USING GUKPOWDER. 



657 



The uext plan was proposed by a French engineer, M. Maillefert, 

 who had used it with great success in the harbor of Nassau 

 This plan was entirely new, and had the great merit of being 

 surprisingly cheap compared with those then in use. It dis- 

 pensed with the costly and difficult process of drilling, but ex- 

 ploded the charges on the surface of the rocks to be removed, 

 while they were covered with the greatest depth of water. 

 Gunpowder burnt in the open air explodes without anything 

 but a harmless Hash. The pressure of the atmosphere is not 

 enough to restrain the dispersion of the gases suddenly gener- 

 ated. Under water, though, it is different ; its pressure con- 

 fines the erases and makes them act with destructive effect on 

 all sides. For a couple of years operations were carried on by 

 M. Maillefert with considerable success. But he was ham- 

 pered by want of means, the money that was spent being 

 raised by private subscriptions; and though the channel -was 

 greatly improved, operations were suspended. It was found, 

 too, that this method was of great service in breaking off iso- 

 lated pinnacles of jagged rock, but when the bed was reached 

 and the rock reduced to a large, smooth, flat surface, progress 

 in the work became slow, doubtful and costly. This process, 

 however, of exploding charges of gunpowder, under water, by 

 means of an electric battery is very valuable in certain situa- 

 tions. 



In 1868 Congress appropriated $85,000 for the needs ot 

 Hell Gate, and bids for the work were opened to the public. 

 The contract was awarded to Mr. S. F. Shelbourne, of New 

 York, who proposed to do the work by drilling and blasting, 

 the machinery to be placed on the bottom and worked by a 

 steam pump placed on a vessel, above. The rock was to be 

 drilled by mushroom drill, as it was called, a diamond drill 

 worked by a small turbine wheel, driven by steam. This drill 

 was tried on the Frying Pan, one of the worst rocks obstruct- 

 ing the channel, but was found to be too delicate and uncertain 

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