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Ch. 13: Blasting Gravel Banks

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BLASTING GRAVEL BANKS.
209
end of each of these drifts two arms (right and left) or cross cuts were driven 70 feet long, thus leaving a space of 40 feet between the ends of the cross cuts from the several main drifts. The powder, in 50-pound boxes, was charged in lots of 1,000 to 1,500 pounds in the different chambers. In each chamber three exploders were placed
Fig. 60.
in the powder, each exploder being carefully connected by an insulated copper wire with the main wires on the outside of the drifts.
The drifts were all well tamped with clay and boul­ders. The wires from the exploders connected outside of the main drifts with two copper wires from an electro­magnetic battery which was situated to the right and about 200 feet from the face of the bank. When every­thing was ready (November 8, 1879) the blast was fired. The back ground was raised bodily 4 or 5 feet, and the face was thrown forward.
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