130 



RELATION OP HEAT TO COMFORT 



FIG. 201 



Experiment 91. What is 

 convection? 



Put a small amount of 

 fine sawdust into a beaker 

 full of water. After some of 

 the sawdust has settled to 

 the bottom, apply heat along 

 one side of the beaker. Ob- 

 serve what happens to the 

 sawdust. Place the bulb of a 

 thermometer just below the 

 surface of the water and 

 read the temperature from 

 time to time. 



Describe convection as a 

 mode of transmission of 

 heat. 



Experiment 92. Is water a good conductor of heat? 



Fill a large test tube about 

 three- fourths full of cold water. 

 Grasp the lower end of the test 

 tube and hold the upper end in a 

 hot flame as shown in Figure 202. 

 Are you able to boil the water in 

 the upper part of the test tube 

 while the lower end is cool enough 

 to hold in your hand? Is water a 

 good conductor of heat? Is glass 

 a good conductor of heat? Poor 

 conductors are called insulators. 

 Do you know of any other sub- 

 stances that are good insulators? 



FIG. 202 



Experiment 93. How does a hot-water heating system 

 work? 



Set up the apparatus as shown in Figure 203. The radia- 

 tors may be made from half-pint milk bottles, and a flask 

 made from a burned-out electric light globe may be used 

 for a boiler if other equipment is not available. If T tubes 

 are not at hand, the system may be set up with a single 

 radiator. The expansion tank should be placed at a level 

 higher than any other part. 



After heating for a short time, observe any flow through 

 the system. Try to answer these questions. What part of the 

 radiators heats first? On the basis of Experiment 91, can 

 you establish a possible cause for the circulation of the 

 water in the system? Can you suggest an experiment to 

 test this point further? Why is the expansion tank impor- 

 tant? Record your results. 



The . - part of the radiators heats first. This would 



seem to indicate that water is heavier than water. 



How might this be tested further? The circulation of the 



water in a hot-water system is caused by currents. 



In a hot-water heating system the hot-water pipe should 



leave the furnace near the and the return or cold-water 



pipe should enter near the of the furnace. 



Experiment 94. How does a steam heating system 

 work? 



Set up the apparatus as indicated in Figure 204. Half-pint 

 milk bottles may be used for radiators and a boiler may 

 be made from an old electric light bulb if other equip- 

 ment is not at hand. Glass T tubes may be secured from 



FIG. 203 



any apparatus supply company. This experiment may be set 

 up with a single radiator. It is important to have the glass 

 tubes slope as shown in the illustration and to have one 

 radiator open. The boiler should be about half full of 

 water. This water must be boiling to supply the necessary 



FIG. 204 



