3. Name five objects outside of the laboratory that have been acted upon by electrolysis. How in each case?
4. Why is table ware silver plated? Why are many iron objects nickel plated?
5. How is the electrolysis of water pipes prevented?
6. Two grams of silver are to be deposited on a spoon by a current of 1 ampere. Find the time required.
7. How long will it take to deposit 20 g. of silver in an electroplating bath if a current of 20 amperes is used?
8. If 1000 g. of silver are deposited on the cathode of an electrolytic reduction plant in 10 minutes, what is the current intensity employed?
(2) The Storage Battery and Electric Power
287. Differences Between Voltaic and Storage Cells. Voltaic cells in which electric currents are produced by the chemical action between metal plates and an electrolyte are often called primary batteries. In voltaic cells one or both plates and the electrolyte are used up or lose their chemical energy in producing the current and after a time need to be replaced by new material, the chemical energy of the electrolyte and of one of the plates having been transformed into electrical energy.
A different proceeding obtains with another type of cell. This is called a storage battery, or an accumulator. In these cells, the same plates and electrolyte are used without change for extended periods, sometimes for a number of years. For this reason storage batteries have displaced many other types of cells, and they are now used (a) to operate many telephone, telegraph, and fire-alarm circuits, (b) to work the spark coils of gas and gasoline engines, (c) to help carry the "peak" load upon lighting and power circuits and (d) to furnish power for electric automobiles. Since a storage battery can deliver an electric current only after an electric current from an outside source has first been sent through it, they are often called secondary batteries.
288. Construction and Action of a Storage Cell.—The common type of storage cells consists of a number of perforated plates made of an alloy of lead and a little antimony. (See Figs. 265, 266, 267.) Into the perforations is pressed a paste of red lead and litharge mixed with sulphuric acid. The plates are placed in a strong solution (20 to 25 per cent.) of sulphuric acid. The plates are now ready to be charged. This is accomplished by sending a direct current from an electric generator through the cell. The hydrogen ions are moved by the current to one set of plates and change the paste to spongy metallic lead. The sulphions move to the other set of plates and change the paste to lead oxide. This electrolytic action causes the two plates to become quite different chemically so that when the cell is fully charged it is like a voltaic cell, in having plates that are different chemically. It has, when fully charged, an E.M.F. of about 2.2 volts. The several plates of a cell being in parallel and close together, the cell has but small internal resistance. Consequently a large current is available.