GRAVITATIONAL WATER 



22 i 



Water Draining from Eight Fact of Saturated Hands. Percentage Based on Dry 



Soil, 4 King 



The table shows the amount of water draining from eight feet 

 of saturated saml soil in 268 days. The drainage, of course, was not 

 continuous during this time, but varied with conditions of tem- 

 perature and atmospheric pressure. During the last 259 days of 

 intermittent drainage the sand lost from 6.56 to 9.15 pounds of 

 water per square foot, or from 1.2 to nearly 1.8 inches of water. 

 Percolation is only possible when the air can enter the soil, hence a 

 slight rain falling on the surface may retard or entirely stop perco- 

 lation by sealing the surface so that the air cannot get out. This 

 has been observed at the Rothamsted drain gages. 



QUESTIONS 



1. Define gravitational water. 



2. W'hat is tin 1 maximum water capacity? 



JJ. Which may have the greater gravitational water capacity, sand or clay? 



4. Define water table. 



5. How does the movement of water through soil vary? 



C. Compare the number of pores in a sand soil, particles ().().") mm., with a 

 silt soil, particles 0.0f> mm. 



7. What about the etl'ect of shape and si/.e of particles in the same soil 



on percolation ? 



8. What part does granulation play in percolation? 

 !). (live the effects of organic matter on percolation. 



10. Explain the effect of viscosity on percolation. 



11. What things affect the viscosity of water? 



12. Explain variations caused by changes in atmospheric pressure. 

 !.'{. What other factors aid percolation? 



14. Describe the Kothamsted drain gages. 



15. What conclusions may be drawn from the results? 



10. Give King's experiment regarding drainage from sands. 



REFERENCES 



'King, F. If., Physics of Agriculture. 1007. p. 134. 

 1 King. V. H.. The Soil, 1007, p. ISO. 



3 Mall, A. 1)., The Hook of the Kothamstcd Experiments. lf)05. p. 2.'<. 



4 King. F. II., Wisconsin Station, lltli Ann. Keport, p. 28.1. 



General References -King. F. 11.. Principles and Conditions of the 

 Movements of Ground Water. I". S. Geol. Survey, 19th Ann. Report, Part 



11, 1S07-08, pp. (i7-20(i. 



