twenty-four. If they were to run longer, they would be dead in a few
weeks. If they run two hours a day, they will last three or four
years.

The life of the cells must be expressed upon the principle of ampere
hours or the amount of energy given off by them. Street car service
requires that the cells work their hardest for fifteen or sixteen
hours a day. The life of the cells has to be divided; first, into the
life of the box which contains the plates. This box, if appropriately
constructed of the best materials, will last many years, because there
is no actual wear on it. The life of the negative plates will be very
considerable, because no chemical action is going on in the negative
plate. The negative plate consists almost entirely of spongy lead, and
the hydrogen is mechanically occluded in that spongy lead. Therefore
the depreciation of the battery is almost entirely due to the
oxidation of the positive plates. If we were to make a lead battery of
plates ¼ inch thick, it would last many years; but for street car
work that would be far too heavy. Therefore we make the positive
plates a little more than one-eighth of an inch thick. I find that the
plates get sufficiently brittle to almost fall to pieces after the car
has run fifteen hours a day for six months. The plates then have to be
renewed. But this renewal does not mean the throwing away of the
plates. The weight is the same as before, because no consumption of
material takes place. We take out peroxide of lead instead of red
lead. That peroxide, if converted, produces 70 per cent. of metallic
lead, so that there is a loss of 30 per cent. in value. Then comes the
question of the manufacture of these positive plates, which, I
believe, at the present day are rather expensive. But I believe the
time will come when battery plates will be manufactured like shoe
nails, and the process of renewing the positive plates will be a very