170 Copper Mines of Lake Superior. (April, 
_ box divided into two compartments, each of which is in 
communication with an adjacent compartment in which the 
sieve is fixed and into which the copper that passes through 
the sieve falls. The pistons of the two hutches are pressed 
down by a single rock shaft, and each piston is lifted back 
into position by a spring—a desirable motion—as the down- 
stroke is thus sharp and rapid, and the up-stroke slower. 
But the hutch is open to the objection that, as each piston 
covers only half the corresponding sieve, a wave is propa- 
gated from one end of the sieve to the other, which inter- 
feres with the regular subsidence of the ore. As the ore is 
imperfeCtly sized, some collects in the sieve and is removed - 
from time to time, but most falls into the bottom, whence it 
is carried away by the flow of water. 
The hutches are arranged, with a view to saving labour, 
in tiers one below the other, so that the scimpings from one 
flow into a hutch on a tier below, and the concentrate is 
re-concentrated in like manner. Water being the carrier, 
no handling, or very little, is required from the time the ore 
is thrown into the stamps till it is shovelled from the 
receiving tank as 80 to go per cent copper. 
One of the most perfect mills on the lake shore is that of 
the old South Pewabic mine—now the Atlantic. In it, the 
stuff crushed by Ball’s stamps is concentrated by 112 
hutches arranged in seven tiers. There, also, the rotating 
German buddle is found to save the copper from the slimes 
effectually and cheaply. In the Quincy Mill, the old- 
fashioned percussion-table takes out the coarse slimes, and 
tributers re-treat the refuse from the whole mill in a sepa- 
rate building with English buddles. The coarse concentrate 
generally runs to nearly go per cent of copper, the fine, 
which cannot be separated, without repeated washing, from 
the iron—which we have seen is a constituent of the trap 
matrix—sometimes stands as low as 50 per cent; but all 
the mills aim at delivering an average of 80 per cent to the 
smelting works. 
Side by side with the Quincy Mill is the Pewabic Mill, in 
which Ball’s stamps are used. A comparison of the tailings 
from the two mills, made by Mr. Macfarlane, is interesting. 
He found— 
Quincy MILL. Pewasic MILL. 
Scimpings from coarse 0°06 per cent. From head of run. . 4°93 per cent. 
rageing . ... « » middleof run. 3°00 ra 
Scimpings from fine ar 4 endiof rn) #2 3S 0a eee 
ragging . . a iS. » heap outside of | 0.66 
Buddle tailings. . . 046  ,, run-house. od 
5). “Gand bank ) 7.” aioo as 
. 7% 
