I can't remember where I first saw this density bottle. It might've been from Educational Innovations at one of our ASM summer camps...or maybe from Flinn Scientific at one of their NSTA workshops.
Either way, I have one of those bottles in my classroom, and nearly every student who plays with it love and is fascinated by it.
There's so much goin on with the bottle (the full video of which you can watchin real time at 4:30).
There's solubility concepts - salt water and isopropyl alcohol being immiscible.
There's polarity concepts - food coloring being differently attracted to the two liquids (I recommend green food coloring not the red that Mould uses here. Just add green food coloring and see what happens.)
There's density concepts - the five substances in the bottle (air, isopropyl alcohol, salt water, white/translucent beads, blue beads) line themselves up by density.
There's polymer concepts - the two beads are made of different polymers (the company wouldn't tell me what polymers, and I've asked). The blue beads are sold as pony beads. The top beads - at least the ones in my bottle from Ed Inn - are sold as UV-detecting beads.
There's electromagnetic wave concepts - turns out that the less dense beads are UV beads. I'd had the bottle for years without knowing that because my classroom at the time had no windows, so I hadn't noticed that. Now that I know it, though, it's pretty cool.
There's IMF concepts - the bottle is shrinking a bit as liquid evaporates even through the bottle over the course of years. That's stunning to me, but I swear that I haven't opened the bottle even once in those years. Something must be going on.
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