2 M. Berzelius on the Theory of Substitutions ofM. 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 [remplacemetit]* 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 [remplacement']*. 



In the Comptes Rendus of 1839, {l^"^^ 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 C'^ H^ 



O^ 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 C* H® 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 

 chlor acetic 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 ehher pariicipation or succession? 



With regard to the practice of rendering the French remplacer, remplace- 

 ment, by the English 'replace', ' replacement', which answer to the French 

 replacer, &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. 



