This precise apparatus is designed for demonstrating Boyle’s Law (elasticity of gases). The apparatus illustrates accurate readings over a wide range of pressure. Two glass tubes, one with a closed top and the other with an 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 vertically on a metal H-shaped base. Supplied without mercury.