US1774688A - Refining of lead bullion - Google Patents

Description

Sept. 2, 1930. G, K.l w|| '1AMs 1,774,688

REFINING oF LEAD BULLION Filed March 28, 1929 Jg Z j2me/Wr Patented Sept. `2, 1930 UNITED f sTATEs PATENT OFFICEl REFINING F LEAD BULLION Application led March 28, 1929, Serial No. 350,832, and 1n Australia April 11, 1928.

This invention\relates to the refining of" lead lbullion containing other metals such as copper, gold and silver, and refers more especially to the refining of bullion working l under similar conditions to what is known as the Parkes process, that is to say, wherein zinc is added for the formation of alloys in the form of crusts.

For the purpose of avoiding unnecessary lo repetition in this specification the following terms will have the following meaning:

-Alloying metals will means suchmetals as copper or gold or silver which form alloys with zinc (with or without lead) and which being present in the initialHbullion, it is desired to remove, both for their own values and for the'purposel of providing lead sufficiently free therefrom for commercial purposes. Crusts will mean and include alloys of the said alloying metals in the form of crustsl which are formed by the cooling of the bullion with a View to separation from the lead bullion. a5

Residual bullion will mean the bullion remaining after one or more of the alloying metals has been separated therefrom in the form of crusts and is relatively low in such alloying metal or metals.

In the refining of lead bullion bythe wellknown IParkes process, it is the practice to Incorporate a certain amount of zinc with the molten bullion suicient for the formation of certain" alloys of the alloying metals desired to be removed. The bullion is then cooled, whereby the said alloys separate from the bullion in the form of crusts, which, owing totheir specific `gravity being lower than that .ofthe liquid bullion, rise to the surface 40`and are then removed, leaving residual bullion relatively low in such alloying metals. The crusts obtained by the aforesaid Parkes process contain a considerable amount of v entangledlead, the removal of which has '45 Vbeen effectedeither oysubjecting the saidI crusts to -liquatiomor to'presses. Y',

- p According to a patent in the United States of America which has been granted to me No. 1,6'87 ,187 ,the treatment for the refining f-llof4 is effected by incorporating zinc `with the said bullion in sufficient quantity and maintaining such temperatures that molten layers of conjugate solutions are formed, the upper of which consists of an alloy rich in certain alloyng metal or metals and separating such alloy. In the operation of this process it has been applied to effect a continuous refining of lead bullion', by continuously7 feeding the molten bullion into a vessel and continuously withdrawing the residual bullion v from the bottom thereof, and continuously or intermittently removing the alloy rich in certain alloying metal or metals from the top.

It has hitherto not been possible to effect a continuous refining of lead bullion by the "35 Parkes process. by reason of the fact that it` is necessary to add the requisiJ quantit of zinc, and to heat the bullion'for effecting the solution thereof in the lead, and to then lcool the mass whereby the alloys are separated out as crusts. The nature of this operation has hitherto necessitated the carrying out of this said Parkes process as an intermittent or batch treatment operation. 'l

Now, the object of this invention is to provide a method of operation whereby the essential conditions and characteristic of the Parkes process may be obtained in a c ntinuous operationl as distinct from, on the one hand the intermittent or batch treatment at 80 present practised, and on the other hand from the formation of conjugate solutions as described in the aforesaid Patent No. 1,687 ,187

I accomplish this object by incorporatin with the bullion an amount of zinc governe 35 bythe content of alloying metals in\the initial bullion on the one hand and in the residual bullion on the'other hand and subjecting the `said bullion during its continuous flow to a dereasingrange of temperatures, the 11p- ,9u per of which is sufficiently high for the solution of thev zinc in thef bullion and below the melting point 'of the alloy comprising the crusts to be removed, Whilst the lower of 'such range is just above the eutectie tempera- 95 ture of the residual bullion .desired to be produced, continuously withdrawing the residual bullion and continuously or intermittentp ly removing the crusts accumulating.

.The amount of zinc incorporated with the l bullion is, as stated, governed by the content of the alloying metals in the initial bullion and in the residual bullion, and in determining the amount of zinc additions necessary fregard will be had to the alloys which are formed in the cooler zones and which are redissolved in the bullion in the zones of higher temperature.

The refining operation is carried out in one or more stages the essential feature of the invention being the continuous flow of the bullion through each stage. In practice each stage 1s represented by the flow of the bullion through a kettle or series of kettles or other suitable vessel in which the Zinc is incorporated with the bullion and the same subjected to the necessary decreasing range of temperatures. In normal practice of the Parkes process a stage is generally equivalent to what is known as a zincing, The invention however may be carried out in other suitable apparatus such as reverberatory furnaces in which the bullion may be subjected to the necessary decreasing range of temperature.

In the drawings:

Figure 1 is a view in sectional elevational of a series of two externally heated kettles adapted for carrying out the invention; and

Figure 2 is a diagrammatic view in elevation illustrating an alternative arrangement of apparatus, and hereinafter is fully de! scribed,

In carrying out this invention the molten bullion is preferably fed into the top of a suitable kettle (see Fig. l of the drawings) where the requisite quantity of zinc necessary for the later formation of alloys in the form of crusts is incorporated with the bullion the temperature being at the upper part of the said kettle sufliciently high for the incorporation in the bullion of the requisite quantity of zinc, but below, the'melting point of the alloys comprising the said crusts, whilst the temperature at the bot-tom of the kettle is maintained just above the eutectic temperature of the residual bullion, and continuously withdrawing the said residual bulh on from the bottom of the kettle, and c-ontinuouslyor intermittently removing the crusts from the top of the said kettle.

The shape and dimensions of the kettle in which the operation is conducted may be as shown in Fig. l and are such that the bullion 1n passing therethrough at a certain rate of flow is subject to decreasing temperatures within the limits mentioned and for this purpose the kettles are so mounted in the brickwork that independent flues E and F surround the same so that differential temperatures may be applied thereto by suit-able means.

In practice the bullion may be pre-heated to any desired temperature before being fed into the top of the kettle such as by means of suitable reverberat-ory furnaces (Figure 2).

The necessary amount of zinc is incorporated with or dissolved in the molten bullion at the top of the kettle either in the f-orm of virgin zinc in solid or liquid condition, or in the form of crusts obtained from a previous operation. In practice this zinc is supplemented by the formation of alloys in the form of crusts in the cooler zones which are re-dissolved in the bullion in the hotter zones.

As the bullion passes downward through the kettle into the cooler zones, crusts are formed which rise to the upper part of the kettle, whilst the residual bullion is continuously withdrawn from the bottom of the kettle in molten condition, either by being pumped or siphoned, or overflowing therefrom through a suitable spout such as A? which discharges from the bottom and delivers ust below the surface of the bullion. The crusts accumulating on the surface are removed, either continuously or intermittently by manual or mechanical means as may be desired.

As with the Parkes process this invention is applicable to the treatment of bullion for the differential separation of alloying metals or for the collective separation thereof. For example, the operation may be conductedby first obtaining crusts rich in one alloylng metal, such as gold, followed by a subsequent separation of crusts rich in another alloy, such as silver, or alternatively crusts may be obtained rich in two or more alloying metals, such as gold and silver.

Instead of conducting the operation in one kettle, in which the residual bullion is withdrawn just above its eutectic temperature, the operation may be conducted in two or more kettles in series in which case it would only be necessary that the te-mperature should be maintained just above the eutectic temperature of the residual bullion at the outflow from the last kettle of the series, though it j will be understood that t-he operation may also be conducted with the temperature at the bottom of all of the kettles in the series just above the eutectic temperature of the residual bullion.

The operation of the Parkes process at present practised is the subject of a number of different well known `modifications involving mostly the different points at which the additions of Zinc are made, and this invention is applicable to any of the said modifications, the essential point being that the cooling of the bullion for the formation of crusts is effected during the continuous passage of the bullion as distinct from the intermittent or batch treatment which has hitherto been incidental to the operation of the said Parkes process. For example the invention is applicable to the well known modification of the Parkesprocess in which two successive zincings are employed, the necessary zinc for the first zincing being obtained L v from crusts produced from the second zincing of a previous operation whilst virgin zinc is used for the second zincing. l

In applying this invention to this modification of the Parkes process, it is desirable to make use of two kettles as shown in Fig. 1 in series, the outflow from kettle A being delivered into the top of kettle B. The crude bullion is continuously fed into the top of kettle A, preferably having been preheated toa temperature suiiicient for the incorporation of the requisite Damount of Zinc in the form of crusts and below the melting point of the orusts which it is desired to remove from the top of this first kettle. This. preheating may be effected in a suitable reverberatory furnace C as shown in Figure 2 The crusts skimmed off from the top of kettle B areregularly delivered into the top of kettle A with the feed of molten crude bullion. The temperature is maintained indebtain in one the bottom of kettle A at just above the eutectic temperature of the residual bullion being delivered from kettle A and is governed by the grade of the metal which it iS desired to deliver to kettle B. The bullion outiiows from A kettle into kettle B, and virgin zinc is regularly suppliedto the top of this kettle B in such quantities as are necessary for the formation of the alloys with the alloying metals contained in the'crude bullion. .The'top of kettle B is maintained at a temperature suiiiciently high to ensure the incorporation in the bullion of the zinc to be added, but below the melting point of the crusts formed in the said kettle B. In practice the temperatures at the top of both kettles are approximately the same. The

` bottom of kettle B uis maintained at the temoutflows therefrom.

,perature justl above the eutectic temperature of the residual bullion, which continuously In operation these two kettles` areworking e' in series in the same manner as obtains with the Parkes process, kettle Abeing directed'v l 'to the formation of crustsof as high a grade Cal i kettle B. lIn this case it will be necessary to as is possible in alloying metals, whilst the kettle B is directed towards the production of a residual. bullion of as low a content of alloying metals as is practicable.

ln another \application of this invention operating in two kettles working in series, the virgin zinc requisite for the formation of the alloys with the alloying metals contained in the crude bullion may be added to kettle A as well as the crusts obtained from maintain a higher temperature in the top of kettle A than in the previous example in view of the higher concentration of zinc and alloying metals, but such temperature must be below the melting point of the alloys comprising the crusts desired to be removed.

The temperature may be maintained at the bottom of kettle A somewhat above the euteclarger quantity of low tic temperature of the bullion flbwing therefrom Vand may beapproximately the same as the top of kettle B, but the temperature at athe bottom of kettle B is just above the eutectic temperature of the residual bullion.

In practice, however, it is desirable. that the kettle B should be maintained at a ensuring a more consistent content ofr alloying metal in the residual bullion discharged from the bottom -of the` said kettle B. It will be obvious that in operating with two kettles inseries with the temperatures Vof the bottom of kettle Asubstantially the same as the top of kettle B the two kettles are performin the same functions as will kettle of dimensions equalpto the combined depth of the two, the crusts formed in the lower part and cooler zone of the combined kettle being redissolved in the bullion in its upper part and hotter zone, and these crusts will correspond in some degree with those crusts which would have.

been skimmed off from kettle B and regularl fed into'the top of kettle A.

onsequently the invention .may be conducted for the refining of bullion in one kettle, the dimensions of such kettle being such as tonensure 'that the decreasing temperatures may be maintained from that at the top, which is below the melting point of crusts desired to beremoved, and sufficiently high` to ensure the-solution or absorption of the zinc added and the low grade crusts rising to the surface from the cooler zones, to that at the bottom which is just above the eutectic temperature of the residual bullion Y delivered therefrom.

Instead of subjecting the top ofthe kettles or other apparatus in which the operation is conducted to external heat for the purpose of obtaining the necessary temperature, I may preheat the bullion `flowing into the kettle to such a degree as is necessary. vOr alternatively I may preheat the bullion only to a limited extent with a view to reducing the' external heating of thel top ofthe kettle.

.In conducting-the operation, therefore, it is preferable to preheat the bullion flowing into the kettle A in a small reverberatory furnace C and I have found in practice that external heating of the kettles may be entirevly dispensed with. By interposinga small reverberatory furnace immediately before the inflow into `the kettles and causing the bullion to iow therethrough and be preheated'therein to the necessary temperature to ensure that the bullion has the required degree in the top ofthe kettles the operatin may beseonducted without any heating of the kettles'. -The maintenance of the decreasing- .of two kettles.

temperatures in the kettles to the temperature at the bottom ust above the eutectic temperature of the residual bullion may bc obtained by regulating the rate of fiow of the bullion through the kettle or by subjecting the lower portions of the kettles to cooling means.

The invention therefore lends itself to an exceedingly simple arrangement of plant comprising a series of kettles Gr and H andv small reverberatory furnaces C and D, the bullion being caused toflow continuously through from one reverberatory furnace C to a kettle and thence into another reverberatory furnace D from which it -passes to the next kettle B in series, the regulation of the temperatures in the kettles being wholly or in part controlled by the temperatures in the said reverberatory furnaces C and D.

The followingr example will illustrate one application of this invention in which preferential removal of crusts relatively rich in gold is first obtained followed by the removal of crusts relatively rich in silver.

Exemplar-A crude bullion assaying approximately 60-ozs. silver, 100 grains gold per ton, and 0.1% copper was continuously preheated in a reverberatory furnace and fed into a kettle at the rate of 20 tons per hour, together with an amount of zinc in regular additions equivalent to 1 0-lbs. per ton of bullion treated. The preheating of the bullion was such as to ensure a temperature at the top of the kettle of 500 C. and the temperature at the bottom of the kettle at 330 C. The residual bullion was continuously withdrawn from the bottom of the kettle by an overflow spoilt delivering just below the surface of the metal in the kettle and the crusts accumulating on the surface of the kettle were skimmed off intermittently.

The residual bullion was found to assay 0.8 grains per ton gold and 55-ozs. per ton silver, whilst the crusts removed assayed 8-oZs. per ton gold and 200-ozs. perton silver.

The residual bullion flowing from. the above degolding treatment was then passed through another reverberatory furnace C for preheating and fed into kettle G of a series The preheating in the reverberatory furnace C was such as to'ensure a temperature of ,450 C. at the top of kettle G and a temperature of 330 C. to- 340 C. at the bottom thereof. The bullion delivered y from thebottoni of kettle G was then passed through a furtherreverberatory furnace D and again preheated and fed to the top of kettle H. The temperature maintained in this last reverberatory furnace was such as to ensure that the temperature at the top of kettle H was 450 C. and an amount of zinc equivalent to 16-lbs. per ton of bullion treated lating in the to of kettle H were skimmed from time to time and added regularly to the top of kettle G. The crusts accumulating in the top of kettle G were removed oil' from time to time and were found to assay 2000 ozs. silver per ton, whilst the residual bullion discharging from the bottom of kettle H assayed 0.15 ozs. silver per ton.

By the application of this invention the refining of bullion may be effected with a considerable saving in labor as compared with the operation of the Parkes7 process as hitherto practised. The continuous fiow of the bullion through the kettles or other vessels employed dispenses with the labor incidental to the cooling of the kettles as at present practised, and the transfer of bullion from one kettle to another. The arduous and laborious operation of scraping the kettles as required in the present operation of the Parkes process is obviated. If the invention is operated in one kettle of suitable dimensions as described, the skimming of crusts from kettle B is entirely dispensed with, reducing the labor involved in the skimming by over as compared with the Parkes process as at present practiced with two zincings. In addition more consistent results can be obtained due to the fact that there is less dependence upon manual labor. Again, by dispensing with the intermittent heating and cooling of the kettles and maintaining even temperatures upon the kettles during 4the. iow of bullion therethrough. maintenance costs can be reduced due to less wear and tear and breakage of kettles, whilst a considerable saving in fuel can be eeli'cted. In addition a reduced plant is necessary for handling a given quantity of bullion, thereby effecting a considerable saving in capital cost.

I claim:

1.k In th-e continuous refining of lead bullion, incorporating` with the bullion an amount of zinc sufficient for the formation of alloys of one or more of the alloying metals desired to be removed and a residual bullion relatively low in the said alloying metal or metals and subjecting the said bullion during lits continuous flow to a decreasing range of temperatures the upper 'of which is sufliciently higlrfor the solution or incorporation of the said zinc in the bullion and below the melting point of the alloy comprising the crusts to be removed, whilst the lower of such range is just above the eutectic temperature of the residual bullion desired to be produced, continuously withdrawing the residual bullion and continuously or intermittently removing the crusts accumulating.

2. In the continuous refining of lead bullion in one or more stages, incorporating with the bullion in each stage of an amount of zinc in the form of virgin zinc and/or I of which is suiciently high for the solution or incor oration of the said zinc in the bulf'lion but4 elow the meltinpoint of the alloy comprising the crust to e removed whilst the lower of such range in the-last stage is just above the eutectic temperature of the residual bullion desired to be produced, continuously withdrawing the residual. bullion from the last stage and continuously or intermittently removing the crusts accumulating in each stage.

3. In thel continuous refining of lead bullion in one or more stages, incorporating with the bullion in each stage of an amount of zmo in the forml of virgin zinc and/or crusts suicient for the formation ot alloys of one or more of the alloying metals desired tobe removed, and a residual bullion relatively low in the said alloying metal or metals, and subjecting the bullion in each y stage during its continuous iiow therethrough to a descreasing range of temperatures, the upper of which is suiiciently high for the solution or incorporation of the said-zinc in the bullion but below the melting point ofthe alloyy comprising the crust to be removed whilst theJ lower of such ian'ge in the lastE sta-ge is just above the eutectic ,temperaturef of the residual bullion desired to be, pro' duced, continuously withdrawing'the residual bullion `from the last stage and continuously or intermittently removing the crusts accumulating'in each stage, and returning the `crusts accumulating in the second or sucmetals, and' subjecting the bullionin eac stage during ceeding stages topa preceding sta e.

4. In the continuous refining 0% lead bullion in one or more stages, incorporating with the bullion in each stage of an amount of zinc in the form of virgin zinc and/or crusts sufficient for the formation of alloys of one or more of the alloying metals desired to be removed, and a residual bullion relatively low inthe said alloying metall or its continuous low therethrough to a decreasing range of temperatures the upper of which is suiliciently high for the solution or incorporation of the said zinc in the ,bullion but below the melting oint of the alloy.comprising the crust to be removed whilst the lower of 'such'Y range in the last stage is just abovethe eutectic temperature of the residual bullion desired to be producedp'continuously withdrawingi P the residual bullion fromv the'last stage continuously or intermittently removingl the crusts accumulating in each stage, pre eating'fthe bullion previous to any one stage `to all `form of virgin zinc and/or crusts for kettle or last kettle to be removed, and a residual bullion relatively low in such alloying metal or metals.

and subjecting the bullion in each stage to a decreasing range of temperatures, the upper of which is suiiciently high for-the solution and incorporation of the -said zinc whilst the lower of such rangein the last sta residual bullion relatively low in the said alloying metal or metals to be removed, continuously or intermittently removing -the crusts accumulating in each stage and returning the crusts accumulating in the second and succeeding stages to a preceding stage, continuously withdrawing the said residual bullion, incorporating with the said residual bullion in one or more stages of a amount of zinc in the form of virgin zinc the remaining alloyingmetal or metals,

loying metal or metals, and subjecting the bullion in each stage'to a decreasing range of temperatures, the u per of which is sufis just above the eutectic temperature o they ficiently high for the solution and incorporation of the said zinc whilst the lower of such range in the last stage is just above the eutectio temperature of the residual bullion desired to be roduced, withdrawing the said residual bulllon continuously, and continu,- ously or intermittently removing the crusts, accumulating in each stage and returning the crusts accumulating in succeeding stages to a preceding stage.

6. In the refining of lead bullion,`feeding the .bullion continuously through a kettle or series of kettles, incorporating with the the second and bullion the necesi-:aryI amount of zinc in the the formation of alloys of one or more ofPthe alloying metals desired to be removed an a residual bullion relatively low in the said4 alloying metal or metals, maintaining the bullion in the. top of the said kettles or irst kettle inthe series at a temperature suiiiciently hi h for the solution or incorporation of the said zinc in thel bullion'but below the melting point ofthe alloy comprising the crusts to be produced, maintaining the temperature o the bullioifat the bottom of the in the series at a temerature just above the eutectictemperature vof the residual bullion desiredvto be produced, continuously removingthe residual bullion from thev b last kettle in the series an\d continuously o1( ttom of the kettle er 'e /l intermittently removing the crust accumulating.

7. In 'the refining of lead bullion, feeding the bullion continuously through a kettle together with the necessary amount of zinc for the formation of alloys of one or more of the alloying metals desired to be removed and a residual bullion relatively l'ow in the said alloying metal or metals, maintaining the bullion in the top of the said kettle at a temperature sufficiently high for the solution' or incorporation of the said Zinc in the bullion but below the melting point of the alloy comprising the crusts desired to be removed, maintaining the temperature of the bullion at the bottom of the kettle just above the eutectic temperature of the residual bullion desired to be produced, withdrawing the residual bullion continuously from the bottom o f the said kettle and continuously or intermittently removing the crusts accumulating on the top of the said kettle.

8. In the refining of lead bullion, feeding the bullion continuously through a series of two or more kettles together with the necessary amount of zinc in the form of virgin Zinc and/or crusts for the formation of alloys of one or more of the alloying metals desired to be removed and a residual bullion relatively low in the said alloying metal or metals, maintaining the bullion at the top of the first kettle in the series at a temperature sufficiently high for the solution or incorporation of the zine in the bullion but below the melting point of the alloy comprising the crusts to be removed from the said kettle, maintaining the temperature of the bullion at the bottom of the last kettle in the series just above the eutectic temperature of the residual bullion to be produced, feeding the crusts accumulating on the surface of the second and succeeding kettles into the top of a preceding kettle, withdrawing the residual bullion continuously from the bottom of the last kettle in the series and continuously or intermittently removing the crusts accumulating on the top of the first kettle.

9. In thev refining of lead bullion, feeding the bullion continuously through a kettle or series of kettles, incorporating with the bullion the necessary amount of zinc in the form of virgin zinc and/or crusts for tip.: formation of alloys of one or more of the alloying metals desired to be' removed and a residual bullion relatively low in the `said alloying metal or metals, preheati'ng the said bullion in a reverberatory or other suitable furnace to such a temperature as is necessary for maintaining the bullion in the top of the kettle or the first kettle in the series at a temperature sufficiently high for the solution at the bottom of the kettle or the last kettle in the series at a temperature just above the eutectic temperature of the residual bullion desired to be produced, withdrawing the residual bullion continuously from the bottom of the said kettle or the last kettle in the series and continuously or intermittently removing the crust-s accumulating on the top of the said kettle.

l0. In the refining of lead bullion, feeding the bullion continuously through a series of two or more-kettles, incorporating with the bullion the necessary amount of Zinc in the form of virgin zinc and/or crusts for the formation of alloys of one or more of the alloying metals desired to be removed and a residual bullion relatively low in the said alloying metal or metals, preheating the said bullion in a reverberatory or other furnace prior to the said bullion being delivered into the top of each of the said kettles in the series whereby the temperature of the bullion is raised therein duringits passage to such a degree as is necessary for maintaining the bullion in the top of each of the said kettles at a temperature sufficiently high for the solution or incorporation of the zinc either as virgin zinc or in the form of low grade crusts in the bullion, but below the melting point of the alloy comprising the crusts desired to be removed, maintaining the temperature of the'bullion at the bottom of the last kettle in the series just above the eutectic temperature of the residual bullion desired to be produced. feeding the crusts accumulating on the surface of the second or sueceeding kettles into the top of a preceding kettle, withdrawing the residual bullion continuously from the bottom ofthe last kettle in the series and continuously or intermittently removing the crusts aecumulating'on the top of the said kettle.

ll. In the refining of lead bullion, feeding the bullion continuously through two or more series of kettles, incorporatingwith the bullion during its passage through the first series the necessary amount of zine in the form of virgin zinc and/or crusts for the preferential formation of alloys of one or more of the alloyi'ag metals and a residual bullion relatively low in such alloying metal or metals maintaining the bullion at the top of the first kettle of the first series at a temperature sufficiently high for the solution or incorporation of the said Zinc in the bullion, but below the melting point of t-he alloy comprising the crusts to be removed, maintaining the temperature of the bullion at the bottom of the said last kettle of the first series just below the eutectic temperature of the residual bullion relatively low in the said alloying metal or metals to be preferentially removed, continuously discharging the residual bullion into the succeeding series incorporating with the bullion during its passage through the said succeeding series the necessary amount of zinc in the form of vi'rgin zinc and/or crusts for theV formation of alloys of the remaining alloying metal or metals desired to be removed and obtaining a residual bullion desired to be produced and relatively low in such alloying metals, withdrawing the said residual bullion continuously from the bottom of the last kettle and continuously or intermittently removing the crusts accumulat ing in the said succeeding series of kettles' relatively high in the said remaining alloying metal or metals. l2. In the rening of lead bullion, feeding the bullion into a reverberatory or other suitable furnace for preheating it to the required temperature and discharging the said preheated bullionv into the top of the first of two series of kettles, togetherA with the necessary amount of zinc for the formationof alloys in the form of crusts relatively rich in one or more of the alloying metals (such as gold) and obtaining a residual bullion relatively rlow in the said alloying metal or metals continuously passing the said bullion through the first series of kettles and discharging the same continuously from the bottom of the last kettle .in the rst series at a temperature just above the eutectic temperature of the residual bullion relatively low in the said second series, withdrawing the residual bullion continuously from the bottom of the second kettle in the second series relatively low in the said alloying metal or metals and continuously or intermittently removing the crusts accumulating in the top of the first kettle of the second series relatively high ir the said alloying metal -or metals.

In witness whereof -I hereunto af'x my signature.

GEORGE KENNETH WILLIAMS.

alloying metal or metals, continuously or intermittently removing the crusts relatively rich in such alloying metal or metals from the top of the first kettle, in the first series, feeding the bullion to a' reverberatory or other suitable furnace in which it is preheated-to the desired temperature and then feeding the same continuously through the second series of kettles, feeding anamount of Zinc into the' first kettle of the second series sufficient for the formation of alloys in the form of crusts l relatively high in the remaining alloying same Into the second kettle of the second se# ries, feeding the crusts accumulating on the surface of --the second kettle of the second series into the top ofthe first kettle of the

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