THE 
LONDON AND EDINBURGH 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
♦ 
[THIRD SERIES.] 
JANUARY 1840. 
I. 0)1 the Theory of Substitutions in Chemistry^ proposed by 
M. Dumas. In a Letter to M. Yq\ouzq from M. Berzelius*. 
"Y^OU will perhaps permit me to. return once more to M. 
^ Dumas’s theory of substitutions, especially after the 
new development that this skilful chemist has lately given it, 
a development which, according to him, threatens to over- 
turn the theory of chemistry in general, and especially electro- 
chemical notions. You remember that in a preceding letter, 
I declared my opinion, that the application which has been 
made of the theory of substitutions, in considering chlo- 
rine, which takes the place of hydrogen, as acting the same 
part as this latter, is contrary to the principles of the science, 
and I quoted some examples on this subject, which I think 
prove it in an unequivocal manner. In begging you to com- 
municate the contents of this letter to the Academie des Sci- 
e?ices, I hoped that M. Dumas would have the goodness to 
explain under what point of view he regards the theory in 
question. He has, indeed, complied with this request, and in 
a manner which, with the exception of some details foreign 
to the question, has entirely satisfied me. 
In the Comptes llendus of 18 vS 8 , semestre, p. 699 and 
the following pages,) M. Dumas has disclaimed this explana- 
tion of the theory of substitutions : “ If I am made to say 
that chlorine takes the place of hydrogen in such a way that 
the former acts the same part as hydrogen, an opinion is im- 
puted to me,” says M. Dumas, ‘^against which I protest, for it 
is opposed to all that I have asserted on these matters. The 
theory of substitutions merely asserts the simple affinity be- 
tween hydrogen and the chlorine which takes its place in 
equal volume. It is an. empirical law which deserves our at- 
tention only as long as it holds good, and if any one has 
made it of more importance it is not my fault.” ' 
* From the Ann. de Chim, et de Phys,^ vol. Ixi. p. 137. 
Phil Mag, S. 3. Vol. 16. No. 100. Jan, 1840. B 
