92 



DRESSING OF ORES 



Tho work of one pulveriser is said to be equal to that of 24 Cornish heads of stamps, 

 and the saving in working cost, in favour of tho former, one-third loss, the wear and 

 tear in both cases being considered equal. 



669 



The first cost of 24 heads of stamps is about 200^., of the pulveriser 1501. The 

 grinding surfaces of the pulveriser lose 3 cwts. per month, whilst the stamps are said 

 to lose 20 cwts. in the same time. At a comparative trial made at Wheal Jane, 

 in Cornwall, on tin ' rows,' the cost of pulverising was Is. \d. per ton ; of stamping, 

 2s. l%d. per ton. 



Arrastre or TaJiona. This machine is extensively employed in tho mining districts 

 of Mexico, for grinding silver ores previous to their amalgamation. 



It consists of a strong wooden axle A (fig. 670), moving on a spindle in a beam s 

 above it, and resting on an iron pivot beneath, turning in an iron bearing, which is 

 inserted into a post of wood c, which rises about a foot above tho ground in tho centre 

 of the arrastre. The shaft A is crossed at right angles by two stout spars D D, which 

 form four arms, each about 5 feet long, one excopted, which is 9 feet long, to admit of 

 two mules being attached to it; by this arm the machine is worked. Tho grinding is 

 performed by four large porphyritic or basaltic stones, two of which are shown, E B. 

 These are loosely attached by thongs of leather, or small sized rope, to tho four .-inns, 

 'and are dragged over the ore, which is put in with water, until it is ground to a 

 very fine slime or mud, called tho lama. One of these machines, when in good working 

 condition, will grind from 600 to 800 pounds weight of ore in twenty-four hours. In 

 Guanaxuato, where the best and finest grinding is obtained in tin; arrastres. the lining 

 or foundation and the grinding stones are, of coars.-rrraiiird porphyry, and forma 

 rough surface. The cost of this apparatus in Mexico, including tho paving of the 

 bottom, and the four mrtapilcs or stones, is on an aver.ipe, 11. The original weight of 

 a metapile is about 700 pounds, its dimensions aro 2 feet 8 inches long, IS inches 

 broad* and 18 inches deep. Notwithstanding tho hardness of tho stones employed, 



