STORAGE BATTERIES. The storage, secondary or reversible battery, and accumu lator are different terms applied to a form of eell based on the principle demonstrated by Faraday in 1834, that chemical and electrical energy were mutually convertible. In 1859, after experiments with various metals, Plantil decided upon the use of lead plates in dilute sulphuric acid, because in discharge both plates were active ; that is, not only (lid the per oxide of lead plate combine with hydrogen. but the reduced metallic lead combined with oxygen. Plante's cell was originally eonst meted with two plates of sheet lead, separated by gutta-percha strips, one sheet being laid over the other, with two gutta-percha strips between them, and two more laid on the upper sheet, as shown at A, Fig. 1.
They were then rolled together and clamped, as shown at II, a strip of lead being left attached to the corner of each sheet in cutting, by which connection could be made. The sheets thus rolled together were placed in a jar of glass or ebonite, containing a 10 per cent. solution of sulphuric acid. The jar had an ebonite cover, with binding screws to which the connecting strips were attached ; also clamps for holding wires to show the heating effect of the discharge.
The electrical preparation of the plates was ac complished by charging them with a battery of two or more cells, one cell being insufficient to overcome the resistance from polarization. The current was continued till the oxygen evolved at the positive pole ceased to combine with the lead and was given off as gas. The cell was then disconnected from the battery, and discharged by making connection between its electrodes, and a fresh charge given in reverse order, and continued as before until gas was given off. This process was continued for several months. with intervening periods of repose, during which the cell remained charged, and the time of charging was increased from a few minutes on the first day to several hours subsequently. In like manner. the periods of repose were increased from hours to weeks and months. Three distinct periods are thus required in this process : that of charging, of repose, and of discharging, during each of which a distinct chemical reaction occurs. During, the charging, peroxide of lead collects on the plate connected with the + pole, and hydrogen on the one connected with the — pole. At first only a thin film of the peroxide is formed and a small amount of hydrogen collected. The plates are then discharged, and during the discharge the peroxide, which is insoluble in sulphuric acid, is reduced to monoxide, Phu, which is immediately reduced go sulphate of load by the acid present in the solution, while the oxygen atom taken from the peroxide unites with the lead on the opposite plate, forming monoxide, which, in turn, is reduced to sulphate, the result being a thin film of sulphate on each plate. The plates are then charged
in reverse order, and the sulphate on the plate, now connected with the -4- pole, is reduced by the oxygen to peroxide, while that on the opposite plate is reduced by the hydrogen to spongy lead, which adheres to the plate in a finely divided condition. As each subsequent charge, after discharge and reversal, produces the same result, each coating eontinnes to increase in thickness, and the spongy lead affording increased facility for the formation of the peroxide, the chemical reaction proceeds more rapidly. The increased thickness of the peroxide soon interposes a strong resistance to this reaction hence a period of repose previous to the dis charge becomes necessary. and during this period, local action, as it is called, takes place. This consists in the reduction of the peroxide to sulphate from the reaction of the sup porting lead plate. The metallic lead having a affinity for oxygen. the peroxide parts with the atom of its oxygen which unites with the lead, and the resulting monoxide is immediately reduced to sulphate by the acid. The result of the chemical reaction of the discharge having formed sulphate of lead on both plates, this sulphate lying next to the plates forms a resistance which impedes local action which takes place during the period of repose. The peroxide being limited in quantity and in close contact with the spongy lead, is rapidly reduced to sulphate, while the original peroxide coating on the other plate. from its greater thickness and the resistance of an excess of sulphate, is reduced much more slowly. These various chemical reactions result in an increased thickness of the peroxide deposit with each charge, while an increased thickness of spongy lead remains on the opposite plate after each reversal ; and when the process has been continued long enough to produce a sufficient thickness of each coating for a practically serviceable cell, the alternate charging and discharging with reversal is discontinued, and the cell being ready for use, it is always thereafter charged in the same direction. When the cell is put into practical use, these chemical reactions continue the same as during the forming process, sulphate being reduced to peroxide by each charge, and peroxide to sulphate by each discharge ; and the electric energy varies as to reaction, and ceases when the chemical affinities are satisfied. In the storage cell the electric energy must first be supplied from an external source, and the action, both chemical and electrical, is limited, dependent on the amount of electrical charge given.