The Romance of Modern Chemistry

CHEMISTRY AND ELECTRICITY of mutual indebtedness. It is a long time now since Volta first showed how chemical forces might be utilised in the production of an electric current—how chemical energy might be converted into electrical energy. The chemical cell which Volta constructed consisted merely of a plate of copper (C) and a plate of zinc (Z) immersed in water to which a little sulphuric acid had been added Volta found that if the two plates were joined by a wire outside the liquid, then an electric current passed through the wire. The electric current obtained from such a cell is not manu- factured out of nothing: there is a quid pro quo. While the cell is running and producing cur- rent, chemical changes are going on which mean a lowering of the store of energy in the cell. As has been pointed out by the Fig. 12.—Volta’s Cell. author of “The Romance of Modern Electricity,” this is exactly analogous to what happens in the case of a “grandfather’s clock.” The store of energy in the clock- weights at any time depends on the height to which they have been wound by muscular force, and the driving of the clockwork for any given time is possible only at the cost of so much of the energy residing in the weights; they will be lower down at the end of the period than they were at the beginning. Similarly we can get a current out of a chemical cell only in so far as chemical changes go on which lower the amount of available energy in the cell. The nature of the changes which may thus be utilised in the pro- 291