252 ELEMENTS OF ELECTRICAL ENGINEERING. 



sure that the grids are not connected by a block of detached ac- 

 tive material. Sulphatation and buckling are usually due to long- 

 continued standing at discharge, which is brought about by an 

 unnoticed internal short-circuit of the cell. 



A storage cell should not be allowed to stand discharged for 

 any length of time. 



A storage battery standing unused should be partly discharged 

 and immediately recharged at least once per week. 



When a storage battery is to be put out of service for a long 

 time, it should be partly discharged, the electrolyte should then 

 be drawn off from each cell and pure water poured in immedi- 

 ately, then the battery should be short-circuited until the voltage 

 (on open-circuit) falls to about 0.5 volt per cell. The cells 

 should then be rinsed with several changes of water, allowing 

 the plates to soak thoroughly in each, and the final washing water 

 should be drawn off and the plates allowed to dry. When the 

 battery is again put into commission it is only necessary to pour 

 in electrolyte and give the battery a long-continued over-charge. 



Sulphatation of the grids of a lead storage cell consists * of 

 the conversion of portions of the active material wholly into lead 

 sulphate. This pure sulphate is a very poor conductor and, once 

 it is formed, it is difficult to make it act as anode or as cathode 

 and thus reconvert it to lead peroxide or to spongy lead respec- 

 tively. A layer of pure lead sulphate sometimes forms between 

 the active material and the metallic lead of the grid, and some- 

 times the external surface of the active material becomes covered 

 with a crust of pure sulphate. Pure lead sulphate is white and 

 whenever white spots appear on the grids of a lead storage cell, 

 the cell should be subjected to a very long-continued over-charge 

 in the attempt to reduce the pure lead sulphate into active 

 material. 



The normal discharge rate of a lead storage cell, on the basis 

 of an eight-hour discharge, is from 6 to 7 amperes per square foot 



*It is claimed by some authorities that Sulphatation consists in the formation of hy- 

 drated lead sulphate. 



