DRESSING OF ORES 137 



speed of the arms and diagonal launders must vary with the nature of the stuff to be 

 operated upon ; for rough sands eight revolutions per minute have been found sufficient, 

 but for fine slimes from fourteen to sixteen revolutions in the same time are necessary. 

 The inflow of slime and water should also be proportioned to the speed and density 

 of the stuff to be treated. No precise instructions can be offered on this head, but an 

 experienced dresser would easily determine the proportions after a few trials. The 

 bed is 18 feet diameter, and has a declination of about 6 inches from the edge to the 

 point where it unites with the horizontal portion of the floor. 

 Experiment on slime ore, very fine and much intermixed with carbonate of iron : 



Per cent. 



Produce before entering buddle . . 6 



Heads of buddle averaging 3 inches deep ^ 191. arirl ^A n? nf H'IVAT Y\AI tnn nf In 1 id 



and 22 inches wide . . . . / 

 Middles of buddle averaging If inch. ) fi , , , 



deep and 18 inches wide . . if*** 1 



Tails of buddle averaging f inch deep. 3 and 5 of oz. 



Castaways 



Time required to fill buddle, 3 hours ; number of arms in buddle, 4 ; number of 

 revolutions of arms per minute, 8. 



Experiment on fine slimes, much associated with carbonate of iron : 



Produce before entering the buddle . ... 3 per cent. 



Heads 3 inches deep, 16 inches wide . - -V . . 7 



Middles 14 do. 12 do. ,%-.. . 1 



Tails . . j , . .> . ,'y - f ./. . traces. 



Number of revolutions of arms per minute 14 ; time required to fill buddle 5 hours. 

 In working this buddle one month upon the fine and rough slimes, indicated in the 

 two foregoing experiments, the results obtained were : 



Mean 

 Assay of ptuffvbefore entering the buddle . . 5'0 per cent. 



Heads afforded 12'5 



Middles . .5*0 



Tails :-"?- r* 0-77 



Experiment on slime ore containing 7 per cent, of lead : 



In 12 hours 4 tons were washed, and gave 14 cwts. of crop, 28 cwts. middles, 

 12 cwts. tails, and 26 cwts. of waste. The 14 cwts. of crop were washed in 3 hours, 

 and afforded 3 cwts. dressed slime ore, 5 cwts. of middles, 4 cwts. of tails, and 1 cwt. 

 of castaways. The middles resulting from both operations, viz. 33 cwts. were washed 

 in 8 hours, and gave crop 4 cwts., middles 12 cwts., tails 4 cwts. and waste 13 cwts. 

 The tails were now washed in 3 hours, and afforded 4 cwts. of middles and 12 cwts. 

 of castaways. 16 cwts. of middles were also washed in 3 hours, and furnished 2 cwts. 

 crop, 6 cwts. middles, and 8 cwts. of castaways. In addition, 10 cwts. of crop ore were 

 washed during 3 hours, and gave 1^ cwt. of slime ore, crop 1 cwt., middles, 6 cwt., 

 castaways 1 cwt. 



The results, therefore, show that 4 tons of rough slimes were washed in 32 hours, 

 and afforded 5J cwts. slime ore at 43 per cent., leaving 1 cwt. of crop at 31 per cent., 

 and 12 cwts. of middles yielding 4^ per cent. A comparison was also made with the 

 shaking table ; 5 tons of the same slimes were washed in 48 hours, and gave 7 cwts. 

 of dressed ore, 1 cwt. of heads, and 8 cwts. of middles. 



The Table at top of following page shows the results of an experiment made between 

 the concave buddle and the ordinary round buddle ; time occupied, 24 hours. 



The tails lying upon the horizontal part of the concave buddle contained 27i per 

 cent, of zinc and 2 per cent, of lead. 



It will be perceived that the much larger crop from the concave buddle was more 

 than twice as rich for lead, whilst it was only 2 per cent, richer for zinc. 



Quartzose ore without blende was then tried, and a similar weight gave 1,570 Ibs. 

 of crop, affording 56^ per cent, or S88 Ibs. of lead, and 3,450 Ibs. of middles of 

 H per cent, produce, equal to 483 Ibs. of lead, or together 5,020 Ibs. of stuff con- 

 taining 1,372 Ibs. of lead. The round buddle. on the contrary, gave 455 Ibs. of crop 

 ore, of 6H per cent., equal to 290 Ibs. of lead, 2,900 pounds of middles, of 18 per 

 cent., representing 541 Ibs. of lead, or a total of 3,365 Ibs. of stuff, containing 831 Ibs. 

 of lead. 



Fig, 733 represents a buddle arranged for the treatment of fine slimes. It is entirely 

 constructed of metal, and every part is carefully fitted in order to secure an even and 

 delicate action. The stuff is introduced into the hopper A, from whence it passes into 



