(Plate V.) which may be made from a piece of tin the size of the arch, being bent so as to form such a concavity as may best suit the purpose to which it is to be applied; this being done, two square pieces of tin, aa, must have an arch cut out of them, of such a size that the diameter thereof may be about three-fourths of an inch less than the diameter of the concave piece before stated; these being soldered to each end of the first-mentioned piece, will form a stand for the hollow part of the mould, and the thickness of the muffle moulded in this will be exactly determined by the edge at each end. A piece of hollow tin, bb, may be soldered along the top edge of the mould, to form a better resistance to the great pressure within. The next part of this mould is a flat piece of tin, Fig. 2, cut exactly to fit the inside of the mould, the use of which is, to form a solid back to the muffles used for chemical purposes.

The second tool for this purpose is a piece of sheet brass, Fig. 3, about six inches long and one broad, which being bent in a semicircular form, and screwed to a piece of wood extending beyond its breadth about an inch, is used for cutting the small air holes c (Fig. 11), in the aforesaid muffles.

The third is the tool or frame, Fig. 4, for preventing the contraction of the muffles in drying, which is made of four pieces of beech, about three quarters of an inch broad, and half an inch thick; the length must be adjusted to the mould of the muffle; two of these being laid parallel within the inside of the mould, and being joined across by the other two, the ends of which should extend so far beyond the outer edges of the other two, that they may rest upon the edges of the muffle mould, and thereby prevent its falling into the mould.

The fourth is the tool for spreading the composition into the moulds, which is formed of iron or steel, (Fig. 5), about thirteen inches in length, one inch and a half broad, and about one-eighth thick; its face under h being rounded in such a manner that its curve may exactly fit the inner curve of the muffle mould (Fig. 6, is a section of it); this should likewise have a point or tongue, extending from each

end,

end, long enough to be bent in the form of a bricklayer's trowel, and by the wooden handles which must be put on, hanging down, it will be found, that, as it is moved either backwards or forwards, it will always present an edge to smooth the composition, and condense it in the mould.

The fifth is a frame (dd), Fig. 15, of which the bottom and farthest side only are shown, and in which frame the tin mould, Fig. 1, is placed, simply constructed by joining two pieces of wood, the one as broad as the bottom of the muffle mould, and having two narrow groves (e c), cut in it, so that the edges of the tin mould may be confined therein; the other board being joined to this, at its edge, should come up so high as just to be under the edge of the mould.

The sixth is the tool for cutting the muffles of different lengths (Fig. 7), and is made of a piece of wood, to the end of which is fixed a thin piece of brass (f), which extending about one inch and one-fourth beyond the top of the wood, is bent at right angles, and made thinner at the end, that it may the more conveniently cut the muffle; under this piece of wood is used another straight piece (g), with two steady pins, which being shifted at the will of the workman, will cut them of any length.

The seventh is the mould for forming the bottom of the close muffle (Fig. 8), which is made of a mahogany or oak plank, about sixteen inches long, ten wide, and about three-eighths of an inch thick; upon this is fixed a ledge on each side, one inch broad, and nearly half an inch thick, and at each end a ledge of the same kind is placed, at such a distance as is best suited to the length of the bottom required. Fig. 9 and 10, are circular moulds for muffle bottoms of dial plates. Fig. 11, a complete muffle standing on its bottom. Fig. 12, a roller for rolling the composition in the first mould. Fig. 13, a tool for making small holes in the muffle.

The usual composition for making muffles is as follows: viz. two parts pipe clay and one part sand, such as is used by the bricklayers, sifted, and mixed together to a proper consistence;

consistence; this is very expensive, on account of the high price of pipe clay, which is about ten shillings the hundred weight, whereas I employ in my improved mode of making them the coarser kind of Stourbridge clay, which can be had at the glass-houses, in the ground state, for six shillings the hundred weight, and this I sift also, to separate the finer part, which I employ for making other smaller articles necessary in my business; using only the grosser or coarser part for muffles, to which I add one-eighth part only of pipe clay, mixing them well together with water, so as to form a mass of a pretty thick consistence. The tin mould being first greased, I place it in the frame Fig. 15, shown under Fig. 1, and having spread the composition in the mould, and smoothed it with the spreader, Fig. 5, till the mould is quite full, the flat piece of tin is then to be well greased, and thrust in at one end of the mould, and the back of the muffle is then formed by spreading the composition, and firmly pressing it against the part already formed. The next thing to be done is to cut the holes in the sides of the muffle, which is done by pressing the semicircular cutter, Fig. 3, into the sides thereof, while it is yet wet, and bringing the piece out entire: the tin mould must now have the frame, Fig. 4, put in to keep the sides of the muffle from contracting, and being set up end-ways, and a little inclined, it must be dried in the sun, until it has shrunk sufficiently-to leave the mould, after which it must be completely dried and burned in the usual manner.

The composition of the smaller implements, or muffle bottoms for dial plates, for the mould Figs. 9 and 10, is made of the finer part of the Stourbridge clay, with a small proportion of pipe clay.

The rings are made from two parts of Dutch black lead pots, powdered, and one part of pipe clay. I have made repeated trials of English black lead, in various states, as a substitute for the Dutch black lead pots, but without finding it to answer properly.

Should any difficulty appear in any part of my process, I shall be happy in attending the committees, and performing the whole operation before them, whenever they

shall

shall be pleased to appoint; when the great simplicity and advantage will appear evident.

I am, my lords and gentlemen,

your most obedient and respectful servant,

EDMUND TUrrell.

Certificates from Messrs. J. Haynes and Son, Westmoreland Buildings; John Kelly, Hooper Street, Clerkenwell; John Foster, Author Street, St. Luke's, and William Foster, Author-Street, St. Luke's, state, that they have been in the habit of using for upwards of twelve months, Mr. Turrell's muffles, and that they are greatly superior to any they have hitherto been able to procure, and that it is their opinion their durability may be completely attributed to his improved method of moulding them.

XXXVI. Description of a Mac' ine for raising Coals or other Articles from Mines. By Mr. GILBERT GILPIN*,

SIR,

THE improvement of the machines in use for raising coal

and ore from the mines, has long been a desideratum of the Society for the Encouragement of Aris, Manufactures, and Commerce, and they have repeatedly offered a premium for that purpose.

Those in general use (from the increased expense of horse labour), are worked by a steam engine, attached to a crank of twenty-one inches radius, wedged on a shaft along with a fly wheel, eleven or twelve feet in diameter, and pinion wheel, of eleven tecth, which latter works in another of sixty four teeth, on the shaft of which is a plain cylindrical barrel, from four to six feet diameter, and nine or ten feet

* From Transactions of the Society for the Encouragement of Arts, Manufac tures, and Commerce, for 1807.--Twenty guineas were voted by the Society to Mr. Gilpin for this invention.

long;

long; some have barrels formed of frustums of cones, (whose perimeters are in the proportion of about five to four), united at their bases, and of various diameters; the axes of both kinds are placed at right angles with the centre line of the pit, and at each end a rope of six inches in circumference is made fast by a staple, which ropes work (in contrary directions at the same time) over two pulleys, placed in a frame parallel to each other, and at an equal distance from the centre of the pit; to the ends of these ropes the baskets of coal and ore to be raised are hooked.

The simplicity of their general structure is such as, perhaps, not to admit of any considerable improvement; but the forms of the barrels are very defective.

On putting one of these machines in motion each rope forms a triangle, the lines thereof from the pulley to the first and last coil, and the surface of the barrel, forming its three sides. Upon the cylindrical barrel the load always tends, from gravitation, towards the nearest point of contact with the centre of motion of the barrel, and, in consequence, the ascending rope at first bends around it in receding coils from the subtending side of the triangle, diminishing their distances as they approach the nearest point of contact, (where the rope crosses the centres of the pulley and barrel at right angles,) thereby leaving a great part of the latter uncovered by the rope, and hence the necessity of such long ones; afterwards coiling hard against itself as it approaches the other side of the triangle, to its great injury in wear.

The barrels formed of frustums of cones, united at their bases, whose perimeters are in the proportion of about five to four, are equally defective, on account of the rope, for the reason before mentioned, binding hard against itself, and even sometimes (in wet weather, when its rigidity is increased by absorption of water,) folding at first in receding coils, and afterwards so hard against itself as to force those receding coils to slip suddenly towards the small perimeter of the cone, thereby making a large portion of the rope to descend the pit in an instant, breaking the rope by the sudVol. 31. No. 123. Aug. 1808.

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