milar test and examination of the plates and electrolyte of a
battery through which a current has been sent from some outside
source, such as a generator, until the current can no longer cause
chemical reactions between the plates and electrolyte, we will find
that the electrolyte is now composed of water and Sulphuric acid, the
acid comprising about 30%, and the water 70% of the electrolyte. The
negative set of plates will be composed of pure lead in a spongy form,
while the positive will consist of peroxide of lead.

The foregoing description gives the final products of the chemical
changes that take place in the storage battery. To understand the
changes themselves requires a more detailed investigation. The
substances to be considered in the chemical actions are sulphuric
acid, water, pure lead, lead sulphate, and lead peroxide. With the
exception of pure lead, each of these substances is a chemical
compound, or composed of several elements. Thus sulphuric acid is made
up of two parts of hydrogen, which is a gas; one part of sulphur, a
solid, and four parts of oxygen, which is also a gas; these combine to
form the acid, which is liquid, and which is for convenience written
as H2SO 4, H2 representing two parts of hydrogen, S one part of
sulphur, and 04, four parts oxygen. Similarly, water a liquid, is made
up of two parts of hydrogen and one part of oxygen, represented by the
symbol H2O. Lead is not a compound, but an element whose chemical
symbol is Pb, taken from the Latin name for lead. Lead sulphate is a
solid, and consists of one part of lead, a solid substance, one part
of sulphur, another solid substance, and four parts of oxygen, a gas.
It is represented chemically by Pb SO4. Lead peroxide is also a solid,
and is made up of one part of lead, and two parts of oxygen. In the
chemical changes that take place, the compounds just described are to
a certain extent split up into the substances of which they are
composed. We thus have lead (Pb), hydrogen (H), oxygen (0), and
sulphur (S), four elementary substances, two of which are solids, and
two gases. The sulphur does not separate itself entirely from the
substances with which it forms the compounds H2SO4 and Pb SO4. These
compounds are split into H2 and SO4 and Pb and SO4 respectively. That
is, the sulphur always remains combined with four parts of oxygen.

Let us now consider a single storage cell made up of electrolyte, one
positive plate, and one negative pla