RESPIRA TION. 5 5 



out of either arm of the tulju. If the open arm of the glass tube is closed with 

 the finger, the cylinder may be inclined so as to let a portion of the potash 

 solution run up among the peas to come directly in contact with the COa remain- 

 ing there. Now rest the cylinder on the table and observe the result. The 

 mercury now stands, if it did not before, higher in the inner arm of the S tube, 

 showing that some constituent of the air within the cylinder was consumed 

 during the formation of the COj. This constituent of the air must be oxygen, 

 since the carbon can only come from the plant. Where the baryta water was 

 spilled over an abundance of the white precipitate of the barium carbonate is 

 formed. 



128. Simple experiment to demonstrate the evolution of 

 CO, during germination. — Where there area number of stu- 

 dents and a number of large cyhnders are not at 

 hand, take bottles of a pint capacity and place 

 in the bottom some peas soaked for 12 to 24 

 hours. Cover with a glass plate which has 

 been smeared with vaseline to make a tight 

 joint with the mouth of the bottle. Set aside 

 in a warm place for 24 hours. Then slide the 

 glass plate a little to one side and (juickly 

 pour in a little baryta water so that it will run 

 down on the inside of the bottle. Cover the 

 bottle again. Note the precipitate of barium 

 carbonate which demonstrates the presence of Fig. 47. 

 CO, in the bottle. Lower a lighted taper. ,^Z. dioxfdeTvLe! 

 It is extinguished because of the great quan- ^5*1,8^7°""'""'*' "'''"' 

 tity of CO,. 



129. If we now take some of the baryta water and blow our 

 " breath " upon it the same film will be formed. The carbon 

 dioxide which we exhale is absorbed by the baryta water, and 

 forms barium carbonate, just as in the case of the peas. In 

 the case of animals the process by which oxygen is taken into 

 the body and carbon dioxide is given off is respiration. The 

 process in plants which we are now studying is the same, and 

 also is respiration. The oxygen in the vessel was partly used up 

 in the process, and carbon dioxide was given off. (It will be 

 seen that this process is exactly the opposite of that which takes 

 place in carbon conversion. ) 



