become thin
and weak, and may be spoken of as being corroded.

1. Impurities. Those impurities which attack the lead grids, such as
acids other than sulphuric acid, compounds formed from these acids, or
substances which will readily form acids dissolve some of the lead
which composes the grids. The grids gradually become weakened. The
decrease in the amount of metal in the grids increases the internal
resistance of the cell and give a tendency for temperatures to be
higher in the cell. The contact between grids and active material is
in time made poor. If the action of the impurities continues for any
length of time, the plate becomes very weak, and breaks at the
slightest touch.

2. High Temperatures. Anything that raises the temperature of the
electrolyte, such as too high a charging rate, causes the acid to
attack the grids and form a layer of sulphate on them. The sulphate is
changed to active material on charge, and the grids are thereby
weakened.

3. Age. Grids gradually become weak and brittle as a battery remains
in service. The acid in the electrolyte, even though the electrolyte
has the correct gravity and temperature, has some effect upon the
grids, and in time this weakens them. During the life of a battery it
is at times subjected to high temperatures, impurities, sulphation,
etc., the combined effects of which result in a gradual weakening of
the grids.

Granulated Negatives

1. Age. The spongy lead of the negative plate gradually assumes a
"grainy" or "granulated" appearance. The lead then seems to be made up
of small grains, like grains of sand, instead of being a smooth paste.
This action is a natural one, and is due to the gradual increase in
the size of the particles of the lead. The plate loses its porosity,
the particles cementing together and closing the pores in the lead.
The increase in the size of the particles of the spongy lead decreases
the amount of surface exposed to the action of the electrolyte, and
the plate loses capacity. Such plates should be thrown away, as
charging and discharging will not bring the paste back to its original
state.

2. Heat will also cause the paste to become granulated, and its
surface to become rough or even blistered.

Heating of Negatives Exposed to the Air

When charged negatives are exposed to the air, there is a decided
increase in their temperature. Spongy lead is in an extremely finely
divided state, the particles of lead being very min