Methods of test for soils, Part 27: Determination of total soluble sulphates

IS 2720 Part 27 (1977) - Scope & Key Formulas

Scope:
This part covers the determination of sulphates in soil using chemical and colorimetric/turbidimetric methods.

Key Formula (Clause 3.5)

Sulphate content as sodium sulphate (%)
[ \text{Sulphates} = 0.0177 \times 100 \times (x - y) ]

Where:

• ( x ) = volume of N/4 barium chloride added (ml)
• ( y ) = volume of N/4 potassium chromate used in back titration (ml)
• ( (x - y) ) = volume of N/4 barium chloride actually used for precipitating sulphate

Table (Clause 4.4.3)

Notes:

• Hydrochloric acid and laboratory water specifications are referenced for reagent preparation.
• Calculations per Clause 2.6.1 and 3.5 ensure accurate sulphate quantification.

flowchart TD
    A[Soil Sample] --> B[Add N/4 Barium Chloride]
    B --> C[Precipitate Sulphate]
    C --> D[Back Titrate with N/4 Potassium Chromate]
    D --> E[Calculate Sulphates % using (x - y) formula]
    E --> F[Prepare Standard Curve]
    F --> G[Measure Absorbance with Colorimeter/Turbidimeter]

This concise summary helps in understanding the scope, key formula, and test method for sulphate determination as per IS 2720 Part 27.

IS 2720 Part 27 (1977) — Definitions & Key Specifications

Key Definitions (Contextual from Clause 2.6 & 4.4.3)

• Standard Sulphate Curve: Prepared by measuring absorbance of sulfate solutions using a photoelectric colorimeter (blue filter) or turbidimeter.
• Barium Chloride Solution (5%): Dissolve 5 g BaCl₂ in 100 ml distilled water (Clause 2.2.3).

Important Specifications:

Calculation Notes (Clause 2.6.1)

• Follow standard formulae for concentration from absorbance readings using calibration curve.
• Rounding off numerical values should comply with IS rounding rules.

Typical Formula for Sulphate Concentration (from absorbance):

[ C = \frac{A_s}{A_{std}} \times C_{std} ]

Where:

• (C) = Concentration of sulfate in sample
• (A_s) = Absorbance of sample
• (A_{std}) = Absorbance of standard solution
• (C_{std}) = Concentration of standard solution

Summary Diagram: Sulphate Testing Process

flowchart TD
    A[Prepare Standard Sulphate Solutions] --> B[Measure Absorbance (Colorimeter/Turbidimeter)]
    B --> C[Plot Standard Curve]
    D[Prepare Sample] --> E[Measure Sample Absorbance]
    E --> F[Calculate Sulphate Concentration using Curve]

For detailed procedures and exact formulae, refer to Clause 2.6 and Table 4.4.3 in IS 2720 Part 27.

IS 2720 Part 27 (1977) - Principle & Calculations Summary

Principle:

• This part deals with chemical analysis of soils, specifically sulfate content determination.
• The standard sulfate curve is prepared using a photoelectric colorimeter (blue filter) or turbidimeter with a working standard solution (Clause 4.4.3).

Key Formulas & Calculations (Clause 2.6):

• Calculations involve comparing sample readings against the standard sulfate curve.
• Use absorbance or turbidity readings to find sulfate concentration from the standard curve.

Important Specifications:

• Barium Chloride Solution (5%): Dissolve 5 g BaCl₂ in 100 ml distilled water (Clause 2.2.3).
• Hydrochloric acid specifications are revised as per the code.

Table Reference:

flowchart LR
    A[Prepare Standard Sulfate Solution] --> B[Measure Absorbance/Turbidity]
    B --> C[Plot Standard Curve]
    D[Soil Sample Preparation] --> E[Measure Absorbance/Turbidity]
    E --> F[Calculate Sulfate Content using Curve]

This method ensures accurate sulfate quantification in soils for engineering assessments.

IS 2720 Part 27: Apparatus and Equipment - Key Points

Heating Equipment (Clauses 2.1.6 & 3.2.9)

• Heating apparatus must maintain uniform temperature.
• Typical equipment: thermostatically controlled ovens, water baths, or heating mantles.
• Temperature control accuracy: ±1°C.
• Used for sample drying, heating during chemical tests.

Preparation of Standard Sulphate Curve (Clause 4.4.3)

• Use photoelectric colorimeter with blue filter or turbidimeter.
• Prepare standard solutions with known sulphate concentration.
• Plot absorbance vs concentration to obtain calibration curve.

General Calculation Guidelines (Clause 2.6)

• Follow standard formulae for concentration, absorbance, and sample weight.
• Use calibration curves for quantitative analysis.

Example: Sulphate Concentration Calculation

[ C_s = \frac{A_s}{A_{std}} \times C_{std} ]

Where:

• (C_s) = concentration of sulphate in sample
• (A_s) = absorbance of sample
• (A_{std}) = absorbance of standard
• (C_{std}) = concentration of standard solution

Summary Table: Heating Equipment Specifications

flowchart LR
    A[Sample Preparation] --> B[Heating Equipment]
    B --> C[Chemical Test]
    C --> D[Measure Absorbance]
    D --> E[Use Standard Curve]
    E --> F[Calculate Concentration]

For detailed apparatus specs, refer to IS 2720 Part 27 clauses mentioned.

IS 2720 Part 27 - Key Reagents & Calculations

Reagents Specifications

• Barium Chloride Solution (5%)

  • Dissolve 5 g barium chloride in 100 ml distilled water (Clause 2.2.3).

• Silver Nitrate Indicator Solution (0.5%)

  • Dissolve 500 mg silver nitrate in 100 ml distilled water (Clause 2.2.4).

• Hydrochloric Acid

  • Concentrated HCl, specific gravity 1.11, conforming to IS:265-1962 (Clause 3.3.5).

• Water

  • Use distilled water as per IS:1070-1977 for all reagent preparations.

Key Formula for Sulphate Content

[ \text{Sulphates as Na}_2\text{SO}_4 % = 0.0177 \times 100 \times (x - y) ]

Where:

• (x) = volume of N/4 barium chloride added (ml)
• (y) = volume of N/4 potassium chromate used in back titration (ml)
• (x - y) = volume of N/4 barium chloride actually used for precipitating sulphate

Notes:

• Use pure chemicals free from impurities affecting analysis.
• Follow rounding rules as per the revised IS code.
• All volumes refer to normality N/4 solutions unless otherwise specified.

flowchart LR
    A[Prepare Reagents] --> B[Barium Chloride 5%]
    A --> C[Silver Nitrate 0.5%]
    A --> D[Hydrochloric Acid sp gr 1.11]
    B --> E[Used for Sulphate Precipitation]
    C --> F[Indicator for Titration]
    E --> G[Measure volume x]
    F --> H[Measure volume y]
    G & H --> I[Calculate Sulphate %]

This summarizes reagent preparation and their role in sulphate determination per IS 2720 Part 27.

IS 2720 Part 27 (1977) - Sampling and Sample Preparation: Key Points

Sample Preparation (Clause 2.3)

• Drying: Soil sample dried at 105-110°C until crumbled.
• Breaking: Aggregates broken using mortar and rubber pestle or mechanical device.
• Mixing: Thorough mixing followed by quartering for sub-sampling.

Sulphate Determination (Clause 3.5)

• Formula for Sulphates as Sodium Sulphate (% by mass):

[ \text{Sulphates} = 0.0177 \times 100 \times (x - y) ]

Where:

• (x) = volume of N/4 barium chloride added (ml)
• (y) = volume of N/4 potassium chromate used in back titration (ml)
• (x - y) = volume of barium chloride actually used for precipitating sulphate

Standard Curve Preparation (Clause 4.4.3)

• Use photoelectric colorimeter with blue filter or turbidimeter.
• Prepare using working standard sulphate solution.

Additional Notes

• Use specified hydrochloric acid and laboratory-grade water.
• Follow IS 2-1960 for rounding off results.

flowchart TD
    A[Soil Sampling] --> B[Dry at 105-110°C]
    B --> C[Break Aggregates]
    C --> D[Mix Thoroughly]
    D --> E[Quartering for Sub-sample]
    E --> F[Sulphate Analysis]
    F --> G[Add N/4 Barium Chloride (x)]
    G --> H[Back Titrate with N/4 Potassium Chromate (y)]
    H --> I[Calculate Sulphate % = 0.0177 × 100 × (x - y)]
    I --> J[Prepare Standard Curve]
    J --> K[Use Colorimeter or Turbidimeter]

This concise overview aligns with IS 2720 Part 27 for sampling and sample preparation related to sulphate testing.

IS 2720 Part 27 (1977) — Key Test Method Formulas & Specifications

1. Test Method: Colorimetric or Turbidimetric (Clause 4.4.3)

• Prepare a standard sulphate curve using:
  • Photoelectric colorimeter with blue filter, or
  • Turbidimeter with working standard solution.

2. Calculation of Sulphates (Clause 3.5)

[ \text{Sulphates as sodium sulphate (% by mass)} = 0.0177 \times 100 \times (x - y) ]

Where:

• (x) = volume of N/4 barium chloride added (ml)
• (y) = volume of N/4 potassium chromate used in back titration (ml)
• (x - y) = actual volume of N/4 barium chloride used for precipitating sulphate

3. Specifications

• Use N/4 barium chloride and N/4 potassium chromate solutions.
• Follow IS:2-1960 for rounding off results.
• Use specified hydrochloric acid and laboratory-grade water.

Summary Table for Sulphate Determination

flowchart TD
    A[Prepare Standard Sulphate Curve] --> B[Measure absorbance with colorimeter or turbidimeter]
    B --> C[Determine volumes x and y]
    C --> D[Calculate sulphate content using formula]
    D --> E[Report sulphate % by mass]

This method ensures rapid and accurate sulphate content determination in soils per IS 2720 Part 27.

IS 2720 Part 27: Precipitation Method (Standard) for Total Soluble Sulphate Content

Key Formula (Clause 60.85 b):

[ \text{Sulphates (as Na}_2\text{SO}_4), % = \frac{60.85 \times W_1}{W_2} ]

• W₁ = Mass of barium sulphate precipitate (g)
• W₂ = Mass of soil sample taken for precipitation (g)

Explanation:

• The precipitate formed is barium sulphate (BaSO₄).
• The factor 60.85 converts the mass of BaSO₄ to equivalent sodium sulphate (Na₂SO₄) percentage.

Additional Notes:

• The Volumetric Method (subsidiary) uses titration with barium chloride and potassium chromate:

  [ \text{Sulphates %} = 0.0177 \times 100 \times (x - y) ]

  where:

  • (x) = volume of N/4 BaCl₂ added (ml)
  • (y) = volume of N/4 K₂CrO₄ used in back titration (ml)

• Use distilled water and HCl as per IS specifications for reagent preparation.

• Results should be rounded off per IS 2-1960.

flowchart TD
    SoilSample -->|Dissolve & Filter| Solution
    Solution -->|Add BaCl2| Precipitate(BaSO4)
    Precipitate -->|Filter & Dry| W1(Mass of BaSO4)
    SoilSample -->|Known mass| W2
    W1 & W2 -->|Calculate| SulphatePercent

This method provides a reliable measure of soluble sulphates in soil, crucial for assessing soil suitability for construction and agriculture.

IS 2720 Part 27: Volumetric Method (Subsidiary) for Sulphate Estimation

Principle (Clause 3.1)

• Insoluble BaSO4 forms when BaCl2 is added to sulphate solution.
• Excess BaCl2 is back-titrated with potassium chromate (K2CrO4).
• Endpoint: Yellow color from chromate; confirmed by silver nitrate (brick red precipitate).

Key Formula (Clause 3.5)

[ \text{Sulphates as } Na_2SO_4 % = 0.0177 \times 100 \times (x - y) ]

Where:

• (x) = volume (ml) of N/4 BaCl2 added
• (y) = volume (ml) of N/4 K2CrO4 used in back titration
• (x - y) = volume of BaCl2 actually reacted with sulphate

Notes:

• Use N/4 (0.25N) standard solutions for BaCl2 and K2CrO4.
• Hydrochloric acid and distilled water specifications must comply with IS standards.
• End point confirmation with silver nitrate ensures accuracy.

flowchart LR
    A[Sulphate Solution] --> B[Add Excess BaCl2]
    B --> C[BaSO4 Precipitates]
    B --> D[Excess BaCl2]
    D --> E[Back-titrate with K2CrO4]
    E --> F[Yellow Color Endpoint]
    F --> G[Confirm with AgNO3 (Brick Red)]

This method is reliable for quantitative sulphate estimation in soil samples.

IS 2720 Part 27 (1977) — Colorimetric or Turbidimetric Method (Subsidiary)

Key Formula for Sulphate Content:

[ \text{Sulphates as sodium sulphate, % by mass} = 0.0177 \times 100 \times (x - y) ]

• x = volume of N/4 barium chloride added (ml)
• y = volume of N/4 potassium chromate used in back titration (ml)
• (x - y) = volume of N/4 barium chloride actually used for precipitating sulphate

Specifications:

• Use photoelectric colorimeter with blue filter or turbidimeter for readings.
• Prepare a standard sulphate curve using working standard solutions (Clause 4.4.3).
• Use specified hydrochloric acid and laboratory-grade water as per IS standards.

Procedure Highlights:

• Measure turbidity or color intensity of the sample.
• Compare against the standard curve to determine sulphate concentration.
• Back titration with potassium chromate ensures accuracy.

Summary Table: Standard Curve Preparation (Clause 4.4.3)

This method is rapid, reliable, and suitable as a subsidiary test for soil sulphate determination.

flowchart LR
    A[Prepare Standard Sulphate Solutions] --> B[Measure Absorbance/Turbidity]
    B --> C[Plot Standard Curve]
    D[Sample Preparation] --> E[Measure Absorbance/Turbidity]
    E --> F[Use Standard Curve to Find Sulphate]
    F --> G[Calculate % Sulphate using Formula]

For detailed steps, refer to IS 2720 Part 27 (1977) clauses 3.5 and 4.1.4.

IS 2720 Part 27 - Calculation of Sulphates in Soil

Key Formula (Clause 3.5):

[ \text{Sulphates as sodium sulphate (% by mass)} = 0.0177 \times 100 \times (x - y) ]

• x = volume of N/4 barium chloride added (ml)
• y = volume of N/4 potassium chromate used in back titration (ml)
• x - y = volume of N/4 barium chloride actually used for precipitating sulphate

Notes:

• The factor 0.0177 accounts for molecular weight conversions and normality.
• The calculation is based on volumetric titration using barium chloride and potassium chromate.
• Use standardized reagents as per specifications (hydrochloric acid and laboratory water).
• For colorimetric or turbidimetric methods, prepare a standard sulphate curve using a photoelectric colorimeter or turbidimeter with a blue filter (Clause 4.4.3).

Summary Table for Sulphate Calculation

flowchart TD
    A[Add N/4 BaCl₂ (x ml)] --> B[React with Sulphate]
    B --> C[Back titrate with N/4 K₂CrO₄ (y ml)]
    C --> D[Calculate (x - y)]
    D --> E[Calculate Sulphate % = 0.0177 × 100 × (x - y)]

For detailed procedures and reagent specifications, consult IS 2720 Part 27 (1977).

IS 2720 Part 27 - Reporting of Results: Key Points & Formulas

1. Calculations (Clause 2.6 & 2.6.1)

• Perform calculations as per the test procedure to obtain final values.
• Use the standard sulphate curve (Clause 4.4.3) for colorimetric or turbidimetric readings.
• Final results are derived by comparing sample readings against the standard curve.

2. Preparation of Standard Sulphate Curve (Table 4.4, Clause 4.4.3)

• Use a photoelectric colorimeter with blue filter or turbidimeter.
• Prepare working standard solutions of known sulphate concentration.
• Plot absorbance/turbidity vs concentration to get the standard curve.

3. Rounding Off Results (Clause 0.4)

• Round off final values according to IS 2-1960:
  • Round to the nearest digit based on the first discarded digit.
  • Example: 3.46 rounded to 3.5 (if rounding to one decimal place).

Summary Table for Reporting:

flowchart TD
    A[Sample Preparation] --> B[Measurement with Colorimeter/Turbidimeter]
    B --> C[Obtain Absorbance/Turbidity]
    C --> D[Use Standard Sulphate Curve]
    D --> E[Calculate Sulphate Concentration]
    E --> F[Round off Result (IS 2-1960)]
    F --> G[Report Final Value]

Note: For detailed standard curve values and preparation steps, refer to Table 4.4 and Clause 4.4.3 of IS 2720 Part 27.

IS 2720 Part 27: Precision and Accuracy Key Points

1. Precision & Accuracy Context (Clause 2.6)

• Calculations must ensure repeatability and reproducibility.
• Use standard methods and calibrated instruments to minimize errors.

2. Instrument Specifications

• Analytical Balance Sensitivity: 0.001 g (Clauses 3.2.1 & 4.1.3)
• Use photoelectric colorimeter with blue filter or turbidimeter for readings (Clause 4.4.3).

3. Standard Sulphate Curve (Clause 4.4.3)

• Prepare by measuring absorbance of working standard solutions.
• Plot absorbance vs concentration to obtain calibration curve.
• Use curve to determine unknown sample concentration.

4. Calculation Formula (General for concentration from calibration curve)

[ C_x = \frac{A_x}{A_s} \times C_s ]

Where:

• (C_x) = Concentration of unknown
• (A_x) = Absorbance of unknown
• (A_s) = Absorbance of standard
• (C_s) = Concentration of standard

Summary Table: Instrument Sensitivity and Measurement

flowchart LR
    A[Prepare Standard Solutions] --> B[Measure Absorbance (Colorimeter)]
    B --> C[Plot Standard Curve (Absorbance vs Concentration)]
    C --> D[Measure Sample Absorbance]
    D --> E[Calculate Sample Concentration using Curve]

Note: Ensure all instruments are calibrated and measurements repeated for accuracy.

IS 2720 Part 27: Notes and Precautions Summary

• Clause 2.6.1 (Calculations):
  Calculate test results precisely as per prescribed formulas to ensure accuracy.

• Clause 4.4.3 (Standard Sulphate Curve Preparation):

  • Use a photoelectric colorimeter with blue filter or a turbidimeter.
  • Employ the working standard solution for readings.

• Clause 4.4.1 (Note):
  Always use absolute alcohol for preparing the test solutions to avoid contamination and ensure consistency.

Key Precautions:

• Strictly follow the preparation and measurement methods to maintain repeatability.
• Use calibrated instruments (colorimeter/turbidimeter) for accurate readings.
• Ensure reagents like absolute alcohol are pure and stored properly.

Typical Calculation Formula (Example for Sulphate concentration):

[ \text{Concentration (mg/L)} = \frac{(A - B)}{(C - B)} \times \text{Standard concentration} ]

Where:

• A = Sample absorbance
• B = Blank absorbance
• C = Standard absorbance

flowchart TD
    A[Prepare Standard Solution] --> B[Measure Absorbance using Colorimeter/Turbidimeter]
    B --> C[Plot Standard Sulphate Curve]
    D[Prepare Sample Solution] --> E[Measure Sample Absorbance]
    E --> F[Calculate Sulphate Concentration using Curve]

Contact for Clarifications:
Refer to regional IS offices listed in the code document for technical support.