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Physics. — “/svtherms of monatomie gases and of their binary 
mirtures. VIL. Isotherms of argon between + 20° C. and 
— 150° C.” By Prof. H. KAMERLINGH Onnzs and C. A. CROMMELIN. 
Comm. N°. 118° from the physical laboratory at Leiden. 
(Communicated in the meeting of October 29, 1910). 
§ 1. In the first publication *) of determinations of: isotherms of 
gases at low temperatures made when these had already been a 
long time in progress mention was made of the desirability of an 
investigation of argon and helium; to these we may now add neon *). 
We were able to publish helium measurements as early as 1907 °*), 
but argon data were not accessible until a sufficient quantity of 
argon (about 25 L.) with not more than 0.1°/, impurity was obtained 
at a much later period (1909). The method of obtaining this has 
already been deseribed*). This degree of purity is sufficient for 
isotherm determinations. Measurements of vapour pressures, of eritical 
constants‘) and also ef coexisting liquid and vapour densities *) have 
already been made with the same gas as was used for the isotherms. 
As was the ease with hydrogen") care was taken in the determi- 
nation of the argon isotherms given below that the observed points 
should be appropriately distributed over each isotherm and that 
suitable temperatures for these should be selected. Still, the shape 
of the isotherms made it desirable that the points observed should 
not be so closely packed in normal positions as was the case with 
hydrogen. 
Since all required densities cannot be obtained with one and the 
same piezometer reservoir, points for each isotherm must be divided 
into groups. The various groups of points which afterwards constitute 
a single isotherm were as far as possible observed at the same 
temperature by suitable adjustment of the cryostat pressure ; corrections 
given by graphical evaluations of a were subsequently applied 
1) Proc. April 1901, Comm. No. 69. 
2) Proc. June 1909, Comm. No. 112. 
35) Proc. Dec. 1907, Febr. and March 1908, Comm. No. 102, a, b and c. 
4) Proc. May 1910, Comm. No. 115, and CG. A. Crommenin, Thesis for the 
doctorate, Leiden, 1910. 
5) Proc. Dec. 1910 Comm. No. 1182. 
6) Proc. March 1907. Comm, 97a, Dec. 1907, Comm. No. 99a, Dec. 1907, 
Comm. No. 100. 
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