When the liquid air is allowed to warm up a little, the nitrogen gas evaporates, while the oxygen remains behind in the liquid. The pure nitrogen then can be pumped into the fixation ovens. To fix the nitrogen in the carbide it is necessary to cool the latter after it comes from the electric furnaces and grind it to a very fine powder. This powder is then placed in furnaces that look like steel barrels but are three or four times larger than an ordinary barrel. The oven filled with calcium carbide is then electrically heated with a carbon rod running through the center. When the temperature is about as hot as that of molten iron the pure nitrogen gas from the liquid air plant is pumped in and allowed to act on the calcium carbide for about a day and a half. When the carbide has absorbed all it will absorb the crude cyanamid formed is removed from the oven as a single large cake which is run through pulverizing drums and then put through an elaborate process of refinement and finally bagged for shipment in carload lots to fertilizer factories throughout the country. The fertilizer manufacturers mix the cyanamid with other ingredients to make a balanced plant food and so ship it to farmers for feeding their crops. In 1914 7,500,000 tons of fertilizer worth $175,000,000 were consumed in this country. This seems like a large quantity, but it allows only a scanty application per acre cultivated. Germany, on one-fourth of our cultivated acreage, uses almost twice as much fertilizer as the entire United States. As a consequence she raises 30 bushels of wheat where we average 14 bushels per acre; 52 bushels of oats where we average 30; and 196 bushels of potatoes per acre where we raise 97 bushels per acre. The explanation is simple, German farmers pay only about one-half as much for their plant food as American farmers pay. Where the German farmer gains $2.00 to $3.00 increase in crop from fertilizer that costs him $1.00 the American farmer pays $2.00 for the same fertilizer, which leaves him less profit and less incentive to use fertilizer. [Illustration: A CARBIDE COOLING SHED] [Illustration: CYANAMID OVEN ROOM] [Illustration: _Photo by William H. Rau_ FOREVER RUSHING AND FOREVER WONDERFUL Niagara Falls from Prospect Point on the American side, looking southwest, across and up the stream. The American Falls may be seen in the foreground rushing past to make their plunge of 165 feet to the rocks below.]