Dealing first with the correction for the lifting power of
the gas, this, according to Pole, is a deduction of _h_(1 -
_d_)/828 where _d_ is the specific gravity of the gas and
_h_ the height (in inches) of the top of the gasholder above the
water level. This strictly applies only to a flat-topped bell, and hence
if the bell has a crown with a rise equal to about 1/20 of the diameter
of the bell, the value of _h_ here must be taken as equal to the
height of the top of the sides above the water-level (= _h'_), plus
the height of a cylinder having the same capacity as the crown, and the
same diameter as the bell, that is to say, _h_=_h'_ +
_d_/40 where _d_ = the diameter of the bell. The specific
gravity of commercially made acetylene being constantly very nearly 0.91,
the deduction for the lifting power of the gas becomes, for acetylene
gasholders, 0.0001086_h_ + 0.0000027_d_, where _h_ is the
height in inches of the top of the sides of the bell above the water-
level, and _d_ is the diameter of the bell. Obviously this is a
negligible quantity, and hence this correction may be disregarded for all
acetylene gasholders, whereas it is of some importance with coal-gas and
other gases of lower specific gravity.
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