You can cool water below its stated freezing point and then crystallize it into ice on command. This is known as supercooling. Here are step-by-step instructions for supercooling water at home.
The simplest way to supercool water is to chill it in the freezer.
- Place an unopened bottle of distilled or purified water (e.g., created by reverse osmosis) in the freezer. Mineral water or tap water will not supercool very well because they contain impurities that can lower the freezing point of the water or else serve as nucleation sites for crystallization.
- Allow the bottle of water to chill, undisturbed, for about 2-1/2 hours. The exact time needed to supercool the water varies depending on the temperature of your freezer. One way to tell your water is supercooled is to put a bottle of tap water (impure water) into the freezer at the same time as the bottle of pure water. When the tap water freezes, the pure water will be supercooled. If the pure water also freezes, you either waited too long, somehow disturbed the container, or else the water was insufficiently pure.
- Carefully remove the supercooled water from the freezer.
- You can initiate crystallization into ice in several different ways. Two of the most entertaining ways to cause the water to freeze are to shake the bottle or to open the bottle and pour the water onto a piece of ice. In the latter case, the water stream will often freeze backward from the ice cube back into the bottle.
If you don't have a couple of hours, there is a quicker way to supercool water.
- Pour about 2 tablespoons of distilled or purified water into a very clean glass.
- Place the glass in a bowl of ice such that the level of the ice is higher than the level of water in the glass. Avoid spilling any ice into the glass of water.
- Sprinkle a couple of tablespoons of salt onto the ice. Do not get any of the salt in the glass of water.
- Allow about 15 minutes for the water to cool below freezing. Alternatively, you can insert a thermometer into the glass of water. When the temperature of the water is below freezing, the water has been supercooled.
- You can make the water freeze by pouring it over a piece of ice or by dropping a small piece of ice into the glass.