328 Prof. F. Horton on High Potential 



plates, for the plates supplied by some makers last much 

 longer than those of others. 



When this type of small storage-cell was first made it was 

 usually provided with an indiarubber cover, but it was 

 afterwards thought that the contact of the rubber and the 

 lead was the cause of rotting which occurs. The lead rods 

 of the electrodes were therefore covered with short glass 

 tubes to prevent this contact ; and this device has generally 

 been found to lengthen considerably the life of the cell. 

 More recently, wooden tops well soaked with paraffin-wax 

 have been substituted for the rubber and glass tubes ; but 

 these wooden lids have been found by the writer to be quite 

 as bad as the old indiarubber ones. About 20 per cent, of 

 the positives of a new battery of 320 such cells recently fitted 

 up in this laboratory rotted through in the course of 3 months. 

 The remaining positives, and the new ones replacing those 

 spoilt, were therefore covered with glass tubes where they 

 pass through the wooden covers; but though, as usual, this 

 increased the length of service of the plates, after a few 

 months broken positives were continually being found and 

 the battery was never reliable. 



The rotting of the positive plate in this way is due to 

 electric conduction across the lid of the cell which is wet 

 with sulphuric acid. In the case of the wood and india- 

 rubber covers which fit tightly round the lead, the action goes 

 on more rapidly than when the rods from both plates pass 

 loosely through glass tubes. The rotting may be prevented 

 altogether by doing away with the cover. It is then 

 necessary to adopt some other device for keeping the plates 

 in position and to prevent the splashing of the acid when 

 the cell is being charged. It would be convenient to have 

 the glass cells made with ridges to keep the plates vertical, 

 but such cells cannot be obtained at the present time. In a 

 long row of cells in series the connecting wires can be made 

 to keep the plates in position, but a safer device is to cut a 

 strip of thin celluloid of width equal to the distance apart of 

 the [dates and to bend this into a f| and place it between the 

 plates of the cell. The top of the celluloid separator should 

 be below the level of the acid in the cell, and a small hole 

 should be made in the top of it to allow the gases to escape 

 when the cell is being charged. The splashing of the acid can 

 be prevented in the usual way by covering the surface with 

 a thin layer of oil ; the liquid petroleum sold by chemists for 

 medicinal purposes does very well. A battery of secondary 

 cells arranged in this way has been working satisfactorily 

 for several months. 



