PNEUMATIC DISPATCH. 139 PNEUMATIC TOOLS. lustration. In the sending apparatus two sec- tions of the tube are supported in a swinging frame so that either can be brought into line with the main tube, through which there is a constant current of air. After a carrier has been placed in an iron trough it passes into an open tube section and is then swung into position so that it is in line with the main tube and the carrier is swept along by the pressure. The ear- 6iS ^ q K x ~N l~^ ~-^, --^ ^i-J >--- / ^^ E3 SESDUiG APPAKATU^. riers usually have a headway of from five to fifteen seconds each, and may be dispatched auto- matically. There are various forms of receivers, the use of which depends upon various conditions of atmospheric pressure. The action of the re- ceiving apparatus is automatic, and as soon as a carrier arrives in the receiving chamber the latter is tilted and the carrier is discharged and the receiving chamber returned to its normal horizontal position. Automatic apparatus is also employed at the intermediate stations and the carriers designed for a particular station are turned aside from the main line tube. The use of pneumatic apparatus is constantly increas- ing and there are cities in the United States in which it is being installed for the transmission of small packages. to discharge a quantity of high explosive. The most successful pneumatic gun, the invention of Capt. E. L. Zalinski, U.S.A., is designed to dis- charge projectiles loaded with a high explosive, such as dj-namite, the shock of the discharge be- ing kept low by the use of air. Pneumatic guns have not been taken up by governments, because it is felt that the problem of projecting a mass containing high explosives is not thoroughly solved by such means. See AlE Gux; Obd- >"AXCE. PNEUMATICS. The branch of mechanics which treats of the properties of gases, either at rest or flowing, and of solids immersed in gases. See Gases, General Peopebtie.s of. PNEUMATIC TOOLS. The name given to a class of portable, self-contained-motor tools ( generally hand tools ) , for metal and wood work- ing, operated by compressed air. Pneumatic tools are of two types, viz. percussion tools and ro- tary tools. In the first type work is done by rapidly repeated percussive blows and in the sec- ond type by a rotary or boring action. The motive power used in both is air under pressure, and the motor is contained within the tool. The variety of purposes to which pneumatic tools are put is very great ; a recent authority has stated that there are between 70 and 80 dillferent styles of such tools in use and that new appli- ances are being constantly discovered. Some of the general mechanical operations to which such tools are applied are hammering, ramming, calking, chipping, riveting, shaving, drilling, boring, screwing, clipping, carving, and ex- panding tubes. As w-ill be seen, these operations are nearly all of the sort which permit the j)rimary mechanical actions of the tool — percus- sion and rotation — to be employed without modi- fication. It will be sufficient for a general under- standing of pneumatic tools, therefore, to describe briefly typical percussive and typical rotary tools. Pebcis.siox Tools. The mechanism employed for utilizing compressed air to secure percussive NoseRece NoseRece Nose '^fe_^;f[;i;;£,.21if "T- J^^^P'"^ Lock Spring Throttle Lever-.,, Valve Box Top,
- ^ fia.'nrrer
Valve Box Bottorr RivetSet Rivet SetCiamp Cylinder >2 Clamping Bolt- -^/f— , ThrottleBUshing] Throttle BushingHug Pin Throttle BushingPlug Throttle I ever ■Pin ^.Handle Throttle Spr. Throttle Valve Throttle Bush- ng Spring Air Strainer SECTION OF EELLEB PSEPMATIC BAMMEE ARRANGED FOE RIVETING, SHOWING OPERATING PARTS. BiBLiOGRAPiiv. For a comprehensive descrip- tion of the Batcheller pneimiatic dispatch sys- tem, particularly as installed at Philadelphia, Pa., see Batcheller, The Pneumatic Dispatch Tube System (Philadelphia, 1897). The results and conclusions of the committee appointed to investi- gate the subject of pneumatic dispatch for the Post-office Department have been published by the Postmaster-General under the title of Pneu- matic Tube Scriice (Washington, D. C, 1900). PNEUMATIC GUN. A gun in which the expansive force of air under pressure is employed Vol. XVI.— 10. action is essentially the same in all pneumatic tools of this t.vpe, and it will be sutticient to de- scribe the mechanism in one of them only, and for this purpose the hammer will perhaps serve best. The pneumatic hammer consists essentially of a c.vlinder containing a piston which, by means of suitable cylinder inlet and exhaust openings for air under pressure, is made to reciprocate back and forth in the cylinder. A tool is inserted into the front end of the cylinder loosely in such a way that the reciprocating piston or hammer strikes its near end at each forward stroke, the
