It is Consists of two glass tubes – one having both ends open and the other having its upper end closed. Both the tubes are mounted on vertical support rods with the help of sliding brackets that can be positioned anywhere along the length of the rod and are connected to each other through a flexible pressure rubber tubing. A meter rule graduated 0-100cm × 1 mm, reading in both directions, is located between the two support-rods on a wooden back plate and facilitates liquid level reading in both the tubes. Complete apparatus mounted on a stable cast-metal base with leveling screws. Requires mercury for use, not included. It is to Demonstrates the relationship between pressure and volume of a given mass of gas at a fixed temperature