An electric arc consuming about 4000 horse-power of energy is passing between the U-shaped electrodes which are made of copper tube cooled by an internal current of water.  On the sides of the chamber are seen the openings through which the air passes impinging directly on both sides of the surface of the disk of flame.  This flame is approximately seven feet in diameter and appears to be continuous although an alternating current of fifty cycles a second is used.  The electric arc is spread into this disk flame by the repellent power of an electro-magnet the pointed pole of which is seen at bottom of the picture.  Under this intense heat a part of the nitrogen and oxygen of the air combine to form oxides of nitrogen which when dissolved in water form the nitric acid used in explosives.]

[Illustration:  Courtesy of E.I. du Pont de Nemours Co.

A BATTERY OF BIRKELAND-EYDE FURNACES FOR THE FIXATION OF NITROGEN AT THE
DU PONT PLANT]

We might have expected that the fixation of nitrogen by passing an electrical spark through hot air would have been an American invention, since it was Franklin who snatched the lightning from the heavens as well as the scepter from the tyrant and since our output of hot air is unequaled by any other nation.  But little attention was paid to the nitrogen problem until 1916 when it became evident that we should soon be drawn into a war “with a first class power.”  On June 3, 1916, Congress placed $20,000,000 at the disposal of the president for investigation of “the best, cheapest and most available means for the production of nitrate and other products for munitions of war and useful in the manufacture of fertilizers and other useful products by water power or any other power.”  But by the time war was declared on April 6, 1917, no definite program had been approved and by the time the armistice was signed on November 11, 1918, no plants were in active operation.  But five plants had been started and two of them were nearly ready to begin work when they were closed by the ending of the war.  United States Nitrate Plant No. 1 was located at Sheffield, Alabama, and was designed for the production of ammonia by “direct action” from nitrogen and hydrogen according to the plans of the American Chemical Company.  Its capacity was calculated at 60,000 pounds of anhydrous ammonia a day, half of which was to be oxidized to nitric acid.  Plant No. 2 was erected at Muscle Shoals, Alabama, to use the process of the American Cyanamid Company.  This was contracted to produce 110,000 tons of ammonium nitrate a year and later two other cyanamid plants of half that capacity were started at Toledo and Ancor, Ohio.