M. Dumas on the Law of Substitutions. 4'43 



gas of the acetates, because it contains hydrogen, and no 

 lonfver an electro-negative body? 



Before mentioning m}' opinion, which is however well 

 known, it is necessary that the three points which make the 

 difficulty, and which are the definition of chemical types, 

 should be well understood, that of the fundamental properties, 

 and the confounding of the function {yvle) which hydrogen 

 and chlorine perform among chemical bodies. Prepossessed, 

 for a long while with the necessity of establishing a good 

 natural classification of organic bodies, I have sought for its 

 basis in their chief characters. The discovery of chloracetic 

 acid gave me an opportunity of developing a view of this 

 nature. Acetic acid and chloracetic acid, as distinct bodies, 

 constitute two species, which I have classed in one genus, by 

 reason of the analogy of their fundamental properties and of 

 the identity of their formula?. 



Thus I propose uniting into one genus all the compounds 

 which unite identical formula with similar chemical properties. 

 Chloroform, bromoform, iodoform, constitute one genus; 

 olefiant gas and the various chioridated bodies, products 

 which are derived from it, constitute another ; acetic acid 

 and chloracetic acid represent a tliird, &c. 



I class then in one genus, or what comes to the same 

 thing, I consider as belonging to the same chemical type, the 

 bodies which contain the same mimber of equivalents, united in 

 the same manner and which possess the same fundamental che- 

 mical properties. 



The definition of a chemical type carries with it then that 

 of the properties which I call fundamental. Now, by what 

 do we recognize a fundamental property ? This is a question 

 easily answered by examples which appear to be conclusive. 

 When we boil chloracetic acid with an alkali, it is at once 

 destroyed and is changed into carbonic acid and chloroform. 

 If we class, as I have done, acetic acid and chloracetic acid 

 in one genus, we are compelled to conclude from this that 

 acetic acid treated with alkalies will change to its turn into 

 carbonic gas, and into a carburetted hydrogen corresponding 

 to chloroform, and into marsh gas {gas des marais). This is 

 precisely the result which is given by experiment. 



But, say MM. Pelouze and Millon, these approximations 

 are purely fortuitous. If acetic acid heated with barj'tes 

 changes into carbonic acid and into marsh gas, it is that ba- 

 rytes simply determines the formation of the carbonic acid, 

 that it takes from acetic acid all the carbonic acid which its 

 constitution allows it to supply. 



Let us admit this first point for the moment ; why should 

 2 G 2 



