I found it in the Atlantic unit study over at Homeschool Share.
After one of our readings of the book Atlantic, which the kids really enjoyed, we talked about how salt gets into the ocean and also about the process of evaporation. Then came the experiment:
1. "Painting" very salty water onto a piece of black construction paper
2. Blow drying the paper
3. What's left after the heat evaporates the water? Salt!
I didn't think to take a picture of the final result, but what you end up with is salt crystals all over the black paper.
Another fun thing we did one day was to play in an indoor "sandbox".
Messy but fun! Thanks to Jen U. for this idea. :)