614 
) 
must rapidly increase. If minimum 7, is exactly on the ether 
& . 
| ta) Tb 
side. then —— = — — and so at first the approximate value of 
a da by dx 
1 dp 1 db, 
] oar . ye . » . 
—_—_ = —-—-—,, But if (rs) differs appreciably from 8, an appreciable 
pda by da ; 
deviation can also occur in this. We find, namely, for p; not exactly 
al 1 a 64 dpi: 1 da db = (73) 
on shut pre gesn ONG OR ae ee 
27 by Di b,’ (rs)? pkda a da byda (rs)d 
lda _1-db, d(rs) Ee 8 
the relation O0 = —— — — — holds for minimum 7, also 
ade b,dw — (rs)da 
dpi: 1 db, d(rs) d 
Set. Ag, however, at present, both for ether and 
prde b, dx _ (rs)de 
for water the observations at 7, are not sufficient to allow us to 
judge about the variability of 4, it must be considered impossible 
for the present to decide whether (7s) differs for these substances, 
; dpx 
and if so for which of them (rs) is greater. The value of ; 
prda 
1 dh, 
which seems greater than — ‚ — would lead us to expect that (rs) 
is smaller for water than for ether. If this variability of 6 is attributed 
to the compressibility of the molecule, the water molecule would be 
more compressible than the ether molecule in spite of its simple 
structure. 
Physics. — “The calculation of the thermodynamic potential of 
mietures, when a combination can take place between the 
components.” By J. J. van Laar. (Communicated by Prof. 
H. A. LoRENTz.) 
1. In Dr. HoeNeN’s Thesis for the Doctorate recently published *) 
the usual method of calculation also followed by me in the Arch. 
Tryter ?) and elsewhere is critised on p. 2—4, with which criticism 
I cannot entirely concur. 
In the cited paper in Tryter the problem in question has been 
treated briefly and not very clearly (in a footnote of a few lines), 
1!) Theorie der thermodynamische functies van mengsels met reageerende com- 
ponenten en hare toepassingen in de phasenleer; Nijmegen, L. C. G. MALMBERG, 
1912. 
2) Théorie générale de l'association de molécules semblables et de la combinaison 
de inolécules différentes; Arch. Treyrer (2) 11, 5me partie, p. 1—97. 
