Evening star. [volume] (Washington, D.C.) 1854-1972, 1914-01-18
BY JAMES S. SKINNER.

The following is intended to elaborate
a little on four pertinent points concern
ing the care of lead storage batteries
These points are covered more or less in
standard instruction books. but instruc-
ton books must necessarily be brief and
very seldom give many of the why's and
wherefores.
The electrolyte in lead storage battery
consists of dilute sulphuric acid. At the
end of full charge this is of about LOO
specific gravity. which means about 40 per
ent acid and 60 per cent water. At the
end of full discharge the specific gray
fly may be as low as 1.100. which means
about IA per cent acid and Sc per cent
water. Evidently acid has either been
taken out of the electrolyte during dis
charge or water has been added. As a
matter of fact, both of these things have
taken place. In discharging. the active
material of both plates has absorbed acid
|and given off elements which combine to
form water and further dilute the cleo
Itrolyte.
The voltage of a battery depends upon
3the strength of the acid in contact with
the active material As the discharge
proceeds the strength of the acid de-
creases and the voltage with it. The de-
crease in voltage proceeds faster than
gravity and the voltage will reach be-
Fore all of the acid in the electrolyte is
Ised up. This is because the lead sui
3phate which is formed durin@ dis
charge clogs UP the pores of the
pilates and prevents the fresh mac
hive acid between the plates from
teaching the undischarged active material
at the middle of the plates When the
3rolta~e of cell falls to o the actual cleo.
}.roIyte in contact with the undischarSed
iaI loS haay 60
hts acid as to have become practically
{pure water. although the main body OF
the electrolyte between the plates may
still contain a large percentage OF acld.
This however cannot be of any service
because of the lead sulphate lying be-
tween it and the undischarged active
material
Thin Plate Batteries.
A great advantage in thin plate bat
| teries lies IN the fact that the acid does
mot have to work its way so far in order
to reach the middle of the plates and
lean, therefore work much more efficient
Ily and thoroughly. In thin plate bat
Iteries about 30 per cent more material
land 80 per cent more acid are actually
FUSED than in thick plate batteries. and
about 30 per cent more capacity is there
10y obtained in the same space and from
tine same weight Oh
During charge the acid which was
previously absorbed is given off again
into the electrolyte. and at the end OF
charge the amount should be the same IS
bat the end of the previous charge. This
alternate absorption and giving out OF
|hcid is characteristic of the discharge
land charge of a lead storage battery.
Providing acid is not spilled out 7 is
practically never necessary to adj fresh
|acid. A little acid may be lost in the
|gas which is given off toward the end of
zach charge. but unless the gassing is
kery violent this loss need not be COM
|pensated for more often than once every
six months or so and then only after a
|rery long full charge. so as to be sure
that ali the acid is out of the plates. In
itself the gas is not sulphuric acid vapor.
(It is merely decomposed water and the
|acid which is lost is simply the very small
amount which it carries along mechan-
tcally.
1t is important that the acid used be
|of the highest purity. Any foreign mat
her in it. especially metals other than
lead, will tend to set up local act on in
the battery. which will discharge the
pilates without the production of any
useful current. A battery containing i'm
|pure acid will not hold its charge. For
|the same reason it is important that acid
|of a higher specific gravity than 1-3C0
should not be placed in a battery, since
such acid also tends to discharge the
pilates without the production of any use
|ful current. Furthermore, sulphuric acid
stronger than leo specific gravity is
likely to hasten the disintegration of the
wood separators.
Importance of Acid Level.
II is not detrimental to the life of the
battery to use acid of lower specific