An important rival to mercury in this respect is gallium, and here is why. Mercury boils at the comparatively low temperature of about 300°C (572°F). This makes mercury thermometers useless for measuring high temperatures. But it takes a temperature of 2000°C (3670°F) to turn gallium into a vapour.

   Not a single metal can remain in the liquid state for so long, i.e., has such a large interval between its melting and boiling points, as gallium. This makes gallium an excellent material for high-temperature thermometers.

One more thing, and this is quite remarkable. Scientists have proved theoretically that if there existed a heavy analogue of mercury (an element with a very large atomic number an inhabitant of, the imaginary seventh floor - eighth period - of the Big House, unknown on Earth) its natural state at ordinary conditions would be gaseous.

   A gas possessing the chemical properties of a metal!

   Will scientists ever have such a unique element to study?

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