( 268 ) 



H\ >N -» ()N< >N 



\__/ NO \ / H 



Fischer and Ed. Hkpp liaxe made a elosei- stiKk of this reaction 

 and found it to be a general one ^) ; it also takes place with 

 diphenylnitrosamine. 



It was deemed of importance to study the exact conditions under 

 which this transformation takes place and particular!}' to learn its 

 order bj' means of a determination of the reaction \ elocitv. A method 

 which permitted the quantitative estimation of the two isomers in 

 presence of each other with sufticient accuracy, was not at hand. 

 The chemical behaviour of the two isomers does not differ greatly 

 and the nitrosobase (at least in this case) is far too weak to be 

 titrated. It was therefore attempted to utilise the difference in colour 

 of the two isomers ; diphcnylnitrosamine has a faint yellow colour, 

 which in dilute solutions ma^^ be neglected. The nitrosobase however, 

 in combination ^villi hych-ocldoric acid forms a brown powder whose 

 dilute alcoholic sohition is dee}) yello\v, whilst more concentrated 

 solutions are dark brown or red. 



It was therefore decided to carry out the measurements by means 

 of a colorimelric i)rocess using the polarisation-coU)rimeter of Krüss. 

 An unexpecled difficulty arose, however, owing to the fact that 

 different prepai'ations of the hydrochloride gave greatly different results 

 when examined in the colorimeter, although they had been prepared 

 in exactly the same manner. As it was, of course, necessary to 

 prepare the standard liquids with the perfect]}' pure salt, I have 

 taken a great deal of trouble to obtain this. It appeared that a 

 solution of this salt is slightly decomposed and darkened by the 

 oxygen of the air and by |)rolonged contact with excess of hydro- 

 chloric acid ; the salt was therefore prepared in an atmosphere of 

 carbonic acid and under S[)ecifietl conditions. The compound was 

 taken as pure when different preparations gave the same result in 

 the colorimeter ; an analysis was of no service. And after it had 

 been found that the free base (which in the solid state forms steel- 

 blue needles) exhibits the same colour as the hydrochloride in dilute 

 alcoholic solutions, the basis of the measurements was obtained. 



From the colorimetric identity of the free base and the hydro- 

 chloride it follows that the latter, in very dilute solutions, must l)e 

 completely alcoholytically dissociated and also that only solutions of 

 a certain degree of dilution are comparable with each other. 



1) Ber. 19. 2*101. 20. 1247. 2471. 21. 8G1. Ann. 255. 144. (188G— 1889) etc. 



