AIR COMPRESSOR 



by them, while certain sea-weeds have actual 

 air-bladders. These last are not cells in the 

 technical sense, nor are the so-called air cells 

 in the bodies of birds, which may be inflated 

 when the bird prepares for flight. These en- 

 closed, air-filled areas are most fully developed 

 in birds of strong, powerful flight, such as the 

 albatross. 



AIR COMPRES'SOR, a mechanical device 

 for compressing air by forcing it into a recep- 

 tacle, where it is kept until required for use. 

 The most widely used form of compressor con- 

 sists of a cylinder, with necessary valves, in 



ONE FORM OF AIR COMPRESSOR 

 which a piston is worked back and forth by 

 steam or other power. The piston sucks air 

 into the cylinder through one set of valves, 

 which close as the piston commences its return 

 stroke. The strokes of the piston compress the 

 air and force it through other valves into a 

 reservoir, or receiver. From the receiver the 

 air is sent through pipes to points at which its 

 power is required. Some appliances are so 

 powerful that the compressed air exerts a 

 pressure of 3,500 pounds per square inch. 



Drilling and riveting, in bridge and ship- 

 building, are usually performed by tools oper- 

 ated by compressed air, which is also used for 

 pneumatic dispatch tubes, ventilating, rock 

 drilling, air cleaning and many other purposes. 

 A more simple form of air compressor is found 

 in the pumps for forcing air into bicycle and 

 automobile tires. Tln\so have a valve in the 

 cylinder to admit air, and a valve through 

 which the air is forced into the tire by the 

 pressure of a piston. See AIR; COMPRESSED 

 AIR; PNEUMATIC TOOLS; AIR BRAKE. 



120 AIR ENGINE 



AIR ENGINE, an engine in which heated or 

 compressed air is used as the motive power. A 

 invat many engines of this type have been in- 

 vented, but most of them have been failures. 

 It has been found impossible to get very much 

 power in return for the amount of heat up- 

 plied, because the expansion of air is so small 

 compared, for instance, with that of water in 

 the form of steam. In the form of motors for 

 producing very small amounts of power, air 

 engines have been found convenient for use on 

 farms, but even here they have proved so ineffi- 

 cient that they are rapidly being replaced by 

 gasoline engines. 



The most common and the most effective air 

 engine is the Erickson engine, which burns 

 wood or solid fuel or gas. It consists of a 

 heating chamber surrounding an iron cylinder, 

 with a burner at the bottom, the flames of 

 which play on the bottom of the cylinder. 

 The heating chamber is insulated, and t^he heat 

 is applied directly to the cylinder itself, to 

 avoid waste. Within this cylinder is a piston, 

 which is alternately lifted and dropped by the 

 heating and cooling of the air. Such an engine 

 is started by giving the wheel a revolution or 

 two by hand in order to lift the piston and thus 

 to drive the cool air to the bottom, where the 

 flame heats and expands it so that it gives the 

 piston another impulse. 



The motion of this piston is up and down. 

 It may be connected with a rocker arm which 

 is in turn attached to the crank on a driving 

 shaft, or, if it is used for pumping, the piston 

 in the cylinder may be connected directly with 

 the piston of the pump and the up and down 

 motion transmitted directly to it. 



An interesting use of an air engine has been 

 made in some fans which were designed to take 

 the place of electric fans, wherever electricity 

 was not available. Enclosed in the base of the 

 fan is a tiny air engine, exactly similar in prin- 

 ciple and construction to a large engine, with 

 an alcohol lamp for furnishing the necessary 

 heat for expanding the air. 



The first air engine, invented in 1816 by 

 Rev. R. Stirling, was the subject of two pat- 

 ents, one in 1827 and another in 1840. A 

 double-acting Stirling engine of fifty horse- 

 power was used for some years in a Dundee 

 (Scotland) factory. There is a modern engine, 

 known as Robinson's, which is modeled on the 

 original Stirling engine. In 1833 John Ericsson, 

 later famous as the builder of the Monitor, in- 

 vented an air engine to be used in the ship 

 Calcoric, but it did not prove a success. 



