Bis[1-[(3-ethyl-4-nitrophenyl)azo]-2-hydroxy-3-naphthalenesulfonic acid]calcium salt C??? ??, ??, ??

Bis[1-[(3-ethyl-4-nitrophenyl)azo]-2-hydroxy-3-naphthalenesulfonic acid]calcium salt ?? ?? ? ???

???

?? ??

Bis[1-[(3-ethyl-4-nitrophenyl)azo]-2-hydroxy-3-naphthalenesulfonic acid]calcium salt ?? ??