EXERCISE 14 



WHAT HAPPENS TO WATER VAPOR WHEN IT COMES IN CONTACT WITH 



A COLD OBJECT? 



Materials. A polished metal cup, preferably aluminum, or a new tin cup ; ice ; salt. 



Directions. Place water which has approximately the temperature of the room in a bright metal 

 cup. Add ice or snow to the water. While the water is cooling watch for any deposit on the outer 

 surface of the cup. What is the deposit ? Where did it come from ? Why is there not a similar 

 deposit on other objects in the room ? If all of the air in the room were cooled to the temperature 

 of the air in contact with the cup, what would happen ? 



NOTE. If no deposit is obtained above, a lower temperature may be secured by adding a handful of salt 

 to the ice and water mixture. 



Additional problems. When a person who wears glasses goes from the cold out of doors into a warm 

 room, the glasses often become u cloudy." Why ? 



What causes the moisture to collect in summertime upon a glass or pitcher of ice water ? 

 What is dew ? What causes it to appear ? 



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