Which instrument is used to measure the purity of milk?

Appeared in: RML MAINS 2025

Explanation

A lactometer is a specialized instrument designed specifically to test the purity of milk.
It operates on the principle of buoyancy by measuring the specific gravity (density) of the milk.
Pure milk has a standard density range. A lower density reading on the lactometer indicates that the milk has been adulterated, typically by adding water, thus assessing its purity.

Option A: A hydrometer is a general instrument for measuring the density of any liquid, not specifically calibrated for milk purity.
Option C: A hygrometer measures humidity, which is the amount of water vapor in the atmosphere.
Option D: A barometer measures atmospheric pressure and is primarily used in meteorology for weather forecasting.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Scientific Measurement Instruments as background academic context rather than a clinical decision trigger.
Ensuring milk purity is a critical public health measure to prevent economic adulteration (adding water) and contamination, which can reduce nutritional value and introduce pathogens.
In the context of community health and food safety in India, food safety officers often use lactometers for rapid, on-the-spot field testing of milk quality at collection centers and dairies.
What if? If a lactometer reading is abnormally low, it strongly suggests adulteration with water. The immediate nursing or public health action would be to flag the sample for further laboratory analysis to confirm adulteration and test for other harmful substances like urea, detergents, or starch.

How to Approach the Question

First, identify the core subject of the question, which is finding an instrument for 'purity of milk'.
Look for specific clues in the options. The prefix 'Lacto-' is derived from the Latin word for milk ('lac'). This strongly suggests that 'Lactometer' is related to milk.
Consider the function of each instrument. A lactometer is specific, while a hydrometer is general. A hygrometer (humidity) and barometer (pressure) measure properties of the atmosphere, not liquids.
Eliminate the obviously incorrect options (Hygrometer, Barometer).
Between the specific (Lactometer) and general (Hydrometer) tool, choose the one that is specifically designed for the task mentioned in the question (measuring milk purity).

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 2 — Subpart B (pp 233-449 of 464) p. 66-68

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