2,7-Naphthalenedisulfonic acid,4-amino-6-[[4-[[4-[[8-amino-7-[(2-cyanophenyl)azo]-1-hydroxy-3,6-disulfo-2-naphthalenyl]azo]benzoyl]amino]phenyl]azo]-3-[(2-cyanophenyl)azo]-5-hydroxy-, tetrasodium salt