Chap, i.] CONSTITUTION OF MATTER. 1 



pound radicals. This notion of compound radicals ha^ a pre- 

 dominant importance in the chemistry of organic substances, so 

 called because nearly altogether they constitute the substance 

 of living bodies. It simplifies extremely their apparent com- 

 plexity. It is thus that, according to Mulder, the formula of 

 albumineis 10(C*<'B:3lN5Ol2)^-S2PL If we limit ourselves to 

 totalising the atoms, this formula gives CWOH^ioN^ooiao + g2pij_ 

 a molecule of frightful complication. But if we admit a com- 

 pound radical, proteine (C^^H^'N^O^^), comporting itself as a 

 simple atom, the molecular structure of albumine is enormously 

 simplified : it approaches that which we are accustomed to meet 

 in the chemistry called mineral. It is probably also from this 

 notion of compound radicals that we must seek the explanation 

 of what has been called isomeria. If bodies having the same 

 elementary composition, such as the tartaric and paratartaric, 

 maUc acid, citric acid, sugars, gums, have nevertheless distinctive 

 properties, we must probably attribute the dissimilarities to 

 difEerences of molecular structure, to the existence, in the very 

 heart of these isomeric bodies, of dissimilar compound radicals. 



There is another notion not less important than that of com- 

 pound radicals for the easy comprehension of the formulas of 

 the chemistry called organic, the notion, namely, of autosaturar 

 tion. In efiect, the atomicity of a simple body does not always 

 expend itself on atoms of a different species ; it may manifest 

 itself between atoms of the same species. The atoms of carbon, 

 for instance, can saturate themselves. An atom of carbon, which 



is tetratomic, — c — , may, by expending merely a quarter of its 



I 

 atomicity, unite itself with another atom of carbon, which, in its 



turn, will neutralise in this combination a quarter of its attrac- 

 tive energy ; there will result thus therefrom a molecule hexa- 

 valeut, that is to say, capable of still enchaining six atoms ; 



I I 

 — c — c — 



