RES P IRA TION. 99 



an excess of CO 2 in the cylinder. At any rate lift the cylinder 

 with the hands in such a way as to hold firmly at the same time 

 the glass tube. Lift it up and down in such a way as to spill a 

 portion of the baryta water over against the wall of the cylinder, 

 and to dash the potash solution into a spray. Be careful not 

 to toss the mercury out of either arm of the tube. If the open 

 arm of the glass tube is closed with the finger (should the 

 apparatus be set up as indicated in fig. 78), 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 CO, 

 remaining there. Now rest the cylinder" on the table and 

 observe the result. The mercury now, if it did not before, 

 stands 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 CO 2 . 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. 



If desired the experiment can be set up as shown- in figure 

 78, with the potash solution in the bottom of the cylinder, and 

 the peas supported on a circular piece of wire netting held in 

 place between two small corks inserted in a glass rod. At the 

 close of the experiment when the cylinder is being agitated the 

 escaping baryta water- forms a large quantity of the whitish 

 precipitate as it washes down the side of the cylinder. 



being set free than oxygen is being consumed. This feature of the ex- 

 periment demonstrates what is known as intramolecular respiration, a kind 

 of respiration which can go on independently of the entrance of the oxygen. 

 See the author's larger " Elementary Botany " page 58. 



