The Romance of Modern Chemistry

CHEMISTRY AND ELECTRICITY the fused salt itself, decomposition took place, with the result that the metallic part of the salt was liberated at one wire (the cathode), and the acidic part of the salt at the other wire (the anode). Investigation, indeed, has shown that the passage of an electric current through a salt solution consists in a general movement of the metallic part towards the cathode, and a general move- ment of the acidic part in the opposite direction; but most obvious to the onlooker is what happens at the wires or electrodes. What the observer sees taking place at the electrodes is sometimes only the secondary, not the direct, result of electrolysis. I1 or instance, if we were to pass a current through a solution of common salt, or sodium chloride, to give it the systematical chemical name, the metallic part of the salt, the sodium, would be liberated primarily at the cathode. Any particle of sodium, however, which was thus liberated, would immediately be set upon by the surrounding water molecules; hydrogen gas would be evolved, and caustic soda would be formed in solution round the cathode. The action of water on sodium prevents our obtaining this metal by the electrolysis of an aqueous solution of any sodium salt. Sometimes the wire or plate which forms the anode is attacked and dissolved by the acidic part of the salt which is being electrolysed. An interesting example of this is furnished by the electrolysis of a solution of copper sulphate between copper electrodes. During this process the metallic part of the salt, the copper, is deposited on the cathode, which therefore becomes gradually heavier. The sulphate, or acidic part of the salt, instead of being liberated at the copper anode, attacks it, forming copper sulphate, which dissolves in the water. So the net 298