LECTURE x.] HISTORY OF CHEMISTRY. 185 



chemistry. In particular, these views led to new characteristics 

 for the recognition of polybasic acids, and this was of great 

 importance at that time, when so few of these acids were 

 known. 



The underlying idea with respect to coupled substances, 

 that the majority of compounds could be regarded as made up 

 of the residues of other substances, was of very great value for 

 the progress of the science, simply because it was opposed to 

 the rigidity and immutability of the radicals. How fertile these 

 ideas were is shown, for example, by the discovery of the 

 anilides and the anilid-acids. 



According to Gerhardt the amides are to be looked upon as 

 compounds of the residues of ammonia and of acids ; thus he 

 supposes oxamide to be formed according to the equation : 31 



C 1 H a 4 +2NH I = C 1 H a 2 .(NH) 2 + 2H a O [=12, O=i6], 

 that is to say, by the replacement of two oxygen atoms by 

 twice the imid- residue NH. Regarding a similar replacement 

 as also possible by means of the residue of aniline, the nature 

 of which had been settled by Hofmann's comprehensive and 

 interesting researches, 32 and then trying to show this replace- 

 ment by direct experiment, he succeeds in preparing oxanilide, 

 the formation of which is represented by the following equa- 

 tion : 



C 2 H 2 O 4 + 2C 6 H 7 N - C 2 H 2 O 2 (C 6 H 5 N) 2 + 2 H 2 O. 

 He carries the analogy between ammonia and aniline still 

 further by the discovery of the anilid-acids, which he regards 

 as analogous to the amid-acids. 33 Thus he writes the formula 

 of sulphanilic acid, which he obtains by the action of sulphuric 

 acid upon oxanilide, SH 2 O 8 . C 6 H 5 N, and, in its existence, finds 

 a new proof of the dibasic character of sulphuric acid. 



It may perhaps seem strange that Gerhardt introduces the 

 residues NH and C 6 H B N into these compounds, instead of 

 NH 2 and C 6 H 6 N. In this he may have been influenced by 

 Laurent, who had already tried, a few years previously, to 



31 Comptes Rendus. 20, 1032. 32 Annalen. 45, 250 ; 47, 37. 33 Journ. 

 de Pharm. [3] 9, 405 ; 10, 5 ; compare Annalen. 60, 308. 



