Ice cubes rely on a solid-to-liquid phase change (er, they melt) to cool a drink. I propose similar-sized cubes of stainless steel, filled with a suitable substance with a melting point of perhaps 80C. A quick Google search suggested sodium ammonium phosphate; not very nice but fine as long as it stays within the cube. Alternatives might be safer or have more appropriate melting points; a plastic outer might permit microwave use if this could be done safely.
Once heated up above the melting point, they would cool to 80C relatively quickly, then stay at that temperature until all the salt had solidified.
Put a couple in your coffee; it'll stay warmer for longer. Best of all, they're reusable!-- david_scothern, Jul 11 2006 http://antoine.fros...ice-and-water.shtml the contribution that phase change makes in energy absorbed by melting ice [xaviergisz, Jul 11 2006] Ooooh http://www.pbase.co...uber/image/24272958Ahhhh [2 fries shy of a happy meal, Jul 11 2006] I think you just invented the coffee cup grenade +-- xenzag, Jul 11 2006 Googling for Hot Cubes turns up something similar, but without the phase change. As proposed here, they would be more effective.-- david_scothern, Jul 11 2006 Surprisingly logical and useful for a halfbakery idea.-- wagster, Jul 11 2006 is there something that would keep baby milk at the right temperature. the little mites hate cold milk
:)-- po, Jul 11 2006 In my current experience, her mother is ideal for this purpose :) although to make a baby bottle with this feature and a colour-changing temperature indicator built in would be good. Perhaps immerse it, filled with milk, in boiling water until it changes colour, at which point it is fractionally above the correct temperature and can be relied upon to maintain optimum conditions for a long period.-- david_scothern, Jul 11 2006 I wouldn't use a baby bottle with anything less than an lcd display and onboard computer.-- wagster, Jul 11 2006 with built-in MP3, GPS, and bluetooth. Let's not get cheap, [wagster].-- NotTheSharpestSpoon, Jul 11 2006 Stirling or cold fusion for power?-- Galbinus_Caeli, Jul 11 2006 stirling of course-- tatmkr, Jul 11 2006 halfbakery