CARBON DIOXIDE 77 



need be only one-fourth of an inch thick, but it should be 

 placed near the wick end of the candle. Fill the saucer 

 with water, place the candle upon the water, light it, and 

 cover with the glass. Tell what happens. 



b. How high did the water rise? The candle has 

 used all of the oxygen and left the nitrogen. How much 

 of the air is nitrogen and how much is oxygen, according 

 to your experiment? Why did not the candle go out at 

 once? Why did not the water begin to rise when the 

 candle was covered? Before answering this question 

 you must think of the effect of heat upon a gas. See 

 Experiment 24. Why did the water continue to rise 

 after the candle went out? 



Note : The same experiment may be repeated with 

 a large bottle, having straight sides, and a cake pan, or 

 bread pan, to see if the same results will be re- 

 peated. 



The following experiment is for the teacher : \ j 



Experiment 39. The Amount of Carbon Diox- j| 

 ide in the Air. 



Apparatus: A twenty-ounce glass-stoppered 

 bottle, glass measure graduated in cubic centi- 

 meters, medicine dropper graduated to hold one- 

 third of a cubic centimeter. 



Materials: Limewater solution (pure water 

 left in contact with slaked lime until the water 

 will not take up any more lime. Dilute the clear 

 decanted liquid with 99 times its own volume), 

 phenolphthalein solution (dissolve one part of 

 phenolphthalein in 500 times its own weight of 50 

 per cent alcohol.) 



