TKEATMENT OF THE COMSTOCK OEES. 197 



ment is possible. These slimes form a variable and in some mills a large per- 

 centage of the whole amount crushed; in some instances, it is staled, more than 

 ten per cent. ; and although they have a high assay value they have not until re- 

 cently been worked successfully and with profit. When one or more of the 

 settling tanks in the mill have been filled the stream is diverted from 

 such to others that have been emptied, and the full ones are in their turn 

 cleaned out, the sand or crushed ore being then subjected to the grinding 

 and amalgamating process of the pan. 



Geinding and Amalgamation. — Pans. — The pans employed for this 

 purpose present a great variety in the details of construction. Since 

 the first "common pan," a very simple form of apparatus, came into use, 

 many inventors have exercised their ingenuity in devising improvements, 

 and at present there are several different patterns, each of which has some 

 special claim for excellence, and finds its advocates among the practical 

 mill-men of the district. A more detailed description of some of these will 

 be found further on. The common features are a round tub, see Plates XXI 

 and XXII, usually of cast-iron, but sometimes with wooden sides, 4 to 

 6 feet in diameter and about 2 feet deep, having a hollow pillar cast in the 

 center, within which is an upright shaft projecting above the top of the pillar 

 that may be set in revolution by gearing below the pan. To the top of this shaft 

 is attached, by means of a key or feather, a yoke or driver by which the muUer 

 or upper grinding surface is set in motion. To the bottom of the pan, on the 

 inside, is fixed a false bottom of iron, cast either in sections, commonly called 

 dies, or in one piece, having a diameter a little less than that of the pan, and 

 with a hole in the center adapted to the central pillar. This serves as the 

 lower grinding surface. The muller, forming the upper grinding surface, is 

 usually a circular plate of iron corresj)onding in size and form to the false bottom 

 just described, having a diameter nearly equal to that of the pan, and a flat, 

 conical, or conoidal form, according to the shape of the pan-bottom. Its un- 

 der side is furnished with shoes or facings of iron, about an inch thick, that may 

 be removed when worn down and replaced by new. The muller is attached to 

 the driver, which is put on and over the central pillar of the pan and, being 

 connected with the interior upright shaft as above described, is thus caused to 



