48 A TREATISE ON DREDGES AND DREDGING 



but in very seamy soil this quantity was greatly reduced, being 

 at times not more than 10 ft. per 10-hour shift. Eight Ingersoll- 

 Sergeant and two Sullivan drills having 5J in. cylinders \\ere used for 

 this work. Each drill was mounted on wooden blocking bolted to 

 two lines of sills bedded in the bottom of the pit. An extension 

 clinch was used to facilitate the handling of the drill steel, by giving 

 plenty of clearance between the drill and the face of the rock 

 ledge. 



The long lift holes were charged with dynamite. At first the 

 sticks of dynamite w r ere inclosed in tin tubes, but owing to the 

 tendency of these tin tubes to catch on irregularities in the sides 

 of the hole it was decided to use only plain paraffined paper cartridges. 

 These dynamite sticks were 24 to 30 in. long and made in four sizes 

 to fit the taper of the drill hole, 2J, 3, 3J- and 4 in. in diameter. 

 About 38 tons of dynamite was used for charging 203 lift holes, and 

 it was furnished by the National Powder Co. of New York. Nearly 

 half of the quantity had 60 per cent of nitroglycerine and the balance 

 75 per cent. Since it was expected that some of the dynamite would 

 be under water three weeks before the firing of the blast, the manu- 

 facturers wrapped each stick with two layers of paraffin paper and 

 aftcrw r ard coated the sticks with a paraffin composition. 



Nine hundred electric exploders were used, especially constructed 

 for subaqueous work by the Star Electric Fuse Works of Wilkes- 

 Barre, Pa. To fire the exploders there were used 110 volts and 75 

 amperes, the 900 exploders being divided into 45 groups of 20 each. 

 The 20 exploders were joined together in series. Each of these 45 

 groups was joined parallel to the main wires. By this method of 

 wiring every exploder received 1J amperes. 



The firing station was located 1000 ft. away from the nearest 

 point of the coffer-dam, in which a breach was made at low tide, 

 in order to flood the pit and thus secure a water tamping, as well 

 as cushion to take up the shock of the explosion. Even at high 

 tide there were a few parts of the rock ledge visible. The blast 

 was fired at 4.10 P.M. Sections of the coffer-dam fell in the water 

 at a distance that appeared to be nearly 800 ft. away from their 

 original position. A huge column of water, timber and rock rose 

 to a height of perhaps 150 ft. and at the same time a sort of tidal 

 wave rushed across the narrow 800-ft. channel to a height of several 

 feet. The shock was scarcely felt by those at any considerable 

 distance, for the explosive appeared to have expended nearly all 



