l8 THE PHYSICAL PROPERTIES OF SOILS 



SECOND EXERCISE 



DETERMINATION OF THE SPECIFIC 

 GRAVITY OF SOILS 



The specific gravity of soil varies from about 2 

 up to 2.90, the average being about 2.65, which is the 

 specific gravity of quartz crystal. That is, the soil 

 calculated free of air spaces weighs about 2.65 times 

 as much as an equal volume of water. The density 

 will vary with the mineral constituents of the soil and 

 with the amount of organic matter present, the specific 

 gravity decreasing as the organic matter increases. 



METHOD OF DETERMINATION 



With specific gravity fiasks or pycnometers (T) 

 of 50 cc. capacity make duplicate determinations of the 

 specific gravity of soils No. i, No. 4, and No. 5. 



Fill the fiask with distilled water and boil for a few 

 minutes in a salt bath to expel the air. Cool the flask 

 to 30° C, insert the stopper, wipe dry, and when 

 it has cooled to room temperature, weigh. Pour out 

 about half of the water in the flask and introduce into 

 it about ten grams of soil. Again place the flask in 

 the salt bath and boil for a few minutes. Fill the flask 

 with boiled water, cool to 30° C, stopper and weigh 

 again at room temperature. Transfer the soil to a 

 porcelain dish, evaporate, and dry in the oven to 

 determine accurately the amount of soil used. 



CALCITLATION 



The weight of the soil used divided by the weight of 

 the water displaced will give the s])ccific gravity of 

 the soil. 



