ESTIMATION OF ATMOSPHERIC GASES 



235 



only blue violet rays to pass, and determine how much carbon 

 dioxide is used. Care must be taken to carry on the tests in the 

 same temperature and intensity of illumination. It may be neces- 

 sary to use shades or shields to prevent unchanged light entering 

 the inner cylinder from the upper exposed part. A thermometer 

 should be placed in the cylinder in such position that it may be 

 read during the course of the exposure. The various solutions 

 will doubtless exhibit different diathermanic properties, and the 

 temperatures may be regulated by any convenient method (See 

 color filters 200). 



302. Volumetric Estimation of Atmospheric Gases. The follow- 

 ing method will be found suitable for estimation of atmospheric 

 gases in all tests of exchanges between the plant and the air, both 



Fig. 118. Apparatus for estimation of atmospheric gases. A, bell -jar covering 

 plant, with capillary tube closed by rubber tube and clamp, and burette with stop- 

 cock. B, Hempel's gas burettes. C, gas pipette containing solution of potassium 

 hydrate. D, gas pipette containing sticks of phosphorus. 



in photosynthesis and respiration, and also commends itself from 

 the fact that the apparatus consists of standard chemical burettes, 

 etc., kept in stock everywhere. 



Place the experimental plants on a suitable ground-glass plate 



