THE COMPOSITION OF THE AIR 



67 



dissolved in it), and with fresh green leaves. Put a 

 glass funnel upside down inside the cylinder, and 

 over this an inverted test-tube full 

 of water. 



Place the whole thing out in 

 sunlight. 



Soon bubbles of gas will begin 

 to rise from the leaves and collect 

 in the test-tube. When enough 

 has been collected, remove the test- 

 tube, keeping it closed with the 

 thumb. Turn it up and lower into 

 it a piece of red-hot wood. 



The wood will glow brightly, 

 owing to the presence of nearly 

 pure oxygen gas. 



We have now learnt that the 

 air is a mixture of two gases, oxygen and 

 nitrogen. That burning bodies are combining 

 with the oxygen to form new substances. 



That during the burning of animal or 

 vegetable substances, or the breathing of 

 animals, the charcoal they contain is being 

 converted into carbonic acid gas by combining 

 with oxygen. 



That this carbonic acid gas is absorbed 

 by the leaves of plants, and during daylight 

 decomposed, the plant keeping the charcoal 

 and returning the oxygen. 



FIG. 15. 



