THE INTRODUCTION OF ACETYLENE GAS
When the incandescent mantle had been perfected so as to be an economical as well an as efficient light-giver, the position of coal gas as an illuminant seemed again secured against the encroachments of its rivals, the arc and incandescent electric lights. But just at this time another rival appeared in the field that not only menaced the mantle lamp but the arc and incandescent light as well. Curiously enough, this new rival, acetylene gas, had been brought into existence commercially by the electric arc itself. For although it had been known as a possible illuminant for many years, the calcium carbide for producing it could not be manufactured economically until the advent of the electric furnace, itself the outcome of Davy's arc light.
Even as early as 1836 an English chemist had made the discovery that one of the by-products of the manufacture of metallic potassium would decompose water and evolve a gas containing acetylene; and this was later observed independently from time to time by several chemists in different countries. No importance was attached to these discoveries, however, and nothing was done with acetylene as an illuminant until the last decade of the nineteenth century. By this time electric furnaces had come into general use, and it was while working with one of these furnaces in 1892 that Mr. Thomas F. Wilson, in preparing metallic calcium from a mixture of lime and coal, produced a peculiar mass of dark-colored material, calcium carbide, which, when thrown into water, evolved a gas with an extremely disagreeable odor. When lighted, this gas burned with astonishing brilliancy, and, as its cost of production was extremely small, the idea of utilizing it for illuminating was at once conceived and put into practice.
The secret of the cheap manufacture of the carbide lies in the fact that the extremely high temperature required—about 4500° Fahrenheit—can be obtained economically in the electric furnace, but not otherwise. Thus electricity created its own greatest rival as an illuminant. It followed naturally that the ideal place for manufacturing the carbide would be at the source of the cheapest supply of electricity, and as the "harnessed" Niagara Falls represented the cheapest source of electric supply, this place soon became the centre of the carbide industry. Here the process of manufacture is carried out on an enormous scale. In practice, lime and ground coke are thoroughly mixed in the proportion of about fifty-six parts of lime to thirty-six parts of coke. When this mixture has been subjected to the heat of the electric furnace for a short time an ingot of pure calcium carbide is formed, surrounded by a crust of less pure material. The ingot and crust together represent sixty-four parts of the original ninety-two parts of lime and coke, the remaining twenty-eight parts being liberated as carbon-monoxide gas.
Calcium carbide as produced by this process is a dark-brown crystalline substance which may be heated to redness without danger or change. It will not burn except when heated in oxygen, and will keep indefinitely if sealed from the air. Chemically it consists of one atom of lime combined with two atoms of carbon (CaC2); and to produce acetylene gas, which is a combination of carbon and hydrogen (C2H2) it is only necessary to bring it into contact with water, acetylene gas and slaked lime being formed. One pound of pure carbide will produce five and one half cubic feet of gas of greater illuminating power than any other known gas. The flame is absolutely white and of blinding brilliancy, giving a spectrum closely approximating that of sunlight. The light is so strongly actinic that it is excellent for photography.
Here was a gas that could be made in any desired quantities simply by adding water to a substance costing only about three cents a pound; its cost of production, therefore, representing only about one sixth of the dollar-per-thousand-feet rate usually charged for illuminating gas in our cities. It could be used in lamps and lanterns made with special burners and with the simple mechanism of a small water tank which allowed water to drip into a receptacle holding the carbide; or—reversing the process—an apparatus that dropped pieces of carbide into the water tanks. It was, in short, the cheapest illuminant known, generated by an apparatus that was simplicity itself.
There were, however, two defects in this gas: its odor was intolerable—the "smell of decayed garlic," it has been aptly called—and when mixed with air it was highly explosive. The first of these defects could be overcome easily; when the burner consumed all the gas there was no odor. The second, the explosive quality, presented greater difficulties. These were emphasized and magnified by the number of defective lamps that soon flooded the market, many of these being so badly constructed that explosions were inevitable. As a result a strong prejudice quickly arose against the gas, some countries passing laws prohibiting its use.
But further inquiry into the cause of the frequent disasters revealed the fact that when the burner of a lamp was constructed so that the air for combustion was supplied after the gas issued from the jet, there was no danger of explosion. And as lamps carefully constructed on this principle replaced the early ones of faulty construction, confidence in acetylene was restored. Methods were devised for supplying the gas for house-illumination like ordinary gas, and the occupants of country houses were afforded a means of lighting their houses on a scale of brilliancy hitherto unapproached, yet with economy and relative safety.
It was found also that the brilliancy of the acetylene flame was of such intensity that it could be used, like the electric arc light, as a search-light. It thus furnished a simple means of supplying small boats and vehicles with such lights, which they could not otherwise have had. It also supplied army signal-corps with an apparatus for flashing messages—an apparatus that was ideal on account of its simplicity and small size.
At the Pan-American Exhibition at Buffalo the various illuminating exhibits were among the most conspicuous and attractive features. But even amid the dazzling electrical displays the Acetylene Building was a noteworthy object. "It was the most brilliantly and beautifully lighted building in the grounds," declared one observer. "It sparkled like a diamond, and was the admiration of all visitors. In it were generators of all types—most of them supplying the gas for their own exhibits—several being the latest exponents of the art, so simple that they can be safely managed by unskilled labor; in fact, 'the brains are in the machines,' and when the attendant has charged them with carbide and filled them with water—given them food and drink—they will work steadily until they need another meal." Indeed, these exhibits at the Pan-American Exhibition demonstrated conclusively that acetylene gas occupies a field by itself as a practical illuminant.
At the same exposition a standard was established for good stationary acetylene generators for house-lighting, and the fact that a large number of generators fulfilled the requirements of the set of rules laid down showed how thoroughly the problem of handling this gas has been solved. Some of these rules used as tests are instructive to anyone interested in the subject, and a few of them are given here. They specified, for example, that—
"The carbide should be dropped into the water," the reverse process of letting the water drip on the carbide, as was done in most of the early generators, being condemned. "There must be no possibility of mixing air with the acetylene gas. Construction must be such that an addition to the charge of carbide can be made at any time without affecting the lights. Generators must be entirely automatic in their action—that is to say: after a generator has been charged, it must need no further attention until the carbide has been entirely exhausted. The various operations of discharging the refuse, filling with fresh water, charging with carbide, and starting the generator must be so simple that the generator can be tended by an unskilled workman without danger of accident. When the lights are out, the generation of gas should cease. The carbide should be fed automatically into the water in proportion to the gas consumed."
Perhaps the most significant thing, showing the stage of progress that has been made in overcoming the danger of explosions from acetylene gas, is that the use of generators meeting some such requirements as the above is not prohibited by fire underwriters. This in itself is very convincing evidence of their safety.