bed of mortar of clay, in order to model perfectly the intrados of the arch, and to hinder the concrete from forming one body with the bricks.

The construction of the centre being finished on the 17th of August, we established, three days after, the masonry of the two heads of the arch of brick, which were completed on the 26th of the same month.

IV.-Construction of the Arch. Immediately after the construction of the two heads, we wrought them into the general mass of concrete, forming the arch; this operation was finished on the 5th of September, with the exception of the backing up, which was accomplished, on both sides, the 11th of the same month. The courses of concrete of the arch were composed in the same manner as those of the abutments, and manipulated by the same process; but we added to it 2 cubic feet of cement for every 35 cubic feet, orth, of the mass, to augment the strength of the mortars of the body of the arch, This construction was made without following any regular order, and the concrete was cast in masses, upon the centre, to the thickness of 2 feet, which formed the first general bed, or layer, on the development of the arch. The first bed being finished, we formed the second in order to reach the thickness of 3 feet at the key, the spandrel backing, and the abutments being levelled up. A coping of hydraulic mortar was then placed over the whole extent of the arch, and covered immediately with a layer of clay, strongly beaten.

V.-Striking the Centre.

All was left in this state until the 25th of January, 1841; we then proceeded to the operation of striking the centre of the arch. The 28th of January, the centre of bricks was taken away, ând the intrados of the arch appeared very even in all its parts. After three months, it manifested not the smallest settlement in its masonry, and, since then, the bridge has stood through the summer, without incurring the least sinking capable of affecting its solidity. This bridge has a clear opening of 393 feet between the abutments; the middle is placed in the axis of the canal, which has two towing paths; its breadth is 19 feet between

497

the heads, or faces, of the rings; and the arch is formed of a segment of a circle of 393 feet chord, and 54 feet rise, or versed sine.

The entire mass of the abutments is of concrete, except the four angles on the sides of the towing paths, which are of large stone, rounded on the arris, on account of the rubbing of the towing lines. The arch is also of concrete, as are the faces of the tympans, or spandrels, and the intrados, with the exception of the arrises of the soffit, or rings of the heads, which are of brick masonry.

M. Lebrun has annexed to his memoir, along with a plan of the bridge of Grisoles, many certificates, from the mayor of this commune, and from the engineer of the lateral canal of the Garonne, proving the complete success of the works, and the solidity of the construction, which has endured the proof of the passage of loaded carriages, the numerous influences of heat, and some very severe frosts, without having indicated the least subsidence or disturbance.

VI.-Explanation of the Figures. Fig. 1 is an external elevation of the bridge.

Fig. 2 a sectional elevation.

a, canal; b, abutment of concrete; c, mass of arch, also of concrete; dd, towing paths; e, angles of bridge upon the tow-paths, built of large stone, with the angles rounded; f, arrises of the soffit, or bands of brick at each head of the arch, instead of the usual ring-stone.

INSTITUTION OF CIVIL ENGINEERS. MINUTES OF PROCEEDINGS-SESSION 1843. February 28.

"Description of the roofs over Buckingham Palace, covered with Lord Stanhope's composition." By Peter Hogg, Assoc. Inst. C. E.

The mixture invented by Lord Stanhope, and used by the late Mr. Nash, for covering the nearly flat fire-proof roofs of Buckingham Palace, is described in the paper as being composed of Stockholm tar, dried chalk in powder, and sifted sand, in the proportions of three gallons of tar, to two bushels of chalk, and one bushel of sand, the whole being well boiled and mixed together in an iron pot. It is laid on in a fluid state, in two separate coats, each about ths of an

inch in thickness, squared slates being imbedded in the upper coat, allowing the mixture to flush up between the joints the whole thickness of the two coats, and the slates being about an inch.

The object in embedding the slates in the composition, is to prevent its becoming softened by the heat of the sun, and sliding down to the lower part of the roof, an inclination being given of only 1 inch in 10 feet, which is sufficient to carry off the water, when the work is carefully executed. One gutter, or water-course, is made as near to the centre as possible, in order to prevent any tendency to shrink from the walls, and also that the repairs, when required, may be more readily effected. It is stated, that after a fall of snow it is not necessary to throw it from the roof, but merely to open a channel along the water-course, and that no overflowing has ever occurred; whereas, with metal roofs it is necessary to throw off the whole of the snow on the first indication of a thaw.

These roofs have been found to prevent the spreading of fires, and it is stated, that on one occasion, to test their uninflammability, Mr. Nash had a bonfire of tar barrels lighted on the roof of Cowes castle.

Another advantage is stated to be, the facility of repair which the composition offers, as if a leak occurs, it can be seared and rendered perfectly water-tight, by passing a hot iron over it; and when taken up, the mixture can be remelted and used again.

The author proposes to obviate the disadvantage of the present weight of these roofs, by building single brick walls at given distances, to carry slates, upon which the composition should be laid; instead of filling the spandrels of the arches with solid materials, as has been hitherto the custom.

The reported failures of this species of covering at Mr. Nash's house in Regentstreet, and in other places, are accounted for by the composition having been used in one thin coat, laid upon an improper foundation of laths and tiles.

The durability of the roofs, which were carefully constructed with good materials, has been, it is contended, fully proved at Lord Palmerston's house, which was covered with the composition in 1807, Lord Berwick's, in 1810; Sir James Langham's, in 1812; the Pavilion at Brighton, in 1816 and 1823; and nearly the whole of Buckingham Palace, in 1826 and 1829; the latter -roofs are stated to be in perfect order at the present time, and have scarcely demanded any repairs since their completion.

The papers illustrated by a drawing, showing the mode of constructing the roofs, and the improved method proposed by the author,

with specimens of the composition, with slates imbedded, taken from the roof of the palace during some recent alterations.

Mr. Poynter presented a drawing of the mode of setting the pots for melting and preparing the composition, the proportions of which he stated somewhat differently from those given in the paper.

Three measures of ground chalk, dried and sifted very fine, were mixed and kneaded up with one measure of tar; these ingredients were melted in an iron pot, set in such a manner that the flame should not impinge too violently upon it. The first, or "skimming" coat of the covering being laid on of a thickness of ths of an inch, the finishing coat was composed by adding to the former mixture three measures of hot sifted sand, well mixing the whole together; the composition was laid on with a tool similar to a plasterer's trowel, but much stronger.

Mr. Nash, when he first tried the composition, found that the surface became disintegrated by exposure to the weather; he therefore added the slates imbedded in the second coat, and subsequently never used the mixture without them.

In reply to questions from the President and other members, Mr. Nixon stated, that he was employed under Mr. Nash when the palace roofs were executed, and he could bear testimony to their durability and soundness. The roofs at East Cowes castle, which were covered with the composition in the year 1808, and those of the Pavilion at Brighton, in 1816, were now in as good a state as when they were finished. The failure at Mr. Nash's house in Regent-street arose from the roof having been originally composed of mastic, which soon cracked. One coat of the Stanhope composition was spread over it, to stop the leaks, but it was insufficiently done, and ultimately Mr. Rainy had a new roof, properly constructed, with two coats of composition, which had remained sound to the present time. The price of these roofs, when well constructed by the person who did those of the palace,* was about five guineas per square.

Mr. Hogg observed, that the chalk was only exposed to such a heat as would evaporate any moisture it contained. The weight of the two coats of Stanhope composition, including the slate imbedded in it, was about 12 lbs. per superficial foot.

Mr. Sibley considered the Seyssel Asphalte, when carefully laid, preferable to any composition of a similar nature; he had used it

Mr. Millson, No. 6, Frances-street, Tothill Fields, Westminster,

THE PLAN OF SMELTING IRON BY STEAMBLAST has been tried, and failed. "B. G. D." will find it thus alluded to by Sir J. W. F. Herschell in his "Disc. Nat. Phil. :"

"Instead of employing this power to force air into the furnace, through the intervention of the bellows, it was, on one occasion, attempted to employ the steam itself, in apparently, a much less circuitous manner, viz., by directing the current of steam, in a violent blast, from the boiler at once into the fire. From one of the known ingredients of steam being a highly inflammable body, and the other that essential part of air that supports combustion, it was imagined that this would have the effect of increasing the fire to tenfold fury; whereas, it simply blew it out-a result which a slight consideration of the laws of chemical combination, and the state in which the ingredient elements exist in steam, would have enabled any one to predict without a trial."

THE CHINESE PUMPS are in China all worked by wooden chains, made of a series of square links; but it does not by any means follow that wood is better than iron; in point of fact, there can be no comparison between them, so far as durability is con cerned. Now that the "Iron Barbarians" have enforced a freer intercourse with their "Celestial" friends, we may reasonably hope to see the wooden chains, ere long, superseded by iron of good British manufacture. And when that consummation is realised, it will be only making a fair return to the Chinese for the pump itself, which was the first good one, the world beyond the "wall" ever knew.

Mr. NAYLOR'S PHANTASMAGORIA.—Sir, -Having tried the method of constructing the phantasmagoria for the exhibition of moving figures, according to the diagram and statement of your correspondent, T. W. Naylor, in No. 1027, and found it will not answer the representations of Mr. N., I should feel obliged if he would state whether there is any mistake of the printer, or engraver of the diagram. Yours truly, X. Y.

CHROME AND IRON.-To separate these two metals from each other, they are precipitated by ammonia, or carbonate of ammonia, and the humid precipitate is treated by a slight excess of sulphurous acid; all the iron is dissolved, as well as a certain quantity of chrome, and the remainder of the latter metal is converted into pure subsulphite. The solution is boiled until decoloured, and it then contains no more iron; in order afterwards to precipitate this metal from it, the sulphurous acid is driven off, either by means of sulphuric acid, or by means of nitro-muriatic acid, and an alkali, or an

alkaline carbonate is afterwards added to it, or else, without decomposing the sulphite, the iron is precipitated by an alkaline hydrosulphate. When a solution of chrome contains at the same time a sufficient quantity of alumina, all the oxide of chrome is carried away by this earth when it is precipitated by sulphite of ammonia. Hence we have a means of separating chrome from iron, manganese, &c. The metals being dissolved, any solution of alumina-alum, for example--is added to the liquor, then sulphite of ammonia is poured in, and it is boiled until it is no longer turbid; it is filtered, and if it still retains its green tint, alum and sulphite of ammonia, &c., are again added to it. The precipitate contains all the chrome, and all the alumina, without any mixture of other oxides; by treating it with caustic potassa, without heat, it is entirely dissolved, but the solution abandons the chrome at the boiling heat, and alumina alone remains. - Berthier.

THE PANAMA CHAINS are a remnant of the extraordinary skill to which the ancient Mexicans had attained in works of gold and silver, but are every day becoming rarer and rarer. The mode of making them is said to be kept a secret to this day among the Indians of Panama, Ewbank, who examined one which came from Carthagena, gives the following account of it:-" The length, had it been cut, was 8 feet 2 inches; its section, which was hexagonal, did not exceed one twentieth of an inch in diameter. It was formed of one or more fine wires, which seemed to have been interwoven or interlaced, like the plaiting of a whip handle. When a single thread was examined by a microscope, it was found to be composed of several wires, which, separate, were scarcely perceptible; the weight of the chain was 11 pennyweights, and it appeared to be as flexible as a piece of twine-certainly far more so than any chain formed of links; no end of a wire could be detected, and not a particle of solder was used."

DR. ARNOTT'S HYDROSTATIC BED.-"A Sleep Wisher" states that Plutarch, in his life of Alexander, mentions that the Babylonians used, during the dog days, to sleep "on skins filled with water," and asks whether this does not show the invention to have been old, and therefore vitiate Dr. Arnott's patent? We answer, first, that the use of the invention by the ancient Babylonians, is no proof that it was ever known to the modern; and second, that Dr. Arnott never took out any patent. "Sleep Wisher" has, therefore, only to "rest and be thankful."

INVENTION OF ROLLER SPINNING.The claim of Mr. John Wyatt to the invention which formed the basis of the colossal

fortune of the Arkwrights, was fully discussed in our review of Mr. Baines's History of the Cotton Manufacture (vol. xxii., p. 424). Mr. Baines, and after him, Mr. Barlow, agree with our correspondent, "H. C. C.," in considering that Arkwright but perfected what Wyatt first invented. We have given, in the article referred to, some reasons for being of a contrary opinion. We have shown it to be in the highest degree probable, that Arkwright knew nothing of what Wyatt had previously done-that there is no valid evidence of Wyatt having, in fact, accomplished any thing-and that if any person has a better claim to the invention of roller spinning than Arkwright, it is not John Wyatt, but Lewis Paul.

FILE-CUTTING BY MACHINERY.-Several machines have been contrived for this purpose, but they have been all decided failures. The best files are still those made by hand. Those called "bastard cut" are an intermediate, or hybrid class of files, neither rough nor smooth, but something between the two.

THE ATMOSPHEric Proof of GunpowDER, consists in exposing equal weights of different sorts to the atmosphere for a number of days, seldom less than fourteen, and then re-weighing them. The increase of weight should not exceed one per cent.; if it is more, the powder is considered bad or indifferent.

THE ARTIFICIAL RUBIES are made, according to Aikin ("Chem. Dic.") by mixing with glass, in a state of fusion, the purple precipitate of cassius, or gold precipitated from a nitro-muriatic solution, together with the oxide of tin. The usual way of making it is to dilute very largely a solution of gold in aqua regia, and add to it, drop by drop, a very dilute nitro-muriate of tin. The liquor immediately becomes of a purplish red colour, and by standing, a precipitate of several varieties of shade slowly subsides.

CYLINDER PRINTING was invented by the late eminent journalist, and ingenious mechanic, Mr. William Nicholson, who took out a patent for it in 1791. The merit of its introduction into use is due, however, to König, who re-patented (and it may be, reinvented) it, in March 1810. The Times of November 28, 1814, was the first sheet ever printed in this way. Mr. Cowper, who, in conjunction with Mr. Applegath, invented the improved machines, which have long since driven those of König out of the field, once asked his German precursor whether he was not aware that he had been anticipated by Mr. Nicholson, when König answered that

"he made a point of not reading any thing that other persons had done, in order that it might not be said he borrowed from any one!" We meet with this ridiculous sort of affectation not unfrequently among inventors, and would-be inventors, but we have always observed that those who indulge in it most, are those who owe most to their reading, and least to their own ingenuity.

NOTES AND NOTICES.

Chemistry and the Customs." As the latest fashion of chemical nomenclature is to convert the German affix stoff (stuff) into the Greek λn, whence a great tribe of yles, or ules, have sprung up in the text books, may I humbly suggest, that in future our Professors in describing the novel naphtha (from New York) the merits of which Dr. Ure has so admirably exposed, should style it in their next editions, paranomyle (or mule), which is by interpretation, illegal stuff, in English, and unrechtmäss-igstoff in German?"-A Chemist.

Cheap and effective Fire Engine for Union Houses and other dwellings.-At a meeting of the Guardians of St. Faith's Union, Norwich, it was proposed by Mr. Thomas Watts, seconded by John Longe, Esq., Chairman, and carried by a large majority," That one of Mr. Shalders', jun., six guinea portable fire engines be ordered, and be kept under the Governor's lock, for the security of the building, in the event of fire; and also for employment in the garden, cleaning windows, &c., or for allaying dust." It was also remarked, that in case of a fire in the neighbourhood both engine and help might conveniently be sent to assist.-Norfolk Chronicle.-Mr. Shalders informs us that the entire weight of a brass engine, such as referred to in the preceding notice, is only 26 lbs., exclusive of the reservoir steadying stand, and that it can be used wherever a lad 4 feet high can find elbow room; a man working the lever with one hand and guiding the jet-pipe with the other, delivers at a moderate speed eight gallons of water per minute to an elevation, in calm air, of 45 feet, or to a distance of 60 feet. It is not subject to choke or to get out of order, whether it is much used or remains for months idle. Access is had to the hydraulic working parts merely by turning one large screw.

The Turkish Steamer "Peiki Tiguret."-Sir,Allow me to correct an error in my letter of last week, in your esteemed Magazine, which has arisen, (and escaped accidentally undetected,) either from misstatement or the misapprehension of the individual who furnished the data. The error is, in stating the speed of the Peiki Tiguret, to be 15 miles with and 12 miles against tide. It should have been 15 miles with the tide, or 12 miles through the water; her speed against strong tide being somewhat under 10 miles in the hour. I am, Sir, your obedient servant, JUSTICE.

P.S.-On Sunday last. at about quarter before twelve at noon, the Peiki Tiguret let Blackwall for the Turkish empire, with some cargo and passengers, and reached Dover at a quarter before six o'clock, making the passage in seven hours. had a whole tide, it is true, in her favour; still it is an unprecedented result for a sea steamer.-J.

She

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