This lab is performed to determine the specific gravity of soil by using a Pycnometer or Specific Gravity Flask. Specific gravity is the ratio of the mass of a unit volume of soil at a stated temperature to the mass of the same volume of gas-free distilled water at a stated temperature.
Procedure
1. Determine and record the weight of the empty clean and dry Pycnometer (Wp)
2. Place 10 grams of a dry soil sample (passed through the sieve No. 10) in the Pycnometer. Determine and record the weight of the Pycnometer containing the dry soil (Wps)
3. Add distilled water to fill up to the half or three-fourth of the Pycnometer. Soak the sample for 10 minutes.
4. Apply a partial vacuum or heat the contents for 10 minutes, to remove the entrapped air.
5. Fill the Pycnometer with distilled water (to the mark), clean the exterior surface of the Pycnometer with a clean, dry cloth. Determine the weight of the Pycnometer and contents (Wb)
6. Empty the Pycnometer and clean it. Then fill it with distilled water only (to the mark). Clean the exterior surface of the Pycnometer with a clean, dry cloth. Determine the weight of the Pycnometer and distilled water, (Wa)
Calculate the specific gravity of the soil solids using the following formula:
Specific Gravity (Gs) = Wo / (Wo + (Wa – Wb))
Wo = Weight of sample of oven-dry soil, g = Wps – Wp
Wa = Weight of Pycnometer filled with water
Wb = Weight of Pycnometer filled with water and soil
Calculations
Sample name: ……………
Sample description: ……………
Pycnometer or Specific Gravity Flask Number
Wp = Mass of empty, clean Pycnometer (grams):
Wps = Mass of empty Pycnometer + dry soil (grams):
Wb = Mass of Pycnometer + dry soil + water (grams):
Wa = Mass of Pycnometer + water (grams):
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