Metallic Mercury Ice Cube Tray

Ice cube trays come in two main varieties, plastic and aluminium. The plastic ones, if you buy quality, make getting the cubes out relatively easy. A simple lengthwise twist or two and you can usually manage to hook a fingernail in enough to retrieve a cube. Aluminium is a better heat conductor and should freeze the cubes more quickly, but it's inflexible, leaving banging the tray upside down on the counter top the only viable cube removal method.

Solution: metallic mercury freezes solid at around -39C. This is a lot colder than the standard domestic freezer, which is around -20C, so we will need super-cold compartment, or retrofit some form of heat pump. Once we have that, we make our ice cube tray. The tray will be simple in design, just a plan tray half filled with mercury. To fit into this is a ice-cube mould/mold which is pushed down into the mercury and clamped into place. Now, place the whole shebang into the small -45C freezer compartment we created earlier. The mercury freezes. At this point, you take it out, remove the positive- displacement cube moulding lid and pour in water. Quickly transfer it back into the -45C freezer compartment. Soon, you'll have frozen water ice cubes in a frozen mercury ice cube tray.

Here's the clever bit, you take the tray out and place it in the regular freezer. At -20C the mercury will melt, but the water remains frozen. Mercury, being a lot denser than water will flow down into the bottom of the tray, the water ice cubes will sort of merrily float about on top, easily plucked and inserted into a waiting glass.