A galvanic cell is a chemical source of electric current based on the interaction of two metals and/or their oxides in an electrolyte, named after the Italian scientist Luigi Galvani.

Later, the scientist assembled a battery from copper-zinc cells, which was later called the Voltaic Column (see figure). It consisted of several dozen zinc and copper circles, folded in pairs and separated by cloth soaked in acid. This invention was subsequently used by other scientists in their research. For example, in 1802, Russian academician V.V. Petrov constructed a giant battery of 2,100 cells that produced a voltage of about 2,500 volts and was used to produce a powerful electric arc that created such a high temperature that it could melt metals.

There are galvanic elements of other designs. Let's consider another copper-zinc galvanic cell, but one that operates using the energy of a chemical reaction between zinc and a solution of copper sulfate (Jacobi-Daniel cell). This element consists of a copper plate immersed in a copper sulfate solution and a zinc plate immersed in a zinc sulfate solution (see figure). Both solutions are in contact with each other, but to prevent mixing they are separated by a membrane partition made of porous material.

Another type of galvanic cells is the so-called “dry” manganese-zinc Leclanche cells (see figure). Instead of a liquid electrolyte, such a cell uses a gel-like paste of ammonia and starch. To ensure that moisture evaporates as little as possible, the top of such an element is filled with wax or resin with a small hole for gases to escape. Typically, Leclanche elements are made in cylindrical cups, which simultaneously serve as both a negative electrode and a vessel.
All chemical current sources (galvanic cells and batteries made from them) are divided into two groups - primary (disposable) and secondary (reusable or reversible). In primary current sources (in common parlance - batteries), chemical processes occur irreversibly, so their charge cannot be restored. Secondary chemical current sources include batteries; their charge can be restored. For widely used batteries, the charge-discharge cycle can be repeated about 1000 times.

Batteries have different voltages and capacities. For example, traditional alkaline batteries have a nominal voltage of about 1.5 V, and more modern lithium batteries have a nominal voltage of about 3 V. Electrical capacity depends on many factors: the number of cells in the battery, charge level, ambient temperature, cut-off current (at which the device does not works even with available charge). For example, a battery that no longer works in a camera often continues to work in a watch or remote control.
The amount of electricity (charge) in batteries is measured in ampere-hours. For example, if the battery charge is 1 ampere-hour, and the electrical device it powers requires a current of 200 mA, then the battery life is calculated as follows: 1 Ah / 0.2 A = 5 hours.
Technological advances have increased the variety of miniature battery-powered devices. Many of them required more powerful batteries, while being quite compact. Lithium batteries are the answer to this need: long shelf life, high reliability and excellent performance over a wide temperature range. Today, the most advanced are lithium-ion power sources. The potential of this technology has not yet been fully revealed, but the immediate prospects are connected with them.

Of particular value in technology are nickel-cadmium batteries, invented back in 1899 by the Swedish scientist W. Jungner. But only by the middle of the 20th century did engineers come to an almost modern design for such sealed batteries. Due to their compactness and autonomy, rechargeable batteries are used in cars, trains, computers, telephones, cameras, video cameras, calculators, etc.
The main characteristics of the battery are capacity and maximum current. The battery capacity in ampere hours is equal to the product of the maximum current and the duration of discharge. For example, if a battery can produce a current of 80 mA for 10 hours, then the capacity is: 80 mA · 10 h = 800 mAh (or, in international designations, 800 mAh, see figure).

Kuznetsova Alla Viktorovna (Samara)

GALVANIC CELLS, primary elements, sources of electrical energy obtained directly in the devices themselves due to the chemical energy of the substances included in them, capable of electrolytic dissociation. There are known cases (concentration circuits) when galvanic production of electrical energy is possible, not associated with chemical transformations; therefore, the broader concept of a galvanic circuit also covers a group of phenomena of a purely physical nature, which, however, are not used as a source of electrical energy in the form of a special device.

The internal structure of any galvanic cell includes the following parts: 1) an ionized medium composed of second-class conductors (electrolytes), which in practically used galvanic cells (hydroelectric cells) represent aqueous solutions of chemical compounds; 2) electrodes made of first-class conductors (metals, oxides with metallic conductivity, etc.), in contact with electrolytes and equipped with leads to an external circuit. The above components d. b. correctly composed into a galvanic circuit, the symbol of which, formed, for example, from metals M 1 and M 2 and solutions of their salts M 1 X 1 and M 2 X 2, is as follows:

where the arrows indicate the direction of the current of the internal and external circuits, and the EMF arising at the points of contact of dissimilar parts of the circuit should be directed from one electrode to another.

In fig. Figure 1 shows a correctly constructed circuit: the resulting EMF is directed from one electrode to another; in fig. 2 - incorrectly constructed circuit: two short-circuited circuits, the EMF of which is directed along the electrodes and the resulting one is zero. The current flow diagram in a closed galvanic circuit is shown in Fig. 3.

For the electrode on which negatively charged ions (anions) are discharged, the name anode has been established in electrochemistry; for the same one on which the discharge of positive ions of cations occurs) - the cathode. Thus, in the internal circuit of a galvanic cell, the anode is the negative electrode, and the cathode is the positive one. When current is passed from outside, the resulting reverse direction of current, or the discharge of anions on the positive electrode, will make it an anode, and the discharge of cations will make the negative electrode a cathode. From a chemical point of view, the process occurring at the anode is identical to the oxidation reaction, and the reverse process at the cathode is identical to the reduction reaction.

I. Theory of galvanic cells. As a source of electric current, a galvanic cell is studied: 1) from its electrical characteristics, 2) from the chemical transformations associated with the passage of current, and 3) from the physical state and physicochemical properties of the active substances.

General characteristics of a galvanic cell. The characteristic quantities of any galvanic element are: E - EMF; V = f(I, R, t) - voltage of a closed element as a function of current I, external resistance R and discharge time t; r - internal resistance, depending on the size of the electrodes and the resistance of the electrolyte; sometimes r = f(t, t"), i.e. r is a function of discharge time t or storage time t"; Polarization emf Ep = f(I, t) is sometimes combined with r under the general name - internal losses, sometimes Ep is expressed as a % of E. The equations relating these quantities are as follows:

Assuming the polarization emf is proportional to the current strength, i.e. Ep = k∙I, which is close to reality, and taking k + r = c, we obtain the expression for the external characteristics of the galvanic cell:

where c" = c∙V, and current strength:

when n elements are connected in series into a battery:

when connecting n elements in parallel:

Other groupings of elements in batteries are almost never used at present. Electromotive force:

power

maximum power at R = s

Graphically, the external characteristics for a galvanic cell, in which E = 1 V and c = 1 Ohm, are shown in Fig. 4; It is obvious that galvanic cells are essentially designed to operate at very low discharge power, since the maximum useful power is only 25% of what is possible for a given current and circuit voltage = source emf.

Current capacity; with I = Const,

with R = Const,

where t 0 is the discharge period in hours.

Energy capacity:

with I = Const,

with R = Const,

Thermodynamic theories. From the point of view of thermodynamics, chemical processes taking place in galvanic cells are considered to be isothermally reversible and, by applying the free energy equation to them, an expression is obtained that relates the thermal effect of a chemical reaction to the electromotive force of galvanic cells. Helmholtz equation:

where E is the emf of the galvanic cell in V; Q - thermal effect in cal; n is the number of valences of ions entering a chemical reaction, the thermal effect of which is Q; F - Faraday = 96540 C = 26.8 Ah; 0.239 - conversion factor J to cal; T is the absolute temperature of the chemical process; dE/dT - temperature coefficient of emf; for galvanic cells it is usually less than 1 mV per 1° (see Table 1).

For a given galvanic cell, the temperature coefficient of the EMF can change its value and sign depending on the concentration of the reacting substances and T°. The given table 2, which gives the values ​​of the emf of galvanic cells at different temperatures, also makes it possible to calculate the corresponding values ​​of the temperature coefficient of the emf and verify its variability.

Galvanic elements with the lowest temperature coefficient, subject to a number of other conditions, are used as EMF standards. When the value of dE/dT is close to or equal to zero, a simpler formula (Thomson’s rule) is applicable to calculate the EMF of galvanic cells:

The use of the above formulas requires experimental determination of dE/dT and accurate accounting of the total thermal effect of chemical reactions of galvanic cells, which is difficult and not always possible. This difficulty is eliminated with the help of the 3rd law of thermodynamics, which makes it possible to calculate the EMF of galvanic cells from thermal data alone.

Osmotic theory of galvanic cells. The contact potential ε of an electrode-electrolyte pair based on Nernst’s osmotic theory of galvanic cells is expressed by the following formula:

where n and T have the meanings indicated above; R/F – electrolytic gas constant, the numerical value of which is 0.864x10 –4, if ε is expressed in V; P is the elasticity of dissolution of the electrode material; p = kC is the ion pressure in the solution, where C is the ion concentration, expressed in gram ions/l. The Nernst formula allows one to study separately the phenomena at the anode and cathode. It is more convenient to use its expression depending on the concentration of ions in the electrolyte:

where ε 0 is a constant value characteristic of each ion, called the electrolytic potential of the corresponding electrode relative to the electrolyte containing 1 test gram ion per liter (ε 0 is given for 18° with the sign corresponding to the electrode in the reference tables of normal potentials), (0.058∙ log C)/n is a correction term for changes in concentration, taken with a sign (+) in the case of the formation of cations Mà M + and with a sign (-) in the case of the formation of anions Xà X – . The EMF of a galvanic circuit is obtained as the potential difference of the individual electrodes:

When directly measuring ε, auxiliary electrodes are used as a conditional zero, usually normal: hydrogen ε n or calomel ε c, related by the equation:

The absolute potential (not a generally accepted value) of the test electrode through the auxiliary one is determined from the equations:

or graphically - see Fig. 5 and table. 3.

In fig. 5 C indicates the potential relative to the calomel electrode, H - relative to the hydrogen electrode, pH - the concentration of hydrogen ions, N - normal solution.

Phenomena in a closed circuit (polarization of a galvanic cell). When current passes, the potentials of the electrodes, and with them the emf, change their initial values ​​in an open circuit depending on the current density on the electrodes and the discharge time of the galvanic cell, due to a change in the resistance of the electrolyte and partly the electrodes and due to changes in the composition and concentration of active agents over time. substances. The combined effect of these reasons, expressed in the increase in internal losses of the galvanic cell as it is discharged, is called the polarization of the galvanic cell. The nature and degree of polarization (in this general sense) determine the most important technical properties of the galvanic cell. The following types of galvanic polarization are distinguished (Table 4):

Depolarization. When applied to galvanic cells, depolarization usually means only cathodic depolarization in view of the fact that no measures are taken against the anodic, due to its insignificance. Hence, the name depolarizer does not mean an additional material, but the main substance acting on the cathode, which, of course, is not entirely correct. Due to technical and economic reasons, galvanic cells in which solid metal, the so-called, is used as an anode, have acquired the greatest practical importance. soluble electrode, and as a cathode - a porous, insoluble, mostly oxygen electrode.

Open circuit phenomena(self-discharge of galvanic cells). Side processes in galvanic cells are associated with secondary reactions that take place when the external circuit is open. They are of great importance for storing galvanic cells, causing the so-called self-discharge of the cells. Internal causes (excluding, of course, short circuits, careless manufacturing, etc.) of self-discharge are grouped in table. 5.

The degree of action of metal pairs (group A, a) is determined not so much by the EMF of the circuit

how much emf of the following circuit:

which is determined by the amount of additional voltage (overvoltage) required for the release of hydrogen on the surface of a given material. The values ​​of these additional stresses for the most important materials with a smooth surface are given in Table 6.

This, for example, explains the harmlessness of the presence of lead in zinc galvanic cells.

II. Main types of galvanic cells. is visible from the table. 7.

This summary proves that with regard to the anode the issue was technically satisfactorily resolved already in Volta's first galvanic cell. Zinc to this day, with the exception of very rare cases, is an indispensable material as an anode. The entire history of galvanic cells is connected with the search for the most suitable material as a cathode in general, an oxygen electrode in particular, and partly the composition and processing of the electrolyte.

Can be produced according to different characteristics. The constructive division into elements with one and elements with two fluids is currently outdated. Of significant importance, confirmed by the history of elemental science, is the chemical composition and initial physical state of the cathode material (Table 8).

Images of typical representatives of different groups of galvanic cells are given in table. I, where the basic chemical processes and the corresponding electromotive forces are indicated.

A) Galvanic cells with liquid cathode material(depolarizer). Galvanic cells of group “a” - in most cases, elements with two liquids, with or without a permeable partition, have ch. arr. historical interest and academic significance (classical Daniell galvanic circuit). Meidinger elements without a diaphragm find more noticeable use in telegraph practice. Later galvanic cells of this group are Schuster elements with a diaphragm:

and L. Darimont with a semi-permeable membrane in the pores of the septum.

b) Galvanic cells with solid cathode material. Galvanic elements of group “b” are currently of greatest practical importance. According to category “A” they include, in addition to those indicated in the table. I element with silver chloride used for medical purposes, known as normal element voltage standards - Clark:

Zn+Hg 2SO 4 =ZnSO 4 + 2Hg , EMF 1.433 V at 15°,

and Weston:

Cd + Hg 2 SO 4 = CdSO 4 + 2 Hg , EMF 1.0184 V at 20°;

According to category “B”, this group of galvanic cells includes, in addition to numerous forms of execution of the well-known Leclanchet elements with a neutral electrolyte, several types of cells with an alkaline electrolyte (Lalande, Edison, Wedekind and others), operating according to the following scheme:

chemical reaction:

One of these modern American designs is shown in Fig. 6 (the left picture is a galvanic cell that has not been used, the right picture is discharged); the bit graph is shown in Fig. 7.

These elements are used for railway and other signaling and are manufactured in sizes for 100-600 Ah capacity.

Due to their low voltage, they are expensive to operate; These elements are sensitive to temperature fluctuations. Elements of this group with an acid electrolyte are also known, operating according to the following scheme:

chemical reaction:

The form of an element of this type for a flashlight is shown in Fig. 8.

V) Galvanic cells with gaseous cathode material. Galvanic elements of group “B” have begun to acquire industrial importance in recent years (until now, mainly in France); are known as elements with air depolarization, or rather, depolarization by air oxygen. The element Feri was one of the first to gain wider recognition. With his work with the gas electrode, Feri not only provided a way to resolve the issue of significant savings in the consumption of zinc in galvanic cells, but also successfully avoided the difficulties associated with the transition of oxygen from a gas to the ionic state, simultaneously illuminating the depolarization mechanism experimentally. The essence of the device (Fig. 9) of this element is as follows: at the bottom of the vessel there is a horizontal zinc plate; in close proximity to it there is a vertical carbon electrode, specially manufactured, with high porosity and electrical conductivity, protruding above the electrolyte (ammonium chloride solution).

Physico-chemical processes of the Feri element. Theoretical equation

not entirely accurate. In fact, the process breaks down into two phases. In the first phase:

ZnCl 2 is formed, as in a conventional Leclanche cell, but then, as work progresses, the electrolyte separates into three layers: specifically heavy ZnCl 2 (weakly acidic medium) remains at the bottom and covers the zinc (Fig. 10), protecting it from uneven corrosion; the specific lighter solution of NH 4 OH formed on coal floats to the top (weakly alkaline medium), and in the middle there remains a predominantly neutral solution of unconsumed NH 4 Cl as the outer layers come closer and the total content of NH 4 Cl in the solution decreases, the second phase of the process begins:

moreover, NH 4 Cl is partially regenerated, and a precipitate of zinc oxide falls at the boundary of the junction of the outer layers; the lower part of the carbon electrode, facing the zinc, remains clean all the time and, most importantly, immersed in a ZnCl 2 solution.

Oppositely directed EMF of a liquid pair (Fig. 11)

approximately equal to 0.25 V, does not reduce the main EMF, since it is short-circuited with a carbon electrode.

The carbon (gas) electrode in the lower part is saturated with adsorbed hydrogen, in the upper part - with oxygen. The degree of depolarization of this electrode is determined by the operation of a short-circuited pair:

with EMF ~ 0.5-1.0 V.

This explains the stability of the element’s operation, which depends on Ch. arr. on the quality of the carbon electrode.

Comparison of galvanic cells with gas, solid and liquid cathode material. A comparative graph of the discharges of the Fery element with the Leclanche element is shown in Fig. 12.

The comparative consumption of materials in elements with different physical states of the cathode material is shown in table. 9 for the case of discharge with a very weak current or a stronger current intermittently.

Feri gives the following comparative costs of producing one Ah:

In addition to Feri elements, elements with air depolarization by Le Carbone and with an alkaline electrolyte by Ney, Nyberg and Jungner are currently known. In fig. Figure 13 shows the discharge graph of galvanic cells from Le Carbone, type AD 220, for a constant resistance of 5 Ohms.

Galvanic cells wet and dry distinguished by the state of their electrolyte: in the form of a liquid aqueous solution, or converted into a jelly-like, sticky mass with some kind of thickener (starch), or, finally, in the form of a sedentary and non-pouring one, for which a porous inert filler mass is impregnated with a liquid electrolyte (wood sawdust, gypsum, sand, cardboard).

Galvanic cells of the Leclanche type with a dry electrolyte have long received the greatest practical application and industrial importance. In this regard, a lot of work has been done recently to illuminate the physicochemical processes occurring in it. Galvanic circuit diagram of this element:

The deoxidation of MnO 2 to Mn 2 O 3 has been established. In contrast to the Feri element (vertical arrangement of electrodes and the presence of ZnCl 2 in the electrolyte), separation of the low-mobility electrolyte occurs here to a lesser extent. There are three stages of chemical reactions:

In addition, the interaction of NH 4 OH and ZnCl 2 under certain conditions is also accompanied by the formation of zinc oxychloride according to the following equation:

The actual consumption of MnO 2 is sometimes less than required by equations 1, 2 or 3, which is explained by the participation of atmospheric oxygen in the reactions, since access to the latter is ensured, or there may be other, still poorly understood adsorption phenomena at the cathode. The polarization of the electrodes is caused mainly by an increase in the concentration of OH- and, to a lesser extent, Zn++ ions (Table 10).

Mechanical polarization also takes place (see Table 4) by ZnCl 2 ∙2NH 3 deposits; Zn(OH) 2 and Zn(OH)Cl. The last two are especially harmful, blocking the access of the electrolyte inside the porous cathode (agglomerate). The self-discharge of dry elements compared to wet ones, with the exception of the Feri element, is significantly less, but largely depends on the method and quality of manufacture.

Classification of dry galvanic cells. If it is necessary to have a supply for several years, as well as in other specific operating conditions (for example, in tropical countries), they prefer to use uncharged or not fully charged galvanic cells for long-term storage, which must be brought into working condition before use. But it must be borne in mind that the service life of such elements is shorter than that of conventional dry galvanic cells.

In view of the wide variety in the design of dry galvanic cells, below is their classification (Table 11) according to design features with a brief indication of the extent and how long-term storage conditions are met; in addition, in table. II shows exemplary forms of implementation of some of them.

III. Application of galvanic cells. Cost of electrical energy from galvanic cells. The theoretical consumption of materials that can be used as electrode materials, and the cost ratio (before the 1914-18 war) of these materials per 1 Wh (Table 12) show that the choice of the latter is limited either by high cost (especially Cd, Ag, Ni , Pb), or technical difficulties, for example, Al, H 2).

In addition, if we consider that the cost of 1 useful Wh from the practically most economically operating Feri element costs about 80 kopecks, taking into account the consumption of materials alone, it will become clear that for both economic and technical reasons, Galvanic elements are used only in cases of consumption a receiver with low energy consumption in general and with low discharge power in particular. In addition, in many cases, the use of galvanic cells is dictated not so much by their efficiency as by their irreplaceability and a number of practical conveniences. The latter explains the predominant distribution of elements of the Leclanche type, especially dry ones.

Electrically, the use of galvanic cells can be combined in the modes indicated in table. 13.

If we compare the technical data of elements of various types, for example, elements of the Fery type with dry elements of the Leclanchet type, it turns out that the same specific use of about 50 Wh/l can be obtained with a specific load for elements of the Leclanchet type of 0.1-0.25 A/l, for elements of the Feri type only at 0.02-0.05 A/l. This explains the comparatively small success of galvanic cells of the Feri type, despite their advantage in terms of efficiency. For a more complete comparative assessment, it is also necessary to take into account the permissible range of discharge voltage and a number of other conditions. To date, the Leclanche system should be considered the most successful system, which is more easily adapted than others to the various operational modes of receivers encountered in practice, which explains its wide distribution.

Industrial production of galvanic cells. The galvanic cells of group “1, b” (Table 13), i.e. dry with a jelly-like electrolyte, are of greatest industrial importance. The scale of production of these galvanic cells can be seen from Table. 14.

Currently, many countries have normalized the production of galvanic cells. In Germany, 8 types of dry cells, 2 types of wet cells and 1 type of pocket batteries are standardized. In America there are 2 types of dry cells, 5 types of pocket batteries and 2 types of anode radio batteries. The draft all-Union standard for zinc-carbon-manganese peroxide galvanic cells with a fixed electrolyte (Table 15) provides for 7 types of dry and water-filled galvanic cells.

The production of radio batteries (anode and filament), especially the former, is subject to the highest requirements, for example, with regard to the homogeneity of the elements. At present, their design cannot yet be considered definitively established, not only here, but also abroad, although recently, especially in America, the technique of their manufacture has reached great perfection.

In fig. 14 shows graphs of periodic discharge of the anode battery, and FIG. Figure 15 shows a view of one of the elements of the radio battery.

Basic materials for the production of dry elements. Manganese peroxide or dioxide, due to its low conductivity, is most often used in a close mixture with graphite powder, in the form of so-called agglomerates - porous (up to 40%) bodies surrounding a carbon conductor rod (see Table II). The balance of the cost of materials mainly consists (in percentage) of:

Industrial requirements for the maximum use of active materials in galvanic cells should be considered from two sides: a) from the side of the resistance of these materials to spontaneous consumption and b) from the side of their activity during operation. The first requirement applies primarily to the anode, the second to the cathode. With regard to zinc, it has been established that no less (if not more) a role than the chemical composition is played by the state of its surface and crystalline structure, i.e., properties that depend on the processing of this rolled material. The following are used as manganese dioxide: a) manganese ore (pyrolusite), b) artificial (chemically obtained) manganese peroxide, c) a mixture of both, for example, 2 parts by weight of the first and 1 part by weight of the second. The first is distinguished by greater resistance and electrical conductivity, the second by greater activity. The mineralogical origin and degree of polymerization of pyrolusite are also of great importance. In the USSR, Chiatura pyrolusite is used almost exclusively. The use of MnO 2 in the agglomerate is highly dependent on: a) the nature of the graphite used, b) the degree of grinding of both ingredients (grain size is about 0.05 mm), c) their electrical conductivity, d) the composition of the mixture and its preparation (pressure), and, finally, e) the adsorbing capacity of MnO 2 and graphite. On average, with continuous discharge to 0.7 V, the use of pyrolusite in dry cells is no more than 20-30% (deoxidation to Mn 2 O 3), and artificial manganese peroxide (MnO 2) is 60-70%. The ratio (MnO 2 /graphite) in modern elements is 2-4.

Electrolyte of dry galvanic cells. The quality of dry galvanic cells, especially the ability to be stored, strongly depends not only on the chemical composition of the electrolyte, but also on the physical properties, filling method, etc. The dependence of the corrosion of smooth metallic zinc in solutions of ammonia of various concentrations is shown in Fig. 16, from which it can be seen that minimal corrosion occurs with a 20% pure NH 4 Cl solution (the effect of individual impurities is considered by Drucker).

According to theory, it is desirable to have a maximum concentration of NH 4 Cl in the electrolyte of dry cells. One useful additive in terms of reducing zinc dissolution is zinc chloride (see Nernst equation), as can be seen from Fig. 17, for a solution containing 25 g of NH 4 Cl per 100 cm 3 of ZnCl 2 solution of various concentrations.

From this graph it is also clear that the effect of zinc amalgamation significantly affects corrosion only in the absence of ZnCl 2, and also that an increase in the ZnCl 2 content over 25% (specific gravity 1.24) affects corrosion much less, moreover, as follows from the theory , is unfavorable with regard to the rapid formation of Zn(OH) 2. It is interesting to note that the apparently optimal concentration of ZnCl 2 corresponds to the ZnCl 2 ∙2NH 4 Cl complex. Among other properties of the electrolyte, its viscosity is significant. According to Drucker, a 5% paste of NH 4 Cl solution has less effect on zinc than a 10% paste. There are two known methods for gelatinizing an electrolyte: 1) the cell is filled with liquid electrolyte and then heated until a paste forms (usual method) 2) gelatinization is carried out at ordinary temperature using zinc chloride. A mixture of two parts by weight of starch to one part by weight of flour is usually used as a thickener. It has been established that the most suitable for dry elements is a viscous yellowish mass, which is obtained in the case of a composition with the shortest gelatinization time. The effect of ZnCl 2 concentration on the rate of gelatinization of solutions can be seen in Fig. 18.

The resulting ratios make it possible to use two separately non-thickening compositions (Table 16), which, when merged together at room temperature, give a lot of the required properties, and, moreover, in a pre-calculated time.

This valuable quality of ZnCl 2, along with those noted above, as well as in view of its hygroscopic and preservative properties, explains both the seemingly incomprehensible introduction of a material into a fresh galvanic cell, which is formed as a product of the cell’s operation, and those advantages in terms of capacity and shelf life , which are possessed by factory-made dry elements before liquid ones and their other forms without the use of ZnCl 2. The formation of double compounds with NH 3 has recently been prevented by the use of an electrolyte without NH 4 Cl, namely magnesium chloride with the addition of manganese chloride. The method of saturating the agglomerate with electrolyte and filling the cell should be considered in relation to its preservation as protecting Zn from the action of atmospheric oxygen on it. Necessary for proper functioning and harmless to the zinc located at the bottom in Feri-type cells, air oxygen in dry galvanic cells, on the contrary, has a strong destructive effect on zinc, especially in combination with a concentration couple (Fig. 19) acting along the electrode when it is vertical location.

Technological methods for the production of galvanic cells. Factory production of galvanic cells is divided into the following main operations: a) production of zinc poles, b) preparation of cathodes (agglomerates), c) preparation of electrolyte and d) assembly of these components. The first operation consists of the usual mechanical techniques: cutting zinc sheets, pattern bending and soldering; Stamping and electric welding of zinc poles are also used. The preparation of agglomerates from graphite and pyrolusite sifted to a certain grain and mixed in a certain proportion consists of pressing briquettes of the required size. Two methods of pressing are known: 1) pressing directly onto coal and 2) pressing onto a template rod that is then removed, followed by inserting the coal into the formed channel. The advantage of the first method is to reduce the sinter-coal contact resistance; the second is the possibility of using high pressures during pressing. Recently, automatic pressing has become widespread. The pressed agglomerate, placed on coal, is placed in a fabric or paper cover, usually tightened in a spiral with a thin cord, to give greater mechanical strength and to protect the mass from chipping. This technique is called sinter tying and is usually done manually. In America, a more advanced technique is practiced - cardboard sheathing of the agglomerate without troublesome tying, and the cardboard sheath, filling the entire space between the agglomerate and zinc, simultaneously serves as a separator and also plays the role of a filler for the electrolyte. One of the possible methods of such mechanization of strapping for small samples is shown in Fig. 20, according to which agglomerates with covers put on them are pressed with slight friction through the hole of a cold or heated matrix, and a correspondingly arranged punch seals the bottoms.

Semi-automatic machines are also used for putting on clamps - brass caps. The device of one of them is shown in Fig. 21.

Technical data: weight 96 kg, power consumption 1/2 l. s., productivity 1500 pcs. in hours. Similarly, in mass production b. or other methods of assembling galvanic cells have been mechanized.

Testing of galvanic cells. Electrical properties are tested using two methods: 1) constant current I = Const and 2) constant resistance R = Const. Due to simplicity, the second method is more common. Tests are divided into the following types: 1) Test of external characteristic or internal resistance; to obtain a linear dependence V = f(I), the V reading must be taken at its steady-state value. 2) Capacity testing by continuous discharge V = f(t) at I = Const or R = Const. 3) Storage ability test; a reliable method has not yet been developed; indirectly and far from accurately judged by the change in EMF or by the increase in internal losses over a certain period of time of storage of galvanic cells. 4) Testing maximum output under conditions b. or m. close to the actual operating conditions of galvanic cells (periodic discharge according to American standards). In the USSR, ch. arr. the first two types of tests; Currently, there are attempts to use the third type; The most common discharge of galvanic cells is 10 Ohm resistance.

It has been established that the form of the function V = f(t) at R = Const for galvanic cells with MnO 2 is very closely expressed by the equation:

where V H. is the initial voltage, b is the element constant, t is time. This relationship makes it possible to analytically determine the average voltage V avg. up to any final voltage V K . from Eq.

and, consequently, the corresponding capacity of the galvanic cell

where t 0 is the discharge period in hours. The first of the equations is applicable up to V K. = 0.7V and below at discharge modes up to 500 hours.

For longer modes (usually not used in practice), an observed deviation (not for all galvanic cells) of the curve from its original parabolic shape is possible (in Fig. 22 and 23 - curves taken for galvanic cells of the same sizes and under the same conditions ).

In these cases, applying the equation

limited by higher final voltage. The nature of the change in the capacity of galvanic cells of Russian products under different modes R = Const is shown for several sizes of elements in the “discharge time-capacity” diagram (Fig. 24).

It is clear from the diagram that the points corresponding to the same modes for different sizes of galvanic cells lie on straight lines drawn from the origin of coordinates (resistance rays), as follows from the equation

since, with very slight fluctuations in V H., V cp. = Const, and, consequently, the value of I avg. , which determines the inclination of the resistance beam to the coordinate axes, also = Const, in other words, the average discharge current can practically be taken to be independent of the size and shape of the galvanic elements and is determined only by the conductivity of the external circuit (discharge resistance). The simple relationships obtained make it possible to easily determine the capacitance from the discharge time graph up to the final voltage for which the diagram is constructed. As for changing the capacity of galvanic cells with a discharge mode, a number of formulas that have appeared recently make it possible to carry out the necessary calculations with sufficient accuracy for practice. When using these formulas, one must not only forget that they are empirical and therefore, strictly speaking, applicable only to the products and under the conditions in which these formulas were derived. For discharges at I = Const, Peukert’s formula is applicable to dry cells (see Electric batteries):

where t 0 is the discharge period in hours; for Russian products, the value of the indicator n up to V K. = 0.7 V was found equal to 1.3. For American products, the validity of the Peukert formula was also established, and up to V K. = 0.75 V for one of the types of dry elements the value n = 2; the constant k depends on the size of the element. For discharges at R = Const, the formula takes the form:

where n is equal to 1.5 to VK. = 0.75 V for American products and 1.3 to V K. = 0.70 V for Russian products. In general, regarding constant n and k, it should be borne in mind that both of them depend on V K. and, in addition, k is determined by the amount of depolarizing mass and the degree of its use, and n is determined by the shape of the element and mainly by the thickness of the active layer of the depolarizer.

The dependence of the discharge voltage of dry elements on temperature and discharge resistance is visible in Fig. 25, which shows that –22° is the critical temperature for discharges b. or m. significant current.

The equipment for testing galvanic cells consists of: 1) a discharge board with a set of resistances and a voltmeter switch (Fig. 26);

2) installations for intermittent testing according to American standards, in which relays C, controlled by clock mechanism A, close and open circuits E under test (Fig. 27);

3) installations for testing periodic discharge of batteries fired for 2 hours a day (Fig. 28).

Various galvanic elements have been used in electrical engineering for a long time. We can say that it was they who stood at the origins of scientific research into such a phenomenon as electricity. To understand the nature of electric current, it is necessary, first of all, to understand what a galvanic element is.

Characteristics

Each galvanic cell is a chemical source of current. The generation of electrical energy here occurs as a result of redox reactions. This results in a direct conversion of chemical energy into electrical current.

A standard galvanic cell includes dissimilar electrodes, one of which contains an oxidizing agent and the other a reducing agent. During the reaction, both of them come into contact with the electrolyte. According to the validity period, elements can be disposable, reusable or continuous. The most widespread is the ordinary electric one, which is used in many modern devices.

Principle of operation

The element consists of two metal electrodes, different in their physical properties. As a rule, they are placed in an electrolyte, which is a viscous or liquid medium. When the electrodes are connected using an external electrical circuit, a chemical reaction begins. At this time, the movement of electrons from one electrode to another begins, due to which electric energy appears.

The negative pole of the cell consists of an electrode that loses its electrons; its materials are lithium or zinc. During the reaction, it plays the role of a reducing agent. Accordingly, the other electrode is an oxidizer and functions as a positive pole. The material for it is magnesium oxides; mercury or metal salts are less commonly used.

The electrolyte itself, where the electrodes are located, is a substance that is not capable of transmitting electric current under normal conditions. When the electrical circuit becomes closed, the substance begins to disintegrate into ions, resulting in electrical conductivity. The materials for electrolytes are most often dissolved or molten acids, as well as potassium and sodium salts.

The entire structure of the galvanic cell is placed in a metal container. The electrodes are made in the form of metal meshes into which an oxidizing agent and a reducing agent are sprayed. Over time, electrochemical reactions become weak as the supply of oxidizing and reducing materials gradually decreases.

Galvanic cells and batteries

A galvanic element, or galvanic couple, is a device consisting of two metal plates (one of which can be replaced by coke plates), immersed in one or two different liquids, and serving as a source of galvanic current. A certain number of voltaic elements connected to each other in a known manner constitute a galvanic battery. The simplest element in terms of structure consists of two plates, immersed in a clay or glass glass, in which a liquid corresponding to the type of plate is poured; the plates should not have metallic contact in the liquid. D. elements are called primary if they are independent sources of current, and secondary, if they become effective only after a more or less prolonged exposure to sources of electricity that charge them. When considering the origin of voltaic elements, one must begin with the voltaic column, the ancestor of all subsequent galvanic batteries, or with the Voltaic cup battery.

Voltage column. To compose it, Volta took pairs of dissimilar metal circles, folded or even soldered at the base, and cardboard or cloth circles moistened with water or a solution of caustic potassium. Initially, silver and copper mugs were used, and then usually zinc and copper. A pillar was made from them, as shown in the diagram. 1, namely: first, a copper plate is placed and a zinc plate is placed on it (or vice versa), on which a moistened cardboard circle is placed; this constituted one pair, on which was superimposed a second, again composed of copper, zinc and cardboard circles, superimposed on each other in the same order as in the first pair.

Continuing to apply subsequent pairs in the same order, you can create a pillar; the pillar shown in the devil. 1, on the left, consists of 11 volt pairs. If a pole is installed on a plate of an insulating, i.e., non-conductive, substance, for example, glass, then, starting from the middle of it, one half of the column (the bottom in our drawing) will be charged with positive electricity, and the other (the top in the drawing) - negative. The intensity of electricity, imperceptible in the middle, increases as it approaches the ends, where it is greatest. Wires are soldered to the lowest and highest plates; bringing the free ends of the wires into contact gives rise to the movement of positive electricity from the lower end of the pole through the wire to the upper and the movement of negative electricity in the opposite direction; an electric, or galvanic, current is formed (see this word). Volta considered two plates of dissimilar metals to be a pair, and attributed to the liquid only the ability to conduct electricity (see Galvanism); but according to the view established later, the pair consists of two dissimilar plates and a liquid layer between them; therefore, the topmost and bottom plates of the pillar (Fig. 1 on the right) can be removed. Such a pillar will consist of 10 pairs, and then its lowermost plate will be copper, and its uppermost one will be zinc, and the direction of movement of electricity, or the direction of galvanic current, will remain the same: from the lower end of the pillar (now from zinc) to the upper (to copper). The copper end of the pole was called the positive pole, the zinc end was called the negative pole. Subsequently, in Faraday's terminology, the positive pole is called anode, negative - cathode. The Voltaic column can be laid horizontally in a trough, covered inside with an insulating layer of wax fused with harpius. Nowadays the voltaic pole is not used due to the great labor and time required to assemble and disassemble it; but in the past they used pillars made up of hundreds and thousands of pairs; Professor V. Petrov used it in St. Petersburg in 1801-2. during his experiments with a column, sometimes consisting of 4200 pairs (see Galvanism), Volta built his apparatus in another form, which is the form of later batteries. Volta's battery (corona di tazze) consisted of cups located around the circumference of a circle into which warm water or a salt solution was poured; in each cup there were two dissimilar metal plates, one opposite the other. Each plate is connected by wire to a dissimilar plate of the adjacent cup, so that from one cup to another along the entire circumference the plates constantly alternate: zinc, copper, then again zinc and copper, etc. In the place where the circle closes, in one cup there is zinc plate, in the other - copper; along the wire connecting these outer plates, current will flow from the copper plate (positive pole) to the zinc plate (negative pole). Volta considered this battery less convenient than a pole, but in fact it was the form of the battery that became widespread. In fact, the structure of the voltaic column was soon changed (Cruikshank): an oblong wooden box, divided across by copper and zinc plates soldered together, into small compartments into which liquid was poured, was more convenient than an ordinary voltaic column. Even better was a box divided into compartments by wooden cross walls; copper and zinc plates were placed on both sides of each partition, being soldered together on top, where, in addition, an eyelet was left. A wooden stick passing through all the ears served to lift all the plates from the liquid or to immerse them.

Elements with one liquid. Soon after, separate pairs or elements began to be made that could be connected into batteries in various ways, the benefits of which were especially clearly revealed after Ohm expressed the formula for the strength of the current depending on the electroexcitatory (or electromotive) force of the elements and on the resistances encountered by the current as in external conductors and inside elements (see Galvanic current). The electrical excitatory force of the elements depends on the metals and liquids and their components, and the internal resistance depends on the liquids and the size of the elements. To reduce the resistance and increase the current intensity, it is necessary to reduce the thickness of the liquid layer between dissimilar plates and increase the size of the immersed surface of the metals. This is done in Wollaston element(Wollaston - according to the more correct pronunciation Wulsten). The zinc is placed inside a bent copper plate, in which pieces of wood or cork are inserted to prevent the plates from touching; a wire, usually copper, is soldered to each of the plates; the ends of these wires are brought into contact with an object through which they want to pass a current flowing in the direction from copper to zinc along the outer conductors and from zinc to copper through the internal parts of the element. In general, the current flows inside the liquid from a metal on which the liquid acts chemically more strongly, to another, on which it acts less strongly. In this cell, both surfaces of the zinc plate serve for the flow of electricity; This method of doubling the surface of one of the plates later came into use when arranging all elements with one liquid. The Wollaston element uses dilute sulfuric acid, which decomposes during the action of current (see Galvanic conductivity); the result of decomposition will be the oxidation of zinc and the formation of zinc sulfate, dissolving in water, and the release of hydrogen on the copper plate, which thereby comes into a polarized state (see Galvanic polarization and Galvanic conductivity), reducing the current strength. The variability of this polarized state is accompanied by variability in the current strength.

Of many elements with one liquid we call media elements(Smee) and Grene, in the first - platinum or platinized silver among two zinc plates, all immersed in dilute sulfuric acid. The chemical action is the same as in Wollaston's element, and is polarized by hydrogen in platinum; but the current is less variable. The electrical excitation force is greater than in copper-zinc.

Grenet's element consists of a zinc plate placed between two tiles cut from coke; the liquid for this element is prepared according to different recipes, but always from dichromopotassium salt, sulfuric acid and water. According to one recipe, for 2500 grams of water you need to take 340 grams of the named salt and 925 grams of sulfuric acid. The electrical excitation force is greater than in the Wollaston element.

During the action of the Grenet element, zinc sulfate is formed, as in previous cases; but hydrogen, combining with the oxygen of chromic acid, forms water; chrome alum is formed in the liquid; polarization is reduced, but not destroyed. For the Grenet element, a glass vessel with an expanded lower part is used, as shown in Fig. 7 table "Galvanic cells and batteries". So much liquid is poured in that the zinc plate Z, which is shorter than coke WITH, it was possible by pulling the rod attached to it T, remove from the liquid for the time when the element should remain inactive. Clamps V, V, connected - one with rod rim T, and therefore, with zinc, and the other with a rim of coal, are assigned to the ends of the conductor wires. Neither the records nor their frames have metallic contact with each other; the current flows along the connecting wires through external objects in the direction from coke to zinc. The carbon-zinc element can be used with a solution of table salt (in Switzerland, for telegraphs, calls) and then it is valid for 9-12 months. without care.

Element of Lalande and Chaperone, improved by Edison, consists of a slab of zinc and another pressed from copper oxide. The liquid is a solution of caustic potassium. The chemical action is the oxidation of zinc, which then forms a compound with potassium; The separated hydrogen, oxidized by the oxygen of zinc oxide, becomes part of the resulting water, and copper is reduced. Internal resistance is low. The excitatory force is not determined with precision, but is less than that of the Daniel element.

Elements with two liquids. Since the release of hydrogen on one of the solid bodies of hydrogen elements is a reason that reduces the strength of the current (actually electrically exciting) and makes it unstable, then placing the plate on which the hydrogen is released in a liquid capable of donating oxygen to combine with hydrogen should make current is constant. Becquerel was the first to construct (1829) a copper-zinc element with two liquids for the named purpose, when the elements of Grenet and Lalande were not yet known. Later Daniel(1836) designed a similar element, but more convenient to use. To separate liquids, two vessels are needed: one glass or glazed clay vessel, which contains a cylindrical, clay, slightly fired, and therefore porous, vessel into which one of the liquids is poured and one of the metals is placed; in the ring-shaped space between two vessels another liquid is poured into which a plate of another metal is immersed. In Daniel's element, zinc is immersed in weak sulfuric acid, and copper is immersed in an aqueous solution of copper (blue) sulfate. Fig. 1 of the table depicts 3 Daniel elements connected into a battery;

cylinders bent from zinc are placed in outer glass glasses, copper plates, also in the shape of a cylinder or bent like the letter S, are placed in inner clay cylinders. You can place it the other way around, i.e. copper in external vessels. The current flows from copper to zinc through external conductors and from zinc to copper through the liquid in the cell or battery itself, and both liquids decompose simultaneously: zinc sulfate is formed in a vessel with sulfuric acid, and hydrogen goes to the copper plate, at the same time copper sulfate (CuSO 4) decomposes into copper (Cu), which is deposited on the copper plate, and a separately non-existent compound (SO 4), which by a chemical process forms water with hydrogen before it has time to be released in the form of bubbles on the copper. Porous clay, easily wetted by both liquids, makes it possible for chemical processes to be transmitted from particle to particle through both liquids from one metal to another. After the action of the current, the duration of which depends on its strength (and this latter partly on external resistances), as well as on the amount of liquids contained in the vessels, all copper sulfate is consumed, as indicated by the discoloration of its solution; then the separation of hydrogen bubbles on copper begins, and at the same time the polarization of this metal. This element is called constant, which, however, must be understood relatively: firstly, even with saturated vitriol there is a weak polarization, but the main thing is that the internal resistance of the element first decreases and then increases. For this second and main reason, at the beginning of the action of the element, a gradual increase in current is noticed, the more significant, the less the current strength is weakened by external or internal resistances. After half an hour, an hour or more (the duration increases with the amount of liquid with zinc), the current begins to weaken more slowly than it increased, and after a few more hours it reaches its original strength, gradually weakening further. If a supply of this salt in undissolved form is placed in a vessel with a solution of copper sulfate, then this continues the existence of the current, as well as replacing the resulting solution of zinc sulfate with fresh dilute sulfuric acid. However, with a closed element, the liquid level with zinc gradually decreases, and with copper it increases - a circumstance that in itself weakens the current (from an increase in resistance for this reason) and, moreover, indicates a transition of liquid from one vessel to another (transfer of ions, see Galvanic conductivity, galvanic osmosis). Copper sulfate seeps into the vessel with zinc, from which the zinc releases copper purely chemically, causing it to precipitate partly on the zinc and partly on the walls of the clay vessel. For these reasons, there is a large waste of zinc and copper sulfate that is useless for current. However, Daniel's element is still one of the most constant. A clay glass, although wetted by liquid, presents great resistance to current; by using parchment instead of clay, the current can be significantly increased by reducing the resistance (Carré element); the parchment can be replaced by an animal bubble. Instead of diluted sulfuric acid, you can use a solution of table or sea salt for zinc; the excitatory force remains almost the same. Chemical effects have not been studied.

Meidinger element. For frequent and continuous and, moreover, fairly constant, but weak current, the Meidinger element (Fig. 2 of the table), which is a modification of the Daniel element, can be used. The outer glass has an extension at the top, where a zinc cylinder is placed on the inner lip; At the bottom of the glass is placed another small one, in which is placed a cylinder rolled up from sheet copper, or a copper circle is placed at the bottom of the inner vessel, which is then filled with a solution of copper sulfate. After this, a solution of magnesium sulfate is carefully poured on top, which fills the entire free space of the outer vessel and does not displace the vitriol solution, as it has a higher specific gravity. Nevertheless, through the diffusion of liquids, vitriol slowly reaches zinc, where it gives up its copper. To maintain the saturation of this solution, an overturned glass flask with pieces of copper sulfate and water is placed inside the element. Conductors go outward from the metals; their parts in the liquid have a gutta-percha shell. The absence of a clay jar in the element allows it to be used for a long time without changing its parts; but its internal resistance is high, it must be moved from place to place very carefully, and it contains a lot of copper sulfate, which is useless for current; in the flask of even a small element about 1/2 kilogram of vitriol is placed. It is very suitable for telegraphs, electric calls and other similar cases and can stand for months. Callot and Trouvé-Callot elements similar to Meidinger elements, but simpler than the latter. Kresten in St. Petersburg he also arranged a useful modification of the Meidinger element. Thomson element in the form of a dish or tray there is a modified Daniel's; porous flat membranes made of parchment paper separate one liquid from another, but you can do without membranes. Siemens element And Halske also belongs to the category of Daniel's. Element of Minotto. A copper circle is at the bottom of a glass jar, on which crystals of copper sulfate are poured, and on top there is a thick layer of siliceous sand, on which a zinc circle is placed. Everything is filled with water. Lasts 1 1/2 to 2 years on telegraph lines. Instead of sand, you can take animal charcoal powder (Darsonval). Trouvé element. A copper circle on which is a column of circles made of pass-through paper, impregnated with copper sulfate on the bottom and zinc sulfate on the top. A small amount of water wetting the paper activates the element. The resistance is quite high, the action is long and constant.

Grove element, platinum-zinc; platinum is immersed in strong nitric acid, zinc in weak sulfuric acid. The hydrogen released by the action of the current is oxidized by the oxygen of nitric acid (NHO 2), which turns into nitric anhydride (N 2 O 4), the released red-orange vapors of which are harmful to breathing and spoil all copper parts of the apparatus, which are therefore better made of lead. These elements can only be used in laboratories where there are fume hoods, and in an ordinary room they should be placed in a stove or fireplace; they have a high excitatory force and low internal resistance - all the conditions for a high current strength, which is the more constant the larger the volume of liquids contained in the element. Fig. 6 of the table shows such a flat-shaped element; outside it on the right there is a bent zinc plate connected to the platinum sheet of the element Z the second element, in the fold of which there is a flat clay vessel V for platinum. On the left is a platinum sheet clamped to the zinc element and belonging to the third element. With this form of elements, the internal resistance is very small, but the strong effect of the current does not last long due to the small amount of liquids. The current flows from the platinum through the outer conductors to the zinc, according to the general rule stated above.

Bunsen element(1843), coal-zinc, completely replaces the previous one and is cheaper than it, since expensive platinum is replaced by coke tiles. The fluids are the same as in the Grove element, the electrical excitation force and resistance are approximately the same; the direction of the current is the same. A similar element is shown in Fig. 3 tables; charcoal tile marked with letter WITH, with a metal clamp with a + sign; this is the positive pole, or anode, of the element. From zinc cylinder Z with a clamp (negative pole, or cathode) there is a plate with another clamp, applied to the carbon slab of the second element in the case of a battery. Grove was the first to replace platinum in his element with coal, but his experiments were forgotten. Darsonval element, carbon-zinc; for coal, a mixture of nitric and hydrochloric acid, 1 volume each, with 2 volumes of water containing 1/20 sulfuric acid. Fora element.- Instead of a coke tile, a bottle made of graphite and clay is used; Nitric acid is poured there. This apparently external change in the Bunsen element makes the use of nitric acid more complete.

Sosnovsky element.- Zinc in a solution of sodium hydroxide or potassium hydroxide; coal in a liquid consisting of 1 volume of nitric acid, 1 volume of sulfuric acid, 1 volume of hydrochloric acid, 1 volume of water. Remarkable for its very high electrical excitatory power.

Callan element.- Carbon of Bunsen elements is replaced by iron; the excitatory force remains the same as when using coal. Iron is not exposed to nitric acid, being in a passive state. Instead of iron, cast iron with some silicon content can be usefully used.

Poggendorff element differs from the Bunsen element by replacing nitric acid with a liquid similar to that used in the Grenet element. For 12 parts by weight of potassium dichromate dissolved in 100 parts of water, add 25 parts of strong sulfuric acid. The excitatory force is the same as in the Bunsen element; but the internal resistance is greater. The oxygen in the said liquid given up for the oxidation of hydrogen is less than in nitric acid at the same volume. The absence of odor when using these elements, combined with other advantages, made it the most convenient to use. However, polarization has not been completely eliminated. Imshenetsky element, carbon-zinc. Graphite (carbon) plate in a solution of chromic acid, zinc in a solution of sodium sulfide salt. Great excitatory force, low internal resistance, almost complete utilization of zinc and very good use of chromic acid.

Leclanche element, carbon-zinc; instead of an oxidizing liquid, it contains powder (large) of manganese peroxide at the coal slab, mixed with coke powder (Fig. 5 table) in an inner, liquid-permeable clay jar; A zinc stick is placed outside in one of the corners of the specially shaped flask. The liquid - an aqueous solution of ammonia - is poured from the outside and penetrates into the clay jar to the coal (coke), wetting the manganese peroxide; the top of the jar is usually filled with resin; holes are left for gases to escape. The excitatory force is average between the Daniel and Bunsen elements, the resistance is high. This element, left closed, gives a current of rapidly decreasing strength, but for telegraphs and home use it lasts for one to two years when adding liquid. When ammonia (NH 4 Cl) decomposes, chlorine is released into zinc, forming zinc chloride and ammonia with coal. Manganese peroxide, rich in oxygen, passes little by little into a compound of a lower oxidation state, but not in all parts of the mass filling the clay vessel. To make more complete use of manganese peroxide and reduce internal resistance, these elements are arranged without a clay jar, and tiles are pressed from manganese peroxide and coal, between which coke is placed, as shown in Fig. 4 tables. These types of elements can be made closed and easy to carry; glass is replaced by horn rubber. Geff also modified this element, replacing the ammonia solution with a solution of zinc chloride.

Element of Marie-Devi, coal-zinc, contains, with coal, a dough-like mass of mercuric sulfate (Hg 2 SO 4), moistened with water, placed in a porous clay jar. Weak sulfuric acid or even water is poured onto the zinc, since the former will already be released from the mercury salt by the action of a current, in which hydrogen is oxidized, and with coal metallic mercury is released, so that after some time the element becomes zinc-mercury. The electrical excitatory force does not change from using pure mercury instead of coal; it is slightly larger than in the Leclanche element, the internal resistance is large. Suitable for telegraphs and in general for intermittent current action. These elements are also used for medical purposes, and they prefer to be charged with mercuric sulfate oxide (HgSO 4). The form of this element, convenient for medical and other purposes, is a tall cylinder of horn rubber, the upper half of which contains zinc and coal, and the lower half contains water and mercury sulfate. If the element is turned upside down, it acts, but in the first position it does not generate current.

Warren Delarue element- zinc-silver. A narrow silver strip protrudes from a cylinder of fused silver chloride (AgCl) placed in a tube of parchment paper; zinc has the shape of a thin rod. Both metals are placed in a glass tube sealed with a paraffin stopper. The liquid is a solution of ammonia (23 parts of salt per 1 liter of water). The electrical excitation force is almost the same (a little more) as in the Daniel element. Silver metal is deposited from silver chloride onto the silver strip of the element, and no polarization occurs. Batteries made from them were used for experiments on the passage of light in rarefied gases (V, Warren Delarue). Geff gave these elements a device that makes them convenient to carry; used for medical induction coils and for direct currents.

Elements of Duchaumin, Partz, Figier. The first is zinc-carbon; zinc in a weak solution of table salt, coal - in a solution of ferric chloride. Unstable and little explored. Partz replaced zinc with iron; a solution of table salt has a density of 1.15, a solution of ferric chloride has a density of 1.26. Better than the previous one, although the electrical excitatory force is less. Figier uses one liquid in the iron-coal element, obtained by passing a stream of chlorine through a saturated solution of iron sulfate. Niode element, carbon-zinc. The zinc is shaped like a cylinder surrounding a porous clay cylinder containing a coke slab covered with bleach. The element is sealed with a stopper filled with wax; a solution of table salt (24 parts per 100 parts water) is poured through the hole in it. The electrical excitatory force is large; with constant, somewhat prolonged action on external small resistance, it soon weakens, but after an hour or two of inactivity of the element it reaches its previous value.

Dry elements. This name can be given to elements in which the presence of liquid is not apparent when it is sucked into the porous bodies of the element; it would be better to call them wet. These include the above-described copper-zinc Trouvé element and the Leclanche element, modified by Germain. This latter uses fiber extracted from coconuts; a mass is prepared from it that strongly absorbs liquid and gases, appears dry and only takes on a wet appearance under pressure. Easily portable and suitable for traveling telegraph and telephone stations. Gasner elements (carbon-zinc), which contain gypsum, probably impregnated with zinc chloride or ammonia (kept secret). The excitatory force is approximately the same as in the Leclanche element, some time after the onset of the latter’s action; internal resistance is less than that of Leclanche. In a dry Leclanche-Barbier cell, the space between the outer zinc cylinder and the inner hollow cylinder of agglomerate, which includes manganese peroxide, is filled with gypsum, a saturated solution of unknown composition. The first, rather lengthy tests of these elements were favorable for them. Gelatin-glycerin element Kuznetsova there is copper-zinc; consists of a cardboard box soaked in paraffin with a bottom lined with tin inside and out. A layer of crushed copper sulfate is poured onto the tin, onto which a gelatin-glycerin mass containing sulfuric acid is poured. When this mass hardens, a layer of crushed amalgamated zinc is poured in, again filled with the same mass. These elements make up a battery like a voltaic column. Designed for calls, telegraphs and telephones. In general, the number of different dry elements is very significant; but in the majority, due to the secret composition of liquids and agglomerates, judgment about them is only possible practical, but not scientific.

Elements of large surface and low resistance. In cases where it is necessary to glow short, rather thick wires or plates, as, for example, during some surgical operations (see Galvanocaustics), elements with large metal surfaces immersed in liquid are used, which reduces the internal resistance and thereby increases the current. Wollaston's method of surface doubling is applied to the composition of surfaces from a large number of plates, as shown in Fig. 2, where y, y, y- plates of the same metal are placed in the spaces between the plates ts, ts, ts, ts other metal.

All plates are parallel to each other and do not touch, but all of the same name are connected by external wires into one whole. This entire system is a uniform element of two plates, each with a surface area of ​​six times that shown, with a thickness of the liquid layer between the plates equal to the distance between each two plates shown in the drawing. Already at the beginning of this century (1822), devices with a large metal surface were installed. These include the large Gare element, called the deflagrator. Long lengths of zinc and copper sheets, separated by flannel or wooden sticks, are rolled into a roller in which the sheets do not come into metallic contact with each other. This roller is immersed in a tub of liquid and produces a very high current when acting on very small external resistance. The surface of each sheet is about 50 square meters. feet (4 sq. meters). Nowadays, in general, they try to reduce the internal resistance of the elements, but give them a particularly large surface for some particular applications, for example, in surgery for cutting off painful growths with a hot wire or plate, for cauterization (see Galvanocaustics). Since conductors of low resistance are heated, current can be obtained precisely by reducing the internal resistance. Therefore, a large number of plates are placed in galvanocaustic elements, arranged similar to those shown in Fig. 2 texts. The device does not present any special features, but is adapted for convenient use; such, for example, are carbon-zinc cells or Chardin batteries with chrome liquid, used in Paris, Lyon, Montpellier and Brussels. Operators should be alerted to the need to use a very low-resistance current meter (ammeter, or ammeter) to ensure that the battery is in good condition before operation.

Normal elements must retain their electrically exciting force or have a constant potential difference for as long as possible when they are kept open in order to serve as a normal unit of measure when comparing electrically exciting forces with each other. For this purpose, Rainier proposed a copper-zinc pair, in which the surface of copper is very large compared to zinc. The liquid is a solution of 200 parts of dry table salt in 1000 parts of water. Under this condition, the polarization of copper is very weak if this element is introduced into a circuit with high resistance and for a short time. Normal element Latimer Clark consists of zinc in a solution of zinc sulfate, mercury and mercury sulfide salt (Hg 2 SO 4). Normal element Fleming, copper-zinc, with solutions of copper sulfate and zinc sulfate of a certain, always constant density. Normal element London Post and Telegraph Office, copper-zinc, with a solution of zinc sulfate and crystals of copper sulfate with copper is very suitable. For the electrical excitatory force of the Fleming element, see the plate at the end of the article.

Secondary elements, or batteries, originate from the secondary pillars of Ritter (see Galvanism), which remained without special attention for 50 years. A Ritter column, consisting of copper plates immersed in some liquid, became polarized after the action of a voltaic column on it, and after that it could itself generate a current, the direction of which was opposite to the primary current. In 1859, Plante constructed an element consisting of two lead sheets, coiled in a spiral like a Gare deflagrator, without mutual metallic contact, and immersed in weak sulfuric acid. By connecting one lead sheet to the anode (positive pole), and the other to the cathode of a battery of at least 2 Bunsen or Poggendorff cells connected in series, and thus passing a current flowing in the liquid from lead to lead, thereby causing the separation of oxygen on the lead plate , connected to the anode, and hydrogen on a sheet connected to the cathode. A layer of lead peroxide forms on the anode plate, while the cathode plate is completely cleared of oxides. Due to the heterogeneity of the plates, they form pairs with a large electrical excitatory force, giving a current in the direction opposite to the previous one. The great excitatory force developing in the secondary element and directed opposite to the excitatory force of the primary battery is the reason for the requirement that the latter exceed the first. Two Poggendorff elements connected in series have an exciting force of about 4 volts, but a Plante element only about 2 1/2. To charge 3 or 4 Plante elements connected in parallel (see Galvanic batteries), in fact, the previous 2 Poggendorff elements would be sufficient, but their action would be very slow to oxidize such a large surface of lead; therefore, to simultaneously charge, for example, 12 Plante elements connected in parallel, you need the action of 3-4 Bunsen elements with an exciting force of 6-8 volts for several hours. Charged Plante cells connected in series develop an electrical exciting force of 24 volts and produce more incandescence, for example, than a charging battery, but the effect of the secondary battery will be shorter. The amount of electricity set in motion by the secondary battery is not more than the amount of electricity passed through it from the primary battery, but, being passed through the external conductors at a greater voltage or potential difference, is expended in a shorter time.

Plante cells, after various practical improvements, were called batteries. In 1880, Faure came up with the idea of ​​covering lead plates with a layer of red lead, i.e., ready-made lead oxide, which, due to the action of the primary current, was further oxidized on one plate and deoxidized on the other. But the method of attaching the red lead required technical improvements, which essentially consisted in the use of a lead grid, in which the empty cells are filled with a dough of red lead and litharge in weak sulfuric acid. The Fitz-Gerald battery uses lead oxide tiles without any metallic base; In general, there are a lot of battery systems and here is an image of only one of the best (Fig. 8 of the table). The Hagen lead grille is composed of two protrusions facing each other, which prevents pieces of lead oxide from falling out of the frame; specially depicted cuts along the lines ab And CD The main drawing explains the structure of this frame. One frame is filled with red lead, the other with litharge (the lowest oxidation state of lead). An odd number, usually five or seven, of plates are connected in the same way as explained in the devil. 2; in the first case 3, in the second 4 are covered with litharge. Of the Russian technicians, Yablochkov and Khotinsky benefited from the design of batteries. These secondary elements, which present one technical inconvenience - a very large weight, have received various technical applications, among other things, for home electric lighting in cases where it is impossible to use the direct current of dynamos for this purpose. Batteries charged in one place can be transported to another. They are now charged not with primary elements, but with dynamos, in compliance with some special rules (see Dynamos, Electric lighting).

Composition of galvanic batteries. The battery is composed of elements in three ways: 1) series connection, 2) parallel connection, 3) combined from both previous ones. In fig. Table 1 shows a series connection of 3 Daniel elements: the zinc of the first pair, counting from the right, is connected by a copper tape to the copper of the second pair, the zinc of the second pair to the copper of the third. The free end of the copper of the first pair is the anode, or positive terminal of the battery; the free end of the third pair is the cathode, or negative terminal of the battery. To connect these same elements in parallel, all the zincs must be connected to each other with metal tapes and all copper sheets must be connected with tapes or wires into one whole separate from the zinc; the complex zinc surface will be the cathode, the complex copper surface will be the anode. The action of such a battery is the same as the action of a single cell, which would have a surface area three times larger than a single cell of the battery. Finally, the third connection method can be applied to at least 4 elements. By connecting them two in parallel, we get two complex anodes and the same two cathodes; By connecting the first complex anode with the second complex cathode, we obtain a battery of two elements with a double surface. Damn it. 3 texts depict two different complex compounds of 8 elements, each represented by two concentric rings separated by black spaces. Without going into details, we note that in appearance the method of composing these batteries differs from those just described.

In (I) 4 elements are connected in series, but at one end the two outer zincs are connected by a metal strip KK, and on the opposite side, the two outer copper plates are connected by a plate AA, which is the anode, whereas QC - cathode of a complex battery, equivalent to 4 elements of double the surface connected in series. Drawing 3 (II) shows a battery equivalent to two elements of a quadruple surface connected in series. Cases when batteries are needed, composed in a certain way, are completely clarified by Ohm's formula (galvanic current), subject to the rule arising from it that in order to obtain the best effect on any conductor with a given number of galvanic elements, it is necessary to compose a battery from them in such a way that inside it the resistance was equal to the resistance of the external conductor, or at least as close as possible to it. To this we must also add that with a series connection, the internal resistance increases in proportion to the number of connected pairs, and with a parallel connection, on the contrary, the resistance decreases in proportion to this number. Therefore, on telegraph lines, which present great resistance to galvanic current, batteries consist of elements connected in series; in surgical operations (galvanocaustics), a battery of parallel-connected elements is needed. Depicted in hell. 3 (I) the battery represents the best combination of 8 cells to act on an external resistance that is twice the internal resistance of a single cell. If the external resistance were four times less than in the first case, then the battery should be given the appearance of hell. 3 (II). This follows from calculations using Ohm's formula. [On elements and batteries, see the work of Niodet (in the Russian translation by D. Golov - “Electrical elements” 1891); less detailed: "Die galvanischen Batterien", Hauck, 1883. Articles in the magazine "Electricity", 1891 and 1892]

Comparison of galvanic cells between themselves. Notes related to this were partly given in the description of the elements. The merit of a galvanic cell is measured by the strength of the current it develops and the duration of its action, namely the product of the first quantity by the other. If we take the ampere as the unit of current (see Galvanic current), and the hour as the unit of time, then we can measure the performance of the galvanic cell in ampere-hours. For example, batteries, depending on their size, can provide from 40 to 90 ampere-hours. For methods of measuring the work delivered by electric current, equivalent to the work of the so-called steam horse for one hour, see Work, Energy of Electric Current.