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MOLECULAR ARCHITECTURE 



417 



represent the added atoms of hydrogen, hydrogen and 

 chlorine, hydrogen and oxygen, etc. 



Gerhardt (1839) on residues. A third aspect of the 

 theory of substitutions, differing both from Dumas's empirical 

 conceptions and from Laurent's ideas of conservation of 

 type, was developed in 1839 by Charles Gerhardt 

 (1816-1856), a pupil of Liebig, who left Germany to 

 become Professor of Chemistry at Montpellier and after- 

 wards at Strassburg. 



Berzelius had laid stress on the formation of compounds 

 by direct addition, e.g. 



= BaSO 4 . 



Dumas had been impressed by the action of chlorine in 

 displacing hydrogen from organic compounds, e.g. 



C1CN + HC1. 



Gerhardt directed attention to the formation of new com- 

 pounds by COPULATION, i.e. by the combination of two 

 substances with the simultaneous "production of a very 

 simple compound, such as water, hydrochloric acid, hydro- 

 bromic acid, etc." (Ann. Chim. Phys., 1839, 72, 196). 

 From a series of over twenty examples of copulation, the 

 following may be selected for representation by modern 

 equations : 



or NH 3 +C 7 H 5 OC1 = HC1 + (NH 2 )C 7 H 5 O 



Benzoyl chloride. 



Benzamide. 



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