The age-herald., 1902-05-04
INcANDEscENT LAMPS.
The Process by Which They Are
 Manufactured.

From Cassier's Magazine.
 Although used so universally, very few even of those who have spent years in the electrical business .haye ever seen an in- candescent lamp in process of manufac- ture The best absorbent cotton is gen. erall,. used as the basis of the filament. The raw cotton Is placed in a pot or yes sel, treated with zinc chloride, and work ed to a pulpy mass which permits or nl- tration and is then carefully filtered through fine mesh platinum filters. Ar ter being filtered several times the densi- ty is brought to the desired value for what is known as the squirting process. The mass" as the pulpy material is called is then placed in soheroidal-shap- e. vessels, which are provided with open ings at both top and bottom. The lower ends are provided with platinum dies, the openings in which are of sufficient size to permit the passage of the mass and orm 1t into a thread of a certain di- ameter depending upon the kind of lamp desired. This is accomplished by sub jecting the mass to air pressure which varies from four to twelve pounds per square inch, depending upon the condi- ton of the mass, temperature atmos- pheric conditions, etc. The temperature ol the water-bath in which the vessels are placed at the time of squirting is about 90 degrees c.
 "The filament passes from the die into a glass jar, whicn Is filled with methyl alcohol, containing ten per cent. solu- ton of hyLro-chloric acid. It immed- ately hardens In this solution, and the acid neutralizes any alkaline effect which may have been retained from the zinc chloride treatment. At this point the filament Is of a yellowish- white color, if r,ae ha dIa and coils itself in the alcoholic solution 1t looks very much like vermicelli. After remaining in this solution for three or four hours, the filament is washed in acid solutions, in pure distilled water, and finally In a bath of methyl alcohol, the entire washing process taking about twenty-four hours. It is then wound upon velveteen drums, which are about eight cen inches in diameter, and is allowed to dry. When thoroughly dried 1t is cut to the desired lengths, and the indvidu- al flaments are made up in punches of ten or more. They are next wrapped around carbon forms to produce the de- sired shape
 These forms, each accommodating a number of fllaments, are placed in a cru- cible and packed in graphite, then a number of forms, etc., the top layer be- ing graphite. The cover is then placed on the crucible and the whole is sealed small openings being left for the escape of the gases, which are driven off in the carbonizing process. Tn, crucible Is placed in the carbonzing furnace and the temperature is gradually raised to about 250O degrees Fahrenheit and main- tained at this point for about twenty four hours. The temperature is then raised to about 4500 degrees Fahrenheit and kept at this point for several hours longer. after which the crucbles are al- lowed to cool slowly. The time occupied in the carbonizing process depends upon the size of the f1laments and for very large filaments may be much longer than the aforementioned period The crucible Is finally unpacked and the flaments are removed, the graphite and forms being preserved for further use.
 After having been sorted the f1laments are again classified according to their electrical resistance, and are then ready for the flashing process.
 'The earlier forms of filaments were far from being of uniform cross section. and the flashing process was introduced to render them more uniform. The pro- cess consists essentially in placing the flaments in a jar containing hydrocar- bon vapor-genrally gasoline or pentane and raising them to incandescence by sending an electric current through -lem. The high temperature decomposes the hydrocarbon vapor and pure graphite carbon is deposited upon the surface of the filament. If the latter is uniform the deposit occurs equally over all portions. II, however, the electrical resistance is abnormally large in some portions, a greater temperature results in those portions due to the increased expendi- ture of energy at these points. and larger deposit of carbon occurs there, the filament being more uniform"