8G 



DRESSING OF ORES 



nearer to or separated farther from each other. To keep the rollers in contact and 

 yet allow the action to take place, a weighted lever A is placed on each side, which by 

 means of tension bars connected with one of the bearings, keep a constant pressure 

 upon the rollers. The ore to be crushed is lodged upon a floor c, and introduced into 

 a hopper D, from which it falls between the rolls ; the requisite crushing pressure being 

 attained by increasing or decreasing the weights applied to the end of the lever. The 

 crushed ore passes from between the rollers B B into the higher extremity of an in- 

 clined cylinder E, made of coarse gauze, or perforated plate, which being set in 

 motion by the same power as the rollers themselves, separates the pulverised material 

 into two classes. That portion which passes through the sieve falls into a waggon 

 placed on the floor of a house, whilst the other, which is too largo to escape through 

 the openings, is carried to the lower end of the cylinder from whence it passes into 

 an inverted bucket-wheel F, by which it is again conveyed into the hopper to bo 

 re-crushed. 



The modifications to the foregoing arrangement may be thus briefly noticed. 



In some machines the feed-hopper is made of sufficient capacity to hold from 20 to 

 25 cwts, of stuff, which is introduced by means of a tram waggon, and renders hand 

 feeding unnecessary. The shoot conveying the crushed ore to the rotating sieve, E, 

 is sometimes divided at the bottom into two parts, one to deliver rough, and the other 

 fine stuff, In connection with each division, is a cylindrical riddle revolving and 

 separating the work according to the fineness or coarseness of the mesh employed. 



A circular sieve divided midway into two parts, each of a different mesh, is in some 

 instances advantageously substituted for two sets of seives ; whilst, in other cases, 

 circular sieves are omitted, the operation of sizing being performed by fixing perforated 

 plates on the periphery of the inverted wheel. 



663 



Instead of one roll being drawn towards the other, they are frequently kept in con- 

 tact by direct pressure, which is effected as shown infgs. 663, 664, 



