The Mystery of Cryolite

Stephen R. Wilk

The search for an item for a lab demo takes the author surprisingly far afield.



Every year I participate in a workshop for pre-teens called “Hands-On Science.” For my last presentation, I wanted to introduce kids to the concept of index matching—combining solids and liquids with similar refractive indices, so that the solid seems to disappear into the liquid. I had a few classic examples lined up—Pyrex and vegetable oil, hydrated sodium polyacrylate marbles and water, Teflon tape and ethanol—but I wanted to impress the students with a rarely seen combination.

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