ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Daniell cell. Invented by the British chemist John Frederic Daniell (1790-1845), the Daniell cell (left) is made from two half-cells, the electrolytes of which are separated by a porous partition. The positive electrode is copper immersed in copper sulphate solution, the negative electrode is zinc immersed in dilute sulphuric acid. Zinc ions migrate across the porous partition, continuously forming zinc sulphate, while copper is plated out onto the copper electrode. It is the movement of ions which creates the electrical current of about 1.1 volts, which can be measured with a voltmeter (right).
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