ALVEOLAR AIR. 109 



that the dome of the meniscus stands precisely at the 10 c.c. 

 mark. 



The tap C is now turned so that A and D are alone in com- 

 munication (as shown in II) and the reservoir, B, taken off the 

 hook by the left hand and slightly elevated, after which a is 

 partly unscrewed and b held open by the right hand. The 

 mercury rises in A so that the air passes into D where the CO 2 

 is absorbed from it. By cautiously raising and lowering B 

 the air is passed several times (five) between A and D, extreme 

 care being taken when lowering B to see that the NaOH solu- 

 tion does not rise into the narrow tubing d. If this should 

 happen, or a broken column of solution get into the tube d, 

 the clamp b should be instantly closed. Finally, the clamp 

 b is closed, B placed on hook 2 and the level of mercury ad- 

 justed by using b and a until the NaOH solution stands exactly 

 at the original level in d. If there has been no leakage, the 

 mercury should stand precisely at the 10 c.c. mark (since 

 atmospheric air contains too small a percentage of CO 2 , 0.03, 

 to be measurable in such a burette). 



Having thus tested the reliability of the apparatus, analysis 

 may be made of alveolar air collected as described on p. 110. 

 To transfer the gas from the syringe to the burette, the former 

 is attached to the rubber tubing at H after this has been filled 

 to the top with mercury, as described above. With the reservoir 

 on hook 2 and the clip a partly opened clamp b is cautiously 

 opened and the piston of the syringe gently pressed so that 

 the air slowly enters the burette to just below the 10 c.c. mark. 

 The further steps are precisely as described for atmospheric 

 air. In this case, however, the volume will be found to have 

 become considerably reduced and the exact reading on the 

 burette is noted and the percentage of CO 2 calculated. 



At least three similarly collected samples of alveolar air 

 are to be analysed and the results should check to within 

 0.25 per cent. 



When all analyses have been completed the burette is filled 

 with weak acid (0.5 per cent H 2 SO 4 ). This is accomplished by 

 turning C into position I, filling the burette with mercury and 

 the syringe with weak acid, inserting the nozzle of the syringe 



