228 HISTORY OF CHEMISTRY. [LECTURE XII. 



first studied by Buckton and Odling. 32 Highly important was 

 the discovery of potassium and of sodium ethyl which was 

 made by Wanklyn, 33 whilst Friedel and Crafts 34 showed how 

 to obtain silicium ethyl, etc. 



I have intentionally referred to these compounds here 

 because they exercised a distinct influence upon the further 

 development of the theory of conjugated radicals. Kolbe was 

 the first to explain correctly the nature of cacodyl ; he calls it 

 methyl coupled with arsenic, As CH 3 [C = 6] ; 35 and even if 

 we do not now employ the word "coupled," still we have in 

 other respects retained this view with regard to the substance, 

 and our conception of the relation of the metal to the radical 

 has not become much clearer. 



Kolbe has a similar way of looking at other organic com- 

 pounds ; all of them contain conjugated radicals, most of them 

 with carbon as the copula. Thus, in acetic acid and the allied 

 compounds, he assumes the radical C 2 C H 3 which, following 

 the example of Liebig, he calls acetyl ; 36 and he writes : 



(C 2 H 3 fC 2 O, HO Aldehyde, 



(CoHjfGjOa, HO. Acetic acid, 



(C 2 H 3 )~C 2 C1 3 Regnault's chloride of acetyl, 37 



(C 2 H 3 )~C, Acetamide [C = 6, O = 8]. 



Although this formula for acetic acid does not differ essen- 

 tially from that of Berzelius, still there was much that was new 

 and valuable in the considerations underlying these symbols. 

 For example, Kolbe now draws attention to the fact that the 

 four carbon equivalents of acetic acid (equivalents in Gmelin's 

 sense) do not really possess the same function, but that two of 

 them are contained in it in the form of methyl, while the other 

 two serve as a point for engaging the affinity of the oxygen. 



The formulae of the other fatty acids are obtained from that 



32 Proc. Roy. Soc. 14, 19; Annalen. Supplementband 4, 109. 33 Proc. 

 Roy. Soc. 9, 341 ; Annalen. 108, 67. 34 Ibid. 127, 31. :Jr > Ibid. 75, 

 211, and 76, i. ' M Compare p. 137. :!7 Annalen. 33, 319. 



