Sodium Acetate

This is a solution of water and sodium acetate. Sodium acetate is a colourless salt with very interesting properties, not least that it is the main flavour ingredient in salt and vinegar crisps, listed as ingredient E262. It is used in extremely diverse applications for its acidic properties, such as in the tanning and dyeing industries as well as part of concrete and rubber production. It is fairly easy to make it at home with distilled vinegar and baking soda, because it is the sodium salt of acetic acid (the main component of vinegar).

When sodium acetate is dissolved in distilled water at a high concentration, the solution becomes ‘supersaturated’, and in this state is all set for a remarkable process to occur. If the liquid is triggered (either by a shock wave or the seeding it with a pre-existing crystal) the liquid transforms into a solid, with large crystals forming before your eyes. This reaction is exothermic and gives off heat, giving rise to the use of this material in reusable commercial hand-warming pouches. To re-use them, all one needs to do is boil the pouch to melt the crystals and thus reinstate the supersaturated solution.