AIR GUN 



AIR PUMP 



Engines working by compressed air, which 

 can easily be conveyed long distances, are used 

 in mining and tunneling, and compressed air 

 tools are used in riveting, in drilling and cut- 

 ting rock, in boring holes in concrete, and in 

 many similar operations, but these do not come 

 strictly under the term air engine and will be 

 found under other headings. See COMPRESSED 



A IK. C.B.M. 



AIR GUN, a weapon designed to project bul- 

 lets or darts by means of compressed air. The 

 stock contains a chamber into which air is 

 forced by compressing a spring, which works a 

 piston in a cylinder. When the trigger is 



AIR GUN 

 A dangerous weapon used by boys. 



pressed, the spring is released and the air is 

 forced into the barrel, propelling the charge in 

 front of it. The force applied by compressed 

 air is far less than that of gunpowder or other 

 explosives, and the range of air guns is corre- 

 spondingly short. 



The so-called toy gun used by boys for target 

 shooting, and sometimes for killing small birds, 

 has a range of not more than 150 feet, and 

 even at that distance cannot be relied on for 

 accuracy. The careless use of these weapons 

 has been the cause of many grave accidents, 

 and, while they are not sufficiently powerful to 

 kill, many boys have suffered the loss of an 

 eye and other injuries through reckless shoot- 

 ing. In most cities the use of air guns is for- 

 bidden, and the weapons are liable to confisca- 

 tion by the police. 



AIR PLANTS or EPIPHYTES, cp 1 ifitt*. 

 Most plants send down roots into the ground 

 to draw up food from the soil, but there are 

 some, known as air plants, which receive all 

 their nourishment from the air. They fasten 

 themselves upon other plants, but, unlike para- 

 sites (which see), they do their hosts no harm. 

 Few, if any, flowering air plants grow in the 

 i>ei&te regions, for there is not to be found 

 there the intense heat and moisture which th. \- 

 must have, but in the jungles of South Ar 

 ica, Asia and Africa gorgeous air-fed orchids 

 rish. Practically the only air plants with 

 n in temperate regions are famil- 

 iar ;r .sees and lichens. 



AIR PUMP, a device for exhausting air or 

 other gases from a closed vessel. The air 

 pump designed for use in schools is the form 



that comes readily to mind when the term is 

 mentioned. The accompanying illustration is 

 one of the many forms used for experimental 

 purposes, and is designed for demonstrating the 

 physical laws governing the pressure of air 

 rather than for practical vise in business or in- 

 dustry. The principle governing the operation 

 of all such pumps is the same; a receiver, 

 such as r in the illustration, is made air-tight, 

 and the air is pumped out through the tube t. 

 A dimple arrangement of valves in the pump 

 prevents the air from returning through the 

 tube into the receiver. The ordinary suction 

 pump for raising water from a well is con- 

 structed on the same principles as the air pump, 

 and before the water reaches the top of the 

 pipe the air has been exhausted by the pump, 

 which then pumps the water. The vacuum 

 cleaner (which see), is another practical appli- 

 cation of the principles of an air pump. 



Some Things to Be Learned from It. The 

 air pump may be used in a variety of simple 

 experiments which illustrate some of the prin- 

 ciples of physics. For example, if a lighted 

 candle is placed under the receiver, it will go 

 out the moment the air is exhausted, thus illus- 

 trating the well-known fact that oxygen is nec- 

 essary to combustion. If the air is gradually 

 exhausted from a receiver under which a glass 

 of water has been placed, bubbles will begin to 

 rise to the surface of the water, thus showing 

 that the water contains air, which tends to ex- 

 pand and rise as the air pressure in the receiver 

 is gradually decreased. Another simple experi- 

 ment can be made to show that air is necessary 

 to the spread of sound. The ringing of a bell 

 suspended inside the receiver by a thread can 

 be heard when the receiver is filled with air, 

 but when the air is exhausted no sound is 

 heard. Scientists know, what this simple test 

 proves, that sound is a vibration of the air. 



Description of a Simple Air Pump. In order 

 that the operation of an air pump may be 

 understood beyond any i ubt. the 



! form illustrated herewith will be ex- 

 plained in detail. It must not be forgotten 

 that there are several varieties of air pumps, 

 and that the explanation given here would not 

 apply, without slight changes, to any other 

 form. In the illustration r is the receiver, 

 \\hich is made to fit closely upon a flat plate, 

 usually of metal. The bottom edge of the re- 

 ceiver is often greased to make an air-tight 

 connection. From r a tube, indicated by the 

 letter t, leads to a cylinder c, in which there is 

 a piston p. In the base of the cylinder is a 



