When Willis Carrier
invented his “Apparatus for Treating Air” back in 1902, he did so
with a single purpose: to control
heat and humidity
that’s adversely affecting the paper being manufactured in the
paper mill he was working in—but how exactly does heat and humidity
affect paper?
Air is a compound,
which means it contains a lot of other gases which includes oxygen,
nitrogen, and water vapor. Specific temperatures allow air to only
hold a maximum amount of water vapor, which is measured by virtue of
relative humidity or RH. As an organic material, paper can readily
absorb water vapor when it is exposed to great amounts.
Relative humidity is
closely related to the terms “dryness” and “wetness.” They
both denote the proportion of water vapor present in the air. At a
certain stage called the “dew point”, which occurs at low
temperatures, the air is very saturated—it holds every ounce of
water possible which manifests in forms of dew or mist. On the other
hand, rising temperatures cause the dew to be suspended mid-air where
it hovers until the temperature is lowered again.
The continuous rising
and falling of temperatures spell doom to paper because of this. This
is why paper manufacturers, as well as document archivists, must
invest in efficient air conditioning so as to preserve the paper they
store.
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