CH. l] RESPIRATION. 9 



the graduations on (r, after bringing the water in the two 

 tubes to one level. To absorb the CO..,, H is connected 

 with the india-rubber tubing C of the absorption pipette 

 (fig. 4). F is raised, and L and the clamp C opened. The 

 gas is thus forced over into D, where it is retained for a 

 minute or so and gently shaken in contact with the KHO, 

 the clamp C and stop-cock L being closed meanwhile. 

 When absorption is believed to be complete the gas is 

 sucked back into G (fig. 5) by lowering F, C and L being 

 open. L is then closed and G and F brought to a level 

 so that the diminished volume of gas can be again read 

 off. The difference gives the amount of CO2 originally 

 present. To make sure of complete absorption the gas 

 may be again passed into D, shaken and returned, when 

 it should show no further reduction in volume. 



When any potash is sucked back into G along with 

 the gas the tubes must be carefully washed clean before 

 being used for another sample of gas. 



(5) Timiriazeff's Eudiometer. 



The modification of TimiriazefF's eudiometer which 

 we employ for the analysis of gas given off by assimilating 

 water plants (see exp. 52, p. 45) may be conveniently 

 employed for respiration experiments. Five or six germi- 

 nating peas are placed in a test-tube (15 c.c. capacity) 

 which is tightly closed by means of a rubber cork. It 

 may be inverted in water or mercury, and the contained 

 gas analysed after two hours. For this purpose it is un- 

 corked while the mouth of the test-tube is under water and 

 about 0'5 c.c. poured up into the funnel of the eudiometer. 



