US1193633A - thomson - Google Patents

Description

I J. THOMSON. ELECTRIC FUMING 0R DlSTiLLlNG FURNACE AND CONDENSER THEREFOR.

, APPLICATlON FILED OCT- Z1915. 1,193,633. Patented Aug. 8, 1916.

5 SHEETSSHEET I.

1. THOMSON. ELECTRIC FUMING 0R DISTILIJNG FURNACE AND CONDENSER THEREFOR.

APPLICATION FILED OCT. 2, H5. 1 1 93,633 Patented Aug. 8, 1916.

5 SHEETS-SHEET 2- J. THOMSON. ELECTRIC FUMING 0R DISTILLING FURNACE AND CONDENSER THEREFOR.

APPLICATION FILED OCT. 2. I915.

a A I m 1; THOMSON. ELECTRIC FUMING 0R DlSTlLLING FURNACE AND CONDENSER THEREFOR.

APPLICATION FILED OCT- 2. I915.

Patented Aug. 8, 1916.

5 SHEETSSHEET 4.

v drawings, forming a part hereof.

UNITED STATES PATENT OFFICE.

JOHN THOMSON, OF NEW YORK, N. Y., ASSIGNOR T0 JOHN THOMSON PRESS COMPANY, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

ELECTRIC FUMING OR DISTILLING FURNACE AND CONDENSER THEREFOR.

T 0 all whom it may concern Be it known that I, JOHN THOMSON, a citizen of the United States, and a resident of the borough of Manhattan of the city of New York, in the county and State of New York, have invented certain new and useful Improvements in Electric Fuming or Distilling Furnaces and Condensers Therefor, of which the following is a specificat on, reference being made to the accompanying This invention relates to the metallurgy of metals which are capable of being volatilized and then condensed or precipitated, and the particular object thereof is to refine an impure metal, or alloy, -pro ducing a'high grade of coalesced metal, or dust, or oxid, as the case may be.

The invention essentially resides in the employment of an electric furnace of the resistor type and coordinating elements designed to accomplish the above object in an effective and economical manner.

The general principles involved Wlll be concurrently pointed out with special reference to the metallurgy of zinc, in connection with the description of the accompanying drawings; which are presented as representative embodiments of the invention.

Figure 1 is atransverse center section of the furnace, viewed as on the line B of Fig. 2, except that its resistor is shown in end elevation, having a metal condenser on its left-hand side and a blue-powder con-. I

forms produced by rods or plates; and with denser, or precipitator, on its right-hand side. Fig. 2 is a longitudinal center section, the resistor and a terminal being shown I in side elevation and being viewed on the line C of Fig. 1. Fig. 3 is a top plan and partial horizontal section, as viewed from the planes denoted by D and E, of Fig. 1. Fig.4 is a top plan view, enlarged, of the terminals, resistor and connector. Fig. 5 is a transverse section of the resistor, as viewed on the line F of Fig. 4. Figs 6 and 7 are detached sectional views showing modifications in the cross-sectional form of the resistor. Fig. 8 is a detached view, enlarged, of one of the terminals showing means for water cooling it. Fig. 9 is a detached view developed from the furnace chamber, .as in Fig. 2, showing a modification in the disposal of its septum-plates. Fig. 10 is a detached plan view of the liquid.

condenser, enlarged, its cover-plates being Specification of Letters Patent.

Patented Aug. 3, 1916.

Application filed October 2, 1915. Serial No. 53,733.

H or I of Fig. 1'. Fig. 13 is a vertical cross section of the blue-powder condenser or precipitator, as viewed on the line J of Fig. 1, except that its water-jackets are shown in end elevation. Fig. 14. is a plan View of the slidable valve for withdrawing blue-powder,

it being shown above in longitudinal section in Fig. 13; and Fig. 15 is an enlarged detail view of an aspirator the application of which is indicated on the blue-powder condenser, Fig. 1.-

The fuming chamber K of the furnace L is heated by a resistor M the type of which was originally proposed by F. A. J. Fitz Gerald, E lcctroclwmz'cal and Metallurgical Industry, page 215 of 1905; that is a carbon bar or slab 16 or "16 having a series of transverse staggered slots 16, alternately cut partially through from one side and then from the other, thereby producing a zig-zag circuit of limited cross sectional area the resistance of which may usually be sufiiciently high to come within the voltage-range of standardized generators or transformers. The Fitz Gerald resistor, sometimes termed the zig-zag resistor possesses the unique advantages of being more readily suspended-and more closely controllable as to its temperature than other .the furnace. The structure is secured together by means of tapered carbon pins 19,

or. screws may be used if desired. The resistor-slabs instead of beingsquare or rectangular in cross section are trapezoids, the beveled sides 20 of which face downwardly, the-bottoms of the slots 21 preferably corresponding to the outer angles; 1 Theupper side-faces 22 of the zinc-trough 23 are availed of as a support for the ends of th connector. Consequently, by simply removing the bricks in the end wall of the furnace the resistor complete with its connector of short-circuiting. The variation in depth of the bath, as will later be pointed out, is merely nominal, whereby the utmost effectiveness in transfer of heat is realized.

Three particular advantages ensue by forming the resistor-slabs, in their crosssection, as trapezoids. Thus, see Fig. 5, the transverse stability, as respects sagging, is greater than if the sldes of the slab and bottoms of the slots were vertical; the heat is radiated from the sloped sides at a rightangle thereto, that is toward the bath, as denoted bythe arrows a; the downwardly radiating surface is thereby increased about 15% and as the transverse length of the circuit, between each slot, corresponds with the angles of the sides, as b maximum, 0 mean and d minimum, the greatest currentdensity is along the lower zone, that is to say nearest to the bath and precisely where required. Obviously, if the heat was to be utilized upwardly, or sidewise, the position of the resistor would be correspondingly reversed. It is preferable, in practice, if the trapezoidal angles are somewhat acute, to leave a small extent of theupper edges vertical 26, as a sharp intersection is liable to be broken in handling. Fig. 6 denotes the trapezoidal section developed to about its maximum extent, that is limited by the intersection of the lower edges 27 of the slots, and Fig. 7 indicates a modification in which the connecting trapezoidal circuit sections 28 are produced in the form of curvedv segments.

Clos. regulation of the temperature is-of first importance. In using the Fitz Gerald .zig-zag type of resistor as a compound element in series, the connector. should have an excess of section over that of the restricted circuit and be thoroughly well attached with a largearea of surface contact.

This is well realized, as See Fig. 1, by fit:-

ting the trapezoidal ends to corresponding recesses 28 in the connector and then keying them together by tapered or threaded pins. Another feature not to be neglected is the water-coolingof the terminals, as this tends to closeness of temperature regulationas a WllOlQ and avoids troublesome air burning at or within the brick-work. An effective means to this end is shown in Figs: 2 and 8,

consisting in boring a relatively deep hole 29 along the axial center of the terminal and inserting a metal tube 30 which contains a smaller axial tube 31 and an outer transverse tube 32. Both ends of the large tube are tightly closed while both ends of the other tubes are open. Cold water is forced in, as arrow e, impinges against the ferent depths in the terminals. Heat is extracted from the center, where most efie tive, and as the pipe-joints may be brazed the system is very safe against accidental leakage of water.

The trough 23 is filled and replenished from time to time exclusively with melted metal, pre-fused extraneously, which is poured in through the chute 33, Figs. 2 and 3, the inner end 34 of which is normally beneath the surface of the bath, acting as a seal against ingress of air or egress of fume. This mode of charging is most effective, as hot metal can be fed in small quantity and at relatively short intervals, thereby not' sensibly disturbing the metal in the bath or interfering with the rate of fume-evolution; which is a feature of prime importance. Also, in this manner the depth of the bath may be maintained with slight variation, say within a fractional part of an inch, as from the level I). to i, Fig. 2, and the thermal condition with respect'to the resistor will remainpractically perfect for an indefinite period of time.

It has been found in practice that the most advantageous manner of constructing the chute, as see Figs. 2 and 3, is by boring a hole in a rod or bar of amorphous carbon or Acheson graphite and disposing it at an pered, the larger diameter being at the bottom. As carbon is a good conductor of heat, the metal contained within the chute is less liable to freeze; but, if such should occur, the bore being tapered and disposed as de-' scribed, the solid plug of metal can readily be driven down into the molten bath. Then, when charging fluid metal, there is much less liability of its splashing or disturbing the continuity of the bath than would be the case were the chute set vertically. Incidentally, too, it is much more convenient for utilization as a peep-hole.

The foregoing conditions, that is radiation of heat uniformly to all portions of the bath-surface, the localized blistering effe t produced by the closeness of the resistor to the bath and the very. slight disturbance caused therein either by convection or charging small volumes of hot fluid metal, results in a very important advantage, namely, little if any circulation is caused in the bath, whence its surface is uniformly the hotter portion thereof. Consequently, as thelatent heat of vaporization of metals, and particularly zinc, is the principal source 0 sorption of energy, essentially all of the heat flowing from the resistor to the bath is effectively utilized.

At considerable intervals, depending upon the quantity of foreign matter contained in the primary charges, the residue must be withdrawn; the bulk of which, in the instance of zinc, being lead, iron, copper, etc., will ordinarily precipitate to the bottom of the trough.' This is provided for by the tap-hole 35, 2, or if it is desirable to quickly empty the trough the plate 36 is removed exposing the larger opening 37 As a further means for conserving the heat developed by the resistor, especially that radiated from its upper surface, and also to efiect a very uniform dispersion of the fume into the higher reaches of the furnace chamber, as O, a septum is provided formed by a series of refractory plates 38, Figs. 1, 2 and 3, which may be perforated or set to leave intervening slits 39. The fume, as arrows j, is thereby caused to dis perse and pass uniformly and vertically upward, expanding, as it leaves the slits, into the overhead or sub-chamber whence it will impinge against the cover, 40; but the heat emitted from the resistor impacts against the plates a considerable portion of which is necessarily reflected backwardly, as denoted by arrows is. In any event, depending upon the thickness and character of the plates, the resistor-temperature will be substantially less above the septum and the effect of this reduction, together with the beforementioned expansion of the fume and its impingement upon the cover, serves both to reduce the temperature of the fume, prior to its entry into the condenser, and also to lessen the radiation loss to atmosphere from the outer surface of the cover. Or otherwise stated, the heat radiated to atmosphere, through the cover, is that derived from the fume plus that conducted through the septum. A modified disposal of the septumplates is shown in Fig. 9, wherein two series of plates 38, 38* are employed, spaced longitudinally, as 38*, each overhead plate covering an underlying space, as 38 of about equal breadth. In this wise, a somewhat more free and greater area may be furnished for escape of fume and no heat vertically radiated from the resistor will pass directly into the upper chamber.

With the terminals located in the same end of the furnace, the charging chute and f ab-- surplus fume 1s regained in the form of tions as are residual port being in the other end, both sides of the furnace are left entirely free for application of condensers, of which two are shown: a liquid metal condenser Q, on

the left-hand side and a dust or blue-powder condenser P on the right-hand side, these being supplied with fume through the ports 41, 42. By means of'the valves 43, i4, either condenser may be operated independently of the other, or a pair of metal condensers, or of dust condensers, may be employed. There are, however, certain advantages to be derived in operating one of each kind. For example, as between a variable supply of power, and a cold, dry atmosphere or a warm moist atmosphere, there may be times when the rate offuming or of condensation will be out of balance. If the capacity of the metal condenser is less than that of the fuming capacity of the furnace, then the valve A may be somewhat opened, as shown, whereby the furnace can be run at its highest rate, the metal condenser taking all that it can coalesce into fluid while the dust or oxid. The aforesaid valves are also utilizable when both condensers are of the same character and employed for the same purpose, in that if one runs ahead of the other, so to speak, they can thereby be quickly brought into a state of balance.

The condensers here shown embody certain principles which have already been set forth in patents previously granted to the present applicant; but with the reservation that those cases related to zinc smelting operations wherein fume is produced by chemical reaction between ore and carbon as a reagent and is combined with monoxid of carbon, the volume of which, at the instant of evolution, is approximately equal to that of the zinc-fume and is not diminished in volume except by a partial withdrawal of its heat. Therefore, the details in this application will be restricted to such adaptaparticularly applicable to a distilling furnace, in which essentially no gas or vapor is produced other than metallic fume. WVhich is to say, this means that a condenser, whether adapted to produce liquid metal or dust would be operating theoretically perfectly when taking fume at its entrance at full capacity, under such head or pressure as might be necessary to cause it to adequately flow, while at the extremity there would be no volume other than thatof the liquid metal produced and no pressure. P67 contra, if the entering volume is completely condensed before the exit is reached, then there may be a vacuous condition and, if the conditions permit, an opposing back-pressure from atmosphere may result.

Having regard to the foregoing principles and referring to Figs. 1 and 3, the metal 30 way 50. The several plates are preferably slid along the rod to produce spaces between them which gradually diminish the area of the lateral flow-ways-from the inner to the outer end of the chamber. Consequently, the velocity of the fume and the area of plate-surface are maintained approximately constant from inlet to outlet. This produces a flow along a general horizontal plane during which the fume is subjected to numerous impingements, expansions, contractions and deflections, as denoted bv the arrows m, and establish conditions which are highly conducive to the condensation and coalescence of fume, into liquid metal. A more complete practical development of these principles is shown in Figs. 10 and 11, in which between the baflle-plates 48 other shorter plates 51 are set to produce gradually diminishing spaces, the fume flowing therethrough in parallel, as the arrows denote. When liquid metal is accumulated, as 52, Fig. 1, the

lower portions of the plates are immersed' therein; therefore, the floor of the chamber becomes in reality a large surface of fluidified metal which performs the double function of stabilizing the proper temperature in the plates and affording an affinitive medium for coalescence of fume. In the assemblage, it is important to observe that the alternate ends of the baffle-plates are in contact with the side-walls and the same refers to the cover-plates of the condensing chamber, whereby to rapidly conduct heat from the interior to the exterior. It may here be observed that, in practice, the condenser is set on a downward slope.

Referring now to Figs. 1, 3 and 12, it will be perceived that the condenser is supported on three narrow brick ledges, 53, 54, 55, between side-walls, 56, 57, set to leave vertical free spaces, 56, 57 In this wise, nearly the entire outer surface of the condenser is, or may be, freely exposed to atmosphere; but the extent of heat-radiation is susceptible of complete control by means of the simple expedient of placing or removing heat insulating sheets, wooden boards or the like, over the top, as 58, beneath, as 60. At the initial start of the furnace, for the distillation of zinc, it is highly essential to pre-heat the interior of the condenser, every portion and part of it, to a temperature well above that of the melting point of spelter, else more or less of blue-powder will be initially formed and accumulated. Also,

such as asbestos,

59, and across the front, as,-

in the event of a temporary cessation of the fume-supply, as when withdrawing residual matter from the trough, it is of the first importance to be able to promptlyapply external heat to the condenser and maintain its interior at a temperature above that at which blue-powder may be produced. To this end, preferably two auxiliary resistors are disposed in channels, 63, 64., beneath the condenser. For this purpose the resistor may be a bed of broken carbon, as depicted by IV in Fig. 12, interpolated between terminals, 65, 66. Thus, current may quickly be turned on, either to one or both, and the desired temperature be imparted and maintained indefinitely, whether the fuming furnace is in operation or not.

Reference should now be had to Figs. 1, 3, 13 and 14. In the blue-powder, or dust, condenser P (perhaps the word precipitator is the more exact term) the same fundamental principles inhere but the mode of execution is quite divergent from that of the liquid condenser. Its fume-chamber T' is formed by a sheet-metal casing 67 the lower edge of which rests within the flanged recess 68 of a cast iron casing 69, into which the blue-powder 7O gravitates and is collected. The top of said fume-chamber is inclosed by a flat metal plate 71 which need not be rigidly confined, whereby in the event of an explosion it will freely blow off. Tight joints are effected as by means of cement 72, or interposed gaskets may be used. Within said chamber are a series of baffle-plates 73 preferably curved in crosssection toward the inflowing fume, all being conveniently strung on two free rods, 74, 75, as in the instance previously described. On each outside of the casing, and in contact therewith, is a sheet-metal water-tank, as 7 6, 77, which may reston the flange of the cast iron casing. These tanks may be open at their tops, as shown. The nipples, 78, 7 8 and 7 9, 7 9 are for attachment of rubber tubing to supply cold water and withdraw it when warm, or water may be continuously circulated, as may be desired. In its dimensions, the width of this fume chamber is relatively substantiallv less than its height and length, in fact generally following the design of the metal condenser except that it stands in its lesser dimension vertically instead of horizontally. Following the courses denoted by the flow-arrows n, it will be perceived that the fume, as it is received from the furnace, suffers a considerable expansion and is thereafter caused to flow forth and back across the baflle-plates and to acutely impinge against andflow along the watercooled sides of the casing. As a consequence, a large volume of fume may be chilled with great rapidity; which is then free to immediately gravitate into the underlying collecting chamber Z from whence it is intermittently withdrawn by the slidable valve 80. As shown, this valve is a simple block having an opening 81 mounted in a slide-way blue-powder in the metal condenser is very objectionable; and it should be borne in mind that the production of dust is contingent upon a chilling temperature, that is a temperature 'less than the melting point of zinc. Yet, blue-powder may be and usually is produced in an oxidizing atmosphere. The presence of oxid of zinc (ZnO) is still more objectionable and this refers either to the metal condenser or to the blue-powder condenser. The formation of ZnO, however, involves the presence of air in considerable volume and is more or less independent of the temperature. The blue-powder of commercehitherto has been nearly if not entirely a residual by-product and the opinion is generally held that even the most infinitesimal of its globules is imprisoned in a film of oxid. So being, it is an oxid of zinc in which the content of oxygen is a minimum. But when the production is by distillation from metal, whether pure or impure, and the contaminating effects of C0, C0 hydrous vapor or atmospheric air are excluded, both in the fuming furnace and the condenser, then there can be no oxidization; there is no coloring of blue due to the oxid and the product is a pure grayish zinc-dust, the particles of which are exceedingly minute. Consequently, graydust is much purer and more effective in several of its applications in the arts than ordinary blue-powder. The latter is classed, commercially, as an explosive; gray-dust, ridden of its protecting films of oxid, is considerably more explosive.

The foregoing premises lead to the concluding coordinating element of the present application, denoted in Figs. 1 and 15, consisting in an aspirator Y for inductively exhausting "air from the furnace and the condensers and also for positively maintaining therein a slightly vacuous condition; or, otherwise expressed, a condition of minortension which shall be somewhat less than that of atmospheric pressure. This effect is produced by the simple expedient of supplying a vertical tube 83, screwed upon a nipple 84, applied to a condenser cover or plate 47, 71, and having thereon one, two or more inciting-tubes, as 85, 86, declined from the horizontal at an angle or angles of about 45. Now, by connecting these inciting tubes, as by means of rubber tubing, with means for supplying air under pressure, any contained air, or gas, or fume, or combination thereof, will beforcibly driven upwardly and out of the main tube 83, as see arrow '0', by the impulse of the jet or jets, and a vacuous condition will necessarily be produced below, thereby causing an induced flow from within the condenser, as denoted by arrow m. If an excess of uncondensed fume reaches the far end of the condenser, the aspirator need not be used; for, by simply shutting off the inciting air, it will then serve as a free outlet, or burner, in the usual manner. This device may also be availed of when first starting the furnace, as a somewhat pronounced inductive effect may be produced whereby to withdraw a portion of the contained air and cause it to be more quickly displaced by hot fume than would otherwise be the case. But this latter use of an aspirator, that is to remove the relatively large volume of air primarily contained in the furnace and condensers, is comparatively limited in that if a sufficient vacuum were produced a fresh supply of air would doubtless be drawn in through the brickwork. Consequently, a means has been developed for this purpose; which consists either in producing within the furnace an inert gas, formed, say, by an oil containing a minimum content of carbon, or by making such a gas externally and conveniently introducing it through the charging chute, thereafter or prior thereto inserting fluid metal. The result of this procedure is that essentially all of the air is displaced by the gas, finding vent through the condenser openings; then as fume is produced it in turn displaces the gas, whence no oxid of the metal will be formed.

A general feature of the design which has purposesly not been earlier adverted to but is ofthe first importance relates tothe large heat radiating surface of the resistor with respect to the heat absorbing surface of the bath. In practice, these may be about equal. Therefore, as thetemperature of the resistor will be nearly if not entirely uniform at every square inch of its surface, there will be no hot spots over the bath; the evolution of fume will proceed with great uniformity and all the ra idity at which calories may be supplied an absorbed. This means that the temperature at and upon the surface of the bath need never be, nor can it well be, but little if any above,the free boiling point of the metal to be vaporized. This also means that all other lower portions of the bath will be at a lesser temperature; hence, when zinc is being distilled, metals like lea-d, tin, copper and iron will not be vaporized, (as may occur in hot-spot zones) and they will tend to settle out of the relatively thin boiling plane, according to their respective densities. And factors not to be overlooked in the above connection are the coordinating performances of the sloped chute, whereby small quantities of hot fluid may frequently be charged without suspending the production of fume and without seriously disturbing the bath; also the septum plates which at once afford a very rapid and unobstructed flow from the fuming chamber and yet prevent superheating of the fume with the contingent loss of energy which would therebyensue.

Various modifications, or even substitutions, may be made in the details without departing from, or evading, the spirit and essence of this invention. For example, while it is contended that the type, form and disposal of the zig-zag resistor herein described is distinctly the best for the contemplated purpose, yet it is not per se a pre-requisite when taken in connection with some of its co-' ordinating functions. It may be operated in parallel; or may be double-compounded; or resistors formed by rods, interlocking plates and broken carbon sustained on gratebars might be substitutedwhich would leave certain other elements of the invention as they stand. The elongated trough may be made approximately square or in the form of an ovoidal basin. The single charging chute may be variously disposed, even to supplying the molten metal centrally, between the resistor slabs, or a plurality of chutes may be employed.

Brief mention has herein been made that the furnace may be used for producing oxids, such as of zinc, ZnO. Such is, in fact, entirely feasible, but the means of its production from pure fume has not been shown in that the principles involved and the elements required are in many respects dissimilar from the more closely coordinating functions of metal and dust condensers.

lVhile a complete citation of various other purposes to which features of this invention can be applied will be omitted, this is not to be construed as indicating that the intimated utilizations have escaped due consideration, and it may be pointed out, in conformity with the opening paragraphs, that this system is well adapted for the treatment of metals other than zinc which are capable of being vaporized and thereafter condensed or precipitated in the form of coalesced metal, dust, or oxid, such say, as cadmium, lead, antimony, etc. Moreover, when an alloy of various metals is charged, each having a distinct vaporizing temperature, the operation may be carried on, in effect, by fractional-distillation. Thus, as a single example, taking an alloy of zinc and lead, the

former may first be coalesced at its lower fuming temperature while the latter may be later vaporized at its considerably high fuming temperature.

lVhat I claim is 1. A zig-zag plate-resistor, its inner end, or ends, being attached to and sustained by a bar, or connector, resting upon ledges in the furnace and along which the said bar or connector may be slid in or out.

2. A zig-zag plate-resistor having a cross section in the form of a trapezoid, the sideangles of which are presented to the surface, or in the direction, where the radiated heat is to be utilized.

3. A zig-zag plate-resistor the cross-section of which is such that the current-density is greatest at or near to the surface, or surfaces, from which its radiated heat is utilized.

4. A zig-zag plate-resistor the cross-section of which is in the form of a trapezoid having its greatest current-density in a horizontal zone between the lower portions of the converging sides.

5. An electric fuming furnace having the following elements disposed in horizontal zones and in the order named: a trough containing a bath of molten metal; a zig-zag resistor whose heat is radiated downwardly and upwardly; a system of spaced or perforated plates and an over-lying chamber into which the ascending fume flows and expands.

6. An electric fuming furnace having a trough containing molten metal, a resistor horizontally suspended above the trough, a spaced septum horizontally suspended above the resistor and a free space above the septum for receiving the vaporized products.

7. An electric fuming furnace having a trough containing molten metal, a resistor above the trough, a portion of whose heat is radiated upwardly and a septum composed of spaced plates suspended above the resistor through which fume may freely escape but by which the upwardly radiated heat is considerably reflected toward its original source.

8. An electric fuming furnace having a resistor-chamber divided by a septum composed of spaced plates horizontally situated between the resistor and the outlet port or ports leading to the condensing system, the construction and arrangement being such that the fume is caused to primarily disperse and flow uniformly into all portions of the sub-chamber from which the said condensing system is supplied.

9. An electric fuming furnace having a liquid metal condenser provided with a series of bafiie-plates so disposed as to cause the fume to flow forth and back, but progressively forward, along a general horizontal plane; the fiow-spaces between the plates becoming less and less from the inlet to the outlet.

10. An electric fuming furnace having a liquid metal condenser having a series of baffle-plates and one or a plurality of interposed spaced shorter plates, whereby the fume, between pairs of bafiie-plates, is caused to flow through the spaces in parallel.

11. An electric fuming furnace having a liquid metal condenser provided with plates for causing a sinuous flow of fume; the flowspaces diminishing and the area of surfacecontact increasing from inlet to outlet.

12. An electric fuming furnace having a condenser provided with plates for producing a sinuous flow of fume, the said plates being strung upon and sustained by a free rod or rods.

13. An electric fuming furnace having a liquid metal condenser, relatively shallow with respect to its other dimensions, provided with a plate-system for producing a sinuous flow of. fume along acontinuous horizontal plane, the condensed metal forming a bath in which the lower portions of all the plates are immersed and a floor over which uncondensed fume is caused to continuously flow.

14. An electric fuming furnace having a liquid metal condenser, relatively shallow with respect to its other dimensions, pro vided with a plate-system for producing a sinuous flow of fume, the upper and lower edges and one end of said plates being in physical contact with the condenser-casin 15. An electric fuming furnace having a liquid metal condenser set in brick-work having underlying channels in which resistors and suitable terminals are disposed for primarily or intermittently heating the said condenser to a temperature above that at which the fume will be precipitated in the form of dust, and means for quickly intercepting the heat flowing from said resistors to the condenser.

16. An electric fuming furnace having a condenser for producing dust, in the interior of which are a series of curved or bent bafiieplates, the inner surfaces of the curvatures being opposed to the fume-flow.

17. In an electric metallic distilling furnace, a coalescing metal condenser on one side and a dust condenser, or precipitator, on the other side, and controlling valves in each entry port, whereby one of said condensers may be operated to its full capacity while the other may take any surplus of fume, if such exists.

18. In an electric zinc distilling furnace, an aspirator applied to the far end of its condenser, or condensers, comprised in an open vertical tube having a plurality of declined inciting tubes to which air under pressure is conducted, whereby a regulatable flow may be induced from the interior of the said condenser, or condensers.

19. In an electric zinc distilling furnace, an aspirator applied to the far end of its condenser, or condensers, comprised in a main open vertical tube having a plurality of declined inciting tubes, the main tube being applied to a nipple in the condenser cover, whereby when an induced flow is not required the aspirator may be left in place and used as a Vent or burner.

This specification signed and witnessed this 30th day of September, A. D., 1915.

JOHN THOMSON.

Signed in presence of RALPH M. THOMSON, J. R. AGNEW.

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