ack walls, to bind the house more firmly together. The spring beams or
iron bars fastened to them must reach quite through the back wall, and be
keyed or screwed up tight; and they must be firmly fastened to the lever
wall on each side, either by iron bars, firm pieces of wood, or long strong
stones, reaching far back into the wall. They must also be bedded solidly,
and the residue of the opening must be built up in the firmest manner.

424. _Q._--If there be a deficiency of water for the purpose of
condensation, what course should be pursued?

_A._--If there be no water in the neighborhood that can be employed for the
purpose of condensation, it will be necessary to make a pond, dug in the
earth, for the reception of the water delivered by the air pump, to the end
that it may be cooled and used again for the engine. The pond may be three
or four feet deep, and lined with turf, puddled, or otherwise made water
tight. Throwing up the water into the air in the form of a jet to cool it,
has been found detrimental; as the water is then charged with air which
vitiates the vacuum.

425. _Q._--How is the piston of a pumping engine packed?

_A._--To pack the piston, take sixty common-sized white or untarred
rope-yarns, and with them plait a gasket or flat rope as close and firm as
possible, tapering for eighteen inches at each end, and long enough to go
round the piston, and overlapped for that length; coil this rope the thin
way as hard as possible, and beat it with a sledge hammer until its breadth
answers the place; put it in and beat it down with a wooden drift and a
hand mallet, pour some melted tallow all around, then pack in a layer of
white oakum half an inch thick, so that the whole packing may have the
depth of five to six inches, depending on the size of the engine; finally,
screw down the junk ring. The packing should be beat solid, but not too
hard, otherwise it will create so great a friction as to prevent the easy
going of the engine. Abundance of tallow should be allowed, especially at
first; the quantity required will be less as the cylinder grows smooth. In
some of the more modern pumping engines, the piston is provided with
metallic packing, consisting for the most part of a single ring with a
tongue piece to break the joint, and packed behind with hemp. The upper
edge of the metallic ring is sharpened away from the inside so as to permit
more conveniently the application of hemp packing behind it; and the j