1,3-Naphthalenedisulfonic acid, 7-((1,8-dihydroxy-3,6-disulfo-2-naphthalenyl)azo)-, tetrasodium salt 29637-28-3 EINECS 249-745-5 Tetrasodium 7-((1,8-dihydroxy-3,6-disulphonato-2-naphthyl)azo)naphthalene-1,3-disulphonate