Gold is a Noble metal. What this means is that it’s particularly tough, that it doesn’t corrode very easily. Which is one of the reasons we humans have been using it as a precious metal for a long time – your gold ring will stay nice and shiny and attractive for a very long time. So when they were deciding what to make Nobel prizes out of, well, it’s the obvious choice. We like the nice things in our lives to have permanence, and gold delivers while being shiny at the same time.
But what if your shiny gold medal was about to get you killed. What then?
This is the problem renowned scientist Niels Bohr had.
It’s the middle of World War Two. Bohr’s institute in Copenhagen was well known as a safe haven for Jewish scientists. In fact, two Jewish German Physicists, Max Von Laue and James Franck, who had both won the Nobel prize, sent their Nobel medals to Bohr for safe keeping – the Nazis were confiscating all the gold they could find in Germany, and Von Laue and Franck wanted to keep their medals, as you might imagine.
But the Nazis have just occupied Denmark, and are in the process of rolling into Copenhagen. This puts Von Laue and Franck in terrible danger – if their Nobel medals are discovered they will almost certainly be tried for treason, as it was illegal to send gold out of Germany. And their medals have their names printed right on them.
So Bohr and a chemist named Georgy de Hevesy, who was working at the institute at the time, have to get rid of these Nobel medals. They thought of burying them, but dismissed it as the Nazis would almost certainly dig up the grounds. Gold is difficult to hide, and difficult to get rid of. That permanence was now a liability.
But de Havesy knew just what to do. Gold is tough, but it’s not invincible. There’s something called Aqua Regia – a mixture of nitric acid and hydrochloric acid. Now, either of these acids by themselves couldn’t touch gold. But when you mix them, well, then chemistry happens.
If you could shrink down to an atomic scale and look at some gold floating in nitric acid, what you would see is the nitric acid peeling off gold atoms, and then other gold atoms bouncing back and rejoining the gold piece. So the gold is essentially unchanged. But if you introduce hydrochloric acid into the mixture, when the nitric acid peels off some gold atoms, the hydrochloric acid jumps in and eats into the gold, transforming it and dissolving it.
So de Havesy puts each of these Nobel prizes into a jar of Aqua Regia, and waits the few painful hours as the gold dissolves, racing the Nazis who were making their way to the front door. He makes it just in time, and puts this jar of curiously coloured liquid on the top of the shelf in the lab. When the Nazis arrived, they tear the place apart, but leave that random jar on the top shelf alone.
After the war, de Havesy returns to the institute, reaches up to that top shelf, takes the jar home and precipitates the gold back out. He sends the gold back to the Nobel Institute, who are only too happy to remake the two Nobel medals. Von Laue and Franck re-received their medals in a ceremony in 1952.
So, maybe nothing is truly permanent. But if we know our chemistry, we can certainly try our best to make it that way.