PHYSICAL PROPERTIES OF SOILS 185 



7. If a soil has an apparent specific; gravity of 1.4, what is the weight of 



the surface soil per acre? 



8. Why is color of soils so important? 



9. What color is imparted by organic matter? 



10. What effect does limestone have on color? 



11. What colors are due to iron? 



12. Why are subsoils in swamps so frequently gray or drab? 



13. The subsoil above the tight clay stratum is usually gray in color. Why 



is this? 



14. What is peculiar of the subsoils of the Piedmont Plateau? 



15. What soil constituents impart color? 



1(5. Explain how soils may undergo change in color. 



17. What can be said of the odor of soils? 



18. If soil particles average 0.02 inch in diameter, how many could be placed 



in a one-inch cubical box with columnar arrangement? If 0.02 mm.? 



19. How many particles in a gram of soil if the particles average 0.005 mm. 



in diameter? 



20. Upon what does the shape of the particles depend? 



21. What property does this affect? 



22. Define internal surface of a soil. 



23. How does the internal surface vary? 



24. How do the areas of spheres vary ? 



25. If a cubic foot of soil has an internal surface of 50,000 square feet and 



it contains 20.8 pounds of moisture, how thick would the film of 

 water be if uniformly distributed over the surface? 



26. What is the internal surface in acres of an acre of coarse sandy soil 



4 feet deep ? ( Table page 181.) 



27. Of an acre of the clay soil as given in the table on page 182? 



28. What two arrangements for soil particles? 



29. If a two-inch cubical box is filled with shot one-sixteenth of an inch 



in diameter arranged in columnar form, how many will it hold? 



30. What per cent of air space will remain? 



31. How is the porosity modified? 



32. What effect does wetting have on total pore space? 



33. How is porosity of a soil determined? 



34. How is the porosity of a soil under field conditions determined? 



35. What relation betwen the total pore space and the si/e of the pores? 

 30. If soil particles are one-thousandth of an inch in diameter, spherical 



and arranged vertically in a one-inch cube, what will lie the total 

 sectional area of the pores? Of a single pore? 



37. In the table on page 183 why is the porosity of the compact in ."> less 

 than in 4? 



REFERENCES 



Toffey, O. X., Hull. 85. Bureau of Soils, p. 42. 



'Wilev, II. W., The Principles and Practice of Agricultural Analyses, 100(i, 



p! 94. 

 'King, F. II., Physics of Agriculture, Mrs. F. H. King, Madison. Wis., 1901, 



p. 124. 

 * Unpublished data Soil Physics Division, University of Illinois. 



