is a design for a heat exchanger, from the primary sodium-potassium-eutectic coolant loop of a space-based nuclear reactor to the secondary mercury coolant loop. Not quite the chemical fun of a liquid-sodium/water heat exchanger, but I think sodium and potassium both dissolve enthusiastically in mercury to produce amalgams combining the toxicity and gets-everywhere of mercury with the violent reactivity with everything of the alkali metals.
See http://www.dself.dsl.pipex.com/MUSEUM/POWER/mercury/mercury.htm for more examples of the lure of boiling mercury to power-station designers; it seems to be a very appealing improvement on normal superheated steam, at least if you're not too concerned about expense, weight or neurotoxicity.
In a similar vein, http://www.dself.dsl.pipex.com/MUSEUM/POWER/steamwheel/steamwheel.htm talks at length about a variety of designs for steam engines with liquid-metal pistons, dating all the way back to James Watt. You have the choice between mercury, which is not good for kittens and other living things, or bismuth/tin-based alloys, which solidify when the steam-engine is turned off, and sometimes expand enough to burst the engine.