Appletons' annual cyclopædia and register of important events of the year .. . GROUND-PLAN OF TUNNELS AND GALLEK1ES AT HAL-LETTS POINT. mercury. The explosive material was nitro-glycerine and the compounds of nitro-glycer-ine, except in spots where the rock was suf-ficiently laminated to require only the impracticability of heavy blasts HELL-GATE, IMPROVEMENT OF. 381 and simultaneous discharges, and of enlargingthe excavation as it advanced, the progress wasslow compared with land-tunneling. Up toJuly, 1872, the drilling was mostly done byhand. The Burleigh steam percussion-m
Appletons' annual cyclopædia and register of important events of the year .. . GROUND-PLAN OF TUNNELS AND GALLEK1ES AT HAL-LETTS POINT. mercury. The explosive material was nitro-glycerine and the compounds of nitro-glycer-ine, except in spots where the rock was suf-ficiently laminated to require only the impracticability of heavy blasts HELL-GATE, IMPROVEMENT OF. 381 and simultaneous discharges, and of enlargingthe excavation as it advanced, the progress wasslow compared with land-tunneling. Up toJuly, 1872, the drilling was mostly done byhand. The Burleigh steam percussion-mu-chine was then adopted. It proved to bemuch better than the hand-drill, even for thesmall holes required by these operations, drill-. BURLEIQH DRILL AT WORK. ing 30 feet of holes in eight hours, at a cost of 36to 37 cents per foot, including repairs, againsta cost of 95 cents per foot by the manual pro-cess. Experiments were made with the Inger-soll percussion-machine, which proved not in-ferior to the other; the diamond drill was alsoused, whicli was found to be an excellent in-strument, but useful here only for exploringthe rock ahead, the varying dip of the rockand the frequent quartz-veius rendering it in-capable for general work. The new Randdrill was employed later, with approved suc- Tho bottom was accurately surveyed in 1871,and the plans and calculations for the workwere based on as many as 16,000 sound-ings. The inclination of the tunnel was variedso as always to leave a roof of 6 to 15 feetthickness with an average of 10 feet betweenthe mine and the water. The tunnels werekept free from water by constant pumping; insome of these the floor was inclined so as toconvey off the water. The total mass of theree
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Keywords: ., bookcentury1800, bookdecade1870, bookidappletonsann, bookyear1876
