The discovery of carborundum nearly thirty years ago, brought into use a new and exceptionally efficient abrasive. In 1891, experiments with electric furnaces showed that when clay and crushed coke were heated through a piece of carbon in an electric furnace, the heat fused the two ingredients, and that when the carbon was withdrawn, minute crystals adhered to it. These tiny crystals were found to be amazingly sharp and hard. Subsequent tests proved that the material had great value as an abrasive, and it is now in general use.
The principal materials entering into the manufacture of carborundum are coke, which supplies the element of carbon, and sand, which supplies the silicon. The coke is crushed in a mill, and is then mixed with the sand. The mass of raw material is then placed in an electric furnace for 36 hrs. and a current of 2000 electrical horse-power is passed through it.
The resistance thus interposed results in the generation of enormous quantities of heat, so great is the temperature of the resistance path; the surrounding mass of coke and sand is heated to a point which is between 4000° and 4500° F. In this terrific heat all known metals not only melt, but volatilize (disappear in the form of a gas). Iron and steel are turned to vapor and granite rocks melt away. All the impurities and substances in the coke and sand other than carbon and silicon are destroyed or driven off in gaseous form, and the atoms of these two elements fly together and unite as carborundum.
The total energy used in a single run of a carborundum furnace is 72,000 horse-power hours. Incidentally, enough electric power is consumed to operate an arc light continuously night and day for twelve years, or to operate one 16 candle-power carbon incandescent lamp for two hundred and twenty years.