EXERCISE 50 



Problem. What gas is given off by plants during starch-making ? 



What to use. A watered plant such as geranium or hydrangea ; bell jar with 

 large opening ; cork ; taper ; matches ; piece of glass for base ; vaseline ; candle. 



What to do. Place corked jar over plant and lighted candle. After flame 

 has gone out, prove that the air in the jar will not support combustion by tilting 

 the cork and thrusting the lighted taper into the jar. Recork jar ; place in 

 sunlight and repeat test at close of another day of sunshine. 



Record. Describe results and explain what changes were brought about in 

 the air. 



Questions. 1. When a flame is present we know that carbon dioxid is one of the results of 

 combustion. What happened to the carbon dioxid produced by the candle ? 



2. Of what value are parks in a crowded city ? 



3. When are plants of value in a sleeping-room ? 



4. What is the value of green plants in an aquarium ? 



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