A seed crystal can be dropped into a saturated solution of sodium acetate. The solution will suddenly crystallize and turn to solid. Alternately, the solution may be slowly poured out onto a seed ...

The first contains a fine iron powder, salt, and water in a pouch that is permeable to air. When it is exposed to air, the iron begins to rust. This rusting process produces heat. The second contains ...

The liquid in the hand warmer is a very concentrated solution of a salt called sodium acetate. The sodium and acetate ions are ready to bond with each other and with water molecules to form a crystal.