Mercury dissolves many metals. Put a little on normally steadfast aluminum and it will slowly eat it away. Mix it with some silver, copper, and other metals, and you've got a dental filling. Mix it with sodium, and you've got a great reducing agent.
Sodium amalgam acts much like sodium, but it's got the added advantage of being a liquid - since reactions require collisions, you're not limited by the small surface area of a solid. Paradoxically, it's actually a little safer and less explodey than sodium. Unfortunately, the mercury part makes it a bit of a liability for, say, pharmaceuticals or food additives.
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Back in 1966 or 1967 this got me a semifinalaist spot in the Westinghouse Science Talent Search.
I'd stumbled in my home lab, dropping a chunk of sodium into an open beaker of mercury. There was an intense exothermic reaction, and a solid product.
I then made combinations with various rations of Hg and Na, put them under a layer of molten wax to seal out air, and measured melting point with home-made thermocouples.
There were extrema in the melting point curve which corresponded, I surmised, to stochiometric Hg2Na and Hg6Na. I suggested that x-ray crystallography be the next step, sent in my report, and got honored.
Then switched to Physics, started at Caltech at age 16 on full scholarship, changed to Astronomy, finally got double B.S. in Math and English, M.S. in Computer Science, first dissertatioon on what's now called nanotechnology, 20 years in space program, and so forth.
I wonder if I gave myself mercury poisoning.
But I still remember the Mercury-Sodium fun. I called it "Amalgam-X", a pun on Malcolm-X.
Have you ever made sodium amalgam? It's a Lewis acid-base neutralization. Spear a little chunk of sodium and thrust it beneath a mercury pool. WHOA! Adding even modest percentages of sodium will heat mercury to a vigorous boil. Water condensers are of questionable value. The product is a nasty solid if you let it cool and fully solidify before chopping it. The product is a nasty solid if you don't let it cool and fully solidify before chopping it.
sodium amalgam used for reductions is solid, actually. Whern it becomes liquid, it is a sign you need to add some more.
Na-amalgam formation is extremely exothermic, the recommended procedure is to impale a cube of sodium on a wire and under flow of Ar quickly stick Na under the Hg level, so that the Na does not burst into flames. When the appropriate amount of Na has been dissolved, you pour the hot amalgam into a wide jar under Ar, let it solidify and then crush it - it is quite brittle.