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By Walter H. Bruckner, George B. Clark

Since the end of World War 11 interest has been increasing in the use of shaped charges in the mining industry and in other industries using explosives for blasting purposes. Shaped charges employ the principle known as the "Munroe effect," which was discovered by Charles E. Munroe more than 50 years ago (in 1888). Details of their design have been explained elsewhere.1,2,3 Fig I shows the essential features of design of two types of shaped charges (with conical and hemispherical cavities) and a schematic sketch of their action upon detonation. The following discussion deals with the behavior of the metal in the cavity liners when they are subjected to intense Pressures exerted when the explosive charge is detonated. Among the conclusions reached in research on shaped explosive charges, the following have been established conceming cavity liners:1'2 I. The optimum wall thickness of a conical cavity liner is dependent upon the apex angle of the cone as well as On the base diameter of the charge. Acute apex angles require thinner walls for optimum perfonnance and more obtuse angles require thicker walls for the same base diameter. '. Cones were more effective in forming a penetrating jet when the walls were tapered; that is, the thickness of the wall of the cone increased from the apex down. 3. The physical and mechanical properties of metals have a marked effect upon their performance as cavity-liner material. Boiling point, ductility, malleability, ten-sile strength, and hardness are among the properties that influence the effectiveness of a metal used as a cavity liner. Lead, for example, makes a wide, flat crater in steel plates. Aluminum makes a deeper crater than lead, and an aluminum alloy having a high tensile strength makes a deeper hole, but slightly smaller in diameter. Cast iron makes a deep, narrow hole. These findings, together with the following analysis under Metallographic Survey of slug, offer solutions to many of the problems involved in solving the mechanism of the formation of Munroe jets. It has been fairly well established that cavity liners collapse in a manner similar to that indicated in Fig 2, Conical liners are known to collapse upon themselves while hemispherical liners are believed to turn inside out in the process of jet formation. The first has been definitely proved by recovery of collapsed portions of cones, while liners from partly detonated charges show that hemispheres may turn inside out. Fig 3 shows a sketch of a recovered slug from a 6-in. shaped charge using a 45" cone made of cast iron. (This size of charge drilled holes up to 3 ft in depth in solid granodiorite.)

Jan 1, 1949

By Sherwin F. Kelly, Bela Low, William B. Creagmile

Electrical methods and instruments for geophysical exploration have been almost exclusively applied, during these years of development of the art, by a few companies specializing in this field. The control of patents, the cost of the instruments and the general lack of published information on details of field procedure and office interpretation have given these owners a monopoly in carrying out electrical surveys. The development of the Megger Ground Tester1 seems likely to change this situation, and to enable mining engineers and geologists, without special training in geophysics, to carry out simple reconnaissance electrical surveys. Nevertheless, the need for such special training and experience in planning surveys and interpreting their results remains, and probably i always will remain, indispensable for a successful outcome. The unique thing about, the Megger Ground Tester, which gives rise to this hope for its general use, is its simplicity of operation. The four binding posts of the instrument are connected by insulated wires to four stakes driven into the ground at appropriate points. The crank of the Megger is then turned, and the resistance of the ground between the two inside stakes is read directly, in ohms, by the deflection of a pointer over a scale. The apparatus is shown in Fig. 1. Fundamentally, the principle of operation is that of determining the resistance of a four-terminal conductor, as applied by Frank Wenner to the measurement of earth resistivity. "A four-terminal conductor is a conductor provided with two terminals to which current leads may be connected and two terminals to which potential leads may be connected. The resistance of such a conductor is the difference in potential between the potential terminals divided by the current entering and leaving

Jan 1, 1932

By E. G. Leonardon, C. Schlumberger, M. Schlumberger

In the search for practical geological problems amenable to solution by the potential methods, the geophysicist is led to study mathematically various theoretical cases. In these idealistic discussions, the media under consideration are generally supposed to be homogeneous and iso-tropic. The geophysicist, of course, realizes perfectly that these conditions do not occur in their entirety in reality. However, the assumptions made are justified, because very often they are necessary in order to render possible an exhaustive study of a given problem, which otherwise would be too complicated, and would not lend itself to a complete mathematical analysis. Of the above two assumptions, that concerning the homogeneity of a given geological formation is satisfactorily realized except in so far as isotropy is concerned, since this property is not often encountered in practice. As a consequence, it is very desirable for the geophysicist to have quite an extensive knowledge of the properties of anisotropic formations, and of the laws that govern the propagation of electric current therein. With such principles in mind, he will be able to decide whether the conclusions arrived at in simple, isotropic conditions are still correct in more complex cases, or in what way they must be modified or adapted in order to constitute a sound basis for the interpretation of the results obtained in anisotropic media. On the other hand, the fact that in anisotropic formations the mobility of the ions is greater along the strike than perpendicular thereto can be utilized for determining the direction of the dip by induction measurements. We therefore propose to study in three successive chapters the following points: 1. Propagation of the electric current in anisotropic media. 2. Some consequences of the anisotropy of geological formations with reference to the surface electrical measurements, and their interpretation. 3. Determination of the direction of the dip of anisotropic formations by surface induction measurements.

Jan 1, 1934

By G. S. Scott, G. W. Jones

ECONOMIC waste caused by mine fires may become considerable,15 especially if a fire is allowed to spread or temporarily to get beyond control. It is important, therefore, to act promptly whenever a fire is suspected and to make every action count. To contribute toward its extinction effectively it is necessary to know at the earliest possible moment, and continuously thereafter, what is happening at the seat of the fire, which may be in a remote or inaccessible area, and also to recognize what may be expected as a result of any proposed combative measure. In combatting a fire the mining engineer and the chemist should cooperate, first deciding upon the course of action to be taken and then drawing upon the mining engineer's intimate knowledge of the physical structure of the fire area, the cost and time required to carry out proposed operations, and the probable efficiency with which these operations could be performed, and upon the chemist's knowledge for the results to be expected therefrom. After the initial steps to be taken have been decided, it devolves upon the mining engineer to see that they are carried out and upon the chemist to evaluate the results and to keep the mining engineer continuously informed in regard to a variety of matters-such as the composition and toxic or asphyxiating properties of the atmosphere in which the men may be working, whether the fire is increasing or decreasing in intensity and its probable temperature, the quantity of air leakage and the explosion hazards of the fire area. The purpose of this paper is to discuss what the chemist can and cannot contribute as a member of the fire-fighting personnel. The technical literature contains several hundred papers relating directly and indirectly to mine fires, and this fact alone is testimony to the complex nature of the phenomena involved in the birth, life, and final demise of a fire. A fire may be stopped (I) by preventing oxygen from reaching the coal or (2) by removing the conditions necessary for the rapid reaction of coal with oxygen; i.e., decreasing the temperature. All methods of prevention or control. necessarily must be based upon one or the other, or both, of these two principles. . The chemistry of a fire may be understood readily if the low-temperature oxidation of coal is considered as a starting point; then oxidation at higher temperatures (or combustion) ; and with these, the composition of the solid and gaseous products resulting from the oxidation or from the effects of the heat liberated. This discussion refers particularly to Pennsylvania anthracite, although much of the material applies equally well to coals of lower rank. OXIDATION OF COAL Oxidation of coal fundamentally is confined to the surface; that is, the rate at which oxygen penetrates into the interior of a solid block of coal is so slow that it may be ignored.6,16 Oxidation starts when a fresh surface is exposed, and the rate is

Jan 1, 1942

By R. Dawson Hall

The stresses in the simplest structures are often those we find most difficult to analyze. The most complex condition in mine stresses is found in simple tunnels where the roof, the sides, and the floor are a monolith. The functions of the parts are like the parts themselves not distinct and spccialized, and the problems to be solved are like those in a metal structure with riveted joints or a redundancy of bars. This difficulty explains perhaps why the condition has not been treated. But just because it cannot be discussed in its entirety is no reason why it should be treated as an action of parts with spccialized functions as a roof beam with supports and a foundation. The problern cannot be ignored on the ground that it is not of sufficient importance to warrant careful consideration, because conditions of complete monolithism, of which the tunnel is the type, are found materially unchanged in room-and-pillar and in longwall work. This unity between roof, sides, and floor, which to the coal miner is a difficult conception, really deserves a scientific appellation, and perhaps holoid (from holos, whole, and eidos, form) will serve the purpose as well as any other. In a simple tunnel the roof, the sides, and the floor form integral parts of one and the same structure, and the distortion of one cannot be conceived without a consequent strain in the others. Thus when the roof of the tunnel droops by reason of its weight, the upper parts of the sides are drawn in becausc they are integrally connected with the roof and must approach each other whenever, by the sagging of the roof, the distance between any two points in it is diminished. (See Fig. 1.) Thc sides in their turn operate on the floor of the holoid structure, producing a tensile stress. The writer has always been impressed with the value of soap as a means of illustrating the action of mine stresses. With that idea in mind' a cake of naphtha soap measuring 43/8 by 2¼ by 19i in. was taken and a tunnel was made through it 13/4 in. long, 21/2 in. wide and 1¼ in. high. (See Fig. 2.) A load was then placed at the mid-span of the tunnel. Eventually, the upper bar, or "roof," broke at the

Jan 1, 1916

By G. C. Gould

The nature of freckle segregation is determined by chemical analyses, microradiograplzy, and electron microprobe. In addition, the influence of chemistry variation on freckle formation is studied in laboratory experiments. It is demonstrated that controlled laboratory solidification can produce freckle segregation. "FRECKLE" segregation is a discontinuous, rod-like segregation observed in vacuum consumable -electrode ingots. Figs. 1 and 2 show this segregation as pencil-like, dark etching areas of segregation found in longitudinally and transversely sectioned consumable-electrode ingots. In most cases the segregation is perpendicular with respect to gravity and parallel to the longitudinal axis of the ingot. The segregation is most often encountered at or around midradius in large vacuum consumable-electrode ingots. The austenitic alloys, A-286* and 718, † have shown particular susceptibility to this mode of segregation. The origin of these rodlike pockets of segregation is not well-understood. It has been suggested that the segregation is a result of a portion of the electrode dropping off and passing through the arc un-melted. On the other hand, smeltzer1 has demonstrated the freckle segregation in A-286 to be comprised of low-melting constituents relative to the matrix melting point. The discontinuous nature of the segregation is the most perplexing facet of the freckle-segregation problem. It was to gain some insight into this part of the problem that this work was undertaken. I) PROCEDURE At the outset of the work identification of the phases present and the elements concentrated in the freckle areas was undertaken. The electron micro-probe was used to determine general enrichment as well as -specific phase chemistry. Microradiography using cobalt and chromium radiation was also used on the freckle areas again to determine the elements involved in the segregation. X-ray diffraction patterns were made from portions of these same foil specimens. Optical microscopy and Knoop hardness measurements were also used

Jan 1, 1965

By E. W. McAllister

The decision of the California Oil Umpire's' office to accept well potentials established from subsurface-pressure data has brought to the attention of many operators for the first time the application of such data to production problems. This paper reviews the development and application of subsurface-pressure data in kettleman Hills, where these data have been used in production work since 1932. The Kettleman Hills field was discovered in October 1928. The first subsurface-pressure surveys were made early in 1932 and by the middle of 1933 the two major operators in the field were making routine pressure runs in thcir respective wells. Shortly therefter, these companies agreed to exchange pressure data, and later a third company entered into the agreement. This made it possible to analyze the effects upon the reservoir pressure of past production practices, which are discussed in the latter part of the report. It is interesting that many of the applications of subsurface-pressure data discussed herein were anticipated by C. L. Clark and C. B. Kimberlint in a report2 dated March 1933. PRODUCTIVITY Index In the majority of individual well problems involving the use of subsurface- pressure data, it is necessary to use a factor known as the "productivity index," which indicates the ability of a well to produce and represents the number of barrels of oil or oil and water per day that will enter the well bore for each pound per square inch pressure drop made opposite the producing interval of the well. The productivity index may be determined from pressure and production data for one or more rates of flow and a static or shut-in pressure survey or from production and pressure data for two or more rates of flow. Productivity indices may be based upon either net oil or total fluid production. All indices referred to in this report are based upon net oil. The value of the productivity index for Kettlcman Hills wells decreases generally with time and it is not uncommon for the index to vary in value at any specific time fur various rates of flow. The decline of the productivity index may be attributed partly to the loss of reservoir pressure. As the reservoir pressure decreases, gas originally in solution is released from the oil, congesting the flow of fluids through the formation and increasing the viscosity and surface tension of the oil; thus the flow resistance of the fluids through the formation is increased, resulting in a decrease of the productivity index. For convenient reference, the productivity indices for each well are plotted against time and a curve is drawn through the points showing the trend of the average index value. Plotted on Fig. I are index values for five

Jan 1, 1941

By E. W. McAllister

The decision of the California Oil Umpire's' office to accept well potentials established from subsurface-pressure data has brought to the attention of many operators for the first time the application of such data to production problems. This paper reviews the development and application of subsurface-pressure data in kettleman Hills, where these data have been used in production work since 1932. The Kettleman Hills field was discovered in October 1928. The first subsurface-pressure surveys were made early in 1932 and by the middle of 1933 the two major operators in the field were making routine pressure runs in thcir respective wells. Shortly therefter, these companies agreed to exchange pressure data, and later a third company entered into the agreement. This made it possible to analyze the effects upon the reservoir pressure of past production practices, which are discussed in the latter part of the report. It is interesting that many of the applications of subsurface-pressure data discussed herein were anticipated by C. L. Clark and C. B. Kimberlint in a report2 dated March 1933. PRODUCTIVITY Index In the majority of individual well problems involving the use of subsurface- pressure data, it is necessary to use a factor known as the "productivity index," which indicates the ability of a well to produce and represents the number of barrels of oil or oil and water per day that will enter the well bore for each pound per square inch pressure drop made opposite the producing interval of the well. The productivity index may be determined from pressure and production data for one or more rates of flow and a static or shut-in pressure survey or from production and pressure data for two or more rates of flow. Productivity indices may be based upon either net oil or total fluid production. All indices referred to in this report are based upon net oil. The value of the productivity index for Kettlcman Hills wells decreases generally with time and it is not uncommon for the index to vary in value at any specific time fur various rates of flow. The decline of the productivity index may be attributed partly to the loss of reservoir pressure. As the reservoir pressure decreases, gas originally in solution is released from the oil, congesting the flow of fluids through the formation and increasing the viscosity and surface tension of the oil; thus the flow resistance of the fluids through the formation is increased, resulting in a decrease of the productivity index. For convenient reference, the productivity indices for each well are plotted against time and a curve is drawn through the points showing the trend of the average index value. Plotted on Fig. I are index values for five

Jan 1, 1941

By K. H. Coats

This paper describes an approximate technique for handling the problem of percolation of evolved gas upwards through the oil column in computer simulation of natural depletion. This technique has been incorporated into a general model for simulating three-phase flow in one, two or three dimensions. The mathematical model for perfonning these calculations is described in detail in a separate article. 1 While vertical gas percolation occurs during natural depletion in a reservoir of any configuration, it is especially pronounced in the pinnacle reel or bioherm. The reel may have an areal extent less than one section with a thickness of up to 800 It. The upward percolation of evolved gas often limits the time step in calculations as little as one day. Using this small time step, computer expense for a single 30- to 40-year simulation on even a one-dimensional basis has exceeded 92,000. The method described here for handling the percolation allows time steps of 60 days or more (depending on reservoir size and production rate), resulting in a considerable reduction in computing expense. The method also allows calculations in which secondary gas caps build up in tight zones of the oil column below the main gas cap. The validity of the method is indicated in connection with an example pinnacle reef field. Calculated results using a 2-day time step (where the method in question is not needed and not invoked) are compared with results using the method and a 60-day time step. The comparison shows good agreement. Results from one- and two-dimensional simulations of the reef are presented along with the corresponding computing times on the CDC 6600 computer. A three-dimensional simulation was also performed and the required computing time is given. INTRODUCTION A general analysis for simulating three-dimensional, three-phase flow in reservoirs has been developed. 1 In applying this model to reservoirs undergoing natural depletion, a time-step restriction was encountered due to the flow of evolved gas upwards through the oil column and toward the gas cap. A remedy for this problem has been incorporated in the analysis and is described here. The time-step restriction is encountered only in calculations which include flow in the vertical or near vertical direction. The restriction occurs to some extent in reservoirs of any geometrical configuration, but it is especially pronounced in the pinnacle reef or bioherm where the ratio of thickness to areal extent is unusually large. This paper describes the problem, a method of handling it, incorporation of the method in the three-dimensional, three-phase model, and, finally, a test of the method's validity in an application to an example pinnacle reef reservoir. THE PROBLEM During the early stages of reservoir depletion, pressure falls below bubble point in progressively lower regions of the oil column. Continuing production results in evolution of dissoived gas throughout the oil column. This gas then percolates upwards toward the top of the reservoir. If the gas encounters a sufficiently low permeability zone in its travel upward, then it can accumulate and form a secondary gas cap. If no zones are encountered which are tight enough to hold gas against the gravity forces, then the gas travels on until it reaches the top of the sand or the main gas cap. Numerical simulation of multiphase flow in reservoirs is generally performed with time steps such that the flow of a fluid into or out of a block in one time step is a fraction (considerably less than one) of the total amount of that fluid present in the block. Use of a time step where the time step's

Jan 1, 1969

By H. R. Deeth, C. J. Koenig

ABOUT ten years ago nepheline syenite was introduced to the ceramic industry and the material has now found application in the various branches of the industry, namely, as a vitrifying agent in white-wares and as a source of alumina and alkalies in glasses, glazes, and porcelain enamels. Spence1 described the early mining and processing developments regarding this material. Since the time of his article many research papers have appeared relating to the usage of nepheline syenite but little has been published relative to subsequent mining and processing methods. A complete indexed review of the literature was issued recently by Ohio State University.2 Since "Lakefield" nepheline syenite from Blue Mountain, Ontario (Fig I); is the only commercial ceramic-grade nepheline syenite now being marketed on this continent, discussion is limited to this operation carried on by American Nepheline Limited, Lakefield, Ont., and its subsidiary in the United States, American Nepheline Corp. at Rochester, N. Y. THE DEPOSIT Blue Mountain is a long ridge rising to an elevation of about 350 ft at its highest point above the surrounding country and extending for about six miles in a northeasterly direction across Methuen township, Peterborough County. The rock of the Blue Mountain central alkaline intrusive is fine grained, light colored and of even granitic texture. The solidified mass consists predominately of the minerals albite, nepheline and microcline in order of abundance. The average mineralogical composition for the deposit obtained by a study of 112 samples taken regularly over the whole formation is as follows:3 [VOLUMETRIC MINERAL PER CENT Albite54 Microcline20 Nepheline22 Muscovite2 Mafics2 (Biotite, hastingsite, magnetite) Total100] The mineral nepheline (or nephelite) belongs to the feldspathoid group but is lower in silica content than are the feldspars. It is a silicate of soda, potash, and alumina (NaKAl2O32SiO2). Its presence with albite (Na2O A1203 6SiO2) and microcline (K20 A12O3 6SiO2) gives the Blue Mountain deposit an alkali content of 15 pct and an alumina content of approximately 24 pct. While this huge alkaline mass is somewhat variable mineralogically, it has a uniform chemical composition. When the iron, mostly in the form of magnetite, is removed during processing, a remarkably uniform finished product is obtained. Geological surveying has disclosed many million tons of nepheline syenite in the Blue Mountain deposit. Diamond drilling in the area where mining is now being carried out indicates a block of about one million tons.

Jan 1, 1947

By John R. Gould

A mathematical treatment of multiple-pass floating-zone refining of semiconductors, including the evaporation of solutes from the melt at reduced pressure, is presented. Vapor pressures and evaporation rate constants for phosphorus, arsenic, and antimony in germanium have been determined from floating-zone experiments conducted at 10 mm Hg. Rate sensi-tivity of arsenic in germanium has been examined over the range of 1 to 10 in. per hr growth rate. The equilibrium value of the segregation coefficient of arsenic in germanium, as determined by an extrapolation of these data, was found to be 0.09. PFANN has treated the segregation of nonvolatile solutes in the zone-melting process, Bradshaw and Mlavsky2 considered the evaporation of solutes in a vacuum during the growth of crystals by pulling from the melt, and van den Boomgaard3 has shown that it is possible to bring a volatile impurity element homogeneously into an ingot by means of zone-melting under a constant pressure of that element. This paper is concerned with the volatilization of solutes during zone - melting in a vacuum. The mathematical analysis by Lord4 of multiple-pass zone melting is extended to include evaporation of solutes. A method is presented in which evaluations of vapor pressures, evaporation rate constants, and distribution coefficients may be derived from the variation of solute concentration in the floating-zone refining of germanium at 105 mm Hg. EXPERIMENTAL Ingots of zone refined germanium, approximately 1/4 in. in diam and 10 to 12 in. in length, were subjected to several floating-zone passes at 105 mm Hg in order to provide intrinsic material for these studies. These ingots were then seeded in a [Ill] direction and solid-doped to a constant impurity concentration of approximately 1015 atoms per cmS in a forming gas ambient (10 pct H - 90 pct A) at 1/2 atm gage. The resulting crystals were subjected to repeated floating-zone passes at 105 mm Hg and a concentration profile along the length made after termination of each pass. Concentrations were determined from four-point probe resistivity measurements, and proper precautions were taken to prevent contamination during handling. A constant zone length, crystal cross section, and growth rate were maintained during zoning. A stationary coil and moving crystal system were employed for floating-zone growth with neither the section of crystal above nor below the melt rotated.

Jan 1, 1962

By AIME AIME

UNTIL recently, practically all geophysical prospecting in Australia was conducted by government departments, either by the Aerial, Geological and Geophysical Survey of Northern Australia or the New South Wales Department of Mines. At present, in addition, the Shell company is carrying out an extensive geophysical campaign in South West Queensland. The Northern Australia Survey has now been in operation for over six years, its work being carried out principally in the northern and central parts of Australia over an area of about a million square miles. At present this Survey is being brought to a conclusion but it appears certain that the geophysical section will be transferred to a Commonwealth Government department on a permanent basis. At present the officers of the Geophysical Section are preparing or have issued some 150 reports on their field work and also a special technical report on the geophysical practice of the Survey.

Jan 1, 1942

By T. Cameron Kenney

INTRODUCTION Whereas the design of rock slopes in open-pit mines is done largely by mining engineers and geologists, the design of slopes in overburden at this point in time is a problem for which civil engineers or geotechnical engineers are best prepared to deal. The reasons for this situation are to be found in the educational curricula and the technical journals of the two groups, where soil mechanics has received little attention by mining engineers and geologists, and rock mechanics has similarly received little attention by civil engineers. In ten years' time this paper will hopefully be considered by young mining engineers to be a repeat of the material that they studied at university. However, even in ten years time I believe that the civil (or geotechnical) engineers will be extensively used as consultants on overburden- slope problems of open pit mines because mining companies will find this more expedient than maintaining their own geotechnical staff, special field equipment and special testing laboratories. For this reason, the purpose of this paper is not to condense several university soil mechanics courses into a twenty-page text for mining engineers and geologists. Rather, the purpose of the paper is to offer a general explanation of various factors affecting slope stability so that mining engineers and geologists will have a better understanding of the behaviour of overburden soils in slopes. A great deal has been written in soil mechanics literature on the subject of slope stability. No attempt will be made to reference all this material but rather only a selected number of references will be cited. Excellent general treatments of the subject of stability of overburden slopes are available (1,2,3,4). Further information of a more specialized nature is to be found in such publications as the Journal of the Soil Mechanics and Foundation Division of the American Society of Civil Engineers, Geotechnique (printed by the Institution of Civil Engineers, England), Canadian Geotechnical Journal, and the proceedings of the conferences of the International Society for Soil Mechanics and Foundation Engineering. FACTORS INFLUENCING SLOPE STABILITY There are two general scales of slope-stability problems, gross stability and local stability. Gross stability refers to large volumes of soil, and gross instability would involve large rotational-type shear failures. Local stability refers to something much smaller and examples

Jan 1, 1972

By H. F. McCullough

The success of a coal-mining venture as relates to operations at the gob or break-line, such as the drawing of pillars or the working of long-faces, depends upon the control of face conditions. The measures required to control the latter are dependent upon the action of the coal seam, roof and floor at and in the vicinity of the faces, but the manner in which these will act is dependent upon the rate of face movement as well as upon the facc characteristics and upon the forces exerted. Yet the merits of a method of working—the practicability of controlling face conditions and the means required for such control when applied to any particular case—are usually judged only upon a consideration of the characteristics of coal seam, roof and floor, and the manner in which they have been observed to act. Practically every coal-mining man knows that face conditions are influenced by the rate of face movement, but few have appreciated that this is as much of a factor in the control of face conditions as are the face characteristics and the forces exerted. Fewer yet have recognized or taken advantage of faster rates of face movement as one of the principal means of establishing control of face conditions or of securing more favorable face conditions. Seemingly inherent difficulties, particularly in the control of roof conditions, but also in the control of conditions of the coal seam and floor, are frequently mitigated or disappear when the rate of movement of the faces is sufficiently increased. The characteristics of the coal seam, roof and floor and the forces exerted upon them do determine the general trend or tendency of face action, but the manner in which the coal seam, roof and floor will act and be aeted upon and the magnitude of the action during the time the site of mining operations remains at any particular point are very largely determined by the rate of movement of the faces. Progressive Nature of Forces Exerted Coal seam, roof and floor are composed of materials having definite properties or characteristics. The potential or ultimate values of the

Jan 1, 1927

By C. A. Stetefeldt

The purpose of this paper is to convince the managers of silvermills that their customary reports in regard to the percentage of silver saved are far from the truth. It may be unpleasant for them to have the proofs of this fact brought before the public, and for this rezson the author refrains from giving the names of the mines and mills from which the statistics here recorded were obtained. It may be asked: What is gained by informing the stockholders of our silver-mines that they receive incorrect reports? Will this increase their dividends or lessen their assessments? In the first place, it is always better to publish honest facts than fiction. In the second place, many superintendents believe in the correctness of their reports, and have no idea how much they deceive themselves. Finally, the knowledge that hitherto unexpected losses of silver take place may lead to the adoption of methods by which these losses are greatly reduced. These remarks refer also to smelting-works. The present paper, however, is concerned exclusively with amalgamation and lixiviation. The first and most important error is found in the inaccuracy of the commercial assay; the second in the incorrect sampling of tailings in amalgamation. Further, mills not doing custom-work, but reducing exclusively ores from mines to which the mills belong, are in the habit of weighing the ore only approximately and without making moisture-tests. Thus, a correct basis for calculating the actual percentage of silver extracted is lacking. The superintendent, then, finds it convenient to report the apparent extraction, i.e., the extraction indicated by comparing the value of the roasted ore, minus soluble salts, with the value of the tailings. How many errors are thereby committed it is not necessary to point out.

Jan 1, 1895

By Frederick L. Knouse

The south border of Espirito Santo begins about 400 km. north of Rio de Janeiro and extends along the Atlantic Coast northward some 325 km. and inland 100 to 150 km. The area under consideration, where quartz crystal of strategic grades has been mined, extends from 19º to 21º and 30º south latitude; and from 40º to 41º and 30º west longitude. This includes the central part of Espirito santo, chiefly south of the Rio Doce from the Atlantic ocean, and west across the border into Minas Gerais near the town of Aimores, in the municipalities of Aimores, Minas Gerais; Baixo Guandu, Santa Teresa, Santa Leopoldina, Colatina, Joao Neiva, Fundao and Domingo Mar-tines, Espirito Santo (Fig. I). During 1943 and the first half of 1944, this region accounted for approximately 3 to 5 per cent of the quartz crystal produced in Brazil. Shipments of crystal have been made chiefly by rail to Rio de Janeiro. This region is serviced by the E. F. Minas-Vitoria and E. F. Leopoldina to Rio de Janeiro through vitoria; and by the E. F. Minas-Vitoria and E. F. Centra] do Brasil through Bello Horizonte, Minas Gerais to Rio de Janeiro. The major deposits are accessible from the railheads by dirt roads, some being 5 to 30 km. off the road, reached by trail. In 1943 and the first half of 1944, the bulk of the production was from inter- mountain marshes and adjoining hillside alluvial placer deposits in the zone surrounding the town of Santa Teresa. Most of these deposits were formed from the erosion of pegmatite~, quartz veins and pockets in the gneiss, with minor quantities produced from miarolitic cavity fillings in the granitic rock. Early Operations Mining of quartz crystal in this region began in 1928 and has been stimulated by the market demand for military uses. Before 1936 little attention was given to it, either in Espirito Santo or eastern Minas Gerais. From 1936 to 1941 the Japanese sent agents to various points of production or potential production to acquire quartz through purchase. They bought crysta1 as small as 10 grams. Since '94' only the United States and Great Britain have received quartz from Brazil. The United States purchases crystals of 100 grams and larger for strategic purposes. The first known discoveries were made either in the municipalities of Aimores, Minas Gerais, or in Baixo Guandu, 01 Domingos Martines, Espirito Santo. Marketable quartz crysta1 was first found either in the massive quartz replacement veins of the Victor Hugo mine in the municipality of Domingo Martines, or in the large 'ores of quartz in the pegmatites near Baixo Guandu, extending into Minas Gerais. Production The production of quartz in Espirito Santo from 1936 through 1941 as recorded

Jan 1, 1948

By Frederick L. Knouse

The south border of Espirito Santo begins about 400 km. north of Rio de Janeiro and extends along the Atlantic Coast northward some 325 km. and inland 100 to 150 km. The area under consideration, where quartz crystal of strategic grades has been mined, extends from 19º to 21º and 30º south latitude; and from 40º to 41º and 30º west longitude. This includes the central part of Espirito santo, chiefly south of the Rio Doce from the Atlantic ocean, and west across the border into Minas Gerais near the town of Aimores, in the municipalities of Aimores, Minas Gerais; Baixo Guandu, Santa Teresa, Santa Leopoldina, Colatina, Joao Neiva, Fundao and Domingo Mar-tines, Espirito Santo (Fig. I). During 1943 and the first half of 1944, this region accounted for approximately 3 to 5 per cent of the quartz crystal produced in Brazil. Shipments of crystal have been made chiefly by rail to Rio de Janeiro. This region is serviced by the E. F. Minas-Vitoria and E. F. Leopoldina to Rio de Janeiro through vitoria; and by the E. F. Minas-Vitoria and E. F. Centra] do Brasil through Bello Horizonte, Minas Gerais to Rio de Janeiro. The major deposits are accessible from the railheads by dirt roads, some being 5 to 30 km. off the road, reached by trail. In 1943 and the first half of 1944, the bulk of the production was from inter- mountain marshes and adjoining hillside alluvial placer deposits in the zone surrounding the town of Santa Teresa. Most of these deposits were formed from the erosion of pegmatite~, quartz veins and pockets in the gneiss, with minor quantities produced from miarolitic cavity fillings in the granitic rock. Early Operations Mining of quartz crystal in this region began in 1928 and has been stimulated by the market demand for military uses. Before 1936 little attention was given to it, either in Espirito Santo or eastern Minas Gerais. From 1936 to 1941 the Japanese sent agents to various points of production or potential production to acquire quartz through purchase. They bought crysta1 as small as 10 grams. Since '94' only the United States and Great Britain have received quartz from Brazil. The United States purchases crystals of 100 grams and larger for strategic purposes. The first known discoveries were made either in the municipalities of Aimores, Minas Gerais, or in Baixo Guandu, 01 Domingos Martines, Espirito Santo. Marketable quartz crysta1 was first found either in the massive quartz replacement veins of the Victor Hugo mine in the municipality of Domingo Martines, or in the large 'ores of quartz in the pegmatites near Baixo Guandu, extending into Minas Gerais. Production The production of quartz in Espirito Santo from 1936 through 1941 as recorded

Jan 1, 1948

By A. C. Watts

For several years, a mine in Colorado experienced considerable trouble from small fires caused by the blasting of coal. Although a well-known make of permissible powder was used, it was first thought that the powder ignited gas that might be present and that this, in turn, set fire to line brattices or to the coal. Experiments were, therefore, conducted with another make of powder, but the results convinced the superintendent of the mine, Robt. Williams, Jr., that the fires were not caused by the powder but by the high-voltage electric current used for detonating the shots. The mine "makes" gas very freely, giving off from three-fourths to one million cubic feet of methane every 24 hours. The coal is a good grade bituminous of a very free burning quality. Electric shot-firing from the outside, after all men and animals were outside, had been practiced for a number of years. The shooting circuit was connected with the main power circuit at the mouth of each entry. Shooting circuit switches were mounted in boxes, which were kept locked with the handle of the switch, in open position, showing through the bottom of the box. The door of the box could not be shut and locked when the shooting switch was closed. At the entrance to each room, or working place, a small switch, called the miner's switch, was placed on the shooting line. It was the duty of the miner, when entering his place at the beginning of the shift, to see that this switch was open and that it was kept open until he left the placc at the end of the shift to go out of the mine. Grounded return was used for main power lines. The current was 500 volts, direct current, with 100 to 300 amp. The nearest working face was 9600 ft, from the shot-firers' switch outside the mine and the most remote working face was 2½ miles. The various working faces were scattered over a wide area between these two points. A description of the main power line would be valueless; the conductors were of sufficient size, the drop in voltage being not more than

Jan 1, 1927

By R. Kossowsky

USING etch-pit techniques, Johnston and Gilman' have shown that the stress dependence of dislocation velocity can be represented by the expression where r, is the dislocation velocity, a is the applied stress, and oa, is the stress to produce a unit velocity. Noble and Hul12 showed that the exponent m is strain-dependent and increases rapidly in the work-hardening region. This was explained by arguing that in the work-hardened material the applied stress required for any given velocity will be greater than in the annealed material by an amount equal to a back stress due to work hardening. schadler3 has stressed the importance of substructure as a possible source of error in dislocation velocity measurements, and took care to make velocity measurements in which dislocations moved such short distances that interactions with boundaries were avoided. schadler3 also pointed out that, if standard testing equipment is used, measurements of m from flow stress data could be seriously in error in materials with a high initial work-hardening rate. Noble and Hu112 have further argued that, due to the strain dependence of m , the extrapolation to zero strain4 to obtain the true value of m can be justified only in the preyield region. Microstrain experiments in high-purity iron5,6 have led to the conclusion that aiA (Ref. 5) (defined as the stress to first produce a permanent set of 10-6 in. per in.) and oflow are not controlled by the same deformation mechanism. It has been proposed5,6 that aA is governed by the lattice resistance to the motion of screw dislocations in a given slip plane and that oflow is controlled by the lattice resistance to a full-scale cross slip. The purpose of this note is to extend Noble and Hull's argument further and to show that measurements of m from flow stress data can be in error due to the rapid increase in stress in the microstrain region6 when stress is increased beyond aA. Double z-one-refined single crystals of molybdenum (with the (101)[ 111] slip system operating and a Schmidt factor of 0.475) were used in an experimen-

Jan 1, 1968

By A. L. Hay

The Sydney coal field, the largest and most valuable in Nova Scotia, is situated on the northeastern coast of the Island of Cape Breton, extending from Mira Bay on the south to Cape Dauphin on the north, a distance of 30 miles, and has a general dip northeast under the sea. (Fig. 1. The field embraces the mining villages of Morien, Birchgrove and Reserve and the towns of Dominion, Glace Bay, Waterford and Sydney Mines. The city of Sydney is situated about midway between the northern and southern extremities of the field and on the western fringe of the productive coal measures. Sydney harbor crosses the coal field, cutting off direct rail connection between Sydney Mines and the greater part of the field to the southeast. (Fig. 2.) The coal measures are exposed in the cliffs on the coast line, which rise to an average height of 30 ft., and are almost continuous throughout the length of the field. The portion of the coal field under land forms a small segment of a circle, the greatest distance from the coast landwards is 9 miles, and it occupies an area of 200 sq. miles. The greatest distance developed seawards from the shore by mining operations is 2 miles. The strata maintain a regularity of dip at this distance, proving a submarine area of about 70 sq, miles. How much further the coal field extends seawards is unknown, but the indications are that it extends far beyond the present economical working limit and in all probability there is a vast submarine coal field. The productive coal measures are of Carboniferous age, these being underlain by beds of sandstone, locally classed as millstone grit, which define the southern limit of the field, while a spur of syenitic hills cuts off the coal-bearing strata on the north. Two main anticlinal folds having a general course easterly divide the field into three basins named from north to south: Sydney Mines-Lingan, Glace Bay and Morien. So far as the portion of the coal field already developed is concerned the general effect of these folds is to vary the direction and dip of the strata at different points of the several basins. The strata dip seawards at the average rate of 6 per cent. along the axes of the basins. On both sides of the several basins, the strata have a dip varying from 7 to 40

Jan 1, 1930