tayed around in
the first place because there was always plenty of sulphate ions with
whom they liked to play.

When the hydrogen ions try to get away from each other they go to the
other plate of the battery, and there they will get some electrons, if
they have to steal in their turn.

I won't try to tell you all that happens at the other plate. The
hydrogen ions get the electrons which they need, but they get something
more. They get some of the oxygen away from the plate and so form
molecules of water. You remember that water molecules are made of two
atoms of hydrogen and one of oxygen. Meanwhile, the lead atoms, which
have lost their oxygen companions, combine with some of the sulphate
ions which are in that neighborhood. During the mix-up electrons are
carried away from the plate and that leaves it positive.

The result of all this is a little lead sulphate on each plate, a
negative plate where the spongy lead was, and a positive plate where the
lead peroxide was.

Notice very carefully that I said "a little lead sulphate on each
plate." The sort of thing I have been describing doesn't go on very
long. If it did the battery would run down inside itself and then when
we came to start our automobile we would have to get out and crank.

How long does it go on? Answer another question first. So far we haven't
connected any wire between the two plates of the battery, and so none of
the electrons on the negative plate have any way of getting around to
the positive plate where electrons are badly needed. Every time a
negative sulphate ion combines with the spongy lead of the negative
plate there are two more electrons added to that plate. You know how
well electrons like each other. Do they let the sulphate ions keep
giving that plate more electrons? There is the other question; and the
answer is that they do not. Every electron that is added to that plate
makes it just so much harder for another sulphate ion to get near enough
to do business at all. That's why after a few extra electrons have
accumulated on the spongy lead plate the actions which I was describing
come to a stop.

Do they ever begin again? They do just as soon as there is any reduction
in the number of electrons which are hopping around in the negative
plate trying to keep out of each other's way. When we connect a wire
between the plates we let some of these extra electrons of the negative
plate pass along to the positive plate where they will be