852 



METHODS OF KINETIC MEASUREMENTS 



CHAP. 25 



can be determined gravimetrically, titrimetrically, electrometrically or 

 manometrically. The tests are made either in samples of the air or sohi- 

 tion taken from the reaction vessel before and after a period of photosyn- 

 thesis, or, more conveniently, in circulating gas, before and after its pas- 

 sage through the reaction chamber — a method first introduced by Kreusler 



Source lamp _,/ Entrant slit of spectograph 



___^^ _^ 1-Concave mirror 



Flat mirror' 



to B 



Plant growth 

 chamber 



-Nutrient 

 supply 



Fig. 25.5. Apparatus for continuous spectroscopic measurement of carbon dioxide 



exchange in plants (after McAlister 1937). 



(1885), and used also in the classical work of Willstatter and StoU (1918) 

 It is convenient to use methods of analysis not requiring the taking of 

 samples, e. g., to measure the conductivity of the absorbing solution in 

 equilibrium with the gas (cf. Newton 1935, and Clark, Shafer and Curtis 

 1941). The smallest amounts of carbon dioxide that can be determined 

 in this way are of the order of 10"'' g. 



Several methods of continuous determination of carbon dioxide in sohi 

 tion have been suggested. In working with (unbuffered) solutions, the 



