The reverse reactions take place on charge. The iron and nickel compounds are probably hydrated, but are here treated as pure oxides, for the sake of simplicity. It will be noted that the same amount of KOH is decomposed, according to the left-hand members of these equations, as is re-formed, simultaneously, as shown on the right. For this reason, the chemical composition, or specific gravity, of the solution does not change appreciably throughout the cycle of charge and discharge.

CHAPTER II

How Storage Batteries Differ in Construction-Batteries Using Other Than Lead Plates-Details of Planté Process-Advantages of Faure Process -Lead Plate Construction-Gould Plates-Combination Faure and Planté Batteries-Exide Plates-Exide "Iron Clad" Plate-Edison Alkaline Battery-Function of Separators.

How Storage Batteries Differ in Construction.-It is not reasonable to expect that any one type of storage battery can be applied universally. Naturally, batteries must be proportioned for the work they are to do. Batteries for stationary work in power plants can be of the open-cell type; those intended for vehicle or boat use should be sealed to prevent danger of splashing out the electrolyte. Various forms of storage batteries are illustrated at Fig. 5. The stationary type in glass or rubber jars is used for isolated lighting plants, telephone, telegraph and signal service and yacht lighting. The larger stationary cells are assembled in leadlined wood tanks, and are used for electric railways, stand-by service in central stations for lighting and power and in large isolated lighting plants. Special types in rubber jars are assembled in trays for electric vehicle service, and still others for trainlighting service. The usual starting, lighting and ignition battery for automobile use is a unit in which three or more cells are imbedded in insulating compound and carried in a substantial wooden case. The usual practice is to burn all the connecting straps to the plate group terminals and cover the whole with sealing compound. Special gas vents are needed with these batteries. The "couple" type is carried in glass jars and is widely used for signal, fire alarm and private telephone service.

Storage Batteries Using Other Than Lead Plates. While there is really only one make of cell that is commercially practical that does not use lead plates, this being the Edison, inventors have endeavored to improve storage battery action for some time by try

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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-Automobile 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 (NH)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