This alloy will melt in boiling water.
Robert-Houdin calls it Arcet's metal, but I cannot find the name elsewhere.
The eating of burning brimstone is an entirely fake performance.

A number of small pieces of brimstone are shown, and then wrapped in cotton which has been saturated with a half-and-half mixture of kerosene and gasoline, the surplus oil having been squeezed out so there shall be NO DRIP.

When these are lighted they may be held in the palm of any hand which has been anointed with one of the fire mixtures described in this chapter.

Then throw back the head, place the burning ball in the mouth, and a freshly extinguished candle can be lighted from the flame.

Close the lips firmly, which will extinguish the flame, then chew and pretend to swallow the brimstone, which can afterwards be removed under cover of a handkerchief.
Observe that the brimstone has not been burned at all, and that the cotton protects the teeth.