Page:Popular Science Monthly Volume 78.djvu/305

Rh by him—the fixation of atmospheric nitrogen, that is, the conversion of this gas, inert and non-utilizable, into nitrogen compounds which could be assimilated by the plant and from this pass to the animal for the building and repair of its tissues. There was the problem for the chemical engineer and the chemical engineer has worked out its solution. The principle employed is to burn the nitrogen of the atmosphere through the agency of the oxygen, by passing the air through a flaming electric discharge. Although this sounds simple, the commercial operation was most complex. The shape and size of the electrodes and their container, the correlation of quantity and intensity of the electric current, of the temperature and volume of air, all demanded patient care as well as expert knowledge. Not only must oxidation be controllable, but the costs must be studied and reduced until a commercial success was assured. The first companies did not succeed and went into bankruptcy, but now, using the power of the mountain streams of Norway and the Tyrol, the nitrogen of the air yields its freedom and leaves the factory as calcium nitrate and sodium nitrate, which go to be mixed with the other constituents of artificial plant foods, or as nitric acid, which is used in so many technical processes. There are now in operation chemical plants which can place upon the world's markets annually 100,000 tons of pure calcium nitrate thus obtained through the use of atmospheric nitrogen.

While one group of chemists were following this solution of the nitrogen problem others had taken another line, influenced partly by a different motive. This was the development and an outgrowth of the calcium carbide industry. After the French chemist, Moissan's, brilliant work upon the production of carbides by the electric furnace the field was occupied commercially and in many places where cheap waterpower could be obtained—Niagara Falls, Norway, Switzerland and others—calcium carbide was made for acetylene lighting. The annual output is about 200,000 tons. But this is more than is called for in the preparation of acetylene. There must be some way of using the excess, and the services of the chemist were in demand.

When free nitrogen is led over calcium carbide at the proper temperature it is absorbed, forming calcium cyanamide. The latter is decomposable by steam, its nitrogen being evolved as ammonia, a valuable plant food. There is the same decomposition when the calcium cyanamide is placed in the ground; the decomposition is then so slow that the ammonia does not escape into the air, but is held in the soil until it is utilized by the plant.

Thus the chemist has built another bridge over the gulf between free and combined nitrogen, cyanamide, or "nitrolime," acting as the middle pier. Nearly 200,000 tons can be annually furnished by the works now built or under construction.