2,7-Naphthalenedisulfonicacid,4-amino-5-hydroxy-3-[2-[4-[[4-[2-[4-hydroxy-2-[(2-methylphenyl)amino]phenyl]diazenyl]phenyl]amino]-3-sulfophenyl]diazenyl]-6-[2-(4-sulfophenyl)diazenyl]-,sodium salt (1:4