HOT ICE

Get some sodium acetate trihydrate. Though it’s an inexpensive, nontoxic ingredient, it’s not commonly available in stores and will probably be easiest to purchase online.


Dissolve the sodium acetate trihydrate crystals. Dissolve as much sodium acetate as you can in hot, almost boiling water.

 Touch the solution with a bit of the solid sodium acetate on a toothpick. The solution should turn into a solid as soon as it is touched. By introducing a "seed" crystal, you just created a nucleation center, triggering the process of solidification.

Place your hands near the outside of the container with the newly formed solid. It should radiate heat (the solid is 130°F, or 54°C) because the formation of crystals releases energy. This is why sodium acetate is used in heating pads and hand warmers.