82 AIR 



dioxide we exhale small, invisible particles of decayed 

 animal matter which also are poisonous unless diluted 

 with plenty of fresh air. You all know the story of the 

 Black Hole of Calcutta, and the fatal results from the lack 

 of fresh air. 



Carbon dioxide has its use and it is a most important 

 one. Plants absorb it and break it up into its parts, car- 

 bon and oxygen. The plants keep the carbon, making- 

 wood of it, and give out the oxygen to the air again. 

 Thus plants purify the air. For that reason we should 

 have plants in our school rooms and houses. Plants owe 

 their ability to take in carbon dioxide to the green color- 

 ing matter in their leaves and stalks. We have learned 

 that the sunlight causes plants to be green, and so you 

 see that it is the sun which causes plants to grow. That 

 is why plants grow in the direction of the sun. 



Experiment 41. Carbon Dioxide from Combustion 

 and from the Breath. 



Apparatus: Candle, funnel, syringe bulb, glass tube, 

 10" long, test tube. 



Materials: Limewater (all the slaked lime that will 

 dissolve in water ; use the clear liquid only.) 



a. Arrange apparatus as shown in the illustration, 

 light candle, and force the gases which come from the 

 candle into the limewater. What happens? What 

 caused the change? 



b. Blow out candle and repeat. In this case it is 

 the air of the room which is being forced into the lime- 

 water. Does the change take place? 



c. Take the apparatus out of doors and repeat. Do 



