962 
§ 6. Discussion. ~The slope of the diameter is given by 
bar = — 0.0026235. 
This coefficient is very large, larger than has been found for any 
other substance yet investigated with the exception of xenon, for 
which PATTERSON, Cripps and WryrLaw-Gray ') have found —0.003055. 
Comparison of the values of this constant for the two monatomic 
substances argon and xenon again reveals the influence exerted upon 
it by the values of the critical temperature. 
With respect to the critical density the following remarks must 
be made. If we assume that the diameter remains rectilinear right 
up to the critical point, we then tind 
Ord = 0.53078. 
(Op dp ) 
oT oe ae ge koex.k. 
(0d: 
Using the equation 
the value 
Ok.s.. 
was previously found from the argon isotherms.*) The difference 
between these two values is of the same order of magnitude and 
is in the same direction as the differences found for other substances, 
carbon dioxide”), methyl chloride), sulphur dioxide *) amongst others. 
The fairly large deviation from rectilinearity of the experimental 
diameter apparent in the neighbourhood of — 125°.17 Cin sr. agrees 
well with this behaviour. 
3.283 was the value previously ©) obtained for the critical coefti- 
cient on taking Kyg = Ky,: we now find 
Kyq == 3.424 
which is therefore slightly greater than that for oxygen’) (3.346) 
If, therefore, we leave Kya = 3.13 for helium out of account, oxygen, 
and not argon, is the substance for which Kyq lies nearest the theo- 
— 
retical value, 2.67, deduced from van DER Waars’s equation. 
1) PATTERSON, Cripps and WuytLaw-Gray, Proc. R.S. (A.) 86 (1912), p. 579. 
2) G. A. GROMMELIN. Proc. Dec. 1910, Comm. No. 118a, and Thesis for the 
doctorate, Leiden 1910. 
3) W. H. Keesom. Proc. Jan. 1904. Comm. No 88; H. KAMERLINGH ONNES 
and W. H. Kersom, Proc. Febr. 1908. Comm. No. 104a 
4) C. H. BRINKMAN, Thesis for the doctorate, Amsterdam 1904, 
5) E. CARDOSO, Arch. se. phys. et Nat. Genève. (4). 34. (1912) p. 127. 
6) H. KAMERLINGH ONNES and C. A. GROMMELIN. Proc. March 1911. Comm 
No. 121a. 
7) E. Maruras and H. KAMERLINGH ONNES. Proc. Febr, 1911. Comm. No. 127. 
