68 



Care should be exercised to fill the molds as nearly as possi1)le in the same man- 

 ner in each test. 



With this same roll of mud make four tests, using varying amounts of water. The 

 jjroportion of water may be reduced by adding more dry soil. Test each of the four 

 types of soil in the above manner, using the highest test of 

 each for comparisons of maximum adhesiveness. 



Exprrhiientx Xoi^. 11 uud 12. 



MECHANUAL ANALYSIS OF SOILS. 



A modification of the method used in the laboratory of the 

 Bureau of h^oils of the United States Department of Agricul- 

 ture. (PI. XIV, fig. 1.) 



Twenty grams of "fine earth" are weighed out and placed 

 in a porcelain or glass mortar. Enough water is added to 

 give the soil the consisteiicy of paste. The mixture is then 

 rubbed with a rubber-tipped pestle. 



In rubbing there should be just enough i)ressure to detach 



Flw. 19.— Ai>]irtmtiis for testing the adhesiveness of soils. 



adhering particles and not enough to break the grains. After five minutes' rubbing 

 more water may be added, and after letting it stand for two or three minutes the 

 turbid liquid 'is decanted into a Ijeaker, "A." Repeat this pestUng and decanting 

 until an examination through the microscope shows the grains to be jjerfectly clean. 

 When clean the grains show sharp outlines and are transparent, while any adhering 

 finer particles make them round and deeply colored. This pestling may require 15 

 minutes to an hour or more. 



When the material is thoroughly disintegrated, it is transferred from the mortar 

 to a No. 2 or No. 3 beaker, which is then filled with water, stirred and allowed to 

 stand a few minutes, after which it is carefully decanted, leaving the last 20 or 30 cubic 

 centimeters, the liquor being added to the beaker "A." This is repeated until the 

 santl is free from clay, fine silt, and much of the silt. The sand should Ije tested 

 with the microscope. All particles smaller than 0.05 millimeter are silt or fine silt 



