Wood's metal
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Wood's metal is a fusible alloy that becomes liquid at approximately 70 °C. It is a eutectic alloy of bismuth, lead, tin, and cadmium with the following percentages by weight: 50 % Bi, 26.7 % Pb, 13.3 % Sn, 10 % Cd.
Typical applications are as low-melting solder, low-temperature casting metal, as a high temperature coupling fluid in heat baths, and as a fire-melted valve element in building sprinkler systems. Its inventor, Dr. Wood at MIT, was infamous for casting teaspoons from the alloy which would melt when used to stir hot coffee. Note that the lead and cadmium components of the alloy makes it toxic.
Because of its low melting temperature, Wood's metal is useful for repairing antiques. To repair a bent piece made of sheet metal, a die can be cast from a good example, and the low temperature of the alloy makes it unlikely that the original will be harmed by the process. The damaged piece can then be clamped in the die and slowly tightened to form it back into shape.
Other low-melting solders and fusible alloys include Rose metal, Galinstan, NaK, and alloys of Indium and Bismuth.de:Woodsches Metall