482 Albert P. Mathews 



tional mass, and states that the cohesive attraction of two 

 molecules is proportional to the product of the two sums of 

 the square roots of the atomic weights of the atoms of the 

 molecules. This relationship, however, is of very limited 

 applicability, if indeed, it correctly expresses the cohesion of 

 any. 



As regards valence, I can find but one other suggestion, 

 that of Sutherland. 1 He showed that the number of equiva- 

 lents, or valences, in simple substances, such as sodium 

 chloride, influenced the value of their cohesion. He was 

 unable to 'establish this relationship for more complex bodies. 

 Nevertheless he assumed that it existed in them and correctly 

 surmised from it the relationship between cohesion and 

 chemical affinity, and adduced it as evidence of the electro- 

 static or magnetic nature of cohesion, "a" was made pro- 

 portional to the square root of the valence. 



The relationship between cohesion and the properties of 

 molecular weight and the number of valences can be inter- 

 preted best by Sir J. J. Thomson's theory of the electrical 

 constitution of matter and valence, and, so far as I can see, 

 on no other hypothesis. It speaks, therefore, for the electro- 

 static, or electro-magnetic theory of cohesion, and, in my 

 opinion, for the latter. 



The relation, M 2 K = (/)(Val" > VMol. WtJ /s , seems at first 

 peculiar. It is odd that the valence of an atom should be of 

 as much importance in cohesion as the weight of the atom; 

 it is a relationship which one would not have anticipated. 

 The significance of this fact, if I am not mistaken, is that the 

 electron couples constituting the molecules are of two kinds, 

 namely, those of the atoms themselves, which added together 

 presumably give the molecular weight; and the valence elec- 

 trons, which differ from the others so that they cannot be 

 added to them. Hence the formula is not M 2 K = (/) (Wt. + 

 Val.), the cohesion being proportional to the sum; but the 

 mass of cohesion is proportional to the cube root of each of 



1 Sutherland: Phil. Mag., [6] 4, 632 (1902). 



