Stalagmometer (drop count method) A stalagmometer is primarily used to measure which property of a liquid by counting drops formed at a capillary tip?

Introduction / Context:
The stalagmometer (drop count method) is a classic laboratory instrument for evaluating interfacial properties. By counting the number of drops of a liquid that fall from a capillary of known dimensions and comparing to a reference, one can determine surface tension using simple relationships that balance gravitational and capillary forces.

Given Data / Assumptions:

• Uniform drops form at a capillary tip under controlled flow.
• Temperature is controlled to ensure consistent physical properties.
• Calibration is performed with a reference liquid (often water).

Concept / Approach:
At detachment, the weight of a pending drop is balanced by the surface tension force acting around the perimeter of the capillary. For a given tip and temperature, the number of drops per unit mass (or per unit volume with density correction) is inversely related to surface tension. Comparing sample and reference drop counts yields the sample’s surface tension. This principle is different from viscometry (kinematic viscosity), refractometry (refractive index), and polarimetry (optical activity).

Step-by-Step Solution:

Verification / Alternative check:
Results can be cross-checked with du Nouy ring or Wilhelmy plate tensiometry; agreement within method precision validates the measurement.

Why Other Options Are Wrong:

• Kinematic viscosity: Measured by capillary viscometers (e.g., Ostwald).
• Refractive index: Determined with refractometers.
• Optical activity: Determined by polarimeters for chiral solutions.

Common Pitfalls:
Ignoring density correction; surface tension comparisons require accounting for sample/reference densities and wetting corrections.

Final Answer:
Surface tension