## Calculating Specific Gravity and the Equivalent Weight of a Liquid

The specific gravity of a liquid is a measurement that indicates how dense a substance is by comparing it to the density of water or the ratio of the density of a substance to the density of some substance (as pure water) taken as a standard when both densities are obtained by weighing in air. Removal of suspended particles by sedimentation depends upon the size and specific gravityof those particles. Suspended solids retained on a filter may remain in suspension if their specific gravity is similar to water while very dense particles passing through the filter may settle.

Water has a specific gravity of 1.0, which means it weighs 8.34 lbs/gallon.

The equivalent weight of a liquid is 22.3 lbs per gallon. What is its specific gravity?

Specific Gravity = equivalent weight of particular liquid
Equivalent weight of water

Specific Gravity =         22.3 lbs per gallon
8.34 lbs per gallon

Specific Gravity = 2.67

You are adding liquid alum to the water to help with flocculation. The specific gravity of liquid alum is 1.336. What would the liquid weigh per gallon?

Specific Gravity = equivalent weight of particular liquid
Equivalent weight of water

Thus

Equivalent weight of a particular liquid = Specific Gravity * Equivalent Weight of Water

Equivalent weight of the liquid alum = 1.336 x 8.34

Equivalent weight of the liquid alum = 11.14 lbs per gallon

Check out the Test Your Knowledge – Calculating Specific Gravity and the Equivalent Weight of a Liquid post for additional practice problems.