A method of preparing carm’ ic acid. The aqueous extract of cochineal is precipitated with plumbic acetate ‘acidulated with acetic j acid; the precipitate is decomposed with hydrogen sulphid, and filtered. The filtrate is evaporated to dryness on a water-bath, and the residue dissolved in absolute alcohol; this solution is allowed to evaporate, when the crystals of carminic acid separate. They are washed with cold water to remove impurities, the water dissolving only the carminic acid.

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Definition of  SCHALLER’S METHOD