Bulletin . ected directly with the mainshaft. The ore hoppers haye a capacity of 100 to 500 tons each,although at some mines the capacity of the mill hopper is morethan 500 tons in order to hold ore enough to supply the mill duringan extra shift. If hoisting is done from more than one shaft, theore is trammed to the mill hopper oyer inclined or horizontal tram-ways, or, where the distance is too great, by aerial tramways orsurface motor haulage. The capacity of the surface tram cars is1 to 3 tons. POWER. Electricity, natural gas, coal, and oil are all used in the districtas sources of power. N
Bulletin . ected directly with the mainshaft. The ore hoppers haye a capacity of 100 to 500 tons each,although at some mines the capacity of the mill hopper is morethan 500 tons in order to hold ore enough to supply the mill duringan extra shift. If hoisting is done from more than one shaft, theore is trammed to the mill hopper oyer inclined or horizontal tram-ways, or, where the distance is too great, by aerial tramways orsurface motor haulage. The capacity of the surface tram cars is1 to 3 tons. POWER. Electricity, natural gas, coal, and oil are all used in the districtas sources of power. Natural gas seems to be most fayored, owingto its cheapness; coal and oil the least. Howeyer, during the wintermonths when the gas pressure becomes low, coal is used to a largeextent. At many of the properties the miU is driyen by electricmotors or gas engines and the hoisting and compressor engines aredriyen by steam, whereas at others electric power is used throughout. BUREAU OF MINES BULLETIN 164 PLATE XI. A. FOREPOLING IN SOFT GROUND.
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