Thomas Jefferson Papers

Enclosure: Report on Desalination of Sea Water, 21 November 1791

Report on Desalination of Sea Water

Novemr. 21. 1791

The Secretary of state, to whom was referred by the H. of Representatives the petition of Jacob Isaacks of Newport in Rhode island, has examined into the truth and importance of the allegations therein set forth and makes thereon the following report.

The petitioner sets forth that by various experiments, with considerable labor and expence, he has discovered a method of converting salt water into fresh, in the proportion of 8 parts out of 10. by a process 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 ships provisions, and offers to convey to the government of the U.S. a faithful account of his art or secret to be used by or within the U.S. 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.

In order to ascertain the merit of the petitioner’s discovery, it becomes necessary to examine the advances already made in the art of converting salt water into fresh.

Ld. 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 tho’ the most obvious, was not the first idea, in the essays for converting salt water into fresh. Filtration was tried in vain, and congelation could be resorted to only in the coldest regions and seasons. In all the earlier trials by distillation some mixture was thought necessary 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 Sr. Richd. 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 worthy noting on the present occasion except the very simple still contrived extempore by capt. 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 hole was bored to receive perpendicularly a short wooden tube made with an inch and half auger, which perpendicular tube received at it’s 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 thro a cask of cold water. With this simple machine he obtained 2 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 1762. Dr. Lind, proposing to make experiment 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 confesses, 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 firing or precipitating it’s 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 express; or instead of the wooden lid and upright tube he proposed a teakettle (without it’s lid or handle) to be joined 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 passing thro a cask of water the whole luted with equal parts of chalk and meal moistened with salt water.

With this apparatus of a pot, teakettle and gun barrel the Dolphin a 20. gun ship in her voyage round the world in 1768. from 56 galls. of sea water, and with 9. lb. of wood and 69. lb. of pit coal made 42. galls. of good fresh water at the rate of 8. galls. an hour. The Dorsetshire, in her passage from Gibraltar to Mahon made 19. quarts of pure water in 4. hours with 10 lb. of wood. And the Slambal in 1773. between Bombay and Bengal with the hand pump, gun barrel and a pot of 6. galls. of sea water made 10 quarts of fresh water in 3. hours.

In 1771. Dr. Irving 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 £5000. from the British parliament. He wet his tube constantly with a mop instead of passing it through a cask of water. He enlarged it’s bore also in order to give a freer passage to the vapour and thereby increase it’s quantity by lessening the resistance or pressure on the evaporating surface. This last improvement was his own. It doubtless contributed to the success of his process: and we may suppose the enlargement of the tube to be useful to that point at which the central parts of the vapour passing thro it would begin to escape condensation.1 Ld. Mulgrave used his method in his voyage towards the North Pole in 1773. making from 34. to 40. 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 succesfully a still which had been contrived in 1763 by Poyssonier, so as to guard against the water being thrown over from the boiler into the pipes by the agitation of the ship, in which 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 obtaining fresh from salt water when Mr. Isaacks the petitioner suggested his discovery.

As the merit of this could be ascertained by experiment only the Secretary of state asked the favor of Mr. Rittenhouse President of the Amer. Ph. soc. of Dr. Wistar professor of Chemistry [in the college of Philadelphia,] and Doctor Hutchinson professor of chemistry in the University be present at the experiments. Mr. Isaacks fixed the pot of a small Cabouse, with a tin cap, and strait tube of tin passing obliquely through a cask of cold water. He made use of a mixture the composition of which he did not explain and from 24. pints of sea water taken up about 3. miles out of the capes of Delaware at flood tide he distilled 22. pints of fresh water in 4. hours with 20. lb. of seasoned pine which was a little wetted by having lain in the rain.

In a 2d experiment of the 21st. of March performed in a furnace and 5. gallon still at the College, from 32. pints of sea-water he drew 31. pints of fresh water in 7. H. 24. M. with 51 lb. of hiccory which had been cut about 6. months. In order to decide whether Mr. Isaacks 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 omission 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 31. pints of fresh water, in 11’ more of time and with 10. lb. less of wood.

On the 24th. of March Mr. Isaacks performed a 3d. experiment. For this, a common iron pot of 3 1/2 galls. was fixed in brickwork, and the flue from the hearth wound once round the pot spirally, and then passed off up a chimney. The cap was of tin and a straight tin tube of about 2. I. diam. passing obliquely through a barrel of water served instead of a worm. From 16. pints of seawater he drew off 15. pints of fresh water in 2 H. 55’ with 3 lb. of dry hiccory and 8 lb. of seasoned pine. This experiment was also repeated the next day, with the same apparatus, and fuel from the same parcels, but without the mixture. 16. pints of sea water yeilded in like manner 15. pints of fresh in 1’ more of time and with 1/2 lb. less of wood. On the whole it was evident that Mr. Isaacks mixture produced no advantage either in the process or result of the distillation.

The distilled water in all these instances was found on experiment to be as pure as the best pump water of the city: it’s taste indeed was not as agreeable; but it was not such as to produce any disgust. In fact we drink in common life in many places and under many circumstances and almost always at sea a worse tasted, and probably a less wholesome water.2

The obtaining fresh from salt water was for ages considered as an important desideratum for the use of Navigators. The process for doing this by simple distillation is so efficacious, the erecting an extempore still with such utensils as are found on board of every ship is so practicable, as to authorize the assertion that this desideratum is satisfied to a very useful degree. But tho’ this has been done for upwards of 30. years, tho it’s reality has been established by the actual experience of several vessels which have had recourse to it, yet neither the fact nor the process is known to the mass of seamen, to whom it would be the most useful, and for whom it was principally wanted. The Secretary of state is therefore of opinion that, since the subject has now been brought under observation, it should be made the occasion of disseminating it’s knowlege generally and effectually among the sea-faring citizens of the U.S. The following is one of the many methods which might be proposed for doing this. Let the Clearance for every vessel sailing from the ports of the U.S. be printed on a paper on the back whereof shall be a printed account of the essays which have been made for obtaining fresh from salt water, mentioning shortly those which have been unsuccesful, and more fully those which have succeeded; describing the methods which have been found to answer for constructing extempore stills of such implements as are generally on board of every vessel, with a recommendation, in all cases where they shall have occasion to resort to this expedient for obtaining water, to publish the result of their trial in some gazette on their return to the U.S. or to communicate it for publication to the office of the Secretary of state in order that others may, by their success be encoraged to make similar trials, and may be benefited by any improvements or new ideas which may occur to them in practice.

MSS (MHi and DLC); the MS from MHi comprises the entire report with the exception of the long, last paragraph, which was carefully penned by TJ at a different time and dated by a clerk as 21 Nov. 1791. The report was probably begun in the spring of 1791 after much research on the subject, as the five pages of references to experiments and sources attest (see note 2 below). Tr (DNA: RG 59, SDR). PrC of Tr (DLC).

The history of this report is discussed in Editorial Note and group of documents on experiments in desalination of sea water to test the claims of Jacob Isaacks, at 26 Mch. 1791. TJ sent a printed copy of his report to Isaacks on 23 Nov. 1791 (letter printed as Document xi).

Upon receipt of the report, the House of Representatives read and tabled it on 22 Nov. 1791, thereby signifying its agreement with TJ’s assessment of Isaack’s lack of scientific originality. Then on 8 May 1792 it passed a resolution in words almost identical to the last sentence of the report instructing the Secretary of the Treasury to provide U.S. collectors with printed clearance forms, one side of which should contain descriptions of desalination methods (JHR description begins Journal of the House of Representatives of the United States, Washington, D.C., 1826, 9 vols. description ends , i, 459, 604–5). This resolution was immediately approved by the Senate and the President (JS description begins Journal of the Senate of the United States, Washington, D.C., 1820–21, 5 vols. description ends , i, 443, 444).

1The previous two sentences were copied and inserted by TJ from a note he wrote on the verso of an undated memorandum from Caspar Wistar (RC in MHi).

2The MS at MHi ends here, but is followed by five pages of notes on related sources and experiments in TJ’s hand. Although it is not among those listed, TJ probably made use of Caspar Wistar’s “Experiments and Observations on Evaporation in Cold Air,” a paper read before the American Philosophical Society in September 1787 and printed in the Society’s Transactions in 1793. TJ’s undated detailed notes on this experiment are in MHi, docketed by him: “Evaporation by Dr. Wistar.”

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