4-Hydroxy-3-[4'-(4-hydroxyphenylazo)-2,2'-dimethyl-4-biphenylylazo]-2,7-naphthalenedisulfonic acid disodium salt

disodium 4-hydroxy-3-[[4'-[(4-hydroxyphenyl)azo]-2,2'-dimethyl[1,1'-biphenyl]-4-yl]azo]naphthalene-2,7-disulphonate