4io HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



method. Malaguti (Comptes rendus, 1837, 5, 334) had 

 succeeded in introducing four atoms of chlorine into 

 ordinary ether. 



C 4 H 10 + 4 C1 2 = C 4 H 6 C1 4 + 4 HC1. 



The simplest explanation was to suppose that chlorine 

 had entered the ethylene or ethyl radicals ; but this would 

 imply the co-existence in the electro-positive radical of hydro- 

 gen and chlorine. Berzelius preferred, therefore, to recon- 

 struct the whole molecule and to write it thus : 



the molecule then no longer contained any trace either of 

 ethyl or of ethylene, but was now composed of methyl oxide 

 and carbon chloride (Comptes rendus, 1838, 6, 634; Ann. 

 Chim. Phys., 1838, 67, 310). 



Chlorine, in organic compounds, " takes the place " and 

 " plays the part " of hydrogen. Dumas at first accepted 

 Berzelius's view that the chlorination of an organic compound 

 might involve a reconstruction of the radicals which it con- 

 tained and in replying to Berzelius' letter emphasised the 

 fact that the theory of substitution " is an empirical rule " 

 (Comptes rendus, 1838, 6, 702). 



"The theory of substitutions expresses then a simple 

 relation between the hydrogen that goes out and the chlorine 

 that enters. In the majority of cases this relation is one of 

 volume for volume. In announcing it, I believe that I 

 rendered a real service to science. Indeed, before it had 

 been signalised, there existed hardly a single exact analysis 

 of a compound formed by the action of chlorine on an 

 organic substance. Since it has fixed the attention of 

 chemists on this kind of reactions, the facts have multiplied, 

 the analyses have received a precision of which the impor- 

 tance has been recognised " (Comptes rendus, 1838, 6, 699). 



It was not long, however, before the amazing complexities 

 of Berzelius's formulae, and the extreme simplicity of the 

 theory of direct replacement, compelled him to adopt the 



