Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . tingthread. The filaments are then carefully measured as totheir length and diameter, and assorted for the different sizesof lamps in which they are to be used; the length of fila-ment is nearly proportional to the voltage, and the surface,to the candle power. The filaments are next treated by the flashing process,the object of which is to insure strength and uniformity inresistance. This is accomplished by inserting the filamentin a closed vessel containing hydrocarbon gas and then
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Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . tingthread. The filaments are then carefully measured as totheir length and diameter, and assorted for the different sizesof lamps in which they are to be used; the length of fila-ment is nearly proportional to the voltage, and the surface, to the candle power. The filaments are next treated by the flashing process, the object of which is to insure strength and uniformity inresistance. This is accomplished by inserting the filamentin a closed vessel containing hydrocarbon gas and then rais-ing it to incandescence by passing an electric current throughit. The action deposits carbon on the filament and if somepoints are of a higher resistance than others, their tempera-ture will be correspondingly higher and more carbon will bedeposited at such places. Measuring instruments are insertedin circuit with the filament under treatment and the depositcontinued until the desired resistance is attained. The fila-ment is then ready for mounting upon the platinum leading- 424 PRACTICAL ELECTRICITY.. in wires and is secured to them by a paste of carbon andmolasses. The platinum wires, P, are sealed in the end of aglass tube, A, Fig. 383, which is sealed into the blown glassbulb of the ordinary shape. The upper end of the bulb terminates in a glass tube which isconnected to the air pump. Afterthe proper degree of exhaustion thistube is heated and sealed leavingthe pointed tip, T, on the end of thelamp. 382. Commercial Rating of In-candescent Lamps.—After ex-haustion and sealing of the bulb thelamp is compared with a standard ofillumination, while measurements ofthe pressure at its terminals andcurrent flowing through it are made.The pressure is marked on eachlamp, also the corresponding candlepower and the watts consumption.The standard lamp in general use israted as equivalent to the light givenby 16 candles, and may consumefrom 50 to 60 watts. A 110-yolt55-watt 16-can