DRESSING OF ORES 



89 



it, and moved by ine teeth of a wheel. The shoe is so regulated, that too much 

 ore can never fall upon the cylinders and obstruct their movement. A small stream 

 of -water is likewise let into the shoe, which spreads over the cylinders, and prevents 

 them from getting hot. The ore, after passing between the fluted rollers, falls upon 

 the inclined planes N N, jig. 666, which turn it over to one or other of the pairs of 

 smooth rolls. 



These, the essential parts of this machine, are made of iron, and the smooth 

 rolls are case-hardened, or chilled, by being cast in iron moulds. The gudgeons 

 of both kinds move in brass bushes fixed upon iron supports k, made fast by 

 bolts to the strong wood-work basis of the whole machine. Each of the horizontal 

 bars has an oblong slot, at one of whose ends is solidly fixed one of the plummer- 

 blocks or bearers of one of the cylinders /, and in the rest of the slot the plummer- 

 block of the other cylinder g slides : a construction which permits the two cylinders 

 to come into contact, or to recede to such a distance from each other as circumstances 

 may require. The moveable cylinder is approximated to the fixed ones by means of 

 the iron levers x x, which carry at their ends the weights P, and rest upon wedges M, 

 which may be slidden upon the inclined plane N. These wedges then press the iron 

 bar o, and make it approach the moveable cylinder by advancing the plummer-block 

 which supports its axis. When matters are so arranged, should a very large or hard 

 piece present itself to one of the pairs of cylinders, one of the rollers would move 

 away, and let the piece pass without doing injury to the mechanism. 



Besides the three pairs of cylinders which constitute essentially each crushing 

 machine, there is sometimes a fourth, which serves to crush the ore when not in large 

 fragments, for example, the chats and cuttings (the moderately rich and poorer pieces), 

 produced by the first sifting with the brake sieve. The cylinders composing that 

 accessory piece, which, on account of their ordinary use, are called chats-rollers, 

 are smooth, and similar to the rollers z z and z' z'. One of them is usually placed 

 upon the prolongation of the shaft of the water-wheel, of the side opposite to the 

 principal machine ; and the other, which is placed alongside, receives its motion from 

 the first, by means of spun wheel-work. 



The general arrangement of a portable crushing mill may be gathered immfig. 667. 

 The rollers A A are kept in close contact by means of the spring arrangement B B. 



667 



The spring itself is formed of discs of India-rubber alternating with discs of iron, 

 both encircling an iron bar passing through and held firmly by the lug c. The stuff 

 is thrown into the hopper D, and on motion being given to the rollers the inclined 

 shoot E receives a percussive action by means of a horizontal lever or pallet 

 attached to the shoot, and moved by one of the two cog wheels fixed on the ends 

 of the rollers. The angle of the shoot is varied by lowering or raising the hook F, 



