To demonstrate the statistical nature of irreversible processes.
The Maxwell Demon demonstrator consists of a sealed flask containing 5 white and 5 black spheres. The demonstration begins with the balls in the stem of the flask in the unmixed condition. Inverting the flask mixes the balls and a discussion of the probability of the balls unmixing on inverting the flask again can follow. With 5 black and 5 white balls the odds against reproducing the initial array are 252 to 1.
Maxwell's Demon can be introduced and his task illustrated in the following manner; rotate the flask in a stem up position to impart a swirling motion to the spheres. Turn the flask to the stem down position and slowly reduce the rotation rate and the balls will spiral back into the neck. With a little practice the initial array is restored.
The "demonability" resides in the fact that the black spheres are constructed so as to rapidly lose momentum (see diagram).