Which of the following methods is used to find the specific gravity of soil in a laboratory?
Try it first: pick an option, then read the explanation.
Correct answer: A. Pycnometer method
Detailed Explanation
As in Q19, this question asks which laboratory method is used to determine the specific gravity of soil, listing similar (but not identical) answer choices.
Why "Pycnometer method" Is Correct
The pycnometer method is the standard laboratory technique for determining specific gravity of soil solids. Hydrometer analysis (option b) is used for sedimentation-based particle-size analysis, not specific gravity; the radiation method and sand bath method are both used for water content, not specific gravity.
Key Point
Hydrometer analysis and pycnometer method are easy to conflate because both involve suspending/mixing soil in a liquid — but they answer completely different questions (particle-size distribution vs. specific gravity).
Key Concepts for Students
- See Q19 for the fuller comparison table of specific-gravity determination methods (density bottle, pycnometer, flask, gas jar, shrinkage limit method).
- Hydrometer analysis is a sedimentation technique used specifically for the fine-grained (silt/clay) fraction of a particle-size distribution test.
- Sand bath and radiation methods both belong to the water-content family of tests, not the specific-gravity family — a recurring distinction throughout this topic.
- The pycnometer method's larger volume (~900 ml) makes it well suited to coarser, cohesionless soils.