30 LABORATORY EXERCISES 



imagination. Tie a bit of absorbent cotton about the bulb of 

 the thermometer, put some gasoline on the thermometer, and 

 wave the thermometer back and forth. Does the reading show 

 any change? What is it? 



c. Get the weight of a beaker half full of water, and keep the 

 water boiling for 10 minutes. Does the temperature change 

 during the boiling? Test it with a thermometer. Has the 

 amount of water changed? How much? 



If 536 calories of heat are needed to evaporate 1 gram of 

 water at 100 C., how many calories were added to the water in 

 the beaker? Where did the heat come from? How was it 

 produced? 



EXERCISE 27 

 KINDLING TEMPERATURE 



Apparatus. Burner, wire gauze. 



a. Hold or support a piece of wire gauze (it should be at least 

 10 cm. square) about 5 cm. above the top of a Bunsen burner. 

 Have the air holes at the base of the burner open. Now turn 

 on the gas supply, and bring a burning match over the middle 

 of the gauze. Does the gas take fire above, or below, the gauze? 

 Prove that there is gas below the gauze. 



b. Let the gauze become cool, and then bring the middle of 

 it down into a Bunsen flame. Does the flame go through the 

 gauze? Why? Hold the gauze in the flame until it is red hot. 

 Does the flame now go through the gauze? Tell why. 



EXERCISE 28 

 MIXING MATERIALS OF DIFFERENT TEMPERATURES 



Apparatus and Materials. Measuring cup and woolen material to 

 fasten around it, cardboard cover, thermometer, water, burner. 



