700 Mr. S. 0. Bradford on the 



in this direction is sufficient to overcome the unbalanced 

 surface forces. And. of those that so escape, any which 

 come again within the range of attraction of the solid 

 particles will be reclaimed, so that solution will continue 

 until the number of particles leaving and returning to the 

 solid is equal. As in the ease of the vaporization of a liquid, 

 the kinetic theory shows, in so far as it is applicable, that in 

 this state the number of molecules in unit volume of the 

 liquid n a , will be equal to the number of those in unit 



s 2 



volume of the solid, ?ij, multiplied by e a ' where a is the 

 most probable speed of the molecules, that is : 



n a = n h e « 2 ........ (2) 



The value of s is given by the relation that the momentum 



normal to the surface, ^ms 2 . of a particle of the solute 



having this velocity is just sufficient to balance the forces 



acting against it. 



The force tending to prevent the solution of a solid 



particle, with greater cohesion than that of the solvent, is the 



difference between the attractions for it of the solid particles 



and of the particles of the solvent. It will therefore be 



,. , . M/ M S M ? , , ,, m , 



proportional to — -, — • t- , where the sumxes s and w 



1 t , r/ r su ? 



correspond to the solute and solvent respectively. The 



average distance, r sw , separating particles of solute and 



solvent will usually differ from that between the particles of 



the solid, partly on account of the natural difference in 



molecular volumes and partly because of the change in 



volume due to the different attracting forces. Solution of a 



particle of solid will, however, be favoured by the difference 



in the attractions of the particles of the solvent for the 



solute particle and for themselves. This may be repre- 



sented as proportional to —4 —^. Inus tne resultant 



force hindering solution is proportional to 



If the molecular cohesion of the solute be less than that of 

 the solvent, the adhesive forces will be greater .than the 

 cohesion of the solute but less than that of the solvent. 

 The solution of a particle of solute will be favoured by the 

 difference between its attractions to other particles of the 



