Lactometers (used to determine the purity of a sample of milk) and hydrometers (used to determine the density of liquids) are based on the ______ principle.

Detailed Solution
Lactometer (used to determine the purity of a sample of milk) and hydrometer (used to determine the density of liquids) are based on the Archimedes principle.
Lactometer determines the purity of milk by the density of milk.
Hydrometer and Lactometer are based on the density of the substance.
The hydrometer basically consists of a weighted, sealed, long-necked glass bulb immersed in the measured liquid; the flotation depth shows the liquid density, and the neck can be calibrated to read the actual gravity value.