1904.J DUDLEY — PASSENGER CAR VENTILATION. 249 



in Parke's Practical Hygiene, and it is found that when the car- 

 bonic acid naturally in the air, is increased by two cubic feet per 

 10,000 from human beings, it is possible to begin to detect the 

 odor mentioned. So that when an analysis of the air in any closed 

 space, which is occupied by human beings, shows not more than 

 six cubic feet of carbonic acid per 10,000, it is claimed that the 

 .space may be regarded as well ventilated. 



The third point to be discussed is, since carbonic acid is given 

 off from human beings, and since the amount of it in the air from 

 this source is an essential element in ventilation, it is necessary to 

 know how much carbonic acid per person per* hour goes into the 

 air. The same authority already quoted, namely, Parke's Practical 

 Hygiene, gives the results of a very large number of experiments on 

 this subject. Men usually give off more than women, and children 

 less than either. A man in vigorous work gives off more than in 

 idleness. The mean of a mixed community, such as may be 

 assumed to ride on cars, is 0.60 cubic foot per person per hour. 

 It will be seen in a moment where these figures apply. 



Fourth, one of the most important questions in car ventilation 

 is, ** How much air per car per hour is it necessary to take through 

 a car in order to have it well ventilated?'' If the data above 

 given are to be trusted, it will be evident that when a car contains 

 sixty people, each one giving off on the average 0.60 cubic foot of 

 carbonic acid per hour, there will be per hour thirty-six cubic feet 

 of carbonic acid to deal with, and the problem becomes how much 

 fresh air is it essential to mix with these thirty-six cubic feet of 

 carbonic acid, in order that it may be diluted to such an extent 

 that it will not add to the carbonic acid already in the air, more 

 than two cubic feet per 10,000. The problem maybe stated in the 

 form of proportion. If 10,000 cubic feet of air are to contain two 

 cubic feet of carbonic acid in addition to its normal amount how 

 many cubic feet are essential to contain thirty-six ? Reducing the 

 proportion and the astounding figure is reached that, in order to 

 have a passenger car well ventilated according to the data already 

 given, it is essential to take through the car 180,000 cubic feet of 

 fresh air per hour. This figure may be stated in another way, and 

 this is the form in which it is usually given in treatises on ventila- 

 tion, namely, it requires 3,000 cubic feet of fresh air per person 

 per hour to maintain the air in any closed space in the conditions 

 required for good ventilation, according to the standards already 

 mentioned. This is hardly the place to discuss the validity of this 



