Modern Views of Electricity (Volta's Force)


I THINK that the difficulty which Mr. Burbury expresses on p. 439 (March 12), under the above heading, probably rests on a misapprehension. He says: “When zinc is isolated, a negative charge is on it, and therefore at an outside point there is a positive slope of potential upwards from the zinc.” My statement, on the contrary, is that a piece of zinc immersed in an oxidizing medium possesses no charge so long as it is isolated, but experiences a lowering of potential by reason of the chemical tendencies of its surface-film—i.e. the contiguity of a number of negatively charged oxygenations. In this film, indeed, there is an electrical double-layer, consisting of equal opposite charges, the negative facing the zinc, the positive facing outwards; but there is no charge such as will produce the slightest effect at an external point. Contact with copper of course changes all this; displacing negative electricity from zinc to copper across the junction, from copper to zinc through the air. It is this displacement which affects all external points; and it is this which electroscopic experiments have displayed. There is nothing whatever to be detected in the neighbourhood of a piece of isolated zinc, unless its surface-film itself be explored. The range of its effect is sharply bounded by the thickness of its infinitesimal air-film, on which the whole of the molecular strain is thrown: much as is expressed by Mr. Chattock in the latter half of his letter on p. 367.

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LODGE, O. Modern Views of Electricity (Volta's Force). Nature 43, 463 (1891) doi:10.1038/043463d0

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