CAPILLARY WATER 215 



moisture contained and the wilting coefficient will give the avail- 

 ahle moisture. A small amount of gravitational moisture may be 

 used by plants. Ordinary plants live but make little growth when 

 the soil is saturated. The diagram (Fig. 94) shows the relation of 

 the soil constants and the different forms of moisture. 



QUESTIONS 



1. How does capillary moisture differ from hygroscopic? 



2. (Jive law governing height. 



3. What causes the film on a water surface? 



4. Under what conditions will the Him exert pressure? 



5. If the tension of water film is 73.!) dynes per square centimeter, what 



pressure will the film exert if the radius of curvature is 2.5 mm.? 



6. Explain the movement of moisture from one soil particle to another. 



Illustrate. 



7. How is moisture held in soil columns? Why is the film thicker on 



the lower particles? 



8. What effect does fineness of particles have on capillary pull? 

 !>. What determines the height to which water will rise in soils? 



10. Why should a clay with a higher moisture content than a sand soil 



extract moisture from the latter when in close contact with it? 



11. What is the moisture equivalent of soils? 



12. Why should clay have such a high moisture equivalent compared with 



other soils? 



13. Find the moisture equivalent if the hygroscopic coefficient is 0.3 per cent. 



14. What determines the rapidity of capillary movement? 



15. What is the significance of the experiment with the clod? 



10. What effect does capillary movement have on root development? 



17. (Jive King's experiment with the covered soils. 



18. Define viscosity. What effect on surface tension does it have? On 



capillary movement? 

 10. What effect does temperature have on capillary movement? Why? 



20. What effect do mineral sul>stances in solution have upon tension? 



Organic substances? 



21. What effect will an application of manure have on surface tension? 



22. Why does water rise faster in medium- than fine-grained soils? 



53. Compare columns 1. 3, and 5 in the table on page 207 and explain dif- 

 ferences. 



24. Compare !>, 10, 11. and 12 and explain differences. 



25. From the standpoint of capillary movement, is organic matter desirable 



in soils? 

 2f>. How is the maximum capillary capacity of soils determined? 



27. What about the delivery of large amounts of water by capillarity for 



crops ? 



28. Hive the conclusions reached from the drain gaires at Rothamsted. 

 20. Describe the method of determining capillary pull of soils. 



30. Will water rise 20.8 feet Hgh in clav? 



31. What part does osmosis plav in moisture movement? 



32. f!ive uses of capillary moisture. 



33. What is the wilting coefficient ? 



34. If (lie hygroscopic coefficient is 0.2 per cent, what is the wilting co- 



efficient ? 



35. What is meant hv available moisture? 



