80 



COMPANION TO TROPICAL READERS 



Fig. 31. Preparation of 

 Nitrogen 



show that it will neither support combustion nor take 



fire. 



(c) Carbon Dioxide. Expose a saucer (preferably a 



blue one) containing some freshly- 

 made lime-water to the air for a 

 number of hours. Observe the 

 milky precipitate found on the 

 surface. 



(d) Water Vapour. Put a glass 

 of cold water in a warm room. 

 Observe the drops of water con- 

 densing on the outer side of the 

 vessel. 



(e) Impurities. Note the par- 

 ticles seen floating in the path 

 of a sunbeam. Shake a dusty 



coat or cushion near by and see how the number in- 

 creases. 



Expt. 191. Plants and Animals depend on one 

 another for the Gases they breathe. 



(a) Animals require Oxygen. If an insect be put in 

 a jar containing no oxygen it will soon die. 



(b) Plants give out Oxygen. Put some shoots of water- 

 cress or other water plant in a vessel of water; observe 

 the bubbles of oxygen rising. Collect as shown in 

 fig. 25, and test for oxygen by carefully removing the 

 test tube and inserting a glowing match. 



(c) Plants require Carbon Dioxide. Char a bit of wood, 

 proving the presence of carbon in plants. 



(d) Animals give off Carbon Dioxide. Breathe through 

 a tube into lime-water, and observe the heavy precipi- 

 tate, proving the presence of carbon dioxide in the 

 gases breathed out. 



Expt. 192. Oxygen necessary for Combustion. Put 

 a lighted candle in a wide-mouthed bottle or jar, cover 



