g8 



BOTANY. 



stand for about 24 hours. The apparatus should be set up quickly so that 

 forming carbon dioxide will not displace the air. 



172. Carbon dioxide given off during germination while 



oxygen from the air is con- 

 sumed. — 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 pre- 

 cipitate is barium carbonate. 

 Some of the carbon dioxide 

 given off by the peas is ab- 

 sorbed by the baryta water 

 forming the insoluble barium 

 carbonate. Carbon dioxide is 

 also absorbed by the caustic 

 potash solution in the bottom 

 of the cylinder. Owing to 

 the slowness with which the 

 carbon dioxide 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 mer- 

 cury in the outer arm of the 

 tube.* 



In about 24 hours observe 



Fig. 78. Fig. 79. 



Experiment to demonstrate respiration. 

 Fig. 78. — At beginning of experiment; mer- 

 cury in each arm equal. No oxygen has been 

 consumed in vessel. 



Fig. 79.— At close of experiment ; mercury „,.„. : c c +ill nio-n^r in t-no n „tpr 

 in inner arm has risen. Some oxygen has been ^.ury IS bllll nigner in me OUtcr 



c ° nsumed ' arm it shows that there is still 



* When this inside pressure is produced it shows that more CO, is 



the experiment. If the mer- 



