Note:  Do not rely on this information. It is very old.

Local Action

Local Action in electric batteries is caused by the presence in plates of commercial zinc of impurities in the form of small particles of metals electro-negative to zinc, such as iron. These particles, when in the exciting fluid, form short-circuited voltaic couples with the zinc, and produce rapid waste. The action does not occur with pure zinc, and can be to a large extent obviated by amalgamating the surface of commercial zinc with mercury.