Which instrument is used to measure liquid specific gravity?

Which instrument is used to measure liquid specific gravity?

• A. Hydrometer
• B. Hydroscope
• C. Refractometer
• D. Pycnometer

Answer: (A)

Measuring liquid specific gravity relies on buoyancy: a hydrometer floats at a level that depends on the liquid’s density. The denser the liquid, the less the hydrometer sinks, and the scale on the stem is calibrated to read the specific gravity relative to water at a standard temperature. Temperature matters because water’s density shifts with heat or cold, so readings are most accurate when the liquid is near the calibration temperature or with a temperature correction. Hydrometers are the go-to tool for quick SG readings in both fields and labs. Other devices have different purposes: a hydroscope is used for inspecting tanks rather than measuring density; a refractometer measures how light bends to give refractive index (often used for sugar content or salinity, not direct SG); a pycnometer can determine density by weighing a known-volume container very precisely, but it’s more of a lab-grade method than a fast SG reading.

Measuring liquid specific gravity relies on buoyancy: a hydrometer floats at a level that depends on the liquid’s density. The denser the liquid, the less the hydrometer sinks, and the scale on the stem is calibrated to read the specific gravity relative to water at a standard temperature. Temperature matters because water’s density shifts with heat or cold, so readings are most accurate when the liquid is near the calibration temperature or with a temperature correction.

Hydrometers are the go-to tool for quick SG readings in both fields and labs. Other devices have different purposes: a hydroscope is used for inspecting tanks rather than measuring density; a refractometer measures how light bends to give refractive index (often used for sugar content or salinity, not direct SG); a pycnometer can determine density by weighing a known-volume container very precisely, but it’s more of a lab-grade method than a fast SG reading.