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Water, Purification Of

Pure water is incapable of putrefaction, but ordinarily water contains a small quantity of organic matter in solution which quickly undergoes decomposition even in closed vessels. This is particularly the case when the water is kept in wooden casks, or in open cisterns, into which leaves and insects are driven by the wind. As a beverage, putrescent water is highly unwholesome. Among the various methods that are adopted for purifying foul water, are the following. 1. Filtration through or agitation with powdered freshly-burnt charcoal, either animal or vegetable, but preferably the latter. This removes both mechanically-suspended matter, and part of the calcareous and gaseous impurities held in solution. 2. Free exposure to the action of the air, by which the organic matters become oxidised and insoluble, and speedily subside. This may be effected easily by agitating the water in contact with fresh air, or by forcing air through it by means of bellows. 3. Add a little sulphuric acid; fifteen to twenty drops are usually sufficient for a gallon. This addition may be advantageously made to water intended for filtration through charcoal, by which plan at least two-thirds of the latter may be saved (Lowitz). 4. An ounce of powdered alum (dissolved) well agitated with a hogshead or more of foul water, will purify it in the course of a few hours, when the clear portion can be decanted. When the water is very putrid, about half a drachm (or even one drachm) per gallon may be employed. 5. A solution of ferric sulphate acts in the same way as alum; a few drops are enough for a gallon. 6. Sea-water may be rendered fit for use as a beverage by distillation. The waste heat of the cook's galley is amply sufficient for this purpose. There are several patent contrivances for the distillation of water on ship-board.