Beneath and bolted to the spider is the cone (20); under that is the water sleeve (21), which slides up and down in the water box (22). All the water which is to he used in jigging passes through these two boxes, and flowing out through the annular openings, keeps the bearings free from grit. The water, under pressure of 8 ft. head, enters through the :3-in. pipe (4/), provided with a valve (42) to regulate the quantity.
The trunnion piece (7) is kept in place by the upper and )ower collars, which are provided with set-screws. The links (5) connect the jig with the lever beam. The jig shaft passes up through the horizontal bevel-gear wheel (1) by which it is rotated ; the shaft moves freely up and down, but it is provided with splines in which fit keys attached to the gear wheel. The pinion is driven by belt from the rear driving shaft (33). The pulleys to transmit the rotary motion are conical, reversed in order to change the speed. The cam wheel (26) is provided with 6 cams, and is keyed to the shaft, which is driven by a belt 8 in. wide, passing over the 86-in. driving pulley (27). The cam wheel makes 43 revolutions per minute, 'giving about 200 jars per minute to the jig. The lever beam is set to move the jig up and clown about in., giving a slow up and a quick down motion. The jig makes seven revolutions per minute. The practice in dressing iron ores at Lyon Mountain. as described by 31r. F. S. Ruttman, Trans. Ant. Inst. Miuin,o. Engrs., vol, xvi, 609. is as follows : The crushed ore is brought from the hoppers to the jigs by chutes provided with gates at the lower end, just above the screen plates. The screens are first covered closely with pieces of heavy ore about the size of hickory-nuts : the crushed ore is then spread over this until it is level with the collar of the spider, about 2!, in. to 3 in. deep. The spring pole is connected with the lever beam by the strap, the water turned on, and the jig started.
The water flows upward through the screen plates and over the collar of the spider, carry ing the gangue to the tail race : the ore settles through the screen. is collected at the bottom of the tub, and thence raised by the elevators to bins. The rotation of the jig produces an equal distribution of the crushed ore on the screen plates, and also forces the particles to traverse a path longer than the radius of the sieve. The crushed ore is allowed to fall on the screen as near the outer periphery as possible. The jig has a capacity of treating 5 tons of ore per hour, requiring 135 gallons of water per minute, or 1,620 gallons per ton treated. One man or boy is sufficient to attend to two jigs.
The MeLanahan Improved Jig, operating on the same principle as the common Hartz jig, is a rough jig designed for dressing iron ores, They are built in sets of four, in tanks 18 ft.
long, 14 ft. wide, and 12 fL. deep. The framework of the tank extends to sufficient height to carry the sizing trommel and the elevators. the total height being 24 ft. The tank is divided into four jig compartments, besides an elevator pit at each end. The pulsating movement of the water in each jig compartment is effected by a central piston working in a cylinder. The stroke of the piston is adjusted by an eccentric, as in Hartz jigs. The trommel above the tank is divided into four sections, each being covered with a screen of the proper size to suit the ore being washed. The jigs are fed by spouts from the various sections of the trommel. The jigs discharge concentrates continuously into a launder leading to the elevator pit at one end of the tank, by which they are raised to storage bins for shipment. Tailings are conveyed to the elevator at the other end of the tank• by which they are raised and loaded into ears to be carried to the waste dump. The water in these jigs is used over and over again, with a small loss.