disodium 4-[(2,4-dihydroxyphenyl)azo]-5-hydroxynaphthalene-2,7-disulphonate

4-(2,4-Dihydroxyphenylazo)-5-hydroxy-2,7-naphthalenedisulfonic acid disodium salt

1-[(2,4-Dihydroxyphenyl)azo]-8-hydroxynaphthalene-3,6-disulfonic acid disodium salt