Wood's metal

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, 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; teaspoons which would melt when used to stir hot coffee. Note that the lead and cadmium components of the alloy makes it toxic.

Other low-melting solders and fusible alloys include Rose metal, Galinstan, NaK, and alloys of Indium and Bismuth.