WEIGHT OF THE AIR 111 



The winds, which are to be studied in Section 94, show con- 

 clusively that air has weight. Otherwise, winds could not 

 exist, or, if air did move, its effect would be invisible and unfelt. 



Experiment 41. Weight of Air. 



Apparatus : Flask 250 c.c., rubber stopper to fit, ring stand, 

 asbestos mat, burner, balances and weights. (Home-made 

 balances will do.) 



a. Put about 50 c.c. of water into the flask and let it boil 

 vigorously. This drives out the air. While the water is 

 boiling, insert the stopper and remove from the heat immedi- 

 ately. A cloth wet with cold water and wrapped around the 

 flask will prevent all danger of an explosion. Weigh the flask. 

 Then remove the stopper, thus admitting the air, and weigh 

 again. Conclusions ? 



The home-made balances may be constructed from a stick 

 three feet long with a cross section of 1" X J". Insert an iron 

 screw eye in the edge of the stick at the middle, and suspend 

 the stick by a string through the screw eye. A piece of iron, 

 lead, or stone may be attached by loop of string, on one side of 



