What does specific gravity measure?

Specific gravity is a measure that compares the weight of a substance to the weight of an equal volume of water at a specified temperature. This comparison allows for an understanding of whether a substance will float or sink in water, as well as providing insight into the density of the substance in relation to water.

When the specific gravity is greater than 1, the substance is denser than water and will sink. Conversely, if the specific gravity is less than 1, the substance is less dense than water and will float. This property is crucial in various fields, including pharmacology, where understanding the density of substances can impact formulation and efficacy.

The other options address different weight comparisons or contexts that do not accurately describe what specific gravity measures. For example, comparing to air is not the standard measurement for specific gravity and would lead to confusion regarding buoyancy and density in relation to fluids.