DRESSING OF ORES 



101 



the stuff, a piece of canvas hangs over the grate. The top of the cast-iron anvil, is 

 of the same diameter as the shoe, and is from 4 to 6 inches high ; the bottom is com- 

 monly square, large enough to extend from side to side of the battery box, the corners 

 being removed, so that it may be withdrawn by the use of a pick point. The shoe is 

 of the hardest white iron, 8 inches diameter and 6 inches high, with a shank tapering 

 from 2 to 4 inches. The shoe is attached to the head, by placing strips of pine wood, 



677 



of an inch thick and an inch wide around the shank. The strips of wood are 

 tied by means of cord, and the head lifter gently driven home, the shoe striking a piece of 

 timber until it is firmly fixed. When it is necessary to remove a shoe it is accomplished 

 by driving a key into a key-way formed in the head for this purpose. The lifter is 

 usually turned to a diameter of 3 inches, and is from 10 to 12 feet long; the head is of 

 tough cast iron, 8 inches diameter and 15 inches high. At the top is a hole, slightly 

 conical, about 7 inches deep, with a drift way for forcing the lifter from the head. 



A stout wrought-iron hoop is put on hot at the top and bottom of each head so as to 

 give it additional strength. To fix the lifter in the head a few blows of the hammer 

 are first necessary, then a few beats in the ordinary way. 



The gib tappet is 8 inches in diameter and 8 inches long, and made hollow so as to 

 receive the lifter. The" gib itself is two inches wide, nearly as long in the tappet, and 

 with its inner face curved, to correspond to the circular hole, through which the 

 lifter passes. The gib being fixed in place and the tappet put upon the lifter, is 

 forced against the latter by means of two keys which are driven to such an extent as 

 to maintain the tappet firmly in its position. This method is found to be in all re- 

 spects satisfactory, and is superior to screw threads or key seatings. A partial revo- 

 lution of the head is effected at each lift, and continues to some extent during the fall, 

 causing, as it is alleged, a grinding as well as a stamping effect, and wearing the shoe 

 more evenly than if no circular movement occurred. Guides of hard wood are pre- 

 ferred to iron. One set is placed below the tappet, about a foot above the battery box, 

 a second set within 6 inches from the top. The width of guide is from 10 to 15 inches. 

 Each cam piece has usually two arms, with faces 2 or 3 inches wide, the casting itself 

 being of tough cast iron ; the curve of the face is the involute of a circle the radius of 

 which ig equal to the distance between the centre of the cam axle and the centre of the 

 lifter. The bottom of the cam is consequently perpendicular to the radius of the curve 

 of the cam, and the gtamp-head is uniformly lifted ia a vertical line, IB practice, the 



