jacket encases the entire cell. The most common storage battery in use today is the rechargeablelead-acid type used in automobiles. The first such battery was devised in 1859 byGaston Plante, a French physicist.The 12-volt battery commonly used in automobiles has six 2-volt cells connectedin series. The electrolyte is dilute sulfuric acid. Each electrode is made ofconnected plates. Between the two sets of plates are thin separators made ofwood, glass, or plastic that do not enter into the chemical reaction. Theseparators are porous so that electrolyte can flow around the plates.Each plate has a framework, or grid, made of a hard alloy of lead andantimony. The grid of a new positive plate is filled with lead dioxide (PbO2). Thenegative plate contains spongy metallic lead.Lead dioxide attracts electrons more strongly than metallic lead and startsdrawing current when the external circuit is closed. This leaves lead ions (Pb++)in the negative plate. Each of these ions draws a sulfate ion (SO4=) from thesolution, making lead sulfate (PbSO4) in the negative plate.This leaves free in the solution two hydrogen (2H+) ions for each sulfate ionwithdrawn. Oxygen ions released by the lead dioxide join the hydrogen ions,forming molecules of water (H2O). This action keeps the positive plate clear todraw current. Since there is no polarization, the battery works as long as anyacid is left to furnish sulfate ions and until each plate contains lead sulfate only.Once this condition is reached, the battery can be recharged by sendingcurrent through it in reverse. This changes lead sulfate in the plates back to leaddioxide and spongy lead and restores acid to the solution. The nickel-cadmium battery, another rechargeable type, was first usedon a large scale in 1917 to help light the subway trains in Paris. Previously anatural gas system did the job, but when it exploded disastrously, costing manylives, the change was made.So-called "open" or "vented" nicke...
