lEEATMENT OF THE COMSTOCK OEES. 201 



The settler is usually placed directly in front of the pan and on a lower 

 level, so that the pan is readily discharged into it. In some mills two pans are 

 discharged into one settler, the operation of settUng occupying four hours, or 

 the time required by the pan to grind and amalgamate another charge. In 

 other mills the settling is allowed only two hours, and the two pans connected 

 with any one settler are discharged alternately. 



The consistency of the pulp in the settler is considerably diluted by the 

 water used in discharging the pan and by a further supply, which in many 

 mills is kept up during the settling operation. In other mills, however, the 

 pulp is brought from the pan into the settler with the addition of as little 

 water as possible, and allowed to settle for a time by the gentle agitation of the 

 slowly revolving muller, after which cold water is added in a constant stream. 

 The quantity of water used, affecting the consistency of the pulp, and the 

 speed of the stirring apparatus are important matters in the operation of set- 

 tling or separating. Since the object of the process is to allow the quicksilver 

 and amalgam to separate themselves from the pulp and settle to the bottom of 

 the vessel, it is desirable that the consistency should be such that the lighter 

 particles may be kept in suspension by a gentle movement, while the heavier 

 particles fall to the bottom. If the pulp be too thick the metal will remain 

 suspended ; if it be too thin the sand will settle with it. Too rapid or too 

 slow motion may produce results similar to the above-named, because by too 

 violent motion the quicksilver will not be allowed to come to rest on the bot- 

 tom, while if the motion be too slow the coarser sand will not be kept in cir- 

 culation. 



A discharge hole, near the top of the settler, permits the water carrying 

 the lighter portion of the pulp to run off, and at successive intervals the point of 

 discharge is lowered by withdrawing the plugs from a series of similar holes, 

 h, h, in the side of the settler, one below the other, so that finally the entire 

 mass is drawn off, leaving nothing in the settler but the quicksilver and 

 amalgam. There are various devices for discharging these. Usually, there 

 is a groove or canal in the bottom of the vessel, as shown in Figs. 1 and 

 2, Plate XVII, leading to a bowl, B, from which the fluid amalgam may be 

 dipped or allowed to run out by withdrawing the plug, p, from the outlet- 

 pipe. 



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