The submarine also had the effect of lessening the importations from Chile of sodium nitrate, which prior to the war were depended upon entirely in the production of nitric acid. It became necessary, therefore, to develop other methods of production. After investigations a plant for the fixation of nitrogen under what is known as a modified Haber process was erected at Sheffield, Ala., while a plant for the same purpose using the cyanamide process was erected at Muscle Shoals, Ala. Both of these were equipped for the oxidation of ammonia to nitric acid, each using a different process. When the armistice was signed these plants were just coming into production. The existence of these two nitrate plants insures the independence of this country in its supply of commercial nitrogen, either for peace or for war. There were also in course of erection, though not in operation on November 11, 1918, great plants for the extraction of nitrogen from the air, at Toledo and Cincinnati, Ohio, but construction on these two plants, each of which was to cost $25,000,000, was stopped when the armistice was signed. PROPELLANTS. In army usage the term "propellant" includes both smokeless powder and black powder. At the outbreak of the European war, the producing capacity in this country for smokeless powder was approximately 1,500,000 pounds a month. By the time the United States got into the war this capacity had been increased from 25 to 30 times, and under the explosives program laid down by us it was indicated that even this capacity would have to be greatly increased. The increase in the production of smokeless powder was helped by the construction of two of the largest smokeless-powder plants in the world--one known as the Old Hickory Plant, located almost on the site of Andrew Jackson's old home at Nashville, Tenn., and the other at Nitro, near Charleston, W. Va. The Old Hickory Plant was the larger and more complete of the two. It is probably the biggest plant of its kind in the world and is entirely self-contained; in other words, the plant actually takes the crude, raw cotton and, producing both the acid and solvents used, puts it through every process until the final product is attained. Nine powder lines were planned for this enterprise, each with a capacity of 100,000 pounds per day, although developments from the early operations indicated that the ultimate production of the plant would reach 1,000,000 pounds a day. The estimated cost of this huge undertaking was in the neighborhood of $90,000,000. Negotiations were begun in October of 1917 and led to a contract with the du Pont Engineering Co., under which this concern was to construct the plant and operate it for a six months' period after its completion.