1183 
(as in the ease of argon) could not be made, since isothermals in 
the neighbourhood of the critical point are not available. 
The critical coefficient becomes 
CE — 9.976 
RT. 
the smallest value yet found for any substance. 
For a ready comparison with other substances of simple molecular 
structure we subjoin the following table of the critical values, the 
diameter slope and the eritical coefficient, as far as known at the 
time with sufficient accuracy. 
The numbers concerning xenon are taken from the measurements 
of PATTERSON, Cripps and Gray!), the others from the Leiden 
measurements. 
| Op | Oka | 2 Kaa 
x + 16:6 | 1°155 | 0-003055 | 3-607 | 
O, | —118:82 | 0-4299 | 2265 | 3°419 
Ar | —122:44 | 0-5308 26235 | 3-424 
N, | —147:13 | 0:3110 | 1958 | 3-421 
H, | —239:91 0-03102 | 03940 | 3-276 
The data thus obtained, combined with the values of the vapour 
pressure, allow a computation of the heat of evaporation L and 
of the quantity 
d A Pee Geene 
—_—_{ — |= —_ zm — m 
d log T\ T 7 Et iii ly 
(m’ and m being the specific heats of the saturated vapour and the 
liquid respectively). 
In a later paper we hope to communicate the results of these 
calculations not only for hydrogen, but also for oxygen, nitrogen 
and argon. 
For the investigation described in this paper we have had the 
benefit of a grant from the BoNAPARTE-fund allowed by the “Aca- 
démie des Sciences” of Paris, for which we wish here to express 
our profound gratitude. 
1) H. S. PATTERSON, R. S. Cripps and R. W. Gray, London Proc. R.S. 86 
(1912) p. 579. 
