(1.) Parallel currents in the same direction attract each other.
(2.) Parallel currents in opposite directions repel each other.
Fig. 228. Chemical action of electricity. Fig. 229.
Upon these two hang all the varied phenomena of electro-dynamics. That chemical action develops electricity we can perceive with the aid of the two cuts (figs. 228 and 229). If the wires be attached to the collecting-plate of a condenser of electricity and the metal plate of a cell, as shown in the figure (fig. 228), the electricity on the plate will be negative. If the operation be reversed, and the plate be put in connection with the acid, and the metal with the earth, the instrument will be charged with positive electricity. In the other case, when two cups are used, united by a magnet so that the solutions (one acid and the other alkaline) can by capillary attraction unite upon the binding of the magnet, and we place the wires as in fig. 229, the charge on the plate will be positive if it be in connection with the acid, and negative if in communication with the alkaline solution. Every time there is chemical action between two bodies in contact electricity is produced—positive on one negative on the other, and that is the fundamental principle of the voltaic pile.
The decomposition of water can also be effected by means of the electric current. If two tubes or vessels be placed in a vase of water, and the wires from the battery be inserted in them respectively, the oxygen will go to the platinum or positive pole wire, and the hydrogen to the zinc or negative pole. This decomposition or “splitting up” of components was termed Electrolysis by Faraday, who gave a series of names to the action and the actors in these phenomena (fig. 230).
Any liquid body, such as the water we have just decomposed for instance, Faraday termed an electrolyte; the surfaces where the current enters or leaves the body were called electrodes—the “ways,” from odos, a “way”; the entry is the anode; the leaving point the katode, from ana, “up,” and kata, “down.” The electrolyte is divided into two portions, “ions” (“movers”), which move towards the electrodes, which are positive and negative. In the case of the decomposition of water the hydrogen goes to the negative electrode, the oxygen to the positive.
Fig. 230.—Decomposition of water.