Popular Science Monthly/Volume 48/January 1896/The Electric Furnace in Chemistry
By H. MOISSAN.
THE reverberatory electrical furnace with movable electrodes, which we devised in 1802, and in which we have made many improvements, is very simple in construction, has been of great service, and has permitted us to deal with problems which have been hitherto insoluble. By means of this apparatus we have been permitted, by obtaining a sufficient temperature, to produce the diamond, to crystallize metallic oxides, to reduce those which have hitherto been refractory, to melt metals heretofore infusible, to distil lime, silica, zirconia, and carbon, and to cause an abundant volatilization of such metals as platinum, copper, gold, iron, manganese, aluminum, and uranium. Some bodies that could not be brought to a condition of fusion, like magnesia, uranium, tungsten, and molybdenum, could be made to assume the gaseous state in the electric furnace. In our studies we have frequently dealt with the vapor of lime and silica.
When using the currents of machines of from one hundred to three hundred horse power, we have in the midst of the furnace the temperature produced by the electric arc; a few centimetres beneath, the crucible containing the matter to be experimented upon; and at the bottom, a mass of quick-lime in full ebullition. The imperfect conducting power of this substance is a fortunate quality for us. It isolates the heat which the electric arc can furnish into the smallest possible cavity.
This new apparatus permits us to approach the study of a whole series of simple bodies which have been till now mere laboratory curiosities, because of the want of adequate means of obtaining them.
It is easy, with the aid of the electric furnace, to produce abundant meltings of chromium by reducing the sesquioxide. This melting, refined, yields chromium, an unoxidizable metal very different from the specimens which have been hitherto obtained. It can be filed like iron, and takes a fine polish. Chromium, then, more infusible than carbon, can now be used in preparing alloys without the need of the intervention of ferro-chromium, which has the disadvantage of containing up to ten per cent of carbon.
This preparation opens the way for the effective study of the alloys of chromium. In combination with aluminum or copper, it gives interesting results. Pure copper, alloyed with 0•5 per cent of chromium, assumes a double resistance and suffers less change than copper in contact with moist air.
Molybdenum, previously unfused, can also be obtained in notable quantities. By heating, in a continuous electric furnace, a mixture of oxide of molybdenum and charcoal, a melting of the metal is obtained which flows readily and can be easily molded. It furnishes a definite carburet, very well crystallized. It is refined by a new heating in the electric furnace, with an excess of oxide of molybdenum. The melted metal thus obtained has a fine grain and a brilliant surface. It can be filed, and forged, at a red heat, upon the anvil; and with iron it furnishes a steel that can be tempered. These are all new properties.
Tungsten has been heretofore known to chemists only as a powder. Under the action of the electric arc, the oxide of tungsten is reduced by means of carbon, and gives in a few minutes a well-melted bottom, covered with a fine layer of the blue oxide of tungsten. This metal, which is still more infusible than chromium and molybdenum, can be liquefied with great facility. It does not seem to have a strong affinity for carbon, and is obtained without special precautions as one of the purest metals we have prepared.
The different oxides of uranium can not be reduced by carbon at the ordinary temperatures of our furnaces; but when a mixture of the sesquioxide of uranium and carbon is subjected to the high temperature of the electric furnace, the reduction takes place in a few instants. After cooling, an ingot may be drawn from the crucible possessing a brilliant fracture and great hardness. When this uranium is slightly carbureted, it presents the property of striking fire in contact with flint. The particles thrown off burn with an intensity and an energy far superior to those exhibited by a piece of iron.
All these simple bodies melt at more or less high temperatures. By the side of them we may place other metals the minerals of which are rare—such as zirconium and vanadium.
Vanadium, on which Prof. Roscoe has made some interesting studies, was not known, except as a gray powder including hydrogen, oxygen, and a little of some alkali metal as impurities; but Prof. Roscoe has had the pleasure of seeing in my little laboratory at the École de Pharmacie several hundred grains of it, under the form of cast metal pieces, having a crystalline and brilliant fracture. This simple body, the mineral of which occurs more extensively than is generally supposed, is very difficult to melt, it hardly liquefying in the current produced in the Edison dynamo by an engine of forty horse power.
In our studies of titanium, a mixture of charcoal and titanic acid gave, with a machine of four horse power, protoxide of titanium; with a machine of forty-five horse power we obtained only nitride of titanium; under the action of currents of from one hundred to three hundred horse power we prepared by kilogrammes a crystallized carbide, and then real titanium, the properties of which are wholly different from those formerly attributed to the gray powders that bore that name. This substance takes fire in fluorine; decomposes water only at a bright-red heat; and possesses the curious property of burning in nitrogen at a high temperature, yielding the nitride of titanium studied by Friedel and Guérin. It readily combines with carbon and silicon, but does not unite with argon. Its melting point is very high, it resembling carbon in that respect. It differs from carbon, however, in the fact that while carbon under the ordinary pressure and at a great elevation of temperature passes from a solid to a gas without becoming liquid, titanium can, in the electric furnace, be liquefied and then volatilized.
Most of the simple bodies furnish, with carbon, well-defined combinations, crystallized and stable, at a high temperature, which are destined to furnish a new chapter to mineral chemistry.
All these simple bodies which we have obtained by kilogrammes in the electric furnace form also borides and silicides finely crystallized and so hard that some of them easily cut the diamond. What part they are to have in the manufacture of steel, and whether they are destined, like chromium, to give new properties to iron, are questions for the future to answer. But a new chemistry of high temperatures is forming, from which industry will most likely draw numerous applications.
It is recognized on all sides that some of our industries are about to suffer important modifications through the use of electrical forces. We ask of the forces of Nature all they can yield; and they are capable of easy use when transformed into electricity.—Translated for the Popular Science Monthly from La Nature.