« НазадПродовжити »
ing other combinations of metals. A number of other couples or elements have been found that will permit a reversing chemical
Fig. 5.—How Storage Batteries Differ in Construction. A–Automo
bile Type. B-Couple Type. C—Glass Jar, Open Type. DLarge Wooden Tank Type for Heavy Duty Service.
action, but most of these are of such a nature that they are interesting additions to a scientist's laboratory rather than contributions to industrial progress. Storage battery plates have been made up entirely of active material. An experimenter has used a positive plate made entirely of litharge (PbO) mixed with ammonium sulphate (NH4)2SO4, which is pressed into the desired shape. Chemical treatment converts the plate to lead peroxide. The negative plate is the conventional lead type. This is really a lead plate type, and must be considered as distinct from the non-lead types.
It is a known fact that almost any primary cell can be made to
Fig. 6.—Showing Method of Grouping Storage Cells to Form
Starting, Lighting and Ignition Batteries.
have some of the characteristics of a storage battery. The experiments in the electrolysis or decomposition of water by using silver or platinum electrodes demonstrates that these substances can be used, though their prohibitive cost renders them only of scientific interest. Zinc has been used for a negative element instead of lead, the surface zinc being converted into zinc sulphate, which dissolved into the electrolyte. Using zinc instead
of lead gives an increase in voltage, the normal 2.2 augmenting to 2.5 volts. A reduction of weight is also possible, because zinc plates can be lighter than lead one of the same capacity.
The disadvantage is the formation of zinc deposits during charging in the shape of clusters or “trees,” which may short-circuit the cell by extending across to the positive element or increase the sediment by dropping to the bottom. Another disadvantage is that the solution will vary in density at different heights. The zinc sulphate is taken from the top of the liquid during charging. Attempts have been made to prevent this by placing the plates horizontally and thus having practically the same density electrolyte surrounding each plate. The fault of this arrangement is that gas bubbles polarize the cell by collecting between the plates. In a vertical plate cell the bubbles rise to the top of the electrolyte and burst, liberating the confined gas, which reaches the atmosphere easily in an open-type cell and through a vent in the sealed types.
Another cell has a negative plate consisting of thin sheet copper amalgamized with zinc. The positives are made of lead leaves perforated with numerous small holes and riveted together, and are formed by the Planté process. The copper-alkali-zinc battery of Lalande and Chaperon and improved by Edison is reversible in action and can be used as a storage battery. When discharged, the positive plate is porous copper; on charging, the decomposition of the electrolyte follows, metallic zinc is deposited on the regative plate, while the porous copper becomes oxidized on the positive. The electrolyte becomes potassium hydrate. This cell may really be considered the ancestor of the modern Edison cell. This storage battery has been used commercially in a limited way, but is not really practical because of its low voltage, that of one cell being but seven-tenths of a volt. That means that three times as many cells would be needed to obtain a certain voltage given by the smaller number of lead plate cells. The weight factor is a serious one that militates against the wide commercial use of low voltage cells. The lead plate type has many practical advantages, but its ability to stand rapid discharge, its great efficiency and its high E.M.F. are among the most important ones.