From the foregoing description of this machine in its most simple state, it will appear, that a much less proportionate quantity of motion takes place near the centre of the agitator, than near its outside, particularly when the machine is made on a large scale, on which account it is necessary, in large machines, to construct a double agitator, that is to say, one in which the central part turns or moves with greater velocity than the external part, as shown in section at Fig. 5, where IIIIFF show the agitator constructed as before, except that its arms and stirrers are more extended from the centre, so as to make room for the smaller Antral agitator i i i i which may be constructed in the same way as before described, or may have its stirrers fixed into the circular block of wood or metal jj, and the iron axes, instead of being fixed into the central block G, now passes through it, and is fixed to the small or internal agitator. For this purpose, the central block G of the agitator should be lined with a brass box, or have proper bearings upon its ends, so that it may revolve freely upon the iron spindle H ; it has also a bearing at n, in the lower part of the cross frame D D, to assist in supporting it ; and on account of the greater weight that now hangs on the said iron spindle H, two friction wheels are fixed to its upper end, as at o o, which run upon the top of the brass bearing p, and materially dimi nish the friction. When the double agitator is used, two riggers will be neces sary, as at L and W, and the one at W, which communicates with the large external agitator, is made double the diameter of the smaller one L, which is fixed upon the iron axle H, in order that the small internal agitator may move with double the velocity of the large external one. In every other respect, this machine is the same as the one already described. Fig. 6, is an elevation of a machine, with a double agitator introduced, merely to show how such a machine, on a small scale, may be moved by hand. land w are the two riggers of the internal and external agitators, as in the last figure, and motion is communi sated to them by the bands in 1101, which pass round the two riggers v and a, both of the same diameter, and both fixed upon the upright iron shaft rr, which also carries the bevelled wheel y, which is driven by the larger wheel hung upon the main shaft, which also carries a heavy fly wheel a a, and the winch or handle by which the whole is turned. The timber framing t t, for carrying the said wheel and riggers, is too obvious to need description, and may be varied in form, to suit the convenience of the place in which the machinery is fixed ; and when a horse is adopted for machinery of magnitude, it is almost needless to observe, that it must take into, and drive the wheel y, which for this purpose may be fixed higher on its shaft, when the wheel y, with its fly wheel, shaft, and handle, will be unnecessary. In the use of this machine, it is vain to expect to get the ore or other heavy material, separated from the sand, earth, or other material, with which it may be mixed, in a clean and perfect state, by one operation as hereinbefore described, because a considerable portion of sand and earth will inevitably run off with it in the water. The mode proposed by the patentee therefore is, to save all the first portions that run off from the central valve at the first washing, in a tub or otber receptacle by themselves; and when a sufficient quantity is thus accumulated, it is to be again put into a machine, which may be smaller for this purpose, and it is to be treated precisely in the same manner as the crude materials iu the first instance, when it will be further cleansed and purified ; but if not in a sufficiently clean state after this second washing, it must undergo a third, or even fourth, in the same or smaller hand machines, according to the purity required ; which by due and attentive care to the directions herein given, and a little practice, may be carried into any extent required. It is also necessary to observe that the operation of washing and separating ores, or other heavy materials, by the machinery before described, may be effected, (though in a less convenient manner,) without the adoption of either of the bottom central valves, or any valves at all; because such heavy materials, if not permitted to escape by the valves, will accumulate in a heap in the centre of the tub, and will be found upon carefully removing the sand, earth, or matrice from around about it ; or another process may be used, such as the apparatus delineated in the subjoined Fig. 7, is adapted for.
In this case a shallow tub is set within a deeper and larger one T, either with or without the blocks ll to raise it above the bottom of the exterior tub ; or the inner tub may be fixed in a running stream, or a stream may be made to run continually into and out of it. When the apparatus is arranged in this form, the revolving motion of the agitator F F I I will 'have the effect of throwing most cf the water that is introduced with the ore into the shallow tub, over its edges into the external tub, or into the running stream, (as the case may be,) or into a reservoir; and with it nearly all the sand, earth, or matrice will be thrown over, so as to leave the ore, or other heavy material, in a nearly clean state at the bottom of the tub, particularly if a sufficient quantity of water has been used during the process.
The whole agitator is now to be removed, for taking out the clean ore, and when an accumulation of refuse has taken place in the outer tub, (if such a oqe be used,) the inner one is to be removed, and the agitator lowered into the other large tub for stirring up the said refuse and water, while it is drawn off by the plug, or spigot and fauset at S; after which such refuse and water are to be again passed through a machine by way of examination, to ascertain if any ore, &c. had passed over with it ; and if so, it will be obtained at this
second washing. The refuse and water might be led over coarse flannel or cloth, in which the heavy material would deposit itself, if there be any left in the refuse. It may likewise happen in some cases, that the ore, or other heavy substances, cannot be conveniently broken down and reduced to powder, but may contain diamonds, precious stones, lumps, or fragments which would be too large and heavy to be put into motion with the water, as before described; whenever this is the case, the construction of the agitator, shown in Fig. 7, is recommended, which in effect is the same as those already described ; but instead of intersecting the arms F F,which carry the stirrers 1III into the central block of wood already described, a circular kind of funnel or hopper is constructed as shown in section at gggg, of iron, and the spindle revolves into transverse pieces In m within the said hopper ; such pieces being placed with their thinnest dimensions upwards, so as to cause as little obstruction as possible. This hop per is to be fed with ore (previously broken into small pieces), by means of the shoot n n, which may be shook by joggles at r, like a cornmill, or be fed by any other convenient method. Fig. 7 also shows another form of the agitator : double set of arms to carry the stirrers, is not essential ; all that is necessary is, that it should possess sufficient strength and substance to put the whole of the water and heavy materials mixed therewith, into a sufficiently rapid motion, to produce the conical hollow space similar to k k k, Fig. 3, as before described.
In addition to the several modes of working the apparatus explained, it is proposed to work the same in streams, or ponds, where gold-dust, ores, &c. may be found, or suspected to exist, without using a tub, in which case the agitator only is to be used, and must be supported, as before, by its cross-bearers D D, and standards C C. Figs. 1, 2, 3, 5, 6, being either fixed to the bottom of a boat or punt, or supported between two boats or punts, the same being immovably moored or fixed upon the water ; or the machinery may be placed upon a stage with legs, adjustable to the depth of the water, so that the agitator may be put into rapid circular motion as before described ; or as near as pos sible to the bottom of such river or stream, when it will soon, by such motion, remove the soil (provided it is not too hard or strong), and will form itself into a circular hollow space equal to its own diameter, into which space it is to be gradually lowered as the earth is washed away ; when, if any gold-dust, ore, or heavy metals are present, they will be brought to the centre thereof as effec tually as if the first agitator had been worked in a tub ; which done, the posi tion of the central spindle of the agitator is to be worked as accurately as possible, either upon the stage that supports it, or by placing upright straight rods in the ground round about it, when a light metal tube, of tinned or plate iron, open at both ends, and of equal diameter to about one-fourth of the agitator that has been used, is to be lowered over the said central spot, for the purpose of confining and covering whatever may have been so brought to the centre, which may then be raised in the tube, by inserting a pump therein till it reaches the sand ; and after having made with it a partial vacuum by raising this pump, the whole tube is brought out with it ; or by means of proper ladles, augers, screw-worms, or other implements used for boring the earth, and bring ing up the same through tubes for well-sinking, and other well-known pur poses; or the implement shown at Fig. 8 may be used to advantage. It consists of an hexagonal, or other polygonal pipe of iron made nearly to fit and fill up the inside of the light pipe before mentioned (directed to be lowered for covering and securing the materials) ; its lower end is to be formed into as many points as the first polygonal has sides, as at aaa a in Fig. A ; these points should be of steel, not only for durability, but that they may bend inwards and spring open again in the form shown at X, in which state the pipe is to be lowered into the tube above mentioned, and it must he pushed through the soil, or whatever the agitator may have brought to the centre, by slackening and turning it round ; while, at the same time, the central chain which communicates by branch chains with each of the first points, as seen at Y, is to be strained with suffi cient force, either by the lever Z or in any other way, to bring all the first points a a a, &c. together, in which state they will be retained, until the contents thus confined to the pipe are brought up out of the water, and discharged on the boat or platform.
Having now described a variety of processes for obtaining the ores of copper, lead, tin, gold, silver, and some other metals, we will refer the reader to the article COAL, (VOL I. pp. 374 and 375,) where a sectional engraving of a coal mine and iron mine is given, with an accurate description of the mode of work ing the same. It is au astonishing and highly interesting sight to a stranger in the neighbourhood of Birmingham, and in other coal and iron districts, to behold, at one view, a great number of steam engines, with all their massive machinery and apparatus, simultaneously at work in the open air; some employed in drawing up the iron ore, others coal ; which, as they emerge from the earth, are sometimes lifted upon an elevated rail-road, from whence, by their own gravity, or by the aid of machinery, they are conveyed with rapidity to their destination; the contents are instantly discharged, and the emptied skip brought back in continuous succession.