1-(2,4-Xylylazo)-2-naphthol-3,6-disulfonic acid disodium salt 2,7-Naphthalenedisulfonic acid, 4-((2,4-dimethylphenyl)azo)-3-hydroxy- 23480-90-2 3761-53-3 68928-54-1 7481-49-4 C.I. 16150 Ponceau 2R Ponceau xylidine