444 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



After the discovery of the benzoyl-radical in 1832, Liebig 

 became the champion of the theory of radicals, whilst Berzelius 

 was chiefly concerned that the dissection of organic compounds 

 should be carried out in such a way as to segregate completely 

 the electro-positive and the electro-negative elements. Dumas, 

 who had much to do with the development of the theory of 

 radicals, soon broke away from Berzelius's interpretation of that 

 theory and became the chief exponent of the rival theory of 

 "substitution." 



D. THE THEORY OF SUBSTITUTION. 



Dumas, in 1834, showed that by a process of substitution or 

 metalepsy the hydrogen of organic compounds could be replaced 

 by an equivalent quantity of chlorine or oxygen, e.g. 



Prussicacid. . HCN+ C1 2 = HC1 + C1CN (Gay- Lussac, 1815) 



Ethylene chloride C 2 H 4 Cl 2 + 4Cl 2 = 4HCl + CoCl 6 (Faraday, 1821) 



Oil of bitter C 7 H 6 O + C1 2 = HC1 +C\II 5 OC1 



almonds (Wohler and Liebig, 1832). 



In some cases, hydrogen was removed without replacement, e.g. 

 Oxalic acid . H 2 C 2 O 4 + O gave H 2 O +2CO 2 . 



In such cases, it was assumed that hydrogen was present in the 

 form of water : thus in the preparation of chloral by the action 

 of chlorine on alcohol, 



Ethylene. . C 2 H 4 +3C1 2 gave C 2 HC1 3 +3HC1 



Water . . H 2 O + C1 2 gave O +2HC1 



therefore 



Alcohol . C 2 H 6 O + 4C1 2 gave C 2 IIC1 3 



E. ORGANIC TYPES, NUCLEI AND RESIDUES. 



Laurent, a pupil of Dumas, asserted that substitution was 

 not merely an empirical rule, but, in defiance of all Berzelius'' 

 electro- chemical conceptions, that chlorine took the place 

 and played the part of hydrogen in organic compounds. 

 Dumas, in 1839, adopted this view by suggesting that substi- 

 tution could take place without any change of type ; this idea 

 was cleverly ridiculed in an anonymous letter written by Wohler 

 in 1840. Dumas distinguished between chemical types, in which 



