Test Method for pH Determination in Soil
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Test Method for pH Determination in Soil

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Test Method for pH Determination in Soil

1) Principle:  

pH of soil is determined by electrometric method which gives a direct reading of the pH value of soil suspension in water.   

2) Reagents and Apparatus:  


I. Balance  

II. Pestle and mortar  

III. Test sieve  


IV. Non-corrodible tray  

V. pH meter  



VI. Buffer solutions  




VII. 100 mL beakers  

VIII. Two 500 mL volumetric flasks 
 
IX. Wash bottle  

X. Measuring cylinder  


3) Procedure:  


3.1) Preparation of test specimen  


Obtain an initial sample. Allow the sample to air-dry by spreading out on a tray exposed  to air at room temperature. Sieve the sample on a 2 mm test sieve (if appropriate,  guarded by a 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 the 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 a representative test sample of  30 g to 35 g.  

3.2) Electrometric method of pH determination  


Weigh 30+0.1 g of soil sample in a 100 mL beaker. Add 75 mL of distilled water, stir the  suspension for few minutes, cover with cover glass and stand for at least 8 hours. Stir the  suspension again immediately before testing. Calibrate the pH meter by using the  standard buffer solutions, following the procedure recommended by the manufacturer.  Wash the electrode with distilled water and immerse in the soil suspension. Take two or  three readings of the pH of the suspension with brief stirrings between each reading.  These readings shall agree to within 0.05 pH units before being accepted. Remove the  electrodes from the suspension and wash them with distilled water. Re-check the  calibration of the pH meter against one of the standard buffer solutions. If the instrument  is out of adjustment by more than 0.05 pH units, set it to the correct adjustment and  repeat steps until consistent readings are obtained.  


4) Reference:   


BS 1377 Part 3:1990 Amd 9028 :1996   

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