PRACTICE XXXI 



A STUDY OF THE PHYSICAL COMPOSITION OF SOILS 



Two weeks will be devoted to studying the physical composi- 

 tion of a large number of soils. It is quite important that one 

 should be able to estimate approximately the proportion of gravel, 

 sand, silt, clay, and organic matter in soils, and it is the object 

 of this exercise to enable the student to do this. 



Each student will be given a sample of the same soil to be 

 studied according to the outline below. 



The work is to be done rapidly, and the graduated cylinder 

 may be used as an aid in estimating the amount of each constit- 

 uent. Place 10 cc. of soil with 75 to 90 cc. of water in the cylinder. 



Shake thoroughly and allow it to stand one-half minute or 

 longer. Note the amount of sand in cubic centimeters and esti- 

 mate the percentage from this. 



The cylinder is an aid in sandy soils but is of little value 

 with silt or clay soils. 



Dry 



Color 



Pulverulent, crumbly, or cloddy 

 Moist 



Color 



Floury, mealy, or gritty 



Friable or plastic 

 Composition (estimated) 



Organic matter in per cent 



Gravel in per cent 



Coarse and medium sand in per cent 



Fine sand in per cent 



Silt and clay in per cent 



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