Mercury boils at 357 ° C, i.e. When most metals are still far from the melting point. This was known in ancient times, and this method has long been based on methods of extracting metallic mercury from ores. The very first method was burning cinnabar with the condensation of mercury vapors on cold objects and, in particular, on freshly cut green trees. Later, retorts made of ceramics and cast iron began to be used. Since 1842, mercury from ores is extracted in reflective furnaces, and since 1857 – in cascade. In the XX century. They were joined by mechanical multi-hop, as well as rotating tubular furnaces.
In cinnabar, 86.2% of mercury, but in ores considered rich, it accounts for an average of 8%. In poor mercury ores, not more than 0.12%. Such ores must necessarily be enriched in one way or another, “sifting” useless components.
And now mercury is extracted from ores and concentrates mainly by pyrometallurgical methods. Firing occurs in shaft, reflector or tube furnaces at 700 … 750 ° C. Such a high temperature is needed for the cinnabar to oxidize, not to sublimate, and so that the oxidation of HgS + O2> Hg + SO2 goes to the end. As a result of firing, a vaporous mercury is obtained, which is converted into a liquid metal in special condensing apparatuses.
Although the gases formed during roasting pass several stages of purification, not so much metallic mercury condenses as the so-called mortar – a finely dispersed mixture consisting of minute droplets of mercury and fine dust of complex chemical composition. In the mortar there are compounds of both mercury itself and other elements. It is subjected to piling, seeking to destroy dust films that prevent the fusion of microscopically small droplets of liquid metal. The same goal is pursued and repeated distillation. But it is not possible to extract all the mercury from the stupa, and this is one of the currently unsolved mercury metallurgy problems. But this is one of the oldest sections of metallurgy.
The ability of mercury to evaporate at a relatively low temperature was used to apply gold coatings to non-noble metals. This is the way the dome of St. Isaac’s Cathedral is gilded in Leningrad. Now this method is out of use because of the virulence of mercury vapor. Electrochemical methods of gilding are more perfect and safe.
But to see only the poison in mercury vapor is wrong. They can bring and bring many benefits.
In 1936, a report appeared that one of the foreign oil firms acquired a mercury mine. It turned out that mercury is needed by this company for the organization of the mercury vapor system intended for oil purification. Nowadays, mercury vapor is increasingly used in the oil refining industry: they help very accurately regulate the temperature of processes, which is extremely important for refining.
Earlier, at the beginning of the 20th century, the attention of heat engineers was attracted by the report on the work of Dr. Emmett from the United States. Emmett was the first to try to use mercury in steam boilers. His pilot plant with a capacity of 2000 liters. from. Worked and consumed 45% less fuel than a conventional steam boiler with a generator. Of course, there were some discussions: mercury is not water, you will not scoop it out of the river! There were more than enough objections to the use of mercury in steam boilers. Studies, however, continued.
The work of Soviet scientific research institutes on the use of a mercury boiler and turbine was very successful. The economics of mercury vapor turbines and the possibility of creating a so-called mercury-water binary cycle in which the heat of a condensing mercury vapor is used in a special condenser-evaporator to produce water vapor have been proved. And before that, the mercury vapor manages to twist the generator shaft. The resulting water vapor drives the second electric turbogenerator. In such a system, operating only on water vapor, it is possible at best to achieve an efficiency of 30%. The theoretical efficiency of the mercury-vapor cycle (45%) is much higher than that of a gas turbine (18 … 20%) and diesel (35 … 39%). In the 1950s, several such power plants with a capacity of up to 20,000 kilowatts existed in the world. Further business, unfortunately, did not go, mainly because of a shortage of mercury.
Vacuum installations in our time are very important for science and industry. And here mercury is found not only as filler tubes vacuum gauge. As early as 1916, Irving Langmuir created a vacuum pump in which mercury evaporated and condensed. At the same time, the residual pressure in the system associated with the pump was hundreds of millions of times less than the atmospheric pressure.
Modern mercury diffusion pumps give an even greater vacuum: one hundred millionths of a millimeter of mercury.
The study of ultraviolet rays progressed slowly until an artificial source of these rays was created. They were mercury vapor in a vacuum. When mercury vapor passes an electric current, they emit a visible blue glow and many ultraviolet rays. The higher the temperature of the mercury vapor, the more intense the ultraviolet radiation in the mercury-quartz lamp.
The visible glow of mercury vapor is used in the construction of powerful lighting lamps. Fluorescent lamps are discharge tubes containing inert gases and mercury vapor. And what is a “cold light”, it is probably unnecessary to explain. Of every ruble that we pay for “light,” only four kopecks fall to the share of really light radiation. The remaining 96 – for unnecessary heat, emitted by conventional electric lamps. Lamps of daylight are much more economical.