Dr. Hofmann on the Metamorphoses of Indigo. 403 



I made a great number of experiments to discover under 

 what conditions this body was formed, but as yet I have not 

 been able to produce it at will. In most cases I obtained in- 

 stead a resinous body, which was precipitated in the form of 

 yellow flakes from the nitric acid by addition of water, and 

 which possessed the same property as nitropicric acid of tin- 

 ging the skin. This substance is soluble in alcohol and aether, 

 but cannot be obtained from the solution in a crystalline form. 

 It is also soluble in the alkalies and ammonia, and is again 

 precipitated by acids. By boiling the ammoniacal solution 

 till the excess of ammonia is removed, and then adding nitrate 

 of silver, a reddish-yellow precipitate is formed, which I was 

 able to obtain only on one occasion in a crystalline form. My 

 substance was, however, ail expended ere I could discover a 

 good method of preparation. Further experiments are neces- 

 sary to decide the correctness of the forementioned hypothesis. 



Action of Anhydrous Baryta and Lime on Chloraniline. 



Though the examples are numerous in which the hydrogen 

 of organic bodies has been replaced by chlorine, yet chemists 

 have seldom been able to expel, without complete disorga- 

 nization of the body, the assumed chlorine and refix the 

 hydrogen in its old position. Indeed I know of no other in- 

 stance than that of the regeneration of acetic acid from the 

 chloracetic, performed by Melsens, by the employment of 

 potassium amalgam. 



From chloraniline aniline can likewise be reproduced. If 

 a few crystals be placed in the end of a combustion-tube and 

 lime in small pieces be laid before it, on heating the lime to a 

 low red heat, there distils over a yellow oil which no longer 

 becomes crystalline, and by all its reactions is at once recog- 

 nised as aniline. At the same time a considerable quantity 

 of ammonia is evolved, and there remains in the tube chloride 

 of calcium and a large quantity of carbonaceous matter. 



The regeneration of aniline is, as must be at once seen 

 essentially different from that of the acetic acid. In the repro 

 duction of acetic acid from the chloracetic the hydrogen as- 

 sumed is derived from the water present, its oxygen serving 

 to oxidize the potassium; in the case of aniline the requisite 

 hydrogen is furnished by that substance itself, which must 

 consequently be partly decomposed. One equivalent of the 

 chlorinated base contains just sufficient hydrogen to convert 

 its nitrogen into ammonia, its own chlorine and that of another 

 equivalent of base into hydrochloric acid, and finally, to fur- 

 nish the required equivalent of hydrogen to the now regene- 



2 E2 



