264 



EAST RIVER BRIDGE. 



Through the roof pass the 

 water-supply and air-shafts, two 

 of each, composed of one-quar- 

 ter-inch boiler-iron, and arrang- 

 ed in pairs for convenience in 

 working, as well as to guard 

 against accidents and delays. 



Before being bolted, each tim- 

 ber in a course is forced into 

 place, both vertically and hori- 

 zontally, by heavy iron clamps or 

 dogs and wedges. The bolts and 

 clamps, acting together, make 

 the whole as near as possible 

 like one solid piece. The joints 

 of each course are filled with 

 j>itch, and the surface dressed 

 off smooth and level, and again 

 pitched and dressed before the 

 succeeding course is applied. 



The lower part of the V, 

 which by its narrow edge is to 

 aid the settling of the caisson 

 into the earth, is shod with a 

 cast-iron shoe, oval on the bot- 

 tom, 8 inches wide on the top, 

 and 2 inches through the thick- 

 est part, and cast in sections of 

 eight feet in length, bolted to 

 the bottom of the first course 

 with four drift-bolts, and pro- 

 tected and held in place by an 

 armor of boiler-iron, extending 

 vertically three feet on the out- 

 side, and also three feet up the 

 inner slope, and firmly bolted 

 through and through. The fig- 

 ure shows a section of the shoe 

 on a larger scale. The outside 

 seams and those of the thir- 

 teenth roof-course are calked 

 Avith the heaviest twelve-thread 

 calking, and the inside seams 

 well calked, but less heavily. 

 This heavy calking rendered it 

 necessary to use a large num- 

 ber of bolts to prevent the joints 

 from opening under the press- 

 ure. As a further precaution 

 against leakage, a layer of tin, 

 between two of felt, is placed 

 around the outside up to the 

 thirteenth, and over the roof, 

 between the thirteenth and four- 

 teenth courses. The sheeting 

 of tin is soldered to angle-irons 

 about the shafts placed for that 

 purpose, and on the outside is 

 covered by a sheathing of plank 

 four inches thick. To prevent 

 water from following the bolts 

 which pass through the tin and 

 felt, a rubber washer is placed 

 next the felt, which, like the 

 other washers, are by the press- 



