( 867 ) 
The eritical end-point lies at 68° according to SCHREINEMAKERS; the 
two vapour-pressures indicated for higher temperature refer to mixtures 
of the critical concentration; they have been derived from VAN DER 
Ip 
Lee *), who has also determined the value of ar for the plaitpoint 
1 
line. This is 197600 mm. of mercury per degree, and so it is of an 
entirely different order of magnitude than the increase of the three- 
phase pressure in the neighbourhood of the critical end-point (about 
10 mm. of mercury). So these data are in flat contradiction to the 
thesis mentioned, unless we should be ready to accept a very steep 
ascent of the three-phase pressure in the immediate neighbourhood 
of the critical end-point, where no measurements have been made, 
but this supposition is diffieult to reconcile with the rise of the two- 
phase pressures of mixtures in the neighbourhood of the critical con- 
centration, as appears from the last values of the table. 
To have somewhat more material at our disposal, we have made 
some more determinations. Though the conclusion, being of a purely 
thermodynamic nature, must not depend on the nature of the system, 
yet we have fixed our choice on mixtures of normal substances. 
With the measurements we have approached the critical end-point 
as closely as possible. We have chosen one case of splitting up of 
the plaitpoint line (cyclohexane —+ aniline) and one of retreat 
(hexane and nitrobenzene), for which system the course of the plait- 
point line had been accurately determined by one of us before ®). 
The substances used were very pure; we refer to the cited commu- 
nication for further details. 
The apparatus used is the same as had already been used by one 
of us*) for determinations of vapour-tension by a static way. A 
further discussion is not necessary. [t was placed in a large thermo- 
stat (80 L.); the pressures were read with a kathetometer with an 
accuracy of 0.05 mm., after it had appeared by repeated measure- 
ment that the equilibrium had set in. The measurements (which were 
all made by Mr. Timmermans), were first made with rising tempera- 
ture, then with falling temperature; the results always agreed to 
1 mm., which may be considered sufficient for the end in view. All 
the pressures were finally reduced to mm. of mercury at 0°. The 
results obtained are found in tables II and III; in the fourth column 
of these tables we have given the vapour pressure of the most 
1) Thesis for the doctorate Amsterdam 1898. 
2) J. Timmermans. These Proc. XIII p. 507. 
°) Pm. KornsrauM. Thesis for the doctorate. Amsterdam 1901, p. 183. Comp 
also vAN Datrsen. Thesis for the doctorate. Amsterdam 1906 p. 10. 
