By Sean Lancaster, Updated Mar 24, 2022
Salt (sodium chloride) dissolves readily in water. The classic method for extracting salt from seawater relies on evaporating the water until crystals appear. In this guide we’ll walk you through the process in a controlled laboratory setting, highlighting the key principles of solubility and crystallization.
Fill a clean beaker with room‑temperature water. Gradually add table salt while stirring with a glass rod. Continue adding until no more salt dissolves; the solution is now saturated, meaning it contains the maximum amount of salt that water can hold at that temperature.
Place the beaker on a hot plate and gently raise the temperature by a few degrees Celsius. Warm water can hold more salt, so this increases the solubility limit.
While the solution is still hot, keep adding salt until it no longer dissolves. The mixture is now supersaturated—more salt than can normally remain dissolved at that temperature.
Turn off the hot plate and let the solution cool naturally. As the temperature falls, the water’s capacity to hold salt decreases, and the excess salt begins to precipitate.
To trigger crystal growth, either scratch the inner wall of the beaker below the solution level with the rod, or introduce a small piece of pre‑formed salt crystal. The scratch or seed provides a nucleation site where salt ions can start arranging into a crystal lattice.
By following these steps, you can observe the transformation from a clear, saturated liquid to crystalline salt, illustrating the fundamental science behind evaporation ponds and ancient salt production.
