Search Documents

By Robert Gillham, Victoria Yablonsky, Grover R. Castle

INTRODUCTION The commercial paper market, unique to the United States, is a direct exchange of funds between high-grade borrowers and large lenders; because it eliminates both the bank's role as middleman and also some significant transaction costs, commercial paper is the lowest cost short term instrument in the world. For this reason, virtually all borrowers would like to enter the market, but only issuers with the highest rating from Moody's and Standard & Poor can attract purchasers at the best rates. COMMERCIAL PAPER The commercial paper market, in existence for over 100 years, has traditionally been used for short-term financings, with most paper maturing within 30-45 days. Under the U. S. Securities Act of 1933, (section 3(a)3) industrial paper can avoid registration only if it matures within 270 days and is used for current transactions. It was first used to finance the short-term seasonal working capital needs of manufacturing companies. Since World War II, commercial paper use has grown steadily, serving in the 1950's as the market in which finance companies financed the explosion in consumer credit purchases of heavy consumer durables. LETTER OF CREDIT BACKING As far as is known, the use of letters of credit to support energy-related commercial paper began about 13 years ago with an arrangement to finance the nuclear fuel for Con Edison's Indian Point 3 Plant. Goldman, Sachs was the architect of this financing and Chemical Bank provided the letter of credit support. After an early burst of interest, this type of financing wobbled severely in the difficult credit markets of the mid-seventies before regaining serious momentum in 1976 and 1977. A mining project would not normally qualify as a borrower in the commercial paper market because of its credit standing and because its large capital needs require long term financing. However, lately, commercial paper has begun to take the place of a bank term loan in limited recourse project financings. L/C backed commercial paper took this new and startling turn in 1982 when it was used as part of the $700 million financing for the development of the Newlands-Collinsville coal mines of Mount Isa Mines Ltd. in Australia. This was the first use of L/C backed commercial paper in a long-term limited recourse project financing. First Boston acted as financial advisor and, again, Chemical Bank provided sole letter of credit support of $155 million. The $785 million BHP financing for the acquisition of the Queensland (Australia) coal assets of Utah International from General Electric Company followed the next year; there we acted with two other Front Banks to provide $270 million of L/C support. These two important transactions indicate that not only has commercial paper become an integral part of a long-term financing package, but also that it is no longer the exclusive domain of the best known U. S. companies. Lesser-rated companies and a multitude of foreign borrowers have gained access to this "exclusive club." How has this become possible? OPERATION OF AN L/C An instrument of the commercial banks, the "direct pay" letter of credit, has enabled lesser-rated companies to issue commercial paper in their own names. The letter of credit allows the issuer to substitute the credit rating of the supporting bank for its own. The L/C in effect allows a lesser-rated company to rent the bank's credit rating. This upgrading is possible because the bank is unconditionally obliged to pay the note-holders at maturity and then turn to the Issuer for reimbursement. The Issuer commonly "rolls over" a new short-term issue and reimburses the supporting bank from the sale of the new issue until cash flows from the project allow the borrower to reduce the level of paper outstanding. The commitment for an L/C facility, up to 12 years in the case of the Broken Hill transaction, governs the life of the commercial paper tranche of the financing. The term of the L/C commitment thus has the power to extend the ordinary 30-45

Jan 1, 1985

By Paul M. Tyler

YEAR after year, the kaolin industry of the United States has been setting new production records and making better products. High-grade paper, pottery, and rubber clays are produced in this country mostly in the South. Georgia alone contributes over 70 pct and South Carolina almost 20 pct of the total domestic output. Residual kaolin is mined in North Carolina, highly plastic but naturally sandy Tertiary (Eocene) potting clays are worked in north central Florida, and good white clays are produced in several other states, but the main sources of kaolin or china clay have been numerous deposits in the Tuscaloosa (Upper Cretaceous) formation. This formation of generally sandy sediments is called the Middendorf member in older geologic reports and corresponds in age with some of the New Jersey clays. As shown in fig. 1, it crops out almost continuously in a generally southwesterly direction across South Carolina and Georgia and into Alabama. Clay is mined from this formation in all three states but the principal producing centers lie within about 10 miles of a straight line drawn between Aiken, S. C., and a point about 10 miles south of Macon, Ga. The white kaolins of the South were recognized and used prior to the Civil War but suitable treatment processes were not introduced until World War I when imports, chiefly from England, were curtailed. Although imports of high-grade clays were resumed after 1918, the domestic industry managed to treble its prewar production record during the early 1920's and has continued to grow. Whereas the 1909 to 1913 average total production in the United States was only 132,104 short tons valued at $705,352 f.O.b. mines, the output in 1948 was 1,-568,848 tons worth $19,756,738. Paradoxically, it seems in retrospect that the early failure of the American industry to meet foreign competition was due to the superior quality of our sedimentary clays in their natural state. Kaolin, of course, is the principal decomposition product of feldspars which originate in acidic igneous rocks such as granite, aplite, alaskite, granodiorite, quartz porphyry, etc. English china clays occur in residual deposits and before they can be marketed they have to be treated to remove accompanying quartz, mica, and other impurities. Notwithstanding the relatively crude methods employed, the final product is a beneficiated clay which is subject to a certain amount of technical control as to quality and uniformity. Although the naturally concentrated deposits in Georgia and South Carolina contain some of the finest crude white kaolin in the world, even it can be made better by suitable treatment. In recent years well over half of the high-grade china clay produced in the United States has been used in making paper. Some qualities of paper clays are still produced by the dry process, or air flotation, but the paper industry's specifications have grown so exacting that wet processing was adopted and more refined methods had to be perfected. Notwithstanding notable advances in clay-preparation technology during the past decade, or possibly because these advances have implemented and encouraged technologic changes in consuming industries, demand has grown for products of higher uniform quality than can be obtained from even the best natural deposits without rigidly controlled fractionation. Largely as a result of the wide adoption of machine coating for paper, the clay industry has been obliged not merely to eliminate virtually all mineral impurities but also to segregate the clay substance itself into narrow particle-size ranges. By extraordinary coordination of sales effort and production technology, several Georgia companies manage to market a wide variety of specialized joint products but the commercial success of many producers depends upon their mining only the best parts of their deposits and then skimming the cream of this almost pure clay in order to obtain a maximum yield of kaolinite finer than about 2 microns in maximum particle size and possessing low viscosity as well as the more familiar attributes of suitable color and brightness, or reflectance. To the casual visitor from another mineral industry, the kaolin mines and plants may appear to be

Jan 1, 1951

By H. L. Overton, J. B. Lipson

The concept of sodium single-ion equivalent activity as developed by Gondouin, Tixier and Simard,' was used to determine the filtrate resistivity-activity relationships for 150 laboratory and 49 field drilling muds. With the exception of the native and phosphate high-resistivity muds and the calcium-treated muds, the filtrate resistivity-activity relationships were found to be within 20 per cent of that for pure sodium-chloride solutions. Gondouin, et al,* previously suggested a method of treating the high-resistivity muds in quantitative electrical log analysis. A new treatment is presented which uses the P-alkalinity of the filtrate as a correlating parameter in handling the calcium-treated muds in quantitative electrical log analysis. INTRODUCTION Gondouin, Tixier, and Simard in 1957 introduced new interpretive procedures for analyzing the self-potential curve of electric logging. They re-emphasized the previous work of the Schlumberger brothers, Wyllie and others, and re-defined the activity concept in terms of a number which they termed the effective resistivity. Their procedures are particuarly effective when the connate-water resistivities are less than 0.08 ohm-m or greater than 0.3 ohm-m. For gyp muds where the calcium content is known, a procedure was presented which allows calculation of the connate-water resistivity with improved accuracy. These procedures assume that one of the fluids in the system is a pure sodium-chloride solution, but they are not limited by the assumptions. For the fresh and saline connate waters, for instance, it is assumed that the drilling mud filtrate is a pure sodium-chloride solution. For the gyp mud interpretive procedure, it is assumed that the connate water is a pure sodium-chloride solution. Brown,' on the other hand, has suggested that it would be extremely fortuitous if drilling mud filtrates could all be treated electrochemically as sodium-chloride solutions, and he cites some examples where discrepancies exist. A study has been made of the deviations of sodium single-ion equivalent activities, an of drilling mud filtrates from that of pure sodium-chloride solutions. Drilling fluids in common use on the Texas and Louisiana Gulf Coast and laboratory-controlled muds were investigated. Using a cell patterned after Gondouin, et al, (Fig. I), the equivalent activities were measured. It should be remembered here that the activity measured is merely an index which uses numbers that represent the sodium single-ion equivalent activity a,., of the mud filtrate. The membrane potential developed across the cell was determined with a null-type potentiometer. The resistivities of the solutions were measured by the four-electrode method. The resistivity system was calibrated by using saturated KC1 solution as a standard. Chemical properties of the drilling fluids studied were measured with standard API-approved equipment for the particular property in question. For the activity measurements, two shale discs were chosen to serve as cationic membranes. These two discs were both 1 1/4 in. in diameter and, respectively, 1/4 and 1/8 in. in thickness. The membrane potential, Em, was determined using the shale discs as cationic selective membranes separating two standard sodium-chloride solutions of known mean activity. Then by comparing the constant Km in the following equation, with the theoretical value of — 59 mv at 75OF, the perfection of the membrane was determined. The variation of Km for the two membranes used in this experimental work, as well as one of the many unsuitable membranes, is shown in Fig. 2. The measurement of the activity of mud filtrate involves the balancing of its combined individual activities against a standard solution of known mean activity. At the point where there exists zero potential across the membrane cell, the activity effects may be assumed equal for all practical purposes. The mechanics of making a null reading of this sort requires having a large number of different mean activity solutions. A more practical method involves

By Werner Joseph, Richard R. Knobler

When the first batch of refined copper ingots was cast at Mantos Blancos in January 1961, eight years of exploration, development and metallurgical pioneering by Mauricio Hochschild & Co. had come to a successful conclusion. This Chilean copper deposit, located in the Atacama Desert 30 miles from Antofagasta, is now producing approximately 20,000 tons of copper per year. The Mantos Blancos deposit has been known since 1912 and various attempts had been made to work the high-grade zones before the present operation was started. The major drawback of the ore to any previous development was its chloride content which varies between 0.4% and 1.5% C1. Although the chloride ruled out the conventional leaching-electrolysis scheme, it did lend itself to the process of precipitating the copper as cuprous chloride.

Jan 1, 1962

Henry Louis, Newcastle-upon-Tyne, England (communica, tion to the Secretary): I have been much interested in Mr. Schmitz's description of the copper-ore bed in the Permian formation of Texas. He compares it with the Mansfeld Kupferschiefer; but it seems to me to present closer analogies with a small deposit on the same side of the Atlantic, in Nova Scotia, which I examined in 1877. I quote entirely from my fieldnotes, made then, and from specimens still in my possession. These copper-deposits are known in several places; but I examined them at the village of New Annan, on the banks of the French river. This district has been determined by Sir J. W. Dawson as being of Permian age, and this determination seems to have been confirmed as recently as 1891 by the operations of the Canadian Geological Survey. The following is the section, very imperfectly exposed in a few shallow levels, described in ascending order: Red sandstone, moderately fissile and markedly false-bedded. Lower nodule-bed, 1 inch to 6 inches thick, of fissile mica, ceous sandstone, containing obscure plant-remains converted into anthracite, chalcopyrite, chalcocite and iron pyrites. Very coarse grit or, in places, red sandstone; thickness and character variable. Upper nodule-bed, 6 inches to 2 feet thick exceptionally, generally about 10 inches. Soft, gray, friable shaly sandstone, with nodules of copper-ore. Red sandstone. All these strata lie flat, in places quite horizontal, in places dipping towards the river at 5° to 10°.

Jan 1, 1897

By E. A. Holbrook

AS A whole, engineering schools have not awakened A to the fact that the workmen compensation laws passed in most of our states between 1914 and 1917 effected a quiet but none the less real revolution in. the relations between labor and management; no longer are industrial accidents unfortunate or careless happenings over which we feel a humanitarian interest and sorrow, they are a cost of the process and the finished product, as vital as improved design and increased efficiency. Last year the writer and others made a committee report to. the American Institute of Mining and Metallurgical Engineers on the cost of accidents in the coal industry of Pennsylvania. Comparatively the accident record in Pennsylvania coal industry is not high, yet the direct compensation cost plus the interference with operation cost of accidents was over 5 per cent. of the total cost of producing the coal. This stands out more vividly -if you realize that about 70 per cent. of the' cost of producing the coal is for payment of labor, wages that are fixed and over which engineering efficiency and management skill have little or no direct effect. This leaves 30 per cent. of the cost chargeable .to hoisting, haulage, overhead 'and other items subject to engineering control. One sixth of this is due to cost of accidents. Surely a direct place 'for an engineering attack.

Jan 1, 1925

By Bryan J. Travis, Thomas L. Cook

INTRODUCTION Our growing concern for adequate and secure sources of energy and minerals has stimulated vigorous exploration for new sources, research toward a better understanding of geological processes, and development of new extraction technologies. The need for control, or at least prediction, of subsurface fluid flow is important for many of these technologies for example: primary, secondary and tertiary recovery of oil; ground water and waste management; in-situ fossil energy extraction (oil shale, coal, tar sands); and solution mining of uranium, copper and other minerals. These technologies, especially the last two, are characterized by highly complex systems. A partial list of the physical processes occurring would include flow in porous/fractured media, multi-phase and multi-component flow with heat transport, chemically active fluids and soils, tracers, diffusion and dispersion, fracturing and dissolution. A great deal of understanding of how these processes behave and interact can be obtained from models. MODELS Theoretical models are valuable because they: 1) provide a frame of reference for interpreting results of laboratory and field experiments; 2) once validated by experiments, allow a variety of geometries, injection/production strategies, etc., to be examined (at relatively low cost) for efficiency and stability; 3) can provide guidance to the design of experiments and field operations. Most models are based on the fundamental principles of mass, momentum and energy balance. But from this starting point, many paths can be taken. For example, there is the theory of Payatakes (1973) which concentrates on the microscale dynamics. In this approach, the rock or soil matrix is represented by a complex of characteristic channels (such as periodically constricted smooth tubes). Detail of flow within the characteristic channel is calculated very accurately. A difficulty with this model is that description of a representative channel can require several parameters which may not be easily measured. Also, it is not clear how the channels can be combined practically to model a large scale flow. Another type of model is the "global" one described by Bear (1972). Here, the continuum equations for conservation of mass, momentum and energy are averaged over a distribution of pore channels, resulting in a set of conservation equations in which the small scale structure of the medium is replaced by quantities such as porosity, permeability, dispersion coefficients and tortuosity. This approach allows computation of large scale flows. However, additional constitutive equations are needed which relate averaged quantities such as permeability to observables such as local saturation, particle size distributions, and others. An important difference between models is the way they handle the momentum equation. Payatakes' model solves the full equation. In others, it is replaced by a simpler relation such as Darcy's law (valid for slow flow rates) or by Forchheimer's equation which extends Darcy's law to higher flow rates. These simple relations can nevertheless match a great deal of experimental data (Dullien 1975). The permeability term which appears in Darcy's law and in Forchheimer's expression has been related to other quantities such as porosity and particle surface area. The Kozeny-Carmen equation is a well-known example, valid for some ranges of porosity and particle sizes and for some materials. Several other semi-theoretical, semi-empirical formulations have been devised, none of which are entirely satisfactory. One goal of researchers has been the ability to predict permeability of a porous material from basic measurable quantities such as grain size distributions without recourse to adjustable parameters. This effort has proceeded from consideration of distributions of idealized, non-intersecting channels, to intersecting channels, to consideration of both distributed pore radii and pore neck radii. This last approach has been used successfully to predict permeabilities (ranging over several orders of magnitude) in sandstones (Dullien 1975). Additionally, studies on explicit networks of channels (e.g., Fatt 1956) and percolation theory (e.g., Larson et. al. 1981) have been used to examine interconnectivity effects in porous media with the hope of eventually being able to predict permeability accurately. To be of more than theoretical interest, a model must be compared s controlled laboratory conditions where boundary and initial conditions and relevant material properties can be accurately determined. Also, extraneous forces can be eliminated so that the interactions between processes of interest can be clearly seen and flow models can be vigorously tested. In contrast to the well-defined environment and

Jan 1, 1982

By J. W. Leonard, B. A. Donahue

A method is described for incorporating coal petrography into mining and preparation plant quality control based on conventional analyses. Complete analyses are made of each of the uniform and relatively distinct petrographic bands in a coal face. With this information it is possible to develop petrographic standardization curves. These curves permit diverse coal characteristics to be rapidly monitored by application of a few standard coal tests. Single seam quality control is discussed in this paper. Inquiries continue to be made about coal petrography, and specifically, about whether coal petrography should be applied more extensively in the coal industry. Coal petrography is the study of the distinct physical, optical, and chemical increments which make up the organic rock mixture which we know as coal. Petrography can be applied by any coal company or at any coal mine where conventional coal analytical facilities are available and where additional resources can be allocated for an increased number of determinations. This first paper of a two part series includes (1) a proposed conventional approach to single seam petrography based on the development of petrographic standardization graphs and (2) some informative and supplemental interrelationships involving coal characteristics developed as a result of this research. In the second part of this series, to be published at a later date, those petrographic characteristics of bands taken from many different coal seams located over wide geographic areas which can be closely related to each other will be considered. These findings will be examined looking toward the development of a comprehensive, conventional approach to coal petrography which can be used as a common basis for multi-rank petrographic standardization graphs. Implicit to the understanding of coal petrography is the well established fact1,2 that the individual analyses of distinct petrographic bands often differ widely from the average analysis which is used to characterize a whole coal seam. In fact, a distinct and minor banded increment of coal in a high volatile seam may actually be a medium or low volatile coal with an analysis similar to the average analyses of seams located in distant coal fields. During the mining of coal, much degradation is caused which tends to randomly scatter coal bands. The degraded, scattered, and physically separated constituents of distinct petrographic bands are processed side by side in the coal preparation plant as distinct petrographic fractions with particles grouped according to a narrow size range (which derives in part from common hardness), specific gravity, and-or surface chemistry. Tile data obtained from numerous analyses made on each of the bands of any given coal seam, although diverse, can be readily interrelated. Indeed, these interrelationships can be developed into a series of nomographs or petrographic standardization graphs to serve as a basis for developing a conventional petrographic* program. Thus, by analyzing one property (for example, ash) of a selected petrographic fraction collected or separated from the flow of coal in a preparation plant, it should be possible to estimate the other physical, chemical, and thermal properties of this fraction by referring to the petrographic standardization graphs. It follows that any or all petrographic fractions in the total coal flow originating from a single coal seam can be rapidly monitored for many properties on the basis of a single analysis run on each fraction. In recent years coal petrographic research has concentrated heavily on that phase of this work which involves microscopic reflectance measurements made at many minute and selected points on a coal briquette surface.3,4 Thus, the percentage of the total number of reflectance measurements that fall into each of a consecutive series of arbitrarily chosen reflectance classes are used to characterize coal. This procedure is analagous to using the face of a coal briquette to represent the reflectance characteristics present at the face of a coal seam. Moreover, by analyzing petrographic fractions of known and uniform optical properties it is possible to closely relate reflectance to other coal characteristics. For example, reflectance has long been known to be related to such

Jan 1, 1968

By Carl Wagner

AT elevated temperatures. most metals react with oxygen, sulphur, or halogen rather rapidly, although a coherent layer of the reaction product is formed and separates the two reactants from each other. The reaction proceeds, since one of the reactants or both dissolve and diffuse across the reaction product. In many cases the rate is diffusion-controlled as is indicated by the validity of the parabolic rate law of Tammann' and Pilling and Bed-worth. wott and Gurney' have suggested that diffusion processes also play an important part in the case of reduction reactions. This is confirmed by observations reported below. In general, however, the rate of reduction reactions is determined not exclusively by diffusion processes. Reduction of Silver Sulphide Above 179°C silver reacts with liquid sulphur very rapidly. Since the volume of silver sulphide is much greater than that of the equivalent amount of silver, a coherent layer of silver sulphide is formed in accordance with a rule established by Pilling and Bedworth.' According to Wagner','' silver ions and electrons migrate from the Ag-Ag,S interface across the silver sulphide layer to the Ag,S-S interface where the following chemical reaction takes place: 2 Ag +2 e + S Ag,S If silver sulphide is reduced by means of hydrogen, the equivalent volume of the reaction product, silver, is less than that of the initial substance. Accordingly, no coherent layer of silver is formed. Instead, fine filaments of silver grow from the silver sulphide surface into the ambient gas. This phenomenon has been investigated by many authors, especially by Kohlschiitter," who has also reviewed previous literature. Kohlschiitter has interpreted the observed phenomena by migration of "silver" dissolved in silver sulphide. According to Wagner,' silver ions and electrons are the migrating particles. The sequence of consecutive steps involved in the reduction of silver sulphide is shown in Fig. 1. Every- where at the silver sulphide surface, hydrogen reacts with sulphur so that excess silver ions and electrons are formed, which migrate at random until they are captured by a nucleus of metallic silver. If such a nucleus lies on the surface and material is furnished only from the base, the original nucleus is pushed outward and thus a filament grows. Removal of sulphur and formation of metallic silver may also take place at different points when silver sulphide is reduced by copper. The reaction is usually formulated as: AgL,S + 2 Cu = Cu.S + 2 Ag but the actual reaction products are silver and a solid solution of the two sulphides. Primarily, excess silver and electrons dissolved in silver sulphide are formed. After a certain degree of supersaturation has been reached, nuclei of metallic silver may form. If, however, a silver foil is in contact with the silver-sulphide phase, as is shown in Fig. 2, silver ions and electrons will migrate to the Ag,S-Ag interface where they are captured. To confirm this scheme, a composite sample, with the geometry shown in Fig. 2, was made by pressing silver sulphide tablets 0.6 cm in diam and 0.4 cm high together with a copper cylinder and a silver foil in crucibles of iron, which does not react appreciably with silver sulphide at 400°C. After heating for 3 to 7 hr at 400°C. the specimens were cut normal to the phase boundaries. It was found that the thickness of the silver foil had increased from 0.01 cm as initial value to a maximum value of 0.06 cm. In the interior of the silver sulphide tablets only traces of metallic silver were observed. These observations show clearly that silver ions and electrons may migrate over distances of several millimeters before they form metallic silver. Reduction of Cuprous Sulphide by Iron The behavior of cuprous sulphide is very similar to that of silver sulphide, since the lattices of the high temperature modifications are identical, but in Cu.S there is a variable deficit rather than an excess of metal. To investigate the displacement of copper by iron, cuprous sulphide powder covered by a copper foil was pressed in iron crucibles and heated up to 800 °C for 3 to 7 hr. The thickness of the copper foil increased from an initial value of 0.005 cm to a nlaximum value of 0.029 cm. In the interior of the

Jan 1, 1953

By J. E. Owen

A model of a porous body is presented in which the pore space consists of a system of voids and interconnecting tubes. Relationships between porosity and resistivity formation factor are determined partly by calculation, partly by experiment. Con triction effects characteristic of the model are shown to be sufficient to account for high formation factors. It is shown that constriction may be combined with moderate amounts of tortuosity to give model pore systems exhibiting to a first approximation porosity and resistivity properties similiar to those of natural porous bodies. INTRODUCTION The relationship between the electric resistivity of a fluid-filled porous body and the geometry of its pore space is so complex that the calculation of the resistivity of a natural porous rock is a practical impossibility. Both the resistivity of a body and its porosity are measurable quantities, however, and previous successes at relating them have been reached by an empirical approach. Efforts at obtaining theoretically derived formulae relating them have generally been unsatisfactory. One of the reasons for this may lie in the pore geometry that has been assumed. THE TORTUOSITY CONCEPT A Parameter called the formation factor is useful in dis-cussing the resistivity of a fluid-filled porous body. This parameter is the ratio of the resistivity of a fluid saturated porous body to the resistivity of the saturating fluid. Formation factors are often available from measurements on cores or from electric logs, and many attempts have been made to correlate formation factors and porosities of geological formations. Whenever a successful correlation is found, the engineer working with electrical logs has a useful tool for the determination of porsities of pay section?. One of the more successful formulae applicable to these correlations is the familiar equation empirically obtained by Archie.' which F is the formation factor. $ is the porosity, and rn is an exponent called the cementation factor. When the for- mula applies, the cementation factor usually is found to be between 1.3 and 2.2. The values for formation factors experimentally obtained are often higher than simple pore geometry would lead one to expect. In an effort to account for such high values certain formulae have been derived based on a so-called "tortuosity concept." In deriving these formulae a synthetic porous body is usually assumed in which the solid material is an electrical non-conductor. and in which the pore system consists of three sets of fluid-filled tubes of uniform diameter connecting opposite faces of the body which, for convenience, is considered to be cubical in shape. The three sets of tubes account for the whole of the effective porosity of the body, and usually, it is specified that they do not interconnect. By considering that the pore tubes are not straight but tortuous, their resistance to the flow of electric currents can be made as high as needed to explain high formation factors. Such an explanation has some basis in fact, but it appears that the tortuosity concept is often incorrectly applied when other factors are largely responsible for observed high resistivities. Recently, Wyllie and Spangler have recognized that tortuosity as calculated by conventional formulae has little if any physical significance.' RESISTIVITY AND THE CONSTRICTION CONCEPT Any explanation of high formation factors which depends solely on tortuosity of uniform pore paths necessarily ignores the effect that variations in the cross-sectional area of the conducting paths have on the resistivity of a body. Although, as previously pointed out, the calculation of such paths for an actual body is impossible, it will he shown that a synthetic pore network can be devised which will yield to analysis, and lead to results in agreement with the experimental data represented by Equation (1). The porous body to be considered is assumed to be homogeneous and isotropic or, for present purposes, identical in its characteristics in the three directions parallel to its coordinate axes. It will he assumed to be built of identical unit cubes, each of which contains a single pore network connecting all faces of the unit cube. A unit of such a pore network is shown

Jan 1, 1952

By C. W. Allen, B. D. Cullity

The proportional limit of iron crystals in torsion is governed by the resolved shear stress in the most highly stressed slip systems, averaged around the specimen circumference, and does not obey a critical resolved shear stress law. Crystals of most orientations exhibit a stage of easy plastic deformation, akin to easy glide in tensile or shear specimens. Transient deformation, similar to that which occurs in single crystals of other materials, is also observed. THE torsional deformation of single crystals of magnesium (hcp) and aluminum (fcc) has been described recently by Choi et al.,&apos; especially with respect to the criterion for the orientation dependence of the onset of plastic flow in these materials. The purpose of this paper is to present results of torsion tests of iron single crystals and thus to extend this yield criterion to a bcc metal. In addition to considering the variation of proportional limit with crystal orientation, this paper also briefly treats work hardening, transient deformation, and the mechanism of plastic flow in iron. The effects of the method of surface polishing and the chemical purity of the iron have been investigated. STRESS DISTRIBUTION It is convenient to express the stress at any point of a cylindrical crystal stressed in torsion in terms of t0, which is the shear stress acting at the surface on a plane normal to the axis of the cylinder and in a direction tangential to the cylinder. This stress is given by To = 2T/pr3 [1] where T is the applied torque and r the specimen radius. The shear stress t, resolved in any chosen slip system is given in terms of 7, by1 Ts/TO = sin 0, cos d sin (0, -) + cos , sin d sin d - ) [2] where 0 and d are the angles between the specimen axis and the slip plane normal and slip direction, respectively; h is the angular circumferential position on the specimen at which t, is being determined, measured from an arbitrary reference plane which includes the axis;o and d are the angular coordinates of the projections of the slip plane normal and slip direction on a transverse section with respect to this same reference plane. Slip in iron occurs in a <1ll> direction on the {ll0}, (1121, and (123) planes, which together comprise 48 slip systems. A complete evaluation of the stress distribution in an iron crystal stressed in torsion would therefore require a calculation of Ts/T0 as a function of for 48 different slip systems. Fortunately Gough,&apos;who studied the behavior of iron crystals in alternating torsion, was able to simplify this problem considerably. He showed that it was sufficient to consider a kind of average slip plane for each slip direction, namely the mathematical plane of maximum resolved shear stress containing the slip direction considered. This simplifying approximation is possible because, for each slip direction, the active slip plane or planes lie very near this mathematical plane of maximum shear stress. Vogel and rick&apos; have critically reviewed the early work of Taylor and Elam,13 Taylor,14 and Fahrenhorst and schmid8 from which the identification of the above crystallographic planes as slip planes in the bcc lattice largely stems. While their criticism is clearly justified, their own results do little to clarify the issue. The role of cross slip (screw dislocations changing glide planes) is evidently so important in this case, as Read3 has suggested, that methods for deducing slip systems from observations of gross slip traces are inadequate, such traces commonly arising from complex dislocation motion. Thus the treatment given here involving the plane of maximum resolved shear stress seems a logical simplification especially in view of Gough&apos;s2 study of a iron. There is, however, an assumption built into the subsequent treatment the comparative validity of which is difficult to assess, namely, that slip in all slip systems in iron may be characterized by a common critical resolved shear stress. The shear stress 7, resolved in a slip direction defined by d andd, and on the plane of maximum shear stress containing this direction, is found by first maximizing 7s/70 with respect to either Oo or 4,. The slip plane coordinates are then eliminated by using the relation between 0, ,o and d, d, namely,

Jan 1, 1963

By AIME

THE history of the Mine La Motte area covers a greater period of time than any other mining operation west of the Mississippi, for it was almost exactly four centuries ago that the white man first visited the region. In May 1541 a few men from the party of Fernando de Soto traversed the place looking for silver which they understood the Indians had found in the vicinity. Some historians say that De Soto himself visited the place sometime later. No other white man came through again until the early 1700&apos;s. In 1712 King Louis XIV of France granted to Antoine Crozat a charter for transacting all business and government in the vast domain of the New Continent stretching from the Gulf of Mexico northward indefinitely. This

Jan 1, 1947

By H. Foster Bain

FROM time to time geologists and mining engineers, impressed by the heavy demands made on our mineral reserves&apos; by modern industry, and particularly by the steadily mounting rate of production necessary to meet that demand, have issued warnings as to the danger of exhaustion. There can be no dispute as to the fact that mineral deposits are exhaustible. New mineral, is not created to replace that taken from the earth and when a crop of mineral is once harvested another cannot be grown in the same area. The evidence of exhaustion &apos;of particular oreshoots, deposits, or even of whole districts is familiar to all who have mined. If one were to judge solely from the abandoned mills and prospect holes he would rightly conclude that mining is but a short-lived industry. If one were, furthermore, to assemble the data as to known reserves of almost any of the commonly used minerals, and divide them by the annual tonnage mined, he would come to the same conclusion. If, again, one were to consider the most carefully made estimates of competent men seeking to measure the earth&apos;s reserves of minerals and plot against them a projection of the curve of past consumption, he would be justified in viewing the situation with alarm.

Jan 1, 1930

By H. Foster Bain

THE "miracle of production." which was such an essential element in winning the European war, was nowhere more in evidence than in our Western States. In shipbuilding alone the Pacific Coast States -et a mark never before equaled, and in production of war goods of many kinds, both Rocky Mountain and Coast States accomplished more than their proportionate share if measured by population standards. This was only possible because of the building of immense new plants of many types, largely financed with Government money. Their operation has built up payrolls in the West and brought a measure of prosperity which Westerners are naturally anxious to have made permanent. A widespread doubt obtains, however, throughout the nation and even in the Western States themselves, as to whether, and if so to what extent, this may prove possible. The question has been raised as to whether the national treasury has not been raided to stock the Western ranges with a voracious breed of white elephant .

Jan 1, 1945

By John W. Padan, John E. Crawford

Beginning with a small but positive participation in undersea mining, the Bureau of Mines continues its active investigations into this potentially tremendous field. The Bureau began its active role in undersea mining in September 1963, with a small task force of three dedicated scientists and a secretary, establishing headquarters at the old Tiburon Naval Net Depot about seven miles up the coast from San Francisco. The past months have been both busy and productive. With 22 Federal agencies involved in oceanography, it logically was the intent of Congress that the Bureau of Mines undertake research concerned only with the technology of marine mineral production and utilization. The Bureau has maintained this purpose in its activities at Tiburon, for while institutes, universities, the Navy and other Government agencies have developed exceptional programs in the fundamental science of the oceans, commonly called oceanographic research, little has been done toward advancing man&apos;s ability to exploit the ocean floors other than by drilling for oil and gas and sulfur.

Jan 3, 1965

By M. R. Geer, H. F. Yancey

THE performance of coal-washing equipment, that is, the effectiveness with which coal and impurity are separated, is a subject of undisputed interest to all concerned with the preparation of coal. Through the years much has been written in both American and European literature on the performance of coal-washing equipment and its interpretation, but until recently no effort has been made to consolidate this wealth of information into a single, comprehensive treatment of the subject. A splendid effort in this direction was made at the First International Conference on Coal Preparation held in Paris in June 1950 in which representatives from virtually every coal-producing country participated. Although the scope of the conference covered the entire field of coal preparation, many of the sixty-odd papers and a great deal of the discussion dealt with the subject of evaluating washery performance. Prominence was given this subject by the Centre d&apos;Etudes et Re-cherches, des Charbonnages de France, which sponsored the conference. This research organization, generally referred to as Cerchar, was formed in 1948 following the nationalization of the French coal industry. Since that date it has conducted an intensive study of coal preparation. Perhaps because of a fresh viewpoint, Cerchar realized immediately that complete information on the performance of French washeries and a thorough understanding of the mechanism of gravity separation were the fundamental prerequisites in a program to improve preparation practice. For this reason Cerchar concentrated on obtaining performance data and on a comprehensive study of methods of evaluating such information. Some idea of the magnitude of this work will be appreciated from the fact that 175 performance tests were made in 44 plants. The work performed by Cerchar emphasized a condition that is recognized by many of those concerned with coal preparation, namely that the lack of uniformity in presenting data on washery performance, the diversity of methods used in evaluating such information, and the frequent confusion of the terms related to performance have been prime factors militating against the progress from art to science. Thus, Cerchar feels that standardization of the methods employed for evaluating washery performance, not only in France but in the entire world, is essential to progress, and the prime objective of the Paris conference was to seek international standardization of the evaluation methods advocated by Cerchar. At the conclusion of the conference the question of standardization was referred to the International Standards Organization. A careful study of the dozen papers on the subject of evaluating washery performance presented at the conference reveals that none of the methods is new; most of them date back over a decade. Nevertheless, the intensive scrutiny of these methods brought about by the conference unquestionably has resulted in a valuable exchange of ideas and a clarification of thought that could scarcely be achieved in any other way. The object of the present report is to make available to the American coal industry the ideas developed at the conference which seem most important from an American viewpoint and to provide a critical analysis of some of the evaluation methods advocated by Cerchar. The various methods of evaluating washery performance are illustrated partly with data that have been published in American literature, and some new data have been obtained as the result of experimental work undertaken since the conference to provide information on certain controversial points. An English translation of the proceedings of the conference, including the discussion as well as the papers, will be available,&apos; and previous to the conference Coal Age2 published a very brief description of some of the principal evaluation methods used by Cerchar. Americans will appreciate as well as do the French the desirability of standardizing both the termi-

Jan 1, 1952

By A. P. Svenningsen

IN the early stages of design it was not considered necessary that separate crushing plants be built for the new sulphide concentrator and smelter until sometime in the future. The plan was to use the existing crushing facilities for both oxide and sulphide ore. A few additions were contemplated for the existing plants, such as increased bin capacity, and possibly two new secondary crushing units. The more the problem was studied and discussed with the plant operators, the more it became evident that it was complex. It involved the classification of different kinds of ore from the open pit mine -sulphide, oxide and mixed-and how best to separate them so that each kind of ore was given the proper processing and treatment. It also involved the problem of keeping the different ores from being contaminated in bins, hoppers and chutes. Added to these, transportation became complicated and would involve additional handling and loading of ore from crushing plants to conveyors, to bins, and finally to railroad cars which were to be hauled to the concentrator and dumped into the fine ore bin. General In the early part of 1951 it was decided that the concentrator be constructed with ten grinding units instead of seven as originally authorized. The smelter was to be increased proportionally and naturally also the overall tonnages of ore to be handled by the new sulphide plant. Due to this increase in plant capacity and the larger tonnages involved, the difficulties which would arise by using the existing crushing plants were increased to a point where it became evident that the building of new crushing plants for sulphide ore exclusively was technically, as well as economically, advantageous. Authorization was, therefore, given by the company to construct new crushing plants to handle 30,000 tons of ore per day, and capable of reducing the run-of-open-pit ore to the proper size feed for the 10x14-ft rod mills in the concentrator. The ore, mined in the open pit, sometimes comes in pieces as large as 6 to 7 ft diam. The rod mills may call for ore crushed to 3/4 in. The large .size of ore delivered from the open pit determined that a 60-in. gyratory crusher be used as primary breaker. Such a crusher will have a capacity considerably in excess of 30,000 tons per day. The crusher will be a single discharge unit driven by a 500-hp electric motor through a tear coupling and a floating shaft. This type of drive has proven successful at a number of other crusher installations which our company has operating in the United States, Mexico and South America. The tear coupling will protect both the crusher and motor against damage in case of overload. No new features are incorporated in the design of the crusher itself, except that the, discharge chute is made the full width of the crusher with parallel sides instead of the usual converging sides. This change in detail should eliminate, a feature which has been a bottleneck in some of the operating plants and has caused loss of production due to ore hanging up and blocking the chute. The secondary crushing plants will have three 7-ft standard Symons cone crushers and six 7-ft short head Symons crushers. Between the primary and secondary crushing plants a coarse ore bin will be constructed with a nominal draw-off capacity of 30,000 tons of ore. The standard Symons and the short head Symons will be in separate buildings. All the crushing plants and the coarse ore bin are interconnected with conveyor belts for transporting the ore to the crushers at the tonnage rate desired. The final product of the new crushing plants is produced by the short head crushers. It will be delivered onto a conveyor belt leading to the top of the fines ore bin in the concentrator. A separate conveyor belt running the full length of the fines ore bin and provided with a movable tripper of rugged design will discharge the sulphide ore into the bin. The concentrator bin is planned and designed so that the installation of this additional conveyor will not interfere with the operation of the two railroad tracks on which crushed ore is brought from the existing oxide plant. Thus when completed the bin can be filled simultaneously by ore from the new crushing plant and by ore from the existing leaching plant.

Jan 1, 1952

By Thomas L. Kesler

IF all of the 14 million tons of kaolin produced in Georgia through 1949 had been mined from a single deposit 20 ft thick, it would represent a mined-out area of less than 1 sq mile. This measure of depletion is in such strong contrast with the large size of the area shown in Fig. 1, from which most of the output has come, that there has developed an optimistic outlook concerning future supplies of kaolin equal in grade to that already mined. Dozens of mines are widely but not evenly distributed within this area, which consists mostly of parts of Twiggs, Wilkinson, and Washington counties. There are scarcely half a dozen kaolin mines elsewhere in the state that have been appreciably productive, although the areas in which they occur may have good possibilities. Most of the efforts to find new deposits, therefore, will be confined to the area shown in Fig. 1, for it is here that the industry has established its facilities, and prospecting is encouraged by relatively numerous outcrops and opened deposits of kaolin.

Jan 10, 1951

By Stanley L. Lopata, Eric B. Kula

SEVERAL methods are available for determining pole figures by X-ray means.&apos; The earlier film methods have been replaced by techniques in which the intensities are measured by Geiger counters on an X-ray diffractometerZm7. These methods utilize either flat transmission or reflection samples,214°8 cylindrical specimens,3 or spherical specimens.7 A single transmission or reflection sample will not yield information over the complete pole figure. The cylindrical specimens suggested by Nortod and the spherical specimen of Jetter and Borie7 have the advantage of allowing the whole pole figure to be obtained without any corrections to the intensity for absorption, There is a lower limit to the size of sheet which can be conveniently studied, however, and sample preparation can be rather tedious. Probably the most common method today for determining the complete pole figure is that developed by Schulz. A flat reflection sample is used for determining the pole figure from the center out to about 70". Because of the geometry of the system used, little or no correction for absorption or irradiated volume is necessary.4&apos;6 A separate transmission sample is used for the region near the edge of the pole figure. This procedure requires two separate samples, one of which must be a thin carefully-prepared transmission sample. Furthermore, since the reflection and transmission data are in different arbitrary intensity units, a region of overlap must be obtained, and the intensity data from one set of measurements converted to units of the other. These are serious disadvantages of this method, and they point out the need for a simplified procedure. Since the reflection technique can be used for planes whose normals lie up to about 70° from the sample surface normal, it is apparent that a complete pole figure can be obtained by reflection alone if sample surfaces are cut at oblique angles to the rolling plane Specifically, if a rolled sample is cut so that the normal to the surface formed lies equidistant (54" 44&apos;) from the rolling plane normal, rolling direction, and transverse direction, then complete information for one quadrant of the pole figure can be obtained by reflection from the surface. Fig. 1 shows this oblique surface, as well as the position of the pole of this surface in the pole figure. When a surface has been cut oblique to the rolling plane, the standard polar stereographic net is inconvenient to use, and it would be more desirable to have the center of the net coincide with the pole of the oblique plane. Fig. 2 shows such a net, where the center has been offset 54&apos; 44&apos; to correspond to a specimen cut as in Fig. 1. This net was in effect obtained by rotating a standard polar stereographic net 54" 44&apos; with the help of a Wulff net. With the experimental setup used. a sample can be cut from plate of 1/2-in. thickness or br Gen- erally thinner sheet is under investigation, and a composite specimen must be used. A convenient procedure has been to bond together, using epoxy resin, sufficient sheets to form a cube. These are clamped in a vise, and when dry, the whole vise is rotated and a flat surface ground at the required angle. The sample is then mounted inside a larger steel ring using Koldmount, the backside ground flat and parallel to the approximate desired thickness. The sample is then polished and etched to remove any effects of cold working during grinding. With this method only one quadrant of the pole figure is obtained. Often pole figures show symmetry around the rolling and transverse directions, and any slight asymmetry is due to scatter. Should the pole figure not be symmetrical, four oblique surfaces, corresponding to the four quadrants of the pole figure, would have to be examined. In most cases there is symmetry at least around the rolling direction, which reduces to two the number of quadrants to be investigated. For many purposes all that is required is an average polefigure for the four quadrants. This canreadilybe obtained with composite specimens of sheet material, where sheets Corresponding to each of the four quadrants can be intermixed. The four quadrants can be obtained by considering sheet in the normal position, and by rotatiolls of 180" around the sheet normal, the rolling direction, and the transverse direction. If desired, the whole thickness of the sheet can be used, yielding an average of the surface and interior textures; or the surface material can be removed from each sheet, resulting in a pole figure for the center alone. Eugene S. Meieran of the Massachusetts Institute of Technology has independently developed the same method. His results, adapted to a pole figure goniometer with a specimen spiraler, will be described in another publication.

Jan 1, 1962

By F. V. Lene, E. J. Westerman

The recrystallization behaviors of two extruded and cold-drawn experimental sintered aluminum powder alloys, containing 1.75 and 3.0 pct Al2O3 by weight, were compared with that of extruded and cold-drawn commercially pure alumirzum. The kinetics of recrystallization of the alloys are described semiquantitatively. For the alloy containing 1.75 pct A l203 the rates of nucleation and of growth were also semiquantitatively determined. THE most striking property of aluminum alloys strengthened by a dispersion of Al2O3, the so-called SAP alloys, is their stability at elevated temperatures. One of the manifestations of this stability is their resistance to recrystallization after they have been cold worked. Most of the commercial grades of either the Swiss SAP or of Alcoa&apos;s Aluminum Powder Metallurgy Products have not been recrys-tallized after cold working, even when they are heated for a long time at a temperature near the aluminum melting point. Lenel, however, observed that the dispersion strengthened aluminum alloys with a larger spacing between the oxide particles than that of most commercial grades would recrys-tallize.1 It appeared to be of interest to further investigate the mode and kinetics of recrystallization of these alloys, and to compare their recrystallization behavior with that of commercially pure aluminum. Because homogeneous deformation of these SAP alloys in tension did not provide sufficient cold work to induce recrystallization, they were cold worked by wire drawing; the nonuniformity of this deformation unavoidably complicated the interpretation of the recrystallization studies. EXPERIMENTAL DETAILS Extrusions—Two types of sintered aluminum powder extrusions were used in this study. One type, designated AT-400, was produced from Reynolds atomized aluminum powder consisting of spherical particles averaging 3µ in diam and containing 1.75 wt pct of Al2O3. This powder was very similar to the R3M powder from which extrusions were previously prepared with an average spacing of 0.9µ between oxide particles.2 The second type, designated MD 2100, was produced from Metals Disintegrating Co. flake powder containing 3.0 wt pct of Al2O3, with an average flake thickness of 0.8µ. The average spacing between oxide platelets in MD 2100 extru- sions was 0.45µ.2 Powder compacts of 3/4-in. diam were extruded at 1000°F into 0.097-in. diam (AT-400) and 0.093-in. diam (MD 2100) wires by methods previously described.3 In order to compare the recrystallization behavior of sintered aluminum powder extrusions with that of wrought commercially pure aluminum 3/4 in. rod stock of 1100 F aluminum was extruded at 1000°F into 0.102-in. diam wire. Wire Drawing—Tungsten carbide dies were used for the AT-400 and 1100 F alloys. They had an included angle of about 15 deg and reduced the wire area approximately 7 pct per pass. Steel dies with an included angle of 11 to 13 deg and an average reduction per pass of 10 pct were used for drawing the MD 2100 alloy, because drawing this alloy through the carbide dies produced overdrawing defects. Heat Treatment—The cold-drawn wires were cut into small samples, and the deformed ends were etched off. The samples were each wrapped tightly in a single layer of aluminum foil, and individually isothermally annealed in a lead bath. Metallography—The modes and kinetics of recrystallization were determined by metallography. Mounted and polished specimens were anodized in a solution of 1.8 pct HBF4;4 examination under polarized light clearly revealed their grain structures. The recrystallized grains were generally much larger than those of the unrecrystallized matrix, and could clearly be distinguished because they alternated between maximum and minimum light reflection when the microscope stage was rotated, while the unrecrystallized matrix had a comparatively homogeneous "salt and pepper" structure. The fractional recrystallized volumes of the dispersion hardened alloy wires were determined by cutting and weighing of recrystallized and total transverse areas on photomicrographs. The recrystallized grains in the 1100 F alloy were too small to be cut out individually; therefore a combination of cutting and lineal analysis was used in this case. RESULTS AND DISCUSSION Modes of Recrystallization—The modes of recrystallization of the three alloys varied widely. In the 1100 F alloy nucleation and growth started in the region midway between the center and the surface;

Jan 1, 1961