514 Prof. R. Meldola on the Theory of the 



discussion is briefly as follows : — By the action of diazotized 

 metanitraniline upon paranitraniline an unsymmetrical diazo- 

 amido-compound is obtained, which has a melting-point of 

 211°. The same compound is obtained by reversing the order 

 of combination, i. e. by acting upon metanitraniline with 

 diazotized paranitraniline. According to Kekule's view, this 

 substance could have only one of the two formulae : — 



(p) N0 2 . C 6 H 4 . N, . NH . C 6 H 4 . N0 2 (m), 



II. 



(m) N0 2 . C 6 H 4 . N s . NH . C 6 H 4 . N0 2 (p) . 



By replacing the H-atom of the Nil-group by ethyl an 

 ethyl-derivative (of m.p. 148°) is formed; and this, on the 

 same theory, could have only one of the two corresponding 

 formulae : — 



m. 



(p) N0 2 . C 6 H 4 . N 2 . N(C 2 H 5 ) . C 6 H 4 . N0 2 (m), 



IV. 

 (m) N0 2 . C 6 H 4 . N 2 . N(C S H 5 ) . C 6 H 4 . N0 2 (p). 



If the unsymmetrical compound had the formula I., its 

 ethyl-derivative (III.) might have been expected to be iden- 

 tical with the compound produced by the action of diazotized 

 paranitraniline upon ethylmetanitraniline ; if it had the for- 

 mula II., its ethyl-derivative (IV.) might have been expected 

 to be identical with the compound produced by the action of 

 diazotized metanitraniline upon ethyl-paranitraniline. As 

 a matter of fact, it has been found that the ethyl-derivative of 

 the unsymmetrical compound is identical ivith neither of the 

 compounds prepared by the action of the diazotized nitr anilines 

 upon the ethyl-nitr anilines. We have therefore to allow the 

 existence of three isomeric ethyl-derivatives containing para- 

 and metanitraniline residues, a fact which cannot be repre- 

 sented by Kekule's formula. The properties of these and all 

 the allied compounds prepared by us in the course of the 

 inquiry are summarized in the following Table : — 



