Indian Standard reference temperature for specific gravity of soil solids As per IS practice, specific gravity (Gs) is defined as the ratio of the unit weight of soil solids to that of water at the reference temperature of:

Introduction / Context:
Specific gravity of soil solids is a dimensionless parameter used in phase relationships. For consistency, a standard reference temperature is specified because water unit weight varies slightly with temperature. Indian Standards adopt a particular reference temperature for this definition and related laboratory tests.

Given Data / Assumptions:

• We follow IS practice for geotechnical testing.
• Reference fluid is water at a specified temperature.

Concept / Approach:

IS codes (e.g., IS 2720 series) commonly refer to 27°C as the standard reference temperature for water when defining properties like specific gravity, ensuring consistent inter-lab comparison.

Step-by-Step Solution:

Verification / Alternative check:

Many Indian Standard test methods specify conditioning and reporting at 27°C ± 2°C, aligning with this reference.

Why Other Options Are Wrong:

Other listed temperatures correspond to practices in different jurisdictions or general laboratory temperatures but are not the IS reference for Gs definition.

Common Pitfalls:

Assuming 20°C or 4°C (maximum water density) by default; mixing ASTM and IS conventions.

Final Answer:

27°C