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By David Davison

Metafex®* is an inert material that is more energetic than explosives when activated. Because Metafex is inert until activated (a moment before use), it can profoundly change the logistics of systems and processes that require energetic materials. We have obtained positive test results for a Metafex configuration (called a flat pack) that operates at the practical voltage of ~20 kV. We describe the outcome of the testing and potential uses of the material.

Jan 1, 2006

By Toshio Suzuki, Machiko Ode, Won Tae Kim, Seong Gyoon Kim

"The Ostwald ripening and growth and coarsening of the secondary dendrite arm are studied using a phase-field model. The phase-field parameters are obtained at a thin interface limit proposed by Kim et al. In Ostwald ripening analysis, the difference of the concentration due ·to· the curvature effect is shown. The third power of the average particle radius Rav is proportional to time and the ripening constant shows a good agreement with the value by Deppers et al. The particle radii distribution shows the transition behavior to attain a self-similar stationary shape. The growth and coarsening behavior of the secondary dendrite arm is also analyzed using a phase-field model. The estimated arm spacing and its dependence on time are in good agreements with experimental data.IntroductionThe ripening or coarsening process controls the microstructure during the late stage of solidification. The ripening phenomena are recognized firstly by the Ostwald [1]. The first quantitative analysis for the Ostwald ripening in the limit of vanishing solid fraction was provided by Lifshitz, Slyozov and Wagner (LSW) [2,3]. In their study, that the mean radius grows proportional to the cubic root of time and the size distribution of precipitations shows a ""self-similar"" shape are shown. Most of the studies for the Ostwald ripening confirm or predict these two general rules above. In case of finite solid fraction, the general rules are observed but the ripening constant is larger and the self-similar shape is wider than the LSW prediction respectively [4-6]. To analyze· the high solid fraction system, the theories that consider the solute field correlation are proposed [4,7-8]. In the theory, however, since the particle is treated as the point, the effect of the concentration field deviation from the monopole field should be taken into account. Recently the numerical simulation, in which not only diffusive transportation of solute but also convection effect is considered, has been done using a phase-field model [9]."

Jan 1, 2000

By AIME AIME

COUNCIL. PRESIDENT OF THE COUNCIL. CHARLES KIRCHHOFF NEW YORK, N. Y. (Term expires February, 1912.) VICE-PRESIDENTS OF THE COUNCIL. BENJAMIN B. LAWRENCE NEW YORK, N. Y. JOSEPH W. RICHARDS SOUTH BETHLEHEM, PA. ALBERT SAUVEUR CAMBRIDGE, MASS. (Term expires February, 1912.) B. CHRISTY BERKELEY, CAL. W. A. LATHROP PHILADELPHIA, PA. GARDNER F. WILLIAMS WASHINGTON, D. C. (Term expires February, 1913.)

Sep 1, 1911

An incremental-analysis-based stope design and cutoff grade calculation method was developed for an underground metal mine project. Traditional stope design methods are typically very time consuming and lack consistency and accuracy by manually drawing stope shapes. For quick reserve calculation and economic analysis, a new method named "3D incremental analysis based stope design" was created for mine-wide stope designs. The key idea of this method is to replace engineers' manual checking of each incremental ring with one calculation of all the rings, and to build the final stope shape with the maximum values. This process was realized through a 3D ring grid setup and proper naming conventions for rapid calculations. With this unique but practical method, multiple options for a mine design were completed within a short time before the final selection of optimal cutoff grade and best stope designs for the project.

Jan 1, 2012

By C. Clark, R. Pakalnis, B. Seymour, L. Martin, M. Stepan, M. Roworth, C. Caceres

The National Institute for Occupational Safety and Health (NIOSH), Office of Mine Safety and Health, Ground Control Engineering Branch is investigating the use of shotcrete in weak rock mass mines with the objective of reducing fatalities and injuries resulting from rock fall accidents. When shotcrete is used as part of a multielement ground support system, there is a need to know the support characteristics that the shotcrete contributes to the overall system. To quantify the support provided by the shotcrete, flexural strength tests were conducted with two common, commercially available fiber-reinforced shotcrete (FRS) mixes using the round determinant panel (RDP) test method, ASTM C 1550. A portable RDP test machine developed by NIOSH researchers was used to determine the peak flexural load and residual load capacity for a steel FRS and a synthetic poly FRS that were sprayed using dry mix procedures and equipment. Besides the flexural strength and loading behavior determined from these tests, a method was also developed for measuring the width of cracks exposed on the underside of a shotcrete panel during a RDP test and relating these measurements to residual load values. Quantifying the peak flexural load and residual loads of a shotcrete mix through on site testing at a mine and visually assessing the loading cycle and load-carrying capability of the shotcrete applied to underground workings will improve mine safety by providing a better assessment of the stability of shotcrete supported entries.

Jan 1, 2010

By Jim Truskoski, Alain Bouchard, Andy Kerr, Germain Labonté, Jim Barrett

"Improving mill grade recovery relationships is always good business. INCO’s Clarabelle Mill has just undergone a $16 million process upgrade that was designed to improve nickel recovery by 2%. The “Mill Redesign Project” was completed on time, under budget and delivered the promised improvement in recoveries.This paper describes the methodology of the Mill Redesign Team, details of the process improvements and the critical success factors that helped the team deliver on its promises.With a payback of under one year, the Mill Redesign Project will play a key role in ensuring a competitive edge as INCO embarks on its second century of operation.INTRODUCTIONIt is not uncommon in milling operations to encounter a crisis. That is the point when the process does not behave as expected and fails to respond to the increasingly desperate efforts of the metallurgists and operators. Flowsheet and process changes are attempted and abandoned. With luck, one or more of the changes achieves some mitigation of the original problem or more usually, the original cause of the problem disappears. Regardless, the metallurgist can sit back and bask in the apparent success of his or her endeavours.Less common is when a problem is carefully diagnosed, a team put together to explore all avenues and recommend a path of action that is implemented on time, on budget and immediately delivers on the promises which are sustained over time. This is one such story. It is the story of the Mill Redesign Project at INCO’s Clarabelle Mill in Copper Cliff, Ontario.BACKGROUNDThe Clarabelle Mill was built in 1971 on the southern rim of the Sudbury basin. At that time it was one of four mills operated by INCO in the Sudbury area. During the 1970’s, 80’s and 90’s, the need for increased process efficiency, higher levels of sulphur rejection to tails and the concurrent development of high capacity mills and flotation cells, resulted in the consolidation of INCO’s Sudbury area milling operations into a single, expanded facility at Clarabelle."

Jan 1, 2003

By John A. Legge Jr.

"ACCOMPANYING Alberta's great natural endowments of oil, wheat, scenery, fishing, and hunting is also a generous endowment of geophysical problems to plague the interpreting geophysicist. These problems — by no means unique to Alberta — are sufficiently numerous and outstanding to be of major concern in exploration. Some of them have been adequately solved, others are well on their way to being solved, and still others remain almost completely unsolved. Often a problem readily solvable in one area can be solved only with great difficulty in another. Many are closely allied with the geological conditions and require the best co¬ordinated efforts of the geologist and geophysicist for their solution.It is a fairly general practice to study rather carefully the geophysical characteristics of known producing reefs in order to obtain data on which to base an interpretation of unproven areas. This practice obviously has a very sound basis, for, as discoveries become more and more widespread in the Alberta basin, it is found that the variation' in geological conditions has a marked effect on the seismic results, as would be expected. By carrying this analysis over an area it is possible more and more to anticipate the geophysical picture which should be obtained in connection with reefing under the varying geological conditions. Another phase of this procedure, and one that has received less attention, though it is certainly of importance, is the analysis of the all too numerous failures. A study of these failures may be more fruitful than a study of the successes for it may indicate weaknesses of field procedure, computations, or in¬terpretation not particularly obvious in the discovery areas. These studies must not only include the geophysical characteristics of the observed `anomalies', but should also be coupled with a thorough geological study to ascertain whether some unanticipated geological condition is responsible for the erroneous geophysical interpretation."

Jan 1, 1953

By William Seymour

"INTRODUCTION Byproduct-coke manufacture is one of our country's most essential in¬dustries; its importance was strikingly accentuated by the demands of World War II. This paper reviews recent progress in various phases of byproduct-coke operations for the production of metallurgical coke particularly that used as blast-furnace fuel.In the early days of the by-product-coke industry in the United States high-grade bituminous coking coals, both high-volatile or gas coal and low-volatile Pocahontas coal, were plentiful, and the selection and mixing of coals for coke-oven use were minor problems.The demands of World War I for the production of iron, steel, and coke aroused and stimulated new interest in the investigation of the reserves, characteristics, and properties of our coking coals. During that war the increased demand for coke reached a critical stage, and the shortage of high-grade coking coals necessitated the use of cols of inferior quality and of different coking characteristics than those previously used.The period of prosperity following World War I brought much progress and development in the by-product-coke industry. Methods of testing coal and coke were improved. The search for satisfactory coking coals was continued, and construction and design of byproduct ovens were improved."

Jun 1, 1946

By Joe H. Skidmore

This paper, describing mining and milling methods and costs at the Gold Hill mine, is one of a series being published by the Bureau of Mines. Boise Basin, in which the geld Hill mine is located, is in the central part of Boise County, Idaho, about 30 miles by air line northeast of Boise. The mine, owned and operated by Talache Mines, Inc., is at the southern end of the town of Quartzburg. About 115 to 125 tons daily is mind by square-setting and is treated in an amalgamation plant.

Jan 1, 1938

By H. L. Teichman, E. M. Sipprelle

ENACTMENT' of Public Law 290 by the 78th Congress authorized the U. S. Department of the Interior, Bureau of Mines, to conduct an experimental program to develop the technology for obtaining oil from oil shale. In adopting and later extending this legislation, the Congress recognized the impending necessity of supplementing ground petroleum reserves with synthetic fuels. Under the provisions of this legislation, the Bureau of Mines, among other things, was charged with the responsibility of developing mining techniques, methods, and equipment for mining the oil shales of the Green River formation of Colorado, Utah, and Wyoming. The oil shales of western Colorado are apparently richer, more accessible, and more amenable to exploitation than elsewhere in the Rocky Mountain region. The site chosen for the Bureau's Experimental mine is about 10 miles west of Rifle in northwestern Colorado. It is within a 1000-sq-mile area from which, it has been estimated, 300 billion barrels of shale oil could be produced from a 500-ft measure near the top of the formation. One hundred billion barrels of this amount could be produced from the Mahogany ledge, a 60 to 100-ft section near the bottom of the 500-ft measure. This ledge is considered to have economic importance at present. The Green River formation was laid down as sediment in the bottom of vast, shallow inland lakes during Eocene time. The deposit is flat-lying, and there are no faults, fissures, or local rolls. Oil shale is actually a strong, tough magnesium marlstone, which will stand unsupported over relatively wide spans. These and other natural physical characteristics favor mechanized, low-cost mining, which is essential for establishment of an oil-shale industry. It was realized from the outset that an extensive research program would be necessary to develop mining methods, equipment, and techniques for a mechanized, low-cost operation. The program was designed to include research. into all the productive phases of mining, such as drilling, blasting, loading, transportation, and maintenance of the mine structure. The methods, equipment, and techniques developed as a result of this research have established a production of 116 tons per man-shift total labor at a direct cost of $0,292 per ton. Another important phase of the research program that has received little publicity because of its theoretical nature is study of the roofstone behavior and determination of mine structure stresses. This paper purposes to discuss this phase of the research program. Preliminary studies of the physical properties of the Green River oil-shale formation were made in the Barodyramics Laboratory at Columbia University during the latter part of 1945 and the early part of 1946.* The purpose of these studies was to determine the maximum size of unsupported underground openings that would be commensurate with safety and still permit the use of large, efficient mining equipment. Also to be determined were the pillar support to extraction ratio and the shape, size, and spacing of supporting pillars. Selected samples of possible roofstones near the top of the Mahogany ledge, as well as representative samples of different rock types found within the ledge, were obtained from the Bureau's oil-shale mine for these studies. The maximum safe unsupported roof span calculated from this work was 200 ft. Using a safety factor of four, it was theoretically determined that openings 60 ft wide could be advanced under a roofstone at the top of the Mahogany ledge. To support the overburden, 60-ft-sq pillars would be left in a checkerboard pattern. From visual observations made of core samples through the selected roofstone at the oil-shale mine, it was determined that the roofstone was actually a plate 6 to 8 ft thick. Because the calculations were theoretical and allowance had to be made for unknown cracks and fractures in the formation, openings 50 ft wide and pillars 60 ft sq were originally contemplated in the Bureau's Experimental mine. This would be the minimum allowable width that would permit use of large underground mining equipment. For lower mining costs and greater efficiency larger openings were desirable. Different but analogous approaches were made to the problem at the Bureau of Mines Applied Physics

Jan 1, 1951

By H. L. Teichman, E. M. Sipprelle

ENACTMENT' of Public Law 290 by the 78th Congress authorized the U. S. Department of the Interior, Bureau of Mines, to conduct an experimental program to develop the technology for obtaining oil from oil shale. In adopting and later extending this legislation, the Congress recognized the impending necessity of supplementing ground petroleum reserves with synthetic fuels. Under the provisions of this legislation, the Bureau of Mines, among other things, was charged with the responsibility of developing mining techniques, methods, and equipment for mining the oil shales of the Green River formation of Colorado, Utah, and Wyoming. The oil shales of western Colorado are apparently richer, more accessible, and more amenable to exploitation than elsewhere in the Rocky Mountain region. The site chosen for the Bureau's Experimental mine is about 10 miles west of Rifle in northwestern Colorado. It is within a 1000-sq-mile area from which, it has been estimated, 300 billion barrels of shale oil could be produced from a 500-ft measure near the top of the formation. One hundred billion barrels of this amount could be produced from the Mahogany ledge, a 60 to 100-ft section near the bottom of the 500-ft measure. This ledge is considered to have economic importance at present. The Green River formation was laid down as sediment in the bottom of vast, shallow inland lakes during Eocene time. The deposit is flat-lying, and there are no faults, fissures, or local rolls. Oil shale is actually a strong, tough magnesium marlstone, which will stand unsupported over relatively wide spans. These and other natural physical characteristics favor mechanized, low-cost mining, which is essential for establishment of an oil-shale industry. It was realized from the outset that an extensive research program would be necessary to develop mining methods, equipment, and techniques for a mechanized, low-cost operation. The program was designed to include research. into all the productive phases of mining, such as drilling, blasting, loading, transportation, and maintenance of the mine structure. The methods, equipment, and techniques developed as a result of this research have established a production of 116 tons per man-shift total labor at a direct cost of $0,292 per ton. Another important phase of the research program that has received little publicity because of its theoretical nature is study of the roofstone behavior and determination of mine structure stresses. This paper purposes to discuss this phase of the research program. Preliminary studies of the physical properties of the Green River oil-shale formation were made in the Barodyramics Laboratory at Columbia University during the latter part of 1945 and the early part of 1946.* The purpose of these studies was to determine the maximum size of unsupported underground openings that would be commensurate with safety and still permit the use of large, efficient mining equipment. Also to be determined were the pillar support to extraction ratio and the shape, size, and spacing of supporting pillars. Selected samples of possible roofstones near the top of the Mahogany ledge, as well as representative samples of different rock types found within the ledge, were obtained from the Bureau's oil-shale mine for these studies. The maximum safe unsupported roof span calculated from this work was 200 ft. Using a safety factor of four, it was theoretically determined that openings 60 ft wide could be advanced under a roofstone at the top of the Mahogany ledge. To support the overburden, 60-ft-sq pillars would be left in a checkerboard pattern. From visual observations made of core samples through the selected roofstone at the oil-shale mine, it was determined that the roofstone was actually a plate 6 to 8 ft thick. Because the calculations were theoretical and allowance had to be made for unknown cracks and fractures in the formation, openings 50 ft wide and pillars 60 ft sq were originally contemplated in the Bureau's Experimental mine. This would be the minimum allowable width that would permit use of large underground mining equipment. For lower mining costs and greater efficiency larger openings were desirable. Different but analogous approaches were made to the problem at the Bureau of Mines Applied Physics

Jan 1, 1951

By A. E. Isaacson

The U.S. Bureau of Mines determined the effect of common sulfide minerals on the corrosion rates of various types of ferrous alloy grinding media. Data obtained from this study will aid in determining the contribution of any electrochemical reactions between sulfide minerals and grinding media to the total grinding media consumption. Common sulfide minerals used in this study were chalcopyrite, galena, and sphalerite. In the presence of oxygen, chalcopyrite was found to increase the corrosion rate, galena was found to decrease the corrosion rate, and the effect of sphalerite was dependent upon the type of grinding media. Possible electrochemical reactions of these minerals in the presence of grinding media are suggested.

Jan 1, 1989

Fundamental results obtained from research on the properties of the edge surfaces of kaolinite particles (~500 nm) are reported. Of particular significance was the development of the experimental protocol. Well-ordered kaolinite edge surfaces were prepared as an epoxy resin sandwich structure having layered kaolinite particles in the center of the epoxy resin sandwich. Images of the sectioned kaolinite edge surfaces were examined by atomic force microscopy (AFM), and the average thickness of kaolinite particles in this study was determined to be 38.3 nm ± 11.7 nm. Furthermore, the surface charge of the kaolinite edge surfaces was evaluated with a super sharp Si tip. The point of zero charge (PZC) of the kaolinite edge surface was determined to be below pH 4, in contrast to the traditional view that the edge surfaces of kaolinite particles may carry a positive charge at pH 4. This lower PZC of the kaolinite edge surface was attributed to the lack of isomorphous substitution in the silica tetrahedral layer when compared to the PZC for the muscovite edge surface. Our results are consistent with the particle aggregation and flotation behavior of kaolinite, and should provide the basis for improved flotation strategies leading to the efficient recovery and utilization of mineral and energy resources.

Feb 23, 2014

By C. A. F. Sweet

The inter-relationship between these parties and the effect on the outcome of the project is often grossly underestimated. There are numerous success stories where the parties have worked as complementary teams aiming at the best outcome for the client company and achieving significant success. While there are a good number of occurrences where either the roles of the parties were unclear or perceived to be different from what others in the team believed or required them to be and the results were less than desired. This usually resulted in ongoing conflict, incorrect focus, working to different agendas and the result being a less than optimum result to Client Company. Mining, by its very nature of exploring where you cannot see, be it a shaft being sunk, tunnel being developed or other excavation that needs to be made, requires a very special working relationship between the parties. To understand this, and it applies equally well to mine and plant construction and other multiple function projects, one needs to start by describing the relationship of the parties. Often people believe that because they manage ongoing complex operations and large numbers of people that they can manage projects and as such the participants will ?fall into line.? At the outset it needs to be stressed that ?Project Management? is a specific type of management and needs to be understood as such. There are enough Colleges and Universities that teach project management, not only as a subject but also as a Master Degree. As you start up your project the relationship you establish between the client, project team (C.P.T) and the Engineering, Procurement, Construction and Management team (EPCM) will largely determine how successful your project will be. It is essential that from the outset a spirit of co-operation, support and respect be nurtured, and that it be actively carried through the project life cycle. There are several methods to facilitate this including team building exercises right at the start. This time and money will be well spent and recouped many times over during the project life cycle.

Jan 1, 2005

By William Petruk

The capabilities of SEM/image analyzers for determining quantitative mineral data which have a bearing on extractive metallurgy have given applied mineralogy a new dimension. The capabilities include automatic mineral identification, unattended operation, search for rare minerals, and measurements of (1) mineral quantities, (2) grain and particle size distributions, (3) liberation characteristics of minerals in ground ores, and (4) mineral associations. Data on mineral quantities define the distributions of elements among minerals, provide background information on characteristics of the samples, and provide a data base for a mineral-materials balance. Size analysis data of the minerals in unbroken ores are used to predict the grind required to liberate minerals. Data on liberation analysis can be used in many ways. One application is to process the image analysis data for feed, concentrate and tails by a materials balancing technique to calculate the recovery of liberated and unliberated grains at each point in a circuit. The calculated recovery data define the behaviour of an ore in a concentrator, pilot plant or bench test, and indicate whether recovery improvements are possible and/or feasible for a particular ore.

Jan 1, 1991

Various methods and software have been trialled for simulation of Au grades at Boddington Mine. This covers in-house and public software as well as sequential and turning bands methods. The diversity of options was further expanded with comparison of point and direct block simulation. Some difficulties were encountered in incorporating high-grade restrictions. Altering parameters or software can make very significant differences and give results varying from estimations. This paper details a new simulation run with validation and tests for local calibration (or progressive correction) of the simulations to the estimations, focusing on reproduction of statistics. This approach brings to the forefront the question æwhat is the purpose of the simulations?Æ Results and some ideas for future applications at Boddington are summarised.

Sep 26, 2011

By Nilo Nogueira da Silva

O objetivo deste trabalho foi investigar os efeitos da temperatura de laminação na microestrutura de um aço microligado ao Nióbio através de simulação por ensaios de torção a quente. Ensaios foram realizados com deformações em resfriamento contínuo para determinar as temperaturas de não recristalização da austenita (Tnr) e de início da transformação austenita-ferrita (Ar3). Foram realizados ensaios de torção simulando diferentes esquemas de laminação a quente em laminador Steckel, variando-se as temperaturas dos passes de acabamento. Foi observado, nas curvas tensão em função da deformação dos ensaios de torção, gradual encruamento da austenita quando a temperatura da última deformação foi inferior à 870°C. Foi também observado que o tamanho de grão ferrítico cresce com temperatura de laminação de acabamento.

Aug 8, 2018

By T D. Sullivan

Risk lies at the heart of all mining and nowhere more so than in pit slope design. Mining is principally about two areas of risk; safety and economics. This paper addresses the main elements of pit slope design and presents a view of the state of the art in terms of safety, design, prediction of performance, success and pit slope management. There has been a recent trend for serious injury and fatalities due to stability in open pit mines. The causes and contributing factors are analysed in relation to geotechnical knowledge, pit slope design and management. Currently there is no standard classification system for mine slope designs and it is considered doubtful if a universal system is possible. Designs are usually formulated in accordance with many different methodologies, various engineering principals and a number of different philosophical approaches, with results often presented in terms of Factors of Safety or Probabilities of Failure. However wide experience has demonstrated that even with apparently detailed engineering investigation and analysis at Feasibility Level, at the Operating Stage mine slope angles are regularly subject to large changes. The general experience is that these changes are ± 5° and 16° overall, which is considerably outside the accepted order of accuracy. For large deep mines these are huge changes and represent significant risks to the operations. The current state of practice in pit slope design is examined for two stages, feasibility and operating.

Jan 1, 2006

By Maria Solórzano, Karina Ramirez

Este proyecto busca incrementar la fuerza laboral femenina en la unidad minera El Porvenir, para lo que se analizan tanto factores externos como internos. Para el análisis externo se realizó una evaluación en colegios, con el fin de conocer si hay interés en carreras relacionadas al rubro de la minería por parte de las estudiantes de cuarto y quinto de secundaria de los colegios aledaños. Asimismo, se evaluaron institutos y universidades para identificar la cantidad de mujeres que estudian carreras relacionadas con el rubro. En cuanto al análisis interno, se identificó la perspectiva tanto de las colaboradoras propias como de empresas terceras, así como se analizó el grado de aceptación por parte de los líderes y colaboradores.

Sep 20, 2019

By Frank L. Antisell

Certain physical and chemical properties of copper are so intimately related that a change in variation of the physical properties indicates a certain chemical change. The standard specifications of copper of the American Society for Testing Materials are based upon physical characteristics with one exception, namely, the copper contents. The physical standard includes electrical properties, defects in the "set or casting," variation in dimensions, weight, etc. Paragraph 4 of the specifications states, " Wire bars, cakes, slabs and billets shall be substantially free from shrink holes, cold sets, pits, sloppy edges, concave tops, and similar defects in set or casting." Shrink holes and concave tops indicate both physical and metallurgical defects; cold sets, sloppy edges, etc., indicate physical defects only; small pit holes may be indicative of either or both physical and metallurgical defects, depending on conditions under which they originated. To the refiner, a copper casting, no matter how made, is known as a "shape," irrespective of whether it is wire bar, ingot, cake, slab, billet, etc. As practically all shapes are cast in an open mold, that is a mold without cope, the surface of the shape cools in contact with the atmosphere and has a coating of oxide. Certain phenomena of the surface indicate the adaptability of the metal for forging or rolling. The writer believes that it is much simpler to produce shapes that are metallurgically correct than those that are mechanically satisfactory. When copper is to be rolled into thin sheets or drawn into very fine wire, the slightest physical defect becomes evident. It is, therefore, of the utmost importance to consider every characteristic of the shape and ascertain the physical and chemical relationship. Pitch and Set.—The appearance of the surface of the copper when cooled is considered as to its "pitch," or the general contour of the surface of the shape (which may vary from a concave to a convex); and the '" set,"' or the detail appearance of the surface of the shape (the wave-like structure). When the shape presents a concave surface, it is known as "low pitch;" a convex surface is known as "high pitch" or "tough pitch;" and a level surface is called "flat pitch." The set of the copper is, in a very large measure, directly related to the pitch; and so intimately are

Jan 1, 1921