54 



MORPHOLOG Y. 



while the cork is pressed in tightly. This allows the mercury to remain at 

 the sairie level in both arms of the tube. Xow remove th^needle and set the 



apparatus aside where'tKe temperature will 

 remain at about 20° C, and let stand for 

 about 24 hours. The apparatus should be 

 set up quickly, so that forming carbon di- 

 oxide will not displace the air. 



127. Carbon dioxide given off during 

 gtrmination while oxygen from the air is 

 consumed. — In a short while there can be 

 seen a whitish film on the baryta water in 

 the vial. In less than an hour this film 

 may become so thick that with a little 

 agitation it breaks and settles as a white 

 precipitate. This white precipitate is ba- 

 rium carbonate, formed when the baryta 

 water absorbs some of the carbon 

 dioxide which is being given off quite 

 rapidly by the germinating peas. The 

 carbon dioxide is also absorbed by the 

 caustic potash solution in the bottom of 

 the cylinder. < )wing to the slowness w'ith 

 which the carbon cioxide diffuses from 

 between the peas into the potash solution 

 an excess may be formed. This excess of 

 carbon dioxide in the cylinder produces a 

 pressure which is shown by the rise of the 

 mercury in the outer arm of the tube."" 



In about 24 hours observe the experi- 

 ment. If the mercury is still higher in the 

 outer arm it shows that there is still an 

 excess of CO2 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 baiyta water 

 over against the wall of the cylinder, and 

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



Fig a,ba. 



* When this inside pressure is produced it shows that more L'( jj is being 

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

 onstrates what is known as intramolecular respiration, a kind of respiration 

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



