I9I2.] BOGERT— CARBON COMPOUNDS. 261 



exhibited in the closer and more logical classification within the 

 groups. The term " organic chemistry," to include both vegetable 

 and animal chemistry, used by Berzelius in his " Handbook," was 

 quite generally adopted. 



In 1836, Laurent advanced his nucleus theory which, although 

 never generally accepted, was used by Gmelin in his " Handbook," 

 with certain alterations, as a foundation for a classification of 

 organic compounds. According to this theory, every organic com- 

 pound contains a group of atoms termed a " nucleus " or " germ." 

 Primary nuclei consist of carbon and hydrogen, and in these the 

 hydrogen may be replaced by other elements or groups of elements, 

 thus giving rise to derived or secondary nuclei, analogous in compo- 

 sition and chemical properties to the primary nuclei. Other atoms 

 may be attached to this nucleus, or they may quite surround it, and 

 when these are removed the primary nucleus reappears. 



In 1839, Dumas developed his substitution theory to a theory of 

 chemical types. An advance was made in the replacement of the 

 dualistic formulas by unitary ones. 



Gerhardt's residue theory appeared at about this time. It may 

 well be explained in comparison with the older radical theory. 

 According to the latter, ethyl nitrate, for example, was regarded as 

 the nitrate of ethyl oxide, (C2H5)20-N205; while, according to 

 Gerhardt, the combination of the nitric acid and alcohol occurs in 

 such a manner that one compound gives up a hydrogen and the other 

 a hydroxyl, forming water, the two " residues " then uniting to ethyl 

 nitrate. 



The discovery of the compound ammonias by Wurtz (1849) ^^'^^ 

 Hofmann led to the arrangement of organic compounds on types 

 of various simple inorganic bodies. For example, it was assumed 

 that the hydrogen in ammonia not only could be replaced atom for 

 atom by other elements, but also by compound radicals. 



Gerhardt's type theory was really a combination of his residue 

 theory with the older radical theory. His four fundamental types 

 were hydrogen, hydrochloric acid, water and ammonia; H — H, 



H — CI, H — O — H, N— H, to which Kekule subsequently added 



\h 



