32 STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



sion, as results obtained during this period would be spurious, owing 

 to the carbon dioxid of the air in the chamber, etc. Thereafter, 

 however, the determinations of the rates appear to be quite concor- 

 dant, depending upon nutritional conditions, and no evidence of 

 traumatic effects was noticeable. We did not find it advisable to 

 run these experiments over 100 hours, as the danger of infection 

 developing after this time became great, and this naturally would 

 introduce serious error. 



To return to the barium-hydroxide solution: 125 c. c. of this 

 solution was introduced into each absorption tube by means of a 

 pipette. After the air-stream had passed through one of these 

 tubes for a definite period, it was disconnected from the apparatus, 

 and the solution, containing the suspended barium carbonate, was 

 transferred to a glass vessel (see fig. 5) and tightly stoppered. By 



.16 



Figure 6. 

 Specific-resistance curve of barium hydroxide at concentrations from 0.05 to 0.12 

 normal. The ordinate represents the specific resistance, while on the abscissa the CO2 

 gram equivalents of 125 c. c. barium-hydroxide solution are plotted for concentrations of 

 0.05 to 0.12 normal. 



rapid manipulation there is no appreciable error introduced from 

 the carbon dioxid of the air. The barium carbonate was allowed 

 to settle until the supernatant liquid was perfectly clear. The 

 vessel was placed in the thermostat kept at 2.5° and the resistance 

 determined by means of the apparatus already described. At 

 frequent intervals the electrodes were dipped in dilute hydrochloric 

 acid and while not in use kept in distilled water. With these pre- 

 cautions the cell-constant remained unchanged for a long time. 



As was described in the previous section, a curve was drawn with 

 the ordinate as specific resistances and on the abscissa the normal 

 concentration. From this data the carbon-dioxid equivalent for 



