70 



THE SUN'S GIFT OF HEAT 



the supply of air has much to do with the fierceness of 

 the fire. 



Experiment 22. Wind a short piece of wire around a small 

 piece of candle and after lighting the candle lower it into a wide- 

 mouthed bottle. Insert a stopper into the 

 mouth of the .bottle. The candle will begin 

 to smoke and will soon go out. 



From the foregoing experiment it 

 appears that a supply of air is necessary 

 for the burning of the candle. Experi- 

 ence shows that this is true in all the 

 forms of combustion familiar to us. 



Experiment 23. (Teacher's Experiment.) 

 Obtain four bottles of oxygen from the 

 chemical laboratory. If not obtainable, place 

 a piece of sodium peroxide (oxone) about as 

 large as the end of a finger in a side-necked 

 test tube provided with a medicine dropper 

 filled with water, as shown in Figure 29. Put 

 the end of the delivery tube under the mouth 

 of an inverted bottle filled with water arranged 

 on the shelf of a pneumatic trough. Drop 

 FIGURE 29 water slowly on to the sodium peroxide and 



collect the gas generated. Fill several bottles. 



Oxygen can also be prepared by heating a mixture of about one 



part manganese dioxide and two parts potassium chlorate in a 



test tube and collecting the gas over water. (Figure 30.) Does 



the appearance of this 



gas differ in any way 



from air? Smell of it. 



Has it any odor? Into 



one .of the bottles of 



oxygen insert a splinter 



of wood having a spark -^ 



at the end. It bursts FIGURE 30 



