, to overcome the friction of the plug
of the water-cock in its barrel. Hence at all times the pressure
obtaining in the service-pipe is uniform, except for a slight jerk
momentarily given each time the cock is opened or closed. When _X_
actuates a carbide-feed arrangement, the work it does may or may not vary
on different occasions, as will appear hereafter. In A^2 the bell itself
carries a perforated basket of carbide, which is submerged in the water
when the bell falls, and lifted out again when it rises. As the carbide
is thus wetted from below, the lower portion of the mass soon becomes a
layer of damp slaked lime, for although the basket is raised completely
above the water-level, much liquid adheres to the spent carbide by
capillary attraction. Hence, even when the basket is out of the water,
acetylene is being produced, and it is produced in circumstances which
prevent any control over the temperature attained. The water clinging to
the lower part of the basket is vaporised by the hot, half-spent carbide,
and the steam attacks the upper part, so that polymerisation of the gas
and baking of the carbide are inevitable. In the second place, the
pressure in the service-pipe attached to A^2 depends as before upon the
net weight of the holder bell; but here that net weight is made up of the
weight of the bell itself, that of the basket, and that of the carbide it
contains.
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