88 Composition of the Atmosphere 



would be expected instead of the constancy indicated. The laboratory 

 is so situated that the wind from the southwest would come from the 

 more residential portion of the city, while the wind from the northeast 

 and east would come from the business and factory part of the city. The 

 power-house of the Harvard Medical School is located exactly north (100 

 meters) from the laboratory, but aside from this, no large factories or 

 other smoke-producing buildings are nearer than 600 meters. 



Errors in first routine. In October 1909 it was found that if the trans- 

 fer of gas from pipette B to the potassium pyrogallate was continued for 

 some time, there was usually a steady, though slight, increase in the per- 

 centage of oxygen, this increase amounting to from 0.001 to 0.002 per cent 

 for each repetition of the routine. Furthermore, the increase continued 

 until the percentage of oxygen had risen from 20.92 to 21 and over, when 

 it could no longer be read accurately, as the graduations extended no 

 farther. It was believed at that time that this increase was due to the 

 distillation of water from the pipette B over into the solution of potassium 

 hydroxide. The theory was that the strong alkali had a tension of aque- 

 ous vapor considerably less than that of water, and that each time that 

 the air was sent over into the potassium pyrogallate it carried with it a 

 slight amount of moisture; this moisture was retained by the strong 

 alkali until all the water was gradually distilled over. 



SECOND ROUTINE, AND RESULTS OBTAINED. 



Since it seemed desirable to minimize as much as possible the trans- 

 fers of air from the measuring pipette into the strong alkali, the first rou- 

 tine was modified somewhat, and a second routine adopted on November 

 3, 1909. The following changes were made in the method : 



The absorption of the carbon dioxide was unchanged, the variation 

 in the routine being chiefly in the determination of oxygen. After the 

 carbon dioxide was absorbed, the gas was sent into the potassium pyro- 

 gallate and allowed to remain for 10 minutes. It was then withdrawn and 

 after being sent into the potassium hydroxide was again returned to the 

 potassium pyrogallate and allowed to remain 5 minutes. Then the first 

 reading was taken. This procedure, i.e., once into the potassium hydrox- 

 ide and a 5-minute sojourn over the potassium pyrogallate, was carried 

 out three times, readings being taken as each routine was concluded. 



Results ivith second routine. The second routine was followed almost 

 without change from November 3, 1909, until February 15, 1911, sam- 

 ples being taken only on the west side of the laboratory. A sample analy- 

 sis made on November 4, 1909, is given in table 52. The detailed results 

 for this series of analyses are given in table 53, in which are incorporated, 

 likewise, the temperature of the outdoor air, the barometer, and data 

 regarding the wind and weather, as well as the times at which the analyses 

 were made. These analyses were continued over a period of more than a 

 year, the summer months only being excepted. 



