xvn MOLECULAR ARCHITECTURE 399 



radicals. The radicals of vegetable substances consist 

 generally of carbon and hydrogen, and those of animal 

 substances of carbon, hydrogen and nitrogen" (Textbook, 

 1817, I, 544). 



Gay-Lussac on the cyanogen radical (1815). An excel- 

 lent example of a compound radical of organic origin was 

 available in the case of prussic acid, which Gay-Lussac had 

 described in 1815 as a compound of hydrogen with the com- 

 pound radical CYANOGEN (p. 245). The analogy between the 

 compound organic radical cyanogen and the simple inorganic 

 radical chlorine was remarkable. It could combine, not 

 only with hydrogen, but with chlorine and with metals such 

 as potassium, silver and mercury; it could also exist alone 

 in the form of a gas, which was evidently the analogue of 

 chlorine gas. The similarity of the two series of compounds 

 may be shown by writing their formulae, as is often done 

 with the symbol Cy (Berzelius, Jahresbericht, 1839, 18, 

 120), to represent the compound-radical CN. Thus we 

 have 



Cyanogen, CN or Cy. Chlorine, Cl. 



Cyanogen gas C 2 N or Cy 2 ^ r^ui r-i 



rt LI -j /^i/^-ivT r*\r* f Chlorine gas . . vJL 



Cyanogen chloride C1CN or CICy / 



Prussic acid . . HCN or HCy Muriatic acid . . HC1 



Potassium cyanide KCN or KCy Potassium chloride KC1 



Silver cyanide . AgCN or AgCy Silver chloride . AgCl 



Mercuric cyanide . HgC 2 N 2 or HgCy 2 Mercuric chloride . HgCl 3 



r ^ Wbhler and Liebig (1832) on the benzoyl radical, 

 The importance of the theory of radicals became evident 

 whenWohler 1 and Liebig, in 1832, published their "Re- 

 searches on the Radical of Benzoic Acid " (Liebig's Ann. 

 der Pharm.) 1832, 3, 249-282). In these researches they 

 showed that oil of bitter almonds could be converted into a 



1 Wohler was already well-known for his preparation of aluminium 

 (Pogg. Ann. der Physik, 1827, 11, 146-161) and for his synthesis of 

 urea, a typical animal product, from inorganic materials (Pogg. Ann. 

 der Physik, 1828, 12, 253-256) ; the urea was obtained in attempting 

 to prepare ammonium cyanate, and is formed as a product of 

 "isomeric change," (NH 4 )CNO CO(NII 2 ). 2 . 



