18. GASHOLDERS.--(_a_) Must be constructed of galvanised iron or
steel not less than No. 24 U.S. Standard gauge in thickness for
capacities up to and including 20 gallons, not less than No. 22 U.S.
Standard gauge for capacities between 20 and 75 gallons, and not less
than No. 20 U.S. Standard gauge for capacities in excess of 75 gallons.
Gas-bells, if used, may be two gauges lighter than holders.
Condensation chambers, if placed under holders, to be of same gauge as
holders.
(_b_) Must be of sufficient capacity to contain all gas generated
after all lights have been extinguished.
If the holder is too small and blows off frequently after the lights are
extinguished there is a waste of gas. This may suggest improper working
of the apparatus and encourage tampering.
(_c_) Must, when constructed on the gasometer principle, be so
arranged that when the gas-bell is filled to its maximum with gas at
normal pressure its lip or lower edge will extend at least 9 inches below
the inner water-level.
(_d_) Must, when constructed on the gasometer principle, have the
dimensions of the tank portion so related to those of the bell that a
pressure of at least 11 inches will be necessary before gas can be forced
from the holder.
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