Pipe-moulding
See CAST-IRON PIPES.
Piston-blowers are machines which force the blast with every alternate motion of the piston. See BLOWER.
Pit is a general foundry term for all holes dug in the floor in which to form moulds in green-sand, or close together and cast such as are formed in dry sand or loam. In the former instance the hole is dug, the pattern inserted, and the sand rammed therein, as described at "Bedding In" (q.v.), while in the latter it may be required only to lower the mould down to a suitable depth for casting (see DRY-SAND MOULDING); or, as in the case of a loam-mould, it may be necessary both for closing, and binding the walls sufficient to resist the pressure of the molten iron within by ramming sand firmly in the space betwixt the pit-sides and the mould. See LOAM-MOULDING; CURB; RAMMING. Pitch is the black residue remaining after distilling wood-tar. Charcoal is made by covering piles of wood to partially exclude the air; this is fired, and the volatile constituents of the wood gradually distil off, leaving the charcoal. If it is desired to produce tar, the resinous woods are employed, and the pit-bottom is made concave. During combustion, the liquid products are separated, collect at the bottom, and flow out through a trough into a reservoir. They consist of tar, acetic acid, and oil of turpentine. When the tar is distilled, essence of turpentine is separated, and what remains is pitch. See TAR.