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and found that the pores were opened by it -he suggested that steam should be blown through the tanks until all the timber in them was raised to a certain temperature, and then by opening the communication with the reservoir, the solution would rush in and fill up the vacuum.

Mr. Cowper believed that it was only necessary to bring the chlorine of the corrosive sublimate and the albumen of the timber into contact, when sufficiently dry, to insure the preservation of the wood. He had occasion to try experiments with paper pulp, and was constantly annoyed by its decaying-but the addition of a small quantity of chlorine had preserved it good for two years, and he believed that it would continue unchanged.

General Pasley confirmed the statement as to the increase of the specific gravity of timber from long immersion at considerable depths. He had found all the timber, except the mainmast, in the Royal George, at a depth of about 90 feet, water-logged. The oak timber had increased on an average more than 50 per cent. above its usual specific gravity.

Mr. Bull had prepared considerable quantities of boards for the Calder and Hebble Navigation, by immersing them in the solution for two or three days, which was about double the period allowed by the patentees. He had some specimens of the boards, and in almost all of them there was an appearance of decay in various stages. An oak board 1 inch thick, kyanized in 1839, had lain ever since upon the damp ground exposed to the air: the sap part was entirely decayed, but the heart remained sound; fungus was, however, growing upon it. Poplar boards, kyanized in 1838, 39, and 40, were all partially decayed-those which were not prepared, and had been exposed in the same situation for the same period, showed however more symptoms of decay. In preparing the timber he had always followed the instructions of the patentees, and had tested the strength of the solution with the hydrometer, but had mixed up fresh solution even more frequently than was supposed to be required. On dismantling one of the tanks for holding the solution, he found the iron-work partially destroyed and entirely covered with globules of mercury.

Mr. Thompson explained that the hydrometer was not a correct testing instrument if any vegetable matter was present in the solution that the tanks on the premises of the Anti-Dry-Rot Company were necessarily made of unprepared timber that the bi-chloride of mercury in solution would penetrate any length of timber, if the extremities of the sap vessels were exposed to

its action, but that it would not penetrat laterally without pressure; it was not therefore surprising that a water-tight tank of unprepared wood should decay on the outside, even if filled with the solution. With regard to the strength of the solution, at first it was believed that 1 lb. of corrosive sublimate to 20 gallons of water was suffi ciently strong, and much timber had been so prepared, but experience had since proved that the strength of the mixture should not be less than 1lb. to 15 gallons, and he had never found any well-authenticated instance of timber decaying when it had been pro ́perly prepared at that strength: as much as 1 in 9 was not unfrequently used. In a cubic foot of wood, prepared under a pressure of 70lbs. per square inch, mercury had been found by the galvanic battery to have penetrated to the heart.

Mr. Horne mentioned that a new process had been invented by Mr. Payne, for rendering timber proof against dry or wet rot, and the ravages of insects; for increasing its durability and rendering it incapable of combustion. The mode of proceeding was tó impregnate the wood with metallic oxides, alkalis, or earths, as might be required, and to decompose them in the interior of the wood, forming new and insoluble compounds.

Mr. Taylor drew the attention of the meeting to a Memoir on the Preservation of Woods, which had been read before the French Academy of Sciences by Dr. Boucherie. It was argued, that all the changes in wood were attributable to the soluble parts they contain, which cause fermentation and subsequent decay, or serve as food for the worms that so rapidly penetrate even the hardest woods. By analysis it was found that sound timbers contained from three to seven per cent. of soluble matter, and the decayed and worm-eaten, rarely more than one or two per cent.; since therefore the soluble matters of the wood were the causes of the changes it underwent, it became necessary for its preservation, either to abstract these soluble parts, or to render them insoluble, by introducing substances which should prevent their fermenting. This might be done by many of the metallic salts or earthly chlorides. Pyrolignite of iron was particularly recommended as being a very effective substance, and cheaper than corrosive sublimate. The process was, to immerse the end of a tree, immediately after it was felled, in the solution of metallic salt, when, the vital energies not having ceased, the fluid was absorbed throughout all the pores of the tree, by a process which is termed "aspiration.' The fluid had been applied in bags, to the base of the trees

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DEFRIES' DRY GAS METER.

when in a horizontal position, or to one of the branches, or by boring holes to the heart a few branches and a tuft of leaves being always left at the top of the principal stem. It was necessary to apply the process speedily after felling the timber, as the' vigour of the absorption was found to abate rapidly after the first day, and became scarcely perceptible about the tenth day, whilst in dead wood, or where there was any accidental interruption of the flow of the sap during growth, the "aspiration entirely failed: resinous trees absorbed less of the fluid than any other.

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The ends proposed to be attained by this process, were chiefly preserving from dryrot; increasing the hardness and the elasticity; preventing the usual changes of form or splitting; reducing the inflammability and giving various colours and odours, according to the nature of the fluid absorbed.

Mr. Bethell remarked that the process described in Dr. Boucherie's pamphlet, was identical with that patented by him July 11th, 1838, two years before Dr. Boucherie's was mentioned in Paris, which was in June, 1840.* The specification filed by Mr. Bethell stated, "that trees just cut down may be rapidly impregnated with the solution of the first class, hereafter mentioned, (among which is included the pyrolignite of iron,) by merely placing the butt-ends in tanks containing the solution, which will circulate with the sap throughout the whole tree; or it may be done by means of bags made of waterproof cloth affixed to the butt-ends of the trees, and then filled with the liquid."

Mr. Bethell found that some solutions were taken up more rapidly by the sap, and circulated with it more freely than others, and the pyrolignite of iron seemed to answer best; he had not hitherto introduced the process in England, because it was much more expensive than the oil of tar, the pyrolignite costing from 6d. to 9d. per gallon, and the oil being delivered at 3d. per gallon.

Mr. Bethell had used similar tanks to those described in Mr. Timperley's paper, for preparing wood with the oil of tar, but as the oil is very penetrating, previous exhaustion of the air had been found unnecessary; the hydrostatic power being sufficient. The mode of working the tanks was to charge then with timber, close them, and fill them with the oil: a hydrostatic pressure of from 100 lbs. to 150 lbs. to the inch, was applied by means of the force-pumps, and kept up for about six hours; this was sufficient to cause the wood to absorb from 35 to 40 gallons per load. By this means a

• See 74th vol. of Annales de Chimie, &c.

409

charge of timber was easily prepared daily, the cost being about 14s. per load.

This was the plan pursued at Manchester for the Manchester and Birmingham Railway, by Mr. Buck, (upon the recommendation of Mr. Robert Stephenson,) and also at Bristol and Bridgewater by Mr. Brunel. Mr. Bethell preferred egg-shaped ends for the tanks, as they resist the pressure better than flat ends.

The solution of corrosive sublimate used at Hull, appeared to Mr. Bethell to be very weak. The advice given by Sir Humphrey Davy to the Admiralty many years since, was to use 1 lb. of corrosive sublimate dissolved in 4 gallons of water, and Mr. Kyan, in the specification of his patent, states that strength; but according to the paper, it appeared that 45 gallons of water were used to 1 lb. of the salt, instead of 4 lbs.

In answer to a question from Mr. Pellatt, Mr. Bethell stated that his experiments on the use of silicate of potash or soluble glass, for rendering wood uninflammable, were not yet concluded: he had proved its efficacy in this point-that as soon as the prepared timber was heated, the glass melted and formed a filmy covering over the surface, which protected it from the oxygen of the air and prevented its catching fire. The silicate also hardened the wood and rendered it more durable. This process was included in his patent of July 11, 1838.

Professor Brande could add but little to what had been said on the subject, but he mentioned a curious appearance in a beech tree in Sir John Sebright's park in Hertfordshire, which on being cut down was found perfectly black all up the heart. On examination, it was discovered that the tree had grown upon a mass of iron scoriæ from an ancient furnace, and the wood had absorbed the salt of iron exactly in the same manner as had been described in the new

process. The degrees of absorption of various solutions by different woods, demanded careful experiments, as some curious results would be obtained: it was a question whether a solution of corrosive sublimate in turpentine, or in oil of coal tar, would not be advantageous, as both substances were so readily absorbed by timber.

Mr. Defries explained the construction and action of his dry gas meter, which was exhibited before it was fixed in the gallery of the Institution.

The instrument consists of a hexagonal case with three solid partitions radiating from the centre to the circumference, across each division thus formed is a flexible partition, to the centre of which is fixed a plate, connected by a lever and shafts with the

valves on the top of the case; by means of a combination of levers and cranks, with a worm and screw, a circular motion is given to dials, indicating the quantity of gas which passes through the machine.

The gas, on entering the upper chamber, passes through the valve into the first division, and distends the flexible partition until the lever is carried to a certain point, when, by means of the connecting shaft, the inlet valve is closed, the outlet valve is opened, and the second division commences its action, which is continued by the third, thus producing an equal flow of gas; and an uniform motion is given to the counter-dials, which necessarily indicate the number of times the divisions have been inflated and emptied, and thus measure the quantity which has passed through in a given time.

The instrument which was presented to the Institution, had its sides formed of glass, in order to show the action of the machinery.

March 15, 1842.

"Description of the Iron Skew Bridge across the Regent's Canal, on the Eastern Counties Railway." By Edward Dobson, Assoc. Inst. C. E.

This bridge is built with a direct span of 54 feet, at an angle of 79°, with the centre line of the canal. The level of the rails is 14 feet 6 inches above the water, and it is constructed to have a waterway of 44 feet, with a clear headway of 10 feet above the towing-path.

As an appendix to this paper, a description is given of a bridge over the same canal, on the line of the London and Birmingham Railway, on account of the similarity of its construction. The span of this latter bridge is 50 feet, but being made for two double lines of rails, it was thought expedient to have three main ribs instead of two, as in the former. The details of construction of this bridge are also given, with a drawing of one of the main ribs and its tie-bar.

March 15, 1842.

"Remarks on the Ravages of the Worm (Teredo Navalis) in Timber." By Robert Davison, M. Inst. C. E.

This communication describes the ravages committed by the "Teredo Navalis" upon the fir piles of the foundations of the old bridge at Teignmouth, five arches of which, after having been built only twelve years, fell suddenly; the construction of a new bridge thus became necessary, and it is now in progress under the direction of Messrs. Walker and Burges. The worm is described

as entering the wood through a hole not larger than a pin, and perforating the timber in all directions, but chiefly in the direction of the fibre, at the same time increasing the size of the holes even sometimes to an inch diameter; a few of the worms had been found of the extraordinary length of 3 feet. They confine their operations between lowwater mark and the bottom of the river, showing that they cannot exist out of water.

A specimen of part of a log, picked up off Jersey, was as much perforated, but in a different manner, the worms having penetrated the wood indiscriminately all over the surface; in some cases leaving in the holes a coat resembling the tail of a lobster about 3 inches in length, which showed that the ravages had been committed by the "Lymnoria Terebrans."

The paper was also accompanied by a specimen of wood sheathing charged with nails from the bottom of a vessel believed to be about 100 years old, together with some of the worms ("Teredo Navalis") for the purpose of showing the peculiar shape of the head-resembling a pair of forceps, with which they cut away the wood.

March 15, 1842.

"Description of the Roof of Messrs. Simpson and Co.'s Factory." By John Boustead, Grad. Inst. C.E.

The truss of this roof is double, consisting of two frames of Memel timber. The principals are fitted into cast-iron shoes, resting on the walls, with projections let into the wall-plates; they taper towards the ridge, and there abut against a cast-iron ring-piece, through which a wrought-iron bolt, 14 inch diameter, passes, and answers the purpose of a king-post in supporting the collar-beam. To the under side of this beam is attached a heel and eye-plate, to either end of which are linked bolts passing between the principals, and secured by nuts at the backs of the shoes, thus forming efficient ties to resist the thrust of the principal rafters.

The slate-boards are supported by five purlins 4 feet apart, and abut against a ridgepiece resting on the kings.

The span of the roof is 34 feet 3 inches. The pitch is about 3 to 1, and the principals are placed 9 feet apart.

The scantlings of the principal timbers are-Principals 9 by 2 inches, tapering to 6 by 2 inches; collar-beam 7 by 31 inches; purlins 6 by 4 inches; wall-plates 6 by 4 inches; slate-boards 1 inch thick; ridge-piece 10 by 2 inches.

The principals were sawn out by a template, so as to insure the given taper and the

THE TURBINE.

accuracy of the angles of the ends; they were then laid in a horizontal position placed at the required angle, and the collar-beam inserted inch deep into each principal, and secured by bolts inch diameter; the mode of raising the roof is then described.

Some of the advantages of roofs of this construction are stated to be, economy in materials and workmanship, with lightness and simplicity, and that all sagging of the timbers may be rectified by screwing up the nuts of the kings and shoes.

The truss is recommended for buildings where lofty apartments or coved ceilings are required, and also for its presenting so few points for the suspension of heavy weights that may subject the timbers to strains for which no provision has been made.

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From the examinations that have been made, this roof seems to answer satisfactorily it has been erected three years and a half, and has sustained heavy falls of snow, but the ridge and rafters have preserved their lines perfectly, and the walls show no signs of having been subjected to undue pressure. The design of the roof is simple, its appearance light, and it may be considered an interesting specimen of the art of simple carpentry, assisted by iron-work.

March 22, 1842.

"Remarks on Machines recipient of Water Power: more particularly the Turbine of Fourneyron." By Professor Gordon (Glasgow.)

Notwithstanding the diminished importance of water power since the almost universal application of the steam-engine, some situations may still be found, in the mining districts of Cornwall, of Derbyshire, and of Cumberland, the Highlands of Scotland, and generally in the districts comparatively destitute of cheap fuel, where it is desirable to render falls of water available.

The theory of water power as it now stands may be announced in general terms thus: "The mechanical effect obtained is equal to that of the moving power employed, minus the half of the vis viva which the water loses on entering the machine, and minus the half of the vis viva which the water possesses when it quits the machine."

Bernoulli recognized the second cause, and soon after, Euler, the first. Borda, in his "Mémoire sur les Roues Hydrauliques," in 1767, gave the proposition in precise and general terms: whence he concluded, that to produce its total mechanical effect: "the water serving as moving power, must be brought on to the wheel with impulse, and quit it without velocity."

This principle being admitted, the cir

411

cumstances next to be considered are, the height of fall, the supply of water, and the nature of the work to be done.

These positions being laid down, the author proceeds to examine the relative efficiency of water-wheels of various constructions.

The undershot wheel acted upon by the velocity of the water when confined in a rectilinear course, or when hung freely in a stream: in the former case the efficiency of the machine is equal to 32 per cent., or nearly rd; in the latter the ratio is 42 per cent, or about ths.

The breast wheel is generally applied to falls of from 4 to 8 feet; in these the efficiency reaches as high as 60 to 65 per cent. of the mechanical effect of the fall of water. The buckets being filled to rds of their capacity, their velocity is seldom less than from 7 to 9 feet per second.

The consideration of this wheel led Poncelet, in 1824-25, to the invention of the "undershot wheel with curved floats," the efficiency of which has been found equal to from 65 to 75 per cent. The velocity of this may be 55 to 60 of that of the effluent water-a velocity equal to that due to nearly the whole height of fall; hence the efficiency becomes "about double that of the ordinary undershot wheel." This wheel has not been much employed in Great Britain, although frequently used in France and Ger

many.

The overshot wheel is most generally employed in Great Britain for falls beyond 10 feet in height, and some excellent examples occur for work of every description, from rolling iron to spinning silk. Its efficiency averages 66 per cent., but has risen as high as 82 per cent.

The economical use of water as a moving power, varying in particular cases, rendered desirable the discovery of a receiver capable of general application, in all circumstances of height of fall, quantity of water, and amount of work to be done; and after intense study Fourneyron produced the Turbine, the peculiarities of which form the subject of the paper.

The imperfect horizontal water-wheels which have been used for centuries in the mountain districts of central Europe, and in the northern Highlands, are mentioned; then are noticed the experiments of MM. Tardy and Piobert, and the allusion by Borda to horizontal wheels; then a general description is given of the numerous experiments made up to the year 1825, when M. Burdin constructed wheels in which the water was received at the circumference of a vertical cylinder, descended in conduits, placed in a helical form round the surface of

the cylinder, and made its escape at the bottom: the efficiency of these wheels was stated to be 75 per cent., but no exact experiments were ever instituted.

The defects in all the previous machines, led to the invention of the Turbine, as it is now designed by M. Fourneyron: its construction may be compared to one of Poncelet's wheels with curved buckets, laid on its side, the water being made to enter from the interior of the wheel, flowing along the buckets, and escaping at the outer circumference: centrifugal force here becomes a substitute for the force of gravity.

The mechanical construction of the Turbine is then given, and its action is thus described. The water, when admitted to the reservoir, rises to a certain level, exercising a hydrostatic pressure proportional to the height of the column, and on the sluice being raised it escapes with a corresponding velocity in the direction of the tangent to the last element of the guide curves, which is a tangent to the first element of the curved buckets; the water pressing without shock upon the buckets at every point of the inner periphery, causes the wheel to revolve, then passes along the buckets, and escapes at every point of the outer periphery; by which arrangement the size of the machine, even for a large expenditure of water, is kept within narrow limits.

The advantages of the Turbines are stated to be

1st. That they are with like advantage applicable to every height of fall, expending quantities of water proportional to the square root of the fall, their angular velocities being likewise proportional to these square roots. 2nd. That their net efficiency is from 70 to 75 per cent.

3rd. That they may work at velocities much above or below that corresponding to the maximum of useful effect, the useful effect varying very little from the maximum nevertheless, and

4th. They work at considerable depths under water, the relation of the useful effect produced to the total mechanical effect expended not being thereby notably diminished.

These advantages are stated to have been realized in the extensive practice of M. Fourneyron, of M. Brendel in Saxony, and of Herr Carliczeck in Silesia, as well as other engineers.

A comparison of the theory and practice of the construction is then instituted, and the following conclusion is drawn:-That if one Turbine has been constructed which works well under a known fall, expending a volume of water exactly measured, this Turbine would serve as a type for all others,

Knowing the fall and the volume of water to be expended, the Turbine would be made similar to its type. Its linear dimensions would be those of the type, directly as the square roots of the volume of water, and inversely as the fourth roots of the heights of fall. Its angular velocity would be to that of the type, directly as the fourth roots of the cubes of the heights of fall, and inversely as the square roots of the volumes of water. These practical rules were first made manifest by M. Combe, of the Ecole des Mines.

A general review is then given of most of the Turbines erected by M. Fourneyron at Pont sur l'Ognon, at Fraisans, at Niederbronne, and at Inval, upon which last were tried the experiments which completely established the reputation of the Turbine as an applicable machine. The details of these experiments are given, whence the mean results appear to be, that the height of fall being 6 feet, 6 inches

With an expenditure of 35 cube feet of water per second, the efficiency was

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