What is a density bottle? How is it used to find the density of a liquid?

A density bottle is a specially designed bottle which is used to determine the density of a liquid. The figure of density bottle is shown below:

Determination of Density of a Liquid using the Density Bottle

1. Measure the mass of empty density bottle using a beam balance. Let it be M₁ g.
2. Remove the stopper of the bottle and fill it with water. Replace the stopper, wipe the outside of bottle dry and measure its mass again. Let it be M₂ g.
3. Empty the bottle and dry it. Fill it with the given liquid, replace the stopper and wipe the outside of bottle dry. Measure its mass. Let it be M₃ g.
4. Calculate the mass of water (M₂ - M₁) and the mass of liquid (M₃ - M₁).
5. Since density of water is 1 g cm^-3, mass of water contained in bottle is the volume of bottle. Thus,
       Mass of liquid = M₃ - M₁
       Volume of liquid = M₂ - M₁

$\therefore \text{Density of liquid} = \dfrac{\text{Mass of liquid}}{\text{Volume of liquid}} \\[1em] = \dfrac{\text{M}_{3}-\text{M}_{1}}{\text{M}_{2}-\text{M}_{1}}{\text{ g cm}^{-3}}$