Last week's article speculating that gold may have been stolen from the Royal Canadian Mint secreted in acid revived our much earlier discussion of Aqua Regia (and don't try this at home, kids, it's dangerous). It also generated a new query regarding the Nobel Prize medals - are they cast or struck? -Editor Leon Saryan writes:
It's my impression that gold metal does not dissolve in hydrochloric acid as such. It does however, dissolve in Aqua Regia, which is a mixture of nitric and hydrochloric acids, volume ratio of 18 ml nitric to 82 ml hydrochloric.
I think you should run a sweep on how many e-mails you get pointing out that hydrochloric acid would not have dissolved the RCM's gold on its own. I suspect I am not the first.
To do the trick one part of concentrated fuming nitric acid needs to be added for every three parts of concentrated fuming hydrochloric. This of course produces what is commonly known as aqua regia or king water.
It will cheerfully dissolve gold and platinum but loses its efficacy if allowed to stand. If you are planning a heist along these lines, it needs to be mixed fresh for best results. From experience, I recall that you also need a bit of patience.
The Franck and von Laue medals are a great story. Of course, it wasn't the medals that were hidden so much as their gold. This was precipitated after WWII and returned to the Nobel Institute who used it to restrike/recast their medals.
Now there's a question: are Nobel medals cast or struck?