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THE MINING AND MILLING PEACTICE.
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mill have been tried, but were found impracticable, the variable hardness of the ore (only a small proportion being hard quartz and rock) making hand-feeding imperative.
The battery which is almost universally in use is that of the Hall type, invented and patented by Mr. Frank "\V. Hall, of Dahlonega. The usual weight of the stamp is 450 pounds. Figs. 16 and 17 give the two vertical sections of this mill. It represents novel features both in the battery and in the setting. The long battery blocks and a bed-rock foundation have been entirely dispensed with. The mill can be set upon any level piece of ground, a 2-inch plank platform forming practically the only foundation. The plan of construction (well shown in the drawing) makes the frame self-contained, the blow of the stamp and the reaction being absorbed and neutralized in the setting. Elasticity is maintained by the guy-rods. A suspended platform gives access to the props, cams, etc. The mortar is held in place by a rib on the bottom fitted in a corresponding gain in the mortar block. It is held down on the latter by wedges driven against blocks bolted on the inside of the battery posts. The small inside dimensions of the mortar are still more narrowed down by chilled-iron liners, which reach to within an inch of the dies. The main purpose of these liners is to bring the ore, on being fed, immediately under the shoes. They also protect the mortar against wear, and help to some extent in collecting and secreting amalgam. Quicksilver is fed to the batteries, and in some cases a considerable amount of amalgam collected is obtained from the mortars. The liners are fitted with dovetails and lugs at" the end, and are finally held in place by two large keys driven against the screen frame, which is shod with wear iron on each side. On removing the front liner the mortar is opened to the floor. The dies, which sit in -§-inch depressions, are easily withdrawn, the back and side liners drop out, and the mortar can be cleaned in a few minutes. The whole clean up in a 10-stamp mill is accomplished in the space of half an hour. The front liner determines the height of discharge, which, when the dies are new, is about 2 inches. An annealed copper plate, 1 feet long and of the full width of the mortar, is in most cases considered sufficient for the outside amalgamation. The weight of the 450-pound stamp-mill is divided as follows:
Pounds.
Stem or spindle ............................................. 175
Head of boss................................................ 150
Tappet with keys........................................... 50
Shoe .....................................-................. 73
Total weight of stamp................................... 450
Die ......................................................... 50
Mortar .....................................................2100
Jjiners for same ............................................ 240
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