443 
M. Dumas on the La'w of Substitutions. 
gas of the acetates, because it contains hydrogen, and no 
longer an electro-negative body ? 
Before mentioning my 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 {rvle) 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 formulae. 
Thus I propose uniting into one genus all the compounds 
which unite identical formulae with similar chemical properties. 
Chloroform, bromoform, iodoform, constitute one genus; 
olefiant gas and the various chloridated bodies, products 
which are derived from it, constitute another ; acetic acid 
and chloracetic acid represent a third, &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 number 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 barytes 
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 
