PRACTICE XIV 



DETERMINATION OF POROSITY (FIRST METHOD) 



Use sand or sandy loam, gray silt or gray silt loam, brown 

 silt loam, clay or clay loam, and peat. 



The weight of soil and volume of tube as found in Prac- 

 tice XI may be used here, or one may weigh a Nessler jar or 

 graduated cylinder and fill to the 100-cc. mark with soil not 

 compacted, and weigh. 



Compute the amount of water-free soil, using the average 

 per cent of hygroscopic moisture from Practice VI which was 

 given for Practice XI. The real specific gravity will be deter- 

 mined or furnished by the instructor. 



(Volume of soil x real specific gravity) weight of water-free soil ^ _ 

 Volume of soil x real specific gravity 



per cent of pore space or porosity. 



What effect does size of particles have on total amount of 

 pore space ? 



Does the amount of pore space increase or decrease with the 

 amount of organic matter ? 



Which of the soils have the largest pores ? Does this mean 

 the greatest amount of pore space ? 



REFERENCES. 



" Soils," Lyon and Fippin, pp. 84-94. 

 " The Soil," Hall, pp. 60-63. 

 " Soils," Hilgard, pp. 108-109. 



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