What does specific gravity measure?

Specific gravity is a dimensionless number that measures the weight of a substance compared to the weight of an equal volume of water. It is a critical concept in understanding how various liquids behave in relation to water, which has a specific gravity of 1. If the specific gravity of a liquid is less than 1, it will float on water, whereas a specific gravity greater than 1 indicates that it will sink. This property is essential in hazardous materials operations to determine how chemicals interact with water, which is often used in firefighting and cleanup processes.

Other options do not accurately define specific gravity. The first option refers to the weight of vapors, which involves different comparisons and does not pertain to liquids and water. The third option discusses the density of solids in relation to air rather than liquids and water. Lastly, the fourth option concerns the volume of gases and does not relate to the direct comparison of a substance's weight with water. Understanding specific gravity is vital for correctly handling and assessing the risks associated with hazardous materials.