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is fused with feldspar; the solvent for tender porcelain is silex, potash, and lead; it is not volatilized like the preceding, because the fire is much inferior to that of the hard porcelain.

These colours being previously fused do not in the least change when applied.

The blues for glass are the same as for tender porcelain.

Concerning Greens.

The greens, employed in painting, are made with the green oxide of copper, or sometimes with a mixture of yellow and blue. They must be previously melted with their flux; without this precaution they would become black; but they do not change after the first fusion.

They must not be treated with a violent fire or they would totally disappear. The green grounds by strong heat are made with the oxides of cobalt and nickel, but it is only a brownish green.

The bluish greens, named sky-blue, formerly a colour very much in esteem, can only be used on tender porcelain; they always scale off from hard porcelain, because there is potash in their composition. These greens cannot be used on glass because they afford a dirty colour: it is necessary to put a yellow on one side, and a more or less pale blue on the other, in order to produce a green. This colour may likewise be fabricated by mixing a blue with the yellow oxide of iron. Brongmart hoped to obtain a green from the oxide of chrome; and the experiments he made promised to be attended with success. The pure chromate of lead fixed on porcelain by means of a strong fire, afforded him a very deep and very fixed blue, of considerable beauty.

Concerning Bistres and Brown Reds.

These are obtained by mixtures of different proportions, of manganese, brown oxide of copper, and the oxide of iron, called amber. They are likewise previously fused in their solvent', so that they do not in the least change on tender porcelain; lead not having the same action on the oxide of manganese as it has on that of iron. This colour may be employed very well on gnus.

The brown red, ground by strong heat, known by the name of fonds cuille, are made in the Same manner: feldspar is their flux. There is no titanium in their composition, though generally asserted in

VOL. III.

books. Titanium was not known at Sevrc when Brougniart first came to that manufactory. He treated this singular metal in various ways, and never obtained any grounds but a slight obscure yellow, and very uncertain in its quality.

Concerning the blucks.

Black colours are the most difficult to be obtained very beautiful. There is no metallic oxide which, singly, affords a fine black. Manganese gives the best; iron, an opaque, dull, blistered black, which easily turns to red. The makers of colours have therefore combined several metallic oxides which, singly, do not afford blacks, and they have' obtained a very beantiful colour, but it is subject to scale and become dull.

The oxides are those of manganese, the brown oxides of copper, and a little of that of cobalt. Grey is obtained by suppressing the quantity of copper and increasing the quantity of flux.

The Sevres manufactory is the only one • which has as yet produced beautiful blacks with a strong fire. This is more owing to the quality of the biscuit than to any peculiarity of process. It is by its mixture of blue with the oxides of manganese and iron that they make this very brilliant black.

The blacks for opaque glass are made the same as for painting, by giving different doses of solvent.

After the display of the principles of fabricating each principal colour, it is clear that by mixing these colours all possible >hades may be obtained: and also that care in the preparation, choice of materials, and just proportions of doses, must exhibit very sensible differences to the experienced eye of a painter. A knowledge of the composition of colours does not give the requisite care and neatness in making them up.

On recapitulating the facts here just stated, in order to present them in a general view; we see, first, that amongst the colours usually employed for hard porcelain, one only is susceptible of change, namely, the carmine; and this may be replaced by the reds of iron, and then no colour changes.

M. Brougniart presented to the Institute an unbaked head made in this manner, and a painting of two roses, the one baked and the other in its first state. There was not any difference between them.

Secondly, That amongst the colours of soft porcelain and enamel, several change considerably, particularly the reds of iron C

and gold, with the yellows, greens, and browns. None have been substituted instead of them, this species of painting being almost abandoned.

Thirdly, That several of these colours change likewise upon the glass by becoming perfectly transparent, particularly the yellows and violets.

Fourthly, That neither an additional calcination, nor an additional fusion, as has been suspected, will prevent them from changing: for this method alters the colours that change, and does nothing to the rest. The change which several colours undergo on tender porcelain, and on glass, does not therefore relate to the nature of their composition, but rather to that of the body on which they are placed. Consequently, by suppressing the carmine of gold from the colours of hard porcelain we shall have a series of unchangeable colours.

ENARGEA, in botany, a genus of the Hexandria Monogynia class and order. Essential character : calyx none ; petals six, oblong, ovate, concave, acute, three outer, three inner, green spotted; berry threecelled.with four or five globular seeds.There is but one species, rti. E. marginata, a native of Terra del Fuego.

ENCALYPTA, in botany, a genus of the Cryptogamia Musci class and order. Capsule cylindrical; fringe simple, of sixteen linear erect distinct teeth; veil companulate, inflated lax. There are six species.

ENCAUSTIC, the same with enamelling and enamel. See Enamelling.

Encaustic painting, a method of painting made use of by the antients, in which wax was employed to give a gloss to their colours, and to preserve them from the injuries of the air.

ENCHASING, or Chasing, the art of enriching and beautifying gold, silver, and other metal work, by some design, or figures represented thereon, in low relievo. See Relievo and Sculpture.

Enchasing is practised only on hollow thin works, as watch-cases, cane-heads, tweezer-cases, or the like. It is performed by punching or driving out the metal, to form the figure1, from within side, so as to stand out prominent from the plane or surface of the metal. In order to this they provide a number of fine steel blocks, or puncheons, of divers sizes; and the design being drawn on the surface of the metal, they apply the inside upon the heads or tops of these blocks, directly under the

lines or parts of the figures; then with 9 fine hammer, striking on the metal, sustained by the block, the metal yields and the block makes an indenture or cavity on the inside, corresponding to which there is a prominence on the outside, which is to stand for that part of the figure.

Thus the workman proceeds to chase and finish all the parts by successive application of the block and hammer, to the several parts of the design. And it is wonderful to ponsider with what beauty and justness, by this simple piece of mechanism, the artists in this kind will represent foliage, grotesques, animals, histories, &c.

ENCHELIS, in natural history, a genus of the Vermes Infusoria. Worm invisible to the naked eye, very simple, cylindrical. There are fifteen species. An account of these may be found in Adams "On the Microscope."

ENCROACHMENT, in law, an unlawful gaining upon the rights or possessions of another. It is generally applied to the unlawful occupation of wastes and commons.

ENDEAVOUR, where one endeavours actually to commit felony, &c, he is punishable as for a misdemeanour; and an assault, with intent to rob, is punished by transportation. Stat. 7, Geo. II. c. 21.

EN DECAGON, a plane geometrical figure of eleven sides and eleven angles. If each side of this figure 1, its area will be 9.3656399 = ^ of the tangents of 73^ degrees to the radius one.

ENDEMIC, or Enoemical disease*, those to which the inhabitants of particular countries are subject more than others, on account of the air, water, situation, and manner of living.

ENDIVE, in botany, &c. broad-leaved succory. See Cichorium.

ENDOWMENT, in law, is the widow's portion; being it third part of all the freehold lands and tenements, of which her husband was seized at any time during the coverture. Of lands not freehold, her portion varies according to the custom in different places.

ENEMY, in law, an alien or foreigner, who in a public capacity invades any country, and who cannot be punished as a traitor, but must be subjected to martial law. An alien residing here, under the protection of the king's peace, may be dealt with as a traitor, because he owes it qualified allegiance.

ENFRANCHISEMENT, in law, the incorporating a poison into any society or body politic; such as the enfranchisement of one made a citizen of London or other city, or burgess of any town corporate, because he is made partaker of its liberties, or franchises.

ENGINE, in mechanics, is a compound machine, made of one or more mechanical powers, as levees, pullies, screws, &c. in order to raise, cast, or sustain any weight, or produce any effect which could not be easily effected otherwise.

Engines are extremely numerous; some used in war, as the battering-ram, ballista, waggons, chariots, &c.; others in trade and manufactures, as cranes, mills, presses, &C. ; others to measure time, as clocks, watches, &c, ; and others for the illustration of some branch of science, as the orrery, cometarium, and the like.

In general we may observe, concerning engines, that they consist of one, two, or more of the simple powers variously combined together; that in most of them the axis in peritrochio, the lever, and the screw, are the const itutent parts; that in all a certain power is applied to produce an effect of much greater moment; and that the greatest effect or perfection is when it is set to work with four-ninths of that charge which is equivalent to the power, or will but just keep the machine in equilibria.

In all machines the power will just sustain the weight, when they are in the inverse ratio of their distances from the centre of motion.

Engine, fire, by Rowntree. We have selected an engine by this maker to give a drawing and description, as it is greatly superior to the common engine with two force pumps. As that kind of engine has so often been described by various authors, and its principle so easily comprehended from the • description of a force-pump; we judged it unnecessary to give any drawing of it.

The fire engine, by Rowntree, is a double force-pump, of a peculiar construction, similar in its action to the beer-engine (described under that article), but as it is on a much larger scale, its constructions are of course varied. Plate Rown tree's Engine, fig. 1 and 2, are two elevations at right angles to each other, of the external part of the engine mounted on four wheels. Fig. 3 and 4, are two sections perpendicular to each other, of the body of the engine or pump : fig. 5 and 6, are parts of the engine. The same letters are used as.far as they

apply in all the figures, A, A, A, A ; fig. 3 and 4, is a cast-iron cylinder truly bored, it is ten inches diameter and fifteen long, it has a (lunch at each end ,whereon to screw two covers, with stuffing boxes, a, a, in their centres, through which the spindle, B, B, of the engine passes, and being tight packed with hemp round the collar, makes a tight joint; the piston, D, is affixed to the spindle within the cylinder, and fits it tight all round by means of leathers, applied as described in the beer-engine; at E, fig. 4, a partition called a saddle, is fixed in the cyUnder, and fits against the back of the spindle tight by a leather.

We have now a cylinder divided by the saddle, E, and piston, into two parts, whose capacity can be increased and diminished by moving the piston, with proper passages and valves to bring and convey away the water: this will form a pump. These passages are cast in one piece with the cylinder: one, d, for bringing the water is square, and extends about \d round the cylinder; it connects at bottom with a pipe, e; at its two upper ends opens into two large chambersi/g'; extending near the whole length of the cylinder, and closed by covers, h h, screwed on : i k, are square openings (shewn by dotted squares in fig. 3.) in the cylinder, communicating with the chambers :fg, I in, are two valves, closing their ends of the curved passage, d, and preventing any water returning down the passage, d: no, are two passages from the top of the cylinder to convey away the water; they come out in the top of the cylinder, which, together with the top of the chambers ,/,ff, form a large flat surface, and are covered by two valves, p, j, to retain the water which has passed through them. A chamber, K, is screwed over these valves; and has the air-vessel, k, fig. l and 2, screwed into its top; from each side of this chamber a pipe, w w, proceeds, to which a hose is screwed, as shewn in fig. 1. Levers, x x, are fixed to the spindle at each end, as shown in fig. 1, and carry the handles, H H, by which men work the engine. When the piston moves, as shown by the arrow in fig. 4, it produced a vacuum in chamber, f, and that part of the cylinder contiguous to it; the water in the pipe, e, then opens the valve, m, and fills the cylinder. The same motion forces the water contained in the other part of the cylinder through the valve, q, into chamber, K, and thence to the hose through the pipe, w; the piston being turned the other way, reverses the operation with respect to the valves, though it continues the same in itself. The pipe, e, is screwed by a flanch to an upright pipe, P, fig. 5,connected with another square iron pipe, fastened along the bottom of the chest of the engine; a curved brass tube, G, comes from this pipe through the end of the chest, and is cut into a screw to fit on the suction hose when it can be used; at other times a close cap is screwed on, and another brass cap at H, within the chest is screwed upwards on its socket, to open several small holes made in it, and allow the water to enter into the pipe; in this case the engine chest must be kept full of water by buckets. The valves are made of brass, and turn upon hinges. The principal advantage of the engine is the facility with which it is cleaned from any sand, gravel, or other obstruction', which a fire-engine will always gather when at work.

The chambers, /, g, being so large, allow sufficient room to lodge a greater quantity of dirt than is likely to be accumulated in the use of the engine at any one fire, and if any of it accidentally falls into the cylinder, it is gently lifted out again into the chambers by the piston, without being any obstruction to its motion: to clear the engine from the dirt, two circular plates, t' r, five inches diameter, are unscrewed from the lids, h h, of the chambers, fg, and when cleaned are screwed on again: these screw covers fit perfectly tight without leather, and can be taken out, the engine cleared, and enclosed again in a very short time, even when the engine is in use, if found

necessary.

The two upper valves, p o, and chamber, K, can also be cleared with equal ease, by screwing out the air-vessel, k k, fig. 1, which opens an aperture of five inches, and fits airtight, without leather, when closed. The valves may be repaired through the same openings. The use of the air-vessel, kk, fig. 1 and 2, is to equalize the jet from the engine during the short intermittance of motion at the return of the piston stroke; this it does by the elasticity of the compressed air within it, which forces the water out continually, though uot supplied quite regularly from the engine.

The engine from which our drawing was taken was made for the Sun Fire Insurance Company, in London, and from some experiments made by their agent, Mr. Samuel Hubert, appears to answer every purpose.

Engine for raising water. The frame of the machine is of cast iron, nearly in the form of the letter A; there are two of these

frames, B B, (fig. 1, Plate Pump- Engine,) screwed together by means of five wrought iron pillars, a a a a; D, is another smaller frame, to support the axis of the fly-wheel, connected with the other frame by three short pillars; E, is the fly wheel turned by winches on the end of its axis; it has a pinion (13) of 13 leaves upon its axis, turning a wheel (48) of 48 teeth, on whose axis are two cranks, 4 b, opposite to each other, to work the pumps; c e, are the two crank rods, made each in two branches, and jointed at the lower end into two other rods, ff, which slide through holes made in the fixed bars, g g, fig. 2; the crank rods receive these bars between their two branches, and by this means, though the rods,//, are confined by their guides to move truly vertical, the crank rods, e e, can partake of the irregular motion of the crank. The pump rods of the pumps are screwed to the rods,//, by two nuts, and go down into the pumps, G H, supported from the iron frame by eight iron braces, A h. The pumps consist of two barrels, G H, with valves at the bottom, allowing water to enter them freely, but preventing its return; the buckets fixed to the pump rods fit the barrels truly, and have valves in them shutting downwards; I, is a chest bringing water to the valves in the bottom of the barrels; K, is another communicating with the top of the barrels by two crooked passages to carry away the water from them; the barrels are close at top, and the pump rods pass through close stuffing boxes, through which no water will leak by them. The action of the pump is the same as the common sucking pump; when the bucket is drawn up, the valve in it closes, and it forms a vacuum in the lower part of the barrel; this causes the water to ascend into it through the chest, I, to restore the equilibrium, at the same time it raises all the water which was above it through the chest, K; on the descent of the bucket the valve at the bottom of the barrel shots, and prevents the escape of the water; the valve in the bucket opens, and the water passes through it, ready to be raised at the next stroke. The barrels in question are :>) inches diameter, and 8 inches stroke. As the two cranks, b-b, are opposite each other, when one bucket is rising, the other is going down; by this means the power required to turn the machine by the handles is equalized, and also the quantity of water raised by the engine.

Engines for raising water by the pressure and descent of a column inclosed in a pipe

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have been lately erected in different parts of the country. The principle now adverted to was adopted in some machinery executed in France about 1731, and was likewise adopted in Cornwall more than forty years ago; but the pressure engine, of which we are about to give a particular description, is the invention of Mr. R. Trevithick, who probably was not aware that any thing at all similar had been attempted before. This engine, a section of which on a scale of [i\ of an inch to a foot is shewn in Plate PressureEngines, one was elected about eight years ago at the Druid copper mine, in the parish of Illogan, nearTruro. A B, represents a pipe six inches in diameter, through which water descends from the head to the place of its delivery to run off by an adit at 8, through a fall of 34 fathoms in the whole; that is to say, in a close pipe down the slope of a hill 200 fathoms long, with S6 fathoms fall; then perpendicularly six fathoms, till it arrives at B, and thence through the engine from B to S two fathoms; at the turn, B, the water enters into a chamber, C, the lower part of which terminates in two brass cylinders, four inches in diameter; in which two plugs or pistons of lead, D and E, are capable of moving up and down by their piston rods, which pass through a close packing above, and are attached to the extremities of a chain leading over and properly attached to the wheel, Q, so that it cannot slip.

The leaden pieces, D and E, are cast in their places, and have no packing whatever. They move very easily; and if at any time they should become loose, they may be spread out by a few blows with a proper instrument, without taking them out of their place. On the side of the two brass cylinders, in which D and E move, there are square holes communicating towards, G, with a horizontal trunk, or square pipe, four inches wide, and three inches deep. All the other pipes, G, G, and R, are six inches in diameter, except the principal cylinder wherein the piston, H, moves; and this cylinder is ten inches in diameter, and admits a nine foot stroke.

The piston rod works through a stuffingbox above, and is attached to, M N, which is the pit rod, or a perpendicular piece divided into two, so as to allow its alternate motion up and down, and leave a space between, without touching the fixed apparatus, or great cylinder. The pit rod is prolonged down in the mine, where it is employed to work the pump; or if the engine was applied to mill-work, or any other use,

this rod would be the communication of the first mover, K L, is a tumbler, or tumbling bob, capable of being moved on the gudgeons, V, from its present position to another, in which the weight, L, shall hang over with the same inclination on the opposite side of the perpendicular, and consequently the end, K, will then be as much depressed as it is now elevated.

The pipe, R S, has its lower end immersed in a cistern, by which means it delivers its water without the possibility of the external air introducing itself; so that it constitutes a Torricellian column, or water barometer, and renders the whole column from A to S effectual, as we shall see in our view of the operation.

The operation. Let us suppose the lower bar, K V, of the tumbler to be horizontal, and the rod, P O, so situated, as that the plugs, or leaden pistons, D and E, shall lie opposite to each other, and stop the water ways, G and F. In this state of the engine, though each of these pistons is pressed by a force equivalent to more than a thousand pounds, they will remain motionless, because these actions being contrary to each other, they are constantly in equilibrio. The great piston, H, being at the bottom of its cylinder, the tumbler is to be thrown by band into the position here delineated. Its action upon, O P, and consequently upon the wheel, Q, draws up the plug E, and depresses D, so that the water way, F, becomes open from A B, and that of G to the pipe R: the water consequently descends from A to C, thence to F, until it acts above the piston F. This pressure forces down the piston, and if there be any water below the piston, it causes it to pass through G G G into R: during the fall of the piston, which carries the pit rod, M N, along with it, a sliding block of wood, I, (dotted) fixed to this rod is brought into contact with the tail, K, of the tumbler, and lowers it to the horizontal position beyond which it oversets by the acquired motion of the weight L.

The mere rising of the piston, if there was no additional motion in the tumbler, would only bring the two plugs, D and E, to the position of rest, namely, to close G and F, and then the engine would stop; but the fall of the tumbler carries the plug, D, upwards, quite clear of the hole, F, and the other plug, E, downwards, quite clear of the hole, G: these motions require no consumption of power, because the plugs are in equilibrio, as was just observed. In this new situation the column, A B, no longer

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