METHOD FOR DETERMINING RESPIRATORY EXCHANGE IN MAN 595 



specific gravity of the KOH should be 1.55, which is obtained approximately by dis- 

 solving the sticks (pure by alcohol) in an equal weight of water. The mark (13) on 

 the stem of the bulb indicates the level at which the solutions should stand. Enough 

 pyrogallate solution is introduced through tube 15 to fill bulbs 12 and 14 two-thirds 

 full. Then pyrogallate solution is poured into tube 16 until the difference in level 

 of fluids is sufficient to produce enough pressure to raise the level of the pyrogallate 

 solution in 12 to the level 13 on the stem. Stopcock 8 must be open during this pro- 

 'cedure. It may be necessary to add or take away a little pyrogallate solution through 

 ''15 to attain the above level. 



Care must be taken to allow for complete absorption of oxygen from the air that 

 AS entrapped between 14 and 16 before an analysis is made; otherwise changes will 

 be produced in the level of the pyrogallate solution. The air in the capillary tubing 

 connecting the burettes with the absorption bulbs must also be freed of CO 2 and O 2 . 

 This can be accomplished by making a dummy analysis of atmospheric air before the real 

 analysis. Great care must be taken to have atmospheric pressure in all the tubes at 

 the start of the analysis. This is accomplished by opening the stopcock in the burette 

 first to atmospheric air and then to the absorption bulbs, until no further change 

 in the level of the fluids in the stems of the absorption bulbs occurs. This level is 

 then marked and used as the standard. A small amount of water in the burette over 

 the mercury assures saturation of the air with water vapor. Time for drainage must 

 be allowed before making readings. 



A very serviceable sampling tube for the transfer of air can be made from a 30 

 c.c. ground-glass syringe, to which is attached a two-way stopcock. A cut of this is 

 shown in Fig. 181. The dead space in these syringes is washed out by working the 

 piston back and forth several times. A thin coating of vaseline prevents leakage of 

 the gas. We have found that these sampling tubes will retain a sample of expired 

 air without change up to eight hours. 



MANIPULATION OF APPARATUS. The sampling syringe (20} is attached to opening 2 

 of the burette, and its stopcock (17) opened to atmospheric air. The level of the 

 mercury is raised to the level of the stopcock of the syringe and is then turned so that 

 syringe and burette are in communication. The bulb of mercury is lowered so that 

 the mercury falls in the burette. This draws the piston of the syringe with it, and fills 

 the burette with air from the syringe. It is advisable to put a little positive pressure 

 on the piston of the syringe in the maneuver to prevent possible leakage. When all 

 of the air is in the burette a slight positive pressure is produced in the burette by 

 gently pressing on the piston, and immediately thereafter the stopcock on the syringe 

 (17) is again turned to the original position. This allows the pressure of air in the 

 burette to come to that of the atmosphere. The height of the mercury is now adjusted 

 to a convenient 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 the fluids. 

 The reading is then taken on the burette. 



The next step in the analysis consists in turning stopcock 8 to communicate 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 complete, 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 2 absorbed. 



