Methods of test for soils, Part 25: Determination of silica sesquioxide ratio

IS 2720 Part 25 (1982) — Scope Summary & Key Specifications

Scope:
This part of IS 2720 covers the determination of the silica sesquioxide ratio in soil samples, important for soil classification and engineering properties.

Key Points:

• Silica Sesquioxide Ratio (SSR):
  [ SSR = \frac{\text{SiO}_2}{\text{(Fe}_2\text{O}_3 + \text{Al}_2\text{O}_3)} ]

• Calculation:

  • Take three determinations of SSR from the soil sample.
  • The average of these three values is the final SSR.

• Units:

  • All quantities follow the SI units system (e.g., length in meters, mass in kilograms).

Relevant Tables:

Important Notes:

• Final results must be rounded off as per IS 2:1960 to maintain consistency with specified significant figures.
• SSR helps in soil classification and assessing soil behavior.

flowchart TD
    A[Soil Sample] --> B[Chemical Analysis]
    B --> C[Three SSR Determinations]
    C --> D[Calculate Average SSR]
    D --> E[Use SSR for Soil Classification]

For detailed procedures, testing methods, and further calculations, refer directly to IS 2720 Part 25 (1982).

IS 2720 Part 25 (1982) - Apparatus and Materials: Key Points

1. Apparatus

• Must be suitable for soil chemical analysis.
• Instruments should provide accurate and reproducible results.
• Typical apparatus includes:
  • Analytical balance (precision ±0.1 mg)
  • Glassware (beakers, pipettes, burettes)
  • Heating devices (water bath, hot plate)
  • Filtration setup
  • pH meter and conductivity meter (if applicable)

2. Materials (Clause 2.14)

• Use pure chemicals free from impurities affecting test results.
• Common reagents include:
  • Hydrochloric acid (HCl)
  • Sulfuric acid (H2SO4)
  • Sodium hydroxide (NaOH)
  • Ammonium hydroxide (NH4OH)
  • Distilled water

3. Calculations (Clause 4.2)

• Silica sesquioxide ratio = Average of three determinations.

4. Units (SI Units)

• Length: metre (m)
• Mass: kilogram (kg)
• Time: second (s)
• Force: newton (N) = 1 kg·m/s²
• Pressure: pascal (Pa) = 1 N/m²

Summary Table: Common Reagents & Apparatus

flowchart LR
    A[Soil Sample] --> B[Chemical Treatment]
    B --> C[Measurement of Silica Sesquioxide]
    C --> D[Repeat 3 Times]
    D --> E[Calculate Average]
    E --> F[Silica Sesquioxide Ratio]

Note: Follow IS 2-1960 for rounding off results consistent with specified significant figures.

IS 2720 Part 25 — Procedure: Key Points & Formulas

1. Rounding Off Results

   • Final test results must be rounded as per IS 2-1960.
   • Retain the same number of significant figures as specified in the standard.

2. Silica Sesquioxide Ratio Calculation

   • Take average of three determinations for the silica sesquioxide ratio:
     [ \text{Silica Sesquioxide Ratio} = \frac{X_1 + X_2 + X_3}{3} ]

3. Units and Symbols (SI Units)

   Quantity	Unit	Symbol
   Length	metre	m
   Mass	kilogram	kg
   Time	second	s
   Force	newton	N
   Pressure/Stress	pascal	Pa

4. General Procedure Notes

   • Follow standard soil sampling and testing methods.
   • Use calibrated equipment and maintain consistency in test conditions.

flowchart TD
    A[Sample Collection] --> B[Preparation]
    B --> C[Three Determinations]
    C --> D[Calculate Average]
    D --> E[Round Off as per IS 2-1960]
    E --> F[Report Results]

Summary: Use averages of three tests for ratios, round results per IS 2-1960, and express values in SI units as specified.

IS 2720 Part 25: Initial Treatment of Soil Specimen

Key Steps (Clause 3.1)

• Sample size: 10 g dried clay fraction (<2 micron) separated by centrifuging.
• Removal of exchangeable cations: Use dialysis or ion-exchange resin.
• Oxidation of impurities: Treat with hydrogen peroxide to remove colloidal and organic impurities.
• Iron oxide removal: Dissolve iron oxides with oxalic acid.
• Washing: Wash clay fraction free of oxalate ions and dry.
• Use: Prepared specimen used for estimation of silica (SiO₂), aluminum oxide (Al₂O₃), and iron oxide (Fe₂O₃).

Calculations (Clause 4.2)

• Perform three determinations of silica and sesquioxide contents.
• Take the average of these as the silica sesquioxide ratio.

Typical Formula for Silica Sesquioxide Ratio:

[ \text{Silica Sesquioxide Ratio} = \frac{\text{SiO}_2}{\text{Al}_2\text{O}_3 + \text{Fe}_2\text{O}_3} ]

Summary Table: Initial Treatment Process

This procedure ensures accurate chemical characterization of clay minerals in soil samples as per IS 2720 Part 25.

IS 2720 Part 25: Estimation of Silica – Key Points

Procedure Summary (Clause 3.2)

• Take ~1 g dried clay in a platinum dish.
• Mix with fusion mixture (5-6 times clay weight).
• Ignite at ~900°C in a muffle furnace; cool.
• Place dish in 800 ml distilled water + few ml concentrated HCl; cover.
• After effervescence stops, wash dish into beaker.
• Evaporate to dryness on sand bath until HCl disappears; repeat if needed.
• Continue evaporation for 1 hour to remove residual acid.
• Add 200 ml distilled water, heat 10 min, filter (Whatman No. 42), wash free of acid.
• Place silica + filter paper in pre-weighed crucible.
• Ignite until constant weight; cool & weigh.
• Silica weight = (weight crucible + silica) - (weight empty crucible).

Calculations (Clause 4.1 & 4.2)

• Silica sesquioxide ratio = (Gram molecular % SiO₂) / (Sum of Gram molecular % Al₂O₃ + Fe₂O₃)
• Take average of three determinations for final ratio.

Notes

• Molecular weights: SiO₂ = 60, Al₂O₃ ≈ 101.96, Fe₂O₃ = 159.7
• Use platinum dish and muffle furnace for high-temp ignition.
• Ensure complete removal of HCl to avoid errors.

flowchart TD
    A[Weigh ~1g dried clay]

Estimation of Aluminium Oxide (Al₂O₃) and Iron Oxide (Fe₂O₃) as per IS 2720 Part 25

Procedure Summary (Clause 3.3)

1. Sample Preparation:

   • Fuse sesquioxide (Fe₂O₃ + Al₂O₃) with fusion mixture.
   • Dissolve in HCl and add to filtrate.
   • Add 5 ml bromine water and make volume to 250 ml.
   • Split into two halves:
     • Half for Al₂O₃ + Fe₂O₃ estimation.
     • Half for Fe₂O₃ only estimation.

2. Estimation of Fe₂O₃ (Clause 3.3.3):

   • Add excess concentrated NaOH to second half; boil.
   • Filter iron hydroxide precipitate (Al hydroxide dissolves).
   • Wash, dissolve precipitate in minimum HCl.
   • Add solid ammonium chloride, heat, cool.
   • Add excess ammonium hydroxide; filter, dry precipitate + filter paper.
   • Ignite in muffle furnace; cool and weigh.
   • Weight after ignition = weight of Fe₂O₃.

3. Estimation of Al₂O₃:

   • Calculate Al₂O₃ by difference:

   [ \text{Weight of } Al_2O_3 = (\text{Weight of } Al_2O_3 + Fe_2O_3) - \text{Weight of } Fe_2O_3 ]

Key Calculations (Clause 4)

Notes:

• Use pre-weighed crucibles for accurate mass determination.
• Ignition must be complete to convert hydroxides to oxides.
• Bromine water acts as an oxidizing agent to maintain iron in the ferr

IS 2720 Part 25 - Key Calculation Details:

• Silica Sesquioxide Ratio (Clause 4.2):
  The average of three determinations shall be taken as the silica sesquioxide ratio of the soil sample.

• Rounding Off (IS 2-1960):
  Final calculated values must be rounded off to the same number of significant digits as specified in the standard.

Important Units & Symbols (SI Units):

Typical Calculation Approach for Silica Sesquioxide Ratio:

[ \text{Silica Sesquioxide Ratio} = \frac{\text{SiO}_2}{\text{Fe}_2\text{O}_3 + \text{Al}_2\text{O}_3} ]

• Take 3 test results → Calculate average → Report as final ratio.

Summary Diagram:

flowchart TD
    A[Soil Sample] --> B[3 Determinations of SiO2, Fe2O3, Al2O3]
    B --> C[Calculate Silica Sesquioxide Ratio for each]
    C --> D[Average of 3 Ratios]
    D --> E[Final Silica Sesquioxide Ratio]

This standard emphasizes precision in averaging and rounding as per IS 2-1960. For detailed chemical analysis formulas and soil testing procedures, refer to IS 2720 Part 25 full text.

Precision and Accuracy as per IS 2720 Part 25

1. Rounding Off (Clause 0.3):

• Final test results shall be rounded according to IS 2-1960.
• The number of significant figures in the rounded value must match that of the specified value in the standard.

2. Average Calculation (Clause 4.2):

• The average of three determinations is taken as the final value (e.g., silica sesquioxide ratio).
• This enhances accuracy by minimizing random errors.

Key Points on Precision and Accuracy:

Important Units (SI Units) for Reference:

Summary Formula for Average (Precision):

[ \text{Average} = \frac{X_1 + X_2 + X_3}{3} ]

Where (X_1, X_2, X_3) are three test results.

flowchart LR
    A[Perform 3 Tests] --> B[Obtain Results X1, X2, X3]
    B --> C[Calculate Average]
    C --> D[Round off as per IS 2-1960]
    D --> E[Final Result]

Note: Use pure chemicals to ensure accuracy in chemical analysis (Clause 2.14).

IS 2720 Part 25 - Reporting of Results: Key Points

1. Rounding Off Results (Clause 0.3)

   • Final test values must be rounded as per IS 2:1960.
   • The number of significant figures in the result should match that of the specified value in the standard.

2. Calculation of Silica Sesquioxide Ratio (Clause 4.2)

   • Take the average of three determinations as the silica sesquioxide ratio of the soil sample.

3. Units and Symbols

   • Use SI units consistently (e.g., length in meters, mass in kg, pressure in pascals).
   • Refer to the standard SI units table for quantities like force (N), energy (J), pressure (Pa), etc.

Summary Table: Key Specifications

Example: Rounding Off Rule (IS 2:1960)

flowchart TD
    A[Test Results] --> B[Rounding Off per IS 2:1960]
    B --> C[Match Significant Figures]
    C --> D[Report Final Value]
    A --> E[Three Determinations of Silica Ratio]
    E --> F[Calculate Average]
    F --> D

Note: Always ensure test results are reported clearly with units and rounded values as per IS guidelines for consistency and compliance.