Wrap the spool pulleys with bicycle-tape, to keep the rubber-band belts from slipping.
The Battery. A dry battery is too heavy for the motor truck to carry; so we must make a special two-cell battery like that shown in Fig. 204. Two glass tumblers to hold the solution, a pair of battery zincs, a pair of carbons, and a bi-chromate of potash solution, are needed. Old battery
Fig. 204.—Two Home-Made Battery Cells Connected in Series.
zinc pencils with several inches of the eaten end cut off (Fig. 206) will do for the zincs, and the carbons from worn-out dry-battery cells cut to a corresponding length will do for the carbons. Fasten together the zincs and carbons with rubber-bands, as shown in Fig. 207, after wrapping a piece of bicycle-tape around the upper end of the carbon and inserting a small wad of it between the lower ends of the carbons and zincs, to keep them from touching one another.
Figure 205 shows a completed cell, and Fig. 204 how the two cells are connected in series, that is, with the carbon
