What is the ratio called that compares the weight of a volume of liquid to the weight of an equal volume of water?

• A. Flammable/explosive range.
• B. Flash point.
• C. Specific gravity.
• D. Vapor density.

Answer: (C)

Specific gravity is the ratio that compares the weight of a volume of liquid to the weight of an equal volume of water. Since it’s based on density, it’s a dimensionless number: water’s density is about 1 g/mL at 4°C, so the liquid’s density (and weight per volume) relative to water gives the SG value. If the liquid is heavier than water, the ratio is greater than 1; if lighter, it’s less than 1. This concept helps compare how different liquids will behave in buoyancy and dosing, among other things. The other terms describe flammability properties or vapor characteristics (not density), so they don’t fit the question.