94 



APPLIED SCIENCE 



sometimes expressed thus: At constant temperature volume of 

 gas varies inversely as the pressure. 



To calculate the volume of a gas at a given pressure, multi- 

 ply the old volume by the old pressure and then divide by 

 the new pressure. 



= V : V 

 = P r x V 



P X V 



: P' 

 X V 



V = 



P' 



Where P and P' are the original and new pressures, and V and 

 V f the original and new volumes. 



The quotient will be the new volume. When a volume of gas 

 is given it is understood to be at a pressure of 1 atmosphere 



unless some other pressure is 

 expressed. One atmospher? 

 is equal to 15 Ibs. air pressure. 



NOTE. In order to convey to 

 the mind the relationship be- 

 tvrcen quantities, such as be- 

 tween volume and pressure, the 

 expressions " varies directly " and 

 "varies inversely" are used. 

 The expression " varies directly " 

 is used to convey to the mind 

 the idea that one quantity grows 

 larger in the same proportion as 



FIG. 57. Wood-boring Machine 

 Operated by Compressed Air. 



the other. When the relation between two quantities is such that 

 one quantity grows larger in the same proportion as the other grows 

 smaller, the first quantity is said to vary " inversely" as the other. 



97. Pneumatic Tools. A pneumatic tool consists of a 

 cylinder with a handle, which contains a working (percus- 

 sion) piston with various air ports, a cap nut, and a spring. 

 Air is usually supplied to pneumatic tools from air tanks. The 



