sides better than any that had been sent before. Captain Wilson says, the same consumption that before carried him six days and a half, carried him with this coal nine days. Some of the commanders of the Mediterranean packets have represented the strength of the Llangennech coal to be as 16 to 11 of the Newcastle. It was upon this report. and for a number of other reasons, the Company tried the experiment of sending it to India, and it appears to have answered extremely well. "Is there any large supply of that coal? -There is a very great supply; there is a large tract of country, called the Great Coal Basin of South Wales; it contains a great quantity of coal of different kinds, and of this sort a considerable portion. There is another Company which has a railroad; their coal does not appear to be so powerful as this. The Llangennech Company said, when they had got all their works completed, they thought they could supply any demand that might be made upon them; at all events, they would be able to supply all the demands of the East India Company. "Have you had any experience of the Forest of Dean coal ?-No; none at all. "Is the Llangennech coal chosen as peculiarly adapted for steam?—Yes; it was recommended by the commanders of the Mediterranean packets. The Court had a letter from the Bombay Government stating that a great deal of the coal which had been sent for steam purposes had taken fire in the storehouses, that it had done a great deal of injury, and was unfit for steam furnaces, so much so that they were quite certain no private individual would have thought of purchasing it. On the receipt of this letter inquiries were instituted in all quarters. I wrote to Messrs. Maudslay and others, requesting their opinion of the different kinds of coal used for steam furnaces, and espe cially asking their opinion as to this Llangennech coal, of which I had heard before, and of the coal which had taken fire. A young engineer, who went out with the last iron boats, went round to several of the great breweries and engineers, and got their opinions about all sorts of coal. The majority of opinions were that the Llangennech coal was the best for steam purposes. There are others very good, but opinions appeared to be unanimous in favour of that; I have since heard one opinion, that the Graigola coal, a Welch coal from the same district, is better; but the majority of opinions are that the Llangennech coal is the best. Mr. William Morgan told me that he preferred the Graigola coal to any other Welch coal. By using only the best coals containing the smallest proportion of sulphur. The Court had brought to its knowledge several instances of spontaneous ignition of coal: three at Bombay, one in a vessel carrying out coals for the Hugh Lindsay, two in private ships at Calcutta, the London and the Roxburgh Castle, and one at St. Helena in the public store-yard, where it was said to have happened several times previously, but it had not been before reported. I inquired of the owners of the Roxburgh Castle what kind of coal they had on board; they told me the Scremerstone Engine coal; I procured a specimen, and found it was full of iron pyrites. "What coal do you recommend as the best?-The Llangennech coal has no sulphur in it; it is always sold in large pieces; it was put, hand-picked, on board the vessel which took it to Bombay. It is not liable to spontaneous ignition: there are three things necessary to spontaneous ignition; first, that there should be a large quantity of sulphur ; next, that the coal should be in a state of powder; and next, that it should get wet. It generates a sort of gas, which, the mos ment it is exposed to the air, takes fire. When they opened the hatches of the Lon don, in Calcutta, the flames burst out; they wondered that the fire had not occurred before. The captain told me he was certain if they had been at sea 24 hours longer they would all have been lost, and he brought me some specimens of the coal as they took it out, half burnt. They half scuttled the vessel; they sunk her in shallow water to extinguish the fire. "Has not this danger been always known? -It has always been known, but it has been much more frequently observed since the alteration of the coal laws; when they were bought by measure the coals used to be more screened, but now they throw in the dust to make up weight." DISTILLATION OF SALT WATER. The subject of the distillation and purification of salt water having been frequently discussed in the Mechanics' Magazine, a correspondent has favoured us with a copy of a report made by Mr. Secretary (afterwards President) Jefferson to the American Congress, " on a claim for a reward for a discovery, alleged to have been made on that subject." It contains some very interesting historical and scientific particulars respecting it, which, we believe, are not generally known; and shows, that at the date of the report, as much was known upon the subject as at the present day, and that, save a knowledge gained from experience in one instance, rather costly of a few plans that will not answer, we are no nearer the attainment of the desired object than we were half a century ago. Experiments by T. Jefferson, Esq., Secretary to the United 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.) The petitioner sets forth, that, by various experiments, with considerable labour and expense, he has discovered a method of converting salt water into fresh, in the propor tion of eight pints out of ten, 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 ship'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 expenses, 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. 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 most obvious, was not the first idea in the essays 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 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 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 ma terials 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 centre of which a great hole was bored to receive, perpendicularly, a short 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 cask of cold With this simple machine he obtained two quarts of fresh water an hour, and observed, that the expense of fuel would be very trifling, if the still was contrived to stand on the fire along with the ship's boiler, water. 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 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 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 express; 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 passing 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 ship, 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 passage from Gibraltar 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 handpump, gun-barrel, and a pot, of six gallons of sea water made ten quarts of fresh water in three hours. In 1771, Dr. Irvine 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 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 pounds less of wood. of 5,000l. from the British Parliament. He the next day, the same quantity of sea water 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 passage to the vapour, and thereby increase its quantity by lessening the resistance or pressure on the evaporating surface: this last improvement was his own, and it doubtless contributed to the success 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, passing 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 Poyssonier, so as to guard against the water being thrown over from the boiler into the pipe, by the agitation of the ship. 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 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 favour of Mr. Rittenhouse, president of the American Philosophical Society, of Dr. Wistar, Professor of Chemistry in the College of Philadelphia, and Dr. Hutchinson, Professor of Chemistry in the University of Pennsylvania, to be present at the experiments. Mr. Isaacks fixed the pot of a small iron cabouse, with a tin cap, and straight 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 twenty-four pints of sea water, taken up about three miles out of the Capes of Delaware at flood tide, he distilled twentytwo 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. 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 On, the 24th of March, Mr. Isaacks performed a third experiment. For this, a common iron pot of 3 gallons was 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 day, with the same apparatus and fuel, from the same parcel, but without the mixture. teen pints of sea water yielded, in like manner, fifteen pints of fresh, in one minute more time, and with half a pound 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. Six The distilled water, in all these instances, was found on experiment to be as pure as the best pump-water of the city. Its 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 worst tasted, and, probably, a less wholesome water. The obtaining fresh from salt water, for ages, was considered as an important desideratum for the use of navigation. 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 authorise the assertion, that this desideratum is satisfied to a very useful degree. But though this has been done for upwards of thirty years, though its 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 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 its knowledge generally and effectually among the seafaring citizens of the United States. 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 United States be printed on a paper, on the Sir, Mr. Woodhouse, in the construction of this machine, availed himself of the important principle in hydrostatics, that a vessel in water, or any other fluid, displaces a mass equal to itself in weight; and that in the case of a suspended body, whatever its weight or magnitude, if counterpoised by an equal weight connected with it by a chain, &c. over a pulley, a very small additional power, if applied on one side, will be sufficient to raise or depress the other. The machine, adapted to a twelve feet lift, was erected some years since at Tardebigg in Worcestershire, and was in very successful operation there for several weeks. It consisted of a vessel called a conductor, large enough to hold a narrow boat, and to allow her to swim in and out freely, built with three-inch deal planking, and caulked like a boat, with screw-pins through the gunnel and bottom, to save room; this vessel, whith the water in it, weighed 64 tons, and was counterpoised by 8 weights of 8 tons each. A brick wall of eight feet thick, high enough to allow for the 12 feet lift, was built close by the side of the lock which contained the conductor, and eight interstices were left in it of 6 or 7 feet in depth, sufficient to allow eight cast-iron wheels, each of 36 feet circum 95 C ference, to revolve freely there in vertical planes, the pivots of these wheels working in sockets bedded in cast-iron on the top of the wall. The eight counterpoise weights were connected with the conductor by means of chains and iron rods, going round the peripheries of the wheel. These weights were composed of solid masonry, and were kept, on ascending, in the same planes by guide-posts, one on each side; and, in descending, they passed into well-holes, similar to the paddle-pits at common locks. Suppose ABCD a longitudinal section of the lock in which the conductor moves; the levels of water in the canal at the summit and below the lift being denoted by the horizontal dotted lines; the conductor is shown in the upper level at A Dab, and similarly at the lower level; the wall with the eight wheels, &c. being also shown in section; the lines c d, &c., are the chains round the wheels, fastened to the conductor on this side, and to the weights on the other side of the wall. The communication between the conductor and the two levels of the canal is made by a sluice at each end of the lock to draw up like a paddle or flood-gate: there is also a similar sluice at each end of the conductor. In each of the canal sluices there is a small paddle, as e and f, to be drawn up by hand :-if the conductor is at the lower level, the paddle e is drawn up, and the water enters the space e g between the two sluices, and sets them floating, so that they can both be drawn up with ease, by a small force as applied to a windlass to raise them, and then a boat may enter the conductor; and when it does this, it displaces, or sends out of that vessel, its own weight of water. The sluices at g and e must then be dropped, and the conductor being now on a balance with the weights behind the wall, the strength of two men will be found amply sufficient to raise it to the upper level, which being done, the small paddle ƒ is drawn up to set the two upper sluices floating in the same manner as described for the two lower ones; the upper sluices are then drawn up as before, and the boat may be passed out. The loss of water with this arrangement is only that contained between either pair of the sluices. The time of getting a boat up or down with this lift was about five minutes, and the motion of the conductor, when in order, is described as having been so perfect, that the surface of water in it was often unruffled during the whole ascent and descent. There are several particulars wanting to render the above description complete, but I have not been able to obtain them at present, and can only add, that the machine having been injured by lightning soon after it was put up, was not repaired afterwards; indeed, it has now been quite out of use for several years, and I cannot learn that the principle has been elsewhere applied; it being found, I suppose, too complex for general use, and that the expense of its construction and repair would be such, in most cases, as to outweigh the disadvantage of an occasional scarcity of water. Whatever may have been the cause of its rejection, however, much credit is unquestionably due to its originator for his ingenuity, as displayed in this invention, and for his perseverance afterwards in bringing it so nearly to a successful practical issue. I am, Sir, yours, &c. Welford, May 18, 1835. Jos. GILBERT. P. S.-Since writing the above, I have made further inquiries to ascertain the mode of fixing the chains to the conductor, and the precise method adopted in applying the power of two men to move the conductor and sluices; but have been unable to obtain any satisfacfactory information on these points. I think it probable, however, that the conductor was suspended by the chains like a scale, and that it was put in motion, together with the sluices, by means of racks and a series of pinions on the same iron axis, with a windlass at each end. The loss of water for each boat amounted to a few gallons only; and the estimated cost of the machine somewhat exceeded 1,000l.-J. G. THE SMOKE NUISANCE. Sir, Having recently passed through the manufacturing districts, the horrible nuisance from smoke was forced upon my consideration; and to get rid of it appeared more than ever a desideratum. I have thought,—but whether it can be accomplished or not, perhaps repeated experiments alone can prove—that it is possible to pump out the air, soot, and smoke, from a furnace, and convey it into a drain or sewer, when the soot and smoke may be separated from the air and mixed with water, and thus converted into manure. Your correspondent, Mr. Alfred T. J. Martin, in his Hydraulic Blast-Wheel, has furnished me with a hint, and I therefore ask him, whether his machine could not be employed as advantageously in drawing air through a furnace as in blowing air into one? We all know that in a room where there is a fire in cold weather, the cold air rushes through the key-hole of the door and every crevice with violence; and, consequently, it is thought, if the fuel chamber of a furnace were exhausted of its air, fresh air would rush through an aperture, or many apertures, if found more desirable in various positions, with as great velocity as can be forced in by bellows or other means. It is supposed that it can only be ascertained by experiment:-1. What power will be required to put the machine in motion? And, 2. What quantity of water and length of drain will be necessary to wash the smoke and soot out of the air from a furnace consuming a given quantity of fuel? It will be perceived, that if machines of this kind could be made available for furnaces, they would also be applicable to private dwellings and cities, and F |