The acid mixture that dissolved two Nobel medals hidden at Bohr’s institute in 1940 was aqua regia. The medals belonged to German physicists Max von Laue and James Franck, whose gold awards were at risk after Nazi Germany occupied Denmark.
Hungarian chemist George de Hevesy dissolved the medals in aqua regia, a highly corrosive mixture of hydrochloric acid and nitric acid. In solution, the gold no longer looked like a valuable medal, so the container could remain unnoticed among ordinary laboratory chemicals at the institute.
After the war, de Hevesy recovered the gold by precipitating it from the solution. The Nobel Foundation then had the medals recast and returned them to Laue and Franck. A common mix-up is to name nitric acid or hydrochloric acid alone; either is an ingredient, but the medal-saving mixture was aqua regia.