Fig. 82.
The first storage cells were made of plain lead plates, rolled up in such a way that they were close to each other, but did not touch. These were placed in dilute sulphuric acid. They were charged in alternate directions several times, until the lead became properly acted upon, at which time the cell would furnish a current.
A great improvement was made in 1881, by Faure, who coated the plates with red lead.
Fig. 83.
The method now generally practiced is to cast a frame of lead, with raised right-angled ribs on each side, thus forming little depressed squares, or to punch a lead plate full of holes, which squares or holes are then filled with a pasty mixture of red oxide of lead in positive plates, and with litharge in negatives. In a form called the chloride battery, instead of cementing lead oxide paste into or against a lead framing in order to obtain the necessary active material, the latter is obtained by a strictly chemical process.
Fig. 82 shows a storage cell with plates, etc., contained in a glass jar. Fig. 83 shows a cell of 41 plates, set up in a lead-lined wood tank. Fig. 84 shows three cells joined in series. Many storage cells are used in central electric light stations to help the dynamos during the "rush" hours at night. They are charged during the day when the load on the dynamos is not heavy.