Preparation and operation: in a 250 ml beaker of sodium acetate crystals (NaAc-3H2O) 60 grams and 40 ml of distilled water, and then heated in a water bath until the crystals are all dissolved, and then continue for a few minutes, take out of the beaker with the solution, and leave it to cool to room temperature.

With a glass rod into the solution, gently rub the wall of the cup or stir the solution or to the solution into a grain of sodium acetate crystals as the "seed crystal", the solution will be precipitated needle crystals, and quickly spread throughout the entire bottom of the beaker, as if it had formed a "block of ice! ".

Extended information:

< p>Liquids whose temperature is below the freezing point but still do not solidify or crystallize are called subcooled liquids. The subcooled liquid is unstable and with a small input of crystals of the substance, crystallization can be induced and the temperature of the subcooled liquid can be brought back to the freezing point. This unstable state, which can be quickly transformed under small perturbations, is called a substable state.

When a saturated solution is slowly cooled in an appropriate manner, it can be made to become supersaturated without precipitating crystals of the solute, a phenomenon also known as subcooling, and the solution is called a supercooled solution. A supercooled solution is also unstable.

Baidu Encyclopedia - Ice