In 1836 Edmund Davy, an English chemist, secured a by-product to the production of metallic potassium which would decompose water with the evolution of a gas containing acetylene.

In 1862 Woehler announced that calcium carbide, which he had made by heating an alloy of zinc and calcium with charcoal to a very high temperature, would decompose water and yield a gas containing acetylene like Davy's compound.

Up to 1892 these two substances-calcium carbide and its product, acetylenewere practically forgotten.

In the mean time the modern electric furnace. had been developed, and in the year 1892 Mr. Thomas L. Wilson, while conducting experiments at Spray, North Carolina, for the purpose of preparing metallic calcium by operating on a mixture of lime and coal, secured a melted mass of dark color.

This mass, when thrown in a neighboring stream, evolved a great quantity of gas which, on being lighted, burned with a brilliant but smoky flame.

Thus were calcium carbide and acetylene gas first prepared on a scale large enough to be of value commercially.

Calcium carbide is now produced commercially in many places-notably at Niagara Falls, New York, where the requisite electric current to produce the high temperature needed (4500 Fahrenheit) can be readily and cheaply obtained.

Ground coke and lime are intimately mixed in the proper proportions and placed in the electric furnace-, the result is that fifty-six parts of lime and thirty-six of coke will make sixty-four parts calcium carbide and liberate twenty-eight parts carbon monoxide.

If the lime and coke are pure, an ingot of pure carbide will be formed, surrounded by a crust of material less pure because partially unconverted.

Calcium carbide is dark brown or black; crystalline and brittle; has a specific gravity of 2.22 to 2.26; may be heated to redness without change; will soften and fuse in an electric furnace; will not burn except when heated in oxygen; and will keep indefinitely if sealed from the air, but will absorb moisture from the air and gradually slake like ordinary lime. If placed in water, or in any liquid containing water, it will effervesce vigorously and liberate acetylene gas.

Calcium carbide consists of lime and carbon (Ca C2). In contact with water, the lime combines with the oxygen of the water, making slaked lime, and the carbon with the hydrogen, making acetylene gas (C, H2). One pound of absolutely pure carbide will produce five and one-half cubic feet of gas; but, as absolutely pure carbide is not made commercially, the usual ratio is one pound of carbide to four and one-half cubic feet of acetylene.

Acetylene is a colorless gas possessing an offensive odor similar to decayed garlic, and so penetrating that one part of gas in ten thousand of air is distinctly noticeable -a valuable property, as by it leaks can be known long before they become dangerous. The odor is entirely due to impurities in the coke and lime; pure coke and pure lime will yield pure carbide. When the gas is burned in a proper jet, there is no odor.

Water will dissolve its volume of acetylene if intimately mixed, but if the acetylene rests on top of the water, the top layer of water becomes saturated and prevents the gas from penetrating farther.

Like all gases which burn in the air, it will explode when mixed with air in the proper proportions, prior to ignition. One part of acetylene with twelve and one-half parts of air will produce perfect combustion; the same proportions will also produce the most violent explosion, though it will also explode with a greater or less proportion of air, varying from three to eighty-two per cent.

Acetylene gas, unmixed with air, is not explosive at ordinary pressure, and modern burners are so constructed that the air for combustion is supplied after the gas issues from the jet.

The illuminating power of acetylene, in a proper burner, is greater than that of any other known gas; the flame is absolutely white and of great brilliancy; its spectrum closely approximates that of sunlight, and consequently it shows the same colors as daylight. It is strongly actinic and well adapted for photography. It neither heats nor pollutes the air so much as coal-gas.

It is one of the cheapest illuminants known-kerosene being its closest rival in economy. One pound of calcium carbide, costing at the present price three and one-half cents, will make four and one-half cubic feet of acetylene gas, which will produce two hundred and twenty-five candlepower for one hour. It will take fifty-six and one-fourth cubic feet of ordinary city gas to give the same amount of light, and at one dollar per thousand feet, city gas would cost five and six-tenths cents to produce the same light as acetylene.

Although there are many other uses of this new gas, the most important and the most valuable is as an illuminant, and the very fact that its generation, by adding water to carbide, is so easy, has flooded the Patent Office with a number of crude appliances-the inventors of which did not understand the properties of the gas nor the simple precautions to be taken to insure its safe generation.

At the Pan-American Exposition-where I had the honor to be the chairman of the Committee on Awards to which was assigned the examination of the acetylene generators exhibited-a set of requirements was drawn up by the committee which, if followed, would produce a nearly ideal generator. The generators were examined and tested, not only according to the directions given by the makers, but also by experiments which might be made by extremely careless and ignorant attendants the object being to find out how nearly "fool-proof" the generators had been made.

Each requirement was given a certain weight, by which the marks given to the requirement were to be multiplied.

The highest mark given to any one requirement was ten, and in order to compute the final rating of the generator this mark was multiplied by the weight given to each requirement in the table below. A generator which complied with every requirement would thus receive a total of one thousand one hundred and sixty points.

If an intending purchaser would use this method in examining a generator and refuse to buy one which did not receive ninety-five per cent. of the above number of points, or one thousand one hundred and two points, he would be sure to select a safe and satisfactory generator.

Requirements for a Good Stationery Acetylene Generator for House Lighting

In addition to the above, generators must conform to the rules and regulations of the fire underwriters.

The purchaser of a generator should ob serve the following additional precautions:

• Carbide should be kept in air-tight cans and stored in a dry place.
• The generator should be situated in a place where the water will not freeze.
• All pipes should be very carefully tested for leaks. A leak can be found by putting soapy water in the suspected part. Never hunt for a leak with a light.
• The generator should be charged in day-time, and no light should be brought within twenty feet of it.
• It is a good plan to discharge the refuse in a sewer, as it is a good disinfectant.

The Acetylene Building is the most brilliantly and beautifully lighted in the grounds; it sparkles like a diamond, is the admiration of all visitors. In it are generators of all types-most of them supplying the gas for their own exhibits - several being the latest exponents of the art, so simple in operation 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.

Acetylene gas has proved its case so far as house-lighting is concerned.

Among its other applications are: searchlights for small yachts (the same generator also lighting the yachts) ; mast- and sidelights for steamers; car-lighting; lighting railroad stations; bicycle-lamps; carriage lanterns; photography; lights for stereopticons; and signaling devices-the latter having recently been improved and made light and portable, promising to be of great utility to the United States Signal Service.

It is also used for heating purposes in cooking and laundry stoves and in Bunsen burners, and explosively in gas-engines.

One peculiarity of acetylene is that the greatest light which can be successfully and economically obtained from a single burner is about fifty candle-power. The same power is produced more conveniently from what is known as the fourth-order kerosene lamp in the light-house service; consequently there is no object in using acetylene gas for light-house purposes at stations provided with keepers.

Experiments are now in progress at the light-house depot at Tompkinsville, Staten Island, New York, to determine its value for lighting beacons for forty days continuously without attendance; the idea being that a number of beacons so lighted need be visited but once a month, thus reducing the cost of maintenance.

The special application in view is at Mobile Bay, Alabama, where there are sixteen beacons to mark the channel; and if the experiments prove successful, these beacons can be charged in one day every month, and will need no further attention.
No device which is both practical and safe has yet been made to use acetylene for gas-lighted buoys; liquefied acetylene has been tried, and though it gave a good and light, difficulties were encountered in its successful operation, and besides, it has not yet been demonstrated that acetylene in this form can be handled with absolute safety.

* The author is indebted for many of the facts in this article to a pamphlet entitled, " The Application of Acetylene Illumination to Country Homes," written by Prof. G. G. Pond, Ph.D.