Our second, solar thermal project was to make a very simple water purifier.
This was really a follow up to our boiling tonic water "experiment". If you recall, when we tried to make a glowing cloud-in-a-jar by using tonic water instead of water, we discovered the tonic water glowed under UV light, but the condensation "cloud" in the jar did not. When the water turned to steam, and then condensed back into water droplets, as it reached the colder air at the top of the jar - it had left the quinine (the part of the tonic water that glows under UV light) behind.
We found instructions for a solar water purifier, using a very similar process, but powered by the sun. Of course we had to try it. Besides, what else were we going to do with half a bottle of left over tonic water? Okay, I might have had a few ideas, but they can keep for another day.
We took the plunge, and pulled out two bowls, one large and one small. We placed the small bowl into the center of the large bowl, and poured our tonic water between the two (so it was in the large bowl, but not the small one).
We covered the the large bowl, loosely, with plastic wrap, securing it in place with a stretchy hair band.
Then we placed a marble on top of the plastic, over the small bowl...
...and moved the whole thing outside into the sun.
The marble kept rolling off the bowl, thanks to a light breeze (maybe we should be studying wind power), so we replaced it with a rock.
As the sun heated the tonic water in the large bowl, it turned to steam, and condensed back into water drops when it came in contact with the plastic, where it rolled down toward the dip in the plastic created by the rock, and finally dripped down into the small bowl.
After a few hours, we had a couple of tablespoons' worth of water in the small bowl, so we brought them back inside, and separated them, drying off the outside of the small bowl...
...so we could check the water in each bowl with a UV light. The tonic water in the large bowl glowed green, indicating the presence of quinine...
...the water in the smaller bowl did not glow green - the quinine was gone, just as we expected. It wasn't a lot of water, but it was clean, or at least quinine free.
Questions for additional thought:
Will this type of purification remove everything harmful from contaminated water?
Would it be more efficient to purify more water (in a larger bowl) at a time, or to use several smaller bowls of water, all set in the sun at the same time?
How does the temperature of the day effect the results of the experiment? Is it better to try this on a cold, but sunny day, or a hot, and sunny day?
What if the larger bowl was black, instead of clear?