A galvanic cell is a source of electrical energy, the principle of operation is based on chemical reactions. Most modern batteries and accumulators fall under the definition and belong to the category under consideration. The physically galvanic cell consists of conductive electrodes immersed in one or two liquids( electrolytes).
Galvanic cells are divided into primary and secondary in accordance with the ability to produce electric current. Both species are considered sources and serve different purposes. The first produce current during a chemical reaction, the second function only after charging. Below we discuss both varieties. By the number of liquids, two groups of electroplating elements are distinguished:
- A vivid example of devices with a single liquid is the volt column( 1800) and the element of Wollaston, which Georg Ohm originally used in his own research. It consisted of copper plates rolled into hollow cylindrical surfaces: the first one was inserted into the second one. Both are protected from contact with wooden struts. The electrolyte is dilute sulfuric acid. The result is a doubling of the working surfaces. During the reaction, copper sulfate is formed with the release of hydrogen, and zinc is oxidized. In batteries, one electrode is usually coal.
- The elements with two liquids use an electrolyte with an excess of oxygen to immerse the electrode, where hydrogen is formed. As a result, a chemical reaction of water formation takes place, the instability of the current is compensated and smoothed. The first idea of using sources put forward in 1829, Becquerel. Initially, a vessel made of weakly baked clay was used to separate the vessels, which had good porosity. To compensate for the release of hydrogen on the copper electrode, it is permissible to use blue vitriol.
Volatility of power supplies with a single liquid noticed Ohms, revealing the unacceptability of the Wollaston electroplating cell for experiments on the study of electricity. The dynamics of the process is such that at the initial moment of time the current is large and first increases, then in a few hours it falls to an average value. Modern batteries are capricious.
The history of the discovery of chemical electricity
Little is known of the fact that in 1752 galvanic electricity was mentioned by Johann Georg. The publication The study of the origin of pleasant and unpleasant feelings, released by the Berlin Academy of Sciences, even gave the phenomenon a completely correct interpretation. Experience: silver and lead plates were connected at one end, while opposites from different sides were applied to the tongue. At the receptors the taste of ferrous sulfate is observed. Readers have already guessed that the described method of testing batteries was often used in the USSR.
Explanation of the phenomenon: apparently, there are some metal particles that irritate the receptors of the tongue. Particles are emitted by a single plate upon contact. Moreover, one metal dissolves. Actually, there is a principle of operation of a galvanic cell, where the zinc plate gradually disappears, giving away the energy of chemical bonds to an electric current. The explanation was made half a century before the official report to the Royal Society of London, Alessandro Volta, on the opening of the first power source. But, as often happens with discoveries, for example, electromagnetic interaction, the experience went unnoticed by the general scientific community and has not been studied properly.
We add that this turned out to be connected with the recent abolition of persecution for witchcraft: few have decided, after the sad experience of the "witches", to study obscure phenomena. The situation was different with Luigi Galvani, who had been working at the Department of Anatomy in Bologna since 1775.His specializations were considered irritants of the nervous system, but the star did not leave a significant mark in the field of physiology. A student of Beccaria was actively involved in electricity. In the second half of 1780, as follows from the memoirs of the scientist( 1791, De Viribus Electricitatis in Motu Muscylary: Commentarii Bononiensi, Volume 7, p. 363), the frog was once again prepared( experiments and then lasted for many years).
It is noteworthy that an unusual phenomenon was noticed by the assistant, exactly as with the deviation of the compass needle by the wire with electric current: the discovery was made only by people indirectly connected with scientific research. The observation concerned jerking of the frog's lower limbs. In the course of the experiment, the assistant touched the inner femoral nerve of the animal being prepared, the legs twitched. Nearby, there was an electrostatic generator on the table, a spark slipped on the device. Luigi Galvani immediately set about trying to repeat the experience. What succeeded. And again on the car slipped a spark.
A parallel connection with electricity was formed, and Galvani wanted to find out whether a thunderstorm would act on a frog in a similar way. It turned out that natural disasters do not have a noticeable impact. The frogs attached by copper hooks to the spinal cord to the iron fence, twitched regardless of weather conditions. The experiments could not be implemented with 100 percent repeatability, the atmosphere did not have an impact. As a result, Galvani found a host of pairs made up of different metals, which, in contact between themselves and the nerve, caused a twitching of the frog's legs. Today, the phenomenon is explained by different degrees of electronegativity of materials. For example, it is known that aluminum plates cannot be riveted with copper, metals make up a galvanic pair with pronounced properties.
Galvani rightly observed that a closed electrical circuit is being formed, suggesting that the frog contains animal electricity, discharged like a Leyden jar. Alessandro Volta did not accept the explanation. Having carefully studied the description of the experiments, Volta put forward an explanation that the current occurs when two metals are combined, directly or through the body's electrolyte of the biological being. The cause of the current lies in the materials, and the frog is a simple indicator of the phenomenon. Quotation Volta from a letter addressed to the editor of a scientific journal:
Conductors of the first kind( solids) and second kind( liquids), when they come into contact in some combination, generate an impulse of electricity, today it is impossible to explain the causes of the phenomenon. The current flows in a closed loop and disappears if the integrity of the circuit is broken.
pillar Leptu was introduced by Giovanni Fabroni in a series of discoveries, who reported that when two electroplating plates were placed in water, one began to break down. Therefore, the phenomenon is related to chemical processes. And Volta, meanwhile, invented the first power source, which served for a long time for the study of electricity. The scientist was constantly looking for ways to enhance the effect of electroplating pairs, but he did not find it. During the experiments, the design of a voltaic column was created:
- Zinc and copper circles were taken in pairs in close contact with each other.
- The resulting pairs were separated by wet circles of cardboard and placed on top of each other.
It is easy to guess that we got a series connection of current sources, which, summing up, amplified the effect( potential difference).When touched, a new device caused a perceptible blow to a man’s hand. Like the experiments of Mushenbruck with a leyden jar. However, it took time to repeat the effect. It became obvious that the source of energy is of chemical origin and is gradually being renewed. But getting used to the concept of new electricity was not easy. The voltaic column behaved like a charged Leyden jar, but. ..
Volta is organizing an additional experiment. Equips each of the circles with an insulating handle, brings it into contact for a while, then opens and conducts a study with an electroscope. By that time, the Coulomb's law had already become known, it turns out that zinc charged positively, and copper negatively. The first material gave electrons to the second. For this reason, the zinc plate of the volt column is gradually destroyed. To study the work appointed a commission, which presented the arguments of Alessandro. Even then, by inference, the researcher found that the voltage of individual pairs is added up.
Volta explained that without wet circles laid between metals, the design behaves like two plates: copper and zinc. Amplification does not occur. Volta found the first row of electronegativity: zinc, lead, tin, iron, copper, silver. And if we exclude intermediate metals between the extreme ones, the “driving force” does not change. Volta established that electricity exists while the plates touch: the force is not visible, but is easily felt, therefore, it is true. On March 20, 1800, the scientist wrote to the President of the Royal Society of London, Sir Joseph Banks, who was first approached by Michael Faraday.
English researchers quickly discovered that if water was dropped on the upper plate( copper), gas was released at the specified point in the contact area. They did the experiment from both sides: the wires of a suitable circuit were enclosed in flasks of water. Gas investigated. It turned out that the gas is combustible, it stands out only from the only side. The wire was noticeably oxidized from the opposite. It is established that the first is hydrogen, and the second phenomenon occurs due to an excess of oxygen. It was established( May 2, 1800) that the observed process is the decomposition of water under the action of an electric current.
William Crookshank immediately showed that it was acceptable to do the same with metal salt solutions, and Wollaston finally proved the identity of the volt column to static electricity. As the scientist put it: the action is weaker, but has a longer duration. Martin Van Marum and Christian Heinrich Pfaff charged a leyden jar from an element. And Professor Humphrey Davy found that clean water cannot serve as electrolyte in this case. On the contrary, the more the liquid is capable of oxidizing zinc, the better is the volt column, which is quite consistent with Fabroni's observations.
Acid greatly improves performance by speeding up the process of generating electricity. In the end, Davy created a coherent theory of the Volt pillar. He explained that metals initially possess a certain charge, when closing contacts causing an element. If the electrolyte is able to oxidize the surface of the electron donor, the layer of depleted atoms is gradually removed, revealing new layers capable of producing electricity.
In 1803, Ritter assembled a pillar of alternating circles of silver and wet cloth, a prototype of the first battery. Ritter charged him with a volt pillar and watched the process of discharge. The correct interpretation of the phenomenon was given by Alessandro Volta. And only in 1825, Auguste de la Reve proved that the transfer of electricity in a solution is carried out by ions of a substance, observing the formation of zinc oxide in a chamber with pure water separated from the neighboring membrane. The statement helped Berzelius create a physical model in which an electrolyte atom appeared to be composed of two oppositely charged poles( ions) capable of dissociating. The result was a slender picture of the transfer of electricity over a distance.