Oven-drying method – moisture content formula from container weights: A container weighs W1. The container with moist soil weighs W2. After oven drying, the container with dry soil weighs W3. What is the correct expression for water content w of the soil (decimal or % as desired)?

Introduction / Context:
Accurate water content is foundational for phase relationships, compaction control, and strength predictions. The oven-drying method determines the mass of water removed relative to the mass of dry soil using simple weighings of a tared container before and after drying.

Given Data / Assumptions:

• W1 = mass of empty container.
• W2 = mass of container + moist soil.
• W3 = mass of container + dry soil after oven drying (105–110 °C).
• No loss of solids during drying; moisture fully removed.

Concept / Approach:
Water content w is defined as Mw / Ms, where Mw is mass of water and Ms is mass of dry soil. Mw equals the difference between moist and dry masses; Ms equals dry mass excluding the container. Substituting measured quantities gives the standard laboratory expression.

Step-by-Step Solution:

Verification / Alternative check:
Sanity check: if W2 ≈ W3 (very dry sample), numerator tends to zero and w tends to zero as expected.

Why Other Options Are Wrong:

• Option B reverses signs producing negative or nonsensical values.
• Option C uses moist mass in denominator; definition requires dry mass.
• Option D divides by moist mass of soil plus container, not the dry mass of soil.

Common Pitfalls:
Using percent in calculations without converting to decimal; spillage during drying; not cooling in a desiccator leading to buoyancy/evaporation errors.

Final Answer:
w = (W2 − W3) / (W3 − W1)