e is made too strong, the plates and also the
separators will be attacked by the acid, and the resistance of the
electrolyte will also increase. The voltage increases as the
proportion of acid is increased, but the other factors limit the
concentration. If the electrolyte is diluted, its resistance rises,
and the amount of acid is insufficient to give much capacity. The
density of 1.280-1.300 is therefore a compromise between the various
factors mentioned above.

(d) Circulation of Electrolyte. This refers to the passing of
electrolyte from one plate to another, and depends upon the ease with
which the acid can pass through the pores of the separators. A porous
separator allows more energy to be drawn from the battery than a
nonporous one.

Operating Conditions.

Considering now the operating conditions, we find several items to be
taken into account. The most important are:

(e) Rate of discharge.
(f) Temperature.

(e) Rate of Discharge. As mentioned above, the ampere hour rating of a
battery is based upon a continuous discharge, starting with a specific
gravity of 1.280-1.300, and finishing with 1.150. The end of the
discharge is also considered to be reached when the voltage per cell
has dropped to 1.7. With moderate rates of discharge the acid is
abstracted slowly enough to permit the acid from outside the plates to
diffuse into the pores of the plates and keep up the supply needed for
the chemical actions. With increased rates of discharge the supply of
acid is used up so rapidly that the diffusion is not fast enough to
hold up the voltage. This fact is shown clearly by tests made to
determine the time required to discharge a 100 Amp. Hr., 6 volt
battery to 4.5 volts. With a discharge rate of 25 amperes, it required
160 minutes. With a discharge rate of 75 amperes, it required 34
minutes. From this we see that making the discharge rate three times
as great caused the battery to be discharged in one fifth the time.
These discharges were continuous, however, and if the battery were
allowed to rest, the voltage would soon rise sufficiently, to burn the
lamps for a number of hours.

The conditions of operation in automobile work are usually considered
severe. In starting the engine, a heavy current is drawn from the
battery for a few seconds. The generator starts charging the battery
immediately afterward, and the starting energy is soon replaced. As
long as the engine runs, there is no load on the