disodium 5-[(2-hydroxy-5-methylphenyl)azo]-2-[2-(4-nitro-2-sulphonatophenyl)vinyl]benzenesulphonate

5-[(2-Hydroxy-5-methylphenyl)azo]-2-[2-(4-nitro-2-sulfophenyl)ethenyl]benzenesulfonic acid disodium salt