. A laboratory course in plant physiology. Plant physiology; Plant ecology. PHOTOSYNTHESIS 109. stopper and tube are lifted from the chamber and placed upright in the pneumatic trough, deeply enough to allow the stopper to be taken off with- out the admission of air to the tube. The zero mark of the tube is then brought exactly to the water surface; the upper stop- cock is cautiously opened, permitting the water to rise slowly to the zero rrark, when the stop-cock is again closed, shutting into the tube exactly 10 cc. of the gas to be analyzed. First the quantity of carbon dioxide in the tube
. A laboratory course in plant physiology. Plant physiology; Plant ecology. PHOTOSYNTHESIS 109. stopper and tube are lifted from the chamber and placed upright in the pneumatic trough, deeply enough to allow the stopper to be taken off with- out the admission of air to the tube. The zero mark of the tube is then brought exactly to the water surface; the upper stop- cock is cautiously opened, permitting the water to rise slowly to the zero rrark, when the stop-cock is again closed, shutting into the tube exactly 10 cc. of the gas to be analyzed. First the quantity of carbon dioxide in the tube is determined, which is accomplished by aid of the reagent tube described on page 105. Next a determination of the percentage of oxygen present is made by another reagent tube, containing pyrogallate of potash, used in the same manner. Some slender vessel is then slipped under the measuring-tube, which is removed and supported for observation, as shown in the figure. Corrections are to be treated as described earlier (page 105). The measuring-tube should always be washed quite free from the reagents at the close of every analysis, and the ground joints should be kept slightly lubricated by the usual wax. In studying the process with beginners, the demon- stration is the more striking and conclusive to them if a second instrument is set up like (and beside) the first, but covered completely from light; while even a third, like these two except that it has no plant, may advan- tageously be added. When interpreting the final results it must te remembered that the experiment is started with only 90% (if 10% carbon dioxide is used) of air, that is, 72% of nitrogen and 18% of oxygen. It is quite possible to adapt a photosynthometer from a graduated tube, the bulb of a calcium-chloride tube, and a rubber stopper, as shown by the accompanying figure (Fig. 27), the principle of its use being nearly identical with that of the instrument just described. Its capacity must of course he accu
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