THE COAL-TAR COLORS 139 



to the formation of indigo. The first practical method, devised 

 by Baeyer in 1880, involved the action of potassium hydroxide 

 on ortho-nitropropiolic acid; but many other methods have 

 been devised since then, such as the action of melted potas- 

 sium hydroxide on bromacetanilid, the action of halogenated 

 acetone on aniline, etc. Indigo is one of the most reliable dye- 

 stuffs, both as to brilliancy and permanency, and there is 

 little difference in these respects between the natural and 

 artificial products. The finished compound can, however, only 

 be used after reduction to the soluble indigo-white, and 

 this makes its use in dyeing and printing somewhat cumber- 

 some. In some of the methods for preparing artificial indigo, 

 the fibre can be impregnated with one ingredient and the other 

 applied either in the dye- vat or from the printing-rolls; con- 

 sequently, indigo can be and is often directly prepared in 

 the quantities and in the places in which it is needed. 



LIST OF COLORS. The following are some of the best 

 known commercial coal-tar colors, their molecular formulas, 

 and the principal methods employed in their manufacture. 



Aldehyde Green. See Aniline Green below. 



Aniline Black, C3oH 25 N 3 , made by the oxidation of aniline with mineral 

 salts. 



Aniline Blue (triphenyl-rosaniline hydrochloride), CssHssNaCl, made by 

 heating rosaniline, benzoic acid, and aniline, and subsequently adding 

 hydrochloric acid. 



Aniline Brown, Bismarck Brown, or Phenylene Brown (triamidoazo- 

 benzene), C^HisNs, made by the action of nitrous acid on metaphenylene- 

 diamine. 



Aniline Green, or Aldehyde Green, 221127^820, made by the action 

 of ordinary aldehyde on an acid solution of rosaniline sulphate and the sub- 

 sequent addition of sodium hyposulphite. 



Aniline Orange. This name is applied to various compounds made by 

 the action of amidosulphonic acids on phenols. The name is often applied 

 to the so-called Victoria Orange, CrHeN^Os. 



Aniline Red. See Fuchsin below. 



Aniline Scarlet, Ci8Hi S N 2 O4SNa, made by the action of diazoxylene on 

 naphthol-sulphonic acid. 



Aniline Violet. See Mauveih below. 



