671 
the liquid volumes were first calculated directly from the positions 
of the meniscus top in the stem and in the appendix, without 
applying any correction. To the numbers so obtained the following 
corrections were then applied: 
1. A fairly large correction for the diminution of the volume at 
low temperature, seeing that the calibration of the dilatometer had 
been reduced to + 20° C.; the correction was obtained by means 
of a formula from a former Communication *). 
2. A correction for the increase of volume due to the pressure. 
For this correction, which was so small as to be negligible in almost 
every case, approximate values were calculated from data contained 
in two previous Communications °). 
3. <A correction for the volume of the argon meniscus. KeLvIN’s 
graphical method *) was employed for the evaluation of this by no 
means negligible correction. To obtain the volume of the menisci it 
was usually sufficient for our purpose to regard the surface of the 
liquid as half of an oblate ellipsoid of revolution. Only at the higher 
temperatures was it necessary to apply GurpiN's theorem to the 
KrLvin diagram in order to determine the body of revolution. 
1) Proc. Sept. 1906, Comm. no. 95b. 
2) Proc. April 1902, Comm. no. 78, Proc: March 1907, Comm. no. 97a. 
5) The capillary constant for argon and its variation with temperature must be 
known for the construction of these diagrams. Now Baty and Donnan (Journ, 
of the Chem. Soc. Trans. 81. 907, 1902) have determined capillary constants for 
liquid argon but only between — 189 C°, and — 183° C. so that the question 
now arose as to how to interpolate in the most rational manner possible from 
— 183°. C. to the critical temperature. A comparison between the results giving 
the reduced capillary constant (see J. D, vAN DER Waals, Cont. I. p. 
We 
LT ),'/spz"ls 
176) as a function of the reduced temperature by Bary and Donnan (l.c.), for 
argon, by DE Vries (Ziitingsversl. Febr. 1893, Comm. no. 6, and Thesis for the. 
doctorate, Leiden 1893) for ether, by VerscHarreLT (Zittingsversl. Juni 1895, 
Comm no. 18) for carbon dioxide and nitrous oxide was fruitless, seeing that the 
last three correspond well, while argon deviates strongly from them. A suitable 
rational method is given by the assumption of the validity of the Eörvös formula 
(Ann. d. Phys. und Chem. 27 (1886) p. 448) according to which the quantity 
KANE 
Ww ( 3 is a linear function of the temperature. According to BALy and Donnan 
? liq 
MM 2 
we get for argon w, i = 2.020 (145.44 — T); from this formula our esti- 
OP lig 
mates have been made except that for the highest temperature, + — 125° C., at 
which one is so close to the critical temperature that the Eörvös formula no 
longer holds, and for which interpolation was resorted to in correspondence with 
the curves given by other substances, 
