Knight's American mechanical dictionary : a description of tools, instruments, machines, processes and engineering, history of inventions, general technological vocabulary ; and digest of mechanical appliances in science and the arts . of the native metallurgistsof Asia and Africa. This was much earlier than the air-pumpsof Ctesibus, 15<J b. c. See Spiritalia Heronis. It is believed that Papins pistons were of wood, and thatCartwright was the first to use a metiiUic piston. One of Cartwrighfs valves was in the piston, and was trippedby the contact of the valve-stem with the eml of the cylin
Knight's American mechanical dictionary : a description of tools, instruments, machines, processes and engineering, history of inventions, general technological vocabulary ; and digest of mechanical appliances in science and the arts . of the native metallurgistsof Asia and Africa. This was much earlier than the air-pumpsof Ctesibus, 15<J b. c. See Spiritalia Heronis. It is believed that Papins pistons were of wood, and thatCartwright was the first to use a metiiUic piston. One of Cartwrighfs valves was in the piston, and was trippedby the contact of the valve-stem with the eml of the cylinder. James Watt found the piston imperfectly fitted in a roughlybored cylinder. The principal packing was a body of wateron the upper surface. He patented the lubricant, 1769, preferring mutton tallow,but hemp and tallow had long been used. To this he some-times added plumb:igo-dust. A common piston till a compara-tively late date was a double cone of wood banded with leatherstrips. This was superseded by a metallic piston, turned to fit neatlyin the cylinder, and having a circular plate on each .*idc clamp-ing two leathers, cupped and chamfered off to an angle of 45°. The piston for the atmospheric engine was a plate of cast-. iron, about ^ inch less in diam-eter than the cylinder, and Hinch in thickness, with a rimabout 4 inches from the this a fiat ring is fittedand the parts nre screwed to-gether, after hemp and tallowhave been inserted betweenthem to form the packing. The hemp-packed pi^^ton (n. Fig 3757) is in common use. Thebottom is accurately fitted to the cylinder, and a portion of theperiphery is cut away to admit of a gasket of nnspun hemp orsoft rope to be wound evenly around it, to form the is compressed by means of a plate and screws, so as to ex-pand it against the inside surface of the cylinder, making asteam-tight joint. The pi?;ton-rod is attached by an enlarged head, screw-nut,and key to the bottom of the cylinder, which has a centr
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