4-amino-3-[[4-(1-naphthylazo)-1-naphthyl]azo]naphthalene-2,7-disulphonic acid, sodium salt

4-Amino-3-[[4-(1-naphthalenylazo)naphthalene-1-yl]azo]-2,7-naphthalenedisulfonic acid/sodium,(1:x) salt