John Frederic Daniell (1790-1845)
John Frederic Daniell was born in London, England, on 12 March 1790 as the son of a lawyer. He received a good education, while attending private school. He received either an earned or a honorary degree from Oxford University.
Upon completing school with a good background in technology, he went to work for a relative who owned a sugar refinery. While working in the refinery he improved its technological operations and processes. After awhile he left the refinery to enter the field of education and research by taking a position as professor of physics at the University of Edinburgh, Scotland, when just 23 years of age. In 1823, he was elected as a Fellow in the Royal Society of London.
In addition to his classes in physics he also worked as a chemist at the university, and began research in meteorology. Concurrent with his university responsibilities he successfully managed the Continental Gas Company in 1817.
Daniell 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.