44'4' M. Dumas on the La*w of Substitutions, 



the remainder of the elements of the acetic acid constitute 

 marsh gas rather than anything else ? There are four equa- 

 tions, which, at the low temperature at which the action takes 

 place, are alike admissible. The acetic acid always furnish- 

 ing carbonic gas, it may give besides, 



1. Carbon and hydrogen C'*+H^, 



2. Methylene and hydrogen C^H^ + H^, 



3. defiant gas and hydrogen SC^H'^+H*, 



4. Marsh gas C^ H^ 



Thus, when we only consult the general forces of chemistrj', 

 at least four suppositions are presented between which there 

 is nothing to authorize a choice ; these are the possible ac- 

 tions. When the consideration of the types is allowed to in- 

 tervene, it chooses between these four possible actions the 

 necessary action, that which will give rise to four volumes of 

 a hydrocarburetted gas corresponding to chloroform, which 

 it represents in this decomposition. 



It is not sufficient then to explain the decomposition of the 

 acetic acid by the alkalies, by saying that those determine the 

 formation of all the carbonic acid which can be produced ; 

 we must besides give an account of the production of marsh 

 gas. Now if four equations alike possible are presented, how 

 shall we choose? 



We see well that the notion of organic types meets the 

 same difficulty as the law of substitutions. The types are 

 sent back to the general forces of chemistry, as the substitu- 

 tions were sent back to the equivalents. 



The reply is then the same: when we put into play the ge- 

 neral forces of chemistry only, the decomposition of acetic 

 acid into carbonic acid and marsh gas is a possible fact. 

 When we set out from the analogv which exists between 

 acetic acid and chioracetic acid, it is a necessary fact. In the 

 first case we should have perfectly understood that some 

 carbon was deposited, that some methylene or olefiant gas 

 was disengaged. In the second, some marsh gas must abso- 

 lutely be disengaged. 



But it is very evident, that the production of carbonic gas, 

 and of marsh gas by the decomposition of acetic acid by 

 means of alkalies is a fact which does not shock the general 

 ideas of chemistry, who explains herself by the play of the 

 general affinities at her disposal. That need not have been 

 demonstrated : a true fact is always possible. 



Thus in the view taken by general chemistry, marsh gas 

 might be formed ; but viewed by the theory of organic types, 

 it was necessary that that compound should be formed. 



