Page:Popular Science Monthly Volume 89.djvu/847

 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 the 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.

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