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Critical Point Apparatus

Critical Point Apparatus

£5,322.59 exc. 20% VAT(£6,387.11 Inc. VAT)


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  • Experiment apparatus for gas laws
  • High precision studing of compression and liquefaction
  • Easy to set up
  • Mercury free
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Critical Point Apparatus

The Critical Point Apparatus is 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 experiment is quick and easy to set up and provides clear and reliable results. 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).

Features of the Critical Point Apparatus

The apparatus includes leak and compression resistant transparent measuring cell the volume inside the cell is changed via a finely adjustable hand-wheel, with any adjustments 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 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 favourably with standard reference values.

Qualitative Observations:

  • Liquid and gaseous states
  • Dynamic compression and expansion
  • Critical opalescence
  • Formation of the transition point at various temperatures

Quantitative Measurements:

  • Display of the critical point and temperature
  • Recording of isotherms in p-V (Clapeyron) diagrams
  • Recording of isotherms in pV-p (Amegat) diagrams
  • Pressure curves for a saturated vapour

Differences between real gases and ideal gases


  • 1 x Critical point device filled with hydraulic (castor) oil. Includes built in safeguarded connection nozzle for MINICAN gas canisters
  • 1 x Oil filling device
  • 1 x Angled 1.3-mm hexagonal spanner (for grub screw on rotary scale)
  • 1 x Plastic hose, 3 mm internal diameter
  • 1 x 1/8" pipe screw connection (SW 11)
  • 1 x Grease gun


  • Critical temperature: 318.6K (45.5°C)
  • Critical pressure: 3.76MPa (37.6 bars)
  • Critical volume: 197.4cm3/mol
  • Critical density: 0.74g/mol
  • Temperature range: 10 – 60°C
  • Maximum pressure: 6.0MPa (60 bars)
  • Maximum volume: 15.7cm3
  • Manometer diameter: 160mm
  • Bore for temperature sensor: 6mm diameter
  • Temperature control connections: 7mm diameter
  • Reducing valve connection: 1/8" diameter
  • Standard gas connection: 3.5mm diameter
  • Dimensions: 380x200x400mm³ approx.
  • Weight: 7kg approx.

Important 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, a MINICAN gas cannister is advised, the connection of which 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.

Required Equipment

Additionally required in cause of degassing hydraulic oil:

Compatible Equipment

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