High temperature bath chemicals I have an electric mantle that I want to bathe reaction vessels at temperatures up to $\mathrm{750^{\circ}C}$.  Obviously that rules out oils.  What substances are used as bath media at such temperatures?

I was thinking of using lead or Rose's alloy, but wondering if there are more standard high-temperature bath chemicals?  I suppose an ideal one would be both inert to lab steel, glass, and a standard atmosphere, and liquid down to room temperature.
Different types of solder can give a very high operating temperature, are cheap and offer excellent conduction and heat contact when molten. We have used lead and cadmium free solder to 500 degrees C with no problem. Your issue may be the melting point (ours was 230C), but the right mix may bring this down for you. If you have the time and inclination, you could modify a commercial mix yourself. Otherwise,  sand would get my vote.