30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 63 



by Baron von Liebig, who recommended that in phthisis the respira- 

 tory action should be lessened/ 



The Boston Nutrition Laboratory of the Carnegie Institution of 

 Washington has undertaken a most painstaking series of investiga- 

 tions bearing on this subject. They include an examination of the 

 comparative oxygen-content of uncontaminated outdoor air under 

 all conditions as to wind direction and strength, temperature, cloud 

 formation, barometer, and weather. In addition, samples of air were 

 collected on the Atlantic Ocean, on the top of Pike's Peak, in the 

 crowded streets of Boston, and in the New York and Boston sub- 

 ways. The results of the analyses of uncontaminated outdoor air 

 showed no material fluctuation in oxygen percentage in observations 

 extending over many months and in spite of all possible alterations 

 in weather and vegetative conditions. The average figures are 

 0.031 per cent of carbon dioxide and 20.938 per cent oxygen. The 

 ocean air and that from Pike's Peak gave essentially similar results. 



The extraordinary rapidity with which the local variations in the 

 composition of the air are equalized is accentuated by the observa- 

 tions on street air in the heart of the city, where the contaminating 

 factors might be expected to be of sufficient magnitude to affect 

 perceptibly the analytic data. Only the slightest trace of oxygen 

 deficit is shown, with a minute corresponding carbon-dioxide incre- 

 ment. Observations such as these tend to demonstrate the extent 

 of the diffusion of gases and the establishment of equilibrium by air- 

 currents. 



Most unexpected are the figures in regard to the extremely small 

 extent to which the air was vitiated in the modern " tube " or sub- 

 way, even during " rush " hours. There was, on the average, a 

 fall of 0.03 per cent in oxygen accompanied by a rise of 0.032 

 per cent in the carbon dioxide. Professor Benedict points out that 

 while the measurement of carbon dioxide has been taken as an index 

 of good or bad ventilation, the fact that the proportion of oxygen 

 is actually lowered by an increase in the carbon dioxide has never 

 before been clearly demonstrated. As a result of this, the determina- 

 tion of the content of carbon dioxide in the air, which can be made 

 with ease and accuracy, suffices to establish the approximate percent- 

 age of oxygen. For every o.oi per cent increase in the atmospheric 

 carbon dioxide one may safely assume a corresponding decrease 

 in the percentage of oxygen. Aside from minor fluctuations ex- 



' See Edward Smith : Consumption, Its Early and Remediable Stages. 

 Blanchard and Lea, Philadelphia, 1865. 



