has observed the circumstance that, keeping 7’ constant the 
curve p=f(e,v) in the mixture of HCl and C,H, shows a maxi- 
mum. In Cont. II p. 86. I have discussed such a locus, and 
proved that for great volumes it has an asymptote parallel to the 
volume-axis, and that for small volumes it moves to the side of the 
component for which b is greater. In fig. 7 the dotted line passing 
through P and Q, represents this locus. On the left of this curve 
en is positive, and on the right negative. All the isobars must 
US oT 
then possess a tangent parallel to the z-axis in the points where 
they cut this locus. In fig. 7 the course of some curves of equal 
pressure has been traced. The temperature is assumed to be so 
low that the plait on the y-surface stretches over the whole breadth 
dy 
of the diagram, and so the curve, for which ee = 0, continues 
vaart 
to consist of two isolated branches. The curves LPM and L'Q M' 
represent these branches, viz. the dotted ones. 
The limits of the unstable region are somewhat wider, and they 
are also indicated as passing through Z,P and M, or L', Qand M'; 
in the figure they are indicated by lines of alternately larger and 
smaller dots. That these limits of the unstable region must pass 
through P and Q, follows from the property, that if () is equal 
vs yT 
to 0, the condition: 
op dey Lf dw )= 
da? de? de dv 
2 
is satisfied in the points, in which ee Tt (2) = 0 is. 
u” GEAR 
If we closely examine the character of the points P and Q, we 
conclude that p in the point Q is really a maximum. The point Q, 
