For years it was the dream and life-ambition of the world’s greatest scientists to discover how to make the supplies of nitrogen in the air available to plants as food. The only way that this could be done in nature was through the agency of bacteria working on the roots of certain plants, such as clovers, but this process was entirely too slow for practical purposes and could be applied on only a small acreage at one time. The free nitrogen of the air cannot be utilized directly by plants. It must first be converted into some combination with other chemicals, as a solid or liquid, which can be absorbed by the plant. Among others who worked on the problem of fixing atmospheric nitrogen were two German chemists, Doctors Caro and Frank, who found that a compound of calcium and carbon heated to a high temperature would absorb nitrogen and retain it in a form that could be applied to the soil and serve as a food for plants. [Illustration: SUGAR CANE CROP FERTILIZED WITH CYANAMID MIXTURES. GROWN IN CALUMET, LA.] This discovery is the basis of the Cyanamid “Atmospheric Nitrogen” industry or the making of fertilizer from the nitrogen in the air. After the discovery was made and tested on the laboratory scale it took several years to put it on a practical basis, as can well be imagined when it is understood what the problems involved were. Besides air this process required as raw materials limestone and coke. The limestone must be burned to quicklime and the quicklime and coke must be fused together to form calcium carbide. Only the most powerful electric furnaces are capable of performing this work. Any other means of heating is far from adequate. For instance, the hottest flame that can be produced by the burning of gas, namely, the oxy-hydrogen blow-pipe flame, can be directed against a stick of burnt lime without doing anything beyond making the lime glow brilliantly, thus producing the calcium or lime-light formerly much used in theaters as a spot-light. In the electric furnaces, however, the lime is heated so powerfully that it actually melts to a liquid, and in this condition it dissolves the coke with which it is mixed and the compound resulting is calcium carbide which can be run off from the interior of the furnace in liquid form. [Illustration: TWO OF THE CARBIDE FURNACES AND ELECTRODE REGULATORS]