he electrolyte, and is not
precipitated as metallic iron. The iron in solution travels from the
positive to the negative plate, and back again, causing a local
discharge at each plate. It is, moreover, very difficult to remove the
iron, except by pouring out all of the electrolyte. Manganese acts the
same as the iron.

2. Impurities Which Attack the Plates. In general, this class includes
acids other than sulphuric acid, compounds formed from such acids, or
substances which will readily form acids by chemical action in the
cell. Nitric acid, hydrochloric or muriatic acid, and acetic acid
belong in this class of impurities. Organic matter in a state of
decomposition attacks the lead grids readily.

Impurities in the second class dissolve the lead grids, and the plate
disintegrates and falls to pieces, since its backbone is destroyed.
When a battery which contains these impurities is opened, it will be
found that the plates crumble and fall apart at the slightest touch.
See Fig. 210.

Separators which have not been treated properly introduce acetic acid
into a cell. The acetic acid attacks and rots the lead, especially the
lugs projecting above the electrolyte, and the plate connecting
straps. The plates will generally be found broken from the connecting
strap, with the plate lugs broken and crumbled.

As for remedies, there is not much to be done. Impurities in the first
class merely decrease the capacity of the battery. If the battery is
fully charged, and the negatives then washed thoroughly, some of the
impurities may be removed. Impurities of the second class have
generally damaged the plates beyond repairs by the time their presence
is suspected.

The best thing to do is to keep impurities out of the battery. This
means that only distilled water, which is known to be absolutely free
from impurities should be used.

Impurities which exist in the separators or acid cannot be detected
readily, but in repairing a battery, separators furnished by one of
the reliable battery makers should be used. Pure acid should also be
used. This means that only chemically pure, or "C. P." acid, also
known as battery acid should be used. In handling the acid in the
shop, it should always be kept in its glass bottle, and should be
poured only into a glass, porcelain, earthenware, lead, or rubber
vessel. Never use a vessel made of any other material.

Corroded Grids

When the grids of a plate are attacked chemically, they