Comparative Air-Analyses 



105 



Table 63. Analyses made at the Nutrition Laboratory of air confined in a steel cylinder. 



Series 5. 



Of especial importance are the percentages for December 2 and 4, 1911, 

 as they establish the absence of any effect upon the determination of car- 

 bon dioxide and oxygen resulting from the temperature of the reagents. 

 The percentages found were constant, independent of an alteration of 

 over 10 C. in the temperature of the water-bath, which ranged during 

 these analyses between 20.4 C. and 32.5 C. These experiments with im- 

 proved technique substantiate fully the observations on p. 97. 



CONCLUSIONS FROM RESULTS WITH FIFTH ROUTINE. 



From the results of anatyses given in tables 61 and 62, it will be seen 

 that the apparatus gives constant oxygen percentages for outdoor air; 

 for any particular day or for a period of 3 or 4 days, the apparatus also 

 gives constant results for the oxygen content of the cylinder air, although 

 these are measurably lower than those for outdoor air. These facts dem- 

 onstrate that the constant readings are not due to any peculiarity in the 

 construction of the apparatus. Furthermore, since it is obvious from an 

 examination of the results that there is a steady, though slight, decrease 

 in the oxygen content of the cylinder air, the evidence in favor of both 

 the accuracy and the sensitiveness of this apparatus becomes conclusive. 



On the basis of this series of observations, then, we may state that the 

 uncontaminated air of Boston is of constant oxygen content irrespective 

 of conditions of weather, humidity, temperature, barometer, wind direc- 

 tion, and season. 



It may further be stated that the percentage of carbon dioxide does 

 not undergo any material alteration under these conditions. 



And, finally, from the evidence thus secured, we may assert that in 

 uncontaminated outdoor air the approximate percentage of carbon di- 

 oxide is 0.031 and oxygen 20.938. 



