Humans have been harvesting salt since prehistoric times. Get in on the action by creating a model ocean and harvesting your own chunky, flaky salt at home!
Add water to liquid measuring cup. Heat in microwave until water is steaming, 1 to 1½ minutes. Use oven mitts to remove measuring cup from microwave (ask an adult for help).
Add 1 teaspoon of salt to hot water. Stir with spoon until salt is completely dissolved and water is clear. Continue adding salt, 1 teaspoon at a time, and stirring until all salt is dissolved into water.
Set baking dish in place where it won’t be disturbed. (A warm, sunny spot will help speed up evaporation.) Carefully pour saltwater into baking dish—this is your model of the ocean.
Leave baking dish undisturbed for 24 to 48 hours, or until all water has evaporated. Use hand lens to observe model ocean a few times as it evaporates. What do you notice?
The big square or rectangular salt crystals you harvested came from the tiny crystals of kosher salt you started with! When you dissolve salt in water and then let the water slowly cool and evaporate, the structure of the salt crystals left behind can change.
When mixed with water, salt crystals dissolve into tiny ions. The hotter the water, the more salt you can dissolve into it. When dissolved salt ions find one another, they lock together, kind of like puzzle pieces, and fall out of the solution. As more salt joins them, the salt crystal grows bigger and bigger. The slower a salt solution cools, the more time the salt ions have to find one another and grow larger crystals. Since you let your salt solution cool slowly, you were able to form some big salt crystals!
All salt comes from the sea. Some comes from the oceans that cover most of the earth today. Other salt comes from underground salt deposits left behind when ancient oceans dried up millions of years ago.
Here are the two main ways that people harvest salt:
To retrieve salt from underground deposits, manufacturers pump in water to dissolve the salt. Then machines pump the saltwater mixture into big tanks, which heat up. The heat causes the water to evaporate, leaving the salt behind.
To harvest salt from the ocean, manufacturers start with large, shallow ponds of salty seawater. Over time, the water evaporates and big salt crystals sink to the bottom. Manufacturers use special rakes to collect the salt. This is similar to how you made your salt! (Some sea salt is made from seawater that’s heated to speed up evaporation.)
The salt you made has large, flaky crystals. It’s more like sea salt than kosher salt or table salt. Use your hand lens to observe your salt crystals up close.