30 



STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



dilating the specific resistance from these values, those of Noyes 

 are for 0.10 normal 48.97 and for 0.05 normal 92.98, while our results 

 were respectively 49.80 and 92.20. 



In view of the fact that our determinations were not made for 

 the purpose of obtaining physical-chemical constants, and we 

 required only relative values for the determination of respiration- 

 rates, the agreement is quite satisfactory. 



Table 7. — Specific resistance of various concentrations of barium-hydroxide solution, 

 determined at 25°. 



Cell constant = 1 .2255. 



The curve plotted from these determinations is given in figure 6. 

 On the basis of these values it was possible to calculate the amount of 

 carbon dioxid represented by any given reduction in the concen- 

 tration of the absorbing barium-hydroxide solution. The manner 

 in which this was employed is given in the following section. 



3. The Procedure of the Respiration Experiments. 



Before using the apparatus just described, it was of course tested 

 for small leaks, the absorption capacity of the soda-lime train at the 

 required rate of the air-stream was determined, and the limits of 

 complete absorption by the barium-hydroxide solution were estab- 

 lished. While the apparatus seems to be rather complex, for con- 

 tinuous use for an extended series of determinations the various 

 appliances proved very reliable and efficient. 



Before each experiment the respiration chamber was washed out 

 with a solution of formaldehyde and then with distilled water. 

 Thereafter filtered air was drawn through the chamber until the 

 last trace of formaldehyde was removed. All nutrient solutions 

 were also steriUzed by heating twice in an autoclave. 



Only the purest chemicals available were used. The sugars 

 were Pfanstiehl brand. Some inconvenience was occasioned by the 

 difficulty of procuring reliable amino-acid. At the time these 

 experiments were begun amino-acids were not procurable or only at 

 an exorbitant price and of a quality utterly unfit for physiological 

 work. We were therefore obliged to devote about three months 



