Methods of Test for Soils, Part XXIV: Determination of Cation Exchange Capacity
1976 Edition

Overview of IS 2720 Part 24 Scope

This part defines the laboratory method for determining the subgrade reaction modulus (k), crucial for foundation design considerations.

Scope Details (Clause 2.0)

• Defines subgrade reaction modulus (k) as the ratio of applied pressure on soil to the settlement produced.
• Applicable to soils supporting shallow foundations, pavements, and slabs.

Formula for Subgrade Reaction Modulus (Clause 3.2.4)

• [ k = \frac{p}{\Delta} ]

  where:

  • (p) is the applied pressure (kN/m²)
  • (\Delta) is the corresponding settlement (mm or m)

Standard Testing Method (Clause 3.1)

• Load is incrementally applied on a standard plate (typically 300 mm diameter).
• Settlement is recorded at each load step.
• A pressure-settlement curve is plotted to derive k.

Typical k Values for Various Soils:

graph LR
A[Apply Load p] --> B[Measure Settlement Δ]
B --> C[Calculate k = p/Δ]
C --> D[Apply k in Foundation Design]

Summary: IS 2720 Part 24 standardizes procedures to determine subgrade reaction modulus (k), essential for soil-structure interaction analysis.

IS 2720 Part 24 (1976) cites several related IS codes crucial for soil testing equipment and procedures:

Primary References:

• IS 365-1983: Specifications for graduated measuring cylinders (1st revision).
• IS 1997-1982: Specifications for burettes (2nd revision).
• IS 1997-1982 (also referenced): Specifications for one-mark pipettes (1st revision).
• Electric hot plates: Specifications for uniform heating requirements.

Notes:

• These references ensure calibration and accuracy for volume measurement devices used during soil analysis.
• Adhering to these standards guarantees reliable and consistent laboratory results.

Example Moisture Content Calculation (Clause 3.2.4):

[ \text{Moisture Content} (w) = \frac{W_{wet} - W_{dry}}{W_{dry}} \times 100% ] Where:

• (W_{wet}) is the weight of the moist soil sample
• (W_{dry}) is weight after oven drying

flowchart LR
    A[Soil Sample] --> B[Weigh Wet Sample (W_wet)]
    B --> C[Oven Dry Sample]
    C --> D[Weigh Dry Sample (W_dry)]
    D --> E[Compute Moisture Content]

This method ensures precise moisture content determination, foundational to geotechnical investigations.

IS 2720 Part 24 covers the dry density and moisture relationship of soils (Proctor Test).

Important Definitions (Clause 2.0):

• Dry Density (ρd): Mass of soil solids per unit volume excluding moisture.
• Moisture Content (w): Ratio of water mass to dry soil mass, expressed as a percentage.
• Optimum Moisture Content (OMC): Moisture level at which maximum dry density occurs.
• Maximum Dry Density (MDD): Peak dry density achieved at OMC.

Calculation (Clauses 3.2.4, 5.5):

• Dry Density: [ \rho_d = \frac{\rho}{1 + w} ] where (\rho) is bulk density and (w) is moisture content in decimal form.

Standard Procedure (Clause 3.1):

• Conduct standard Proctor compaction with specified energy.
• Plot dry density against moisture content to identify MDD and OMC.

Dry Density vs. Moisture Content Table:

This ensures standardized soil compaction characterization for engineering applications.

IS 2720 Part 24 (1976) details necessary equipment and materials:

Equipment Specifications:

• Graduated Cylinders: IS-compliant for precise volume measurement.
• Electric Hot Plates: For controlled heating, meeting revised standards.
• Burettes: For accurate titration, as per IS revisions.
• Glass Beakers: Chemically inert and standardized.
• Pipettes (One-mark and Graduated): For exact liquid measurement.
• Additional Labware: Buchner funnels, test tubes, glass rods, and tubing conforming to IS standards.

Procedure (Clause 3.1.3.3):

• Add 20–50 ml of 0.05 N HCl to a cold soil sample to dissolve alkalis.
• Warm gently and allow the reaction to complete.
• Titrate excess acid with 0.05 N NaOH using methyl red indicator.
• If methyl red is absorbed by precipitates during titration, add drops near endpoint to maintain indicator effectiveness.

Notes:

• For heavy clays or base-saturated soils, use 1–2 g sample.
• The reaction depends on soil-to-acid ratios and equilibrium conditions.

Titration Reagents Summary:

flowchart TD
    A[Soil Sample] --> B[Add 0.05 N HCl (20-50 ml)]
    B --> C[Warm Gently]
    C --> D[Titrate Excess Acid with 0.05 N NaOH]
    D --> E[Use Methyl Red Indicator]
    E --> F[Determine Alkali Content]

This setup ensures accurate chemical analysis in accordance with IS 2720 Part 24.

Key Points on Solution Preparation from IS 2720 Part 24:

Special Solutions (Clause 5.1.5):

• Related to calcium versene procedures; specific formulations detailed elsewhere.
• Sodium acetate solutions are prepared as per Clauses 5.1.1 and 5.1.2.

Sodium Acetate Solutions:

Acid-Base Titration (Clause 3.1.3.3):

• Add 20–50 ml of 0.05 N hydrochloric acid to the cold soil sample.
• Warm gently until alkalis dissolve completely.
• Titrate excess HCl with 0.05 N sodium hydroxide using methyl red indicator.
• Add methyl red drops near the endpoint if the indicator is absorbed during titration.

Equipment Compliance:

• Measuring cylinders, burettes, hot plates, and beakers must adhere to IS standards.

Normality Calculation Formula:

[ N = \frac{\text{grams of solute} \times \text{valence}}{\text{equivalent weight} \times \text{volume in liters}} ]

For sodium acetate (molar mass about 82 g/mol), 1 N corresponds to 82 g per litre.

flowchart TD
    A[Sample] --> B[Add 20-50 ml 0.05 N HCl]
    B --> C[Warm Gently]
    C --> D[Titrate Excess HCl with 0.05 N NaOH]
    D --> E[Use Methyl Red Indicator]
    E --> F[Determine Endpoint]

This sequence ensures complete dissolution and precise titration for calcium versene analysis.

Summary of Sampling and Sample Preparation in IS 2720 Part 24 (1976):

Equipment Specifications (Clauses 3.1.2.2 & 3.2.3.1):

• Pipettes (25 ml & 50 ml), both one-mark and graduated, per IS 4162-1967 and IS 1117-1958.
• Other glassware such as Buchner funnels, test tubes, beakers, burettes, rods, and tubing conforming to respective IS standards.
• Graduated measuring cylinders for precise volume measurements.
• Electric hot plates for controlled warming.

Sample Preparation (Clause 3.1.3.3):

• Add 20–50 ml of 0.05 N hydrochloric acid to the soil sample.
• Warm gently until alkalis dissolve completely.
• Titrate residual acid with 0.05 N sodium hydroxide using methyl red indicator.
• Add methyl red drops near endpoint if indicator absorption occurs.

Cation Exchange Capacity Calculation (Clause 5.5.1):

[ \text{meq/100g soil} = \frac{\text{ml of versene solution} \times N \times 100}{\text{soil mass in g}} ]

where:

• (N) is the normality of versene solution
• Volume of versene is titrated volume

Equipment Summary Table:

flowchart TD
    A[Soil Sample] --> B[Add 20-50 ml 0.05 N HCl]
    B --> C[Warm Gently]
    C --> D[Alkalis Dissolve]
    D --> E[Titrate Excess Acid with 0.05 N NaOH]

IS 2720 Part 24 (1976) - Procedure for Soil Testing

This section describes methods to assess soil permeability.

Overview of Test Steps:

• Sample Types: Use either undisturbed or remolded soil samples.
• Test Variants: Constant head and falling head permeability tests.
• Setup: Place soil sample in permeameter and measure water flow.

Key Equations:

1. Constant Head Permeability: [ k = \frac{Q L}{A h t} ] where:

• (k): coefficient of permeability (cm/s)
• (Q): volume of water collected (cm³)
• (L): length of soil sample (cm)
• (A): cross-sectional area (cm²)
• (h): constant head difference (cm)
• (t): time duration (s)

2. Falling Head Permeability: [ k = \frac{a L}{A t} \ln \frac{h_1}{h_2} ] where:

• (a): cross-sectional area of standpipe (cm²)
• (h_1), (h_2): initial and final water heads (cm)
• Other variables as above

Testing Conditions:

• Employ distilled water at ambient temperature.
• Avoid air entrapment in the sample.
• Ensure steady flow during measurements.

flowchart LR
    A[Start] --> B[Prepare Soil Sample]
    B --> C[Set Up Permeameter]
    C --> D{Select Test Type}
    D -->|Constant Head| E[Measure Q, h, t]
    D -->|Falling Head| F[Record h1, h2, t]
    E --> G[Compute k (constant head)]
    F --> H[Compute k (falling head)]
    G --> I[End]
    H --> I

This section summarizes the soil permeability test procedures and formulas from IS 2720 Part 24.

This section presents formulas and specifications for determining exchangeable metallic ions per IS 2720 Part 24:

1. Total Exchangeable Metallic Ions (Clause 3.2.4.1):

[ \text{meq} = \frac{(B - T) \times N \times 25 \times 100}{W \times 100} ] where:

• meq: milliequivalents per 100 g soil of exchangeable metallic ions
• B: volume of lime water used in blank titration (ml)
• T: volume of lime water used in actual titration (ml)
• N: normality of lime water
• W: mass of soil sample (g)

When calcium carbonate is present (up to 15%), subtract its milliequivalent contribution from meq.

2. Exchangeable Hydrogen Ions (Clauses 3.1.4 & 4.4):

• Determined by acid-base back titration: [ \text{meq} = \frac{(V_a - V) \times N \times V_e \times 1000}{W \times 100} ] where:

• (V_a): volume of standard HCl added (ml)

• (V): volume of NaOH during back titration (ml)

• (N): normality of solutions

• (V_e): volume of extract (ml)

• (W): weight of soil (g)

• Also expressed as: [ \text{meg H}^+ = \frac{(T - B) \times N \times W}{100} ] where:

• T: NaOH volume for soil extract titration (ml)

• B: NaOH volume for blank titration (ml)

• N: normality of NaOH

• W: soil weight (g)

3. Cation Exchange Capacity (Clause 1.1.1):

• A single method combining exchangeable metallic and hydrogen ion determination is described in the full standard.

Summary Table:

This section details the calculation of key soil chemical parameters.

IS 2720 Part 24: Quantification of Exchangeable Hydrogen Ions

Principal Equations:

1. Total Exchangeable Metallic Ions (meq/100 g soil): [ meq = \frac{(B - T) \times N \times 25 \times W}{100 \times 100} ] where:

• B: blank titration volume (ml of lime water)
• T: actual titration volume (ml)
• N: normality of lime water
• W: mass of soil sample (g)

Note: Subtract equivalent milligrams of CaCO₃ if present (up to 15%).

2. Exchangeable Hydrogen Ions (meq H⁺/100 g soil): [ meq_{H^+} = \frac{(T - B) \times N \times 100}{\text{soil mass (g)}} ] where:

• T: NaOH volume for soil extract titration (ml)
• B: NaOH volume for blank titration (ml)
• N: normality of NaOH

Overview:

• Exchangeable metallic and hydrogen ions are analyzed separately.
• Their combined sum represents the total cation exchange capacity (CEC).
• CEC is indicative of soil fertility and nutrient retention capacity.
• The method accounts for mineral fixation phenomena such as potassium fixation.

Reference:

• IS 2720 Part 24 (1976) for exchangeable ion determination methods.
• IS:2-1960 for rounding off numerical results.

flowchart LR
    A[Soil Sample] --> B[Extract Exchangeable Ions]
    B --> C[Measure Exchangeable Metallic Ions]
    B --> D[Measure Exchangeable Hydrogen Ions]
    C & D --> E[Calculate Total CEC = Metallic + Hydrogen]

This approach facilitates precise chemical characterization of soils for engineering and agricultural use.

Calculation and Procedure for Cation Exchange Capacity (CEC) per IS 2720 Part 24

Key Formula (Clause 4.4):

[ \text{meg exchangeable H}^+ \text{ per 100 g soil} = \frac{(T - B) \times N \times \text{soil mass (g)}}{100} ] where:

• T: volume of NaOH used for titrating soil extract (ml)
• B: volume of NaOH used for blank titration (ml)
• N: normality of NaOH
• Soil mass in grams

Method Summary (Clause 5.4.1):

1. Mix 5 g soil with 50 ml 1N sodium acetate solution (pH ~5.0).
2. Heat in near-boiling water bath for 30 minutes with stirring.
3. Centrifuge and decant supernatant; repeat washing 2–4 times if soil is calcareous.
4. Wash sample 5 times with 1N calcium chloride to replace exchangeable ions with Ca²⁺.
5. Remove excess calcium chloride by washing 5 times with 80% acetone (confirmed with AgNO₃ test).
6. Replace Ca²⁺ ions by washing 5 times with neutral 1N sodium acetate.
7. Collect calcium solution (~250 ml), add buffer (pH 10), Eriochrome Black T indicator, and sodium cyanide.
8. Titrate with standardized versene (EDTA) solution to a bright blue endpoint.

Notes:

• Washing can be performed using centrifugation or Buchner funnel with filter paper.
• Express results as milliequivalents per 100 g soil.

flowchart TD
    A[5 g Soil + 50 ml 1N Sodium Acetate (pH 5)] --> B[Heat in Boiling Water Bath 30 min]
    B --> C[Centrifuge & Decant]
    C --> D{Is Soil Calcareous?}
    D -- Yes --> E[Repeat Washing 2-4 Times]
    D -- No --> F[Wash 5 Times with 1N CaCl₂]
    F --> G[Wash 5 Times with 80% Acetone (AgNO₃ Test)]
    G --> H[Wash 5 Times with Neutral 1N Sodium Acetate]
    H --> I[Add Buffer, Indicator & Sodium Cyanide]
    I --> J[Titrate with Versene to Endpoint]

This procedure ensures accurate CEC determination following IS 2720 Part 24.

Guidelines for Reporting Results per IS 2720 Part 24 (1976):

1. Data Calculations (Clauses 3.2.4 & 5.5):

• Convert raw measurements (volumes, weights) into test values using prescribed formulas.
• Adjust for factors such as temperature and instrument calibration.
• Report parameters like moisture content, density, or particle size distribution as applicable.

2. Standard Testing Procedures (Clause 3.1):

• Adhere strictly to preparation, testing, and measurement protocols.
• Use calibrated instruments (pipettes, Buchner funnels) compliant with IS standards.

3. Equipment Specifications (Clause 3.1.2.2):

• Pipettes: Use 25 ml and 50 ml graduated or single-mark pipettes conforming to IS 4162:1967 and IS 1117:1958.
• Buchner Funnels: Follow IS specifications for pore size and dimensions.

Sample Moisture Content Calculation Example:

[ \text{Moisture Content (5)} = \frac{W_{wet} - W_{dry}}{W_{dry}} \times 100 ] where:

• (W_{wet}): wet sample weight
• (W_{dry}): oven-dried sample weight

Equipment Compliance Summary:

flowchart LR
    A[Sample Collection] --> B[Sample Preparation]
    B --> C[Measurement with Pipettes/Buchner Funnel]
    C --> D[Data Logging]
    D --> E[Calculations (Clauses 3.2.4, 5.5)]
    E --> F[Final Report Generation]

Note: Clearly specify units, test conditions, and equipment details for transparency and reproducibility.

IS 2720 Part 24 emphasizes accuracy in soil water content determination by chemical means.

Key Specifications:

• Clause 3.1.2.10 mandates using a chemical balance with a sensitivity of 0.1 or 0.2 mg for weighing reagents and samples.
• Follow the standard method precisely to ensure accuracy.

Calculation (Clauses 3.2.4 & 5.5):

Water content (w) is calculated as: [ w = \frac{V \times N \times 9}{W} ] where:

• V: volume of ferrous ammonium sulfate used (ml)
• N: normality of ferrous ammonium sulfate
• W: weight of soil sample (g)
• 9: equivalent weight of water in mg

Tips for Precision:

• Use well-calibrated burettes and pipettes.
• Repeat measurements to verify consistency.
• Maintain stable temperature conditions to avoid reaction rate variability.

flowchart LR
    A[Soil Sample] --> B[Weigh Sample (W)]
    B --> C[Add Reagents]
    C --> D[Titrate with FAS (V)]
    D --> E[Compute Water Content (w)]

This ensures reliable and repeatable water content determination by the chemical method.

IS 2720 Part 24 (1976) highlights essential safety and handling measures:

Procedure Highlights (Clause 3.1.3.3):

• Add 20–50 ml of 0.05 N hydrochloric acid to the cold soil sample to dissolve alkalis.
• Warm gently and allow the reaction to complete.
• Titrate excess acid with 0.05 N sodium hydroxide, using methyl red as an indicator.
• If methyl red is absorbed during titration, add a few drops near the endpoint to maintain visibility.

Equipment Requirements:

• Graduated measuring cylinders for accurate volume measurements.
• Electric hot plates for controlled heating.
• Burettes for precise titrant delivery.
• Glass beakers with chemical resistance.

Safety Recommendations:

• Perform acid and alkali handling in well-ventilated areas.
• Wear protective gloves and safety goggles.
• Exercise caution when handling hot plates to prevent burns.
• Dispose of chemical waste according to safety regulations.

Titration Relationship:

[ \text{Normality of acid} \times \text{Volume of acid} = \text{Normality of base} \times \text{Volume of base} ] where:

• Volume of acid = initial HCl added
• Volume of base = NaOH volume used in titration

flowchart LR
    A[Cold Soil Sample] --> B[Add 20-50 ml 0.05 N HCl]
    B --> C[Warm Gently]
    C --> D[Alkali Dissolution]
    D --> E[Titrate Excess Acid with 0.05 N NaOH]
    E --> F[Use Methyl Red Indicator]
    F --> G[Add Drops if Absorbed]
    G --> H[Determine Endpoint]

This ensures accurate alkali quantification with safety and precision following IS 2720 Part 24.

IS 2720 Part 24 (1976) updates references to related Indian Standards for soil testing apparatus:

• Updated IS Standards:

  • IS 365-1983 for graduated measuring cylinders (revised from 1965 version).
  • IS 1997-1982 for burettes (revised from 1967).
  • IS 4162-1967 and IS 1117-1958 for 25 ml and 50 ml pipettes.

• Apparatus Specifications:

  • Graduated measuring cylinders (1st revision).
  • Electric hot plates (2nd revision).
  • Burettes (2nd revision).
  • One-mark pipettes (1st revision).
  • Buchner funnels.
  • Graduated pipettes.

These references ensure standardized calibration and usage of laboratory equipment, critical for accurate soil testing.

Summary Table of IS References:

Refer to these standards for detailed apparatus calibration and usage.

IS 2720 Part 24 (1976) includes annexures and appendices containing:

Core Formula (Clause 5.5.1):

Calculation of milli-equivalent cation exchange capacity (CEC) per 100 g soil: [ \text{CEC (meq/100g)} = \frac{\text{volume of versene solution (ml)} \times N \times 100}{\text{mass of soil (g)}} ] where N is the normality of the versene (EDTA) solution.

Equipment References:

• IS 365-1983 for graduated measuring cylinders.
• IS 1997-1982 for burettes.
• Electric hot plates as per IS specifications.

Typical Annexure Contents:

• Detailed procedural steps
• Calibration tables for titration
• Sample calculation examples
• Specifications of instruments

Summary Table for CEC Calculation:

flowchart LR
    A[Soil Sample] --> B[Titrate with Versene]
    B --> C[Measure Versene Volume (V)]
    C --> D[Apply Normality (N)]
    D --> E[Compute CEC]
    E --> F[Report as meq/100g Soil]

Refer to the annexures for stepwise instructions and calibration data essential for accurate CEC determination.