1.0 Scope:
In this method the water-soluble salts in soils are quantitatively
determine by shaking the material for 24 hours with water and determining the
mass of salts present in a filter aliquot
2.0
Apparatus:
2.1
Sieves.
2.2
Mortar and pestle.
2.3
Flasks 500 ml capacity.
2.4
Shaker.
2.5
Buchner funnels.
2.6
Evaporating dish.
3.0
Preparation of test specimen:
3.1
Fine aggregates:
a)
Dry about 400 g of the test
sample at a temperature not exceeding 80°C for at least 16 h and then grind it
until it all passes a 1.70 mm sieve. By means of a sample splitter or by coning
and quartering obtain a test specimen of mass about 100 g, and grind it until
it all passes a 425 m sieve.
b)
Dry the test specimen at a
temperature of 75-80°C until, after two successive drying periods of 4 h, the
decrease in mass does not exceed 0.1% of the total mass, and cool it to room
temperature in a desiccator.
3.2
Base course materials:
a)
Dry a mass of the test sample
estimated to contain about 400g of material passing a 425m sieve for at least
16 h at a temperature not exceeding 80°C, allow to cool, and sieve on a 4.75 mm
sieve and a1.70 mm sieve superimposed on a pan.
b)
Break up any aggregation of
smaller particles in the portion passing the 4.75 mm sieve and retained on the
1.70mm sieve by placing it in the mortar and rubbing it with the pestle.
c)
Sieve this portion again on the
1.70mm sieve, add it to the material in the pan, and sieve the mixture on a
425m sieve. Place the portion retained on the 425 m sieve in the mortar, rub it
as in above, and again sieve thoroughly on the 425m sieve.
d)
Combine the fines and mix well.
By means of a sample splitter or by coning and quartering obtain a test
specimen, of mass about 100g, of the fines, and dry and cool it.
4.0
Procedure:
4.1
Extraction of water soluble
salts:
a)
Weigh out accurately about 25g
of the test specimen in to a flask and add exactly 500ml of water. Stopper the
flask and shake continuously for 24 h on the shaker. Remove the flask from the
shaker and allow the undissolved material to settle by allowing the flask to
stand undissolved for at least 1 h.
b)
Place a dry 600 ml beaker in
the filter apparatus and a double layer of glass fibre filter paper of fine
texture on the Buchner funnel, and wet the paper
with a few drops of the aqueous extract.
c)
Using low vacuum and ensuring
that the sediment in the flask is not disturbed, filter about 400ml of the
aqueous extract through the filter paper. Then shake the flask vigorously until
all the Buchner funnel, attempt to transfer as much
as possible of the undissolved material into the funnel. Do not add additional
water to the flask to aid in this operation. Complete the filtration by
evacuation but do not allow the filter paper to become dry. Do not wash the
residue on the filter paper.
d)
Add
about 0.5 g of dry filter paper pulp to the filtrate and stir until the paper
pulp has disintegrated completely and is in suspension. Cover the residue in
the Buchner funnel with a glass fiber filter paper of the texture and filter
the filtrate through the Buchner funnel again, using low vacuum, into a clean
and dry suction flask. Do not wash the residue in the Buchner
funnel.
e)
The Filtrate should now be
clear and contain no undissolved material in suspension. If this is not the
case, repeat above.
4.2
Recovery of water soluble salts:
a)
By means of pipette transfer
200 ml of the filtrate to a beaker of capacity about 400ml , boil until the
volume of the solution is about 50 ml, and transfer quantitatively to the dry
tare evaporating dish, washing the beaker three times with warm water and
adding the washings to the solution in the evaporating dish.
b)
Evaporate the contents of the
evaporating dish to dryness on a water bath, then transfer the dish to an oven
maintained at a temperature of 105-110°C and dry for 1 h. Cool the evaporating
dish and its contents to room temperature in a desiccator, determine its mass,
and calculate the mass of the contents of the evaporating dish.
4.3
Blank Determination:
Carry out a blank determination by following the
procedures given in 3.1 and 3.2 but omitting the 25 g of test specimen.
Subtract the mass of any residue found in the evaporating dish from the mass
found in 3.2(b) above and this corrected mass (Mass A) as the mass of water
–soluble salts in the 200ml of filtrate.
5.0
Calculation:
4.1
Calculate, as follows, the
water-soluble salts content of the fine aggregate or the fines
A x 5
Total water-soluble salts content (m/m) = --------- x 100
B x 2
Where:
A = mass of soluble salts found in 200ml of the extract, g
B = mass of the specimen taken for extraction, g
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