THE WATER IN THE SOIL 21 



Conclusion. — Figure the percentage of gravity and 

 film moisture in the soil. If others have worked with 

 different kinds of soil, compare your results with theirs. 



13. How Film Moisture works its Way upward in the 

 Soil. — The film moisture held in the soil tends to work 

 its way upward toward the surface. This is called capil- 

 lary action. We may know that water will rise a short 

 distance in a very small glass tube when we thrust it into a 

 pail of water. We know a lamp wick pulls up oil by the 

 same process. The soil is full of these tiny tubes, which 

 are not straight, to be sure, since they consist of irregular 

 openings between the soil particles ; and through them 

 the moisture rises from the subsoil. Do these tubes 

 vary in size in different soils ? 



EXERCISE 8 



Object. — To record the rate at which film moisture rises 

 in different soils. 



Procedure. — Repeat Exercise 4, but set the lower end 

 of the chimneys in pans of water instead of adding water at 

 the top. Raise the lower end of the chimneys slightly from 

 the bottom of the pan by thrusting a toothpick or spUnter 

 under one side. Otherwise the water may not enter freely. 



Conclusion. — Record the length of time it took the 

 moisture to reach the surface of the soil in each cylinder 

 or chimney. Tell why it rose quickly in some and slowly 

 in others. 



Since the moisture in the soil rises through these capil- 

 lary tubes, as we have just shown, is it not important to 

 keep them unbroken? 



EXERCISE 9 



Object. — To study the effect of breaking the capillary 

 tubes in the soil by plowing under clods or heavy straw. 



