THE ELECTRIC FURNACE
Moissan’s Great Work—What we owe to the Electric Furnace— The Blowpipe—The Thermit Process.
SOME metals, such as tin and lead, melt at very low temperatures. Silver, gold, and copper require greater heat, yet all melt at or about a temperature of a thousand degrees centigrade. Iron is more difficult, for it takes a temperature of 1600 degrees centigrade to melt wrought iron, while metals of the platinum type demand still higher temperatures to reduce them.
Until the invention of the blast furnace, man had at his command no way of obtaining a heat fit for making steel, and even in a blast furnace the temperature does not exceed 1600 degrees centigrade. Fifty years ago chemists and others were already realizing the need for higher temperatures,
but the question was how to get them. In the year 1892 Henri Moissan, a French chemist, attached, like the Curies, to the University of Paris, had made a rather rough electric furnace of the "resistance" type, so termed because the heat is produced by the high electrical resistance of the material with which the furnace is charged. A little later Moissan went to work on different lines, and constructed an arc furnace in which the current is led in by two carbon rods which meet just above the substance under experiment. The points in contact are raised to a white heat, and are then separated, whereupon the electric current bridges the gap and an immensely high temperature is produced.
The body of Moissan’s furnace, also the lid, were constructed of blocks of lime, lime being one of the most perfect of nonconductors of heat. With his comparatively simple device, but using a powerful current, Moissan found himself able to command temperatures up to 4000 degrees centigrade. The lime itself began to melt, and the heat of the central furnace was so intense that it was necessary for the operator to wear glasses to protect his eyes. Ordinary metals did not merely melt; they actually boiled. When copper was placed in the furnace, flames of green copper gas streamed out of the holes through which passed the carbon rods.
In Siemen’s furnace it had taken an hour to melt a pound of iron, but in Moissan’s the metal was fluid within three minutes. Moissan next began to experiment with unyielding substances such as chromium, manganese, tungsten, vanadium, and silicon. These had hitherto been mere chemical curiosities, obtainable only in very small quantities; but the new furnace provided a means of obtaining them in larger quantities, and in this way proved of immense value to mankind. These substances, you see, have the power of influencing steel when mixed with it in proper proportions. Chromium makes steel extraordinarily tough, manganese and tungsten make it hard, vanadium gives it strength. A great deal of the steel used for the frames of motor cars is strengthened by the use of vanadium. Mix silicon with steel and you get a metal suitable for making springs.
Moissan’s electric furnace was the starting point of a new age in steel manufacture. Modern guns, armor-plate cars, and high-speed tools could never have been made had it not been for the developments here mentioned.
Another of Moissan’s achievements was the manufacture of artificial diamonds from carbon. These diamonds were but the tiniest fragments of crystalline carbon, and were enormously costly to produce. Moissan’s method of making them was to dissolve coke dust in molten iron, using a crucible made of carbon. When the intense heat of the electric furnace had rendered the whole mass fluid, the crucible and its contents were suddenly dashed into cold water. The sudden cooling of the iron set up such tremendous pressure that the melted carbon was crystallized and turned into minute diamonds. The precious stone which we call the diamond is nothing but pure carbon (or charcoal) in a crystallized form.
Natural graphite, commonly called blacklead, is another form of carbon. In its natural form it had always been scarce, yet new uses for it were constantly appearing. It was needed not only for lead pencils, but for stove blacking, for electrical appliances, and, above all, for lubricating purposes. Before the invention of the electric furnace the idea of manufacturing graphite would have been scouted as ridiculous; but once Niagara was harnessed, and its huge electric power made available, the operation became as simple as making soap. Graphite being merely pure carbon, by treating anthracite coal in the electric furnace the hard black lumps are turned into a fine black powder, greasy to the touch, and capable of a hundred uses. To-day every ounce of blacklead used for polishing a kitchen range or stove is the product of one of these wonderful electric furnaces.
Some years before Moissan made his attempts at turning black carbon into crystal diamond, another experimenter was in the field. This was Mr. E. G. Acheson, one of Mr. Edison’s band of brilliant young chemists. Not having electric heat, he made use of the oxyhydrogen flame, and perhaps for that reason failed to produce diamonds. Later, Mr. Acheson was one of the pioneers of electric lighting in Europe, and installed the first electric-lighting plants in Milan, Genoa, Venice, and Amsterdam. When this work was finished he returned to America, and was placed in charge of the new power works at Niagara. The amount of electricity obtained from this mighty fall of water was far greater than any yet procurable, and Mr. Acheson decided to make a fresh attempt at the production of artificial diamonds. But he had also another object in view. At that time emery (oxide of aluminium) was the material in universal use for grinding down rough metal castings, and Mr. Acheson thought it might be possible to produce some hard substance which would do the work of emery. Such a material, if it could be cheaply made, would certainly have great value.
After considering the matter, the chemist believed that carbon mixed with clay would produce an extremely hard substance, and that if, in cooling, the carbon should separate from the clay, the result might be real diamonds. He therefore mixed clay and coke dust together, placed them in a crucible, inserted the ends of two electric-light carbons into the mixture, and connected the carbons with a dynamo. The fierce heat fused the clay and carbon together, and, when the resultant mass had been cooled, a few small purple crystals were found. These were so hard that they scratched glass; but after examining them, Mr. Acheson was sure they were not diamonds. He thought, however, that they might be rubies or sapphires. He then repeated this experiment, getting similar but larger crystals, and these, to his amazement, proved to be harder than rubies, even scratching the diamond itself. He showed them to jewelers, chemists, and geologists, who nearly all pronounced them to be natural gems dug from the bosom of Mother Earth. One of the authorities to whom they were shown was Professor Geikie, the celebrated Scottish geologist. After he had examined them he was told that the crystals had been manufactured in America, but this statement he flatly refused to believe. "Those Americans!" he exclaimed quite crossly. "What won’t they claim next? Why, man, those crystals have been in the earth a million years."
Mr. Acheson named his new gems "carborundum", and soon found that he had discovered exactly what he had been looking for, namely, a cheap and perfect substitute for emery. In 1893 he made seven tons of carborundum, and by 1902 was producing no less than 2700 tons yearly. The mixture used is 34 per cent. coke, 54 per cent. sand, 10 per cent. sawdust, and 2 per cent. common salt. After the cooling the carborundum is found in large crystals round the carbon core; and outside is another substance, called "siloxicon", which is used for furnace linings. The furnaces used for making carborundum have to be built up afresh for use each time. The heat is so terrific that many of the bricks melt like cheese, and new ones must be supplied.
The heat produced in the electric furnace is probably equal to that of the sun itself, and is no doubt amply sufficient for the production of diamonds. Science, however, has not yet learned Nature’s secret of producing the gigantic pressure which is equally essential.
Far more important than carborundum is another product of the electric furnace called "calcium carbide." This was first made by accident at the works of the Cowles Electric Smelting Company at Cleveland, Ohio. On the dump were found some lumps of porous gray stone which, when dropped into water, gave off a gas which exploded at the touch of a match. Calcium carbide is produced simply by heating together carbon and common lime. The two unite into a sort of extremely hard and heavy grayish stone, the great value of which is that it gives off, when damped, the gas called acetylene. Acetylene burns with a white flame, giving a most wonderful light strongly resembling that of the sun; and many private houses all over the world are lit with acetylene gas, which is very simple and easy to make and store. It is even more simple to burn, for it does not require a mantle, as does coal or petrol gas.
But the great value of acetylene gas is for welding purposes. Previous to the discovery of acetylene, welding was accomplished by means of the oxyhydrogen blowpipe flame, by which a temperature of 2000 degrees centigrade could be obtained. But with acetylene, which is more easily handled and cheaper, a flame twenty per cent. hotter could be obtained. With the oxyacetylene blowpipe a man can attack sheets of armor plate up to a thickness of an inch and a half, and cut it like cheese. An elliptical manhole—say sixteen inches by ten inches—can be cut in a one-inch boiler plate by this method in four minutes, and an armor plate six inches thick can be cut at the rate of a yard in ten minutes. For repair work, and especially for repairing damaged battleships, oxyacetylene is simply invaluable. It must, however, be confessed that the discovery has another and less pleasant side, in that it has been adopted by criminals; the oxyacetylene flame has been used again and again by safe breakers to open steel safes. Workers with the oxyacetylene blowpipe have to take precautions against the intense heat and dazzling glare. They must wear blue glasses, and work behind a shield, for otherwise they would very soon be blinded and scorched.
Even now we have not come to the end of the benefits conferred upon mankind by the use of the electric furnace, for without the great heat which it produces we should be deprived of our supply of that wonderful, light, and useful metal known as aluminium.
One of the most important of the works at which aluminium is extracted stands on the south shore of Loch Ness in Scotland, and is worked by water power from the famous Falls of Foyers. The great Girard turbines work under a vertical head of three hundred and fifty feet of water, and five thousand horsepower is employed day and night (so long as the water lasts) in the production of aluminium. The bauxite comes from the north of Ireland; the metal, as produced at Foyers, is 99.5 per cent. pure.
Aluminium is rapidly becoming the most valuable of all metals to man. Its most noticeable feature is, of course, its wonderful lightness. Bulk for bulk, it is only one third the weight of cast iron and less than one fourth that of lead. It is so ductile that wires can be made of it less than one hundredth of an inch in diameter, and so malleable that it can be hammered out into sheets 1/40000 of an inch in thickness. It is also a good conductor of electricity. As a substitute for iron in the manufacture of cooking utensils it is coming into very wide use, for it is an excellent conductor of heat, yet is not easily tarnished or affected by acids. It is easily cleaned, and has the great advantage over enameled ware that it does not chip. For military canteens, or for travelers’ or explorers’ outfits, its lightness makes it invaluable. Nearly all the great firms, which make such things as meat extracts, mineral waters, margarine, sweets, sugars, jams, and milk preparations use vessels made of aluminium. For optical and scientific instruments aluminium is used more and more every year. Motor-car manufacturers would be lost without this metal, for it is the ideal material for gear cases and pistons. Various alloys, or mixtures, of the metal are used for motor-car bodies and the like. The framework of the modern airship is built entirely of aluminium alloys. One of the most valuable properties of this metal is its readiness to mix with others; and some of the alloys, while little heavier than the pure metal, are almost as strong as steel. Never a month goes by without some new use being found for this wonderful gray metal, and it might almost be said that an aluminium age is succeeding the age of iron and steel.
In addition to those substances already mentioned there are other productions of the electric furnace. One is carbon bisulphide, which is formed by running melted sulphur over red-hot carbon, and another is phosphorus, of which the world’s chemists are now using more than a thousand tons a year.
Time and again we notice how each step forward in the path of progress leads to new and unexpected discoveries. The use of the electric arc led to the mass production of aluminium; this metal in its turn has of late years become a cheap and convenient agent for the production of high temperatures. When it is powdered and mixed with the oxides of other metals the mixture burns so fiercely that the whole mass melts at a white heat, the aluminium combining with the oxygen of the oxide, while the other metal remains in the crucible in a pure state.
This new process, by which chromium, manganese, vanadium, and similar metals are easily produced from their oxides, has been given the name of aluminothermy. One of its most interesting developments has been the welding of iron and steel by means of thermit. This is simply a mixture of aluminium powder and ferric oxide, or iron rust. When this mixture is ignited in a crucible, the reaction is so violent that the temperature rises to 3000 degrees centigrade. The iron collects at the bottom of the crucible, and can be poured at once over any parts that need to be welded. Thus car rails can be joined after they have been laid in position. If a ship breaks her stern post, it is easy to repair it in dry dock and make it as good as new within a few days. Formerly the casting and fitting of a new stern post would have taken many weeks.
There are plenty of other uses for thermit. You will have heard of the incendiary bombs that were dropped on London during the Great War. They produced such a heat that if one fell in the middle of the street the woodwork on each side was scorched. These bombs were filled with thermit.