27. GASHOLDERS.--(_a_) Must be of sufficient capacity to contain at
least 4 cubic feet of gas per 1/2-foot burner of the rating.
This is to provide for the requisite lighting period without the
necessity of making gas at night, allowance being made for the
enlargement of burners caused by the use of cleaners.
(_b_) Must be provided with suitable guides to direct the movement
of the bell throughout its entire travel.
28. PRESSURE RELIEFS.--Must in all cases be provided, and must be so
arranged as to prevent pressure in excess of 100-tenths (10) inches water
column in the mains.
29. PRESSURES.--Gasholders must be adjusted to maintain a pressure of
approximately 25-tenths (2.5) inches water column in the mains.
CHAPTER V
THE TREATMENT OF ACETYLENE AFTER GENERATION
IMPURITIES IN CALCIUM CARBIDE.--The calcium carbide manufactured at the
present time, even when of the best quality commercially obtainable, is
by no means a chemically pure substance; it contains a large number of
foreign bodies, some of which evolve gas on treatment with water. To a
considerable extent this statement will probably always remain true in
the future; for in order to make absolutely pure carbide it would be
necessary for the manufacturer to obtain and employ perfectly pure lime,
carbon, and electrodes in an electric furnace which did not suffer attack
during the passage of a powerful current, or he would have to devise some
process for simultaneously or subsequently removing from his carbide
those impurities which were derived from his impure raw materials or from
the walls of his furnace--and either of these processes would increase
the cost of the finished article to a degree that could hardly be borne.
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