1813.] On the Cause of Chemical Proportions. 445 



tion that when two bodies, A and B, combine in different pro- 

 portions, the additional portions of the one are always multiples 

 by whole numbers, 1, 2, 3, 4, &c. lead us to conclude the exist- 

 ence of a cause in consequence of which all other combinations 

 become impossible. Now what is that cause P It is obvious 

 that the answer to this question must constitute the principal 

 basis of chemical theory. 



When we reflect on this cause it appears at first evident that 

 it must be of a mechanical nature ; and what presents itself as 

 the most probable idea, and most conformable to our experience, 

 is, that bodies are composed of atoms, or of molecules, which 

 combine 1 with 1, 1 with 2, or 3, 4, &c. ; and the laws of 

 chemical proportions seem to result from this with such clear- 

 ness and evidence, that it seems very singular that an idea so 

 simple and so probable has not only not been adopted, but not 

 even proposed before our own days. As far as I know, the 

 English philosopher, Mr. John Dalton, guided by the experi- 

 ments of Bergman, Richter, Wenzel, Berl holler, Proust, and 

 others, was the first person who endeavoured to establish that 

 hypothesis. Sir H. Davy has lately assured us that Mr. Higgins, 

 in a book published in 1789, established the same hypothesis. I 

 have not seen the work of Mr. Higgins, and can only notice the 

 circumstance on the authority of Davy.* 



Notwithstanding the great clearness and simplicity which cha- 

 racterize this hypothesis, it is connected with great difficulties, 

 which make their appearance when we apply it to a number of 

 chemical phenomena. These difficulties naturally excite doubt6 

 as to the truth of the hypothesis. Among the numerous experi- 

 ments which I have made in order to discover the chemical 

 proportions in which bodies unite, 1 have met with cases when, 

 notwithstanding the completest agreement with the laws which I 

 conceived myself to have discovered, the composition of a body 

 could not be explained according to the hypothesis which we are 



» Tlir work of Higgins on Phlogiston is certainly possessed of much merit, 

 and ai.lkipaicd some of the most striking subsequent discoveries. But, when 

 he wrote, metallic oxides were so little known, .and so few exact analyses 

 existed, that il was not possible to be acquainted with the grand fact that 

 oxygen, &c always unite in determinate proportions which aic multiples of 

 the minimum proportion. The atomic theory «as taught by Mergman, Collen, 

 Black, &c, jtul as far as i< was by Higgins. The latter, indeed, states 

 si>iu< striking iact> respecting tin- gases, and anticipitated Gay-Lussac'a 

 theory o( volumes j but Mr. Dalton fust generalised tin- doctrine, and 

 thought oT determining the weight of the ati.itis of bodies. He >howod 

 me his table of symbol*, and the weights of the atoms of six or eight 

 bodir-, in 1 804 1 and I believe the same yeat explained the subject In London 

 in a coui e of lectures delivered in the Royal Institution. The subject could 

 w been hroa er, Bui about the same lime several other 



: n truck with the i lie oxides pub» 



in mi \ ( bemlstri ; and the doctrine woald have certainly bceu started by 

 oiheij if Daltini hud missed it. I 



