184 ANILINE-RED 



solution of great richness and purity of colour. If, in tho treatment of aniline with' 

 arsenic acid, the latter be considerably beyond tho proportion of aniline employed, 

 violet and blue dyes may bo formed. The production of such has boon patented by 

 Girard and De Laire. 



Laurent and Casth^laz have obtained aniline-red direct from benzol, without tho 

 preliminary isolation of aniline. Nitrobenzol is treated with a mixture of iron and 

 hydrochloric acid, or with ferric chloride. On heating the mixture, the ferric chloride 

 reacts on the aniline contained in the mixture, transforming it into aniline-rod. It is 

 doubtful if the colouring-matter obtained by this process is equal in beauty to that 

 procured from the aniline, and tho process is no longer employed. Tho name of 

 erythrobenzol was given by the discoverers to the colouring-matter thus obtained, but 

 it probably consists principally of rosanilino. 



The processes described are amongst the best yet devised for the preparation of 

 crude aniline-red. Numerous other methods have been patented, amongst others tho 

 following : 



Messrs. Kenard Brothers include in their patent the ebullition of aniline with 

 stannous, stannic, mercurous, and mercuric sulphates, with ferric and uranic nitrates 

 and nitrate of silver, and with stannic and mercuric bromides. 



Messrs. John Dale and Caro patent tho action of nitrate of lead upon aniline, or 

 hydrochlorate of aniline. 



Mr. Smith claims the ebullition of aniline with perchloride of antimony, or tho 

 action of antimonic acid, peroxide of bismuth, stannic, ferric, mercuric, and cupric 

 oxides upon hydrochlorate or sulphate of aniline at the temperature of 180. 



M. Gerber-Keller (Heilmann in England) claims the production of aniline red from 

 all the metallic salts of the oxacids of nitrogen, sulphur, chlorine, bromine, iodine, 

 phosphorus, arsenic, and, in fact, almost every compound within the range of chemistry. 

 It may well be said of such patents, that ' scientific men cannot speak otherwise than 

 in terms of reprehension. Their claims are founded on random guesswork, not on tho 

 results of patient investigation. They are attempts to pro-occupy the whole field, and 

 forestall all the rewards which should be left open to real inventive genius to cultivate 

 and win.' 



These processes have reference to the preparation of crude aniline-red. The crude 

 colours contain some undecomposed aniline, mostly in the form of salts. They con- 

 tain also tarry matters, some insoluble in water and dilute acids ; others soluble in 

 bisulphide of carbon, naphtha, or in caustic or carbonated alkalis. If, therefore, tho 

 crude red be boiled with an excess of alkali, the undecomposed aniline is expelled, 

 the acid which exists in the product being fixed. On treating the residue with 

 acidulated boiling water, the red is dissolved, while certain tarry matters remain 

 insoluble. If now the boiling solution be filtered, and then saturated with an alkali, 

 the colouring-matter is precipitated in a tolerable state of purity. By re-dissolving the 

 precipitated red in an acid, not employed in excess, a solution is obtained which 

 frequently crystallises, or from which a pure red may be thrown down by a new 

 addition of chloride of sodium, or other alkaline salt. The hydrochlorate of aniline- 

 red is employed in dyeing in France, while the acetate is used in England. 



To Dr. Hofmann we are principally indebted for the investigation into the nature 

 of aniline-red. In his paper on the ' Formation of Aniline-Red,' he says, he is 

 ' painfully aware of the imperfections of his researches upon this subject : as yet only 

 a corner of the veil which conceals tho truth is raised. The genesis and constitution 

 of aniline-red still remain to be investigated, though the chemical nature and compo- 

 sition of the substance itself are no longer doubtful.' 



Aniline-reds are salts of a very remarkable compound, which plays tho part -of a 

 well-defined base, and to which Dr. Hofmann gave the name of rosaniline. This 

 compound, in its anhydrous state, is represented by tho formula of C 19 H 1 9 N 3 . (See 



ROSANILINE.) 



The formation of aniline-red will be best given in Dr. Hofmann's own words : 

 ' It had been observed by many manufacturers that some varieties of commercial 

 aniline yield much more rosaniline than others. Samples of aniline, boiling at tem- 

 peratures much higher than the boiling point of the pure compound, are found to be 

 particularly adapted for the production of tho red. This observation led Dr. 

 Hofmann to examine carefully tho deportment of pure aniline under the influence of 

 the several agents by which commercial aniline is converted into aniline-red. To this 

 examination ho subjected a sample of pure aniline derived from indigo, and other 

 samples made from pure benzol ; this being derived in some cases from benzoic acid, 

 in other cases from coal-tar. These experiments elicited the remarkable fact, that 

 pure aniline, from whatever source obtained, is incapable of furnishing the red dye a 

 result fully confirmed by Mr. E. C. Nicholson, who indeed had been long acquainted 

 with this circumstance. It thus became obvious that commercial aniline must contain 



