Gallium

Through the magic of ebay, I bought some gallium. It's strange stuff. Apparently whether it's listed as liquid or solid on periodic tables depends on where the table is printed; the melting point is 30°C, so it's solid at room temperature if the room's in Canada in March. But it'll melt in your hand, though it's a slow process.

Gallium is a crystalline solid; I suppose many metals are, but the crystals are really obvious when gallium solidifies. I thought I'd take a video of gallium crystallizing, but it has a tendency to supercool, so after sitting at room temperature for hours it was still liquid. I dropped a crystal of gallium in, though, and I got this beautiful slow crystal formation:

This video is shown at twelve frames per second, each frame is 60 seconds of real time. (It starts when it does because that's when I realized nothing was going to happen immediately; it ends when it does because that's when my camera overheated (!).)

Those vague angular patterns on the surface are actually crystals forming underneath. When I tipped the dish so the liquid flowed away I saw this:


Unfortunately, gallium is directly below aluminum on the periodic table, so, like aluminum, it reacts very rapidly with air, forming a sticky surface scum. When gallium is liquid, though, this scum can't stay in place to protect the surface; instead it sticks to everything around it. Rolling gallium through your fingers feels very peculiar — it's decidedly denser than water, though not tangibly more viscous, and it doesn't feel cool (its vapor pressure at room temperature is tiny). But because of the oxidation, it leaves a gray scum all over your hands. Pieces of gallium left in air also quickly start looking dull and dirty.