Melted!

At the Bureau of Standards, Washington, thorium oxide, most resistant to heat of all known substances, was melted (for the first time in history) by C. O. Fairchild and C. G. Peters. Platinum melts at a temperature of about 3,200 degrees Fahrenheit, but that does not begin to phase thorium oxide. Its melting point is probably over 6,000 degrees, which, of course, no thermometer can measure. It is used commercially in gas mantles. A gas flame does not affect it, but an electric arc may. The oxide does, however, shrink in volume at high temperatures. Thorium oxide has been utilized to make crucibles for holding molten platinum. The oxide itself was melted only in a hollow formed in a heap of its own powder.