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, hke 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 



