CH. l] RESPIRATION. 5 



air suction may be carried to any part of the room by 

 means of fine lead-tubing. 



Between the flask and the aspirator two washing 

 bottles P, G, containing baryta water are fitted in which 

 the CO2 produced by respiration of the plants is caught 

 and precipitated as BaCOg. 



The amount of the precipitate may be estimated by 

 titration, for which see Sutton, Volv/metric Analysis, 5th 

 Ed. pp. 80—89. 



(4) Intramolecular respiration. 



To demonstrate the fact, the following simple form of 

 experiment may be tried. 



Soak 6 peas in water for 12 hours, when the seed- 

 coats can easily be removed without injury to the embryo; 

 the removal of the testa is necessary to avoid introducing 

 air with the peas, the object of the experiment being to 

 show that CO2 is produced in the absence of free oxygen. 

 Fill a test-tube with mercury and invert it in a mercury 

 trough which should stand in a strong wooden tray. This 

 precaution is advisable in all experiments involving the 

 use of mercury, so that .if any accident occurs the mercury 

 may not escape and get into the cracks of the floor. It is 

 desirable to use clean mercury which has been redistilled, 

 but the experiment will succeed perfectly without any 

 special care being taken in its treatment. 



Pass the peeled peas one at a time under the rim of 

 the test-tube so that they float up into the mercury, and 

 occupy the upper end of the test-tube. On the following 

 day it will be found that the test-tube is half full of gas, 



