468 TEE MECHANICS OF VENTILATION. 



servation shows that there are certain amounts of moisture which when 

 exceeded lead to a rapid deterioration of the air. From 4.5 to 5.0 grains in 

 a cubic foot of air at 60°-62° is the limit of good ventilation. 



c. Organic impurities from the bodilj^ exhalations. There is always 

 present in illy-ventilated apartments, especially school-rooms where chil- 

 dren from the poorer classes are present, a certain unpleasant smell which 

 a medical friend of large experience in ventilation characterises as "cheesy." 

 In simple justice it must be said that this smell is by no means confined to 

 school-rooms of the kind indicated. Excellent examples of it are frequently 

 noticed in concert halls, theatres, lyceums, and in private houses where 

 even an intimation of uncleanliness would bo a rank injustice. Organic 

 analysis has thus far been unable to do more than detect the simple pres- 

 ence of this ill-smelling enemy of the human race. It has been found, how- 

 ever, that a rapid increase of the organic impurity takes place when carbonic 

 acid exceeds six volumes in 10,000, or when moisture rises above five grains 

 in a cubic foot of air at 60°-62°. The reason for the limit of carbonic acid 

 and moisture as above given is therefore apparent. 



d. Heat thrown off from occupants and from the lights at night. It has 

 ■ been determined by observation that an adult gives out 470-490 units of heat 

 per hour, and that an ordinary sperm or tallow candle gives out in burning 

 one hour substantially the same amount. The specific heat of air is 0.238 

 when water is taken as unity, consequently the heat from a single ^^erson 

 or single candle in one hour would raise 1074 lbs. of air 1°, or, since, a pound 

 of air at 60°-62° equals thirteen cubic feet (exactly 13.09 at 60°) we have 

 heat enough to raise 25,662 cubic feet 1°. It will be shown, hereafter, that 

 2000 cubic feet of air per hour is a fair allowance for an adult. It follows 

 that every person, and over}^ candle, gives out heat enough in an hour to 

 raise the supply per hour for each person, from 12° to 13°. If a room were 

 constructed of a capacity equal to say ten persons, and the air supply ex- 

 actly regulated to give each 2000 cubic feet per hour, the bodily heat alone 

 would increase the temperature of the supply from 12° to 13°. 



A large majority of buildings are now lighted by coal gas ; we will, there- 

 fore, consider the amount of heat produced by the combustion of a cubic 

 foot, having ascertained which it will of course be easy to calculate the ele- 

 ments for rooms of any given capacity and number of lights. 



The average of a large number of analyses of coal gas of from twelve to 

 eighteen candle power is as follows : 



Hydrogen, 43.76 



Marsh Gas, -• 40.47 



Carbonic Oxide, 5.94 



Olefiant Gas, 6.58 



Nitrogen, • 1-05 



Oxygen, 0.47 



Carbonic Acid, 0.75 



Aqueous Vapor, 1-00 



100.02 



