Question

Name the instrument used to measure the specific gravity (relative density) of a liquid.

Hint:

Think of the floating instrument used in dairies to check if milk has been diluted with water, and in batteries to check acid strength.

Answer 1

Step 1: Specific gravity of a liquid means how heavy it is compared with water of the same volume.

Step 2: A hydrometer is a sealed glass tube with a heavy bulb at the bottom and a graduated stem at the top. It is dropped into the liquid and left to float freely.

Step 3: The instrument works on the principle of flotation. In a denser liquid the hydrometer sinks less, so more of the stem stays above the surface. In a lighter liquid it sinks deeper.

Step 4: The reading on the stem at the liquid surface directly gives the specific gravity of that liquid.

Answer: The instrument used to measure specific gravity is the hydrometer.