Energy efficiency
(1970-1845)
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Daniell was a British chemist and meteorologist. Born in London on March 12, 1790, Daniell got a degree from Oxford University. He became the first professor of chemistry at King's College in London in 1831 and taught there until 1845. He invented the Daniell Cell in 1836, which was a big improvement in the battery. His battery was the first reliable and lasting source of direct-current electricity. Because Daniell's battery was so reliable, it was used exclusively in the late 1830's to power British and American telegraph systems.

Among Daniell's other inventions was a new type of dew-point hygrometer to measure humidity and a pyrometer to measure the heat in a furnace. His other scientific work included using physical laws to explain the atmosphere, suggesting improvements in meteorological instruments and researching the effects of solar radiation.

aniell not only excelled because of his ability to make useful observation, classifications, and improvements in the physical sciences of his time; but he also demonstrated skill for scientific manufacturing enterprises with the development of a new process for general gas. His research in 1820 led to the invention of a dew-point hygrometer that measured relative humidity which afterwards became a standard instrument. His hygrometer was made with two thin glass bulbs that were hung from a base and joined with a glass tube. One of the glass bulbs held ether and a thermometer that collected and dissipated dew when the other bulb was slowly cooled and reheated. The condensing temperature was produced by evaporation of the ether. Daniell's hygrometer, as it was called, enabled the easy determination of vapor that existed in a given mass of atmosphere. The average temperature recorded by the device was the dew point. In 1823, he published Meteorological Essays which soon became a popular book. In a later edition he also discussed the meteorological effects of solar radiation and the cooling of the Earth. Daniell's Essay on Artificial Climate Considered in Its Applications to Horticulture showed the importance of humidity in greenhouses.

Then in the early 1830s, Daniell became deeply interested in the work of his friend Michael Faraday so turned to electrochemistry for his main research interest at that time. A major problem with the Volta pile was that it could not provide current for a sustained period of time. Sturgeon worked on the problem when in 1830 produced a battery with longer life than that of Volta by amalgamating the zinc. Contributing to the major problem with batteries was a thin film of hydrogen bubbles that formed over the positive electrode. The thin film of hydrogen caused increased internal resistance of the battery that reduced its effective electromotive force (voltage). This process of a thin film of hydrogen collecting on the electrode is known as polarization.

Daniell began experiments in 1835 in an attempt to improve the Voltaic battery with its problem of being unsteady and as a weak source of electrical current. His experiments soon led to remarkable results. In 1836, he invented a primary cell in which hydrogen was eliminated in the generation of the electricity. Daniell had solved the problem of polarization. In his laboratory he had learned to alloy the amalgamated zinc of Sturgeon with mercury. His version was the first of the two-fluid class battery and the first battery that produced a constant reliable source of electrical current over a long period of time. That is, the power remained constant with this type of battery upon repeated application without removing the which was a source of weakness in all single fluid batteries. Until now the current of other batteries declined rapidly. His placement of a barrier between the copper and zinc plates stopped the hydrogen from forming.

The Volta battery (pile) emitted free hydrogen by the electrolyte which then migrated to the positive copper pole. The hydrogen accumulated on the pole to form a barrier that soon stopped the flow of the current. Both single fluid and two-fluid batteries used solutions to create the electricity. Daniell's battery consisted of a cylindrical copper vessel that served as the passive plate (pole). Placed inside the outer copper vessel was a porous earthenware container or partition that held a zinc rod or active plate (pole). The space between the copper and the porous cup was filled with a solution of copper sulfate which was kept saturated by crystals of the salt lying on a perforated shelf. The porous cup was filled with dilute sulfuric acid. The porous earthenware kept the fluids from mixing without hindering the passage of current; it allowed ions to move through while the reaction of the cell was taking place. The contents of the battery had to be dismantled when not used to stop the chemical reactions and conserve the metals. The sulfate of copper that was in contact with the passive plate served to take up hydrogen. The amalgamated zinc rod (anode) had a binding screw. The top of the copper cylinder contained the other binding screw (cathode).

Daniell's last work on a gravity type of battery was later to become one of the most popular in the 1850's. He fused two electrolytes; copper sulfate (CuSO4) and zinc sulfate (ZnSO4). A copper electrode was placed in the bottom half of a glass battery jar, and then copper sulfate was added in crystal form. Next the zinc sulfate solution was floated on top of the copper sulfate. This approach decreased the need for a porous ceramic diaphragm to separate the two electrolytes, and decreased the internal resistance of the system. When the circuit was opened and let standing while open the copper ions would diffuse upwards and self discharge onto the zinc anode which resulted in loss of power. The operator added copper sulfate crystals to maintain a constant saturated solution that then could constantly produce its current.


Daniell's invetions


Daniell's hygrometer

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His research in 1820 led to the invention of a dew-point hygrometer that measured relative humidity which afterwards became a standard instrument. His hygrometer was made with two thin glass bulbs that were hung from a base and joined with a glass tube. One of the glass bulbs held ether and a thermometer that collected and dissipated dew when the other bulb was slowly cooled and reheated. The condensing temperature was produced by evaporation of the ether. Daniell's hygrometer, as it was called, enabled the easy determination of vapor that existed in a given mass of atmosphere. The average temperature recorded by the device was the dew point. In 1823, he published Meteorological Essays which soon became a popular book. This work is "the first attempt to collect scattered facts on the subject, and to explain the main phenomena of the atmosphere by physical laws. Daniell insisted on the paramount importance of extreme accuracy in meteorological observation, and kept a model record of atmospheric changes. He called attention to the necessity of attending to the moisture of hothouses, and caused a revolution in hothouse management." In a later edition he also discussed the meteorological effects of solar radiation and the cooling of the Earth. Daniell's Essay on Artificial Climate Considered in Its Applications to Horticulture showed the importance of humidity in greenhouses.

Interest in the atmosphere enabled Daniell to improve hothouse plant growing. He really revolutionized hot house management by stressing the value of atmospheric moisture. Daniell was the first to use physical laws in trying to explain the phenomenon of atmosphere. His work leading to improvements in hothouse management earned him the silver medal award from the Horticultural Society in 1824.

Daniell's pyrometer

In 1830, he invented a pyrometer that was successful in measuring heat. Daniell found that in fusing metals a liquid is constantly moved by the cooling of its exterior. His research in chemistry enabled him to produce gas from resin and measure very high temperatures. He also invented a water barometer in 1830.

He was the first professor of chemistry and meteorology at the then new King's College of London, and worked there from 1831 to 1845. While at King's College he was responsible for establishing a department of applied science. In 1832, he was awarded the Rumford Medal of the Royal Society of London for his earlier work with the pyrometer.


Daniell's battery

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The chemical reaction within the battery consisted of a decrease of zinc and an increase of copper; the zinc crowded out copper from its sulfate so that the copper sulfate continuously changed into zinc sulfate by replacement. Beard and Rockwell expressed the chemical reaction with the equation:

Zn + H2SO4 + CuSO4
ZnSO4 + H2SO4 +
Cu

A scheme of Daniell's battery - does not correspond to the real structure of it.

Daniell's nattery

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Daniell's nattery was called a constant battery because it did not evolve gas, and therefore did not polarize, supplying a constant current. It furnished the unit of electric potential, the volt, as a column of mercury did the unit of resistance, the ohm. The Daniell cell still used the familiar copper and zinc electrodes. The zinc electrode was put in a cup of unglazed earthenware and bathed in dilute sulphuric acid. The copper was surrounded by crystals of copper sulphate that maintained a saturated solution. Instead of releasing hydrogen, the electrons were furnished to the copper ions in the electrolyte, which plated out as copper metal on any nearby surface. The purpose of the cup was to keep the solutions separate while allowing electrical conduction by ion migration. If the solutions mixed, local action ruined the battery. When the cell furnished current, the zinc dissolved to form zinc sulphate solution, and copper from the copper sulphate plated out on the copper electrode.

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No gases were involved at all, so the cell did not polarize. The cell has a fairly large internal resistance, but this was not a serious defect in view of the small currents required, and actually proved an advantage in many applications. It also protected the cell against damage if shorted. The copper sulphate even kept algae under control. However, the porous cup, intended to keep the solutions separate, was rendered impervious after a time by deposition of copper on it as the cell operated.

 
   
 
 
 
     

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