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apparatus is set going, and at the moment when the bubbles 

 are beginning to stream through the absorbing liquid, the water 

 level in the vessels and the time is to be noticed. When a definite 

 amount of air has passed through the apparatus, the cocks are 

 turned 90° to stop the air current, and the baryta solution is 

 poured into the titration vessel. The baryta solution is titrated 

 with HCl solution, and from the difference between this value 

 and the first titration value the amount of C0 2 in the air can 

 be calculated. When the air current is passed under pressure 

 through the apparatus (as was done in my first experiments) 

 this value will often be too great, say 0.6 mg G0 2 per 1. or 

 more, since bacteria in the glass and india rubber tubes in spite 

 of sterilisation frequently cause an evolution of G0 2 . This may 

 often be an advantage, since when during assimilation the C0 2 

 content is diminished, it will lie near the natural content of atmo- 

 spheric air. 



The estimation of the G0 2 assimilation is carried out in a similar 

 manner. The leaf is put in the plant receiver, the same amount of air 

 as above is drawn through the apparatus, the baryta solution is 

 titrated, and the difference between this and the former mentioned 

 titration indicates the amount of the assimilated G0 2 . The leaf area 

 (upper + lower surface) is determined by drawing the leaf 

 on paper, cutting it out and weighing. Hence the G0 2 assimilation 

 per hour and per 100 cm 2 surface (= 50 cm 2 of the upper surface 

 -j- 50 cm 2 of the lower surface) may be calculated. 



An example will show how the calculations are carried out. 



The experiment was carried out with Rumex acetosella, 2 leaves 

 with a leaf area of 32 cm 2 (upper + lower surface). 



30 cm 3 of the baryta solution corresponded with 30.2 cm 3 



HCl. When 2 1. air were drawn through the apparatus, the 

 titer of the baryta solution was 24.6 cm 3 jjq HCl. 1cm 3 ^ HCl 

 = 0.2 mg G0 2 . The amount of C0 2 in the air was consequently 

 0.56 mg G0 2 per 1. ? 



After the leaves was put in the apparatus, 2 1. air were passed 

 through in 54 minutes, and the titer of the baryta solution was then 



found to be 27.0 cm 3 ^ HCl. Hence it may be calculated that the 

 amount of C0 2 assimilated in this time is 27.0 ^-24.6 = 2.4 x 0.2 

 mg. The G0 2 assimilation per 100 cm 2 per hour is therefore 



2.4 x 0.2 x g x ~ = 1.7 mg. GO r 



