56 



A PRIMER OF BIOLOGY 



Experi- 

 mental 

 demon- 

 stration 

 of respira- 

 tion. 



by day as well as by night, is easily proved by the 

 following experiment (Fig. 22). 



Place a vigorously growing green plant beneath a 

 suitable bell-jar (A) which communicates by means 

 of two bent glass tubes with gas-wash bottles, 

 and cover the bell- jar with black cloth or black 

 paper to shut off sunlight from the plant. The 

 two gas-wash bottles B and C, and D and E are half- 

 filled with lime-water. The outer end of the bent 

 tube B' communicates with the air directly, but since 



"-N + C<\. 



rh f 



FIG. 22. Apparatus for demonstrating respiration in 

 plants during the day. 



the end of the tube inside the wash- bottle passes 

 below the level of the lime-water, all the gas which 

 enters the apparatus must pass through the lime- 

 water in B. Now when carbon dioxide and lime- 

 water meet, carbonate of lime (or calcium carbonate) 

 is formed. This latter substance is insoluble in 

 water and appears as a white precipitate in the lime- 

 water. The second bottle (C) is interpolated between 

 B and the bell- jar to catch any carbon dioxide that 

 may have passed over unaffected by the lime in 

 bottle B. On the other side of the bell-jar, the two 

 bottles D and E also contain lime-water. If now 

 any carbon dioxide be formed by the plant it will 

 give rise to a white precipitate in bottle D, while 



