The electric fixation of nitrogen

One of the most pressing of modern problems is the supply of combined nitrogen for agricultural purposes. There are three substances essential to vegetable life which are constantly being extracted from the soil by the crops or plants growing thereon. These are nitrogen phosphorous and potassium. The continual abstraction of these substances renders necessary their periodic replacement if the soil is not to be impoverished. In early agricultural operations animal fertilizer sufficed for the needs of the time, but in recent years the supply has become inadequate, and it has become essential that some form of artificial fertilizer be employed. Nitrate of soda and sulphate of ammonia have been extensively used for this purpose with very satisfactory results. The increased demand for these drugs, however, has limited the supply. It is estimated that the consumption of Chili saltpetre has increased in the period from 1850 to 1903 from 250,000 tons to 1,540,000 tons annually, and at the present time the rate of consumption is in the neighborhood of 2,000,000 tons per year. For many years Peruvian guano has been used, but the supply is practically exhausted. The sewage from cities if utilized in an efficient manner would prove at best but an insignificant item in the total world´s demand. It has been estimated that in England alone there is wasted through her sewers the equivalent of $80,000,000 per year. No efficient method has as yet been proposed for the satisfactory utilization of city sewage. Sulphate of ammonia is now manufactured in large quantities as a by-product in gas works. It is improbable, however, that this form of combined nitrogen can successfully replace Chili saltpetre when the latter shall have become exhausted. Nitrogenous compounds are unstable chemically, and this instability has rendered the fixation of nitrogen difficult by artificial means, a critical temperature of dissociation existing so near the temperature of combination that disintegration- is prone to occur immediately after the combination has been brought about. There are two proved methods for fixation — the Birkland-Eyde process, and the cyanamide process of Caro and Frank. A modification of the Birkland-Eyde process due to Dr. Schonherr and operated by the Badische Aniline und Soda Fabrik is worthy of description. The principle upon which all these processes is based, is the treatment of air to a high temperature while passing through a strong electrostatic field. Under this influence the nitrogen of the air combines with oxygen, but decomposes practically as soon as the combination occurs. This decomposition has been prevented by removing the high temperature in the static field as soon as the combination of nitrogen and oxygen has been obtained, or, in other words, the air is subjected to a rapid periodic treatment. In the Birkland-Eyde process a high-tension alternating-current flame is blown into a disc transversely to a direct current magnetic field. The gases mixed with steam are passed directly over lime. This process is modified in the Badische Aniline und Soda Fabrik. In the latter, long thread-like arcs are employed. The air is blown tangentially so as to circulate spirally around the arc. The difficulties encountered in the development of these processes in the past, have been the high cost of electric power and the fact that the process of nitrogen fixation in the flame is a reversible one. At certain critical points the combined nitrogen is again decomposed and it is with the perfection of this detail that the development has been concerned, cheap water power having been available in many places for some time.