Page:Popular Science Monthly Volume 49.djvu/814

790 an address by W. R. Addicks, of Boston, Mass., delivered before the New England Association of Gas Engineers at their twenty-sixth annual meeting:

The electric furnace is of ordinary brick, two and a half by three feet (inside measurements) at the bottom. The front side consists of four iron doors. The electric current enters at the bottom and top; the lower electrode is an iron plate covered with eight inches of carbon (pieces of carbon pencils or a mixture of coke and coal tar). Sixteen copper cables 0·75 inch in diameter convey the electricity from the dynamos to the bottom electrode; sixteen other cables are connected with the top electrode, which is composed of six carbon pencils each four inches square and thirty-six inches long; these are bound together by a sheet of iron, so as to really form only one pencil. The upper electrode is so arranged that it can be raised or lowered by means of a screw. Dynamos giving a current of from fifty to one hundred volts and seventeen hundred to two thousand ampères are used, actuated by a water wheel of three hundred horse-power capacity. To start the furnace a little carefully ground and mixed lime and coke (this being done by special grinding and mixing machinery, which forms an essential part of the plant) is thrown on the bottom of the furnace, the current turned on, and the upper electrode lowered until an arc is formed between it and the mixture. The carbide soon begins to form, and new material is shoveled in as the ingot is built up. The end of the pencil is kept covered with about a foot of the mixture, and is gradually raised by the attendant until the capacity of the furnace is reached; then the current is turned off and the furnace left to cool. This constitutes the whole process, and is extremely simple and inexpensive, requiring no skilled labor and little machinery. Much time has been lost at Spray in waiting for the furnace to cool, which requires from four to eight hours. In the new plant of the Philadelphia company at Niagara the lower electrode and the bottom of the furnace consist of a car, which, as soon as the run is finished, can be drawn out and a fresh car substituted, thus obviating the loss of time and heat in waiting for the furnace to cool. Many other improvements, including an arrangement by which the mixed lime and coke are automatically fed into the furnace, are expected to materially reduce the cost of manufacture at the Niagara works.

The proportions of lime and coke are roughly calculated by means of the atomic weights involved in the reaction, but in practice it is found that, owing to impurities and loss in the process, these amounts have to be exceeded somewhat. After the mass in the furnace has cooled sufficiently, it is dumped on a grate which holds the carbide and permits the unreduced material,