954 
have been partly, but not entirely surmounted. The obvious 
choice lay between nitrogen and carbon monoxide and it fell on 
nitrogen partly because for this substance more thermodynamical 
data are available than for carbon monoxide, whereby the import- 
ance of the investigation is much enhanced and partly because we 
could use the very pure nitrogen, with which determinations of 
the critical constants") had been made. A separate experiment’) 
showed that the nitrogen was indeed of very high purity. 
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Fig. 1. 
§ 2. Apparatus. The apparatus were practically the same as 
used for the determination of the diameter for argon; we, therefore, 
') This number of the Proc., H. KAMERLINGH ONNES, C. DORSMAN, and G. Horst, 
Comm. NO, 1455. 
2) Comp. this number of the Proc. CG. A. GROMMELIN, Comm. N°. 145d. 
