38 Heat of Dissolution of Gases in Liquids. 



drawn from the comparative magnitude of the various values 

 is one which is decidedly in favour of the existence of chemical 

 compounds in solution, namely, that more heat is evolved in 

 every case here investigated by the dissolution of a substance 

 in water than in the other two solvents examined, this being- 

 very significant in view of the fact that water undoubtedly has 

 a much greater tendency to form definite molecular compounds 

 than either acetic acid or benzene. It is scarcely necessary 

 to mention that pyridine in acetic acid is not an instance of 

 dissolution strictly comparable with the others, since the 

 pyridine acetate which is formed is a compound of a different 

 order of stability from the hydrates or analogous compounds 

 which, I believe, are present in solutions. 



We have thus most of the main characteristics of chemical 

 combination attending the dissolution of gases in liquids — a 

 selective attraction, a considerable evolution of heat, and an 

 action which is more energetic in the very case where che- 

 mical combination is known to occur more readily ; and all 

 that is wanted to convert this evidence of the truly chemical 

 nature of the action into proof, is to find that the combination 

 which does occur, occurs in definite molecular proportions. 

 This last proof I have already obtained. Series of different 

 strengths of all the solutions here dealt with have been 

 examined as to their freezing-points, and in nearly every case 

 changes of curvature, some of them very marked, have been 

 found to occur at various definite and simple molecular 

 proportions. These results I hope shortly to publish. 



I believe that the chief objection now urged against the 

 view that the nature of solution is truly chemical, is the ab- 

 sence of any explanation of how chemical combination could 

 lead to such a condition of the dissolved matter, that calcula- 

 tions based on the idea that it is uncombined with the solvent, 

 and even that it is split up into independently acting ions, 

 should lead to so many correct results. This absence, 1 

 believe, no longer exists ; for in a recent communication to 

 the German Chemical Society {Ber. xxiv. p. 3629) I have 

 shown that this state of quasi-independence of the dissolved 

 substance, and also of the ions of an electrolyte, would be a 

 direct consequence of the existence of hydrates (or similar 

 compounds) of a high degree of complexity in solutions. 



