Salt, or Sea-Water, (eau de mer, Fr.) that which is strongly impregnated with salt, and is very sensible to the taste.

Method of converting Salt-Water into fresh.

Many attempts have been made to render saltwater fresh and potable; but they have, in general, been little else than different modes of distillation, though many of the authors of them, either from ignorance of the real nature of sea-water, or from a design of rendering their process mysterious, have mixed different ingredients with the water, either before or after its distillation.

Sir R. Hawkins, in the reign of Queen Elizabeth, obtained fresh-water by distillation.

Dr. Hales informs us, that Sir Theophilius Oglethorpe, in the reign of Charles II. applied lime as an ingredient to improve distilled sea-water.

Dr. Lister proposes the freshening of sea-water by means of sea-plants; these vegetables, like other plants, continually exhaling a large quantity of water in form of vapour, and that being all fresh, hr proposes on this basis a distillation without fire. The body of a large still was filled three parts with sea-water, and several fresh sea-plants in their growing posture put into it: the head was then fitted on, and a receiver adapted to the nose; then the continual ascent of vapour from the plant condensed into water in the head, and conveyed into the receiver sweet and clear water fit for drinking; the quantity thus produced, though considerable, is only small in proportion to the wants of a ship's company.

Mr. Hauton, therefore, attempted a more general method of doing it in quantities; for this purpose a great quantity of sea-water is to be taken up in a proper vessel, and as much oil of tartar, per deliquium, is to be added to this as will render it turbid, and cause a large precipitation. After this, the water is to be distilled, the furnace of the still being so contrived as to take up very little room, and consume only a small quantity of fuel; the sea itself may serve as a worm tub, the worm passing out of the ship at one place, and in again at another. When the water is thus distilled, it is mixed with an alkaline earth, and, after stirring it thoroughly about, the earth is to be suffered to subside to the bottom, and the water poured off; it is then said to be perfectly sweet, and in no way distinguishable from river water.

The process of Mr. Appleby, published in 1734 by order of the lords commissioners of the Admiralty, consisted in mixing with twenty gallons of sea-water six ounces of a fixed alkali, prepared with quicklime, as strong as lapis infernalis, and six ounces of bones calcined to whiteness and finely powered, and drawing off in a common still, with a slow fire, fifteen gallons. See Phil. Trans. Vol. XLVIII. p. 69.

Dr. Butler, instead of the Lapis infernalis and calcined bones, proposed the use of soap-leys.

Dr. Hales, in his Philosophical Experiments, suggested a method by keeping the sea-water close shut up till putrified and has again become sweet, and then distilling the water; upon which he found that three-fourths of the sea-water was free from bitterness and the acid. In another place he recommends the use of powered chalk and ventilation, by blowing up through the distilling water with a double pair of bellows. See Phil. Trans. Vol. XLIX. p. 312. &c.

Captain Chapman, in 1757, obtained fresh water by distilling sea-water with wood-ashes.

Dr. Lind, in 1761, discovered that sea-water, distilled without the addition of any ingredients, yielded pure fresh-water; and, in 1762, and account of this was read to the Royal Society, and soon after published by authority of the lords commissioners of the Admiralty.

In 1763, M. Poissonnier invented a still for this purpose, and Lord Mulgrave, in his voyage towards the North Pole in 1773, has done equal justice to its practicability.

Dr. Irving, in 1770, by whom distillation was generally introduced into the British navy, obtained a parliamentary reward of £5000; his invention consisted of a tea-kettle made without a spout, with a hole in the lid in the place of a knob; when filled with sea-water, the fresh vapour will arise as it boils and issue through the hole in the lid; into which the mouth of a tobacco-pipe is fitted, letting the stem incline a little downwards, and the vapour of fresh-water will take its course through the steam of the tube, and may be collected by fitting a proper vessel to its end. He also adapted a tin, iron, or copper tube, of suitable dimensions, to the lid of the common kettle used for boiling the provisions on ship-board; the fresh vapour, arising from boiling the sea-water in the kettle, passes through this tube into a hogshead, which serves as a receiver; and that the vapour may be readily condensed, the tube is kept cool by constantly wetting it with a mop dipped in a tub of cold water.

It appears from the testimony which was delivered to the lords commissioners of the Admiralty, by many respectable officers who witnessed an experiment made at Spithead, in January 1771, on board the Arrogant, that eighty gallons of sea-water did, in twenty-five minutes, after being put into the copper, and a fire made, distill in the proportion of twenty-five gallons per hour into fresh water, perfectly well tasted, and of less specific gravity than the best spring water in that neighbourhood; and the said officers gave it as their opinion, that five hundred gallons of fresh water might be distilled in the course of twenty-four hours, with the same quantity of fuel, in proportion to the time, as it required in the ordinary business of the ship. Every ship's kettle is divided into two parts, by a partition in the middle; one of these is only used when peas or oatmeal are dressed; but water is, at the same time, kept in the other to preserve its bottom. Dr. Irving has availed himself of this circumstance; and, by filling the spare part of the copper with sea-water, and fitting on the lid and tube, he has shewn that sixty gallons of fresh-water may be drawn off during the boiling of the above-mentioned provisions, without any additional fuel. He recommends also the preserving of the water, which may be distilled from the coppers in which peas, oatmeal, &c. are dressed, as salutary for the scorbutic, and the most proper kind of water for boiling salt water provisions. He likewise particularly remarks, that only three fourths of the sea-water should be distilled, as the water distilled from the remaining concentrated brine is found to have a disagreeable taste; and the farther continuation may be injurious to the vessel.

For an account of several experiments made on some of the best distilled water, prepared by Dr. Irving from sea-water, by Dr. Watson, see his Chem. Ess. vol. 2, p. 168, &c.

Dr. Priestley has suggested a proposal to give to this distilled water the briskness and spirit of fresh spring water, and, at the same time, of rendering it, perhaps, a remedy or preventive against the scurvy, by impregnating it with the gas or fluid called fixed air, obtained by mixing chalk with oil of vitriol.

A patent has lately been taken out by a Mr. Archbold, for a method of converting salt-water into fresh, both on land and on-board ship, which is produced by distilling to pure fresh water, on a principle of filtration. For this purpose, stills of a new construction are used, each of which has an outward case of metal; between the interior sides and the bottom, and the exterior bottom and sides of the still, a place is left vacant; but the still is inserted in the case in such a manner, that there shall be no egress for the steam from the case, except by a safety-valve. The head and neck are fixed to the still; thus the water in the cases, not having the pressure of the atmosphere,, will rise much beyond the boiling heat, and make the stills which are inserted in them boil also; and there being no egress for the steam from the case, except by the safety-valve; a small fire will suffice to keep up this degree of heat. From that part of the case which comes in immediate contact with the fire, a flue may be inserted, which, making some horizontal revolutions along the bottom, may pass out into the chimney. The back also of the fire-place can be a narrow boiler, which may communicate with the cases of the still. When performed on-board ship, a reservoir of salt-water is placed upon the deck of the vessel, through which the chimney of the fire may pass and impart its heat; and from the pipes, having a cock attached to each, lead into the cases and stills for the purpose of their supply. From the necks of the stills pipes are brought, conducting the steam into vessels for cooking provisions. The range has two metal doors in front, each of which is attached by hinges to iron bolts: these fit into staples fixed in the side of the range, so that when the fire is not wanted for cooking, it can be enclosed by these doors; but when required, the doors can be drawn out the length of the bolts, fitting into the staples at the side of the range, and form a screen. between which and the fire the meat can be roasted. For the purpose of condensing steam on-board of ships, the tube containing it may pass through the ship, and along any part of the outside of it which lies immediately in the water, and again entering the ship, it discharges the condensed water into the water designed for its reception: after the sea-water has been distilled in this manner, it is passed through a filterer, consisting of a small cylinder case made of tin or other metal, and being filled with pounded charcoal, each end is stopped by a circular cover perforated with holes, fine enough to prevent the charcoal from passing through. One end of thus case is inserted into a cask, also partly filled with pounded charcoal, and the water being poured into the cask, filters out through the case. See the article Filtering Machine.

A patent has also been taken out by Mr. Lamb, for the invention of an apparatus for rendering salt-water perfectly fresh and pure by distillation. The apparatus is attached to a new-constructed ship's firehearth; and it is said, that while a hearth, fitted on this principle, proportioned to the size of a fifty-gun ship, produces 25 gallons of fresh water per hour, without the slightest interruption to cooking, it effects a saving of one-fourth the consumption of fuel.

In consequence of certain experiments which have been made on-board his Majesty's ship Trusty, the invention has received the approbation of the lords commissioners of the Admiralty. Captain Hodgson, of the Trusty, before whom the experiments were made states, that the fire-hearth fully answers all its intended purposes; that he feels no hesitation in saying, that the invention will be attended with the greatest utility to the navy in general; that it consumes considerably less fuel, and that the coppers boil in one-third less time than by any mode before employed; that it produces fresh-water from sea-water at the rate of 20 to 25 gallons per hour; and that the water is as good, if not better, than any he ever drank at sea.

William Burney: A New Universal Dictionary of the Marine, being, a copius Explanation of the Technical terms and Phrases usually Employed in the Construction, Equipment, Machinery, Movements, and Military as well as Naval, Operations of Ships: with such parts of Astronomy, and Navigation, as will be Useful to Practical Navigators. Illustrated with a Variety of Modern Designs of Shipping, etc. together with separate views of the Masts, Yards, Sails, and Rigging. To which is annexed, A Vocabulary of French Sea-phrases and Terms of Art, Collected from the Best Authorities. Originally Compiled by William Falconer, Author of the Shipwreck, &c. Now Modernized and much Enlarged, by William Burney, LL.D. Master of the Naval Academy, Gosport.
T. Caldell & W. Davies, London, 1815. 4to, xvii, 708, 88 pp, 35 plates.

Transcribed by Lars Bruzelius

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