of wooden strips or steel wedges driven between them after they are set in position. The shell linings are so arranged that they form a series of ridges which have a slightly spiral course in such a direction as to feed the ore and crushing balls towards the feed end of the cylinder. The material to be crushed is fed into one end of the apparatus through the hollow trunnion and crowds its way to the other end, where the discharge takes place through another hollow trunnion. The rate of discharge is governed by the rate of feeding, on account of the fact that the ore naturally tends to move towards the feeding end, and travels in the opposite direction only when forced to do so. The balls which accomplish the crushing are about 2 inches in diameter, are made of chilled white iron, and weigh approximately 2 pounds each. It requires about three tons of these balls. to each crushing barrel, and in order to make up for wear, it is necessary to occasionally charge new balls in with the ore. The feed end of the machine is provided with spiral arms which prevent any material inside from backing out through this end. A series of experiments to test some of these machines gave the following results: The material fed to the crusher consisted of 60 per cent. ore broken to screen four mesh; 30 per cent. to eight mesh; and 10 per cent. finer than eight mesh. The product from the barrel which passed through 100-mesh screen amounted to thirty tons in twenty-four hours. In pulverizing ore this fine, about 50 per cent. of it was reduced as fine as 150 mesh, and the remaining 50 per cent. varied between 150 mesh and 100 mesh. The wear and tear on the balls amounted to only three pounds per ton of material pulverized. The crushing was done wet and the wear on the balls made up by charging new balls into the machine without stopping. The speed of the pulverizing barrel was from 12 to 15 revolutions per minute, requiring about 17 H. P.

One great advantage that this style of pulverizer has over other crushing machines is that no sizing or screening is necessary. The material fed to the crushing barrel is passed through finishing rolls first and discharged sufficiently

uniform in size for its desired purpose. When crushing wet in the above experiments, from five to seven gallons of water per minute were required for each barrel. The crushing may be accomplished dry, and when this is the case, the wear on the balls is increased.

In the illustration the discharge arrangement has been removed from the front end of the machine and a portion of the casing broken away to show the inside of the barrel.

55. Globe Mill.-The mill shown in Fig. 48 differs essentially from those described, as only one ball b is employed

FIG. 48

The

to do the crushing, and the cylinder a is stationary. ball moves about in the cylinder, motion being imparted to it by the frictional contact of two steel disks c fastened to the main shaft g, and flaring slightly away from each other, but pressing lightly against the ball. The machine revolves

at the rate of about 300 revolutions per minute, giving the ball in a 5-foot mill a velocity of about 75 feet per second, so that after it once gets well in motion, very little friction from the disks is necessary to keep it going, and the wear on the disks is, consequently, surprisingly small. The ore is fed into the machine by an automatic feeder at the top and falls into the grooved path of the ball b, which is pressed strongly outwards by the centrifugal force due to its rapid motion. The crushing action occurs along the whole path of the ball, as its rapid motion draws the ore around with it. The mill is adapted for either wet or dry crushing. The pulp is discharged through screens in the ends of the drum, against sheet-iron splash plates, whence it falls into the discharge boxes. The wet-crushing mill can be fitted with inside amalgamated plates if desired, and the coarser gold saved inside the mill.

AUTOMATIC ORE FEEDERS

56. Objects Attained.-Automatic feeders for stamp batteries have almost universally replaced hand feeding. When running with a uniform ore, automatic feeders, once carefully adjusted, will work day in and day out with very

FIG. 49

little attendance, giving the maximum capacity of the stamps and the minimum wear, besides saving the wages of the feeders. Modern feeders cut out a certain amount of ore at each stroke of a certain stamp and push it off into the motor, making the feed regular.

57. The Roller

Feeder. Another and more modern form of roller feeder

is shown in Fig. 49. The roller, like that in the previous machine, revolves a little with each drop of the driving stamp, and carries out with it a little ore each time. The feed from this machine is apt to be irregular, as the roller may slip without bringing out any ore, and large pieces may clog the machine.

58. Tulloch Feeder.-The Tulloch feeder, shown in Fig. 50, feeds perfectly, is cheap, light, and so very simple

in construction and operation that any blacksmith can make whatever repairs may be necessary. The feeder is of the shaking-tray type. The hopper a holds about 1,500 pounds of ore, which runs into it directly from the crusher or is dumped in from a car.

The tray b is hung from the frame timbers in such a manner that it swings forwards of its own weight until lugs beneath strike the jar rod. It is swung backwards by an arm on the rocker-shaft c, connected to the under side of the tray. The crank-arm d of the rocker-shaft is connected with the short arm of the lever e, the long arm of which is connected with the tappet rod f. This tappet rod of 1-inch

steel is opposite and parallel to the middle stamp stem and passes through a hole bored through the lower stem guides. The head of the rod, upon which is set a rubber buffer g, is struck by the stamp tappet towards the end of its fall, and pressing down the lever e, throws the tray back. Some of the ore in the tray in front of the door is pushed off, the amount corresponding to the length of the swing of the table, while the tray, falling back into position again as soon as the tappet rod is released by raising the stamp stem, carries forwards an equal amount of ore from the inside of the hopper. A spring is sometimes used at the back of the tray to assist the forward motion. The frame of the feeder is mounted on rollers, so that the machine can be readily moved about. The feed regulates itself automatically; if the bed of ore on the dies becomes too thick, the lowest position of the stamp is raised in consequence, shortening the length of the stroke of the tappet rod, and consequently diminishing the feed of the machine, until the bed has worked down again. If the bed gets too thin, on the other hand, the feed of the machine increases correspondingly.

59. Challenge Feeder.-The Challenge feeder, shown in Fig. 51, is particularly adapted for very wet and sticky ore, on account of the fact that the ore is scraped off in place of being shaken off. It is heavier and more expensive than the Tulloch and much more intricate in construction, but is very strong and durable and feeds well. The hopper feeds on to the inclined cast-iron plate or disk a, which is revolved by a bevel gear beneath, driven by a friction disk ƒ—or, in a modification of the Challenge, by a ratchetand-pawl arrangement-which is connected by a system of levers to a tappet rod, as in the Tulloch feeder, and turns a short distance with each blow on the rod. The friction disk (or pawls) and the levers and tappet rod are brought back into position after each blow by a flat steel spring s and link 7. With each partial revolution of the plate, the wing b scrapes off a little ore into the machine being fed. The highest