240 ELEMENTS OF ELECTRICAL ENGINEERING. 



a current immediately starts to flow through the circuit, leaving 

 the cell at the copper or carbon electrode (the cathode) and enter- 

 ing the cell at the zinc electrode (the anode). This current decom- 

 poses the sulphuric acid (H 2 SO 4 ), the hydrogen is liberated at 

 the copper or carbon cathode and escapes from the cell as a gas, 

 and the sulphuric acid radical (SO 4 ) which is set free at the zinc 

 anode combines with the zinc and forms zinc sulphate (ZnSO 4 ) 

 which goes into solution. The combination of Zn and SO 4 

 develops more energy than is required for the decomposition of 

 the H 2 SO 4 so that the chemical action in this cell is a source of 

 energy. 



The available energy of the reaction which takes place in the 

 above cell may be greatly increased by providing an oxidizing 

 agent in the neighborhood of the cathode so that the hydrogen 

 may be oxidized and form water (H 2 O) at the moment of its 

 liberation by the current. The energy of this oxidation is then 

 added to the available energy of the total chemical action in the 

 cell* 



103. Voltaic action and local action. Two kinds of chemical 

 action are to be distinguished in a voltaic cell : (a) The chemical 

 action which depends upon the flow of current, and does not 

 exist when there is no current ; and () the chemical action which 

 is independent of the flow of current, and which exists whether 

 the current is flowing or not. 



The chemical action which depends on the current is propor- 

 tional to the current, it is essential to the operation of the voltaic 

 cell as a generator of current, its energy is available for the main- 

 tenance of the current, and it is called voltaic action. 



The chemical action in a voltaic cell which is independent of 

 the flow of current does not help in any way to maintain the 

 current, it represents absolute waste of materials, and it is called 

 local action. Local action takes place more or less in every type 



* The student is referred to Professor H. S. Carhart's Primary Batteries, published 

 by Allyn and Bacon,* Boston, Mass., for full information on primary batteries, and 

 primary battery tests. 



