What is specific gravity a measure of?

Specific gravity is a measure of the ratio of a substance's weight to the weight of an equal volume of water. This dimensionless quantity allows for comparisons of the density of the substance to that of water, which has a specific gravity of 1 at standard temperature and pressure. When you determine the specific gravity, you essentially gauge how much heavier or lighter a substance is compared to water.

Understanding specific gravity is critical in various fields, including engineering, chemistry, and fluid dynamics, especially when dealing with liquids and gases in a boiler system. It helps in selecting appropriate materials and understanding buoyancy for fluid management.

The other options provide incorrect references: the first focuses on air, which is not relevant to specific gravity; the third suggests a comparison of weight to mass, which doesn't align with the definition; and the fourth confuses mass with weight and highlights a comparison to mass instead of weight. This emphasizes the importance of recognizing that specific gravity relies on weight comparisons to water, not mass or air.