Public Health Sanitarian Practice Test

When milk is adulterated with water, its specific gravity decreases. Specific gravity is a measure of the density of a substance compared to the density of water. Pure milk has a specific gravity of about 1.030 to 1.040, which is greater than that of water. When water, which has a specific gravity of 1.000, is added to milk, it dilutes the milk's composition.

This dilution leads to a reduction in the overall density of the mixture because the proportion of the heavier components (such as fats, proteins, and solids) relative to the lighter component (water) decreases. Hence, the specific gravity of the resulting adulterated milk is less than that of pure milk. This phenomenon is significant in milk quality control, as a lower specific gravity can indicate the presence of added water, thus signaling potential adulteration.