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Page:Popular Science Monthly Volume 38.djvu/374

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THE POPULAR SCIENCE MONTHLY.

becoming oxidized, a large proportion of the shot did not satisfy this condition, and the method was abandoned.

Lead wire was then substituted for the shot, and was found very efficient. Lead wire, however, is very expensive; and, to obviate this, Simmen invented a very ingenious and economical PSM V38 D374 Lead shot accumulator.jpgLead-shot Accumulator. process of manufacturing it. This consists in pouring molten lead into heated iron boxes, the bottoms of which are perforated with suitable-sized holes. The metal flows through these holes, and is suddenly cooled by dropping into cold water. The wire thus manufactured does not possess the same regular character as drawn wire, but is perfectly suited to the purpose for which it was intended. The wire, after removal from the water, is compressed into sheets, which, under the microscope, resemble, in texture, coarse felt. Simmen placed pieces of this felt in frames of cast lead, which acted as supports and improved the electrical contact.

Reynier sought to increase the exposed surface by taking thin lead foil and forming it into accordion-plaits. The compressed plaits were then attached to supporting frames. When Reynier's battery was charged, an unexpected phenomenon PSM V38 D374 Lead wire plate.jpgLead-wire Plate. presented itself. The lead, in taking up the oxygen, had increased its weight. At the same time it had been transformed into peroxide of lead, which is less dense than pure lead—i. e., a pound of it would occupy more space than a pound of the metal. The plaits, therefore, required more room, and in expanding they buckled the frames holding them. To obviate this, Reynier then cut a longitudinal opening in the plaits after they had been placed in the frame, and when the battery was charged this opening was closed by the expansion.

In all the styles of lead batteries mentioned, the oxide of lead on one plate and the spongy metallic lead on the other were formed from the lead of the electrodes themselves. Camille Faure, however, lessened the loss of time in formation by using lead plates as a support, and covering them with a paste made of some powdered oxide of lead mixed with sulphuric acid. This paste he kept in place by covering with sheets of felt. When the charging current was connected, the oxide on one plate was changed to a