PROCEDURE
Step 1. Clean the density bottle and stopper. Dry by rinsing with acetone or an alcohol-ether mixture and then blowing warm air through it at 105 °C to 110 °C. Weigh the bottle with the stopper to the nearest 0.001 g (m1).
NOTE: In order to avoid distortion, the density bottle should not be dried by placing it in an oven.
Step 2. Transfer the first soil specimen to the density bottle direct from its sealed container. Weigh the bottle, contents and stopper to the nearest 0.001 g (m2).
Step 3. Add sufficient air-free distilled water or other liquid just to cover the soil in the bottle, without disturbing the soil excessively. Place the bottle and contents, without the stopper, in the vacuum desiccator. Evacuate the desiccator gradually, reducing the pressure to about 20 mm of mercury. Take care during this operation to ensure that air trapped in the soil does not bubble too violently, which could lead to small drops of suspension being lost through the mouth of the bottle. When using a water pump, because of variations in mains pressure, take care to ensure that the required vacuum is maintained. Leave the bottle in the evacuated desiccator for at least 1 hour until no further loss of air is apparent.
NOTE: With certain soils, e.g. those containing soluble salts, kerosene (paraffin oil) or white spirit may be preferred to distilled water. If one of these is used, record the fact and carry out a separate experiment to determine the density of the liquid at the temperature of the test.
Step 4. Release the vacuum and remove the lid of the desiccator. Stir the soil in the bottle carefully with the Chattaway spatula, or vibrate the bottle. Before removing the spatula from the bottle wash off any particles of soil adhering to the blade with a few drops of air-free liquid. Replace the lid of the desiccator and evacuate it again as specified in Step 3.
Step 5. Repeat Steps 3 and 4 until no more air is evolved from the soil.
NOTE: Experience has shown that the largest source of error in the test is due to the difficulty in ensuring the complete removal of air from the sample. To obtain reliable results the soil should be left under vacuum for several hours, preferably overnight.
Step 6. Remove the density bottle and contents from the desiccator and add more air-free liquid to fill the bottle. Insert the stopper and immerse the bottle up to the neck in the constant-temperature bath. Leave the bottle in the bath for at least 1 hour or until the contents have attained the constant temperature of the bath.
NOTE: If a constant-temperature room or cabinet is available then this procedure need not be carried out in a water bath.
Step 7. If there is an apparent decrease in the volume of the liquid, remove the stopper, add more liquid to fill the bottle and replace the stopper. Return the bottle to the bath and again allow the contents to attain the constant temperature.
NOTE: If surplus liquid other than water exudes through the capillary in the stopper it should be carefully absorbed on a filter paper to avoid contamination of the water bath.
Step 8. Repeat Step 7 if necessary, until the bottle remains completely full.
Step 9. Take the stoppered bottle out of the bath, carefully wipe it dry with the minimum of handling and weigh the whole to the nearest 0.001 g (m3).
Step 10. Clean out the bottle, fill it completely with de-aerated liquid, insert the stopper and immerse in the constant temperature bath for the period specified in Step 6.
Step 11. If necessary, fill the bottle as specified in Steps 7 and 8.
Step 12. Take the stoppered bottle out of the bath, wipe it dry as specified in Step 9 and weigh it to the nearest 0.001 g (m4).
NOTE: If step 10 is used to find the volume of the density bottle then the test may be carried out at any temperature provided it is constant throughout the test.
Step 13. Repeat Steps 1 to 9 using the second specimen of the same soil so that two values of particle density can be obtained. If the results differ by more than 0.03 Mg/m3 repeat the test.
NOTE 1: Many soils have a substantial proportion of heavier or lighter particles. Such soils will give erratic values for the particle density even with the greatest care in testing and a number of repeat tests may be needed to obtain a good average value.
NOTE 2: Clean quartz and flint sands generally have a specific gravity close to 2.65; low values would suggest the presence of organic matter.
CALCULATIONS
Calculate the specific gravity or particle density, Gs (in Mg/m3), from the equation below:
Where,
m1 is the mass of density bottle (in g);
m2 is the mass of bottle and dry soil (in g);
m3 is the mass of bottle, soil and water (in g);
m4 is the mass of bottle when full of water only (in g).
Calculate the average of the two results if they differ by no more than 0.03 Mg/m3.
Express the average value of the particle density to the nearest 0.01 Mg/m3.
TEST REPORT
The test report shall affirm that the test was carried out in accordance with
BS 1377-2:1990 and shall include the following information:
a) the method of test used;
b) the average value of the particle density of the soil specimen;
c) the information required by clause 9 of BS 1377-1:1990.
