The formation of water vapor
Whenever water is left freely exposed to the air, it evaporates;
that is, it passes into the gaseous state and mixes with the gases
of the air. Even snow and ice give off water vapor, though in very
small quantities. The quantity of water vapor which can enter a
given volume of air is definitely limited. For instance, at the
temperature of freezing water 2.126 grains of water vapor can enter
one cubic foot of air, but no more. When air contains all the water
possible, it is said to be saturated, and evaporation then ceases.
The practical effect of this is the well-known experience that on
the seashore, where the air is often very nearly fully saturated
with water vapor, the drying of clothes goes on very slowly, whereas
in the interior, like the dry-farming territory, away from the
ocean, where the air is far from being saturated, drying goes on
very rapidly.
The amount of water necessary to saturate air varies greatly with
the temperature. It is to be noted that as the temperature
increases, the amount of water that may be held by the air also
increases; and proportionately more rapidly than the increase in
temperature.
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