Gold is the third in our series of films created to tie in with Friday’s Elements event (the previous two were tin and silver). This beautiful metal has played a huge and important part in human history, but how much do you know about its actual properties?
One of the appealing features of this metal is its constancy; it doesn’t tarnish or change over time. But it isn’t as unreactive as it seems. One of the experiments that Andrea demonstrates in the film above is what happens when you drop mercury onto gold leaf. The gold dissolves into the mercury, leaving an amalgam. This process has been used to separate out gold in the mining process, after which the mercury and gold amalgam is heated and the mercury evaporates away again. However, mercury is toxic, and Andrea pointed out that in some places careless use of this process allows mercury to escape into the environment and into water systems.
Another way of dissolving gold is to use ‘aqua regia’, which is also demonstrated in the film. Andrea told me that Niels Bohr used this trick to dissolve his gold Nobel Prize to keep it out of the hands of the Nazis. The gold Nobel Prize solution was left untouched by them during the war, and he was able to retrieve it afterwards, precipitate out the gold and send it back for recasting.