324? M. Dumas on the La'm of Substitutions, 
weighing 1294-. These quantities are the chemical equiva* 
lents of those bodies ; all chemical action takes place between 
them and their multiples. 
Now, to say that from an organic compound, an equivalent 
of hydrogen may be subtracted, and that its place may be 
taken by an equivalent of chlorine, is manifestly announcing 
a law in perfect harmony with the general law of the recipro- 
cal action of bodies by equivalents. Every one comprehends, 
that if a crystallized body could produce another, likewise 
crystallized, by losing hydrogen and gaining chlorine, which 
could not be represented by equivalents, we must conclude 
from this that the theory of equivalents is false. The law of 
substitutions ought to be in accordance with the theory of 
equivalents, as moreover the general expression which has 
been given to it suggests. 
But from thence to assert that the law of substitutions has 
no peculiar character, that it is only a particular case of the 
theory of equivalents, there is either an equivocation or an 
immense leap. That this leap was made when the law of 
substitutions was at first put forth, that nothing allowed the 
cause of it to be foreseen, in order to connect it with a theo- 
retical principle, 1 concede without difficulty. This also did 
not fail to be the case, and amongst the objections of the 
German chemists to the law of substitutions, it always figures 
first. The philosophers who some years ago viewed it in 
this manner, were right without doubt, but they must have 
been very much surprised to see so many skilful men persist 
in finding in it a special character. 
With regard to myself, if I believed in the future prevalence 
of the law of substitutions, in its importance, five years ago, 
when I was the only one who defended it, it is not to be sup- 
posed that I can change my opinion, when the most eminent 
English chemist, Mr. Graham, adopts it without reserve; 
when M. Liebig, after sharply criticising it, now receives it 
as admitted in science ; when so many labours, undertaken 
often to combat it, have come within this very circle, to give 
it a complete consecration ; when, lastly, far from seeing in the 
law of substitutions a simple experimental fact, we are now 
able to ascend to its cause. 
Thus, to assert, as M. Pelouze has done, that the phas- 
nomenon of substitution, when it is observed, is only a par- 
ticular case of the theory of equivalents, is to announce as a 
novelty two things perfectly known, viz. : first, that in the 
action of two bodies, substitution does not always take place; 
secondly, that when it is effected, it takes place by equiva- 
lents. This does not hinder the phaLmomenon of substitution 
