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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.

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    $\begingroup$ What about sand? $\endgroup$ – Todd Minehardt♦ Feb 13 '16 at 16:20
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    $\begingroup$ @ToddMinehardt You did beat me by seconds :D. Sand is an excellent option, both in terms of good heat transfer and lab safety. $\endgroup$ – Klaus-Dieter Warzecha Feb 13 '16 at 16:22
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    $\begingroup$ @KlausWarzecha and Todd - Good suggestion. The reason I was thinking of liquids is that the electric mantle doesn't apply heat very evenly, but natural convection in a liquid would maintain even temperature. $\endgroup$ – feetwet Feb 13 '16 at 16:28
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    $\begingroup$ Gallium may be nice $\endgroup$ – Mithoron Feb 13 '16 at 16:32
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    $\begingroup$ @feetwet And gallium would probably also steadily form oxides at any air-exposed surface; not so good for long experiments. $\endgroup$ – hBy2Py Feb 13 '16 at 22:51
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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.

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