. Electrical world. ther carrier of the current in thearc flame must be found. The material which in an arc lamp electrode,by replacing the carbon used at present, would constitute an essen-tial advance in the art of illumination, must, therefore, fulfill the fol-lowing conditions: It must be a good conductor when solid and its vapors must beconductors of the arc. It must be incombustible so as to give a long burning arc. It must give a spectrum of high brilliancy; that is, an arc of highefficiency. The light must be distributed approximately uniformly over thewhole spectrum; that is, it must
. Electrical world. ther carrier of the current in thearc flame must be found. The material which in an arc lamp electrode,by replacing the carbon used at present, would constitute an essen-tial advance in the art of illumination, must, therefore, fulfill the fol-lowing conditions: It must be a good conductor when solid and its vapors must beconductors of the arc. It must be incombustible so as to give a long burning arc. It must give a spectrum of high brilliancy; that is, an arc of highefficiency. The light must be distributed approximately uniformly over thewhole spectrum; that is, it must give a white light. In magnetite, or the black oxide of iron, one of the most commoniron ores, a substance was found having the required characteristics. By very extensive investigations of the phenomena taking placein the electric arc with different materials as arc terminals, it wasfound that the material which carries the arc flame issues from thenegative terminal as a high velocity which, when striking the. FIG. 3.—MAGNETITE ARC. positive, produces heat. If, therefore, the positive terminal cannotconduct this heat away, it may get hotter than the negative and doesso in the carbon arc. Therefore, in the carbon arc the positive terminal burns away morerapidly. The greater heat produced at the positive terminal is thereason for introducing arc-coloring substances in the flame carbonarc lamps into the positive electrode. They are introduced into thearc by evaporation, and at the hotter positive electrode evaporationis more rapid. This also has led to the misconception that the posi-tive terminal feeds the arc while in reality it has no direct influenceon the phenomena in the arc, but the spectrum of the arc is that ofthe negative terminal, except where material of a boiling point lowerthan the temperature of the arc flame is introduced into the arc. If the positive terminal is made large enough and a good conductorof heat so as to carry away the heat, it does not wear a
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectelectri, bookyear1883
