Pullback to Pyroxylin

Pullback to Pulsating current

proof; or a proof of a form on a hand press.

Pullback. (Plast.) Device to bring the press platen to the open po­sition by the operation of hydrau­lic cylinders; also used to operate ejection devices. SEE PuSHBACK.

Pull broach. (Mach.) A tool for cut­ting internal grooves or finishing holes of some shape, usually other than round, by being pulled through the work. SEE BROACH.

Puller. (Auto.) Any mechanical or hydraulic device for removing, by pulling action, parts which are tightly fitted; e.g.. wheel puller or gear puller.

Polley. (Mech. Engin.) A wheel used to transmit or receive power through a belt which travels over its face.

Pulley block. (Mech.) A sheave pul­ley or series of such pulleys, en­closed betwen metal or wooden side plates which carry the shaft or pin on which the pulleys re­volve.

Pulley lathe. (Mach.) A lathe used for turning either a straight crowned face on pulleys.

Pulley stile. (Arch.) The venical sides of a double-hung window frame, on which are fastened the pulleys for the sash weights.

Pulley tap. (Mach.) A tap with a very long shank, used for tapping set-screw holes in the hubs of pul­leys.

Pull-out. (Aero.) The maneuver of transition from a dive to horizon­tal flight. (Print.) Anything pulled out from a form by the suction of the rollers of a press.

Pull pin. (Mach.) A device for throw­ing mechanical parts in or out of gear, or for shifting in or away from a fixed relative position.

Pull-up. (Aero.) A maneuver, in the vertical plane, in which the air­plane is forced into a short climb, usually from approximately level flight.

Pulp. (Paper) A mixture, as of wood fibers or rags, reduced to a soft, wet .nassand forming the basis from which paper is made.

Pulpboard. (Papermkg.) A crude board made of mixed paper stock, mechanical wood pulp, or a mix­ture of such materials.

Pulping. (Papermkg.) The manufac­turing process for transforming pulpwood, rags, or other raw ma­terial, into a pulp for papermak­ing.

Pulpit. (Arch.) A raised platform, with enclosed front, for a preacher in a church.Pulsating current. (Elec.) A direct current whose value is not cons­ Push button to Pyroxylin same operations as a "pull broach" but is pushed through the work. SEE BROACH.

Push button. (Elec.) A device which completes an electric circuit as long as a smalI button or knob is depressed.

Push-button drive. (Aulo. Mech.) A system of gear shift control oper­ated manually or electrically by a set of push buttons mounted as a unit on the instrument panel.

Push-button starter. (Aulo.) A start­ing system in which the starting motor circuit is closed by a push button instead of a foot switch.

Push-button switch. (Elec.) A switch in which the electrical contacts are closed by pushing one button and are 'opened by pushing an other.

Push-down. (Aero.) The opposite of pull-up.

Pusher airplane. (Aero.) An airplane with the propeller or propellers aft of the main supporting sur­faces.

Pusher propeller. (Aero.) A propel­ler mounted to the rear of the engine or on the rear end of the propeller shaft.

Push rods. (Auto.) In overhead-valve engines, the rods between the outer end of the'rocker arms and the cam followers.

Putlog. (Masonry) A crosspiece in a scaffolding, one end of which rests in a hole in the wall.

Putty. (Chern. and Bldg.) A composi­tion of whiting and linseed bil, used for filling small holes in woodwork, and securing panes of glass in sash. Puzzolan or slag cement. Cement made of volcanic ash or from blast furance slag. It is slow-setting and slow-hardening, and not as strong as natural Portland cement. It is not extensively used.

Pyramid. (Malh.) A figure' having for its base a plane polygon, and for its sides several traingles with a common vertex.
Pyridine. (Chern.) A nitrogenous base (CsHsN) obtained as a yel­ low oil from the dry distillation of bones, It is used in denaturing alcohol.

Pyrite. (Chern.) A naturally occur­ring sulphide of iron, FcSz, brass yellow in color. Also known as fool's gold or sulphur diamonds.

Pyrographing. The producing of a design, as on leather or wood, by means of a red-hot needle or fine flame.

Pyrolusite. (Metal.) An important manganese ore of iron-black color found in many countries. Besides being a source of metal manga­nese, it has use in electric batter­ies and as a paint dryer. Pyrometer {Mech. Engin.) An in­strument for measuring very high degrees of heat, as in furnaces.

Pyroxylin (Chern.) A solution of ni­trocellulose in ether, ethyl acetate, and amyl acetate. Used in the manufacture of photographic films, celluloid, rayon, etc. It is inflammable and explosive.