132 FIRST YEAR COURSE IN GENERAL SCIENCE 



may be used instead of two metals. There must be chem- 

 ical action between the liquid and one metal, or there will be 

 no current. Such a combination is called a cell, and two or 

 more cells make a battery. Electricity, produced in this way 

 is called current electricity or Voltaic electricity, from Volta, 

 one of its discoverers. (LABORATORY MANUAL, Exercise 

 XIV.) 



The two pieces of metal, the liquid between them, and the 

 wire connecting them make a circuit, or path for the current 

 of electricity. The ends of the metals where the conducting 

 wire is attached are the electrodes. If this circuit is broken 



Simple Cell Battery 



FIG. 66. A SIMPLE CELL AND A BATTERY OF THREE CELLS 



The wider piece of metal represents zinc, the other copper. Weak 

 acid acts more strongly upon zinc than upon copper. The current starts 

 with the zinc, is conducted by the acid to the copper, and thence by wire 

 back to the zinc. 1. How many substances are there in the circuit? 2. 

 What change would be produced if the wire were broken? 



This battery contains two different liquids as well as two metals. The zinc 

 in weak acid is in a porous cup, which stands in a jar of blue vitriol solution. 

 The current passes in the same direction as in a simple cell, but its quantity 

 and intensity vary with the number of cells and the connection of the plates. 



by separating the conductors at an electrode, or by taking 

 one metal from the liquid, no current passes. 



At the instant of breaking the circuit, and of connecting it 

 again, a little spark at the electrodes shows the presence of 

 electricity. The heat of this spark is sufficient to light 

 the gas at a burner constructed for " self-lighting." An 



