Daniell cell

The Daniell cell is a type of electrochemical cell invented in 1836 by John Frederic Daniell, a British chemist and meteorologist, and consists of a copper pot filled with a copper (II) sulfate solution, in which is immersed an unglazed earthenware container filled with sulfuric acid and a zinc electrode.

The Daniell cell was a great improvement over the existing technology used in the early days of battery development.

The definitions of electrical units that were proposed at the 1881 International Conference of Electricians were designed so that the electromotive force of the Daniell cell would be about 1.0 volts.

In the above wet-cell during discharge, nitrate anions in the salt bridge move into the zinc half-cell in order to balance the increase in Zn2+ ions.

A 0.5 inch diameter zinc rod hung inside this ox-gullet tube suspended from wooden supports.

Daniell states that a porous earthenware tube may be used instead of the ox gullet for practical ease but this arrangement will produce less power.

[9] Over time, copper buildup will block the pores in the earthenware barrier and cut short the battery's life.

Nevertheless, the Daniell cell provides a longer and more reliable current than the Voltaic pile because the electrolyte deposited copper, which is a conductor, rather than hydrogen, which is an insulator, on the cathode.

With an operating voltage of roughly 1.1 volts, it saw widespread use in telegraph networks until it was supplanted by the Leclanché cell in the late 1860s.

A disadvantage of the gravity cell is that a current has to be continually drawn to keep the two solutions from mixing by diffusion, so it is unsuitable for intermittent use.

A variant of the Daniell cell was invented in 1837 by the Guy's hospital physician Golding Bird who used a plaster of Paris barrier to keep the solutions separate.

A surprising result from Bird's experiments was the deposition of copper on the porous plaster and in veins running through it without any contact with the metal electrodes.

Bird himself had to carefully examine his apparatus for inadvertent contact, perhaps through the growth of copper "whiskers", before he was convinced of the result.

[13][14] John Dancer, a Liverpool instrument maker, in 1838 was the first to take commercial advantage of the unique features of the Daniell cell for copper plating.