tetrasodium 4,4'-bis[[2-methoxy-5-methyl-4-[(4-sulphonatophenyl)azo]phenyl]azoxy]stilbene-2,2'-disulphonate

2,2'-(1,2-Ethenediyl)bis[5-[[2-methoxy-5-methyl-4-(4-sulfophenylazo)phenyl]ONN-azoxy]benzenesulfonic acid]tetrasodium salt