Page:Electricity (1912) Kapp.djvu/58

54 conditions is about 1.4 volts, drops to a much smaller figure. If left standing idle a little while, the cell recovers and its e.m.f. rises again to 1.4 volts. It will be obvious that by joining up in the same sense a sufficient number of Daniell cells, or cells of any other type, any desired voltage may be obtained between the ends of the series of cells.

A special type of cell is the so called accumulator or storage cell, in which both electrodes are lead and some oxide of lead. This is a so-called reversible cell. On forcing a current through in one direction, the oxide on the plate where the current enters the electrolyte (dilute sulphuric acid) is reduced, and the other electrode becomes more highly oxidised. Thus the cell is charged. If then the cell is connected to any working circuit, it gives a current in the reverse direction; the previously strongly oxidised electrode being reduced and the other becoming more oxidised, the cell discharges. These lead accumulator cells are made up into storage batteries, which are extensively used in electricity works.