tetrasodium 4,5-dihydroxy-3,6-bis[(4-nitro-2-sulphonatophenyl)azo]naphthalene-2,7-disulphonate

4,5-Dihydroxy-3,6-bis[(4-nitro-2-sulfophenyl)azo]-2,7-naphthalenedisulfonic acid tetrasodium salt