126 



ELEMENTARY LESSONS ON [CHAP. HI. 



the copper portion dipped into the other cup. The 

 difference of potential between the first and last cups 

 is again proportional to the number of pairs of metal 

 strips. This arrangement, though badly adapted for 

 such a purpose, is powerful enough to ring an electric 

 bell, the wires of which are joined to the first zinc and 

 the last copper strip. The electrical action of these 

 combinations is, however, best understood by studying 

 the phenomena of one single cup or cell. 



152. Simple Voltaic Cell. Let a glass jar be 

 taken and filled with water, having a few drops of 

 sulphuric acid added to it (Fig. 71). Let two clean 



strips, one of zinc 

 Z, and one of copper 

 C, be separately 

 placed in the dilute 

 acid without touch- 

 ing. If they are 

 now examined by 

 an electroscope or 

 electrometer it will 

 be found that they 

 are all zinc, copper, 

 and water, at very 

 nearly the same 

 .potential ; neither 

 fof them is negative 

 or positive. A still 

 more delicate elec- 

 trometer will show 

 that both the zinc 

 and the copper are very slightly negative, while the acid is 

 slightly positive. If no acid has been added to the water, 

 the water will be slightly negative, and the metals slightly 

 positive ; but in either case the metals will be as nearly 

 as possible at the same electrical potential. Now, let a 

 piece of copper wire be affixed to the top of each strip 



Fig. 71. 



