959 
The coefficient of inclination of the diameter is: 
bar = — 0.0019577, 
and thus a good deal smaller than the coefficients of argon (—-0.0026235) 
and of oxygen (— 0.002265). 
The “undisturbed” critical density derived from the diameter using 
as the eritieal temperature —147°.13') is found to be: 
ord = 0.31096. 
A comparison with the value for the “undisturbed” critical density 
: 5 3 > n Op dp 
which might be derived by the aid of the equation ( ,) = (ar) 
7 hf OI A Pe 
from the vapour-pressure curve and the isotherms near the critical 
point (as this was carried out for argon) is impossible for nitrogen, 
as isotherms are not available in the mean time. 
The critical coefficient is 
Kad = da, 
a comparatively small value, as was to be expected in connection 
with the simple molecular structure of nitrogen, its deviation from 
the theoretical value } is in the same direction and to much the 
same degree as that of argon (3.424) and that of oxygen (3.419) ’). 
The liquid densities at the lower temperatures are in fairly 
good agreement with those found bv Baty and Donnan *), the diffe- 
rences being of the order of 1°/,. 
Physics. — J/sothermals of di-atomic substances and their binary 
mixtures. XVI. Vapour-pressures of nitrogen between the 
critical point and the boiling point” By Dr. C. A. CROMMELIN. 
(Communication N°. 145d from the Physical Laboratory at 
Leiden). (Communicated by Prof. H. KAMERLINGH ONNss). 
(Communicated in the meeting of December 30, 1914). 
The determination of the density-curves and the diameter of 
nitrogen *) offered a welcome opportunity for determining the vapour- 
pressures of nitrogen between the critical point and the boiling 
point, therefore in the region of the higher pressures, and thus 
making a contribution towards the knowledge of the equation of 
1, H. KAMERLINGH ONNES, C. DoORSMAN and G. Horsr, This number of the 
Proc. Comm. 1455. 
2) Calculated with the critical constants of Comm. 1455. 
8-1. €. 
4) E. Maruias, H. KAMERLINGH ONNES and G. A. CROMMELIN, This number 
of the Proc., Comm. N°. 145c. 
