Relationship between Molecular Cohesion 483 



these kinds of electrons and so is proportional to the cube root 

 of their product. The valence electrons are probably more 

 labile, more easily removed and replaced. They have a 

 different degree of liberty and they cannot be summed with 

 the atomic. 



The formula thus confirms the correctness of Drude's 

 promise that the electrons of the valences differ in their 

 properties from the electrons of the atoms. He concluded 

 that only the valence electrons would be sufficiently free to 

 vibrate synchronously with light and hence these electrons 

 must be particularly concerned in the refraction and dis- 

 persion of light. Drude's 1 suggestion of electrons of different 

 degrees of liberty confirmed, as it was, by experiments show- 

 ing a relation between valence and dispersion, is thus con- 

 firmed also from the wholly different field of cohesion. 



A still more interesting conclusion may be drawn from 

 this relationship, namely, that a neutral, uncharged atom 

 having no valence will have no cohesion. Since it will have 

 no chemical affinity either, if chemical affinity is, as it ap- 

 pears to be, of an electrical nature, it is thus seen that a close 

 relation must exist between chemical affinity and cohesion. 

 Such neutral atoms will presumably still have gravitational 

 attraction. A free electrical charge on the atom is, therefore, 

 necessary for cohesion, but not for gravitation. Furthermore, 

 the cohesional effect is the same whether the charge be positive 

 or negative; and it is proportional to the number of charges. 

 The formula shows, also, that the effect of a free charge on any 

 atom is proportional to the weight of the atom; that is, the 

 effect of the valence charge is multiplied, as it were, by the 

 number of electron couples in the atom; and the effect of the 

 total number of valence charges in the molecule is multiplied 

 by the whole number of atomic electron couples in the mole- 

 cule. Just how such an effect could be produced, and why the 

 attraction, or cohesive mass, should ultimately prove to be 

 proportional to a linear function (the cube root) of the product 



Drude: Annalen der Physik., [4] 14, 677 (1904)- 



