Specification: Item  First grade Second Grade Colour Index 10 max  20 max Purity  90% min  85% min Sulphate as SO4   0.001% max  0.002% max  Chloride as CL 0.003% max 0.005% max  Iron as FE  0.0001%max   0.0005%max  Evaporation residue 0.006% max   0.02% max