Bis[1-[(4-methyl-3-nitrophenyl)azo]-2-hydroxy-7-naphthalenesulfonic acid]calcium salt C??? ??, ??, ??

Bis[1-[(4-methyl-3-nitrophenyl)azo]-2-hydroxy-7-naphthalenesulfonic acid]calcium salt ?? ?? ? ???

???

?? ??

Bis[1-[(4-methyl-3-nitrophenyl)azo]-2-hydroxy-7-naphthalenesulfonic acid]calcium salt ?? ??