INFLUENCE OF ATMOSPHERIC TEMPERATURE. 159 



of water is 2.09 millimeters of mercury and at —20" C, it is 

 0.92 millimeters. Hence, with an average humidity of about 

 80, the water deficit of the air at Harbin during- the epidemic 

 would be represented by from 0.4 to 0.2 millimeters of mercury. 

 Under these circumstances, evaporation could take place only 

 with extreme slowness. 



In India, with a temperature of -|-30° and a humidity of 70, 

 the water deficit of the air would be represented by 9.46 milli- 

 meters of mercury. In other words, evaporation would take 

 place from twenty-five to fifty times more rapidly in India than 

 in Harbin. 



During the plague epidemics of both India and Manchuria, 

 the fact that the poor people were much overcrowded in their 

 living quarters undoubtedly hastened the spread of the disease. 

 In Manchuria, on account of the bitterly cold weather, the doors 

 and windows of the overcrowded houses were kept tightly closed. 

 Under these circumstances, another factor is introduced of 

 perhaps no small importance in its bearing upon the rate of 

 disappearance by evaporation of droplets of sputum in the air; 

 namely, the moisture in the expired air. In the cold, the moisture 

 from the breath of the inmates of an overcrowded room would 

 quickly saturate the air and reduce evaporation to a minimum, 

 whereas the air of a similar warm room could take up large 

 quantities of moisture without becoming saturated. 



The following hypothetical case will illustrate the point in 

 question. Let us assume that there are 10 men in a room 4 

 meters by 4 meters with the ceiling 4 meters high and that the 

 room is without ventilation. If the air of the room had a 

 humidity of 50 and a temperature of 30° C, it would become 

 saturated after about four hours, for the room contains 64,000 

 liters of air. The expired air, which has a temperature of 

 37° and is saturated with moisture, totals about 4,800 liters 

 per hour. The vapor pressure of air saturated at 37° is 46.7 

 millimeters of mercury, and of half-saturated air at SO'' it is 15.7. 

 Therefore, the men would have to breathe r^.i or approximately 

 one-third of the air of the room in order to cause saturation 

 of all of it. This would require h of "^^ or about four hours. 



If the air of the room had a humidity of 50 and a temperature 

 of 8 C, the men would have to breathe /«." or approximately one- 

 twelfth of it in order to produce saturation, and this would require 

 T J of *|^ or approximately one hour. Hence the air of the room at 

 the lower temperature would become saturated in about one- 

 fourth of the time required at the higher temperature. 



