Method of test for soils, Part 26: Determination of pH value

IS 2720 Part 26: Scope & Key Specifications

This part of IS 2720 covers methods for determining pH of soils using electrometric and indicator paper methods.

1. Scope (Summary)

• Applicable for pH measurement of soils using:
  • Electrometric method (using pH meter)
  • Indicator paper method (colorimetric)
• Covers sample preparation, measurement, and interpretation.

2. Key Formulas (Clause 2.6 - Calculations)

• pH Calculation (Electrometric Method):

[ pH = pH_{calibration} + \frac{E_{measured} - E_{calibration}}{S} ]

Where:

• (E_{measured}) = electrode potential of soil suspension
• (E_{calibration}) = electrode potential of standard buffer
• (S) = slope of electrode (mV/pH unit) typically 59 mV at 25°C

3. Indicator Paper Method (Clause 3.2.1)

4. Data Recording

• Use Appendix A data sheet for electrometric observations.
• Record pH values, temperature, and electrode conditions.

flowchart LR
    A[Soil Sample] --> B[Prepare Suspension]
    B --> C{Method}
    C -->|Electrometric| D[Measure Potential with pH Meter]
    C -->|Indicator Paper| E[Dip Paper & Compare Color]
    D --> F[Calculate pH using formula]
    E --> F
    F --> G[Record pH in Data Sheet]

Summary: IS 2720 Part

IS 2720 Part 26 (1987) — Electrometric Method for Soil pH Determination

Key Specifications:

• Instrument: pH meter (direct reading type) as per IS 2711-1979, equipped with:

  • Glass electrode (measuring electrode)
  • Calomel reference electrode (or equivalent)

• Sample Preparation: Soil suspension prepared by mixing soil passing through a specified sieve with distilled water (usually 1:2.5 soil-to-water ratio).

Procedure Summary:

1. Calibrate pH meter with standard buffer solutions (pH 4, 7, and 9).
2. Immerse electrodes in the soil suspension.
3. Record the stable pH meter reading.

Data Recording (Appendix A):

Important Notes:

• Follow rules for rounding off numerical values as per the standard.
• Ensure electrodes are clean and properly maintained.
• Temperature corrections may be applied if necessary.

Typical Formula:

No explicit formula is needed; pH is directly read from the meter calibrated against standard buffers.

flowchart TD
    A[Soil Sample] --> B[Passing through Sieve]
    B --> C[Mix with Distilled Water (1:2.5)]
    C --> D[Prepare Soil Suspension]
    D --> E[Calibrate pH Meter]
    E --> F[Immerse Electrodes]
    F --> G[Read pH Value]
    G --> H[Record Data]

This method ensures accurate, reproducible soil pH values critical for agronomy and geotechnical assessments.

IS 2720 Part 26 - Apparatus and Materials: Key Points

1. Mortar and Pestle

   • Use a mortar with rubber-covered pestle (Clause 2.1.6) to avoid contamination.
   • Glass apparatus must be alkali-resistant.

2. Indicator Papers (Clause 3.2.1)
   Supplied in booklets or rolled tapes with color charts. Common indicators include:

3. Data Sheets
   • Electrometric method data sheet: Appendix A (Clause 2.5.1)
   • Colorimetric methods data sheets: Appendices B & C (Clause 3.3.1)

Summary Table of Indicator Papers

| Indicator          | pH Range        |
|--------------------|-----------------|
| Bromocresol green  | 3.8 – 5.4       |
| Bromothymol blue   | 6.0 – 7.6       |
| Methyl orange      | 3.1 – 4.4       |
| Methyl red         | 4.4 – 6.2       |
| Thymol blue        | 1.2–2.8 & 8.0–9.6 |
| Titan yellow       | 11.0 – 13.0     |
| Chlorophenol red   | 4.8 – 6.4       |

Note: Always refer to the respective appendices for

IS 2720 Part 26: Buffer Solutions Key Details

Buffer Solutions Preparation (at 25°C)

Important Specifications:

• Use pure chemicals free from impurities affecting analysis.
• For alkaline buffers (pH 9.2), ensure distilled water is free from carbon dioxide to avoid pH drift.
• Prepare solutions by dissolving the chemical fully and then diluting to the specified volume with distilled water.

Testing Method:

• Use Universal Indicator Method (Clause 3.1) to verify buffer pH.

Summary Table:

flowchart LR
    A[Start] --> B[Dissolve chemical in distilled water]
    B --> C[Make up solution to 500 ml]
    C --> D{Buffer pH?}
    D -->|4.0| E[Use 5.106 g potassium hydrogen phthalate]
    D -->|9.2| F[Use 9.54 g sodium tetraborate]
    F --> G[Ensure distilled water is CO₂ free]
    E & G --> H[Use Universal Indicator to verify pH]

This ensures accurate and consistent pH buffer solutions for soil testing as per IS 2720 Part 26.

IS 2720 Part 26: Soil Specimen Preparation & pH Determination

Key Specifications for Soil Specimen Preparation (Clauses 2.3 & 2.4)

• Sample Preparation:
  • Break soil aggregates so particles passing 425 µm sieve are discrete.
  • Mix thoroughly and subdivide by quartering or riffling to get representative sub-sample.
• pH Test Suspension:
  • Take 30 g soil + 75 ml aerated distilled water in 100 ml beaker.
  • Stir briefly, cover, stand 1 hour with occasional stirring.
  • Stir again before testing.

pH Determination (Clause 2.5.1 & 3.1.2)

• Electrometric Method:
  • Use pH meter on prepared suspension.
• Indicator Method:
  • Take 20 g soil + 50 ml aerated distilled water.
  • Stir continuously for 10 min, stand 1 hour.
  • Pipette 20 ml clear solution, add 2-3 drops universal indicator.
  • Compare color with standard pH chart.
• Note: Add barium sulphate to accelerate settling:

  Soil Type	BaSO4 : Soil Weight Ratio
  Sand	1 : 3
  Silt	1 : 1
  Clay	3 : 1

Summary Table for pH Test Suspension

flowchart TD
    A[Soil Sample] --> B[Break aggregates]
    B --> C[Mix & Subdivide]
    C --> D[Take 20-30 g soil]
    D --> E[Add aerated distilled water]
    E --> F[Stir & Stand 1 hour]
    F --> G{pH Test Method}
    G -->|Electrometric| H[pH Meter Reading

IS 2720 Part 26: Electrometric Method for Soil pH Determination

Key Specifications & Procedure Summary

• Purpose: Determine soil suspension pH using a pH meter (electrometric method).
• Sample Preparation: Soil sample passing through Sieve No. 4 is used.
• Measurement: pH meter reading on standard pH scale.
• Reporting: pH value rounded to the nearest 0.1 pH unit.
• Documentation: Use the data sheet format as per Appendix A to record:
  • Soil Identification
  • Sample passing sieve number
  • pH meter reading

Important Notes

• The test must explicitly mention it was carried out by the electrometric method.
• Follow standard calibration and maintenance of the pH meter for accuracy.
• Rounding off follows IS 2 rules (nearest 0.1 unit).

Typical Data Sheet Layout (Appendix A)

Summary Diagram of Procedure

flowchart TD
    A[Soil Sample] --> B[Pass through Sieve No. 4]
    B --> C[Prepare Soil Suspension]
    C --> D[Calibrate pH Meter]
    D --> E[Measure pH Electrometrically]
    E --> F[Record pH to nearest 0.1 unit]
    F --> G[Fill Data Sheet (Appendix A)]

For detailed calibration and measurement steps, refer to the full IS 2720 Part 26 document.

IS 2720 Part 26 - Recording Observations

• Clause 2.5 & 3.3: Emphasize systematic recording of observations during soil resistivity tests.

• Clause 2.5.1: Use the data sheet in Appendix A for electrometric method observations. It typically includes:

  • Electrode spacing
  • Measured resistance or voltage
  • Current applied
  • Calculated resistivity

• Clause 3.3.1: Use Appendix B and C for colorimetric method observations, which record:

  • Sample identification
  • Color intensity or scale reading
  • Corresponding resistivity values from calibration charts

Key Points for Recording Observations:

• Maintain clarity and accuracy.
• Include all test parameters (e.g., electrode spacing, current, voltage).
• Use standard data sheets as per Appendices for consistency.
• Observations form the basis for calculating soil resistivity using:

[ \rho = 2 \pi a R ]

Where:

• (\rho) = soil resistivity (Ω·m)
• (a) = electrode spacing (m)
• (R) = measured resistance (Ω)

flowchart TD
    A[Start Test] --> B[Measure Resistance/Voltage]
    B --> C{Method Used?}
    C -->|Electrometric| D[Record in Appendix A]
    C -->|Colorimetric| E[Record in Appendix B/C]
    D --> F[Calculate Resistivity]
    E --> F
    F --> G[Analyze & Interpret Data]
    G --> H[End]

Use these guidelines to ensure standardized and reliable soil resistivity data recording.

IS 2720 Part 26: Calculation and Reporting

1. Calculations (Clauses 2.6 & 3.4)

• Calculations involve determining soil parameters (e.g., shear strength, compressibility) from test data.
• Use standard formulas for parameters like:
  • Shear strength: ( \tau = c + \sigma \tan \phi )
  • Void ratio: ( e = \frac{V_v}{V_s} )
  • Water content: ( w = \frac{W_w}{W_s} \times 100% )
• Interpretations require averaging multiple test results and checking for consistency.

2. Presentation of Results (Clauses 2.7 & 3.5)

• Results must be tabulated clearly, including:
  • Sample identification
  • Test conditions (e.g., moisture, density)
  • Calculated parameters with units
• Include graphical plots where applicable (e.g., stress-strain curves).
• Report anomalies or deviations from standard behavior.
• Use SI units consistently.

Example Table Format for Reporting:

This ensures clarity and uniformity in reporting soil test results per IS 2720 Part 26.

IS 2720 Part 26: Colorimetric Methods (Subsidiary Methods) - Key Points

1. Indicator Papers (Clause 3.2.1)

• Indicator papers are supplied as booklets or rolled tapes with a color chart.
• Common indicators include:
  • Bromocresol green
  • Bromothymol blue
  • Thymol blue
  • Methyl orange
  • Titan yellow (Clayton yellow)
  • Methyl red
  • Chlorophenol red

2. pH Measurement (Clause 2.7.1)

• pH value of soil suspension must be reported to nearest 0.1 pH unit.
• Measurement is by the electrometric method, but colorimetric methods serve as subsidiary checks.

3. Data Recording (Clause 3.3.1)

• Observations from colorimetric methods are recorded on data sheets given in Appendix B and Appendix C.

Typical Data Sheet Structure (Summary from Appendices)

Notes:

• Colorimetric methods provide a quick, visual estimate of soil pH or other chemical properties.
• For accuracy, electrometric methods (pH meter) are preferred.
• Use the color chart supplied with indicator papers to match the color and estimate pH.

flowchart LR
    A[Soil Sample] --> B[Prepare Suspension]
    B --> C[Add Indicator Paper]
    C --> D{Color Change}
    D --> E[Match with Color Chart]
    E --> F[Estimate pH or Property]
    F --> G[Record on Data Sheet]

This summarizes the key points for colorimetric methods per IS 2720 Part 26. For detailed procedures and exact color charts, refer to Appendices B & C of the code.

IS 2720 Part 26: Universal Indicator Method (Clause 3.1)

Preparation of Universal Indicator (3.1.1)

• Dissolve in 100 ml alcohol:
  • 0.06 g Methyl yellow
  • 0.04 g Methyl red
  • 0.08 g Bromothymol blue
  • 0.10 g Thymol blue
• Titrate with 0.1 N NaOH until yellow color is obtained.

Color-pH Correlation

Notes:

• The universal indicator provides a continuous pH scale useful for soil pH determination.
• The titration to yellow color standardizes the indicator solution.
• The color changes correspond to specific pH values, aiding visual estimation.

graph LR
A[Prepare Indicator Solution] --> B[Titrate with 0.1N NaOH]
B --> C{Color Observed}
C -->|Cherry red| D[pH 1]
C -->|Red orange| E[pH 3]
C -->|Orange red| F[pH 4]
C -->|Yellow green| G[pH 7]
C -->|Blue green| H[pH 9]

For detailed indicator paper method, refer to Clause 3.2.

IS 2720 Part 26: Indicator Paper Method for Soil pH

Key Specifications & Procedure (Clause 3.2)

• Indicator Papers: Supplied as booklets or rolled tapes with color charts, including:
  • Bromocresol green
  • Bromothymol blue
  • Methyl orange
  • Methyl red
  • Titan yellow (Clayton yellow)
  • Chlorophenol red
  • Thymol blue

Procedure (Clause 3.2.2)

1. Weigh 20 g of representative soil sample.
2. Add 50 ml distilled water; stir continuously for 10 min.
3. Let stand for 1 hour.
4. Pipette 20 ml clear supernatant into a clean test tube.
5. Dip indicator paper strip into solution.
6. Match the color on paper with supplied color chart to read pH.

Notes:

• pH is read directly from the color scale.
• This method is quick and suitable for field or lab use.
• Accuracy depends on indicator paper range and color matching.

flowchart TD
    A[Soil Sample (20g)] --> B[Add 50 ml Distilled Water]
    B --> C[Stir 10 min]
    C --> D[Stand 1 hour]
    D --> E[Pipette 20 ml Clear Solution]
    E --> F[Dip Indicator Paper]
    F --> G[Compare Color with Chart]
    G --> H[Determine pH]

This method is standardized in IS 2720 (Part 26) - 1987 for soil pH estimation using indicator papers.

IS 2720 Part 26: Colorimetric Methods - Key Points

1. Indicator Paper Method (Clause 3.2.1)

• Indicator papers supplied as booklets or rolled tapes with a color chart.
• Common indicators include:
  • Bromocresol green
  • Bromothymol blue
  • Thymol blue
  • Methyl orange
  • Titan yellow (Clayton yellow)
  • Methyl red
  • Chlorophenol red

2. pH Measurement (Clause 2.7.1)

• pH is recorded to the nearest 0.1 pH unit.
• The standard method is electrometric, but colorimetric methods serve as subsidiary.

3. Data Recording (Clause 3.3.1)

• Observations to be recorded on data sheets provided in Appendix B and C.

Typical Procedure Summary:

1. Dip indicator paper into soil suspension.
2. Compare resulting color with the color chart.
3. Record color and corresponding pH value on the data sheet.

Example Color-pH Relation (Indicative):

flowchart TD
    A[Soil Suspension] --> B[Dip Indicator Paper]
    B --> C{Color Change}
    C --> D[Match with Color Chart]
    D --> E[Record pH on Data Sheet (Appendix B/C)]

For exact color charts and detailed steps, refer to Appendices B & C of IS 2720 Part 26.

IS 2720 Part 26: Presentation of Results

Key Clauses Summary:

• Clause 2.6 & 3.4 (Calculations & Interpretations):

  • Perform all calculations clearly, showing intermediate steps.
  • Use standard formulas relevant to soil tests (e.g., moisture content, density, shear strength).
  • Interpret results based on soil behavior and test objectives.

• Clause 2.7 & 3.5 (Presentation of Results):

  • Present results in tabular form with clear headings:
    • Sample ID
    • Test parameters (e.g., moisture content %, density, shear strength)
    • Calculated values (e.g., dry density, void ratio)
  • Include graphical plots where applicable (e.g., stress-strain curves, compaction curves).
  • Provide units, test conditions, and any deviations from standard procedures.
  • Summarize key findings and conclusions.

Common Formulas for Presentation:

Recommended Presentation Format:

IS 2720 Part 26: Electrometric Method Data Sheet Key Points

• Data Sheet Location: Appendix A of IS 2720 Part 26 provides the format to record electrometric method observations.

• Equipment Specification:

  • Use a pH meter (6H meter) as per IS 2711-1979.
  • Must have a glass electrode and a calomel reference electrode or equivalent.

• Measurement Reporting:

  • pH values are recorded to the nearest 0.1 pH unit.
  • Clearly state that the test was done using the electrometric method.

Typical Data Sheet Fields (from Appendix A):

Notes:

• Soil suspension preparation ratio is critical (commonly 1:2.5 soil to water).
• Calibration of electrodes before measurement is essential for accuracy.

flowchart LR
    A[Soil Sample] --> B[Prepare Suspension (1:2.5)]
    B --> C[Calibrate pH Meter]
    C --> D[Measure pH with Glass & Calomel Electrodes]
    D --> E[Record pH (±0.1) on Data Sheet (Appendix A)]

This ensures standardized, accurate pH measurement following IS 2720 Part 26.

IS 2720 Part 26: Colorimetric Method Reference Charts

Key Points from the Code:

• Indicator Papers (Clause 3.2.1) include:

  • Bromocresol green
  • Bromothymol blue
  • Methyl orange
  • Methyl red
  • Titan yellow (Clayton yellow)
  • Chlorophenol red
  • Thymol blue

• pH Determination (Clause 4.1):

  • The color of the soil suspension solution is compared against a standard color chart to determine pH.
  • pH values are reported to the nearest 0.1 pH unit (Clause 2.7.1).

Data Recording:

• Use Appendix B and C data sheets for recording colorimetric observations (Clause 3.3.1).

Typical Procedure Summary:

1. Prepare soil suspension.
2. Dip indicator paper or add indicator solution.
3. Compare the resulting color with the standard colorimetric chart.
4. Record pH to 0.1 unit accuracy.

Example: pH Color Chart (Indicative)

flowchart LR
    A[Prepare Soil Suspension] --> B[Add Indicator Paper/Solution]
    B --> C[Observe Color Change]
    C --> D[Compare with Standard Color Chart]
    D --> E[Record pH Value (±0.1)]

Note: For exact color charts and detailed data sheets, refer to Appendix B and C of IS 2720 Part 26 (1987).