132 



DRESSING OF ORES 



machines are illustrated under this head, nnd many more might have boon added, it 

 does not follow that they may be advantageously employed for every variety of ore. 



Thus an apparatus which would enrich slimes by one operation from 1 J to 5 per 

 cent, might bo both economical and desirable for treating copper ore, but would not 

 be so important in the case of lead ore of the same tenure ; for after deducting the 

 loss of metal incident to the enrichment, chargiug the manipulative cost on the full 

 quantit}' of stuff, and estimating the relative value of the two products, it might be 

 found that one would scarcely leave a margin of gain, whilst the other would yield a 

 satisfactory profit. 



The proper sizing and subdivision of slime is as necessary as in the case of coarser 

 work. In some of the German mines four or five distinct classes of slime are made, 

 each class being treated on suitable enriching tables. 



Richards' Slime Separator. The water and stuff from the slime separated, is de- 

 livered through a launder into a pit, at the head of which is fixed a slightly inclined 

 plank, divided into channels by slips of wood set in a radial direction from the aper- 

 ture of the delivery launder. This pit has the form of an inverted cone, and since 

 the water passes through it at a very slow rate, the more valuable and heavier matters 

 will be deposited at the bottom. This apparatus thus becomes not only a slime pit, 

 but also a slime separator. 



The ordinary slime pit has usually vertical sides and a flat bottom ; the slime and 

 water enter it at one of its ends by a narrow channel, and leave from the other by the 



same means. 



A strong central current is thus produced through the pit, which not only carries 

 with it a portion of valuable slime, but also produces eddies and counter-currents 

 towards the sides, which have the effect of retaining matters which from their small 

 density should have been rejected. 



The improved pit, jig. 724, receives its slimes from the launder B, and lets off a 



portion of them at c, whilst the richer and heavier matters, which fall to the bot- 

 tom, escape through the launder D, regulated by means of the plug A, and screw A'. 



In many cases sand and slime stuff are much commingled with clay, and require 

 to be broken and disintegrated before the ore can be extracted. A method for accom- 

 plishing this is shown in jig. 725. A is the circumferential line of a round buddlo; 

 B, launder, leading to such buddle ; c, sifting trommel ; D, rotating paddles ; E, tor- 

 mentor ; F, driving shaft. 



A modification of this method is found in the slime trommel, fg. 726. A, hopper, 

 into which slimes are lodged; B, launder, delivering clean water into hopper A; c, 

 trommel of sheet iron, fitted in the interior with spikes for the purpose of dividing 

 the stuff; D, disc, perforated to prevent the passage of pieces of chips or bits of clay 

 and stone ; E, Archimedean pipes fitted into a disc of sheet iron, conveying water 

 into gauze or perforated trommel F; o, slime cistern; H, cistern for receiving the 

 rough stuff; j, slime outlet, communicating with round buddle, or other suitable 

 apparatus ; x, outlet for trommel raff, which may be delivered to a sizing cistern. 

 The speed of the gauze trommel for fine slimes varies from 80 to 100 feet per 

 minute. 



Hand Huddle. This apparatus (fig. 727), is somewhat extensively employed inlead- 

 Eiines for the concentration of stuff which contains but a small proportion of ore, such 



