ON THE PHENOMENA AND THEOBIES OF SOLUTION. 447 



sein d'une dissolution. lis constituent alors un systeme en equilibre, 

 dans lequel les proportions relatives de chaque hydrate varient avec la 

 quantite d'eau, la temperature, _ ainsi qu'avec la presence des autres 

 corps, acides, bases on sels, capables de s'unir pour leur propre compte, 

 soit a I'ean, soit au corps primitivement dissous. Ce serait le degre 

 inegal de cette dissociation des hydrates, variable avec la tempera- 

 ture, qui ferait varier le coefficient de solubiUte du corps dissous lui- 

 meme.' 



We may now turn to those writers who, whilst referring the 

 phenomena of solution to a molecular attraction of some kind, do not 

 attribute solubility to the formation of chemical compounds of definite 

 composition. 



Graham is one writer who distinctly ranges himself on this side. He 

 says : — ' The attraction between salt and water which occasions the 

 solution of the former, diflFers in several circumstances fi'om the affinity 

 which leads to the production of definite chemical compounds. In 

 solution combination takes place in indefinite proportions, a certain 

 quantity of common salt dissolving in or combining with any quantity of 

 water, however large. . . . But the maximum proportion of salt 

 dissolved or the saturating quantity has no relation to the atomic weight 

 of the salt, and indeed varies exceedingly with the temperature of the 

 solvent. The limit to the solubility of a salt seems to be immediately 

 occasioned by its cohesion.' And again : " The force which produces 

 solution differs essentially from chemical affinity in being exerted be- 

 tween analogous particles, in preference to particles which are very unlike 

 and resembles more in this respect the attraction of cohesion.' 



Brande, also, appears to have taken a similar view, for, although he 

 makes no formal statement of his opinion, the following passage occurs 

 in his ' Manual ' (5th edition, 1841), p. 110 : — ' When common salt is 

 dissolved in water its particles may be regarded as disposed at regular 

 distances throughout the fluid ; and if the quantity of water be consider- 

 able, the particles will be too far asunder to exert reciprocal attraction ; 

 in other words, they will be more powerfully attracted by the water than 

 by each other.' 



Daniell, in his ' Chemical Philosophy ' (1842), ascribes the phenomena 

 of solution to the conflict between the ' heterogeneous adhesion ' of liquid 

 to solid and the ' homogeneous attraction' of cohesion. 



In Miller's 'Chemistry,' vol. i. (2nd edit. 1860), p. %7, we find 

 the following passages, which show more in detail the application of 

 the same idea : — ' Adhesion is frequently manifested between solids and 

 liquids with sufficient force to overcome the power of cohesion, and the 

 substance is then said to become dissolved, or to undergo solution. . . . 

 Anything that weakens the force of cohesion in the solid favours solution. 

 Thus if the substance be powdered it becomes dissolved more quickly, 

 both from the large extent of surface which it exposes and from the 

 partial destruction of cohesion. In the same way heat, by increasing the 

 distance between the particles of the solid, lessens its cohesion, and 

 probably thus contributes so powerfully to assist in producing solution. 

 If a solid body be introduced in successive portions into a quantity of a 

 liquid capable of dissolving it, the first portions disappear rapidly, and as 

 each succeeding quantity is added it is dissolved more slowly, until at 

 length a point is reached at which it is no longer dissolved. When this 

 occurs the force of cohesion balances that of adhesion, and the liquid is 



