Page:1902 Encyclopædia Britannica - Volume 25 - A-AUS.pdf/48

28 are rectangular and the plate, is thicker. The positive lower or higher one, horizontal ribs are seen. To give grid has quite a different shape (Fig. 6). For the quickest greater strength, thicker vertical ribs are obtained by cutdischarges (up to onel hour or less) the grid has the form ting out one tooth of each rack at intervals. The grooves of thin vertical ribs T ^th inch apart, strengthened at inter- are about -j^th inch apart and ^ inch deep. The positive vals by horizontal ribs. Between the vertical ribs are deep plates are about inch thick, and are formed (that is, narrow grooves, which hold the active material. The nega- covered with pertive grid is like Fig. 5, the holes being rectangular in shape. oxide) by charging them, and leaving them on open circuit (repose) alternately. Later, charging and discharging are substituted. Here, as asssaasss H1 in Plante’s work, niiiiiuifmiuiimi charging and discharging become more prolonged as the formation proceeds. As much as five or six weeks is required. The negative plate is a pasted plate. Litharge* mixed with sulphuric acid is placed in the holes of a lead grid, to which, before pasting, is Fig 7 given a superficial Fig. 7 shows the general appearance of the two-hour coating of peroxide discharge cell, illustrating the method of connecting, and by making it a terFig. 9. the greater thickness of the positive over the negative minal in an acid plate; also, the clearance between the plates and the bottom bath and charging it as a positive for a short time. This of the cell. There are other types of grids besides those gives a greater attachment between the grid and the spongy mentioned, to suit the varying conditions of electrical lead when subsequently reduced. The negative plate is work, for high discharge, traction, &c. about x4y th inch thick. Another cell of pasted type is that known as the There are many other types of cells. An interesting “ Hart ” accumulator. The positive and negative plates, one is that known as the Lithanode. Originally, this was are Hart cell similar in size and shape, are pasted an attempt to prevent local action by making the positive of with red lead and litharge respectively. The peroxide alone, and to form it so slowly that its mechanical grid is in the form of lattice-work, arranged alternately on arrangement and strength would facilitate diffusion and either side, with strong leaden ribs running diagonally prevent disintegration. It has not yet been largely used. across the plate. The active material in each plate is split the type of cell may he, it is important to attend to up into a number of small pellets, each of which is gripped theWhatever following working requirements :-—(!) The cells must be fully hard on its surface equal to the maximum demand, both in discharge by means of a leaden rate and capacity. (2) All the cells in one series Erecting ce s "* lip attached to the ought to be equal in discharge rate and capacity. This involves similarity of treatment. (3) The cells are erected on grid and turned strong wooden stands. Where floor space is too expensive, they over by a special can be erected in tiers ; but if possible this should be avoided. process. In joining They ought to lie in rows, so arranged that it is easy to get to up, a special ter- one side (at least) of every cell, for examination and testing, and need be to detach and remove it or its plates. Where a second minal is used. The if tier is placed over the first, sufficient clearance space must be lugs are first faced allowed for the olates to be lifted out of the lower boxes. The cells up against each are insulated by supporting them on glass or mushroom-shaped other and tightened oil insulators. If the containing vessels are made of glass, it is to put them in wooden trays which distribute the weight by a temporary desirable between the vessel and insulators. To prevent acid spray from master connector. filling the air of the room, a glass plate is arranged over each This then gives way to a non-corrosive bolt, which is cell. The positive and negative sections are fixed in position conically tapered and gives a large connecting surface. with insulating forks or tubes, and the positive terminal of one Fig. 8 gives a view of the cells and also of the connector. cell is joined to the negative of the next by burning or bolting. If the latter method is adopted, the surfaces ought to be very Mixed Type.—In this type, of which the “Tudor” clean and well pressed home. The joint ought to he covered by cell is a well-known example, the positives are prepared by vaseline or varnish. When this has been done, examination ought to be made of each cell to see that the plates are evenly “Tudor” a ^)lire formation from a carefully-made spaced, that the separators (glass tubes or ebonite forks between il. lead casting, and the negatives by pasting. ce the plates) are in position and vertical, and that there are no scales lig. 9 shows the unformed positive plate. A or other adventitious matter connecting the plates. The floor of mould is made by supporting narrow gun-metal racks on the cell ought to be quite clear ; if anything lies there it must be each side of a cast-iron frame. The teeth of the racks removed. (4) To mix the solution a gentle stream of sulphuric form vertical grooves in the faces of the casting; and as acid must be poured into the water (not the other way, lest too heating cause an accident). It is necessary to stir the narrow spaces are left between one rack and the next great whole as the mixing proceeds and to arrange that the density is