Appearancewhite needle crystal or powder Assay99.5% min Melting point199-201 ( f+5 deg. C ) Loss on drying0.5% max Heavy metals0.001% max Arsenic0.0001% max Iron0.001% max Hydroquinone0.001% max Ph value5.0-7.0 in 1% aqueous solution Clarity of water solutiontransparency, colorless Specific optical rotationf++-f+d 20 = - 66 f+ 2fp Infrared signature peak1515cm-11220cm-11050 f+ (5~8) cm-1 Microbiological test: Bacteria300cfu/g max Fungus100cfu/g max Packing in 10kg carton, inner sealed with 1kg x 10 aluminum foil bag. Packing in 25kg cardboard drum, inner sealed with 25kg aluminum foil bag.