2,7-Naphthalenedisulfonic acid, 4-((2,4-dihydroxy-5-((4-nitrophenyl)azo)phenyl)azo)-5-hydroxy- 4-((2,4-Dihydroxy-5-((4-nitrophenyl)azo)phenyl)azo)-5-hydroxy-2,7-naphthalenedisulfonic acid 67786-16-7