6-Amino-4-hydroxy-3-[[4-(sulfomethyl)phenyl]azo]-2-naphthalenesulfonic acid disodium salt

(4-Aminophenyl)methanesulfonic acid?diazo, in alkaline conditions and 6-Amino-4-hydroxynaphthalene-2-sulfonic acid? coupling.

red light brown. Soluble in water for red orange brown. The strong sulfuric acid for red, diluted into orange. Adding strong hydrochloric acid in aqueous solution for orange; Add thick sodium hydroxide solution for orange brown.