The first records of mercury that have come down to our days date back to about the 5th century BC. In those days, it was mined by the only method known then - roasting cinnabar (compound with sulfur) together with coal. When heated, cinnabar breaks down into its constituent mercury and sulfur, the latter combines with oxygen and forms a volatile compound. At room temperature, the density of mercury (kg / m3) is 13,545.7 kilograms per cubic meter, while it is the only metal that under ordinary conditions we observe in a liquid state.
In nature, the relative density of mercury is low and is estimated at approximately 0.03 - 0.09 mg per kilogram of rock. Concentrated deposits are quite rare, mainly mercury compounds are literally sprayed over the entire surface layer of the earth's crust. Worldwide, about 5,000 deposits of this metal are known, of which only about 500 have been mined. According to modern science, a much higher density of mercury (relative to other components) is observed in the earth's mantle, from where it enters the surface and into the atmosphere during volcanic eruptions. earthquakes, tectonic faults, etc. The so-called mercury respiration of the planet evaporates from the bowels of the order of 3,000 tons of mercury per year; humanity (according to scientists' estimates) adds about 4,000 tons more annually. On a planetary scale, the value may seem small, however, the extremely low solubility of most mercury compounds should be taken into account, because of which they are practically not excreted from the body.
The ability of heavy metals to gradually accumulate is a very unpleasant feature, especially when you consider that they accumulate not only in the human body, but also in the tissues of animals that serve as our food. The relative density of mercury accumulated in the animal’s body is not the same for different species; in addition, habitat and age have an effect. For example, predator fish gradually accumulate mercury-containing compounds in their tissues; the density of these compounds grows faster in predators than in fish that eat plant foods. This factor must be taken into account, especially if the reservoir where the fish were caught from is exposed to wastewater. Similar conclusions are also true for terrestrial animal species and for birds.
Despite the high toxicity of mercury, refusal to use it is hardly possible. Probably its best known use is in medical thermometers (a good combination: medicine and overt poison). The use of mercury in measuring temperature is dictated by an unusually advantageous combination of its qualities: 1) a large range of measured temperatures; 2) more uniform than other liquids extensibility (which allows to increase the measurement accuracy); 3) the complete absence of wetting the glass with mercury; 4) low heat capacity, providing a quick response of the thermometer to a change in external conditions.
No less common are fluorescent lamps, in which radiation is formed by mercury vapor under the influence of a glow discharge. Typically, the density of mercury (more precisely, its vapor) in the lamp bulb is low, the main pressure is formed by an inert gas. Visible light appears due to the phosphor deposited on the glass surface: the ultraviolet radiation of mercury vapor is completely absorbed, and the energy is redistributed in the visible range. The quality of light (color, spectrum continuity) depends on the specific composition of the phosphor. For a living room, it is recommended to choose a lamp with warm light (or a combination of warm and daylight lamps in a set), for an office the daylight is optimal, i.e. slightly cooler lighting.