<P> In current practice, zinc is produced by electrowinning of zinc sulfate or pyrometallurgical reduction of zinc with carbon, which requires an energy input . The energy produced in the lemon battery comes from reversing this reaction, recovering some of the energy input during the zinc production . </P> <P> From 1840 to the late 19th century, large, voltaic cells using a zinc electrode and a sulfuric acid electrolyte were widely used in the printing industry . While copper electrodes like those in lemon batteries were sometimes used, in 1840 Alfred Smee invented a refined version of this cell that used silver with a rough platinum coating instead of a copper electrode . Hydrogen gas clinging to the surface of a silver or copper electrode reduces the electric current that can be drawn from a cell; the phenomenon is called "polarization". The roughened, "platinized" surface speeds up the bubbling of the hydrogen gas, and increases the current from the cell . Unlike the zinc electrode, the copper or platinized silver electrodes are not consumed by using the battery, and the details of this electrode do not affect the cell's voltage . The Smee cell was convenient for electrotyping, which produced copper plates for letterpress printing of newspapers and books, and also statues and other metallic objects . </P> <P> The Smee cell used amalgamated zinc instead of pure zinc; the surface of amalgamated zinc has been treated with mercury . Apparently amalgamated zinc was less prone to degradation by an acidic solution than is pure zinc . Amalgamated zinc and plain zinc electrodes give essentially the same voltage when the zinc is pure . With the imperfectly refined zinc in 19th century laboratories they typically gave different voltages . </P> <Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2015) (Learn how and when to remove this template message) </Td> </Tr> </Table>

Fruits that can be used as a battery