196 MINING INDUSTEY. 



The stamps vary in weight from 500 to 1,000 pounds; they are lifted and 

 drop about 8 or 9 inches, making from seventy to ninety blovrs per minute; they 

 are arranged in batteries, which consist, each, of one mortar with usually four 

 or five stamps. Wet crushing is always employed for these ores ; that is, a 

 stream of water is admitted to the mortar with the ore, and, flowing off, carries 

 with it the pulverized ore as soon as the latter is sufficiently reduced in size 

 to pass through the screens placed in front of the discharging apertures of the 

 mortar. 



The screens through which the crushed material is discharged from the 

 mortar are either of brass wire-cloth, having 35 or 40 meshes to the lineal 

 inch, or more frequently of Russia sheet-iron, perforated with fine holes. 

 Screens of the latter sort, in general use, are known as Nos. 5 or 6. In the 

 last named the hole has a diameter of -^ of an inch. 



In former years the amalgamation of the precious metals of the ore with 

 quicksilver was carried on in the mortar, a supply of quicksilver for that pur- 

 pose being introduced with the rock into the mortar. This feature of the proc- 

 ess has, however, now been given up in the mills of the Washoe district. 

 The stufi" being discharged from the battery is conveyed in troughs by means 

 of the flowing water to settling tanks, of which there is a series placed in front 

 of the batteries. These tanks are usually built of plank, are 3 or 4 feet deep 

 by 5 or 6 or more feet square, and are so arranged as to have communication 

 with each other near the top, so that the stream of water carrying the crushed 

 ore in suspension, having filled one tank may pass into the next, and so on 

 through several, depositing the material and not finally leaving the tanks un- 

 til it has become tolerably clear. The number of tanks must be sufficient to 

 allow of a certain portion being emptied while others are receiving their sup- 

 ply, and the conveying troughs are provided with gates so an^anged that the 

 stream can be admitted to one portion of the tanks and shut off from the other 

 at pleasure. The stream, having deposited in these tanks the bulk of the ma- 

 terial, is still charged with slimes, or rock reduced to an impalpably fine con- 

 dition, which is only settled by a slow process. For this purpose the stream 

 is sometimes permitted to pass through other large settling tanks, or to slowly 

 deposit its charge in a pond or dam outside the mill, where such an arrange- 



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