1,3-Naphthalenedisulfonic acid, 7,7'-(iminobis(carbonyl(2-methyl-4,1-phenylene)azo))bis-, tetrasodium salt 28706-21-0 EINECS 249-168-9 Tetrasodium 7,7'-(ureylenebis((2-methyl-p-phenylene)azo))dinaphthalene-1,3-disulphonate