THE SOIL AND SOIL WATER 



Capillary Attraction. Water also will rise through a 

 lamp wick or other porous substance. In the experi- 

 ment shown in Fig- 

 ure 6, the water 

 passes through the 

 wick from the left 

 bottle into the right 

 one. If the bottle 

 contained porous 

 soil, as in Figure 5, 

 the water would rise 

 through the soil to 

 the top of the bottle, 

 where it would slow- 



FIG. 6. Illustrating capillarity. ly pass off into the 



air. The force which causes oil, water or any other 

 liquid to rise through a porous substance, is called 

 capillary attraction or capillarity. 



When soil is saturated, the water fills all the spaces 

 between the soil particles. In time much of this drains 

 away. The water that drains away is called free, or gravi- 

 tational, water. That which remains after the free water 

 has passed off is called capillary water. It exists as thin 

 layers around the particles of soil, and is held to the par- 

 ticles by capillary attraction. 



Evaporation. If we rub the blackboard with a damp 

 cloth, the board does not remain wet long, because the 

 water passes off into the air. We hang wet clothes upon 

 a line so the water in them will pass off into the air and 

 they will become dry. The passing off of water from a 

 wet surface into the air, we call evaporation. 



