Electronic current in liquids

In an iron conductor, an electron current appears by the directed movement of free electrons and that with all this, no configurations of the substance from which the conductor is made occur.

Such conductors, in which the passage of an electron current is not accompanied by chemical changes in their substance, are called first class conductors... These include all metals, coal and a number of other substances.

But there are also such conductors of electron current in nature, in which chemical phenomena occur during the passage of current. These conductors are named guides of the second kind... These include essentially different mixtures of acids, salts and alkalis in water.

If you pour water into a glass vessel and add a few drops of sulfuric acid (or some other acid or alkali) to it, and then take two iron plates and attach conductors to them by lowering these plates into the vessel, and connect a current source to the other ends of the conductors through the switch and the ammeter, then gas will be released from the solution, while it will last continuously as long as the circuit is closed. acidified water is indeed a conductor. In addition, the plates will begin to become covered with gas bubbles. Then these bubbles will detach from the plates and come out.

When the electron current passes through the solution, chemical configurations occur, as a result of which gas is released.

Conductors of the second kind are called electrolytes, and the phenomenon that occurs in an electrolyte when an electron current passes through it is.

Iron plates dipped in an electrolyte are called electrodes; one of them, connected to the positive pole of the current source, is called the anode, and the other, connected to the negative pole, is called the cathode.

What is the reason for the passage of the electron current in the watery conductor? It turns out that in such mixtures (electrolytes), acid molecules (alkali, salt) under the action of a solvent (in this case, water) decompose into two component parts, while one particle of the molecule has a positive electronic charge, and the other negative.

Particles of a molecule that have an electronic charge are called ions. When an acid, salt or alkali dissolves in water, a huge amount of both positive and negatively charged ions appears in the solution.

Now it should become clear why an electron current passed through the solution, because a potential difference was created between the electrodes connected to the current source, in other words, one of them turned out to be positively charged, and the other negatively. Under the influence of this potential difference, positive ions began to mix towards the negative electrode - the cathode, and negative ions - towards the anode.

Thus, the chaotic movement of ions has become an ordered counter movement of negatively charged ions in one direction and positive ions in the other. This process of charge transfer is the flow of electron current through the electrolyte and occurs until the time when there is a potential difference across the electrodes. With the disappearance of the potential difference, the current through the electrolyte stops, the ordered movement of ions is disrupted, and chaotic movement begins again.

As an example, let us consider the phenomenon of electrolysis when an electron current is passed through a solution of copper sulfate CuSO4 with copper electrodes lowered into it.

The phenomenon of electrolysis when current passes through a solution of copper sulfate: C - vessel with electrolyte, B - current source, C - switch

There will also be a counter movement of ions to the electrodes. The positive ion will be the copper ion (Cu), and the negative ion will be the acid residue (SO4). Copper ions, when in contact with the cathode, will be discharged (attaching to themselves the missing electrons), that is, they will be converted into neutral molecules of pure copper, and will be deposited on the cathode in the form of the thinnest (molecular) layer.

Negative ions, having reached the anode, are also discharged (donate extra electrons). But with all this, they enter into a chemical reaction with the copper of the anode, as a result of which a copper molecule Cu joins the acid residue SO4 and a molecule of copper sulfate CuS O4 appears, which is returned back to the electrolyte.

Because this chemical process takes a long time, copper is deposited on the cathode, which is released from the electrolyte. With all this, the electrolyte instead of the copper molecules that have gone to the cathode receives new copper molecules due to the dissolution of the second electrode - the anode.

The same process occurs if zinc electrodes are taken instead of copper ones, and a solution of zinc sulfate Zn SO4 serves as the electrolyte. Zinc will also be transferred from the anode to the cathode.

So Makar, difference between electronic current in metals and watery conductors consists in the fact that in metals, charge carriers are only free electrons, i.e., negative charges, while in electrolytes, electricity is carried by oppositely charged particles of matter - ions moving in opposite directions. Because they say that electrolytes have ionic conductivity.

The phenomenon of electrolysis was discovered in 1837 by B.S. Jacobi, who created countless experiments on the study and improvement of chemical current sources. Jacobi found that one of the electrodes placed in a solution of copper sulfate, when an electron current passes through it, is covered with copper.

This phenomenon called electroforming, finds at the moment a very huge practical application. One example of this is the coating of iron objects with a narrow layer of other metals, i.e. nickel plating, gilding, silver plating, etc.

Gases (including air) do not conduct electron current under ordinary conditions. For example, naked wires of overhead lines, being suspended parallel to each other, are isolated from one another by a layer of air.

But under the influence of the highest temperature, a large potential difference and other circumstances, gases, like watery conductors, are ionized, that is, they appear in a large number of particles of gas molecules, which, being carriers of electricity, facilitate the passage of an electron current through the gas.

But at the same time, the ionization of a gas differs from the ionization of a watery conductor. If a molecule disintegrates into two charged parts in water, then in gases under the action of ionization, electrons are always separated from each molecule and the ion remains in the form of a positively charged part of the molecule.

One has only to finish the ionization of the gas, as it will finish being conductive, while the liquid always remains the conductor of the electron current. As it follows, the conductivity of a gas is a temporary phenomenon, depending on the action of external circumstances.

But there is another type of discharge called arc discharge or just an electronic arc. The phenomenon of the electronic arc was discovered at the beginning of the 19th century by the first Russian electrical engineer V.V.Petrov.

VV Petrov, doing countless experiments, found that between 2 charcoals connected to a current source, a continuous electronic discharge appears through the air, accompanied by a bright light. In his own writings, V. V. Petrov wrote that with all this "the black calm can be quite brightly illuminated." So, for the first time, electronic light was obtained, which was actually used by another Russian electrical engineer Pavel Nikolayevich Yablochkov.

"Candle Yablochkov", whose work is based on the use of an electronic arc, made a real revolution in electrical engineering at that time.

The arc discharge is used as a light source in our day, for example, in spotlights and projection devices. The highest temperature of the arc discharge allows it to be used for the construction of an arc furnace. Currently, arc furnaces powered by a very high current are used in a number of industries: for smelting steel, cast iron, ferroalloys, bronze, etc. And in 1882 by N.N. Benardos the arc discharge was used for the first time for cutting and welding metal.

In gas tubes, fluorescent lamps, voltage stabilizers, to obtain electric and ion beams, the so-called glow gas discharge.

A spark discharge is used to measure huge potential differences with a ball spark gap, the electrodes of which are two iron balls with a polished surface. The balls are moved apart, and a measurable potential difference is applied to them. Then the balls are brought together until a spark jumps between them. Knowing the diameter of the balls, the distance between them, pressure, temperature and humidity of the air, they find the potential difference between the balls according to special tables. In this way, it is possible to determine, with an accuracy of up to several percent, the potential difference of the order of 10 thousand volts.

That's all for now. Well, if you want to find out more, I recommend paying attention to Misha Vanyushin's disc:

"About electricity for beginners in video format on DVD"

« Physics - Grade 10 "

What are the carriers of electric current in a vacuum?
What is the nature of their movement?

Liquids, like solids, can be dielectrics, conductors, and semiconductors. Dielectrics include distilled water, conductors - solutions and melts of electrolytes: acids, alkalis and salts. Liquid semiconductors are molten selenium, sulphide melts, etc.

Electrolytic dissociation.

When electrolytes dissolve under the influence of the electric field of polar water molecules, electrolyte molecules decompose into ions.

The disintegration of molecules into ions under the influence of the electric field of polar water molecules is called electrolytic dissociation.

Dissociation degree- the proportion in the dissolved substance of molecules that have decayed into ions.

The degree of dissociation depends on the temperature, the concentration of the solution, and the electrical properties of the solvent.

With increasing temperature, the degree of dissociation increases and, consequently, the concentration of positively and negatively charged ions increases.

Ions of different signs, when they meet, can again combine into neutral molecules.

Under unchanged conditions, a dynamic equilibrium is established in the solution, at which the number of molecules that decay into ions per second is equal to the number of pairs of ions, which again combine into neutral molecules during the same time.

Ionic conductivity.

Charge carriers in aqueous solutions or molten electrolytes are positively and negatively charged ions.

If a vessel with an electrolyte solution is included in an electrical circuit, then negative ions will begin to move to the positive electrode - the anode, and positive ions - to the negative - to the cathode. As a result, an electric current will flow through the circuit.

The conductivity of aqueous solutions or electrolyte melts, which is carried out by ions, is called ionic conduction.

Electrolysis. With ionic conduction, the passage of current is associated with the transfer of matter. On the electrodes, the release of substances that make up the electrolytes occurs. At the anode, negatively charged ions give up their extra electrons (in chemistry, this is called an oxidative reaction), and at the cathode, positive ions receive the missing electrons (reduction reaction).

Liquids can also be electronically conductive. Liquid metals, for example, have such conductivity.

The process of release at the electrode of a substance associated with redox reactions is called electrolysis.

What determines the mass of a substance released over a certain time? Obviously, the mass m of the released substance is equal to the product of the mass m 0i of one ion by the number N i of ions that reached the electrode during the time Δt:

m = m 0i N i. (16.3)

The mass of the ion m 0i is equal to:

where M is the molar (or atomic) mass of the substance, and N A is Avogadro's constant, that is, the number of ions in one mole.

The number of ions reaching the electrode is

where Δq = IΔt is the charge that has passed through the electrolyte during the time Δt; q 0i is the charge of the ion, which is determined by the valence n of the atom: q 0i = ne (e is the elementary charge). During the dissociation of molecules, for example KBr, consisting of monovalent atoms (n = 1), ions K + and Br - appear. Dissociation of copper sulfate molecules leads to the appearance of doubly charged ions Cu 2+ and SO 2-4 (n = 2). Substituting expressions (16.4) and (16.5) into formula (16.3) and taking into account that Δq = IΔt, a q 0i = ne, we obtain

Faraday's law.

Let us denote by k the coefficient of proportionality between the mass m of the substance and the charge Δq = IΔt passed through the electrolyte:

where F = eN A = 9.65 10 4 C / mol - Faraday constant.

The coefficient k depends on the nature of the substance (values ​​of M and n). According to formula (16.6), we have

m = kIΔt. (16.8)

Faraday's law of electrolysis:

The mass of the substance released at the electrode during the time Δt. with the passage of an electric current, it is proportional to the strength of the current and time.

This statement, obtained theoretically, was first established experimentally by Faraday.

The quantity k in formula (16.8) is called electrochemical equivalent of this substance and is expressed in kilograms per pendant(kg / Cl).

From the formula (16.8) it can be seen that the coefficient k is numerically equal to the mass of the substance released on the electrodes during the transfer of a charge equal to 1 C by ions.

The electrochemical equivalent has a simple physical meaning. Since M / N A = m 0i and en = q 0i, then according to formula (16.7) k = rn 0i / q 0i, that is, k is the ratio of the ion mass to its charge.

By measuring the values ​​of m and Δq, it is possible to determine the electrochemical equivalents of various substances.

You can be convinced of the validity of Faraday's law by experience. Let's assemble the installation shown in Figure (16.25). All three electrolytic baths are filled with the same electrolyte solution, but the currents passing through them are different. Let us denote the strength of the currents through I1, I2, I3. Then I 1 = I 2 + I 3. By measuring the masses m 1, m 2, m 3 of substances released on the electrodes in different baths, one can make sure that they are proportional to the corresponding strengths of the currents I 1, I 2, I 3.

Determination of the electron charge.

Formula (16.6) for the mass of the substance released on the electrode can be used to determine the electron charge. From this formula it follows that the modulus of the electron charge is equal to:

Knowing the mass m of the released substance during the passage of the charge IΔt, the molar mass M, the valence of n atoms and Avogadro's constant N A, we can find the value of the modulus of the electron charge. It turns out to be equal to e = 1.6 10 -19 C.

It was in this way that the value of the elementary electric charge was obtained for the first time in 1874.

Electrolysis application. Electrolysis is widely used in technology for various purposes. Electrolytically cover the surface of one metal with a thin layer of another ( nickel plating, chrome plating, gold plating etc.). This durable coating protects the surface from corrosion. If you ensure good peeling of the electrolytic coating from the surface on which the metal is deposited (this is achieved, for example, by applying graphite to the surface), then you can get a copy from the embossed surface.

The process of obtaining peelable coatings - electrotype- was developed by the Russian scientist B.S. Jacobi (1801-1874), who in 1836 applied this method to make hollow figures for St. Isaac's Cathedral in St. Petersburg.

Previously, in the printing industry, copies from a relief surface (stereotypes) were obtained from matrices (an imprint of a set on a plastic material), for which a thick layer of iron or another substance was deposited on the matrix. This made it possible to reproduce the set in the required number of copies.

With the help of electrolysis, metals are purified from impurities. Thus, crude copper obtained from the ore is cast in the form of thick sheets, which are then placed in a bath as anodes. During electrolysis, the copper of the anode dissolves, impurities containing valuable and rare metals fall to the bottom, and pure copper settles on the cathode.

With the help of electrolysis, aluminum is obtained from bauxite melt. It was this method of producing aluminum that made it cheap and, along with iron, the most widespread in technology and everyday life.

With the help of electrolysis, electronic boards are obtained, which serve as the basis for all electronic products. A thin copper plate is glued onto the dielectric, on which a complex pattern of connecting wires is applied with a special paint. Then the plate is placed in an electrolyte, where areas of the copper layer not covered with paint are etched out. After that, the paint is washed off, and the details of the microcircuit appear on the board.

According to the degree of electrical conductivity, liquids are divided into:
dielectrics (distilled water),
conductors (electrolytes),
semiconductors (molten selenium).

Electrolyte

It is a conductive liquid (solutions of acids, alkalis, salts and molten salts).

Electrolytic dissociation
(disconnection)

During dissolution, as a result of thermal motion, collisions of solvent molecules and neutral electrolyte molecules occur.
Molecules break down into positive and negative ions.

The phenomenon of electrolysis

- accompanies the passage of electric current through the liquid;
- this is the release of substances included in electrolytes on the electrodes;
Positively charged anions, under the action of an electric field, tend to the negative cathode, and negatively charged cations, to the positive anode.
At the anode, negative ions donate extra electrons (oxidative reaction)
At the cathode, the positive ions receive the missing electrons (reductive reaction).

Electrolysis law

1833 - Faraday

The law of electrolysis determines the mass of a substance released at the electrode during electrolysis during the passage of an electric current.

k is the electrochemical equivalent of a substance, numerically equal to the mass of a substance released at the electrode when a 1 C charge passes through the electrolyte.
Knowing the mass of the released substance, it is possible to determine the electron charge.

For example, dissolving copper sulfate in water.

Electrical conductivity of electrolytes, the ability of electrolytes to conduct electric current when an electric voltage is applied. The carriers of the current are positively and negatively charged ions - cations and anions that exist in a solution due to electrolytic dissociation. The ionic conductivity of electrolytes, in contrast to the electronic conductivity characteristic of metals, is accompanied by the transfer of matter to the electrodes with the formation of new chemical compounds near them. The total (total) conductivity consists of the conductivity of cations and anions, which move in opposite directions under the action of an external electric field. The fraction of the total amount of electricity carried by individual ions is called the transfer numbers, the sum of which for all types of ions participating in the transfer is equal to one.

Semiconductor

Monocrystalline silicon is the most widely used semiconductor material in industry today.

Semiconductor- a material that, in terms of its specific conductivity, occupies an intermediate place between conductors and dielectrics and differs from conductors in a strong dependence of conductivity on the concentration of impurities, temperature and exposure to various types of radiation. The main property of a semiconductor is an increase in electrical conductivity with increasing temperature.

Semiconductors are substances with a band gap of the order of several electron volts (eV). For example, a diamond can be attributed to wide-gap semiconductors, and indium arsenide - to narrow-gap... Semiconductors include many chemical elements (germanium, silicon, selenium, tellurium, arsenic and others), a huge number of alloys and chemical compounds (gallium arsenide, etc.). Almost all inorganic substances of the world around us are semiconductors. The most widespread semiconductor in nature is silicon, which makes up almost 30% of the earth's crust.

Depending on whether the impurity atom donates an electron or captures it, the impurity atoms are called donor or acceptor. The nature of the impurity can vary depending on which atom of the crystal lattice it replaces, in which crystallographic plane it is embedded.

The conductivity of semiconductors is highly temperature dependent. Near absolute zero temperature, semiconductors have the properties of dielectrics.

The mechanism of electrical conduction [edit | edit wiki text]

Semiconductors are characterized by both the properties of conductors and dielectrics. In semiconductor crystals, atoms establish covalent bonds (that is, one electron in a silicon crystal, like diamond, is linked by two atoms), electrons need a level of internal energy to release from an atom (1.76 10 -19 J versus 11.2 10 −19 J, which characterizes the difference between semiconductors and dielectrics). This energy appears in them with an increase in temperature (for example, at room temperature, the energy level of the thermal motion of atoms is equal to 0.4 · 10 −19 J), and individual electrons receive energy to detach from the nucleus. As the temperature rises, the number of free electrons and holes increases; therefore, in a semiconductor that does not contain impurities, the electrical resistivity decreases. It is conventionally accepted to consider as semiconductors elements with an electron binding energy less than 1.5-2 eV. The electron-hole conduction mechanism is manifested in intrinsic (that is, without impurities) semiconductors. It is called the intrinsic electrical conductivity of semiconductors.

Hole [edit | edit wiki text]

Main article:Hole

During the breaking of the bond between the electron and the nucleus, a free space appears in the electron shell of the atom. This causes the transition of an electron from another atom to an atom with free space. On the atom from which the electron passed, another electron enters from another atom, etc. This process is caused by the covalent bonds of atoms. Thus, there is a movement of a positive charge without moving the atom itself. This conditional positive charge is called a hole.

A magnetic field

A magnetic field- a force field acting on moving electric charges and on bodies with a magnetic moment, regardless of the state of their motion; magnetic component of the electromagnetic field.

The magnetic field can be created by the current of charged particles and / or the magnetic moments of electrons in atoms (and the magnetic moments of other particles, which usually manifests itself to a much lesser extent) (permanent magnets).

In addition, it arises as a result of a change in the time of the electric field.

The main force characteristic of the magnetic field is vector of magnetic induction (vector of magnetic field induction). Mathematically - a vector field that defines and concretizes the physical concept of a magnetic field. Often, the vector of magnetic induction is called simply the magnetic field for brevity (although this is probably not the most strict use of the term).

Another fundamental characteristic of the magnetic field (alternative magnetic induction and closely interconnected with it, practically equal to it in physical value) is vector potential .

Sources of magnetic field [edit | edit wiki text]

A magnetic field is created (generated) by a current of charged particles, or a time-varying electric field, or the intrinsic magnetic moments of particles (the latter, for uniformity of the picture, can be formally reduced to electric currents

>> Physics: Electric current in liquids

Liquids, like solids, can be dielectrics, conductors, and semiconductors. Distilled water is among the dielectrics, and solutions and melts of electrolytes: acids, alkalis and salts are conductors. Liquid semiconductors are molten selenium, sulphide melts, etc.
Electrolytic dissociation. When electrolytes dissolve under the influence of the electric field of polar water molecules, electrolyte molecules decompose into ions. This process is called electrolytic dissociation.
Dissociation degree, i.e., the proportion of molecules in the solute that decayed into ions depends on the temperature, the concentration of the solution, and the electrical properties of the solvent. With increasing temperature, the degree of dissociation increases and, consequently, the concentration of positively and negatively charged ions increases.
Ions of different signs, when they meet, can again unite into neutral molecules - recombine... Under unchanged conditions, a dynamic equilibrium is established in the solution, at which the number of molecules that decay into ions per second is equal to the number of pairs of ions, which again combine into neutral molecules during the same time.
Ionic conductivity. Charge carriers in aqueous solutions or molten electrolytes are positively and negatively charged ions.
If a vessel with an electrolyte solution is included in an electrical circuit, then negative ions will begin to move to the positive electrode - the anode, and positive ions - to the negative - to the cathode. As a result, an electric current will be established. Since charge transfer in aqueous solutions or electrolyte melts is carried out by ions, this conductivity is called ionic.
Liquids can also be electronically conductive. Liquid metals, for example, have such conductivity.
Electrolysis. With ionic conduction, the passage of current is associated with the transfer of matter. On the electrodes, the release of substances that make up the electrolytes occurs. At the anode, negatively charged ions give up their extra electrons (in chemistry, this is called an oxidative reaction), and at the cathode, positive ions receive the missing electrons (reduction reaction). The process of release at the electrode of a substance associated with redox reactions is called electrolysis.
Electrolysis application. Electrolysis is widely used in technology for various purposes. Electrolytically cover the surface of one metal with a thin layer of another ( nickel plating, chrome plating, copper plating etc.). This durable coating protects the surface from corrosion.
If you ensure good peeling of the electrolytic coating from the surface on which the metal is deposited (this is achieved, for example, by applying graphite to the surface), then you can get a copy from the embossed surface.
In the printing industry, such copies (stereotypes) are obtained from matrices (an imprint of a set on a plastic material), for which a thick layer of iron or another substance is deposited on the matrices. This allows the set to be reproduced in the desired number of copies. If earlier the circulation of a book was limited by the number of prints that can be obtained from one set (when printing, the set is gradually erased), now the use of stereotypes can significantly increase the circulation. True, at present, with the help of electrolysis, stereotypes are obtained only for high-quality print books.
The process of obtaining peelable coatings - electrotype- was developed by the Russian scientist B.S. Jacobi (1801-1874), who in 1836 applied this method to make hollow figures for St. Isaac's Cathedral in St. Petersburg.
With the help of electrolysis, metals are purified from impurities. Thus, crude copper obtained from the ore is cast in the form of thick sheets, which are then placed in a bath as anodes. During electrolysis, the copper of the anode dissolves, impurities containing valuable and rare metals fall to the bottom, and pure copper settles on the cathode.
With the help of electrolysis, aluminum is obtained from bauxite melt. It was this method of producing aluminum that made it cheap and, along with iron, the most widespread in technology and everyday life.
With the help of electrolysis, electronic boards are obtained, which serve as the basis for all electronic products. A thin copper plate is glued onto the dielectric, on which a complex pattern of connecting wires is applied with a special paint. Then the plate is placed in an electrolyte, where areas of the copper layer not covered with paint are etched away. After that, the paint is washed off and the details of the microcircuit appear on the board.
In solutions and molten electrolytes, free electric charges appear due to the decay of neutral molecules into ions. The movement of ions in the field means the transfer of matter. This process is widely used in practice (electrolysis).

???
1. What is called electrolytic dissociation?
2. Why does a substance transfer occur when a current passes through an electrolyte solution, but does not transfer a substance when passing through a metal conductor?
3. What are the similarities and differences in intrinsic conductivity in semiconductors and in electrolyte solutions?

G.Ya. Myakishev, B.B. Bukhovtsev, N.N. Sotsky, Physics Grade 10

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Liquids, like any other substance, can be conductors, semiconductors, and dielectrics. For example, distilled water will be a dielectric, and solutions and molten electrolytes will be conductors. Semiconductors will be, for example, molten selenium or sulphide melts.

Ionic conductivity

Electrolytic dissociation is the process of decomposition of electrolyte molecules into ions under the action of the electric field of polar water molecules. The degree of dissociation is the fraction of molecules that have broken down into ions in a solute.

The degree of dissociation will depend on various factors: temperature, solution concentration, solvent properties. As the temperature rises, the degree of dissociation will also increase.

After the molecules are divided into ions, they move chaotically. In this case, two ions of different signs can recombine, that is, they can again combine into neutral molecules. In the absence of external changes in the solution, a dynamic equilibrium should be established. With it, the number of molecules that decayed into ions per unit time will be equal to the number of molecules that will unite again.

Ions will be charge carriers in aqueous solutions and electrolyte melts. If a vessel with a solution or melt is included in the circuit, then positively charged ions will begin to move towards the cathode, and negative ions towards the anode. As a result of this movement, an electric current will be generated. This type of conductivity is called ionic conductivity.

In addition to ionic conductivity in liquids, it can also have electronic conductivity. This type of conductivity is typical, for example, of liquid metals. As noted above, in the case of ionic conduction, the passage of current is associated with the transfer of matter.

Electrolysis

Substances that are part of electrolytes will settle on the electrodes. This process is called electrolysis. Electrolysis is the process of release of a substance at an electrode associated with redox reactions.

Electrolysis has found wide application in physics and technology. With the help of electrolysis, the surface of one metal is coated with a thin layer of another metal. For example, chrome plating and nickel plating.

With the help of electrolysis, a copy can be obtained from a relief surface. For this, it is necessary that the layer of metal that settles on the surface of the electrode can be easily removed. For this, graphite is sometimes applied to the surface.

The process of obtaining such easily peelable coatings is called electroplated plastic. This method was developed by the Russian scientist Boris Yakobi in the manufacture of hollow figures for St. Isaac's Cathedral in St. Petersburg.