If the whole contents
of the seal cannot conveniently be run into an open vessel in which the
mixing can be performed, the sealing water must be drawn off a little at a
time and a corresponding quantity of the protective reagent added to it.
Care must be taken also that motives of economy do not lead to excessive
dilution of the reagent; the seal must be competent to remain liquid under
the prolonged influence of the most severe frost ever known to occur in the
neighbourhood where the plant is situated. If the holder is placed out of
doors in an exposed spot where heavy rains may fall on the top of the
bell, or where snow may collect there and melt, the water is apt to run
down into the seal, diluting the upper layers until they lose the frost-
resisting power they originally had. This danger may be prevented by
erecting a sloping roof over the bell crown, or by stirring up the seal
and adding more preservative whenever it has been diluted with rain
water. Quite small holders would probably always be placed inside the
generator-house, where their seals may be protected by the same means as
are applied to the generator itself. It need hardly be said that all
remarks about the dangers incidental to the freezing of holder seals and
the methods for obviating them refer equally to every item in the
acetylene plant which contains water or is fitted with a water-sealed
cover; only the water which is actually used for decomposing the calcium
carbide cannot be protected from frost by the addition of calcium
chloride or glycerin--that water must be kept from falling to its natural
freezing-point.
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