7,7'-(Carbonyldiimino)bis[4-hydroxy-3-[[2-sulfo-4-[(4-sulfophenyl)azo]phenyl]azo]-2-naphthalenesulfonic acid hexasodium salt

7,7'-(Carbonyldiimino)bis[4-hydroxy-3-[[2-sulfo-4-[(4-sulfophenyl)azo]phenyl]azo]-2-naphthalenesulfonic acid hexasodium salt