18 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 
