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opposite direction to that described above. This method can not 

 be recommended. 



The speed of the air current is regulated by a capillary glass 

 tube, fitted in the india rubber tube connecting the flasks A and B. 



The whole apparatus can easily be made portable, and the 

 experiments can therefore be carried out anywhere. 



It is clear, that the area of the assimilating leaf, the speed 

 of the air current and the concentration of the baryta solution 

 must correspond with one another. As mentioned already Brown 

 and Escombe experimented with very large leaves with an area of 

 300 — 800 cm 2 . Therefore they had to use a very quick air current. 

 I prefer to use a leaf area varying from 4.4 — 100 cm 2 (upper -f- 

 lower surface). In this case 2 1. air per hour, containing about 

 1 mg G0 2 , is sufficient to supply the leaf with C0 2 . The leaf area 

 should vary with the intensity of assimilation. In intensive assi- 

 milation a small leaf area is used and vice versa. Generally the 

 C0 2 tension in the air should not be diminished more than \ by 

 the assimilation, for otherwise the assimilation also will be di- 

 minished too much. 



The C0 2 , that is not absorbed by the leaf, is absorbed by 

 baryta solution and its amount determined by titration with 

 HCl. The strenght of the two solutions is the same and can be 

 varied from ^ — ^ . If the first concentration is used the expe- 

 rimentation time should be 2 hours, and the amount of the 

 supplied air 4 1. 3 absorption tubes will be sufficient. It is best 

 to have 2 apparatus working at the same time. In the latter 

 case 3 — 4 absorption tubes should be used, and the experimen- 

 tation time can be diminished to \ hour. The amount of air to 

 be supplied is 1 1. In my experiments I have most frequently 

 used solutions and an experimentation time of 1 hour. 



The experiments are carried out in the following manner. 



At the beginning the solutions are prepared, 500 cm 3 of each 

 and every day new solutions are made. The titration value of 

 the baryta solution is estimated in the following manner. 10 cm 3 

 of the baryta solution is filled into each of the absorption 

 tubes and the stops with the glass tubes are set in. The stops 

 are again taken out, and the content of the tubes is poured into 

 the titration vessel and titrated with, the HCl solution with 

 Phenolphthalein as indicator. 



Now the C0 2 content of the air is to be determined. 10 cm 3 

 baryta solution is filled into each of the absorption tabes; the 



