74 CHEMICAL PROPERTIES OF SOIL 



51. Determination of True Specific Gravity. 



The specific gravity is generally determined at 20° C. 

 in an ordinary specific gravity bottle. 



A 100 C.C. capacity specific gravity bottle is weighed, 

 then filled with freshly boiled distilled water and 

 weighed again. Ten grams of the soil dried at 100° C. 

 are boiled for a short time in a beaker with a few 

 c.c. of water in order to expel the air. The soil 

 is then completely washed into the gravity bottle 

 with boiled distilled water, cooled to 20°, and filled to 

 the mark with the water. The bottle is then weighed 

 again. 



The weight of soil used divided by the weight of 

 water displaced gives the specific gravity of the soil. 



52. Determination of Apparent Specific Gravity. 



In order to ascertain the apparent density of a soil 

 the best method is to get a smooth open measure, such 

 as a pint pot or a specimen jar, fill it with the soil, with 

 gentle tapping, strike off the upper surface flush with the 

 top of the pot, and weigh. The volume of the vessel is 

 measured by filling it with water and the apparent 

 density obtained by dividing the weight of soil by the 

 volume. 



Pore-space. 



53. Direct determination in Sand. 



Fifty grams of sand are weighed out and transferred 

 to a dry measuring cylinder. The latter is tapped 

 gently on the bench and the volume occupied by the 

 sand noted. (The apparent density may be measured 

 from this datum.) The sand is now removed and 50 

 c.c. of water poured into the cylinder, after which the 

 sand is carefully returned to the vessel, the mixture 



