Three plates are used in each cell. Each cell will have an E. M. F. of two volts when fully charged. In order therefore to have a battery capable of delivering six volts, three cells will be necessary. Nine plates will be required for three cells.
The body of the plates should then be drilled full of holes about one-eighth of an inch in diameter as shown by B in Figure 39.
The plates are now ready for pasting. Select three of the plates and mark them with a small cross. These are to be *positive* plates when finished. The paste for these plates is made by mixing red lead with diluted sulphuric acid. The paste should form a good stiff mixture. Lay the three plates upon a smooth board and press the paste carefully into the holes with a flat stick. They are then laid aside to dry and harden.
[Illustration: FIG. 40.—A set of three Plates composed of One Positive and Three Negatives assembled to form a Cell.]
The six remaining plates are to be *negatives* when finished and they are pasted in identically the same manner as the positives except that the paste is made of a mixture of yellow lead and dilute sulphuric acid instead of red lead.
A pasted plate is shown at the right in Figure 39.
Cut six rectangular pieces, three by three and one-half inches, of heavy blotting paper or thin whitewood. The thin wood used in the construction of fruit baskets may be used for this purpose. These rectangles are to be used as "separators" between the plates.
[Illustration: FIG. 41.—Glass and Rubber Storage Cell Jars which are on the market for the Electrical Experimenter and may be purchased very reasonably.]
The plates should then be assembled in groups of three, as shown in Figure 40. The positive plate is placed in the centre with a separator on either side. Two negative plates are then placed on the outside. The lugs on the negative plates should come opposite to each other. A square lead block having a hole bored through the centre may be placed between the two negative lugs. The lugs are then clamped together with a binding post and a screw. The plates are held in a compact bundle by two heavy rubber bands passing around them.
Each group of plates is then placed in its proper jar and the jar filled full of a mixture composed of: