trisodium 2-[2-(4-nitro-2-sulphonatophenyl)vinyl]-5-[[4-[(4-sulphonatophenyl)azo]-1-naphthyl]-N,N,O-azoxy]benzenesulphonate

2-[2-(4-Nitro-2-sulfophenyl)ethenyl]-5-[[4-[(4-sulfophenyl)azo]naphthalen-1-yl]-NNO-azoxy]benzenesulfonic acid trisodium salt