180 M. Dumas on the Law of Substitutions, 



Thus to fix our ideas, in the theory of types the essence of 

 bitter almonds is a type in which we can substitute for an equi- 

 valent of hydrogen an equivalent of chlorine, of bromine, of 

 iodine, of oxygen, or of amidogen, without the type being 

 altered, 



C 28 H 12 O 2 

 C 28 H 10 O 2 



Ch 2 



C 28 H 10 O 2 



O 



C23 JJ10 O 9 



s 



C 28 H 10 O 2 - 

 Az 2 H 4 . 



But whilst admitting that an element might be substituted 

 for the system C 28 H 10 O 2 , the theory of types does not con- 

 sider it as an invariable group. It believes that hydrogen 

 may be taken from that group, that chlorine may take its 

 place, or that it may be made to undergo every other modifi- 

 cation without its fundamental nature being altered by it. 



In a word, by a reciprocity easy to foresee, and which to 

 receive all its development would require a detail of formulae 

 which I cannot enter upon here, we arrive at the conclusion, 

 that in the same manner that it is possible in an organic com- 

 pound to substitute sulphuric acid, which fulfils the same 

 function for hydrogen, so we may in certain organic matters 

 substitute a simple body for a group of molecules representing 

 a compound body. 



To say that nitrous vapour takes the place of hydrogen in 

 nitrobenzine, is the same as if we said that in aether potassium 

 may take the place of aetlryle. 



But we must not conclude from this that aethyle is a perma- 

 nent, immutable (innnuable), unchangeable compound, for ex- 

 perience proves the contrary. Only by losing some hydrogen 

 and gaining chlorine everything leads us to suppose that it 

 preserves its character, as does the aether, of which it makes a 

 part. 



But I admit that in a given type there are certain compound 

 groups for which simple bodies may be substituted, and which 

 in so far would deserve the name of radicals. They fulfil the 

 same function as ammonium, which takes the place of the po- 

 tassium in alum, for example. 



Thus I cannot consider these groups as immutable bodies, 

 for experience has pronounced the contrary, and every theory 

 which would absolutely rest on this basis would go too far. 



Amongst the researches which contribute the most to mo- 



