1 8 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



the trace of hydrogen that is clinging to the carbon plate and 

 form H 2 SO 4 . In this cell, however, the greater part of the 

 liberated hydrogen has, of course, escaped, and the reversed 

 chemical action due to a reversed current cannot long continue. 

 Local action, on the other hand, being independent of current, is 

 not affected by a reversal of the current. 



9. The storage cell.* A voltaic cell which is free from local 

 action and in which all of the materials which take part in the 

 voltaic action are conserved in the cell, may be regenerated after 

 use by sending through it a reversed current. This regeneration 

 is due to the reversed chemical action that is produced by the 

 reversed current as explained in the previous article. A voltaic 

 cell that is adapted to be thus regenerated, that is, a voltaic cell 

 in which there is no local action and in which all of the materials 

 which take part in the voltaic action are conserved in the cell, is 

 called a storage cell. The process of regeneration is called 

 charging, and the use of the cell as an- electric generator is called 

 discharging. A storage cell always requires more energy to 

 charge it than is delivered by the cell during the discharge. 



The lead storage cell. The voltaic cell which, up to the 

 present time, has been found to be most satisfactory when used 

 as a storage cell, is a voltaic cell having a cathode of lead peroxide 

 (PbO 2 ), an anode of spongy metallic lead, and an electrolyte of 

 dilute sulphuric acid. The lead peroxide and the spongy metallic 

 lead are both converted into insoluble lead sulphate (PbSO 4 ) 

 when the cell is discharged. When this cell is charged, the 

 lead sulphate is converted back into lead peroxide and spongy 

 lead respectively. The lead peroxide and the spongy lead are 



*The description here given of the action of the lead storage cell is a simple 

 working theory of the cell. The actions as described do, no doubt, take place, but 

 they are complicated by more complex actions such as the formation of persulphates 

 at the anode and of subsulphates at the cathode. See The Theory of the Lead 

 Accumulator, by Friedrich Dolezalek (English translation by C. L. von Ende, 

 published by John Wiley & Sons). A good engineering treatise on the storage 

 battery is Storage Battery Engineering by Lamar Lyndon (McGraw Publishing 

 Company). 



