From Charles Douglas Wehner:

Re: Scientists work on sun-charged "heat battery" (Oct. 27): Two other examples of "Heat Batteries" spring to mind.

Firstly, we have water. It is unique in the sheer quantity of "heat of melting" that it requires. Substances like wax melt easily, but water stays at exactly zero degrees for a considerable time, whilst it expands. The expansion of water explains why it floats in winter, instead of sinking. Only after this internal molecular rearrangement (phase change) does it melt.

The disadvantage is that it is simply too cold. One needs something with a large latent heat that melts at perhaps a comfortable TWENTY degrees Celsius, not at zero.

Secondly, there was a novel hollow frying pan containing an alloy similar to Wood's Metal. This was placed on the stove until the metal melted. Then it could be put on the side, and the curve of temperature had a "plateau" at the melting point, allowing it to continue to fry the food all on its own.

The disadvantage of the frying pan was that the "latent heat of melting" of the alloy was just too little. The gadget worked, but the effect was hardly magical.

If the research into Ruthenium compounds should lead to substances with spectacular latent heats, things may change.