will serve, by their going through both the front and back 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 junk ring is made much the same as if no metallic packing were employed.

426. Q.—­Will you explain the mode of putting the engine into operation?