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GENERAL SCIENCE 



112. Refrigeration. From the facts in 1 1 1 , we 

 can easily understand that gases can be used for cooling 

 purposes. When fruits and vegetables are placed in 

 cold storage a freezing temperature is not desired, so air 

 can be used to keep the building cool. The air is com- 

 pressed and forced through metal pipes with water run- 

 ning over them to cool the condensed air. This air is 

 then allowed to escape in the storage rooms, which are 

 thus kept at a low temperature. 



AMMONIA CONDENSING PIPES ON THE ROOF OF AN ICE PLANT 



Liquids, when tiiey evaporate, take up a great amount 

 of heat; this we know from our experience with water. 

 To experience the cooling effect of evaporating liquids, 

 place a few drops of the following compounds on the back 

 of your hand in the order named: ether, alcohol, 

 ammonia, and water. The one that evaporates the fast- 

 est will feel the coolest, because the faster the molecules 



