252 NA TURE-STUD Y REVIEW 



fitting cover against the mouth of the bottle and after turning it 

 mouth up, lower into it for an instant a lighted match 

 or candle (attached to a piece of wire), sliding aside and then 

 returning the cover. 



(b) Also pour into the bottle a little clear lime-water and shake. 

 (Lime-water may be bought at a drug store or may be pre- 



.pared by slacking a little fresh lime in a bottle of water. After 

 the extra lime has settled, the clear lime-water may be poured 

 or siphoned off into another bottle.) 



(c) Do the same with the other bottle. 



Note in which bottle the flame is extinguished. Why not in 

 the other? Also note which makes the lime-water more milky. 



(d) Try the candle test in a bottle filled with breath (expired 

 air) which has not stood in the sunlight. Result? (The flame 

 is extinguished as before.) 



(e) Try the candle in a bottle oi fresh air. After covering the 

 bottle, allow the candle to remain till the flame is extinguished. 

 Remove the candle an 3 test the candle's "breath" with lime-water. 



(f) Vary the experiment by lowering the candle into the 

 bottle first and then blowing in the breath slowly through a long 

 tube reaching to the bottom of the bottle. 



What do both the candle's * 'breath" and the human breath 

 contain? — (Carbon dioxide or carbonic acid gas which changes 

 the lime in lime-water to lim.estone. 



We are like the burning candle in that we take oxygen from 

 fresh air and by com.bining it with the carbon of fat or starch 

 or sugar, make carbon dioxide while producing heat or other 

 energy.) 



(g) A bottle filled with the "breath" (products made by 

 burning ) of a candle (e) and containing a cutting from a green 

 plant may be exposed to the sunhght, as in the first part of Exp. 

 2, and then tested as in (a) and (b) . 



(h) Repeat the experim.ent with the bottle containing a cutting, 

 but allow it to stand not in the sunshine but in a dark closet. 



Test as before. Compare and account for the difference in 

 result. 



Encourage the children to try the experiments at home. 



Conclusions : 



Teach that green plants in the sunlight remove from the air 

 carbon dioxide gas which we exhale in our breath. They put 



