MAGNETIC SEPARATOUS.—The Bachanan Magnetic Separator (Fig. 12) consists of two iron rolls, journaled in two horseshoe magnets. These magnets are wound with insulated copper wire and excited by a dynamo. The direction of the winding is such that one roll is of north and the other of south polarity, thus forming a powerful magnetic field between the two. The ore is fed into hoppers above the rolls, and the stream of ore from them is regulated by hand levers. As the ore is drawn into the magnetic field between the rolls, all that is magnetic is attached to the faces of the rolls and carried around to the opposite sides, where the rolls are non-magnetic, and dropped.
The gangue being non-magnetic, falls directly between the rolls. One of the rolls is movable, so that the distance between them, and consequently the strength of the magnetite field, may be adjusted. An interesting comparison between this machine and kydraulic jigs was made at the Croton mines at Brewster, V., where the ore, a dense magnetite, was crushed by Cornish rolls so as to pass a 16-mesh screen.
Ore assaying 37•963 per cent, iron, and 29.30 per cent. silica, gave concentrates, with the Buchanan separator, assaying 64.554 per cent. iron, and 5'350 per cent. silica. A few years before the introduction of the magnetic machine, plunger jigs had been used, when the following results were obtained : Fine jigs, crude ore assayed 36•4S per cent. iron ; concentrates, 65'56 per cent. iron ; 14-31 per cent. iron. Coarse jigs, crude ore, per cent. iron ; concentrates 59.78 per cent.
Iron, and tailings, 22'16 per cent. iron.
The Ball-Norton Electro-maynetic Separator, sometimes called the " Monarch," consists of apartiallycloscdehest, having an opening at f, Fig, 13, from the feed hopper, h, through which the ore is delivered to the machine from a storage bin, provided with means for regulating the flow of ore. Other openings are provided for the dis charge, at 1„of tailings at m, of middlings ; and at c, of concentrates ; also at e for allowing free in gress of air to the chest at that point, and at 8, where a powerful exhaust fan is connected. The
openings at t and at are kept sealed against ingress of air at those points by means of hinged and weighted valves, a a, which discharge the products from the hoppers, p and k, eontinuously, and in the same proportion as received from above, when a sufficient weight has accumulated upon the inside to cause the contents of the hoppers to leak by the valves. The machine is also provided with two drums• 1 and 2, turning upon the shafts, i and/ These shafts, to gether with the magnets, a and b, which they also serve to support, stand still, while the drums may be rapidly revolved around the magnets and out of contact therewith. It will be noticed that the magnet occupies a sector of the drum. the proportions being such that, approximately, one.third of the periphery of the drum is within the influence of the magnetic field, while the upper two-thirds is outside of the field and removed from the magnetic influ ence. The magnet is so constructed as to present a series of poles of alternately opposite polarity near the inner surface of the drum. In accordance with the well-known phenomena of magnetic attraction, which in the case of powerful magnets is exerted at a considerable distance from the magnetic poles, any magnetizable matter bronght near the outer surface of the drum. Within the are covered by the magnet, will he powerfully attracted and drawn into firm contact with the outer surface of the drum. These drums are composed of a non metallic and neutral material, such as wood, paper, etc., and they torn in the direction ineli eated by the arrows near the top of the drums. Just below the feed hopper, an apron of neutral metal, 3, is arranged, curving downward and forward in the direction of the rotation of the drum, its lower portion describing a short are concentric to the surface of the drain. This serves as a chute to direct the stream of ore falling from the feed hopper within the influence of the first two or three poles of the magnet. A similar but somewhat shorter apron, 4, is arranged in like relation to the second drain and magnet., b.