( 874 ) 
the mixtures rich in aniline were very viscous, and showed great 
super-heating, which sometimes ascended as high as 25° degrees, 
and rendered any measurement impossible. The results have been 
collected in tables IV and V. 
Further consideration and comparison of these data shows that we 
have to do here with systems interesting for more than one reason. 
In general the rule holds that of two substances that with the larger 
molecule has also the greater a, and accordingly is the less volatile 
one. In accordance with this most of the examined systems belong 
to the righthand or to the middle region of the general diagram of 
isobars. Now the mixtures of aniline with hexane and cyclohexane 
present systems with a very pronounced difference in volatility. 
Whereas hexane and cyclohexane have a vapour tension of 125 mm. 
à 150 mm at + 33°, that of aniline is less than 0,1 mm. at that 
temperature‘). Notwithstanding this aniline has the smallest 
6 (0.006123 in the ordinary units *), 0.006247 for cyclohexane and 
0.007849 for hexane). That in spite of this the aniline is so much 
less volatile is owing to this that here the @ does not rise, as it 
usually does, and even rapidly, with inerease of 6, but even decreases. 
The a for aniline is in the same units 0.05283 to 0.05190 for cyclo- 
hexane and 0.04928 for normal hexane. So we have either systems 
with continually decreasing temperature of the unsplit mixture (lefthand 
region) or systems with a minimum 7% (middle region); in which 
case we are, will depend on the value of a,,. Now theory teaches 
that the existence of a point where z, =, (maximum in the p‚r- 
curve, minimum in the 7’,x-curve) is in the closest connection with 
the presence of a minimum critical temperature of the unsplit mixture. 
These two properties occur namely at the lowest temperatures for 
the same value of z; at higher temperature the mixture where 
2, =, shifts always further to the lefthand side (smaller 5, so here 
to the aniline-side)*). Now as the point 2,= 4, is not present in 
the boiling-point line, so at higher temperature, we must conclude 
for the present that really the differences in column 5 of table II 
must be ascribed to difference of purity between the substances 
investigated by us and by Sypney Youre. If a further investigation 
should prove the contrary, so that at lower temperature a maximum 
does exist, then we should meet here for the first time as far as 
we know with a case that is in opposition to the rule given by 
1) Kautpaum. Z. phys. Ch. 26 p. 603 (1898). 
2) See Lanpott and Börnsrein's tables. 
3) Théorie moléculaire § 9. Cf. further van per Waats, These Proc, IV. 549 
and Kounstamm Z. phys. Ch. 75, p. 527 (1910). 
