EXPERIMENTS BY T. JEFFERSON ESQ. SECRETARY TO THE UNI

TED STATES OF AMERICA, ON THE DISTILLATION OF SALT WATER.

Being a report by him to the American Congress on a claim for a reward for a discovery, alleged to have been made on that subject.

1

THE petitioner sets forth, that, by various experiments, with considerable labour and expence, he has discovered a method of converting salt water into fresh, in the propor tion of eight pints out of ten, by a procefs so simple, that it may be performed on board of vessels at sea by the common iron cabouse, with small alterations, by the same fire, and in the same time, which is used for cooking the fhip's provisions; and offers to convey to the government of the United States, a faithful account of his art, or secret, to be used by or within the United States, on their giving to him a reward suitable to the importance of the discovery, and, in the opinion of government, adequate to his expences, and the time he has devoted to the bringing it into effect.

very,

In order to ascertain the merit of the petitioner's discoit becomes necefsary to examine the advances already made in the art of converting salt water into fresh.

Lord Bacon, to whom the world is indebted for the first germs of so many branches of science, had observed, that, with a heat sufficient for distillation, salt will not rise in vapour, and that salt water distilled, is fresh. And it would seem that all mankind might have observed, that the earth is supplied with fresh water chiefly by exhalation from the sea, which is in fact an insensible distillation effected by the heat of the sun. Yet this, though the

Jan. 2. most obvious, was not the first idea in the efsays for converting salt water into fresh. Filtration was tried in vain, and congelations could be resorted to only in the coldest regions and seasons. In all the earlier trials by distillation, some mixture was thought necefsary to aid the operation by a partial precipitation of the salt, and other foreign matters contained in sea water. Of this kind were the methods of Sir Richard Hawkins, in the 16th century, of Glauber, Hauton, and Lister, in the 17th, and of Hales, Appleby, Butler, Chapman, Hoffman, and Dove, in the 18th nor was there any thing in these methods worth noting on the present occasion, except the very simple still contrived extempore by captain Chapman, and made from such materials as are to be found on board every ship, great or small. This was a common pot with a wooden lid of the usual form in the center of which a great hole was bored to receive perpendicularly a fhort wooden tube, made with an inch and half auger, which perpendicular tube received at its top, and at an acute angle, another tube of wood also, which descended till it joined a third, of pewter, made by rolling up a dish, and passing it obliquely through a cafk of cold water. With this simple machine he obtained two quarts of fresh water an hour, and observed, that the expence of fuel would be very trifling, if the still was contrived to stand on the fire along with the ship's boiler.

In 1792, Dr Lind proposing to make experiments of several different mixtures, first distilled rain water, which he supposed would be the purest, and then sea water, without any mixture, which he expected would be the least pure, in order to arrange between these two supposed extremes the degree of merit of the several ingredients he meant to try. "To his great surprise," as he confefses, "the sea water distilled without any mixture was as pure as the rain water." He pursued the discovery,

and established the fact, that a pure and potable fresh water, may be obtained from salt water by simple distillation without the aid of any mixture for fining or precipitating its foreign contents. In 1767, he proposed an extempore still, which, in fact, was Chapman's, only substituting a gun barrel instead of Chapman's pewter tube, and the hand pump of the ship to be cut in two obliquely, and joined again at an acute angle, instead of Chapman's wooden tubes bored exprefs; or instead of the wooden lid and upright tube, he proposed a tea kettle, (without its lid or handle,) to be turned bottom upwards, over the mouth of the pot, by way of still head, and a wooden tube leading from the spout to a gun barrel pafsing through a. cask of water, the whole luted with equal parts of chalk and meal moistened with salt water.

With this apparatus, of a pot, tea kettle, and gun barrel, the Dolphin, a twenty gun fhip, in her voyage round: the world in 1768, from fifty six gallons of sea water, and with nine pounds of wood, and sixty-nine pounds of pit coal, made forty two gallons of good fresh water at the rate of eight gallons an hour. The Dorsetshire, in her pafsage from Gibralter to Mahon, in 1769, made nineteen quarts of pure water in four hours with ten pounds of wood. And the Slambal, in 1773, between Bombay and Bengal, with a hand pump, gun barrel, and a pot, of six. gallons of sea water made ten quarts of fresh water in. three hours..

In 1771, Dr Irvin putting together Lind's idea of distilling without a mixture, Chapman's still, and Dr Franklin's method of cooling by evaporation, obtained a premium of L. 500s from the British parliament. He wet his tube constantly with a mop instead of passing it through a cask of water: he enlarged its bore also, in order to give a freer pafsage to the vapour, and thereby increase its quantity by lefsening the resistance or prefsure on the e*

Jan. 25 vaporating surface: this last improvement was his own, and it doubtlefs contributed to the succefs of his models; ́and we may suppose the enlargement of the tube to be useful to that point at which the central parts of the vapour, pafsing through it, would begin to escape condensation. Lord Mulgrave used his method in his voyage towards the north pole, 1773, making from thirty four to forty gallons of fresh water a day, without any great addition of fuel, as he says.

M. de Bougainville in his voyage round the world, used very successfully, a still which had been contrived in › 1763, by Poyfsonier, so as to guard against the water being thrown over from the boiler into the pipe, by the agitation of the fhip. In this, one singularity was, that the furnace or fire box was in the middle of the boiler, so that the water surrounded it in contact. This still, however, was expensive, and occupied much room.

Such were the advances already made in the art of ob taining fresh from salt water, when Mr Isaacks, the petitioner, suggested his discovery.

As the merit of this could be ascertained by experi ment only, the secretary of state asked the favour of Mr Rittenhouse, president of the American philosophi cal society, of Dr Wistar, professor of chemistry in the college of Philadelphia, and Dr Hutchinson, professor of chemistry in the university of Pensylvania, to be present at the experiments. Mr Ifsaacks fixed the pot of a small iron cabouse, with a tin cap, and straight tube of tin, passing obliquely through a cafk of cold water; he made use of a mixture, the composition of which he did not explain, and from twenty-four pints of sea water, taken up about three miles out of the Capes of Delaware at flood tide, he distilled twenty-two pints of fresh water in four hours, with twenty pounds of seasoned pine, which was a little wetted by having lain in the rain.

In a second experiment on the 21st of March, performed

in a furnace and five gallon still at the college, from thirty-two pints of sea water he drew thirty-one pints of fresh water in seven hours, twenty-four minutes, with fifty-one pounds of hickory which had been cut about six months. In order to decide whether Mr Isaack's mixture contributed in any, and what degree, to the success of the operation, it was thought proper to repeat his experiment under the same circumstances exactly, except the omif sion of the mixture. Accordingly, on the next day, the same quantity of sea water was put into the same still, the same furnace was used, and fuel from the same parcel. It yielded, as his had done, thirty-one pints of fresh water in eleven minutes more of time, and with ten pound lefs of wood.

On the 24th of March, Mr Isaacks performed a third experiment. For this, a common iron pot of 3 gallonswas fixed in brick work, and the flue from the hearth wound once round the pot spirally, and then passed off up a chimney. The cape was of tin, and a straight tin tube of about two inches diameter, passing obliquely through a barrel of water, served instead of a worm. From sixteen pints of sea water he drew off fifteen pints of fresh water, in two hours fifty-five minutes, with three pounds of dry hickory and eight pounds of seasoned pine. This experiment was also repeated the next nay, with the same apparatus and fuel, from the same parcel, but without the mixture. Sixteen pints of sea water yielded in like manner, fifteen pints of fresh, in one minute more time, and with half a pound lefs of wood. On the whole, it was evident that Mr Isaacks's mixture produced no advantage either in the process or result of the distilla

tion.

The distilled water, in all these instances, was found on experiment to be as pure as the best pump water of th