417 
Physics. — “On the second virial coefficient for di-atomic gases”. 
By Dr. W. H. Krrsom. Supplement N°. 25 to the Communications 
from the Physical Laboratory at Leiden. (Communicated by 
Prof. H. KAMERLINGH ONNEs). 
§ 1. Introduction. Synopsis of the more important results. In 
Supplements N°. 24a ($ 1) and 5 (§ 6), in which the second virial 
coefficient was deduced from different particular assumptions concern- 
ing the structure and action of the molecule, a comparison was 
contemplated between the results then obtained and such experi- 
mental data as are at present available. The present paper will 
discuss some results obtained by carrying out such a comparison in 
the case of di-atomic gases. The importance of such a comparison, 
as well as of a comparison of the second virial coefficients for 
various gases, especially for di- and mon-atomic gases, from the point 
of view of the law of corresponding states, was emphasized in 
Comm. N°. 127c, § 1 (these Proceedings p. 405). That such a comparison 
can now be made with any fruitful result is due to the extensive 
series of accurate isotherm determinations made by KAMERLINGH ONNES 
and his collaborators, BRAAK, CROMMELIN, and W. J. pre Haas. 
In the present investigation a beginning is made with the di-atomic 
gases, especially with hydrogen, for these reasons: In the first place 
the most immediately indicated simplified hypothesis that can be made 
concerning the genesis of molecular attraction and can give any 
hope of agreement with experimental results ') is that first intro- 
duced by Remeanum, which represents it as originating in the mutual 
electrostatic action of doublets of constant moment immovably attached 
to the molecules at their centres; this, together with the assumption 
that the molecules collide as if they were rigid spheres of central 
symmetry, leads to a value of the specific heat which agrees most 
closely with that of the di-atomic gases dissociating with difficulty at 
ordinary temperature; for these gases a law of dependence of # 
upon the temperature quite definite, and therefore ready to be tested, 
was deduced in Suppl. N°. 246 §6 from the above assumptions. In 
the second place, values of 5 for hydrogen are known over a much 
more extensive temperature range than for any other gas with the 
') See M. REINGANUM, Ann. d. Phys. (4) 38 (1912), p. 649 for the rejection of 
the explanation of molecular attraction by gravitation, or (at least of the total 
molecular attraction, cf. p. 429 note 2) by the magnetic action of series of rnag- 
netons assumed to be present in the molecules of paramagnetic and ferromagnetic 
substances. 
