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Local Action; Amalgamatimg the Zinc

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-348

2025-12-28

326

 When a strip of zinc is placed in the acid, hydrogen bubbles are given off from its surface. This is due to the setting up of an electric current between impurities in the zinc and the zinc itself through the acid and is called local action. The existence of these impurities can be proved by leaving the zinc in the acid for five minutes, when it will be found covered with a black deposit that can be wiped off.

If a particle of carbon is at A (Fig. 1), a local current will be set up between it and the zinc, and as a result hydrogen. will be set free. In order to prevent this action, which reduces the surface of the plate for the main current, the zinc is cleaned by dipping it in dilute sulphuric acid and then rubbing with mercury. This has the property of dissolving the zinc and forming a covering over the particles of carbon as shown at B in Fig. 1, thus preventing the carbon from coming in contact with the acid.