dryness, in order to expel the excess of acid, and dissolved in water. The addition of a solution of tin and muriatic acid will shew the presence of gold by a purple precipitate; and platina will be indicated by a precipitate, on adding a solution of muriate of ammonia. When gold and platina are both contained in the same solution, they may be separated from each other by the last mentioned solution, which throws down the platina, but not the gold. In this way platina may be detached also from other metals.

For extracting "silver" from its ores, the nitric acid is the most proper solvent., The silver may be precipitated from nitric acid by muriate of soda. Every hundred parts of the precipitate contains seventyfive of silver. But, as lead may be present in the solution, and this metal is also precipitated by muriate of soda, it may be proper to immerse in the solution, a polished plate of copper. This will precipitate the silver, if present, in a metallic form. The muriate of silver is also soluble in liquid ammonia, which that of lead is not.

"Copper ores" may be analyzed by boiling them with five times their weight of concentrated sulphuric acid, till a dry mass is obtained, from which water will extract the sulphate of copper. This salt is to be decomposed by a polished plate of iron, immersed in a dilute solution of it. The copper will be precipitated in a metallic state, and may be scraped off and weighed. If silver be suspected with copper, nitrous acid must be employed as the solvent; and a plate of polished copper will detect the silver.

"Iron ores" may be dissolved in dilute muriatic acid, or, if the metal be too highly oxydized to be dissolved by this acid, they must be previously mixed with one-eighth of their weight of powdered charcoal, and calcined in a crucible for an hour. The iron is thus rendered soluble. The solution must then be diluted with ten or twelve times its quantity of water, previously well boiled, to expel the air, and must be preserved in a well-stopped glass bottle for six or eight days. The phosphate of iron will within that time be precipitated, if any be present, and the liquor must be decanted off. The solution may contain the oxides of iron, manganese, and zinc. It may be precipitated by carbonate of soda, which will separate them all. The oxide of zinc will be taken up by a solution of pure ammonia; distilled vinegar will

take up the manganese, and will leave the oxide of iron. From the weight of this, after ignition, during a quarter of an hour, twenty-eight per cent. may be deducted.

"Tin ores." Boil 100 grains, in a silver vessel, with a solution of 600 grains of pure potash. Evaporate to dryness, and then ignite moderately for half an hour. Add boiling water, and if any portion remain undissolved, let it undergo a similar treatment. Saturate the alkaline solution with muriatic acid, which will throw down an oxide of tin. Let this be redissolved by an excess of muriatic acid: again precipitated by carbonate of soda; and being dried and weighed, let it, after lixiviation, be once more dissolved in muriatic acid. The insoluble part consists of silix. Into the colourless solution, diluted with two or three parts of water, put a stick of zinc, round which the reduced tin will collect. Scrape off the deposit, wash, dry, and fuse it under a cover of tallow in a capsule placed on charcoal. A button of pure metallic tin will remain at the bottom, the weight of which, deducted from that of the ore, indicates the proportion of oxygen. The presence of tin in an ore is indicated by a purple precipitate, on mixing its solution in muriatic acid with one of gold in nitro-muriatic acid.

"Lead ores" may be analyzed by solution in nitric acid, diluted with an equal weight of water. The sulphur, if any, will remain undissolved. Let the solution be precipitated by carbonate of soda. If any silver be present, it will be taken up by pure liquid ammonia. Wash off the excess of ammonia by distilled water; and add concentrated sulphuric acid, applying heat, so that the muriatic acid may be wholly expelled.

"Mercury" may be detected in ores that are supposed to contain it, by distillation in an earthen retort with half their weight of iron filings or lime. The mercury, if any be present, will rise and be condensed in the receiver.

"Ores of zinc" may be digested with the nitric acid, and the part that is dissolved boiled to dryness, again dissolved in the acid, and again evaporated. By this means the iron, if any be present, will be rendered insoluble in dilute nitric acid, which will take up the oxide of zinc. To this solu tion add pure liquid ammonia, in excess, which will separate the lead and iron, if any should have been dissolved; and the excess of alkali will retain the oxide of zinc. This

cylindric tube, of a mixture of lead and tin; AB, (fig. 6) open at one end, and nearly closed at the other by a lump of the same metal, E, which is circular for about twothirds round, and fits the end of the pipe; the other third is a straight edge: the upper edge of the conical pipe, F, is bent to be parallel to this, and thus forms a small cleft similar to the wooden one for the pas sage of the air, the lower edge of the cylindrical pipe, A B, is bent into the line of the cleft and cut sharp, to divide the current of air; these pipes are open at top, and are brought to tune by bending the pipe at the top, and thus altering its bulk: a is a piece of metal, called the ear, soldered upon the pipe at each end of the cleft, to prevent the stream of air being dispersed before it meets the sharp edge of the pipe, BA; in the small pipes this is not applied.

The bellows of the organ are double, as shewn in fig. 1, Plate I; that is, they are two distinct pairs, E, F, connected together at their hinge; so that when one is opening, and filling with air, the other is forcing its air out into the regulator, D; the bellows receive their motion by a rod, d, from a crank, a, on a spindle which comes through the box, in which the machine is enclosed, and has a handle on it by which it is turn ed. The regulator, D, is exactly similar to another pair of bellows, and is filled with air from the bellows, E F, below it, through two valves in the bottom board over the bellows; from this regulator the air proeeeds through the passage, bef, (seen better in the section), fig. 2, &c.

Fig. 2, Plate I, to a long trunk, g, going under the pipes called the air-chest, which communicates with them by a small valve, h, under each it is kept shut by a small wire spring, and is opened by a wire fixed to the end of a rod, G; above the valve, the passage enlarges, and goes under two small wooden sliders or stops, nm, and from thence in two distinct passages to the wooden and metal pipes, N M.

The air-chest, g, is common to all the pipes, and each pair (of wooden and metal pipes) has a valve, h, and spring to them selves; the small passage above each valve belongs to each pair of pipes, and has no connection with the other; the two stops belong to all the pipes; m, to the metal, and n, to the wooden ones; they are long slips of wood drilled with so many holes as there are pipes, and at the same intervals, (the disposition of the pipes is shown in fig. 3, which is a plan of the whole instrument put

together); so that when the holes are over the passages, the air has free communication from the valve to the pipes; but when the stops are drawn out, the interval between each hole applies itself to the holes under the pipes, and thus stops the passages.

We now come to describe the apparatus which opens the valves, h, at the proper time, to perform the note of a piece of music.

The axle, on which the crank, a, (fig. 1, 2, and 3) is formed, has an endless screw, o, (fig. 3,) cut upon it to turn a wheel, p, by the teeth cut in its circumference; this wheel is in the same piece with a cylindric barrel, HH, shown separately (in fig. 4, Plate II); it has a great number of short pins stuck in it, which, as it revolves upon its pivots, catch the ends of a number of small levers called keys, rrr, and raise them; this depresses the other, ttt, ends, which are attached to the rods, G, and consequently open the valves. There are as many of the levers, or keys, as there are pipes, each answering to a different note of the gamut; the pins in the barrel are so disposed, as to lift the keys in the same order and time as any piece of music for which the barrel has been previously made. The keys all turn upon one wire, as a centre, and to prevent their shifting sideways; and by that means missing the pins in the barrel intended for them, they move in small notches, cut by a saw in two pieces of brass plate, which are screwed to the edge of a piece of wood, K, and project below it; the wire which forms the centre for the keys is also fixed to the piece of wood, K, which is called the key-frame. A number of small pieces of mahogany are fixed to the keys at t, and to these the rods, G, are jointed by a piece of leather glued to both: vv, are small screws going through the key-frame, and touching the piece of wood, t, their use is to adjust the levers, so that the ends, rr, shall form one straight line.

The key-frame is not fastened down to the frame of the machine, but has a piece of iron plate, w, fastened to each end, and turning upon screws fixed to the frame of the instrument upon which the whole key. frame can be fitted as a centre; two screws through its ends, resting their points upon the frame, support it, and by screwing these out, the whole frame can be raised or lowered, to adjust the ends of the keys the proper distance from the centre of the bar rel, H.

By inspecting the plan and elevation, (fig. 1 and 3) it will be seen, that the barrel is longer than the set of keys, by the distance of one of the keys from the other, the barrel can be moved along endways this quantity, and for this purpose it is mounted in a frame, (fig. 4) which slides in a groove, shown in the section (fig. 2); a small pin, P, (fig. 4) is fastened to the frame, and comes through the case of the instrument; it has notches cut in it which receives the sharp edge of a bolt, L, (fig. 7) fixed there, and which holds the barrel in any place it is set. By moving the barrel endways a short distance, an entire new set of pins is presented to the keys, rr, which pins are disposed differently to the former ones, and consequently play a different tune; there are often five different sets, and as many notches, on the pin, P, (fig. 1). Without some contrivance when the barrel is moved end. ways, its pins might catch some of the keys, and break or bend them: to avoid this, the bolt, P, which confines the barrel, and prevents it being moved either way, is held down by another bolt, R, (fig. 7) sliding across the end of it; this bolt has a pin fastened to the back of it, which goes through the case of the instrument, (marked x, fig. 2 and 3) and when drawn back, presses down the end of a lever, y, the other end of which lifts up the key-frame, and thus raises the keys up clear of the pins in the barrel, before it can be moved endways to play another tune.

ones; for fuller music, the stop, m, is push ed in, and ʼn drawn out; the wooden pipes are then used, and, for very grand and loud music, both sets are used, by drawing out both stops, and when both are in the soundcases, though the handle is still turned. For changing the tune, the bolt, R, is drawn back, this raises the key-frame; the other bolt is then drawn back, and the pin, P, moved in or out to another notch; the bolts are then to be returned. Several barrels are adapted to the same organ, to perform a great variety of tunes.

ORGANICAL, in the ancient music, was that part performed by instruments. The organical comprehended three kinds of instruments, viz. the wind instruments, as trumpets, flutes, hautboys, &c.; stringed instruments, as lutes, lyres, violins, harpsichords, &c.; and pulsative instruments, or those played by beating with the hands or sticks, as drums, &c.

ORGANICAL description of curves, is the description of them upon a plane by means of instruments, and commonly by a continued motion. The most simple construction of this kind is, that of a circle, by means of a pair of compasses. The next is that of an ellipse by means of a thread and two pins in the fòci, or the ellipse and hyperbola, by means of the elliptical and hyperbolic compasses.

ORGANZINE, in commerce, a description of silk usually imported from Italy into this country. It is of the utmost imporThe regulator, D, is pressed down by two tance to the manufacturer, as none of the wire springs, which equalize the pressure principal articles could be fabricated withupon the air contained in it, when, by the out it; and the Italians aware of this, long bellows forcing in more air than the pipes kept the art of throwing it a most profound require, and consequently it accumulates in secret. It was introduced into this country the regulator, it lifts up its lid, and the han- by the enterprize and skill of Messrs. dle of a small valve, z, seen in the eleva Thomas and John Lombe, the latter having tion, (fig. 1) is pushed against a part of the at the risk of his life, and with wonderful frame; this opens the valves, and allows ingenuity, taken a plan of one of these comthe air to escape, until the regulator sinks plicated machines, in the King of Sardinia's by the action of the two wire springs. dominions, from which, on his return, they established a similar set of mills in the town of Derby; and in consideration of the great hazard and expense attending the undertaking, a patent was granted to Sir Thomas Lombe, in 1718, for securing to him the exclusive privilege of working organzine for the term of 14 years; but the construction of buildings and engines, and the instruction of the workmen took up so much time, that the 14 years were nearly expired before he could derive any advantage from it, in consequence of which he petitioned parliament, in 1731, to grant him a further

From what we have said, a description of the operation of the instrument will be scarcely necessary. By turning the han dle, the crank, a, works the bellows, and supplies the air to the pipes; the endless screw turns the barrel, and its pins lift up the keys at the proper time, opens the valves, and admits the air into the pipes. When soft music is to be played, the stop, m, (fig. 2) which has a handle coming through the case, is drawn out, and the other shoved in; this stops the passages to the wooden pipes, and opens the metal VOL V.

F