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Les cartes, planches, tableaux, etc., peuvent etre film6s d des taux de r6duction diff6rents. Lorsque le document est trop grand pour 6tre reproduit en un seul clich6, il est film6 d partir de Tangle sup6rieur gauche, de gauche d droite, et de haut en bas, en prenant le nombre d'images n6cessaire. Les diagrammas suivants illustrent la mdthode. errata 1 to e pelure, :on ik T\ 1 32X ^ Jl/, f C^ i ' > I A NEW PROCESS FOR THE EXTRACTION OF COPPER FROM ITS ORES, WITH NOTKS ON THE TREATMENT OP GOLD AND SILVER ORES. BY DR. T. STERRY HUNT, F.R S., AND JAS. DOUGLAS, Jr., Esq. (second and enlarged edition.) MONTREAL. 1870. A NEW PUOCESS FOK THE EXTRACTION ov if COPPER FROM ITS ORES, WITU NOTES ON THE TREATMENT OF GOLD AND SILVER ORES. MY DR. T. STERRY HUNT, F.R.S., AND JAS. DOUGLAS, Jr., Esq, (SECOND AND BNLAKGBD EDITION.) This new process, for which Letters Patent liave been granted in the United States, Groat ISritain, Canada, Kowfouudlaiid and Chile, (besides an exclusive privilege for Bolivia) may be understood from the siH-cilication of the liritish j)at patent in Canada is Jan. 14, 186y, in the United States, Feb. 9., 180;>, and in the United Ivingdom, Aug. 13, 1809, SPECIFICATION. 1. For the extraction of copper from its ores by this process it should be in the state of an oxyd or some compound thereof, as oxychlorid or carbonate. These oxydized forms of copper are decomposed under proper conditions by protochlorid of iron, ■with the production of dichlorid of copper, which is soluble in certain saline solutions, and in some cases a portion of protochlorid of copper, together with insoluble peroxyd of iron, and more or less insoluble oxychlorid or basic persalt of iron, which may be rendered soluble by the action of sulphurous acid. 2. Tlie naturally or artificially oxydizcd ores are to bo digested ■with a watery solution of neutral protoclilorid of iron, with or without the addition of an earthy or alkaline ehlorid, as common salt. The neutral protochlorid of iron may be conveniently prepared b}'- double decomposition ot protosulpliate of iron with an ccpiivalcnt of ehlorid of calcium or ehlorid of sodium. In preparing the solution, here- inafter designated as the bath, we may proceed as follows : 8. One hundred and t onty (120) pounds of salt, or one hundred and twelve (112) pounds of dry ehlorid of calcium, or its equivalent of hydrated ehlorid, are to be dissolved with two hundred and eighty (280) pounds of protosulphate of iron, (green copperas,) in one hundred (100) imperial gallons of water. In place of the above salts we may substitute an amount of protochlorid of iron prc})arcd by any other method, containing fifty-six (50) pounds of metallic iron. To the bath prepared in eitlicr way, two hundred (200) pounds of sea salt are then added, wlicn the solution is ready for use, and will bo found capable of chloridizing and dissolving about ninety (00) pounds of copper. The power of brine to dissolve the dichlorid of copper formed increases greatly with the strength and tcioperature. The proportions above given are convenient, but in the case of poor ores, a solution of one-half the strength may be used with advantage. 4. In the treatment of copper ores by this process, they may be divided into two classes, non-sulphuretted and sulphuretted ores. 5. The first class or non-sulphuretted oxydiscd ores, includes the native oxyds of cop[)cr, the carbonates, and the oxychlorid. To prcjiare these for treatment they should be finely pulverized, and the carbonates may with advantage be gently calcined before or after grinding, in order to expel carbonic acid. The red oxyd, if alone or greatly predominating, should also be gently calcined after grinding to convert it into protoxyd ; but if it be mixed with a considerable proportion of protoxydized ore this is not necessary. 6. The pulverized oxydized ores thus prepared are to be digested in the above bath, with frequent agitation. Heat is not necessary, but it accelerates the solution of the oxyd of copper, which in practice should not be more than sufficient to yield sixty or seventy pounds of copper to the above bath of one hundred gallons. When 8 the solution is complete and the liquid drawn ilT, the insoluble residue should be lixiviated with a small volume of hot strong brine. The liquid is then digested with metallic iron, by whicli the copper is thrown down as cement copper, two parts of iron yielding three parts of ractallic copper. 7. The bath thus freed from copper contains a large amount of regenerated protochlorid of iron, and can be used at once to treat a fresh portion of oxydized ore. A small loss of cldorinc, Avhich separates as oxyclilorid of iron, has, however, to be supplied by adding to the bath, from time to time, protochlorid of iron or the salts required to produce it. This need not, however, exceed for each repetition, one-eighth of the original quantity, and by careful exclusion of the air the quantity to be added each time may be reduced to much less. The strength of the bath in protochlorid of iron should be determined from time to time by appropriate tests. 8. In localities Avhere it may be desirable to economize the proto- chlorid of iron a modification of the pro jess maybe adopted, which consists in treating with sulphurous acid the iron-compoinids preci- pitated by the oxyd of coi)per. To this end sulphurous acid from the roasting of sulphuretted ores, or from any other source, may be made to pass over or through the bath after or during the process of dissolving the oxyd of copper. In this case the protosalts of iron are constantly regenerated, and serve to chloridize fresh portions of oxyd of copper. A small amount of protochlorid of iron, with the aid of sulphurous acid, may, in this modification, be used to convert a large (quantity of copper into dichlorid, the excess of which is pre- cipitated, and may be washed out with hot strong brine. As this deposits a large quantity in cooling, the same brine may be employed indefinitely for dissolving dichlorid by heating and cooling it each time. 9. The solid dichlorid is rapidly reduced by contact with metallic iron, especially when wot with brine, and yields metallic copper and protochlorid of iron, one part of iron giving two of copper. To prevent any precipitation of oxychlorid of copper irom the dichlorid solution by the air, it is Avell in all cases to have a small portion of protosalt of iron present. A little free sulphurous acid will also prevent such precipitation ; but any excess of this gas should be expelled or allowed to escape from the solution before adding metallic iron. 10. In the case of sulphuretted ores, the first stop in the appli- cation of our process has for its object to convert the metal into an oxyd soluble in the bath already described. This conversion is effected by calcination hi the air, by which means all copper, iron and sulphur arc oxydized. [Pyritous ores, holding much iron and 8ul})]uir, may be roasted in kilns, then ground and rccalcined, but native sul[)hurets rich in copper, or regulus, should be ground before calcination, which is best done in a muffle lurnace. In either case] a low red heat suffices, and what is called a dead roast is to be avoided, not only because it involves a waste of time and fuel, but because the high temperature renders a portion of the oxyd of copper insoluble in the protochlorid of iron bath. The roasting need be continued only until the complete oxydation of the sulphuret of copper, and its conversion into a mixture of oxyd with a variable proportion of sulphate of copper. This product may be treated directly with the bath, without addition, as directed for non-sulphu- retted ores, but the excess of sulphates thus introduced renders the bath impure, and much more metallic iron is required for the subsequent precipitation than when the whole of the copper is in the form of oxyd. 11. We therefore prefer to proceed as follows : We determine in the roasted ore the amount of copper present as sulphate, which will vary very little for any given ore roasted under constant conditions, and we add thereto an equivalent of lime, which gives rise to insoluble sul[)hate of lime and oxyd of copper. In practice it is well to leave undecomposed a small amount of sulphate of copper, which, in a subsequent stage of the process, will give with metallic iron the sulphate of iron required to replace the small loss already mentioned as occuri-ing when sulphurous acid is not used. To an ore, for instance, with eight per cent, of copper, which after roasting contains three per cent, of copper as oxyd, and five per cent, as sulphate, we may add lime enough to decompose four-fifths of the latter, at the rate of 28*0 parts of pure lime for 31*7 parts of copper, or about an e(|ual weight of ordinary non-magncsian lime ; being four pounds of finely ground lime for each one hundred pounds 6 of the above roasted ore. An equivalent quantity of carbonate of lime, or other alkaline or earthy base, maybe used instead of (juick- lime, but with less advantage. The roasted ore and lime may be added to the bath together, or better, the ore is to be added first. The subsequent part of the process is to be conducted as already described for the ores of the first class. 12. When protosulphate of iron is used instead of the proto- chlorid in preparing the bath, or in keeping up its strength, as in the case of ores of the first class, sulphate of soda is formed, which may in great part be crystallized out by extremes of heat and cold- The formation and accumulation of this sulphate may, however, be prevented by the use of chlorid of calcium, as already set forth. The still larger production of sulphate of soda, which would take place if calcined ores of the second class were added directly to the bath, js prevented by the use of lime as already described, and that portion which must result from the excess of sulphate of copper, as recommended, may be decomposed by the addition of small portions of chlorid of calcium from time to time. By attending to these precautions the strength of the bath in chlorid of sodium, and its sol- vent power may be indefinitely maintained. 13. We do not claim the use of any particular form of furnace, nor of any special arrangement for calcining, lixiviating or precipi- tating, reserving to ourselves the choice of the best forms of appa- ratus for these purposes ; neither do we claim the use of protosalts of iron otherwise than in solution, nor the use of perchlond or other persalts of iron, nor yet the use of sulphurous acid save and except in connection with protosalts of iron, as already set forth. 14. What we claim as our invention is : I. The use and application of a solution of neutral protochlorid of iron, or of mixtures containing it, for the purpose of converting the oxyd or suboxyd of copper, or their compounds, into chlorids of copper. II. The use of sulphurous acid for the purpose of decomposing the oxychlorid of iron formed in the preceding re-action. III. The use of a process for the purpose of extracting copper from its naturally or artificially oxydized compounds by the aid of the first, or the first and second of the above reactions, substantially in the manner already set forth. 6 EXPLANATIONS. CIdoridizing the Copper. — The reaction between protoxyd of copper and protoclilorid of iron gives rise to peroxyd of iron, and a mixture of the two clilorids of copper, two thirds being dichlorid, and one tliird protoclilorid of copper, as shewn in the c(pxation A. The red oxyd or dinoxyd of copper in like manner gives rise to peroxyd of iron, hut yields a mixture of two thirds dichlorid and one third of metallic copper, as shown in the ecpiation B. A. — 3Cu.O- + 4FcCl = L .^0, + 2Cu,Cl + 2CuCl. 3CU3O3 li. — 3Cu,0 + 2FcCl = FelOl + 2Cu^Cl + 2Cu. ^3' '3" Inasmuch as the metallic copper (2Cu) set free in B. is readily converted into dichlorid by the protochlorid, (2CuCl) of A., it fol- lows that if not more than one half of the copper be dinoxyd, the remainder being protoxyd, the whole tvill be chloridized by the action of the protochlorid of iron bath. Svhihillfy of tJie Diclilorid of Cojiper. — While the protochlorid of copper is very soluble, the dichlorid is insoluble in water, but readily solu])lc in a strong solution of sea-salt, and of most other chlorids. A saturated brine at a temperature of 104° Fahrenheit, (90° Centigrade,) will hold in solution more than IG per cent, of dichlorid of copper, and at 104° F. (40° C.,) more than 8 per cent. A brine containing fifteen parts of salt to one hundred of water, dis- solves at 194° F. (90^ C.) 10-0 per cent., atl04°F. (40^ C.) G-0 per cent., and at 57" F. (14° C.) 8-5 per cent, of dichlorid of cop- per. When these strong solutions are diluted Avith Avater they deposit much of the dichlorid as a white crystalline powder. A solution made Avith five parts of salt to one hundred of Avatcr, dissolves at 194^ F. ;90^ C.) only 2-6 per cent., and at 104° F. (40° 0.) only 1"1 per cent, of dichlorid of copper. The above figures arc approximate, and a little below the results of actual experiment. 100 parts of dichlorid contain G4 parts of metallic copper. Composition of the Bath. — The equivalent Avcight of protosul- phate of iron or copperas is 139, and that of common salt 58*5, while that of copper is 31-7 and that of iron 280. In prescribing proportions for the bath, numbers a little exceeding these are given, to allow for impurities in the salts employed. To chloridize three equivalents, say O.rl pounds of copper, which are in the state of protoxyd, two e([uivalcnt3 of [)rotochlorid of iron are produced from 280 pounds of copperas and 120 pounds of salt, dissolved in 100 imperial gallons or 1000 pounds of water. This solution should convert one third of the copper into protochlorid and two thirds into dichlorid, equal to 98-() pounds of dichlorld of copper. To render this soluhle wo have prescribed the addition of 200 pounds or 20 per cent, additional of salt to the bath, while, as we have seen, a solution holding but 15 per cent, will dissolve at 11)1° F., considerably more than this quantity. While these are the theoretical (juantities, there is in practice, from a secondary re-action resulting in the formation of an insoluble basic per-salt, a loss of protochlorid of iron amount- ing to from five to ten per cent., so that the chloridizing power of the bath is somewhat less than above represented. • Moreover, if a considerable portion of dinoxyd of copper be present in the ore the amount of dichlorid will be larger than above calculated. For both of these reasons it is not well to add to the above bath more than GO or 70 pounds of copper for each 100 gallons. The solution of the copper from a properly prepared ore will be found complete by several hours digestion or percolation, even in the cold, but is more rapid in proportion as the heat approaches the boiling point. Preparation of tJie Ores. — In the calcination of carbonates, as recommended, the object is lo expel the carbonic acid, which would otherwise cause much effervescence in the bath. When the red or dinoxyd predominates in the ore, this should bo, in part at least, con- verted into protoxyd by calcination in the air, since when alone it leaves one third of its copper undissolved in the bath. In oxydiz- ing sulphuretted ores by roasting till all the sulphur is oxydized there is obtained a mixture of sulphate of copper with protoxyd and a portion of dinoxyd, which latter, according to Plattner, may amount to 20 or 30 per cent, of the copper. Farther roasting at a high heat will convert both this and the sulphate into protoxyd, but this con- dition is less advantageous, inasmuch as both time and fuel are consumed and the copper is rendered less soluble. The large pro- portion of dinoxyd, moreover, suffices, as already explained, to con- 8 vert much of the protochlorici of copper into diohlorid, thereby effecting a saving of iron in precipitating. Consumption of 3IetalUo Iron. — With few exceptions the copper extracted by sohition from its ores is thrown down in the metallic state as cement copper, by moans of metallic iron. In theory there are required less than 89 (88-3) parts of pure iron to precipitate 100 parts of copper from a solution of protosulphate or protochlorid, but in practice two or three times as much are consumed. This great consumption of metallic iron is duo to two principal causes : 1st. In the ordinary processes for extracting copper from its ores by the moijt way, acids (and somotimos persalts of iron) are employed to render the copper soluble, either as the principal agents or as auxiliaries. When these are employed the solutions contain more or loss of persalts of iron, which consume the metallic iron that would otherwise throw down the copper. Thus an amount of persul})hate holding four e(;[uivalents of iron consumes five equivalents of metallic iron, which are there1>y converted into pro- tosulphate, four equivalents of iron at the same time being de- posited in the form of an insoluble basic persalphate, which contami- nates the cement copper. 2nd. The second cause of the waste of iron is the action of the air. In order to separate the whole of the copper from the solutions a digestion of several days with metallio iron is resorted to. The protosaltof iron, which is formed in this re action, greedily absorbs oxygen from the air and is thereby converted into a mixture of an insoluble and a soluble pcrsalt. The latter, as above shown, dis- solves a quantity of iron in its turn, and yields another portion of insoluble pei-salt, which falls with the cement copper. The result of the above causes combined is that instead of 89 parts of iron there are consumed, according to circumstances, from 200 to 800 parts of metallic iron to produce 100 parts of metallic copper in the form of cement copper. This too is rendered impure by an admix- ture of insoluble persalts of iron generally amounting to from 20 to 40 per cent., and even more. The present process avoids both of these fiults, and enables us to obtain a pure cement copper with a very small consumption of iron. The solution obtained with the bath V 9 ^7 3r ie a is ;3 Q d 3 C fc S of protochlorid of iron can contain no persalt of iron in solution, and if protoxjd of copper alone has been employed will hold three equi- valents of copper combined with two e(|uivalents of chlorine, so that they will be p"scipitated by two equivalents of iron, being at tho rate of 59 parts of metallic iron for 100 parts of metallic copper. If, from the presence of much dinoxyd, or from other reasons, tho greater part of the copper be present as dichlorid, it will be remem- bered that this requires only one equivalent of iron to precipitate two equivalents of copper, being at the rate of -15 parts of iron for 100 parts of metallic copper. The precipitation of copper from the solutions is at first rapid, especially if these are hot, and kept in agitation. Inasmuch as the waste li(piors are not rejected in this, as in the ordinary process, the long digestion with iron required to remove the last portion of copper is dispensed with, and tho rKjuid, after having given up the greater part of its metal, is withdrawn and used for the treatment of a fresh portion of ore. The prolonged action of the air on the bath is thus avoided, and wc obtain a cement copper almost entirely free from insoluble iron salts, and with the consumption of a minimum quantity of iron. T/iJ Regenerated Bath. — If tlio action of the air be excluded it will, be found that the bath, after complete precipitation of the cop- per by iron, will be nearly as rich in protochlorid of iron as before the solution of the copper. The loss, which is due to the separation of a portion of oxychlorid of iron during the solution, is variable, and in some cases docs not exceed six per cent. Tiie various ways of supplying this loss are three : (1) Tho direct addition to tho bath of a portion of protosulphate or protochlorid of iron. (2) The addi- tion of a portion of suli)hate of copper from the roasted ore, and (B) the use of sulphurous acid. Of those the first reiiuires no explana- tion, and the second and third will be explained under the two fol- lowing headings. The proportion of iron in tho bath should bo determined from time to time by the following method : A small por- tion of the bath, freed from copper by digestion for some hours with metallic iron in a stoppered bottle, is diluted with 50 parts of water, and strongly acidulated with sulphuric acid. A standard solution of permangauato of potash of known strength is then added from a 10 graduated tube so long as it is decolorized. By comparative experi- ments of this kind on the regenerated bath its strength in proto- chlorid of iron is readily determined. The Protosalts of Iron. — In preparing the bath we have recom- mended either protosulphate or protochlorid of iron. The former salt, being an article of commerce, is to be obtained in many places where the latter cannot readily be procured, and may be easily manufactured for the purpose in regions? where neither of these can be readily obtained, provided sulphuretted copper ores are to be had. It is well known that in roasting these a considerable portion of the copper is converted into sulpliate, which may be readily dissolved by water from the roasted ore. If to each 63-4 pounds of copper thus dissolved, we add 120 pounds of common salt, and digest the liquid with metallic iron in a close vessel, best with the aid of heat, till the copper is precipitated, the solution will contain such an amount of protochlorid of iron that it will only be necessary to add 200 pounds of common salt and a sufficient amount of water, to make 100 gallons of the bath of the stren- th before prescribed. If a roasted ore, charged with sulphate, be added directly to the bath of protochlorid of iron, it will be found, after precipitating the copper by metallic iron, that the regenerated bath will contain not only the protosalt of iron corresponding to that originally present in the bath, but also that resulting from the action of the mctalHc iron on the sulphate of copper introduced, wliich has given r'.se to proto- chlorid of iron and sulphate of soda by double decomposition ; thus rendering tlie bath impure l)oth fiom the presence of sulphates and from an excess of protochlorid of iron. To obviate these results we add to such roasted ores, (as already descril)ed in § 11), so much lime as may be necessary to convert the whole or the greater i)art of the sul- phate of copper present into insoluble suljiliate of lime and protoxyd of copper, which latter is at once solu1)le in the protochlorid bath. A small portion of sulphate of copper, as above prescribed, may bo left undccom posed l»y lime, and by its re-action with metallic iron will give the protosuli)hatc of iron re(|uired to supply the small loss already explained, and keep up the regenerated bath to its original standard, as shown by the test with permanganate. 11 The use of protosulphate of iron for making the bath, introduces a large proportion of sulphate of soda. A great part of this, it is true, crystaUizes out when the bath is exposed to cold, and may thus be got rid of. The use of a portion of chlorld of calcium may also, as already explained, be resorted to with advantage where this substance can be cheaply procured. In districts where hydrochloric acid is a bye-product of little value it will be best to obtain the protochlorid of iron directly by saturating the crude acid with scrap iron and employing the product as already ex[)lained in § 3. Use of Sulphurous Acid.— Whon the mixture resulting from the action of oxyd of copper upon the bath of protochlorid of iron is heated, and exposed to the action of an excess of sulphurous acid, the whole of the separated peroxyd of iron is converted into a pro- tosalt, and the bath, after preci[)itation by metallic iron, is found to contain much more protosalt than at first. Such a result is gene- rally to bo avoided, but by passing into or over the bath a small portion of sulphurous acid, it is easy to dissolve such a portion of the prcci[)itated oxychlorid or oxyd of iron as to prevent the loss of iron which otherwise occurs, and keep up the standard of the regenerated bath without the addition of a salt of iron or of sulphate of cojiper. The introduction of air with the sulphurous acid is to be prevent- ed as much as possible, since it tends to convert the dichlorid of copper into protochlorid, and thus increase the consumption of metallic iron. Peroxyd of Iron. — The prcci[titatcd hydrated peroxyd of iron, holding more or less oxychlorid and basic pcrsidphatc,* is in part retained by the gangue, but the greater portion of it accumulates in the settling-tank. When susi)ended in water and heated with an excess of sulphurous acid gas, it is converted into a mixture of in- soluble protosulphite and soluble protosulphate of iron, which latter • Wlieu, as in ordinary cases, the batli hoMs suliiliates, the precipitateJ peroxyd contains a hasic persulphate, with but little of the oxychlorid which is found in a ba th where chlorids only are present. ,12 may be used for the copper bath*. The oxyd may also be dried and used as a pigment, or reduced to metallic iron to be em])loyed for the precipitation of copper. To this end it may be mixed with one fourth its weight of carbonaceous matter and heated to redness in suitable vessels, by which means it will be converted into iron- sponge : or else compressed into cakes and smelted, with the addition of lime, in a small blast furnace, yielding thus cast iron. WORKING OF THE PROCESS. Preparation of the Ores. — The new method above describ- ed is now in use at the Harvey Tlill mine in Leeds, near Quebec. The ores there treated are a mixture of yellow and purple suljtliurets of copper, dressed for the purpose to 15 or 20 per cent., and ground so as to pass through a seive of forty meshes to the linear inch. The roasting is at present effected on a small scale in a muffle fur- nace thirty feet long, with a wood fire, tlie heat passing in flues beneath tlie floor of the muffle only. With this arrangement, however, only about two tons of ore can be roasted in twenty-four hours, and it is proposed to erect, at once, larger and more convenient furnaces. A proper arrangement for roasting, tliough an indispensable prelimin- ary to tlie treatment of suli)hurettcd ores, constitutes no distinctive part of the new process (pages 4-5), which has for its object the solution and precipitation of copper from naturally or artiflcially oxydized ores. Solution. — A Freiberg barrel was used in the earlier trials, but has since been advantageously replaced by two circular tubs, made of three-inch spruce plank, measuring seven feet in diameter by five feet in height, and furnished with closely fitting covers. The stirring apparatus consists of two obli(|ue blades fiistoned to a vertical shaft, their ends being withhi an inch of the sides, and about twelve inches from the bottom of the tub, which is somewhat convex, so as to diminish the space beneath the revolving blades near the centre, and thus prevent an accumulation of ore in that part. Such a tub •This use has been pointed oul in the specification of tlie United States pat**at, tPhere it is stated that instead of employing sulpliurons acid during the process of solntion, " the residue after the solution of the copper maj' be exposed to the action of the sulphurous acid gas," in order to obtaiu a soluble protosalt of iroa for the bath. 13 will hold about five tons of liquid, and may bo three-quarters filled. With twenty or twenty-five turns of the stirrer in a minute it is easy to keep one and a-half or even two tons of roasted ore suspended in three tons of liquid, and if allowed to subside the ore falls so as to leave the stirrer free. The bath used at present is even weaker than that indicated in the foregoing specification, marking about 19"^ Baume, (specific gravity 1*1-1T), and containing ten grains of iron to the fluid-ounce, or a little over two per cent. Such a bath will, by continued agitation, at a temperature of 120° to 180*^F. dissolve the-oxyd of copper from a properly roasted ore holding 15 percent, in six or eight hours. At the end of this time a sample of the washed gangue should not yield to strong boiling acetic acid more than two or three thousandths of copper. Should boiling nitric acid remove a farther portion, it shows a defective roasting of the ore. The stirrer boing stopped, the liquid is quickly drawn olf through an open- ing near the bottom by a two-inch india-rubber hose into a large covered settling-tank, where it deposits the finely divided portions of the gangue aad the suspended peroxyd of iron. The gangue is •washed by agitating for a few minutes with a portion of fresh bath or of brine, in order to remove the copper solution which it retains, and is then shovelled out through a trap eight inches square in the bottom of the tank. Precipitation. — After three or four hours repose in the settling tank the clear copper solution is drawn off to the precipitating-tanks, which arc built like the dissolving-tanks, but with flat bottoms. Here scrap iron, cither of wrought or cast metal, is placed on racks of basket-work near the top and bottom of the tank, which is filled with the hot li((uor and closely covered. After tweli'e hours, if the exposed surface of iron be suificicnt, tiic precipitation of the copper is very nearly complete, and the liquid may be drawn off, passing through a flannel filter to retain any suspended particles of metallic copper, and is ready to be transferred to the dissolving-tank for the treatment of a fresh charge of roasted ore. A little steam injected from time to time cither into the dissolving or precipitating-tank suffices to keep the bath at about 150"^ F., at which temperature the processes of solution and precipitation proceed with rapidity. As a charge of bath can be used once every twenty four hours, the loss of heat in covered vessels is slight. The vats for the three ope- 14 ' rations arc arranged at different levels, so that the liquors flow from the dissolving to the subsiding and thence to the precipitating-tanks. From tlie last tlie regenerated bath is discharged into a tight vessel from which, by the pressure of steam, it is raised to the level of the dissolving-tanks,, As both iron and copper are attacked by the copper solutions, the use of tliese metals must be avoided in those parts of the ajjparatus which are exposed to its action. The use of lime and of sulphurous acid in this process has been already explained on pages 4 and 11. The ores used at Harvey Hill are, however, so calcareous that lime is not needed to decom- pose the sulphate of copper formed in roasting. A small amount of sulphurous gas from the roasting of the ore is made to pass over the surface of the bath, through a tube enterinir one side of the closely covered dissolving-tank, while from the otiier side an escape- tube passes into a chimney, thus establishing a draught. In this way it has been easy at llarvcy Ilill to keep up, and even to aug- ment at will, the iron content of the bath. If this becomes exces- sive, its amount is readily reduced by adding a little lime, or in the case of the calcareous ores now used, by running one or more charges without the use of sulphurous acid. Baths which have been used twelve and fifteen times at Harvey Hill, at each time taking up and precipitathig two or three per cent, of copper, are unaltered in their composition and as good as at first. The consumption of metallic iron in precipitating, as determined by numerous trials on solutions prepared as above, and holding trora fifty to sixty pounds of copper to the ton, will not exceed fourteen hundred pounds of iron to the ton of pure copper thrown down. The costs of worknig copper ores by this process are comprehend- ed under four heads : 1. The roasting and grinding of the ores, and the furnaces and mills for the pur})ose. I'oor ores may be kiln-roasted beibre grind- ing, but rich ores and regulus should be pulverized before roastin<^ (See page 4). 2. The necessary vats and stirring-apparatus, and the handling of the materials in dissolving and preci[)itating. 3. The first cost of the baths and the small amount of salt rec^uir- ed to supply unavoidable waste, besides, in some cases only, a por- tion of lime. 15 4. The metallic Iron required for precipitating tlic copper, which is not more than from one-half to one-third the amount consumed in the ordinary processes for obtaining cement copper, (page 8). Solvent Power of Protochlorid of Copper. — Protochlorid of cop- per readily attacks metallic copper, forming with it dichlorid. Hence, as already ex])lained, the metallic copper which is separated when the protochlorid of iron bath acts on dinoxyd of copper, is at once dissolved if an eciuivalcntofi.rotoxydofcopperbe present to yield the reciuisite amount of protochlorid. The protochlorid of copper will also attack certain sulphuretted compounds of copper. Copper glance, purple copper ore, or artificial products, as regulus, approaching these in composition, are readily dissolved by a solution of protochlorid of copper mixed with common salt, dichlorid of cop- per being formed. Hence, a sulphuretted ore imperfectly roasted, and still containing a portion of sulphuret rich in copper, will give it up to the action of a bath containing protochlorid of copper. Some specimens of kiln-roasted Spanish pyrites, still holding kernels of regulus, have been found to yield the whole of their cop- per to the action of such a bath, but the kiln-roasting is seldom complete enough to give this result, and a grinding and recalcina- tion will in most cases be found necessary. The present process has, from the above reaction, an important advantage over those in which the copper is dissolved as a sul- phate. The protochlorid of copper in the bath exerts a powerful solvent action on any portions of sulphuret or of metallic copper (derived from suboxyd or otherwise) present in an imperfectly roasted ore. The sulphate of copper, on the contrary, possesses no such solvent power, so that a com})lete roasting of the ores becomes necessary. TREATMENT OP COPPER ORES HOLDING SIVER AND GOLD. The bath of protochlorid of iron and salt, after being more or less comi>lctely saturated with copper, chloridizes and dissolves silver or any of its compounds, in virtue of the well known action of proto- chlorid of copper. Repeated experiments with the silver and gold- bearing sulphuretted copper ores of Colorado and other regions, 16 have shown that when a properly roasted ore of this kind (or a regulus from such ore) is treated in tlie way just described for the removal of its copper, all of the silver is, at the same time, dissolved as a chlorid in the bath, and may be thrown down in the metallic state by digesting it with metallic copper, or causing it to filter through a bed of cement copper. After thus separating the silver the cop[)er is precipitated as usual by metallic iron. The residue from the bath, having lost its copper and silver, contains any gold which may liavc been present in the ore, in a favorable condition for removal by ehh)rination. Trials on a considerable scale have shown that when a regulus holding at the same time copper, silver and gold, is treated by the present process for the extraction of the copi)er, it is })ossible, with but little additional expense, to separate from it at the same time all the silver a)id the gold. The removal of the silver from the bath requires only the use of a portion of the cement copper from a previous operation ; ■while to obtain the gold from the residue the ordinary ajjparatus for chlorination may be employed.* In the case of copper ores containing nickel this metal gradually accumulates in the bath, and when in sufficient quantity may be extracted, after first peroxydizing and precipitating the iron, ■which would probably be best eft'octed by forcing a current of air through the liquid previously mingled with pulverized carbonate of lime. For further information address, T. Sterry Hunt, diontreal, Canada^ James Douglas, Jr., Quebec, Canada, or their Agents, James Lewis & Son, 1, Fcmcich Street, Liverpool, Eiujland. Montreal, Canada, April, 1870. • See the Engimerin% and Mining Journal of New York, for March 8 and 16, also ihQ American Gaslight Journal and Chemical Repertory^ for Miucli 0, 1870.