Comparative Air- Analyses 115 



glass and the mercury, the contraction as measured is invariably too 

 large by the volume of the water so held. Unfortunately no quantita- 

 tive measurements of this water are possible with the Sonden apparatus. 

 In this study, however, we have aimed to secure constancy in the amount 

 of water thus trapped, knowing that the absolute amount could not be 

 measured. The analyses of both outdoor and cylinder air with the potas- 

 sium pyrogallate employed in this research, as well as the analyses made 

 with Haldane's strong solution, showed invariably that the correction of 

 + 0.014 should be added to the results given to make them comparable 

 with analyses made with the Haldane solution. 



The atomic weights of but few of the chemical elements are known to 1 

 part in 2000, and hence it may now rightly be said that air is a physical 

 mixture with the definiteness of composition of a chemical compound. 



(5) While the combustion of fuel and the vital processes of men and 

 animals result in a local increase in carbon dioxide and decrease in oxy- 

 gen on the one hand, and vegetable growth results in a decrease in carbon 

 dioxide and increase in oxygen on the other, the extraordinary rapidity 

 with which the local variations in the composition of the air are equalized 

 is accentuated by the observations on street air, which show but the 

 slightest trace of an oxygen deficit. 



The ratio between the increment in carbon dioxide and the decrease 

 in oxygen leads naturally to the conclusion that carbon-dioxide deter- 

 minations may be taken as excellent indications of the oxygen content 

 and thus the necessity for elaborate and time-consuming oxygen determin- 

 ations disappears. For every 0.01 per cent increase in the atmospheric 

 carbon dioxide, one may safely assume a corresponding decrease in the 

 percentage of oxygen. 



Nutrition Laboratory of the Carnegie Institution op Washington, 

 Boston, Massachusetts, February 19, 1912. 



