THE COAL-TAR COLORS 135 



in the former, orange in the latter instance. Replacing either 

 or both of the phenyl groups (C 6 H 5 ) by more complex hydro- 

 carbon groups deepens the tone (with a tendency toward the 

 redder tints), increases the affinity for fibres, and dimin- 

 ishes the liability to fade. The earlier dyes of this class, such 

 as "aniline yellow," "Bismarck brown," chrysoidin, etc., 

 were singularly brilliant, but were not fast; whereas the 

 browns and the many reds, ranging from scarlet to purple, 

 which are now produced under the names of ponceaux or 

 bordeaux, congos, quinoline red, etc., are exceedingly per- 

 manent. In manufacturing this class of dyes, nitrous acid is 

 allowed to act upon an ice-cold solution of the salt of any 

 primary base (like aniline), and the "diazo-salt" formed 

 is allowed to act on another base or a phenol; an endless 

 variety of combinations is thus possible. 



TRIPHENYL-CARBINOL DERIVATIVES. These represent the 

 first discoveries in the aniline dyes, and some of them are 

 still produced on the largest possible scale. The fundamental 

 compound of the class is triphenyl-carbinol (CeH^sCOH, 

 and its derivatives are properly subdivided into rosanilines, 

 rosolic acids, and phthalems. 



In the rosaniline group, two or three amido-groups (NH 2 ) 

 are introduced in place of hydrogen atoms of the phenyls 

 (C 6 H 5 ). The di-amido-compounds are green; the fri-amido- 

 compounds are red, violet, or blue. Strictly speaking, the 

 compounds thus obtained are not themselves dyes, but are 

 bases which must first be combined with suitable acids, and 

 thus brought into a soluble form. Their salts in the solid 

 condition are beautifully crystalline bodies, showing colors 

 quite different from those of the solutions, and having pecu- 

 liar lustres like those of beetles' wings. The solutions have 

 very intense colorations and stain animal fibres readily and 

 permanently, although they do not fix themselves easily 



