... residue with 80 cc. of hot water for ten minutes on a steam bath with frequent shaking, and let cool. Treat the solution with 20 cc. (for roasted coffee) or 10 cc. (for unroasted coffee) of 1-percent potassium permanganate and let stand for 15 minutes at room temperature. Add 2 cc. of 3-percent hydrogen peroxid (containing 1 cc. of glacial acetic acid in 100 cc.). If the liquid is still red or reddish, add hydrogen peroxid, 1 cc. at a time, until the excess of potassium permanganate is destroyed. Place the flask on the steam bath for 15 minutes, adding ... — All About Coffee • William H. Ukers
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