The technique that gets a dissolved solid back — by deliberately throwing the liquid away.
It works because the solvent changes from a liquid to a gas at a much lower temperature than the solute. Heat a salt solution and the water turns to vapour and leaves; the salt has a far higher boiling point, so it simply stays where it is, as the residue.
This is the answer to the problem from the last lesson. Salt cannot be filtered out of salt solution because it has dissolved — evaporation should be used instead.
Want the solid (salt from seawater) → evaporation. Want the liquid (drinking water from seawater) → distillation. Same mixture, opposite techniques, decided entirely by the goal.
In a salt mine, hot water is pumped deep into the ground to dissolve the salt. The salt solution is pumped up into pans on the ground, and the water is allowed to evaporate under the sun, leaving solid salt behind in the pans.
Water is essential for decomposition, so removing it preserves food. Evaporation is used to dry herbs, spices and small fish — galangal, wolfberries, dried shrimp and ikan bilis. This also extends shelf life and so reduces food wastage.