Mercury has a very large thermal expansion which remains constant over a considerable temperature range. As such, Mercury has often been used in thermometers to indicate changes in temperature.
The triple point of mercury, -38.8344 C, is a fixed point used as a temperature standard for the International Temperature Scale (ITS-90).
Ligiuid Mercury was sometimes used as a coolant for nucleur reactors; however, sodium is proposed for reactors cooled with liquid metal, because the high density of mercury requires much more energy to circulate as a coolant.
Gaseous mercury is used in mercury-vapour lamps and some "neon sign" type advertising signs and fluorescent lamps.
A mercury battery is a non-rechargeable electrochemical battery, a primary cell. The voltage during discharge remains practically constant at 1.35 volts, and the capacity is much greater than a similarly sized zinc carbon battery. Mercury batteries were used in the shape of button cells for watches, hearing aids, and calculaters. However, due to the content of mercury, it is now banned in several countries.
Mercury occurs in deposits throughout the world mostly as cinnabar (Mercuric Sulfide) The red pigment Vermillion, a pure form of Mercuric-Sulfide, is mostly obtained by reaction of mercury, with sulfur.