Method for Water-Soluble Chloride Analysis Test in Soil
Principle.
Reagents and Apparatus.
I. Burette, 50 mL
II. Weighing balance
III. Stoppered conical flask, 500 mL
IV. Wide mouth screw-capped plastic or metal bottle,
2L capacity.
V. Measuring cylinder
VI. Filter paper, medium grade
VII. Filter funnel
VIII. Mechanical shaker
IX. 6 M Nitric Acid Solution
X. 0.1 N Silver Nitrate Solution
XI. 0.1 N Potassium Thiocyanate Solution
XII. 3-5-5-Trimethylhexan-1-ol
XIII. Ferric alum indicator
Procedure:
Standardization of thiocyanate solution
Preparation of test specimen.
Obtain an initial sample. Dry this sample in an oven at 105 °C to 110 °C and allow to cool to room temperature in the desiccator. Sieve the sample on a 2 mm test sieve (if appropriate, guarded by a test sieve of larger aperture) and crush retained particles other than stones to pass through the 2 mm test sieve. Reject the stones, ensuring that no fine material adheres to them, e.g., by brushing.
Record the mass m2 (in g) of sample passing the 2 mm test sieve to the nearest 0.1 %. Throughout these and subsequent operations ensure that there is no loss of fines.
Divide the material passing the 2 mm test sieve by successive riffling through the 15 mm divider to produce the following: a) a test specimen of about 500 g; and b) a specimen of about 50 g for a qualitative check test to determine whether chlorides are present.
Dry the specimens in the oven at 105 °C to 110 °C. The specimens are deemed to be dry when the differences in successive weighing carried out at intervals of 4 h, do not exceed 0.1 % of the original mass of the sample.
Allow the specimens to cool to room temperature in the desiccator.
Qualitative check for chlorides.
Preparation of water-soluble chloride extract.
Analysis of extract.
Take 100 mL of the filtered extract by means of the pipette and transfer to the 250 mL conical flask.
Add 5 mL of the nitric acid solution to the flask followed by silver nitrate solution from a burette until all the chloride has been precipitated, and then add a little excess silver nitrate.
Record the total volume V (in mL) of silver nitrate solution added.
Add 2 mL of 3,5,5-trimethylhexan-1-ol, fit the stopper, and shake the flask vigorously to coagulate the precipitate.
Carefully loosen the stopper, avoiding loss of solution, rinse with distilled water, and collect the washings in the solution.
Add 5 mL of the ferric alum indicator solution, followed by the standardized thiocyanate solution from a burette until the first permanent color change occurs, that is from colorless to brick-red. Record the volume V3 (in mL) of thiocyanate solution added.
Calculation.
Reference.
BS 1377 Part 3:1990 Amd 9028 :1996