British chemist and meteorologist (1790–1845)
Daniell was the son of a London lawyer. He started work in the sugar-refining factory of a relative and, on the basis of early researches, he was elected to the Royal Society at the age of 23. He was appointed as first professor of chemistry at the newly opened King's College, London, in 1831.
Daniell invented a number of scientific instruments, including a hygrometer (1820) to measure humidity in the atmosphere. His theories on the atmosphere and wind movements were published in Meteorological Essays and Observations (1823). He also stressed the importance of moisture in hothouse management.
Daniell is best remembered for his introduction in 1836 of a new type of electric cell. The voltaic cell, introduced by Alessandro Volta in 1797, lost power once the current was drawn. This was due to bubbles of hydrogen collecting on the copper plate and producing resistance to the free flow of the circuit (polarization). With the growth of telegraphy there was a real need for a cell that could deliver a constant current over a long period of time. In the Daniell cell a zinc rod is immersed in a dilute solution of sulfuric acid contained in a porous pot, which stands in a solution of copper sulfate surrounded by copper. Hydrogen reacts with the copper sulfate. The porous pot prevents the two electrolytes from mixing, and at the positive (copper) electrode, copper is deposited from the copper sulfate.
