438 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



leads to the view, that carbon is tetratomic (or tetrabasic) " 

 (Ann. Chem. Pharm., 1858, 106, 153). 



" If one introduces carbon as a tetratomic radical into the 

 types, one obtains for several of its known compounds 

 relatively simple formulae " (ibid, footnote). 



The QUADRIVALENCY of the single carbon atom was shown 

 in the following compounds in which it is combined with 



When two carbon atoms were united, the valency of the 

 double carbon atom, C 2 , was not 2x4 = 8, but 6, since two 

 units of combining-power were used in holding the two 

 carbons together, as in : 



Ethane . . C 2 H 6 Acetonitrile . C 2 H 3 N'" 



Ethyl chloride . Q>H 5 C1 Cyanogen . C 2 N 2 '" 



Ethylene chloride C 2 H 4 C1 2 Aldehyde . C 2 H 4 O" 



Carbon trichloride C 2 C1 6 Acetyl chloride C 2 H 3 C1O", etc. 



(ibid., p. 154). In reference to such a group of compounds 

 Kekule suggests that 



" If one compares together compounds, which contain the 

 same number of carbon atoms in the molecule and can be 

 converted into one another by simple metamorphoses 

 (e.g. alcohol, ethyl chloride, aldehyde, acetic acid, glycollic 

 acid, oxalic acid, etc.) one comes to the conclusion, that 

 they contain the carbon atoms arranged in the same way, 

 and that only the atoms attached to the carbon-skeleton 

 change (ibid., 155-156). 



Structural formulae of organic compounds. Graphic 

 formulae. Kekule's recognition of the quadrivalency of 

 carbon, and of the CARBON-SKELETON as the nucleus of all 

 organic compounds, provided a complete solution of the 

 ^problem of molecular structure. In order to show the 

 structure of any compound it was only necessary to indicate 



