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Page:Popular Science Monthly Volume 38.djvu/370

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THE POPULAR SCIENCE MONTHLY.

electrical storage batteries, or accumulators, as they are sometimes called.

The employment of these names for the apparatus is very unfortunate. They are the cause of the popular idea that electricity, which is considered as a subtle, indefinite, and intangible something, is stored up in them, as valuables are stored in a vault. The commercial current electricity can not, in large quantities, be stored and still preserve its character. It has but a flitting existence, and is no sooner produced than it dissipates itself and is converted into some other form of energy. It was because of this momentary existence that science had to wait so long for an accident to reveal to Galvani that such a thing could exist.

The energy which a current may at any instant be said to possess is immediately transformed into heat in the circuit, which will under certain conditions produce light; into chemical energy; into motion, which may or may not produce sound; or into magnetic and electrotonic conditions. The last may either be permanent or have the same evanescent existence as the original current.

When electricity is employed to charge a storage battery, only that part which is transformed into chemical energy is used. The rest is dissipated. The battery, then, instead of being a place where electricity is laid away, is a place where chemicals are left by the current, with the expectation that they will in turn produce a current when called upon. This may seem a fine distinction, but it is only apparently so. For instance, the current might be produced by a dynamo turned by Niagara water-power. The chemical left by it might be zinc deposited from a solution of zinc sulphate. This might be transported, preserved, bought and sold, and finally be employed by some physicist to produce another current. Were the electricity itself stored in its original form, then the imaginative reader can best tell what would become of it and how it must be handled.

To understand this transformation more clearly, and to obtain a clear idea of what goes on in a storage battery, one must first become acquainted with that part of electricity which treats of the phenomena resulting when a current of electricity passes through a liquid. This is called electrolysis, and the liquid through which a current can be made to pass is called an electrolyte.

If a current of electricity flows into a liquid solution of any metallic salt by means of a wire, and if, after traversing it, it flows out through another wire, then it will, by its passage, separate the salt into two parts and deposit the metal upon the latter wire.

If, for instance, the solution be one of silver cyanide, then silver will be deposited on the second wire. If a brass fork be connected with this wire and dipped in the solution, then it will receive a