But when water is offensive in consequence of being long kept, the most effectual and expeditious method of sweetening it is by exposing it to the air in as divided a state as possible. Boiling will not expel the putrid effluvia contained in water; but such is the attraction of air for this offensive matter, that the water need only be thoroughly exposed to it to be rendered quite sweet. This is best done by a machine invented by Mr. Osbridge, a lieutenant of the navy. It consists of a hand pump, which is inserted in a scuttle made at the top of a cask, and by means of it the water, being raised a few feet, falls through several sheets of tin pierced like cullenders, and placed horizontally in a half cylinder of the same metal. The purpose of it is to reduce the water into numberless drops, which being exposed in this form to the open air, is deprived of its offensive quality. The same method will serve to separate the superfluous quick lime in the water. It is a machine very deservedly in common use, and the working of it is a moderate and salutary exercise to men in fair weather. The following contrivance will be found to afford a sufficient supply of sweet water to particular messes, and may be considered as an artificial and more expeditious sort of dripping stone.--Let the narrow mouth of a large funnel be filled with a bit of sponge, over which let there be a layer of clean gravel or sand covered with a piece of flannel, and over the whole another layer of sand. Muddy or offensive water being poured upon this, runs or drops out clear; and care must be taken to change the sand, sponge, &c. frequently, as they will become loaded with the impurities of the water[81]. There should be in every ship an apparatus for distilling water in case of distress. This consists merely of a head and worm adapted to the common boiler, and distillation may go on while the victuals are boiling. More than eight gallons of excellent fresh water may be drawn off in an hour from the copper of the smallest ship of war[82]. I refer for a more particular account of all this to the works of Dr. Lind, who was the original inventor and recommender of this method. This invention seems to have escaped others so long, from the idea that the _desideratum_ in freshening sea water was some substance to be added to it while under distillation. No such substance is necessary, and, the more simple the mode of distillation, the fresher the water will prove. Rain water at sea is always pure and wholesome, and may be saved occasionally by means of a sail or awning. CHAP. III. Of CLOTHING.