A CENTURY OF CHEMISTRY. 103 



out the idea that organic compounds might he 

 brought into line with inorganic compounds by sup- 

 posing that they contained compound radicals, like 

 cyanogen, which behaved like elements. In mineral 

 substances the radicals are simple; in organic sub- 

 stances they are compound. 



Substitution. — About 1840, Dumas' idea of " sub- 

 stitution '^ was added to the conceptual formula? of 

 the organic chemist. ^' It was found that one or more 

 atoms in an organic compound, notably of hydrogen, 

 might be replaced by an equal number of atoms 

 of other elements, and that such products of substi- 

 tution retained similar qualities, and could be mutu- 

 ally converted into each other, the type of the com- 

 pound remaining the same." * 



Dumas showed that chlorine may replace hydrogen, 

 atom for atom, in many organic compounds, and " it 

 may be easily imagined how distasteful such a dis- 

 covery would be to iBerzelius and the school of electro- 

 chemists, involving as it does the idea that a negative 

 element may be exchanged for a positive element, 

 without a fundamental alteration in the chemical 

 character of the resulting compound." f 



According to Roscoe, the idea of substitution was 

 the germ of Williamson's researches on etherification 

 and those of Wurtz and Hofmann on the compound 

 ammonias — investigations which lie at the base of the 

 structure of modern chemistry — and had also a pro- 

 found influence on the development of organic 

 synthesis. 



Nuclei and Types. — The older radical theory, in- 

 fluenced by the facts of substitution, gave place to 

 the " type theory " of Laurent and Gerhardt and the 



* Merz, History, Vol. I., p. 410. 

 t Tilden, Short History, p. 15. 



