Page:Popular Science Monthly Volume 38.djvu/373

Rh 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 current 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 Planté battery to its full capacity. After being subjected to the current for a day or two, if the plates be removed and examined, it will be found that the one which received the oxygen has changed its physical character: instead of having a smooth surface, it presents 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 exposed and to the spongy character of it.

This original charging of a new battery, to change the character 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 directions.

As the process of electrical formation is necessarily an expensive one, it was thought that the same end could be attained by mechanical means. Planté 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, thinking 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