HEATING THE HOME 7 



The circulation of air through these pipes is maintained 

 through the effect of heat on gases. When air is heated it 

 expands and so becomes lighter, while the air coming in 

 from outdoors is colder and heavier. When two gases of 

 unequal weight are brought into contact, the tendency is 

 for the heavier body to sink to the bottom and push the 

 lighter gas up. So here the cold air rushes in under the warm 

 air, which is thus forced upwards. 



DEMONSTRATION i 



Purpose. To study the principles applied in the hot-air 

 furnace. 



Apparatus. Flask, rubber stopper with a single hole to fit, 

 glass tubing about a foot long, alcohol lamp or Bunsen burner, 

 tumbler, chimney, touch paper or piece of cloth, candle. 



Directions, i. Push the glass tubing through the hole in the 

 stopper and insert the stopper in the flask. Fill the tumbler 

 with water and place the end of the tube in it. Heat the flask 

 gently and notice what happens at the' end of the tube. What 

 is the explanation ? Remove the lamp but allow the end of the 

 tube to remain in the water. Explain what happens. 



2. Light a candle. On the table on each side of the candle 

 put a match ; on the matches place a lamp chimney. Light a 

 joss stick or piece of cloth and hold at the lower end of the 

 chimney near the matches. What do you notice inside of the 

 chimney ? What does this show ? 



3. How are the principles illustrated by these two experiments 

 applied in the hot-air furnace ? 



The hot-water system. In the hot-water system the water 

 is heated in the basement by the furnace and is then con- 

 ducted through pipes to radiators situated in the various 

 rooms. (See figure 2.) In the attic is placed a tank con- 

 nected with this set of pipes. The hot water passes to this 

 tank and to the radiators, and then back to the furnace, 

 where it is reheated. 



