325 
and the Theory of Chemical Types, 
from possessing a special character, from constituting a case 
of chemical action so particular, that it was absolutely neces- 
sary to distinguish it from every other, as I have done. 
To be convinced that the theory of substitutions is not ge- 
neral, there is no need of new facts; it will suffice to read my 
memoir on chloracetic acid, which has been so often quoted 
for some time. We there see that besides the chloracetic 
acid produced by substitution by means of the action of 
chlorine on acetic acid, oxalic acid and carbonic acid are de- 
veloped, the production of which by substitution we may be 
at a loss how to explain, at least for the present. 
And better still, it suffices to glance at my memoir relative 
to indigo : we there see that the white indigo, under the 'in- 
fluence of oxygen, loses an equivalent of hydrogen without 
gaining anything. In this case then there is no substitution ; 
I convinced myself of it. At a later period MM. Liebig 
and Woehler observed facts of the same nature in their admi- 
rable researches upon uric acid. Quite recently, Mr. Kane 
observed similar facts in the colouring matter of Heliotrope. 
Thus, the phsenomenon of substitutions is not general ; still 
more, this is one of its most essential characters, as we shall 
presently see. 
Not only it is not general, because a body may, under the 
influence of oxygen, lose hydrogen without gaining anything, 
but it is not general also for the contrary reason. Olefiant 
gas, for example, may lose 4? equivalents of hydrogen and 
take 6 of chlorine; every one knows this. Any one who had 
not analysed all the intermediate degrees of this action, as 
M. Regnault has done, would, in comparing the first and 
last term, have found the law of substitutions defective. 
At present it may be explained and understood without 
difficulty, when we say that if white indigo loses hydrogen 
without gaining anything, it passes into a new molecular 
type ; when we know that olefiant gas may produce a chlo- 
ride of carbon of the same type as itself, and, by a fresh 
addition of chlorine, a new chloride of a different type. 
Thus, the law of substitutions prevails when the bodies pre- 
serve their initial type; it is no longer applicable in the con- 
trary case; and, by this very means, it serves to distinguish 
the bodies which have preserved their molecular type from 
those which have lost it. 
But there is no occasion to return to this explanation, which 
my wish to express myself clearly has induced me to give 
en passant, to justify the necessity of distinguishing the law of 
substitutions from other chemical actions {reactions,). 
The law of substitutions expresses, that in an organic body, 
