HOW DO WE USE AIR? 



61 



formed. Actually we do not produce a complete vacuum, 

 for there is always a little air left. It is practically im- 

 possible to remove all matter from a space, hence we call 

 any space from which nearly all the 

 air has been removed a vacuum. 



Demonstration 4. Making a Vacuum by 

 Condensing Steam in a Glass Flask. 



Stretch the neck of a rubber balloon over 

 the neck of a flask which is filled with steam. 

 As the steam condenses, a partial vacuum is 

 formed. Explain the action. 



A Useful Vacuum Maker. The 



demonstration shows how the atmos- 

 phere presses towards a vacuum. 

 There are simpler ways of making a 

 vacuum than by condensing steam. 

 The rubber bulb is a common and 

 useful device for making a vacuum. 

 After a vacuum has been made, it is a 

 simple matter to get the atmosphere 

 to work for you. Take the medicine 

 dropper. Place the open end under water ; squeeze the 

 bulb. Did anything come out? Release the bulb. The 

 elasticity of the rubber makes it spring back to its original 

 size. The air that was squeezed out has left some room in 

 the tube so that the atmospheric pressure on the water 

 outside the tube can push water up into the tube. A 

 fountain pen has a rubber bulb which is squeezed by a 

 lever to make the vacuum, after which atmospheric pres- 

 sure lifts the ink into the reservoir of your pen. 



The Atomizer. Another use of the rubber bulb in 

 producing movement of a liquid is in the atomizer used 

 for perfume or for spraying your throat. This bulb has 

 a valve so that it can send a series of puffs of air through. 

 As each puff of air is forced across the open end of the 



