Action:
A large Florence flask containing a clear colorless liquid is sitting on the demonstration table. You take a small crystal or two of a white salt and drop it into the flask. A beautiful star-shaped mass of white crystals immediately begins to radiate out from the point of impact, soon completely turning the liquid to a solid white mass. Turning the flask upside down, you show that all the liquid has frozen.

You Need:
Two- or 3-liter Florence flask; sodium acetate trihydrate.

Why:
The supersaturated solution of sodium acetate requires only one or two "seed" crystals of the salt to cause massive crystallization. So much solid is formed that the water is trapped in the mass and appears to be completely frozen.

How:
The supersaturated solution is prepared by heating in the flask sodium acetate tribydrate and water, in the ratio of 130 grams: 100 ml., until the salt has dissolved. Make up enough solution to approximately half-fill the flask. Allow the solution to cool slowly without any disturbance.

Remarks:
Great care must be taken to avoid jarring the solution lest it crystallize too soon. Place a beaker over the mouth of the flask while it is cooling lest dust particles cause crystallization. This demonstration is a very striking example of the concept of supersaturation.