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　　Preparation method:

　　20g of potassium dichromate was dissolved in 40ml of water, constantly stirring 400ml of concentrated sulfuric acid was slowly added.

　　Caution:

　　1. for washing glassware are dried organics and oil pollution.

　　2. highly corrosive, to prevent burns skin, clothing.

　　3. can be used repeatedly if the lotion into the dark green failure, may be added to concentrated sulfuric acid Cr3 + will continue to be used after oxidation.