The boys and I have been experimenting some this summer.
This one involved putting a stalk of celery in colored water. We chose red, hoping for big contrast. It was supposed to happen over night. After a disappointing result the first morning, M had the idea to put it in more direct sun to speed things up. It worked much better, but still wasn't the "wow" I was hoping for.
Here we put blue and yellow food coloring in the bowls, used a folded paper towel as a wick and soon had green water in the third bowl. This one was quick and easy and worked very well.
We also did three others where I completely forgot to take pictures.
One was about condensation and involved ice and salt in a metal bowl with a lid. We talked about the ice on the outside of the bowl and how it got there. The boys thought the water was leaking through the bowl at first.
A major fail was the experiment where we tried to grow a gummy bear. We soaked fruit chews over night in plain water. There was, of course, supposed to be some expansion. I think regular fruit chews are moister than a good old fashioned gummy bear and didn't expand so much as disintegrate.
Lastly, was an experiment called Invisible Skin. We coated our hands with a few drops of vegetable oil and compared how the water acted compared to just a plain hand. We learned about water molecules and that polar bears have an oily coating that acts as a protective layer against very cold water.