502 M. Dumas on the Law of Substitutions, 



genus, to the same chemical type : the others could not take 

 their place there. What place can be properly assigned to 

 these kinds of bodies ? 



We have not to wait long for a reply, and it carries the 

 law of substitutions to a degree of generality and importance 

 which it does not belong to me to develop here, but which 

 the order of ideas obliges me to indicate. 



The admirable work of M. Regnault on the aethers has 

 indeed given an unexpected development to the theory of 

 types. There is nothing more natural than to class in one 

 genus bodies which approach so near as acetic acid and chlor- 

 acetic acid : but there must be good reasons for admitting 

 that there is a true analogy between 



Marsh gas C* H^ H^ 



Methylic aether C* O H^ 



Formic acid C^ H^ O^ 



Chloroform C^ H^ Ch« 



Bromoform C^ H^ Br« 



Iodoform C4 HH« 



Chloridated methylic aether < ^12 



Bichloridated methylic aether \ y-,i 4 



Perchloridated methylic tether C'* O Ch*^ 



Hydro-chlorate of methylene C^ Ch^ H^ 



r C^ Ch^ H* 

 Chloridated hydrochlorate of methylene < /-ii 3 



f C^ Ch^ H^ 

 Bichloridated hydrochlorate of methylene \ r^^± 



Chloride of carbon C* Ch^ Ch^ 



Amongst these bodies, to which, without forcing anything, 

 we might add prussic acid and ammonia, we meet with acids, 

 bases, neutral bodies, and consequently substances the most 

 unlike in an ordinary chemical view. 



M. Regnault admits, and, he purposes to prove, that all the 

 bodies so unlike, chemically speaking, which this series con- 

 tains, that all those which can be united in analogous series, 

 have this in common, that they belong to the same mechanical 

 system. 



I repeat that it is not for me to explain views which 

 will be explained hereafter by their inventor, but I have to 

 show in what these views differ from those which preceded 

 them, to cause it to be felt how they complete what may now 

 be called the general theory of substitutions. Moreover, it is 



