through which the hot water will ascend; and when the bucket descends to
the bottom of the pump barrel, the warm water which was below it will all
have passed above it, and cannot return. When the bucket next ascends, the
water above it, not being able to return through the bucket valve, will be
forced into the hot well through the delivery valve S. The hot water pump
M, pumps a small quantity of this hot water into the boiler, to compensate
for the abstraction of the water that has passed off in the form of steam.
The residue of the hot water runs to waste.

102. _Q._--By what expedient is the piston rod enabled to pass through the
cylinder cover without leaking steam out of the cylinder or air into it?

_A._--The hole in the cylinder lid, through which the piston rod passes, is
furnished with a recess called a stuffing box, into which a stuffing or
packing of plaited hemp is forced, which, pressing on the one side against
the interior of the stuffing box, and on the other side against the piston
rod, which is smooth and polished, prevents any leakage in this situation.
The packing of this stuffing box is forced down by a ring of metal
tightened by screws. This ring, which accurately fits the piston rod, has a
projecting flange, through which bolts pass for tightening the ring down
upon the packing; and a similar expedient is employed in nearly every case
in which packing is employed.

103. _Q._--In what way is the piston rod connected to the great beam?

_A._--The piston rod is connected to the great beam by means of two links,
one at each side of the beam shown at _f g_, (fig. 21.) These links are
usually made of the same length as the crank, and their purpose is to
enable the end of the great beam to move in the arc of a circle while the
piston rod maintains the vertical position. The point of junction,