698 



The modern electrical theory of atomic structure appears 

 to allow more insight into the nature of! solution than has- 

 hitherto been possible. Atoms should attract one another 

 in the same way as electric doublets. Usually there would 

 be a residual field of force surrounding a molecule, with the 

 result that molecules should attract one another, whether 

 alike or unlike, with a force varying inversely as the 

 fourth power of the distance. A theory of molecular 

 attraction of this kind was treated at some length by 

 Sutherland in a series of papers in this journal. The idea 

 has recently been developed by Sir J. J. Thomson [1914]. 

 Representing the force between two atoms A and B as 



A . p , where Ca and Cb are the moments of the corre- 

 r 



sponding electric doublets and r the distance between their 



centres, the force between two molecules AB and CD 



will be ( C a + ( "b)(Cc + Ci>) which showg that the effect c£ 



atoms and radicles will be additive. 



The forces arising from electrons and positive charges 

 ■will depend on the orientation of the atoms and will not 

 always be radial. It is only by taking the mean value that 

 they can be treated as radial and determined by distance. 

 In the position of comparatively close packing, as in liquids, 

 the attraction of a pair of unlike molecules may be influenced 

 by their configuration, as affecting the distance of the electric 

 charges, and may differ considerably from that deduced from 

 their mutual attractions or from their behaviour in regard to 

 other molecules. This effect must be taken into account in 

 attempting to calculate solubility. It is the more likely to 

 come into play in adsorption by solid substances, in which 

 the orientation of the attracting molecules is more or less 

 fixed, and may account, at least in part, for selective 

 adsorption. 



Thus, as has usually been supposed hitherto, the electrical 

 theory implies attraction within a narrow radius as a 

 universal property of the molecules of matter. It follows, 

 as Laplace supposed, that solids and liquids alike must have 

 an enormous surface energy due to the unbalanced molecular 

 attractions at their surfaces, while internally the forces are 

 in equilibrium on account of the equal molecular attractions 

 on all sides. 



Since, according to the kinetic theory, all molecules of 

 matter, above the absolute zero of temperature, are in 

 constant motion, while their momentum changes continually 

 in direction and amount, molecules at the surface of a 



