430 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



largely of mixed types to represent the structure of com- 

 pounds, e.g. (loc. cit. 135, 136, 137) 



H| H \ 



gave SO 2 { (sulphurous acid, H 2 SO 3 ) 

 H 



cn ci \ 



H/ cj-v / (chlorosulphonic acid, C1SO 3 H, prepared 



H 



Qfx j \Lftiur umtpnunit uciu, v^iov^ 3 iA, jji 



2 \ r> by combining SO 3 + HC1) 



H ; 



H l 



H >N jj VN (carbamic add, the parent substance 



H j gave of ammonium carbamate, 



CO 



H 1 

 jj VN 



CO \n 

 H / U 



Gerhardt (1855) on conjugated radicals. A parallel 

 method of subdividing the molecules of organic compounds 

 was devised by Gerhardt, who found that the process of 

 " copulation " could be applied, not only to complete 

 molecules, but also to the radicals of which those molecules 

 are composed. In his Treatise (1852, IV. 604-610) he 

 makes use of CONJUGATED RADICALS to represent simul- 

 taneously " two or several systems of double decomposition 

 of the same body." This method of representation was 

 applied with great success to the fatty acids. Most of 

 their double decompositions (formation of salts, chlorides, 

 amides, esters, etc.) could be expressed by formulae of the 

 water-type, thus : 



Formic acid, o|^ HO Propionic acid, 



Acetic acid, O- Butyric acid, 



But "the acid radicals of the formula CnHgn-TO may be 

 viewed as composed of the carbonyl radical CO and an 

 alcohol radical C n H 2n+1 : 



CO(H) formyl CO(C 2 H 5 ) propionyl 



CO(CH 3 ) acetyl CO(C 3 H 7 ) butyryl." 



