Plante Positive.— The Plante plate is also subject to the continual, slow washing away of its lead peroxide, but the original layer is more durable than the peroxide made from red lead, so it lasts a considerable time in spite of its thinness. Moreover, all the while that the original layer is disintegrating and falling away, the electrolytic action is penetrating farther into the metallic lead of the plate and forming fresh active material, in the manner of the Plante formation, and thus there is a balance between loss and gain, and the capacity of the plate is maintained for a long period, say about performs the electrochemical function of the plate.
The combined mechanical and electrical en durance of this type of plate has given it a very broad field of application; its weight, roughly triple the pasted type, and its consequent cost constitute its chief limitations.
two or three times as long as in the case of the pasted plates. For effecting this extended life, however, there is required a large reserve of pure lead; so that in actual practice the Plante plaid weigh itom two Li, three 1.11111:b as much as pasted plates of equal capacity.
Figs. 13 and 14 show a Plante type of plate known in this country as the used largely in Europe, and consisting of an integral one-piece casting; while Fig. 10, though actually a negative, may be used as illustrating the Gould type, made from rolled sheet lead, by a spinning process.
In this country and in England a modified Plante plate, known as the "Manchester?' has largely superseded all of the above, chiefly on account of its superior mechanical construction. The Plante plate is made of pure lead, because this metal is attacked by the electrolytic action at about the right rate to replace the loss of lead peroxide; hut pure lead is very soft, hence these plates are much subject to buckling and breaking. The Manchester plate (Fig. 15) differs in that a rigid grid, or frame, of anti Ironclad Type.— During the past five years a third type of positive plate has come into prominence in this country, founded on the principle first successfully developed by Phili part, in France, about the year 1898. This plate, known as the gronclad,D is shown in Fig. 18, and differs from those heretofore dis cussed in that a porous exterior envelope retains the active material in place, so that the large reserve necessary with other types is here unnecessary.
mony-lead alloy furnishes mechanical strength, while snial!, pure lead, spirally wound "but toils° (Fig. 16) inserted in holes of the grid (Fig. 17) furnish the active material which The plate consists of a number of cylindrical pencils, one of which is shown in section in Fig. 19; a central-lead ant' mony core fur nishes support and conductivity for the stir rounding mass of active material, itself again enveloped by the perforated hard rubber tubes (Fig. 18). The perforations in the tube consist of minute saw cuts of the order of one one hundredth inch wide; and so effective are these tubes as "retainers" that the plates which em ploy them have a life approximating 1,000 come the °separators? Considerations of space, weight and electrical resistance all demand that adjacent positive and negative plates be main tained as close together as possible, yet without touching anywhere. To fulfil these require ments spacers or separators of some sort are inserted between them. Here again countless schemes have been tested out, but to-day prac tically only two types have survived, and these often used in conjunction.
The older of the two is the perforated rub ber separator, shown in Fig. 20, as a flat sheet of perforated hard rubber, and often, when used alone, provided with a series of parallel ridges on one side, to afford sufficient acid cycles of charge and discharge, being two to three times that of the flat plates, Fig. 11, in which the active material is left exposed.
The life of the Ironclad plate is thus about the same as that of a Tudor or Manchester plate, while its capacity-weight ratio is about on a par With the pasted types.
With the Ironclad plate loosening and wash ing out of the active material is reduced to a space between plates. When so used, however, even though the holes be small, "trees" of lead are very apt to develop on the negative plates, which in time find their way through to the positives and cause short-circuits.
The perforated rubber separator used by itself is therefore not satisfactory and has been almost entirely replaced by the wood separator, examples of which are shown in Figs. 21 and 22.
minimum, and, contrary to what might be ex pected, the protective rubber tube offers but very slightly increased resistance to the passage of the electric current.