486 Albert P. Mathews 



involve the number of valence electrons, is the relation be- 

 tween the magnetic and cohesive properties, since here we 

 touch, I think, the very kernel of the problem of the nature 

 of cohesion. 



The connection between the magnetic properties and 

 cohesion is brought out very clearly, in an empirical way, 

 by Pascal's 1 investigations on the relation between magnetic 

 susceptibility and the molecular properties. In a series of 

 papers Pascal has shown that there is a remarkable con- 

 nection between the specific susceptibility of diamagnetic 

 elements and the atomic weights and valences. Thus if 

 elements of the same family having the same valence are 

 arranged in their order of increasing specific susceptibility, 

 they are in the order of their atomic weights; and, on the 

 other hand, a close dependence on valence may be observed. 

 In elements of nearly the same weight but of different valence 

 numbers, the atomic magnetic susceptibility, X a , increases 

 with the number of valences. An empirical relationship 

 was found between them, X a io~ 7 e a + l * a where a is 



about 2.1, /? about 0.004 and a the atomic weight, a and p 

 depend only on valence. But here, also, double bonds made 

 their effect felt, though less pronouncedly than in refraction. 

 Double bonded molecules have, in general, a lower molecular 

 susceptibility than that calculated. Other effects of molecular 

 form are seen; for example, the benzene nucleus augments 

 the diamagnetism, although the double bonds it is supposed 

 to contain should have an opposite effect. The factor of 

 molecular structure appears, then, to influence diamagnetism. 

 On the whole, however, calculation of the number of valences 

 in the molecule by this procedure agrees better with the calcu- 

 lation from the cohesion, than does the calculation from the 

 refractivity or dispersion. Thus, double bonds are of less 

 action on the diamagnetism and in the benzene nucleus they 



1 Pascal : "Sur im mode de contr61e optique des analyses magne" tochimiques, ' ' 

 Comptes rendus, 152, 1852 (1911). Recherches magne to-chimiques sur la struc- 

 ture atomique des halogenes," Comptes rendus, 152, 826 (1911). Ann. Chim. 

 Phys., [8] 19, 1-80 (1910). 



