The Birmingham age-herald., 1902-09-09
lNcANDEscENT LAMPS.
Details of the Process, Long Regarded
 as a Trade Secret.

From the Electrical World.
 The manufacture of an incandescent electric lamp Is of special interest be- cause many of the operations have here tofore been regarded as trade secrets and carefully kept from the public.
 The delicate filaments which produce the light are formed by squirting paste made from cellulose (wood puip) 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.
 They are then packed in carbon dust anu subjected to intense heat for many hours. The celiulose is completely chsrred, and the hlament now practically consists of charcoal. It is then suspended in an atmosphere of hydrocarbon vapor. in vessel in which partial vacuum has been made, and a current of electricity sufficient to bring 1t to incandescence IS sent through it. This decomposes the hy- drecarbon. and a carbon soot somewhat resembling graphite is deposited on a flsment This is technically known as flashing" after this treatment the fla ment has a metallic luster resembling polished steel
 The glass bulbs are blown in mouls to secure absolute uniformity, and as they come from the glasshouse they are per- fectly smooth at the rounded end, and have long open neck. To the rounded end is fused a short length of glass tubing opening into the interior of the bulb. This is subsequently used for connecting the bulb to the exhaust pump.
 For making the connection through the glass between the carbon filament and the wire bringing current the most satisfac- tory material is platinum. because 1t ad- heres very firmly to fused glass and be- cause it expands and contracts at the same rate. 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 1t 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 a f1ange at one end, is now called the mount or stem.
 Next the flament is fastened to the ends of the platinum wire which projects from the stem. This is accomplished by means of special cement which will stand red heat. Over this paste Is de- posted layer of carbon. The paste is then dried in an oven, and the stem, with it's attached filament Is fastened onto the bulb by fusing the flange on it's upper end about the neck of the bulb.
 After this joint is carefully tested to be sure there are no leaKs, the eX2aus ton of the air is accomplished by means of a mechanical air pump, the iasu traces of gas or air being removed from the bulb by chemical means. When the va- cuum is sufficiently high the tube through which the air has been exnaust ed is sealed off by means of a small lamp leaving the small round tip seen on the spherical end of the finisned lanhS.
 The lamp Is now practically completed and is sent to the testing department. Here it is subjected to a serres or seyere tests before 1t is considered ready for the market. If 1t passes rnese success fully the base (he portion by means O. which it is screwed into a bracket) is oemented on, and the completed lamp goes to the shipping department.