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By A. W. Hann

THE importance, to geologists and metallurgists, of knowing the mineralogical forms in which the silver occurs in ores has increased during the past few years, and will continue to increase as long as working hypotheses are converted into proved theories and rule of thumb methods are supplanted by scientific data. The methods used for the determination of these silver minerals have been: (1) careful study of polished ore sections with the microscope, and more recently, (2) metallurgical separation of the ground ore by flotation, tabling and panning, supplemented by microscopic examination of these separated minerals, and chemical analyses. During the course of some experimental work carried on by the testing department of the International Smelting Co. and myself, it became important to determine, in a general way, the distribution of the silver values in the minerals, as they exist in Tintic Standard and North Lilly siliceous oxidized lead-silver ores. These mines are in the East Tintic Mining District, State of Utah. In this work the second method was used. Differential flotation tests were run, separating the sulfide from the oxidized minerals, and the products were assayed. Various concentrates were carefully panned and the separated products assayed; special samples of ore were selected and assayed. The microscope was used only for the purpose of determin; ing whether the individual minerals were in the so-called "free" state. Analysis of Tintic Ores These chemical and mineralogical determinations showed the silver to be present as native silver, argento jarosite, argentite, and combined or inherent in the tetrahedrite, chalcopyrite, galena, pyrite, cerussite, anglesite, mimetite, malachite, iron oxide and occluded in the quartz. Careful microscopic work would probably show other forms in small amounts, such as the halide silver minerals and some of the antimony sulfide combinations. The tabulation of the analyses of the various products (Table 1) shows no evidences of fixed ratios of silver to any particular base metal.

Jan 1, 1929

By R. W. Regehr, R. A. Burmeister

Epitaxial growth of GaAs 1-xPx on germanium substrates was achieved using an open tube vapor transport system. The compositional range of 0.3 < x < 0.4 was examined. The best results were obtained with (311) orientation of the germanium substrate. The physical and chemical properties of the resulting layers were investigated using several techniques. Spectrographic analyses of the layers indicate substantial incorporation of germanium into the GaAs t-X Px layer. Evidence is presented which indicates that this incorporation occurs via a vapor phase transport process rather than by solid phase dijfu-sion. Electrical measurements suggest that the germanium thus incorporated behaves predominantly as a deep donor in the compositional range of 0.33 < x * 0.40 and has a deleterious effect upon the luminescent properties of GaAs1-x Px. The increasing technological importance of GaAs1-xPx for use in light-emitting devices has led to an evaluation of several aspects of existing growth processes. The method most commonly used to prepare GaAs1-xPx for electroluminescent device applications is vapor phase epitaxial growth on GaAs substrates.&apos;-4 In a typical electroluminescent diode structure the active region of the diode is entirely within the epitaxial layer and thus the electrical properties of the substrate are relatively unimportant since it is effectively a simple series resistance (assuming hetero-junction effects to be negligible). The use of germanium rather than GaAs as the substrate material is of interest for several reasons. First, GaAs of reasonable structural quality has been epitaxially grown on germanium4-2 and it is reasonable to expect that GaAs1-xPx could subsequently be deposited on the GaAs layer. Second, germanium substrates are readily available with both lower dislocation densities and larger areas than GaAs. Finally, single crystals of germanium are more economical than GaAs single crystals. The principal objective of the present investigation was to test the feasibility of growing GaAs1-xPx epi-taxially on germanium substrates, and to evaluate the properties of such layers with regard to electroluminescent device requirements. The approach used was to a) demonstrate epitaxial growth of GaAs1-xPx on germanium, and b) characterize the relevant structural, electrical, and optical properties of the GaAs1-xPx layers. The possibility of germanium incorporation into the grown layers was of special interest since there was some indication of this in previous studies of GaAs growth on germanium.5&apos;11,12 Although a study of the electrical properties of germanium in GaAs1-xPx was not an intent of this investigation, several features of the electrical properties of the layers grown in the present study which appear to be due to germanium are described. EXPERIMENTAL PROCEDURE The open-tube vapor transport system used for the epitaxial growth of GaAs1-xPx is illustrated in Fig. 1. This system utilizes the GaC1-GaC13 transport reaction and is similar in most respects to the larger system described elsewhere.&apos; The germanium substrates were n-type, with a resistivity of 40 ohm-cm (Eagle-Picher Co.). These were cut to the orientations of {100), {111), and (3111, and were mechanically polished and chemically etched in CP-4 (5 min at 0°C) prior to growth. In some cases, a GaAs substrate was employed in addition to the germanium. The orientation of the latter was {loo}, and they were also mechanically polished and chemically etched prior to growth. The initial composition of the deposited layer was pure GaAs. After approximately 10 microns of GaAs was deposited on the germanium substrate, the phosphorus content of the layer was gradually increased over a distance of approximately 15 microns to the desired concentration and maintained at this value throughout the remainder of the growth. Typical operating parameters used during growth are given in Table I. Selenium was used as a n-type dopant in several runs to facilitate comparison of the electrical properties of the layers grown on germanium with those of layers grown on GaAs substrates, which are usually doped with selenium. The concentration of H2Se in the gas phase was adjusted to a value which would normally yield a carrier density of 1 to 5 x 101 7 at room temperature in layers grown on GaAs substrates. The terminal surfaces of the epitaxial layers were examined by optical microscopy for structural characteristics. Laue back-reflection photographs (Cu radi-ation) were also made on the terminal surface to verify the epitaxial nature of the deposit. After these steps

Jan 1, 1970

By Milton E. Wadsworth, W. Martin Fassell, William H. Dresher

A study of the rate of dissolution of molybdenite (MoS2) in alkaline solution was carried out under carefully controlled conditions. Effects of temperature, oxygen over-pressure, and KOH concentration were evaluated. Studies were made in the temperature range 100°C to 175°C and in the pressure range 0 to 700 psia of oxygen. Under these conditions molybdenite was found to leach according to a linear mechanism. Both oxygen over-pressure and KOH concentration were found to control the rate of leaching. The mechanism has been explained in terms of adsorption of oxygen at the molybdenite surface followed by configurational rearrangement of the adsorbed molecules. The hydroxyl ion dependency is believed to be diffusion-controlled. Laboratory batch studies have shown that molybdenite can be readily dissolved in alkaline solutions under moderate conditions of temperature and pressure. Commercial application of this process to the production of ferro-molybdenum and molybdenum chemicals is promising in view of the ease of dissolution of molybdenite and the relatively noncorrosive conditions involved in the process.

Jul 1, 1956

By Brian J. Gorval, Robert L. Kemeny

INTRODUCTION Financing, or providing adequate capital at low cost for developing and bringing a natural resource property into production, is a fundamental requirement for profitable operation. Under the present economic environment the cost of financing any project is gaining more importance than ever. The fundamental keys for success in mining are "the Four M&apos;s": Mineral, Market, Management and Money. In recent years, with capital and operating costs skyrocketing, increased emphasis on obtaining adequate and low cost capital funds for bringing in a prospect is essential. For a small mining company there are limited sources for raising funds. In most cases these companies have neither a substantial asset base, nor any cash flow, and they are deemed as risky investments. The issue of shares of capital stock of such a company is probably the most common method of raising funds via the public purse. Alternatively, debt could be used and a source of such capital might be private investors or financial institutions. The company which intends to raise funds from the investing public by way of the sale of equity, subsequently lists those shares for trading on a stock exchange. Going and staying public commits a company to a multitude of complex laws, rules and reporting requirements. The governing bodies are the watch dogs for the public. The largest of such an organization of this kind in the world is the Securities and Exchange Commission (SEC) in the United States. In Canada, the Securities Laws come from within provincial jurisdiction. Most provinces have their own Securities Act, and Securities Commission. It is the Commission which administers the Act, and hence controls the distribution and trading of securities within the province. Extra provincial registration is required for trading and distribution in more than one province. In British Columbia, prior to a public offering, the approval of the Superintendent of Brokers (SOB) and of the VSE must be obtained. THE VANCOUVER AND TORONTO STOCK EXCHANGES There are five stock exchanges in Canada which supply a trading forum in which mining companies may operate. The stock exchanges are located in Montreal, Toronto, Winnipeg, Calgary, and Vancouver. Of the five stock exchanges, the Vancouver Stock Exchange (VSE) and the Toronto Stock Exchange (TSE) are the most heavily used for resource-based issues and are the focus of this paper. The objective of this section is to provide a brief background on the VSE and TSE. The Vancouver Stock Exchange The VSE is Canada&apos;s predominant stock exchange for financing resource-based, junior issues. Since 1907, the VSE has acted as a source of funds for mining, exploration and energy companies throughout Canada and the world. Currently, there are over 1400 companies listed on the VSE. During 1983, over 3.1 billion shares traded at a value exceeding CDN$3.96 million. The VSE has developed a reputation as one of the few exchanges where a speculative resource venture may obtain a listing and subsequent financing in a relatively short time, generally five to ten months. The SOB, the Investment Dealer&apos;s Association of Canada (IDA), and the VSE all regulate trading at the Exchange. Any irregularities in a company&apos;s stock dealings are investigated and trading may be halted by the VSE until a satisfactory explanation has been received from the suspended company. Companies can be suspended from trading or delisted for various reasons. One reason is misrepresentation of facts in documentation submitted to the SOB, VSE, or to the public, through news releases.

Jan 1, 1985

By R. E. Hudrlik, G. W. Preckshot

The diffusion coefficients of silver from solid silver in molten lead were measured to within ± 0.8 pet in a columnar type diffusion cell ower, the temperature range of 326° to 530°C. Fick&apos;s law describes the process up to 530°C where the laminar mechanism appareltly breaks down. These is negligible resistance at the interface as shown by mathematical analyses. The diffusion coefficients are found concentration independent. IT would seem that diffusion in liquid metals would be free of such effects as molecular structure, dissociation. polarization. and compound formation. This view was taken by Gorman and preckshot in their study of diffusion of copper from solid copper into molten lead. They reported diffusion coefficients which were independent of the concentration over the range of 478° to 750°C. They found that the Stokes-Einstein equation with constant radius of the diffusing specie represented the diffusion data better than Eyring&apos;s rate theory equation and Sheibel&apos;s correlation. The radius of diffusion was found to be that of the doubly charged copper. There appeared to be no resistance across the solid-liquid boundary. In the present work the diffusion coefficients for silver in liquid lead were measured over a range of temperatures of 350° to 505°C. The solubility of silver in lead over the range of 303° to 630°C was also obtained. These results are compared with calculated or correlated values or with data in the literature. EXPERIMENTAL Procedure—The experimental equipment techniques and procedures were those reported in detail by Gorman and preckshot9 and will not be repeated here. Measured values of WT, Co, A. L were obtained for various diffusion times and the diffusion coefficient was computed for the case of no resistance at the interface9, 11 by: WT/CoAL = 1- 8/p2 n=1 1/(2n - 1)2 exp[-(2n - 1)2p2 Dt/4L2] [1] or where there was resistance at the interface by: WT = 1- ?n=1 2h2/ap2L [sxp [-Dan2t]/[(h2 + an2) L + h] The roots an are those of the transcendental equation3 tan (an L) = Iz/cun. The diffusion coefficient is that defined by Hartley and Crank.7 The total silver in the lead cylinder and equilibrium slug was determined by a cupellation technique&apos; with proper correction for losses. Analysis of known samples showed that this method is surprisingly accurate. The amount of silver in the lead adhering to the silver cylinder was obtained in the same fashion as shown by Gorman and preckshot.9 The small errors involved in this determination are not critical since the silver in this adhering lead layer is only 3 to 15 pet of the total diffused. Materials—Electrolytic silver containing 99.9+ pet Ag obtained from General Refineries of Minneapolis, Minn. was used for all but runs 7 and 8. For the balance of the runs this silver was reduced with hydrogen at 1100°C and its oxygen content was found to be about 0.017 pet. For the runs. 7 and 8, phosphorous-reduced silver of the same purity was obtained from Handy and Harman Co. of Chicago, Ill. The densities of the phosphorus-reduced silver and the hydrogen-reduced electrolytic silver were 10.484 and 10.487 g per cm3, respectively. These values agree with those reported for pure silver. Silver which was reduced at 900 C had an average density of 9.998 g per cm3, indicating porosity. This silver was used for a number of runs which were not tabulated in Table I. These are indicated by crosses on Fig. 2. The 99.999 pet Pb was obtained from the National Lead Co. Research Laboratory of Brooklyn, New York. DISCUSSION OF RESULTS The diffusion and solubility results are reported in Table I for eleven runs using either phosphorus-reduced electrolytic silver or hydrogen-reduced silver at 1100° C. The solubility data shown in Fig. 1 show the excellent agreement with that reported by Heycock and Neville.8 The data of Friedrichs5 apparently are in error. The experimental solubility data of this work are reported to 0.3 pet. The experimental diffusion coefficients computed from Eq. [1] are reported within 1.2 pet of the mean and are plotted in Fig. 2. These are expressed within +0.8 pet of the experimental values over the entire temperature range by: D= 8.26 x 10 -5 e-1925/RT . [3] There appears to be little difference due to the

Jan 1, 1961

By P. A. Laxen, H. R. Spedden

WHEN a mineral particle is fractured, bonds between the atoms are broken. The unsatisfied forces that appear at the newly formed surface are considered to be responsible for the adsorption of ions at the mineral surface. A knowledge of the mechanism and extent of ion sorption from solution onto a mineral surface is of interest in the development of the theory of flotation.&apos;*&apos; Study of the adsorption of sodium from an aqueous solution oftheon quartz offers a simple approach to this complicated problem. The availability of a radioisotope as a tracer element meant that accurate data could be obtained."." Three main factors which appeared likely to affect the adsorption of sodium are: l—concentration of sodium in the solution, 2—concentration of onotherof cations in the solution, and 3—anions present in the solution. Hydrogen and hydroxyl ions are always present in an aqueous solution. By controlling the pH, the concentration of these two ions was kept constant. The variation in thesethe amount of sodium adsorbed with variation in sodium concentration was then determined under conditions standardized in regard to hydrogen ion. The effect of concentration of hydrogen ions and of other cations was also measured. A few experiments were made to get a preliminary idea on the effect of anions. The active isotope of sodium was available as sodium nitrate. Standard sodium nitrate solutions were used throughout these experiments except when the effects of other anions were studied. It was found that sodium adsorption increased with sodium-ion concentration, but less rapidly than in proportion to it. Increasing hydrogen-ion concentration, or conversely decreasing hydroxyl-ion, brings about a comparatively slight decrease in sodium-ion adsorption. Increasing the concentration of cations other than hydrogen or sodium decreases somewhat the adsorption of sodium ion. It would appear as if the kind of anion is a secondary factor in guiding the amount of sodium ion that is adsorbed. Materials and Methods Quartz The quartz was prepared as in previous work in the Robert H. Richards Mineral Engineering Laboratory&apos; except for the refinement of using de-ionized distilled water for the final washing of the sized quartz, prior to drying." To minimize the laborious preparation of quartz, experiments were made to determine .whether the sodium-covered quartz could be washed free of sodium and re-used. The experiments were successful as indicated by lack of Na" activity on the repurified material and by its characteristic sodium adsorption. Table I gives the spectrographic analyses of the quartz used. The quartz ranged from 16 to 40 microns in size, averaging about 23 microns (microscope measurement), and had a surface of 1850 sq cm per g (lot I), 2210 (lot 11) and 2000 (lot 111) as determined by the Bloecher method." Radioactive Sodium Method of Beta Counting for Adsorbed Sodium: Na22, the radioisotope of sodium, possesses convenient properties.&apos; It has a half-life of 3 years, thus requiring no allowance for decay during an experiment. On decay it emits a 0.575 mev ß+ radiation and a 1.30 mev r radiation. The decay scheme is illustrated in the following equation: ß+ NaR-------&apos;8&apos;77NeZ2 3 years The /3 radiation is sufficiently strong to penetrate an end-window type of Geiger-Mueller counting tube. This, in turn, makes it possible to use external counting, a great advantage in technique. Furthermore, it permits the assaying of solids arranged in infinite thickness, while assaying evaporated liquors on standardized planchets. The equipment used was standard and similar to that employed by Chang.R The original active material was 1 ml of solution containing 1 millicurie of Na" as nitrate. This active solution was diluted to 1000 ml. Five milliliters of this diluted active solution was found to give a quartz sample a sufficiently high activity for accurate evaluation of the sodium partition in the adsorption measurements. Also, 1 ml of final solution gave a sufficiently high count for precision on the liquor analyses. The sodium concentration of the diluted active solution was 1.2 mg per liter, so that 6 mg of sodium for 60 ml of test solution and 12 g of quartz was the minimum amount used. The active solution was stored in a Saftepak bottle. Procedure for Adsorption Tests: The method consisted of agitating 12 g of quartz with 60 ml of solution of known sodium concentration for enough time to establish equilibrium between the solution and the quartz surface. The quartz was separated as completely as possible from the solution by filtering and centrifuging. The activity on the quartz and in the equilibrium solution was measured and the partition of the sodium was calculated from the resulting data. The detailed procedure for the adsorption test is set forth in a thesis by Laxen." In brief, it included the following steps: 1—Ascertainment of linearity between concentration of Na" and activity measured. 2—Evaluation of factor to translate activity on solid of infinite thickness in terms of activity on an evaporated active film of minute thickness, on the various shelves of the counter shield. 3—Taking precautions to avoid evaporation of water during centrifuging

Jan 1, 1953

By P. A. Laxen, H. R. Spedden

WHEN a mineral particle is fractured, bonds between the atoms are broken. The unsatisfied forces that appear at the newly formed surface are considered to be responsible for the adsorption of ions at the mineral surface. A knowledge of the mechanism and extent of ion sorption from solution onto a mineral surface is of interest in the development of the theory of flotation.&apos;*&apos; Study of the adsorption of sodium from an aqueous solution oftheon quartz offers a simple approach to this complicated problem. The availability of a radioisotope as a tracer element meant that accurate data could be obtained."." Three main factors which appeared likely to affect the adsorption of sodium are: l—concentration of sodium in the solution, 2—concentration of onotherof cations in the solution, and 3—anions present in the solution. Hydrogen and hydroxyl ions are always present in an aqueous solution. By controlling the pH, the concentration of these two ions was kept constant. The variation in thesethe amount of sodium adsorbed with variation in sodium concentration was then determined under conditions standardized in regard to hydrogen ion. The effect of concentration of hydrogen ions and of other cations was also measured. A few experiments were made to get a preliminary idea on the effect of anions. The active isotope of sodium was available as sodium nitrate. Standard sodium nitrate solutions were used throughout these experiments except when the effects of other anions were studied. It was found that sodium adsorption increased with sodium-ion concentration, but less rapidly than in proportion to it. Increasing hydrogen-ion concentration, or conversely decreasing hydroxyl-ion, brings about a comparatively slight decrease in sodium-ion adsorption. Increasing the concentration of cations other than hydrogen or sodium decreases somewhat the adsorption of sodium ion. It would appear as if the kind of anion is a secondary factor in guiding the amount of sodium ion that is adsorbed. Materials and Methods Quartz The quartz was prepared as in previous work in the Robert H. Richards Mineral Engineering Laboratory&apos; except for the refinement of using de-ionized distilled water for the final washing of the sized quartz, prior to drying." To minimize the laborious preparation of quartz, experiments were made to determine .whether the sodium-covered quartz could be washed free of sodium and re-used. The experiments were successful as indicated by lack of Na" activity on the repurified material and by its characteristic sodium adsorption. Table I gives the spectrographic analyses of the quartz used. The quartz ranged from 16 to 40 microns in size, averaging about 23 microns (microscope measurement), and had a surface of 1850 sq cm per g (lot I), 2210 (lot 11) and 2000 (lot 111) as determined by the Bloecher method." Radioactive Sodium Method of Beta Counting for Adsorbed Sodium: Na22, the radioisotope of sodium, possesses convenient properties.&apos; It has a half-life of 3 years, thus requiring no allowance for decay during an experiment. On decay it emits a 0.575 mev ß+ radiation and a 1.30 mev r radiation. The decay scheme is illustrated in the following equation: ß+ NaR-------&apos;8&apos;77NeZ2 3 years The /3 radiation is sufficiently strong to penetrate an end-window type of Geiger-Mueller counting tube. This, in turn, makes it possible to use external counting, a great advantage in technique. Furthermore, it permits the assaying of solids arranged in infinite thickness, while assaying evaporated liquors on standardized planchets. The equipment used was standard and similar to that employed by Chang.R The original active material was 1 ml of solution containing 1 millicurie of Na" as nitrate. This active solution was diluted to 1000 ml. Five milliliters of this diluted active solution was found to give a quartz sample a sufficiently high activity for accurate evaluation of the sodium partition in the adsorption measurements. Also, 1 ml of final solution gave a sufficiently high count for precision on the liquor analyses. The sodium concentration of the diluted active solution was 1.2 mg per liter, so that 6 mg of sodium for 60 ml of test solution and 12 g of quartz was the minimum amount used. The active solution was stored in a Saftepak bottle. Procedure for Adsorption Tests: The method consisted of agitating 12 g of quartz with 60 ml of solution of known sodium concentration for enough time to establish equilibrium between the solution and the quartz surface. The quartz was separated as completely as possible from the solution by filtering and centrifuging. The activity on the quartz and in the equilibrium solution was measured and the partition of the sodium was calculated from the resulting data. The detailed procedure for the adsorption test is set forth in a thesis by Laxen." In brief, it included the following steps: 1—Ascertainment of linearity between concentration of Na" and activity measured. 2—Evaluation of factor to translate activity on solid of infinite thickness in terms of activity on an evaporated active film of minute thickness, on the various shelves of the counter shield. 3—Taking precautions to avoid evaporation of water during centrifuging

Jan 1, 1953

By K. A. SPENCER

THE production of soft coal from strip mines in the United States has shown a remarkable growth in the last sixteen years, increasing from one and one-quarter million tons in 1914 to approximately twenty-two million tons in 1929. This is a growth of approximately 1660 p& cent, as compared with a growth of approximately 20 per cent in the underground mines for the same period. But even with this marked in- crease the total tonnage produced by open-face mining represents only 4 per cent of the nation&apos;s soft coal tonnage.

Jan 1, 1931

By Douglas W. Fuerstenau, Kalanadh V. S. Sastry

A mathematical model is developed for flotation in a countercur-rent column where continuously generated air bubbles rise through a downward flowing pulp. The model is based on the assumption of axially dispressed plug flow of both the liquid and air-bubble phases. An appropriate flotation-rate expression, which takes into account the changing concentration of solid particles on the bubble surface, is formulated and applied to the column flotation process. Although a complete solution of the resulting equations is not possible for the general case, solutions for specific limiting cases have been obtained. From these, it is possible to predict theoretically the dependence of the column performance on certain variables. Specifically, concentration profiles as a function of height in the column have been calculated for various values of the characteristic dimensionless parameters. The effect of axial dispersion on the perforance of the equipment is pointed out. In recent years, there has been considerable progress in delineating the fundamental physicochemical principles underlying the unit operation of flotation and in advancing methods for kinetic analysis and process modeling of flotation.&apos; In general, nearly all such process research has been concerned with the analysis of conventional flotation equipment and circuits. From these investigations, the possibility of developing and designing flotation apparatus for more efficient separation appears limited with conventional equipment. How- ever, recently there has been an attempt to apply coun-tercurrent flow techniques to flotation in the context of a flotation column.- some of the results from pilot-plant studies2 indicate possibilities for success of this process at least in obtaining higher-grade concentrates though not higher recoveries. A flotation column operates on countercurrent principle in which bubbles continuously generated at the bottom of the column rise through the downward flowing slurry. A schematic diagram of the flotation column is shown in Fig. 1. The physicochemical principles of bubble-mineral attachment, using this flotation column, are essentially the same as those which prevail in conventional equipment, the only differences being in the flow patterns of the various phases. The salient operating feature of the column as compared to those of a conventional cell is that neither mechanical nor turbulent pneumatic agitation is employed. The column is

Jan 1, 1971

By AIME AIME

AS director of Battelle Memorial Institute and as Chairman of the important O.P.M. advisory committee on metals and minerals, Clyde E. Williams numbers his acquaintances in the mineral industries by the thousands and h because his principal hobby is liking human beings, most of his acquaintancs are also his friends. Clyde is one of the many outstanding metallurgist, in the United States who started as a chemist. After graduating from the University of Utah in 1915 he was successively chemist for U.S. Smelting Refining and Mining Co., and at the Bureau of Mines station at Ithaca, N.Y. He then got into, metallurgical work and in 1920 he was appointed superintendent of the Northwest Station of the Bureau of Mines at, Seattle. Subsequently he was assistant to H. Foster Bain in metallugical work for the

Jan 1, 1942

By E. S. Machlin, C. W. Chen

THIS investigation is concerned with the origin of the intercrystalline voids and cracks formed in metals and alloys subjected to stress at elevated temperature. There have been many suggestions in the recent literature relating to this problem. Greenwood&apos; suggested that the voids may be produced by vacancy condensation. Zener has stated that shear-stress relaxation across grain boundaries could initiate high tensile stresses at the regions blocking grain boundary slip and thereby cause the formation of cracks. Chang and Grant3 have described the formation of cracks at grain boundary triple points and have experimentally verified Zener&apos;s mechanism for the grain boundary regions in the vicinity of a triple point. Subsequent to the completion of this investigation, Gifkins4 developed a model which made use of Stroh&apos;s5 mechanism of fracturing to produce sub-microscopic fractures that subsequently grow by grain boundary slip. Chen and Machlin,6 in answer to Gifkins, described a model deduced from the present investigation, in which grain boundary slip provides both the stress to fracture at grain boundary jogs and the deformation required to separate fractured jog surfaces. The possibility of gas condensation to form intercrystalline voids and cracks is eliminated as a basic mechanism because such voids and cracks are developed in vacuum melted material containing minute amounts, if any, of gaseous impurities. In a theoretical evaluation of this problem, Machlin7 concluded that void nucleation by vacancy condensation during creep-rupture is improbable but that vacancy condensation on supercritical sized voids to produce growth is probable. This investigation was begun to evaluate the suggested mechanisms for intercrystalline fracture. In particular, in order to correlate vacancy supersaturation ratios produced in creep with those determined by Bal-luffi and Seigle8 as critical for , the nucleation of voids, specimens were obtained from the same heat of brass as used by the latter authors, through the courtesy of Dr. Seigle. The experiments conducted in this investigation fall into the following categories: 1) Brass—observation of voids produced under a variety of conditions, including creep under compression, to evaluate the mechanisms of void nucleation and growth. 2) Bicrystal experiments to check the mechanism of void nucleation deduced in this investigation. 3) Morphology of intercrystalline voids produced in a variety of metals. Each set of experiments will be described and discussed separately. Experimental Techniques A special creep-rupture test rack was constructed which made it possible to apply the stress to the specimen in a controlled atmosphere of inert gas, reducing gas, or vacuum. All the creep-rupture tests on a-brass (30 pct Zn) were conducted in nitrogen under a pressure slightly above atmospheric. Either dead weight loading or constant elongation rate loading could be applied with the load measured by means of a strain gage dynamometer. In order to obtain a coarse-grained crystal structure stable at

Jan 1, 1958

By H. H. Stoek

Danville, the county seat of Montour county, Pa., was one of the earliest and best-known centers of the iron intlustry in the State. It is situated on the north bank of the north branch of the Sosquehanna river, twelve miles east of the confluence of the north and west branches of that river at Northurnberlttnd. The ore-belt, extending for a distance of twelve miles along the north bank, has been developed in a number of places, but nowhere so extensively as in the immediate vicinity of Danville. Hence, a description of the mines in that locality will suffice, as typical of the workings of the entire section. Geology. The Montour ridge consists of an anticlinal fold extending from the source of Wapwollopen creek on the east to the west branch of the Susquehanna, which it reaches at the mouth of Chilisquaque creek. According to the reports of the First Geological Survey of Pennsylvania, the length of the ridge is nearly twenty-seven miles, with an average breadth of three-fourths of a mile, and a maximum elevation of six hundred feet in the vicinity of Danville, where it also attains its greatest width. Just north of Danville the Mahoning creek cuts through it, exposing the iron-ore on the hill-side, where advantage has been taken of this to work the beds on the southern slope of the ridge by means of drifts. The sections given in Fig. 1 are taken from the reports of the First Geological Survey of Pennsylvania, made in 1858, by H. D Rogers, whose description of the Moatour ridge was so complete and accurate that the entire report was reprinted as an appendix to Vol. G 7 of the Second Geological Survey. The approximate crosssection shows that near Danville the top of the ridge is of Clinton vol, xx.—24

Jan 1, 1892

By Ovid W. Eshbach

ENGINEERING education has been powerfully affected by the impact of war, just how powerfully can be better understood after considering the postwar problems regarding students, staff, and plant. In time of war no one will question the necessity of expediency of military training. With the cessation of hostilities, expediency gives way to the evolutionary process of strengthening engineering education as need is exemplified by experience. During the war, except for the Navy V-12 program, engineering education was at its lowest ebb of the century. Freshman enrollments were largely limited to those graduating from high school at the age of seventeen; and the upperclass, to those disqualified for active service. In most schools the experienced staff was either in service or government and industrial research. Many may never return to their former occupations. The most immediate problem is that of maintaining and building a staff to meet the enrollment of returning veterans. It is estimated that out of the eleven

Jan 1, 1945

By A. Eilers

NO one who has visited our Western mining districts, and studied the economical part of the beneficiation of the ores occurring all over that vast extent of country, can underrate the high importance of the above subject. By far the larger number of the districts which contain smelting ores, i. e., argentiferous and auriferous lead, or copper ores, are situated in the Great Basin, that great plateau between the Rocky Mountains on the east, and the Sierra Nevada on the west, almost the whole of which is comprised at present in the boundaries of Nevada, Utah, and part of Arizona. This region is essentially a barren country. The extreme dryness of the atmosphere permits but a scanty vegetation in the plains; and even in the detached mountain-chains running through it-generally from N. to S., or from N. W. to S. E.-there are no trees found except dwarfed pines and mahogany, at the head of sheltered ravines, and a few cottonwoods and willows, which fringe the insignificant streams, before the water sinks in the arid plains. Nearly all the mountain-chains in this region are rich in silver ores. That class of these ores which is adapted to amalgamation, and rich in silver, has been worked with profit for more than ten years. But before the advent of the transcontinental railways, mining was restricted to these ores alone, and the consumption f fuel could be met with the scanty supply of forest trees in the immediate vicinity of the mining districts. Since, however, the Union and Central Pacific Railroads have brought the Great Basin nearer to the commercial centres of the East and the Pacific coast, thus reducing the expenses of freight and labor materially, other silver deposits, containing poorer ores in greater abundance, have been rapidly taken

By J. R. Long, T. R. Graham, R. S. Dean

FOLLOWING the development of elec¬trolytic manganese production by the Bureau of Mines, an extensive program was planned to study the character of this high-purity product and its possible utilization in various alloy combinations. Previous work reported in the literature concerning alloys containing substantial amounts of manganese dealt largely with material prepared from relatively impure grades of the metal, and in many instances the impurities thus introduced did not permit true evaluation of manganese as an alloying element. One phase of the Bureau&apos;s program included a general review of the system and the establishment of the physical properties of copper-manganese-zinc alloys, using electrolytic manganese, and with particular emphasis directed to com¬positions within the alpha solid solution area. A number of reports of the work on alloys in this system, giving specific data concerning the equilibrium system and some of its alloys, have already been published. One study1 established the alpha solid solution area at various temperature levels and composition ranges up to 50 pct manganese. Other investigation reports presented the properties of selected alloys; namely, a 65 pct copper, 10 pct manganese, 25 pct zinc alloys&apos; a sensibly white manganese brass composed of 70 pct copper, 20 pct manganese, 10 pct zinc,3 and a series of alloys with a constant copper content of 60 pct and 5 to 25 pct manganese, balance zinc.4 In these reports tensile properties as influenced by cold-working and subsequent annealing were given in detail. Additional data are now available on other alloys of the alpha region up to 50 pct manganese, and these, together with previously published information, are sufficiently complete to establish the relationship between properties and composition for this portion of the ternary system. The present report is a summary of the tensile properties of wrought alloys in the form of sheet and rod stock. The summary is necessarily limited to data for only one condition of cold-work and a single annealing temperature, since a complete exposition of all the data available would be too extensive for this presentation. Nevertheless, it is possible to make a reasonable approximation of the tensile properties in other conditions of cold-working and annealing by a correlation of the data previously presented on specific alloys and the data given here.

Jan 1, 1947

By Allan J. Clark

THE September issue of MINING AND METALLURGY might almost have served as a review of the advances in the metallurgy of gold during the current year. In addition to a scholarly article by F. W. Bradley, there were able descriptions by W. W. Bradley and W. F. Boericke of the methods followed in California and in Ontario. Considered together, the two last-named articles indicate the many possible combinations of flotation with one or more of the older processes. This, the prominence of flotation as an aid in the beneficiation of gold ores, is probably the most striking of the year&apos;s developments. It would perhaps be nearer the fact to say that the year has not been marked by the gold metallurgists&apos; discovery of the flotation process, but rather by the flotation merchandizers&apos; discovery of gold metallurgy. I say this because native gold was floated successfully more than fifteen years ago, and a reference to these results was published six years ago.

Jan 1, 1933

By Frank E. Woolley, John F. Elliott

Mathematical models of the transient thermal behavior of a high-temperature solution calorimeter1-3 have been developed. The thermal behavior of the calorimeter is appoxirrzated by linear lumped-parameter models, and hence is described by sets of linear ordinary differential equations with constant coefficients The response of the models to various inputs is shown to agree with the response of the real system. Application of the modeling to experimental design and analysis of data illustrates the usefulness of simple models of complex systems. The early eperiments1,2 with the high-temperature solution calorimeter indicated that the change in the temperature of the bath resulting from the addition of a solute sample to the bath involved not only the direct effect due to the solution process but also possibly a secondary effect arising from the change in coupling between the bath and the induction heating coil. Consequently, an extensive analysis of the calorimeter was carried out, and models of the transient thermal processes of the instrument were developed to aid in improving the design and interpreting the behavior of the system. This paper describes the dynamic modeling; the use of it in treating experimental results has been reported earlier.3 The high-temperature solution calorimeter was constructed to measure directly the partial molar heats of solution of solute elements in a variety of liquid metal solvents.1-3 The calorimeter consists of an induction-heated liquid metal bath into which small samples of a solute element can be dropped. The bath temperature is recorded continuously, and the change in the measured bath temperature with time, dTm = f(t), resulting from the solute addition are the raw data from which the enthalpy change caused by the addition is determined. To extract the rmodynamic results from the data, the temperature change must be compared with that resulting from calibration additions of known enthalpy change. Accordingly, it is necessary to understand the transient thermal processes arising as a result of the addition to the bath. Neither modeling nor experimentation alone could provide the required insight into the working of the calorimeter. The alternate use of both methods in conjunction greatly assisted the design of the equipment and experiments, and the interpretation of the data. THE PHYSICAL CHARACTER OF THE SYSTEM The essential parts of the calorimeter, Fig. 1, for model studies are the thermocouple, the liquid metal bath and the surrounding refractories. The system is the solvent metal bath and those refractories around it which undergo a temperature change as a result of an addition to the bath, and which determine the way the temperature of the bath responds to an input. The inputs are the combined transient thermal effects arising when an addition is made to the bath. They include the thermal effects of the addition itself and the results of changed coupling between the bath and the induction coil. The response is the variation in the measured bath temperature, dTm(t) = Tm(t) - Tm(O), from an initial steady state resulting from the inputs. It was assumed in this study that the physical properties of the various elements of the system are independent of the inputs and time, although these properties may vary as the result of changes in the composition and size of the bath during a series of additions. This separation of inputs and the system is equivalent to assuming that the system is linear, i.e., that its behavior can be described by linear differential equations with constant coefficients. Linear behavior can be expected whenever the departure of each portion of the system from its steady-state condition is small enough to cause negligible changes in the thermal properties of the materials and in the various heat-transfer coefficients. Radiative heat transfer is important in this system, so the assumption of linearity should be valid only for small temperature deviations. Several conclusions were drawn from operation of the calorimeter in earlier experimental studies: 1) Radiative heat transport from the top of the bath is a significant portion of the total heat lost from the bath. However, for small changes in the bath temperature the change in transport by this path could be assumed to be proportional to the change in the bath temperature. 2) A very small portion of the heat input is lost through the thermocouple to its water-cooled holder. The thermal resistance and thermal capacity of the thermocouple protection tube are small, so the temperature of the thermocouple should follow closely that of the bath. 3) The remainder of the total heat lost from the bath will pass by conduction through the crucible to, and through, the other refractories, eventually being absorbed by the water-cooled induction coil or by the water-cooled sides and bottom of the enclosure. 4) The thermal resistance between the bath and crucible is very small. Thus the thermal capacity of the crucible will affect the temperature of the bath very soon after an addition of heat to the bath. 5) The thermal resistance between the crucible and the silica sleeve is large, especially if a radiation shield is placed in the gap. The effect of the thermal capacity of the sleeve thus will be significant only at longer times. The thermal resistance through the packing below the crucible also is large, so the packing and the silica sleeve will have similar effects on the behavior of the system. 6) A large temperature drop exists across the gap containing the water-cooled induction coil. Thus for relatively small changes in the thermal input to the bath, the refractories beyond the sleeve

Jan 1, 1970

By E. G. Dean

A method of top slicing has been devised at the Miami Copper Co.&apos;s mine at Miami, Aria., which differs radically in some ways from the customary methods of top slicing. The area of that section of the orebody in which top slicing is used is about 800 ft. square. The ore, while for the most part soft, is, nevertheless, considerably harder than the capping. The latter is siliceous, seldom containing any clay or other binding material, and breaks into fine particles so that it runs like sand if given the opportunity. Because of these facts, and because the ore is above the average grade of the mine ore, it has been mined by top slicing. Haulage levels are opened up 150 ft. apart, vertically, with two sub-levels between at 50-ft. intervals, to facilitate the putting up of ore chutes. These sublevels are used during slicing for distributing air in the ventilation system. On the haulage level the drifts are spaced on 50-ft. centers, and raises along these drifts are also spaced on 50-ft. centers, except the incline raises as hereafter noted. The raises are cribbed where necessary. Where the wear will be excessive, 1/4-in. iron plates are spiked to the top of every third set of cribbing, for its protection. When top slicing was first used, an attempt was made to carry a slicing face from fifty to several hundred feet long. Timber and other supplies were brought in through long drifts from an auxiliary shaft. Great difficulty was experienced in keeping these drifts open, the side pressure breaking the posts and the top weight breaking both caps and posts. Furthermore, the men could not work efficiently while these drifts were being repaired. The slicing faces advanced irregularly, due to varying conditions, and in many ways the results were not all that could be desired. It was then decided to divide the slicing area into blocks 200 ft. square and this was later changed to 250 ft. square. At the center of each block a two-compartment raise is put up as a supply raise, the compartments being 2 ft. 6 in. and 4 ft. by 4 ft. 4 in., the smaller being used as a manway. Station sets of 12 by 12 timber with

Jan 1, 1917

By F. W. Lee

Historical-From the beginning of time, all ingenuity of mankind has been concentrated upon the methods of finding gold and unusual deposits in the earth. An illustration (Fig. 1) from the old treatise by Agricola, "De Re Metallica," published in 1580, will serve to show the im-plicit faith of that generation in divining methods. However, it was not until 1920 that real progress was made in prospecting by using the latest advances of the physical sciences. The public interest was stimulated by the successes of these methods on the part of commercial oper-ators, and governmental agencies received many requests for information concerning their relia-bility. There were also, in the late 1920&apos;s.high- pressure mine-promotion schemes which used geophysical methods in a very questionable manner, symbolized in Figure 2 as of 1928 by an elec-trified forked stick. Authoritative information concerning such practices for public protection was needed to curb such notorious undertakings. Dr. Scott Turner, then Director of the United States Bureau of Mines, thoroughly understood the situation and was first in the governmental de-partments to recognize the possible value of a study of modern prospecting methods. The Bureau of Mines began this investigation by employing Drs. A. S. Eve and D. A. Keys of McGill University for short periods in the summer in 1927. Their first publication [see 1 of "References" at end of paper] served to illustrate the fundamental scientific principles which underlie geophysical prospecting. This was followed by a second publication [21 giving the results of field-tests. In the light of the rapid improvements during the intervening ten years, these two papers take a historical position. Later a full-time position under Civil Service was planned by the Bureau of Mines for con-tinuous investigations and research concerning geophysics and its applications to prospecting. It was Turner&apos;s idea that. since the oil-industry had been making very rapid progress with good results, if mineral mining could also benefit to the same degree, it would be of great help to that industry.

Jan 1, 1940

By R. E. Cuthbertson

AN early appreciation by the management that Climax ore presented a challenging problem of economic concentration was responsible for the establishment, in June 1926, of an ore-testing department at the experimental plant of the Colorado School of Mines at Golden, some ninety miles from Climax. An engineering office was later organized in the same community for the design of all ore-treatment units erected at Climax during the period of rapid growth. Work of the ore-testing and design staffs was effectively co-ordinated under a common head. The primary reason for having the ore-testing and plant design departments in Golden, was to place these activities under the able supervision of A. J. Weinig, consultant for the Climax Molybdenum Co., and director of the experimental plant. A secondary consideration was the availability of excellent facilities for research in ore dressing in a highly favorable environment. Concentration of molybdenite by flotation from an ore of simple mineral composition does not appear, superficially, to present a serious problem in ore dressing but experience belies this apparent simplicity. The molybdenite content of average Climax ore is low and it is finely

Jan 1, 1946