70 Royal Society : — 



•which have been proved (by my method of opposed muscular piles) 

 to be equal in electromotive power ; subject a certain number of them 

 to repeated stimulation, and then, by means of the method of opposed 

 couples, compare the muscles which have been exercised with those 

 which have been left at rest, and it will be found that the latter 

 will manifest a much greater degree of electromotive power than 

 the former. The nervous excitation, which causes muscular con- 

 traction, developes heat, generates mechanical force and consumes 

 chemical affinity ; and as the electromotive apparatus of muscle 

 operates through means of that affinity, it must get weakened, like a 

 pile in which the acid has become weaker. In the Torpedo, on the 

 other hand, there is neither heat nor mechanical force produced, and 

 the electromotive apparatus is set up again, as it were, through the 

 influence of the nerves, after the manner of a secondary pile." 



" Natural History of the Purple of the Ancients." By M. Lucaze 

 Duthiers, Professor of Zoology in the Faculty of Sciences of Lille. 

 Received March 22, 1860. 



" Contributions towards the History of Azobenzol and Benzidine." 

 By P. W. Hofmann, Ph.D. Received July 24, I860. 



Among the numerous compounds into which benzol, when sub- 

 mitted to reagents, is converted, azobenzol and its derivatives have as 

 yet received but limited attention. Although more than twenty- 

 five years have elapsed since this interesting body was discovered 

 by Mitscherlich, both its formation and its constitution remain still 

 doubtful. 



Mitscherlich*, who discovered azobenzol in 1834, when submitting 

 nitrobenzol to the action of an alcoholic solution of potassa, repre- 

 sented this compound by the formula 



C 6 H 5 Nt, 



but left the reaction which gives rise to the formation of azobenzol 

 unexplained. In 1845 this body was reprepared by Hofmann and 

 Muspratt J, who observed among the collateral products of the reac- 

 tion aniline and oxalic acid. They represent the formation of 

 azobenzol by the equation 



2C B H 5 N0 2 + C 2 H e O = C 6 H 5 N + C 6 H 7 N + C 2 H 2 4 -l-H 2 0, 



Nitrobenzol. Alcohol. Azobenzol. Phenylamine. Oxalic acid. 



adding at the same time that they are far from considering this 

 equation as more than the representation of one phase of the trans- 

 formation of nitrobenzol, since several other rather indefinite com- 

 pounds or products are formed simultaneously. 



At about the same period Zinin made the interesting observation 

 that azobenzol is capable of fixing hydrogen and of being thereby 



* Pogg. Ann. xxxii. p. 224. 

 f H = l, = 16, C = 12, &c. 

 t Mem. of the Chem. Soc. vol. iii. p. 113. 



