The true value of "a" of Tan der Waals' epation 

 and the nature of cohesion. 



1ÏY 



A. P. MATHEWS. 



(The University of Chicago, Chicago. December, L916. 



In a recent paper in the Proceedings of the Amsterdam Academy, 

 van Laar *) has severely criticised the law I have discovered expres- 

 sing the mass factor of the cohesional attraction of the molecules, 

 in other words van der Waals' constant a, in terms of the 

 gravitational attraction and the number of valences in the molecule. 

 This law is of such significance and is so important that its basis 

 in fact, upon which it rests, must be scrutinized very closely. The, 

 criticism of any student of the subject is to be welcomed, therefore, 

 altho the tone in which van Laar has expressed his criticism is to 

 be regretted. It is evident that he bas misunderstood a portion at 

 least of my work, for I cannot believe that he has intentionally 

 misrepresented what I have done, altho the misrepresentation appears 

 to me to be inexcusable. I am, nevertheless, glad of the opportunity 

 his attack has given me of presenting the additional evidence which 

 I have obtained since the publication of my first papers, evidence 

 which, I think, removes many of the grounds of 'criticism of my 

 former papers and establishes much more firmly the law of cohesion 

 announced therein. 



The principal result of my work has been the discovery that van 

 der Waals' constant, a, is equal to N 2 (m 2 k X ValjMf lz . 

 In this equation m is the gravitational mass of a molecule: 

 k is the gravitational constant; Val the number of valences; 

 M the molecular weight ; and N the number of molecules in 

 the volume of gas or liquid for which a is computed. This 



a ) Van Laar : Proceedings, Koninklijke Akademie van Wetens, te Amsterdam, 18, 

 1916, p. 1235. 



D 1* 



