US1006876A

US1006876A - Metallurgy of zinc ores and compounds.

Info

Publication number: US1006876A
Application number: US53679110A
Authority: US
Inventors: Augustin Leon Jean Queneau
Original assignee: QUENEAU ELECTRIC ZINC FURNACE Co
Current assignee: QUENEAU ELECTRIC ZINC FURNACE Co
Priority date: 1910-01-07
Filing date: 1910-01-07
Publication date: 1911-10-24
Anticipated expiration: 1928-10-24

Description

A. L. J. QJENEAU. METALLURGY OF ZINC ORES AND COMPOUNDS.

APPLICATION FILED JAN. 7, 1910.

Patented Oct. 24, 1911.

3 SHEETS-SHEET l.

INVENTOR u/g awaaa,

' BY w/j/zw ATTORNEY-5,

A. L. J. QUENEAU. METALLURGY 0F ZINC ORES AND COMPOUNDS.

' APPLICATION FILED 11111.7, 1910,

1,006,876, Patented 001'. 24, 1911.

3 SHEETSSHEET 2.

INVENTORZ ATTORNEYS,

A. L. J. QUENEAU.

METALLURGY 0F ZINC ORES AND COMPOUNDS.

APPLICATION FILED JANJ, 1910.

1,006,876, I I Patented Oct. 24, 1911.

3 SHEETSSHEET 3.

ATTORNEY5.

UNITED STATES PATENT OFFICE.

AUGUSTIN LEON JEAN QUENEAU, OF OVERBROOK, PENNSYLVANIA, ASSIG-NOR T0 QUENEAU ELECTRIC ZINC FURNACE COMPANY, OF PHILADELPHIA, PENNSYL- VANIA, A CORPORATION OF DELAWARE.

Specification of Letters Patent.

Patented Oct. 24, 1911.

Application filed January 7, 1910. Serial No. 536,791.

To all whom it may concern:

Be it known that I, AUGUsTIN LEON JEAN QUENEAU, a citizen of the Republic of France, residing at Overbrook, city and county of Philadelphia, and State of Pennsylvania, have invented certain new and uselurgy of zinc ores and like reducible coinpounds of zinc, and, in its preferred form, is carried out by means of an electrically heated rotatory furnace, provided with a fluid resistor, which furnace and resistor themselves constitute a part of the invention.

In the accompanying drawings, Figure 1 represents a longitudinal central section, partly in elevation, of a furnace and its condenser and feeding devices, adapted for the practice of the invention. Fig. 2 represents on a larger scale and in elevation, one end of the furnace viewed from the right of the line 2-2 of Fig. 1, and with the feeding devices removed. Fig. 3 represents, likewise on a larger scale, a section thereof taken on a plane indicated by the line 3-3 of Fig. 1. Fig. 41 represents, on a still larger scale, a longitudinal sectional View of a portion of one end of the furnace. Fig. 5 represents, in longitudinal section, a modification of the furnace adapted particularly for use in connection with a multiphase current. Fig. 6 represents a sectional view taken on a plane indicated by the line 66 of Fig. 5.

Referring to the drawings, it will'be noted that the furnace is of the rotary type, adapted to be rotated continuously or intermittently in one direction, or alternately in opposite directions, so as to agitate or tumble the charge. The furnace, in both of the modifications shown, is lined interiorly with refractory material of suitable physical characteristics, inclosed in a shell or casing of low carbon steel. The outer blocks a proximate to the steel shell maycons'ist of good heat insulating fire brick, whereas the inner blocks 6 are preferably of chrome brick, or the like, inert to slags and zinc vapors.

It will be convenient, as illustrated in the drawings, to make the metal shell of the furnace cylindrical in form and in a num ber of sections, and to provide these sections With annular flanges d cast or otherwise formed integral with them, these flanges being bolted together so as to assemble the sections to make up the complete shell, and to permit them to be disassembled, when desired. Certain of these flanges will, as shown, constitute tires, resting upon rollers e, the axis of the furnace being usually horizontal. The shell is also provided with a band gear f, driven through the intermediacy ofa gear 9, which constitutes an element of a variable speed drive, adapted to be actuated in either direction from a variable speed electric motor, so that the num ber of revolutions or oscillations per minute of the furnace may be readily varied.

In the form of furnace shown in Fig. 1, the section of the shell at the condenser end of the furnace likewise constitutes an end plate therefor. nace shown in Fig. 1, and both ends of the furnace shown in Fig. 5 are provided with an independent annular metallic plate 71., likewise preferably of low carbon steel or other like appropriate conducting metal. The metallic plate is provided with an annular series of apertures near its outer edge or border, through which apertures pass a corresponding series of headed bolts 2'. These bolts likewise pass through a stationary flange j of the shell and through the slidable ring Z, and are provided at their :inner ends with screwthreads having adjusting nuts, as shown in Figs. 1, 2, 4 and 5. Springs m are interposed-between the The other end of the furflange j and ring Z and encompass the shanks I of the bolts, so that the plates 71. may have a capacity for independent movement, to correspond to the effects of heat expansion in the furnace, but will nevertheless be held instrong, elastic, adjustable contact with the furnace ends. The bolts 5 are held out of electrical contact with the plate flange and ticularly Fig. 4) and are out of electrical contact with the flange j and ring Z, so that no electric current shall pass through the springs, to affect their temper or resiliency.

At the feed end of the furnace the end lining consists of an annular course of chrome bricks or blocks I), backed by a course of fire-bricks a, both of which are incased in a low-carbon steel acket n, which latter is cast integral with a plate 70 having an inturning flange r which serves as a water channel to receive cooling water from the spray pipe an. A copper plate 8 flanged outwardly is interposed between the plates h and 72, and directs the cooling water, sprayed upon the plate p into the carrying-off trough 00. An inner refractory sleeve 0 serves for the introduction of the feed pipe a forming a part of the charging devices hereinafter referred to. So also, at the condenser end of the furnace a like course of chrome bricks or blocks 6 backed by a course of fire bricks a is incased within a like low-carbon steel jacket 12 cast integral with the plate 77 and having the inturning flange r, cooperating with the water spray pipe at, flanged copper plate 8 and trough m. A refractory connection q leads into the condenser A, which condenser and its prolong B revolve with the furnace, being suitably bolted thereto through the intermediacy of the flanges shown. The prolong may be provided with perforated partitions o as showna/It will be noted that the central perforations of the partitions in the prolong are in such alinement that the interior of the furnace can be viewed through them and so that a clearing rod may be inserted to remove any possible obstruction in the refractory connection 9. The noncondensable fumes and gases escaping from the prolong B may conveniently be led away through a suitable stack C, to be further'treated, if desired.

In the practice of my invention, I contemplate applying the electric heating current ,1n the form of a direct current, a singlephase alternating current or a multi-phase alternating current. The construction shown in Fig. 1 is particularly adapted to the employment of a direct current or mono-phase alternating current, one of the leads from the working circuit connecting with the plate 71/ at the feed endof the furnace, and the other lead connecting with the metal shell; whereas, in the form of the furnace shown in Fig. 5, three leads are employed, one of which connects with the metal plate 7L at the feed end of the furnace, the other with the metal plate h at the condenser end thereof, and the third to the metal shell, so that xby this arrangement, a two-phase current derived from any suitable source, as, for instance, from a three-phase circuit, through the intermediacy of the well lmown Scott connection, may be efliciently supplied, as will be hereinaftermore fully pointed out.

Electrical connection between the plate 71 and the working current can be readily established by means of a suitable carbon or metallic brush making contact with an ann'ular projection 42 on the plate, and a like connection is made with the shell of the furnace by means of a similar carbon or metallic brush making contact with a raised surface thereon. For instance, with the furnace shown in Fig. 1, the brush y constitutes one of the leads of the direct current or mono-phase current employed, and the brush 2 constitutes the other lead thereof; whereas, in the construction shown in Fig. 5, the three leads for the two-phase current. supplied are represented by the brushes y, 3 and y In the construction shown in Fig. 1, the metal plate It at the feed end of the furnace is out of direct electric connection with the metal shell, and is intended to be electrically connected therewith indirectly, during the operation of the furnace, through the intermediacy of a molten fluid resistor, which is adapted to extend longi tudinally from end to end of the interior chamber of the furnace. In the construction shown in Fig. 5, a like fluid resistor is employed, extending from end to end of the furnace chamber and completing connection between the end plates 7L thereof, but this fluid resistor likewise completes contact between the plates h and the metal shell, through the intermediacy of an inner annular flange 7c, water-cooled from a spray pipe 00, which discharges into a channel surrounding the said flange. This arrangement secures the necessary current distribution for the employment of a two-phase circuit. It will be noted that, in Fig. 5, the conducting flange la is shown as nearer the feed end of the furnace than the condenser end. This location of the flange k is chosen so that the electric resistance between the flange 7c and the metal plate It at the feed end of the furnace shall be as nearly as possible equal to the electrical resistance between the flange k and the plate in at the condenser end of the furnace, having in view the circumstance that for purposes hereinafter described, the cross section of the fluid resistor is less, and consequently its resistivity is greater, at the feed end of the furnace than at the condenser end.

The fluid resistor, indicated by the letter D, may consist of a metal, a salt, or a slag, adapted to maintain fluidity during the passage of an electric current of suitable voltage and amperage for the reducing action desired. In most instances, I prefer to use for the molten fluid resistor an alloy or comnecessary, a high electrical efiiciency is nevertheless secured, i. e., that the ratio of from six to sixteen per cent. by weight of 'nace. This high percentage of phosphorus increases very considerably the electric rechanged in chemical composition during the resistor, will be practically maintained conas metallic shot, entrapped by the slag or ferro-phosphorus. Thus, I have found that by so compounding cast iron and ferro-phosphorus, the resulting product will analyze phosphorus, and such product will have good physical properties well adapted for its use as a molten fluid resistor in the rotary fursistivity of the metal. For instance, an alloy carrying twelve per cent. of phosphorus (which I recommend in practice) has an electric resistivity about four times that of molten cast iron, and is very fluid at about 1050 centigrade. These qualities are especially advantageous for the reason that they permit me to employ a relatively considerable depth of the molten fluid resistor, thereby obtaining a correspondingly considerable extent of surface contact between the resistor and the charge above it, as indicated in Figs. 3'and 6. Another advantage of the use of the iron-phosphorous alloy or comp'bund is that it Will remain practically unprocess. As we increase the percentage of phosphorus in the molten iron up to these higher amounts, it progressively displaces the carbon, until when the compound attains a composition represented by the formula Fe P, carbon is present in but very small quantity. The percentage of carbon present in solution in the alloy is automatically regulated by the equilibrium law of solution for a given temperature, there being always present in the furnace charge an available excess of readily soluble carbon. The element phosphorus is recommended because it has the property of giving high electrical resistance and high fluidity, and because it has alower chemical afiinity for. sulfur than has iron. There is usually pres ent in the zinc ore charge a sufficiently large excess of iron to satisfy whatever sulfur has remained in the roasted zinc ore. It follows, therefore, especially in view of the acid nature of the slag, that the quantity of phosphorus originally present Tinthe molten stant except for the mechanical losses, such mattes. It will be, of course, apparent that the advantage of high fluidity of the molten resistor is to permit it to quickly adjust its level during the rotation of the furnace, and that the advantage of high specific electrical resistance is that, for the depth of resistor ohmic resistance of the molten resistor to the total of the electric resistances between the molten resistor and the brushes is at a maximum.

v 7, As shown in the drawings, I prefer to arrange for a lesser depth of the molten re-; sistor at that end of the furnace where the charge enters, thereby more highly heating the resistor at that end in order to compensate for the cooling effect of the entering -Condensation of the zinc vapor to the liquid condition will take place in the zinc chamber A, which rotates with the furnace, and this condenser may be heated or it may be cooled, as the case may be, to realize the best condensing conditions. If cooled, it may, in addition to the cooling which it experiences from rotating in the open air, be further acted upon by a jet or jets of air, or otherfluid, directed upon it. So, also, the electrical connections may likewise be fluidcooled, in any desired manner. Any condensable matter carried off from the condenser A into the prolong B is recovered therein and the products of combustion are collected and carried off through the stack C. v

The furnace may be charged in any suitable manner, but I prefer to feed it in a continuous manner with the zinc ore charge, so as to realize a continuous operation between tapping periods. To this end, as illustrated in Figs. 1 and 5, I may conveniently pro ing. The feed pipe rotates with the furnace and has suflicient clearance where it enters the feed bin E to compensate for any slight irregularities in its rotation. At its supply end, the feed pipe a is provided with a positive feed, which may consist of a rotatory screw 5 actuated by suitable gearing from any source of power, and which may be air-cooled; as shown, if desired.- The fact that the feed tube a projects into the zinc ore charge contained in the feed bin or hopper E, serves toseal it as against the admission of air and escape of vapors, and this seal is made the more absolute and reliable by the circumstance that the feed screw 6 terminates at a pointjust within the supply end of the feed tube a whereby there is always present between the free end of the feed screw and the discharge end of the cast iron connection a a body of the zinc ore charge sufficient to fully occupy the Tinterior of the feed connection between those points. Consequently, even though the zinc ing furnace.

ore charge in the feed bin should, through inadvertence, or otherwise, become exhausted, the furnace would still be practically sealed against the escape of vapors from within, or the admission of air from without, through the feed pipe connection a by reason of the existence within such connection of a constant quantity of the zinc ore charge itself. I also prefer to provide the outside of the feed tube a with a screw blade a as shown, operating to feed toward or into the bin, thereby preventing the leakage of the ore mixture from the bin at that point.

In the practice of the invention, before admitting the zinc ore charge, the furnace is heated preliminarily. This heating may be effected, if desired, by a gas or oil flame, or by admitting into the furnace abody of molten lead or other metal of low melting point, and passing the electric current through the furnace, while subjecting it to a slow movement of rotation. When the furnace lining has attained the necessary temperature, the furnace is stopped and the lead or other like metal is tapped off. A known amount of resistor, preferably melted before it is inserted in the furnace, is then introduced, sufficient to reach the level desired, and the feeding in of the zinc ore charge is commenced.

The zinc ore charge may consist of a-mixture of Zinc ore and coke, wherein, the coke is but slightly in excess of that'theoretically required for the reduction of the ore. This mixture is preferably preheated to as high a temperature as the coke will tolerate'without ignition (say to a temperature of 500 (3.), by placing it in a rotary furnace of the muffie type, heated exteriorly by the products of combustion from any suitable heat- The rotation of the ore and coke mixture during the heating operation servesto insure the highest possible homogeneity of the mixture and the uniform heating of the individual particles. In the heated condition, the charge is then supplied to the brick-lined bin-E, from which it is fed into the furnace continuously, upon the surface of the molten resistor. The rotation of the furnace with its molten resistor then proceeds, the electric current maintaining the necessary thermal conditions for the reduction of the ore and the volatilization of the zinc. The gaseous and volatile products of the reducing operation enter the condenser, wherein the zinc vapors are in large part condensed into metallic zinc, the prolong taking care of such of the zinc vapors as may escape condensation in the condenser itself; whereupon the residual fumes and gases will be carried off through the stack G, for further treatment, if desired.

Because of the continuous feed of the zinc screw-threaded plug 6 is in place.

ore charge into the furnace, the reducing operation proceeds with corresponding continuity, until such time as it is deemed advisable to tap off the slag, it being understood that the capacity of the furnace to rotate permits the slag to be tapped off separately from the metal remaining in the furnace.

A suitable provision for permitting the tapping of the furnace is illustrated in Figs. 1 and 5. For instance, a tap hole, tapering outwardly may conveniently be made in the chrome brick lining. The tapering opening, thus provided, is normally tamped with a filling 0 consisting of an electrically conducting mixture of fire clay and graphite, which'is tamped into the opening as indicated-in Figs. 1 and 5. Immediately opposite the tapered opening, the low carbon steel casing is is provided with a screwthreaded aperture occupied by a screw threaded plug 0, the arrangement being such that when the tapered aperture is filled with its content of the fire clay and graphite mixture, thereby plugging the tap-hole, the When the furnace is to be tapped, the screw-plug e is removed, together with the fire brick immediately back of it, and one lead of the electric circuit is put in contact directly with the plug filling of fire clay and graphite, the furnace being stopped in such position that the plug filling will be in contact with the molten resistor. The passage of the current throughthe conducting filling rapidly raises it to such a temperature that it becomes soft and yielding and it may then be readily removed, thereby establishing the tapping outlet.

It will, of course, be understood that before removing 'the conducting filling, the furnace has been further rotated sufficiently to stop it at a place above the level of the charge. As soon as the provision for tapping the furnace has thus been established, the furnace is again rotated to an extent corresponding to the Inasmuch as the slag level is below the surface of the zinc ore charge, and inasmuch as the outflow of the slag proceeds with considerable rapidity, it is not necessary, 1n most instances, to interrupt the continuous feed of the zinc ore charge at the time the tapping is undertaken, although, if so desired, the feed may be temporarily interrupted during this brief period. It will be understood further that the tap-hole may likewise serve for the introduction of the molten resistor into the furnace, in the first instance, or its partial or complete removal, as desired- Where the zinc ore to be'treated contains any of the precious metals, it willbe found desirable to add enough copper ore to the desired tapping operation.

. shortening the time required for the complete chemical action, and not only increasing the daily furnace capacity, but also increasing the heat eflicieney of the furnace, as heat is radiated, for a given charge, durving a shorter space of time, so that the loss of radiated heat is correspondingly less. Furthermore, the rotation of the furnace, by constantly renewing the surface of the lining in contact with the heating medium,

keeps the whole furnace at a high. heat and keeps the lining free from accret-ions that would otherwise tend to accumulate upon it. Evidently, however, the upper part of the furnace will be at all times to some extent cooler than the lower part, which contains the molten resistor. This is a desirable feature, in that it keeps down the tem perature of the issuing gases and zinc vapors, thus facilitating the condensation of the latter. I

Referring further to the conditions of practice of my invention, I desire to state that I may so proportion the zinc ores entering into the charge to each other and to the coke employed as the reducing agent that there will be introduced an appropriate amount of iron to compensate for any mechanical losses of the molten iron resistor, as, for instance, from losses due to the entrapping of portions of the iron, as shot, in the slag, or from any other cause; and, if there is not enough phosphorus present in the slag, to supply with the iron, the

.losses of resistor, I may add to the ore charge as an additional ingredient an' appropriate amount of phosphoretic slag from any suitable source, as, for instance, the phosphoretic slag from a. basic lined Bessemer, open-hearth or electric steel refining furnace. Furthermore, the zinc ore charge is to be so compounded as to produce a highly liquid slag, which is without important corroding effect upon the neutral lining of chrome brick employed.

It is within the contemplation of my invention to run off the fluid metal resistor at any time, if desired, and to permit its place to be taken either wholly or in part by molten slag introduced independently into the reducing chamber or which may be allowed to accumulate from the zinc ore charge itself. If additional slag to that which accumulates from the zinc ore charge be required, it may conveniently be applied from waste slag which has already been tapped off from the reducing chamber, and

its liquidity may be increased, if required, by the addition of fluor-spar or the like. In fact, in some instances, Where it is desired to accumulate in the resistor a large number of calories in order to correspondingly counteract whatever of chilling effect may be incident to the admission of the charge, it may be desirable to practically substitute for the fluid metal resistor a resistor consisting of the molten slag itself, the lesser electric conductivity of the liquid slag as compared to that of the fluid metal resistor permitting the employment of a larger cross section for the resistor when the liquid slag is employed as such and constituting it a larger reservoir or magazine for the storage of heat.

In the practice of charging the zinc retorts of the customary Belgian furnace the charge is supplied to-the retorts in a moist condition, which is necessitated by the circumstance that it is shoveled into the retorts by hand, long-handled shovels being employed for the purpose which cannot be manipulated without scattering about a' large quantity of dust from the material being charged unless the material is first dampened. In the practice of my invention,

on the contrary, the charge is fed into the reducing chamber in a substantially dry condition, for which reason the amount of moisture introduced into the reducing chamber and which in the ordinary practice has an oxidizing effect upon the zinc vapors during the early stages of the operation is substantially eliminated.

In order to realize to the highest degree the condition of dryness desirable for the charge on its admission to the reducing chamber the preheating of the charge to the extent permitted by the presence'of the reducing agent therein is made available for that purpose, and this preheating of the charge has the further characteristic advantage that it lowers the gap between the temperature prevailing within the reducing chamber and that of the entering charge itself so that the calories required for carrying on the operation within the reducing chamber are to a large extent utilized merely for the purpose of realizing the chemical re actionsnecessary for the reducing operation instead of being likewise expended in raising the charge from a cold condition to the higher ranges of temperature. Furthermore, in the ordinary practice care is taken to so compound the zinc ore charge that it shall have a very large excess of the reducing agent (coke) present, and the formation of a highly liquid slag is avoided, the conditions being so balanced in this regard that the large excess of coke shall serve to mechanically absorb as far as possible the slag produced thereby keeping it out of contact as well as may be with the acid walls of the retort which would otherwise be rapidly corroded especially if the slag, for any particular charge, should be essentially basic. The employment of this large excess of coke in the ordinary practice is an element of serious loss and inconvenience, for the reason that it must be ejected from the retort at the end of the operation and is practically a waste material in so far as its carbon content is concerned, its recovery only being attempted in those instances where the expelled material contains in addition important quantities of valuable metals. In the practice of my invention, however, the zinc ore charge is so compounded that the amount of reducing material is present only in slight excess above that required for the chemical reactions necessary for the reduction of the ore,say eighteen to twenty per cent. of fixed carbon to the total amount of the charge. So also, in the practice of my invention, a highly liquid slag is a most desirable feature of the process and in order to give it full liquidity, if the ores themselves do not furnish a sufiiciently liquid slag, additional fiuxing material may be added, as, for instance, an appropriate amount of fluorspar. Moreover, inasmuch as the reducing chamber is heated byan internal source of heat, to wit, the electric current passing through the fluid resistor, it is not necessary, as in the Belgian retort furnace practice, to have the lining of the retorts thin for the transmission of heat from without inwardly, and, therefore, of clay, but they may, as herein contemplated, be provided with a thick non-acid lining, such as chromite brick or the like, which is practically neutral to the liquid slags produced at the temperatures prevailing within the reducing chamber. Furthermore, as hereinbefore pointed out, the sealing of the reducing chamber at the place where the charge is fed into it provides efficiently against the admission of air to the interior of the chamber, therebyinsuring the presence of a reducing atmosphere within the chamber during the period of the vaporization of the zinc and, at the same time, permits the operation to be a practically continuous one, the condensation of the zinc vapors proceeding I continuously, the slag being tapped ofi progressively and the feed being practically continuous.

It is of special advantage for the practice of the invention that the electrical connection of the fluid resistor to the external heating circuit is established through direct contact of the resistorwith leads or terminals of metal. The annular sleeves a and the intermediate annulus being of steel leave nothing to be desired in this regard, inasmuch as they sufficiently approximate the metal of the resistor when the latter is the iron-phosphorous alloy usually preferred, and particularly they do not tend to introduce impurities into the resistor or to reduce its resistivity. At the same time, these terminals are of substantial and simple construction, and the sleeves especially, being each cast in one piece, can be readily .removed and others substituted should the originals become worn or distorted.

VJ hat I claim is i 1. The method of reducing zinc ores and compounds, which consists in establishing within a reducing chamber a fluid resistor, introducing into the chamber the zinc ore charge, and maintaining the temperature of the charge at the reducing point by passing an electric current through the resistor, and imparting a movement of rotation to the chamber; substantially as described.

2. The method of reducing zinc ores and compounds, which consists in establishing within a reducing chamber a fluid resistor, introducing into the chamber in a practically dry condition the zinc ore charge, maintaining the temperature of the charge at the reducing point by passing an electric current through the resistor and tumbling the contents of the chamber; substantially as described.

3. The method of reducing zinc ores and compounds, which consists in establishing within a reducing chamber a fluid resistor, introducing into the chamber the zinc ore charge, its reducing constituent being not materially in excess of that required for the reduction, maintaining the temperature of the charge at the reducing point by passing an electric current through the resistor, and tumbling the contents of the chamber; substantially as described.

4. Themethod of reducing zinc ores and compounds, which consists in establishing within a reducing chamber afluid resistor, introducing into the chamber the zinc ore charge, maintaining the temperature of the charge at the reducing point by passing an electric current through the resistor, and tumbling the contents of the chamber in the presence of a highly liquid slag; substantially as described.

5. The method of reducing zinc ores and compounds, which consists in establishing within a reducing chamber a fluid resistor, introducing into the chamber the zinc ore charge, its reducing constituent being not,

tumbling the contents of the chamber in the presence of a highly liquid slag; substantially as described.

6. The method of reducing zinc ores and compounds. which consists in establishing within a reducing chamber a fluid resistor, introducing into the chamber the zinc ore charge, maintaining the temperature of the charge at the reducing point by passing an electric current through the resistor, tum.- bling the contents of the chamber, and proressively drawing off the slag and supplymgadditional quantities of the charge so as to maintain a practically continuous operation; substantially as described.

7. The method of reducing zinc ores and compounds, which consists in establishing within a reducing chamber a fluid resistor, introducing into the chamber the zinc ore charge, maintaining the temperature of the charge at the reducing point by passin an electric current through the resistor, um-

bling the contents of the chamber, and ex-" eluding oxidizing gases from the atmosphere of the reducing chamber during the period of the recoveryof the zinc vapors; substantially as described.

8. The method of reducing zinc ores and compounds, which consists in establishing within a reducing chamber a fluid resistor, introducing into the chamber the Zinc ore charge, maintaining the temperature of the charge at the reducing point by passing an electric current through the resistor, and tumbling the contents of the chamber in the presence of a highly liquid slag and a nonacid lining; substantially as described;

9. The method of reducing zinc ores and compounds, which consists in establishing within a reducing chamber a'fluid resistor consisting of molten iron carrying a high percentage of phosphorus, introducinginto the chamber the zinc ore charge, and main taining the temperature of the charge at the reducing point by passing an electric cur rent through the resistor; substantially as described.

10. The method of reducing zinc ores and compounds, which consists in establishing within a reducing chamber a fluid resistor consisting of molten iron carrying a high percentage ofphosphorus, introducing into the chamber the zinc ore charge, and maintaining the temperature of the charge at the reducing point by passing an electric current through the resistor, and supplying any lossesvin iron and phosphorus, by contributions from the charge substantially as described;

11, The method of reducing zinc ore and compounds, which consists in establishing within a reducing chamber a fluid resistor, introducing the zinc ore charge into the chamber in a practically dry state and at a temperature approximating that at which its reducing constituent would burn in the open air, maintaining the temperature of the charge at the reducing point by passing an electric current through the resistor and tumbling the contents of the chamber; substantially as described.

12. An electric furnace for the metallurgy of zinc ores and compounds, comprising a reducing chamber, a fluid resistor therein, means for heating said fluid resistor electrically, and means for shifting the surfaces of contact between the fluid resistor, the ore charge and the walls of the 'reducing chamber; substantially as described.

13. An electric furnace for the metallurgy of Zinc .ores and compounds, comprising a rotatable reducing chamber, a fluid resistor therein, and connections for leading current through the resistor, whereby, during rotation of the chamber, the mass of the resistor remains in the lower portion thereof, the furnace charge is agitated and mixed, and the lining of the chamber is heated throughout by successive contact with the hot resistor; substantially as described.

14.- An electric furnace for the'metallurgy of zinc ores and compounds, comprising a rotatable reducing chamber, electric circuit terminals of metal, and a fluid resistor bridging said terminals and in direct contact therewith; substantially as described.

15. An electric furnace for the metallurgy of zinc ores and compounds, comprising a rotatable reducing chamber, electric circuit terminals, each consisting of an outer metal plate having an annular inwardly projecting extension likewise of metal, and a fluid resistor bridging said extensions; substantially as described.

16; An electric furnace for the metallurgy of Zinc ores and compounds, comprising a rotatable reducing'chamber, electric circuit terminals, each consisting of an outer metal plate having an annular. inwardly projecting extension likewise of metal, and a fluid resistor bridging said extensions, said plate being fluid-cooled; scribed.

17. An electric furnace for the metallurgy of zinc ores and compounds comprising a rotatable reducing chamber, provided at its ends with electric circuit terminals each consisting of a steel plate provided with an inwardly projecting extension likewise of steel, and a fluid resistor bridging said extensions and consisting of molten iron containing phosphorus; substantially as described.

18. An electric furnace for the metallurgy of zinc ores and compounds, comprising a rotatable reducing chamber, electric circuit terminals, and a molten resistor bridging said terminals and restricting the passage substantially as de-- of the working current, as the chamber rotates, to a'path maintained below the level of the charge; substantially as described.

19. In an electric furnace for the metallurgy of zinc ores and compounds, comprising a rotatory reducing chamber, having an electrically-heated fluid resistor, means for connecting the fluid resistor to the external heating circuit consisting of an annular ter minal of metal preserving contact with the resistor as the chamber rotates; substantially as described.

20. In an electric furnace for the metaling a rotatory reducing chamber having an electrically-heated resistor, means for connecting the opposite ends of the fluid resistor to the external heating circuit consisting of annular sleeves of metal projecting into the reducing chamber from the ends thereof and preserving contact with the resistor as the chamber rotates, one of said sleeves containing a feed pipe. for

charging the reducing chamber, and the' other containing an exit port leading to a condenser; substantially as described.

22. In an electric furnace for the metallurgy of zinc ores and compounds, comprising a rotatory reducing chamber having an electrically-heated resistor, means for connecting the opposite ends of the fluid resistor to the external heating circuit consisting of annular sleeves of metal projecting into the reducing chamber from the ends thereof and preserving contact with the resistor as the chamber rotates and an intermediate annulus of metal likewise preserving contact with the fluid resistor as the chamber rotates, the external heating circuit being provided with two-phase leads, to which said annular sleeves and the intermediate annulus are respectively connected;

substantially as described.

23. An electric furnace for the metallurgy of zinc ores and compounds, having a reducing chamber provided with a longitudinally'expansible lining, in combination with a conducting end plate held in yielding relationship therewith; substantially as described.

24. An electric furnace for the metallurgy of zinc ores and compounds, comprising a rotatory reducing chamber, having an electrically-heated fluid resistor and having an expansible lining, a casing one of Whose ends constitutes a fixed abutment for the lining and whose other end is closed by a yielding spring-pressed end plate, and means for connecting up the fluid resistor with the external heating circuit; substantially as described.

25. An electric furnace for the metallurgy of zinc ores and compounds, comprising a rotatable reducing chamber having a metallic casing made up of an outer shell and two ends, one of which is electrically insulated from the shell, a fluid resistor within the chamber electrically connected at its opposite extremities to the said ends respectively, and brushes making electric contact respectively with the insulated end of the casing and with its shell; substantially as described.

26, An electric furnace for the metallurgy of zinc ores and compounds, comprising a reducing chamber, a feeder for supplying the ore charge into the chamber, a fluid resistor whose resistivity and heating capacity are greatest at the place Where the charge en ters, means for heating the resistor electrically, and means for shifting the surfaces of contact between the resistor, the ore charge, and the walls of the reducing chamber; substantially as described- 27. An electric furnace for the metallurgy of zinc oresand compounds, comprising a rotatable reducing chamber, a fluid resistor therein of lesser cross section at one end of the chamber than at the other, and means for feeding in the ore charge at that end of the chamber where the cross section of the resistor is less; substantially as described.

28. An electric furnace for the metallurgy of zinc ores and compounds, comprising a rotatable reducing chamber of less internal diameter at one end than at the other, a fluid resistordtherein, means for heating said resistor electrically, and means for feeding in the ore charge at the smaller end of the furnace; substantially as described.

.29. An electric furnace for the metallurgy of zinc ores and compounds, comprising a rotatable reducing chamber, a molten resistor therein, means for heating said resistor electrically, and a feeding device for supplying the chamber with the ore charge as the reducing operation proceeds, said feeding device consisting of a feed pipe rotating with the furnace, a feed bin into which said pipe extends, and a feed screw for forcing the contents of the bin into the feed pipe; substantially as described.

30. An electric furnace for the metallurgy of zinc ores and compounds, comprising a rotatable reducing chamber; a molten resistor therein, means for heating said resistor electrically, and a feeding device for supplying the chamber with the ore charge cupied b the charge material; substantially 10 as the reducing o eration proceeds, said as descri ed feeding device consisting of a feed pipe ro- In testimon whereof I afiix my signature, tafiinlg wigh the furnace, adfeedE bn into in presence 0 two witnesses.

w 10 san 1pe exten s, an a ee screw for forcing he contents of the bin into the AUGUSTIN LEON JEAN QUENEAU feed pipe, said feed screw terminating back \Vitnesses:

of the discharge end of the feed pipe so as L. H. BARLOW,

to leave an intermediate sealing portion 00- L. B. PENFIELD.