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By Edward C. Jeffrey

The use of coke in metallurgy, to any important degree, dates from the middle of the 18th century. Its utilization came most opportunely for European civilization. The forests of Europe, except in the most remote and inaccessible regions, had been largely fed, in the form of charcoal, into the smelting furnaces. For a hundred years—the middle of the 17th to the middle of the 18th century—there .was a stationary condition of population corresponding to the exhaustion of European forests. This situation, which was particularly evident in Great Britain, was due to the fact that the forests had been depleted and the practical utilization of coke had not begun. The coking industry is essential for our metallurgical industries, which in turn are basal to healthy economic progress. But coke is of great importance, not only on its own account, but for its byproducts, which enter fundamentally into all the arts of peace and war. The dyestuff industry and the manufacture of explosives are intimately connected with one another, as was shown by the recent war. The subject of coking coal, therefore, is well worthy the serious attention both of practical industry and the scientific investigator. The most valuable coking coals, from the metallurgical standpoint, are derived from the coals of highest ranks. Coals, for example, that have a carbon ratio of from 70 to 80 per cent. yield the most valuable coke for the blast furnace. The difficulty of investigating these coals, however, is great, for they are rather friable and delicate and possess a high carbon content, which makes them difficult to manipulate. They present, on account of their high carbon content, a considerable degree of opacity when examined, in thin sections, under the microscope. The tenderness of structure and blackness of such high-grade coking coals as those of Connellsville and the Pocahontas region make them extremely difficult to investigate. Two of my colleagues, who are taking part in this discussion, will describe the valuable results that have been reached by studying coal by the methods of the mineralogist. Doctor White and Doctor Thiessen have studied the structure of coal as determined from thin sections that

Jan 1, 1925

By Charles White Merrill

Money is one of the most pervasive elements in human life. The compensation for a workman's daily efforts is expressed as a wage and is measured in money. What an individual may consume depends largely on his income which also is expressed in terms of money. If he would start an enterprise its size would be determined in large part by the amount of money available for capitalization and its success would be measured in net income expressed in money. In short, the most widely used common de- nominator for comparing merchandise, real property, jobs, enterprises, gross national product, or personal success is money. Despite this use of money by almost everyone past infancy to express his appraisal of the innumerable values he sees around himself, the complexity of the device called money makes its nature and workings a mystery to most users. Some of the difficulty in understanding money results from the fact that it has three distinct but interrelated functions: (1) a medium of exchange, (2) a unit of account, and (3) a store of value. In many statements about money the discussion moves from one function of money to another without the speaker or the listener recognizing the changes. For example, the housewife says "We took the money we had saved up to make the down payment and after twelve monthly payments the television will be ours." When this housewife spoke of "saving up the down payment" she referred to money in its function as a store of value; when she spoke of "the down payment" she was using money as a medium of exchange; and when she referred to the "monthly payments" she spoke of money as a unit of account. Another cause of confusion in understanding money is its paradoxical nature in that it represents both the power to produce and the power to consume. For example, when the rich uncle dies one nephew may regard his inheritance as an opportunity to buy a farm and leave the ranks of the wage earners to become an independent producer, whereas the other nephew may regard his portion as the means of living in complete leisure as a pure consumer.

Jan 1, 1964

By S. R. B. Cooke, H. S. Choi, I. Iwasaki

In a previous article1 the function of various fatty acids as collectors for iron ores was reported for the two alternate processes; (a) the flotation of iron-oxide minerals, and (b) the flotation of calcium-activated siliceous gangue. The selectivity of separation was shown to be markedly dependent not only on such common parameters as pH and the levels of collector and activator addition, but also on the structure and the degree of unsaturation of the acids used. The iron ores employed consisted primarily of hematite, goethite, and quartz and as the effectiveness of any one acid on the separation depends on the individual response of each constituent mineral toward the given collector, a comprehensive knowledge of the floatability of the individual minerals is desirable for the interpretation of the results obtained. The mechanism by which a collector ion becomes attached to a mineral-solution interface has been a subject of much investigation. From quantitative studies of the properties of the electrical double layer on mercury2 and on several solid surfaces3,4,5,6 , the adsorption of some flotation reagents at the mineral-solution interface is beginning to be understood. For example, it has been demonstrated from streaming potential measurements made on quartz5 and corundum6 that the interfacial electrical condition is strongly dependent on the pH. Thisoccurs presumably through the following electrolytic reaction at the interface, and in the presence of a flotation collector, controls the floatability of the solids. A concurrent investigation of the flotation behavior of goethite and of quartz carried out at the School of Mines and Metallurgy7 has shown a positive correlation with the electrokinetic behavior of these minerals. The purpose of the present investigation was to collect general information on the floatability of hematite, and to investigate the function of various 18-carbon aliphatic acids on the floatability of hematite, goethite, and of activated quartz. Electrophoretic mobility measurements, simplified flotation tests using a modified Hallimond tube, and contact angle and frothability measurements were employed. The results are of direct application in the interpretation of the batch flotation results on natural ores as

Jan 1, 1961

By Harry M. Roeser

As a result of the publication, several years ago, of some articles on determining the constants of empirical formulas, the determining the constants of types of curves used for estimating the production decline of oil wells was brought to the writer for study. Methods requiring the minimum of time and labor and the maximum of rigor were sought, as it appeared that the nature of the data from which such curves are computed and the relative uncertainty of occurrence of the events predicted from them did not justify close adherence to the theory on which the solution of such problems is ordinarily based. The technical deficiencies of the solutions presented in this paper, from the standpoint of the method of least squares, are readily apparent to those familiar with that method, but their presentation in detail here is irrelevant to the subject matter. However, it is the author's conviction, after a rather exhaustive study of the problem, that the value of the solutions lose little by the approximate application of the conventional theory. It must be understood by those who use these formulas that the solutions herein given, and the formulas based on them, are merely facilities to aid the valuation engineer in forecasting future events. It is assumed, also, that before application is made of them, prescient judgment based on the circumstances in each case, shows that the forecast has some probability of realization. On this basis only will these formulas be found useful.

Jan 1, 1925

By J. E. Andersen, J. Halpern, C. S. Samis

In the presence of oxygen, galena is oxidized in an aqueous medium containing sodium hydroxide, in accordance with the following reaction: PbS + 2O2 + 3OH ? HPbO2 + SO4 = + H2O A novel method was devised for following this reaction which takes place in an autoclave under oxygen pressure, by measuring the concentration of HPbO2- in the solution with a cathode ray polarograph employing stationary platinum electrodes. Using this procedure a study was made of the kinetics of the reaction, in which the effect of a number of variables, including temperature, oxygen pressure, NaOH concentration, and agitation, on the rate, were determined. The results of this study are described and discussed, in terms of possible mechanisms for the reaction. IT is known that sulphide minerals can be oxidized in aqueous media in the presence of oxygen under pressure. Reactions of this type can be classified in two categories depending upon whether the products of oxidation are insoluble or soluble in the aqueous medium. An example of the first type of reaction is the oxidation of pyrite in alkaline solutions, giving rise to an insoluble iron oxide. The kinetics of this reaction have been investigated and its mechanism established.' It has been applied in the oxidation of iron sulphides present in refractory gold ores to improve the subsequent recovery of gold by cyanida-tion.' The second type of reaction finds application where it is desired to recover the metal by leaching during oxidation. In this case a medium is selected in which the oxidized mineral is soluble. For example, nickel, copper, and cobalt sulphide ores can be treated by oxidation in the presence of a solution of ammonia dissolving the nickel, copper, and cobalt as the metal ammine sulphate salts.:' A similar treatment has also been reported to apply to zinc sulphide ores.' It is known that lead sulphate is soluble in solutions of sodium hydroxide or ammonium acetate. It should therefore be possible to dissolve the lead from galena ores by aqueous oxidation with oxygen under pressure using either of these solutions. The applicability of the ammonium acetate treatment has been investigated and confirmed in a recent study.' The present paper describes the results of a similar study in which the kinetics of the oxidation of galena in sodium hydroxide solutions have been investigated. The object of this investigation was pri- marily to obtain information of a fundamental nature relating to the kinetics and mechanism of this reaction. The use of pulps of comminuted ore in a study of this type is undesirable because of the difficulty in controlling and measuring the surface area. The measurements were therefore made using galena crystals of measured surface area and in this way absolute reaction rates were obtained. The reaction was found to proceed as follows: PbS + 2O2 + 3OH ? HPbO2 + SO4 + H2O [I] The products are sodium plumbite and sodium sulphate salts which dissolve in the aqueous solution. The reaction studies were carried out in an autoclave in which a desired pressure of oxygen was maintained. The reaction was followed by measuring the concentration of lead in the solution with a cathode ray polarograph. The results obtained in this investigation are presented and discussed in the present paper. Experimental Materials: The crystals of galena were obtained from Violamac Mines, Sandon, B. C. The following impurities were indicated by spectrographic analysis carried out by the Provincial Assay Office, Victoria, B. C.: Sn, 0.02 to 0.2 pct; Sb, 0.07 to 0.7; Zn, 0.01 to 0.1; Si, Fe, Mg, As, less than 0.05 pct; Ag, 126 oz per ton, the latter determined by standard fire-assaying procedure. After cutting a specimen measuring approximately 5x7x12 mm, the crystal surfaces were ground parallel to the 100 axes using No. 2 emery, washed with water, and the dimensions were measured with a micrometer. Oxygen gas was of commercial grade and supplied in cylinders by Canadian Liquid Air. Solutions were made up with chemicals of chemically pure grade and distilled water. Equipment: Autoclave: The autoclave used in these studies was constructed of stainless steel and

Jan 1, 1954

By George E. Roberts

The maintenance of the common gold standard is the most important cooperative undertaking in the world. The war broke up this relationship and brought about a state of great disorder in the currencies and exchanges. After the war the countries all began to grope their way back to the gold standard as the best means of establishing trade and financial relations with each other. With this movement began a general decline in commodity prices. The question has been raised whether the world's return to the gold standard was not forcing prices back to the prewar level. Also, the question is raised whether the world has not outgrown the supply of gold as the basis of credit. Because Europe readjusted its monetary units to conform to the higher level of prices there is no pressure on prices on this account. Furthermore, a large amount of gold formerly in hand-to-hand circulation passed out of circulation and has been added to the central bank reserves. The gold reserves of 36 countries increased approximately 100 per cent from the outbreak of the war to June 30,1930. The increase is much larger than the average increase of prices in any of the important countries, at any time since 192.5. As gold in the central banks of issue is far more effective for all business purposes than gold in circulation, the gold scarcity argument has little basis as applied to this time. The abnormal distribution due to the war was to the disadvantage of business everywhere. Credit was scarcer and dearer in some countries. The inflation in this country might have been greater had the production of gold been greater. The argument supporting the theory of a scarcity of gold assumes as fundamental that general price changes must be accounted for by changes in the price equation on the side of money. This is disproved in every period of business depression. A downward price movement is characteristic of every period of business recession. Important discoveries of gold must be made even to maintain present gold production, in the face of which the world's business is bound to continue increasing. It cannot be doubted that some way will be found

Jan 1, 1931

By Fredrick Laist, J. P. Cooper

In the spring of 1931 an experiment was made at Anaconda with a small reverberatory furnace, with which was combined a roasting shaft. The arrangement is shown in the accompanying drawing (Fig. 1) and requires but little explanation. The general idea was to roast flotation concentrates, mixed with the proper fluxing materials, by dropping them down a heated shaft, from which the calcines would enter the smelting zone of the reverberatory furnace through an opening in the roof. The hearth of the reverberatory was 3 ft. wide by 21 ft. long. The roasting shaft was 3 ft. square inside and had an effective height of about 20 ft. The reverberatory furnace was arranged so that it could be charged either directly through the roof with regular hot calcines, in the usual manner, or by means of the shaft, at the top of which were a feeding arrangement by which cold flotation concentrates, suitably fluxed, could be fed continuously and a pipe through which cold air was blown in. Means were provided for distributing the feed over the cross-section of the roasting shaft. At first a mechanical arrangement was used but later it was found that a simple cone served the purpose equally well and gave less operating trouble. On account of the small size of the equipment, it was realized that absolute capacity and fuel consumption figures would mean but little. It was not to be expected that ratios comparable to those obtained in large furnaces could be gotten, and the only way in which any idea could be obtained as to the possibilities of the combination furnace was to run it in parallel with the reverberatory furnace charged in the usual manner and operating without the shaft. The results of such parallel runs are given in Table 1. The amount of oil burned in the reverberatory was purposely maintained at substantially the same rate during both runs in order that the benefits resulting from the shaft might be gaged. It was expected that the shaft would considerably increase the capacity of the reverberatory and that a better fuel ratio would be obtained on account of the high temperature at which the calcines would enter the

Jan 1, 1934

By David D. Rabb

Leaching or solution mining, a relatively simple and economical process for beneficiating metallic ores, is likely to find increasing application in the treatment of low-grade ores that are impractical to mine by any other means. This process may be carried out in two different ways: 1) dump leaching, where the ore is moved from its original location to be leached at another site; and 2) In-situ leaching, where the ore is leached in place by introducing the leach solution at the top, letting it flow down through the ore under gravity, and then recovering it plus the dissolved metals it contains. Whichever leaching method is used, it is almost always necessary to break up the ore before leaching. In this paper a study is reported which indicates that rock broken by an explosion-in particular, an underground nuclear explosion-is significantly more amenable to leaching then is rock broken by other methods. These results suggest that the leaching speed and efficiency could be increased by nuclear fracturing of the ore. Not only would the leach time be shortened, but the resulting increase in strength or richness of the solutions would decrease plant installation expense as well as reduce pumping and processing costs. A considerable fund of experience has been accumulated in the course of several hundred experimental underground nuclear explosions, so that the gross results of any given nuclear explosion can now be predicted with a fair degree of confidence.' From this knowledge it seems clear that, under the proper conditions, large ore bodies can be fractured much more economically-macroscopically speaking-by nuclear explosions than by other methods. The present study concentrates on smaller scale effects that is, the cracks in the chunks of rock broken by the explosion-and shows that here too, in the microscopic domain, there are important advantages to nuclear fracturing. The intense shock produced by the very fast acting, high-brisance nuclear explosive fractures the rock in a way that should significantly improve its leachability. Experimental Procedure This study compared rocks broken by nuclear explosives with rocks produced by conventional mining, quarrying, or core drilling. The test samples, granite chunks 6 to 8 in. on a side, plus core sections, came from the area of the Hardhat*2 nuclear explosion and were taken both before and after the explosion. For comparison, several samples of quarried granite were obtained from a local gravestone monument company. The general procedure was to soak the test samples in leaching solution and then determine the extent of penetration. A standard commercial copper leaching solution was used (10 gpl Cu, 10 gpl H2SO4, 5 gpl ferric Fe, 15 gpl total Fe, pH about 1.5), to which a water-soluble penetrant dye, Zyglo 1-c, had been added. Details of the procedure were as follows: 1) Sample leached in solution containing Zyglo penetrant dye. 2) Washed with water. 3) Air-dried. 4) Cut with granite wire saw. 5) One face polished with granite monument polish. 6) Sent directly to be photographed, or heated at 110°C for 2 hr and then sent to be photographed. 7) Photographed under ultraviolet light to show crack patterns. Results After 10 days of leaching at 70-75°F, the samples were removed from the solution, washed, dried, and cut in half with a granite wire saw to study the penetration of the leach solution. Since the Zyglo dye in the leach is visible under ultraviolet light, the degree of penetration of the leach (and hence the cracks in the samples) can be studied on photographs of the crosscut samples made under ultraviolet light. The photos in [Fig. 1] show how the leach solution penetrated various representative samples. Of the 71 rock samples examined, fractures were most frequent and prominent in samples from the rubble produced by the nuclear explosion [(Fig. 1D)]. Fracturing was less apparent in shaft-mined rock [(Fig. 1B)], still less evident in drift-mined rock [(Fig. 1C)], and practically nonexistent in cored or quarried specimens [(Fig. 1A)]. The samples in [Fig. lA-C] were from the same general area as the nuclear explosion, but they were obtained before the explosion. Results of the crack studies are summarized in [Table 1]. The Zyglo-treated leach solution penetrated the test samples at the rate of about 1/2 mm during the first hour, 1 mm by the end of 4 hr, 2 to 3 mm in 12 hr, and 4 to 6 mm in 10 days, showing a progressively slower rate with time.

Jan 1, 1972

By F. D. Wright, H. D. Fara

The solution to the plastic and elastic stresses around a circular shaft in a hydrostatic stress field that has appeared in two editions of a widely used book on rock mechanics1 is in error. Although this is a relatively minor matter, the correct solution was not found by a literature survey, so it appears worthwhile to present it. For a homogeneous, isotropic, rigid plastic-elastic body in plane strain which obeys Tresca's yield criterion the following equations must be satisfied:'," In the plastic zone,

Jan 1, 1963

The earliest record of coal in Indiana is one of the earliest in the country. At the close of the French and Indian War, in 1763, the famous Indian trader, George Croghan, was sent from Pittsburgh on a mission to the western Indians. His party met that of a hostile chief on the lower Ohio and was captured, and were taken up the Wabash River; on June 22nd, he passed the mouth of the Vermilion River-probably the Big Vermilion-and on June 23rd, he made the following entry in his journal: "on the South Side of the Ouabache runs a high hank, in which are several very fine coal mines, and behind this bank, is a very large meadow, clear for several miles."' The mines, of course, were outcrops. A few days after this he met some Indian acquaintances who secured his freedom. This location was at Ouicatanon, 210 miles from "Port Vincent," which was destroyed a few years later, and in what is now Fountain County, probably near Coal Creek. Croghan was familiar with the coal already being worked at Pittsburgh. Surveyors who ran the township and section lines in the first ten years of the last century noted the presence of coal and marked its position on the maps in 1804.2 The next record is by Nicholas J. Roosevelt, who in 1809 examined the Ohio and Mississippi Rivers prior to starting building the first steamboat to navigate these rivers. "Not only did he do this, but finding coal on the banks of the Ohio, he purchased and opened mines of the mineral; and so confident was he of the success of the project on hand, that he caused supplies of the fuel to be heaped upon the shore, in anticipation of the wants of a steamboat whose keel had yet to be laid."3 It is probable that this account confused the date of seeing the coal with that of mining it, as an earlier account by another relative of Mrs. Roosevelt of the first trip of the steamboat New Orleans in 1811 is as follows:

Jan 1, 1942

By Rudolph Emmel

THE mines operated by the South American Development Co. are located in the Zaruma mining district of southwestern Ecuador. They are near the old mining town of Zaruma, which is the only important city in the canton of the same name. The district is situated in the upper end of a valley lying between two spurs of the Cordillera, one of which may be considered the Coast Range and the other an intermediate range. The mining camp proper, known as Portovelo, and the plant are 2.4 km. south of Zaruma, on the north bank of the Amarillo River, a tributary of the Tumbes River, which flows southwestward through Peru to the Pacific. Portovelo is difficult of access; it is reached from Guayaquil by means of river steamers and muleback. Embarking at Guayaquil, the route is down the Guayas River, across the Jambeli Canal, and up the Santa Rosa River to Santa Rosa, a distance of 177 km. From Santa Rosa, the road or trail follows the Santa Rosa River, then across the summit of the Coast Range into Portovelo, a distance of 74 km.-a two-day trip on muleback. The mining property of the South American Development Co. comprises 297 lode claims and 142 placer claims. The combined lode claims cover an area, roughly rectangular in shape, 9000 m. long from north to south by 4000 m. wide; the northern edge of the rectangle is about 3000 m. north of the central plaza of Zaruma. Mineral lands in Ecuador are held by virtue of an annual tax per claim paid to the central government, no surface rights being included.

Jan 1, 1925

By R. J. P. Lyon

It is usually assumed1,2 that ore deposition is relatively slow, taking place over tens of thousands of years. Yet many syntheses and phase changes can be completed in the laboratory in a matter of hours, under essentially the same pressure and temperature conditions to be expected in nature. Much has been written about geothermometry, and Ingerson's recent summary2 an hardly be surpassed. Rather than review the whole field, this article will deal specifically with diffusion rates in solid solutions* of the sulfide minerals. In the study and application of temperature-indicating phenomena to problems of ore genesis, the time factor has often been neglected. In the particular case of sulfide systems, the speed of unmixing and diffusion of the constituent phases in the solid solutions has seldom been considered when laboratory data are applied to the genesis of natural sulfide ores. Chalcopyrite and Bornite Intergrowths: Chal-copyrite and bornite are copper iron sulfides often found in association. In many ores the individual grains appear to have mutual boundaries, but bladed intergrowths are quite common. Early workers in the field, " deduced that while these patterns could have been formed by replacement, they could be experimentally reproduced from the unmixing of solid solutions of the two previously homogenized at 475°C. Much of the ore from Roan Antelope mine in the Rhodesian Copper Belt exhibits these bornite-chalcopyrite intergrowths, from which it has been deduced that the ores could have been subjected to a minimum temperature of 475°C. In several recent interpretations,' this temperature rise has been considered to result from a regional metamorphism of an original syngenetic copper-bearing sediment. The same temperature rise to 475 °C was suggested from similar intergrowths in the sulfide- • The general subject of solid solution in structurally similar minerels is treated in many texts'. :' ' and will not be further elucidated. bearing ore from the Happy Jack uranium mine8 on tile Colorado Plateau, although this temperature had a different origin. In 1931 SchwartzV etermined that 475°C represented the unmixing temperature of his bornite-chalcopyrite solid solutions but, more important, that the characteristic intergrowths of bornite and chalcopyrite could be preserved only if the solid solution were chilled quickly to room temperature. This significant corollary has been almost completely neglected by both Davis and Miller.7,8 By suitably decreasing the cooling rate, Schwartz found that the original pattern of the intergrowth was reformed (Fig. 1). The cooling rate was critical. In cooling from 475°C to room temperature in

Jan 1, 1960

By Reginald S. Dean

THE widespread occurrence of manganese in low grade oxide and carbonate ores not amenable to mechanical concentration has led to extensive investigations of hydrometallurgical methods for producing a pure manganese compound suitable for further treatment. Manganese carbonate is the preferable compound. This product when fully crystalline and of not too fine crystal size is easily filtrable and stable in air. It can be converted to other compounds such as the oxides by heating in air or can be reacted with acids for producing salts. A useful hydrometallurgical process must produce relatively concentrated solutions that can be purified easily, reagents must be cyclically used, and heat requirements must be small. Neither the ammonium sulphate nor sulphur dioxide leaching processes that have been tested extensively fulfill these 'requirements. Other hereto-fore proposed processes have obvious limitations and have not been tried on a large scale. The present process is based on the discovery by the writer of a new group of aqueous manganese-ammonia complex solutions highly concentrated in ammonia, which permit rapid solution of manganous oxide to concentrations of 80 to 100 g Mn per liter and from which a fully crystalline, easily filterable manganese carbonate is precipitated by the addition of carbon dioxide and partial ammonia removal. Although the process may be carried out with many ammonium salts, commercial advantages dictate the use of ammonium carbamate, which is obtained when CO2 is passed into concentrated aqueous solutions of ammonia. If the carbamate is used, the only reagents, ammonia and C02, are volatile and may therefore be recovered from solutions and residues by heating, thus eliminating washing and extensive evaporation. Impurities are controlled easily as most metal oxides are either insoluble in the lixiviant or fail to precipitate with the manganese carbonate. Others are controlled by sulphide addition. The process has been tested extensively on a small scale on a wide variety of ores; including Three Kids, Artillery Peak, Cuyuna, and Chamberlain; as repre-

Jan 1, 1952

By Frances Hurd

WHEN 60:40 brass is heated to 825° C., given a drastic quench to obtain the beta solid solution, and reheated, various changes take place in the structure. Reheating at 200' C. causes a fine, granular, sorbitic structure to appear which has been considered alpha solid solution. These particles coalesce at higher temperatures of reheating, and at 470° C., the alpha forms twins. A further study of these transformations was considered worth investigating.

Jan 1, 1927

By Clemens Jones

The difficulties attending the reduction of ferric sulphate in the determination of metallic iron by the method of Marguerite, are often serious, and affect time, patience and accuracy. They depend upon the condition and purity of the zinc used, the state of saturation of the solution, acidity, and temperature. D. J. Caruegie (Chem. News, lvii., No. 1481), says that ferric solutions are instantaneously reduced by the use of zinc-dust. But there are obvious objections to its employment in quantitative work. Dr.

Jan 1, 1889

By F. P. Dewey

THE Falling Cliff Mine adjoins on the west the Bertha Mine, from which a large amount of first-class ore has been taken, producing the purest zinc known to commerce. The two mines are in the same hill, Bertha being on the northern 'slope and Falling Cliff on the top and opposite slope. The formation is No. 2 limestone. Although considerable exploration has been done by numerous shafts and' tunnels (there being over six hundred feet of the latter), no satisfactory determination of the dip and strike of the .vein could be made on account of its contortions, the ore descending from the top to the. bottom of the tunnels and rising again in very short distances; but enough has been done to indicate a very large mass of

Jan 1, 1882

By F. P. Dewey

The Falling Cliff Mine adjoins on the west the Bertha Mine, from which a large amount of first-class ore has been taken, producing the purest zinc known to commerce. The two mines are in the same hill, Bertha being on the northern slope and Falling Cliff on the toy and opposite slope. The formlation is No. 2 limestone. Although considerable exploration has been clone by numerous shafts and' tunnels (there being over six hundred feet of the latter), no satisfactory determination of the dip and strike of the vein could be made on account of its contortions, the ore descending from the top to the bottom of the tunnels and rising again in very short distances ; but enough has been done to indicate a very large mass of

Jan 1, 1882

By Zden[e]k P. Bažant

Due to their heterogeneity, most rocks fracture with a zone of distributed cracking ahead of the fracture front. This makes linear elastic fracture mechanics inapplicable. The present study describes a mathematical model in which the progressive microcracking is taken into account by strain-softening stress-strain relation. In a simpler version of the model, the triaxial strain-softening stress- strain relation is obtained by direct adjustment of the elements of the compliance matrix. This formulation is rigorous only if the principal stress directions do not rotate during fracture formation within the fracture process zone. As a more sophisticated and generally applicable model, the so-called microplane model which is an analogue of the slip theory of plasticity is outlined. Comparison with fracture data for various rocks are given.

Jan 1, 1984

By Stewart K. Griffiths

A general method-of-lines numerical approach for modeling gas driven fractures has been developed and tested. The numerical solutions agree very well with known similarity solutions for laminar and turbulent flow. Acceptable accuracy is obtained with a very few numerical grid points and with modest execution times. The model has also been checked against the results of several field tests, in which air was used to drive axisymmetric fractures into permeable tunnel-bed tuff.

Jan 1, 1984

By Luther B. Eames

J. V. N. DORR, New York, N. Y.-I have read Mr. Eames' excellent paper on this' subject with great interest, for besides being connected with the design and installation of the first modern countercurrent decantation plant, he was associated with me in the development of the thickener in the Black Hills some years earlier, and has now been operating the largest plant that has used this method of treatment. His, discussion, of the influence of different factors on the results obtained is quite thorough, but several features I think may not be apparent to the reader who has not studied the subject carefully. 1. Grade of Ore That Can Be Treated.-Mr. Eames has shown graphically that' the assay of all solutions increases directly as the grade of the ore treated. He has not emphasized, however, the fact that, as most operators prefer to keep the assay of pregnant solutions down below a certain figure in order to insure complete precipitation, an increase in ore value beyond a certain point means a proportional increase in solution precipitated and therefore not only an increase in the percentage of dissolved gold recovered, but an actual descrease in tailing loss. The importance of the influence of the percentage of moisture in the underflow on loss is made clear, and I. may add that unless it is quite evident that pulp can be safely settled to 50 per cent. solids, or more, it is usually advisable to use a continuous filter at the end of. a decantation plant to reduce losses in cyanide and gold. Dissolution in Thickeners.-The influence of a change of solution on silver dissolution has long been emphasized and most gold operators have. recognized the annoying way in which a gold ore after being agitated until nothing more can be dissolved will loosen up again when almost ready for the dump after the dissolved metal has been removed by decantation or filtration. Continuous decantation gives favorable conditions for this additional dissolution and a chance to recover most of what is thus dissolved. This is especially true if an extra tank is used in the series and barren solution added at the second tank from the end instead, of the first, as shown in Mr. Eames' Fig. 1. It can be calculated that the use of this tank will reduce the mechanical loss of cyanide by one-third and cut the gold loss as well; but the saving in gold or silver that may dissolve when the pulp is first diluted with weak solution may be as important.

Jan 4, 1917