Apparatus for the recording of pressure verses volumes and for investigating Boyle’s Law. The vertical tube is part – filled with the colored liquid and sealed. The trapped air is then compressed progressively, with pressure (p) and volume (v) readings taken at each stage. Before each pair of readings is taken, the liquid should be allowed to settle so that the heat caused by the compressions is dissipated. The air is trapped in a long, graduated vertical tube. This scale is in arbitrary units. These can be taken as indicating the volume of the trapped air. Pressure is applied by using a bicycle pump (or similar) and can be read off the gauge provide. This gauge is calibrated This gauge is calibrated in both kg/cm and p.s.i. A reservoir under the gauge ensures that the pressure reaching the trapped air does not fluctuate too violently. The vertical tube will withstand the pressures required for the demonstration. However replacement of the bicycle pump with a foot pump might result in pressures greater than the apparatus can stand.