476 



HELL-GATE, IMPROVEMENTS AT. 



wires, they being held firmly in place by the 

 sulphur. The inner ends of the wires are 

 united by a small platinum wire. The ends 

 of the wires are then surrounded with fulmi- 

 nate, and the two parts of the tube are put 

 together, that containing the wires slipping 

 within the other. The entire fuse is then cov- 

 ered with gutta-percha. The passage of an 

 electric current through the wires heats the 

 platinum bridge to redness, and causes an ex- 

 plosion of the fulminate. 



The number of pounds of rack-a-rock put 

 into drill-holes was 240,399 ; of dynamite, 42,- 

 831; total, 282, 730 pounds. There were 11,789 

 drill-holes in the roof and 772 in the pillars, 

 and their total length was 113,102 feet, or 

 more than twenty miles. The whole amount 

 of rock to be broken by the final blast was 

 270,717 cubic yards, covering an area of about 

 nine acres. The primary charges, the office of 

 which was by their detonation to produce the 

 explosion of the charges in the drill-holes, were 

 placed along the galleries at intervals of 25 

 i'eet, on timbers extending from wall to wall, 

 and consisted of two 24-inch dynamite car- 

 tridges like those already described lashed to 

 the timber, with one of the " mine-exploders " 

 bound upon them. The entire mine was di- 

 vided into 24 independent circuits. Within 

 each of 21 of these circuits were 25 fuses or 

 mine-exploders, while three circuits contained 

 22 fuses each. A wire from the battery on the 

 surface of the rock at the mouth of the shaft 

 led from one fuse to the next, until the 25 

 fuses were in the same electrical circuit, and 

 thence back to the battery. So far as was prac- 

 ticable, adjacent charges were put on different 

 circuits, so that if any circuit failed through 

 fault in the connections, an explosion of its 

 charges would still be insured through the 

 sympathetic action of the adjoining charges. 

 The whole number of these primary charges 

 was 591. Some of the circuits were nearly a 

 mile long. The battery consisted of sixty cells, 

 all coupled in one series, each of which had an 

 electro-motive force of 1'95 volts and an in- 

 ternal resistance of O'Ol ohm. The plates 

 were 6 inches by 9 inches four carbon and 

 three zinc plates in each cell, separated by a 

 quarter of an inch. The ordinary bichromate 

 solution was used. The poles were constituted 

 of two large mercury cups, into one of which 

 were dipped the 24 lead wires, while the 24 

 return wires terminated in a third cup. Be- 

 tween this third cup and the remaining pole 

 of the battery stood the apparatus for closing 

 the circuit. It consisted of a stout iron cup 

 containing mercury, in which sat a thin glass 

 tumbler also partly filled with mercury. Two 

 large strips of copper connected the mercury 

 in the iron cup with one pole of the battery, 

 and that in the glass with the cup containing 

 the return wires. To close the circuit through 

 the fuses it was only necessary to break the 

 tumbler so as to let the mercury in it mix 

 with that in the iron cup. To do this at the 



proper moment, a quarter-inch iron rod four 

 feet long, terminating at the top in a small 

 round disk, stood with its point in the bot- 

 tom of the glass. It was long enough to pass 

 through the roof of the battery-house. A 30- 

 grain platinum fuse, connected with a small 

 battery at Astoria, was laid on the disk and 

 stuck on with a lump of wax. It had been 

 previously determined by experiment that the 

 blow struck by this fuse on exploding, and 

 transmitted by the iron rod, would be so sharp 

 as to pulverize the tumbler and yet not splash 

 the mercury. 



The mine was flooded by two siphons of 12 

 and 16 inches respectively, in fifteen hours and 

 a half, ending at 3.30 A.M., Oct. 10. The ex- 

 plosion was set for 11 A. M., Oct. 10, but every- 

 thing could not be made ready and tested in 

 time to fire at the appointed moment. The 

 explosion did not take place till 11.13, which 

 caused some confusion in the seismoscopic ob- 

 servations. The whole area of the reef was 

 shattered. The plan of making the excava- 

 tions large enough to swallow all the debris of 

 the reef and leave a channel deep enough, with- 

 out further operations, already abandoned at 

 Ilallet's Point as more expensive than dredging 

 up the broken rock, was never entertained at 

 Flood Rock. Though the charges all exploded 

 at the same instant, the time and the appear- 

 ance of the effect above the water-surface va- 

 ried according to the strength of the rock and 

 the depth of the water. There was no loud 

 report, and no dangerous shock. The break- 

 ing of some panes of glass and the shaking 

 down of a few bricks and loose ceilings consti- 

 tuted all the damage that was done. 



Pending the awarding of a contract for dredg- 

 ing, the work of removing the rock was begun 

 with a scow belonging to the Government, as 

 soon after the explosion as possible. From 

 15 to 30 tons of rock were hoisted out daily, 

 after being slung by divers on chains. A con- 

 tract has been let for the removal of 30,000 

 tons of the rock at $3.19 a ton, the contractor 

 to do his own surface-blasting. This is less 

 than the price for which rock was removed on 

 similar terms at Hallet's Point. The contractor 

 has two grapples at work, and is removing an 

 average of about 120 tons a day. As a whole, the 

 cost of mining a cubic yard of rock has been re- 

 duced 34 per cent, from the cost of doing the 

 same work at Hallet's Point. The total cost 

 of the work done on Flood Rock, including 

 the final blast, amounts to $2.99 a cubic yard 

 of the whole amount of rock broken, or $5.66 

 less than the cost of breaking Hallet's Point. 

 A considerable part of this gain will be ex- 

 pended on the proportionately larger amount 

 of dredging to be done. The net result, how- 

 ever, will show an improvement of not less 

 than 30 per cent. The total cost of the final 

 blast at Hallet's Point was $81,092,24; at 

 Flood Rock it was only $106,509.93, though the 

 blast was 5'6 times as large. The progress 

 with the dredging gives promise that an 18- 



