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Chemical Washing

When precipitation takes place, the deposit requires to undergo edulcoration, or cleansing from the liquid from which it was precipitated. With heavy and bulky precipitates, this is done by repeated washing, and, after the deposit has again settled, decantation of the supernatant liquid (see No. 3847); but when the powder is light, and separates with less facility from the liquid, the washing is better performed by a continuous stream of water passing through a filter on which the precipitate has been previously collected. The apparatus employed for a self-feeding filter (see No. 3840) is admirably adapted for this purpose. Lixiviation, or the separation of soluble matter from an insoluble powder, can be performed in the same way. (See Nos. 14, 23, and 32.)