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.