The current is delivered from the Niagara Power Company under a pressure of 2200 volts. The conductors run first into the transformer-room, which adjoins the furnace-room, and is there transformed down from 2200 volts to an average of about 200 volts. The transformers at these works have a capacity of about 1100 horse-power. About 4 per cent of this power is converted into heat in the process of transformation, making a loss in electrical energy of a little over 40 horse-power. This heat would be sufficient to destroy the transformer if some arrangement were not provided to carry it off. We have already described how this is done through the medium of a circulation of oil. Because of the low voltage and enormous quantity of the current passing from the transformer to the furnace very large conductors are required. The two conductors running to the furnace have a cross-section of eight square inches, and this enormous current, representing over 1000 horse-power, is passed through the core of the furnace, and is kept running through it constantly for a period of twenty-four to thirty-six hours.
Let us consider for a moment what 1000 horse-power means; as this will give us some conception of the enormous energy expended in producing carborundum. A horse-power is supposed to be the force that one horse can exert in pulling a load, and this is the unit of power. However, a horse-power as arbitrarily fixed is about one-quarter greater than the average real horse-power. If 1000 horses were hitched up in series, one in front of the other, and each horse should occupy the space of twelve feet, say, it would make a line of horses 12,000 feet long, which would be something over two miles. Imagine the load that a string of horses two miles long could draw, if all were pulling together, and you will get something of an idea of the energy expended during the burning of one of these carborundum furnaces.
Within a half hour after the current is turned on a gas begins to be emitted from the sides and top of the furnace, and when a match is applied to it, it lights and burns with a bluish flame during the whole process. It is estimated that over five and one-half tons of this gas is thrown off during the burning of a single furnace. This gas is called carbon monoxide, and is caused by the carbon of the coke uniting with the oxygen of the sand. When we consider the vast amount of material that comes away from the furnace in the form of gas it is easy to see why it is necessary to introduce sawdust or some equivalent material into the mixture, in order to give the whole bulk porosity, so that the gas can readily escape. We should also expect that after five and one-half tons had been taken away from the whole bulk that it would shrink in size. This is found to be the case. The top of the mass of material sinks down to a considerable extent by the end of the time it has been exposed to this intense heat. Gradually, after the current has been turned on, the core becomes heated, first to a red, and afterwards to an intense white heat. This heat is communicated to the material surrounding the core, producing various effects in the different strata, owing to the fact that it is not possible to keep a uniform heat throughout the whole bulk of material. Some of it will be "overdone" and some of it "underdone." The material which lies immediately in contact with the core will be overheated, and that, which at one stage was carborundum, has become disintegrated by overheating.
The silica of the compound has been driven off, leaving a shell of graphitic substance formed from the coke.
After the current is shut off and the furnace has cooled down, a cross-section through the whole mass becomes a very interesting study. The core itself, owing to the intense heat it has been subjected to, has had the impurities driven out of the coke, leaving a substance like black lead, that will make a mark like a lead-pencil, and is really the same substance, known as plumbago, in one of its forms. It is the carbon left after the impurities have been driven out of the coke. Surrounding the core for a distance of ten or twelve inches, radiating in every direction, beautifully colored crystals of carborundum are found, so that a single furnace will yield over 4000 pounds of this material. Beyond this point the heat has not been great enough to cause the union between the carbon and silica, which leaves a stratum of partly-formed carborundum; outside of that the mixture is found to be unchanged.
These carborundum crystals are next crushed under rollers of enormous weight, after which the crushed material is separated into various grades for use in making grinding-wheels of different degrees of fineness. This crushed material is now mixed with certain kinds of clay, to hold it together, and then pressed into wheels of various sizes in a hydraulic press, and afterward carried into kilns and burned the same as ordinary pottery or porcelain. These wheels vary in size from one to sixteen inches. The substances used as a bond in manufacturing wheels are kaolin, a kind of clay, and feldspar.
While carborundum has already a large place as a commercial product, there is no doubt but that the uses to which it will be put will vastly increase as time goes on. This product may be called an artificial one, and never would have been known had it not been for the intense heating effects that are obtained from the use of electricity. It certainly never could have been brought into play as one of the useful agencies in manufacturing and the arts. It is not known to exist as a natural product, which at first thought would seem a little strange in view of the evidences of intense heat that at one time existed in the earth. Its absence in nature is explained by Mr. Fitzgerald by the fact that "the temperatures of formation and of decomposition lie very close together."