Simple construction permits the use of water or even air for demonstration of the concepts involved. Comprises a pair of graduated glass syringes of capacities 50 and 20cm3, both having finely ground pistons and provide a cross-sectional area ratio of 3:1 respectively. Both the syringes mounted on a stable, non-skid sheet metal base with loading platform at their top and their nozzles linked to each other through a 3-position valve, by means of which they may be opened to the atmosphere, isolated or interconnected as desired. Both the pistons provided with limit-stop to prevent their complete ejection from the barrels. Thick wall of syringes makes it capable of withstanding pressures involved. The graduated syringe barrels also permit simple Boyle’s Law experiments to be performed.