The essential form of the apparatus gives a natural approach to the empirical basis of Boyle's Law.  It becomes a simple way to approach the experimental side of physics and to introduce at sight the concepts of vacuum, pressure, density, etc. For demonstrating the relationship between pressure and volume of a given amount of gas The apparatus consist of two glass tubes, one with closed top and other open one connected together by a piece of flexible tubing, running parallel to one another on metal rods. This allows one of the tubes to be raised higher or lower than the other and then locked in place. This unit stands vertical on a metal base. Wooden meter scale 0 to 100 cm  fitted on metal base with levelling screws. Supplied without mercury and rubber tube.