THE SEEL INCANDESCENT-LAMP FILAMENT.
A patent has just been issued in this country for an incandescent-lamp filament which is both novel and successful. The following is the method of preparation: threads of cotton, silk, or other vegetable fibre are steeped in a solution consisting of a silicate or salt, gum-senegal, and caustic soda, and then rolled between warm grooved rollers. The thread is then carbonized in the usual manner. To regulate the resistance of the resulting filament, it is placed in a vessel into which melted paraffine is run, and when the latter hardens an electric current is sent through the filament. As the thread heats, part of the paraffine nearest to it is liquefied, and as the heat becomes more intense, carbon is deposited on the filament, the solid outer shell of the paraffine preventing any air from getting to it. The resistance gradually decreases as more carbon is deposited. When it reaches its proper value, the current is cut off, the whole of the paraffine melted, and the thread removed. The gum-senegal completely fills the pores of the filament, making it very strong, while the silicate and caustic soda surround the inner core. We have, then, three layers, -the central carbonized thread, the silicate, and the outer layer of deposited carbon.