The Technical Use of Mercury

Mercury is present in the atmosphere mainly due to volcanic emissions but also as a result of industrial pollution. The total amount of global emissions of mercury to the atmosphere are not accurately known at present, although there is evidence that the atmospheric concentration of mercury has increased by about 1% per year for the last 25 years. The volcanic emissions are very big, between 25 000 and 100 000 tonne/year. They are responsible for a base level of mercury concentration in the ground and water. Mercury from the atmosphere is enriched in the surface layers of the ground, where it forms complexes with humus. Rain water dissolves and transports humus to streams and lakes. Mercury is enriched in the top layers of the bottom sediments. 

As the toxicity of mercury went unrecognized for a long time, the special properties of the element became the basis for a versatile utilization and this remained partly the case up to very recently. As is clear from the following description, mercury may be used in a lot of applications. For aU these, the intention is to find substitutes, which both function well without mercury and are acceptable from the environmental point of view. 

Mercury has been used as a metal in thermometers because its coefficient of expansion is nearly constant, which means that the changes in volume for each degree rise or fall in temperature is the same. It has also had widespread use in many types of scientific apparatus, such as vacuum pumps, barometers, electrical rectifiers, relays and switches. 

In the chemical industry, mercury is used as a catalyst for the manufacture from acetylene of acetaldehyde, vinyl chloride and vinyl acetate. Mercury acetate has been used in paints. The intention has been to protect boats against attack of mold fungus. Mercury fulminate Hg(ONC)2 was earher used in detonators, but is nowadays replaced by lead azide. 

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