124 THE PATH OF SCIENCE 



both contain the group C2 H5, which is known as the radical 

 ethyl. The importance of these radicals was first realized as 

 a result of the work of von Liebig and Wohler on the com- 

 pounds derived from benzoic acid that contain the radical 

 benzoyl, Ce H5 CO. Jean Dumas and P. Boullay had even 

 earlier recognized the existence of the ethylene radical, and 

 Bunsen found the cacodyl radical in the organic compounds 

 of arsenic, which he investigated. Berzelius, who at this 

 time was the recognized leader in chemical science, had 

 formulated the structure of inorganic salts as depending upon 

 the union of two electrically opposed components, these be- 

 ing the oxide of the metal and of the metalloid. Berzelius 

 applied this same idea to the structure of organic compounds, 

 formulating ethyl chloride as directly analogous to sodium 

 chloride. The great generalization of Berzelius was later to 

 be revived in the theory of electrolytic dissociation. But it 

 does not apply to organic compounds, and its advocacy by 

 Berzelius undoubtedly delayed the advance of organic chem- 

 istry for a number of years. The opposition to Berzelius 

 centered around two ideas. Von Liebig believed that the 

 properties of organic compounds depended upon the pres- 

 ence of radicals, so that ethyl chloride was cognate with ethyl 

 alcohol, since both of them contain the radical ethyl, rather 

 than with sodium chloride. Dumas, on the other hand, 

 classified organic compounds into types. Thus he found that 

 the progressive substitution of chlorine for hydrogen atoms 

 in acetic acid left the type of compound undisturbed. Mono- 

 chloroacetic acid, dichloro-, and trichloroacetic acid are all 

 acetic acids. The idea of types was extended by A. W. 

 Williamson, the predecessor of Ramsay at University Col- 

 lege, London. He considered alcohols, ethers, and acids to 

 belong to the water type of compounds; whereas A. Laurent 

 and C. F. Gerhardt regarded the amines as of the ammonia 

 type. 



All this work was leading to the clarification of the struc- 

 ture of organic compounds, but our present structural 

 formulae we owe primarily to August Kekule and A. S. 



