he steam
chests, connecting the several boilers together. The spindles of these
valves should project through stuffing boxes in the covers of the valve
chests, and they should be balanced by a weighted lever, and kept in
continual action by the steam. If the valves be lifted up, and be suffered
to remain up, as is the usual practice, they will become fixed by corrosion
in that position, and it will be impossible after some time to shut them on
an emergency. These valves should always be easily accessible from the
engine room; and it ought not to be necessary for the coal boxes to be
empty to gain access to them.

406. _Q._--Should each boiler have at least one safety valve for itself?

_A._--Yes; it would be quite unsafe without this provision, as the stop
valve might possibly jam. Sometimes valves jam from a distortion in the
shape of the boiler when a considerable pressure is put upon it.

407. _Q._--How is the admission of the water into the boiler regulated?

_A._--The admission of feed water into the boiler is regulated by hand by
the engineer by means of cocks, and sometimes by spindle valves raised and
lowered by a screw. Cocks appear to be the preferable expedient, as they
are less liable to accident or derangement than screw valves, and in modern
steam vessels they are generally employed.

408. _Q._--At what point of the boiler is the feed introduced?

_A._--The feed water is usually conducted from the feed cock to a point
near the bottom of the boiler by means of an internal pipe, the object of
this arrangement being to prevent the rising steam from being condensed by
the entering water. By being introduced near the bottom of the boiler, the
water comes into contact in the first place with the bottoms of the
furnaces and flues, and extracts heat from them which could not be
extracted by water of a higher temperature, whereby a saving of fuel is
accomplished. In some cases the feed water is introduced into a casing
around the chimney, from whence it descends into the boiler. This plan
appears to be an expedient one when the boiler is short of heating surface,
and more than a usual quantity of heat ascends the chimney; but in well
proportioned boilers a water casing round the chimney is superfluous. When
a water casing is used the boiler is generally fed by a head of water, the
feed water being forced up into a small tank, from whence it descends into
the boiler by the force of gravity, while the surplus run