,^ktk?klk^i-H^:^n' ir fast rea Antimony. — It covers the charcoal with a white oxyd or bluish white if in a thin layer. The coating is not close to the assay and is easily driven away. If a great deal of silver be present, the coating appears pink. Zinc. — The coating of the oxyd of zinc is near to the test, appears yellow when hot, and turns white on cool- ing. Heated with the oxydation flame, the coating becomes luminous. Tin. — The coating is quite close to the test. It is yellow when hot and white when cold, resembling the coating of zinc. Becomes also luminous. In the reduc- 2 18 PROCESSES OF SILVER AND GOLD EXTRACTION. tion flame the coating of oxyd can be reduced to the metallic state. Selenium — Gives a steel gray coating of a feeble metal- lic lustre, showing somewhat violet color further oiOfj played upon with the flame, it emits a rotten radish-like odor. Tellurivm. — It fumes and coats the coal white with a red or dark yellow seam. Examining ore on charcoal, it cannot be expected to get always coatings which agree exactly with the de- scription, there being generally different metals present. If, for instance, the ore under examination contains lead, zinc, and antimony, the white coating with a blueish seam will appear first, and is recognized as antimony. But it soon becomes yellow from the oxyd of lead, which, mixed with the white antimony coating appears lighter. The zinc coating which is also yellow colored is not distinguishable at first from the lead coating, but this latter can be blown away with the oxydation flame, leaving the zinc oxyd, which appears luminous when played upon with the oxydation flame. EXAMINATION WITH BORAX AND SODA, On Charcoal. Sec. 7. The borax assumes a globular shape when melted on charcoal with the blowpipe. If pure, it ap- PKOCESSES OF SILVER AKD GOLD EXTRACTION. 19 pears colorless, and dissolves the oxyds of metals. If sulphurets are taken in examination, they must be pow- dered and a small portion of it treated with the reduction flame, on charcoal, in order to drive out the sulphur and arsenic. If the sulphurets melt, the powder may be mixed with charcoal dust and treated to a dark red heat. A very small part of this roasted ore, or not roasted if the test consists of oxyds, is put on the borax pearl, and melted with the oxydation flame. If the color of the glass is not perceptibly changed, another particle of the ore can be dissolved, but it is never advisable to take too much in the first instance. If the globule be too dark in color, it may be flattened by a pair of pin- cers after blowing, before getting stiff, and then observ- ed against the light. A colored borax glass appears often different when cold or warm, also if treated with the outer or inner flame ; there are, however, but a few metals to be con- sidered for our purpose. Iron. — It colors the borax reddish yellow or reddish brown, when hot and played upon with the oxydation flame. It turns yellow, or colorless if in a small quan- tity, when cold. A good reduction flame makes the glass reddish brown, but it becomes bottle green when cold. « Copper — When hot, colors the glass green ; when cold, blue. The presence of other metals renders these 20 PROCESSES OF SILVER AND GOLD EXTRACTION. signs uncertain. The surest way is, to reduce the oxyd of copper which is dissolved in the borax, to a suboxyd by which the glass assumes a light red color, becoming opaque. When the well-calcined test is dissolved in borax, a small piece of tinfoil is laid on the pearl and blown with the reduction flame. If there is only a small quantity of copper in the ore, the borax pearl will appear brick red and opaque when cold. If the color is grayish brown, there is also some antimony in the test. If the pearl becomes black there is a great deal of antimony, which must be driven off by a better roasting. EXAMINATION IN A CLOSED GLASS TUBE. Sec. 8. A particle of ore, of the size as represented in Fig. 7 a, is introduced into a glass tube (Fig. 7 b) and heated by an alcohol lamp. The heat must be raised gradually to redness, also increased, if no sublimate appears, directing the alcohol flame by the blowpipe on that part of the tube where the particle of ore is, till the glass commences to melt. The volatile substances sublimate on the cooler part of the tube (Fig. 7 c), assuming different colors, thus enabling us to recognize the substance. a. A dark yellow or reddish-brown sublimate when hot, turning the sulphur yellow when cold, indicates sulphur. Only such sulphurets which contain two atoms PROCESSES OF SILVER AND GOLD EXTRACTION. 21 of sulphur to one atom of metal emit sulphur in a closed tube. h. A reddish yellow sublimate which appears at a high temperature under the blowpipe, becoming sulphur yel- low when cold, shows iodine. c, A dark reddish-brown, almost black sublimate, becoming red or reddish-yellow after cooling, shows the presence of arsenic and sulphur. d, A black sublimate, quite close to the test, arising by the aid of the blowpipe and turning brownish-red when cold, indicates sulphur and antimony. c. A black sublimate without lustre, rendering a red powder when scratched, indicates sulphur and mercury. /. A grayish-white sublimate, consisting of trans- parent crystals, which can be distinguished under the magnifying glass, indicate^ antimony. Some ore will not yield this sublimate, unless it is treated with the blowpipe. g. A reddish black sublimate, obtained* by the aid of the blowpipe, giving a dark red powder, indicates selen- itiln, which can be observed at the open end, by the odor of rotten radish. h. A gray sublimate indicates mercury. The. quick- silver globules can be perceived by a magnifying glass. 22 PKOCESSES OP SILVER AND GOLD EXTRACTION. EXAMINATION IN A GLASS TUBE, Opek at Both Ends. Sec. 9. For the purpose of examining the ore in an open tube, the test is introduced so as to have it near one end. That part of the tube is heated over the alcohol flame, while the other end is raised a little, so as to create a draft. It is often required to raise the heat by aid of the blowpipe, as described in Section 8. The ore is used in shape of grain, about as large as hempseed ; but, if it was observed to decrepitate in the closed tube, it must be pulverized, and in that state introduced into the tube. There are substances or combinations, which are not volatile in a closed tube, but being in contact with the oxygen of a draft of air in an open tube, they oxydize and escape, either in form of gas, when they can be per- ceived by their odor, or by their action on a strip of moistened blue litmus paper, which is placed in the upper part of the tube, or they sublime in the cooler part, nearer to the test, or further off, according to the degree of their volatility. Care must be taken to raise the heat gradually, otherwise it may happen that a great part of the sub- stance will sublime without change. There are several substances, which, treated in an open tube, can be recog- nized with certainty. Such substances are principally : Sulphur, — Sulphurets, being heated in a tube, emit PROCESSES OF SILVER AND GOLD EXTRACTION. 23 sulphurous acid. The sulphur can be d'etected by the odor at the upper end of the tube, also by the litmus paper, which changes its blue color into red. Antimony. — Antimony yields white fumes, condensing in the upper part of the tube to a white sublimate. The presence of lead makes the sublimate light yellow. Selenium. — Selenium of silver emits at the upper end of the tube the odor of rotten radish. Iodine. — Iodide of silver, if strong heat is applied, gives a yellow sublimate. It changes sulphur yellow when cold. Quicksilver. — Quicksilver gives a sublimate of metallic mercury of a grayish-white appearance. If sulphur is present and strong heat is applied, a black coating will be formed. SYSTEMATIC PROCEEDING Fob Determination of Gold and Silver Ores. Sec. 10. The use of the following systematic proceed- ing can be understood easily by an example : A silver mineral, for instance, approved as such by examination on silver, must be observed first as to what lustre it shows, or whether it is dull. Suppose, then the mineral has a metallic lustre (see I). The color must 24 PROCESSES OF SILVER AND GOLD EXTRACTION. be observed next and compared with those under I. The ore is further found to be " lead gray." We have then to proceed from the indicated letter B on the right side to B on the left, and examine accordingly, whether the mineral gives a sublimate or not. If, for instance, no sublimate has been obtained, we must pro- ceed to c as indicated. On the described examination under c the mineral appears tough, it can be cut with a knife. We go over to Section 16, and see the numbers 2 and 20, Silverglance and Hessite. The description of both will lead to the right determination of the mineral. I. LUSTRE-METALLIC OR SUB-METALLIC. Color — white, grayish white, yellowish white, or yeUow, see . . . A Color — ^lead-gray, blackish lead-gray, or iron-black B (7oZor— hght steel-gray C Color — reddish lead-gray D Color — ^pinchbeck brown U II. LUSTRE-RESINOUS AND ADAMANTINE. Color — ^pearl-gray, yellowish green, green, olive-green, lemon yellow or light yeUow, see F III. DULL. Color — ^red, dark red (sometimes externally lead-gray), see. . . G- Color — ^blackish blue jff Color — greenish black / PROCESSES OF SILVER AND GOLD EXTRACTION. 25 A It can be cut with a Knife, see a A Can not be cut, is brittle 5 ^ In a closed tube, no sublimate, even under the blowpipe o B It ^ves a sublimate, with or without the blowpipe d (7 In a closed tube, no sublimate e O It gives a subHmate / i) In a closed tube, dark red, sublimate. See Sec. 16 (8 or 9). J^ In a closed or open tube, no subhmate. Sec. 16 (4). J^ In a closed or open tube, no sublimate , g F Gives, with aid of the blowpipe, a slight sublimate h G In a closed tube, red-brown or reddish yellow sublimate. Sec. 16 (10). G- It gives three sublimates, black, yellow, and gray. Sec. 16 (16). jB" In an open or closed tube, no subhmate. Sec. 16 (3 a'). / In an open or closed tube, no sublimate. Sec. 16 (11 a'). a It melts on charcoal to a metaUic white globule. Sec. 16 (1). a It melts on charcoal to a metalHc yellow or yellowish globule. Sec. 15 (1). h It melts on charcoal to a globule of metalUc lustre, coating the coal white. Sec. 16 (17). h It decrepitates somewhat, giving, before fusing, a sUght, very volatile whitish coating. Sec. 15 (4) or Sec. 16 (22 or 23). c It can be cut with a knife. Sec. 16 (2 or 20). c It can not be cut, is brittle. Sec. 16 (3 or 4, a or 6), or Sec. 16(2). c? in a closed tube it gives a reddish yellow subHmate. Sec. 16 (6 a'). e On charcoal it fiises, giving a yellow and white coating. Sec. 15 (8). / In a closed tube, by aid of the blowpipe, a dark red sublimate. Sec. 16 (11). 26 PROCESSES OF SILVER AND GOLD EXTRACTION. g On charcoal it fuses, emits an acrid odor, and leaves globules of silver ; in a closed tube with bisulphate of potassa, emits no colored vapors. Sec. 16 (12). g It gives, with bisulphate of potassa, red-brown vapors. Sec. 16 (13 or 14). A In a closed tube, with bisulphate of potassa, violet vapors. Sec. 16 (15). ANALYSIS OF RETORTED AMALGAM, Or Bullion Metal. Sec. 11. Black amalgam is first tried with the magnet on a small particle. If attracted, there is a great deal of iron in the amalgam. If it does not follow the mag- net, it may still contain iron, which must be examined in a different way. A small piece is introduced into a closed tube and heated by the alcohol lamp to redness. It generally gives out a whitish sublimate, consisting of minute glob- ules of mercury, which can be detected by the magnify- ing glass, or by a piece of flattened gold, which, when introduced into the tube and rolled over in the sublimate, gets a coating of quicksilver. Heated in an open tube, it sometimes colors litmus paper red. This proves the presence of sulphurets in the amalgam. Under such circumstances a black subli- mate appears, consisting of sulphur and mercury. A small particle of bullion metal or retorted amalgam is laid on charcoal and heated with the oxydation flame. PROCESSES OF SILVER AND GOLD EXTRACTION. 27 A slight yellow coating indicates lead ; a bluish-white, antimony ; or the coating is yellowish, and further off bluish white, proviiig the presence of both lead and an- timony. On a clean spot of the charcoal, some borax is melted into a transparent globule. The metal is placed against the borax and played upon with the reduction flame for half a minute. The oxydation flame would oxydize the silver, and color the pearl white enamel-like in cooling. The metal globule, when yet hot, is seized by a pair of pincers and taken out, leaving the borax pearl on the coal. To this pearl is added some tinfoil of the size of a small pinhead, and blown again only a short time with the reduction flame. If the pearl turns gray enamel-like or black, it shows the presence of antimony, which, on account of its small amount, could not have been per- ceived as a coating on the charcoal. In this case another small particle of the same test must be played upon with the pure oxydation flame for about one minute, in order to get rid of the antimony, and then treated with borax and tinfoil as above described. If there be copper in the metal, the glass would appear brick-red or dark brown when cold under the influence of the tinfoil. The same pearl is played upon again with a good reduction flame for half a minute in order to reduce the copper to a metallic condition. If then, the glass appears transparent greenish or bottle green, there is iron pres- ent in the metal. If it does not become transparent, a longer blowing or better reduction flame is required. 28 PROCESSES OF SILVER AND GOLD EXTRACTION. BLOW-PIPE ASSAY. Sec. 12. For the purpose of determining a silver min- eralj it is not absolutely necessary to ascertain the amount of silver or the specific gravity. In some cases, however, it may be desirable to know both. To ascer- tain the silver by fire assay, would not answer ; firstly, because there are generally different silver minerals in the ore, the separation of which in the required quantity would be almost impossible, and because the fire assay is not accurate enough for this purpose. In analyzing silver ore it is important to examine it with the magnifying glass, and to select pieces which are of the same quality in regard to toughness, color, lustre, and fracture. A preliminary examination with the blow-pipe will inform us of the compound, and enable us to know whether the difierent pieces are substantially the same. Rich silver ore should be examined carefully with the aid of a magnifying glass, and the small par- ticles of native silver adhering to the mineral removed by a pair of pincers. This precaution must be observed, likewise, in selecting pieces for the determination of spe- cific gravity. One grain of the silver mineral is sufficient for the blowpipe assay, and, if properly conducted, will always yield the same amount of silver, as found in the classifi- cation, provided it is a mineral with an invariable amount of silver, for instance silverglance. For the purpose of assaying, the mineral must be pul- PROCESSES OF SILVER AND GOLD EXTRACTION. 29 verized in the agate mortar to the finest powder. Tough silver ore can be used in little pieces. Of this prepared ore, 1 grain or yVVo ^^ weighed out on the assay balance (see Sec. 3) with the utmost precision, and emptied into the mixing scoop (see Fig. 3). Some powder always remains in the balance cup which must be swept with a little hair brush into the capsule. (Fig. 3.) The required quantity of borax glass and lead (Sec. 4) depends on the ore. About j^^-^ of borax will generally answer, but if the test appears difficult to be melted, some more borax may be added during the smelting operation. Three times as much lead as silver ore should be used. If there is a great deal of copper in the mineral, a double quantity of lead is required. The ore, lead, and borax are mixed carefully in the capsule with an iron spatula. When this is done, the spatula is brushed above the capsule and the mixture introduced into the paper tube (Sec. 3). To effect this, the paper tube is gently held between the thumb and forefinger. The capsule is held with the thumb and fore- finger of the right hand, and the mouth of the capsule introduced so far into the tube that it can be held, together with the tube, by the left hand. The assay slides into the tube by gently knocking with the spatula upon the capsule. The remaining dust must be swept into the tube with the hair brush. The tube is then closed, folding the paper with the fingers, and is thus prepared for melting. For this purpose, a hole is made in a sound piece of 30 PROCESSES OF SILVER AND GOLD EXTRACTION. charcoal with the little drill (Fig. 2) deep enough to receive the prepared tube, which is introduced. The hole must be always made across the grain of the coal near the edge. The reduction flame is now conducted so as to cover the tube by easy blowing: A strong blast would carry oflf the paper which was folded, and cause some loss. When the tube paper is burned and the assay commences to melt, a strong heat must be applied with a pure reduction flame which is chiefly turned upon the borax, not upon the lead button. The latter gains in size by the joining of other globules. When the melting has proceeded so far that only slag and the lead button are perceived, the blowing must be inter- rupted, in order to bring the bottom of the tube, which may be yet under the slag, to the top, by tapping the coal with the finger. The application of the reduction flame is continued till no particles of lead are seen on the slag. The charcoal must be inclined in different directions, so that the lead button may touch all sides of the slag, gathering up the small lead globules. When this is performed, the oxydation flame must be used, chiefly for the purpose of driving out the sulphur. The assay must be kept as far from the flame as possible. The blast is directed right on the lead button. It will soon be perceived, that many little lead globules arise in the slag, but they do not contain silver. The lead oxyd, produced by the oxydation flame, is dissolved by the borax, and, in contact with the glowing coal, reduced to the metallic state. After a time the melting PROCESSES OF SILVER AND GOLD EXTRACTION. 31 is interrupted, and when it is observed that the lead button turns black on cooling, the blowing must be con- tinued for half a minute more. If the lead, when hard- ened, has a light lead-color it may be broken out, with a pair of pincers, and cleaned of slag on the anvil with the little hammer. The button is now ready for cupellation. The bone- ash cupel (Fig. 4:,h) is heated in the oxydation flame, and the lead button introduced. The object of this operation is the oxydation of the lead, which is thereby separated from silver. The lead button in the cupel is played upon with the oxydation flame, using a strong heat. As soon as the lead becomes bright and active the cupel is held a little further off from the flame and a moderate heat is applied, but not so low as to stop the action. The flame must be directed on the lead. The litharge accumulates behind the button, which, when reduced to the size as represented by c (Fig. 4), must be separated from the litharge, by using more heat on and around the button, holding at the same time the capul a little inclined, so that the globule may slide off on a clean spot. The cupel is held nearer to the flame, which must play around the button, in order to heat the cupel, by which the litharge as it is formed sinks into the mass, leaving finally a pure silver globule. When the last particles of litharge are emitted, the globule assumes the color of the rainbow, which indicates the finishing operation requiring a few seconds more blow- ing. If there was too much copper in the assay, the 32 PROCESSES OF SILVER AND GOLD EXTRACTION. silver button will appear dark or black. An addition of lead of the size of a pin-head, and treated again with the blowpipe for a moment will render the button bright. The silver button is taken from the cupel, laid edge- ways on the anvil and the adhering boneash hammered off. It is then weighed on the balance and the per cent- age is found directly by noticing the weight. If required to express the per centage in ounces per ton, it may be calculated in the following way : for instance, one hundred parts of silver ore assayed in the described way, yielded a button, weighing sixty-three. This mineral contains, then, sixty-three per cent, of sil- ver, consequently twenty times so much per ton of 2,000 lbs., of which one pound contains 14*58 ounces Troy. The calculation accordingly is : 63 X 20 = 1260 X 14-58 = 18,370-80 ounces per ton. The silver button, when dissolved in nitric acid, leaves sometimes a black particle of gold, which is always insignificant and without influence in classifica- tion. The application of too much heat in cupellation may cause a serious loss of silver. It is therefore necessary to keep the cupel sufficiently far off from the flame and allow the litharge to become stiff, as soon as it parted from the metal. But also in this case a certain loss must be suffered, which, as found by experience, must be added to the weight of the button. PROCESSES OP SILVER AND GOLD EXTRACTION. 33 The following extract from Plattner^s Table of Silver Losses by Cupellation will serve our purpose : If the silver button weighed : Ores containing 30 to 59 per cent, of copper, required 11 parts of lead to 1 part of ore. 1 1 Ores containing under 7 per cent, of copper, or free from it, require 6 parts of lead to 1 of ore. The loss of silver in cupellation will be : 80 0*44 70 0-82 0-40 60 50 0-74 0-56 0-36 0-32 40 0-55 0-27 30 0-50 0-25 20 0-45 0-22 10 0-40 0-20 9 0-35 017 8 0-28 015 7 0-23 013 6 0-20 Oil 5 0-18 0-10 4 016 009 According to this table the real amount of silver in the supposed assay of the silver ore (which, in the absence of copper was mixed with 5 parts of lead) must be equal to 63 -|- 0-37 = 63-37 per cent. SPECIFIC GRAVITY. Sec. 13. The determination of specific gravity, for the purpose of the classification of silver ore is not abso- lutely necessary, but in some cases it may be of service. The specific gravity of a mineral is its weight, com- pared with the weight of an equal body of distilled or pure water. 3 34 PROCESSES OF SILVER AND GOLD EXTRACTION. It is necessary to know the absolute weight of the mineral, then that of an equal volume of water, and to divide the first by the last. The mineral by immersion loses exactly so much in weight as an equal bulk of water weighs. The loss of weight of a mineral by immersion expresses, therefore, the weight of an equal volume of water. If the absolute weight of a mineral is divided by its loss under water, the quotient will show the specific gravity. For instance, a piece of native gold (Comstock) weighs. 183-8 . The same piece under water 170-8 Difference 13-0 183'8 The difference, 13, is the loss of weight bj immersion, and -Tg~ = 14-1 spe- cific gravity of gold. The blowpipe-balances are provided for hydrostatic weighings, as represented by Fig. 8. On the little hook of the scale, a, is fastened a fine silk thread prepared with a sling (for the mineral, which may weigh two or three grains). The scales are set to balance, including the thread. The mineral is then suspended on the thread, weighed, and the weight noticed. A small tum- bler, c, is placed under the scale, a, and the suspended mineral, h, immersed about one-fourth of an inch below the surface of the water. If any bubbles are perceived on the mineral, they must be removed by the aid of a small hair brush. It is weighed again now, and the loss by immersion found. PROCESSES OF SILVER AND GOLD EXTRACTION. 35 HAEDNESS. Sec. 14. In regard to gold and silver ores, the hard- ness is not very important, inasmuch as there is no con- siderable variation among these minerals. Chapman's arrangement, by which the hardness can be ascertained without the use of minerals, representing the scale of hardness, will sufficiently answer our purpose. Hardness = 1-5 yields with difficulty to the nail. Hardness = 2-5 does not yield to the nail ; does not scratch a copper coin, but is easily scratched by it. Hardness = 3-5 scratches a copper coin easily, but is scratched by it with difficulty. CHAPTER II DESCRIPTION OF GOLD AND SILVER ORES. A. GOLD ORES. Sec. 15. Gold appears mostly in metallic condition, but never free from silver. It is found generally in the form of grains, scales, dust, also in the shape of leaves, threads or crystals. It is not ascertained but supposed, that a part of the gold in iron pyrites does not exist in metallic state, but combined with sulphur, or with arsenic in the arsenical pyrites. The gold is found in combina- tion with the following metals : 1. Silver — In dijfferent proportions. The gold of Gold Hill lode, N. T., contains forty-seven to fifty per cent, of silver; -that of the Comstock lode thirty to forty-five. Gila River and Australian gold three to five per cent., according to the amount of silver the gold appears more or less whitish. Sixty per cent, of silver renders the alloy white. On charcoal, treated with the oxydation flame, it gives sometimes a bluish-white coating of antimony. With PROCESSES OF SILVER AND GOLD EXTRACTION. 37 borax, played upon with reduction flame, a reaction of copper may be observed. 2. With Tellurium. — It contains gold 26, silver 14, tellurium 59, with traces of lead, copper, and antimony, hardness 1*5, gravity, 5*7 to 5*8, lustre metallic, color light gray. In an open tube it emits white fumes, and gives a gray sublimate of tellurium. Directing the flame on the sublimate, it melts into transparent drops. The fumes have a peculiar sour odor. On charcoal it melts to a dark gray globule. Played upon with the pxyda- dation flame it gives a white coating, which disappears with a bluish-green color under the oxydation flame. Continued blowing yields a yellow, bright gold button. 3. With Tellurium and Lead. — Gold 9, tellurium 32, lead 54, with traces of copper, sulphur, and antimony ; H. = 1*5, Gr. = 7-7*2, color dark lead-gray. In an open tube it fumes, and yields a gray sublimate, the upper part of which, formed by antimonous acid, can be driven away by the flame. On charcoal it fumes and gives two coatings : a white one, which is volatile, consisting of tellurous and antimonous acids and sul- phate of lead ; the other coating is yellow, less volatile, and consists principally of oxyd of lead. Continued blowing leaves a small metallic button, showing gold color when cupeled. 4. With Mercury and Silver, — Gold 36, silver 5, mer- 38 PROCESSES OP SILVER AND GOLD EXTRACTION. cury 58. The gold is found also alloyed with molyb- denum, platinum, and rhodium. B. SILVER ORES. Sec. 16. Silver is found mostly in combination with sulphur, also alloyed with other metals and substances. It appears often in metallic condition. 1. Native Silver — Is found crystalized, in threads or filaments. It often contains a small amount of anti- mony, arsenic, iron, gold, or copper. The native silver (one variety) of the Comstock lode, N. T., contains : Sil- ver 60-85, gold 1-9, lead 8-30, copper 1-5, H.= 2-7 -3, Gr. = 10-6-11-3. Heated on charcoal it becomes covered with lead globules, disappearing again when red hot. It gives a yellow coating of lead, and further off a bluish-white of antimonous acid. It colors the borax glass green with the oxyd of copper. a. Combination with Sulphur. 2. Silver Glance (Sulphuret of Silver). — Silver 87, sulphur 12-9, H.= 2-5, Gr. = 6-9-7-2, lustre metallic, color and streak blackish lead-gray, streak shining. It may be cut like lead. On charcoal, it melts into a dark blue globule, generally emitting metallic silver on the surface on cooling, especially if a small particle of borax glass is added, which dissolves impurities. It yields a silver globule when melted with soda. PROCESSES OF SILVER AND GOLD EXTRACTION. 39 3. Stromeyerite (Silver-copper Glance). — Silver 50-53, copper 31, sulphur 15, H. = 2*5, Gr. ^ 6-2, lustre metallic, color blackish lead-gray. In a closed tube gives some- times a little sulphur sublimate, in an open tube sulphur- ous acid. On charcoal it fuses to a steel blue globule, emitting sometimes metallic silver on cooling. Melted with soda, it gives a copper button, which yields silver when refined. It occurs in the Heintzelman mine (Ari- zona). d. A variety of this ore, containing 40-43 per cent, of silver with a dull blackish-blue color, streak shining, can be cut, occurs in Arizona. 4. Sternbergite (Sulphuret of Silver and Iron). — Silver 30-33, iron 36, sulphur 30, H. = 1, Gr. = 4-2, me- metallic lustre, color pinchbeck-brown, streak black. In thin laminas flexible, resembling graphite. In an open tube it gives out sulphurous acid. It melts to a globule on charcoal, emitting silver, and follows the magnet. a\ A variety of this ore is found in the Gold Hill lode, N. T. It consists of silver 33-25, iron 34*05, H. = 2-8, Gr. = 5*2, color dull bluish-gray ; the fracture has a metallic lustre and dark lead-gray color. The powder is blackish-brown. It is found in small fragments of indistinct cubic shape. On charcoal it melts with a spongy appearance to a dull gray globule, following the magnet. A slight yellow coating indicates a trace of lead. In melting it gives out a great deal of sulphur- ous acid. Treated with soda a silver globule is easily obtained. 40 PROCESSES OF SILVER AND GOLD EXTRACTION. h. Combinations with Sulphur and Antimony, or Arsenic. 6. Brittle Silver Ore. — Silver 70, antimony 13*9, sul- phur 15*7, H. = 25, Gr. = 62, lustre metallic, color and streak iron black or blackish lead-gray. In a close tube it decrepitates, melts to a globule and gives a blackish sublimate which turns red-brown when cold, consisting of sulphide of antimony. In an open tube it melts, evolving sulphurous acid, and fumes. On charcoal it fuses, and coats the coal white with antimonous acid. By continual blast, the coating assumes a pink color, derived from the oxyd of silver. It occurs frequently in the Comstock lode. 6. Folyhadte (Eugen Glance). — Silver 64-72, copper 3-10, sulphur 17, H. = 2*5, Gr. = 6-2. It contains also antimony, arsenic, iron, and sometimes zinc. Lustre metallic, color iron black, streak black. In a closed tube it yields nothing volatile. In an open tube it gives anti- monial fumes and sulphurous acid. It occurs also in Gold Hill lode, N. T. a\ The polybasite of the Comstock lode contains 64 per cent, of silver. It gives in a closed tube, with the aid of the blow-pipe, a reddish brown sublimate with a yellow edge. In an open tube, white fumes arise and some white sublimate deposits. On charcoal, with the reduction flame, it evolves an odor of garlic. Played upon with the oxydation flame, it gives out sulphurous acid and a white coating of antimonous acid. It melts PROCESSES OF SILVER AND GOLD EXTRACTION. 41 to a globule with a metallic lustre. If the hot blast is changed suddenly to a cold one, and directed on the globule, holding the blow-pipe point close to it, metallic silver is emitted. If the cold blast is stopped too soon, the silver will disappear again. 7. Miargyrite. — Silver 35-8, antimony 42*8, sulphur 21, H. = 2*5, Gr. = 5*2-5.4. Lustre metallic adamantine, color iron black, streak dark cherry red. In a closed tube it decrepitates, melts easily, and gives out a subli- mate of sulphide of antimony. In an open tube sul- phurous acid and antimonial fumes are emitted, deposit- ing a white sublimate of antimonous acid. On charcoal it melts quietly, emitting sulphurous acid and antimo- nial fumes. It covers the coal with a white coating, which becomes pink colored by continual blast. Melted with soda a silver button is obtained, which, treated with borax and tin, reacts on copper. 8. Darlt Red Silver Ore ( Pyrargyrite, Antimonial Blend). — Silver 58*9, antimony 23-4, sulphur 17*5, H. = 2*5, Gr. = 5*7. Lustre metallic-like adamantine, color dark red, powder cochineal-red. In a closed tube, by the aid of the blowpipe, it yields a sublimate of sul- phide of antimony, black while hot, but varying from red to reddish-yellow when cold. In an open tube it gives antimonial fumes and sulphurous acid. On char- coal it melts easily and deposits a white coating of anti- monous acid. With soda it gives a silver globule. It occurs also in the Gold Hill lode, N. T. 42 PROCESSES OF SILVER AND GOLD EXTRACTION. 9. Light Red Silver Ore (Proustitej Arsenical Blend). Silver 65*4, arsenic 15-1, sulphur 19-4, H. = 2-5, Gr. = 5* 5-5-6, color similar to dark red silver ore, but lighter. Behaves like the preceding, except the arsenical fumes. 10. Xanthocone. — Silver 64, arsenic 13-4, sulphur 21*3, H. = 2, Gr. = 5-5-2, color dull red to clove brown^ powder yellow. When heated in a closed tube it be- comes dark red, melts and gives some sublimate of sul- phide of arsenic. While hot, it is dark brownish red, and red to reddish-yellow when cold. In an open tube and on charcoal it behaves like the preceding. 11. Silver FaUerz (Argentiferous gray copper ore). Silver 17-71-31-29, antimony 26-63-24-63, sulphur 23-52-21-17, copper 25-23-14-81, iron 3-72-5-98, zinc 3-10-0-99, lustre metallic, color light steel gray. In a closed tube it sometimes decrepitates, melts and gives, by aid of the blowpipe, a dark red sublimate of tersul- phide of antimony with antimonous acid. In an open tube it fuses^ gives antimonial fumes and sulphurous acid. On charcoal it fuses easily and gives a bluish- white coating of antimonous acid and antimonial fumes. There is also a yellowish coating close to the test which appears white on cooling. This coating is created by oxyd of zinc. d. The Reese River ore from the Comet lode seems to be a metamorphosed silver fahlerz. The sulphur is rep- resented by carbonic acid, so that almost all copper and PROCESSES OP SILVER AND GOLD EXTRACTION. 43 silver is a carbonate. It contains silver 22*35, copper 17, antimony, and some lead. It has a dull greenish-black or black color, streak shining, powder greenish-gray. In a closed tube it yelds nothing volatile. In an open tube some sulphurous acid can be observed. On charcoal fuses slowly, but boils up suddenly in contact with glow- ing coal, leaving a button of silver and copper. This button, when played upon with the oxydation flame on another spot of the charcoal, gives first a bluish coating of antimonous acid, then a yellow one nearer to the assay of the oxyd of lead. The silver can be separated from copper by cupellation with lead. v. The silver fahlerz of Sheba lode (Humboldt) con- tains silver, 8-20, gold 0*008, some antimony and lead, but very little copper. It has a light-gray metallic lustre. It is also called gray silver ore. c. Combination with Chlorine, Bromine, and Iodine. 12. Horn Silver (Chloride of Silver).— Silver 75*2, chlorine 24*6, H = 1*5, Gr. = 5*5-5*6, lustre adaman- tine, color gray, greenish or blackish, streak shining. It looks like horn 'or wax. It is translucent and may be cut like wax. Occurs frequently in the Comstock and Gold Hill lodes ; also in California. It fuses in a candle flame. On charcoal it is easily reduced and gives an odor of chlorine. If treated under the reduction flame with an addition of copper, it forms a chloride of copper and colors the flame azure-blue. 44 PKOCESSES OF SILVER AND GOLD EXTRACTION. 13. Embolite (Chlorobromide of Silver). — Silver 66*9 to 75, H = 1-1*5, Gr. = 5-3-5-4, lustre resinous, color yellowish-green or green. On charcoal it fuses easily, evolves vapors of bromine, and gives metallic silver. Mixed with oxyd of copper it colors the flame greenish- blue. 14. Bromyrite (Bromic Silver). — Silver 57-56, bromine 42-44, H. = 1-1-5, Gr. = 5-8-5-6. In a closed tube, treated with bisulphate of potassa, it emits brown va- pors. On charcoal it fuses easily and yields a globule of silver. It is yellow or greenish, and may be cut like chloride of silver. 15. lodyrite (lodid of silver). — Silver 46, iodine 54, H. = 1-5, Gr. = 5*5. Lustre adamantine. Color yel- low, also greenish. It is translucent. In scale shape it is always lemon-yellow. When heated in a closed tube it becomes fire red, but assumes its former color when cold. It fuses easily, and gives, by the aid of the blow- pipe, a reddish yellow sublimate, getting lemon-yellow on cooling. With bisulphate of potassa, it emits beauti- ful violet vapors. In an open tube it .gives an orange sublimate, lemon-yellow on cooling. On charcoal it assumes a fire red color before it fuses, and spreads on the coal and yields many minute silver globules. With an addition of oxyd of copper, it makes an intensely green flame with a bluish tinge. PROCESSES OF SILVER AND GOLD EXTRACTION. 45 16. lodid of Silver and Mercury. — Silver 40-42, iodine, quicksilver, and sulphur (chlorine?) Color dull, dark red. Streak shining. Powder dark red, but changes soon into lead-gray if exposed to the light. In a closed tube it gives three sublimates, separated in rings. The nearest to the assay, is black (sulphide of mercury), the second yellow, (subchloride of mercury ?) the third is gray (metallic mercury). An addition of bisulphate of potassa causes it to yield violet vapors, which come from the iodine. In an open tube it gives the same sub- limate, but the black is very slight ; it gives also yellow fumes. A gold particle in the tube becomes amalga- mated. Litmus paper at the upper end is colored red by the sulphur. Heated on charcoal, it turns black, fuses easily, and yields silver globules. Melted with soda, it draws partly into the coal. If this crust is broken out, and laid on a blank piece of silver, with a drop of water, the sulphur in it will cause a black spot on the silver. Heated with a small piece of pure lead, it gives a beautiful green coating with a yellow border nearest the assay. This coating (iodine and lead) is far off from the test. With copper oxyd, like the iodyrite. This mineral occurs to my knowledge only in the Heintzelman mine (Arizona), d. Combination with Antimony. 17. Antimonial Silver. — Silver 77-84, antimony 23-16, H. = 3-5, Gr. = 9-4-9-8. Lustre, metallic ; color and streak, silver-white. On charcoal it fuses easily to a 46 PROCESSES OF SILVER AND GOLD EXTRACTION. globule, coating the coal white. A continual blast ren- ders the white coating reddish. e. Combination with Selenium. 18. Naumannite (Selenid of silver). — Silver 73, Selen- ium 26, H. = 2*5, Gr. = 8. Lustre, metallic ; color, iron black. It melts easily on charcoal, but with intu- mescence in the reduction flame. It emits the selen- ium odor of rotten radish. With soda it yields metallic silver. 19. Eucairite (Selenid of silver and copper). — Silver 43*1, selenium 31*6, copper 25*3. Lustre, metallic -, col- or, lead-gray. On charcoal it melts to a gray metallic globule, fumes and reacts on borax with copper. This mineral is soft, and can be cut with a knife. /. With Tellurium. 20. Hesdte (Tellurid of silver).— Silver 62*42, tellu- rium 36-96, iron 0-24, Gr. = 8-4-8-6. Lustre, metallic ; color, lead-gray, or steel-gray. It is soft, and can be cut like lead. According to Mr. Blake, this mineral is found in California also. He describes the reaction as follows : " In an open tube the mineral fuses quietly, coloring the glass a bright yellow under assay ; a white or gray sublimate is deposited at a short distance, immediately over it, which, on being heated, fuses into transparent drops resembling oil. On charcoal it fuses to a leaden PROCESSES OF SILVER AND GOLD EXTRACTION. 47 colored globule, which on cooling becomes covered with dendrites. This globule flattens under the hammer. With the addition of soda, a silver globule is obtained." /. With Bismuth. 21. Bismuth Silver. — Silver 60, bismuth 10, copper 7*8, and some arsenic. Lustre, metallic ; color, tin white or grayish. On charcoal it melts easily, covering the coal dark orange. It is yellow while hot, and lemon-yellow when cold. The oxyd of copper in it colors the borax green when melted on charcoal. g. With Merouky. 22. Silver Amalgam. — Silver 34*8-26-2, quicksilver 65-2-73.7, H. = 3-5, Gr. = 13.7-14. Lustre, metallic ; color, silver-white ; brittle. In a closed tube the mer- cury sublimates. 2^. Arquerite—^WvQv 86*49, quicksilver 13-51. It behaves like the amalgam. CHAPTER III. METALLURGY OF GOLD AND SILVER ORES. FIRE ASSAY OF ORES. The modes of assaying here described are those best suited for the purpose of the miner and millman. The apparatus and method of procedure are as simple as is possible; consistent with correctness. TOOLS. Sec. 17. A fine assay balance, as described in Sec. 3. A pair of less delicate scales, capable of weighing about three ounces. The weights are Troy ounces ; one ounce divided into ^^^. Such a scale may cost in San Francisco from $10 to $12. French clay crucibles No. 7; some glass matrasses; dry cups (small crucibles of pipe clay); a fine wire cloth sieve on a wooden frame, 60 holes to the inch (2,500 to a square inch); one pair of crucible tongs; one pair cupel tongs ; a pair of pincers ; a tooth brush and an iron mortar; two or three muffles, 10 inches long, 4 inches wide, and 3 inches high. PROCESSES OF SILVER AND GOLD EXTRACTION. 49 Cupels. — The fabrication of cupels requires a brass mould and boneashes. The bones are burnt white for this purpose. Pieces not well burnt, showing a black inside, do not answer. The bones are then pulverized and sifted through a fine sieve, forty holes to the inch. The bone powder is sprinkled with water, mixed and rubbed with the hands till it appears uniformly moistened and allows itself to be formed into a ball by a squeeze of the hand, without wetting it. The mould is then filled and beaten with the pestle by a wooden mallet. The pestle is drawn out in a twisting way and the cupel is pressed out by the ball of the hand. MATERIALS. Sec. 18. 1. Litharge. — Sifted, well mixed, and kept always under cover. One ounce and a half, mixed with 10 grains of wheat flower, melted in a crucible, will yield a button, which must be cupeled, and the weight of the small silver grain noticed. This weight must be sub- tracted from all assays, where this quantity of litharge was used. 2. Wheat Flour. — It is used instead of charcoal to reduce a part of the litharge to lead. A mixture of one hundred parts of soda and twelve parts of wheat flour serves as a flux for lead assays. 3. Soda (Carbonate of Soda).— If this soda is crys- tallized, it must be exposed for some time to the air, till 4 50 PKOCESSES OF SILVER AND GOLD EXTRACTION. it turns into a white powder, thus losing half of its water of crystallization. Bicarbonate of soda or soda-ash an- swers the purpose likewise. 4. Glass, — Broken glass is pulverized in an iron mor- tar and sifted. It serves as a flux. 5. Salt — Common table salt is freed from water of crystallization by heating in a sheet iron box, like a coffee roaster, till the decrepitation ceases. The salt fuses quicker than the assay mixture, and prevents the contact between air and the assay. 6. Iron. — It is used in small pieces of wire one-fourth or three-sixteenths inch thick, cut into pieces of differ- ent lengths from one-fourth to one-half inch. The pur- pose is the desulphuration of the sulphurets. GOLD AND SILVER ASSAY. Sec. 19. The ore intended for the assay must be broken first in small pieces, of which about one pound is taken without selection, afterwards well mixed and pounded finer. From this another portion is taken, about three ounces, pulverized and sifted through the sieve, described in Sec. 17. Ores from new lodes should be assayed for the purpose of ascertaining the highest yield, and the darkest parts of the ore selected and pul- verized. In taking samples of tailings, it is the safest way to procure three or four boxes of about one cubic PROCESSES OF SILVER AND GOLD EXTRACTION. 51 foot each, and have them filled from the discharge at different times, say at the commencement, at the middle and at the end of the discharge time. The box must be removed as soon as the water reaches the brim. After some hours, when the sand and mud have settled, the water is poured off, and the contents of all the boxes mixed and dried. These tailings are spread out, and small quantities are taken from different parts of the surface to the amount of three or four pounds. This sample is mixed well and treated in the same way, taking four or five ounces, which must be sifted and poundedj if any coarse sand is present. The mortar must be cleaned carefully after pounding each sample, especially if it was rich. In this latter case the mortar must be washed, or a small piece of quartz pounded in it and then wiped out with a clean cloth. The prepared sample and fluxes are weighed in the following proportion : a. Ores or Tailings containing but little Sulphurets. Ore 250 grains. Glass 125 grains. Flour 8 grains. Litharge 1)^ ounces. Soda 1 ounce. h. Ores containing about fifty per cent, of Sulphurets. Ore 250 grains. Glass 125 grains. Iron 50 grains. Litharge 1>^ ounces. Soda 1 ounce. 52 PROCESSES OE SILVER AND GOLD EXTRACTION. c. Ore being nearly all Sulphurets. The mixture is like the preceding, but double the amount of iron (one hundred grains) must be used. The soda and litharge are first introduced into the crucible, then the balance of the mixture. By aid of an iron spatula, the end of which is rounded, ore and fluxes are mixed in the crucible carefully over a sheet of paper. If in mixingj some powder should be spilled, the test can not be considered proper. It is better to repeat the weighing. If there are several assays made at the same time, the crucibles must be numbered out- side with red chalk. The charged crucible is tapped several times against the table, in order to settle the mixture, and is covered with salt, about one-fourth of an inch deep. Thus prepared, the assay is ready to be melted. The crucible is placed in the middle of the furnace, on the muffle, or, if there are two or three assays to be melted, the crucibles, standing on the muffle must touch each other, leaving space between them and the walls, as rep- resented in Fig. 9. The furnace is charged with charcoal only to the top of the crucibles, and set on fire by some live coal. It is not advisable to fill the furnace entirely, unless No. 8 crucibles are used, because the assay effervesces in melt- ing and may overflow. The covers are taken off^, the charcoal, by replacing, kept level with the top of the crucibles until the melting mass has gone down. The PROCESSES OF SILVER AND GOLD EXTRACTION. 53 assays are covered again, the furnace filled with coal to the line, h, and closed by an iron cover, a. The cupels are placed now in the muffle, d, and closed by the shut- ter, e. In about half an hour the charcoal is burnt down so far that the tops of the crucibles are exposed. By means of the crucible tongs the covers are removed first, the crucibles then, one after another, are seized with a pair of tongs (as represented in Fig. 10 c') and the contents poured into an iron mould (Fig. 12), containing four or five hollows, three-fourths of an inch deep. In pouring, the crucible must be kept close to the mould and slowly inclined, by degrees almost perpendicularly, so that the slag may drop out entirely. This melting operation takes nearly one hour's time. Care must be taken not to let the coal burn down below the line, /, else the upper part of the crucible might get too cool. The lead button in the mould is cooled off in one or two minutes, freed from slag by hammering it into a square shape, and, by means of the cupel tongs, intro- duced into the light red hot cupels. It melts in a short time, and the oxyd on the surface draws to the sides of the cupel. The lead appears bright, and fuming, and minute spots of litharge, constantly appearing, glide to the sides, being absorbed by the cupel mass. The muf- fle is kept open, but the ash holes, g and g\ are closed. The front edge of the cupels will cool off by the draft, and appear dark red ; the button inside is bright. The temperature must be kept as low as possible, but sufii- 54 PROCESSES OF SILVER AND GOLD EXTRACTION. cient to keep the button in action. If, however, the temperature be too low, and the lead, covered with oxyd, appearing dull, a piece of live charcoal is placed in front of the cupels, and the muffle is closed. By increasing the heat, the button soon resumes its activity, the muffle is opened again, and the coal removed. The furnace must be charged with charcoal, so that the muffle is always covered. The button becomes gradually smaller, but looks bright as long as litharge is separating from it. As soon as the last particles disappear, a play of rainbow colors is perceived on the remaining silver button, indicating the end of the cupellation. Generally, the crucibles are taken out of the furnace, when all the coal is burned down, placed in a cool place, and broken when cold. It is, however, a great saving in time, if the melted mass is discharged in the described way. A comparative trial will show that the results are equal, if well performed. If there is not too much importance connected with the assay, the crucibles may be used over four or five times, but care must be taken not to use crucibles in which rich assays were made. The silver button is freed from adhering to boneash by hammering edgeways and weighed. The weight, multiplied by 1-16, gives the amount of ounces per ton of ore of 2,000 lbs., which may be illustrated by an example. For instance, a button is found to weigh — PROCESSES OF SILVER AND GOLD EXTRACTION. 55 300 50 6 356 X 1*16 = 412-9 ounces per ton of ore. After weighing, the silver button is introduced into a glass tube, adding about half an ounce of pure nitric acid, and heated by the alcohol flame. It soon begins to boil, emits reddish-brown vapors and leaves the gold, if any in the assay, in undissolved particles of a black color in the tube. The nitric acid, containing the dis- solved silver is poured off slowly, and the tube filled with distilled water. When all the particles of gold have settled, this water must be poured off again care- fully and the tube filled once more with water, to the brim. The tube is then covered with the dry cup and quick- ly turned over, as represented in Fig. 11. The gold falls to the bottom of the cup, but, being very light and sometimes in minute particles, the tube must be kept for a while in this position, till no suspended particle is visible. It requires now some practice to lift the tube without spilling some water, which would invariably carry out some gold. The easiest and surest way is to gradually lift up the tube, till the water, the brim of the tube and the dry cup are level (Fig. 11, a). A slide of the tube in the direction of a' leaves the gold in the cup undisturbed. A slight tapping of the cup will bring the gold particles together, the water is poured 66 PROCESSES OF SILVER AND GOLD EXTRACTION. off and the cup dried over the alcohol flame till the gold assumes a yellow color. This gold is now carefully weighed and calculated upon as follows : The gold was found to weigh, for instance, yf f o? ^^^ the silver button before dissolving jV/o- ^^ ^^^ S^^^ i^ subtracted from the silver which contained this gold, we find thus the pure silver — 356-35 = 321 silver X 1'16 = 372-3 ounces per ton. and 35 gold X 1-16 = 40-6 " " To find the value, the ounces of gold must be multi- plied with 20*67 and those of silver with 1-30. These numbers in their fractions are not perfectly correct, but will serve our purpose. Continuing the calculation we find- Silver = 372-3 ounces X 1*30 = $483-99 Gold = 40-6 " X 20-67 = 839-20 Total value $1,323-19 per ton. In assaying gold ore, the button will not dissolve in nitric acid. In this case it must be melted (after weigh- ing) on a piece of charcoal before the blowpipe, with the addition of three times its weight, of pure silver and then dissolved and treated as above described. In case the ore for the assay has been weighed out by half an ounce, equal to two hundred and forty grains, the calculation is made in the same way as before with the exception, that the number 1-215 must be substi- PROCESSES OF SILVER AND GOLD EXTRACTION. 57 tuted for 1*16. The procedure of the preceding exam- ple would be as follows : The weight of the button was three hundred and twentj-one. This multiplied with 1*215 will give the amount of ounces per ton of ore of 2,000 pounds. 32 (321) X 1*215 = 390 ounces. The quantity of fluxes used for two hundred and fifty grains of ore will also serve for half-ounce assays. LEAD ASSAY. Sec. 20. In using lead ore for the purpose of melting silver ores, the amount of lead in the ore must be ascer- tained. The lead ores of Nevada Territory and Califor- nia are represented chiefly by sulphuret of lead (galena), but also to some extent by carbonate of lead. The lead ore must be sifted in the same way as the silver ore (Sec. 19) and mixed with fluxes in the follow- ing proportions : a. Ore containing Sulphuret of Lead. Ore }4 ounce. Soda with 12 per cent, of wheat flour 1)^ ounces. Glass }4 ounce. Iron 100 grains. h. Ore containing Carbonate, Oxtd, or Molybdate of Lead. The mixture is the same as that of the ore, a, but no iron is taken, as there is no sulphur in the ore. If it is pure galena, one hundred grains of iron are used. If 58 PROCESSES OP SILVER AND GOLD EXTRACTION. therefore the ore, a^ contains a great deal of earthy matter and less galena, or if the ore, ^, is mixed with sulphurets, the quantity of iron may be taken more or less, according to the supposed quantity of sulphurets. The melting is performed in the same way as is done with the silver assay. The lead button, resulting from the assay, is weighed on the ounce scale. As one ounce is divided {^^, the per centage of lead in the ore is easily found by doubling the weight of the button. CHAPTER IV. EXTRACTION OF GOLD. Sec. 21. The process of extracting free gold, and the manipulation itself, is very simple, requiring only a proper friction and contact with quicksilver. But there are combinations of gold with other substances in Cali- fornia, refusing to liberate the gold by friction. Such ore, as arsenical, and some iron pyrites, or tellurium of gold, require a different treatment. There are two principal methods of gold extraction : By amalgamation, and by chlorination. A. BY AMALGAMATION. a. Amalgamation in the Battery. For this purpose the batteries are provided with amal- gamated copper plates, three to five inches wide, having the length of the battery ; one at the discharge, the other at the feed side ; the latter being protected by the iron feed plate. They are fixed with a pitch of about thirty-five to forty degrees towards the dies. Other bat- 60 PROCESSES OF SILVER AND GOLD EXTRACTION. teries are so constructed as to have sufficient space where the amalgam may accumulate. In this case, the stamps are three to four inches apart from one another and from the sides of the mortar ; also, iron vertical grates inside the sieves are in use. The amalgam deposits readily between the rods. The amalgam adheres best to copper plates which are coated with quicksilver. This is per- formed by rubbing quicksilver on the copper with a piece of cloth tied to a wooden handle, using some drops of nitric acid, which may be diluted with the fourth part water. The quantity of quicksilver depends upon the quan- tity of gold in the ore. One ounce of gold requires one ounce of quicksilver, but when the gold is very fine, one and one-fourth to one and one-half ounces may be used. The quicksilver is introduced every half-hour, or every hour by the feeder, during the stamping, in each bat- tery, in portions of one-quarter of an ounce, more or less, as the ore requires. This may be observed at the discharge. When the amalgam appears very hard or dry, some more quicksilver may be used ; but if, on the contrary, the amalgam is too soft, or if quicksilver drops are perceived, less quicksilver must be introduced. The amalgamation goes on very rapidly. One hour after the quicksilver is put in, no yellow gold particles come out of the battery, except in cases when the quartz, containing lead, antimony, or other volatile metals, is burned for the purpose of rendering it easier to break. Many particles of gold appear coated, and are discharged without being amalgamated. PROCESSES OF SILVER AND GOLD EXTRACTION. 61 If the proper proportion of quicksilver, and the regu- lar times of charging be observed, when the ore contains heavy gold (800 fine), sixty to seventy-five per cent, may be saved in the battery and the copper-plated platform ; but light gold (300 to 400 fine), like Washoe gold, gives a less favorable result. A great many fine particles of amal- gam adhere together, involving also manganese scum, if present, and form small spongy, blackish lumps, which are so light as to float, and on account of being coated with foreign matters, will not unite with the accumulated amalgam. Of this amalgam but very little can be saved; it floats over blankets, copper plates, or ripples. It is therefore an error to use quicksilver in the bat- tery, if concentration is in use, and the tailings are not saved. The finest gold is easier retained by concentra- tion than this floating amalgam. There is also no evi- dence of any advantage in battery amalgamation, when the whole mass of pulverized rock is amalgamated in pans, unless the mass or the concentrated part is intended for roasting. b. Amalgamation on Copper-Plated Platforms, Troughs, AND OTHER COPPER FIXINGS. (Yery imperfect, and mostly abandoned.) c. Amalgamation in Arrastras. This is a very old, primitive method, but gives com- paratively a good result on the free gold, if, under good management, sufficient time is allowed. The construe- 62 PROCESSES OF SILVER AND GOLD EXTRACTION. tion is well known. There is a stone bottom, ten to fourteen feet diameter, and wooden sides, twenty to twenty-five inches high. Four or six large stones are dragged in a circular way by chains, fastened to four arms of the upright shaft. They make from six to ten revolutions per minute, and grind one and one- half to two tons of rock (broken in pieces as large as a hen's egg or smaller) in twenty -four hours. This is, however, too much for a proper amalgamation. When in motion, the arrastra is charged with about two hundred pounds of ore, with some water. One quarter of an hour afterwards the balance of the whole charge, from four hundred to five hundred pounds, is introduced. As soon as the ore is turned into mud, one or two ounces of quicksilver are pressed through a dry cloth over the thick pulp. A sample is taken from time to time with the horn spoon, washed and examined. When free gold is perceived, after the amalgamation has been going on for some time, some more quicksilver may be added. The first charges require a little more quicksilver. After four or five hours the pulp is diluted with water and discharged. The next charge is treated in the same way, and so on till one hundred or one hun- dred and fifty tons are worked through. The quicksilver must be used always in proportion with the gold, one or one and one-half ounces to an ounce of gold. The amalgam imbeds in the crevices of the bottom, and must be always dry. The use of too much quicksilver makes the amalgam thin, causes an imperfect amalgamation, PROCESSES OF SILVER AND GOLD EXTRACTION. 63 and a loss in quicksilver, vsrhich is often found beneath the bottom rock. d. Amalgamation in Iron Pans. The pan amalgamation is a highly improved arras fcra amalgamation, and at present the most perfect gold manipulation. The two conditions, friction and contact with quicksilver, are accomplished in a high degree by Wheeler's pans, the description of which will be found in Section 50. The supposition that a slow motion is favorable for the amalgamation is erroneous and en- tirely refuted by recent experience. To what degree, however, velocity may be advantageously increased is not yet ascertained ; but sixty revolutions 'per minute of a properly-constructed muUer answers most satisfac- torily, but the quicksilver is destroyed by friction to some degree. There is no chemical process required for amalgama- tion of gold, except with such ore as is mentioned in Sec. 21. By the pan manipulation the gold is extracted as close as ninety-five per cent, of the fire assay. The loss of gold in the pans does not result from defective amalgamation, but from improper discharge. Ores, containing gold in such condition, that it can- not be liberated by grinding, must be subjected to roast- ing without salt, before treating in pans. The treatment of gold ores does not differ from that of silver ores, except that no heat and no chemicals are required. 64 PROCESSES OF SILVER AND GOLD EXTRACTION. B, BY CHLORINATION. Sec. 22. This process is based on the property of chlorine, which enables it when placed in contact with gold to form a terchloride of gold without the applica- tion of heat. The silver, when in the metallic state or as sulphate, undergoes the same change, forming chlo- ride of silver, but the chloride of gold is soluble in water, chloride of silver only in a hot solution of salt. This process is executed in Nevada, California. An- other establishment, belonging to Mr. Deetken, in San Francisco, beneficiates concentrated sulphurets from different parts of California. The chloHnation of gold ores is a very simple pro- cess, still there are some delicate points in it. Compara- tively, very few hands are employed ; and there is neither motive power nor steam. This process, if well managed, extracts the gold very closely. Coarse gold particles, generally not found in the tailings, would resist chlorination, or require too much time. Accord- ing to Mr. Deetken's experience, low gold (in fineness) in the tailings is preferable, it being sooner transformed into chloride. The tailings are subjected first to calcination in a roasting furnace, without being sifted. No salt is used, as it sometimes causes a loss of gold. The roasting is performed in the usual way by stirring the mass at a low temperature till all the sulphurets or arseniurets are decomposed. An addition of charcoal powder favors the PROCESSES OP SILVER AND GOLD EXTRACTION. 65 roasting. After six or eight hours, when no odor of sulphurous acid is observed, the ore is discharged, spread on a proper place and cooled. The tailings or ore is then sprinkled with water and shoveled over sev- eral times. A little too dry or too wet has a great influ- ence on the result of chlorination. When moistened, the stuff is introduced into wooden tubs about seven feet in diameter and twenty-five or thirty inches deep. These tubs have a prepared bot- tom, which allows the entrance of chlorine gas from be- neath into the mass of tailings. Near the bottom are two holes, one for the discharge of the solution, the other communicates by a lead pipe with a leaden gas generator. The generator is filled to a certain height with peroxyd of manganese and salt. Sulphuric acid is introduced by a lead pipe. As soon as the mixture becomes hot, by the fire underneath the generator, the chlorine gas commences to be evolved and enters the tub through the connecting lead pipe. After some hours the whole mass is strongly pen- etrated and the greenish gas lies heavy on the tailings. The tub is closed by a wooden cover. In this condition it remains for ten or fifteen hours, when the cover is removed and clean water introduced. As soon as the water reaches the surface of the tailings, the discharge pipe is opened, and the water, containing the dissolved chloride of gold, is led into glass vessels. An addition of sulphate of iron, precipitates the gold in metallic con- dition as a black-brown powder. If there are silver 5 66 PROCESSES OF SILVER AND GOLD EXTRACTION. sulphurets in the ore, they, by roasting without salt, are converted mostly into sulphates, and in subsequent contact with chlorine, into chlorides which are not solu- ble in water, and remain in the tailings. The gold is therefore 995 fine. CHAPTER V. EXTRACTION OF SILVER. The extraction of silver, as practiced in Nevada Ter- ritory and California, may be described as follows : I. WET PROCESS. Amalgamation in Iron Pans. II. ROASTING PROCESS. a. Amalgamation in Barrels. h. Amalgamation in Yeatch Tubs. c. Amalgamation in Iron Pans. III. COLD PROCESS. Amalgamation in Heaps (Patio). IV. MELTING PROCESS. Extraction of Silver by Lead. I WET PROCESS. Sec. 23. About two years ago, Mr. Smith attracted attention by his " Smith's Process," using the ore without roasting, in iron pans four feet in diameter. The sur- 68 PROCESSES OF SILVER AND GOLD EXTRACTION. face of the bottom was diminished by a center-piece and by many shoes, so that only fifty lbs. of ore could be charged, and worked for five to six hours. Since that time there has been little improvement in the exclusively chemical part of this process; but the whole pan arrangement has been gradually so perfected, that now-a-days a four-foot pan (Wheeler's) is charged with seven hundred and fifty or eight hundred pounds of ore, and the amalgamation is finished in three hours including charge and discharge. But this mechanical improvement comprehends also that of the chemical part. It is known that friction and iron decompose tough silver sulphurets, without chemicals. Friction and iron are powerful chemicals in themselves. Silver ore, treated with chemicals in a stone arrastra for twelve hours, will not yield half so much silver as one Wheeler's pan in three hours, without any chemicals. A great advantage of this process, is the working of unroasted ore. Dry crushing, injurious to machinery, is not required ; the immediate working of the pulverized ore prevents the waste, and the silver, resulting from this process, is generally very fine (970 to 997). It is comparatively a cheap process. But, although improved, the result of this method cannot be considered yet quite satisfactory. In regard to chemicals, an important dis- covery can hardly be expected. Almost everything, between blue vitriol and tobacco or tea decoction, which reasonably or unreasonably permitted a supposition that it might effect the decomposition of the sulphurets, has PKOCESSES OP SILVER AND GOLD EXTRACTION. 69 been experimented on, and yet, there are no chemicals known by means of which more than fifty or sixty per cent, of the silver can be extracted. If a higher per centage is obtained, it is on account of the gold, or the prevalence of silverglance. But the decomposition of silver sulphurets does not depend on chemicals alone, as is demonstrated by Wheeler's pans, by which the silver can be extracted from ten to fifteen per cent, closer than in common pans. The result, however, depends very much on the quality of the ore, if the latter is not roasted. It must be observed that the above per centage has no reference to gold. Not all silver combinations are suitable for the wet process. Sufficient experiments, however, have not yet been made as to how the different silver ores behave in the pans, but it seems that the difficulty of decomposi- tion grows with the amount of sulphur in the ore, and especially with that of antimony. Arsenical combina- tions are more easily worked than antimonial. Pyrites of arsenic, iron, and copper, are not afibcted at all by chemicals. In cases where such pyrites are argentifer- ous, or antimonial conabinations are prevalent, the roast- ing process must be adopted. CHEMICALS USED IN DIFFERENT MILLS. Sec. 24. 1. Sulphate of Copper or Blue Vitriol. — It con- sists of 31*72 oxyd of copper, 32*14 sulphuric acid, 70 PROCESSES OF SILVER AND GOLD EXTRACTION. 36*14 water. It dissolves easily in water. In contact with iron, metallic copper is precipitated, and in the presence of quicksilver amalgamated. The sulphuric acid combines with iron oxyd to form sulphate of iron. If there are no sulphurets in the ore, or if in propor- tion too much blue vitriol is used, the amalgam retains almost all copper, which is precipitated with iron ; but in contact with silver sulphurets, under some circum- stances of galvanic chemical action, the copper is ex- pelled again from the amalgam, and enters probably into combination with sulphur. As soon as the blue vitriol is introduced, it may be observed that a great part of the bottom gets instantly amalgamated. The surface, to which the quicksilver adheres, is not iron, but copper, being precipitated by iron. This copper amalgam is removed by friction of the muller, and is taken up by the quicksilver ; and yet, the metal after retorting and melting shows only a trace of copper, if the right proportion of the blue vitriol and silver sulphurets was observed. In many cases the amalgam after retorting looks black, yielding a good deal of matt in melting. This matt appears tough, is dark grayish-blue in color, and contains silver in different proportions up to eighty per cent, and sometimes a considerable amount of copper. The silver bar, however, is over 970 fine (*). The matt, * The fineness must be always understood in relation to 1000 parts of the metal ; 970 fine means 970-1000 pure silver and gold, and 30-100 base metals. PROCESSES OF SILVER AND GOLD EXTRACTION. 71 when it has a yellowish color, contains mostly sulphide of iron. The blue vitriol must be used always in solution. In this state it is mixed sooner with the pulp, and kept in suspension, having thus better opportunity to act imme- diately. 2. Sulphate of Iron, Copperas, or Green Vitriol — It con- sists of 27*19 protoxyd of iron, 31-02 sulphuric acid, and 41*79 water. Exposed to the air, it turns into white powder. This salt is obtained by dissolving iron in diluted sulphuric acid. 3. Bisulphate of Soda. — It is composed of 63 sulphuric acid, 37 soda. This salt is obtained in the acid factories producing nitric acid, from Chile saltpetre. Its opera- tion in the pan is due to the fact that it readily parts with one portion of its sulphuric acid, leaving sulphate of soda. 4. Alum. — Potassic alum consists of 33*76 sulphuric acid ; 10*82 alumina (clay) ; 9*59 potassa ; 45*47 water. The sodic alum contains 34*94 of sulphuric acid. 5. Sulphuric Add, — This chemical seems to act partly by direct decomposition of silver sulphurets. Instantly after being introduced into the ore, it emits sulphuretted hydrogen. The silver may be oxydized by the oxygen which is disengaged by the parting hydrogen and con- verted by the acid into sulphate, or it may be set free in 72 PROCESSES OF SILVER AND GOLD EXTRACTION. metallic condition. In both cases it can be amalgamated without salt. But the salt, under the action of the sul- phuric acid, creates muriatic acid. This, however, may be limited. A considerable part of the sulphuric acid is engaged in dissolving iron, forming sulphate of iron, setting hydrogen gas free. There is always so much iron in the pan, from the wear of the stamps when the ore is crushed, and from the shoes and dies or bottoms of the pans, that the pan itself is very little eaten by the acid. 6. Common Salt (Chloride of Sodium). — Salt cannot operate directly on the sulphurets. It does not decom- pose, but it must be first decomposed by another agent, before any action, chiefly chlorination, can take place. Sal ammoniac, chloride of copper, or iron, may replace the salt for the purpose of chloridizing. But, as before mentioned, salt and sulphuric acid create, to some degree, muriatic acid, which acts also on sulphurets. 7. Chloride of Copper. — This salt is composed of 52- 5 chlorine, 47'4 copper. It is obtained by dissolving metallic copper in aqua rcgia. To this purpose muriatic acid, with some nitric, is introduced into a porcelain or enamelled vessel, and some copper pieces, best in shape of plates or sheets ; the acid will dissolve so much of them as to become saturated. Some heat hastens the solution, which assumes a beautiful emerald-green color. The chloride of copper seems to operate with better PKOCESSES OF SILVER AND GOLD EXTRACTION. 73 result than blue vitriol ; but, using this salt with com- mon salt, the amalgam obtained by this process appears often white and clean, crackling between the fingers like pure silver amalgam, still containing a great deal of sulphurets. After retorting, it appears blackish. and renders, by melting, a pure silver bar, but also a rich silver matt, sometimes as much as fifteen per cent, of the bullion, containing eighty per cent, of silver. Such a result is not always obtained, but under some circumstances, not yet sufficiently investigated. When experimented on in small quantities of about twenty- five pounds, and the calculation made also on the silver in the matt, the loss appears between fifteen and twenty per cent. In fact, however, the use of sulphate of cop- per and salt amounts exactly to the same thing, because the copper vitriol, especially if steam is introduced, is soon decomposed by the salt forming chloride of copper and sulphate of soda. 8. Siihchloride of Copper. — It consists of 36 chlorine, and 64 copper. It is obtained by boiling metallic cop- per in copper chloride, as prepared in the above de- scribed way. It changes the color from green into brown, but appears light green, when diluted with water, giving a precipitate. 9. Protochloride of Iron. — It consists of 66 chlorine, and 34 iron. It can be prepared in different ways. Small pieces of iron are dissolved in muriatic acid to 74 PROCESSES OP SILVER AND GOLD EXTRACTION. saturation, supported by a moderate heat. The iron is then removed, or the solution poured over in another porcelain dish, adding so much muriatic acid as was taken for the solution, and heated again, whereupon some nitric acid is added, but carefully, in very small quantities, till the boiling up ceases. It behaves simi- lar to chloride of copper. 10. Chloride of Iron, — It is obtained by boiling or heat- ing metallic iron in aqua regia or muriatic acid. It acts favorably on the silver sulphurets. QUANTITY OF CHEMICALS Per Ton of Ore, as used in different Mills. Sec. 25. In describing the quantity of chemicals, as used in treating silver ores, it may be observed that, according to the amount of sulphurets, also the quantity of chemicals must be proportionate. a. Chloride of copper (Sec. 24. 7) 13 pounds. Common salt 60 pounds. 6. Chloride of iron (Sec. 24. 10) 13 pounds. c. Sulphate of iron 1 pound. Sulphate of copper 8 pounds. Common salt 80 pounds. a, h. c, are calculated for ore containing from two hun- dred and fifty to five hundred ounces of silver in sul- phurets. All chemicals except salt are used in solution. PROCESSES OP SILVER AND GOLD EXTRACTION. 75 The salt is charged half an hour before the chemicals are put in. d. Sulphuric acid 3 pounds. Sulphate of copper 2 pounds. Salt 15 pounds. e. Sulphuric acid 2 Alum 2 pounds. Sulphate of copper 1}^ pounds. /. Sulphate of copper 1-2 pounds. Sulphate of iron 1*0 pound. Sal ammoniac 0'8 pound. • Common salt 2-0 pounds. g. Alum 13^ pounds. Sulphate of copper 1)4 pounds. Salt 40 pounds. h. Muriatic acid 30 ounces. Peroxyd of manganese 8 ounces. Blue vitriol 10 ounces. Green vitriol 10 ounces. i. Common salt 15 pounds. Nitric acid 1 to 2 pounds. Sulphate of iron 1 to 2 pounds. k. Common salt 25 pounds. Blue vitriol 2 pounds. Catechu 2 pounds. These, and a great number of other recipes, formerly honored with the title of " Processes," may not all prove to be the results of experience or scientific specula- tion, especially as to the proportion and quantity. It seems that there is a boundary beyond which the ex- 76 PROCESSES 6f silver and gold extraction. traction of silver can not be effected, whatever may be done in regard to quality or quantity of chemicals, or in regard to time, if the ore is not roasted. But, as a matter of course, some chemicals work much better than others. Some ores are better suited for the pan amal- gamation without roasting than others. The chemicals under a, ^, c, and d, will likely give the most satisfaction. AMALGAMATION IN PANS. Sec. 26. The pans, especially the muUers, have different shapes ; but, although the* results of operations depend considerably on the right form of mullers, effecting more or less perfect grinding, it will be sufficient to describe the principal arrangement of the common pans, and of the Wheeler pans, the latter differing entirely from all others except Yarney's, and lately Hepburn's. (For a description of the common pan, see Sec. 49.) The treatment of ores in iron pans is the most simple amongst all metallurgical operations. The muller is put in motion, the pan charged with some water, and the ore, in pulverized condition, introduced. A four-foot pan may take one hundred and fifty pounds ; a five-foot two hundred and fifty or three hundred, and a six-foot pan four hundred and fifty or five hundred pounds of ore. Wheeler's pan of four-foot, is charged with seven hundred and fifty pounds. The quantity of water is soon found out. The ore must be kept in a thickish condition. If there is too much water, there is not only PROCESSES OF SILVER AND GOLD EXTRACTION. 77 more friction, by the settling of the sand, but also the chemicals are more diluted, and the quicksilver is in one mass on the bottom. But if, on the other hand, the pulp is too thick, the particles of ore cannot change their places quick enough, dead masses will occur, and the amalgamation is delayed. When the pan is thus charged with ore, the quicksil- ver is next introduced, in quantity of thirty-five, sixty, or eighty pounds, according to the sizes of the pans above mentioned. If salt is used, it may be added immediately after the quicksilver, and half an hour's time allowed for dissolving, l3efore other chemicals are charged. The sulphuric acid must be diluted with about four parts of water before being introduced. The pulp of ore must be kept as much as possible in a uniform condition in regard to dilution and heat, and no boiling allowed. The right speed of the muller is between ten and fifteen revolutions per minute. A quicker motion is not injurious to amalgamation, unless there is too much water in the pan, or the mullers are not set right, and throw the ore towards the sides. The temperature seems to answer best when below boiling heat, but still hot enough to be inconvenient to hold the finger longer in the pulp than just to try its condition. Too much heat is injurious, especially when sulphate or chloride of cop- per is used, causing a larger loss in quicksilver, and also in amalgam, which, assuming a black, rag-like appear- ance, does not unite easily with the other amalgam, but swims on the quicksilver. It parts in minute particles, 78 PROCESSES OF SILVER AND GOLD EXTRACTION. and is liable to escape in discharging the tailings. Such black amalgam rubbed in a porcelain mortar, gives a great deal of black powder, consisting of some silver sul- phurets and sulphide of copper, resulting from sulphate of copper, probably by action on sulphurets of silver. Treating the ore cold, using sulphuric acid and salt, the result, in regard to the quantity of amalgam, does not differ much ; but after retorting and melting, the warm amalgamation gains from ^ve to seven per cent, on the value of the bar. Chloride of copper and chloride of iron allow cold amalgamation, but warm amalgama- tion may be better for sorhe qualities of ore. After a run of three or four hours, during which time the ore is ground very fine, water is introduced, and the pulp diluted, so that all quicksilver and amalgam can join in one mass on the bottom, which may require half an hour's time. There are generally three discharge holes to each pan. The lowest one serves for discharg- ing quicksilver and is level with the bottom or even below it, communicating with a groove, which runs to the centerpiece. The uppermost hole is opened and the tailings discharged, under a constant stream of water, into the pan. After one-quarter of an hour the lower plug is removed, continuing the discharge for another quarter of an hour. Both holes are plugged up again, the pan charged with ore and treated as before. The quicksilver may be taken out once or twice a week or oftener according to the richness of the ore. In discharging the tailings, some amalgam is always PROCESSES OF SILVER AND GOLD EXTRACTION. 79 carried out, especially at the end of the operation, when the coarser sand is washed off. To prevent the loss of this amalgam, agitators are applied. They consist of tubs, two or three feet in diameter, and ten or twelve inches high, with a vertical shaft, on which four arms are fixed, having vertical stirrers as represented in Fig. 17. But it is evident that one agitator for many pans, as is the general usage, is not sufficient ; it is only a repetition of the first washing. The greatest part of the amalgam goes out again. These agitators differ very much in construction and size, none, however, offer a satisfactory result. The most proper and time-saving way, in dis- charging the pans where a constant stream of clear water can be obtained, is the use of one or two general agitators, six or eight feet in diameter, in which the' tailings are discharged, leaving the quicksilver with a part of the ore always in the pan. The tailings are not diluted, unless the stuff is too thick. In this case some water may be introduced into the pan before discharg- ing, but not so much as to allow a separation of slime and fine sand. From the agitator the tailings run off in a small stream (three-eighths of an inch thick) into a five- foot pan in which a continual stream (an inch in diameter) of clear water flows, as described in Sec. 27. This strong dilution under a constant stream permits a very close separation of amalgam which unites with the quicksilver in the pan. Such pans are of better service, when the continual discharge is arranged in the centre like Knox's pans, because the motion of the muUer (fifteen 80 PROCESSES OF SILVER AND GOLD EXTRACTION. to eighteen revolutions per minute) creates a strong current on the periphery. When the tailings are discharged, there is always a good deal of sand left in the pan, partly to save time, but chiefly on account of quicksilver and amalgam, of which ai the end of the operation, more is carried out in proportion. Whenever the quicksilver gets thick by the amalgam or at the close of the week, the lowest hole is opened, after the tailings have been removed by the usual dis- charge. The quicksilver runs into buckets, but some of it remains in the pan and must be taken out with the scoop. By means of a piece of blanket and clear water, the quicksilver is washed perfectly clean, and poured into a filter, of sugar-loaf shape (see Fig. 18), of strong canvas or duck. The quicksilver runs through the cloth, leaving the amalgam in the filter, which generally must be pressed over again through a cloth by hand or a press. This amalgam must be separated, the metal from the quicksilver, by retorting (see Sec. 42). All the sand, sulphurets, and amalgam particles from the last discharge and cleaning of the quicksilver, must come back into the pan with the next charge. If, how- ever, the sulphurets and metallic iron from the wear of the shoes accumulate too much, forming a heavy stuf^ which generally retains a great deal of amalgam, it is better to treat it separately in a pan with addition of one, or one and a half per cent, of sulphuric acid, and to save all these tailings, which contain such silver com- PROCESSES OF SILVER AND GOLD EXTRACTION. 81 binatipns, as resist decomposition in pans. These tail- ingSj if accumulated to several tons, must be roasted with four or ^Ye per cent, of salt, and treated in pans without chemicals. AMALGAMATION IN WHEELER'S PANS. Sec. 27. The amalgamation in Wheeler's pans (see Sec. 50, Figs. 24, 25) does not differ much from that of others, but the peculiarity of discharging tailings and quicksilver every time, at once, which is based on the construction and motion of the muller, requires attention to some points, which partly influence the good results of the amalgamation. A quick and fine grinding at the speed of fifty to sixty revolutions depends also on the quality of the shoes and dies. Soft shoes will stand according to the quality of ore thirty to forty days, while hard ones of white iron, will last ten to fifteen days longer, doing at the same time better grinding. The only inconvenience of the hard shoes and dies con- sists in the brittleness of the iron. On this account they must be removed in time, so that not more than three- fourths of an inch are worn off, leaving one-fourth of an inch in thickness. If this be neglected, and the shoes become thinner, a trifling foreign hard matter may effect the break of shoes or dies, and cause a break in the yoke or something else. The advantage of a quick and prompt grinding will be found indirectly in saving silver ore, because it allows 6 82 PROCESSES OP SILVER AND GOLD EXTRACTION. the use of coarser ore in the pan. It is a known, fact that the j&ner the ore is crushed, especially wet, the more silver ore will be turned into slime, of which a great deal will be carried out by the water (*). Crush- ing dry, the loss in dust will increase with the fineness of the sieves. It is therefore advisable to crush coarse and to grind fine. Using common pans, it is preferable to pulverize the ore as fine as possible in order to save time and the shoes of the pan, especially the bottom. Wheeler's pan performs the pulverization much quicker and cheaper than the battery does, at a certain size of grain. The guide-blades must be kept always close to the muUer, in order to prevent ore and quicksilver from fol- lowing the motion of the muller, thus forcing the mass to the centre and under the muller. The present construc- tion is such, that the muller cannot follow the wear of the shoes for more than about half an inch. The grind- ing becomes imperfect. In this case, which may happen once in a week, the key and screw which fasten the yoke to the driving shaft, must be loosened, and the shaft raised half an inch, paying attention that the mul- ler, after all is fixed, can be raised above the dies at least one-eighth of an inch. When this is done, the guide- ^ That the slime is very difficult to work in pans to advantage is known to every millman. On this account and because the slime is often richer than the coarser sediment, especially if brittle|silver sulphurets are present, the coarse crushing is preferable. It was even observed that more quicksilver scum is formed in treating slime than in working coarser material. PROCESSES OF SILVER AND GOLD EXTRACTION. 83 blades have to be lowered by the screw on top of the shaft, so as to have it again close to the muller. If hard shoes are used, this adjusting may not be required for a longer time. It takes, however, only a few minutes. The consistence of the pulp must be thickish, but still so, that a lively motion on the sides and between the guide-blades is perceptible. If the motion be too slack, some water must be added. In regard to amalgamation, a little more or less water is not so important as it is for the separation of amalgam in the agitators. Steam must be introduced three or four inches above the muller, for if too close to the bottom, the pipes re- quire frequent cleaning. The temperature can be kept near to the boiling point. There is no necessity of a steam chamber. The direct use of steam in the pulp does not interfere with the required consistency, but allows a considerable saving of fuel. Eight Wheeler's pans, if the boiler is proportionate, require half a cord of wood in twenty-four hours. In regard to chemicals, after several months' run at Col. Kaymond's mill on Carson River, experience proved that the use of chemicals is entirely useless in treating Ophir ore. I made comparative runs for many weeks, and found that experience confirmed that a better result was obtained without any chemicals whatever. The use of them was therefore abandoned at the Dayton mills. It is, however, a fact, that in treating silver ore in com- mon pans, the use of chemicals always gives a better result. It can not be supposed, therefore, that the 84 PROCESSES OF SILVER AND GOLD EXTRACTION. chemicals prevent a perfect amalgamation in Wheeler's pans, but the amalgam is in a different condition, more liable to be ground into a black floating powder. This is also the reason that it seems as if the quicksilver v^ere protected by the chemicals against being ground to scum, because the black powdered quicksilver is less visible. The loss of quicksilver could not have been ascer- tained yet, as it is not advisable to take out the dies on account of cleaning. As a matter of course, the quicksilver must be turned into scum to some degree, but considering the better yield and expelling of chemi- cals, these pans can afford to lose some quicksilver. In the course of manipulation, however, a great deal of this scum is regained. It is unquestionable that the iron under favorable circumstances decomposes the silver sulphurets just as well or better than the best chemicals ; but if, on ac- count of improper arrangement of grinding, the action of iron on sulphurets is effected in a limited degree, the chemicals will then assist. It happens often that in cleaning the agitator, when no chemicals are applied in the pans, a strong smell of sulphuretted hydrogen is ob- served, which arises from the decomposition of sulphur- ets. In washing the tailings, after the iron has been extracted with the magnet, blue sulphurets can hardly be discovered. The difficulty in stating the loss of sil- ver lies partly in the inconvenience of taking out the dies, in order to effect a perfect cleaning, as it is almost PROCESSES OF SILVER AND GOLD EXTRACTION. 85 impossible to place the dies back again as level as be- fore, but the difficulty is chieiBiy found in the attempt to get a reliable average sample for the assay, especially if wet crushing is going on. The sulphurets and gold are always concentrated in the vats, where the ore falls in from the battery, and every inch in it shows a different amount of silver. The next vat shows the same differ- ence, having, besides, already so much slime that a mix- ing for the purpose of having the metal equally distrib- uted in the mass, is impossible without drying. The calculations on the superiority of Wheeler's pans, at least to the present date, are derived from the com- parative yield and the appearance of the tailings, ac- cording to which these pans seem to yield at least ten per cent, more than the best common pans. To find the real loss of silver and quicksilver, it would require dry ore, each charge well mixed, sampled, and weighed, and one pan and agitator exclusively for this purpose. This could not have been performed yet. A great difference as to the result will be found in a comparative working of the finest sediment (the slime) which glides between the mullers of the common pans almost motionless, as if it were one mass, while in Wheeler's pans the slime is forced under the muUer with the same speed as the ore. When the muller is in motion, so much water is intro- duced that it plays over the rim of the muller ; then seven hundred and fifty pounds of wet ore, or six hundred of dry, are charged, and if it is perceived 86 PKOCESSES OF SILVER AND GOLD EXTRACTION. that the motion of the ore is not lively enough, more water is added. The pulp should not cover the guide- blades. After this, one hundred pounds of quick- silver are poured into each pan. The amalgamation and grinding continue for three hours. A longer amal- gamation does not appear to give a better result. The plug of the hole which is nearest to the bottom is taken out, and the whole mass discharged. The pan is charged immediately as before. The charge and dis- charge can be effected in five minutes. Of the hundred pounds of quicksilver, which were introduced, only fifty or sixty pounds were discharged with the ore ; the bal- ance remains between the dies. All the subsequent charges take fifty pounds. Several hundred pounds of quicksilver must be kept at hand, to replace such as re- mains with the amalgam in the agitator. Wheeler's agitator (see Sec. 51), being eight feet in diameter, has such a swift motion on the periphery, that, treating the tailings in the usual way, by diluting with clear water, a great deal of amalgam is carried out. The discharge from the upper hole, where the mud and very fine sand with much water flows out, is free of amalgam, but after all the mud has been removed and the lower hole opened, the floating amalgam, which cannot reach the bottom on account of the sand (which settled in consequence of the dilution), escapes with the tail- ings. The loss increases with the speed and also with the coarseness of the tailings. If the speed is reduced, the motion near the centre will be too slow. PROCESSES OF SILVER AND GOLD EXTRACTION. 87 After different experiments I adopted the following method, by which the above difficulties are avoided: Three inches above the bottom (see Fig. 23) there is a three-eighth-inch pipe, through which the tailings flow out in a thin stream continually, so that in the course of three hours, if three pans are discharged into one agi- tator, the tailings are down to the level of the pipe. The quicksilver and amalgam have time enough to sink by degrees to the bottom, and those particles which escape through the three-eighth-inch pipe are also saved. No water is needed in the agitator, but the pulp must have the proper consistency when discharged. The amalgam accumulates round the centre-bowl. It will be found that this amalgam, and that from the bowl, is richer in gold than that further off, while the fine amal- gam carried out through the pipe contains only one-half of the amount of gold which is found in the average of the agitator amalgam. It occurs often that a great part of the amalgam deposits in the amalgamating pans, sometimes accumulating on the sides, and accidentally on the muUer, which, if perceived at the discharge, must be taken out, else it might accumulate to fifty pounds, or more, pressing the muller on one side, and thus causing a very unequal wear of the shoes. At other times, no deposit of amalgam takes place in the pans, or one pan may retain as much as one hundred pounds, when another has none at all. It seems that this appear- ance depends on a variable electric condition of the iron. 88 PROCESSES OF SILVER AND GOLD EXTRACTION. When the pans are discharged, the quicksilver runs on the inclined bottom to the centre, joining the quick- silver in the bowl, coming out by the siphon, whence it is taken and returned to the pans, fifty pounds to each charge. The amalgam accumulates also in the bowl, preventing finally the passage through the siphon. In this case the agitator must be cleaned. To this purpose, when the last discharge is effected, the lowest one-half inch pipe is opened, and the tailings, when level with the half-inch pipe, are discharged by the hole on the inclined bottom near the bowl. The tailings from this last discharge are led into a separate box, whence it can be transferred immediately into the other agitator, or if only one, back into Wheeler's pan. The agitator is then stopped, the black stuff from the bottom, which is very rich in fine amalgam, removed, the quicksilver strained, and the bowl filled again with quicksilver after the siphon was also cleaned. All this can be done in three hours, so that the agitator is ready for the subsequent discharge of the pans. The shoes of the agitator must be run suspended about one-eighth of an inch above the bottom, in order to allow the settling of sulphurets and amalgam. If the ore contains a great deal of sulphurets of such a nature that a part of them do not yield up their silver without roasting, the agitator may be used as a concen- trator at the same time, by screwing up the shaft, on the arms of which the shoes are fastened, for one-eighth of an inch or more every day. PROCESSES OP SILVER AND GOLD EXTRACTION. 89 All the black stuff from the agitator must be worked over in a common five or six-foot pan without the addi- tion of quicksilver, and the tailings saved to be roasted. Each agitator must have one four or five-foot pan for the reception of the tailings, coming out of the one- eighth inch pipe. The discharge-hole of this pan, about three inches above the bottom, is always open, so that the tailings have only a passage through the pan, the muller of which may make twelve or fifteen revolutions. The fine amalgam, and especially the quicksilver scum, would escape from this pan to the greatest part, if not diluted. A continual stream of clear water, therefore, through a pipe an inch or three-quarters of an inch in diameter, is indispensable. Twenty or thirty pounds of quicksilver are introduced into the pan in order to col- lect the amalgam. In some mills Wheeler's pans are discharged, using only the upper hole, retaining thus the most of the quicksilver. This mode saves the trouble of handling the fifty pounds required for each charge ; but the amal- gam, accumulating in the quicksilver, is too much ex- posed to grinding, causing thus a richer quicksilver scum, of which a considerable part is lost. Wheeler's pans have been improved lately by Mr. Hepburn. The improvement seems to be important. Without having a larger diameter, the conical bottom offers a larger grinding surface. The whole arrange- ment is simplified. On account of the inclined bottom, no guide-blades are required. One of these pans is 90 PROCESSES OF SILVER AND GOLD EXTRACTION. charged with 1,000 pounds, so that four tons of ore may be worked in twenty-four hours by one pan, requiring about two and one-half horse-power each. In regard to the amalgamation, there will be probably the same result as obtained by Wheeler's. All that was said in relation to the manipulation with Wheeler's pans can be applied also to Hepburn's. II. ROASTING PROCESS. Sec. 28. The roasting of silver ore, for the purpose of converting all the silver into a chloride, no matter in what condition it may occur, either in the metallic state, or in a sulphuret, arsenide or antimonial silver, in order to make it fit for easy decomposition and subsequent immediate amalgamation, has been adopted in several extensive works of Nevada Territory. There may be some kinds of silver ore, which under certain circum- stances can be treated raw in pans very advantageously, even if there be a greater loss of silver. Nevertheless, the high importance of roasting can not be overlooked, this being in many instances the surest and the only way to beneficiate such silver combinations as refuse to deliver the silver by amalgamation without roasting. There is no silver ore which can not be treated success- fully by means of roasting. The patio or pan amalgama- tion, working so-called " rebellious " ores, must resort to PKOCESSES OF SILVER AND GOLD EXTRACTION. 91 roasting, or else exclude such ores from the manipula- tion. In regard to the importance of roasting, which in course of time may be more appreciated, a thorough description of this process appears necessary. More- over, it is entirely impossible to carry on a rational and correct roasting according to the quality of ore, or in regard to a special object, if the chemical actions during the roasting are not regarded or understood. It is in- dispensable to get acquainted with the theory of this process, of which the most important actions will be considered. Three agents are active in roasting : the oxygen of the air, the hydrogen of the water-vapors of the air and fuel, and the chlorine of the salt. (By the term "roast- ing" I here always mean " chlorination roasting.") But as the decomposition of salt by heat alone is very im- perfect, sulphur is another important agent, the pres- ence of which is by all means required. The decompo- sition of salt is effected by sulphuric acid in the form of vapor, and by sulphates, produced by the oxygen of the air and the sulphur of the sulphurets in the ore. If, therefore, the silver were combined with antimony or arsenic, with but little or no sulphurets, the chlorination would be very imperfect. In this case an addition of two or three per cent of calcined green vitriol (sulphate of iron) is required. The principal object in roasting must be first, the production of sulphates. The iron pyrites and other 92 PROCESSES OP SIJ.VER AND GOLD EXTRACTION. sulphiirets, when red hot and acted upon by the oxygen of the air, change into sulphates by oxydation of the sulphur to sulphuric acid. The sulphuric acid can not unite with the metal of the sulphuret under decompo- sition, unless it becomes an oxyd. One part of the sul- phuric acid, therefore, transfers oxygen to the metal, being thus reduced to sulphurous acid, while the metal becomes an oxyd and combines with another part of sulphuric acid to a sulphate. During this process, which is performed at a low heat, the salt is almost entirely indifferent, so that it is imma- terial whether it is charged at the same time with the ore, or two hours later. As soon as the sulphates are formed, and no odor of sulphurous acid observed, the heat must be increased. The decomposition of salt begins, being performed in two different ways : 1. The sulphate of iron principally, and other sul- phates, emit sulphuric acid in vapor, which, in contact with saltj forms sulphate of soda, setting free the chlo- rine in a gaseous form. One part of the oxygen of the sulphuric acid is transferred to the sodium of the salt, oxydizing it to soda, which, uniting with another part of sulphuric acid, forms sulphate of soda, while the chlo- rine absconds, combining with free metals in chlorides when in contact with them, and decomposes sulphurets in such a way, that one part of the chlorine combines with the sulphur in volatile chloride of sulphur, while PROCESSES OF SILVER AND GOLD EXTRACTION. 93 another part unites with the freed metal of the sulphuret in a chloride. 2. The other way of decomposition of salt differs in its result, not emitting chlorine gas, but forming chlo- rides during the act of decomposition. The sulphate in contact with salt enters into an exchange of compounds. The sulphuric acid combines with the soda of the salt to sulphate of soda, and the chlorine with the metal of the sulphate to a chloride, the oxygen of the metaloxyd oxydizing the sodium. The chlorination of metals ac- cordingly is performed by the direct action of chlorine gas on the metals and sulphurets, and by contact of salt with sulphates. During this process, besides the chlorine gas, hydro- chloric acid in vapor is created. The hydrochloric or muriatic acid arises partly by the action of water-ab- sorbing sulphuric acid on the salt, whereby the sodium is oxydized by the oxygen of the water, while its hy- drogen unites with the chlorine to form hydrochloric acid in the form of gas. The muriatic acid is also formed by the contact of chlorine gas with compounds of hy- drogen, for instance carburetted hydrogen. The chlo- rine, by its affinity for hydrogen, decomposes the com- pounds of the latter elements. It is also produced by the contact of steam with volatile chlorides, as chlorides of antimony, zinc, lead or copper, etc., reducing the metals to oxyds, or the silver to a metallic state, which, however, in contact with hydrochloric acid or chlorine, is turned again into a chloride. 94 PROCESSES OF SILVER AND GOLD EXTRACTION. The circumstances, accordingly, under which the for- mation of hydrochloric or muriatic acid takes place, are various, but always when water-vapors enter the porous mass of ore. Behayior op Chlorine Gas. Sec. 29. It has been mentioned already that chlorine gas acts directly on sulphurets. Under the action of chlorine gas the following changes occur : a. The Iron (with sulphur or arsenic) changes into protochloride of iron (Fe CI), but, exposed to the air, into sesquichloride (Fe^ CP). This chloride becomes volatile and is sublimable. If in this condition it meets gaseous products* of burning fuel containing vapors of water, or hot air containing steam, a mutual decompo- sition takes place, resulting in oxyd of iron and gaseous hydrochloric acid. h. Manganese (combined with sulphur) changes into protochloride of manganese (Mn CI). It is not volatile. Water-vapors decompose it into sesquioxyd and gaseous muriatic acid. c. Zinc (combined with sulphur) changes into proto- chloride of zinc (Zn CI). It melts before it is red hot, and becomes volatile when red hot. In contact with steam, it forms oxyd of zinc and hydrochloric acid. d. Lead (in combination with sulphur) changes very PROCESSES OF SILVER AND GOLD EXTRACTION. 95 slowly into chloride of lead (Pb CI). It melts easily. In contact with red hot air it evaporates partly, while another part, evolving chlorine, changes into a com- pound of oxyd of lead and chlorid of lead, which is not volatile. e. Copper (combined with sulphur) changes partly into sesquichloride of copper (Cu^ CI), partly into proto- chloride (Cu CI), according to the action of more or less chlorine at a higher or lower temperature. Both com- binations are inclined to evaporate. When red hot, the chloride changes into sesquichloride, emitting half of its chlorine, by which sulphurets are decomposed. Under the action of steam a mutual decomposition takes place, creating gaseous hydrochloric acid and oxyd, or sequi- oxyd of copper, the latter being converted into oxyd by contact with the air. /. Silver (native and in combination with sulphur) changes slowly into chloride of silver (Ag CI.) It be- comes volatile only at a high temperature. g. Gold (free or combined with arsenic, antimony, or tellurium) changes when in a very fine pulverized state, at a low heat, into terchloride of gold (Au CP). It emits two parts of chlorine, below red heat, forming chloride of gold (Au CI). Red heat changes it into metallic gold. h Arsenic (with other metals and sulphur) is trans- 96 PROCESSES OF SILVER AND GOLD EXTRACTION. formed into a very volatile terchloride of arsenic (As CP). i. Antimony/ (with other metals or sulphur) changes into terchloride of antimony (Sb CP). It is like the terchloride of arsenic, very volatile. Behavior of Hydrochloric Acid. Sec. 30. The gaseous hydrochloric acid in contact with metallic silver unites with it at a high temperature to form chloride of silver. The hydrogen is set free. It behaves in like manner with the sulphurets and arsenides, of which the most are decomposed in such a way that chlorides of metals are formed, while the sul- phur or arsenic combines with the hydrogen. Behavior of Salt. Sec. 31. When the roasting of ore has advanced so far that considerable quantities of chlorides, which are partly volatile, are formed, under the action of chlorine, and hydrochloric acid in contact with salt and sulphates, some of the salt, not previously decomposed, evaporates. These salt vapors, and those of the volatile chlorides transfer chlorine to undecomposed sulphurets or arsen- ides, or to already present sulphates, arsenates, or anti- monates, or to free oxyds. Chlorides, which are disposed to transfer chlorine to such metals in combination with sulphur or arsenic as possess more affinity to chlorine, than themselves, are, besides salt, protochloride of iron, PROCESSES OP SILVER AKB GOLD EXTRACTION. 97 protochloride of copper, also the chlorides of zinc, lead, and cobalt. a. Metallic Silver in contact with salt changes partly into chloride of silver, probably in such a way that the silver decomposes the salt in the same proportion as the sodium takes up carbonic acid from the gaseous pro- ducts of burning fuel. h. Sulphurets in contact with salt are not decomposed directly. The sulphurous acid, however, in contact with the air, creates sulphuric acid, which acts on the sodium, freeing thus the chlorine, by which the formation of chlorides in the not yet decomposed sulphurets are effected. c. Arsenides are not changed by the salt. They oxydize, evolve arsenous acid, and are converted into arsenates. Only a very slight decomposition of salt takes place. The presence of sulphates, however, vola- tile chlorine, or gaseous hydrochloric acid, effects the chlorination. d. Oxyds of Metals, with the exception of the oxyd of silver, are changed very little or not at all by salt. The oxyd of silver readily giving up its oxygen, changes perfectly into chloride of silver, if sufficient salt be present. A small portion of the oxyds of copper and lead are changed into chlorides. 7 98 PROCESSES OF SILVER AND GOLD EXTRACTION. e. Sulphates, — Sulphates decompose the salt by mutual exchange of compounds. The sulphate of lead changes into chloride of lead, which, evaporating in contact with air, emits one part of its chlorine, being reduced to a combination of chloride and oxyd of lead. The sul- phate of copper changes into chloride of copper. This becoming volatile, evolves chlorine gas, and forms sesqui- chloride of copper, which is less volatile. Sec. 32. The ores intended for roasting must be examined not only in regard to the quality and quan- tity of sulphurets, but also in regard to the earthy mat- ters accompanying the ore. It is not immaterial whether the ore contains carbonate of lime or quartz. If there is a great deal of lime in the ore, it absorbs sulphuric acid, forming sulphate of lime, remaining in this con- dition through the whole process, without being decom- posed. On this account calcareous ore requires so much more sulphurets or sulphate of iron as is necessary to change all the lime into sulphate. Talcose ores behave like the calcareous. Silicia or quartz, if abundant, in presence of steam decomposes some of the salt, when red hot, forming silicate of soda and hydrochloric acid, the importance of which has been mentioned (see Sec. 30). This behavior of these earths shows that it is disadvantageous to submit pure calcareous or talcose ores to roasting, and that in such a case quartzose ore must be added, if possible. The quantity of sulphurets in the ore is important, a PROCESSES OP SILVER AND GOLD EXTRACTION. 99 certain amount of it being required to decompose so much salt as is necessary for chlorination. In Freiberg (Germany), it was the rule to subject only that ore to roasting which contained enough sulphurets to give twenty-five or thirty per cent, of matt (sulphide of iron), when assayed for that purpose. If less matt was ob- tained, the ore had to be mixed with other ore, or so much iron pyrites was added that the required quantity of sulphurets was obtained. The second class ore of the Ophir and Mexican claims in the Comstock lode, con- sisting of pure decomposed quartz, contains silver sul- phurets, with a small proportion of iron pyrites, yielding from six to eight per cent, of matt. The roasting with salt, however, gives a satisfactory result, which must be attributed chiefly to the pure quartzose condition of the ore. If the ore contains an abundance of sulphurets, the roasting must be performed without salt, for about two hours, till the greatest part of the sulphur is driven off, otherwise it would bake, and cause an imperfect roast- ing. The quantity of sulphurets has a great influence on the result of roasting. Ore like that of the Ophir or Mexican mines, containing silverglance, polybasite, brit- tle silver ore, native silver and gold, some iron, and but little copper pyrites, will give a good result by roasting, even when less attention is paid to the time and dili- gent stirring, than for instance with the so-called " base metal ore," which abounds in copper pyrites, zinc-blend. 100 PROCESSES OF SILVER AND GOLD EXTRACTION. sulphuret of lead, etc. The presence of base metals causes a higher loss in silver. The chloride of silver is not volatile, except at a high temperature (Sec. 29,/). But it has been observed that, in the presence of base metal chlorides, the chloride of silver volatilizes also. 4^he increased heat increases the volatilization, but de- composes the base metal chlorides. By keeping a low heat, the loss of silver is less if the zinc-blend is not argentiferous, the latter requiring a higher heat to effect decomposition. But in roasting at a low heat, the base metal chlorides remain in the ore, and cause more loss of quicksilver in the subsequent amalgamation, and require more metallic iron in the barrels ; besides, the bullion contains a great deal of base metals. In treat- ing such ore in the roasting furnace, the application of steam is advantageous, creating hydrochloric acid by the decomposition of chlorides, at the same time becom- ing a decomposing agent for the sulphurets. The hydrogen of the steam decomposes also the chloride of silver, which, upon being reduced to a metallic condition, by its affinity for chlorine, in turn decomposes the hydro- chloric acid. The silver may thus change repeatedly from metallic condition to the chloride, while the base metal chlorides are reduced to oxyds, and in that state do not interfere with the amalgamation. PROCESSES OF SILVER AND GOLD EXTRACTION. 101 A. ROASTING OF SILVER ORES For the Barrel and Veatch's Steam Amalgamator. Sec. 33. The silver ore for the modes of amalgama- tion without friction, as shown by long experience, must be free from metallic gold, or it must be extracted before the ore is subjected to roasting, as is done in the " Silver State Reduction Works," on Carson River. After roasting, the gold is not like silver, in a soluble and easily decomposable condition, but in a metallic state, generally coated with some oxyd, especially if sul- phuret of lead occurs in the ore. This renders the amalgamation of gold much more difficult. Also, metal- lic silver, when roasting is performed without salt, using charcoal and saw-dust for the purpose of converting the silver-combinations of the ore into the metallic state, will be imperfectly amalgamated in the barrels. The ore does not require to be very fine for the pur- pose of roasting, but it must be fine on account of amal- gamation. Vertical wirecloth sieves at the battery, with nine hundred holes to the square inch, if dry crush- ing is in use, or sixteen hundred holes when wet crush- ing is preferred, on account of extracting gold, will answer the purpose. The pulverized dry ore is spread on a platform and mixed with from six to twelve per cent, of salt, accord- ing to the richness and quality of the ore. It seems, however, that six per cent., as used in one of the 102 PROCESSES OP SILVER AND GOLD EXTRACTION. Washoe valley works for ore, assaying from seventy-five to one hundred dollars per ton, may not be sufficient, still the result is considered quite satisfactory. Very rich ore may require fifteen or twenty per cent, of salt. In dry crushing, the salt may be mixed with the ore in the right proportion before going to the battery. This mode of mixing is the most perfect and most con- venient. The Ked Hot Furnace (see Sec. 53, Figs. 29, 30) is charged with eight hundred or one thousand pounds of ore, and, by means of iron hoes spread over the bottom of the furnace. If the ore is moist, or rich in sulphurets, the heat is kept low. The workman commences to stir the ore with the hoe or an iron rake, back and forward across the hearth, moving slowly from the bridge towards the flue and back. When the ore is perfectly dry, appearing very movable, almost flowing, the heat must be increased. Continual stirring is required, in order to expose new ore on the surface, thus facilitating the oxydation. If there is a great amount of sulphurets in the ore, the sulphur commences to burn when the ore gets dark red hot, evolving so much heat that the firing must be suspended for about one hour and a half, but the stirring continues, touching all spots and corners of the hearth. After a great part of the sulphur is burnt ofi^, the temperature will sink, and the ore appear dark. The temperature must be raised again by firing. The formation of sulphates is going on, disengaging a large quantity of sulphurous gas. The ore at the bridge PROCESSES OF SILVER AND GOLD EXTRACTION. 103 will be heated much more than on the opposite side. The roaster must take the trouble of changing the ore from the bridge to the flue, and the cooler ore to the bridge, several times. If lumps are perceived in the ore, they must be beaten to powder by an iron hammer- like instrument with a long handle. After three or four hours roasting, according to the amount of sulphurets, no sulphurous acid is perceptible. The temperature must be increased to a light red heat. The formation of sulphates, arsenates, antimonates, and oxyds is almost completed. The chlorination has commenced, and as the increased heat is rapidly going on, white fumes arise, and the gases and vapors evolved have a sharp, acrid odor, consisting of some sulphurous acid, chlorine gas, hydrochloric gas, chloride of sulphur, chlorides of iron and copper, etc. The ore assumes a spongy or woolly condition, increas- ing in volume. In the presence of sufficient copper the flame is colored blue by the chloride of copper. After one hour's roasting, at an increased heat and with diligent stirring, the chlorination is finished. The ore is discharged by the back door or the discharge hole in the bottom, although the fumes and gases are still being evolved. If there is a great deal of copper and other base metals in the ore, the roasting may require more time in order to decompose the chloride of copper and sul- phates, the presence of which in the amalgamating barrels or tubs destroys not only more iron, but increases 104 PROCESSES OF SILVER AND GOLD EXTRACTION. the heat too much, causing an injurious division of the quicksilver into small particles and scum. The base metal chlorides, reduced by the iron, enter into the amalgam and make it impure. The time for decompo- sition must be prolonged in the barrels before the quick- silver is introduced, otherwise a destruction of mercury would follow. The decomposition of the base metal chlorides can be effected in the furnace either by carbonate of lime or by heat, the latter requiring more time. The carbonate of lime in pulverized condition decomposes* the chlorides and sulphates, bub not the chloride of silver. The addi- tion of lime rock, after the heat has been increased, must be made gradually in regard to the quantity, com- mencing with two per cent., till the required amount for a certain class of ore is found. It may require as much as six per cent. The first portion of lime is introduced by a scoop, spreading it over the ore and well mixed. A small portion of the ore is then taken in a porce- lain cup or glass, and mixed with some water by means of a piece of iron with a clean metallic surface. If the iron is coated red with copper, or if the water is bluish, some more lime is required. After the lime is charged, half an hour must be allowed for reaction. When another test does not show the above signs of soluble copper, or only in a slight degree, the charge can be taken out. In the absence of lime, wood ashes may be used. If too much lime or ashes is used, the amalgama- tion is injured, and a greater loss of silver will be the PROCESSES OF SILVER AND GOLD EXTRACTION. 105 result. The chloride of copper will also be decompased by longer roasting and increased heat, and samples should be taken in the same way as before to ascertain the decomposition of those chlorides. One furnace requires two men by day and two men by night in order to keep up continual stirring, firing, charging, and so forth. The Central mill at Virginia City employs two men at a time, attending three fur- naces. The stirring is performed at intervals ; roasting six or seven hours, in treating rich ore. Other works having poorer ore finish the roasting in four and a half and five hours. The ore after having been roasted contains from ^Ye to fifteen per cent, of lumps, which are not roasted thoroughly, and contain some undecomposed sulphurets, sulphates, and chlorides. These lumps are separated from the fine, well-roasted ore, pulverized, and with the addition of two or three per cent, of salt are roasted again for two hours. The ore is sifted through two sieves. One has 64, the other 2,500 to 3,600 holes to the square inch. The lumps which do not pass the coarse sieve are pulverized under stamps and reroasted. The ore which passes the first sieve and stops at the second is ground fine and delivered with the fine sifted ore for amalgamation. In the Central Mill there is no grinding after roast- ing. The ore is pulverized under a set of small stamps and sifted while the coarser particles are constantly elevated to the battery. 106 PROCESSES OF SILVER AND GOLD EXTRACTION. B. ROASTING OF SILVER ORES For Pan Amalgamation. Sec. 34. The roasting of ore for the purpose of amal- gamating in iron pans, differs from the already described procedure, in so far as a perfect chlorination of all the silver in the ore is not absolutely required. Consoli- dated fragments or lumps formed during the roasting are not injurious. The extraction of gold before roast- ing is not necessary. The sulphates, remaining in the lumps, and such as were not changed into chlorides by improper roasting, are partly decomposed in the pan by the iron, but most of them are converted into chlorides by the salt, which always remains in small quantities in the ore after roast- ing. This salt dissolves in the pan and changes the sul- phates; which are also soluble, into chlorides, they being decomposed by the iron and amalgamated. The quick- silver, when present in the pan, takes also part in the decomposition, being thus converted into subchloride of mercury or calomel, which, unlike chloride of mercury, not being decomposed by the iron, causes a loss in quick- silver. The sulphate of silver, soluble in hot water, will be decomposed by iron into metallic condition, combining with the quicksilver to an amalgam. It would appear, therefore, that roasting without salt, for the purpose of producing sulphate of silver, which is easily beneficiated PROCESSES OF SILVER AND GOLD EXTRACTION. 107 in the pans, would be more economical by saving salt. It is, however, very difficult to transform all the silver into a sulphate. The sulphates of iron and copper must be formed before the sulphuret of silver can be changed into a sulphate, and if there is not sufficient sulphuric acid emitted by other sulphates, a great deal of the sulphu- ret will be decomposed into sulphurous acid and metallic silver, the presence of which must be avoided. If arse- nic and antimony be present, arsenate and antimonate of silver, which will escape the amalgamation, will be formed. A great part of the arsenate and antimonate of silver will be changed into sulphate of silver, but not all, especially if the ore is poor in iron sulphurets. On the other hand, if the heat is kept too high, the sulphate of silver will be reduced to a metallic state, which, as before remarked, must be avoided ; because, while the sulphate is not volatile, the metallic silver, by means of oxydation, evaporates, and deposits itself in cooler places in a metallic condition, emitting oxygen, causing thus a loss. The chlorodizing roasting requires less attention, and gives a better result. The sulphurets, which may re- main in the ore undecomposed after roasting, will be reduced in the pan by predominant chlorides and sul- phates. Sulphates alone effect very imperfect decom- position of sulphurets in the pan. Mr. Sutro's furnace for this purpose (at Dayton, N. T.) is twelve feet by thirteen, offering about one hundred and fifty square feet of hearth surface. The furnace is 108 PROCESSES OF SILVER AND GOLD EXTRACTION. charged with 2,000 pounds of ore with two per cent, of salt, or when pan-tailings are subjected to roasting, the ore of which had been treated with chemicals and salt, the latter is not added at all. Two men are employed at a time at each furnace for twelve hours. The stirring is kept up constantly at a low, dark red heat four hours long, when the ore is considered well roasted and with- drawn. It contains a great many lumps, so that sifting and pulverizing are required, chiefly on account of the imperfect pan arrangement. In using Wheeler's or Hepburn's pans, it is not necessary to pulverize the roasted stuff. The lumps are not formed in the furnace, but are the consequence of the fine muddy condition of pan-tailings. In roasting dry ore, or well dried and pul- verized pan-tailings, the lumps are formed in small pro- portion. This roasted ore is then introduced into the pan like unroasted ore, and amalgamated in the usual way. A great deal of the base metals will enter the amalgam, if such occur in the ore, but a strange appearance is the iron amalgam which is always obtained in a certain quantity in treating pan-tailings. It separates in melt- ing, swimming on the fused metal in lumps, when it must be removed and melted over with more fluxes. But it sometimes happens that all the amalgam after retorting appears black, spongy, and very light, contain- ing from forty to fifty per cent, of iron. In this case the result in regard to silver extraction is unfavorable. This black retorted iron amalgam, only the result of certain old pan-tailings, must be worked over, treating it like PROCESSES OF SILVER AND GOLD EXTRACTION. 109 ore, in a pan with quicksilver and some sulphuric acid. The iron entering the amalgam is derived principally from the wear of dies and shoes, being in metallic con- dition, but after six hours' roasting, most of it is finally converted into an oxyd. Some chloride of iron or other combinations may still remain in a very limited propor- tion. It is therefore difficult to account for the reason why, and under what conditions the iron is amalgamated, as experiments on ores containing metallic iron from the stamps, when treated in the pans with the addition of sulphate, protochloride, or chloride of iron, always pro- duces amalgam free of iron. At the moment of amal- gamation, the iron is in metallic condition, and also after retorting, but when the retort is opened and the air comes in contact with it, the amalgam assumes a higher glow, and continues so for twenty-four hours. During this time, most of the iron will oxydize, and still be attracted by the magnet. It is, however, very likely that by proper roasting, of a reasonable charge, this singular appearance can be avoided. As a matter of course, only those ores or tailings which contain a sufficient quantity of sulphurets, espe- cially iron sulphurets, can be subjected to roasting. If the quantity be insufficient, one or two per cent, of calcined green vitriol (sulphate of iron) must be added, or the ore must be concentrated, saving the tailings in the usual way. The concentrated ore, after roasting, may be amalgamated with the unroasted tailings, for which the roasted part represents the chemical. 110 PROCESSES OP SILVER AND GOLD EXTRACTION. It is advisable to use not less than four per cent, of salt, and not to charge more than 1,000 pounds at a time, except in a mechanical furnace. The temperature must be kept at a dark red heat for at least two hours, and one hour light red hot, in which time the roasting of 1,000 pounds of ore may be generally completed. In using dry ore, the formation of lumps is moderate, and requires no sifting or grinding, especially if Wheel- er*s pans are used. I have made different experiments with roasted ore in the pans, always obtaining the best results and clean amalgam, except in one instance, pur- posely applying a very low temperature, on which occa- sion, the amalgam, apparently pure, turned black after retorting, and consisted mostly of iron. But when the ore contains a great deal of copper and other base metals, the roasting must be treated more carefully (Sec. 33). The result of this manipulation is a metal more or less impure, between 600 and 700 fine — that is, if the roasting has been properly conducted and the ore not overloaded with base metals.* G. ROASTINa OF SILVER ORES Abounding in Antimony, for Pan Amalgamation. Sec. 35. Ores, containing an abundance of antimony, like that of the Sheba lode (Sec. 16, 11 l>), which is rich in silver, can not be treated in pans without roast- ing. This ore is accompanied by sulphuret of zinc, sul- PROCESSES OF SILVER AND GOLD EXTRACTION. Ill phuret of lead, and carbonate of lead. The carbonate of lead is black, somewhat dull, and also rich in silver. In selecting the ore for this purpose, the sulphuret of lead must be separated as much as possible. Some of the gangue should be left in the sulphurets. Quartz or other earthy matter prevents the baking of the ore while roasting. The hot furnace is charged with six or seven hundred pounds of ore, and while the mass is kept at a very low temperature, below glowing heat, it is diligently stirred. The sulphurets of antimony and lead fuse at a dark red heat, and if they were fused, the roasting would be most imperfect, and result in a loss of silver. Care must be taken to keep the temperature low, especially when the ore is rich in sulphuret of antimony. The oxydation of the sulphur and antimony will soon commence. White fumes of antimonous acid arise, gradually increasing, a strong odor of sulphurous acid is emitted, while constant stirring exposes always a new surface of the ore to the oxydizing air. As soon as it is perceived that the fumes and the formation of sulphurous acid decrease, the heat must be raised gradually, so that about two hours after the charge the ore appears red hot. Sulphates of lead and zinc and some sulphate of silver will be formed with the increasing heat, also antimonate of silver, of which only a small part may be changed into sulphate of sil- ver under the influence of the limited quantity of gas- eous sulphuric acid. This acid is partly disengaged 112 PROCESSES OF SILVER AND GOLD EXTRACTION. from the sulphates of lead and zinc under the increasing heat, which at the expiration of three or three and a half hours must be nearly light red. At this time sam- ples must be taken from the furnace, and if ascertained by odor that none or not much sulphurous acid is emit- ted, the first part of the roasting is finished. During this period a great deal of antimony is vola- tilized, as antimonous acid, and also some oxyds of lead and zinc. One part of the antimonous acid combines with anti- monate, which is not volatile. To disengage this, as well as the antimonate of silver, the roasting must be changed into a chloridizing one. For this purpose, five per cent, of salt, in a fine pulverized condition, is thrown into the furnace with a scoop, in such a way as to scat- ter it over the whole surface of the ore. Soon after the ore and salt are mixed by the usual stirring, white fumes will arise again, consisting chiefly of chloride of antimony which is very volatile. Also some chloride of lead and zinc are volatilized. The sul- phate of silver is changed into a chloride, partly by the decomposition of salt, partly by the volatile chlorine. The formation of hydrochloric acid is here important to assist the decomposition of the antimonate of silver, for which purpose the introduction of some steam in the furnace, under a pressure of three or four pounds, will render good service. The ore increases in volume a great deal, becoming woolly, changing its color by de- grees to light yellow. After the addition of the salt, PROCESSES OF SILVER AND GOLD EXTRACTION. 113 the temperature must be increased a little to a light red heat, and after one hour's chloridizing roasting, the pro- cess is completed and the ore discharged. As a matter of course, some silver is lost, as the chlo- rides of lead, and zinc, and antimony will dispose the chloride of silver to evaporate. The amalgamation of this ore will yield a metal, containing a considerable amount of lead, according to the quantity of lead in the roasted ore. Mr. Sutro has used a very simple way of separating the lead amalgam from the silver amalgam. It is known that the silver amalgam, which is obtained in the pan amalgamation, consists of small regular crystals which are suspended in the quicksilver. The lead amal- gam, on the contrary, is entirely dissolved in the quick- silver when hot. If, therefore, the quicksilver is pressed through a cloth while hot, the dissolved lead amalgam is found in the quicksilver, and the silver amalgam in the cloth. A second filtration of the quicksilver when cold, gives the lead amalgam. The lead contains three or four per cent, of silver. It is, however, not likely that this way of separation would answer when Wheeler's pans are in use, for they yield a finer amalgam; besides, it is dangerous to handle hot quicksilver. A surer and more perfect separation of lead and silver is effected by refining. (Sec. 47.) 8 114 PROCESSES OF SILVER AND GOLD EXTRACTION. D, ROASTING OF SILVER ORES In a Mechanical Furnace. Sec. 36. The difference between roasting in a com- mon and a mechanical furnace is merely a difference of mechanical operation, but on the more or less proper execution of the mechanical operation depends also the chemical result. Gurlt, in his remarks on the new pro- gress of the copper process in England, speaks of a mechanical double roasting furnace with revolving stir- rers, which he saw at the Pembrey Copperworks. He says, one of these double furnaces roasts twenty-four tons of ore in twenty-four hours, and recommends it highly for roasting copper and lead ores, but he thinks it would not answer for roasting where a great deal of attention is required, for instance in roasting silver ore. This remark may be true in Europe, but we, in Nevada Territory, are differently situated. In Germany the roaster works with hands and head, and is responsible for the result. His work can be trusted. Our roasters are inexperienced, frequently green hands, without the least interest in the result. A good mechanical furnace is also reliable in its performance, and responsible for the result. The mechanical furnace which I propose is not in use to my knowledge, but it may be easily perceived that no other furnace offers the same advantage of having i)he ore so uniformly heated. Whatever the construe- PROCESSES OF SILVER AND GOLD EXTRACTION. 115 tion of the roof or arch of a furnace may be, the heat will always be more intense at the bridge than on the opposite side. This requires the troublesome moving of ore from the bridge to the flue and back, and even then the disadvantage of the difference in temperature is not entirely corrected. The revolving bottom of the furnace (Sec. 54, Fig. 31) carries the ore at each revolu- tion through all the different temperatures of the fur- nace, and the ore is twice stirred, thus effecting a very uniform heating of the ore and consequently also a uniform chemical action. 9fich a furnace will roast the ore with much more precision than a common furnace attended by such roasters as we can get in Nevada Territory, and it requires on that account less time. One man can attend several furnaces. The consumption of wood will be less ; and no cooling at the working door can take place as in other furnaces where the door must be con- stantly open, whereby a great mass of cold air is drawn in, diminishing the draft at the fire place. The expenses are thus considerably reduced, but the most important advantage lies in the more perfect roasting which gives a better result in extracting the silver. LOSS OF SILVER In Roasting Different Silver Ores. Sec. 37. In roasting the ore by the oxydation method without salt, the per centage of loss of silver will be 116 PROCESSES OF SILVER AND GOLD EXTRACTION. higher, when there is a great deal of metallic silver in the ore, or when it is produced during the roasting, or when the mass of ore assumes a loose condition, admit- ting the air to permeate it. The loss increases also when the richness of the ore decreases, or when for some reason the temperature must be kept high. The sulphate of silver in contact with the oxyds of other metals suffers a greater loss than arsenate or antimony of silver, because the sulphate is more easily decomposed by oxyds at a high temperature and reduced to the metallic state. In roasting the ore without salt, silver is not only lost mechanically, being carried out with*the draft, but chiefly chemically by the conversion of the metal into the oxyd of silver, which is volatile. If not combined with antimony, it deposits itself in a metallic form, for it leaves its affinity for oxygen at a lower temperature. At Mansfeld, where Ziervogel's method is practiced, in extracting silver from copper matt the loss of silver, according to the recent accounts of Dr. Heinbeck, is 7*06 per cent, in roasting and 1*20 in extracting the silver, making the total loss of 8*26 per cent. This is consider- ed a very flattering result. Taking into account the stuff collected from the dust chambers, the loss will be diminished somewhat. In the chloridizing roasting, if properly conducted and if there are no base metals in the ore, the loss of silver is less than in the oxydizing roasting. However, the circumstances which determine the loss are different PROCESSES OF SILVER AND GOLD EXTRACTION. 117 and numerous, but generally speaking the loss by roast- ing is between five and fifteen per cent. Losses above fifteen or below five per cent, are exceptions. The base metal ore of the Ophir's northern claim on the Comstock lode, containing lead, zinc, iron, copper, and antimony, which I treated for the barrel amalgama- tion, mixing it with fifty per cent, of pure ore (the latter is now worked by itself), after having been care- fully roasted, suffered a loss of between five and eight per cent, of silver. The accounts of the present losses in some works where roasting is going on are consider- ed so low, that, allowing one or two per cent, for the amalgamation, there is hardly anything left for loss in roasting. This is evidently a mistake, founded on an improper mode of taking samples for that purpose. AMALGAMATION OF ROASTED ORE. a Barrel Amalgamation. Sec. 38. The amalgamation in barrels is not adapted to ore containing gold. Unroasted ore has been tried with chemicals unsuccessfully. The construction of the barrels does nor differ much in the different works of Nevada Territory. They have a cylindrical shape, the diameter and depth being nearly equal. The staves are three to four inches thick. There are two sizes in use. The smallest capable of receiving from 1,000 to 1,300 pounds of ore, are thirty-two inches each way; the larger, receiving a ton of ore, measure from forty- 118 PROCESSES OF SILVER AND GOLD EXTRACTION. four to forty-eight inches in the clear. The motion is imparted by cog-wheels although belts fitted directly on the barrel are preferable. The stoppage and starting by means of tightening puUies is more easily efiected with- out jar. Above each barrel is a wooden or sheet iron funnel, large enough to receive one charge. By means of a hose, fastened at the mouth of the funnel, the barrel is charged with the required quantity of ore in a short time. When this is done, from one hundred and sixty to two hundred pounds of wrought iron are introduced. The iron is in pieces of different shape and length, but pieces over five pounds, and such as have rough and sharp edges and ends, wear the staves too much. After the iron, cold water is added in such a proportion as to form a thickish paste. One ton of ore may require five hundred or six hundred pounds of water, according to the fineness of the ore. The barrel is then closed tightly and set in motion, at the speed of about twelve revolutions per minute. After two hours' run, the barrels are stopped and exam- ined. By this time the mass of ore should be of such consistency as to allow the forming of a soft ball with the hand. If the pulp adheres to the hand and fingers so that no ball can be formed, some thirty or fifty pounds of ore may be added, but if, on the contrary, the stuff is so dry that it crumbles into pieces, some more water must be added. After the ore has been found to be in the right condition, the barrels are PROCESSES OF SILVER AND GOLD EXTRACTION. 119 charged with quicksilver. One thousand pounds of ore require five hundred pounds of quicksilver. The open- ing is closed again and secured by means of a screw. The motion must be changed now to eighteen or twenty revolutions per minute. Four hours after the quicksilver has been charged, each barrel must be examined again. For this purpose the barrel is stopped and opened. A wooden stick, about an inch thick, is dipped into the pulp and with- drawn. If the ore is so diluted that it runs down from the stick, forming a long thread, the quicksilver and the iron sink to the bottom, the amalgamation is imperfect, and the iron does useless damage to the barrel. Some dry ore may be added, but after this time no more. If, on the other hand, the ore crumbles from the stick, or if it is so stiff that it does not adhere at all, the suspended quicksilver and iron have no chance to change their places, and the amalgamation will give a very poor re- sult. An addition of water is therefore in this case necessary. The barrels are put in motion again and continued for fourteen hours, so that the period of amal- gamation, from the introduction of quicksilver, will last about eighteen hours, after which the barrels are filled with water, set in motion at a reduced speed, and after one or two hours run, discharged. The discharge is performed in different ways. Oppo- site the feedhole in the barrel is a small hole, shut by an inch screw. Through this hole the quicksilver is let out first, directly into the filter or into a common re- 120 PROCESSES OF SILVER AND GOLD EXTRACTION. ceiver. As soon as the mud appears, the screw is put in, the plug of the feedhole removed, the barrel turned over, and the tailings discharged into a large inclined trough below the barrels, leading into agitators, where the tailings are diluted with more water, in order to allow the settling of the particles of quicksilver and amalgam, requiring five or six hours, when the tailings are discharged. The contents of the barrels, quicksil- ver and tailings are also discharged at once into the agitators, the bottoms of which have a conical shape, like Wheeler's agitator. (See Sec. 51, Fig. 26.) The agitator is a tub, five or six feet in diameter, and about the same in height. On the perpendicular centre- shaft are four arms with staves, three or four inches apart, performing the stirring. The shaft makes twelve revolutions per minute. In Washoe Valley there is an agitator, sixteen feet in diameter. This size can not be recommended. The purpose of the agitator is to have such a motion and such a dilution that, while the earthy particles are kept in suspension, the heavier but minute particles of quicksilver can sink by degrees to the bot- tom. If the mass is too thick, the quicksilver will be kept suspended; if it is too diluted, the sand settles with the quicksilver. The former result will also occur, if the motion is too fast, and the latter, if the motion is too slow. A sixteen feet agitator has a tremendous speed on the periphery when the motion near the cen- tre is right. Even eight feet is too large, unless the agitator is not intended to effect a perfect separation, but is used like Wheeler's agitator. (See Sec. 27.) PROCESSES OF SILVER AND GOLD EXTRACTION. 121 As soon as the barrels are empty, and the iron pieces, which may happen to fall out, replaced, the charging is performed as before. The quicksilver, which came out of the barrels, is strained, and the amalgam retorted. (Sec. 42.) The object of using metallic iron in the barrel is to decompose the sesquichloride, or chloride of iron, and to reduce it to protochloride. The chlorides of silver, copper, and lead, as well as some sulphates, after hav- ing been reduced to the metallic state, combine with the quicksilver, which is introduced after all these reac- tions have been effected by the metallic iron. In the absence of iron these chlorides would be decomposed by the quicksilver, which, forming sub-chloride of quick- silver, would decompose no longer, causing a great loss in mercury, and the amalgamation would be imperfect. Metallic copper, in place of iron, acts with little less energy than the iron, but, not reducing the copper and lead chlorides to the metallic state, it renders a very pure amalgam. It is by no means necessary to use pure copper in the barrels. In treating the copperous silver ore from the Heintzelman mine in Arizona, I was obliged to procure copper by liquation of copperous lead. Be- ing limited in regard to heat, for want of firebrick, the copper could not be refined properly, having a grayish red color, on account of some lead. This cop- per, as well as black copper, bought from Mexicans, gave a very favorable result as to the quality and quan- tity of the silver extracted. 122 PROCESSES OF SILVER AND GOLD EXTRACTION. h. Amalgamation in Dr. Veatch's Steam Tubs. Sec. 39. The principle of this amalgamation, which is performed at the Central Works (Virginia City) is, in regard to chemical procedure, the same as that of the barrel amalgamation. Chlorides and sulphates are de- composed by wrought iron or copper plates. But, while the barrels discharge the quicksilver after each amalga- mation of a new charge, in order to save it from destruc- tion by decomposition, the steam tubs retain it for many charges, according to the richness of the ore. The quicksilver therefore takes an active part in decompos- ing the chlorides, forming calomel. In this combination the quicksilver is always lost. The steam has no chemi- cal action, but it may influence the amalgamation by its temperature. In regard to the mechanical part of amalgamation, these tubs differ entirely from the barrel arrangement. There are wooden tubs about four feet deep and four feet in diameter. The bottom is made of cast iron with three circular openings for the reception of perforated plates, also of cast iron, below which are the steam chambers. The holes are very fine, about two inches apart. In the middle of the tub is an upright shaft, suspended on a box outside of the tub. There are three arms attached to it, each having three copper or iron plates hanging perpendicularly in concentric lines. The movable cover has an opening in connection with a flue by which the steam and some quicksilver are carried into cooling tanks. PROCESSES OP SILVER AND GOLD EXTRACTION. 123 The steam is forced through the perforated plates into the pulp, throwing the quicksilver in globules of all sizes constantly through the whole mass, causing a very perfect contact between the ore and mercury. The iron plates — or if the ore is very copperous, copper plates,— nine in number, have a circular motion, cut the ore with the edge, require very little power, and assist the motion of the pulp. The decomposition of chlorides goes on very rapidly in consequence of the heat and contact with the plates, which expose about 3,600 square inches of surface to a mass of six or eight hundred pounds of ore. Under such circumstances the amalgamation may be effected in five hours, but as a matter of course, the result depends entirely on a proper roasting. With regard to saving the gold in silver ore, this amalgamation may be equal to that of the barrels. Gold requires friction, silver chemical action. I could not ascertain the loss of quicksilver, but very likely it must be greater than in the barrel amalgamation, not only on account of being converted into calomel to some extent, but also by being dispersed by the force of steam, which should for that reason be carefully regulated. The mechanical loss and that by evaporation, in consequence of considerable heat in the tubs, is not important, as the greater part of the quick- silver is condensed in a cooling tank. This amalgamation is superior to barrel amalgama- tion in regard to the time and the amount of power required, still there are some inconveniences which 124 PROCESSES OF SILVER AND GOLD EXTRACTION. have not yet been removed. The choking of the fine holes in the perforated plates by amalgam, the cleaning of which is troublesome, might be avoided by discharg- ing the quicksilver after each amalgamation ; but then the plates would come too much in contact with the different salts of the ore, which doubtless would enlarge the holes and cause more damage than benefit. The cleaning of the tubs is injurious to the health of the workmen, if no time is allowed for cooling or precipita- tion of the vapor of the mercury. The roasted and finely pulverized ore is spread on a platform moistened with water, and, after the plates have been set in motion, the quicksilver, water, and some steam introduced. The amalgamator is charged with six or eight pounds of ore by means of a shovel. If there is too much steam, the ore will be thrown up with the quicksilver against the cover, if on the other hand the steam has too little force, the amalgamation is delayed. The amalgam deposits partly on the plates, where it must be removed by iron scratchers without taking out the plates. After four or six hours, accord- ing to the richness of the ore, the amalgamators are discharged into agitators. c. Amalgamation m Pans. Sec. 40. Ores containing such compounds of silver as cannot be treated satisfactorily in pans, or concentrated tailings of the pan amalgamation, which contain chiefly such silver ore as has resisted the action of chemicals, PROCESSES OF SILVER AND GOLD EXTRACTION. 125 will give the best result after having been subjected to a chloridizing roasting. The presence of base metals will of course render the amalgam impure, but this depends partly on the greater or less attention given to the roasting. A certain amount of copper in the bar is not so injurious after all, increasing only the expense for transportation by express. If the ore is of such a nature that a great deal of lead enters the amalgam, the metal must be refined, and in this case the calculation will show whether there is more economy in working the ore without roasting, even if more silver be lost. Generally, if in treating ore of. about one hundred ounces per ton by means of roasting, not more than ten per cent, of silver were saved, it would not pay to roast. If the ore is very rich, especially when there is also gold in it, the proper way of reducing it, is to amalgamate it in pans without roasting, save the tailings in large tanks, roast them subsequently and work them over in pans, either alone or mixed with raw ore. In this case, although the water always carries off some ore in form of the finest slime, yet the loss is less, or may be a great deal less, than the loss in roasting some qualities of rich ore. We must take into consideration the fact that if the rich ore be treated by roasting previous to amalgama- tion, it must sufier not only the chemical loss but also that caused by the draft of the furnace ; whereas the tailings, when exposed to the furnace after amalgama- tion, will have only the sixth part or so of the value of the original ore. 126 PROCESSES OF SILVER AND GOLD EXTRACTION. Ores containing antimony to excess, like that of the Sheba lode (in Humboldt County, N. T.), or combina- tions with zinc and iron, like the ore from the Rappa- hannock lode (Palmyra District, N. T.), cannot be treat- ed in pans without roasting ; also, auriferous arsenical or iron pyrites require roasting. The amalgamation can be executed in different pans ; but in order to save quicksilver from being changed into subchloride, the arrangement must be made that after each charge tailings and quicksilver be discharged. The construction of Wheeler's and Hepburn's pans makes such discharge necessary. On this account, and because they are superior in many respects, they are preferable to other pans. But the dies in Wheeler's pans form curved grooves in which a part of the quick- silver and amalgam remains after the discharge. They must be replaced by a bottom of one piece of hard iron or dies without space between them. The ore is then introduced according to the ca- pacity of the pan and the volume of the ore ; for instance, five or six hundred pounds into one Wheeler's pan, or ten hundred pounds into Hepburn's, with a sufficient addition of water. The steam must be used moderately. The ore undergoes now the same process as in the barrels. After one hour's time, when the most of the chlorides and sulphates are decomposed and the silver reduced to the metallic state, sixty pounds of quicksilver are introduced. The amalgamation now goes on with the same speed and moderate temperature PROCESSES OP SILVER AND GOLD EXTRACTION. 127 for two hours. Then all is discharged. The pan is charged again, and the procedure is the same as before. Wheeler's and Hepburn's pans alike require about three hours for the amalgamation of a charge. Others may require four or five hours, according to their service- ableness. If the ore renders an impure amalgam, the impurity can be best ascertained after the first discharge by taking a sample of about ten grains of amalgam, which is heated to red heat by fire under draft, in order to get rid of quicksilver. This sample thus retorted must be examined under the blowpipe (see Sec. 11). If there are no other metals in it but iron, there is no remedy save better roasting. The chlorides of other base metals can be destroyed by using some quicklime, pul- verized lime rock, or clean wood ashes. One or one and a half per cent, of lime is charged with the ore. After a quarter of an hour's time, a small portion of the ore is taken from the pan, put into a porcelain cup, and, by means of a piece of copper, stirred with some water and a few drops of quicksilver. If the quicksilver be covered with a black coat instantly, some more lime must be added. Fifteen minutes later another sample is taken in the same way, and so on till the quicksilver does not appear black, or very slightly so. Too much lime is injurious to the extraction of silver. This method is only a temporary remedy. It can be better executed in the furnace. Such ore, introduced with about fifty per cent, of raw ore may prove a very good chemical. 128 PROCESSES OF SILVER AND GOLD EXTRACTION. in. COLD PROCESS. AMERICAN HEAP AMALGAMATION OR PATIO. Sec. 41. The patio amalgamation, where wood and water are scarce, the ore suitable, the climate favorable, and labor cheap, is a very good process, and in many cases cannot be replaced by a better one. The climate of Nevada Territory, at least in the summer, is very favorable for the patio ; but several months of the winter time do not permit this process, without having proper buildings, in which, by the aid of steam and other arrangements, the required temperature is obtain- ed, although the sunbeams and open air assist the process, independent of the temperature. On the other hand, there are the disadvantages that the expenses of steam power, horses, and men are comparatively much heavier here in Nevada Territory, than for instance in Mexico or South America. Besides, it is hardly possible that this process should justify its use, along side of pans working three or four tons of ore in twenty-four hours, with less expense and similar or better results, according to the nature of the ore. Ores containing gold cannot be treated by patio, unless that metal is extracted first in some other way. The best and at the same time cheapest method is to extract gold by the new improved pans, offering also the advantage of the finest grinding, required for the PROCESSES OF SILVER AND GOLD EXTRACTION. 129 patioj but in this case the tailings of poorer ore would not pay to be worked over by the patio process. The ores most suitable for this process are Brittle- silver ore, Polybasite, Rubysilver, Bromyrite, lodyrite, Silverglance, and Chloride of Silver. The last two, on account of their toughness and ductility, amalgamate with little more difficulty thau the other compounds. Silver, combined with copper and antimony, must be slightly roasted before being subjected to patio amalga- mation. It requires generally a very low, dark red heat, being stirred only at intervals for about twelve hours. Such ore can often be treated without magis- tral. If similar ore be taken into the patio without roasting, it remains cold, when the usual quantity of magistral is taken; and an abundance of it does not effect a proper extraction of silver. If on the other hand such ores are roasted too much, the patio appears very hot. It is well to let it rest after roasting for a few days in a moist condition. Argentiferous zincblend, pyrites, and some other com- binations cannot be treated by patio without a perfect roasting. Gold ores and argentiferous lead ores are entirely excluded from this process. The patio process was tried in Virginia City, and is at present practiced in Washoe Valley and on Carson River. The theory of this process does not explain the chemical procedure satisfactorily. Salt and the magis- tral, containing about eighty per cent, of sulphate of copper, prepared from copper pyrites by roasting at a 9 130 PKOCESSES OF SILVER AND GOLD EXTRACTION. moderate temperature, generally with an addition of salt, are the two agents, acting and reacting mutually on each other and on the sulphurets in the presence of quicksilver. To these reactions the amalgamator {azoguero) gives his particular attention by making fre- quent tests with his horn spoon or other instrument. Notwithstanding all his care, it is sometimes found necessary to add to the mass a portion of quick lime, little or much, as the case may require, for the purpose of counteracting the injurious effects of too much magis- tral. The blue vitriol in place of magistral is less fit on account of its vigorous action upon the quicksilver. The loss of quicksilver occurs here, as in other opera- tions, for two reasons : the chemical, or " consume," and the mechanical, or "loss." The chemical is almost inva- riably equal to the weight of the silver extracted. The mechanical depends on the attention and ability of the amalgamator. The ore is first ground very fine ; then from thirty to sixty tons are laid out on the floor (patio) and mixed well with some water to a proper consistency. Samples are taken from all parts of the mass, a fire assay is made of them, and salt is introduced, amounting to two or four per cent, according to the quality of the salt and the quality of the ore. An excess of salt does not in- jure the operation. When the salt is well mixed with the mass, it should remain undisturbed for one or two days to permit the salt to be dissolved. The mass is then turned over and worked, by treading with horses or other means, to a uniform proper consistence. PROCESSES OF SILVER AND GOLD EXTRACTION. 131 The magistral is then incorporated, about one per cent., more or less, according to the quality of the ore, the temperature, and the situation. After the magis- tral has been well tramped in, the quicksilver is next scattered over it by straining through canvass. The amount of quicksilver first introduced is from one-half to two-thirds of the whole that may be required, which is about six pounds to one pound of silver, as ascer- tained by the assay of the sample. v After some days, the first part of the quicksilver has combined with enough silver to form a dry amalgam. When this is the case, one-half of the remainder of the quicksilver is added, mixed and trodden as before, and when after several days it is discovered that there is again dry amalgam, the last part of the mercury is in- troduced. Some days later, the amalgamation is fin- ished, and then some more quicksilver may be added for the purpose of washing more easily. The Torta (mass of the pulp) is tested twice a day by taking a small quantity of the pulp from different parts of the torta, and carefully washing it in a horn- spoon. The mud is washed away, leaving the amalgam on the bottom, also undecomposed sulphurets, and sil- ver partially combined with minute particles of quick- silver {limadura). This limadura is separated from the other parts by a pecuhar shaking of the spoon, and be- comes the principal object for the azoguero's inspection. By its various states and color, the process of the patio is understood. There are, however, so many variations 182 PROCESSES OF SILVER AOT) GOLD EXTRACTION". of appearance, that it requires a great deal of experi- ence to form a correct judgment. In the absence of magistral, for want of copper pyrites, blue vitriol or sulphate of copper is substituted, Mr. W. M. Brown, an experienced practical azoguero, who managed the patio operation at the Mexican mill, Virginia City, and afterwards on Carson Eiver, prepares his magistral by roasting pan-tailings at a proper tem- perature, they containing a certain proportion of salt. These roasted tailings are mixed with the ore and act upon it as magistral. RETORTING. Sec. 42. The amalgam, a combination of gold and silver with mercury, must be separated, for the purpose of having the metal prepared for melting, also to regain the quicksilver for further use. The separation is called "retorting," a very simple process, being a mere distilla- tion at a high heat. The quicksilver assumes a gaseous form, is led off through a cold pipe, and is condensed again to the metallic state, while the other metals re- main in the retort. The retorts used in Nevada Territory differ very much in shape and size. Those having an oval or cylin- drical form are better than flat-bottomed retorts, which always require a separate trough for the amalgam, on account of the obstructive corners ; besides, they have the disadvantage of being more liable to burst. The PROCESSES OF SILVER AND GOLD EXTRACTION. 133 retort most used at present is the cylindrical retort (Sec. 55, Figs. 20, 21.) The egg retort, of an oval shape, but lately introduced, seems to permit a more convenient charging and saving of fuel. This retort contains movable troughs or shelves for the amalgain. Before charging, the lower part of the cylindrical retort must be coated with a soft pulp of fine, sifted wood ashes, by means of a long rod, to one end of which a rag is tied. The same precaution must be ob- served with the troughs for the egg retort. When dry, the amalgam is introduced into the retort in balls or pieces. Sufficient room at the top must be left for the vapors of quicksilver. If overcharged, some amalgam may come out at the pipe-hole. A retort of the size as described in Sec. 55 should not be charged with more than eight hundred or nine hundred and fifty pounds of silver amalgam. When filled, the retort must be closed carefully, so that no vapors of quicksilver can escape anywhere. For this purpose the face of the door is covered with a paste of pure, fine, sifted ashes, about half an inch thick. The paste should be soft, but must not run. The cor- respondent face of the retort is moistened, and the door set in, fastened by the two wedges and tapped with a wooden mallet No force at all is required. If the ash paste has the right consistency, the closing will be per- fectly tight When this is done, the fire can be started imme- diately. As soon as the water, which cools the pipe. 134 PROCESSES OF SILVER AND GOLD EXTRACTION. commences to boil, the fire must be kept very moderate for some hours, and increased when the boiling goes down. In about four hours after beginning, the retort should be dark red-hot, and kept in this state for two or three hours more, when the heat may be increased a little, not allowing a good light red heat, which would melt the silver partly, and also injure the retort. When the pipe gets cool, and no quicksilver drops out, the retorting is finished. The water in the cooling pan, covering the quicksilver, must be clear. If it be- comes milky, the distillation, on account of too much heat, was too sudden. It requires eight or ten hours to drive off all the quicksilver. A forced retorting does not gain much in time ; the amalgam will generally be found not well retorted, and the retort will be used up in half the time. It is not the shape of a retort, but the time that is important for a good retorting. It is also a bad habit to open the retort before all is cooled down. A hot retort, even after the best retorting, con- tains mercurial vapors which are very injurious to the health, although the influence is not perceived imme- diately. When cold, the metal is taken out and broken into pieces for the purpose of melting. MELTING OF KETORTED METAL. Sec. 43. The retorted metal is of a spongy appear- ance, crumbling easily, and on that account is not fit for transportation or handling. To prepare it for transpor- PROCESSES OF SILVER AND GOLD EXTRACTION. 135 tation and to ascertain its value by assay, the retorted metal must be melted into bars. The furnace is of simple construction (Sec. 56, Figs. 13, 14), square or round on the inside, and from ten to fourteen inches in the clear, according to the size of the crucible. The best are the black lead crucibles. Before using, they require to be annealed, that is, heated slowly by degrees to red heat. This may be performed in the same furnace on a moderate charcoal fire, or after melt- ting, when the heat has gone down somewhat. The crucible must always be put first with the brim on the fire, so that the bottom is turned upwards. When the brim appears red-hot, the crucible can be turned without danger of cracking. The most intense heat in the furnace is one and a half or two inches above the grate. The crucible, there- fore, ought to stand always on a piece of fire-brick, so as not to be exposed to the cold draft of the air. When the crucible is placed perpendicularly in the centre and covered, the charcoal is put around it and on and over the cover, some live coals on top, and the furnace is shut by the slides. When the crucible ap- pears redshot, the cover is removed carefully, that no charcoal falls into it, and so much silver as the crucible will hold (from twelve to twenty pounds) is introduced with a pair of longhandled tongs. A handful of borax is also added. The crucible is then covered, and the furnace, after a new charge of charcoal, closed again. In about half an hour the silver is melted down so far 136 PROCESSES OF SILVER AND GOLD EXTRACTION. that another portion of silver can be introduced, and so on, till fifty or sixty pounds, which is about the right amount for a proper bar, are melted down. The borax must be used in proportion to the impuri- ties of the metal. If the retorted metal is white and clear, one handful is sufficient; but if the amalgam looks black, double the quantity is required. The borax dissolves the oxyds of base metals and earthy matters, which may happen to be in the amalgam, and forms a black slag, which covers the metal. Some amalgama- tions furnish amalgam, containing a great deal of sul- phurets. When melted, the sulphur takes up so much silver as to form a combination similar to the silver- glance, containing eighty per cent, of silver. If there is metallic iron in the amalgam or crucible, it combines with the sulphur, setting the silver free. This combina- tion of sulphur and metals, called "matt," is poorer in silver, in proportion to the amount of metallic iron present. . The matt is more liquid than the slag, but heavier. It lies on the metal, below the slag. If rich in silver, the matt is tough, bluish gray ; if poor, it is brittle and has a yellowish gray appearance. After the last charge is melted, the cover is removed and metal and slag stirred well by means of a red-hot iron rod, then covered, and a good heat effected by another charge of charcoal, when the slag is taken off This is generally done by a skimmer (Fig. 16), made of half inch round iron, rolled into a coil at one end. With this skimmer the slag is touched carefully, not dipping PROCESSES OF SILVER AND GOLD EXTRACTION. 137 too deep. The slag adheres to the skimmer, which is taken out immediately after it comes into contact, aud tapped slightly against the stone floor, or a wet board. With this cooled coating the skimmer is dipped again into the crucible, and the adhering slag treated as before. This is done repeatedly, till nearly all the slag is re- moved, when by a smaller and lighter skimmer the sur- face of the metal is cleaned entirely in the same way. It has often been mentioned that when metallic silver is exposed in a melted condition to the air, oxydation takes place and causes a loss by volatilization. By add- ing the borax with the first charge, the silver will be covered by it and protected ; but when, by skimming, all the slag has been removed, and the metal surface appears clear, a handful of charcoal powder must be thrown into the crucible immediately after the last slag has been taken out. The crucible is then covered, and the last heat applied. If there be matt present, it, being more fluid than the slag, does not adhere so well to the skimmer. After the accumulated slag has been knocked off from the skimmer, it is dipped as before, but must be taken out quicker and the matt shaken off by a quick shake over a pan or water tub. This operation continues till all the matt is out. When the metal appears clear, a small piece of borax is introduced, and when melted removed by means of a small skimmer. Charcoal dust is then introduced and a last good heat given. The crucible is taken out by a pair of strong crucible tongs (Fig. 15). 138 PROCESSES OF SILVER AND GOLD EXTRACTION. It is placed before the mould, and the contents poured out in a uniform stream and not too slow. The cast- iron mould must be made hot, and if required, smoked over burning rosin, so that the whole inside appears covered with soot. The mould must stand level. As soon as the metal is in the mould it is covered immedi- ately with charcoal powder. In this simple proceeding, the look of the bar depends entirely on the greater or less purity of the metal. It will however answer the purpose, as there is no neces- sity to spend time and fuel in acquiring a nice bar, unless the bar has to be stamped w^ith the value, ready for the market. If not stamped by a responsible firm, the bar must be remelted for this purpose, no matter how it looks. Hence there is no need for the millman to trouble himself in making a nice bar. If a handsome bar is desired, it must be observed that after slagging, the metal should appear with a smooth, mirror-like surface, so that objects may be reflected by it. If not, if the metal when melted continues to evolve impurities which cloud the surface, a new portion of borax must be added and stirred with a red-hot iron, or a red-hot slip of black lead crucible. Then the heat is raised again, and the operation may be repeated two or three times, always removing the slag before adding borax, till the metal appears lustrous. But in many instances, especially when a great deal of sulphurets come in the amalgam, sulphur and other impurities are so abundant that it would take half a day PROCESSES OF SILVER AND GOLD EXTRACTION. 139 or more to get rid of it merely with borax. In such a case, if there are about sixty pounds of metal in the crucible, after all slag and matt have been removed, four or five ounces of lead are introduced with the addition of some borax. The metal is then mixed well, the crucible covered, and the heat increased. When the charcoal has burned down to the brim of the crucible, the cover is taken off, and the slide doors of the furnace shut partly, so that only three to four inches of opening is left, otherwise the heat is oppressive to the workman. The metal must be stirred over, and the borax which takes up the oxyd of lead and other impurities, separ- ated by the aid of lead, skimmed off and replaced by another piece of borax. The oxyd of lead can be seen distinctly in numerous little spots adjoining the borax. When the last particles of lead separate from the silver, the surface of the metal will brighten for a few seconds, assuming by degrees a clear lustrous appearance. When the borax is saturated by the litharge, the crucible will be attacked. It is therefore necessary to skim often and to add more borax. Such metal, also amalgam from roasted ore, especially if obtained in large quantities, is not only cheaper and more economical to refine in a refining furnace, like the cupel furnace (Sec. 58) which should be of a smaller size, but even the melting into bars is more advanta- geous and a great deal less troublesome than the crucible melting, unless it is very pure metal. Silver, exposed to the draft in a melting condition, suffers a loss which 140 PROCESSES OF SILVER AND GOLD EXTRACTION. increases with time and heat. For this reason the melt- ing in crucibles is preferable, if the metal is pure, but when oxydation of base metals is required, in order to refine the silver, a refining furnace must be used. A new test furnace ought to be dried by a slow fire, at least two days before the heat can be increased. When the test appears light red hot, a small piece of retorted amalgam is introduced in the middle of the test, and the door shut. If it melts into a bright silver button the amalgam can be charged as carefully as possible, otherwise the test might be injured, especially the first charge in a new test. Several handfuls of charcoal dust are introduced, the door closed, and a strong heat applied. The silver will soon commence to melt, making room for another charge. When the test crucible is full, containing sixty, one hundred, two hun- dred, or two thousand pounds, according to the size, good heat must be kept up for about half an hour, then stirred with a red-hot iron hook, the end of which is bent upwards so as not to tear the crucible. The charcoal dust will soon burn ofi", and must be replaced by another charge when the metal appears bright and clear. It is then ready to be dipped up and poured into moulds previously warmed. But if dry, ash-like impurities appear on the surface of the metal bath some litharge may be thrown on it. This will fuse, and be drawn into the mass, taking the impurities with it. The metal must be stirred several times and a strong heat kept up, till after an hour or PROCESSES OF SILVER AXD GOLD EXTRACTIOJ^. 141 two, the surface of the silver will appear like a mirror without agitation. If, however, the silver should con- tain a good deal of foreign matter, twenty or twenty-five ounces of lead may be introduced. The metal will com- mence immediately to work, minute spots of litharge will arise on the surface increasing and gliding towards the test, by which they will be taken up. This will continue for some time, when the whole bath will be perceived to be covered suddenly with a bright cloud which disappears in a few minutes, leaving the metal clear. As a matter of course, no lead is necessary if the amalgam is already alloyed with it, which is easily discovered by the blowpipe (Sec. 2). The hot mould is placed close to the door, and the silver poured into it by means of an iron ladle about six inches in diameter and two inches deep. This ladle must be made red hot before using. Near the close of the operation the heat must be increased and kept on till all the silver is out. A small quantity which cannot be dipped out always remains. This is left till it cools and becomes hard, when it is easily removed by an iron rod. This, however, must be done without delay as soon as the cake gets hard ; otherwise, if too late, the test would certainly get damaged. This is of course not necessary, if another charge of silver has to be melted. All the slag and matt must be carefully gathered till a convenient time is found to remelt it. It happens sometimes that the skimmer takes up a few drops of metal with the slag, especially if there is not sufficient 142 PROCESSES OF SILVER AND GOLD EXTRACTION. heat in the crucible. The matt always contains more or less silver. The slag and matt, when they are to be melted, are broken into small pieces by a hammer and mixed with ten per cent, of soda-ash or soda. An old crucible of a good size (No. 50.) which appears strong enough to stand the melting is placed in the furnace in the same way as for melting retorted amalgam, and the mixture is introduced by means of a scoop, filling two- thirds of the crucible. It requires about one hour to melt one charge. When the fusion is complete, the contents of the crucible is stirred first with a rod of iron a quarter of an inch thick which is bent over like a hook. When after some time, the rod gets red-hot and the hook melts down, some old nails or scrap iron must be added and stirred with a thicker iron rod from time to time. Another test is made with the quarter- inch iron rod, and when that rod no longer assumes a white heat at which it melts ofi', a last strong heat is applied and the slag is removed by an iron ladle which is cooled in water after each dip. When about two- thirds has been removed in this way, the crucible is charged again and managed as before. Silver matt when thus treated transfers its sulphur to the iron, and the silver is reduced to the metallic state, accumulating at the bottom of the crucible. So long as the test iron melts oflf in a short time, more iron must be added. When, after four or five charges from which the slag has always been skimmed ofi", sufiicient metal accumulates in the crucible, it is taken out and the con- PROCESSES OF SILVER AND GOLD EXTRACTION. 143 tents poured into a warm mould. By adding lead, the extraction of silver is more perfect, but then it requires cupellation (Sec. 46.) The borax slag, especially when matt is present, con- tains very little silver, except that slag which involves the matt in small globules. Therefore the shortest way of beneficiating slag and matt, is to throw it on the ore before the battery and to treat it in pans with the ore, provided that no roasting is in progress, because the slag particles melt at a very low heat, thus forming hard little half-melted lumps, which however are not injurious if pan amalgamation is adopted. ASSAY OF THE BAR. Sec. 44. It is not the intention to describe here the way of assaying for the purpose of stamping the value on the bar, as required for the market, but merely to ascertain the value for transportation, or to have some check on the value to be ascertained in the assay office where it is remelted. After the bar has been cleaned and dried, if cooled in water, and that is generally done to save time, two little pieces are cut off from the corners, one on each flat side, and the bar weighed on a good platform-scale. The two pieces are flattened on an anvil thin enough to be cut with a pair of scissors, and heated to a red heat on a piece of charcoal with a blowpipe. As the upper and lower sides of the bar do not differ 144 PROCESSES OP SILVER AND GOLD EXTRACTION. much in regard to fineness, provided that the melted silver was well mixed at the moment before it was poured into the mould, it is sufficient to weigh on the assay balance about five grains of one piece and to add as much of the other, so as to weigh very exactly ten grains in all. It is understood, of course, that the silver chips must be perfectly clean. These ten grains are wrapped in a little piece of sheet lead of about ten grains weight, or more if copper is in the metal, and introduced into a cupel by a pair of cupel-tongs. The cupel must be light red-hot before the assay is intro- duced. It is then cupelled according to the process described in Sec. 19, or the cupellation can be performed by the blowpipe (Sec. 12). The silver button is taken from the cupel with a pair of pincers and cleansed of the adhering particles of bone-ash with a toothbrush. It is then hammered flat on an anvil and annealed again with the blowpipe or in the muffle. It is now weighed on the balance and the weight noted. After this, the amount of gold must be ascertained by parting it from silver. For this purpose, pure nitric acid (about three- fourths of an ounce) is poured into a glass matrass or tube and the silver plate dissolved as described in Sec. 19. The weight of the gold is also noted, and the calcu- lation made as illustrated in the following example : For instance, the bar weighed on the platform scale forty-one and one-half pounds. This must be multiphed by 14*58 to find the amount of ounces. The silver button after cupellation weighed, say, 887 and the gold 131. The value of the bar will be found thus: PROCESSES OF SILVER AND GOLD EXTRACTION. 145 The bap weighs 41-5 X 14*58 = 605-07 ounces. The fineness in silver is 887-131 = 756 X 1*30 = value per oz. $0,98-2 " "gold 131X20-67 « « 2,70-7 Value of gold and silver per ounce $3,68*9 Hence the value of the bar is 605-07 X 3-689 = $2232-10. If the same kind of ore is treated by a permanent process, the fineness of the silver varies generally very little in regard to base metals, except when it comes from the roasting process. It is then, if not required to know the very exact value, sufficient to take the aver- age fineness of some bars, say 887, and to make the assay only on gold, the amount of which should be sub- tracted from 887, leaving thus the silver for the calcula- tion very near the real amount. If, on account of a high amount of gold, the assay should not dissolve in nitric acid, pure silver must be added. (Sec.l9.) IV. MELTING PROCESS. Sec. 45. The melting of silver ore, carried on in sev- eral metallurgical works of San Francisco, other parts of California, and in Pleasant Valley, N. T., is compara- tively an expensive method. It is not very likely that silver ore ever will be worked advantageously by melt- ing, unless the amount of lead or some particular cir- cumstances should decide for it. 10 146 PROCESSES OP SILVER AND GOLD EXTRACTION. Very rich ore, which allows the use of sufficient fluxes, may justify a proper melting; but even then, amalgamation in pans without roasting, with a saving of the tailings to be worked over in pans or barrels after a chlorodizing roasting, will be preferable to the expensive melting, which requires experienced and skillful hands, and a considerable investment of capital. The reverberatory furnaces, which are used in Cali- fornia or Nevada Territory, have nothing peculiar in their construction, and resemble, generally in arrange- ment, shape, and dimensions those described in metal- lurgical books. These furnaces require the best fuel, either imported coal or artificially dried wood, and do not seem to be suitable for the circumstances of Califor- nia and Nevada Territory. This, of course, does not allude to ore like pure galena, which does not require such a heat as the silver ore, the latter being generally accompanied by various foreign substances. However, a description will be given of a crucible furnace which was planned by the writer for melting the rich Ophir ore in San Francisco, and which answered the purpose perfectly. The blast furnaces, where the burning of coke, an- thracite, or charcoal, is forced by compressed air, con- centrated in a small space, thus ajffording a high tem- perature, even if a lower quality of fuel must be used, are more suitable, under our circumstances, for melting silver ore, provided that sufficient lead ore, containing at least fifty per cent, of lead, can be mixed with it. PROCESSES OF SILVER AND GOLD EXTRACTION. 147 This kind of furnace is also more easily constructed, not absolutely requiring fire brick, for which some kinds of sand stone, conglomerate with predominant quartz, or some clay slate may be substituted. The disadvan- tage is the want of power to drive the bellows, which is the soul of the furnace. The shape and dimensions are described in all metallurgical books. Besides, the dimensions and the whole arrangement should be accom- modated to the locality and the ore. The crucible furnace (Sec. 57, Figs. 32, 33, 34), de- rived from the Mexican cupel furnace, can melt, accord- ing to the size and quality of ore and fuel, from half a ton to three tons in twenty-four hours. The ore is pul- verized and sifted in a sieve of about six hundred and twenty-five holes to the square inch. The ore can be melted directly, when mixed with fluxes ; but it is more economical to roast it after it has been pulverized, in order to drive out as much sulphur as is possible, at a low heat. If subjected to melting without roasting, a great deal of metallic iron is required to consume all the sulphur. Iron, lead, silver, and copper, combine with the sul- phur and form a matt which covers the lead below the slag. This matt must be roasted and treated like ore. It will also be formed, to some extent, even after a good roasting, and it would not be advisable to roast so per- fectly as to prevent the formation of matt, because the slag will always be poorer in silver, if some matt is made in melting. 148 PROCESSES OF SILVER AND GOLD EXTRACTION. The roasting is performed in a common roasting fur- nace, at a very low heat, with diligent stirring, continu- ing till no sulphurous gas is emitted, which can be ascertained by the odor. This operation may require three hours. To each new charge of ore some pulver- ized matt should be added, so that it shall not accumu- late. It may be pulverized with the ore, or separately. The roasted ore is then mixed with fluxes, of which there are three classes : 1. Fluxes, dissolving the different earths and oxyds of base metals. Such fluxes are : soda ash, litharge, slag, and silicia or quartz. 2. Fluxes, decomposing sulphurets : metallic iron, lith- arge, and lime ; also, soda ash. 3. Fluxes, collecting the gold and silver : lead, in the the shape of granulated metallic lead, or as lead ore ; litharge, or hearth (the mass from the refining furnace). The litharge, or lead-oxyd, which is obtained from the cupel furnace, consisting of 92-8 lead and 7*17 oxygen, eagerly dissolves the quartz and other earths forming silicates. It is also a powerful agent in decomposing sulphurets by its oxygen, creating sulphurous acid and metallic lead, which latter combines with the metal of the sulphuret and all metallic particles with which it may come in contact. The addition of slag in melting has a double purpose : first, to dissolve the earths and oxyds of metals ; second, to regain the particles of lead and matt which were drawn out with the slag, in cleaning the surface of the PROCESSES OP SILVER AND GOLD EXTRACTION. 149 lead before tapping. If there be not a sufficiency of such slag, poorer slag must be added. The silicia, in the shape of sand, dissolves the oxyd of iron. The addition of sand is required when roasted matt is melted without sufficient ore to mix with it. In this ease, if no sand were used, the oxyds of iron and lead would attack the mass of the hearth considerably. The lime combining with the slag, protects the oxyd of lead against such combination and decomposes the sulphurets indirectly. The hearth of the cupel is used on account of being saturated with litharge. The charcoal in the pulverized state decomposes the oxyd of lead and in part the sulphates. It is used in such proportion as to reduce one part of the litharge, while another part decomposes the sulphurets which may remain in the ore after roasting. Metallic iron (granulated or borings) is the best agent for the decomposition of sulphurets forming iron matt. Metallic lead takes up the gold and silver whenever it comes in contact with' these metals or melted sul- phurets. No melting of silver ores can be performed without lead or materials which produce lead. If there is no lead ore, granulated lead or litharge will answer even better (but not in a blast furnace). Litharge must be pulverized and sifted. The lead requires to be finely granulated. The granulation is effected in a wooden box (Fig. 19). The bottom and sides must be smooth, and the box tight. The box hangs on a rope so as to •m 150 PROCESSES OP SILVER AND GOLD EXTRACTION. allow a swinging motion. Several hundred pounds of lead are melted in an iron kettle and kept in a fused condition by a slight fire underneath. The temperature of the lead is right when a wooden stick thrust into it turns brown without causing a boiling motion. About twenty pounds are then taken with a hot crucible or an iron ladle and introduced into the box, in which a handful of pulverized charcoal was previously put. This must be repeated at each charge. The workman immediately takes hold of the handles, a, and swings the box in such a way that the lead slides from the side, h, over to c, and back, and so on repeatedly. When the lead becomes more compact by cooling, the swinging must be shorter and quicker, so that the lead strikes the sides with force till it falls in dust. The box is turned over and another charge gran- ulated. The lead thus granulated must be sifted in a sieve of about six hundred and twenty-five holes to the square inch. Lead ore is preferable to lead or litharge only in case that it contains some silver, dr if it is cheaper. The ore must be selected carefully and all rubbish separated. It should contain seventy or seventy-five per cent, of lead, never less than fifty. If the ore is galena (sul- phuret of lead) it should be mixed with the ore in the right proportion before pulverization and roasted together with an addition of matt, obtained in course of melting. The proportion of ore and fluxes may be PROCESSES OP SILVER AND GOLD EXTRACTION. 151 changed according to the nature of the ore ; the follow- ing mixtures, however, may be given : No. 1. Mixture for Ores without Roasting and before Litharge is obtained from the Manipulation. Silver ore 100 pounds. Granulated lead (or 200 pounds lead ore) 85 pounds. Soda ash 25 pounds. Iron 25 pounds. Lime (and 25 pounds slag when obtained) 3 pounds. No. 2. Mixture for Roasted Ore. Silver ore 100 pounds. Granulated lead 85 pounds. Soda ash 20 pounds. Iron 8 pounds. Lime ^ pounds. No. 3. Mixture of Silter Ore after Products of Smelting ARE at Hand. Silver ore 100 pounds. Granulated lead 25 pounds. Litharge 75 pounds. Hearth 10 pounds. Soda ash 15 pounds. Charcoal 5 pounds. Iron 8 pounds. Lime 3 pounds. Slag 25 pounds. When .the melting is executed with an addition of lead ore, No. 2. and No. 3 do not require granulated 152 PROCESSES OF SILVER AND GOLD EXTRACTION. lead, but it is always very useful to add sufficient litharge. The quantity of flux required depends much on the quality of ore. If the slag is too thin, it is not necessary to use so much soda ash. When the furnace is white-hot, the mixture is intro- duced by means of a scoop or shovel at the flue door (Fig. 32, i)y and spread to about half the length of the flue, between the door and the crucible. The ore may lie five or six inches deep. The door is closed, and the firing continued so that the flame reaches the end of the flue. The ore soon commences to melt, and runs into the crucible. A new charge must be introduced as often as the melting ore makes room for it. On the melting surface of the ore innumerable lead globules arise, which, taking up silver, grow bigger by joining other globules, and roll down into the crucible, followed by the slag. The lead separates in the crucible from the slag and matt, and it is very important to open the front door, 7c, often, in order to mix the slag and lead well by stirring with an iron rod, which is bent hook- like in such a way that the crucible may not be injured. The more the lead is brought into contact with slag, the poorer the latter will be in silver. The melting goes on till the crucible is nearly full ; but care must be taken to stop charging in time, so that, when the crucible is full, no ore shall be in the flue. The melted mass is now stirred again, the door closed, and a good heat applied for fifteen minutes, after which the- firing is stopped and the slag channel opened by means of a bar. PROCESSES OF SILVER AND GOLD EXTRACTION. 158 The slag runs out in an iron car. The channel is then shut again by a paste, formed of one part of ashes in bulk, and one of loam, well mixed. The paste must be made soft, but still so that it may be formed into round, long pieces, which, after being dipped in water, are laid directly into the hot channel and pressed with a piece of red-hot flat iron. This operation must be repeated after each introduction of the paste till the channel is filled level with the rim of the crucible. The fire is started again, the flue charged with ore, and the melting executed in the same way as before. After the slag has been discharged five or six times, it may be examined by an iron ladle, to ascertain how much lead or matt has accumulated in the crucible, and when it is found that the matt is only three inches be- low the bottom of the slag channel, the slag is first dis- charged into the car, and when it has run out, the re- mainder must be drawn ofi* by an iron hoe through the channel till the matt appears free from slag. The slag thus drawn off is mixed with the ore again, as men- tioned before, for some matt will unavoidably be drawn out likewise. When all the slag has been removed from the crucible, the lead and matt must be tapped into the open hearth, B\ The taphole is opened with a chisel- like pointed bar, boring and picking the loam mixture in the hole, not using too much force, till the lead com- mences to run out. When all is out, the taphole must be closed again without delay. For this purpose a piece of charcoal, 154 PROCESSES OF SILVER AND GOLD EXTRACTION. about two and a half inches long, pointed at one end, wrapped with loam at the other, and shaped like the taphole, is fastened to a rod, and introduced so that the point of the charcoal shuts up the hole in the crucible. Two or three other loam balls are applied on it, tapping each with a wooden rod. The matt, separated from the lead, hardens quicker than the lead below it in the lower hearth, and. can be removed in one piece with an iron fork. The lead is then dipped up with ladles and poured into warm iron moulds. The lead bars weigh twenty-five or thirty pounds, a convenient size for handling at the cupel fur- nace. All the matt is turned into the ore and pulverized with it. In roasting, the sulphur is burnt ojQT and the iron oxydized, being thus a good flux for the silicia, while the silver is absorbed by the lead. SEPARATION OF LEAD AND SILVER, OR CUPELLA- TION. Sec. 46. The lead, obtained from melting silver ores, must be separated from the silver by an oxydizing pro- cess, called cupellation. To this the lead is subjected either directly, or, if very poor in silver, after concen- tration in a smaller quantity of lead, in order to reduce the expense of cupellation. This (Pattinson's) concen- tration has been introduced by Capt. Mead in Pleasant Valley, N. T., the result of which is not yet known. PROCESSES OF SILVER AND GOLD EXTRACTION. 155 Some general remarks on the concentration by crystal- lization will follow, after the cupellation shall have been described. The cupel furnace (Sec. 58, Figs. 35, 36), after having been perfectly dried by a slow fire for two or three days, must be made light red-hot, before the lead can be intro- duced. A piece of lead is placed on the hearth, and observed. First it will melt and become covered with an oxyd. If the heat is too low, the oxyd coat grows thicker, and the lead remcains dark red. In this case the door is shut and the temperature raised by better firing. The oxyd crust will then melt and disappear, leaving a round, bright lead button. When this is perceived, two lead bars are introduced, placed on the fire-tile, and re- placed by others when melted down, till the hearth is full. If the lead is not clean, there remains on the tile a kind of skeleton, mostly of matt, which is pushed into the test before another lead bar is introduced. The doors are closed, and the heat raised. After half an hour's time the surface of the leadbath is covered with a kind of slag, the scrapings, consisting of oxyds of lead and iron, and other foreign matters. These scrapings, to be melted, require more heat than the litharge, and are called froth. This froth is drawn off, over the litharge bridge (Fig. 36, /), in which a small canal, e\ is made just before drawing. For this purpose a piece of flat iron is prepared, about one and a half inches wide by one-half inch thick and five feet long, one end of which is sharpened and stretched a little, so that it assumes 156 PROCESSES OP SILVER AND GOLD EXTRACTION. the shape of a chisel. With this instrument the canal is made by careful picking and scratching, about half an inch deep. Over this canal the scrapings must flow from the furnace. To effect this, the slag is drawn first with a round iron rod over the channel repeatedly, holding the rod light on the surface of the bath, or otherwise some lead might escape. The scrapings, assisted in this way, will soon flow by themselves, but from time to time they require again the aid of the rod. The easy run depends also on the temperature ; if too low, the scrap- ings will freeze and shut up the canal. This slag looks black, is heavy and brittle and shows a glassy surface. By degrees it changes color, becoming more yellow, flowing more easily, and assuming a scaly appearance. The litharge is formed now, and flows freely through the canal, which however must be constantly attended to by widening in case of need, or, by arresting the stream by putting a small lump of the hearth mass in the canal, if any drops of lead escape. The heat must be kept moderate and regulated after the appearance of the litharge. As long as the scrapings continue to run, the temperature requires to be higher so that the scrap- ings flow down to the floor. When so much of this slag is removed that the lead is exposed in the middle of the bath, the blast is introduced, first gently blowing, but it may be increased when litharge arises to such a degree that the lead is slightly moved by the wind and the litharge is driven against the sides. The lead bath PROCESSES OF SILVER AND GOLD EXTRACTION. 157 brightens and must be always lighter in color than the hearth at the sides. When the litharge solidifies on the bridge or shortly below it, the operation requires more heat. The right temperature is then when the litharge flows to the floor, but when it flows on the floor in a red- hot condition, there is too much heat in the oven, caus- ing a greater loss in lead by volatilization. When the litharge ceases to flow at the right temper- ature, the canal must not be made deeper, but another lead bar placed on the tile. It requires much attention to keep the canal as uniform as possible about half an inch wide. This canal will be cut deeper gradually by the litharge. If the temperature is too high the lith- arge attacks the hearth-mass more, the canal will grow deeper and some lead may escape. When, therefore, after a longer use, or with excessive heat, the canal appears too deep, it must be filled with hearth-mass and another canal opened alongside of it as flat as possible, just to permit the flowing of the litharge. The charging of lead bars must continue without interruption, regu- lated by the canal and the formation of litharge as above described. In drawing the litharge, it is an error to let all flow out. Particular attention must be paid to have at least four or five or even more inches of the surface of the lead always covered with litharge, which forms a flat ring on the periphery of the bath. The longer the litharge is in contact with the lead the poorer it is in silver. Another sign for the right temperature is in 158 PROCESSES OF SILVER AND GOLD EXTRACTION. the lead fumes. If the heat is too strong, the lead fumes will arise in such a quantity that it is difficult to see the bath, which interferes very much with the drawing of the litharge. If on the other hand the temperature is too low, the lead vapors will disappear almost entirely, the litharge does not flow right, cools in the channel and stops. The right temperature is indicated by a moder- ate amount of lead vapors, so that most of the litharge can be seen distinctly and the flow is free, over the whole litharge bridge. When after twelve or fifteen hours the whole surface of the bridge has been cut for canals, generally five or six of them, the first one must be opened again or better a new one made, but of course deeper than the first row. The lead bath will stand accordingly also deeper in the test. We now proceed in the same way, making new canals close by, when the first is getting too deep and so on. After from thirty to forty-eight hours of uninter- rupted cupellation, the charging of lead bars is stopped. From this moment the last canal must be made deeper as the drawing of the litharge requires it. During the whole process the formation of litharge can be observed, and it flows constantly on the convex surface of the bath towards the sides joining the ring of litharge, kept purposely to some extent, in large furnaces even twelve inches wide. At the end of the operation when the silver is concentrated and but little lead in it, the litharge appears less, but in larger spots, till at last a shining, playing veil appears, which soon PROCESSES OF SILVER AND GOLD EXTRACTION. 159 covers all the metal. The blast must be moderated now and the heat increased. After some time the bath clears up again, emitting some litharge in minute parti- cles which continue under strong heat for a short time. The blast must be reduced now to the lowest degree and then stopped entirely, when the silver commences to play rainbow colors, but the fire must be kept on. The silver is stirred with a red-hot iron rod once or twice till finally the metal appears bright and clear like a mirror. If there are eighty pounds or more of metal in the test, the silver may be dipped out with an iron ladle into hot moulds. Smaller quantities are cooled by the blast, also some cold water may be poured on the middle of the silver cake, yet only a little at a time, so as not to cool the hearth too much. When the silver hardens, it emits oxygen, forming figures or towers of different shape. The silver is then tried with an iron bar, slightly knocking on it. If it sounds like solid metal, a pointed bar will lift the cake by introducing the point under the edge of the slab. The moment when the silver becomes hard, must be watched in this operation, else, if too late, the test might be considerably damaged. In case the cake is larger than the opening of the litharge bridge, it must be taken out through the fire-place. The cupellation, executed in the described way, yields very fine silver, which need not be refined. Generally the cupellation is interrupted when the brightening 160 PROCESSES OF SILVER AND GOLD EXTRACTION. occurs. In this case, however, the silver is not quite pure and must be refined in a refining furnace. As soon as the silver is taken out, the furnace must be immediately prepared for another operation, if suffi- cient pig lead is at hand. For this purpose, three or four flat iron bars, each five feet long, are introduced into the furnace, so that one end of each may get red-hot, while the other ends remain cold enough to be handled. Meanwhile the same composition, of which the hearth was made (Sec. 58), is prepared with some water to a soft paste, well worked, and formed into cylinder-like pieces, about eight inches long and three or four inches thick, of which from four to six pieces may be required. The canal is cleaned of litharge, and one of the pre- pared oblong pieces dipped into water, and by means of a flat, cold iron, placed in the hot canal. The mass in- troduced must be pressed and slightly beaten with one of the red-hot bars till it seems to be well united. This operation must be performed quickly, so that the oblong mass is quite wet when touching the canal, and is then instantly pressed and beaten. Another slab follows now exactly in the same way, and so on, until the canal is filled level with the hearth, forming a solid mass. When this is done, fuel is introduced into the furnace quite moderately for half an hour, in order to dry the new. litharge bridge. The heat is then increased, and when the furnace appears light red-hot, the charging and cupelling of the lead is performed in the way described. This operation can continue for one or two wee^s, PROCESSES OF SILVER AND GOLD EXTRACTION. 161 according to the quality of the hearth. If, however, it were required to suspend the operation for one or more days, the hearth would crack in cooling, if not provided for. In this case, after the new litharge bridge has been made, the hearth and bridges are covered with ashes, and all draft shut as off close as possible. In mending the canal, much attention must be paid to the right consistency of the mass, and to having it wet immediately before the application. The mass must be soft, but must retain the form given to it. If too hard, or if the dipping into water be neglected, the lead would find its way through, coming forth in drops. In such cases where the drops are perceived, the hearth is hollowed about three inches deep, and stopped with some of the mass, using a red-hot iron. The litharge, if required, can be easily reduced to metallic lead by having a cylinder of cast iron in front of the litharge bridge. The cylinder is hollow, open at both ends, and the sides have a number of inch holes to admit the air. It stands over a cast-iron bowl, or on the floor, in which a hole is made for the reception of lead. The cylinder is filled with charcoal and set on fire, being about four feet high and twelve inches in diameter. The litharge is led over an iron plate into the centre of the cylinder. The oxyd of lead, fused and red-hot, coming into contact with glowing coals, is reduced to lead, and accumulates in the crucible below the cylinder, , which must always be kept filled with charcoal. 11 1^2 PROCESSES OP SILVER AND GOLD EXTRACTION. REFINING OF SILVER. Sec. 47. The refining of silver is the continuation of cupellation, when, as before described, the process is considered finished with the brightening of the silver. To this process all impure silver is subjected, but when copper or impurities are considerable, so that a pro- portionate quantity of lead must be added, requiring also a blast to effect the oxydation, and a litharge canal to draw off the litharge, then the refining is performed by way of cupellation. Retorted amalgam, obtained by the pan amalgamation without roasting, when melted into bars, is generally between 987 and 997 fine, not requiring any further refining. But in some cases the amalgam contains sulphurets, the sulphur of which re- mains to a considerable amount in the silver, when melted in the crucible. In pouring the metal into the mould, sulphurous acid is emitted, and its evolution con- tinues till the metal hardens, causing a dull, uneven sur- face. Such amalgam, as well as that from roasted ore, or silver, generally, if obtained in large quantities, can be melted to advantage in refining furnaces. The refining is performed in different ways. It is done in crucibles, having thus the smallest loss in sil- ver ; but only such silver as contains a small amount of impurities can be treated for this purpose in crucibles, which, on the other hand, besides requiring more fuel, are more dangerous than the hearths, on account of PROCESSES OF SILVER AND GOLD EXTRACTION. 163 being liable to break, and also expensive. The refin- ing is also executed in cast-iron dishes, which are lined with fire-proof material. These tests are placed in the refining furnace, exposed to the flame, or under a muffle, the last method requiring more fuel and silver not too impure. The most proper way is to refine in hearth fiirnaces. (Sec. 59.) There is little difference between them and the cupelling furnaces in regard to size, and no blast is used in either. The consumption of fuel is moderate, and also the loss of silver, if properly attended to. The quantity of silver which can be refined at a time varies, according to the size of the furnace, from one hundred to two thousand pounds. These furnaces may be con- structed to be heated either by flame or gas. The gas is produced by charcoal, coke, or anthracite. The silver is introduced when the test appears white- hot. The door is closed and the fire kept up till all the silver is melted. The retorted amalgam, on account ol its bulk, can be charged at once. Another portion is introduced and so on, till the test is full. When the last charge is melted, the silver must be stirred with an iron rod for a short time, and then the door is closed again for half an hour. If there are still ash-like impurities, swimming on the surface, they may be skimmed off, or one per cent, of lead is introduced into the silver and stirred again. The litharge will appear soon on the surface and, dissolving the dry scrapings, draw into the test. The stirring, at interval of half an hour maj be 164 PROCESSES OF SILVER AND GOLD EXTRACTION. repeated three or four times during the process. The silver becomes gradually clearer and brighter till finally the roof of the furnace is reflected on the lustrous sur- face of the bath. At this point the silver possesses the required fineness of about 999*5, and to prevent its volatilization its surface must be covered with charcoal powder immediately. The metal may be dipped up and poured into moulds, keeping up continually a strong heat, or it may be cooled in the furnace and taken out in the shape of a cake, in the same way as described in Sec. 46. The melting may require two or three hours and about the same time must be spent for refining, so that the whole process takes from five to eight hours, according to the quantity of silver introduced. PATTINSON'S CRYSTALLIZATION PROCESS. Sec. 48. This process, for the purpose of concentrat- ing the silver in the lead, is founded on the fact that lead, if alloyed with silver to a certain proportion, is more liquid than pure lead, or lead alloyed in a very small proportion with silver. The advantage of this process is the reduction of the quantity of lead, which otherwise would have to be separated from silver by cupellation. When a sufficient quantity of lead, containing silver, is melted in a cast-iron vessel and uniformly cooled, small crystals will form, increasing in quantity. These crys- tals, when taken out by means of perforated ladles, will PROCESSES OP SILVER AND GOLD EXTRACTION. 165 be found a great deal poorer in silver than the fluid remainder in the kettle, which again will be found richer than the original lead. On account of the adherence of fluid lead to the crys- tallized, the separation cannot be perfect, but repeated recrystallization of the crystals results finally in two sorts of very poor and rich lead. There is, however, a limit, beyond which no concentration to a higher degree can be effected. According to Professor Reich, the melting tempera- ture of lead, containing 0*0065 per cent, of silver is 610** Fahrenheit. Lead, containing 0*476 per cent, of silver melts af 588° ; but lead containing 2*25 per cent, of silver melts at the same temperature as pure lead, con- sequently no crystallization of poor lead can take place. Alloys of equal parts of both metals, or three parts of lead to one of silver, require a higher temperature of melting than pure lead. The following table shows the proportionate progress of the enrichment of lead, by crystallization of the poor : Amount of silver in pig lead. Amount of silver dipped in crj'stals. Amount of silver in the liquid remainder. 0-704 per cent 0-732 « 0-966 " 0-988 " 1-442 " 0-390 to 0-466 0.318 " 0-374 0-410 " 0-680 0-390 " 0-624 0-682 1-025 1-076 1-450 1-530 1-922 2-090 " 2-011 2-260 2-206 " 2-216 2-246 2-206 " 2-212 2-264 166 PROCESSES OF SILVER AND GOLD EXTRACTION. The good result of this manipulation depends — 1. On the right management of the temperature. If the temperature be too low, no separation can be obtain- ed, and if on the other hand the lead is too hot no per- fect formation of crystals can take place. 2. On the right quantity of lead which is taken into operation. It requires at least two tons and a half, in order to effect a slow change from the fluid into solid condition, affording thus sufficient time to remove the crystallized lead. 3. pn the number and size of iron kettles, depending on the quantity of lead designed for this process and on the amount of silver in it. The right temperature, the time of crystallization, and the preservation of temperature must be found by experiments. The use and advantage of this method depends principally on the quality of the lead and the quantity of silver in it. The process will succeed if the lead is free from other base metals. Antimony and copper aggravate the formation of crystals, from which the liquid lead separates with difficulty. The produc- tion of pure lead, also an object of this method, cannot be obtained in that case. If, therefore, such impure lead is designed for crystallization, it must be subjected first to purification, causing thus expense and loss in metals. This purification of impure lead, especially if antimony is present, may be executed by melting it in a reverb- PROCESSES OF SILVER AND GOLD EXTRACTION. 167 eratory furnace at a very low temperature, keeping it for some time in such condition. It forms then a crust on the surface, which principally consists of oxyd of lead and antimonate of oxyd of lead. This crust must be drawn off as long as it appears, or stirred by increased heat with addition of lime and charcoal dust, by which a great part of the lead is reduced again. But it is evident that under such circumstances, even when the purest lead would result from subsequent crystallization, a direct cupellation in California and Nevada Territory is more advantageous, and that, if the cupellation on account of too small amount of silver would not pay, the crystallization, depending on the purification of lead, would pay still less. If the lead is not overloaded with base metals, but containing, however, so much as to interfere with the crystallization, a more simple refining may be adopted. The lead is introduced into a Pattinson kettle melted and stirred with a wooden rod, by which the lead is brought into a turbulent motion, exposing always a renewed surface to the air, promoting thus the oxyda- tion of the base metals. The impurities are drawn off, till they cease to appear. The number of kettles required for crystallization is determined principally by the amount of silver. The process offers the best advantage, if the lead contains from five to ten ounces per ton. In this case, a few crystallizations render two kinds of lead, one poor, the other rich; the latter ready for cupellation. At a 168 PROCESSES OF SILVER AND GOLD EXTRACTION. higher amount of silver the process is prolonged, caus- ing more expense for fuel and labor ; but under favor- able circumstances, for instance, if very pure lead is obtained which would command a better price, then also lead containing from fifty to sixty ounces per ton could be advantageously subjected to the concentration process. The degree to which the concentration is carried on is important, because, besides the increased expense for labor and fuel, a very rich lead produces a richer lith- arge when cupelled. The concentration accordingly ought not to exceed four or five hundred ounces per ton. Lead, containing silver in such small proportion as will not pay the expense of cupellation, can be worked advantageously by way of crystallization. The low temperature does not much affect the lead, and besides when the lead is pure the loss in silver is insignifi- cant. The loss of lead in England, which is generally pure, amounts to two per cent. Other qualities of lead, in Germany, suffer a loss of three per cent., while the loss in cupellation and the reduction of litharge amounts to from eight to ten per cent. Generally there is no gain on fuel or labor in this process, compared with cupellation. If there is a considerable amount of silver in the lead, the crystallization may be even more expensive, but the gain in lead may cover the differ- ence and leave also a profit. This, however, depends on the price of lead. CHAPTER VI DESCEIPTION OF MACHINERY AND FUENACES. COMMON IRON PAN. Sec. 49. Fig. 22 represents a common iron six-foot pan. Fig. 23 is a vertical section of Fig. 22 on the line A B ; a shows a wooden cross, to which the wooden block, ^, with the iron shoes, c, are fastened by the bolts, d. Each shoe has a pin, e, about one inch long, fitting in the wooden block, in order to prevent movement. On the shaft, y, is the yoke,/, fastened by a key. The two ends of the yoke fit in the holes, h, of the cross, a, but ngt too tight, so that the muUer can follow the wear of the shoes. Pans, having the gear underneath, and the shaft through the cone, e, are so arranged that by means of a screw the muUer can be raised. This ar- rangement for raising the muller is not important, as the muller generally grinds with its full weight. The steam is introduced into the pulp, through the pipe, I; k, Jc, are the discharge pipes -, m represents the false hot- 170 PROCESSES OP SILVER AND GOLD EXTRACTION. torn, made of one piece, two inches thick. This bottom must be one inch less in diameter, so that half an inch of free space is left between the bottom and the pan on the sides, and on the cones. The best way to fasten these bottoms, and also to prevent the quicksilver from getting under them, is the following : Strips of strong cloth, two inches and a half wide, are laid over the space between the bottom and sides, which is filled with a paste of iron filings and wedged with well dried wooden wedges, quite close together, so that the cloth is equal in height on both sides of the wedges, which are driven in tight. The wedges must be a little shorter than the thickness of the false bottom, leaving thus a space above them, which is covered with a paste of iron filings. WHEELER'S PAN. Sec. 50. Fig. 24 shows the ground view of the pan, and Fig. 25 the vertical section of Fig. 24, on the line A B, For the sake of clearness of representation, the yoke, a, and the guide-blade arrangement, g, l\ 3, c, of Fig. 25, are not represented in Fig. 24, but the position of the guides is shown by dotted lines, c. The muller, c?, and the ring, ^, (the two journals of which move in the box,/, fixed to the muller, while the other two, ^, move in the box, ^, of the yoke, a) cover only half of the pan, Fig. 24. The other half shows the dies, /, laid directly on the bottom of the pan, Iz, They are kept in place PROCESSES OP SILVER AND GOLD EXTRACTION. 171 in the centre by the ring,/, and on the sides by the in- clined ledges, L Each die has for this purpose a projec- tion, «2, which is placed under the ledge, I, with the beveled side, as represented in Fig. 26, m\ The dies are one inch thick, beveled on each long side in the same direction, so that, in putting them together, the groves, i% are formed. In Fig. 25 the muUer, d, shoe, n, and die, e, are repre- sented on one side. The muller has twelve oblong openings, d\ two and one-fourth inches wide by ten and three-fourths long. One of the long sides towards the dies is beveled, as shown by the dotted lines, 5. The projection on the shoes is of the same shape, being only half an inch narrower and as much shorter, so that the space of half an inch is wedged with dry pine wood, n\ by which the shoe is fastened to the muller. The shoe below the muller is represented by the dotted lines o. On the outer ledge of the muller are inclined ledges, o\ which, in connection with those of the pan, /, create an upward current of the pulp ; c, c, are guide-blades con- veying the pulp to the centre. These guides have at the outer end a projection, like a hook, as indicated by the dotted lines c, c. This hook catches the blade, p, which is also bent hook-like, fastened to the pan by an iron wedge, between the ribs,jt?*. Thus the guides resist the current of the pulp. The guide-blades, c, are connected with the frame, q, formed of four rods, screwed to the ring, h\ which again is in connection with the lower ring, b, by four bolts, to 172 PROCESSES OF SILVER AND GOLD EXTRACTION. which the guides are attached. The frame rests by means of the screw, ^', on the shaft, r, and can be raised or lowered. a is the steampipe, conveying the steam directly into the pulp ; u shows the steam chamber, if the pulp is to be heated through the bottom. This, however, has proved unnecessary, and it consumes more fuel. On that account no more pans of this kind are made with a steam chamber. As a consequence, the arrangement with the box, t, is also altered, and affords more conve- nience in oiling and handling ; w and w' show the appa- ratus for raising the muller. By screwing the rod, ^, the muller will be raised gradually, but if a sudden lift is required, the rod must be pushed down. The dies, as well as the bottom of the pan, are not so perfect as to fit exactly without giving way a little in one place or another, thus presenting an uneven grind- ing surface, and causing a jarring for many hours after starting. To avoid this, some wet, muddy tailings, or ore, is introduced into the pan and spread uniformly, nearly half an inch deep. Each die is then laid in the proper radial direction, the projection of the outer end under the ledge, I, and imbedded well into the mud, till it lies solid and level. Care must be taken that the stump edge 1, Fig. 24, does not project over the sharp edge 2 of the next die. When all twelve dies are set in, the collar, /, is put over the heads of the dies, and fastened by turning it under the nuts of the centre- piece 3. The spaces, V and if, are filled with wet ore, PROCESSES OP SILVER AND GOLD EXTRACTION. 173 level with the surface of the dies, and the muller placed over them. Some water is poured over the muller, then some diluted mud, and allowed to rest for about two hours before starting, in order to effect the swelling of the wedges, n\ Above the pans a sliding block is required, for the purpose of lifting the muller. The muller must be lifted at least once every week, and pan and muller cleaned from adhering amalgam, which accumulates round the centrepiece, preventing the ore from passing freely under the muller. The first three or four charges require two or three hours' longer grinding, on account of the roughness of the shoes and dies. These pans are made in the Miners' Foundry, San Francisco. WHEELER'S AGITATOR. Sec. 51. Fig. 26 represents a vertical section of the agitator (exclusive of the arms, a, which are shown in a front view). The upright shaft, h, is hollow for the purpose of conveying the water through the arms a, of which there are four, into the pulp, in order to dilute it for an easier separation of the amalgam from the sand. If, however, it is treated as described in Sec. 27, no dilution is required, therefore the hollow shaft and arms are superfluous and may be replaced by solid ones. In case the pulp is too thick, some water may be added in the pan, several minutes before the discharge. 174 PROCESSES OP SILVER AND GOLD EXTRACTION. The shaft, h, slides in the gear, as much silver as possible. The operation becomes extended, so that the loss of silver must increase. The cost of liqua- tion of one hundred pounds of copper will be more than the value of the four and a half ounces of silver. The black copper is first broken in small pieces cold, or it is made red-hot, which facilitates the breaking, or it is melted and poured into cold water (granulated), PKOCESSES OF SILVER AND GOLD EXTRACTION. 233 and then melted with lead. Each ounce of silver requires thirty to thirty-two pounds of lead, but the proportion of lead to copper should not be over 11 : 3. Lead and copper in the proportion of eleven to three, in regard to the above mentioned proportion of lead and silver, are melted in a cupola furnace with aid of the bellows. The alloy is poured into moulds, assuming the shape of a disk eighteen inches in diameter, and from three to three and a half inches thick. These copper disks are laid on two inclined iron plates in an oven, in such a way that a space of one or two inches is left between each disk. They are covered with charcoal, and it ignited. The lead soon commences to trickle from the disks, and runs on the inclined iron plates, through the split which is left between them into a basin underneath. "When the lead ceases to flow, the operation is finished. The lead is given over to the cupellation. The spongy copper contains from ten to twenty per cent, of lead. If this copper is found to be rich in silver, it is fused again with lead and treated as before. If otherwise, it is subjected to the sweating process. The sweating is performed in another furnace at a stronger heat, to get rid of another portion of lead, which however is obtained in an oxydized condition. The unfused copper is purified on a refining hearth. Extraction op Silver by Copper and Lead. The object of this process is the decomposition of the 234 PROCESSES OP SILVER AND GOLD EXTRACTION. sulphides of silver in the ores and matts, combined with an extraction of silver by lead. The decomposition of silver sulphurets by copper is not perfect for the reason that when copper prevails, an alloy of silver, copper, and matt is formed which retains a great deal of sulphide of silver. If there is also lead in the ore or in the melting product, this will be eliminated with the silver while an equivalent quantity of copper enters the matt. Copper-Dissolving Process. The principle of this process is as follows: If ar- gentiferous matt is melted together with copper and plumbiferous products, the copper enters the matt, while the eliminated silver is taken up by the lead. At the same time the lead acts, desilvering the matt. If too much copper is added it does not remain dissolved in the matt, but separates partly again, and enters the lead. If the copper contains silver, this will be also extracted, so that the copper need not be subjected to another extraction, for instance, by liquation or amal- gamation. The usefulness of this process depends gen- erally on local circumstances, especially on the propor- tion of matt and black copper, which is obtained in melting. If too much matt, then the extraction of silver is imperfect ; on the contrary, if too little, the black copper cannot all be dissolved by the matt, but alloys with the lead. Under suitable circumstances, this process is advan- PROCESSES OF SILVER AND GOLD EXTRACTION. 235 tageous. It is preferable to the liquation process, because it allows a more perfect desilverization of the matts. SEPARATION OF SILVER FROM ARGENTIFEROUS LEAD. CUPELLATION OF PiG LeAD. Sec. 71. Cupellation, the object of separating silver from argentiferous lead, is executed in such a way that the lead on the hearth of an oven, under influence of heat and compressed air, is converted by degrees into an oxyd of lead (litharge) which draws to the periphery from the convex surface of the fused lead, exposing thus the metal constantly to the oxygen of the air. Drawing off this litharge as it is formed, the silver finally remains in the hearth. The old cupelling furnace has no separate fire-place, but the lead was melted in the hearth between fire- wood ; the blast was directed on the lead, over which burning wood was maintained till the process was finished. This mode requires much more fuel and the oxydation of lead is imperfect. There are two modes of cupelling in use : The Ger- man on fixed hearths, and the English on movable tests. CupellaUon in unmovahle Hearths, — The German cupel- ling-furnaces are constructed of two principal parts 3 of 236 PROCESSES OF SILVER AND GOLD EXTRACTION. the fire-room and of the cupelling-room, connected by a fire-bridge. The cupelling room is formed by a circular block of mason-work about fifteen inches above the ground, provided with channels for the escape of mois- ture. On the periphery of the block, the wall from twelve to fifteen inches thick is carried up twenty inches, forming a wall-ring, of which the inner space receives the material for the hearth. The coppel or hood is formed of many iron bars well riveted, and with many little hooks for the purpose of holding the clay lining. There have been also clay coppels in use, weighing over a ton ; the iron ones, from 1,100 to 1,300 pounds, are generally preferable for many reasons. By means of a crane, three coppels can be lifted and turned aside. Arches of brick, used in some places, are less convenient. They must form high coppels {^Ye and a half feet) to resist the effect of heat and lead fumes longer; they are a great deal cheaper, but the iron ones stand ten times as long. The iron skeleton of the coppel is lined first with loam, then with a mixture two inches thick of three parts of clay and one part of quartz. In the wall-ring, coarse slag is introduced or rock of the size of one's fist, about twelve inches deep in the centre, and sixteen to eighteen inches deep on the sides, forming a concave surface. Over the slag comes a row of brick and then the hearth-mass. Lixiviated wood- ashes are not much in use, but replaced by the marl which is a much better hearth material. The marl is PKOCESSES OF SILVER AITD GOLD EXTRACTION. 237 cheaper, it does not absorb so much litharge, and the result in regard to the quantity of silver is always better than on a test of ashes. It is pulverized and sifted through a sieve of about sixty-four holes to the square inch, then very evenly moistened, introduced in the hearth and stamped hard from four to six inches thick. The whole mass may be introduced at once, or in portions. The hearth must be hard enough so that no impression can be made with the finger. The con- cave hearth in the centre is six to eight inches deep and from six to ten feet in diameter. The wall-ring is continued about two feet and a half above the hearth, and contracted for several inches on the top, on which the coppel rests. This ring has several apertures : one litharge hole, another hole opposite the fire-bridge through which the lead is introduced, and two holes for the tuyeres. The hearth is charged either at once with so much lead as is intended for one trip, from five to twelve tons, or is filled with lead, and more added during the operation, in the same proportion, as litharge is drawn off. The latter way is preferable for this reason, that a smaller hearth can be used and less wood consumed on the same quantity of lead. A large hearth must be kept at a hig*her heat. This makes the hearth softer, and the mass absorbs more litharge. But the addition of lead, during cupellation, yields an impure litharge which, when reduced, renders a low quality of lead. When the lead is charged, the coppel is placed on 238 PROCESSES OF SILVER AND GOLD EXTRACTION. the wall-ring, all clefts and little cracks are covered with loam and a slow fire started. By increased heat, the lead melts down, leaving all impurities on the surface. These impurities or dry scrapings (German, Ahzug) are skimmed off. They contain a great deal of lead, copper, antimony, arsenic, also silver in oxydized and sulphuretted condition. If the pig lead is of pure quality, the scrapings are not regarded. The surface of the lead after the removal of the dry scrapings does not remain clear for a long time, but becomes again coated by a crust. This crust, after the drawing of dry scrapings or after the melting of pure pig lead, must be scorified by in- creased heat and brought into fusion, admitting at the same time the blast. The fused crust or black-litharge scrapings, or froth (German, Abstrich), must be drawn off likewise. In the commencement it is spongy, black, has an imperfect metallic lustre, but assumes a gray greenish-yellow color at the end of the period. It con- tains metallic and oxydized lead, besides oxyds of zinc, iron, bismuth, antimony, arsenic, etc. ; the antimony especially concentrates in it to a considerable amount. Dry scrapings and the black litharge contain more silver than the litharge. The main part of the com- pound is oxyd of lead which has the property of taking up the sulphides of antimony and arsenic, by which again the sulphides of copper and silver are brought into the combination. While the black litharge is drawn, heat and blast PROCESSES OF SILVER AND GOLD EXTRACTION. 239 must be increased, in order to hasten the scorification. To facilitate the drawing, some moistened coarse char- coal is thrown on the surface by which the froth assumes a spongy condition, when it is easily removed. The quantity of this froth depends on the quality of the lead. When the black color of the froth changes into greenish-brown, assuming a more tough consistency, the oxyds of zinc, iron, and copper are mostly removed, and the black litharge consists in the greatest part only of the oxyds of lead and antimony. The more the latter is eliminated the more the yellow color of the oxyd of lead appears. The tough, scori-like condition disappears, and a short, scaly state appears. The mass flows no more down the floor, but hardens in front of the furnace. As soon as this change appears the drawing of froth is finished, and the temperature must be lowered. The breast of the furnace or the litharge-bridge is cleaned, then a channel cut or scratched by an iron hook or saw-like instrument. Through this channel the litharge runs, wherein it is driven by the blast. The litharge channel, at a proper cupellation should be cut so deep only that the litharge ceases to flow, when the wind is stopped. The formation of litharge is difficult, if the antimony does not depart with the black litharge, because the lead has little inclination to oxydize before the antimony. This explains the long duration of some cupellations. Generally the temperature must be kept as moderate 240 PROCESSES OP SILVER AND GOLD EXTRACTION. as possible, otherwise more lead and silver will volatilize. A hot litharge also eats the channel too much, and causes the escape of some lead. If the cupellation is kept too cold, the silver, which is in the unsufficiently liquid litharge, cannot come in contact well enough with the lead to be reduced again, consequently the litharge from too cold cupellation becomes richer in silver. At a too high temperature, more litharge is absorbed by the hearth, which is injurious, but this cannot be avoided entirely even by the best conducted heat. On the edge of the bath, by escaping moisture and carbonic acid of the hearth a throwing up of bubbles is created, which follow the edge of the bath when the periphery of the lead decreases. The bubbles cease shortly before the brightening or concentration in the centre. It indicates too much heat if this boiling is violent, but it should not be too weak. Care must be taken to keep always a sufficient quantity of litharge on the periphery of the lead-bath. The blast can be regulated in any required direc- tion. In the first part of cupellation the blasts (of two tuyeres) have a divergent direction. According to the difierent position of the litharge the direction can be modified. At the end of the operation the blasts may cross each other. Hot air did not answer in all places. The addition of lead commences as soon as a good run of litharge is observed. It is introduced by the feed-hole and placed on the brim of the hearth. Time and quantity of feeding depend on the progress of PROCESSES OF SILVER AND GOLD EXTRACTION. 241 cupellation, and are indicated by the litharge and lith- arge-channel. At the end of the operation when less litharge is formed, the bath assumes a bright color. This is an indication that the period of brightening is approaching. The bath becomes covered with a net-like coat, movable on the convex surface, consisting of lith- arge-spots, between which the silver glances through. These spots grow larger, till at last the net breaks and the litharge slides to the sides, producing a peculiar shine which is called the brightening, distinguished by a play of colors. The colors are produced by the separa- tion of the last of the oxyd of lead in very thin layers, through which the light passes, being reflected by the silver under a certain color. The kind of color depends on the thickness of the coating, which grows gradually towards the silver of the convex surface, producing the variety of colors, in a certain system. This is going on as long as oxyd of lead is emitted, and ceases when the silver becomes fine. The purification can continue under a strong heat, till to the required fineness, which in large furnaces however is not done on account of the consume of fuel by which the extensive space must be kept at a high temperature. The silver is generally taken out after the brightening, and the five or ten per cent, of foreign substances which are left in it, separated by refining. After the brightening the wind is stopped, the silver cooled first with warm then with cold water and finally broken out by means of a long chisel. 16 242 PROCESSES OF SILVER AND GOLD EXTRACTION. The products of cupelling are the following : a. The black litharge, or froth, is a very impure, ferrif- erous and copperous litharge, obtained in the first part of the operation. This litharge is not suitable for the market, neither for the reduction process. Generally it is melted with the ores. The black litharge contains sometimes as much lead as the yellow. The first lith- arge shows generally a brown or greenish color, caused by iron and copper. The affinity of copper and lead to the oxygen seems to be equal, as there is always some copper in the litharge from the beginning to the end of the process. h. The poor litharge is the second litharge. It first looks yellow, but on getting cold, cracks in all direc- tions. In the clefts arises a red, scaly, easily pulverizing product (the red litharge) while the rapidly-cooled crust retains its color and cohesion (the yellow litharge). The red litharge is the same chemical combination as the yellow, in an isomeric modification, differing only by structure and color. The production of the red litharge can be promoted by drawing the litharge from the cupelling furnace into hollow cylinders of sheet-iron, in which it cools, assuming a red color and the fine condi- tion. This is the best article for the market. The yellow litharge is quite suitable for reduction. c. The Rich Litharge. — This product is obtained in the last hours of cupellation. Being richer in silver this litharge is never sold but melted with the ore. PROCESSES OF SILVER AND GOLD EXTRACTION. 243 d. The Silver, — The fineness of the cupelled silver depends entirely on the time consumed after bright- ening. e. The Hearth. — The hearth always retains more silver than the litharge, the silver of which is taken up by the lead during the longer contact. This is not the case with that litharge which draws into the hearth- mass. When the cupellation is finished and the furnace cooled down, the hearth is broken out and the heavy part, saturated with oxyd of lead, given over to the melting manipulation. Cupellation in Movable Hearths. — This mode is prac- ticed chiefly in England. These cupelling-furnaces differ from the German in two points : firstly, they have a fixed flat arch; secondly, the hearth-mass is generally bone-ash. The tests are prepared outside of the furnace in oval iron test-rings, four feet in the larger and two and a half feet in the smaller diameter. These tests are placed into the furnace from beneath, leveled, and the room between the test-ring and furnace- wall filled with fire-proof material. Generally, the Eng^ lish pig lead is so poor in silver that it must be concen- trated by Pattinson's crystallization process. Fine, pulverized bone-ashes are moistened with water containing some potash, then introduced into the test- ring and beaten in. The test is so cut out that the brim above is two inches, and at the bottom three inches thick, and the bottom itself one inch. On the front u 244 PROCESSES OF SILVER AND GOLD EXTRACTION. side the test brim is five inches wide, containing an opening for the litharge. The test is brought into the furnace, dried, and then heated to red heat. The lead is introduced in fused condition, and the temperature raised till the crust melts, when the blast is thrown in, by which the lith- arge is driven to the front. By the addition of fused lead, the surface is always kept at the same level, till about Rye tons of lead are cupelled. The cupelling is then so far continued that the alloy may contain two or three hundred times as much lead as silver, where- upon the alloy is tapped, the tap-hole shut and the con- centration continued in the same way. When so much rich lead is obtained that a silver-cake of from 3,000 to 5,000 ounces can be expected, the cupellation on it is executed in the described way. Heated steam in place of wind yields a finer litharge. CONCENTRATION OF SILVER IN POOR PIG LEAD, By Pattinson's Crystallization Pkocess. Sec. 72. Most of the English pig lead is poor, being produced from galena, generally under twenty ounces per ton. The silver of such poor lead could not be extracted advantageously prior to the year 1833, when Lee Pattinson patented a new mode of concentrating the silver in argentiferous lead. This procedure permits the extraction if the ore contains only three ounces of silver per ton. PROCESSES OF SILVER AND GOLD EXTRACTION. 245 This method is founded on the fact that if an alloy of lead and silver is melted in an iron kettle and cooled, while often stirred, lead crystals will form at a certain temperature which are poorer in silver than the remain- ing liquid. The crystals are removed by means of per- forated ladles, and several repetitions of the same pro- cess on the crystals and the enriched lead will yield a very poor lead of commerce and a rich part for the cupellation. Besides the advantage of being enabled to extract small quantities of silver, this process yields also a purer and more valuable lead than that of reduced litharge. Although the cupellation of the enriched lead sustains a loss of at least five per cent, of lead, the average is nevertheless below two per cent., while the cupellation of the whole mass would sufier from seven to eight per cent, loss of lead. Very little or nothing is saved, com- paratively, in fuel and labor. This process requires strong rather than skillful hands. Lead, containing about five ounces per ton, offers the best advantage. At a higher amount of silver the expenses for labor and fuel increase, and the process is considerably delayed, still in many places lead with from forty to fifty ounces is concentrated with pecu- niary advantage. Impure lead, containing antimony, arsenic, zinc, or copper, is not suitable for concentra- tion, the separation of silver being imperfect. Such lead is first purified by continued heating in a reverber- 246 PROCESSES OF SILVER AND GOLD EXTRACTION. atory furnace or by stirring in a kettle with an unsea- soned rod, and skimming oflf the impurities. The good result of this process depends also on the right conduction of the temperature. If this be too low, the separation of crystals cannot take place, because the whole mass stiffens too soon. On the contrary, if too hot, no crystals can arise. Only a large quantity of lead will give a good result, because the transition of the liquid into the stiff state is only slow enough in a large quantity to give sufficient time for the removing of the crystallized lead. Many experiments have failed because operated with too small quantities. Generally, in England, such lead is concentrated as contains from five to ten ounces of silver per ton, in lots of from 2*5 to five tons in four or nine cast-iron kettles, taking about fifty tons for one trip in succession. It requires several days to work up this quantity with two or four men. At a battery of nine kettles, for instance, the lead with about ten ounces silver per ton is introduced in one of the middle kettles, and cooled down after it has been melted. The crust from the sides of the kettle is thrust into the liquid lead by means of an iron paddle, stirring at the same time the mass. With an iron perforated ladle (of which the handle is nine feet long, the ladle from twelve to fifteen inches diameter, six inches deep, with three-quarter inch holes in the bottom), the crystal- lized lead is dipped from the bottom of the kettle, and after the liquid lead drops off by shaking the ladle, it is PROCESSES OF SILVER AND GOLD EXTRACTION. 247 laded into the next kettle on the left. This is done till about ^^ of the original quantity, with an average amount of five ounces silver is transferred. The next ~^^ with about ten ounces silver, is laded temporarily into a flat kettle. The last ^^ with twenty ounces of silver is transferred to the first kettle on the right. The lead from the flat kettle with ten ounces of silver, is introduced again into the first, with another portion of the original lead, and proceeded with in the same way as long as there is lead of ten ounces of silver at hand. As soon as the kettle with the crystals on the left with five, and the kettle on the right side with the enriched lead containing twenty ounces of silver per ton, are filled, the separation is executed in both, and afterwards in all the following kettles, in the same manner as it was done in the first one. From the last kettle on the left side the lead is not further concentrated, but laded into moulds for the mar- ket. It contains from one-fourth to one-half ounce of silver per ton. The enriched lead of the last pot has from two hundred to four hundred ounces of silver per ton. The following scheme gives a view of the procedure of the work : 248 PROCESSES OF SILVER AND GOLD EXTRACTION. W ^ 03 m s '^ So 2 g ^ Hi CO >, holes, each half an inch square. By these holes the draft is regulated. The draft-holes of the muffle must be carefully covered with pieces of bro- ken muffles, then the charcoal in large pieces introduced around the muffle. The aperture is closed by a tile with a hole in it, through which the inside of the muffle can be seen. The furnace is filled with charcoal and the fire started. When molten, the silver must be stirred often by means of an iron hook, and the process continued by closed or open muffle, as the temperature may require, till no forming litharge is perceptible, and the metal looks perfectly bright. When this state is obtained, the silver-cake is cooled with water. The metal will soon commence to spit. An iron hook is pressed into the sil- ver, on the spot where the spitting takes place, and by means of it, the silver cake is taken out. At Oker on the Hartz, eight hundred ounces of the introduced silver yields seven hundred and sixty ounces fine silver in five hours. PROCESSES OF SILVER AND GOLD EXTRACTION. 257 Procedure of the Mhxt at Clausthal — The iron test-bowl is filled with wood ashes, well lixiviated, and beaten in level with the edge, whereupon a cavity is cut out about twelve inches in diameter, and from three to four inches deep. There are three furnaces of the preceding des- cription, each for one muffle, and two larger ones, in each of which 'four muffles are placed. The latter fur- naces are provided with four draft-holes on the back wall. The smaller ones have holes on two sides, and one behind. The tests are placed in the furnace as above described, charged with seven hundred ounces, and by closed muffle, melted down in about two hours. After this the muffle is opened and the metal stirred for some time with an iron hook, then shut up for half an hour, and then stirred again. This is repeated three times at intervals of half hours, whereupon the last heat is given, half an hour long. During the stirring, lith- arge eyes are produced on the surface of the bath. At the end of the operation they disappear. As soon as the silver looks perfectly bright, it is cooled by pouring wa- ter on it. The spitting is impeded by keeping an open hole in the centre of the cake with an iron hook. B. Refining in Reverberatoey Furnaces. The reverberatory, or flame furnaces, have movable or fixed hearths, and are covered with an arch or mova- ble cap. They do not difier much from the cupelling furnaces, save the size. The heat is produced by wood, coal, or gas. 17 258 PROCESSES OP SILVER AND GOLD EXTRACTION. The test-rings, or brick hearths, are prepared either with lixiviated wood ashes, or with fine, sifted marl. The properly cut and dried test is placed in the furnace, the silver introduced, covered with small charcoal, and heated to nearly white heat at well closed doors. To avoid losses of silver, it is a principal rule to cover it with fine charcoal or saw-dust, and to - melt it down quickly, and to refine it at a lower temperature. The silver volatilizes at the beginning of the white heat, especially under draft; this must be kept from the sil- ver by the cover of charcoal. The more antimony, arsenic, or lead, the silver contains, the easier it volatil- izes, requiring the charcoal cover to be kept on it so much longer. When molten, and no more silver is add- ed, the slag is drawn off, the metal stirred, and the sur- face cleaned. The temperature is so conducted, that the eyes, swimming on the surface, should not glide too fast towards the sides. At a too high temperature, the sil- ver assumes a vibrating motion, many pearls hasten from the middle towards the periphery, and the silver does not adhere to an iron rod, if quickly dipped in and withdrawn. The temperature is too low, when on the edge of the silver bath commencing refrigeration be observed. If the fusion is not easily obtained, some lead, from four to six per cent., may be added. Easy refrigerating and slow refining silver requires some copper. If, after some stirring, a bright surface is observed, the assay must be taken, by dipping a curved iron rod about half PROCESSES OF SILVER AND GOLD EXTRACTION. 259 an inch deep into the silver till the latter assumes a pear-like shape. It is pure if no spots of litharge or oxyd of copper are perceived on it, and if the silver runs off, or endeavors to drop off, when dipped again. In the reverse case, the refining must continue. When fine, the silver is cooled with water and removed. In Freiberg, the refining furnace is charged at once with from twelve hundred to thirteen hundred pounds of silver. Repining in Crucibles. Generally only the purer silver is subjected to refin- ing in crucibles. The melting is performed either in a black-lead or cast-iron crucible, either with charcoal or with the flame of coal, in reverberatory furnaces, in which the crucible is placed. The black-lead crucibles at Freiberg have been replaced by cast-iron ones in flame -furnaces, offering many advantages over the for- mer in draft furnaces, with charcoal. The loss of silver by volatilization was brought down to the minimum, while, when exposed to the strong draft of the crucible furnace in a black-lead crucible, it was considerable. The use of coal proved more econom- ical than charcoal, and the iron crucibles stood longer than the black-lead crucibles. At a white heat in an uncovered crucible the silver loses about one per cent, per hour. At Przibram (Bohemia) the crucible is charged by degrees, with from 4,800 to 9,600 ounces of silver, and 260 PHOCESSES OF SILVER AND GOLD EXTRACTION. melted in five or six hours. A mixture of two parts lixiviated ashes, and one part bone-ashes, is introduced on the molten silver, by means of an iron ladle, stirred in such a way on two places, as to obtain two openings in the mass, through which the oxygen of the air can come into contact with the silver. The oxyd of lead is taken up by the porous mass, and this removed by means of a ladle. This operation must be repeated at gradually longer intervals, till the silver commences to boil and to show a bright surface. After this, a mixture of one ounce and a half of borax with the same quantity of saltpetre, is introduced, and then the slag skimmed off, after a quarter of an hour's time. The silver is im- mediately covered with charcoal dust and a good heat applied for a quarter of an hour, when the silver is dip- ped into moulds. This method suffers a small loss in silver, consuming comparatively very little fuel, but the operation requires more time. CHAPTER IV EXTKACTION OF SILVER IN THE WET WAY. A. EXTRACTION BY QUICKSILVER OR AMALGAMA- TION. Sec. 75. Where gold and silver ores were found in large quantities, but no fuel, it was necessary to search for other means of reduction than heat, and this was found in quicksilver. Poor silver ores, containing small quantities of lead, are also suitable for amalgamation. The extraction of silver by quicksilver is founded on the property of the latter to form an alloy with the silver, which can be separated by heat. A procedure for extracting the silver from ores by quicksilver was first published by Bartolom^ de Medina in Mexico, in the middle of the sixteenth century. In the year 1784 the amalgamation was introduced in Europe first by Born, at Vienna, in copper kettles, then by Gellert in tubs, and finally by Ruprecht, in barrels. The amalgamation, compared with melting, has the advantage of saving fuel, rendering the silver in a short time, — unlike the melting by which the silver is carried 662 PROCESSES OF SILVER AND GOLD EXTRACTION. through many intermediate products, causing thus more loss in silver, expense of time and money. There are chiefly three modes of amalgamation : 1. European Barrel-Amalgamation. 2. American Amalgamation. a. Heap- Amalgamation (Patio). h. Kettle-Amalgamation. 3. Combined European and American method. European Barrel Amalgamation. The European barrel-amalgamation is more perfect than the patio-amalgamation, yielding the silver in much shorter time and with less quicksilver consume, but makes the use of more machinery and fuel neces- sary. In both methods the silver must be converted into a chloride and decomposed in the barrels by iron, in the patio by quicksilver. The European method is applied to ores, matts, and black copper. Amalgamation of Silver ores. All silver ores are not suitable for amalgamation. Copper, lead, antimony, arsenic, and zinc, are not agree- able customers, partly because they enter the amalgam, and because they effect losses of silver and quicksilver by volatilization, also impede the amalgamation and produce richer tailings (the last is caused by lead). The PROCESSES OF SILVER AND GOLD EXTRACTION. 263 zincblend needs a strong heat, but decomposes the salt very little. Argentiferous blend loses a great deal of silver by volatilization. Iron acts favorably ; manganese, nickel, and cobalt are not injurious. Experience shows that, concerning earthy matters, quartzose ores yield more silver but less pure amalgam, and cause larger loss in quicksilver, while calcareous ores work better on quicksilver, giving also purer amalgam, but less silver. The best economical result is obtained by mixing both kinds. Clayish ores are amalgamated with difficulty. The ores best suitable are the pyritous, sulphuretted silver ores, without regard to richness, but salt and quicksilver must be regulated according to the richness. In roasting the ore with salt, a certain amount of pyrites is necessary for the formation of chlorine, which is ascer- tained by an assay for matt. If there is no pyrites in the ore, iron or magnetic pyrites, matt or green vitriol, must be added. The Roasting — With the intention of forming chloride of silver — is one of the most important preparations of the ore. It must be executed with great care. In Freiberg, one charge used to be four hundred and fifty pounds. It is introduced into the dark red furnace, carefully spread on the hearth, stirred and the lumps broken with a long-handled hammar. After this, a moderate fire is started and continued, gradually raising the heat for about two hours. At this time, the furnace having assumed a light red heat, the sulphur begins 264 PROCESSES OF SILVER AND GOLD EXTRACTION. to burn. In the first period, white vapors arise chiefly of water, antimony, arsenic, and zinc. With the beginning of the burning of sulphur or desulphurization, the second period commences. Under constant stirring the fire must be made to go down, as the burning sulphur creates a sufficient temperature. In this period, lasting again two hours, the principal action on the ore is efiected in an oxydizing manner by the atmospheric air. Sulphurous acid, basic, and neutral sulphates are formed, as well as free oxyds ; but some sulphides remain also undecomposed, resulting from higher sulphur combinations. When the odor of sulphurous acid has disappeared, and the temperature has sunk to dark red heat, the last period begins. The heat must now be raised, under continual stirring; the ore swells up, enlarging its volume, greenish-gray vapors are emitted, and the last period is generally finished in three-quarters of an hour, and the ore drawn out while the evolution of gases is still going on. The sulphates, especially the sulphate of iron, act in this period on the salt, whereby partly free chlorine and partly hydrochloric gas is formed, the latter in the presence of water-vapors which are always supplied by the fuel and air. In passing through the ore, the chlo- rine decomposes principally the sulphides which escaped decomposition by heat, forming volatile chlorides of sulphur, arsenic, antimony, iron, and zinc, also unvola- tile chlorides of gold, silver, copper, lead, nickel, cobalt, PROCESSES OF SILVER AND GOLD EXTRACTION. 265 iron, and manganese. The hydrochloric gas changes principally the oxydated metal combinations into chlo- rides. The chlorination of silver already begins in the second period of roasting, but principally in the third. If the roasting was well performed, all silver must be changed into a chloride, otherwise some sulphurets of silver remain undecomposed and the tailings become rich. Examining the ore during the roasting for chloride of silver, the following procedure will show the result : A sample is taken from the furnace and one ounce of it weighed out, introduced into a filter and lixiviated with a hot solution of salt until a clean piece of copper does not show a white coating of precipitated silver. The ore is then dried and assayed for silver. The roasted ore must be sifted and ground. The coarse part is ground separately and roasted over with two per cent, of salt ; the fine-sifted and ground ore is given over to the amalgamation. Amalgamation, — This is performed in barrels made of oak or pine wood. The first period is the preparation of the pulp. For this purpose water (three hundred pounds) is led into each barrel and 1,000 pounds of roasted ore introduced, also one hundred pounds of wrought-iron. The barrels are shut and started with a speed of fourteen to sixteen revolutions per minute. The water dissolves all soluble salts and exposes in this way the particles of chloride of silver. Tn this period the iron acts decomposingly on the chlorides of iron and 266 PROCESSES OF SILVER AND GOLD EXTRACTION. copper, changing them into sub-chlorides which are not injurious to the quicksilver. The chlorides of copper and iron would transform a part of the quicksilver into sub-chloride which would be lost in the tailings. The dissolved chlorides of silver, gold, and copper are re- duced by the iron to a metallic state. After two hours' preparatory run, during which the pulp has obtained the proper consistency, the barrels must be arrested and the second period (the amalgamation) commences. To each barrel is now added five hundred pounds of quicksilver. When secured, the barrels are started again for twenty hours with a speed of twenty to twenty-two revolutions per minute. By a galvanic action the further decomposition of the chloride of silver takes place. The galvanic action is created by the positive iron, the negative quicksilver, and the dis- solved salts as conductor. The negative chlorine com- bines with the iron, the positive silver with the negative quicksilver. Temperature is produced by these actions. Besides the chloride of silver, also other metal combina- tions are decomposed by the galvanic action, especially copper, lead, antimony, and gold, which combine with the quicksilver. The third period is the separation of amalgam and residue. The amalgam, disseminated in the pulp is separated by water, with which the arrested barrels are charged over two-thirds full, and again brought in mo- tion for two hours, revolving eight or nine times per minute, whereupon the amalgam and quicksilver is dis- PROCESSES OP SILVER AND GOLD EXTRACTION. 267 charged, first, through a small hole in the plug, then the residue through a large hole (five to six inches in diameter). The residue of each five barrels runs into one agita- tor, in which the amalgam still left settles to the bottom, while the tailings are discharged gradually through three holes, one above the other. The amalgam, when discharged from the barrel is led directly into canvass filters. The quicksilver, pressed by its own weight, runs through the cloth into a reser- voir. If it ceases to run, the separation of the remainder of the quicksilver is performed by pressing with the hands or press. Amalgamation op Copber-Matt. The copper-matt amalgamation makes the same man- ipulation necessary as the working of ores. The matt, however, after a first raw roasting is drawn out, mixed with salt and lime, moistened, and the mass after proper drying, roasted again. This modification is based on the amount of copper in the matt, with the object of changing the chloride of copper into oxyd of copper, because the chloride of copper chloridizes a part of the quicksilver when in contact. In the first roasting of the matt, sulphates of copper, silver, and iron are formed. By the action of salt, they are transformed into the chlorides of copper, and silver, and sequi-chlo- ride of iron. The lime decomposes the chloride of 268 PROCESSES OP SILVER AND GOLD EXTRACTION. copper and sesqui-chloride of iron into hydrated oxyds, without changing the chloride of silver. Herein the experience that an addition of lime diminishes the loss of quicksilver is accounted for. The subsequent or the second roasting is performed at a higher temperature, effecting the perfect chlorination of the silver. The amalgamation of the matt is advantageous, if there is no gold in the ore, no lead ore to be had or the fuel is scarce, otherwise melting with lead would be preferable. Amalgamation of Argentiferous Arsenides (Speiss) ob- tained IN Melting. The arsenides, obtained in melting of cobalt ores, are analogous to the matts. In the first place we have arsenic, in the second sulphur combined with metals. The amalgamation of Speiss is executed in Saxony. It requires a very careful roasting and fine grinding, and an addition of sufficient salt. As there is not sufficient sulphur in the ore, by which the salt can be decom- posed, two and a half or three per cent, of green vitriol must be added for that purpose. The tailings contain five ounces of silver to the ton, but the average loss is about thirteen per cent. Amalgamation of Argentiferous Black Copper. Experience proves that the alloy of silver and copper, without sulphur, decomposes the salt forming chlorides of silver and copper. The closer the contact between PROCESSES OP SILVER AND GOLD EXTRACTION. 269 salt and copper, the more chloride of silver is formed. The chloride of copper transfers also chlorine to the silver, being thus reduced to sub-chloride. Black copper requires, as well as the ores, an abund- ance of salt, and deserves preference to the copper-matt amalgamation on account of its simplicity and more perfect extraction of silver. This method has a decided advantage over the liquation process, on black copper, free from lead and gold. In Schmolnitz (Hungary) the black copper contains from one hundred and ten to one hundred and fifty ounces of silver per ton, and eighty-five-eighty-nine per cent, of copper. This copper is heated red in a reverberatory furnace and stamped in glowing condi- tion, then sifted and ground to fine powder. For the roasting, four hundred pounds is taken to each charge and oxyd with seven to nine per cent, of common salt. After roasting, it is ground again, and then amalgam- ated. , The barrels are charged with from 1,200 to 1,500 pounds each, one hundred pounds of copper balls, four hundred pounds of quicksilver, and the required quan- tity of water. The loss of silver is four and three- fourths per cent., of which only two and a half per cent, remains in the residue. The pure copper resulting from this process contains about ten ounces of silver. to the ton. At Tajova, a loss of twenty-seven per cent, of silver occurs and the copper retains twenty ounces per ton. At Ofienbanya (Transilvania) the black copper con- 270 PROCESSES OF SILVER AND GOLD EXTRACTION. tains some lead, and on this account three per cent, of saltpetre is added with the salt in roasting. B, EXTRACTION OF SILVER BY DISSOLUTION AND PRECIPITATION. Augustin's Extraction with Solution of Salt. Sec. 76. This method is based on the solubility of the chloride of silver in concentrated solution of com- mon salt, from which it is precipitated by copper. If water is added to a salt solution with dissolved chloride of silver, the latter will be again separated in form of chloride of silver as a white precipitate. This fact, on which Augustin based his extracting method, has been known a long time. It was first executed on copper- matt at Gottes-belohnung works, and since then at other places, also on other argentiferous products and ores. The best results have been obtained on copper-matts. Extraction of Silver from Copper-Matt. The Copper-Matt — Suitable for extraction must be as rich in copper as possible, otherwise the residue becomes too rich in silver. Poorer copper-matts are therefore concentrated by melting in reverberatory furnaces, being thus enriched to from sixty to seventy per cent. The matt must be free from or should contain very little lead, antimony, zinc, or arsenic, or else a considerable loss in silver might occur. PROCESSES OF SILVER AND GOLD EXTRACTION. 271 Lead — Makes the roasting troublesome, having an inclination to melt, v^hich counteracts the formation of the chloride of silver. At the same time chloride of lead is created, which would also be dissolved in the salt solution, causing an impure precipitation of silver. Sulphuret of zinc, to a certain amount, is injurious in a chloridizing roasting, because, when changed into a sulphate, it requires a high temperature to drive the sulphuric acid out, which must be done, otherwise too much chloride of zinc will be formed. But at a high temperature the matt softens by commencing to melt, causing thus richer tailings and also a larger loss of silver by volatilization. For this reason, zinciferous matt must be freed from zinc by concentration-smelting in reverberatory furnaces. Antimony and Arsenic, in a chloridizing roasting, pro- duce also antimonate and arsenate of silver, neither of which can be decomposed by the chlorine. Introduced steam, however, forms hydrochloric acid, by which the above combinations are decomposed, resulting in chlo- ride of silver and volatile chlorides of antimony and arsenic. The fine pulverized matt, principally consisting of sulphides of iron, copper, and silver, is first roasted without salt, whereby the iron is converted into sul- phate of iron, then sulphate of copper is formed, and finally sulphate of silver. The temperature, under which the sulphate of silver is produced, is so high that almost all the sulphate of iron and a great part of 272 PROCESSES OF SILVER AND GOLD EXTRACTION. the sulphate of copper will be decomposed, so that at the end of roasting the mass consists chiefly of the oxyds of iron and copper, some sulphate of copper and sulphate of silver, as well as some undecomposed sul- phides. From time to time samples are taken, to ascer- tain the condition of the roasting. The sample is placed on a filtering paper and lixiviated with water. The blue color, according to its intensity, shows the pres- ence of more or less sulphate of copper. An addition of salt solution gives a white precipitate of chloride of silver. In the second roasting period the oxydation is con- tinued for a while at an increased heat, in order to decompose all sulphides of iron, copper, and silver. When a sample, taken from the furnace gives a feeble blue-colored water, and with salt solution a strong pre- cipitate of silver, the purpose of the oxydizing roasting is accomplished. Now is the time to introduce the salt and to change the roasting into a chloridizing one. The sulphuric acid, which is principally combined with silver and to some extent with copper, expells the chlorine of the salt, forming sulphate of soda and sulphurous acid. The chlorine, penetrating the mass, creates chloride of silver; but as there is always a super- abundance of chlorine, it creates also some chloride of copper and iron. In this condition the roasted matt is subjected to lixiviation with hot concentrated solution of salt. The desilverization is promoted and perfected if the solution acts under pressure upon the matt. From PROCESSES OF SILVER AND GOLD EXTRACTION. 273 the solution, the silver is precipitated by metallic cop- per. The copper precipitating the silver, enters into solution and is precipitated by the iron. The sub- chloride of copper is produced by decomposition of chloride of silver, and also by decomposition of the chloride of copper in the solution, with metallic copper. The products of this process are : 1. Cement-silver. 2. Cement-copper. 3. Residue melted for copper. 4. Green vitriol or sulphate of iron, and, 5. Glauber's salts. In Freiberg this method offered also a great advan- tage over the liquation process, and is executed in the following way ; The matt, after stamping and sifting, is subjected to roasting in portions of from three hundred to four hundred pounds. The roasting is performed in a double furnace, one hearth above the other. Each charge remains four hours on the upper and four hours on the lower hearth. The roasted matt is then ground fine, and roasted over on the lower hearth for one hour with an addition of five per cent, of salt. The roasted matt in now subjected to the lixiviation. For this purpose it is elevated to the upper story, where 18 274 PROCESSES OP SILVER AND GOLD EXTRACTION. the lixiviating tubs are arranged. They are three feet nine inches high, two feet eight inches in the upper and two feet four inches in the lower diameter, and are filled with from four to six hundred pounds of matt. Each of these tubs has a filtering apparatus on the bottom ; first a wooden cross then a perforated wooden bottom, then a layer of straw and over this a piece of cloth, made tight against the staves of the tub, by being stretched upon a hoop. On the top of the tub, when filled with matt, there is placed a perforated wooden disk. The concentrated hot salt solution is conveyed in a trough to the tubs, into which it drops, coming out through the cock at the bottom saturated with the chlo- ride of silver. This cock is first opened for the escape of vapor, then shut for a quarter of an hour and opened again, taking care that as much salt solution flows into the tub as comes out through the cock. The lixiviation is performed in three periods. The first, with concentrated solution, takes ten hours. The second, also with concentrated solution, continues till a piece of clean copper does not become coated white; and this may require ten or twelve hours longer. The last lixiviation is done with clear water. The products obtained are : 1. Residue, — The tubs are transported on a railtrack to a discharge place, an assay is taken, and in case the tailings should prove to be unsufiiciently desilvered, PROCESSES OP SILVER AND GOLD EXTRACTION. 275 they must be roasted over again v^rith salt. They con- tain from forty to sixty-five per cent, of copper. 2. Silver Salt Solution — Which is conveyed into pre- cipitation tubs. 3. Liximating Water. — This water, obtained from the third period, contains salt. It is led into a basin and used again for lixiviation. The cement-copper, obtained by precipitation with iron, is introduced into the precipitating tubs, about six inches deep, in which the silver-containing solution is conveyed. The tub is provided with a filtrating appa- ratus, through which the desilvered solution is carried into other tubs where the copper is precipitated by iron and used again for precipitating the silver. The precipitated silver is removed at intervals of eight days from the copper on which it accumulates. Sub-chloride of copper and chloride of lead are separ- ated from the precipitated silver by washing it with water and diluted muriatic acid, then melted and re- fined in crucibles. a ZIERVOGEL'S EXTRACTION OF SILVER WITH WARM WATER. SEa 77. ZiervogeFs method of silver extraction from matts is more simple and cheaper than the preceding. No salt is used here. 276 PKOCESSES OP SILVER AND GOLD EXTRACTION. In roasting pure argentiferous copper-matt sulphate of iron is first formed, then sulphate of copper, and finally sulphate of silver. The formation of the last sulphate requires such high temperature that it decom- poses again the first two sulphates, created at a lower heat. The sulphates of iron and copper are decomposed into oxyds, and sulphuric acid which escapes, while the sulphate of silver remains undecomposed. This sul- phate is soluble in hot water, and can be precipitated by copper. It has been observed generally that Ziervogel's method is simpler and cheaper, and the lixiviation is eflTected quicker, but the roasting process is a great deal more difficult, purer matts are necessary, and the tailings are richer than from Augustin's process. The matt is pulverized to a fine powder, and, in charges of five hundred and seventy-five pounds, roast- ed. There are double furnaces used for this roasting. The upper floor is charged with the matt, and this stir- red for one hour and a quarter ; the lumps, if any, are mashed and the mass changed so that the cooler part is brought nearer to the fire, and vice versa. The stirring is continued for one hour and a half, the mass changed again, and now from twenty to twenty-five pounds of coal-dust are added, well mixed, for ten minutes and then conveyed to the lower hearth, through a flue which was covered with an iron plate. The matt is now spread on the red-hot hearth, and stirred for about one hour and a quarter without using any fuel. The mass PROCESSES OP SILVER AND GOLD EXTRACTION. 277 will first ignite on account of the coal dust. It is then raked together and the different heated parts change places. A sample is taken from the bridge-side with an iron ladle, emptied into a porcelain cup, so as to divide it in two partitions. Cold water is then slowly introduced on one side till it penetrates the sample and comes forth on the other. The water must appear feebly-blue color- ed, and several grains of salt must not produce a darker hue but precipitate the silver as a white substance. If such reaction is observed the matt must be shift- ed, firing and stirring continues ; another sample is taken at the bridge-side and examined in the same way till a corresponding result is obtained. But if the water should show a green color from sulphate of iron, or a deep blue from sulphate of copper, the stirring must be continued. As soon as the roasting is finished which is indicated by the above sample, a sign is given to the upper work- man to add coal-dust to the matt of the upper hearth. The roasted matt from the lower floor is removed and sifted through a sieve of sixteen holes to the square inch. The coarse part of the sifting is added to each charge in quantities of twenty to twenty-five pounds and reroasted. The fine-sifted matt is brought to the cooling place, where it remains for six or eight hours. The result of this process depends so much on the roasting that at Freiberg an arrangement is made, according to which 278 PROCESSES OP SILVER AND GOLD EXTRACTION. the roasters receive a premium, if the tailings are found poorer than the allowance. The lixivation is carried on with hot water in wooden tubs similar to those described in Augustin's process. They are arranged in galleries. On the first there are eight wooden cylindrical lixiviating tubs, provided with a filtering apparatus. The tubs are two and a half feet high and the same width. At the bottom there is a cock through which the filtrate is conveyed into clear- ing tanks, thirty feet long, one and one-half feet wide, and one and one-half feet deep, divided into two parti- tions. The lye enters the first partition, then over the parting board into the second. From thence it flows through ten cocks into as many precipitating tubs, which are posted on the second gallery. These tubs are also provided with filters and cocks. Each of them contains ten pounds of granulated copper, and over it in each two hundred and fifty pounds of black copper, fourteen inches long, five wide and one inch thick. The fluid, after passing the tubs of the second gallery, flows into precipitating tubs on the third gallery of which there are five in number, containing likewise copper for precipitation. From this last gallery the fluid flows into a leaden basin, wherefrom it is pumped into another leaden basin and heated by steam till it assumes a temperature of 158° Fahrenheit. , The fine-sifted matt, after having rested for about eight hours is cooled down to about 158° Fahrenheit. In this state it is introduced into the precipitating tubs PROCESSES OF SILVER AND GOLD EXTRACTION. 279 of the first gallery (four hundred pounds in each) and water added till it commences to run out at the cock on the bottom. The water is previously heated by steam to 158*^ Fahrenheit. The water must be stopped as soon as it begins to run through the cock, and then so much of the heated fluid of the leaden basin is allowed to flow on the matt, till a sample from the outflow does not show a precipi- tate of chloride of silver by salt solution. This lixivia- tion takes two* hours and a half The tailings are removed and given over to the copper-smelting process. The precipitation of silver by copper in the precipitating tubs, is similar to the operation described in Augustin's process. D. PATERA'S SILVER EXTRACTING PROCESS. Sec. 78. By a chloridizing roasting the silver is con- verted into chloride of silver, then dissolved in hypo- sulphite of soda, and precipitated by polysulphide of sodium. Gold, diluted hyposulphite of soda dissolves the chlo- ride of silver sooner than a hot concentrated solution of salt. The polysulphide of sodium precipitates the silver as a sulphide, the reduction of which is performed by simply calcining under a muffle. The ore is first subjected to an oxydizing roasting, in which the heat must be increased slowly by degrees, especially if the ore contains many difierent sulphurets. 280 PROCESSES OP SILVER AND GOLD EXTRACTION. When red heat is obtained, some steam is introduced in the furnace and as much as possible without dimin- ishing the necessary heat. The ore must be constantly stirred. In about four hours the first roasting is com- pleted and the ore is discharged. This must be ground fine, mixed with from six to ten per cent, of salt, or more according to the richness, and subjected to the second — chlorodizing roasting. Two or three per cent, of calcined green vitriol is added for the decomposition of salt. When red-hot, the steam is used again, and diligent stirring kept up for five or six hours. Rich ore may require a longer roasting by several hours. The roasted ore is now ready for lixiviation. There are chlorides of different .base metals in the ore, which are soluble in water, while the chloride of silver resists, for this reason two lixiviations are adopted : the first with hot water, which will dissolve and carry off* the chlorides and sulphates of copper, iron, zinc, cobalt, etc., and the second with hyposulphite of soda which dis- solves the chloride of silver. If the roasting is not well performed so that some sulphate of silver remains in the ore, this will be also dissolved by the water and car- ried out with the base metals. Charges of four hundred pounds of roasted ore are thrown into tubs, prepared for lixiviation like those used and described in Augustin's process. Hot water is con- veyed to the tubs for about six hours by a constant stream, purifying thus the mass of base metals. After this cold water is used for the purpose of cooling the PROCESSES OP SILVER AND GOLD EXTRACTION. 281 ore, which is not allowed to be warm for the second lixiviation. When cold, the ore must be removed in other tubs of the same description, but smaller. A cold solution of hyposulphite of soda is brought into the tubs, and con- tinued till in a taken sample no precipitate of silver is obtained by a solution of polysulphide of sodium. The solution, now in precipitating tubs, is mixed together under good stirring with the precipitant (poly- sulphide of sodium). The precipitate (sulphide of silver) appears black. Attention is necessary to use the right proportion of the precipitant, in order to obtain a neu- tral liquor after all the silver is precipitated. This fluid is used over again for lixiviation, but a surplus of the precipitant would render the fluid unsuitable for that purpose and precipitate some silver in the mass during the lixivation. If no more precipitation is observed, a small quantity of the solution is taken in a glass tube and some drops of polysulphide of sodium added. If a black precipitate is produced in a slight degree, some more of the precipitant must be added to the solution in the precipitating tubs ; but if, on the contrary, no precipitate was obtained in the glass tube, another sam- ple must be taken, and tried with some drops of the original solution. If then a black precipitate is formed, too much of the precipitant was introduced into the precipitating tub and must be neutralized by addition of the original solution. The precipitated black sulphide of silver deposits in 282 PROCESSES OF SILVER AND GOLD EXTRACTION. bags which are well pressed, dried, then washed with warm water in filters, dried again and heated under muffles, to which air has access. The sulphur burns off and the silver remains in metallic condition. This is melted finally in crucibles with an addition of some iron and borax. TABLE I SHOWING THE AMOUNT OP SILVER OR GOLD IN OUNCES CON- TAINED IN ONE TON OF ORE (TWO THOUSAND POUNDS) FROM THE WEIGHT OF FINE METAL OBTAINED IN AN ASSAY OF HALF AN OUNCE OR TWO HUNDRED AND FORTY GRAINS OF ORE. 284 PROCESSES OP SILVER AND GOLD EXTRACTION. Ounces of Fine Metal 'per Ton of Ore of 2,000 Pounds, *n o >*i o ^ o a g 1? § 2>g E § 2.i' ^^ 1 1 || 1 1 ^^ 1 1 If ?2. "•* 1 ?s. 1 t OS. o 1 2 H H o 2. ' i i o 1 2 H i 1 <=» 5 : ^, « r r i ^ r " 3. I ci cr; cs 2 g or? c ►1 CO : & • rt • rs » p • ft ri ; i ri :• i p* 1- ; § •030 36-45 •060 72-90 •001 1-21 1 37-66 1 74-11 2 2-43 2 38-88 2 75-33 3 3-64 3 40-09 3 76-54 4 4-86 4 41-31 4 77-76 5 6-07 5 42-52 5 78-97 6 7^29 6 43-74 6 80-19 7 8-50 7 44-95 7 81-40 8 9-72 8 46-17 8 82-62 9 10-93 9 47-38 9 83-83 •010 12-15 •040 48-60 •070 85-05 1 13-36 1 49-81 1 86-26 2 14-58 2 51-03 2 87-48 3 15-79 3 52-24 3 88-69 4 17-01 4 53-46 4 89-91 5 18-22 5 54-67 5 91-12 6 19-43 6 55-89 6 92-34 7 20-65 7 57-10 7 93-55 8 21-86 8 58-32 8 94-77 9 23-08 9 59-53 9 95-98 •020 24-30 •050 60-75 •080 97-20 1 25-51 1 61-96 1 98-41 2 26-73 2 63-18 2 99-63 3 27-94 3 64-39 3 100-84 4 29-16 4 65-61 4 102-06 5 30-37 5 66-82 5 103-27 6 31-59 6 68-04 6 104-49 7 32-80 7 69-25 7 105-70 8 34-02 8 70-47 8 106^92 9 35-23 9 71-68 9 108-13 PROCESSES OP SILVER AND GOLD EXTRACTION. 285 Ounces of Fine Metal per Ton of Ore of 2,000 Founds, >^ o h=J o ^ o 2. g E§ 2> § e. § o 5' E § ^1 1 1 ^^ :3 r^ ^¥ 1 1 s. £ ?s> 1. 1 oa li. ?s. ^ 1 O X 1 3 O « 1 o o Sh i 3 2. ' :2 ^ 2 3 S^ i ^ <=> r r ^ o.gf r 3. 5 g- r ^. 1 1 : Hi *§ 1 . !— • • o ri • o P* 1 : P 5' 2 ; ? •090 109-35 •120 145-80 •150 182-25 1 110-56 1 147-01 1 183-46 2 111-78 2 148-23 2 184-68 3 112-99 3 149-44 3 185-89 4 114-21 4 150-66 4 187-11 5 115-42 5 151-87 5 188-32 6 116-64 6 153-09 6 189-54 T 117-85 7 154-30 7 190-75 8 119-07 8 155-52 8 191-97 9 120-28 9 156-73 9 193-18 •100 121-50 •130 157-95 •160 194-40 1 122-71 1 159-16 1 195-61 2 123-93 2 160-38 2 196-83 3 125-14 3 161-59 3 198-04 4 126-36 4 162-81 4 199-26 5 127-57 1 5 164-02 5 200-47 6 128-79 6 165-24 6 201-69 T 130-00 ; 7 166-45 7 202-90 8 131-22 8 167-67 8 204-12 9 132-43 9 168-88 9 205-33 •110 133-65 ; •uo 170-10 •170 206-55 1 134-86 1 171-31 1 207-76 2 136-08 2 172-53 ■2 208-98 3 137-29 1 3 173-74 3 210-19 4 138-51 ' 4 174-96 4 211-41 5 139-72 1 5 176-17 5 212-62 6 140-94 ! 6 177-39 6 213-84 7 142-15 i 7 178-60 7 215-05 8 143-37 8 179-82 8 216-27 9 144-58 1 9 181-03 9 217-48 286 PROCESSES 0E» SILVER AND GOLD EXTRACTION. Ounces of Fine Metal per Ton of Ore of 2,000 Pounds* >^ o y c ^^ o o 5* E § s.§ E§ o 5' E§ ^1 1 1 l^ I 1 !^ 1 1 1. E ?S, It ?2» If ?2. 11. O i 3 ik ai. o o P 3 O ^ : 8 : 1 a ^ ^ 8 ? g- : ? s- : ? S g' • pj •180 218-70 •210 255-15 •240 291-60 1 219-91 1 256-36 1 292-81 2 221-13 2 257-58 2 294-03 3 222-34 3 258-79 3 295-24 4 223-56 4 260-01 4 296-46 5 224-77 5 261-22 5 297-67 6 225-99 6 262-44 6 398-89 7 227-20 7 263-65 7 300-10 8 228-42 8 264-87 8 301-32 9 229-63 9 266-08 9 302-53 •190 230-85 •220 267-30 •250 303-75 1 232-06 1 268-51 1 304-96 2 233-28 2 269-73 2 306-18 3 234-49 3 270-94 3 307-39 4 235-71 4 272-16 . 4 308-61 5 236-92 5 273-37 5 309-82 6 23844 6 274-59 6 311-04 7 239-35 7 275-80 7 312-25 8 240-57 8 277-02 8 313-47 9 241-78 9 278-23 9 314-68 •200 243-00 •230 279-45 •260 315-90 1 244-21 1 280-66 1 317-11 2 245-43 2 281-88 2 318-33 3 246-64 3 283-09 8 319-54 4 - 247-86 4 284-31 4 320-76 5 249-07 5 285-52 5 321-97 6 250-29 6 286-74 6 323-19 7 251-50 7 287-95 7 324-40 8 252-72 8 289-17 8 325-62 9 253-93 9 290-38 9 326-83 PROCESSES OF SILVER AND GOLD EXTRACTION. 287 Ounces of Fine Metal per Ton of Ore of 2,000 Pounds, >r^ o >=d o Hj o s,g E§ o 5' E § 2> i' E § f 1 1 1 !^ 1 1 ^9 p rt- 5. t ?2, 1. £ ?s. s. t ?2. o 1 i i O i i i 1 ' P O i 3 ^ 1 r i <=> r ^ ^. o g* : 1 f 1 \ 1 . on * ; 8 11 p 1 : & •270 328-05 •300 364-50 •330 400-95 1 329-26 1 365-71 1 402-16 2 330-48 2 366-93 2 403-38 3 331-69 3 368-14 3 404-59 4 332-91 4 369-36 4 405-81 5 334-12 5 370-57 5 407-02 6 335-34 6 371-79 6 408-24 7 336-55 7 373-00 7 409-45 8 337-77 8 374-22 8 410-67 9 338-98 9 375-43 9 411-88 •280 340-20 •310 376-65 •340 413-10 1 341-41 1 377-86 1 414-31 2 342-63 2 379-08 2 415-53 3 343-84 3 380-29 3 416-74 4 345-06 4 381-51 4 417-96 5 346-27 5 382-72 5 419-17 6 347-49 6 383-94 6 420-39 7 348-70 7 385-15 7 421-60 8 349-92 8 386-37 8 422-82 9 351-13 9 387-58 9 424-03 •290 352-35 •320 388-80 •350 425-25 1 353-56 1 390-01 1 426-46 2 354-78 2 391-23 2 427-68 3 355-99 3 392-44 3 428-89 4 357-21 4 393-66 4 430-11 5 - 358-42 5 394-87 5 431-32 6 359-64 6 396-09 5 432-54 7 360-85 7 397-30 7 433-75 8 . 362-07 8 398-52 8 434-97 9 363-28 9 399-73 9 436-18 288 PROCESSES OP SILVER AND GOLD EXTRACTION. Ounces of Fine Metal per Ton of Ore of 2,000 Pounds. g 1 o 1 1 s i i tn \ i S, ^ o p. § 1 1 P o r t '' 8 g 1 11 o 1 1 i 3 j i •360 437-40 •390 473-85 •420 510-30 1 438-61 1 475-06 1 511-51 2 439-83 2 476-28 2 512-73 3 441-04 3 477-49 3 513-94 4 442-26 4 478-71 4 515-16 5 443-47 5 479-92 5 516-37 6 444-69 6 481-14 6 517-59 7 445-90 7 482-35 7 518-80 8 447-12 8 483-57 8 520-02 9 448-33 9 484-78 9 521-23 •370 449-55 •400 486-00 •430 522-45 1 450-76 1 487-21 1 523-66 2 451-98 2 488-43 2 524-88 3 453-19 3 489-64 3 526-09 4 454-41 4 490-86 4 527-31 5 455-62 5 492-07 - 5 528-52 6 456-84 6 493-29 6 529-74 7 458-05 7 494-50 7 530-95 8 459-27 8 495-72 8 532-17 9 460-48 9 496-93 9 533-38 •380 461-70 •410 498-15 •440 534-60 1 462-91 1 499-36 1 535-81 2 464-13 2 500-58 2 537-03 3 465-34 3 501-79 3 538^24 4 ^m-s^ 4 503-01 4 539-46 5 467-77 5 504-22 5 540-67 6 468-99 6 505-44 6 541-89 7 470-20 7 bm-Qb 7 543-10 8 471-42 8 507-87 8 544-32 9 472-63 9 509-08 9 545-53 PROCESSES OP SILVER AND GOLD EXTRACTION. 289 Ounces of Fine Metal per Ton of Ore of 2,000 Pounds. a o a o a o g.g E § ag- Eg ai ^ § ^f T 1 ^1 1 1 ^S it IE f "^ It ?2. It 9^ o 1 i i Ih P o Ik P o , i 3 o g* r ^. o g* f i ^ ^ : 1 "^ g : i=! 1 i ^ g g. p> • rt rt p p, • n 5* t3 • o 5" a • o 5' 5 ' O P s- : » s g- : p3 ? ^ : c3 450 546-75 •480 583-20 •510 619-65 1 547-96 1 584-41 1 620-86 2 549-18 2 585-63 2 622-08 3 550-39 3 586-84 3 623-29 4 551-61 4 588-06 4 624-51 5 552-82 5 589-27 5 625-72 6 554-04 6 590-49 6 626-94 7 555-25 7 591-70 7 628-15 8 556-47 8 592-92 8 629-37 9 557-68 9 594-13 9 630-58 •460 558-90 •490 595-35 •520 631-80 1 560-11 1 596-56 1 633-01 2 561-33 2 597-78 2 634-23 3 562-54 3 598-99 3 635-44 4 563-76 4 600-21 4 6S6'6Q 5 564-97 5 601-42 5 637-87 6 566-19 6 602-64 6 639-09 T 567-40 7 603-85 7 640-30 8 568-62 8 605-07 8 641-52 9 569-83 9 606-28 9 642-73 •470 571-05 •500 607-50 •530 643-95 1 572-26 1 608-71 1 645-16 2 573-48 2 609-93 2 646-38 3 574-69 3 611-14 3 647-59 4 575-91 4 612-36 4 648-81 5 577-12 5 613-57 6 650-02 6 578-34 6 614-79 6 651-24 7 579-55 7 616-00 7 652-45 8 580-77 8 617-22 8 653-67 9 581-98 9 618-43 9 654-88 19 290 PROCESSES OF SILVER AND GOLD EXTRACTION. Ounces of Fine Metal per Ton of Ore of 2,000 Pounds, >^ o N o H^ o a i' e § s^r E§ a §■ ^ § « ? 1 p CD gs 1 1 f g 1 § 1 1 O 2. 2. t ?2. 1. 1 ?2. ^ 1 P O ^ 1 P o ^ 1 B O 2s ' i '^ 2. ' 2 H CD 2. ' § 3 o g* : ^. <= r : ^ ° ^ :" ^. 1 s : ^ 11 : £ 1 S : & S. 2 o o p p o g 1 •^ ? s 1 ; ? ri • o •540 656-10 •570 692-55 •600 729-00 1 657-31 1 693-76 1 730-21 2 658-53 2 694-98 2 731-43 3 659-74 3 696-19 3 732-64 4 660-96 4 697-41 4 733-86 5 662-17 5 698-62 5 735-07 6 663-39 6 699-84 6 736-29 7 664^60 7 701-05 7 737-50 8 665-82 8 702-27 8 738-72 9 667-03 9 703-48 9 739-93 •550 668-25 •580 704-70 •610 741-15 1 669-46 1 705-91 1 742-36 2 670-68 2 707-13 2 743-58 3 671-89 3 708-34 3 744-79 4 673-11 4 709-56 4 746-01 6 674-32 5 710-77 5 747-22 6 675-54 6 711-99 6 748-44 7 676-75 7 713-20 7 749-65 8 677-97 8 714-42 8 650-87 9 679-18 9 715-63 9 752-08 •560 680-40 •590 716-85 •620 753-30 1 681-61 1 718-06 1 754-52 2 682-83 2 719-28 2 755-74 3 684-04 3 720-49 3 756-95 4 685-26 4 721^71 4 758-17 5 686-47 5 722-92 5 759-38 6 687-69 6 724-14 6 760-59 7 688-90 7 725-35 7 761-80 8 690-12 8 726-57 8 763-02 9 691-33 9 727-78 9 764-23 PROCESSES OF SILVER AlCD GOLD EXTRACTION. 291 Ounces of Fine Metal per Ton of Ore of 2,000 Pounds, >ri o ^*i o ►*! o s.§ g, o s. i' s § 2.§ g § «^l 1 i 1 1 ^^ 1 1 1. E 02. 9^ § 1 &' T 1 ' 3 O i 3 5 o i ^ = i i 3 ° §" ^ ^. ^ o ^ ^. • o g- : ^. IJ o IJ »-• 2. ^ I J^ P 1 • ? s 1 : P : P •630 765-45 •660 801-90 •690 838-35 1 766-66 1 803-11 1 839-56 2 767-88 2 804-33 2 840-78 3 769-09 3 805-54 3 841-99 4 770-31 4 806-76 4 843-21 5 771-52 5 807-97 5 844-42 6 772-74 6 809-19 6 845-64 7 773-95 7 810-40 7 846-85 8 775-17 8 811-62 8 848-07 9 776-38 9 812-83 9 849-28 •640 777-60 •670 814-05 •700 850-50 1 778-82 1 815-26 1 851-71 2 780-04 2 816-48 2 852-93 3 781-25 3 817-69 3 854-14 4 782-47 4 818-91 4 855-36 5 783-68 5 820-12 5 856-57 6 784-90 6 821-34 6 857-79 7 786-11 7 822-55 7 859-00 8 787-33 8 823-77 8 860-22 9 788-54 9 824-98 9 861-43 •650 789-75 •680 826-20 •710 862-65 1 790-96 1 827-41 1 863-86 2 792-18 2 828-63 2 865-08 3 793-39 3 829-84 3 866-29 4 794-61 4 831-06 4 867-51 5 795-82 5 832-27 5 868-72 6 797-04 6 833-49 6 869-94 7 798-25 7 834-70 7 871-15 8 799-47 8 835-92 8 872-37 9 800-68 9 837-13 9 873-58 292 PROCESSES OF SILVER AND GOLD EXTRACTION. Ounces of Fine Metal per Ton of Ore of 2,000 Pounds. >ri o Nj o S o o 5" ^ g 2. i* E§ s,§ t § » ? 1 1 - g 1 § ^1 1 1 3. t ?^ s. £ ?2. IE ?2. 'Z 1 P o o 1 P o o 1 P o 2. ' 2 H i 3 O 1 g 3 to O i 2 H i « ^ r * ^. o r : ^. o r r ^ 0<3 • p;^ or? p * t^ on; p t:^ n \ P II '• 8 ; p s 1 ! i •720 874-80 •750 911-25 -780 947-70 1 876-01 1 912-46 1 948-91 2 877-23 2 913-68 2 950-13 3 878-44 3 914-89 3 951-34 4 879-66 4 916-11 4 952-56 5 880-87 5 917-32 5 953-77 6 882-09 6 918-54 6 954-99 7 883-30 7 919-75 7 956-20 8 884-52 8 920-97 8 957-42 9 885-73 9 922-18 9 958-63 •730 886-95 •760 923-40 •790 959-85 1 888-16 1 924-61 1 961-06 2 889-38 2 925-83 2 962-28 3 890-59 • 3 927-04 3 963-49 4 891-81 4 928-26 4 964-71 5 893-02 5 929-47 5 965-92 6 894-24 6 930-69 6 967-14 7 895-45 7 931-90 7 968-35 8 896-67 8 933-12 8 969-57 9 897-88 9 934-33 9 970-78 •740 899-10 •770 935-55 •800 972-00 1 900-31 1 936-76 1 973-21 2 901-53 2 937-98 2 974-43 3 902-74 3 939-19 3 975-64 4 903-96 4 940-41 4 976-86 5 905-17 5 941-62 5 978-07 6 906-39 6 942-83 6 979-29 7 907-60 7 944-05 7 980-50 8 908-82 8 945-27 8 981-72 9 910-03 9 946-48 9 982-93 PROCESSES OP SILVER AND GOLD EXTRACTION. 293 Ounces of Fine Metal per Ton of Ore of 2,000 Pounds. 1 1 2 1 o 1 § i 3 : 1 j 1 it 1 1 ri i' ^ 1 p P o i 3 r ^. ; 8 O p o 1 en p 5 2 » sr r ■ One ton of ore will con- tain — Ounces •810 984-15 1 •840 1020-60 -870 1057-05 1 985-36 i 1 1021-81 1 1058-26 2 986-58 ' 2 1023-03 2 1059-48 3 987-79 1 3 1024-24 3 1060-69 4 989-01 4 1025-46 4 1061-91 5 990^22 5 1026-67 5 1063-12 6 991^44 6 1027-89 6 1064-34 7 992-65 7 1029-10 7 1065-55 8 993-87 8 1030-32 8 1066-77 9 995-08 9 1031-53 9 1067^98 •820 996-30 •850 1032-75 •880 1069-20 1 997-51 1 1033-96 1 1070-41 2 998-73 2 1035-18 2 1071-63 3 999-94 3 1036-39 3 1072-84 4 1001-16 4 1037-61 4 1074-06 5 1002-37 5 1038-82 5 1075-27 6 1003-59 6 1040-04 6 1076-49 7 1004-80 7 1041-25 7 1077-70 8 1006-02 8 1042-47 8 1078-92 9 1007-23 9 1043-68 9 1080-13 •830 1008-45 •860 1044-90 •890 1081-35 1 1009-66 1 1046-11 1 1082-56 2 1010-88 2 1047-33 2 1083-78 3 1012-09 3 1048^54 3 1084-99 4 1013-31 4 1049^76 4 1086-21 5 1014-52 5 1050-97 5 1087-42 6 1015-74 6 1052-19 6 1088-64 7 1016-95 7 1053-40 7 1089-85 8 1018-17 8 1054-62 8 1091-07 9 1019-38 9 1055-83 9 1092-28 294 PROCESSES OF SILVER AND GOLD EXTRACTION. Ounces of Fine Metal per Ton of Ore of 2,000 Pounds, Hrj o 9 c S o a § E§ e. § E§ !^ 1 1 !^ !? 1 1 g. t ?s. 1. E If ?s. 1 ' O 2» ' 2 H 5 o § 3 5^ 1 3 => r r ^. ° r r % *=* o' • 3. 11 • n |i ' n 1 i * n ri ; § 3 s. o : p P 1 • o • 3 •900 1093-50 •930 1129-95 •960 1166-40 1 1094-71 1 1131-16 1 1167-61 2 1095-93 2 1132-38 2 1168-83 3 1097-14 3 1133-59 3 1170-04 4 1098-36 4 1134-81 4 1171-26 5 1099-57 5 1136-02 5 1172-47 6 1100-79 6 1137-24 6 1173-69 7 1102-00 7 1138-45 7 1174-90 8 1103-22 8 1139-67 8 1176-12 9 1104-43 9 1140-88 9 1177-33 •910. 1105-65 •940 1142-10 •970 1178-55 1 1106-86 1 1143-31 1 1179-76 2 1108-08 2 1144-53 2 1180-98 3 1109-29 3 1145-75 3 1182-19 4 1110-51 4 1146-96 4 1183-41 5 1111-72 5 1148-17 5 1184-62 6 1112-94 6 1149-39 6 1185-84 7 1114-15 7 1150-60 7 1187-05 8 1115-37 8 1151-82 8 1188-27 9 1116-58 9 1153-03 9 1189-48 •920 1117-80 •950 1154-25 •980 1190-70 1 1119-01 1 1155-46 1 1191-91 2 1120-23 2 1156-68 2 1193-13 3 1121-44 3 1157-89 3 1194-34 4 1122-66 4 1159-11 4 1195-56 5 1123-87 5 1160-32 5 1196-77 6 1125-09 6 1161-54 6 1197-99 7 1126-30 7 1162-75 7 1199-20 8 1127-52 8 1163-97 8 1200-42 9 1128-73 9 1165-18 9 1201-63 PROCESSES OP SILVER AND GOLD EXTRACTION. 295 Ounces of Fine Metal per Ton of Ore of 2,000 Founds, ^^ o ►^ o ^ o o 5' ^ § o S* E§ 2* i' E§ S"? 5 rt- !^ 1 1 1 § i. E ?s. IE ?2, 5. E ?2, r 1 P o ^ 1 P o o 1 P o 5h i 3 P 3 Sh i 3 s §■ : ^, S r ^ r : i on? c II : 8 IJ •* 8 05-68 3 ( 5 67-70 3 ' r 29-72 4 ( 5 07-75 4 ( 5 69-77 4 ' r 31-78 5 ( 5 09-82 5 ( 3 71-83 5 ' r 33-85 6 ( 5 11-89 6 ( ) 73-90 6 ' r 35-92 7 ( 5 13-95 7 ( ) 75-97 7 1 r 37-98 8 ( 5 16-02 8 ( ) 78-04 8 1 ' 40-05 9 ( ) 18-09 9 ( > 80-10 9 ^ ^ 42-12 316 PROCESSES OF SILVER AND GOLD EXTRACTION. Value of Gold per Ounce Troy at different Fineness. p en Cents Dollars f en o p p r f r i 9 p f ; •360 ^ r 44-19 -390 ^ ^ 06-20 •420 ^ ^ 68-22 1 r r 46-25 1 i ^ 08-27 1 ^ ^ 70-28 2 h' r 48-32 2 ^ ^ 10-34 2 ^ ^ 72-35 3 r r 50-39 3 ^ ^ 12-40 3 ^ ^ 74-42 4 r 52-45 4 ^ ^ 14-47 4 i ^ 76-49 5 I- r 54-52 5 ^ ^ 16-54 5 ^ ^ 78-55 6 f I 56-59 6 i ^ 18-60 6 ^ 3 80-62 7 r r 58-66 7 ^ ^ 20-67 7 ^ ^ 82-69 8 c r 60-72 8 ^ ^ 22-74 8 ^ ^ 84-75 9 >■ r 62-79 9 i ^ 24-81 9 i ^ 86-82 •370 r r 64-86 •400 ^ ^ 26-87 •430 ^ ^ 88-89 1 r I 66-93 1 i ^ 28-94 1 ^ ^ 90-96 2 r r 68-99 2 ^ ^ 31-01 2 1 B 93-02 3 f r 71-06 3 ^ ^ 33-07 3 ^ B 95-09 4 r r 73-13 4 ^ ^ 35-14 4 { B 97-16 5 r r 75-19 5 ^ ^ 37-21 5 ^ B 99-22 6 r r 77-26 6 i ^ 39-28 6 < ) 01-29 7 r r 79-32 7 ^ B 41-34 7 1 ) 03-36 8 r I 81-39 8 ^ ^ 43-41 8 < ? 05-43 9 f r 83-46 9 J ^ 45-48 9 1 } 07-49 •380 r r 85-53 •410 ^ ^ 47-55 •440 i } 09-56 1 r J 87-60 1 i ^ 49-61 1 i } 11-63 2 r r 89-66 2 ^ B 51-68 2 J ? 13-70 3 !■ J 91-73 3 { B 53-75 3 i } 15-76 4 r r 93-80 4 { B 55-81 4 1 } 17-83 5 f r 95-87 5 { B 57-88 5 1 ? 19-90 6 J 97-93 6 \ B 59-95 6 ^ d 21-96 7 B 00-00 7 1 B 62-02 7 ^ 5 24-03 8 B 02-07 8 < B 64-08 8 d 26-10 9 B 04-13 9 < B 66-15 9 9 28-17 PROCESSES OF SILVER AND GOLD EXTRACTION. 317 Value of Gold per Ounce Troy at different Fineness, 1 Cents Dollars f 1 ? o w §• NJ ; F \ ! •450 ( ) 30-23 •480 9 92-25 •510 10 54-26 1 } 32-30 1 9 94-32 1 10 56-33 2 } 34-37 2 9 96-38 2 10 58-40 3 ) 36-43 3 9 98-45 3 10 60-47 4 } 38-50 4 10 00-52 4 10 62-53 5 ) 40-57 5 10 02-58 5 10 64-60 6 ) 42-64 6 10 04-65 6 10 66-67 7 ) 44-70 7 10 06-72 7 10 68-73 8 } 46-77 8 10 08-79 8 10 70-80 9 ) 48-84 9 10 10-85 9 10 72-87 •460 ) 50-90 •490 10 12-92 •520 10 74-94 1 ) 52-97 1 10 14-99 1 10 77-00 2 ) 55-04 2 10 17-05 2 10 79-07 3 } 57-11 3 10 19-12 3 10 81-14 4 ) 59-17 4 10 21-19 4 10 83-20 5 ) 61-24 5 10 23-26 5 10 85-27 6 ) 63-31 6 10 25-32 6 10 87-34 7 ) 65-37 7 10 27-39 7 10 89-41 8 ) 67-44 8 10 29-46 8 10 91-47 9 ) 69-51 9 10 31-52 9 10 93-54 •470 ) 71-58 •500 10 33-59 •530 10 95-61 1 ) 73-64 1 10 35-66 1 10 97-67 2 ) 75-71 2 10 37-73 2 10 99-74 3 ) 77-78 3 10 39-79 3 11 01-81 4 ) 79-84 4 10 41-86 4 11 03-88 5 ) 81-91 5 10 43-93 5 11 05-94 6 ) 83-98 6 10 45-99 6 11 08-01 7 } 86-05 7 10 48-06 7 11 10-08 8 ) 88-11 8 10 50-13 8 11 12-14 9 ) 90-18 9 10 52-20 9 11 14-21 318 PROCESSES OF SILVER AND GOLD EXTRACTION. Value of Gold per Ounce Troy at different Fineness, o 3 2 p en 1 • o CO 1 1" 1 1 ! •540 11 16-28 •570 78-29 •600 12 40-31 1 11 18-35 1 80-36 1 12 42-38 2 11 20-41 2 82-43 2 12 44-44 3 11 22-48 3 84-50 3 12 46-51 4 11 24-55 4 86-56 4 12 48-58 5 11 26-61 5 88-63 5 12 50-65 6 11 28-68 • 6 90-70 6 12 52-71 7 11 30-75 7 92-76 7 12 54-78 , 8 11 32-82 8 94-83 8 12 56-85 9 11 34-88 9 96-90 9 12 58-91 •560 11 36-95 •580 98-97" •610 12 60-98 1 11 39-02 1 12 01-03 1 12 63-05 2 11 41-09 2 12 03-10 2 12 65-12 3 11 43-15 3 12 05-17 3 12 67-18 4 11 45-22 •4 12 07-24 4 12 69-25 5 11 47-29 5 12 09-30 5 12 71-32 6 11 49-35 6 12 11-37 6 12 73-39 7 11 51-42 7 12 13-44 7 12 75-45 8 11 53-49 8 12 15-50 8 12 77-52 9 11 55-56 9 12 17-57 9 12 79-59 •560 11 57-62 •590 12 19-64 •620 12 81-65 1 11 59-69 1 12 21-71 1 12 83-72 2 11 61-76 2 12 23-77 2 12 85-79 3 11 63-82 3 12 25-84 3 12 87-86 4 11 65-89 4 12 27-91 4 12- 89-92 5 11 67-96 6 12 29-97 5 12 91-99 6 11 70-03 6 12 32-04 6 12 94-06 7 11 72-09 7 12 34-11 7 12 96-12 8 11 74-16 8 12 36-18 8 12 98-19 9 11 76-23 9 12 38-24 9 13 00-26 PROCESSES OF SILVER AND GOLD EXTRACTION. 319 Value of Gold per Ounce Troy at different Fineness. H u o H w o H w 9 1-^ o^ r g- o^ -1 g- o^ o -< o 1 r ? 2 3" 1 1 3- P' 5' i •630 13 02-33 •660 13 64-34 •690 14 26-36 1 13 04-39 1 13 66-41 1 14 28-42 2 13 06-46 2 13 68-48 2 14 30-49 3 13 08-53 3 13 70-54 3 14 32-56 4 13 10-59 4 13 72-61 4 14 34-63 5 13 12-66 5 13 74-68 5 14 36-69 6 13 14-73 6 13 76-74 6 14 38-76 7 13 16-80 7 13 78-81 7 14 40-83 8 13 18-86 8 13 80-88 8 14 42-89 9 13 20-93 9 13 82-95 9 14 44-96 •640 13 23-00 ' ^670 13 85-01 •700 14 47-03 1 13 25-06 1 13 87-08 1 14 49-10 2 13 27-13 2 13 89-15 2 14 51-16 3 13 29-20 3 13 91-21 3 14 53-23 4 13 31-27 4 13 93-28 4 14 55-30 5 13 33-33 5 13 95-35 5 14 57-36 6 13 35-40 6 13 97-42 6 14 59-43 7 13 37-47 7 13 99-48 7 14 61-50 8 13 39-53 8 14 01-55 8 14 63-57 9 13 41-60 9 14 03-62 9 14 65-63 •650 13 43-67 •680 14 05-68 •710 14 67-70 1 13 45-74 1 14 07-75 1 14 69-76 2 13 47-80 2 14 09-82 2 14 71-83 3 13 49-87 3 14 11-89 3 14 73-90 4 13 51-93 4 14 13-95 4 14 75-97 5 13 54-01 5 14 16-02 5 14 78-04 6 13 56-07 6 14 18-09 6 14 80-10 7 13 58-14 7 14 20-16 7 14 82-17 8 13 60-21 8 14 22-22 8 14 84-24 9 13 62-27 9 14 24-29 9 14 86-30 320 PROCESSES OP SILVER AND GOLD EXTRACTION. Value of Gold per Ounce Troy at different Fineness. o 1 r 9 f Pi CO 7 p" on Cents P' ; • ': -720 14 88-37 •750 15 50-39 •780 16 12-40 1 14 90-44 1 15 52-45 1 16 14-47 2 14 92-51 2 15 54-52 2 16 16-54 3 14 94-57 3 15 56-59 3 16 18-60 4 14 96-64 4 15 58-66 4 16 20-67 5 14 98-71 5 15 60-72 5 16 22-74 6 15 00-78 6 15 62-79 6 16 24-81 7 15 02-84 7 15 64-86 7 16 26-87 8 15 04-91 8 15 66-93 8 16 28-94 9 15 06-98 9 15 68-99 9 16 31-01 •730 15 09-04 •760 15 71-06^ •790 16 33-07 1 15 11-11 1 15 73-13 1 16 35-14 2 15 13-18 2 15 75-19 2 16 37-21 3 15 15-25 3 15 77-26 3 16 39-28 4 15 17-31 4 15 79-33 4 16 41-34 5 15 19-38 5 15 81-40 5 16 43-41 6 15 21-45 6 15 83-46 6 16 45-48 7 15 23-51 7 15 85-53 7 16 47-55 8 15 25-58 8 15 87-60 8 16 49-61 9 15 27-65 9 15 89-66 9 16 51-68 •740 15 29-72 •770 15 91-73 •800 16 53-75 1 15 31-78 1 15 93-80 1 16 55-81 2 15 33-85 2 15 95-87 2 16 57-88 3 15 35-92 3 15 97-93 3 16 59-95 4 15 37-98 4 16 00-00 4 16 62-02 5 15 40-05 5 16 02-07 5 16 64-08 6 15 42-12 6 16 04-13 6 16 66-15 7 15 44-18 7 16 06-20 7 16 68-22 8 15 46-25 8 16 08-27 8 16 70-28 9 15 48-32 9 16 10-34 9 16 72-35 PROCESSES OF SILVER AND GOLD EXTRACTION. 821 Value of Gold per Ounce Ih-oy at different Fineness. i t I o \ < 1 3' 2 ? 3 2 o 1 1- 2 ( < D 9 9 •810 16 74-42 •840 17 36-43 •870 17 98-45 1 16 76-49 1 17 38-50 1 18 00-52 2 16 78-55 2 17 40-57 2 18 02-58 3 16 80-62 3 17 42-64 3 18 04-65 4 16 82-69 4 17 44-70 4 18 06-72 5 16 84-75 5 17 46-77 5 18 08-79 6 16 86-82 6 17 48-84 6 18 10-85 7 16 88-89 7 17 50-90 7 18 12-92 8 16 90-96 8 17 52-97 8 18 14-99 9 16 93-02 9 17 55-04 9 18 17-05 •820 16 95-09- -850 17 57-11 •880 18 19-12 1 16 97-16 1 17 59-17 1 18 21-19 2 16 99-22 2 17 61-24 2 18 23-26 3 17 01-29 3 17 63-31 3 18 25-32 4 17 03-36 4 17 65-37 4 18 27-39 5 17 05-43 5 17 67-44 5 18 29-46 6 17 07-49 6 17 69-51 6 18 31-52 7 17 09-56 7 17 71-58 7 18 33-59 8 17 11-63 8 17 73-64 8 18 35-66 9 17 13-70 9 17 75-71 9 18 37-73 •830 17 15-76 -860 17 77-78 •890 18 39-79 1 17 17-83 1 17 79-84 1 18 41-86 2 17 19-90 2 17 81-91 2 18 43-93 3 17 21-96 3 17 83-98 3 18 45-99 4 17 24-03 4 17 86-05 4 18 48-06 5 17 26-10 5 17 88-11 5 18 50-13 6 17 28-17 6 17 90-18 6 18 52-20 7 17 30-23 7 17 92-25 7 18 54-26 8 17 32-30 8 17 94-32 8 18 56-33 9 117 34-37 9 17 96-38 9 18 58-40 23 322 PBOCESSES OF SILVER AND GOLD EXTRACTION. Value of Gold per Ounce Troy at different Fineness. 1 CD 9 3 % CO 9 a r 9 3 s o \ 5 ' ••; •900 18 60-46 •930 19 22^48 •960 19 84-50 1 18 62-53 1 19 24-55 1 19 86-56 2 18 64-60 2 19 26-61 2 19 88-63 3 18 66-67 3 19 28-68 3 19 90-70 4 18 68-73 4 19 30-75 4 19 92-76 5 18 70-80 5 19 32-82 5 19 94-83 6 18 72-87 6 19 34-88 6 19 96-90 7 18 74-94 7 19 36-95 7 19 98-97 8 18 77-00 8 19 39-02 8 20 01-03 9 18 79-07 9 19 41-08 9 20 03-10 •910 18 81-14 •940 19 43-15 •970 20 05-17 1 18 83^20 1 19 45-22 1 20 07-23 2 18 85-27 2 19 47-29 2 20 09-30 3 18 87-34 3 19 49-35 3 20 11-37 4 18 89-41 4 19 51-42 4 20 13-44 5 18 91-47 5 19 53-49 5 20 15-50 6 18 93-54 6 19 53'5Q 6 20 17-57 7 18 95-61 7 19 57-62 7 20 19-64 8 18 97-67 8 19 59-69 8 20 21-70 9 18 99-74 9 19 61-76 9 20 23-77 •920 19 01-81 •950 19 63-82 •980 20 25-84 1 19 03-88 1 19 65-89 1 20 27-91 2 19 05-94 2 19 67-96 2 20 29-97 3 19 08-01 3 19 70-03 3 20 32-04 4 19 10-08 4 19 72-09 4 20 34-11 5 19 12-14 5 19 74-16 5 20 36-18 6 19 14-21 6 19 76-23 6 20 38-24 7 19 16-28 7 19 78-29 7 20 40-31 8 19 18-35 8 19 80-36. 8 20 42-38 9 19 20-41 9 19 82-44 9 20 44-44 PROCESSES OF SILVER AND GOLD EXTRACTION. 323 Value of Gold per Ounce Troy at different Fineness. H « Q ^ t) 9 ^^ r^ ^ o ^ o tr -5 a g p* sr * f p' s- o ^ s- ^ S p S p 2 3 a 3 Cl> Cl' P' 5* GD w !• a »*j a s 3 p ? •990 20 46-51 1 -994 20 54-78 •998 20 63-05 1 20 48-58 5 20 56-85 9 20 65-12 2 20 50-65 6 20 58-91 1000 20 67-18 3 20 52-71 1 7 20 60-98 I INT D E X . Page. Abstrich 238 Abzug 238 Acetate of lead 192 Acid, sulphuric 71 Acid, hydrochloric 96 Agitator 120, 173 Alum 71 Amalgamation of gold 59 Amalgamation of gold in arrastras.. .. 61 Amalgamation of gold in batteries 59 Amalgamation of gold in pans 63 Amalgamation of silver 261 Amalgamation of silver in barrels. 117, 262 Amalgamation of silver in pans.. ..76, 124 Amalgamation of silver in Yeatch's Tubs 122 Amalgamation of silver in Wheeler's Pans 81 Amalgamation of copper matt 267 Amalgamation of speiss 268 ^ Amalgamation of black copper 268 ' Analysis of amalgam and bullion metal 26 Annealing of crucibles 135 Antimonial blend 41 Antimonial silver 45 Argentiferous copper ore 190 Argentiferous gray copper ore 42 Argentiferous lead ores 190 Argentiferous pyrites 191 Argentiferous zinc ores 191 Arsenical blend 42 Arquirite 47 Assay of silver with the blowpipe.. 28, 199 Assay of silver by fire 48, 192 Assay of silver and gold 50 Assay of lead 57 Assay of rich silver ores 193 Assay of silver with lead 193 Page. Assay of silver without lead 195 Assay of silver with litharge or acetate of lead 195 Assay of roasted ores 196 Assay of poor ores 196 Assay of ores rich in eulphurets 196 Assay .of ores rich in earths 196 Assay of alloys 197 Assay of silver and lead 197 Assay of silver, tin, and zinc 197 Assay of silver, copper, and brass .... 198 Assay of cupriferous silver 198 Assay in the wet way 199 Assay for matt 227 Augustin's Process 270 Bismuth silver 47 Bisulphate of soda 11 Blast furnaces 146 Blend, antimonial 41 Blend, arsenical 42 Blowpipe, use of 15 Borax 10 Borax glass 11 Brightening 241 Brittle silver ore 40 Bromic silver 44 Bromyrite 44 Calomel 106 Chemical action 265 Chemicals 69,83 Chemicals per ton of ore 74 Chloride of silver 43 Chlorination, of gold ores 64 Chlorine, action on metals 65, 94 Chlorobromide of silver 44 Coating, on charcoal 17 Concentration of silver in lead 164, 244 Concentration of silver in zinc 249 326 INDEX. Page. Consume, of quicksilver 130 Copperas 71 Copper, black 231 Copper, chloride of 72 Copper dissolving process 234 Copper, oxyd of. 12 Copper, subchloride of. 73 Copper, sulphate of. 69 Crucible furnace 179 Crucible cast iron 259 Cupels 49 Cupels, size of 198 Cupel mass 184,236 Cupellation with blowpipe 31 Cupellation under muffle 53, 194 Cupellation on hearth 154, 235 Cupelling furnace 183 Dark red silver ore 41 Division of silver ores 189 Dressing of assay samples 199 Embolite 44 Eucairite '. 46 Eugen-glance 40 Examination of ores for roasting 98 Examination on charcoal 16 Examination with soda and borax 18 Examination in a closed glass tube.. .. 20 Examination in an open glass tube 22 Extraction of gold 59 Extraction of silver, methods 205 Extraction of silver in the dry way... 216 Extraction of silver with lead 216 Extraction of silver from lead with zinc 249 Extraction of silver in the wet way.. 261 Extraction of silver by precipitation.. 270 Extraction of silver from copper matt. 270 Filtering apparatus 274 riame 15 Fluxes for melting ores 148 Froth 155,238, 242 Furnace for assays 52 Furnace for cupellation 183 Furnace for meting bars 135, 179 Furnace for melting ores 180 Furnace for refining silver 186 Furnace for roasting ores 176, 177 Galvanic action 266 Gold 36 Gold with mercury 37 Gold with silver 36 Gold with tellurium 37 Gk)ld with tellurium and lead 37 Page. Granulation of lead 149 Hardness of silver ores 35 Hearth 243 Hessite 46 Hoi-n silver 43 Hydrostatic melting 229 Hyposulphite of soda 279 Incorpomtion 131 lodyrite 44 Iodide of silver and mercury 45 Iron, protochlorid of 73 Iron, chlorid of 74 Iron, as chemical 84 Lead, for cupriferous assays 198, 200 Light red silver ore 42 Limadura 131 Liquation 231 Litharge 148 Litharge ring 157 Litharge fumes 158 Litharge black 238 Litharge red 242 Litharge yellow 242 Lixiviation 273 Loss of lead, remedy for 218 Loss of silver, remedy for 258 Loss of silver in roasting 115 Lustre of ores 24 Magistral 129 Marl 184, 236 Matt 136, 226 Melting of retorted amalgam. 134, 138, 139 Melting of silver ores with lead 205 Melting of rich ores in crucibles 220 Melting in cupelling furnaces 221 * Melting of unroasted ores 222 ^ Melting of roasted argentiferous cop- per ores 224 Melting of rich silver ores 152 Melting furnace 180 Melting process 145 Methods of extraction, choice of. 218 Methods, principal 211 Methods of refining 254 Miargyrite 41 Mixture of ore for melting... 151, 222, 223 Naumannite .' 46 Oxydizing flame 15 Pans, description of 169, 170, 174 Parke's process for desilverising lead.. 249 Patera's process for extraction of sil- ver 279 INDEX. 327 Page. Patio, or American heap amalgama- tion 164, 244 Pattinson's concentration of Bilver in lead 164, 244 Polybasite 40 Polyeulphide of sodium 279 Proustite 42 Protochloride of iron 73 Purification of lead 167 Pyrargyrite 41 Reagents for blowpipe 10, 12 Reduction flame 15 Reduction of litharge 161 Refining of silver 162, 251 Refining in crucibles 162, 259 Refining in hearth furnaces 163 Refining on movable tests 254 Refining under muflles 255 Refining in reverberatory furnaces 257 Refining furnace 186 Retorting 133 Roasting 90 Roasting for barrel amalgamation. 101, 263 Roasting for pan amalgamation 106 Roasting for patio process 129 Roasting for Augustin's process 271 Roasting for Ziervogel's process 276 Roasting for Patera's process 280 Roharbeit 225 Rohstein 225 Ruby silver (see pyrargyrite) 41 Salt, common 72,96, 130 Scheme of Pattinson's crystallization.. 248 Scorification, asbay 193 Scrapings 155, 238 ^ Selenid of silver 46 Selenid of silver and copper . 46 Separation of lead and silver amal- gam 113 Sign of completed roasting 277 Silver amalgam 47 Silver assay 192 Silver bromic 44 Silver, chlorid of 43 Silver chlorobromid :.. 44 Silver copper glance 39 Page. Silver fahlerz 42 Silver glance 38 Silver, iodid of 44 Silver native 38 Silver ores. 38 Silver, sulphuret of 38 Silver, tellurid of. 46 Silver concentration in matt 225 Silver concentration in lead 164, 244 Silver concentration in zinc 249. Silver extraction by mercury 207 Silver extraction by precipitation 208 Silver extraction by lead 228 Skimmer 136 Soda bisulphate 11, 71 Soda carbonate 11, 49 Specific gravity 33 Spitting of silver 253 Spitting of silver, remedy for 257 Steam application in roasting 100 Sternbergite 39 Stromeyerite 39 Sublimation in glass tubes 21 Sulphuret of silver and iron 39 Systematic proceeding in determining gold and silver ores 23 Table, loss of silver by cupellation. .. 33 Table, progress of enriching lead 165 Tailings 80, 89, 108 Temperature in cupelling 157, 258 Tellurid of silver 46 Test-ring 243 Tinfoil 12 Torta 131 Treatment of slag and matt from melt- ing bars 141 Treatment of rich silver ores 125, 209 Treatment of poor silver ores 210 Value of gold and silver per ounce — 145 Vitriol blue 69 Vitriol green 71 Volatility of silver 100 "Weights, for assay 13 Wet assay 199 Wet process 67 Xanthocone 42 h'l^ ; 1 'LXr'( I y\ 'V. ■^. YV FIG. 6 . M.A'I'F. !l. Fl (,7 FLO. la i?^-. y.,Ktou^e.i.uko. S,F 'irulrj^^r /^ly.s /.'i ./A/^inrAdo^/ur-M Srvf/^^ /'//-/A :j^/. v-/ /^^///r// /r'////'//}fJl. riA'n-:.LV. ^ FIO \?L?. FIG fciS n AfYf/f /'/yy y}*. y:-i '> ///r/? /n/Ai'^pA 1 rio'h3.c>miLe5 Ijiiui(/5'd9 LlinroC.S F H^ TE VI \ > \ ^ s jrio ;-^:^^ H.An'1:; VII! if^ dS / Fb,. oO TLATEIZ.. I ^" ':^^-Eji -- ;s i , , \ \ i i !| j ! 1 1 1 'i !l 1 i 1 1 1 1 I II 1 1 -. » M W -'"".. '^ -A' '■^-,' 'PLATE XI. :fi&. 35 Scale Fi^'s. 36. rM 37. /S rneh h rAc^/oo?-. Raliljoume's Iid:i.oe£29 Clay St SP. I