THE EVAPORATION OF WATER 133 
which can enter a given volume of air is definitely 
limited. For instance, at the temperature of freez- 
ing water 2.126 grains of water vapor can enter 
one cubic foot of air, but no more. When air con- 
tains 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 sea- 
shore, where the air is often very nearly fully sat- 
urated 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, as may be seen 
from the table on page 134. 
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. This is generally 
well understood in common experience, as in drying 
clothes rapidly by hanging them before a hot fire. 
At a temperature of 100° F., which is often reached 
in portions of the dry-farm territory during the 
growing season, a given volume of air can hold more 
than nine times as much water vapor as at the tem- 
perature of freezing water. This is an exceedingly 
important principle in dry-farm practices, for it 
explains the relatively easy possibility of storing 
