IS HEAT USED UP WHEN A LIQUID IS CHANGED TO A GAS? 29 



small amount of fine sawdust or tiny shreds of paper. Warm 

 the beaker slowly, and note any movements in the sawdust 

 or paper. What is taking place in the water? What is the 

 meaning of convection? How is the upper part of the liquid 

 heated? Let the hot liquid cool, and note what movements 

 take place. What is the direction taken by the cooler water? 

 By the hotter water? 



6. Convection in Air. Open a door leading from a warm 

 room into a cold room or hall. Hold a lighted candle at the 

 top of the door opening; at the bottom. What is the direction 

 of the air currents in each case? Tell why. 



Hold the lighted candle near the incoming air register of your 

 house or schoolroom. Near the outgoing register. Over the 

 hot- water or steam coils. Give the results. 



Why does so much dust collect on walls and ceilings over hot- 

 air registers, and over steam and hot-water radiators? What 

 does this show as to the direction taken by heated air? 



EXERCISE 26 

 IS HEAT USED UP WHEN A LIQUID IS CHANGED TO A GAS? 



Apparatus and Materials. Ether or gasoline, water, thermometer, 

 absorbent cotton, beaker or measuring cup, balances. 



NOTE. Ether and gasoline are very inflammable. Put out 

 all flames when working with them. 



a. Pour a few drops of ether or gasoline into the palm of your 

 hand, and let the liquid evaporate. What is the result? 

 Explain it. 



Wet your hand with water having the temperature of the 

 room, and wave it back and forth to make the water evaporate. 

 Is there any change in temperature? 



6. If you have a thermometer, find out if the result is only 



