2 M. Berzelius on the Theory of Substitutions ^M, Dumas. 
This assertion of M. Dumas is in perfect harmony with 
my way of thinking; what has led to a misstatement of his 
opinion is probably the improper denomination of theory of 
substitutions, for an empirical law is not a theory, and the 
word ‘ substitution ’ has long since been used in chemistry to 
signify the replacing femjplacemenff of one body by another 
which acts the same part as this body, and M. Dumas has lately 
changed this word for another, which is very well chosen, 
metalepsie, signifying replacement Sjemplacementf^ , 
In the Comptes llendus of 1839, (1®^® semestre, p. 909), M. 
Dumas has more lately given a new explanation of this the- 
ory, but quite opposed to that just mentioned. He made 
the beautiful discovery that crystallizable acetic acid 
H, exposed to the light of the sun in an atmosphere of dry 
chlorine, is gradually decomposed, and that an equal volume 
of chlorine completely takes the place of the hydrogen. A 
new acid composed of FF O^, H, is the result of this ac- 
tion, some of whose properties he has described. 
The conclusions which M. Dumas draws from this fact are 
the following : the chlorine in taking the place of the hydro- 
gen atom for atom, acts the same part as the hydrogen ; an 
acetic acid is the result of this, which differs only from the 
other in containing six atoms of chlorine instead of six atoms 
of hydrogen, and on this account he gives it the name of 
chloracetic acid. It possesses the same properties as the 
ordinary acid, so that if we know the properties of the latter, 
we equally know those of chloracetic acid. This is caused 
by the properties of a body depending rather on the type of 
the composition than on the particular characters of the ele- 
ment which has been exchanged. In organic chemistry, says 
he, there exist certain types, which are preserved even when 
equal volumes of chlorine, bromine, or iodine have taken 
the place of the hydrogen which they contain. He infers 
from this that there are two great leading principles in che- 
mistry, which are isomorphism in mineral chemistry, and sub^ 
stitution in organic chemistry. He supposes that these prin- 
ciples originate from the same cause, and that in due time 
they may be generalised under one common expression. 
M. Dumas adds that neither isomorphism nor the theory 
* As precision in the use of terms is very important in this subject, is 
not metalepsy objectionable as signifying d\t\\cv participation ov succession? 
With regard to the practice of rendering the French remplacer, renplacc- 
ment, by the English ‘replace’, ‘ replacement’, which answer to the French 
replaccr, &c., and have an entirely different meaning, it is a slovenly shift, 
which ought always to have been resisted, as causing constant ambiguity and 
confusion. Can chemists find any authority for such a perversion of both 
languages ? — R, T. 
