AIR AS AFFECTED BY HEAT AND COLD 111 



FIGURE 57 



Experiment 43. Use a convection apparatus or take a tight chalk 

 box and in two places on the top punch holes in a circle not quite 

 as large as the bottom of a lamp chimney. Place a small lighted 

 candle at the center of one of the circles of holes 

 and a lamp chimney, tightly sealed to the box, 

 about each circle. Hold a smoking piece of paper 

 above the chimney which does not inclose the 

 candle. (If a pane of glass is put into one of the 

 vertical sides of the box, better observations can 

 be made.) (Fijgure 57.) What happens? Put 

 out the candle and carefully heat the chimney 

 with a Bunsen burner. Is there the same action 

 as before ? Why is it that sparks rise from a fire ? 

 What is meant by the draft of a stove ? Why in 

 order to ventilate a room is it best to open a window at the top and 

 bottom? 



The refrigerator illustrates the effect of temperature upon 

 the circulation of air (Figure 58). The coldest air in the re- 

 frigerator is nearest the ice. This being heaviest naturally 

 falls. The farther away from the ice it gets the warmer and 



therefore the lighter it be- 

 comes. The falling current 

 of cold air pushes the 

 warmer air up through the 

 compartments on the op- 

 posite side and back to 

 the ice again, thus making 

 a continuous circulation. 



It is not generally recog- 

 nized that an electric fan 



J 



FIGURE 58. REFRIGERATOR 



Diagram illustrating circulation of air 

 when the doors are closed. 



may be made just as use- 

 ful in winter as in summer. 

 The warm air in a room 

 tends to rise to the upper 



