A-B-C of Electricity

by Wm. H. Meadowcroft

THE ALKALINE STORAGE BATTERY

We shall now describe an entirely different type of storage battery, which contains neither lead nor acid. It is one of the many inventions of Thomas A. Edison.

In the alkaline storage battery the gas called oxygen plays a very important part, and we will try to make it clear to you what this part is.

You are well aware of the fact that if you leave your pocket-knife out in the air it will get rusty. The reason for this is that iron or steel quickly tends to combine with the oxygen of the air, and this combination of oxygen and iron is rust, otherwise called oxide of iron, or iron oxide.

This iron oxide, or rust, is therefore the result of a chemical action between the iron and the oxygen.

Now as all chemical actions require the expenditure of energy, there has been developed either heat or electricity in the process. The oxygen may be taken away from the iron oxide, chemically; but here again would be another chemical action which would require energy to be once more expended.

Iron oxide may be made chemically in many different ways. It is frequently made in the form of a powder. Therefore, we do not have to depend upon iron rust for a supply of this material.

Before going further we must consider another oxide—namely, nickel oxide. It is characteristic of nickel that when it is combined with oxygen to a certain degree so as to form the compound known as nickel oxide, it will receive still more oxygen.

Now, if under proper conditions we compel iron oxide to give up its oxygen to some other kind of chemical compound, such as nickel oxide, we must expend energy. But, on the other hand, if this nickel oxide gives back the oxygen to the iron—which it will do if opportunity is given—there is energy produced again in receiving the oxygen. In other words, the energy previously expended, or part of it, is now returned.

This action and reaction are practically those that take place in the Edison alkaline storage battery. For simplicity of illustration we will consider a cell containing only two plates, one positive and one negative.

The negative plate is made up of a number of small, flat, perforated pockets containing iron oxide in the form of a fine powder. The positive plate is made up of small, perforated tubes containing nickel oxide mixed with very thin flakes of metallic nickel. (Fig. 37 illustrates these plates, the positive being in front.)

Fig. 37

These two elements, positive and negative, having wires or conductors attached, are placed in a nickeled-steel can containing the electrolyte, which consists of a potash solution. You will see that this differs from a lead storage battery, in which the electrolyte is sulphuric acid and water. If we were to put this acid solution into a metallic can (except one made of lead) the can would not last long, as the acid would quickly eat holes through it.

Now let us see what takes place in the Edison alkaline storage battery. If an electric current from a dynamo or other source of electricity is caused to pass through the positive to the negative plate the oxygen present in the iron oxide passes to and remains with the nickel oxide. During all the time this is going on the battery is said to be "charging," and when all the oxygen has been removed from the iron oxide and is taken up by the nickel oxide, then the battery is said to be "charged," and the flow of current into the battery is stopped.

A change has now taken place. The powder in the negative plate is no longer iron oxide, but has been reduced to metallic iron, because the oxygen has been removed. The powder in the positive plate is now raised to a higher or super oxide of nickel, because it has taken the oxygen that was in the iron.

But the nickel oxide will readily give up its excess of oxygen, and the iron will receive it back freely if permitted. If the proper conditions are established, this transfer of oxygen will take place, but the iron cannot receive it without delivering energy.

Fig. 38

The proper conditions are established by providing a conducting circuit between the two elements, in which lamps, motors, or other electrical devices are placed. As soon as this circuit is provided, the opportunity is given to the iron to receive the oxygen. This it does, and in so doing develops electrical energy.

This energy is in the form of electric current which is then delivered by the battery on what is called the "discharge," and this current may be used for lighting lamps or for operating motors or other electrical devices.

The battery is said to be discharging as long as the iron is receiving oxygen from the nickel oxide. As soon as it becomes iron oxide once more, the giving out of energy ceases and the battery is said to be "discharged," and must again be charged to obtain further work from it. Such a battery can be charged and discharged an indefinite number of times.

This type of battery is very rugged, and its combinations are not self-destructive. It is very simple, as it provides chiefly for the movement of the oxygen back and forth; besides, it gives much more current for its weight than the lead type of storage battery. (Fig. 38 shows the plates of a standard Edison cell removed from container.)