VAN DER WAALS about the displacement of the point.c, =.v,. Perhaps 
the best way to decide this question will be by a direct determination 
of the plaitpoint line L—G. We hope to carry it out as soon as 
we shall again have a sufficient quantity of cyclohexane at our disposal, 
There is another eircumstance which draws the attention in these 
systems, and which also points in the direction of a non-existence 
of a point z,=#,. We refer here to the very great difference in 
volatility between aniline and the respective other components, of 
which we already spoke. At the temperatures of examination the 
vapour tension of hexane and cyclohexane is more than 1000 times 
that of aniline. Now it does not seem probable that the vapour tension 
of a substance could rise by the addition of a substance so much 
less volatile, as would be required for a maximum. In general this 
is even considered as so self-evident that when the two components 
differ very much in volatility, the validity of van ’r Horr’s law is 
vy 
Oe And Sinise ois 
: dp as 
generally simply accepted ——- = — 1, so lim 
paw vy 
nearly always in accordance with experience. That, however, a great 
difference in volatility does not always justify the supposition 
v 
lin — = 0, the systems aniline with hexane and cyclohexane, and in 
vy 
a still higher degree nitrobenzene with isopentane and hexane prove, 
because in the latter the difference of volatility is still greater. For 
what conclusion we may want to draw from tables II and III 
concerning the existence of the maximum, this is conclusively proved 
by it, that the vapour pressure line descends very little from the 
edge if at all. Take e.g. the measurements of the two-phase pressure 
for a mixture of the critical concentration just above the temperature 
of the critical end-point. These mixtures have a concentration of 
about w—0.5, but their vapour-pressure is not measurable lower 
than that of the volatile component in pure state. And compare 
with this e.g. the mixtures of aniline and nitrobenzene with ether 
examined by Raourr *j. Though at a concentration of 50 °/, the vapour 
pressure has not diminished to half its value, as extrapolation of the 
rule of van ‘t Horr would give for these non-diluted solutions, yet 
the ratio found (about 3/5), differs only comparatively little from it. 
It is true that a similar phenomenon as for the systems mentioned 
was already known for phenol and water, but the abnormality of 
the two components led us to suppose that this was caused by this abnor- 
mality. The three systems examined here show that also for mixtures 
1) Z. phys. Ch. 2 p. 353 (1888). 
