VOLTAIC ELECTRICITY. 



374. The Electric Current. When a strip of 

 copper and one of zinc are placed in 



dilute sulphuric acid, the two strips 

 being connected above the acid by a 

 wire conductor, a current of elec- 

 tricity is produced. In fact, two 

 currents, opposite in kind and direc^ 

 tion, are simultaneously produced, 

 but to avoid confusion the negative 

 current is ignored. When refer- 

 ence is made to the direction 

 of the current, it means the direction of the positive 

 current. The apparatus here described is called a Voltaic 

 or Galvanic element. 



375. Direction of the Current. For this pro- 

 duction of the electric current, it is necessary that the 

 liquid have a greater action upon one metal than upon 

 the other. The metal most vigorously acted upon con- 

 stitutes the generating or positive plate ; the other, the 

 collecting or negative plate. This relation of the plates 

 determines the direction of the current. In the liquid, 

 the current is from the positive to the negative 

 plate; in the mire, it is from the negative to the 

 positive. 



376. The Electric Circuit. When the wires 

 from the two plates are in contact, it is said that the 

 circuit is closed; when the plates are not thus in electric 

 connection it is said that the circuit is broken. 



(a.) When the circuit is closed, hydrogen is set free by the decom- 

 position of the liquid and rises from the surface of the negative 

 plate. The tendency of the hydrogen to adhere to the plate is one 



