Most liquids, cooling, shuffle near,
and freezing packs them tighter still,
so solid wax, dropped in, sinks clear
through melted wax, as solids will.
But water, freezing, holds its hands:
each molecule grips four, no more,
in six-sided rings, like stretching bands,
with empty space at every core.
That frame takes up a little room
beyond the liquid’s jostling crowd,
about a tenth, so through the gloom
of winter, ice floats, light and proud.
And stranger: water packs in best
at four degrees, not one or two;
so four-degree water sinks to rest
below, while colder floats in view.
So lakes freeze from the top, a lid
of ice that keeps the frost away,
and down below, the fish that hid
swim on at four degrees all day.
If ice had sunk, the lakes would fill
from floor to surface, layer on layer,
and many would be frozen still
right through, with nothing living there.
It’s why a pipe can split in frost,
why bottles crack in freezers too:
the water swells, whatever the cost,
it needs more room, and pushes through.
So when the ice cubes bob and clink
on top of your nimbu pani, spare
a thought for fish, and stop to think
how odd it is they’re floating there.
A small experimentWatch water grow
- Fill the cup with water right to the brim, so the surface is level with the rim.
- Put it carefully in the freezer, standing level, and leave it overnight.
- In the morning, look at the top. Then mark the height of the ice on the outside of the cup.
- Let it melt and see where the water level ends up.
What's going on?
The ice bulges up above the rim, because the same water takes up about a tenth more room as a solid. When it melts, the lattice collapses and the water fits back inside the cup.
Safety Use a plastic cup, never glass: glass can crack as the ice expands.