505 
and the Theory of Mechanical Types, 
hydrogen, it is of importance to remark here, that M. Laurent 
insisted on the identity of the function of the chlorine with 
that of the hydrogen in bodies formed by substitution long 
before it had been positively established by experience. 
It will not be my object now to write the history of the 
theory which occupies us ; when experience shall have sounded 
all the parts in succession, it will be useful to go into the dis- 
cussion of the d priori ideas which may have often predicted 
the results. 
Thus putting aside every historical question, and stopping 
only at facts, at the experiments which have served as a basis 
to my own convictions, in a word, consulting only my per- 
sonal impressions, I must say, that the first results in which 
I believed I could recognise in a decisive manner the ele- 
ments of a view arrested by this subject, are those which or- 
ganic chemistry owes to M. Malaguti. In fact, we know that 
this skilful observer has recognised, that aether, whether free 
or combined, may always lose two equivalents of hydrogen 
and gain two equivalents of chlorine, without any of its es- 
sential chemical characters undergoing alteration; for its 
power of combination remains exactly the same ; chloridated 
aether then is still aether. 
My conviction became complete, when I was able to re- 
cognise the precise nature of chloracetic acid, and when I saw 
chlorine take the place of all the hydrogen of the acetic acid, 
without modifying its capacity of saturation, without in any 
way altering what I term its fu7idamental properties ; chlo- 
ridated acetic acid then is still acetic acid. 
It is by setting out from these two facts, it is by adding 
those which M. Regnault had himself observed in the action 
of chlorine on the liqueur des Hollandais^ that I have tried to 
show that there exist, in organic chemistry, types capable of 
undergoing, without being destroyed, the most singular trans- 
formations as to the nature of their elements. 
More recently M. Regnault, in the memoir on the aethers 
which I have already quoted, giving a still greater extension 
to those views, considered the bodies formed by substitution 
as belonging to one mechanical system. We may wait with 
confidence for the developments which he promises to give to 
these first views. 
[To be continued.] 
