If you’ve ever used a chemical hand warmer, you’ll be familiar with sodium acetate. These bags of liquid are supersaturated solutions of sodium acetate that has supercooled to ambient temperature. Clicking a metal disc in the solution creates a nucleation center that causes the solution to rapidly crystallize, releasing heat. Heating the solid turns it back into a liquid, thereby recharging the hand warmer.

There’s no end of fun to be had with these devices, and now Andrew Adamatzky from the University of the West of England in Bristol has added a new trick to the repertoire: Adamatzky has built a computer entirely out of sodium acetate.

The basic idea is to exploit the traveling wavefront of crystallization to perform calculations, rather in the manner of reaction-diffusion computers and the slime mold computer he has also toyed around with. So the speed of the wavefront as it moves through a petri dish and the way it interacts with other wavefronts effectively performs computations.

Adamatzky inputs data by triggering nucleation at multiple points in parallel by immersing aluminum wires powdered with sodium acetate into a supersaturated solution in a petri dish. He “processes” the wavefronts using blobs of silicone to steer them around the dishes and has used the technique to create AND and OR gates.

The results of a computation are determined by recording the movement of the wavefronts and analyzing the edges of the resulting crystal structures.

Adamatazky’s hot ice computer has so far solved several mazes and a number of other computing problems. He has kindly posted some cool videos of his computer here.

But the computer is far from perfect, he says. Following the wavefronts is by no means easy and occasionally results in no solution or circular ones. In other words, the hot ice computer occasionally hangs, resulting in the hot ice equivalent of the BSOD. It’s probably more realistic than even he bargained for.

Ref: arxiv.org/abs/0908.4426: Hot Ice Computer