In the year 1900, Thomas Edison in America and Valdemar Jungner in Sweden both invented storage cells using a solution of caustic potash as the electrolyte. Edison used iron for the negative plate and Jungner used cadmium. Both men used nickel
hydroxide for the positive plate.
Cadmium has certain advantages over iron, and present-day cells are mostly of this type, although it is found that the addition of a little iron to the cadmium improves the efficiency of the cells. The active material is in powder form and is enclosed in perforated pockets in specially constructed steel plates. The container is made of nickel-plated steel (Fig. 34.8).
Although more expensive, alkaline cells have a very much longer life than lead cells and also possess a number of other advantages. Large currents, such as would ruin a lead cell, may be freely taken from alkaline cells without ill effect, and they may be left for months in a discharged condition without harm. They are therefore very suitable for installation in railway rolling-stock and yachts for lighting and other purposes, as they require no special maintenance when out of use for extended periods. Many large ships, hospitals and public buildings are provided with alkaline-battery installations for emergency lighting. One disadvantage is that the e.m.f. of an alkaline ce1\ is only about 1.25 V, and this tends to fa1\ continuously on discharge. Five alkaline ce1\s in series give an e.m.f. about equal to that of three lead ce1\s.