ATR OF NEW YORK SUBWAY—SOPER. 665 
Weight of dust in subway and street air compared.—The average 
weight of dust suspended in the atmosphere of the subway as found 
by the use of sugar filters, using all of the results, was 61.6 mg. per 
thousand cubic feet of air, or 2.25 mg. per cubic meter; in the streets, 
52.1 mg. per thousand cubic feet, or 1.83 mg. per cubic meter; differ- 
ence, 9.5 mg. The maximum amount found in the subway was 
204 meg. 
Twenty-three comparative tests were made to determine with par- 
ticular care the weight of suspended dust per thousand cubic feet of 
air inside of the subway and in the streets at the same time and as 
near the same place as possible. These showed an excess of dust in 
the subway of 47 per cent over that outside. In five cases there was 
more dust outside, the greatest excess being 30 per cent. In the other 
eighteen cases the excess of subway dust over street dust ranged from 
11 to 800 per cent. 
Weight of dust inhaled by passengers.—The weight of dust which 
the average passenger inhaled in one-half hour in the subway was 
very slight. Assuming that 360 ¢. c., or 22 cubic inches. of air were 
taken in at each breath and that the passenger breathed eighteen times 
a minute, the total quantity of air which passed into the lungs in half 
an hour was about 6.88 cubic feet, or 6.50 cubic meters. Using the 
average of all results, or 61.6 mg. per thousand cubic feet, as the 
weight of dust suspended in the atmosphere, it appears that the aver- 
age passenger took into his nose or mouth 0.42 mg. of dust in a ride 
of half an hour. 
The amount of dust found in the air of the subway varied with a 
number of circumstances. More dust was found at the arrival ends 
than at the departure ends of the station platforms. This was prob- 
ably due to the fact that the brakes were applied near the arrival 
ends, and to the fact that the currents of air from incoming trains 
helped to carry dust from those sections of the subway which lay 
between stations to the platforms. 
The stations where the greatest weights of dust were found were 
express stations; there the amount of metallic dust formed by the 
braking of the trains was much greater than at the local stations and 
the travel from the streets was greatest. 
The numbers of bacteria found in the accumulated dust of the sub- 
way were usually smaller than the numbers found in dust which had 
accumulated outside. 
The average result of thirty samples of dust which had accumulated 
in the subway was 500,000 bacteria per gram of dust. The average 
obtained from six samples of dust which had accumulated under what 
appeared to be comparable circumstances in different buildings in 
New York was 600,000. 
