[NM020ABO], Technical Note, Thomas Alva Edison, November 21st, 1886


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[NM020ABO], Technical Note, Thomas Alva Edison, November 21st, 1886

Editor's Notes

706 "The object of this invention is to obtain homogenous carbon filiments for incandescent Electric Lamps The invention consists in the use of the non volitile residues of the resins and bitumens which are Oxygenated Hydrocarbons. With or without infusible conducting or non conducting elements or compounds. The invention further consists in the manner of forming the carboniziable filiment and in the manner of carbonizing the same. Of the oxygenized residues of Resins and bituments I prefer what is known as Asphaltene which is prepared from common refined Asphalt by heating the same at about 250 centigrade in the open air until the volitile matters are driven off-- This is allowed to cool & is then broken up and very finely powdered, it is then put into a mould with a plunger from this mould there is a fine orifice through which the Asphaltene may be forced into a thin filiment the mould being heated to the softening point of the asphaltum.-- The filiments are then hung in small carbon boxes a number of which are placed in a chamber of carbon. The whole is heated for about 15 hours to a heat a little below the softening point until last traces of the voltile matter are thus driven out & then the heat may be raised slowly without melting or softening the filiment until the whole is thorougly carbonized-- If the Asphaltene just before all the voliltile matters are driven off in its preparation is mixed with pure finely divided graphite & then allowed to cool pieces may be put into the filiment forming press without powdering & by a high heat filiments forced out In this case the filiments may be carbonized by the regular methods without previous drying slowly as the Graphite prevents the efffects of soften of the Asphaltene. Infusible Oxides such as lime, Magnesia Alumina may be substituted for Graphite when high resistance filiments are required. I do not wish to confine myself to Asphaltene as it is not an exact compound but claim generally the heating of all Bituminous & Resinous substances until nearly the whole of their volatile constituents are driven off stopping the heat just below the carbonizing or decomposing points. Petroleum, Rosin etc may be used-- If filiments are formed out of infusible oxides They may afterwards be impregnated with asphaltene & accomplish the same purpose The Asphaltene being disolved in Benzol or other solvent which is volitile at low temperatures Seeley-- I find asphaltene the best substnce for impregnating the clay etc filiments you may have to divide this application as its for soaking How would it do to put all the claims in & then when we want to can make an division-- Claim formation of filiments from asphaltene or equivalent substance 2nd Combined with powdered carbon or graphite 3rd Combined with Infusible substances presumably formed filiments of carbon or infusible non-conducting materials impregnated with Asphaltene in proper solvent etc" 707 " "The object of this invention is to make filiments of carbon for incandescent electric lamps which shall be of even texture & of high electrical resistance-- The invention consists of the method of forming the Carbonizable filiment by first taking a filiment of some substance which is soluable in liquids which do not act of the carbonizable material to be placed on its surface for instance Boric Acid can be drawn out when hot into very fine perfectly cylindrical filiments if these be bent in proper form the may be coated with many concentric layers of carbonizable material, for Insance if the Boric Acid filiment be immersed in a solution of Asphaltene in Benzol, once & then allowed to dry which id does quickly it may again be immersed & a second coat put on-- each coat can be made exceedingly thin according to the dilution of the solution after a sufficient thickness of carbonizable material is obtained the whole is thrown into water which disolves the Boric acid & leaves the filiment of asphaltene with a hole in the centre ready for carbonization, as the hole in the center increases the resistance of the filiment a saving in conductors is obtained owing to the great number of concentric layers any defect in one layre is rendered a small factor. It is evident that is tubes of Boric acid be heated and drawn out into filiments the will be hollow & if the liquid containing the Asphaltene be drawn through at intervals it will deposit on the inside of the glass tube-- In this case the Boric acid is dissolved very much quicker I have spoken of Boric acid as a former & Asphaltene as the carbonizable material, but it is evident that these materials can be changed in almost endless ways-- If melted Rosin be drawn out into filiment, It may be coated with layers of Licorice dissolved into, Gum Dextrine starch Tragacanth, Arabic, then if thrown into spirits Turpentine The Rosin may be disolved out. It is not even necessary to disolved the Rosin out as the whole is carbonizable. All that is necessary is that there should be a smooth substance carbonizable or soluable on which to build up the main portion of the filiment by successive concentric films of the material the solvent of which volatilizes Now friend Seeley can you get a broad claim to this process-- concentric multiple layers hollow carbon-- disolvable former or carbonizable on-- etc etc" [drawing may be related]




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Thomas A. Edison Papers, School of Arts and Sciences, Rutgers University
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