Which instrument is used to determine liquid specific gravity?

• A. Densitometer
• B. Hydrometer
• C. Pycnometer
• D. Hydraulometer

Answer: (B)

Measuring liquid specific gravity relies on buoyancy. A hydrometer is a float weighed so it sits lower or higher in a liquid depending on density. The denser the liquid, the less the instrument sinks, so it floats higher and the calibrated scale directly indicates the liquid’s specific gravity (density relative to water, using water at its standard density as the reference). This makes it the quickest, most practical tool for determining SG in many liquids, from fuels to solutions, right in the field or lab.

Other instruments exist for density measurement, but they’re typically more precise or specialized. A densitometer or pycnometer can give exact densities but require more setup and careful handling, while a hydraulometer is used in specific cement or slurry contexts and isn’t as broadly suited for general liquid SG measurements.