Critical Point Apparatus

A high-precision device for studying the compression and liquefaction of a gas, determining the critical point and recording isotherms in p-V (Clapeyron) diagrams. The test gas is sulfur hexafluoride (SF6), which has a critical temperature of 318.6 K (45.5°C) and a critical pressure of 3.76 MPa (37.6 bars), allowing for a simple experiment set-up. The apparatus includes a transparent measuring cell that is highly resistant to leakage and compression. The volume inside the cell is changed via a finely adjustable hand-wheel, the change being indicated by a combination of a fixed and a rotary scale to an accuracy of 1/1000 of the maximum volume. The pressure is generated by a hydraulic system containing castor oil of medically approved quality. The measuring cell and hydraulic system are separated by a cap seal which rolls in as the volume increases. This design means the pressure gradient between the measuring cell and oil chamber is negligible. A manometer measures gas pressure instead of oil pressure without taking up any dead space inside the measuring cell. During transitions from the gaseous to the liquid phases and vice versa, it is therefore possible to observe the formation of the first drops of liquid and disappearance of the last gas bubbles. The measuring cell is enclosed in a transparent water chamber. A circulation thermostat allows the temperature to be maintained at a highly constant value, which can be monitored by means of a thermometer.Practical indications of the volume, pressure and temperature permit easy recording of p-V or pV-p diagrams providing qualitatively correct results. Pressure and temperature-dependent volumetric corrections also provide quantitatively accurate results comparing favorably with standard reference values.Refer also to experiment UE2040300.Qualitative Observations:Liquid and gaseous statesDynamic compression and expansionFormation of the transition point at various temperaturesQuantitative Measurements:Display of the critical point and temperatureRecording of isotherms in p-V (Clapeyron) diagramsRecording of isotherms in pV-p (Amegat) diagramsPressure curves for a saturated vaporDifferences between real gases and ideal gasesImportant Note: In accordance with good laboratory practice, it is advisable to obtain gas via a fixed pipeline if the critical point apparatus is used frequently. In case of occasional usage, it is more expedient to obtain the test gas from MINICAN® canisters. A MINICAN® gas connection is designed similarly to the valve on a common spray can, i.e. it is opened simply by fitting the MINICAN® on the gas connection nozzle.1002670 Includes Only:1 Critical point device filled with hydraulic (castor) oil but without test gas (SF6). Includes built in safeguarded connection nozzle for MINICAN® gas canisters1 Oil filling device1 Angled 1.3-mm hexagonal spanner (for grub screw on rotary scale)1 Plastic hose, 3 mm internal diameter1 1/8" pipe screw connection (SW 11)1 Grease gunAdditionally required:Sulphur hexafluoride SF6Required for periodic degassing or refilling of hydraulic oil:Castor Oil (1002671)High Power Vacuum Pump.