Compressed Air Work And Diving 1909
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CHAPTER VI.
Pneumatic Cylinders and Caissons (continued\*
Compressed air was first usecl for engineering purposes
in this country during the construction of Rochester
Bridge in the year 1851.+ A little before this Dr Potts
had usecl the vacuum process for sinking cylinders and
had also used caissons open to the air which did not
keep the water out. Lord Dundonald had also taken
out several patents for the use of compressed air for
other purposes.
The bridge consisted of three large openings spanned
by cast-iron segmental girders and one opening spån.
The central opening was 170 ft. wide, and the other
two spåns each 140 ft. wide. The river piers were
1,118 sq. ft. in area, and were each supported upon
fourteen cast-iron cylinders 7 ft. in diameter.
The vacuum process was first triecl, and by this
methocl ahout 500 tons were sunk, when it was found
thcit the bottom was of Kentish ragstone, and therefore
this method was unsuitable. Sir Charles Fox, who
was in charge of the construction, then decicled to use
compressed air, and personally made the drawings of
* This chapter was originally written for the Engineer, and has appearcd
in its columns. The author is indebtcd to the Editor for permission to
reproclucc here.
f Proc. Inst. C. E., vols. x. and xxvii