white, and the combustion of the wick so perfect, that no snuffing bustion of the wick so was found to be necessary. An inconvenience arose from the guttering of the candle; but this defect, we conceive, would very likely be obviated by proper attention in the manufacture, and by the admixture of some other oleaginous matter, whose melting point is higher than that of tallow, as to render it harder. There are, doubtless, various substances which would be preferable to tallow for this purpose, if the price of them were not an obstacle.

With the intention of communicating our proposition, to make hollow candles, to our readers, we had the annexed cut executed three or four years ago; but before we could give it insertion, a patent nt was taken out for it by Mr. Poole, as agent for Mons. Gay Lussac, the celebrated French chemist, a report of which patent was given in Vol. III, First Series, page 274. At this time we mentioned to some friends, how we had been forestalled in our invention, when we learned, to our, surprise, that several of our acquaintances had also entertained the same proposition, each imagining himself to be the sole inventor. The subject was dropped by us, and almost forgotten, until recently, when we were informed by a medical gentleman, that he had patented the invention fourteen years ago, and that a large manufaetory was commenced for the manufacture of them, with every probability of success; and that the reason why the manufacture of them was not carried forward, had no reference to the practicability of the scheme. Seeing that the subject has been taken up by the most scientific, as well as by clever practical men, we are the more confirmed in our opinion, that important results may yet flow from prosecuting the plan; and with the hope that some intelligent person will undertake it, we have thrown out the foregoing remarks,

IMPROVED PREPARATION OF CANDLES.

STEEP the cotton wick in lime water, in which is dissolved a considerable quantity of the nitrate of potassa; chlorate of potassa answers still better, but is too expensive for common practice. By this means is obtained a purer flame, and a superior light; a more perfect combustion is insured; snuffing is rendered nearly as superAluous as in wax candles; and the candles, thus treated, do not run. The wicks should be thoroughly dry, before the tallow is put to theni.-Murray-Brewster's Journal.

IMPROVED LIQUOR COCK.

London Street, Greenwich, June 27, 1829. SIR, A salt-water friend of mine, who is what they call a "genus," having constructed a new liquor cock, which I take to be an improvement upon the ordinary kind, I have thought it a fit subject "for your publication, which I have taken in from its commencement, for the sake of the nautical improvements it occasionally contains, and only wish it had a few more. As I have no relish for spinning a long yarn of description, and am a bit of a draftsman, though no fresh-water fish, I send you what I suppose to be a section of the thing.

a, is the channel where the liquor goes out; the passage where it goes out into my brown jug; c a plug, which by turning the handle d, stops up the gangway, and keeps all tight. If you want to know more about it, you may see it in operation in my barley-wiue cask, and at the same time, ascertain the merits of the latter.

JOHN HOLMES.

ASH'S SELF-REGISTERING BAROMETER.

THE intention of this contrivance is to register, by means of two barometers, the highest and lowest pressure in the absence of the observer, as some thermometers do. The tubes are to be common ones, but turned up at bottom like inverted syphons, and within the short legs are to be placed silk valves; that in the one to open upwards to shew the lowest, and that in the other to open downwards to shew the highest pressure. I need hardly say that both valves must be opened, and the mercury allowed to settle before the

A

instruments are left. If it should be thought that silk valves would be too liable to get out of order, I would propose valves formed of glass, as represented in the annexed sketch, A in which A A represents part of the barometer tube, having two pieces of smaller tube b b cemented in, with a disc of glass, c, loose between them, and ground to fit air tight on their ends; these must be always below the surface of the mercury: the disc in one of the barometers must be loaded so as to make it sink or rest on the lower interior tube, by which the mercury will be permitted to rise above the valve, but prevented from returning, and thus the least degree of pressure will be indicated and for indicating the greatest degree, the disc must be made somewhat lighter than mercury, that it may press slightly against the upper interior glass tube, so as to permit the mercury to descend below it, but not to

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return. d is a small platinum or iron wire to open the valve for adjusting the mercury. The same principle may be applied to the barometer described in Number 64 of the Register of Arts, which sets its own vernier.

ON A NEW METALLIC PISTON.

BY THE EDItor.

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IT has been stated by the late Mr. Tredgold, in his excellent **Treatise on the Steam Engine," that it would be an improvement to admit the steam into the interior of the piston, in order that the elastic force of the vapour might be made to keep the packing closely pressed against the sides of the cylinder. While it is with considerable diffidence that we differ from so great an authority, we are disposed to think that some advantage might be taken of the hint thus given to improve the piston. If the steam were itself to enter between the segments, or other pieces of metal of which the piston is constructed, small particles of sand would insinuate themselves by degrees between the sliding joints, which would before long destroy their proper action, and open fissures for the free passage of the steam through them. Mr. Tredgold seemed to consider that the force of the metallic springs, which are employed in Cartwright's and Barton's pistons, were liable to counteraction by the steam getting between the piston and cylinder. Now the springs cannot be pressed back but through the medium of the segments, and the segments cannot be operated upon if the steam be allowed to press upon their upper and under surfaces, which being of greater area than the sidęs receive more pressure, and consequently resist the effect of a

lesser force. But admitting, for argument sake, that such an effect can and does take place, the remedy proposed by Mr. Tredgold is worse than the disease; for, if the steam be allowed to operate with its full force laterally, the friction of the piston against the cylinder will be so great as to neutralize entirely the power of the engine` estimated from the ordinary data.

From the little reflection that we have been enabled to bestow upon the subject, it appears clear to us that a metallic piston should have no more friction against the cylinder than arises from its barely touching the sides of the cylinder. To produce this contact without the employment of metallic springs, but by the elasticity of the steam only, we have to submit the following arrangement of parts.

Fig. 6, Plate I., exhibits a plan of the piston, and Fig. 7 a vertical section, the letters of reference in each indicating similar parts; a b c d are four segments forming the circular area of the upper side of the piston, as shown at a bin the section. Underneath these segments are four other segments (two of which are shown at o o in the section), arranged so as to break joint in the manner of the Cartwright piston. e e are two circular metallic plates, which may cover the whole area of the piston; these are ground conical on one side to fit accurately into a conical cavity ground out of the segments: g is the piston rod which slides through the plates ee, the latter being confined from moving up or down upon the rod by the nut f, yet allowing sufficient freedom for the conical surfaces of the segments sliding against the conical surfaces of the plates e e.

Now, supposing this piston to be put into a cylinder when it begins to wear, the pressure of the steam upon the plates will cause the piston to expand, and keep it always in contact with the cylinder. There can be no fear of a re-action by the steam getting between the cylinder and the piston on account of the superior pressure upon the plates. To keep the piston expanded but very little pressure will be found necessary, consequently, the conical surface of the plates may form a very acute angle with the flat sides ;—a few experiments will determine the degree of obliquity required.

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It should be observed, that these conical plates (which are proposed solely with the view of employing the elastic force of steam instead of metallic springs), are equally applicable to Barton's Patent Piston, which we consider to be decidedly superior to those constructed on the Cartwright principle, for reasons which we have before given in our observations upon metallic pistons generally in a former number. We shall not, however, dwell more upon this subject, hoping that some of our ingenious readers will favour us with their opinions on the matter, with suggestions for the further improvement of this important part of the steam engine.

NEW MOTIVE ENGINE,

Patented by RICHARD WILLIAMS, of Tabernacle Walk, London-Enrolled June, 1829.

THE use of the elastic force of steam, as a prime mover, has become so extensive, and been found so important, that a very considerable portion of the mechanical genius of this country has long been, and still is, devoted to the construction or improvement of machines to economise the fuel used in producing power through the medium of steam, or rendering its application safe and convenient; and hence have proceeded the almost infinite variety of steam-engines, which have at different times been patented and described in the pages of the Register of Arts and Journal of Patent Inventions.

We have on the present occasion the pleasure of adding to the number, one which displays much mechanical ingenuity in the arrangement and adaptation of the several parts of which it is composed. By this remark, we must not, however, be understood to insinuate, that Mr. Williams, by his patent" for certain improvements in the application of elastic and dense, fluids to the propelling of machinery of various descriptions," has invented an engine, which will supersede the steam-engine, as it is usually constructed. His object is to avoid the expensive wear and attendant friction of metallic or packed pistons moving in cylinders; and this he effects by having his steam cylinders open at one end, and inverted in a vessel of dense fluid, which will require a much greater heat to convert it into vapour than water; so that steam being admitted successively into the cylinders, three in number, which are attached by rods to a three-throw crank: they are forced up in succession and give motion to a shaft, which may be attached in the usual way to any machinery requiring to be put in motion.

The action of this engine will be readily understood on reference to the drawing, fig. 1, where

a represents the furnace.

b the boiler, partly filled with water, and partly with steam.

cc the dense fluid vessel, which may be considered as partly filled with oil.'

ddd three cylinders, closed at their upper ends with a spherical top, and open at their lower ends.

e e e steam reservoirs attached to the bottom of the dense fluid vessel.

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fff rod connecting the cylinders with the cranks.

ggg the cranks and shaft for communicating the motion.

VOL. IV,-No. 73.

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1ST AUGUST, 1829.