If they require forming, they must be put through the same forming process which has already been described.
The finished cells when sealed will appear like those shown in Figure 45, according to the sizes of plates and jars used.
[Illustration: FIG. 45.—Three different sizes of Storage Cells which may be purchased ready made or built by the experimenter out of prepared materials as explained.]
Recharging and Caring for Storage Cells.
Storage cells are especially affected by the usage given them. If they are mistreated they will quickly go to pieces, whereas, on the other hand if well treated they will last indefinitely.
It is important that the electrolyte used in the cells should always be of the proper strength. The only accurate method of preparing the electrolyte is with the aid of a *hydrometer*. A hydrometer is an instrument for determining the specific gravity of solutions.
It is a little device which looks somewhat like a thermometer. It is placed in the solution and allowed to float. There is a numbered scale along the upper part of the hydrometer and the *specific gravity* or strength of the solution is indicated on the scale by the point which is level with the surface of the solution.
The normal specific gravity for a storage battery solution should be about 1.250. The strength can be increased by adding more acid and decreased by adding water.
Ordinary commercial or technical grades of sulphuric acid and ordinary water are satisfactory for primary batteries, but the acid and water used in making the electrolyte for storage cells must be *chemically pure* if you wish to obtain good results and desire your batteries to hold their charge while standing.
Storage cells can be recharged with DIRECT current only. A dynamo for recharging storage cells must be SHUNT wound. The voltage of the charging current must be greater than that of the storage cells. About three volts of charging current will be required for each cell of the storage battery. Cells may be connected in multiple when recharging so as to bring the voltage of the cells below that of the charging current. It will of course, however, take much longer to recharge cells connected in multiple than the same cells connected in series, provided that the amperage of the current is the same.