114 



Composition of the Atmosphere 



CONCLUSIONS. 



(1) Apparatus for gas-analysis. The Sonden apparatus here de- 

 scribed fulfills all conditions essential to exact gas-analysis, save that the 

 gas is not measured dry in a dry pipette over mercury. In spite of this 

 one drawback, the technique has been developed so as to insure a con- 

 stancy and sensitiveness found as yet in no other form of gas-analysis 

 apparatus. 



(2) Reagent for the absorption of oxygen. Experimentation with all 

 forms of absorbents for oxygen, including several strengths of potassium 

 pyrogallate solution, leads inevitably to the conclusion that the Haldane 

 potassium-pyrogallate solution is the most efficient agent thus far recom- 

 mended. The analyses of those investigators employing phosphorus or 

 sodium hydrosulphite do not lead one to believe that for efficiency they 

 can supersede the Haldane solution. 



(3) The constancy of the oxygen percentage in outdoor air. The results 

 of analyses of air taken near the laboratory showed no material fluctua- 

 tion in oxygen percentage during a period extending from April 15, 1911, 

 to January 30, 1912. This constancy was maintained in spite of all 

 possible alteration in weather conditions, changes in barometer, ther- 

 mometer, humidity, and wind direction and strength; furthermore, the 

 experiments were made before, during, and after the vegetative season. 

 The average result of 212 analyses showed 0.031 per cent of carbon dioxide 

 and 20.938 per cent of oxygen. The analyses of air collected over the 

 ocean, at two different times of the year, and on the top of Pike's Peak, 

 gave essentially similar results. The average results of all the analyses 

 made in this research of outdoor air are summarized in table 72. 



Table 72. Summary of analyses made at the Nutrition Laboratory of outdoor air. 



1 A correction of 0.014 has been added to the average results obtained in this research to make them 

 comparable with results secured with the Haldane solution. (See p. 113.) 



(4) Tha absolute oxygen content of outdoor air. While this research 

 has dealt mainly with comparative values, certain fundamental difficul- 

 ties in method and technique prevent deductions with regard to the ab- 

 solute oxygen content of outdoor air. The use of the Haldane concen- 

 trated potassium-pyrogallate solution would seem to preclude the pos- 

 sibility of the formation of measurable amounts of carbon monoxide, but 

 we always have to deal with the possible error in the water adhering 

 to the pipette when the change in level of the mercury is made. Since 

 the contraction in volume is assumed to be only that due to absorbed 

 oxygen, and since unquestionably some water is confined between the 



