333W / _d^2_ - 4.54_w_(H - _h_) /
H_d^2_
It follows that _p_ varies with the position of the bell, that is to
say, with the extent to which it is filled with gas. It will be well to
consider how great this variation is in the case of a typical acetylene
holder, as, if the variation should be considerable, provision must be
made, by the employment of a governor on the outlet main or otherwise, to
prevent its effects being felt at the burners.
Now, according to the rules of the "Acetylen-Verein" (_cf._ Chapter
IV.), the bells of holders above 53 cubic feet in capacity should have
sides 1.5 mm. thick, and crowns 0.5 mm. thicker. Hence for a holder from
150 to 160 cubic feet capacity, supposing it to be 4 feet in diameter and
about 12 feet high, the weight of the sides (say of steel No. 16 S.W.G. =
2.66 lb. per square foot) will be not less than 12 x 4pi x 2.66 = 401 lb.
The weight of the crown (say of steel No. 14 S.W.G. = 3.33 lb. per square
foot) will be not less than about 12.7 x 3.33 = about 42 lb. Hence the
total weight of holder = 401 + 42 = 443 lb. Then if the holder is full,
_h_ is very nearly equal to H, and _p_ = (35.333 x 443) / 48^2
= 6.
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