TEEATMENT OF THE COMSTOCK OEES. 229 



motion, avoiding thereby the loss of fine particles of amalgam or quick- 

 silver. 



The method of withdrawing the fluid amalgam or quicksilver from the 

 vessel has already been indicated, and an ordinary contrivance for this purpose 

 is shown in the figures on Plate XVII. Different makers vary this plan in 

 some of the details. In some separators the groove or canal for the collection 

 of the quicksilver is circular, concentric with the pan-bottom, and usually 

 placed midway between the circumference of the bottom and the base 

 of the central cone. The outlet-pipe for the discharge of the quicksilver 

 and amalgam is connected with the bottom of this groove, leading out under" 

 the vessel to a point beyond the circumference, where it may terminate in a bowl 

 or may turn upward and be fitted with a vertical pipe in which the outlet may 

 be fixed at any desired height and the quicksilver allowed to discharge itself con- 

 tinuously as fast as it accumulates in the groove or receptacle in the pan-bot- 

 tom. A cock or plug at the lowest point of the discharge-pipe permits the 

 whole of the quicksilver to be withdrawn when desired. 



Agitators — The agitators, see Plate XXIII, through which the pulp 

 passes after leaving the separators are, in general, wooden tubs, that vary 

 in size from 6 to 12 feet in diameter and 2 to 6 feet in depth. The main 

 object in letting the stream of pulp pass through them is to retain and 

 collect as much as possible of the quicksilver and amalgam and heavy par- 

 ticles of undecomposed ore that are carried out with the pulp discharged 

 from the separator. A simple stirring apparatus somewhat resembling 

 that of the separator keeps the material in a state of gentle agitation, the 

 revolving shaft carrying four arms to which a number of staves are attached. 

 In some mills there are several agitators, in most cases only one, and by 

 some they are not used at all. The stuff" that accumulates on the bottom 

 is shoveled out from time to time, usually at intervals of three or four days 

 and worked over in pans. Beyond these are a number of contrivances for 

 concentrating the most valuable portions of the tailings. Among them are 

 blanket sluices and other variously devised machines, some of which will 

 receive further description in a following section when tailings and sluices 

 will be more particularly noticed. 



General Arrangement of Mills. — The general arrangement of the 



