1029 
O. This would have to make the mixing still more thorough, if possible 
but it did not cause the slightest change of the plaitpoint temperature. 
The eritical phenomenon preserves its characteristic peculiarities 
and the same intensity up to the highest pressures that we have 
examined, which bears further witness to the fact that the plaitpoint 
concentration changes only very little, so that it remains the same 
all over the extensive range of pressure and temperature considered 
here. In this it is absolutely required to keep the pressure per- 
fectly constant during the measurements, as otherwise the VAN DER LEE 
effect *) would disturb the observations. It is fortunately, however, 
easy to distinguish whether the cloudiness which appears in the 
liquid, is the consequence of the slow cooling of the thermostat or 
of an abrupt cooling which takes place in the examined liquid 
itself owing to an expansion by decrease of pressure. [n the 
former case, namely, the cloudiness begins on the ontside, and 
proceeds towards the centre, whereas in tbe latter case it arises 
in the centre, and spreads from there in all directions. The sensi- 
tivity of the vaN DER Ler effect in these circumstances shows that 
the equilibrium of pressure between the manometer and the liquid 
itself sets in almost immediately. A last proof for the accuracy of 
the measurements in the new apparatus is afforded by the compa- 
rison of the results obtained in this way at low pressure with those 
obtained in Cailletet tubes. 
Some values will give an idea of the attainable accuracy. 
a. The plaitpoint temperature remains constant, also after the 
mixture (nitrobenzene + petroleum) under investigation has been in 
the apparatus for two days, under pressures up to more than 500 
atm. As a mean of ten measurements 13.°95 + 0.°06 was found. 
6. The plaitpoint temperature remains constant when the experi- 
ment is repeated with different fillings. 
Water + triethylamine, critical end-point 18.°35 and 18.°36 
The same system in a Cailletet tube yields 18.°33 
c. The increase of the plaitpoint temperature per atmosphere is 
the same for different fillings, and also for determinations in a Cail- 
letet tube. As an example we take the system cyclohexane + aniline. 
dt as 
EE between 1 and 200 k.g. per cm.” yields —+ 0.0067 
jh 
in a Cailletet tube was found. + 0.0066 
1) These Proceedings, XIII p. 517. 
61 
Proceedings Royal Acad. Amsterdam. Vol. XV. 
