If the carbide charged into a hand-fed
generator is in very large lumps there is always a possibility that
overheating may occur in the centre of the masses, due to the baking of
the exterior, even if the generator is fitted with a reaction grid.
Manifestly, when carbide in lumps of reasonable size is dropped into
excess of water which is not merely a thick viscid cream of lime, the
temperature cannot possibly exceed the boiling-point--_i.e._, 100 deg.
C.--provided always the natural convection currents of the water are
properly made use of.
The defect which is, or rather which may be, characteristic of a hand-fed
carbide-to-water generator is a deficiency of gas yield due to
solubility. At atmospheric temperatures and pressure 10 volumes of water
dissolve 11 volumes of acetylene, and were the whole of the water in a
large generator run to waste often, a sensible loss of gas would ensue.
If the carbide falls nearly to the bottom of the water column, the rising
gas is forced to bubble through practically the whole of the liquid, so
that every opportunity is given it to dissolve in the manner indicated
till the liquid is completely saturated. The loss, however, is not nearly
so serious as is sometimes alleged, because (1) the water becomes heated
and so loses much of its solvent power; and (2) the generator is worked
intermittently, with sufficiently long intervals to allow the spent lime
to settle into a thick cream, and only that thick cream is run off, which
represents but a small proportion of the total water present.
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