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

IS 2720 Part 24: Scope Overview

IS 2720 Part 24 deals with Determination of Subgrade Reaction Modulus (k) for soil, essential for foundation design.

Scope (Clause 2.0)

• Defines Subgrade Reaction Modulus (k) as the ratio of pressure applied to soil to the corresponding settlement.
• Applies to soil under shallow foundations, pavements, and slabs.

Key Formulas (Clause 3.2.4)

• Subgrade Reaction Modulus: [ k = \frac{p}{\Delta} ] where:
  • (p) = pressure applied on soil (kN/m²)
  • (\Delta) = corresponding settlement (mm or m)

Standard Method (Clause 3.1)

• Load is applied incrementally on a plate of standard size (usually 300 mm diameter).
• Settlement readings are recorded for each load increment.
• Plot pressure vs. settlement curve to determine (k).

Typical Values of (k) (Indicative)

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

Summary: IS 2720 Part 24 standardizes the determination of subgrade reaction modulus (k), vital for soil-structure interaction analysis.

IS 2720 Part 24 (1976) references several related IS codes for equipment and procedures essential in soil testing:

Key References and Substitutions:

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

Important Notes:

• These referenced IS codes specify calibration and accuracy for measuring equipment used in soil tests.
• Ensuring compliance with these standards guarantees reliable volume measurements during soil moisture and other tests.

Typical Formula from Clause 3.2.4 (Calculation):

For moisture content determination, [ \text{Moisture content} (w) = \frac{W_{wet} - W_{dry}}{W_{dry}} \times 100% ] Where:

• ( W_{wet} ) = weight of wet soil sample
• ( W_{dry} ) = weight of oven-dried soil sample

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[Calculate Moisture Content]

This ensures accurate soil moisture content, a key parameter in geotechnical investigations.

IS 2720 Part 24 deals with Determination of Dry Density-Moisture Relationship (Proctor Test).

Key Definitions (Clause 2.0)

• Dry Density (ρd): Mass of solids per unit volume of solids and voids, excluding water.
• Moisture Content (w): Percentage ratio of water mass to dry soil mass.
• Optimum Moisture Content (OMC): Moisture content at which dry density is maximum.
• Maximum Dry Density (MDD): Highest dry density achieved at OMC.

Calculation (Clauses 3.2.4 & 5.5)

• Dry Density:
  [ \rho_d = \frac{\rho}{1 + w} ] where
  (\rho) = bulk density (mass/volume),
  (w) = moisture content (decimal).

Standard Method (Clause 3.1)

• Use standard Proctor compaction test with specified compactive effort.
• Plot dry density vs. moisture content to find MDD and OMC.

Typical Table: Dry Density vs. Moisture Content

This standard ensures uniformity in soil compaction characterization for design and construction.

IS 2720 Part 24 (1976) - Apparatus and Materials Key Points

Apparatus Specifications

• Graduated Measuring Cylinders: As per IS specifications for accurate volume measurement.
• Electric Hot-plates: Revised standard for uniform heating.
• Burettes: First revision for precise titration.
• Glass Beakers: First revision for chemical compatibility.
• One-mark and Graduated Pipettes: For accurate liquid measurement.
• Test Tubes, Glass Rods, and Tubing: Standard lab glassware specifications.

Key Procedure (Clause 3.1.3.3)

• Add 20 to 50 ml of 0.05 N HCl to cold soil sample to dissolve alkalis.
• Warm gently, then stand until complete dissolution.
• Titrate excess acid with 0.05 N NaOH using methyl red indicator.
• If methyl red is absorbed during titration, add drops before endpoint.

Notes

• Use 1-2 g soil for heavy clays/base saturated soils.
• Values depend on soil-to-acid ratio (equilibrium values).

Summary Table for Titration Reagents

flowchart TD
    A[Soil Sample] --> B[Add 0.05 N HCl (20-50 ml)]
    B --> C[Warm gently and stand]
    C --> D[Titrate excess acid with 0.05 N NaOH]
    D --> E[Use methyl red indicator]
    E --> F[Determine alkali content]

This setup ensures precise chemical analysis per IS 2720 Part 24 standards.

IS 2720 Part 24: Preparation of Solutions (Key Points)

Special Solutions (Clause 5.1.5)

• Used in calcium versene procedure.
• Exact compositions not fully detailed here but refer to Clause 5.1 for sodium acetate solutions.

Sodium Acetate Solutions (Clause 5.1.1 & 5.1.2)

Acid-Base Titration (Clause 3.1.3.3)

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

Equipment Specifications

• Graduated measuring cylinders, burettes, electric hot-plates, and glass beakers must conform to IS specifications (refer IS 2720 Part 24 revisions).

Summary Formula for Normality (N):

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

For sodium acetate (CH3COONa, molar mass ~82 g/mol), 1 N = 82 g/L.

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 accurate titration for calcium versene analysis.

IS 2720 Part 24 (1976) — Sampling and Sample Preparation: Key Points

Equipment Specifications (Clauses 3.1.2.2 & 3.2.3.1)

• Pipettes: 25 ml & 50 ml, one-mark and graduated types per IS: 4162-1967 and IS: 1117-1958.
• Other Glassware: Buchner funnels, test tubes, glass beakers, burettes, glass rods, and tubing as per respective IS standards.
• Measuring Cylinders: Graduated type for accurate volume measurement.
• Electric Hot-plates: For gentle warming during preparation.

Sample Preparation Procedure (Clause 3.1.3.3)

• Add 20-50 ml of 0.05 N HCl to soil sample.
• Warm gently until alkalis dissolve.
• Titrate excess acid with 0.05 N NaOH using methyl red indicator.
• Add drops of methyl red near endpoint to avoid absorption errors.

Key Formula for Cation Exchange Capacity (Clause 5.5.1)

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

Where:

• ( N ) = Normality of versene solution
• Versene volume = volume of versene used in titration

Summary Table: Sample Preparation Equipment

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) - Test Procedure for Soil

This part covers methods for determining the permeability of soils.

Key Test Procedure Summary:

• Sample Preparation: Undisturbed or remolded soil samples.
• Test Types: Constant head and falling head permeability tests.
• Test Setup: Soil sample placed in a permeameter; water flow measured.

Important Formulas:

1. Constant Head Test:

[ k = \frac{QL}{Aht} ]

Where:

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

2. Falling Head Test:

[ k = \frac{aL}{At} \ln \frac{h_1}{h_2} ]

Where:

• (a) = cross-sectional area of standpipe (cm²)
• (L), (A), (t) as above
• (h_1), (h_2) = initial and final head of water in standpipe (cm)

Specifications:

• Use distilled water at room temperature.
• Ensure no air bubbles in sample.
• Maintain steady flow conditions.

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

This summarizes the test procedure and key formulas from IS 2720 Part 24.

Here are the key formulas and specifications from IS 2720 Part 24 for determination of exchangeable metallic ions and related parameters:

1. Total Exchangeable Metallic Ions (Clause 3.2.4.1)

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

• meq = milli-equivalents percent of exchangeable metallic ions
• B = blank titration (ml lime water)
• T = actual titration (ml lime water)
• N = normality of lime water
• W = mass of soil (g)

If calcium carbonate is present (up to 15%), subtract its milligram equivalents from meq.

2. Exchangeable Hydrogen Ions (Clauses 3.1.4 & 4.4)

• From acid-base back titration:

[ \text{meq} = \frac{(V_a - V) \times N \times V_e \times 1000}{W \times 100} ]

• (V_a) = volume of standard HCl

• (V) = volume of NaOH in back titration

• (N) = normality

• (V_e) = volume of extract

• (W) = weight of soil (g)

• Expressed as:

[ \text{meg H}^+ = \frac{(T - B) \times N \times W}{100} ]

• (T) = NaOH volume for soil extract titration
• (B) = NaOH volume for blank
• (N) = normality NaOH
• (W) = mass of soil (g)

3. Cation Exchange Capacity (Clause 1.1.1)

• Single method to determine combined metallic + hydrogen ion exchange capacity (details in full standard).

Summary Table:

IS 2720 Part 24: Determination of Exchangeable Hydrogen Ions

Key Formulas

1. Total Exchangeable Metallic Ions (meq/100g soil):

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

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

Note: Deduct milligram equivalents of CaCO₃ if present (up to 15%).

2. Exchangeable Hydrogen Ions (meq H⁺/100g soil):

[ meq_{H^+} = \frac{(T - B) \times N \times 100}{\text{mass of soil in g}} ]

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

Summary

• Exchangeable metallic ions and hydrogen ions are determined separately.
• Their sum gives the total Cation Exchange Capacity (CEC).
• CEC reflects soil fertility and nutrient holding capacity.
• The method accounts for soil mineral fixation effects (e.g., potassium fixation).

Reference

• IS 2720 (Part 24) - 1976: Methods for exchangeable cations and hydrogen ions determination.
• Follow IS:2-1960 for rounding off results.

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

This concise approach ensures accurate soil chemical characterization for engineering and agricultural applications.

Cation Exchange Capacity (CEC) Calculation & Method (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{mass of soil (g)}}{100} ]

• T = volume of NaOH used in titration of soil extract (ml)
• B = volume of NaOH used for blank titration (ml)
• N = normality of NaOH solution
• Mass of soil = weight of soil sample in grams

Method Summary (Clause 5.4.1):

1. Soil sample: 5 g soil + 50 ml 1N sodium acetate (pH 5.0).
2. Digest in near boiling water bath for 30 min with stirring.
3. Centrifuge and decant supernatant; repeat washing with sodium acetate (2-4 times if calcareous).
4. Wash 5 times with 1N calcium chloride to replace exchangeable cations with Ca²⁺.
5. Remove excess CaCl₂ by 5 washes with 80% acetone (AgNO₃ test for chloride).
6. Replace Ca²⁺ by washing 5 times with neutral 1N sodium acetate.
7. Collect calcium solution (~250 ml), add buffer (pH 10), indicator (Erichrome Black T), and sodium cyanide.
8. Titrate with standardized versene solution to bright blue endpoint.

Notes:

• Washing can be done by centrifuge or funnel with filter paper.
• Results expressed in meq/100 g soil.

flowchart TD
    A[5 g Soil + 50 ml 1N Sodium Acetate (pH 5)] --> B[Boiling Water Bath 30 min]
    B --> C[Centrifuge & Decant]
    C --> D{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

IS 2720 Part 24 (1976) – Reporting of Results: Key Points

1. Calculation of Test Results (Clauses 3.2.4 & 5.5)

• Use standard formulas to convert raw data (e.g., volume readings, weights) into test results.
• Correct for temperature, equipment calibration, and sample conditions.
• Calculate values such as moisture content, density, or particle size distribution as per the specific test.

2. Standard Method (Clause 3.1)

• Follow prescribed procedures for sample preparation, testing, and measurement.
• Use calibrated equipment (pipettes, Buchner funnels, etc.) as per IS specifications.

3. Equipment Specifications (Clause 3.1.2.2)

• Pipettes: Use 25 ml and 50 ml graduated or one-mark pipettes complying with IS 4162:1967 & IS 1117:1958.
• Buchner Funnels: Follow IS specifications for size and porosity.

Typical Calculation Formula (Example: Moisture Content)

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

Where:

• (W_{wet}) = Weight of wet sample
• (W_{dry}) = Weight of dry sample after oven drying

Summary Table: Equipment Specifications

flowchart LR
    A[Sample Collection] --> B[Sample Preparation]
    B --> C[Measurement using Pipettes/Buchner Funnel]
    C --> D[Data Recording]
    D --> E[Calculation (Clause 3.2.4, 5.5)]
    E --> F[Reporting of Results]

Note: Always report results with units, test conditions, and equipment details for clarity and reproducibility.

IS 2720 Part 24 focuses on Determination of Water Content of Soil by Chemical Method. Regarding Precision and Accuracy, key points and formulas are:

Key Specifications:

• Clause 3.1.2.10: Use a chemical balance with 0.1 or 0.2 mg sensitivity for weighing reagents and samples to ensure precision.
• Clause 3.1: Follow the Standard Method strictly to maintain 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 (mg)

Precision Tips:

• Use accurate burettes and pipettes.
• Repeat tests to check consistency.
• Maintain constant temperature to avoid reaction rate variations.

flowchart LR
    A[Soil Sample] --> B[Weigh sample (W)]
    B --> C[Add reagents]
    C --> D[Titrate with FAS (V)]
    D --> E[Calculate water content w]

This ensures accuracy and repeatability in water content determination by chemical method.

IS 2720 Part 24 (1976) — Safety and Handling Key Points

Key Procedure (Clause 3.1.3.3)

• Add 20-50 ml of 0.05 N HCl to cold sample to dissolve alkalis.
• Warm gently; allow reaction to complete.
• Titrate excess acid with 0.05 N NaOH using methyl red indicator.
• If methyl red absorbs during titration, add a drop or two before endpoint.

Equipment Specifications (Referenced)

• Graduated Measuring Cylinders: Accurate volume measurement.
• Electric Hot-plates: Controlled gentle warming.
• Burettes: Precise titrant delivery.
• Glass Beakers: Chemical resistance and volume handling.

Important Tips for Safe Handling:

• Use acid and alkali solutions in well-ventilated areas.
• Wear protective gloves and goggles.
• Handle hot plates carefully to avoid burns.
• Dispose of chemical wastes as per safety norms.

Titration Formula:

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

Where:

• Volume acid = initial HCl added
• Volume base = NaOH used to titrate excess acid

flowchart LR
    A[Cold Sample] --> B[Add 20-50 ml 0.05N HCl]
    B --> C[Warm gently]
    C --> D[Allow alkali dissolution]
    D --> E[Titrate excess acid with 0.05N NaOH]
    E --> F[Use methyl red indicator]
    F --> G[Add drops if methyl red absorbed]
    G --> H[Determine endpoint]

This ensures accurate alkali content determination with safety and precision per IS 2720 Part 24.

IS 2720 Part 24 (1976) - References & Bibliography Key Points

This part primarily updates references to related IS standards for laboratory apparatus used in soil testing:

• Revised IS Standards:

  • IS 365-1983 (Graduated Measuring Cylinders) replaces IS 365-1965.
  • IS 1997-1982 (Burettes) replaces IS 1997-1967.
  • IS 4162-1967 and IS 1117-1958 for pipettes (25 and 50 ml).

• Specifications for Apparatus:

  • Graduated measuring cylinders (first revision).
  • Electric hot plates (second revision).
  • Burettes (second revision).
  • One-mark pipettes (first revision).
  • Buchner funnels.
  • Graduated pipettes.

These references ensure proper calibration and standardization of lab equipment essential for soil testing accuracy.

Summary Table of Key IS References

For detailed apparatus calibration and use, refer to the updated IS standards mentioned above.

IS 2720 Part 24 (1976) - Annexures & Appendices Key Points

Key Formula (Clause 5.5.1)

Calculation of Milli-equivalent Cation Exchange Capacity (CEC) per 100 g soil:

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

• N = Normality of versene solution
• Versene solution volume = titrated volume in ml

Specifications & References

• Use IS 365-1983 for graduated measuring cylinders.
• Use IS 1997-1982 for burettes.
• Use electric hot plates as per the latest IS specifications.

Annexures & Appendices typically include:

• Detailed test procedures
• Calibration tables for titrations
• Sample calculation examples
• Instrument specifications

Summary Table for CEC Calculation

For detailed procedures, always refer to the Annexures of IS 2720 Part 24, which provide stepwise methods and calibration data.

flowchart LR
    A[Soil Sample] --> B[Titration with Versene]
    B --> C[Measure Volume of Versene (V)]
    C --> D[Use Normality (N) of Versene]
    D --> E[Calculate CEC using formula]
    E --> F[Result: meq/100g Soil]