ELECTRICAL INVENTIONS 223 



into copper and chlorine ions. The copper, which a moment 

 before was in a neutral molecular state, now in its ionic condition, 

 bears an excess of two positive charges on each ion. To accom- 

 plish this change two electrons or negative charges have been left 

 on the copper plate. Since countless numbers of copper mole- 

 cules are rapidly making this change, the copper plate is nega- 

 tively charged. At the opposite side of the battery, metallic 

 copper is depositing on the carbon. The positively charged copper 

 ions change to a neutral molecular state by drawing negative 

 electrons from the carbon, so that the latter is left with a positive 

 charge. There is thus produced a difference in electric pressure, 

 and a current flows in the wire in consequence. In all the litera- 

 ture of batteries it has been the custom to speak of the current 

 as flowing in the wire from the positively charged carbon to the 

 negatively charged copper. Now physicists believe that it is the 

 movement of the electrons from the copper plate to the carbon that 

 makes the current in the wire. In spite of this, however, we follow 

 the old custom and speak of the current as flowing from the posi- 

 tive to the negative pole. Before the free ends of the copper and 

 the carbon are connected in such a simple battery, it will be 

 noticed that chemical action is going on rapidly at the copper 

 strip, while little or no action occurs at the carbon. Hydrogen 

 bubbles are rapidly evolving as the copper takes the place of the 

 hydrogen in the acid. When, however, the elements of the 

 battery are connected by the wire, the hydrogen nearly ceases 

 to appear at the copper pole, but accumulates rapidly on the 

 carbon. The copper of the plate drives off the hydrogen in the 

 molecules of acid next to it. This nascent hydrogen is very 

 active, and replaces the hydrogen of the next adjacent molecules. 

 So the hydrogen is passed from molecule to molecule across the 

 battery somewhat as a football might be passed down a line of 

 players. Thus it arrives at the carbon pole without being 

 visible in transit. 



Such a battery will not operate very long, however, for the 

 bubbles of gas accumulate on the positive plate, and prevent the 



