44 NATURAL RESOURCES OF HOME ENVIRONMENT 



What makes the candle burn ? If we were to place a 

 lighted candle in the jar in which the candle went out 

 (page 42), we would find that it does not burn. Evidently 

 some part of the air caused that candle to burn. Let us 

 try to find out whether it is the oxygen. We have seen 

 that wood burns in oxygen and we guess that it is oxygen 

 that makes it possible for the candle or splinter to burn 

 in the air. Suppose we introduce some oxygen into the 

 glass in which the candle will not burn. After mixing 

 we insert a lighted candle and find that it does burn, act- 

 ing very much as it did in the open 

 air. The mixed gases in the tumbler 

 evidently help the candle to burn. 

 There can now be no doubt that the 

 oxygen of the air is needed to make 

 the candle burn. It is equally es- 

 sential to us in breathing as we shall 

 learn a little later. 



Those of you who have started 

 a home laboratory will be interested 

 to collect oxygen in bottles and to 

 burn other substances in it, as sul- 

 phur and iron. For burning iron 

 use picture cord wire. Unravel the 

 end, warm, dip in sulphur, light 

 the sulphur, and thrust into the jar 

 of oxygen. 



Still another gas in the air. If we were to leave a jar 

 containing limewater in the open air overnight,, we would 

 find in the morning a whitish film on the surface of the 

 liquid. If we prepare a gas by pouring a little vinegar or 

 hydrochloric acid upon cooking soda and pass it through 



The limewater test for carbon 

 dioxide. 



