blackish coal-tar colour dye
• (n.) A dark blue dyestuff, of the induline group; -- called also azodiphenyl blue. • (n.) A dark blue dyestuff, of the induline group; -- called also azodiphenyl blue.
Ni'gro·sine noun [ From Latin niger black.] (Chemistry) A dark blue dyestuff, of the induline group; -- called also azodiphenyl blue . 
Nigrosine is a class of black pigments and dyes obtained from aniline hydro-chlorates. They are used in inks and shoe polishes and for dyeing textiles.
any of the class of deep blue or black dyes obtained by the oxidation of aniline, used as coloring agents in inks and shoe polishes and for dyeing leather, wood, textiles, and furs.