1884 Jrnl. Chem. Soc.46 237 The preparation of azo-dyes from the trisulphonic acids of β-naphthol.
1894 G. M. GouldIllustr. Dict. Med.Azo-dyes, a well defined group of the coal-tar colors, all containing the diatomic group N N, bound on either side to a benzene radical.