The daily morning journal and courier., 1903-05-02
rNcANDEscENT LAMPS.
Details of the Process, Long Regard

Details of the Process Long Regarded as a Trade Secret. The manufacture of an incandescent electric lamp is of special interest be- cause many of the operations have heretofore been regarded as trade se- crets and carefully kept from the pub lie.
 The delicate filaments which produce
 the light are formed by squirting a
 paste made from cellulose (wood' pulp) through dies, from which it emerges in the form of fine threads, which when
 dried are tough and flexible. These threads before they are dry are formed | into the desired shape. .T.,.} s # k They are then packed in carbon dust and subjected to intense heat for many 1 hours. The cellulese is completely
 charred, and the fllament now practi- cally consists of charcoal. It is then
 suspended in an atmosphere of hydro- carbon vapor, in vessel in which a partial vacuum has been made. and a current of electricity sufficient to bring it to incandescence is sent through it,
 This decomposes the hydrocarbon, and carbon soot somewhat resembling graphite is deposited on the filament, This is technically known as flashing" !" After this treatment the filament has a metallic Iustre resembling polished steel. The glass bulbs are blown in noulds to secure absolute uniformity, and as they come from the glass-fouse they are perfectly smooth at the rounded end and have a long open neck To the rounded end is fused short length of glass tubing opening into the interi- or of the bulb. This is subsequently, used for connecting the bulb to the ex- haust pump. ....... I
 For making the connection through the glass between the carbon ilament and the wire the most satisfactory ma terial is platinum, because it adheres firmly to fused glass and because it ex- bands and contracts at the same rates. If this were not the case when it got hot through the passage of the current it would either expand more or less than the surrounding glass, and either break it or make a space through which air would leak So through the little glass stopper which will eventually project down into the neck of the bulb are fused two platinum wires. This stopper which has f1ange at one end, is now called the mount or stem.
 Next the filarnent is fastened to the ends of the platinum which projects from the stem. This is accomplished by means of a special cement which will stand a red heat. Over this paste is deposited a layer of carbon. The paste is then dried in an oven, and the stem, with it's attached flament, is fastened onto the bulb by fusing the flange on its upper end about the neck of the bulb. a ,.3 %-r' g
 After this joint is carefully tested to be sure there are no leaks the exhaus- ton of the air is accomplished by
 means of a mechanical air pump, the last traces of gas or air being removed from the bulb by chemical means. When the vacuum is sufficiently high the tube through which the air has been exhausted is sealed off by means of a small lamp, leaving the small round tip seen on the spherical end of the finish- ed lamp.
 The lamp is now practically complet- ed, and is sent to the testing depart ment. Here it is subjected to a series of severe tests before 1t is considered ready for the market. If it passes these successfully the base (the portion by means of which it is screwed into a bracket) is cemented on, and the conl- pleted lamp goes to the shipping depart
 ment.-EIectrical World.