28 



LABORATORY EXERCISES 



Hold the wires horizontal, and place them so that they are 

 heated equally. Which wire first feels hot to the hand, and is 

 therefore the better conductor of heat? 



Put one end of a piece of glass tubing (or a glass rod) , about 

 15 cm. long, into the flame, and heat it until the end is melted. 

 Does the end in your hand become hot? Is glass a good con- 

 ductor of heat? 



b. Conduction by Water. Hold or support at an angle of 

 about 45 degrees a test tube that is % full of water (Fig. 15). 



If you hold the tube, use a test tube 

 holder (a folded strip of paper will 

 do). Place the holder about the 

 lower part of the tube, and hold the 

 tube in a small flame so that the 

 flame may strike the upper part of 

 the tube, but may be below the level 

 of the water. If the flame strikes 

 the tube above the water level, the 

 glass may be cracked. Heat the 

 water to boiling. Is the lower part 

 Does water conduct heat as iron and 



FIG. 15. 



of the test tube hot? 

 copper do? 



EXERCISE 25 

 CONVECTION 



Apparatus and Materials. Test tube and holder, burner, large 

 beaker or flask, wire gauze and ring stand, fine sawdust, candle. 



a. Convection in Water. Take a test tube 5 / 6 full of water, 

 hold it by the upper part, and heat the lower part in a small 

 flame. Is the heating now confined to the part near the burner? 

 Tell why. Over a burner, and on a wire gauze, place a tall 

 glass beaksr or flask 5 / 6 full of water. Put into the water a 



