THE MYSTERIOUS CASE OF THE DISAPPEARING METAL

STORY BY BOB JONES

A specimen of sphalerite from Iron Cap Mine, Graham, Arizona.

CALAMINE CC BY-SA 3.0, VIA WIKIMEDIA COMMONS

When you visit a mineral show and check a dealer’s stock, I’d like to recommend you “think zinc.” The metal comes in a variety of lovely mineral species but not in a pure state. It ranks as the fourth most abundant metal after iron, aluminum, and copper. But unlike copper, iron, lead and some other metals, pure zinc is never found in a natural state. It is so reactive scientists had a heck of a time isolating pure zinc so they could study it.

Zinc has been in use for well over 5,000 years, but it was never found in pure form until 1746, thanks to zinc’s disappearing act! Scientists tried to isolate it as zinc readily forms compounds but can’t stand being alone, so it forms compounds with almost anything that comes along. The problem with zinc is it is very chemically active. Alchemists and later metallurgists and scientists could produce all sorts of chemical reactions involving zinc. Still, as soon as it was isolated, it would combine with something at hand, usually oxygen.

Zinc was so elusive scientists were really stymied to produce it in pure form. Workers would perform a perfect chemical operation to free up zinc only to open their furnace or container and not find anything, no zinc, only unwanted residue. Where was the zinc?

What’s funny is the zinc was right there. The residue weighed less than the original material, so it seems to have disappeared. To find the missing zinc all the scientists had to do was look up the chimney. There it was! The zinc had vaporized from the heat of the reaction and drifted up the chimney, combined with oxygen, and sublimated on the walls of the chimney as white zinc oxide. Mystery solved! But the white powder was still not pure zinc.