Density

The density of a substance is defined as the mass per unit volume. It is a derived quantity. The unit of density in S.I. system is kilogram per cubic metre (kg m-³).

The ratio of the density of the substance to the density of water is called relative density or specific gravity. Since this is a ratio of densities, it is a mere number without any units. A specific gravity bottle is used to measure relative density.

Specific gravity bottle (density bottle) is a glass bottle with a long narrow neck and a glass stopper with a hole fitted into the neck, designed to hold a specific volume of liquid indicated on the bottle. This is used to determine the relative density of liquids.

To find the relative density of a liquid, the density bottle is initially filled with the liquid and then with water and the mass of the bottle in each case is noted. We then use the following relation to find the relative density of the given liquid:

Relative Density = mass of V cm³ of liquid / mass of V cm³ of water Image