Arsenic is a dangerous but necessary substance. What is arsenic? Characteristics, properties and application Arsenic to which family does it belong

Arsenic- a mineral from the class of native elements, semimetal, chemical formula As. Common impurities are Sb, S, Fe, Ag, Ni; more rarely, Bi and V. The As content in native arsenic reaches 98%. Chemical element of the 15th group (according to the outdated classification - the main subgroup of the fifth group) of the fourth period of the periodic system; has an atomic number of 33. Arsenic (crude arsenic) is a solid extracted from natural arsenopyrites. It exists in two main forms: ordinary, so-called "metallic" arsenic, in the form of shiny steel-colored crystals, brittle, insoluble in water, and yellow arsenic, crystalline, rather unstable. Arsenic is used in the production of arsenic disulfide, coarse shot, hard bronze and various other alloys (tin, copper, etc.)

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STRUCTURE

Several allotropic modifications of arsenic have been established. Under normal conditions, metallic or gray arsenic (alpha-arsenic) is stable. The crystal lattice of gray arsenic is rhombohedral, layered, with a period a = 4.123 A, angle a = 54° 10'. Density (at a temperature of 20 ° C) 5.72 g / cm 3; temperature coefficient. linear expansion 3.36 10 deg; specific electrical resistance (temperature 0 ° C) 35 10 -6 ohm cm; HB = w 147; coefficient compressibility (at a temperature of 30 ° C) 4.5 x 10 -6 cm 2 / kg. The melting point of alpha-arsenic is 816 ° C at a pressure of 36 atmospheres.

Under atm. pressure, arsenic sublimates at a temperature of 615 ° C without melting. The heat of sublimation is 102 cal/g. Arsenic vapors are colorless, up to a temperature of 800 ° C they consist of As 4 molecules, from 800 to 1700 ° C - from a mixture of As 4 and As 2, above a temperature of 1700 ° C - only from As 2. With the rapid condensation of arsenic vapor on a surface cooled by liquid air, yellow arsenic is formed - transparent soft crystals of the cubic system with a density of 1.97 g / cm 3. Other metastable modifications of arsenic are also known: beta-arsenic - amorphous glassy, ​​gamma-arsenic - yellow-brown and delta-arsenic - brown amorphous with densities of 4.73, respectively; 4.97 and 5.10 g/cm3. Above 270°C, these modifications transform into gray arsenic.

PROPERTIES

The color on a fresh fracture is zinc-white, tin-white to light gray, quickly tarnishes due to the formation of a dark gray tint; black on a weathered surface. Mohs hardness 3 - 3.5. Density 5.63 - 5.8 g / cm 3. Fragile. Diagnosed by the characteristic smell of garlic on impact. Cleavage perfect according to (0001) and less perfect according to (0112). The fracture is granular. Oud. weight 5.63-5.78. The dash is grey, pewter white. Shine metallic, strong (in a fresh fracture), quickly fades and becomes matte on an oxidized, blackened surface over time. It is diamagnetic.

MORPHOLOGY

ORIGIN

Arsenic occurs in hydrothermal deposits as metacolloidal formations in voids, apparently formed during the last moments of hydrothermal activity. In association with it, arsenic, antimony, and less often sulfur compounds of nickel, cobalt, silver, lead, etc., as well as non-metallic minerals, of various compositions, can occur.

In the literature there are indications of the secondary origin of arsenic in the weathering zones of deposits of arsenic ores, which, generally speaking, is unlikely, given that under these conditions it is very unstable and, rapidly oxidizing, decomposes completely. Black crusts consist of a fine mixture of arsenic and arsenolite (As 2 O 3). In the end, pure arsenolith is formed.

In the earth's crust, the concentration of arsenic is low and amounts to 1.5 ppm. It occurs in soil and minerals and can be released into the air, water and soil through wind and water erosion. In addition, the element enters the atmosphere from other sources. As a result of volcanic eruptions, about 3 thousand tons of arsenic are released into the air per year, microorganisms form 20 thousand tons of volatile methylarsine per year, and as a result of the combustion of fossil fuels, 80 thousand tons are released over the same period.

On the territory of the USSR, native arsenic was found in several deposits. Of these, we note the Sadon hydrothermal lead-zinc deposit, where it was repeatedly observed in the form of reniform masses on crystalline calcite with galena and sphalerite. Large kidney-shaped accumulations of native arsenic with a concentric-shell structure were found on the left bank of the river. Chikoya (Transbaikalia). In the paragenesis with it, only calcite was observed in the form of rims on the walls of thin veins intersecting ancient crystalline schists. In the form of fragments (Fig. 76), arsenic was also found in the area of ​​st. Dzhalinda, Amur railway etc. and in other places.

In a number of deposits in Saxony (Freiberg, Schneeberg, Annaberg, etc.), native arsenic was observed in association with arsenic compounds of cobalt, nickel, silver, native bismuth, etc. All these and other finds of this mineral are of no practical importance.

APPLICATION

Arsenic sulfide compounds - orpiment and realgar - are used in painting as paints and in the leather industry as a means to remove hair from the skin. In pyrotechnics, realgar is used to produce "Greek" or "Indian" fire, which occurs when a mixture of realgar with sulfur and nitrate burns (it forms a bright white flame when burned).
Some organoelement compounds of arsenic are chemical warfare agents, for example, lewisite.

At the beginning of the 20th century, some cacodyl derivatives, such as salvarsan, were used to treat syphilis, over time, these drugs were displaced from medical use for the treatment of syphilis by other, less toxic and more effective, arsenic-free pharmaceutical preparations.

Many of the arsenic compounds in very small doses are used as drugs to combat anemia and a number of other serious diseases, as they have a clinically noticeable stimulating effect on a number of specific body functions, in particular, on hematopoiesis. Of the inorganic compounds of arsenic, arsenic anhydride can be used in medicine for the preparation of pills and in dental practice in the form of a paste as a necrotizing drug. This drug was colloquially and slangy called "arsenic" and was used in dentistry for local necrosis of the dental nerve. Currently, arsenic preparations are rarely used in dental practice due to their toxicity. Now other methods of painless necrosis of the nerve of the tooth under local anesthesia have been developed and are being used.

Arsenic - As

CLASSIFICATION

Our story is about an element that is not very common, but widely known; about an element whose properties are contradictory to the point of incompatibility. It is also difficult to reconcile the roles that this element has played and is playing in the life of mankind. At different times, in different circumstances, in different forms, it acts as a poison and as a healing agent, as a harmful and dangerous waste product, as a component of the most useful, irreplaceable substances. So the element with atomic number 33.

History in abstracts

Since arsenic is one of the elements, the exact date of discovery of which has not been established, we confine ourselves to stating only a few reliable facts:

arsenic has been known since ancient times;

in the writings of Dioscorides (1st century AD), the calcination of a substance that is now called arsenic sulfide is mentioned;

in the 3rd-4th century, in fragmentary records attributed to Zozymos, there is a mention of metallic arsenic; the Greek writer Olympiodorus (5th century AD) describes the production of white arsenic by roasting sulfide;

in the 8th century, the Arab alchemist Geber obtained arsenic trioxide;

in the Middle Ages, people began to encounter arsenic trioxide when processing arsenic-containing ores, and the white smoke of gaseous As2O3 was called ore smoke;

the production of free metallic arsenic is attributed to the German alchemist Albert von Bolstedt and is attributed to about 1250, although Greek and Arab alchemists undoubtedly received arsenic (by heating its trioxide with organic substances) before Bolstedt;

in 1733 it was proved that white arsenic is an oxide of metallic arsenic;

in 1760, the Frenchman Louis Claude Cadé obtained the first organic compound of arsenic, known as Cadé liquid or "cacodyl" oxide; the formula of this substance is [(CH3)2A]2O;

in 1775 Carl Wilhelm Scheele obtained arsenic acid and arsenic hydrogen;

In 1789, Antoine Laurent Lavoisier recognized arsenic as an independent chemical element.

Elemental arsenic is a silver-gray or tin-white substance, in a fresh fracture it has

metallic luster. But it quickly fades in air. When heated above 600 ° C, arsenic sublimates without melting, and under a pressure of 37 atm it melts at 818 ° C. Arsenic is the only metal whose boiling point at normal pressure lies below the melting point.

Arsenic is poison

In the minds of many, the words "poison" and "arsenic" are identical. That's how it happened historically. There are stories about the poisons of Cleopatra. The poisons of Locusta were famous in Rome. Poison was also a common tool for eliminating political and other opponents in the medieval Italian republics. In Venice, for example, experts in poisoning were kept at the court. And the main component of almost all poisons was arsenic.

In Russia, the law prohibiting the sale of “vitriol and amber oil, strong vodka, arsenic and tsilibukha” to private individuals was issued back in the reign of Anna Ioannovna - in January 1733. The law was extremely strict and read: “Who will henceforth trade in that arsenic and other materials mentioned above and will be caught with it or who will be reported to, they will be severely punished and exiled to exile without any mercy, the same will be inflicted on those who past pharmacies and town halls from whom they will buy. And if someone, having bought such poisonous materials, will repair damage to people, those who are searched for will not only be tortured, but they will also be executed by death, depending on the importance of the matter without fail.

For centuries, arsenic compounds have attracted (and continue to attract) the attention of pharmacists, toxicologists, and forensic scientists.

Criminalists have learned to recognize arsenic poisoning unmistakably. If white porcelain-like grains are found in the stomach of the poisoned, then the first thing to do is to suspect arsenic anhydride As2O3. These grains, together with pieces of coal, are placed in a glass tube, sealed and heated. If there is As2O3 in the tube, then a gray-black shiny ring of metallic arsenic appears on the cold parts of the tube.

After cooling, the end of the tube is broken off, the charcoal is removed, and the grey-black ring is heated. In this case, the ring is distilled to the free end of the tube, giving a white coating of arsenic anhydride. The reactions here are:

As2O3 + 3S == As2 + 3SO

or

2As2O3 + 3S = 2AS2 + 3CO2;

2As2+3O2==2As2O3.

The resulting white plaque is placed under a microscope: even at low magnification, characteristic shiny crystals in the form of octahedrons are visible.

Arsenic has the ability to stay in one place for a long time. Therefore, during forensic chemical research, samples of earth taken from six sites near the burial place of a person who could have been poisoned, as well as parts of his clothing, jewelry, and coffin boards, are delivered to the laboratory.

Symptoms of arsenic poisoning are a metallic taste in the mouth, vomiting, severe abdominal pain. Later convulsions, paralysis, death. The most famous and widely available antidote for arsenic poisoning is milk, more precisely, the main milk protein casein, which forms an insoluble compound with arsenic that is not absorbed into the blood.

Arsenic in the form of inorganic preparations is lethal in doses of 0.05-0.1 g, and yet arsenic is present in all plant and animal organisms. (This was proven by the French scientist Orfila back in 1838.) Marine plant and animal organisms contain on average hundreds of thousands, and freshwater and terrestrial - millionths of a percent of arsenic. Microparticles of arsenic are also absorbed by the cells of the human body, element No. 33 is found in the blood, tissues and organs; especially a lot of it in the liver - from 2 to 12 mg per 1 kg of weight. Scientists suggest that microdoses of arsenic increase the body's resistance to the action of harmful microbes.

Arsenic is a medicine

Doctors state that dental caries is the most common disease in our time. It is difficult to find a person who does not have at least one filled tooth. The disease begins with the destruction of the calcareous salts of tooth enamel, and then pathogenic microbes begin their nasty business. Penetrating through the weakened armor of the tooth, they attack its softer interior. A “carious cavity” is formed, and if you are lucky enough to be at the dentist at this stage, you can get off relatively easily: the carious cavity will be cleaned and filled with filling material, and the tooth will remain alive. But if you do not see a doctor in time, the carious cavity reaches the pulp, the tissue containing nerves, blood and lymphatic vessels. Its inflammation begins, and then the doctor, in order to avoid the worst, decides to kill the nerve. The command is given: “arsenic!”, And a grain of paste the size of a pinhead is placed on the pulp exposed by the instrument. Arsenic acid, which is part of this paste, quickly diffuses into the pulp (the pain that is felt at the same time is nothing more than the “last cry” of the dying pulp), and after 24-48 hours it’s all over - the tooth is dead. Now the doctor can painlessly remove the pulp and fill the pulp chamber and root canals with antiseptic paste, and seal the “hole”.

Arsenic and its compounds are used not only in dentistry. Salvarsan, the 606th preparation of Paul Ehrlich, a German doctor who discovered the first effective means of combating lues at the beginning of the 20th century, gained worldwide fame. It was indeed the 606th of the arsenic preparations tested by Ehrlich. This yellow amorphous powder was originally assigned the formula

Only in the 50s, when salvarsan was no longer used as a remedy against lues, malaria, and relapsing fever, did the Soviet scientist M. Ya. Kraft establish its true formula. It turned out that salvarsan has a polymer structure

Value P depending on the method of obtaining, it can range from 8 to 40.

Salvarsan was replaced by other arsenic drugs, more effective and less toxic, in particular its derivatives: novarsenol, miarsenol, etc.

Some inorganic arsenic compounds are also used in medical practice. Arsenic anhydride As2O3, potassium arsenite KAsO2, sodium hydrogen arsenate Na2HAsO4. 7H2O (in minimal doses, of course) inhibit oxidative processes in the body, increase blood formation. The same substances - as external - are prescribed for certain skin diseases. Namely, arsenic and its compounds are credited with the healing effect of some mineral waters.

We think that the above examples are sufficient to confirm the thesis contained in the title of this chapter.

Arsenic is a weapon of destruction

Again, we have to return to the deadly properties of element No. 33. It is no secret that it was widely used, and possibly still being used, in the production of chemical weapons, no less criminal than nuclear ones. This is evidenced by the experience of the First World War. Information leaked to the press about the use of poisonous substances by the troops of the imperialist states in Abyssinia (Italy), China (Japan), Korea and South Vietnam (USA) speaks of the same thing.

Arsenic compounds are included in all major groups of known chemical warfare agents (0V). Among the 0V of general toxic action are arsine, arsenic hydrogen AsH3 (we note in passing that compounds of trivalent arsenic are more poisonous, whose compounds in which arsenic is pentavalent). This most poisonous of all arsenic compounds, it is enough to breathe air for half an hour, a liter of which contains 0.00005 g of AsH3, in order to go to the next world in a few days. AsH3 concentration 0.005g/l kills instantly. It is believed that the biochemical mechanism of action of AsH3 is that its molecules "block" the molecules of the enzyme of erythrocytes - catalase; because of this, hydrogen peroxide accumulates in the blood, destroying the blood. Activated carbon sorbs arsine weakly, so an ordinary gas mask is not a protector against arsine.

During the First World War, there were attempts to use arsine, but the volatility and instability of this substance helped to avoid its mass use. Now, unfortunately, there are technical possibilities for long-term contamination of the area with arsine. It is formed by the reaction of some metal arsenides with water. And the arsenides themselves are dangerous for people and animals, the American troops in Vietnam proved this. . . The arsenides of many metals should also be classified as general action agents.

Another large group of toxic substances - irritating substances - consists almost entirely of arsenic compounds. Its typical representatives are diphenylchloroarsine (C6H5)2AsCl and diphenylcyanoarsine (C6H5)2AsCN.

Substances of this group selectively act on the nerve endings of the mucous membranes - mainly the membranes of the upper respiratory tract. This causes a reflex reaction of the body to get rid of the irritant by sneezing or coughing. Unlike tear agents, these substances, even with mild poisoning, act even after the affected person has escaped from the poisoned atmosphere. Within a few hours, the person is shaking with an excruciating cough, pain in the chest and in the head appears, tears begin to flow involuntarily. Plus, vomiting, shortness of breath, a sense of fear; all this leads to complete exhaustion. And in addition, these substances cause a general poisoning of the body.

Among the poisonous substances with blistering action is lewisite, which reacts with the sulfohydryl SH-groups of enzymes and disrupts the course of many biochemical processes. Absorbed through the skin, lewisite causes general poisoning of the body. This circumstance at one time gave Americans a reason to advertise lewisite under the name "dew of death."

But enough about that. Humanity lives in the hope that the poisonous substances we have talked about (and many more like them) will never be used again.

Arsenic - a stimulant of technological progress

The most promising field of application of arsenic is undoubtedly semiconductor technology. Gallium arsenides GaAs and indium arsenides InAs acquired particular importance in it. Gallium arsenide is also important for a new direction in electronic technology - optoelectronics, which arose in 1963-1965 at the intersection of solid state physics, optics and electronics. The same material helped create the first semiconductor lasers.

Why did arsenides turn out to be promising for semiconductor technology? To answer this question, let us briefly recall some of the basic concepts of semiconductor physics: "valence band", "forbidden band" and "conduction band".

Unlike a free electron, which can have any energy, an electron enclosed in an atom can only have certain, well-defined values ​​of energy. From the possible values ​​of the energy of electrons in an atom, energy bands are added. By virtue of the well-known Pauli principle, the number of electrons in each zone cannot exceed a certain certain maximum. If the band is empty, then, of course, it cannot participate in the creation of conductivity. The electrons of the completely filled band do not participate in the conduction either: since there are no free levels, an external electric field cannot cause a redistribution of electrons and thereby create an electric current. Conductivity is possible only in a partially filled zone. Therefore, bodies with a partially filled band are referred to as metals, and bodies in which the energy spectrum of the electronic state consists of filled and empty bands are referred to as dielectrics or semiconductors.

We also recall that completely filled bands in crystals are called valence bands, partially filled and empty bands are called conduction bands, and the energy interval (or barrier) between them is called the band gap,

The main difference between dielectrics and semiconductors lies precisely in the band gap: if an energy of more than 3 electron volts is needed to overcome it, then the crystal is referred to as dielectrics, and if less, to semiconductors.

Compared to classical group IV semiconductors, germanium and silicon, group III arsenides have two advantages. The band gap and the mobility of charge carriers in them can be varied over a wider range. And the more mobile the charge carriers, the higher frequencies the semiconductor device can operate. The band gap is chosen depending on the purpose of the device. So, for rectifiers and amplifiers designed to operate at elevated temperatures, a material with a large bandgap is used, and for cooled infrared radiation receivers, a material with a small bandgap is used.

Gallium arsenide has gained particular popularity because it has good electrical characteristics, which it retains in a wide temperature range - from minus to plus 500 ° C. For comparison, we point out that indium arsenide, which is not inferior to GaAs in electrical properties, begins to lose them at room temperature. temperature, germanium compounds - at 70-80 °, and silicon - at 150-200 ° C.

Arsenic is also used as a dopant, which gives "classical" semiconductors (Si, Ge) a certain type of conductivity (see the article "Germanium"). In this case, a so-called transition layer is created in the semiconductor, and, depending on the purpose of the crystal, it is doped in such a way as to obtain a layer at different depths. In crystals intended for the manufacture of diodes, it is “hidden” deeper; if solar batteries are made from semiconductor crystals, then the depth of the transition layer is no more than one micron.

Arsenic as a valuable additive is used in non-ferrous metallurgy. Thus, the addition of 0.2-1% As to lead significantly increases its hardness. Shot, for example, is always made from lead alloyed with arsenic - otherwise you will not get a strictly spherical shape of shots.

The addition of 0.15-0.45% arsenic to copper increases its tensile strength, hardness and corrosion resistance when working in a gassed environment. In addition, arsenic increases the fluidity of copper during casting, facilitates the process of wire drawing.

Arsenic is added to some grades of bronzes, brasses, babbits, printing alloys.

And at the same time, arsenic very often harms metallurgists. In the production of steel and many non-ferrous metals, they deliberately go to the complication of the process - if only to remove all arsenic from the metal. The presence of arsenic in the ore makes production harmful. Harmful twice:

firstly, for human health, and secondly, for the metal - significant impurities of arsenic worsen the properties of almost all metals and alloys.

This is Element No. 33, which deserves a bad reputation, and yet is very useful in many cases.

* The two types of conductivity are described in detail in the article "Germanium".

The content of the article

ARSENIC- a chemical element of group V of the periodic table, belongs to the nitrogen family. Relative atomic mass 74.9216. In nature, arsenic is represented by only one stable nuclide, 75 As. More than ten of its radioactive isotopes with a half-life from several minutes to several months have also been artificially obtained. Typical oxidation states in compounds are –3, +3, +5. The name of arsenic in Russian is associated with the use of its compounds for the extermination of mice and rats; The Latin name Arsenicum comes from the Greek "Arsen" - strong, powerful.

Historical information.

Arsenic belongs to the five "alchemical" elements discovered in the Middle Ages (surprisingly, four of them - As, Sb, Bi and P are in the same group of the periodic table - the fifth). At the same time, arsenic compounds have been known since ancient times, they were used for the production of paints and medicines. Of particular interest is the use of arsenic in metallurgy.

Several millennia ago, the Stone Age gave way to the Bronze Age. Bronze is an alloy of copper and tin. Historians believe that the first bronze was cast in the Tigris and Euphrates valley, sometime between the 30th and 25th centuries. BC. In some regions, bronze was smelted with especially valuable properties - it was better cast and easier to forge. As modern scientists have found out, it was a copper alloy containing from 1 to 7% arsenic and no more than 3% tin. Probably, at first, during its smelting, the rich copper ore malachite was confused with the weathering products of some also green sulfide copper-arsenic minerals. Having appreciated the remarkable properties of the alloy, the ancient craftsmen then specifically looked for arsenic minerals. For searches, they used the property of such minerals to give a specific garlic smell when heated. However, over time, the smelting of arsenic bronze ceased. Most likely this happened due to frequent poisoning during the firing of arsenic-containing minerals.

Of course, arsenic was known in the distant past only in the form of its minerals. So, in ancient China, the solid mineral realgar (sulfide composition As 4 S 4, realgar in Arabic means “mine dust”) was used for stone carving, however, when heated or exposed to light, it “spoiled”, as it turned into As 2 S 3 . In the 4th c. BC. Aristotle described this mineral under the name "sandarak". In the 1st century AD the Roman writer and scientist Pliny the Elder, and the Roman physician and botanist Dioscorides described the mineral orpiment (arsenic sulfide As 2 S 3). Translated from Latin, the name of the mineral means "golden paint": it was used as a yellow dye. In the 11th century alchemists distinguished three "varieties" of arsenic: the so-called white arsenic (oxide As 2 O 3), yellow arsenic (sulfide As 2 S 3) and red arsenic (sulfide As 4 S 4). White arsenic was obtained by sublimation of arsenic impurities during the roasting of copper ores containing this element. Condensing from the gas phase, arsenic oxide precipitated in the form of a white coating. White arsenic has been used since ancient times to kill pests, as well as...

In the 13th century Albert von Bolstedt (Albert the Great) obtained a metal-like substance by heating yellow arsenic with soap; this may have been the first sample of arsenic in the form of a simple substance, obtained artificially. But this substance broke the mystical "connection" of the seven known metals with the seven planets; this is probably why the alchemists considered arsenic an "illegitimate metal". At the same time, they discovered its property to give copper a white color, which gave reason to call it "a means that whitens Venus (that is, copper)."

Arsenic was unequivocally identified as an individual substance in the middle of the 17th century, when the German pharmacist Johann Schroeder obtained it in a relatively pure form by reducing the oxide with charcoal. Later, the French chemist and physician Nicolas Lemery obtained arsenic by heating a mixture of its oxide with soap and potash. In the 18th century arsenic was already well known as an unusual "semi-metal". In 1775 the Swedish chemist K.V. Scheele obtained arsenic acid and gaseous arsenic hydrogen, and in 1789 A.L. Lavoisier finally recognized arsenic as an independent chemical element. In the 19th century organic compounds containing arsenic were discovered.

Arsenic in nature.

There is little arsenic in the earth's crust - about 5 10 -4% (that is, 5 g per ton), about the same as germanium, tin, molybdenum, tungsten or bromine. Often arsenic in minerals occurs together with iron, copper, cobalt, nickel.

The composition of the minerals formed by arsenic (and there are about 200 of them) reflects the "semi-metallic" properties of this element, which can be in both positive and negative oxidation states and combine with many elements; in the first case, arsenic can play the role of a metal (for example, in sulfides), in the second - a non-metal (for example, in arsenides). The complex composition of a number of arsenic minerals reflects its ability, on the one hand, to partially replace sulfur and antimony atoms in the crystal lattice (the ionic radii S -2, Sb -3 and As -3 are close and amount to 0.182, 0.208 and 0.191 nm, respectively), on the other hand are metal atoms. In the first case, arsenic atoms have rather a negative oxidation state, in the second - a positive one.

The electronegativity of arsenic (2.0) is low, but higher than that of antimony (1.9) and most metals; therefore, the oxidation state –3 is observed for arsenic only in metal arsenides, as well as in SbAs stibarsen and intergrowths of this mineral with pure crystals. antimony or arsenic (the mineral allemontite). Many compounds of arsenic with metals, judging by their composition, are related to intermetallic compounds rather than arsenides; some of them are characterized by a variable content of arsenic. In arsenides, several metals can be present simultaneously, the atoms of which, at a close ion radius, replace each other in the crystal lattice in arbitrary ratios; in such cases, in the mineral formula, the symbols of the elements are listed separated by commas. All arsenides have a metallic luster, they are opaque, heavy minerals, their hardness is low.

An example of natural arsenides (about 25 of them are known) are the minerals löllingite FeAs 2 (an analogue of pyrite FeS 2), skutterudite CoAs 2–3 and nickelskutterudite NiAs 2–3, nickeline (red nickel pyrite) NiAs, rammelsbergite (white nickel pyrite) NiAs 2 , safflorite (speis cobalt) CoAs 2 and clinosafflorite (Co,Fe,Ni)As 2, langisite (Co,Ni)As, sperrylite PtAs 2, maucherite Ni 11 As 8, oregonite Ni 2 FeAs 2, algodonite Cu 6 As. Due to their high density (more than 7 g/cm3), geologists refer many of them to the group of "super-heavy" minerals.

The most common arsenic mineral is arsenopyrite (arsenic pyrite) FeAsS can be considered as a product of the replacement of sulfur in pyrite FeS 2 by arsenic atoms (ordinary pyrite also always contains some arsenic). Such compounds are called sulfosalts. The minerals cobaltine (cobalt luster) CoAsS, glaucodot (Co,Fe)AsS, gersdorfite (nickel luster) NiAsS, enargite and lusonite of the same composition, but different structure Cu 3 AsS 4 , proustite Ag 3 AsS 3 - an important silver ore, were formed similarly. sometimes called "ruby silver" because of its bright red color, it is often found in the upper layers of silver veins, where magnificent large crystals of this mineral are found. Sulfosalts may also contain noble metals of the platinum group; these minerals are osarsite (Os,Ru)AsS, ruarsite RuAsS, irarsite (Ir,Ru,Rh,Pt)AsS, platarsite (Pt,Rh,Ru)AsS, hollingworthite (Rd,Pt,Pd)AsS. Sometimes the role of sulfur atoms in such double arsenides is played by antimony atoms, for example, in seinjayokite (Fe,Ni)(Sb,As) 2 , arsenopalladinite Pd 8 (As,Sb) 3 , arsenepolybasite (Ag,Cu) 16 (Ar,Sb) 2 S 11 .

The structure of minerals is interesting, in which arsenic is present simultaneously with sulfur, but rather plays the role of a metal, grouping together with other metals. These are the minerals arsenosulvanite Cu 3 (As, V) S 4 , arsenohauchecornite Ni 9 BiAsS 8 , freibergite (Ag, Cu, Fe) 12 (Sb, As) 4 S 13 , tennantite (Cu, Fe) 12 As 4 S 13 , argentotennantite (Ag,Cu) 10 (Zn,Fe) 2 (As,Sb) 4 S 13, goldfieldite Cu 12 (Te,Sb,As) 4 S 13, girodite (Cu,Zn,Ag) 12 (As,Sb) 4 (Se,S) 13 . One can imagine what a complex structure the crystal lattice of all these minerals has.

Arsenic has a uniquely positive oxidation state in natural sulfides - yellow orpiment As 2 S 3, orange-yellow dimorphite As 4 S 3, orange-red realgar As 4 S 4, carmine-red getchellite AsSbS 3, as well as in colorless oxide As 2 O 3, which occurs as minerals arsenolite and claudetite with different crystal structures (they are formed as a result of weathering of other arsenic minerals). These minerals usually occur as small inclusions. But in the 30s of the 20th century. in the southern part of the Verkhoyansk ridge, huge crystals of orpiment up to 60 cm in size and weighing up to 30 kg were found.

In natural salts of arsenic acid H 3 AsO 4 - arsenates (about 90 of them are known), the oxidation state of arsenic is +5; examples are bright pink erythrin (cobalt color) Co 3 (AsO 4) 2 8H 2 O, green annabergite Ni 3 (AsO 4) 2 8H 2 O, scorodite Fe III AsO 4 2H 2 O and simplesite Fe II 3 (AsO 4) 2 8H 2 O, brown-red gasparite (Ce, La, Nd) ArO 4, colorless gernesite Mg 3 (AsO 4) 2 8H 2 O, rooseveltite BiAsO 4 and kettigite Zn 3 (AsO 4) 2 8H 2 O, as well as many basic salts, for example, olivenite Cu 2 AsO 4 (OH), arsenobismite Bi 2 (AsO 4) (OH) 3. But natural arsenites - derivatives of arsenous acid H 3 AsO 3 are very rare.

In central Sweden, there are the famous Langban iron-manganese quarries, in which more than 50 samples of minerals representing arsenates have been found and described. Some of them are not found anywhere else. They were once formed as a result of the reaction of arsenic acid H 3 AsO 4 with pyrocroite Mn (OH) 2 at not very high temperatures. Usually, arsenates are products of the oxidation of sulfide ores. They usually do not have industrial applications, but some of them are very beautiful and adorn mineralogical collections.

In the names of numerous arsenic minerals one can find toponyms (Lölling in Austria, Freiberg in Saxony, Seinäjoki in Finland, Skutterud in Norway, Allemon in France, the Canadian Langis mine and the Getchell mine in Nevada, Oregon in the USA, etc.), the names of geologists, chemists, politicians, etc. (German chemist Karl Rammelsberg, Munich mineral merchant William Maucher, mine owner Johann von Gersdorff, French chemist F. Claude, English chemists John Proust and Smithson Tennant, Canadian chemist F. L. Sperry, US President Roosevelt, etc.), plant names (for example, the name of the mineral safflorite comes from saffron), the initial letters of the names of the elements - arsenic, osmium, ruthenium, iridium, palladium, platinum, Greek roots ("erythros" - red, "enargon" - visible, "lithos" - stone) and etc. and so on.

An interesting ancient name for the mineral nickeline (NiAs) is kupfernickel. Medieval German miners called Nickel the evil mountain spirit, and Kupfernickel (Kupfernickel, from German Kupfer - copper) - "damn copper", "fake copper". The copper-red crystals of this ore looked very much like copper ore; it was used in glass making to color glass green. But no one could get copper from it. This ore was studied by the Swedish mineralogist Axel Kronstedt in 1751 and isolated a new metal from it, calling it nickel.

Since arsenic is chemically quite inert, it is also found in its native state - in the form of fused needles or cubes. Such arsenic usually contains from 2 to 16% impurities - most often it is Sb, Bi, Ag, Fe, Ni, Co. It is easy to grind into powder. In Russia, native arsenic was found by geologists in Transbaikalia, in the Amur Region, and it is also found in other countries.

Arsenic is unique in that it is found everywhere - in minerals, rocks, soil, water, plants and animals, it is not for nothing that it is called "ubiquitous". The distribution of arsenic over different regions of the globe was largely determined in the processes of formation of the lithosphere by the volatility of its compounds at high temperatures, as well as by the processes of sorption and desorption in soils and sedimentary rocks. Arsenic migrates easily, which is facilitated by the rather high solubility of some of its compounds in water. In humid climates, arsenic is washed out of the soil and carried away by groundwater and then by rivers. The average content of arsenic in rivers is 3 µg/l, in surface waters - about 10 µg/l, in the water of the seas and oceans - only about 1 µg/l. This is due to the relatively rapid precipitation of its compounds from water with accumulation in bottom sediments, for example, in ferromanganese nodules.

In soils, the arsenic content is usually between 0.1 and 40 mg/kg. But in the area of ​​occurrence of arsenic ores, as well as in volcanic regions, the soil can contain a lot of arsenic - up to 8 g / kg, as in some areas of Switzerland and New Zealand. In such places, vegetation dies, and animals get sick. This is typical for steppes and deserts, where arsenic is not washed out of the soil. Clay rocks are also enriched in comparison with the average content - they contain four times more arsenic than the average. In our country, the maximum allowable concentration of arsenic in the soil is 2 mg/kg.

Arsenic can be removed from the soil not only by water, but also by wind. But for this, it must first turn into volatile organoarsenic compounds. This transformation occurs as a result of the so-called biomethylation - the addition of a methyl group with the formation of a C–As bond; this enzymatic process (it is well known for mercury compounds) occurs with the participation of the coenzyme methylcobalamin, a methylated derivative of vitamin B 12 (it is also found in the human body). Biomethylation of arsenic occurs both in fresh and sea water and leads to the formation of organoarsenic compounds - methylarsonic acid CH 3 AsO (OH) 2, dimethylarsine (dimethylarsenic, or cacodylic) acid (CH 3) 2 As (O)OH, trimethylarsine ( CH 3) 3 As and its oxide (CH 3) 3 As = O, which are also found in nature. Using 14 C-labeled methylcobalamin and 74 As-labeled sodium hydrogen arsenate Na 2 HAsO 4, it was shown that one of the methanobacteria strains reduces and methylates this salt to volatile dimethylarsine. As a result, the air in rural areas contains an average of 0.001 - 0.01 μg / m 3 arsenic, in cities where there are no specific pollution - up to 0.03 μg / m 3, and near sources of pollution (non-ferrous metal smelting plants, power plants, working on coal with a high content of arsenic, etc.) the concentration of arsenic in the air can exceed 1 µg/m 3 . The intensity of arsenic fallout in the areas of industrial centers is 40 kg/km 2 per year.

The formation of volatile compounds of arsenic (trimethylarsine, for example, boils at only 51 ° C) caused in the 19th century. numerous poisonings, since arsenic was contained in plaster and even in green wallpaper paint. In the form of paint, Scheele greens Cu 3 (AsO 3) 2 were used earlier. n H 2 O and Parisian or Schweifurt greens Cu 4 (AsO 2) 6 (CH 3 COO) 2. In conditions of high humidity and the appearance of mold, volatile organoarsenic derivatives are formed from such paint. It is believed that this process could be the cause of Napoleon's slow poisoning in the last years of his life (as is known, arsenic was found in Napoleon's hair a century and a half after his death).

Arsenic is found in significant amounts in some mineral waters. Russian standards establish that arsenic in medicinal table mineral waters should not exceed 700 µg/l. IN Jermuk it may be several times larger. Drinking one or two glasses of “arsenic” mineral water will not bring harm to a person: in order to be fatally poisoned, you need to drink three hundred liters at once ... But it is clear that you cannot drink such water all the time instead of ordinary water.

Chemists have found that arsenic in natural waters can be found in different forms, which is significant in terms of its analysis, migration methods, and different toxicity of these compounds; thus, trivalent arsenic compounds are 25–60 times more toxic than pentavalent ones. As(III) compounds in water are usually present in the form of weak arsenic acid H 3 AsO 3 ( RK a = 9.22), while the As(V) compounds are in the form of a much stronger arsenic acid H 3 AsO 4 ( RK a = 2.20) and its deprotonated anions H 2 AsO 4 – and HAsO 4 2–.

The living matter of arsenic contains on average 6 10 -6%, that is, 6 μg / kg. Some seaweeds are able to concentrate arsenic to such an extent that they become dangerous to humans. Moreover, these algae can grow and multiply in pure solutions of arsenic acid. Such algae are used in some Asian countries as a remedy for rats. Even in the clear waters of the Norwegian fjords, algae can contain up to 0.1 g/kg of arsenic. In humans, arsenic is found in brain tissue and muscles, it accumulates in hair and nails.

Arsenic properties.

Although in appearance arsenic resembles a metal, it is still rather a non-metal: it does not form salts, for example, with sulfuric acid, but is itself an acid-forming element. Therefore, this element is often called a semimetal. Arsenic exists in several allotropic forms and in this respect closely resembles phosphorus. The most stable of them is gray arsenic, a very fragile substance that has a metallic sheen when freshly fractured (hence the name "metallic arsenic"); its density is 5.78 g/cm 3 . With strong heating (up to 615 ° C), it sublimates without melting (the same behavior is typical for iodine). Under a pressure of 3.7 MPa (37 atm), arsenic melts at 817°C, which is much higher than the sublimation temperature. The electrical conductivity of gray arsenic is 17 times less than that of copper, but 3.6 times higher than that of mercury. With increasing temperature, its electrical conductivity, like that of typical metals, decreases - approximately to the same extent as that of copper.

If arsenic vapor is cooled very quickly to the temperature of liquid nitrogen (-196 ° C), a transparent soft yellow substance is obtained, resembling yellow phosphorus, its density (2.03 g / cm 3) is much lower than that of gray arsenic. Pairs of arsenic and yellow arsenic consist of As 4 molecules that have the shape of a tetrahedron - and here the analogy with phosphorus. At 800°C, a noticeable dissociation of vapor begins with the formation of As 2 dimers, while at 1700°C only As 2 molecules remain. When heated and under the action of ultraviolet, yellow arsenic quickly turns into gray with heat release. When arsenic vapor condenses in an inert atmosphere, another amorphous black form of this element is formed. If arsenic vapor is deposited on glass, a mirror film is formed.

The structure of the outer electron shell of arsenic is the same as that of nitrogen and phosphorus, but unlike them, it has 18 electrons in the penultimate shell. Like phosphorus, it can form three covalent bonds (configuration 4s 2 4p 3), leaving an lone pair on the As atom. The sign of the charge on the As atom in compounds with covalent bonds depends on the electronegativity of neighboring atoms. The participation of the lone pair in the complex formation is much more difficult for arsenic than for nitrogen and phosphorus.

If d orbitals are involved in the As atom, the 4s electrons can be depaired to form five covalent bonds. This possibility is practically realized only in combination with fluorine - in pentafluoride AsF 5 (pentachloryl AsCl 5 is also known, but it is extremely unstable and quickly decomposes even at –50 ° C).

In dry air, arsenic is stable, but in humid air it tarnishes and becomes covered with black oxide. During sublimation, arsenic vapor easily burns in air with a blue flame to form heavy white vapors of arsenic anhydride As 2 O 3 . This oxide is one of the most common arsenic-containing reagents. It has amphoteric properties:

As 2 O 3 + 6HCl ® 2AsCl 3 + 3H 2 O,

2 O 3 + 6NH 4 OH ® 2 (NH 4) 3 AsO 3 + 3H 2 O.

When As 2 O 3 is oxidized, an acid oxide is formed - arsenic anhydride:

As 2 O 3 + 2HNO 3 ® As 2 O 5 + H 2 O + NO 2 + NO.

When it interacts with soda, sodium hydrogen arsenate is obtained, which is used in medicine:

As 2 O 3 + 2Na 2 CO 3 + H 2 O ® 2Na 2 HAsO 4 + 2CO 2.

Pure arsenic is rather inert; water, alkalis and acids that do not have oxidizing properties do not act on it. Dilute nitric acid oxidizes it to ortho-arsenic acid H 3 AsO 3, and concentrated - to ortho-arsenic H 3 AsO 4:

3As + 5HNO 3 + 2H 2 O ® 3H 3 AsO 4 + 5NO.

Arsenic(III) oxide reacts similarly:

3As 2 O 3 + 4HNO 3 + 7H 2 O ® 6H 3 AsO 4 + 4NO.

Arsenic acid is an acid of medium strength, slightly weaker than phosphoric. In contrast, arsenic acid is very weak, corresponding in strength to boric acid H 3 BO 3. In its solutions, there is an equilibrium H 3 AsO 3 HAsO 2 + H 2 O. Arsenic acid and its salts (arsenites) are strong reducing agents:

HAsO 2 + I 2 + 2H 2 O ® H 3 AsO 4 + 2HI.

Arsenic reacts with halogens and sulfur. AsCl 3 chloride is a colorless oily liquid fuming in air; hydrolyzes with water: AsCl 3 + 2H 2 O ® HAsO 2 + 3HCl. Bromide AsBr 3 and iodide AsI 3 are known, which are also decomposed by water. In the reactions of arsenic with sulfur, sulfides of various compositions are formed - up to Ar 2 S 5. Arsenic sulfides dissolve in alkalis, in a solution of ammonium sulfide and in concentrated nitric acid, for example:

As 2 S 3 + 6KOH ® K 3 AsO 3 + K 3 AsS 3 + 3H 2 O,

2 S 3 + 3 (NH 4) 2 S ® 2 (NH 4) 3 AsS 3,

2 S 5 + 3 (NH 4) 2 S ® 2 (NH 4) 3 AsS 4,

As 2 S 5 + 40HNO 3 + 4H 2 O ® 6H 2 AsO 4 + 15H 2 SO 4 + 40NO.

In these reactions, thioarsenites and thioarsenates are formed - salts of the corresponding thioacids (similar to thiosulfuric acid).

In the reaction of arsenic with active metals, salt-like arsenides are formed, which are hydrolyzed by water. The reaction proceeds especially quickly in an acidic medium with the formation of arsine: Ca 3 As 2 + 6HCl ® 3CaCl 2 + 2AsH 3. Arsenides of low-active metals - GaAs, InAs, etc. have a diamond-like atomic lattice. Arsine is a colorless, odorless, highly poisonous gas, but impurities give it the smell of garlic. Arsine slowly decomposes into elements already at room temperature and quickly when heated.

Arsenic forms many organoarsenic compounds, for example, tetramethyldiarsine (CH 3) 2 As–As(CH 3) 2 . As early as 1760, the director of the Servian porcelain factory, Louis Claude Cade de Gassicourt, distilling potassium acetate with arsenic (III) oxide, unexpectedly obtained a smoking liquid containing arsenic with a disgusting smell, which was called alarsin, or Cade liquid. As it turned out later, this liquid contained the first obtained organic derivatives of arsenic: the so-called cacodyl oxide, which was formed as a result of the reaction

4CH 3 COOK + As 2 O 3 ® (CH 3) 2 As–O–As(CH 3) 2 + 2K 2 CO 3 + 2CO 2 , and dicacodyl (CH 3) 2 As–As(CH 3) 2 . Kakodil (from the Greek "kakos" - bad) was one of the first radicals discovered in organic compounds.

In 1854, the Parisian professor of chemistry Auguste Kaur synthesized trimethylarsine by the action of methyl iodide on sodium arsenide: 3CH 3 I + AsNa 3 ® (CH 3) 3 As + 3NaI.

Subsequently, arsenic trichloride was used for syntheses, for example,

(CH 3) 2 Zn + 2AsCl 3 ® 2(CH 3) 3 As + 3ZnCl 2 .

In 1882, aromatic arsines were obtained by the action of metallic sodium on a mixture of aryl halides and arsenic trichloride: 3C 6 H 5 Cl + AsCl 3 + 6Na ® (C 6 H 5) 3 As + 6NaCl. The chemistry of organic derivatives of arsenic developed most intensively in the 20s of the 20th century, when some of them had antimicrobial, as well as irritating and blistering effects. At present, tens of thousands of organoarsenic compounds have been synthesized.

Getting arsenic.

Arsenic is obtained mainly as a by-product of the processing of copper, lead, zinc and cobalt ores, as well as gold mining. Some polymetallic ores contain up to 12% arsenic. When such ores are heated to 650–700°C in the absence of air, arsenic sublimates, and when heated in air, volatile oxide As 2 O 3, “white arsenic,” is formed. It is condensed and heated with coal, and arsenic is reduced. Obtaining arsenic is a harmful production. Previously, when the word "ecology" was known only to narrow specialists, "white arsenic" was released into the atmosphere, and it settled in neighboring fields and forests. The exhaust gases of arsenic plants contain between 20 and 250 mg/m 3 of As 2 O 3 , while the air usually contains about 0.00001 mg/m 3 . The average daily allowable concentration of arsenic in the air is considered to be only 0.003 mg / m 3. Paradoxically, even now it is not the plants for its production that pollute the environment with arsenic, but non-ferrous metallurgy enterprises and power plants that burn coal. Bottom sediments near copper smelters contain a huge amount of arsenic - up to 10 g/kg. Arsenic can also get into the soil with phosphate fertilizers.

And another paradox: they get more arsenic than they need; this is a rather rare occurrence. In Sweden, "unnecessary" arsenic was even forced to be buried in reinforced concrete containers in deep abandoned mines.

The main industrial mineral of arsenic is arsenopyrite FeAsS. There are large copper-arsenic deposits in Georgia, Central Asia and Kazakhstan, in the USA, Sweden, Norway and Japan, arsenic-cobalt deposits in Canada, arsenic-tin deposits in Bolivia and England. In addition, gold-arsenic deposits are known in the USA and France. Russia has numerous deposits of arsenic in Yakutia, the Urals, Siberia, Transbaikalia and Chukotka.

Definition of arsenic.

A qualitative reaction to arsenic is the precipitation of yellow sulfide As 2 S 3 from hydrochloric acid solutions. Traces are determined by the Marsh reaction or the Gutzeit method: strips of paper moistened with HgCl 2 darken in the presence of arsine, which reduces sublimate to mercury.

In recent decades, various sensitive methods of analysis have been developed, with which it is possible to quantify negligible concentrations of arsenic, for example, in natural waters. These include flame atomic absorption spectrometry, atomic emission spectrometry, mass spectrometry, atomic fluorescence spectrometry, neutron activation analysis... If there is very little arsenic in the water, preconcentration of the samples may be required. Using this concentration, a group of Kharkov scientists from the National Academy of Sciences of Ukraine developed in 1999 an X-ray extraction method for the determination of arsenic (as well as selenium) in drinking water with a sensitivity of up to 2.5–5 µg/L.

For the separate determination of As(III) and As(V) compounds, they are first separated from each other using well-known extraction and chromatographic methods, as well as using selective hydrogenation. The extraction is usually carried out with sodium dithiocarbamate or ammonium pyrrolidine dithiocarbamate. These compounds form water-insoluble complexes with As(III), which can be extracted with chloroform. The arsenic can then be brought back into the aqueous phase by oxidation with nitric acid. In the second sample, arsenate is converted to arsenite with the help of a reducing agent, and then a similar extraction is performed. This is how “total arsenic” is determined, and then As (III) and As (V) are determined separately by subtracting the first result from the second. If there are organic arsenic compounds in water, they are usually converted into methyldiodarsine CH 3 AsI 2 or dimethyliodarsine (CH 3) 2 AsI, which are determined by one or another chromatographic method. Thus, nanogram amounts of a substance can be determined using high performance liquid chromatography.

Many arsenic compounds can be analyzed by the so-called hydride method. It consists in the selective reduction of the analyte to volatile arsine. So, inorganic arsenites are reduced to AsH 3 at pH 5 - 7, and at pH

The neutron activation method is also sensitive. It consists in irradiating the sample with neutrons, while the 75 As nuclei capture neutrons and turn into the 76 As radionuclide, which is detected by characteristic radioactivity with a half-life of 26 hours. In this way, up to 10–10% of arsenic in a sample can be detected, i.e. 1 mg per 1000 tons of substance

The use of arsenic.

About 97% of the mined arsenic is used in the form of its compounds. Pure arsenic is rarely used. Only a few hundred tons of metallic arsenic are produced and used annually throughout the world. In the amount of 3% arsenic improves the quality of bearing alloys. Additives of arsenic to lead significantly increase its hardness, which is used in the production of lead batteries and cables. Small additions of arsenic increase the corrosion resistance and improve the thermal properties of copper and brass. Highly purified arsenic is used in the manufacture of semiconductor devices, in which it is alloyed with silicon or germanium. Arsenic is also used as a dopant, which gives "classical" semiconductors (Si, Ge) a certain type of conductivity.

Arsenic as a valuable additive is also used in non-ferrous metallurgy. Thus, the addition of 0.2 ... 1% As to lead significantly increases its hardness. It has long been noticed that if a little arsenic is added to molten lead, then when casting shot, balls of the correct spherical shape are obtained. The addition of 0.15 ... 0.45% arsenic to copper increases its tensile strength, hardness and corrosion resistance when working in a gassed environment. In addition, arsenic increases the fluidity of copper during casting, facilitates the process of wire drawing. Arsenic is added to some grades of bronzes, brasses, babbits, printing alloys. And at the same time, arsenic very often harms metallurgists. In the production of steel and many non-ferrous metals, they deliberately go to the complication of the process - just to remove all arsenic from the metal. The presence of arsenic in the ore makes production harmful. Harmful twice: first, for people's health; secondly, for a metal, significant impurities of arsenic worsen the properties of almost all metals and alloys.

Various arsenic compounds, which are annually produced in tens of thousands of tons, have a wider application. Oxide As 2 O 3 is used in glassmaking as a glass clarifier. Even the ancient glassmakers knew that white arsenic makes the glass "deaf", i.e. opaque. However, small additions of this substance, on the contrary, lighten the glass. Arsenic is still included in the formulations of some glasses, for example, "Viennese" glass for thermometers.

Arsenic compounds are used as an antiseptic to protect against spoilage and preserve skins, furs and stuffed animals, to impregnate wood, as a component of antifouling paints for the bottoms of ships. In this capacity, salts of arsenic and arsenic acids are used: Na 2 HAsO 4, PbHAsO 4, Ca 3 (AsO 3) 2, etc. The biological activity of arsenic derivatives has interested veterinarians, agronomists, and specialists in the sanitary and epidemiological service. As a result, arsenic-containing livestock growth and productivity stimulants, antihelminthics, drugs for the prevention of diseases of young animals on livestock farms appeared. Arsenic compounds (As 2 O 3 , Ca 3 As 2 , Na 3 As, Parisian greens) are used to control insects, rodents, and also weeds. In the past, such applications were widespread, especially in the cultivation of fruit trees, tobacco and cotton plantations, to rid livestock of lice and fleas, to stimulate growth in poultry and pig production, and to dry cotton before harvesting. Even in ancient China, rice crops were treated with arsenic oxide to protect them from rats and fungal diseases and thus increase the yield. And in South Vietnam, American troops used cacodylic acid (Agent Blue) as a defoliant. Now, due to the toxicity of arsenic compounds, their use in agriculture is limited.

Important areas of application of arsenic compounds are the production of semiconductor materials and microcircuits, fiber optics, the growth of single crystals for lasers, and film electronics. To introduce small, strictly metered amounts of this element into semiconductors, gaseous arsine is used. Gallium arsenides GaAs and indium InAs are used in the manufacture of diodes, transistors, and lasers.

Arsenic also finds limited use in medicine. . Arsenic isotopes 72 As, 74 As, and 76 As with convenient half-lives for research (26 h, 17.8 days, and 26.3 h, respectively) are used to diagnose various diseases.

Ilya Leenson

Arsenic (the name comes from the word mouse, used to persecute mice) is the thirty-third element of the periodic system. Refers to semimetals. In combination with an acid, it does not form salts, being an acid-forming substance. Can form allotropic modifications. Arsenic has three currently known crystal lattice structures. Yellow arsenic exhibits the properties of a typical non-metal, amorphous - black and the most stable metallic, gray. In nature, it is most often found in the form of compounds, less often in the free state. The most common are compounds of arsenic with metals (arsenides), such as: arsenic iron (arsenopyrite, poisonous pyrites), nickeline (kupfernickel, so named because of its similarity with copper ore). Arsenic is an inactive element, insoluble in water, and its compounds are poorly soluble substances. Oxidation of arsenic occurs during heating, at room temperature this reaction proceeds very slowly.

All arsenic compounds are very strong toxins that have a negative effect not only on the gastrointestinal tract, but also on the nervous system. History knows many sensational cases of poisoning with arsenic and its derivatives. Arsenic compounds were used as a poison not only in medieval France, they were known in ancient Rome and Greece. The popularity of arsenic as a potent poison is explained by the fact that it is almost impossible to detect it in food, it has neither smell nor taste. When heated, it turns into arsenic oxide. Diagnosing arsenic poisoning is quite difficult, as it has similar symptoms with various diseases. Most often, arsenic poisoning is confused with cholera.

Where is arsenic used?

Despite their toxicity, arsenic derivatives are used not only for baiting mice and rats. Since pure arsenic has a high electrical conductivity, it is used as a dopant, which gives semiconductors such as germanium, silicon, the conductivity of the required type. In non-ferrous metallurgy, arsenic is used as an additive that gives alloys strength, hardness and corrosion resistance in a gaseous environment. In glassmaking, it is added in small quantities to lighten glass, in addition, it is part of the famous "Viennese glass". Nickelin is used to color glass green. In the leather business, sulfate compounds of arsenic are used in the processing of hides to remove hairs. Arsenic is found in varnishes and paints. In the woodworking industry, arsenic is used as an antiseptic. In pyrotechnics, “Greek fire” is made from arsenic sulfide compounds, and is used in the manufacture of matches. Some arsenic compounds are used as chemical warfare agents. The toxic properties of arsenic are used in dental practice to kill the dental pulp. In medicine, arsenic preparations are used as a drug that increases the overall tone of the body, to stimulate an increase in the number of red blood cells. Arsenic has an inhibitory effect on the formation of leukocytes, so it is used in the treatment of certain forms of leukemia. A huge number of medicines based on arsenic are known, but recently they have been gradually replaced by less toxic drugs.

Despite its toxicity, arsenic is one of the most essential elements. When working with its compounds, it is necessary to adhere to safety regulations, which will help to avoid undesirable consequences.

Arsenic compounds (English and French Arsenic, German Arsen) have been known for a very long time. In the III - II millennium BC. e. already knew how to obtain copper alloys with 4 - 5% arsenic. A student of Aristotle, Theophrastus (IV - III century BC), naturally occurring red arsenic sulfide is called realgar; Pliny calls yellow arsenic sulfide As 2 S 3 orpiment (Auripigmentum) - painted in golden color, and later it was called orpiment (orpiment). The ancient Greek word arsenicon, as well as sandarak, refer mainly to sulfur compounds. In the 1st century Dioscorides described the burning of orpiment and the resulting product - white arsenic (As 2 O 3). In the alchemical period of the development of chemistry, it was considered indisputable that arsenik (Arsenik) has a sulfurous nature, and since sulfur (Sulphur) was revered as the "father of metals", masculine properties were attributed to arsenik. It is not known exactly when metallic arsenic was first obtained. Usually this discovery is attributed to Albert the Great (XIII century). The coloring of copper with the addition of arsenic to a white silvery color was considered by the alchemists as the transformation of copper into silver and attributed such a "transmutation" to the powerful power of arsenic. In the Middle Ages and in the first centuries of modern times, the poisonous properties of arsenic became known. However, even Dioscorides (Iv.) recommended that asthma patients inhale the vapors of the product obtained by heating realgar with resin. Paracelsus had already made extensive use of white arsenic and other arsenic compounds for treatment. Chemists and miners of the 15th - 17th centuries. knew about the ability of arsenic to sublimate and form vaporous products with a specific odor and toxic properties. Vasily Valentin mentions the well-known metallurgists of the 16th century. blast furnace smoke (Huttenrauch) and its specific smell. The Greek (and Latin) name for arsenic, referring to arsenic sulfides, comes from the Greek masculine. There are other explanations for the origin of this name, for example, from the Arabic arsa paki, meaning "poison penetrating deep into the body"; probably the Arabs borrowed this name from the Greeks. The Russian name arsenic has been known for a long time. It has appeared in literature since the time of Lomonosov, who considered arsenic to be a semimetal. Along with this name in the ХМVIII century. the word arsenic was used, and arsenic was called As 2 O 3. Zakharov (1810) proposed the name arsenic, but it did not take root. The word arsenic was probably borrowed by Russian artisans from the Turkic peoples. In Azerbaijani, Uzbek, Persian and other oriental languages, arsenic was called margumush (mar - kill, mush - mouse); Russian arsenic, probably a distorted mouse-venom, or mouse-venom.