current passed through the cell restores the chemicals to an active condition so that they can supply en e.m.f.
There are ordinarily three cells in a 6-volt storage battery.
THE LEAD CELL
A typical storage battery with a cut out section of one of the cells is shown in Fig. 13. Note that there are several positive and negative plates in this cell and a porous wood or hard rubber separator between each plate and a bottom support. The separators are so constructed that they will allow the electrolyte to pass through them readily.
The lead plates contain holes or grooves which are filled with a paste made up of red lead or litharge. Alternate plates are connected to different terminals, those connected to the negative terminal being one more in number than those connected to the positive terminal. The plates are placed in a containing vessel and a 20 per cent. solution of sulphuric acid added. A current of electricity is then caused to flow through the cell for a number of hours, the result leaving the paste in one, the form of spongy lead. At the same time, the plate at which the current enters the cell is, converting the paste into lead peroxide. Finally, one plate will be coated with spongy lead, forming the negative plate of the cell , while the other plate is coated with lead peroxide and is termed the positive plate. The cell is now charged and will deliver a current for a certain length of time. This current will flow from the cell in a direction opposite to that of the charging current, the potential being 2.1 volts when the cell is fully charged.
A cell of the above construction is known as the “Exide” and is employed very extensively for radio purposes.
THE ACTION OCCURRING IN THE LEAD CELL
Before we consider the action of the cell it might be well to summarize the above. We have learned that--
The storage cell (also known as the secondary cell or accumulator) is a type of electro-chemical cell, that differs from the primary cell in that for renewal it merely needs to have current flow through it from an outside source.
By conversion of electrical energy into chemical energy, the storage cell forms a portable and convenient source of electrical energy which can be employed when any other source would be out of the question or where it is inconvenient to have a generating plant running continuously.
