Brief Historical Sketch of the Lead Bat The lead storage battery of to-day exists in several distinct types, and as each is the survivor of many unsuccessful attempts, and as development has been gradual, it is con venient to treat it historically.
About the year 1860 Plante, experimenting with a number of electrolytic cells, placed a couple of lead plates in a vessel contaimng weak sulphuric acid, through which, in series with a galvanometer, he passed an electric current. After the current had flowed for some time in one direction, he stopped it, and, bringing the two cell terminals together, was surprised to find from a reverse swing of the galvanometer, still in circuit, that the cell gave back some of the electrical energy that had been applied to it_ Repetition of the experiment showed that the cell slowly but steadily gained in capacity for storing energy, while occasional reversals greatly accelerated the gain.
The explanation of the phenomenon as we now understand it is this: Metallic lead, when placed in sulphuric acid, is immediately at tacked, with the formation of a thin slan of lead sulphate, which, being insoluble, protects the metallic lead inside and prevents further action. Electrolysis, however, converts the sulphate upon the positive to peroxide of lead and permits the sulphuric acid to work a little further into the metal beneath; and it is thus that the action is cumulative and the amount of lead in a porous or °active') state con tinually increases. Electrolysis affects the nega tive, however, merely in reducing the lead sul phate to metallic lead, so there is here but little cumulative action, and hence occasional reversal is necessary to build up the thin sldn of °active materialP on both plates together.
Months of charge, discharge and reversal were required to build up a layer sufficiently thick to rnalce a battery of useful capacity. Hence other inventors set about to shorten this arduous process, lcnown as "formation,/' and finally Faure, in France, and Brush, in America, about simultaneously discovered that they could apply to the plates a thick coating of lead oxide, made into a sort of putty-like paste with sulphuric acid, which, by means of a single slow charge, was converted into thoroughly porous active material.
Subsequent improvements on Plante's proc ess have shortened it until now it is about as quick and as cheap as Faure's process, so that at the present time both are successfully em ployed, the Faure very much the more extensively.
Plante and Pasted Types The Plante and °paste& types as now used differ very distinctively in their design, though electrically the difference is much less than would be expected. The Plante plate consists of pure lead, upon the surface of which there is °formed') a thin layer of °active material' having a thicicness of the order of a few hundredths of an inch. The layer is necessanly thin in order to prevent its peeling off readily; hence a very large surface is required, and this is usually obtained by making the lead plates in the form of a number of parallel transverse leaves, as shown in Figs. 13 and 14.
The surface is increased by this construc tion anywhere up to 8 or 10 times that of a plain sheet of equal superficial area.
The °pasted)) (Faure) type, on the other hand, is characterized by a relatively thick mass of porous active matenal, retained by an open work grid or lattice of lead-antimony alloy, as shown in Figs. 6, 7 and 8.
Both types of plate can be used as either positive or negative, but certain characteristics make the one or the other better suited to particular classes of service, as will appear hereafter.
Negative Exide Negative.— The negative plate of a lead storage battery, at least theoretically, is quite a simple matter; the sponge lead which constitutes the active ma terial has considerable mechanical tenacity and is therefore relatively easy to hold in place upon the skeleton frames or ogrids" to which it is applied. There is no destructive action upon the lead-antimony alloy of which these grids are made, and they may therefore be as light as methods of manufacture will permit. Fig. 6 shows a negative grid of the type which is now standard in the United States, and which is still best known under its original name of the “Exide.* Fig. 7 shows a cross-section of the same grid, and shows how the active ma terial occupying the interior spaces is locked shown in Fig. 9 is used. This plate may be considered as a development of the exide type, inasmuch as the active material is held within two protecting surfaces, which, in the case of the box plate, consist of finely perforated lead sheets, while in the exide type they consist of parallel bars with relatively large openings between.