That's what a Hungarian chemist did to his friend's medal.
Bohr knew he had to do something to make the medals disappear. Bury them? No. The army would upend the entire lab, leaving no stones unturned. Send them away? There was neither DHL(founded 1969) nor FedEx(founded 1973).
On the day the Nazis came to Copenhagen, a Hungarian chemist named Georgy de Hevesy (who would one day win a Nobel Prize of his own) decided to turn to science for help. He decided to dissolve the medals.
But as the minutes ticked down, both medals were reduced to a colorless solution that turned faintly peach and then bright orange. By the time the Nazis arrived, both awards had liquefied inside a flask that was then stashed on a high laboratory shelf.
After the war, Hevesy returned to Copenhagen and did a little wonder of his own. He reversed the chemistry, precipitated out the gold and sent the material back to the Swedish Academy in Stockholm. The Nobel Foundation then recast the prizes using the original gold and re-presented them to Mr. Laue and Mr. Franck in 1952.