A SIMPLE ELECTRIC FURNACE KISSELAND NORBERT KRAMBR. ST. MARY'SACADEMY, SANANTONIO, TEXAS
Wishing to duplicate a few experiments which required rather high temperatures, we found that the only solution to the problem was the bnilding of a furnace which would furnish the required temperature. The cost of a factory-built furnace was prohibitive, and so we set out to supply our own needs. The furnace is of the indirect electric arc type and the arc is established between two one-half inch cored carbons about a foot long. This size of carbons is sufficiently large to carry the rather heavy current which is used. The furnace operates on alternating current, requiring from fifty to a hundred amperes, depending on the temperature to be reached. The shell of the furnace is of heavy iron pipe, measuring six inches inside diameter. All cuts on this pipe are made a t right angles. The shell carries two holes of one and one-quarter inches in diameter, centers being one and three-quarters inches from the top of the shell. The upper opening is fitted with a circle of transite. This circle is made to fit on the inside of the shell, where it is held by means of bolts. A hole is cut in the transite disk as an entrance to the crucible cavity. Another disk, a little smaller than the first, but having MOVABLE ELECTRODE the inner hole cut one-half an inch larger , in diameter, is then cemented to the first with retort cement. A reference to the accompanying diagram will clarify this expfanation. A large fire-clay crucible is used to form the crucible cavity. This should he bored to allow for the entrance of the carbon electrodes. The bottom of this crucible is filled with retort cement in order to hold the smaller crucible a t the proper height. The holes in the shell are fitted with tubular insulators made of porcelain. These can be bought a t an electrical supply house for a trifling sum. They protect the electrodes from making contact with the shell and thereby causing a "short." Clay is used as the heat insulator. However, if it is available, magnesite is far better and lighter. The clay is packed tightly in the interior of the furnace and the bottom is then bolted into place. The bottom transit disk is of the same diameter as the furnace shell and is bolted directly to the latter. The cover is a two-inch section of the heavy piping and is fitted with two transite disks. One fits inside of the pipe and the other on top of the pipe. If desired, a peep-hole can he put in the cover. This is of advantage as one can then watch the arc, without removing the cover of the furnace. This cover is also packed with clay or magnesite. A handle is a very convenient addition to the top. 147
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JOURNAL OF C H E M I C A L E D U C A T I O N
JANUARY, 1932
Brackets are put on the side of the furnace in order to steady and support the electrodes. These are made of brass strips, '/a'' X '/
