The plates are now ready for pasting. They are placed on a smooth slab of stone or glass and pasted with a stiff mixture of red lead and sulphuric acid (two parts water to one part acid). The paste must be pressed carefully into the recesses of the plates with a flat stick. They are then laid aside to dry and harden. [Illustration: Fig. 72.—The Wood Separator.] After they have thoroughly dried they should be assembled as in Figure 73 with one positive plate between two negative ones. The wooden "separators" are easily cut out of wood with a saw and penknife. The thin wood used in the construction of peach baskets is the best for the purpose. The separators should be made the same size as the lead battery plates. Each group of plates is then placed in a jar containing a mixture of sulphuric acid and water (4 parts water to one part acid). In mixing the acid be very careful to pour the acid into the water, stirring the mixture slowly at the same time, and not the water into the acid. [Illustration: Fig. 73.—The Complete Element for a Storage Cell.] The plates are now ready for "forming." The binding-posts on the lugs of the plates may be secured from the carbons of some old dry cells. The simplest method of "forming" the plates is to use four gravity cells and "form" one storage cell at a time. [Illustration: Fig. 74.—A Battery of Home-Made Storage Cells.] Connect the positive pole (copper) of the gravity battery to the positive pole (center-plate) of the storage cell and the negative (zinc) of the gravity battery to the negative (outside plates) of the storage cell. Allow the current to flow through the storage battery for several days or until the positive plate turns to a dark chocolate-brown color and the negatives to a gray-slate. [Illustration: Fig. 75.—Gravity Cells. These consist of zinc and copper elements, immersed in a zinc-copper sulphate solution. They cannot be easily made, and are best purchased. The illustration also shows the star-shaped copper and "crowfoot" zinc element used in a gravity cell.] After the cells have once been "formed" all that they require is occasional recharging from gravity cells or from a dynamo, by connecting the positive pole of the charging current to the positive plates of the storage cells and the negative pole to the negative plates. When the cells are fully charged, bubbles of gas will rise freely from the plates. If a dynamo is used it must be "_shunt_" wound and not a "_series_" machine. Recharging will only require about one-quarter of the time consumed in forming. It is a very good plan to connect twelve gravity cells in series and use them to recharge the storage battery. The gravity cells can always be kept connected to the storage cells when the latter are not in use and thus remain fully charged and ready to supply their maximum current.