Luigi Galvani (1737–1798) of Bologna, Italy, in 1786 unwittingly produced an electric current from chemical action. Because he was eagerly seeking other results he misinterpreted this. Several words in the dictionary are becoming either obsolete or misnomers. For example, galvanism is an old-fashioned word for an electric current. The expression galvanic electricity is a relic of the abandoned idea that there are several kinds of electricity, of which Galvani discovered one. Galvanized iron is wholly a misnomer. It is a name used for iron which has been coated with zinc, and it suggests the idea that somehow the zinc is coated upon the iron by means of an electric current, whereas in fact it is done by dipping the iron into melted zinc.
Alessandro Volta (1745–1827) of Como, Italy, took up the discovery of Galvani, interpreted it correctly, and perfected the method of producing electricity by chemical action. What these two men really discovered was that it is possible to produce continuous currents of electricity. Before that electricity was known only by the instantaneous discharge or spark. From the name of Volta is derived the word volt, which designates the unit of electro-motive force. The adjective voltaic is synonymous with galvanic, as voltaic or galvanic cell, voltaic or galvanic current. For a long time it was thought that such an adjective was needed to designate electric currents generated by chemical action as a peculiar kind of electricity. We no longer think of electricity which is generated by chemical action as different from that generated by a dynamo or from any other source.
For about seventy-five years after the discovery of Galvani chemical action was our only method of generating currents of electricity, and it is largely owing to the inadequacy of this method of production that so few uses for electricity were discovered previous to the perfection of the dynamo about a third of a century ago. Two things have conspired to bring about this age of electricity. (1) The dynamo reduced the cost of production from five dollars to ten cents per kilowatt hour. (2) Mankind grew extravagant, greatly increased the number of things which it considered necessary, and at length became both able and willing to spend more for the things which it demanded.
The so-called voltaic cell is of scarcely more than academic interest now. The school which, as a rule, follows half a century behind practical life, has taught and still teaches the philosophy of the galvanic cell with great particularity. It is now being urged to undertake the teaching of the dynamo. Meanwhile the dynamo has almost driven out of existence all electric battery cells except the storage cell and the so-called "dry cell," and each year the dynamo is encroaching more and more upon the territory of the dry cell. In the present day, when a passenger upon a street car pushes a button to stop the car, he uses, not a voltaic cell, but a 500-volt dynamo current to ring a small buzzer, and it costs the company not one-hundredth part as much as it would to furnish him a battery equipment to do the same thing. Small dynamos and magnetos are displacing dry battery cells in the sparking equipment of motor boats and automobiles.
We lifted a dry battery cell out of its pasteboard case and found that it was contained in a metal cup of sheet zinc. The top of this was sealed over airtight with pitch, the purpose of which is to prevent this "dry" cell from drying up. We dug away the hardened pitch and found a black powder which was distinctly moist. In case the pitch becomes cracked or a hole appears in the zinc cup, the moisture passes out and the cell ceases to act as a generator of electric current.
The zinc cup had a lining of pasteboard on the sides and the bottom, similar to the pasteboard which enveloped the outside, only the lining was quite moist. A corrugated rod of carbon about an inch in diameter occupied the middle of the cup, and the space around it was packed full of a mixture of ammonium chloride, manganese dioxide, and other substances like plaster, etc., which differ with different cells. A dry cell which has been long in use is quite apt to show stains upon its pasteboard case. These are caused by holes which appear in the zinc. The production of electric current by the cell is dependent wholly upon a chemical action between the zinc and the ammonium chloride which results in the destruction of both. This chemical action cannot go on without moisture.
The zinc cup of the particular cell which we were examining appeared to be intact, and we proceeded to dig out the black powder. Its black colour is due to the manganese dioxide. Ammonium chloride is white. We lifted out the carbon rod and scraped the zinc cup clean. The binding posts attached to both the zinc cup and the carbon rod were left intact. Into the zinc cup we now poured a tumblerful of water and added about a quarter of its volume of hydrochloric acid, setting the whole into a large bowl to guard against disaster. Bubbles of gas were formed rapidly, causing the liquid to effervesce as a tumbler of soda water would do. We inverted an empty tumbler over the cup so as to collect this gas. In about two minutes we lifted the tumbler, still holding its mouth downward, and brought a lighted match to it. There was a flash and the contents burned with a pale-blue flame. Some of the zinc had united with some of the hydrochloric acid and set free hydrogen gas, which is one of the constituents of the acid. This is typical of chemical actions. Something similar takes place between the ammonium chloride and the zinc. Three interesting things occur in this experiment:
1. Chemical action, just described, is produced.
2. Heat is produced. This was very evident when we took the zinc cup up in our hands. It was as hot as though boiling water had been put into it.
3. An electro-motive force is produced. This we showed by connecting one end of a piece of copper wire to the binding post of the zinc cup and the other end of the wire to an electric bell. Another wire ran from the bell to the carbon rod. When the carbon rod was lowered into the acid the bell rang.