“Supercriticality”; a dramatic but safe demonstration of the critical point

The image of a fluid passing up through its critical point and back down again is one of the most beautiful and fascinating physical transformations that can be demonstrated to an audience. Unfortunately this image is not often seen; safety issues often restrict educators from carrying out such demonstrations in the public arena. In this article we describe a self contained demonstration apparatus that may be used to illustrate this transition in a very safe and controlled way. The demonstration apparatus may be used as a hands-on teaching instrument in the classroom, or alternatively, with the aid of an LCD projector and screen, be used as an interactive demonstration during larger lectures or exhibitions.