656 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
dioxide was highest between 5.30 and 6 p. m. and lowest between 
1 and 3.a.m. The amount increased from a minimum in the early 
morning hours to about 9 a.m. After this there was a fall to about 
1.30 p. m., followed by a rise to the highest point of the day, which 
occurred between 5.30 and 6 p.m. (See fig. 6.) The average range 
of CO, outside, as determined by hourly results, was 0.8 part per 
10,000. 
In the subway the greatest amount of carbon dioxide for the whole 
day also occurred between 5.30 and 6 p.m. Thereafter there was a 
gradual fall to the lowest point, which was reached between 3 and 
4 a. m. 
From this lowest point the amount increased steadily to about 9 
a. m., after which it fell irregularly to between 1 and 2 p. m. 
The average for the whole day agreed closely with the average 
between 1 and 3 p. m. 
In the late afternoon there was a rapid rise to the maximum fer 
the day, which was reached at about 5.30 p. m. 
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eels etal feleteie taal S50 PET eer SapSeRG 
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POC ANAEUAMAANATUGNAGA PEE 
TS TST ANTS aap ET STP PTT NT TTP STS ea TT Tah Tag 
ETT TST TST TST DST TST TSTPSTS IETS TTS ST TST TA aha BRETT 
Fig, 6.—Variation in the amount of carbon dioxide in the subway and streets as de- 
termined by hourly analyses—average of 1,510 analyses. 
C02, Parts in 10,000 
The samples of air which were analyzed for oxygen were collected 
from 9.30 a. m. to 5.30 p. m., between the Brooklyn Bridge and 
Ninety-sixth Street stations. The average amount of oxygen found 
in the air of the streets was 20.71 per cent; in the subway, 20.60 
per cent; difference, 0.11 per cent. The least amount found in the 
subway was 20.25 per cent. 
BACTERIAL CONDITION OF THE AIR. 
The studies concerning the micro-organisms in the subway related 
chiefly to the number and origin of the bacteria and molds. It was 
not practicable within the time and scope of the investigation to 
determine the various species of bacteria present, but the principal 
sources of many of them were investigated indirectly with fairly 
satisfactory results. 
The bacteria were collected by allowing them to settle from the 
air on circular plates, or Petri’ dishes, 34 inches, or about 9 cm., in 
Eee 
