VIII THE SUPPLY OF NITROGEN PRODUCTS FOR A ARTHUR A. NOYES N adequate supply of nitrogen compounds, particularly of nitric acid and ammonia, was of vital importance in ensuring victory in the war. From nitric acid are made all the important explosives, smokeless powder, picric acid, trinitrotoluol, ordinary black powder, dynamite, and ammonium nitrate. The last of these materials, the simplest of them all, came during the war into the greatest prominence as one of the most important explosives. In fact, one of the leading munition authorities of England declared that the war could be won only with ammonium nitrate, as no other explosive could be produced in quantity adequate to meet the enormous demands of the Allied armies. This development of the use of ammonium nitrate brought about a heavy demand for ammonia; so that while in the early stages of the war our chief concern was an adequate supply of nitric acid, we soon became no less interested in a sufficient and ample production of ammonia. Of these two nitrogen compounds there are only three important sources. (The first source is Chile saltpeter, or sodium nitrate, which is found in a natural state in the dry regions of Chile, and which until recently furnished the total supply of nitric acid of the world. We depended for our own nitric acid supply at the beginning of the war wholly upon the Chilean imports. were scarce. This was, however, a precarious source of supply. For in the first place, it required ships for its transportation, and ships In the second place, there was always danger that enemy machinations, through the purchase of the Chilean mines, destroying the plants, or blowing up the oil supply used for fuel, would reduce the production; or that our supply might be cut off entirely, by the establishment of a hostile submarine base on the Pacific Coast. All of these possibilities made it unsafe to rely for our nitric acid supply on Chile saltpeter alone. But, even if none of them actually came about, it would still be impracticable to get in this way the huge amount of nitric acid that would be needed by the American Army. 66 The second source of nitrogen products is the ammonia produced as a by-product in the manufacture of gas and coke. There has been developed, as will be described later, a process for the conversion of ammonia into nitric acid, so that if we could get, from any source, an adequate supply of ammonia, it could be converted into nitric acid. But unfortunately, this country was still producing most of its coke in the so-called beehive" oven, which is simply a hemispherical kiln, into which the coal is charged and set on fire; the products of the combustion being allowed to pass into the air, whereby the ammonia and valuable hydrocarbons that might be obtained are lost. It is true that during the preceding decade there had been a rapid introduction of the so-called "by-product" ovens, in which the coal is heated in closed retorts, and the gases are passed through condensers and scrubbers by which the hydrocarbons and the ammonia are recovered. It was even claimed before the war by representatives of the by-product industry that this rapidly increasing supply of ammonia would alone suffice to meet the military needs of the Government; but the result proved that it was utterly inadequate. The production by this process is necessarily limited by the fact that the byproduct industry is dependent upon the steel industry; for it is mainly in the metallurgy of steel that coke finds its use, and ammonia can be produced at reasonable cost only in proportion as there is a demand for coke. The third source of these nitrogen compounds is atmospheric nitrogen. During the last fifteen years there have been developed a number of chemical processes by which the nitrogen of the air is "fixed," as we say, whereby ammonia, nitric acid, or cyanide is produced. Only the three fixation processes which had been operated before the war on a commercial scale will be here briefly described. These are the cyanamide process, the synthetic ammonia process, and the arc process. 1. The cyanamide process starts with lime and powdered coke. The first chemical reaction that takes place results in the formation of calcium carbide (CaC), as follows: CaO+3C=CaC, + CO. This is the substance which is used so extensively in the manufacture of acetylene for use as an illuminant and in oxy-acetylene welding. The carbon monoxide escapes as a gas. The first step in the cyanamide process is carried out in huge electric furnaces. The charge of lime and coke in small lumps is fed down through the furnace, in the center of which stands a large carbon electrode; the walls of the furnace form the other electrode. The mixture is heated to a very high temperature, and the melted carbide is tapped off at the bottom from time to time, and allowed to solidify. The carbide is then crushed and subjected to the nitrifying process. It is packed into large basket-shaped containers three to six feet high and two to three feet in diameter. These baskets, which are perforated with small holes, are enclosed in an iron vessel into which is forced nitrogen made by distilling liquefied air. The chemical reaction is started by heat produced by passing an electric current through a resistance wire, placed in the axis of the basket. The reaction which takes place is as follows: CaC2+ N2 = CaCN2 + C. |