The Critical Temperature Unit contains Sulfur Hexafluoride which has a critical temperature of 45.7 degrees C or 318.7 degrees K.  Heat 1500 ml of water to about 60 degrees C and pour it into the Styrofoam container that contains the water pump.  Turn the variac, which is connected to the pump, up to the 50 mark. Observe that the liquid in the cell appears to boil, then the liquid interface disappears, then the entire cell goes opaque with very little boiling which are the observations when taking the liquid from below to above the critical temperature.  You can also observe the cell when it goes from above the critical temperature to below the critical temperature by adding ice to the hot water in the Styrofoam container.  In that case you will observe the cell go from opaque with little boiling, to turbulent with the appearance of an interface, to clear liquid with a definite liquid - gas interface.  

An alternative to using a video camera to observe the Critical Temperature Cell is to use a projector to project the image of the liquid in the cell onto a screen as it goes above and below the critical temperature. A lens may be necessary to enlarge the image for large scale viewing.

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