DRESSING OF ORES 



153 



756 



inclination are given to the table by altering the levers H H. For he purpose of 

 quickening or decreasing the action of the table two cones are employed L i/, upon 

 which the driving band is shifted as may bo 

 necessary. A band from a runner, fitted on 

 the axis of the cone i,, communicates motion 

 to a pulley wheel M, upon the shaft of which 

 are cranks attached to connecting rods o, 

 giving motion to the table. 



When the machine is in operation, the ore 

 flows over at F, into the launder baneath it, 

 whilst the waste is carried over the opposite 

 end into the trough E. 



Professor B. Silliman and Mr. J. D. 

 Whitney give the following particulars of 

 results results realised by this machine : 



The total ' weight of ore stuff dressed 

 during 122 days was 11,948,900 Ibs. of rock 

 stamped and crushed, or 5,080 tons miners' 

 weight. 



The total ore sold from this quantity of 

 stuff was 128 gross tons (2,352 Ibs.), or 

 2^ per cent, of the stuff worked over. By 

 the Captain's vans the average richness of 

 the stamp work (forming much the larger part 

 of what goes to the separators) for 22 weeks 

 was 2-32 per cent. The humid assay of the 

 average work from the stamps for five weeks 

 in July and August gave for the richness 

 of the stuff dressed on the separators 3'28 

 per cent, of ore, or 0'984 per cent, of 

 metallic copper. There is, therefore, an 

 apparent loss in the tailings of ^ per cent, 

 of 30 per cent, ore, or ^ of copper. The 

 amount of ore, however, lost in the tailings 

 does not exceed ^ to ^ per cent., or about 

 ^ per cent, of copper. The actual products 

 of working, therefore, as may be seen, exceed 

 for the machines the average richness of the 

 Captain's vans. 



Of the total ore produced in this time,/ 



181,126 Ibs. came from the separators. 



and 160,858 Ibs. from the jiggers. The whole amount of stuff, therefore, required 

 to produced this amount of ore, estimated from the above ratio (T15 : 1) is 

 768,680 Ibs. This may be taken approximately as the actual quantity which passed 

 over the separators, and if calculated on the Captain's vans, it should have produced 

 177,961 Ibs. of ore, while in fact it did produce 181,126 Ibs., or a variation in excess 

 for the machines of only 3,210 Ibs. Each of the separators, therefore, dresses about 

 14 ton of rock daily, of stuff yielding an average of 2'5 per cent, of 30 per cent. 

 ore. 



Dolly Tub or Packing Kieve. This apparatus is employed for the purpose of exclud- 

 ing fine refuse from slime ore, which has been rendered nearly pure by previous 

 mechanical treatment. In using it the workmen proceed thus : 



The kieve fig. 757, is filled to a certain height with water, and the dolly A intro- 

 duced. A couple of men then take hold of the handle B. and turning it rapidly, cause 

 the water to assume a circular motion. The tossing is then commenced by shovelling 

 in the slime until the water is rendered somewhat thick. After continuing the stirring 

 for a short period, the hasps E E are loosed, and the bar D with the dolly are suddenly 

 withdrawn. The tub is then packed by striking its outside with heavy wooden mallets. 

 When this operation is terminated, the water is drawn off through plug-holes in the 

 side of the tub. 



The object of the rotatory motion created by the dolly is to scour off clayey or 

 other matter adhering to the ore, whilst the packing hastens the subsidence of 

 the denser portions. In one portion of this kind four distinct strata may be procured, 

 as indicated by the lines a b, c d, efg t h c Jc, in fig. 758. 



The upper portion, viz., from A to B, will probably have to be set aside for further 

 washing, whilst the slime c should be fit for market. The conical nucleus in the 

 centre of the tub generally consists of coarse sand, and is usually further enriched on 



