Compressed Air Work And Diving 1909
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ROCHESTER BRIDGE.
51
the apparatus to be Lised. To Sir Charles Fox, there-
fore, must be given the creclit of originating the use
of compressed air for engineering purposes, so far, at
any rate, as this country is concerned. There woulcl
appear, however, to have been some use of compressed
air in France about the same date.
The methocl acloptecl was as follows, and by its
means the remaining 1,700 tons of cast-iron cylinder
were sunk with entire success :—
A wrought-iron cover was bolted to a 9-ft. length
of cylinder, and through this cover projected by about
ci third of their length two D-shaped cast-iron chambers.
In the top of each was a circular door, 2 ft. in diameter,
opening downwards. On the flat side of each chamber
below the cover was a rectangular opening, 2 ft. by
3 ft. 4 in., by which access was obtainecl to the inside
of the cylinder. The buckets were raisecl by an ordinary
windlass fixed inside the cylinder, and a chain passing
over the sheave of a light crane allowecl the buckets to
be swung into the chamber on reaching the level of the
opening. The whole arrangement, except for the method
of hoisting the buckets, is very similar to that of the
Barmouth Lock, shown in Fig. 9. The output was
twenty-five buckets per hour, and each bucket held
2 cwt. of excavated material. On the completion of
the sinking the cylinders were filled with concrete and
brickwork.
This system was acloptecl shortly after by Mr Brunel
for the bridge over the Wye at Chepstow.* This bridge
had one spån of 300 ft., and two others of 100 ft. The
pier supporting one end of the 300-ft. spån consisted of
six cast-iron cylinders' filled with concrete, 8 ft. in
* Proc. Inst. C. E., vol. vii.