562 METABOLISM 



of the atmosphere. The heighl of the mercury is now adjusted to a con- 

 venient height in the burette by closing cock 7 and turning the milled 

 screw 6. The cock 18 is now made to communicate with the absorption 

 bulbs. If the air in the burette is at atmospheric pressure, no change 

 will occur in the level of 1he fluids. The reading is then taken on the 

 burette. 



The next step in the analysis consists in turning stopcock 8 to com- 

 municate with the caustic soda solution in bulb 9, and the leveling tube 

 (5) is raised, forcing mercury into the burette and the air into bulb 9. 

 The gas is passed back and forth several times until absorption is com- 

 plete, as can be determined by the fact that the level of the mercury in 

 the burette remains constant when the fluid in the bulb is returned to 

 its original level (13) on the stem. In this adjustment it is convenient 

 to make the gross leveling by the mercury bulb and the fine leveling by 

 closing 7 and turning 6 until the fluid in 9 is at the original height. 

 The reading on the burette indicates the loss in volume due to the CO, 

 absorbed. 



The oxygen is removed by a similar procedure, the gas being passed 

 into the alkaline pyrogallate solution by turning cock 8 to communicate 

 with bulb 12. The absorption of oxygen is slower than for CO,, and 

 more care must be taken to get complete absorption. The air in the 

 tubing between the fluid in 9 and stopcock 8 must be washed out sev- 

 eral times in order to get the oxygen which is left in it after the absorp- 

 tion of the C0 2 . When this is complete, the final reading on the burette 

 is made and the loss in volume from the second reading represents the 



oxygen. 



THE CALCULATIONS 



The calculation of the percentile composition of the air and of the re- 

 spiratory quotient is represented in the following example of an actual 

 analysis: 



(The temperature and barometric pressure as taken at the time of the 

 experiment were 20° C. and 747 mm. Hg.) 



CO„ analysis — 



1st reading of burette 20.00 



2nd reading of burette after absorption of CO, 19.20 



C0 2 absorbed 0.80 



0.80-^20 = 4.0 per cent C0 2 in expired air. 



O, analysis — 



2nd reading of burette 19.20 



3rd reading of burette after absorption of (X 15.90 



2 absorbed 3.30 



3.30-^- 20 = 16.50 per cent of 2 in expired air. 



