4 Meia^KUM, Deve/opineiif of the Atomic T/ieojy. * 



The time was ripe for a new theory of affinity. That 

 is the explanation of how Berthollet's ideas were taken 

 up so eagerly as was the case. Chemical reactions had 

 been studied in the light of the old theory so thoroughly 

 that numerous anomalies had been discovered, which 

 only the new theory could explain. Even the effect of 

 mass in chemical change had been noted by Bergman. 

 In his "Dissertation on Elective Attractions " (§ lo, 1785) 

 he discusses the reaction, Ad-\-c-—Ac-{-d, where Ac is 

 precipitated. " It now remains to be examined, whether 

 the whole of d can be dislodged b}' a sufficient quantity 

 of r from its former union. It should be carefully noted 

 in general, that there is occasion for twice, thrice, nay 

 sometimes six times the quantity of the decomponent c, 

 than is necessary for saturating A when uncombined." 

 Bergman noted the effect, but could not explain the 

 principle, of mass-action. That principle, leading straight 

 as it does to the doctrine of chemical equilibrium, was 

 quite foreign to the theory of chemical affinity to which 

 he always adhered. 



It seemed to be a necessary consequence of Berthollet's 

 principles that chemical combination takes place in in- 

 definite proportion. He had obliterated the distinction 

 between chemical and physical forces, and regarded solu- 

 tion as produced by affinity between solvent and solute. 

 Hence solutions were compounds.' In the ne.xt place, 

 indefinite proportion seemed to be an obvious corollary of 

 his "mass-action" theorem. In any chemical system the 

 state of equilibrium depends on the quantity present of 

 each of the re-agents involved. Hence the larger the 

 amount of a given constituent that might be present, so 

 much the more of this should enter into the composition 



" " Essai de Slatique chimique," §§ 36, 39. 



