Making Air Fit to Breathe 



Experimenters are washing it and filtering it 

 in order to free it from dust and bacteria 



exposed for three 

 minutes. It is then 

 placed in an incubator 

 for two days at the tem- 

 perature of the room 



In center above : The rate 

 at which fresh air is sup- 

 phed to each person is ob- 

 tained by filling bottles 

 with air and analyzing it 

 for carbon dioxide 



No more than fifty 

 thousand particles per 

 cubic inch should be 

 present under the mi- 

 croscope, although 

 some samples have 

 shown twenty million 



At left: a gelatine plate 

 after two days of incuba- 

 tion. No more than twelve 

 large colonies of bac- 

 teria should result from 

 the air in any room 



IT is only recently that health commissions 

 have studied all the conditions that ha\e 

 to be considered in mechanicalh' counter- 

 acting drowsiness and the sore thnjats we 

 get from being shut up all day in our 

 offices, factories, or schools. 



Already many important and interesting 

 facts have been brought to light. One of 

 the discoveries which will change the 

 beliefs of man>- of us is that the carbon 

 dioxide exhaled in our breath is practically 

 harmless; -it is only when it amounts to 

 quantities eight to ten times the quantity 

 found in the best air that we begin to be 

 uncomfortable. Nowadays, an engineer will 

 analyze the air of a room for its percentage 

 of carbon dioxide only because this per- 

 centage furnishes the best and quickest 

 indication of tlie number of cubic feet of 



fresh air which is required for each person. 



Important work has been accomplished 

 by the Chicago Commission on Ventilation 

 in determining the exact effects of the 

 humidity, or moisture, of the air upon 

 comfort. They have found that a cold 

 room can be made as agreeable as one that 

 is warm, simply by increasing its humidity. 



Dust in the air of a room also lowers the 

 vitality of the people in it, when it is 

 present in 3,000,000 or more particles per 

 cubic inch. 



We now understand win- the previous 

 systems of ventilation — of which some are 

 still in u.se — were not satisfactory. In 

 these systems only the supply of air and 

 its temperature were regulated. They 

 lacked the means to moisten and dry the 

 air ami to cleanse it sufficiently of dust. 



833 



