445 



The azobenzole obtained in this manner is so readily purified that 

 this process is greatly preferable to the action of alcoholic potassa 

 upon nitrobenzole, since the latter process simultaneously produces 

 several substances which can be separated only with difficulty from 

 the azobenzole. 



A portion of the azobenzole obtained in the above process was 

 converted by means of sulphuretted hydrogen into benzidine. Of 

 the beautifully crystallized compound, a platinum salt was made 

 which was analysed by Mr. Noble. 



0-268 grm. of the salt left 0-088 grm. = 32-88 per cent, of 

 platinum. The formula C 12 H,- N, HC1; Pt C1 2 requires 33'09 per 

 cent, of platinum. 



Benzidine exhibits a very interesting deportment with nitrous 

 acid; gently warmed in the gas of this acid, obtained by treatment 

 of starch with nitric acid, it gives rise to a powerful reaction. The 

 substance assumes an orange-red colour, and exhibits, after treatment 

 with water, when recrystallized from alcohol, all the properties of 

 azobenzole. 



The reproduction of this body from benzidine was moreover fixed 

 in the following numbers : 



0*215 grm. of substance gave - 623 grm. of carbonic acid, and 



0-112 grm. of water. 



Theory. Experiment. 



(C ia H.N). 



Carbon 79*12 79'02 



Hydrogen 5'49 5'78 



Nitrogen .... 15*39 



100-00 



The simplest formulae of azobenzole and benzidine only differ by 

 one equivalent of hydrogen, 



Azobenzole C 12 H 5 N 



Benzidine C, 2 H 6 N, 



a relation which sufficiently explains the transformation and repro- 

 duction of azobenzole. 



2x2 



