﻿M. Dumas' s Remarks on Affinity* 95 



In recent times the views of Newton have met with an unex- 

 pected and remarkable support in the beautiful aud important 

 researches which our eminent colleague M. Henri St. -Claire De- 

 ville has devoted to the phenomenon of dissociation — one of the 

 greatest acquisitions, not only of chemistry, but of natural phi- 

 losophy. 



Nothing, in fact, is more in accordance with the laws of me- 

 chanics than to say that a volatile liquid placed in connexion with 

 a free space fills it with its vapour, and that the tension of this 

 increases or decreases regularly in a continuous manner accord- 

 ing as the temperature rises or falls. 



But to say that carbonic acid separates from lime in the same 

 manner, to establish that there is a tension of decomposition 

 analogous to the tension of vapours, and that the evaporation of 

 a liquid and the decomposition of a carbonate take place in virtue 

 of the same laws, and present the same phenomenon of continuity, 

 is to connect chemical combination with cohesion, is to prove 

 that under certain conditions the laws which regulate the aggre- 

 gation or the separation of molecules of the same kind are also 

 applicable in the case of molecules of different kinds. 



Without affirming that in all cases the dissociation of com- 

 pounds presents the character of a continuous phenomenon, it is 

 enough that the case is frequent (as is proved by the researches 

 of our eminent compeer and those of his pupils), to justify our 

 assimilating the purely physical molecular separations and the 

 chemical molecular separations, and to give us the right hence- 

 forth to unite cohesion and affinity the one to the other, and 

 both to universal attraction. 



It follows from this brief summary : — 



(1) That Newton gave of chemical affinity a notion to which 

 nothing has been added, when he connected it with general 

 attraction and showed how, at a certain distance from the centres 

 of molecular action, it may become zero, or even repulsive. 



(2) That Ampere has given the complement to this view by 

 showing that the shape of the components limits the number of 

 combinations which two elements may produce, and that it de- 

 termines the ratios according to which they may unite, and even 

 enables us to predict the ready replacement of one element in a 

 complex molecule by another without its stability being com- 

 promised. 



(3) That Meyer has shown how the impact of molecules, 

 striking against each other with extreme velocity to produce 

 combination, may give rise to the phenomena of heat, of light, 

 and of electricity which accompany chemical action. 



(4) That M. Henri St.-Claire Deville, in discovering the ca- 

 pital phenomenon of dissociation, has opened a new way to science 



