THE STORAGE OF ELECTRICITY. 



359 



I 

 Mill' 



Plante's Accu- 

 mulator. 



be as large as possible. He accomplished both of these ends with 

 economy of space by winding large plates into a spiral form, they 

 being separated from each other by strips of rubber. 



In charging this battery, care must be exercised that the cur- 

 rent be not too strong ; otherwise the gases would 

 be sent off too rapidly for the lead to take them up, 

 and they would then rise to the top of the liquid and 

 escape into the air. The electrical energy which 

 separated them would thus be lost. It accordingly 

 takes a long time to charge a new Plante battery to 

 its full capacity. After being subjected to the cur- 

 rent for a day or two, if the plates be removed and 

 examined, it will be found that the one which re- 

 ceived the oxygen has changed its physical char- 

 acter : instead of having a smooth surface, it pre- 

 sents a spongy appearance, having little holes and 

 cavities in it, and thus exposes a larger superficial 

 area. 



If the battery be now discharged, and be again 

 subjected to the charging current, it will be found 

 that a much stronger current may be used than at first, without 

 any gas escaping. This is owing to the much larger surface ex- 

 posed and to the spongy character of it. 



This original charging of a new battery, to change the charac- 

 ter of the lead surfaces, has been termed formation, and, inasmuch 

 as only one plate is altered by 

 a charge in one direction, a 

 complete formation consists 

 in a charging in two direc- 

 tions. 



As the .process of electrical 

 formation is necessarily an 

 expensive one, it was thought 

 that the same end could be at- 

 tained by mechanical means. 

 Plante" himself suspended the 

 lead plates, for a few days, in strong nitric acid. The acid does 

 not attack the lead, but seems to dissolve out small impurities, 

 which are distributed throughout the metal, leaving it in a much 

 more porous condition than after electrical formation. 



Others cut the plates into fine fringes, thus exposing a large 

 surface with a small weight of lead. 



D'Arsonval, instead of using plates, employed lead shot, think- 

 ing to get the largest surface for the given weight. The particles 

 could be effective, however, only under the condition that they 

 were in good contact with the wires leading to the battery. After 



Plant e's Arrangement of Plates. 



