e kind, and are most conveniently arranged in a chest, which may be
attached in any accessible position to the side of the hot well. There are
two nozzles upon this chest, of which the lower one leads to the pump, and
the upper one to the boiler. The pipe leading to the pump is a suction pipe
when the plunger ascends, and a forcing pipe when the plunger descends. The
plunger in ascending draws the water out of the hot well through the lowest
of the valves, and in descending forces it through the centre valve into
the space above it, which communicates with the feed pipe. Should the feed
cock be shut so as to prevent any feed water from passing through it, the
water will raise the topmost valve, which is loaded to a pressure
considerably above the pressure of the steam, and escape into the hot well.
This arrangement is neater and less expensive than that of having a
separate loaded valve on the feed pipe with an overflow through the ship's
side, as is the more usual practice.

470. _Q._--Will you describe what precautions are to be observed in the
construction of the cocks used in engines?

_A._--All the cocks about an engine should be provided with bottoms and
stuffing boxes, and reliance should never be placed upon a single bolt
passing through a bottom washer for keeping the plug in its place, in the
case of any cock communicating with the boiler; for a great strain is
thrown upon that bolt if the pressure of the steam be high, and if the plug
be made with much taper; and should the bolt break, or the threads strip,
the plug will fly out, and persons standing near may be scalded to death.
In large cocks, it appears the preferable plan to cast the bottoms in; and
the metal of which all the cocks about a marine engine are made, should be
of the same quality as that used in the composition of the brasses, and
should be without lead, or other deteriorating material. In some cases the
bottoms of cocks are burnt in with hard solder, but this method cannot be
depended upon, as the solder is softened and wasted away by the hot salt
water, and in time the bottom leaks, or is forced out. The stuffing box of
cocks should be made of adequate depth, and the gland should be secured by
means of four strong copper bolts. The taper of blow-off cocks is an
important element in their construction; as, if the taper be too great, the
plugs will have a continual tendency to rise, which, if the packing be
slack, will enable grit to get betwe