Precise instrument for demonstrating the relationship between pressure and volume of a given amount of gas. Two glass tubes one closed at one end the other with both ends open are connected by a long rubber tube. The glass tubes are mounted with the help of sliding brackets on two vertical support rods and can be positioned anywhere along the length of the rods. Wooden meter rule permits measurement. Leveling screws on metal base. Requires mercury (Not Included) for performing experiments.