A practical joke played by chemists involves making teaspoons for unsuspecting tea drinkers from which metal?

Gallium is a soft, silver-colored metal that has a melting point of 29.7 C or 85 F. At room temperature (about 25 C or 72 F) a teaspoon crafted from gallium will be a solid object. However when placed into a cup of hot tea, the spoon will melt. The color of gallium is similar to aluminum and the unsuspecting target for the joke will likely not notice a visual difference between a spoon made of gallium or a regular teaspoon.

The melting point of gallium is low enough that by picking up a piece of gallium (or our gag spoon) it will begin to melt in a person's hand. Gallium as a metal is non-toxic, so application of this joke will not harm the participants, unlike metals such as mercury, which can be harmful if mercury vapors are inhaled or mercury is ingested.