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LXV. Memoir on the Law of Substitutions^ and the Theory 
of Chemical Types, By M. Dumas. 
[Continued from p. 329.] 
Chemical Types, 
CONSIDERED in itself, the law of substitutions has a 
practical importance quite sufficient to justify the necessity 
of distinguishing it from the more general actions of che- 
mistry. But this distinction becomes necessary in quite 
another way, when to this kind of instinct which led us to 
view it at first as a law of nature, succeeds the nearly perfect 
certainty that it is connected with one of the most mysterious 
and most important phenomena of the science. 
I mean the existence of chemical types, capable, without 
being destroyed, of undergoing the most singular transforma- 
tions, and of which all the elements might successively disap- 
pear, others being substituted for them. I mean those organic 
types, the admission of which into the domain of organic che- 
mistry seemed to me to be henceforward inevitable, in con- 
sequence of the best-characterized experiments which had 
been suggested by the law of substitutions. 
Thus it being possible to convert acetic acid into chloracetic 
acid by the action of chlorine without its at all losing its ca- 
pacity for saturation, 1 have considered the chloracetic acid 
which results from it as acetic acid in which chlorine had 
been substituted for hydrogen : these two bodies have appeared 
to me to belong to one type, to one kind. 
Now, when I established, five years ago, the analogy of 
iodoform, of bromoform, of chloroform, and of anhydrous 
formic acid, when I added that electro-negative bodies, such 
as sulphur, phosphorus, and arsenic, might be substituted 
for iodine, chlorine, and oxygen, no one raised the least dif- 
ficulty ; this series of formulae entered the science without ob- 
stacle. 
It is then because the development of the experiment has 
led us to look upon chlorine and hydrogen as susceptible of 
taking the place of each other in a compound, that certain 
convictions revolt. We are then led to examine what we 
should understand by an organic type^ and to discuss this point: 
for example, it being possible for iodine, bromine, chlorine, 
and oxygen to take each other’s place in a compound without 
destroying its type, can this power foie) be denied to hydro- 
gen? In other terms, iodoform, bromoform, chloroform, 
oxiform, being admitted as species of the same genus, can 
we refuse this character to hvdroform, that is to say, to the 
