1 8 ECONOMIC GEOLOGY. 



On one side of each cylinder, half way between the ends, is a large opening called a 

 manhole; on the other side, opposite, is a large faucet. By an ingenious contrivance, 

 the manhole can be closed with absolute tightness. Inside, upon the axis of each cyl- 

 inder, is a voltaic pile. Below the vent of the tank is a circular cistern, five feet in 

 diameter and one foot six inches high, called a dolly or agitating tub. An upright 

 shaft, standing on the centre of the bottom of this tub, is made slowly to revolve. 

 From a horizontal cross-piece placed on this shaft, a little above the level of the top of 

 the tub, iron teeth one foot six inches long descend. On the side of this tub opposite 

 the vent of the tank are four holes, one above the other, through which fluid may pass 

 into an amalgamated copper vessel, in shape an inverted hollow truncated cone. In 

 the centre of this copper vessel, called a washer, is a hollow sphere pierced with small 

 holes. In this sphere terminates a water-pipe connected with a reservoir above, and 

 provided with a stopcock to regulate the flow and pressure of the water. Below this 

 washer is another, smaller, but in every respect similar in shape and arrangement. 

 Such is the amalgamating machinery. The amalgamation is effected as follows : From 

 the car above the machinery the pulverized ore is, by a shute, emptied into one of the 

 cylinders through the manhole. Water is then introduced till the cylinder is two thirds 

 full. Any necessary chemicals, and from fifty to one hundred pounds of quicksilver, 

 according to the richness of the ore, are added at the same time. The manhole is then 

 closed so tight that nothing can escape ; and the cylinder is revolved from three to four 

 hours. Then the faucet is opened, and ninety to ninety-five per cent, of the quicksilver 

 runs out into a vessel ready to receive it. Another vessel is substituted for this, and 

 receives a large portion of the amalgam. The remaining contents of the cylinder are 

 then allowed to flow out into the tank, and are washed down into the dolly-tub, where 

 they are constantly agitated by the teeth on the cross-piece before mentioned. From 

 this tub they pass into the washers, in which the jets of water from the holes in the 

 hollow sphere keep the mass constantly in movement, so that any amalgam quicksilver 

 or gold which shall have escaped from the cylinder and the dolly-tub sinks to the bot- 

 tom of the first, or, at any rate, of the second washer. 



The Dodge shaft was sunk 17 feet in 1867; and the rock taken from 

 it yielded $6.25 per ton in the mill. After that, the whole vein on both 

 sides was excavated for a length of several rods to the same depth, the 

 rock yielding only ^3 or ^4 per ton. After the return to sinking the 

 original shaft, $10 per ton was obtained immediately; and the yield for 

 about two years subsequently was nearly the same, averaging $14, and 

 in one instance reaching ^19. The shaft had been excavated to a depth 

 of about 70 feet in 1869; and there are drifts at about 60 feet depth in 

 both directions, particularly to the east. The vein is 16 feet wide here. 

 The rock from this depth seems to have been most productive. It is 



