CHAPTER IV.
VARIOUS VOLTAIC CELLS.
49. Single-Fluid and Two-Fluid Cells. The simple cell (§ 45) is a single-fluid cell. The liquid is called the electrolyte, and this must act upon one of the plates; that is, chemical action must take place in order to produce a current. The simple cell polarizes rapidly, so something must be used with the dilute sulphuric acid to destroy the hydrogen bubbles. This is done in the bichromate of potash cell.
In order to get complete depolarization—that is, to keep the carbon plate almost perfectly free from hydrogen, it is necessary to use two-fluid cells, or those to which some solid depolarizer is added to the one fluid.
50. Open and Closed Circuit Cells. If we consider a voltaic cell, the wires attached to it, and perhaps some instrument through which the current passes, we have an electric circuit. When the current passes, the circuit is closed, but when the wire is cut, or in any way disconnected so that the current can not pass, the circuit is open or broken. (See "Study," § 266.)
Open Circuit Cells are those which can give momentary currents at intervals, such as are needed for bells, telephones, etc. These must have plenty of time to rest, as they polarize when the circuit is closed for a long time. The Leclanché and dry cells are the most common open circuit cells.
Closed Circuit Cells. For telegraph lines, motors, etc., where a current is needed for some time, the cell must be of such a nature that it will not polarize quickly; it must give a strong and constant current. The bichromate and gravity cells are examples of this variety. (See "Study," § 286.)
Fig. 39.