Methods of Test for Soils, Part XXI: Determination of Total Soluble Solids

IS 2720 Part 21: Scope & Key Specifications

This part covers the Determination of Total Soluble Solids in soil samples using a simplified conductimetric method.

Key Points from Clause 2.3.2 & Appendix A:

• Sample Preparation:

  • Oven-dry soil sample mass: ( w ) (g)
  • Volume of clear filtrate taken: 50 ml (standard volume)

• Mass Measurements:

  • Mass of dish with residue after oven drying
  • Mass of empty dish
  • Mass of residue ( w_1 = ) (Mass of dish + residue) - (Mass of dish)

• Calculation for % Soluble Solids:

[ \text{Percentage of soluble solids} = \frac{w_1 \times 100}{w} ]

Where:

• ( w_1 ) = Mass of residue (g)
• ( w ) = Mass of oven-dry soil taken (g)

Notes:

• If solubility > 2%, repeat test with 50 ml distilled water for accuracy.
• Use of conductivity meter or bridge is recommended for conductimetric method.

Summary Table (Proforma for Recording):

This method ensures accurate quantification of soluble solids critical for soil quality assessment.

IS 2720 Part 21: Apparatus and Materials Key Points

Apparatus:

• Porcelain or Glass Dish: For drying residue.
• Conductivity Meter or Bridge: For conductimetric method.
• Glass Rod or Stirrer: For mixing samples.
• Oven: To dry soil samples.
• Measuring Cylinder: For volume of filtrate (typically 50 ml).
• Balance: For weighing soil and residue (accuracy to 0.01 g).

Materials:

• Distilled Water: Used for preparing soil filtrate.
• Soil Sample: Oven-dried before testing.

Key Formula for Percentage of Soluble Solids:

[ \text{Percentage of soluble solids} = \frac{w_1 \times 100}{w} ]

Where:

• ( w ) = Mass of oven-dry soil sample (g)
• ( w_1 ) = Mass of residue after drying filtrate (g)

Recommended Proforma (Appendix A) Summary:

Notes:

• If soluble solids > 2%, repeat test with 50 ml distilled water.
• Follow IS 2-1960 for rounding off results.
• Conductivity method uses conductivity meter for subsidiary testing.

flowchart LR
    A[Soil Sample (oven-dry)] --> B[Mix with distilled water]
    B --> C[Filter solution]
    C --> D[Take 50 ml filtrate]
    D --> E[Evaporate in porcelain dish]
    E --> F[Weigh residue (w1)]
    A --> G[Record mass (w)]
    F --> H[Calculate % soluble solids = (w1*100)/w]

This summarizes the apparatus, materials, and key calculation for total soluble solids per IS 2720 Part 21.

IS 2720 Part 21: Sampling & Sample Preparation for Total Soluble Solids

Key Specifications:

• Sample size: Representative soil passing 2 mm IS Sieve.
• Drying: Oven dry at 105–110°C to constant weight.
• Sample mass: ~10 g oven-dry soil.
• Extraction: Add 100 ml distilled water, shake for ≥15 hours.
• Filtration: Decant and filter through Whatman No. 42 or equivalent; repeat if not clear.

Important Formula:

[ \text{Percentage of soluble solids} = \frac{w_1 \times 100}{w} ]

Where:

• ( w ) = Mass of oven-dry soil taken (g)
• ( w_1 ) = Mass of residue after oven drying (g)

Sampling Record Proforma (Appendix A):

Notes:

• If solubility > 2%, repeat test with 50 ml distilled water.
• Use shaker for thorough mixing.
• Clear filtrate is critical for accurate residue measurement.

flowchart TD
    A[Air dried soil sample] --> B[Pass through 2mm sieve]
    B --> C[Oven dry at 105-110°C]
    C --> D[Weigh ~10g soil (w)]
    D --> E[Add 100ml distilled water]
    E --> F[Shake for ≥15 hours]
    F --> G[Allow settling]
    G --> H[Decant & filter clear filtrate]
    H --> I[Evaporate filtrate in dish]
    I --> J[Weigh residue + dish (w1 + dish)]
    J -->

IS 2720 Part 21 (1977) - Test Procedure Key Points

Test Procedure Summary:

• Test records must be maintained using the proforma in Appendix A.
• The test involves measuring total soluble solids in soil filtrate.
• Use conductimetric method with a conductivity meter or bridge.
• If solubility > 2%, repeat test with 50 ml distilled water.

Proforma for Recording (Appendix A):

Key Formula:

[ \text{Percentage of soluble solids} = \frac{w_1 \times 100}{w} ]

Where:

• ( w_1 ) = Mass of residue after drying (g)
• ( w ) = Mass of oven-dry soil taken (g)

Notes:

• Use 50 ml filtrate for the test.
• Repeat test if solubility > 2% for accuracy.
• Record all observations carefully as per the proforma.

flowchart TD
    A[Take oven-dry soil sample (w)] --> B[Prepare filtrate (50 ml)]
    B --> C[Collect filtrate in dish]
    C --> D[Dry residue in oven]
    D --> E[Weigh dish + residue (mass 5)]
    E --> F[Calculate residue mass w1 = (mass 5) - (mass 6)]
    F --> G[Calculate % soluble solids = (w1*100)/w]
    G --> H[Record data in proforma]

This

IS 2720 Part 21: Measurement of Conductivity - Key Points

Instrument & Accuracy (Clause 3.1.1)

• Use a Conductivity Meter/Bridge with a known, unbreakable cell constant.
• Measurement ranges: 1 mho to 10 mhos (7 or 8 ranges).
• Accuracy: ±3%.

Calibration (Clause 2.2)

• Check equipment with saturated calcium sulphate solution.
• Standard conductivity at 25°C: 2.2 mhos/cm.
• If deviation occurs, clean the conductivity cell.

Measurement Formula

[ \sigma = K \times G ] Where:

• (\sigma) = Specific conductivity (mhos/cm)
• (K) = Cell constant (cm(^{-1}))
• (G) = Conductance (mhos)

Recording Results (Clause 2.3.2)

• Use the proforma in Appendix A for observations.
• Round off results as per IS 2-1960.

Summary Table: Conductivity Measurement

flowchart LR
  A[Prepare Calibration Solution] --> B[Check Conductivity Meter]
  B -->|If deviation| C[Clean Cell]
  B -->|If OK| D[Measure Soil Sample Conductivity]
  D --> E[Calculate Specific Conductivity: σ = K × G]
  E --> F[Record Results as per Appendix A]

This ensures reliable and standardized conductivity measurement of soil pore water or electrolytes per IS 2720 Part 21.

IS 2720 Part 21: Total Soluble Solids (TSS) in Soil

1. Methods for TSS Determination

• Gravimetric (Standard) Method
  • Take 50 ml clear filtrate in pre-weighed dish
  • Evaporate water by heating, then dry at 110°C
  • Cool in desiccator, weigh residue
  • Calculate TSS % based on original soil amount

Formula:
[ \text{TSS %} = \frac{\text{Weight of residue (g)}}{\text{Weight of soil sample (g)}} \times 100 ]

2. Conductimetric (Subsidiary) Method

• Use conductivity meter/bridge readings to estimate TSS qualitatively.

Summary

• Gravimetric method is accurate and standard.
• Conductivity method provides quick qualitative assessment.

flowchart TD
    A[Soil Sample] --> B[Filtration]
    B --> C[50 ml Clear Filtrate]
    C --> D[Evaporate Water]
    D --> E[Dry at 110°C]
    E --> F[Weigh Residue]
    F --> G[Calculate % TSS]

This summarizes the gravimetric procedure visually.

IS 2720 Part 21: Reporting of Results for Total Soluble Solids

Key Reporting Specifications:

• Results Precision: Report results to the nearest 0.01% by weight of oven-dry soil (Clause 2.3.1).

• Percentage of Soluble Solids Formula:

[ \text{Percentage of soluble solids} = \frac{w_1 \times 100}{w} ]

Where:

• (w_1) = Mass of residue after oven drying (g)
• (w) = Mass of oven-dry soil taken (g)

Proforma for Recording (Clause 2.3.2)

Conductivity Interpretation (Clause 3.3.2)

Notes:

• If solubility > 2%, repeat test with 50 ml distilled water (Clause 2.2.2 Note).

flowchart TD
    A[Take oven-dry soil sample (w)] --> B[Prepare filtrate (50 ml)]
    B --> C[Dry residue in dish and weigh (w1)]
    C --> D[Calculate % soluble solids = (w1*100)/w]
    D --> E[Report results to nearest 0.01%

IS 2720 Part 21 (1977) - Precision and Accuracy Key Points

• Balances:

  • Physical Balance sensitivity: 0.01 g (Clause 3.1.2)
  • Chemical Balance sensitivity: 0.001 g (Clause 2.1.3)

• Filter Paper:

  • Use Whatman No. 42 or equivalent for filtration (Clause 2.1.15)

• Recording Observations:

  • Follow the recommended proforma for test records (Clause 2.3.2, Appendix A)

• Rounding Off Rules:

  • Numerical values should be rounded as per IS 2720 Part 21 guidelines to maintain accuracy.

• Precision & Accuracy:

  • Sensitivity of balances ensures measurement precision.
  • Use of standard filter paper and proper record keeping enhances test accuracy.

Typical Formula for Precision (Standard Deviation, s):

[ s = \sqrt{\frac{1}{n-1} \sum_{i=1}^n (x_i - \bar{x})^2} ]

Where:

• (x_i) = individual measurement
• (\bar{x}) = mean of measurements
• (n) = number of observations

Summary Table of Balance Sensitivities

flowchart LR
    A[Sample Preparation] --> B[Weighing on Physical Balance (0.01g)]
    B --> C[Weighing on Chemical Balance (0.001g)]
    C --> D[Filtration using Whatman No. 42]
    D --> E[Record Observations (Appendix A)]
    E --> F[Calculate Precision & Accuracy]

This ensures high precision in soil testing measurements per IS 2720 Part 21.

IS 2720 Part 21 (1977) – Notes and Recommendations Summary

Key Formula for Percentage of Soluble Solids:

[ \text{Percentage of soluble solids} = \frac{w_1 \times 100}{w} ]

• w = Mass of oven-dry soil sample (g)
• w₁ = Mass of residue after oven drying (g)

Recommended Proforma for Recording (Appendix A, Clause 2.3.2):

Important Note:

• If the solubility exceeds 2%, repeat the test with 50 ml distilled water (Clause 2.2.2 Note).

Summary:

• Use 50 ml filtrate for testing.
• Record all weights carefully.
• Calculate soluble solids % using the formula.
• Repeat test if solubility > 2%.

flowchart TD
    A[Take oven-dry soil sample (w)] --> B[Prepare filtrate (50 ml)]
    B --> C[Evaporate filtrate in dish]
    C --> D[Weigh dish + residue (w₁ + dish)]
    D --> E[Calculate residue mass w₁ = (dish + residue) - dish]
    E --> F[Calculate % soluble solids = (w₁ * 100)/w]
    F --> G{Is % soluble solids > 2%?}
    G -- Yes --> H[Repeat test with 50 ml distilled water]
    G --

IS 2720 Part 21: Proforma for Recording Total Soluble Solids

Proforma Table (Appendix A, Clause 2.3.2)

Key Formula

[ \text{Percentage of soluble solids} = \frac{w_1}{w} \times 100 ]

• (w) = Mass of oven-dry soil (g)
• (w_1) = Mass of residue after drying (g)

Conductivity Interpretation (Clause 3.3.2)

Note: If soluble solids > 2%, repeat test with 50 ml distilled water (Clause 2.2.2).

flowchart TD
    A[Take oven-dry soil sample] --> B[Extract filtrate (50 ml)]
    B --> C[Dry residue in dish]
    C --> D[Weigh dish + residue]
    D --> E[Calculate residue mass (w1)]
    E --> F[Compute % soluble solids = (w1/w)*100]
    F --> G[Interpret conductivity

IS 2720 Part 21: Additional Notes on Test Repetition

Key Point from Clause 2.2.2 (Amendment):

• If the percentage of soluble solids exceeds 2%, repeat the test using 50 ml distilled water to ensure accuracy.

Test Repetition Procedure Summary:

Formula for Percentage of Soluble Solids:

[ \text{Percentage of soluble solids} = \frac{w_1 \times 100}{w} ]

• w = Mass of oven-dry soil (g)
• w1 = Mass of residue after drying (g)

Recording Format (Appendix A):

• Use the proforma to record:
  • Sample number
  • Mass of oven-dry soil
  • Volume of filtrate
  • Dish details
  • Mass of residue
  • Calculate % soluble solids

Summary:

• Repeat test if soluble solids > 2% with 50 ml distilled water.
• Use the same formula and proforma for consistent recording.
• Ensures reliable and comparable test results.

flowchart TD
    A[Initial Test] --> B{Soluble solids > 2%?}
    B -- Yes --> C[Repeat test with 50 ml distilled water]
    B -- No --> D[Report results]
    C --> D

This ensures accuracy in soil soluble solids determination per IS 2720 Part 21.