The Romance of Modern Chemistry

CHEMISTRY AND ELECTRICITY change might in fact be represented as follows: iron + copper sulphate-> copper+iron sulphate. Now something exactly similar happens when a piece of zinc is employed instead of the knife-blade. If we were to put a few bits of zinc foil in a solution of copper sulphate, and leave them for some time, we should find that they had entirely disappeared, and that in their place a spongy mass of metallic copper lay at the bottom of the solution. This simple little experiment shows that the change zinc + copper sulphate->copper + zinc sulphate is one which takes place spontaneously. A little reflection will convince the reader that the forces which bring about any spontaneous natural change can, if properly harnessed, be made to do work of various kinds. The force of gravitation, under the influence of which an unsupported body falls to the ground, is harnessed for the service of man in innumerable ways, as, for instance, in the grandfather’s clock. The con- version of quicklime + water into slaked lime is a change which takes place spontaneously, and, as we have seen in an earlier chapter, is accompanied by a considerable increase in bulk. The force of this ex- pansion has occasionally been utilised in blasting coal, by the simple device of packing quicklime into a hole in the coal and moistening it with water. The chemical forces set to work immediately, and the mechanical force of the expansion which accompanies the reaction suffices to split the coal apart. The Daniell cell is another illustration of this same general principle. It is simply a device whereby the spontaneous chemical change zinc + copper sulphate -*copper+zinc sulphate is harnessed and made to do work. The chemical energy of the cell is con- 294