Philadelphia being previously an unusually cleanly and well-ventilated
city, what would be the saving of life, health, and wealth were such
a city as New-York perfectly cleansed and ventilated?
Here it is proper to state again that conflicting opinions are found
in many writers on ventilation, in regard to the position of ventilating
registers to carry off vitiated air. Most writers state that the impure
air is heavier, and falls to the bottom of a room. After consulting
scientific men extensively on this point, the writer finds the true
result to be as follows: Carbonic acid is heavier than common air,
and, unmixed, falls to the floor. But by the principle of _diffusion
of gases_, the air thrown from the lungs, though at first it sinks
a little, is gradually diffused, and in a heated room, in the majority
of cases, it is found more abundantly at the top than at the bottom
of the room, though in certain circumstances it is more at the bottom.
For this reason, registers to carry off impure air should be placed
at both the top and bottom of a room.
In arranging for pure air in dwellings, it is needful to proportion
the air admitted and discharged to the number of persons.
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