1716-22-9 2-((2,4-Dinitrophenyl)azo)-1-naphthol 3,6-disulfonic acid 2-((2,4-Dinitrophenyl)azo)-1-naphthol 3,6-disulfonic acid disodium salt 3,6-Naphthalenedisulfonic acid, 2-((2,4-dinitrophenyl)azo)-1-hydroxy 3-((2,4-Dinitrophenyl)azo)-4-hydroxy-2,7-naphthalenedisulfonic acid 5423-07-4 DNPNS Nitrazine Yellow Nitrazine paper Phenaphthazine