254 RESPIRATION, FERMENTATION AND DIGESTION 



bottles holding about 50 cc. Set one near the jar and pour a 

 small amount of the barium solution into it, allowing the liquid 

 to fall several centimeters in a thin stream from the test-tube. 

 The liquid will be only slightly milky when it is shaken up in the 

 bottle. Now carefully lower the second bottle by means of a 

 cord into the jar and allow it to rest on the seeds. Hold the 

 test-tube at the same distance as before and pour the remainder 

 of the liquid into the bottle in the jar. After a few minutes take 

 it out and shake, noting that it shows the liquid in a much more 

 milky condition than in the first bottle. The two tests show that 

 germinating seeds absorb the oxygen of the air, so that combus- 

 tion is not supported, and that the air confined with the germina- 

 ting seeds contains a larger proportion of the gas (carbon dioxide) 

 which gives the barium solution a milky appearance, due to the 

 formation of insoluble barium carbonate. 



321. Ready Method of Estimation of the Amount of Carbon 

 Dioxide Exhaled. Place about a hundred germinating seeds of 

 wheat, or a number of opening flower buds, or a number of mush- 

 rooms in a state of rapid growth, in an Erlenmeyer flask on a layer 

 of crumpled filter paper. Set one or two small test-tubes half 

 full of saturated solution of sodium hydrate on the seeds, and 

 then close the flask with a rubber stopper perforated to admit a 

 short section of glass tubing bent at right angles twice. Sup- 

 port the flask on a retort stand and connect the free end of the 

 bent tube with a graduated burette by means of a stout piece of 

 rubber tubing wired and make all joints air-tight. Bring a dish 

 full of mercury under the lower end of the burette, and warm it 

 at the middle until a bubble of air escapes, and the mercury in 

 the burette rises to the level of that in the dish on cooling. Mark 

 the exact level. Set the apparatus in a place where it will not be 

 exposed to direct light and note the temperature. The volume 

 of the air in the flask will be decreased by the amount of oxygen 

 absorbed by the seeds, which should be replaced by carbon dioxide 

 excreted. This substance is absorbed by the sodium hydrate, 

 however, as fast as it is formed, so the replacement is effected by 



