e their way to the surface, and in so
doing cause numerous fine particles of active material to break off
and fall to the bottom of the jar. This happens because the lead
peroxide is a granular, non-coherent substance, with the particles
held together very loosely, and the gas breaks off a considerable
amount of active material.

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CHAPTER 7.
CAPACITY OF STORAGE BATTERIES.
------------------------------

The capacity of a storage battery is the product of the current drawn
from a battery, multiplied by the number of hours this current flows.
The unit in which capacity is measured is the ampere-hour.
Theoretically, a battery has a capacity of 40 ampere hours if it
furnishes ten amperes for four hours, and if it is unable, at the end
of that time, to furnish any more current. If we drew only five
amperes from this battery, it should be able to furnish this current
for eight hours. Thus, theoretically, the capacity of a battery should
be the same, no matter what current is taken from it. That is, the
current in amperes, multiplied by the number of hours the battery,
furnished this current should be constant.

In practice, however, we do not discharge a battery to a lower voltage
than 1.7 per cell, except when the rate of discharge is high, such as
is the case when using the starting motor, on account of the
increasing amount of sulphate and the difficulty with which this is
subsequently removed and changed into lead and lead peroxide. The
capacity of a storage battery is therefore measured by the number of
ampere hours it can furnish before its voltage drops below 1.7 per
cell. This definition assumes that the discharge is a continuous one,
that we start with a fully charged battery and discharge it
continuously until its voltage drops to 1.7 per cell.

The factors upon which the capacity of storage batteries depend may be
grouped in two main classifications:

1. Design and Construction of Battery
2. Conditions of Operation

Design and Construction.

Each classification may be subdivided. Under the Design and
Construction we have:

(a) Area of plate surface.
(b) Quantity, arrangement, and porosity of active materials.
(c) Quantity and strength of electrolyte.
(d) Circulation of electrolyte.

These sub-classifications require further explanation. Taking them in
order:

(a) Area of Plate Surface. It is evident th