Comparative Air-Analyses 83 



nected with the gas-analysis apparatus, so that by turning a valve the 

 water-suction pump could be connected with either the west or the east 

 pipe and fresh outdoor air drawn from either side of the building at will. 

 In all analyses care was taken to have the suction pump in full operation 

 for several minutes before taking the sample, thus insuring a complete 

 sweeping out of the pipe by fresh outdoor air. With all analyses simul- 

 taneous records have been made of the weather, the direction and strength 

 of the wind, the outdoor temperature, and the barometer. 



METHOD OF USING THE APPARATUS AND RESULTS OBTAINED. 



The best procedure in the use of this apparatus is by no means obvious 

 from an inspection of its construction; furthermore, as errors appeared in 

 the technique and in the apparatus, the routine has been altered funda- 

 mentally on several occasions. Inasmuch as the results first obtained 

 are so completely in harmony with many of those of the earlier inves- 

 tigators, it seems advisable to give our entire series here, even though we 

 know that the results of the first two years are open to objection, owing 

 to slight errors which disappeared as the routine became more perfected. 



While the investigation was started primarily to study the oxygen- 

 content of the outdoor air, it was necessary to determine beforehand the 

 carbon dioxide, since an alkaline absorbent for oxygen was employed; 

 hence practically all the analyses are accompanied by simultaneous de- 

 terminations of the carbon dioxide in the air. In the especially exact ap- 

 paratus designed by Sonden and Pettersson, the carbon dioxide is de- 

 termined to the third or fourth significant figure, but as the amounts of 

 carbon dioxide that were to be used in our apparatus might at times reach 

 1 per cent, it was impossible to secure this degree of fineness in the cali- 

 bration of the carbon-dioxide pipette, hence readings can be taken only 

 to one-thousandth of 1 per cent. Consequently, since other methods are 

 better adapted for securing accurate carbon-dioxide determinations, little 

 stress has been laid upon the determinations made in connection with 

 this research, although they are probably accurate to within 0.002 in all 

 cases. At one time during the research it was found that the potassium 

 hydroxide reagent chamber C was broken, so it became temporarily 

 necessary to absorb simultaneously the carbon dioxide and oxygen; hence 

 for a short period the percentages represent the percentage of oxygen 

 plus that of carbon dioxide. As soon as possible the reagent chamber 

 was repaired and the research was then continued in the usual way. 



FIRST ROUTINE, AND RESULTS OBTAINED. 



The earlier results in this series are especially interesting as indicating 

 how it is possible by constanc} r in routine to secure duplicate results on 

 practically all samples. Furthermore, it is interesting to note that if the 

 research had been discontinued at the end of the second year, the results 

 could easily have been taken as verifying completely those of the earlier 

 investigators, who showed that fluctuations in the oxygen content of the 

 atmosphere are to be expected, slight though they may be. 



