Electrolysis

(e-lěk-trol'e-sis.) [From Gr. lyo, to loosen or disengage. ] (Chem.) To those substances which, like water, are resolved into their elements by the voltaic current, the term electrolyte has been applied by Faraday, to whom the principal discoveries in this subject and the nomenclature are due. Electrolysis is the decomposition by the voltaic battery; the positive electrode was by Faraday called the anode, and the negative electrode the kath ode. The products of decomposition are io nes; katione, that which appears at the kath ode, and ani one, that which appears at the anode. By means of the battery, the compound nature of several substances which had previously been considered as elements has been determined. By means of a battery of 250 couples, Davy, shortly after the discovery of the decomposition of water, succeeded in decomposing the alkalies po ta and soda, and proved that they were the oxides of the hitherto unknown metals pota ium and sodium. The decomposition of po ta maybe demonstrated with the aid of the battery of4 to 6 elements in the following manner: a small cavity is made in apiece of solid caustic po ta , which is moistened, and adr op of mercury placed in it. The po ta is placed on apiece of platinum connected with the positive pole of the battery. The mercury is then touched with the negative pole. When the current pa es, the po ta is decomposed, oxygen is liberated at the positive pole, wh ilo the pota ium liberated at the negative pole amalgamates with the mercury. On distilling this amalgam out of contact with air, the mercury pa es off, leaving the pota ium. The decomposition of binary compounds, that is, bodies containing two elements, is quite analogous to that of water and of po ta ; one of the elements goes to the positive, and the other to the negative pole. The bodies separated at the positive pole are called electro-negative elements, because at the moment of separation they are considered to be charged with negative electricity, while those separated at the negative pole are called electro-positive elements. One and the same body may be electro-negative or electropositive, according to the body with which it is as so0ciated. For instance, sulphur is electro-negative towards hydrogen, but is electro-positive towards oxygen. The various elements may be arranged in such a series that any one in combination is electro-negative to any following, but electro-positive toward all preceding ones. This is called the electro-chemical series, and begins with oxygen as the most electro-negative element, terminating with pota ium as the most electro-positive. E. is too expensive to be employed in the separation of the commercial metals from their compounds,but this proce is largely applied in the operations of electro typing and electroplating. [s. 322]