CH. l] RESPIRATION. 5 



in detached drops passes, and produces a correspondingly 

 slow suction-current of air at the side tube (c in Detmer's 

 figure). The aspirator should be hung about 70 cm. 

 above the table so as to allow the use of an outflow tube 

 of about 60 cm. in length, which insures sufficient suction. 

 The tube which admits air into F should be fitted with a 

 screw clamp so as to regulate the inflow. If the sink in 

 the laboratory is inconveniently placed the 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, C, containing baryta-water are fitted in which 

 the CO2 produced by respiration of the plants is caught 

 as BaCOg. With 100 peas the amount of BaCOg may be 

 estimated at intervals of 20 minutes or half-an-hour. 



The estimation is made by titration, for which see 

 Sutton, Volumetric Analysis, 5th Ed. pp. 80 — 89. 



Rough quantitative determinations may be readily 



made as follows. Shake up about 21 grams crystallized 



Barium hydrate with 1 liter of distilled water and allow 



it to stand for 12 hrs. in a closed flask, or till dissolved. 



Filter it into a stoppered bottle. Before an experiment 



introduce, with a pipette, 50 c.c. of this solution into the 



bottle P, and a further quantity into G, At the end of the 



experiment, when a considerable quantity of Barium 



carbonate has been precipitated in P, draw off 20 c.c. of 



the solution ^ with a pipette and titrate it quickly against 



^ The liquid need not be clear, as extremely dilute HCl has no action 

 on barium carbonate. For an accurate method of estimating the COj 

 of respiration by titration, see Blackman in the Phil. Trans. 1895, also a 

 full account of his work in Science-Progress, 1895. 



