34 



EXPElUMKXTt^ WITH PLANTS 



substance so that it no longer supports combustion. 

 We may now pour a little lime-water into the jar, 

 replace the stopper and shake vigor- 

 ously. (Lime-water is prepared by 

 placing a little unslaked lime in a 

 metal dish or pail, filling the pail 

 with water and allowing it to stand 

 for a day; the water should then 

 be filtered through filter- paper or 

 through a cotton plug in the neck 

 of a funnel.) If the lime-water 

 turns milky, it indicates that the 

 oxygen has united with the carbon 

 of the plant to form carbon diox- 

 ide, a gas familiar to us as soda- 

 water gas. Arrange an experiment, as shown in Fig. 

 30, by placing a vial of clear 

 lime - water surrounded by 

 soaked seeds in a jar and stop- 

 pering loosely. As a control, 

 use a similar arrangement 

 without the seeds. We may 

 make use of the fact that car- 

 bon dioxide is readily absorbed 

 by lye to perform a further ex- 

 periment. Arrange two bottles 



31. Method of measuring the amount 



(pint or half -pint), as sliown ^L^'S^'',°.?„/St fhet^^w '^ 

 in Fig. 31, by fitting them with J.^,'?)" "' *''°"'"' " "^ 



30. Apparatus for deterniin- 

 ing whether germinating 

 seeds produce carbon diox- 

 ide, the vial is filled with 

 lime-water. (.Seen in sec- 

 tion.) 



