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metal, which result in the production of a lead spray, which falls as a powder when cooled. Nitric acid is used to dissolve this powder, which precipitates as lead chloride when hydrochloric acid is added. After this material is washed and dried it forms the basis of the filling of the negative plates. A mixture of this lead chloride and zinc chloride is melted in crucibles and poured into moulds, which produce small tablets about 34 of an inch square and of a thickness varying from 14 to 5/16 of an inch, depending upon the thickness of the negative plate. These tablets are then assembled in special moulds and held in place by recesses, into which they fit and which prevent movement. They are kept at a distance of about .2 inch from each other and from the mould edges. Molten antimonious lead is then poured in to fill the spaces between the tablets, and to insure a proper flow of metal it is forced into the mould under approximately 75 pounds pressure. Upon cooling, the result is a solid lead grid, in which the small squares of active material are imbedded. The next step is to reduce the lead chloride by placing the plates in a dilute solution of zinc chloride, each plate being separated from its neighbor by a slab of zinc. By assembling the plates in this manner the equivalent of “short circuiting” a cell is obtained, and the lead chloride is reduced to metallic lead. The zinc chloride is removed from the plates by thoroughly washing them.
A new form of negative plate which is now manufactured to replace the chloride type just described consists of a pocketed grid, the openings of which are filled with litharge paste and afterward covered with perforated lead sheets, which are formed by casting integrally with the grid. The grid used for the positive plate is composed of a 5% antimony-lead alloy and is about 17/16 inch thick, having circular holes about 34 of an inch in diameter, staggered so that the nearest points are about 3/32 of an inch apart. Close spirals are rolled up of corrugated lead ribbon of the same width as the plate thickness, and these are forced into the circular holes of the plate. The spirals are formed into active material by the electro-chemical process, and during this the spirals expand sufficiently so they fit closer to the grid sides. This form of positive is known as the Manchester plate
and is illustrated at Fig. 12. The box negative plate, the construction of which has been previously described, is also shown at Fig. 12.
"Iron Clad” Exide Battery.—The capacity of the conventional pasted type Exide plate rises in service for a time and then gradually becomes less. The initial rating is conservative, however, so that if a battery is given a proper initial charge it will give its rated discharge at the start. This will gradually increase in use, so that the output becomes greater, and then there is a dropping off from the maximum. This rise in capacity when the battery
is first put into service results from the increasing porosity of the active material on the positive plate. The more porous this active material the better the electrolyte diffuses through it and more lead peroxide is brought into action on each cycle of charge and discharge. This increase in capacity is evidently made at the expense of the positive active material, because as more is brought into action the active mass becomes softer, and the time comes when some of the material must be dislodged when the battery is charged and it will settle to the cell bottom in the form of sediment. This explains why the life of a battery is shortened by too much charging. The capacity will augment just as long as the rate of increase in the porosity of the active material is greater
than the rate at which the active material loosens from the plate. After a period of use the loss of material will become greater than the gain in porosity, and it is evident that the cell will begin to lose capacity when this condition is reached.
It is evident that if the positive active material could be prevented from dropping off and still be maintained in a healthy operating condition that the plates would have longer life. While improvements have been made from time to time in the construction of the elements, the new form of positive was evolved. This was accomplished by keeping the active material in position by utilizing a pencil of lead peroxide surrounding a conducting core and enclosed in a porous tube having a sufficient elasticity so that as the active material expanded and contracted, because of alterations in its molecular structure, the containing tube compensated for these variations. The positive plate of the “Iron Clad” Exide consists of an alloy framework comprising top and bottom bars integrally connected by conducting cores of the same metal. The uniform pencils of active material surround these cores and are protected by horizontally laminated rubber tubes.
Each tube is formed with narrow vertical ribs diametrically opposite each other, which take the place of the spacing ribs on the ordinary wooden separator and at the same time re-enforce the tube. By thus protecting the active material and holding it in position it remains active for a considerable time. Excellent conductivity and increased accessibility for the electrolyte are obtained, thereby making it possible to secure a relatively high output from a comparatively small quantity of active material. This battery, which is illustrated at Fig. 17 A, having the positive plate shown at B, was given its name because of its remarkable durability. The negative plate of this battery, which is shown at Fig. 17 C, is of the same general construction as the regular Exide negatives, but is made somewhat thicker in order to compensate for the longer life of the positive plate.
The wood separator used between the plates of this battery is a sheet of chemically treated wood and is flat on both sides. No rubber separators are required, inasmuch as the positive plate provides its own separator in having the ribbed rubber tubes to retain