334 



Introduction to the Study of Science 



lead plate. This substance is brownish in color. It is a compound of 

 oxygen and lead, and is called lead peroxid. By way of the plate, 

 marked ( ), hydrogen is thrown off. (See electrolysis of water, 

 page 115.) 



After ten to fifteen minutes open switch No. 1, to cut out the dry 

 cell, and close switch No. 2 to connect the electric bell with the storage 



cell. In the discharge the sub- 

 _ stances are changing and gener- 

 I ating electric current. The lead 

 peroxid is converted into me- 

 tallic lead, which is now soft, 

 spongy, and more easily changed 

 at the next charging. As the 

 cell is small, it has a very limited 

 capacity; but with repeated 

 charging and discharging it in- 

 creases in capacity. That Is, 

 the chemical substances are 

 more easily and abundantly 

 developed in charging, and they 

 in turn produce a larger amount 

 of electric energy in active 

 circuit. 



FIG. 112. Experimental storage cell. 

 Fasten two pieces of sheet lead, A and B, 

 to a piece of wood, C, and connect each 

 with copper wires, E and F, completing 

 the circuit with dry cells, D, and a switch, 

 S\. Make a second circuit with an elec- 

 tric bell and a switch, S%, as shown in 

 diagram. To charge the cell close Si. 

 To discharge the secondary cell, open Si 

 and close S^. 



Principle of the secondary cell. Electricity is not stored in 

 the secondary cell, for just as much escapes in charging through 

 the negative plate as is transmitted through the positive plate. 

 The electric current in interaction with the lead and sulfuric 

 acid solution forms chemical substances which, when the battery 

 is connected in circuit, produce electrical energy. 



SUMMARY 



Increase in electrification of steam railways is due to greater use 

 of water power, improvement of electrical generators, transmission 

 lines, and motors. 



When a wire is moved through a magnetic field, a current is gen- 

 erated. This illustrates the principle of an electric generator. A 

 generator is a machine for transforming mechanical energy into elec- 

 trical energy. 



When a current is passed through a wire in a magnetic field, the 

 wire moves in a definite direction. This illustrates the principle 



