ELECTROLYSIS. I

f platinum plates attached to wires from a battery of two or more voltaic cells be dipped into pure water or pure hydrochloric acid, no change takes place in the liquid, and no current pa es; but if a little of the acid be added to the water, the liquid becomes a conductor, and allows the current to traverse it, while it also undergoes chemical decomposition in the proce . Substances which in aqueous solution conduct electricity are termed electrolytes; they include salts, acids, and bases. Di olved in chloroform, the same substances do not conduct electricity the reason being that they are present in a special condition in water. This condition is known as di ociation. It is supposed that in an electrolytic solution some or all of the molecules of the dis- - solved substance are broken up into their constituent atoms or radicles which are oppositely charged; such charged atoms or radicles are called tons, and the phenomenon is termed ton i zati on. The metallic atom or cation carries positive electricity; the acid or salt radicle is the anion, and carries negative electricity. In the case of an aqueous solution of sodium chloride there are sodium ions and chlorine ions present. These being modified by the charges they carry, do not exhibit in the solution the properties of the elements sodium and chlorine. When a current is pa ed through the solution, the electric forces direct the anions or chlorine ions to the positive pole or anode of the electrolytic cell, and the cations or sodium ions to the cathode or negative pole. At the anode the negative charge of the anion is neutralized, and the ion becomes an ordinary atom, and is liberated as chlorine gas. Similarly at the cathode, the positive charge on the cation is neutralized and the ion liberated as metallic sodium. This sodium at once attacks the water, forming sodium hydroxide in solution and liberating hydrogen, which bubbles off at the cathode. The whole proce is known as electrolysis, and the electrolytic cell is called a voltameter. In the electrolysis of copper sulphate copper electrodes are employed, and the copper ion, when liberated, is deposited on the cathode. Electrolysis forms the basis of many industrial proce es for the isolation and refining of metals, and is also used in electroplating and electrotyping.