Preparation
3-Aminobenzenesulfonic acid diazo, and 5-Aminonaphthalene-2-sulfonic acid and 8-Aminonaphthalene-2-sulfonic acid?coupling, again diazo, and Naphthalen-1-amine?coupling, product to diazo, in alkaline conditions and 7-Amino-4-hydroxynaphthalene-2-sulfonic acid coupling.