Lactometer
Explanation
The purity of milk is determined by measuring its specific gravity (density relative to water). Instruments used for this purpose operate on Archimedes’ Principle of buoyancy, where the depth to which the instrument sinks correlates to the density of the liquid.
- Hydrometer is Incorrect: A Hydrometer is a general instrument used to measure the specific gravity of liquids. While a lactometer is a specialized type of hydrometer, the specific term for the instrument used for milk is a lactometer.
- Lactometer is Correct: A Lactometer is specifically designed to test the purity of milk. Pure milk has a higher density than water. If water is added to milk (adulteration), the density of the mixture decreases, causing the lactometer to sink deeper, which is indicated on its calibrated scale.
- Barometer is Incorrect: A Barometer is an instrument used to measure atmospheric pressure.
- Manometer is Incorrect: A Manometer is used to measure the pressure of a gas or liquid contained within a closed system (e.g., a pipe or tank).
Key Takeaway:
A Lactometer is used to determine the purity of milk by measuring its specific gravity based on Archimedes’ Principle.