SEA-Water, the salt water of the sea. The principal salts contained in sea-water are, 1st, Common marine or culinary salt, compounded of fossil alkali or soda and marine acid; 2dly, A salt formed by the union of the same acid with magnesian earth; and, lastly, A small quantity of selenite. The quantity of saline matter contained in a pint of sea-water, in the British seas, is, according to Neumann, about one ounce in each pint (A).

The saltness of this water is supposed to arise from numerous mines and mountains of salt dispersed here and there in the depths of the sea. Dr Halley supposes that it is probable the greatest part of the sea-salt, and of all salt lakes, as the Caspian sea, the Dead sea, the lake of Mexico, and the Titicaca in Peru, is derived from the water of the rivers which they receive: and since this sort of lakes has no exit or discharge but by the exhalation of vapours, and also since these vapours are entirely fresh or devoid of such particles, it is certain that the saltness of the sea and of such lakes must from time to time increase; and therefore the saltness at this time must be greater than at any time heretofore. He further adds, that if, by experiments made in different ages, we could find the different quantity of salt which the same quantity of water (taken up in the same place, and in all other the same circumstances) would afford, it would be easy from thence, by rules of proportion, to find the age of the world very nearly, or the time wherein it has been acquiring its present saltness.

This opinion of Dr Halley is so improbable, that it is surprising so acute a philosopher could have adopted it. That fresh water rivers should in the course of many thousand years produce saltness in the sea, is quite incredible. If this were the case, every sea or great body of water which receives rivers must be salt, and must possess a degree of saltness in proportion to the quantity of water which the rivers discharge. But

(A) In Bergman's analysis of sea-water taken up in the beginning of June 1776, about the latitude of the Canaries, from the depth of 60 fathoms, the solid contents of a pint of the water were,

<table> <tr> <th></th> <th>Gr.</th> </tr> <tr> <td>Of common salt</td> <td>253^1/2</td> </tr> <tr> <td>Salited magnesia</td> <td>60^1/2</td> </tr> <tr> <td>Gypsum</td> <td>8^1/2</td> </tr> <tr> <th>Total</th> <th>330^1/2</th> </tr> </table>

3. 9 Grs. or 5 1 10^1/2 so far is this from being true, that the Palus Meotis and the great lakes in America do not contain salt but fresh water. It may indeed be objected, that the quantity of salt which the rivers carry along with them and deposit in the sea, must depend on the nature of the soil through which they flow, which may in some places contain no salt at all; and this may be the reason why the great lakes in America and the Palus Meotis are fresh. But to this opinion, which is merely hypothetical, there are unanswerable objections. It is a curious fact that the saltness of the sea is greatest under the line, and diminishes gradually as we advance to the poles: We must therefore suppose, if Dr Halley's theory be true, that the earth contains more salt in the tropical regions than in the temperate zones, and more in the temperate zones than in the frigid; and consequently that the rivers in these different regions contain a quantity of salt proportionable to their distance from the equator. This, however, must be first proved by experiment, and cannot be assumed as an established fact. But there is another circumstance that entirely destroys this theory. If we allow that the sea receives its saltness from the rivers, it must be equally salt or nearly so in every part of the earth. For, according to a simple and well known principle in chemistry, "when any substance is diffused in water with the affluence of agitation, at whatever part of the water it is introduced, it will be equally diffused through the whole liquid." Now though it were true that a greater quantity of salt were introduced into the sea under the line than towards the poles, from the constant agitation occasioned by the wind and tide, the salt must soon pervade the whole mass of water. To say that the superior degree of heat in the tropical regions may dissolve a greater quantity of salt, will not destroy our argument; for it is an established principle in chemistry, that cold water will dissolve nearly as great a quantity of salt as hot water can dissolve.

The saltness of the sea has also been ascribed to the solution of subterraneous mines of salt, which is supposed to abound in the bottom of the sea and along its shores. But this hypothesis cannot be supported. If the sea were constantly dissolving salt, it would soon become saturated; for it cannot be said that it is deprived of any part of its salt by evaporation, since rain-water is fresh. If the sea were to become saturated, neither fishes nor vegetables could live in it. We must therefore despair of being able to account for the saltness of the sea by second causes; and must suppose that it has been salt from the creation. It is impossible indeed to suppose that the waters of the sea were at any period fresh since the formation of fishes and sea-plants; for as these will not live in water saturated with salt, neither will they live in water that is fresh; we therefore conclude that the saltness of the sea has been nearly the same in all ages. This is the simplest hypothesis of the three that has been mentioned. It explains best the various phenomena, and is involved in fewest difficulties. We shall, however, allow that there may be some exceptions; that the saltness of some seas, or of particular parts of the same sea, may be increased by mines of rock-salt dispersed near its shores.

With regard to the use of this salt property of sea-water, it is observed, that the saltness of the sea preserves its waters pure and sweet, which otherwise would corrupt and stink like a filthy lake, and consequently that none of the myriads of creatures which now live therein could then have a being. From thence also the sea water becomes much heavier, and therefore ships of greater size and quantity may be used thereon. Saltwater also doth not freeze so soon as fresh-water, whence the seas are more free for navigation. We have a dissertation, by Dr Ruffel, concerning the medical uses of sea-water in diseases of the glands, &c. wherein the author premises some observations upon the nature of sea-water, considered as impregnated with particles of all the bodies it passes over, such as submarine plants, fish, salts, minerals, &c. and saturated with their several effluvia, to enrich it and keep it from putrefaction: whence this fluid is supposed to contract a soapiness; and the whole collection, being pervaded by the sulphureous steams passing through it, to constitute what we call sea-water; the confessed distinguishing characteristics of which are saltness, bitterness, nitrety, and unctuosity: whence the author concludes, that it may be justly expected to contribute signally to the improvement of physic. The cases in which our author informs us we are to expect advantages from sea-water are, 1. In all recent obstructions of the glands of the intestines and meseentery. 2. All recent obstructions of the pulmonary glands, and those of the viscera, which frequently produce confluences. 3. All recent glandular swellings of the neck, or other parts. 4. Recent tumours of the joints, if they are not suppurrated, or become sibirious or cancerous, and have not carious bones for their cause. 5. Recent defluxions upon the glands of the eyelids. 6. All defecations of the skin, from an erysipelas to a lepra. 7. Diseases of the glands of the nose, with their usual companion a thicknes of the lip. 8. Obstructions of the kidneys, where there is no inflammation, and the stone not large. 9. In recent obstructions of the liver, this method will be proper, where it prevents confluences of the belly, and afflicts other medicines directed in icterial cases. The same remedy is said to be of signal service in the bronchocele; and is likewise recommended for the prevention of those bilious colics that so frequently affect our mariners.

Preservation of Sea-Water from Putrefaction. As it is sometimes necessary to preserve sea-water in casks for bathing and other purposes, it is of importance to know how to keep it from putrefaction. Many experiments were made to determine this point by Mr Henry, and are recorded in the first volume of the Memoirs of the Literary and Philosophical Society of Manchester. His first experiment we shall here present to our readers. "To one quart of sea-water were added two scruples of fresh quick-lime; to another, half an ounce of common culinary salt; and a third was kept as a standard without any addition. The mouths of the bottles being loosely covered with paper, they were exposed to the action of the sun in some of the hottest weather in summer. In about a week the standard became very offensive; and the water, with the additional quantity of salt, did not continue sweet many hours longer; whereas that with lime continued many months without ever exhibiting the least marks of putridity." When he added a dram more of quicklime, the whole of the magnesia contained in the water was separated; and when a further addition was made, a lime-water was immediately immediately formed. He therefore concluded, that two scruples of quicklime are sufficient to preserve a quart of sea-water. The proportions, however, may vary a little, according to the strength of the quicklime employed.

Freshening of SEA-Water. The method of making sea-water fresh was long a deaderatum in navigation. Many methods have been proposed for this purpose. Mr Appleby published an account of a process which he had instituted in the year 1734. He distilled sea-water with a quantity of lapis infernalis and calcined bones; but this process was soon laid aside, as it was not only difficult in itself, but rendered the water unpalatable. Dr Butler proposed soap-leys in place of Mr Appleby's ingredients; but the water was still liable to the same objection. Dr Stephen Hales recommended powdered chalk; but his method was expensive, and did not improve the taste of the water. Dr Lind of Portsmouth distilled sea-water without any ingredients; but as the experiment he made was performed in a vessel containing only two quarts, with a glass receiver, in his study, nothing conclusive can be drawn from it for the use of Dr Irving's sailors. At length Dr Irving brought the process to a very high degree of simplicity and perfection, by which the water is obtained pure, without much expense of fuel or a complicated apparatus. For this valuable discovery he received a reward of 500l. The advantages of this method remain to be stated, which may be reduced to the following: 1. The abolishing all stills, fill-heads, worm-pipes, and their tubes, which occupy so much space as to render them totally incompatible with the necessary business of the ship; and using in the room of these the ship's kettle or boiler, to the top whereof may occasionally be applied a simple tube, which can be easily made on board a vessel at sea, of iron plate, stove funnel, or tin sheet; so that no situation can prevent a ship from being completely supplied with the means of distilling sea-water. 2. In consequence of the principles of distillation being fully ascertained, the contrivance of the simplest means of obtaining the greatest quantity of distilled water, by making the tube sufficiently large to receive the whole column of vapour, and placing it nearly in a horizontal direction, to prevent any compression of the fluid, which takes place so much with the common worm. 3. The adopting of the simplest and most efficacious means of condensing vapour; for nothing more is required in the distillation but keeping the surface of the tube always wet, which is done by having some sea-water at hand, and a perfor to dip a mop or swab into this water, and pass it along the upper surface of the tube. By this operation the vapour contained in the tube will be entirely condensed with the greatest rapidity imaginable; for by the application of the wet mop thin sheets of water are uniformly spread, and mechanically pressed upon the surface of the hot tube; which being converted into vapour make way for a succession of fresh sheets; and thus, both by the evaporation and close contact of the cold water constantly repeated, the heat is carried off more effectually than by any other method yet known. 4. The carrying on the distillation without any addition, a correct chemical analysis of sea-water having evinced the futility of mixing ingredients with it, either to prevent an acid from rising with the vapour, or to destroy any bituminous oil supposed to exist in sea-water, and to contaminate the filled water, giving it that fiery unpalatable taste inseparable from the former processes. 5. The ascertaining the proper quantity of sea-water that ought to be distilled, whereby the fresh water is prevented from contracting a noxious impregnation of metallic salts, and the vessel from being corroded and otherwise damaged by the salts caking on the bottom of it. 6. The producing a quantity of sweet and wholesome water, perfectly agreeable to the taste, and sufficient for all the purposes of shipping. 7. The taking advantage of the drying the ship's provisions, so as to distil a very considerable quantity of water from the vapour, which would otherwise be lost, without any addition of fuel. To sum up the merits of this method in a few words: The use of a simple tube, of the most easy construction, applicable to any ship's kettle. The rejecting all ingredients; ascertaining the proportion of water to be distilled, with every advantage of quality, saving of fuel, and preservation of boilers. The obtaining fresh water, wholesome, palatable, and in sufficient quantities. Taking advantage of the vapour which ascends in the kettle while the ship's provisions are boiling. All these advantages are obtained by the above-mentioned simple addition to the common ship's kettles. But Dr Irving proposes to introduce two further improvements. The first is a hearth, or stove, so constructed that the fire which is kept up the whole day for the common business of the ship serves likewise for distillation; whereby a sufficient quantity of water for all the economical purposes of the ship may be obtained, with a very inconsiderable addition to the expense of fuel. The other improvement is that of substituting, even in the largest ships, cast-iron boilers, of a new construction, in the place of coppers.

As soon as sea-water is put into the boiler, the tube Directions is to be fitted either into the top or lid, round which, if for distillation, a bit of wet linen may be applied, to make it fit close to the mouth of the vessel; there will be no occasion for luting, as the tube acts like a funnel in carrying off the vapour. When the water begins to boil, the vapour should be allowed to pass freely for a minute, which will effectually clean the tube and upper part of the boiler. The tube is afterwards to be kept constantly wet, by passing a mop or swab, dipped in sea water, along its upper surface. The waste water running from the mop may be carried off by means of a board made like a spout, and placed beneath the tube. The distillation may be continued till three-fourths of the water be drawn off, and no further. This may be ascertained either by a gauge-rod put into the boiler, or by measuring the water distilled. The brine is then to be let out. Water may be distilled in the same manner while the provisions are boiling. When the tube is made on shore, the best substance for the purpose is thin copper well tinned, this being more durable in long voyages than tin-plates. Instead of mopping, the tube, if required, may have a case made also of copper, so much larger in diameter as to admit a thin sheet of water to circulate between them by means of a spiral copper thread, with a pipe of an inch diameter at each end of the case; the lower for receiving cold water, and the upper for carry it off when heated.

When only a very small portion of room can be conveniently allow for distillation, the machine (fig. 2.), which is only 27 inches long, may be substituted, as SCYTHES. PLATE CCCCLXXVIII.

Machine for Freshening SEA WATER.

SECTOR

SERIES was done in this voyage. The principal intention of this machine, however, is to distil rum and other liquors; for which purpose it has been employed with extraordinary success, in preventing an emphysema, or fiery taste.

Figure 1. represents in perspective a section of the two boilers taken out of the frame. In the back part at D, E, are seen openings for the cocks. On the top is a distilling tube A, B, C, five inches diameter at A, and decreasing in size to three inches at C; the length from B to C is five feet. Near C is a ring to prevent the water which is applied to the surface from mixing with the distilled water. In the inside of the tube below B, is a small lip or ledging, to hinder the distilled water from returning into the boiler by the rolling of the ship.

In figure 2. A, B, C, D, represent a vertical section of a copper box, 27 inches long, seven inches wide, and 11 in height, tinned on the inside. In the bottom F is an aperture about six inches in diameter, having a ring to fit on the still or boiler. The dotted lines which run nearly horizontal, are vessels of thin copper, tinned on the outside, two feet long, seven inches wide, and three quarters of an inch deep. At G is a funnel to receive cold water, which is conveyed into the vessels by communicating pipes, contrived in such a manner as to form a complete and quick circulation of the water through their whole extent. When the water is become hot by the action of the steam, it is discharged by the horizontal pipe at A. E is a pipe from which the distilled water or spirits run, and is bent in such a form that the liquor running from it acts as a valve, and hinders any steam from escaping that way. On the top of the box, at H, is a safety-valve, which prevents any danger from a great accumulation of vapour not condensed for want of a proper supply of cold water.

We shall now mention a different method, discovered by the Chevalier Lorgna, by congelation of sea-water. Sea-water requires a very great degree of cold in order to become ice. Our author found that a freezing mixture, made by mixing three parts of pounded ice with two parts of common salt, was quite sufficient to freeze it. The cold produced by this mixture is equal to about 4° below 0 of Fahrenheit's thermometer.

A quantity of sea-water is never entirely congealed, a portion of it always remaining fluid; and, what is very remarkable, this fluid part is incomparably more full of salt and more nauseous than the rest; hence, if this be separated from the congealed part, the latter on being melted will be found to contain much less salt than it did before congelation. This we shall call the water of the first purification.

If the water of the first purification be again congealed, a part of it will remain fluid as in the first operation. This fluid portion will contain a greater proportion of salt than the rest, which is of course more pure, and, being melted, forms the water of the second purification. Thus, by repeatedly freezing the same sea-water, and separating the fluid from the congealed part in every operation, it is at last perfectly purified, so as to be entirely divested of salt, and as fit for drink and other purposes as the purest water that is used.

At first the sea-water, in order to be congealed, requires a very great degree of cold, as mentioned above, the ice formed in it consists rather of scales or filaments than of a compact body, and the quantity of the fluid parts bears a considerable proportion to the quantity of ice. But as the water, by undergoing the successive congelations, becomes more and more pure, so it becomes capable of being congealed by a smaller and smaller degree of cold; the ice is at the same time more compact, and in greater quantity; the fluid part at last becoming very inconsiderable.

SEA-Weed, or Alga Marina, is commonly used as a manure on the sea-coast, where it can be procured in abundance. The best sort grows on rocks, and is that from which kelp is made. The next to this is called the peaty sea-weed; and the worst is that with a long stalk. In the neighbourhood of Berwick, the farmers mix it with stable-dung and earth, and thus obtain a great quantity of excellent manure. Sea weed is found also to be a very fit manure for gardens, as it not only enriches them, but destroys the vermin by which they are usually infested.

SEA-Wolf. See ANARRHICAS, ICHTHYOLOGY Index, Saltness of the SEA. See SEA-Water.

South SEA. See PACIFIC Ocean, and SOUTH Sea.