514 Dr. W. W. J. Nicol on the Vapour-pressures 



2. Concentration con- 

 stant. — The effect of rise 

 of temperature is to di- 

 minish the restraining 

 effect of the salt in the 

 case of NaCl, to leave 

 KC1 unaffected, and to 

 increase the effect with 

 NaN0 3 andKN0 3 . The 

 four salts forming again 

 a series in the same order 

 as above. 



3. When both temperature and concentration increase the 

 salts form the same series — diminution of the restraining 

 effect with NaCl and KC1, little or none with NaN0 3 , and a 

 marked increase with KN0 3 . 



4. When the solubility as a function of the temperature is 

 considered, the same series is observed. The solubility of 

 NaCl increases only slightly with rise of temperature, that of 

 KC1 rather more so, Still more marked is the case with 

 NaN0 3 , while the solubility of KN0 3 increases enormously 

 with the temperature. 



5. There is clearly a connection between increase of solu- 

 bility of the salts and the effect they have on the vapour- 

 pressure of the water in which they are dissolved. 



Any attempt to explain the behaviour of the salts must of 

 necessity, in our present state of knowledge of the nature of 

 solution, partake largely of the nature of hypothesis. Still I 

 cannot refrain from pointing out how completely the Theory 

 of Solution I put forward some years ago explains these very 

 varied phenomena. 



According to this theory, solution is an entirely physical 

 process, and results from the action of purely physical forces; 

 thus differing entirely from all the modifications of the 

 Hydrate Theory which have hitherto found favour with expe- 

 rimenters. Solution is the result of the tendency of three 

 forces towards equilibrium. These three forces being the 

 attraction of water for salt, that of salt for salt, and that of 

 water for water. For the sake of brevity the attraction be- 

 tween similar molecules may be spoken of as Cohesion, that 

 between dissimilar molecules as Adhesion. Thus, where the 

 salt is soluble, the adhesion of salt and water is greater than 

 the cohesion of the salt plus the cohesion of the water. When 

 the salt is insoluble, the reverse is the case. When the salt 

 dissolves, the adhesion of water to the salt is more and more 

 diminished by the presence of the dissolved salt till a point is 



