504? M. Dumas on the Law of Substitutions^ 
formed into another which presents the same chemical ac- 
tions, these two products belong to the same genus. 
Alcohol, hydrated acetic acid, chloracetic acid, belong to 
the same natural family. Acetic acid and chloracetic acid 
belong to the same genus. 
Such are the bases of the natural classification of organic 
substances, which I shall have soon an opportunity of deve- 
loping before the Academy. 
Before going further, it is just to notice here the labours of 
the chemists who have directed the science towards the point 
of view which now occupies us. 
M. Regnault not only takes the first place in this respect, 
by the date of his observations, but by the importance of his 
researches and with respect to the ideas he has deduced from 
them, we must consider this young chemist as having ad- 
vanced more than any one the state of the science on this 
point. 
In my own name I can speak more freely than when I was 
commissioned to express the opinion of the Academy, and I 
think it my duty to declare here that the views of M. Reg- 
nault are connected with physical studies of the highest or- 
der, and that they give to the theory of substitutions a de- 
velopment as fortunate as it was unlooked for, in its applica- 
tion to the study of the most intimate physical properties of 
bodies. 
At the same time with M. Regnault, two other chemists 
well known to the Academy, MM. Persoz and Laurent, were 
also occupied in researches concerning the theory of substitu- 
tions. 
One of them indeed, M. Persoz, did not appear to occupy 
himself with the application of this theory ; but the formula 
by the help of which he endeavoured to express the composi- 
tion of a great number of mineral bodies, agreed perfectly 
with the developments which the theory of substitutions re- 
ceived by degrees from experience. The system of formulae 
adopted by M. Persoz, and the views which they express in 
mineral chemistry, have then found a fortunate application 
in a great number of facts which the theory of substitutions 
has led to the discovery of in organic chemistry. 
M. Laurent on his side has made a multitude of researches, 
and has published a great number of memoirs in support of the 
laws by which he sought to foresee and to explain all the 
phenomena of substitutions. As we saw above that the prin- 
cipal difficulty which is opposed to the approximation of 
acetic acid and of chloracetic acid consists in the similar func- 
tion which we are compelled to attribute to chlorine and to 
