(Gregory L. Hansen) wrote in message ...

When I pull the hose from the nitrogen exhaust on my cryostat, chunks of
ice will fall on to the aluminum stand and as they melt they'll move side
to side, sometimes dancing back and forth quite rapidly until they're very
small compared to the puddle they're floating in.

Any ideas why they would dance?

Any ideas why the ice would contain trapped compressed micro-bubbles?

It seems to me I've seen something similar, but with dry ice ...

OK ... check that. Given the temperature of LN2, maybe your water ice
contains bits of solid CO2. Or maybe there are trapped microbubbles
after all ... ordinary ice cubes are full of trapped air, and if they
don't actually dance, they certainly can effervesce. I associate the
effect with colder freezers, but I'm not sure why ... more rapid
freezing, less chance for gas to diffuse out of the solid, more
entrapped bubbles formed from the solid by nucleation after
solidification?

OYTOH ... don't drops of LN2 also dance on on countertops like water
on a hot skillet? Looks like all you need is rapid gas generation,
whatever the source.