Patented Feb. 21, 1928, 1,660,220 UNITED STATES PATENT OFFICE. ANTHONY-G. DE GOLYER, OF BROOKYN, NEW YORK. CoPPER BEFINING. NoDrawing. Application filed April 16, 1927. serial No. 184,443. My present invention relates to a new and copper, cement copper, scrap copper, etc. It improved process for the refining of copper, is also adapted for use in both the produc-65 and relates particularly to methods for the tion of cast shapes to be used in the produc production of copper which is entirely free tion of wire, tubes, sheets and other wrought from dissolved and occluded gas and from articles, and for the production of finished oxygen. or semi-finished castings in sand or other In response to industrial and technical de molds, PE, castings having high 60 mands, many attempts have been made to electrical conductivity, high tensile strength produce oxygen free copper by direct refin and excellent machining qualities. O ing methods and otherwise. While it has Before describing my invention I will been possible heretofore to produce oxygen give, for the purpose of comparison, an out free copper by means of previously proposed line of the pyrometallurgical method which 05 methods, copper so produced did not have has heretofore been generally used for the the necessary additional qualities of high refining of copper, and the aii Opera 5 metallic copper content, high electrical con tions required for the production of deoxi ductivity, and freedom from dissolved or dized copper. occluded gas which, latter, resulted in gas or Electrolytic copper in the form of cath-0 “blow holes in the solid copper. Conse odes has an average metallic copper content quently, copper produced by previously pro of 99.975%, and an electrical conductivity of 20 posed methods does not possess the neces 101% or more (Matthissen standard), and sary properties and qualities to meet the is substantially free from oxygen. How general industrial and technical require ever, cathode copper is not in suitable con- 75 ments, hence, none of such previously pro dition for rolling or other working, and posed processes have been of commercialim must be subjected to a pyrometallurgical re portance. fining process before it can be rolled, drawn, I have discovered that by means of the etc. W hereinafter described process I can produce The cathodes are melted in fuel fired re- 80 copper which is entirely free from dissolved verberatory furnaces, the charges ranging or occluded gas, such as carbon monoxide, from 20 to 250 tons. The major portion of 3) and entirely free from oxygen. Further the melting is accomplished by indirect dis more, the copper so produced contains lower solving, i.e., the solid copper is under the percentages of various impurities, such as surface of the bath and not in direct contact 85 iron and sulphur, than copper produced by with the fuel flames. The charging and heretofore known pyrometallurgical meth melting operations require from 0 to 13 35 ods, and copper produced by means of the hours, regardless of the size of the charge, present invention is entirely free from resid and during this time the molten copperab ual impurities resulting from reagents used sorbs a relatively large amount of sulphur 90 in effecting complete removal of oxygen. from the fuel flames, By reason of the combined advantageous When the charge is molten, air is blown 40 factors-absence of dissolved or occluded into the copper until the bath consists of gases, absence of oxygen, and high metallic the saturated copper-copper oxide eutectic, copper content-copper produced by the op containing .39% oxygen, and, in addition, 95 eration of the present invention possesses some free cuprous oxide, so that the bath higher percentage of electrical conductivity, generally contains from 45% to .55% oxy 45 higher tensile strength and greater reduction gen. Oxidation in this manner removes sub in area and percentage of elongation than stantially all sulphur from the bath, Epper refined by previously known meth as sulphur dioxide; and substantially a 100 OS, M iron, and a portion of certain other impuri The present process is equally adapted for ties, such as arsenic and antimony. The 50 the refining of cathode copper produced by latter impurities are removed from the cop electrolytic refining and the direct refining r as oxides which enter the slag. Fol of copper bearing material which has not owing oxidation, a large proportion of the l been refined electrolytically, such as blister slag is removed. 1660,220 Partial deoxidation of the bath is then un oxygen, in the form of cuprous oxide, in dertaken by "poling’ i. e., logs or poles of such copper renders it entirely or partially green wood are introduced under the surface unsuitable for many industrial applications. of the metal, the wood being converted into Many attempts have been made to pro charcoal which in turn reacts with the cu duce oxygen free copper by means of a com 70 prous oxide of the bath. Reduction of the bination of the above described method and cuprous oxide in this manner is continued un the additional operation of adding a metal til the oxygen content of the bath is between lic deoxidizing agent, such as phosphorus .035% and 055%, within which range the or silicon, to the “poled' copper, i.e., the O metal is said to be “tough pitch’ copper. At copper containing between .035% and .06.0% 75 this stage the copper is cast into wire bars, OXygen. cakes, ingots, etc. While it is possible to produce copper The “poling' operation requires from 3 to which is substantially oxygen free by such 4A hours, and from 4 to 6 hours are con methods, the cast copper is invariably un 5 sumed in casting, and during these peri sound, due to the presence of gas in the 80 ods the copper again absorbs appreciable molten metal, hence it is not suitable for amounts of sulphur, as well as iron and rolling, drawing, or other mechanical work other impurities. - ing. Furthermore, such copper always cont In the refining of copper by the above de tains impurities in the form of residual 20 scribed method it is essential that the oxy metallics of the deoxidizing agent, hence the gen content be maintained within the range percentage of electrical conductivity is ma of from .035% to .055%, as when the oxygen terially reduced, being, in such cases, be exceeds approximately .060% the cast cop tween 85% and 92% (Matthissen standard), per is unsound, apparently due to the pres so that the copper is not suitable for use in 25 ence of a gas. Furthermore, the relatively wire or other wrought forms for the trans 9. high oxygen content reduces the percentage mission of electrical energy. of reduction in area and elongation to such It will be apparent that it is not possible an extent that the copper does not possess to produce copper, by methods heretofore sufficient ductility for mechanical working. available, which possesses the following 30 In a similar manner, when the oxygen combined properties: (a) entire freedom 95 content is reduced to less than .035% the from oxygen; (b) entire freedom from dis cast copper is unsound, the metal invariably solved or carbon monoxide or other gases; rising or “swelling' in the molds, due to (c) metallic copper content of 99.970% or the presence of carbon monoxide, and pos higher; (d) electrical conductivity of sibly other gas, and such copper, termed 100.5% (Matthissen standard) or higher. 00 “over-poled', is also unsuitable for me By means of the process of the present in chanical working by reason of porosity, im vention I convert cathode copper into any paired ductility, low electrical conductivity, desired shapes or forms for use in the manu etc. facture of wrought products, or for use as 40 It will be apparent, therefore, that the finished or semi-finished castings, and the 105 poling operation can not be utilized for the copper so produced is characterized by en production of oxygen free copper having tire freedom from dissolved or occluded car the requisite reduction in area and elonga bon monoxide and other gases; entire free tion, i. e., ductility, tensile strength, elec dom from oxygen; a metallic copper con 45 trical conductivity and other essential or tent as high as, or higher than in the orig 0. desirable physical properties. inal cathode copper; a percentage of elec Copper produced by the above described trical conductivity as high or higher than pyrometallurgical method, generally termed that of the original cathode copper; high electrolytic copper', thus contains between tensile strength; high percentage of reduc 50 .035% and 060% oxygen and has a metallic tion in area, e. g., approximately 80% in 5 copper content of between 99.900% and the case of annealed wrought products. 99.960%. Wire of approximately .080 of an Furthermore, by means of this invention I inch diameter drawn from such copper and also refine copper containing material which annealed, will have an electrical conduc has not been refined electrolytically, such as 55 tivity of from 99.5% to 100.8%; a reduction blister copper, cement copper and scrap 120 in area of from 35% to 47%; elongation in copper, and convert such copper into any 10 inch lengths of from 30% to 38%, and desired forms for use in the manufacture will show an average of between 38 and 44 of wrought products, or for use in finished twists in 6 inch lengths. or semi-finished castings, and the copper so 60 Therefore, the metallic copper content produced is characterized by; entire free 25 and the percentage of electrical conductivity dom from dissolved or occluded carbon - of copper refined by such methods are sub monoxide and other gases; entire freedom stantially lower than the copper content and from oxygen; a metallic copper content ap electrical conductivity of the original cath: preciably higher than in the original copper 65 ode copper. Furthermore, the presence of containing material; a percentage of elec- 130 1,660,320, trical conductivity higher than that of the tively large amount of carbon monoxide, original copper containing material; a rela and in this case the holes caused by the f tively high percentage of reduction in area are smaller and less apparent due to dis e.g., 70% or more in the case of anneale semination of the gas. Wrought products. Copper which has been partially deoxi O The process of the present invention is dized by the reaction of carbon with cuprous based upon my discovery that, under certain oxide, such as by “poling', introduction of conditions, carbon monoxide is soluble in charcoal, coke, etc., may, and undoubtedly molten copper. I have found through ex usually does contain other gases, e. g. hy O tensive research that carbon monoxide which drogen, in addition to carbon monoxide. I 5 is generated or formed within molten copper nave found however, that in the operation dissolves or is occluded in the copper. of the process of this invention the presence I have further discovered that when the of additional gas or gases in molten copper percentage of oxygen exceeds a definite may be disregarded as they are apparently 5 amount, approximately .10% of the total entirely eliminated by the methods used to RO weight of the bath, that any carbon mon prevent the occurrence of carbon monoxide oxide formed within the copper is more or in molten copper. less simultaneously converted into carbon The process of the present invention com dioxide, which is not soluble in molten cop prises the following essential operations: 20 per. On the contrary, when the percentage (a) Partial reduction of the cuprous 85 of oxygen in the bath is less than approxi oxide in the molten copper by reaction with mately .10%, an appreciable proportion of carbon. carbon monoxide generated or formed with (b) Stopping the reduction with carbon in the molten copper remains dissolved or before the oxygen content has been reduced 25 occluded therein as long as the copper is to the “critical oxygen point', i.e., the point molten. at and below which there is not sufficient It appears, therefore, that .10% is what oxygen or cuprous oxide in the bath to react may be termed a “critical oxygen point, with all carbon monoxide present in the i. e., when the oxygen content exceeds this copper to convert it to carbon dioxide; this 30 amount there is evidently a mass reaction critical point being approximately .01% of cuprous oxide with carbon monoxide, Oxygen. probably according to the following: (c) Subsequent removal of all remaining oxygen by means of subjecting the oxygen CuO + CO=2Cu+CO, and oxygen compounds of the bath to re 85 and, as carbon dioxide is not soluble in mol action with a metallic reducing agent, the O ten copper such gas readily escapes from the reaction of which with oxygen or oxygen bath; on the other hand, when the oxygen compounds does not generate carbon mon content is less than this amount the mass re oxide in appreciable amounts. action of cuprous oxide and carbon mon The process of my invention may be suc 40 oxide does not take place, with the result cessfully carried into effect in the following 105 that a portion or all of the carbon mon ae oxide present within molten copper remains Copper or copper bearing material ma occluded or dissolved therein. be melted in any furnace to which a R When molten copper containing carbon cient volume of energy in the form of heat 45 monoxide in solution, or otherwise, is cast may be supplied to melt the copper, and the carbon monoxide is not released until maintain it in a thoroughly molten condi the copper has cooled to a temperature which tion during the necessary operations. When is relatively not much higher than the freez the copper is not sufficiently oxidized co ing point of copper, the result being that incidental with melting, and when the bath carbon monoxide is expelled shortly prior absorbs an appreciable amount of sulphur or 15 to the formation of the crystal and thus other impurities during melting oxidation tends to become more or less concentrated by blowing is necessary. along the crystal boundaries with the con After the desired amount of oxidation has sequent formation of gas holes. Such gas been effected, the bath is partially deoxi holes are, of course, readily detected in the dized by the introduction of carbon into the 20 case of oxygen free copper. However, in the metal. This may be accomplished by “pol case of cast copper containing from 035% ing' in the usual manner, the introduction to .055% oxygen the occurrence of holes due of charcoal, coke, or other carbonaceous ma to the presence of carbon monoxide in the terials into the copper, such as by means of 6) copper when molten is not as readily ap immersion, agitation or otherwise. During 2. - parent, unless the amount of carbon mon the partial deoxidation operation samples oxide has been excessive. It appears that of the copper may be taken from time to in such oxygen, containing copper the cop time to determine the progress of reduction per-copper oxide eutectic, which occurs on of oxygen, or this operation may be timed, the crystal boundaries, acts to retain a rela that is, an approximate weight of carbon 30 4 1,660,220 may be allowed to react with the oxygen atmosphere of the stack, the usual oxidation, of the bath for a predetermined length of or blowing operation of previous refining time. processes is wholly eliminated. Immediately following the partial deoxi When a sufficient quantity of molten cop dation operation, one or more metallic reduc per has accumulated in the hearth this metal 70 ing agents are introduced into the molten is transferred to a second furnace, which is metal, and allowed to react with the remain also heated by the combustion of oil or ing oxygen. I have found that silicon, man powdered coal. Coincidental with the trans ganese, phosphorus and a number of boron fer of the copper to the second, or deoxida containing reagents may be successfully used tion furnace it is separated from substan 75 as the metallic reagents in removing all of tially all slag which may have accumulated the oxygen from the bath. The purpose for thereon. which the copper is intended will usually de The copper is maintained in a thoroughly termine the proper reagent to employ. For molten condition in the second furnace and . example, when it is desired to produce gas partial removal of oxygen is accomplished 80 free and oxygen free copper having an elec by reaction of carbon with the oxygen and trical conductivity of more than 100% it is oxygen compounds of the bath. Such re essential to use a metallic reducing agent moval of oxygen is, according to my process, which will not alloy or otherwise combine stopped before the cuprous oxide content 2 with the copper to lower the electrical con is reduced to the “critical oxygen percent 85 ductivity. In a similar manner when it is age'. The bath is then partially or entire desired to produce copper billets possessing ly covered with charcoal or other carbona the maximum ductility for the manufacture ceous material for the purpose of maintain of seamless tubes by the piercing method it ing a neutral or reducing atmosphere within 2. is also of advantage to use a metallic reduc the furnace; or the bath may be covered 90 ing agent which will not combine with the with oxygen compounds, such as lime, mag copper nor result in residual impurities nesia, etc., which are inert under the prevail therein, either or both of which conditions ing conditions. After the copper has thus would tend to make the piercing operation been protected from possibility of oxidation 30 more difficult. by the atmosphere of the furnace, a metallic 95 When all of the oxygen has been removed reducing agent is introduced into the cop the copper is ready for casting into any de per for the purpose of removing all remain sired commercial shape, or into sand or other ing oxygen. The metallic reducing agent molds for the production of finished or employed must be capable of reacting with 35 semi-finished castings. oxygen and oxygen compounds of copper un 100 While the process of the present invention der the physical conditions prevailing within can be successfully and satisfactorily car the furnace, and it is essential that such reac ried into effect according to the above gen tions do not generate appreciable amounts eral outline of operations, for the purpose of carbon monoxide. When it is desired to 40 of further illustration I give herewith a pre produce copper having an electrical conduc 105 ferred method of operation. tivity of 101% or higher (Matthissen stand In this particular scheme of operation, I ard) it is necessary to use a metallic reduc use a combination stack and reverberatory ing agent which does not dissolve in or furnace for melting the copper, and use oil otherwise combine with, or contaminate cop 45 or powdered coal as the fuel for heating per. As an example of reducing agents O the furnace. The solid copper, which may which are suitable for this purpose I cite be cathodes or metal which has not been aluminum boride, calcium boride and silicon refined electrolytically, is charged into the boride. When electrical conductivity is not stack, and as it passes down through the an objective other metallic reducing agents, 50 stack it is preheated and finally melted. The such, for example, as phosphorus, silicon or 15 molten metal flows out of the stack into the manganese may be used. hearth of the reverberatory portion of the When the oxygen has been entirely re furnace. It will be apparent that the char moved the copper is cast into any suitable acter of the combustion gases in the stack molds in the usual manner. 55 ortion of the furnace may be closely regu Copper produced by means of the process 120 ated and controlled, thus giving advan of this invention is characterized by entire tageous melting conditions. Furthermore freedom from dissolved or occluded carbon by melting in this manner the molten metal monoxide and entire freedom from oxygen does not remain in contact with the fuel and oxides, consequently, castings made 66 flames for more than a few minutes, conse therefrom are characterized by entire free 25 quently, the metal does not absorb an ap dom from holes and other defects due to the preciable amount of sulphur nor other im presence of gas or oxygen in the molten purities. By reason of this, together, with metal. the fact that any desired degree of oxidation A further distinctive advantage of the 5. can be readily obtained by regulating the present invention is that the gas free and 30 oxygen free copper produced by means of I claim: EEE EE higher percentage 1. The method of producing copper which of electrical conductivity, greater t e is entirely free from dissolved or occluded strength and greater percentages of reduc gas and entirely free from oxygen com tion in area and elongation than E. free, pounds which comprises reducing the oxygen 70 or oxygen containing copper which has been content of the copper, while molten, by re refined by previously known methods. action of carbon with the oxygen of the bath . It will be apparent that in the case of to a point above the critical oxygen percent copper which has been oxidized to an appre age at, and below which carbon monoxide is ciable extent that the major portion of re retained in molten copper; subsequently re 75 0 duction of the oxygen of the bath is accom moving from said molten copper all remain plished by means of carbon, which is of de ing oxygen by subjecting such oxygen to re cided economical advantage. action with a metallic reducing agent, the The terms “critical oxygen point' and reaction of which does not generate carbon "critical oxygen percentage used herein and monoxide. 16 in the appended claims refer specifically to 2. The method of producing copper which the percentage of oxygen present in molten is entirely free from included gas and en copper in the form of cuprous oxide, and tirely free from oxygen compounds which such terms are used to designate the per comprises reducing the oxygen content of centage point at which cuprous oxide ceases the copper, while molten, by reaction of car 85 to react with carbon monoxide to oxidize the bon with the oxygen of the bath to a point latter compound. above the critical oxygen percentage at, and I have found also that copper which has below which mass-reaction of cuprous oxide been refined by means of the process of the with carbon monoxide does not occur; subse present invention and which contains rela quently removing from said molten copper tively small percentages of oxygen and/or all remaining oxygen by subjecting such dissolved or occluded carbon monoxide will oxygen to reaction with a metallic reducing possess physical properties approximatin agent, the reaction of which does not gener the physical properties of similarly refine ate carbon monoxide. copper which is entirely free from carbon 8. The process of producing copper which monoxide and oxygen. Although the pres is entirely free from carbon monoxide and ence of even such relatively small amounts of entirely free from oxygen in any form which oxygen, chiefly in the form of cuprous oxide, comprises reducing the amount of cuprous will render copper unsuitable or undesirable oxide in molten copper by reaction with for various applications, I have found that carbon to a point above the critical percent 100 copper refined by means of this process and age at, and below which reaction of cuprous which is substantially free from included oxide with carbon monoxide does not pro carbon monoxide and oxygen can be used for bath;ceed atsubsequently the temperature removing prevailing all remaining in the certain industrial applications. OS 40 Therefore, the herein described refining oxygen by subjecting such oxygen to re - process may be advantageously utilized for action with a metallic reducing agent, the the production of copper which is substan reaction of which does not generate carbon tially free from dissolved or occluded carbon monoxide. monoxide and/or oxygen. It will be evident 4. The process of producing copper which that such small amounts of these impurities is entirely free from cuprous oxide and car 110 may be allowed to remain intentionally or bon monoxide which comprises reducing the otherwise in the refined copper without de amount of cuprous oxide in molten copper parting from the scope of my present inven by reaction with carbon to a point higher tion. As an example, in the operation of the than the critical percentage at, and below process a small percentage of y may be which mass reaction of cuprous oxide with allowed to remain in the copper by the use carbon monoxide does not occur; subse of a quantity of metallic reducing agent Ey, removing all remaining cuprous which is insufficient to remove all of the oxide y subjecting such cuprous oxide to oxygen in the molten metal. It will be un reaction with a metallic reducing agent, the reaction of which does not generate carbon 20 derstood, however, that the physical prop monoxide. erties of such copper containing impurities 5. The process of producing cast copper in the form of carbon monoxide, other oxy which is ity from oxygen and sub gen compounds or oxygen will not be en stantially free m gas holes and other de tirely the same as the physical properties of fects due to the presence of cuprous oxide 25 copper which is entirely free from such im and dissolved or occluded gas which com purities.By the term "substantiallyo as free from prises reducing the amount of cuprous oxide oxygen used herein and in the appended in molten copper by reaction with carbon claims, I refer specifically to copper contain and carbon monoxide to a point higher than ing not more than .008% oxygen. the critical percentage at, and below which 6. 1660,220 reaction of cuprous oxide with carbon mon tinuously from the melting zone of the fur oxide does not proceed in such a manner nace to a hearth situated at a lower eleva as to remove substantially all carbon mon tion than said melting zone; intermittently oxide from the metal; subsequently remov removing molten copper from said hearth, ing all remaining oxygen by subjecting and transferring it to a second furnace in such oxygen to reaction with a metallic re which the copper is maintained in a molten 70 ducing agent, the reaction of which does not condition by the direct heat of the combus generate carbon monoxide. . tion of carbonaceous fuel; reducing the oxy 6. The process of producing cast copper gen content of the molten copper in said O which is entirely free from oxygen, substan second furnace by reaction with carbon to tially free from gas holes and other defects a point higher than the critical oxygen per 75 caused by carbon monoxide, and which has centage at, and below which molten copper a minimum electrical conductivity of 1.01% retains carbon monoxide; subsequently re (Matthissen standard) which comprises re moving from said molten copper all remain 15 ducing the amount of oxygen in molten cop ing oxygen by subjecting the oxygen and per by reaction with carbon and carbon mon oxygen compounds to reaction with a metal 80 oxide to a point higher than the critical per lic reducing agent, the reaction of which centage at, and below which carbon mon does not generate carbon monoxide. oxide is retained in the molten copper; sub 10. The process of producing copper sequently treating said molten copper which which is entirely free from cuprous oxide contains oxygen, but is substantially free and from dissolved or occluded carbon 85 from carbon monoxide, to remove all re monoxide, and which is further character maining oxygen by subjecting such oxygen ized by a minimum metallic copper content to reaction with a metallic reducing agent of 99.985% and a minimum electrical con which is not soluble in molten copper and ductivity of 101% (Matthissen standard) the reaction of which does not generate car which comprises melting copper directly in bon monoxide. the products of combustion of carbonaceous 7. The process of producing cast copper fuel, intermittently removing molten copper which is entirely free from oxygen and sub from the melting furnace and transferring 30 stantially free from holes and other defects it to a second furnace where said copper is caused by carbon monoxide, and which is maintained in a molten condition by direct 95 further characterized by a minimum metal exposure to the products of combustion of lic copper content of 99.985%, a minimum carbonaceous fuel; reducing the cuprous electrical conductivity of 1.01% (Matthissen oxide content of said copper in said second 3. standard) and a minimum reduction of area, furnace to an amount which is in excess of in the annealed condition, of 74%, which the percentage of cuprous oxide necessary 00 comprises reducing the amount of oxygen to react with all carbon monoxide present in molten copper by reaction with carbon and oxidize it to carbon dioxide or other to a point higher than the critical percent compounds which are not soluble in molten age at and below which carbon monoxide copper; subsequently removing from said is retained in molten copper; subsequently molten copper all remaining cuprous oxide 105 removing all remaining oxygen by subject by subjecting such cuprous oxide to reac ES such oxygen to reaction with a metallic tion with a metallic reducing agent which reducing agent which is not soluble in is not soluble in, and does not alloy or other molten copper, and the reaction of which wise combine with molten copper, and the does not generate carbon monoxide. reaction of which does not generate car 10 8. As a step in the process of producing bon monoxide. copper which is entirely free of carbon mon 11. In the process of producing copper oxide and oxygen in any form by means of substantially free from oxygen, which com 50 reducing a portion of the oxygen contained prises removing oxygen from molten cop in molten copper by reaction with carbon, per by reaction with carbon; the step of re 115 stopping the reduction of cuprous oxide with moving carbon monoxide which consists in carbon while sufficient cuprous oxide re stopping the removal of oxygen with carbon mains in the bath to react with all carbon while sufficient oxygen remains in the bath 55 monoxide present in such a manner as to to react with substantially all the carbon oxidize such carbon monoxide to carbon di monoxide present and permitting said oxy 20 oxide or other compounds which are not re gen and carbon monoxide to react to form . tained in molten copper. carbon dioxide or other compounds which 9. The process of producing copper which are not retainable by molten copper. 60 is entirely free from dissolved or occluded 12. The process of producing copper sub carbon monoxide and from oxygen which stantially free from oxygen gas holes and comprises melting copper directly in heat other defects caused by the presence of dis enerated by combustion of carbonaceous solved or occluded gas which comprises re el, allowing the molten copper to flow con ducing the amount of oxygen in molten cop 1,660,220 7 per by reaction with carbon to a point sufi- by subjecting such oxygen to reaction with ciently higher than the critical percentage a metallic reducing agent, the reaction of at and below which reaction of cuprous which does not generate carbon monoxide. 10 oxide with carbon monoxide does not pro- Signed at New York in the county of 5 ceed to remove substantially all carbon mon- New York and State of New York this oxide from the metal; EY subsequently re- twenty-fourth day of March, A. D. 1927. moving substantially all remaining oxygen ANTHONY G. DE GOLYER.