Physics. — ''On the Course of the Values of n and b for Hydrogen 

 at Different Tefnperatares and Volumes." (Continuation of 

 the Paper of April 8t'\ 1903). By Dr. J. J. van Laar. 

 (Communicated by Prof. H. A. Lorentz.) 



(Communicated in the meeting of October 27, 1917). 



1. Introduction. 



In a Paper published in These Proc. Vol. XIX p. 359—367 

 Prof. VAN DKR Waals advanced the supposition that the quantity a 

 of his equation of stale — at least below the critical temperature 

 and for the small volumes — would be dependent on the volume. 

 At the conclusion of his paper he expresses the hope that also other 

 investigators will feel an interest in this question, and that a serious 

 research will be set on foot also above the critical temperature. 



On the appearance of the said paper 1 had already worked on 

 this subject for a long time, also in connection with n)y researches 

 concerning the fundamental values of \^a for the different elements 

 of the Periodic System '), and I had found that a was chiefly a 

 function of the temperature, whereas ^ appeared to be dependent 

 both on T and on v. 



If, however, a were also dependent on i\ then in my opinion 

 the equation 



a j /v]c 



would at least represent the facts equally well as the equation given 

 by VAN DER Waals 



For Fluorbenzene we find e.g. what follows. 



For the lower temperatures, where c/, has not been measured 



1) It is clear thai it is of the highest importance in this, to know accurately 

 in how far a and b are variable from T = cc to T = 0. The more so as some 

 physicists, among others Mathews, assume in their calculations that the values of 

 a at the absolute zero will not differ much from those at the ordinary temperature. 

 We shall see in what follows that this assumption is very far from reality. 



