58 



ELASTICITY OF AIR. 



inasmuch as the quantity of air in R has been increased by one tenth part of 

 its volume. After the second stroke the pressure will be expressed by the 

 number 12. After the third by the number 13, and so on. 



In the form given in practice to the condensing syringe, the necessity for 

 manipulation by the stop-cocks here represented is removed. A silk-valve, 

 such as that described in the exhausting syringe, is placed in the tube C, fig. 

 13, but opening downward. The neck of the receiver R is furnished with a 

 stop-cock and a tube, which terminates in a screw. This screw is connected 



with a corresponding one proceeding from the bottom of the syringe. By this 

 arrangement, the air is capable of passing through the silk-valve from the 

 syringe to the receiver, but not in a contrary direction. A small hole is made 

 through the piston, extending from the upper to the lower surface, and the 

 silk-valve is extended across this hole on the lower surface, so that air is ca- 

 pable of passing through this valve to the cylinder below it, but not in a con- 

 trary direction. 



Now let us suppose that the air in the receiver has the same pressure and 

 density as the external atmosphere, and let the piston P be at the top of the 

 cylinder, the air in the cylinder A, B, also having the same pressure and den- 

 sity as the external air. By pressing the piston toward the bottom of the 

 cylinder, the air enclosed will become condensed, and by its increased pres- 

 sure will open the valve V, and as the piston descends will be forced into the 

 receiver R. When the piston has arrived at the bottom, all the air contained 

 in the cylinder will be transferred into the receiver. It will be retained there, 

 because the valve V, opening downward, will not permit its return. If the 

 piston be now drawn up it will leave a vacuum below it when it begins to as- 

 cend, but the pressure of the atmosphere above will open the valve V', and the 

 air rushing through will fill the cylinder as the piston ascends, and when the 

 piston has arrived at the top of the cylinder, the space below it will again be 

 filled with atmospheric air. By the next descent of the piston this air is forced 

 into the receiver R as before, and so the process is continued. 



It should be observed, that when the piston P is drawn to the top of the 

 cylinder, the air which has passed into A B has not quite so great a pressure 



