EXERCISE 45 



WHAT HAPPENS WHEN WATER BOILS, AND AT WHAT TEMPERATURE DOES 



THIS TAKE PLACE? 



Materials. A flask ; a two-holed rubber stopper to fit ; a thermometer ; a glass tube ; a ring 

 stand with clamps (or other support). 



Directions. Set up an apparatus as shown in the diagram. The flask should be about one half 

 full of water into which has been dropped a few grains of sawdust or very small bits of porous 

 paper. Note the temperature of the water, and then heat gently. Small bubbles will soon appear on 

 the walls of the vessel, or rise through the water. Note the temperature when bubbles first 

 appear. What are these bubbles ? (Set a glass of cold water in the sun or near the radia- 

 tor, and see if the same thing happens.) While heating, observe the movement of the 

 particles and explain why they move as they do. When the temperature is near 100C. 

 or 212F., note the large bubbles which form at the bottom of the flask. What are these ? 

 Do they change in size as they rise through the water ? What causes some to disappear 

 completely ? When the water is boiling vigorously, note its temperature. W 7 hat occu- 

 pies the space above the water in the flask ? Allow it to boil for ten minutes, and then 

 compare the volume left with the original volume. How do you explain the difference ? 

 What do you understand by the statement that water boils at about 100C. or 212F. ? 



Additional problems. What differences are there between ordinary water and steam ? 



Boil a half flask of water and, when at boiling temperature, remove the flame and stopper the bottle 

 air-tight with a rubber stopper. Allow the flask and water to cool for five or ten minutes ; then invert 

 the flask and pour cold water on it. Explain what happens. 



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