Putrid WATER, is that which has acquired an offensive smell and taste by the putrescence of animal or vegetable substances contained in it. It is in the highest degree pernicious to the human frame, and capable of bringing on mortal diseases even by its smell. It is not always from the apparent muddiness of waters than we can.
can judge of their disposition to putrefy; some which are seemingly very pure being more apt to become putrid than others which appear much more mixed with heterogeneous matters. Under the article ANIMALCULE, No 33, is mentioned a species of insects which have the property of making water sink to an incredible degree, though their bulk in proportion to the fluid which surrounds them is less than that of one to a million. Other substances no doubt there are which have the same property; and hence almost all water which is confined from the air is apt to become offensive, even though kept in glass or stoneware vessels. Indeed it is a common observation, that water keeps much longer sweet in glass vessels, or in those of earthen or stoneware, than in those of wood, where it is exceedingly apt to putrefy. Hence, as ships can only be supplied with water kept in wooden casks, sailors are extremely liable to those diseases which arise from putrid water; and the discovery of a method by which water could easily be prevented from becoming putrid at sea would be exceedingly valuable. This may indeed be done by quicklime; for when water is impregnated with it, all putrescent matters are either totally destroyed, or altered in such a manner as never to be capable of undergoing the putrefactive fermentation again. But a continued use of lime-water could not fail of being pernicious, and it is therefore necessary to throw down the lime; after which the water will have all the purity necessary for preserving it free from putrefaction. This can only be done by means of fixed air; and mere exposure in broad shallow vessels to the atmosphere would do it without any thing else, only taking care to break the crust which formed upon it. Two methods, however, have been thought of for doing this with more expedition. The one, invented by Dr Alston, is, by throwing into the water impregnated with lime a quantity of magnesia. The lime attracts fixed air more powerfully than magnesia; in consequence of which the latter parts with it to the lime: and thus becoming insoluble, falls along with the caustic magnesia to the bottom, and thus leaves the water perfectly pure. Another method is that of Mr Henry, who proposes to throw down the lime by means of an effervescing mixture of oil of vitriol and chalk put down to the bottom of the water cask. His apparatus for this purpose is as simple as it can well be made, though it is hardly probable that sailors will give themselves the trouble of using it; and Dr Alston's scheme would seem better calculated for them, were it not for the expense of the magnesia; which indeed is the only objection made to it by Mr Henry. Putrid water may be restored and made potable by a process of the same kind.
Of late it has been discovered that charcoal possesses many unexpected properties, and, among others, that of preserving water from corruption, and of purifying it after it has been corrupted. Mr Lowitz, whose experiments on charcoal have been published in Crell's Chemical Journal, has turned his attention to this subject in a memoir read to the Economical Society at Peterburgh. He found that the effect of charcoal was rendered much more speedy by using along with it some sulphuric acid. One ounce and a half of charcoal in powder, and 24 drops of concentrated sulphuric acid (oil of vitriol), are sufficient to purify three pints and a half of corrupted water, and do not communicate to it any sensible acidity. This small quantity of acid renders
it unnecessary to use more than a third part of the charcoal powder which would otherwise be wanted; and the less of that powder is employed, the less is the quantity of water lost by the operation, which, in sea-voyages, is an object worthy of consideration. In proportion to the quantity of acid made use of, the quantity of charcoal may be diminished or augmented. All acids produce nearly the same effects: neutral salts also, particularly nitre and sea-salt, may be used, but sulphuric acid is preferable to any of these; water which is purified by means of this acid and charcoal will keep a longer time than that which is purified by charcoal alone. When we mean to purify any given quantity of corrupted water, we should begin by adding to it as much powder of charcoal as is necessary to deprive it entirely of its bad smell. To ascertain whether that quantity of powdered charcoal was sufficient to effect the clarification of the said water, a small quantity of it may be passed through a linen bag, two or three inches long; if the water, thus filtrated, still has a turbid appearance, a fresh quantity of powdered charcoal must be added, till it is become perfectly clear: the whole of the water may then be passed through a filtering bag, the size of which should be proportioned to the quantity of water. If sulphuric acid, or any other, can be procured, a small quantity of it should be added to the water, before the charcoal powder.
The cleaning of the casks in which water is to be kept in sea-voyages should never be neglected: they should be well washed with hot water and sand, or with any other substance capable of removing the mucilaginous particles, and afterwards a quantity of charcoal dust should be employed, which will entirely deprive them of the musty or putrid smell they may have contracted.—The charcoal used for purifying water should be well burnt, and afterwards beat into a fine powder.
Sea-Water. See SEA-Water.