and
III. it was pointed out that after-generation only occurs when water is
brought into contact with an excess of carbide. If, then, the opposite
system of construction is adopted, and carbide is fed into water
mechanically, no after-generation can take place; and provided the make
of gas can be controlled in a small carbide-feed generator as accurately
as is possible in a small water-to-carbide generator, the carbide-feed
principle will exhibit even greater advantages in portable apparatus than
it does in plant of domestic size. Naturally almost every variety of
carbide-feeding gear, especially when small, requires or prefers
granulated (or granulated and "treated") carbide; and granulated carbide
must inevitably be considerably more expensive per unit of light evolved
than the large material, but probably in the application to which the
average portable acetylene apparatus is likely to be put, strict economy
is not of first consequence. In portable acetylene generators of the
carbide-feed type, the supply is generally governed by the movements of a
mushroom-headed or conical valve at the mouth of a conical carbide
vessel; such movements occurring in sympathy with the alterations in
level of the water in the decomposing chamber, which is essentially a
small displacement holder also, or being produced by the contraction of a
flexible chamber through which the gas passes on its way to the burner.
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