7854)
cubic inches, and its weight will be (at 62 deg. F.):
(0.7854_pd^2_ x 0.03604) = 0.028302_pd^2_ lb.
Consequently a bell which is _d_ inches in diameter, and gives a
pressure of _p_ inches of water, will weigh 0.028302_pd^2_ lb.
Or, if W = the weight of the bell in lb., the pressure thrown by it will
be W/0.028302_d^2_ or 35.333W/_d^2_. This is the fundamental
formula, which is sometimes given as _p_ = 550W/_d^2_, in which
W = the weight of the bell in tons, and _d_ the diameter in feet.
This value of _p_, however, is actually higher than the holder would
give in practice. Reductions have to be made for two influences, viz.,
the lifting power of the contained gas, which is lighter than air, and
the diminution in the effective weight of so much of the bell as is
immersed in water. The effect of these influences was studied by Pole,
who in 1839 drew up some rules for calculating the pressure thrown by a
gasholder of given dimensions and weight. These rules form the basis of
the formula which is commonly used in the coal-gas industry, and they may
be applied, _mutatis mutandis_, to acetylene holders. The
corrections for both the influences mentioned vary with the height at
which the top of the gasholder bell stands above the level of the water
in the tank.
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