The process was orginally developed for the production of a fertilizer material to replace the more expensive sodium nitrate or ammonium sulphate, but processes have since been devel oped for the conversion of the nitrogen of the cyanamide into ammonia and for the oxidation of the ammonia into nitric acid, thus provid:ng a means for the chemical utilization of the nitrogen of the air. This same result has been secured by the direct oxidation processes for atmospheric nitrogen, which will be considered later.
Graphite.—Artificial graphite was first con sidered as a commercial possibility when it was noticed that in the carborundum furnaces masses of graphite frequently resulted from the overheating of the carborundum in the center of the furnace, the carborundum being decom posed and the silicon volatilized, leaving the carbon as graphite. The process was then car ried on with the intentional overheating of the entire charge, with the result that it was con verted into graphite. It was eventually found that all carbides decompose with the formation of graphite and the volatilization of the metal, and that it was not necessary to make up a carborundum charge to secure graphite, but that any carbonaceous material could be graphi tized that carried a uniform mixture of metal lic oxides, for example, coke or anthracite coal. The next step was the graphitization of molded carbon matenals, particularly electrodes, it be ing only necessary to incorporate tuuformly throughout the body, while in the process of manufacture, a small percentage of some metal lic oxide, preferably Fe203, this being largely volatilized out in the course of the graphitiza tion. The amount of amorphous graphite pro duced in this way now amounts to about ten million pounds annually, and the electrode material graphitized to at least half that amount Alumina.— Electrically fused alumina under the trade-names of ualundump and 4aloxite is used mainly for abrasive purposes and to a lesser extent as a refractory material mainly for laboratory apparatus. The process consists in fusing down pure calcined bauxite in an electric furnace. The furnace is of the crucible type with two electrodes dipping into it. When the furnace is filled it is shut down, the sides stripped off and the block of alumina, weighing about five tons, is cooled slowly and then broken to lump form for shipment. The furnace works at 110 volts and 2,500 amperes, consuming 275 lcilowatts. The energy consumption is about 2.1 kilowatt hours per kilogram of alumina. This is about half the power requirement for car borundum, but the raw material is more ex pensive, so that the product is a trifle more expensive than carborundum.
Fused Quartz.— Fused silica ware is now made by several manufacturers, and almost any shape can be secured that is made in glass, pro viding the size is not too great. The price of the material is still quite high. Pure silica is fused in a small electric furnace and the main difficulty encountered is the heating of the silica to a sufficient temperature for it to flow easily (2,000° C. or 3,600° F.) without excessive volatilization and without the silicon combining with the carbon electrodes to form siloxicon or silicon carbide.
Phosphorus.— The disadvantages of the old chemical methods for the manufacture of phos phorus were considerable, the reduction of phos phoric acid or a phosphate giving a very low yield. The operation is now carried on electro thermally, reducing a mixture of bone ash, calcined phosphate rock or calcined wavellite (A1P0.) with carbon and sand. The phos phorus distils off and is collected under water, and the calcium or aluminum silicate slag is drawn off intermittently. The yield of phos phorus is 80 to 90 per cent and the furnace requires 11.6 kilowatt hours per kilogram of phosphorus.
Carbon Bisulphide.— The chemical manu facture of this substance was attended with con siderable difficulty, but the electrothermal pro duction works very easily, and one plant sup plies the entire demand of this continent. A current of electricity passing through a granu lar carbon resistor volatilizes sulphur to vapor, which passes up through a column of hot char coal above the resistor, forming CS., which is drawn off from the top of the furnace and con densed. The energy consumption is about 1.15 kilowatt hours per kilogram of CS,, an efficiency of about 35 per cent.
Nitrogen Fixation.— The direct oxidation of the nitrogen of the atmosphere for the pro duction of nitric acid and ammonia is a re sult long sought by numerous investigators, but it is only within recent years that it has become a commercial possibility. This has now been accomplished in three types of processes. One of these, the direct combination of nitrogen with hydrogen to form ammonia, is more chem ical than electrothermal, and so does not con cern us here. The second type of process is a more or less indirect conversion of the nitro gen, largely electrothermal in character and is treated in the preceding paragraphs on Cal cium Carbide and Cyanamide. The third type of process is the direct combination of atmospheric nitrogen and oxygen to form nitrous oxide under the influence of a high tension electric discharge. This process is gen erally known as the arc process, while the pre ceding process is known as the cyanamide process.