937 
as the measurements of the dielectric constant lie partially in the 
field of temperature, where the values for B calculated on the 
assumption of bipoles deviate from those determined experimentally, 
and moreover the supposition upon which the calculations are 
based will not entirely correspond to the facts. 
Finally, I should like to draw attention to the conclusions, which 
follow from these calculations, for the determinations made by 
Pu. A. Gure!) and his fellow-workers of the molecular weight of 
gases from the weight of a litre under normal circumstances and 
the compressibility. These measurements, which have been made 
with the greatest care, have not always led to a satisfactory 
agreement between the molecular weight determined in this and 
other ways, especially in the case of easily compressible gases. 
From our calculations it follows 15 that for an accurate determination 
of the compressibility the measurements must be so arranged that 
they ‘enable us to determine?) with the necessary accuracy not only 
B but also C; and 2"! that when it is not established in another way 
that a given gas behaves as a normal substance, the compressibility 
for that gas must be specially determined. 
Our calculations demonstrate that the deviations from the law of 
corresponding states, which in various substances may be very 
important as regards the value of 5, may be even greater for C, 
so much so that the sign*) for substances with and without bipoles 
may be different. The fact that for some gases including ammonia 
a correct value for the molecular weight was obtained by making 
use of the law of corresponding states, even where this was not to be 
expected according to the preceding discussion, must therefore be 
regarded as due to accident. And it is not to be expected that at 
other temperatures an equally good agreement would be found. 
1) See for instance Mém. de la Soc. de Phys. de Genéve (35) 1905—1907. and 
further Journ. d. Chem. Phys. various volumes. 
2) This conclusion was also drawn by H. KAMERLINGH ONNEs and W. H. Kersom 
Enc. Math. Wiss. V 10 p. 902. They alsc point out here (p. 909) the influence 
of the deviations from the law of the corresponding states upon the determinations 
of the molecular weight. 
3) Whereas B changes its sign for all substances examined, a possible difference 
of sign at equal reduced temperatures may thus be ascribed to the choice of the 
critical quantities as corresponding, this is not the case with C. For normal 
substances (see H. KAMERLINGH ONNES Comm. Leiden NO, 74, p. 10) C is every- 
where positive and increases with falling temperature. 
60 
Proceedings Royal Acad. Amsterdam. Vol. XIX 
