SECT. m. THE ANILINE COLOURS. 12 -i> 



Rosaniline or roseine, a white substance, is the base 

 of aniline. It is a powerful alkali, readily combining 

 with acids to form highly coloured salts, many of 

 which have a tendency to crystallize, like magenta. 

 This base is most easily extracted from the acetate of 

 aniline. The boiling solution of that salt decomposed 

 by a large excess of ammonia, yields a crystalline 

 precipitate of a reddish colour, and when the colourless 

 liquid is separated by nitration from the precipitate, 

 it deposits on cooling perfectly white needles and tablets 

 of pure rosaniline. This substance unites to acids in 

 three different proportions forming three kinds of salts. 

 The salts that contain one equivalent of acid are ex- 

 tremely stable compounds ; for the most part they have 

 a green metallic reflection like some insects' wings ; 

 by transmitted light they are red, and their solutions 

 in alcohol have the magnificent crimson colour of 

 magenta. 



A bright purple dye is furnished by mixing equal 

 weights of magenta and aniline. When this mixture 

 is kept at the temperature of 329 for some hours and 

 then mixed with water and hydrochloric acid to remove 

 any excess of magenta or aniline, the result is an in- 

 soluble purple residuum or precipitate, but which when 

 well washed with water becomes soluble in alcohol and 

 boiling water slightly acidulated with acetic acid. When 

 the insoluble purple residue is boiled several times with 

 dilute hydrochloric acid, a fine blue dye is formed ; 

 azuline, the most beautiful of the blue dyes, which resists 

 the action of the strongest acids, and which is produced 

 by oxidizing aniline under high pressure. It was first pre- 

 pared at Lyons from phenic acid, a product of the dis- 

 tillation of coal ; when pure it appears under the form 

 of copper bronze-coloured crystals soluble in alcohol, to 

 which they communicate a magnificent blue colour 

 tinged with red ; but most of the blue dyes are derived 



