Some Applications of Heat 



103 



Experiment to Show Radiation. To show the transference 

 of heat in matter by radiation, suspend a small heated ball in the 

 middle of a room so that it will be a few feet above the floor. 

 By several trials, find out in what directions and at what distances 

 your hand will feel the heat without touching the ball. Is the 

 heat given off equally in all directions, upward, downward and 

 sideways ? What conclusion 

 may be drawn from this ex- 

 periment ? 



Convection. Convection 

 is the transfer of heat 

 by the flowing of gases or 

 liquids. It depends for its 

 effect on the fact that liquids 

 and gases expand when heated 

 and tend to set up currents 

 within themselves. These cur- 

 rents serve to carry the heat 

 to other portions of the gas or 

 liquid. 



Experiments to Show Con- 

 vection. To show the circula- 

 tion of water by convection 

 currents due to its unequal 

 heating, place a small amount 

 of fine sawdust in a flask and 

 partly fill the flask with water. 

 Heat the water gradually and 

 notice what happens. Why 

 does the sawdust act as it 

 does? The upward move- 

 ment of the water forms con- 

 vection currents. This may also be shown with magenta 

 crystals instead of sawdust. With these a colored effect is 

 produced. 



To show that air expands when heated, partly fill a small 

 bottle with eosin solution or some other colored liquid. Close the 



CONVECTION CURRENTS IN A LIQUID 



As the water heats, it rises, carrying the 

 sawdust with it. 



