200 MINING INDFSTEY. 



which is generally supposed to be analogous to that produced by the same re- 

 agents in the Mexican "patio" process, is but imperfectly understood, and their 

 efficiency, at least in the manner and 'proportions in which they are at present 

 employed, may well be doubted. This is apparent from the fact that in some 

 mills both sulphate of copper and salt are used, in others only the first is 

 used without the second, and in others only the second without the first, or, if 

 at all, in proportions so minute that its efficient action is incredible; others have 

 dispensed with the use of "chemicals" altogether, and under all these varying 

 circumstances equally good results have been obtained. Some mills, accus- 

 tomed to use both salt and sulphate of copper, have dropped either one or the 

 other, while working continuously on the same kind of ore, without perceiving 

 any difference in the result ; and it is the opinion of many intelligent mill-men 

 that neither salt nor sulphate of copper, in the manner and quantity as at 

 present employed, are essential to the efficient working of the ore in pans. 

 This subject will be further discussed on a following page. 



Two hours having been devoted to the grinding, and two or three more to 

 amalgamation, the pan is discharged and its contents received by a settler or 

 separator. The discharge of the pan is usually aided by a supply of water, 

 which dilutes the pulp and permits it to run freely from the pan into the set- 

 tler. The pan being emptied and partly washed out by the stream of water, 

 is again charged with a fresli quantity of sand and the grinding operation is 

 resumed without delay. 



Settlers or Separators. — These, like the pans, differ somewhat in details 

 of construction, but they usually are round tubs of iron or of wood with cast-iron 

 bottoms, resembling the pans in general features, but larger in diameter. A 

 hollow pillar or cone, (7, Figs. 1 and 2, Plate XVII, is cast in the center of the 

 bottom, within which is an upright shaft, &. This shaft is caused to revolve 

 by gearing below the pan. To its upper end is attached a yoke or driver, i>, 

 that gives revolving motion to arms. A, extending from the center to the cir- 

 cumference of the vessel. The arms carry a number of plows, or stirrers, oi 

 various devices, usually terminating in blocks of hard wood, P, that rest lightly 

 on the bottom. No grinding is required in the operation, but a gentle stirring 

 or agitation of the pulp is desired in order to facilitate the settling of the 

 amalgam and the quicksilver. The stirring apparatus, or muller, makes about 

 fifteen revolutions per minute. 



