Diamonds, gems, and the precious metals being scattered in minute quan tities over extensive surfaces of ground, chiefly of alluvial soil, the process of obtaining and separating them from the matrices and earths with which they are naturally combined, is extremely tedious when conducted by the ordinary processes of washing, stamping, and picking ; any improvements, therefore, in the apparatus, by which the labour can be considerably abridged, is of essential importance to those who are interested in such pursuits. The improvements which have been patented by Mr. Hardeben, appear to us to be deserving of that character ; and having been informed that they have been very successfully introduced in some of the gold mining districts of America, we shall here annex a detailed description of his apparatus, prefacing our account with the obser vation, that its application is not confined to the more precious metals, but may be advantageously employed in the separation of other solid substances of dissimilar specific gravities. If the matrices in which metals are found are of a hard and stony nature, they must, in the first instance, be reduced by hammers, or by the operation of an ordinary stamping-mill, to powder or dust ; for the smaller the particles are, the more effectually will they be separated by the subsequent process. The materials so prepared are put into a deep conical or cylindrical tub, with a quantity of water sufficient to permit the whole of the ore, soil, or other powdered materials, to float about in a perfectly free and liquid state whenever the water is stirred round by the agitators, which we shall presently describe ; and with a force and velocity so as to drive the water xip the sides of the tub in such marine; that a hollow space, in the shape of an inverted cone, may be formed in the water within the tub. F. 1 of the previous engravings, is a side view of the apparatus ; Fig. 2 a plan of the same; and Fig. 3 a sec tion of the tub, to show the form of the agitator, and the means used to suspend and move it ; the same letters of reference are used to denote the same parts in all the figures. A is the tub, quite smooth in the inside, supported upon a platform B, forming a part of the frame of the machine, and from which the two standards, C C, rise that support the horizontal cross-frame D D, which carries the agitator F G H I. This agitator may be made of wood or iron, according to the magnitude of the machine, and consists of four double arms F F F F, which support and carry the stirrers I III, which bang vertically. These stirrers may be screwed or morticed into the double arms F F F F, which are in like manner screwed or morticed into the strong central block G; through the centre of this block (which is also the centre of the agitator), the iron spindle H passes, being fixed by a nut and screw beneath the block, and ter minating at its upper, end in the handle k, which serves to turn the agitator round ; on which account the spindle has two turned bearings, which run in brass boxes a a. As the power and velocity of the winch K would not be suf ficient in large machines, a rigger is hung at L, upon the iron spindle H, so that the agitator may be turned by a band passing round it; and round a large rigger moved by a horse-wheel (or any sufficient power) as shown in Figs. 1 and 2, where M is the band, and N the large rigger fixed upon the vertical shaft 0, the bevel pinion of which at P takes into the teeth of a large horse wheel, not shown in the drawings because it does not constitute any part of the invention. By this mode of working any required number of machines can be placed round the horse-wheel, and be worked at the same time. The external bars of the stirrers I I come very nearly in contact with the sides, and their extremities very near to the flat bottom of the tub, so as to insure the agitation of the whole quantity of material that may be mixed with the water, and prevent, as far as possible, the deposit of any part of the same, either on the bottom, or on the sides of the tub ; and for the due adjustment of the ends of the stirrers to the bottom of the tub, the horizontal cross-frame D D is movable np and down in long morticed grooves, made for that purpose at Q Q, near the tops of the two standards C C, (as dis tinctly seen in Fs,. 1, 2, and 6,) and is fixed at the required height by means of the iron screw-bolts R It, which pass into any of the series of holes made in the side of the standards, Fig:. 3 and 5. A temporary elevation of the agitator may, at times, be necessary in first setting the machine to work, if the powdered ore or sand put into the water is of such a dense or heavy nature as to prevent the agitator from moving ; while, by lifting it in the first instance, and then set ting it in motion, and afterwards lowering it gently while in motion, it will gradually lay hold of the materials, and soon put them into a whirling motion. In the underneath Rg. 4, a perspective figure is given of the agitator, detached from the other parts of the machine ; and for the purpose of so detaching it, the cross-frame D D, together with its brass boxes, are made to take asunder longitudinally, as seen in Figs. 1 and 2, but are bolted together whilst the machine is in use. S is a cook, or spigot and faucet for drawing off the water from the tub whenever it may be necessary ; in addition to this, the centre of the bottom of the tub is furnished with a peculiar valve, the use and construction of which forms one of the leading features of this invention. This valve admits of different constructions, as will appear when its use has been described. One form of it is shown in section at Fig. 3, and another form at Fig. 5. In Fig. 3 c c is a brass or other metal cylin der, which must be bored in its inside like a pump barrel, in order that the piston d, which is packed with hemp, leather, or other fit material, may move in a water-tight manner within it ; ef is an iron lever, turning on the fulcrum/ for the purpose of moving the piston with which it is connected by the rod g; and h is at iron loop or guide, which not only causes the lever e, to move up and down without external action, but alsotea and restrains its quantity of motion, which is necessary, because when the e of the lever is drawn up to its highest possible elevation, the piston d should be at the top of the barrel c c, with its convex upper surface just projecting into the tub, as shown by the curved dotted line ; and when the end e of the lever is at its greatest depression, the piston must be at the bottom of the said barrel, but must never move out of it ; and when the said piston is in its lowest situa tion, as shown in the figure, its upper surface must be just below a row of large holes, which are formed round the said barrel as at f f ; consequently, while the piston is in its position, any fluid that may happen to be in the tub will flow out of it, through these holes, into a shallow tub E, placed underneath to receive it; but if the piston is raised rather more than its own thickness, it will cover all the said hole ff, and prevent the discharge of anything from the tub, although it will leave all the upper part of the barrel c c open, as a well or receptacle to receive anything that may fall into it; and this well, or receptacle, may, in a moment, be annihilated by pushing the piston upwards.
The other form of the valve, shown in Fig. 5, is similarly placed in the centre of the bottom of the tub, and for the same purpose, though rather more simple in its construction. It consists merely of a conical brass or other metal stopper, turned and ground, or packed so as to fit tightly into the hole of the metal plate t t, which is let into the bottom of the tub : this stopper is moved, as in the former valve, by the iron or metal lever e f, and attached to the plug or stopper by the iron rod g, so that the valve may be opened or shut at pleasure, by applying the hand to the end of the lever. It will be observed in all the above figures, and particularly in the perspective view of the agitator at Fig. 4, that there are no stirrers I I I in the centre of the agitator, but that a certain space, fully equal to the size of the central valve, is left free for them, not only for the purpose of permitting the valve to rise between the stirrers, but also to prevent the same degree of motion being given to the central part of the con tents of the tub, that is given to the sides of it. Having so far described the general form and construction of the apparatus, we shall next proceed to describe the manner of using it, for the purpose of extracting the gold, silver, or other metals or materials, from the sand, earth, or other matrices with which they may happen to be mixed. For this purpose the tub A A must be about half filled with water, or, what is better, may communicate by a pipe, shoot, or trough, with water, which can at pleasure be permitted to run into the tub, or may be stopped ; the cock 3 and central valve being of course closed at this time. The ore and matrice, or other material to be operated upon, reduced to a state of powder, must now be thrown in, in such quantity that it will not exceed in weight more than about half the weight of the water in the tub at any one time ; but a greater or less quantity may be added, according to its density, which will be easily ascertained by practice. The agitator is then to be put into motion, beginning slowly at first, but quickening it until the whole quantity of water, and the materials that have been thrown into it, are put into rapid motion, and the whole of the ore, or other material, however heavy, has become completely incorporated with, and floats in, the water. It will soon be found, that the water, by its centrifugal force, will rise against the sides of the tub, and leave a hollow space in the middle of it, in the form of an inverted cone, as shown by the dotted lines k k k k, in the section of lig. 3. This effect takes place to such an extent (if the height of the tub and the size of the agitator are properly proportioned to one another, and the motion is sufficiently rapid), that the central valve at the bottom of the tub can be distinctly seen from above, and may even be opened without danger of discharging much of the water ; and if, after continuing this rapid motion for two or three minutes, it is gradually abated, and the agitator is brought to a state of rest, it will be found that all the gold or silver, or other metals, so mixed with the water, will be deposited in a heap in the centre of the tub, immediately over the central valve, with very little admixture of the sand or earth that was previously mixed with it; and, consequently, if the piston d of the tub-valve in /rig. 3 is lowered, so as to form the chamber or cavity, at the same time that the motion of the agitator is slackened, such heavy material will be deposited in the said chamber or cavity, and may be drawn off with a little of the sand, earth, and water accompanying it, into the receiving tube E, by lowering the said piston below the holes described at fff in the figure; but if the discharge should be followed by too much sand, earth, and water, it may instantly be stopped by raising the piston above the holes. Should the ore or other material not be sufficiently heavy to deposit itself in the centre of the tub, then the stopper valve, shown in Fig. 5, is to be used in preference, which is not to be opened until the fluid in the tub has been moved for a minute, and the central hollow cone is formed in the middle, when the stopper may be raised, and the speed of the agitator diminished, until the water begins to flow gently from the valve, when, in running, it will bring the ore, or other heavy materials with it, and must be permitted to run so long as this is the case; the valve is then to be closed, and the agitator again put into rapid motion ; after which the valve is to be again opened, and so in succession, until the whole of the ore, or other heavy mate rial, is obtained, which will be known by its ceasing to run from the lower cen tral valve, when the remaining refuse is to be drawn off by opening the valve and spigot S, having previously placed another tub, called the waste-tub, under the machine for the purpose of receiving it; and while so running off, the agitator must be kept in motion to stir it up and wash out the contents of the tub. When empty, the waste-tub, with its contents, must be removed, and the tub A A must be supplied with a fresh quantity of water and ore, or other heavy material, to resume the operation.