CH. XXTX. 



THE VOLTAIC PILE. 



261 



which is the one now commonly used for simple experi- 

 ments. Jn this battery each piece of zinc is joined to one 

 of copper, and where the two are not united they are in the 

 same cup, so that the liquid acts as a link to them. We 

 know now what Volta did not know, that a chemical change 

 is going on between the zinc and the acid water, which sets 

 the action going, but we do not yet know exactly what the 

 electricity itself is. The movement in Fig. 46 begins on 

 the left-hand side at z. Here the current is set up by the 

 action of the acid and water upon 

 the zinc, and is passed on to the 

 copper, c ; then along the wire #, to 

 the next z, and so on till it reaches 

 the last cup, when it is carried by 

 the wire b back to the first piece of 

 zinc, and so the round is completed. 

 This battery is called the ' Crown 

 of Cups,' but though it is so simple, 

 it has not become as famous as the 

 second battery made by Volta, which 

 is still called the * Voltaic Pile ' (see 

 Fig. 47). In this battery the metals 

 are laid one above the other, and 



j a i z, Zinc, c, Copper, a, a, Rod 



have small pieces of card or flannel con nectin g the top layer of 

 between them which are wetted with 

 salt and water. The battery ends 

 with a plate of zinc at the bottom, and of copper at 

 the top, and these are connected by the wire, a a. The 

 action passes round this battery just as it did through the 

 cups, and if the wire, a a, is cut in the centre and tipped 

 vrith charcoal (which, being a bad conductor, causes the 

 electricity to pass with difficulty), a bright spark will glow 

 between the points as long as the battery is at work. Early 



FIG. 47. 

 The Voltaic Pile (Fownes). 



copper with the bottom layer 

 of zinc. 



