In April 1940, early in the Second World War, Nazi Germany invaded and occupied Denmark. To prevent the Germans from discovering Max von Laue 's and James Franck's gold Nobel medals, Bohr had de Hevesy dissolve them in aqua regia. In this form, they were stored on a shelf at the Institute until after the war, when the gold was precipitated and the medals re-struck by the Nobel Foundation. Bohr's own medal had been donated to an auction to the Finnish Relief Fund, and was auctioned off in March 1940, along with the medal of August Krogh. The buyer later donated the two medals to the Danish Historical Museum in Frederiksborg Castle, where they are still kept, although Bohr's medal temporarily went to space with Andreas Mogensen on ISS Expedition 70 in 2023-2024.