EXERCISE 10 

 THE WEIGHT OF SOIL PER CUBIC FOOT 



Object. To determine the weight of soil per cubic 

 foot. 



Explanation. The weight of soil depends upon the 

 weight of the material of which the soil is composed and the 

 amount of open space or pore space hi the soil. If a cubic 

 foot of soil contained no pore space and were composed 

 entirely of rock particles, it would weigh a little more than 

 two and one half times as much as a cubic foot of water, or 

 about 165 pounds per cubic foot. A cubic foot of soil 

 never weighs this much. A soil always contains some pore 

 space, and this reduces its weight. A soil also contains some 

 organic matter, and since organic matter is lighter than the 

 rock particles, the more organic matter it contains the less 

 it weighs. Thus the weight of soil per cubic foot varies 

 with its organic matter content and the amount of pore space 

 in the soil. 



Equipment. 1. Four soil tubes, like those used in 

 Ex. 9. 



2. Cheesecloth. 



3. Shears. 



4. Torsion balances weighing to half a gram. 



5. Four soils: gravel, sand, loam, and clay. 



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