John Daniell (1790-1845)

John 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 zinc with mercury. His version was the first battery that produced a constant reliable source of electrical current over a long period of time.

To make the Daniell cell, a copper plate is placed at the bottom of a glass jar. Copper sulfate solution is poured over the plate to half-fill the jar. Then a zinc plate is hung in the jar as shown and a zinc sulfate solution poured very carefully into the jar. Copper sulfate is denser than zinc sulfate, so the zinc sulfate "floats" on top of the copper sulfate.