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THE COMPOSITION OF EXPIRED ALVEOLAR AIR. 



By Ethel C. Pinkerton, B.Sc. (Syd.), Science Research 

 Scholar in the University of Sydney. 



(From the Physioloyical Laboratory of the University of Sydney.) 



In a previous communication (1) dealing with the percentage 

 of carbon dioxide in expired alveolar air, it has been shown that 

 the amount of carbon dioxide in the last 625 c.c. of expired air 

 does not vary beyond the error of the analytical method, when the 

 expulsion has been performed within two seconds, for quantities 

 of air of two litres or over, and within one second for quantities 

 of one to two litres of expired air. The investigation of the com- 

 position of expired alveolar air has now been extended to the 

 estimation of oxygen as well as carbon dioxide, and more accu- 

 rate analytical methods have been employed for the determinations 

 of the amounts of the gases. 



Methods. — The samples of air have been obtained in tlie same 

 way as in the previous research (i) b}^ collecting them through 

 small capillary pipes set in a long brass tube, into which the sub- 

 ject of the experiment breathed. The tube is the same as used 

 previously, and the capillary tubes have been fixed 250, 500, 1750 

 and 2000 mm. from the mouthpiece. The analyses of the gases of 

 the samples have been performed in a large Haldane apparatus, 

 the carbon dioxide being absorbed by potash, and the oxygen by 

 alkaline pyrogallic acid. The carbon dioxide can be estimated to 

 001 c.c. in a measurement of 1 c.c, giving an analytical error of 

 1 in 100. The percentages of carbon dioxide in the samples are 

 calculated, therefore, to the second decimal place. The error in 

 the determinations of oxygen has been ascertained in a series of 



